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CHAPTER - 1

INTRODUCTION

Section 1.1: Basic kinetic terms

1.1.1: Laws of chemical kinetics

1.1.2: Theories of reaction rates

1.1.3: Oxidation and reduction

1.1.4: Kinetics of catalyzed reaction

Section 1.2: Micelle catalysis

1.2.1: Behavior of surfactants

1.2.2: Phenomenon of micellization

1.2.3: Role of micelle catalysis in the present work

Section 1.3: Fluoroquinolones as substrate

1.3.1: Fluoroquinolones as micro contaminants in aquatic environment:

1.3.2: Oxidation of fluoroquinolones

1.3.3: Environmental impact of fluoroquinolones

Section 1.4: Chloramine-T and potassium permanganate as oxidants

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INTRODUCTION

Surfactants and their properties have received considerable attention from last few

decades as the use of these surface active compounds are increasing day by day. Apart

from their other specific properties, the ability of surfactants to affect the rates of

chemical reactions has become quite important as it can play a role of catalyst for various

physical, organic, biochemical and physiological reactions. Varieties of surfactants are

available depending upon the charges present at its polar head group and the length of its

tail portion. A wide structural variation is also possible within each class of molecules

because both the length of hydrophobic tail and the nature of the hydrophilic head group

may be varied. As the concentration of the surfactant in an aqueous solution is increased,

many of the chemical and physical properties of the solution change abruptly (in a

continuous manner) over a concentration range known as the critical micelle

concentration, after achievement of this particular concentration, micelles or aggregates

are supposed to be formed in the solution. The rate of various reactions is found to be

influenced by the micelles formed from surfactants. Fendler and Fendler (1975) have

provided a comprehensive review of effort in this field. There are a number of

bimolecular reactions for which the rate-surfactant profiles have been interpreted in terms

of the distribution of surfactants between the aqueous and micellar pseudophase [Albert,

2005].

The kinetics of the bimolecular reaction between a neutral substrate and a charged

reagent is usually strongly modified, in aqueous solutions, by the presence of micellar

aggregates of ionic surfactants. This phenomenon of “micellar catalysis” has been

investigated by many researchers for several systems [Mittal, 1979; Mittal, 1977; Mittal,

1984; Laurent et al. 1999; Gaillon et al. 1997; Ramamurthy et al. 1990; Denver, 1981;

Françoise et al. 1984; Bunton et al. 2000; Raimondo et al. 1993; Houshang et al. 2002;

María Múñoz et al. 1999; Gall et al. 2003]. Micellar catalysis is observed when reactants

are taken into the micellar pseudophase and there have a greater reactivity than in bulk

solution. Ionic micelles typically increase rates of reactions of reactive counter ions with

hydrophobic as well as hydrophilic substrates. These rate enhancements are due to higher

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local concentrations of both the reactants at the micelle-water interface as compared to

their stoichiometric concentrations [Romsted, 1977; 1984; Martinek et al. 1977; Bunton

& Savelli, 1986; Bunton et al. 1991]. In present investigation our objective is to carry out

a kinetic comparative study of the oxidation of two of the most widely used antibacterial

Fluoroquinolone family drugs, i. e. ciprofloxacin and norfloxacin in water and micellar

medium.

Recently, presence and accumulation of pharmaceuticals and personal care products

(PPCPs) in the aquatic environment have received increasing attention and putting a new

challenge to drinking water, waste water and water treatment systems [Chen & Chu,

2012; Hai Yang et al. 2010; Kolpin et al. 2002; Ternes et al. 2004]. Due to their large

quantities of uses, antimicrobial chemicals are continuously introduced to the aquatic

environment via treated, untreated sewage, sludge, agricultural waste and runoffs. In this

context, fluoroquinolones (FQs) are probably among the most important class of

synthetic antibacterial agents as these are most commonly used in human and veterinary

medicines. In fact most of these antibacterial agents are not fully metabolized in the body

[Watkinson et al. 2007], therefore entered the environment through wastewater effluents

[Kummerer et al. 2000]. A perusal of literature shows that not so many studies focusing

the biodegradability and fate of FQs in the environment have been reported [Pereira et al.

2007; Haque & Muneer 2007; Hektoen et al. 1995; Merengo et al. 1997]. However,

strong binding can be expected to delay degradation and may partly explain the apparent

recalcitrance of FQs [Heinz-Georg et al. 1997]. Several recent studies have reported the

environmental presence of FQs in many countries such as Switzerland, United States,

Australia and China [Ikehata et al. 2008]. The presence of broad spectrum antibiotics like

these in aquatic environment, even at low concentrations, may pose serious threats to the

ecosystem and human health by inducing proliferation of bacterial drug resistance [Golet

et al. 2002]. Studies on the oxidation of few FQs [Taicheng et al. 2010; Xander Van et al.

2011; Taicheng et al. 2010; Naik et al. 2009; Nanda et al. 1999] have been reported.

However in natural water reservoirs already containing various surfactants as well as

oxidants, the fate of these drugs is a new immerging aspect for researchers. This study

reports the absolute kinetics and effects of various surface active agents on the oxidative

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transformation of two of the FQs, ciprofloxacin (CIP) and norfloxacin (NOR) by oxidants

chloramine-T (CAT) and potassium permanganate. This may be explaining how CIP and

NOR get transformed in the presence of an oxidant (CAT)/KMnO4 and surfactants in

aqueous media. During the water chlorination process behaviors of some FQs have been

reported [Micheal et al. 2005]. Present investigation is based upon the influence of

anionic, cationic and nonionic surfactants on the transformation of CIP and NOR by

CAT/KMnO4. The CAT itself is used as an antiseptic drug [Das et al. 2001] and also

most commonly used for various water treatment processes, disinfectant, deodorant, etc.

[Norman et al. 1980].

SECTION 1.1

BASIC KINETIC TERMS

Kinetic investigations cover a wide range from various viewpoints. The chemist uses

kinetics as a tool to understand fundamental aspects of reaction pathways, a subject that

continues to evolve with ongoing research. The applied chemist uses this understanding

to devise new and/or better ways of achieving desired chemical reactions. This may

involve improving the yield of desired products or developing a better catalyst. The

chemical engineer uses kinetics for reactor design in chemical reaction or process

engineering. A legitimate objective of chemical kinetics is to enable us to predict

beforehand the rate at which given chemical substances react, and to control the rate in

some desirable fashion; alternatively, it is to enable us to “tailor” chemical reactions so as

to produce substances with desirable chemical characteristics in a controllable manner,

including choice of an appropriate catalyst [Ronald et al. 1999].

Chemical reactions occur in various phases such as the gas phase, in solution using

various solvents, at gas-solid, and other interfaces in the liquid and solid states. Many

techniques have been employed for studying the rates of these reaction types and even for

following fast reactions. Chemical kinetics deals with quantitative studies of the rates at

which chemical processes occur, the factors on which these rates depend and the

molecular acts involved in reaction processes. A description of a reaction in terms of its

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constituent molecular acts is known as the mechanism of the reaction. From

interpretations of macroscopic kinetic data in terms of molecular mechanisms, one can

gain insight into the nature of reacting systems, the processes by which chemical bonds

are made and broken, and the structure of the resultant product [Hill, 1977]. The present

investigation deals with the kinetic, catalytic and mechanistic aspects of the title reaction.

1.1.1: Laws of chemical kinetics

The rate of a chemical reaction is expressed as a change in concentration of some species

with time. Therefore, the dimensions of the rate must be those of concentration divided

by time. A reaction that can be written as

has a rate that can be expressed either in terms of the disappearance of A or the

appearance of B. Because the concentration of A is decreasing as A is consumed, the rate

is expressed as -d[A]/dt and the concentration of B is increasing with time, the rate is

expressed as +d[B]/dt. The mathematical equation relating concentrations and time is

called the rate equation or the rate law. If we consider a reaction that can be shown as:

the rate law will usually be represented in terms of a rate constant and function of the

concentrations of A and B, and it can usually be written in the form

where x and y are the exponents on the concentrations of A and B, respectively. In this

rate law, k is called the rate constant and the exponents x and y are called the order of the

reaction with respect to A and B, respectively.

The overall order of the reaction is the sum of the exponents x and y. Thus, we speak of a

second-order reaction, a third-order reaction, etc., when the sum of the exponents in the

rate law is 2, 3, etc., respectively. These exponents can usually be established by studying

the reaction using different initial concentrations of A and B. When this is done, it is

possible to determine if doubling the concentration of A doubles the rate of the reaction.

If it does, then the reaction must be first-order in A, and the value of x is 1. However, if

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doubling the concentration of A quadruples the rate, it is clear that [A] must have an

exponent of 2, and the reaction is second-order in A. One very important point to

remember is that there is no necessary correlation between the balancing coefficients in

the chemical equation and the exponents in the rate law. They may be the same, but one

can not assume that they will be same without studying the rate of the reaction. If a

reaction takes place in a series of steps, the study of the rate of the reaction gives

information about the slowest step of the reaction.

Suppose we have a chemical reaction that can be written as:

and let us also suppose that the reaction takes place in steps that can be written as:

The amount of C (known as an intermediate) that is present at any time limits, the rate of

the overall reaction. The sum of Eqs. (v) and (vi) gives the overall reaction that was

shown in Eq. (iv). The formation of C depends on the reaction of one molecule of A and

one of B. That process will likely have a rate that depends on [A]1 and [B]

1. Therefore,

even though the balanced overall equation involves two molecules of A, the slow step

involves only one molecule of A. As a result, formation of products follows a rate law

that is of the form Rate = k [A][B], and the reaction is second-order (first-order in A and

first-order in B). It should be apparent that we can write the rate law directly from the

balanced equation only if the reaction takes place in a single step. If the reaction takes

place in a series of steps, a rate study will give information about steps up to and

including the slowest step and the rate law will be determined by that step [House, 2007].

1.1.2: Theories of reaction rates

1.1.2.1: Collision Theory

Normally, the rate of a reaction is expressed in terms of a rate constant multiplied by a

function of concentrations of reactants. As a result, it is the rate constant that contains

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information related to the collision frequency, which determines the rate of a reaction in

the gas phase and the rate constant is given by the Arrhenius equation:

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Ea is related to the energy barrier over which the reactants must pass as products form.

For molecules that undergo collision, the exponential is related to the number of

molecular collisions that have the required energy to induce reaction. The pre-exponential

factor, A, is related to the frequency of collisions. Therefore, we can describe the reaction

rate as:

Rate = (Collision frequency) x (Fraction of collisions with at least the threshold energy)

or

where ZAB is the frequency of collisions between molecules of A and B and F is the

fraction of those collisions having sufficient energy to cause reaction [House, 2007].

The main features of collision theory are

• molecules are hard spheres, i.e. there are no inter molecular interactions,

• vibrational and rotational structures of reactants and products are ignored,

• the activated complex plays no part in the theory, and

• redistribution of energy on reaction is ignored [Wright, 2004].

The rate of reaction will be proportional to the number of collisions per unit time between

the reactant, but it has been observed that not every collision between the reactant

molecules results in a reaction. When we compare the calculated number of collisions per

second with the observed reaction rate, we find that only a small fraction of the total

number of collisions is effective. There can be following reasons why a collision may not

be effective.

(i) During the collisions some of the molecules having low energy (less than the energy

of activation) are not capable of undergoing transformation.

(ii) The molecules are not properly orientated or aligned during the collisions. The

importance of the proper orientation of molecules during the collision may be

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considered with the following example (Figure 1.01) where alignment (a) leads to

reaction while alignment (b) does not. In case (b), the molecule BB is not properly

oriented and one B atom is far away and not capable of forming bond with any atom

of A.

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Figure 1.01: Achievement of transition state after the molecular collision resulting in product

formation.

On the basis of above discussions we can express the rate as the product of three factors

as:

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Or

Although the collision theory of reaction rates is evidently satisfactory when applied to a

number of reactions, it fails conspicuously in many cases such as rapid chain reactions,

i.e. reactions involving complex molecules etc. [Upadhyay, 2006].

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1.1.2.2: Transition State Theory or Activated Complex Theory

The transition state theory (also known as absolute reaction rate theory) was developed

by Erying and Polanyi (1935) [King, 1983]. According to this theory, the reactant

molecules are first transformed into intermediate transition state (also known as activated

complex). The activated complex is formed by loose association or bonding of reactant

molecules or by redistribution of energy.

Assumptions:

Transition state theory (TST) is based on these three postulates:

1. In passing from the initial state to final state over the potential energy surface, the

reacting system must travels a region of the reaction path, called the transition

state, whose potential energy is the highest energy on the path.

2. The chemical species in the transition state is in equilibrium with the reactant

state.

3. The rate of reaction is equal to the product of the concentration of transition state

species formed from the reactant state and the frequency with which this species

passes on to the product state [Kenneth, 1990].

TST assumes that all supermolecules that cross the critical dividing surface from the

reactant side become products. This is reasonable, since once a supermolecule crosses the

critical surface it is a downhill journey to products. A second assumption of TST is that

during the reaction, the Boltzmann distribution of energy is maintained for the reactant

molecules. This assumption was also used in the hard-sphere collision theory also

[Levine, 2009].

The activated complex is unstable and breaks into the products at a definite rate as

follows:

Transition state theory describes the changes of geometrical configuration which occur

when suitably activated molecules, having the required critical energy, react. It gives a

detailed account of the absolute rate of reaction. The activated complex theory begins by

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postulating an activated complex for each elementary reaction, the high-energy ground-

state species formed from the encounter of reactant molecules. An elementary

bimolecular reaction:

can be viewed as the formation of the activated complex (AB) and its eventual decay to

form products:

where A, B, and (AB)# are in local equilibrium with one another, and K

# is a kind of

equilibrium constant. Decay of the activated complex to form products is simply related

to the vibrational frequency of the species imparted by thermal energy:

where kB is Boltzmann's constant and h is Planck's constant. This is a useful formulation,

since intrinsically chemical aspects of the reaction are contained in the value of K#

[Wright, 2004].

-5

0

5

10

∆G#

∆G#

∆G#

Fre

e en

ergy/

kca

l m

ol-

1

Reaction coordinate

-5

0

5

10

∆G#

∆G#

∆G#

Fre

e en

erg

y/

kca

l m

ol-

1

Reaction coordinate

Figure 1.02: Free energy versus reaction coordinate profile.

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1.1.3: Oxidation and reduction

In simple terms:

• Oxidation is the loss of electrons or an increase in oxidation state by a molecule,

atom, or ion.

• Reduction is the gain of electrons or a decrease in oxidation state by a molecule,

atom, or ion.

Oxidation is better defined as an increase in oxidation state, and reduction as a decrease

in oxidation state. Redox (portmanteau for reduction-oxidation) reactions describe all

chemical reactions in which atoms have their oxidation state changed. This can be either

a simple redox process, such as the oxidation of carbon to yield carbon dioxide (CO2) or

the reduction of carbon by hydrogen to yield methane (CH4).

Ross Stewart [Steward, 1964] has proposed the following general definition. “An

oxidation and a reduction if the products differ from the reactants in a way that cannot be

accounted for simply by an exchange of protons, hydroxide ions, halide ions, ammonium

ions, alkali metal ions, amide ions etc. or is equivalent by an exchange of water,

hydrogen, halide, ammonia etc.”

Present investigation is based upon the kinetic study of oxidation reduction reactions

between commonly used oxidants during waste water treatment and two of the most

frequantly used Fluoroquinolone drugs, i.e. Ciprofloxacin and Norfloxacin. Since the

present atmosphere is oxidative in nature, mostly drug transformations under the natural

environment are most likely to follow oxidation path. One of the metal oxide facilitated

oxidation can be represented as [Zhang & Huang, 2005]:

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1.1.4: Kinetics of catalysed reaction

Since past few decades, the kinetics of micelle catalyzed reactions has been an attractive

field for the researchers. In the year 1959, it was reported that the anionic surfactants

show inhibition effects whereas the cationic surfactants exhibit rate enhancements effects

on the reaction rate [Duynstee et al. 1959]. This discovery marked the beginning of the

study of micellar-catalyzed reactions but for the first order reactions, a complete kinetic

treatment was given by Menger and Portnoy in 1967 [Menger & Portnoy, 1967]. Later

micelles were treated as enzyme-like particles and micellar catalysis was initially

sometimes used as a mimic for enzyme-catalyzed reactions [Romsted, 1984]. As the

effect of micelles on higher-order reactions is more complex, and led to the development

of the pseudo-phase model [Berezin et al. 1973; Martinek et al.1977] and various forms

of pseudo-phase model,[Romsted, 1977]. For a first-order reaction, the main kinetic

effect of micelles is due to the formation the specific local (micellar) reaction

environment, comparable to a difference in solvation. Particularly, the polarity differs

from that of the bulk solution. The substrate may experience different types of

microenvironments depending on its exact location within the micelle [Ta¸scio˘glu, 1996;

Sepulveda, 1986]. Micellar effects on reaction rate constants have been compared, for

instance, with rate constants in concentrated electrolyte solutions, the latter mimicking

the Stern layer [Buurma et al. 1999]. For bimolecular reactions following the second-

order path, differences in salvation in the aqueous and micellar phases, plays important

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role. Secondly the concentrations of both the reactants in the micellar phase are also quite

contributing. Many organic substrates having an affinity for the micellar phase over the

aqueous phase, concentrate in the micelles, which make up only a relatively small part of

the total volume of the system. The result is a general rate enhancing effect for

bimolecular reactions. The effect diminishes at higher surfactant concentrations because

both reactants are diluted over increasingly more micelles. Other possible effects include

a partial alignment of the reactants, which can either facilitate or complicate the reaction,

and result in a shift in regio- or stereoselectivity [Ta¸scio˘glu, 1996] Different models

have been developed to quantify the effects that micelles have on reaction kinetics. The

most intuitive and easily applied model is the pseudophase model. In the pseudophase

approach, the micellar solution consists of an aqueous phase (w) and a micellar (pseudo-

)phase (m). One or more reactants partition over these two phases, with partition

coefficients PX = [X]m/[X]w. In each phase, the reaction proceeds with a particular rate,

characterized by the corresponding rate constants, km and kw. A complication for second-

order reactions is that either a concentration term enters the micellar rate constant, or in

order to eliminate the concentration term, the micellar reaction volume has to be

estimated. In the latter case, the concentration effect is not incorporated into the micellar

rate constant, but described explicitly by the model. This approach allows direct

comparison between the rate constants in the aqueous and micellar phase. The observed

second-order rate constant is expressed as follows:

C is the concentration and V the molar volume of micellized surfactant. km and kw are rate

constants in micellar and aqueous phases. PA and PB are the partition coefficients

[Yatsimirski et al. 1971; Martinek et al. 1975].

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SECTION 1.2

MICELLE CATALYSIS

Micelle catalysis is the acceleration of a chemical reaction in solution by the addition of a

surfactant at a concentration higher than its critical micelle concentration so that the

reaction can proceed in the environment of surfactant aggregates (micelles). Micelle

formation can also lead to a decreased reaction rate. The biologically important

aggregates i.e. micelles are capable of forming a new reaction medium, concentrating the

reagents at the (lipid/water) interface, the stern layer [Swain, 1950]. A micelle-bound

substrate will experience a reaction environment different from bulk water, leading to a

kinetic medium effect. Hence, micelles are able to catalyze or inhibit organic reactions. A

micelle or a micellar aggregate constitutes an inhomogeneous microreaction

environment, which is highly dynamic, in the sense that its constituents (surfactant

monomers) are in rapid equilibrium with surfactant monomers in aqueous phase. Thus, in

a strict sense, a micelle or a micellar aggregate is not a separate phase like aqueous phase

although it does provide microreaction medium, which is called pseudophase, in which

micellar-mediated reactions occur. The kinetic data are treated using the pseudophase

model, regarding the micellar solution as consisting of two separate phases [Menger &

Portnoy, 1967].

1.2.1: Behavior of surfactants

The name stands for “surface active agents” pointing out that the main feature is the

ability to absorb at the interface between two immiscible phases and lower the interfacial

tension between them. Surfactant molecules are constituted by two parts, connected by a

rigid linker, each of them showing affinity for a different medium. Common amphiphiles

bear a hydrophilic “head”, usually a polar functional group and a lipophilic “tail”, alkylic

and either linear or branched. The “head” gives the criterion on which they are classified,

therefore we have anionic, cationic, non-ionic and zwitterionic surfactants and the choice

depends tightly on the application and the function they have to carry out. Rate of a

micellar-mediated reaction may be influenced by one

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or more than one of the following factors: (1) micellar medium effect, (2) micellar effect

on keeping reactant molecules apart from each other, that is, proximity effect, (3)

electrostatic effect, (4) hydrophobic effect, (5) ionic strength effect of ionic micellar

surface, (6) ion exchange between two counterions of ionic micelles, and (7) the effect of

ion-pair formation between counterions or ionic head groups of ionic micelles and ionic

reactants. For present study we undertook three surfactants: CTAB (Cationic), SDS

(anionic) and TX-100(non ionic).

Cetyltrimethylammonium bromide (CTAB) is one of the components of the topical

antiseptic cetrimide. The addition of CTAB to biphasic hydroformylation catalysts has

been suggested as a means to improve reaction activity while retaining selectivity to

linear aldehydes [Fell & Papadogianakis, 1991]. The addition of cationic surfactant,

CTAB, enhanced the oxidation of D-mannose by cerium (IV) [Kabir-ud-Din et al. 2008],

oxidation of aminoalcohols [Pandey & Upadhyay, 2005], hydrolysis of methyl violet

[Singh et al. 2011] and D-fructose oxidation by permagnate [Andrabi et al. 2007]. Li,

Jian-zhang et al. showed that hydrolysis of p-nitrophenyl picolinate increases with pH of

the buffered CTAB micellar solution [Jian-zhang et al. 2011] and Zoya Zaheer and

Rafiuddin reported inhibitory effects of CTAB in the permanganate oxidation of

phenylalanine [Zaheer & Rafiuddin 2009].

Sodium dodecyl sulfate (SDS or NaDS) also named as sodium laurilsulfate or sodium

lauryl sulfate (SLS), is an organic compound with anionic head group. It is used in many

cleaning and hygiene products. In SDS, the surfactant polar head is composed by the

sulfate group with one negative charge and by the positive sodium counterion.

Counterions are partially bound to the heads, partially dispersed in the diffuse layer. Ma

Loreto Luna et al. found that reaction between N,N-dimethyl-p-phenylenediamine (DPD)

and N,N-dimethylaniline (DA) to form Bindschedler's Green leuco base, oxidized by

hydrogen peroxide was found to be accelerated by SDS [Lunar et al. 1992]. Some

examples of micellar catalysis include acid-catalyzed enolization of acetone in the

presence of bromine [Maruthamuthu & Lakshmikanthan, 1981], Ni2+

aq/pyridine-2-azo-

p-dimethylaniline complexation reaction [Ywm et al. 1994] , paracetamol oxidation by

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chromium(VI) [Ilyas et al. 2007], redox reaction of ascorbic acid-vanadium(V) system

[Malik et al. 2008].

Figure 1.03: surfactants belonging to different classes.

Triton X-100 is a nonionic surfactant which has a hydrophilic polyethylene oxide group

(on average it has 9.5 ethylene oxide units) and a hydrocarbon lipophilic or hydrophobic

group. The hydrocarbon group is a 4-(1,1,3,3-tetramethylbutyl)-phenyl group. Some of

the cited examples of miceller catalysis of TX-100 include reduction of methylene blue

(MB) by ammonia [Kundu et al. 2003], oxidation of aspartic acid by colloidal MnO2

[Akaram 2007], hexavalent chromium reduction [Basu & Saha 2010], aquation of Iron II

bipyridil complex ion in bimiceller system [Owoyomi et al. 2005] etc.

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1.2.2: Phenomenon of micellization

When surfactants are added to water, they preferentially adsorb at the surface replacing

the high-energy water molecules. The hydrophilic head groups immerse in water and the

hydrophobic tail groups align in air, as a result, the free energy of the system as a whole

is dramatically lowered.

Figure 1.04: Formation of self assembly of surfactants above CMC.

At some high concentrations, surfactants can self assemble to form aggregates in a bulk

solution. It has been observed that, depending on their structures and conditions (solvent,

concentration, temperature, etc), surfactants can form a variety of aggregation patterns

such as spherical, cylindrical, reverse micelles, vesicle, and lamella (Figure 1.04, 1.05 &

1.06). All of the self-assemblies are in dynamic equilibrium and surfactant molecules

constantly join and leave these aggregates on a timescale of microseconds. In aqueous

solutions, the tendency of self-assembling mainly originates from water/water

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intermolecular interactions being stronger than those between water/hydrophobic chain

(namely hydrophobic effect). The first-formed aggregates in water are generally spherical

micelles. The hydrophobic tails are directed towards the interior of the micelle and the

hydrophilic heads are orientated towards the solvent. Thus, exposure of the hydrophobic

parts to the surrounding water molecules is minimized, so is the free energy. The

properties at low concentrations in water are similar to those of simple electrolytes except

the surface tension. However, these properties (interfacial and bulk) all show a sharp

break at a particular concentration. This peculiar phenomenon indicates formation of self-

associated units - micelles. The concentration at which micelles start to form

(micellization) is called the critical micelle concentration (CMC). Each surfactant has a

characteristic CMC value at a given temperature. Above the CMC; the concentration of

surfactant unimers remains constant while the concentration and structure of micelles

vary with increased surfactant concentration. Above CMC monomers and micelle exist in

dynamic equilibrium [Fox, 1972]

At concentrations close to CMC, micelles are small and spherical, rarely spheroidal

[Fendler, 1975; Void & Vold, 1983]. As the surfactant concentration increases they

become larger, and after a certain concentration they convert into rod like micelles. The

presence of salt or organic additives can affect the conversion concentration depending

on the nature of the additives [Bunton et al. 2005]. Aggregates can also form in a polar

solvent. In such cases head groups of surfactant molecules locate inside to form a polar

core and hydrocarbon tails are directed towards the bulk solvent, to form the outside shell

of the micelle. These are called reversed (reverse) or inverted (inverse) micelles [Fendler

et al. 1972].

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Figure 1.05: Picture showing the difference between reverse micelle having polar core

and a normal micelle.

If there is any water in the medium, it will be entrapped in the core [Seoud et al. 1994].

This surfactant solubilized water is often referred as a water pool and reverse micelles are

sometimes called microemulsions. They are able to solubilize relatively large amount of

water in their cores and this enables them to solubilize water soluble substances in

nonpolar solvents. They are also reported to form near- and supercritical fluids [Furusaki

& Kishi, 1992].�

Surfactants of various structures have been synthesized and extensively studied like

anionic, cationic and non-ionic surfactants. When the skeleton feature is considered,

surfactants can also be classified as the following types: single-tailed, bolaform, gemini

(or dimeric) and oligomeric, and polymeric. The catalytic potential of micellar aggregates

has received special attention. Menger and Portnoy in 1967 defined micelles as enzyme-

like particles, not surprisingly, as micellar catalysis was initially sometimes used as a

mimic for enzyme-catalyzed reactions [Romsted, 1984]. The effect of micelles on higher-

order reactions is more complex, and led to the development of the pseudo-phase model

[Berezin et al. 1973; Martinek et al. 1977] and its variants. Different models have been

developed to quantify the effects that micelles have on reaction kinetics. Most accurate

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models for micelle structure are presented by Hartley, Menger and Portnoy, Berezin, Dill

Flory, Green and Fromherz. These models are discussed in later chapters.

Table 1.1: Factors governing micelle formation.

Surfactant Aggregate

Single chain, Large HG Spherical/ellipsoidal

Single chain, Small HG Cylindrical/rod like

Double, Flex chains, Large head groups Vesicle, Flexible bilayers

Double Rigid bulky chains, Small HG Reversed/inverted micelle

Figure 1.06: Formation of lamellar micelle.

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1.2.3: Role of micelle catalysis in the present work

Present investigation is an attempt to explore the role of different kinds of surfactants on

the oxidative transformation of two fluoroquinolone family drugs, i.e. ciprofloxacin and

norfloxacin. As surfactants are used in wide quantities in our day to day life, their

presence and accumulation in the environment is quite obvious. Therefore micelle media

has been selected to study the oxidation of drugs by commonly used chlorinating agent

chloramines-T, during waste water treatment.

SECTION 1.3

FLUOROQUINOLONES AS SUBSTRATE

Fluoroquinoles are drug class of synthetic broad spectrum antibiotics. Fluoroquinolones

(FQ), as widely used antibacterial agents in clinic, are the second-generation derivatives

of quinolones, obtained by addition of a fluorine atom in position 6 and a piperazine

substituent in position 7 [Suh & Lorber,1995]. Numerous derivatives of FQ family drugs

have been synthesized in an effort to enhance the antimicrobial spectrum and

pharmacological properties as listed in Table 1. Diversities in structures of

fluoroquinolone family are mainly within R1 and R7 (Figure 1.07). Conjugations

between groups are limited, and the groups have relatively independent properties.

Presence of both the reducible groups on C3 and C4 and the double bond between C2 and

C3 makes FQ interesting in analytical view point.

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Figure 1.07: The matrix of all fluoroquinolone antibacterials.

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In Ciprofloxacin at position R1 cyclopropyl group appears to be optimum for activity.

Amino group enhances absorption e.g Sparfloxacin. At position 6 addition of a fluorine

atom resulted in a dramatic increase in anti-bacterial potency. The addition of piprazinyl

ring at position 7 was found to extend the spectrum of activity leading to broad-spectrum

FQs.

Table 1.1: Structure detail of some FQs.

Name of FQ R1 R7 R5

Norfloxacin -C2H5

H

Ciprofloxacin

H

Ofloxacin

H

Lomefloxacin -C2H5

F

Sparfloxacin

F

The fluoroquinolones are small molecules with weights between 300 and 500 Da. Many

of these compounds are Zwitterions and exhibit different solubility characteristics with

changes in pH. The frequent usage of these antibacterial agents has led to their ubiquitous

presence in the environment. The potential toxicities of these antibacterial micro-

contaminants in the environment necessitate further investigation on their transformation

in order to properly evaluate their risks. Although FQs have relatively low log Kow

values

(e.g.0.28 and 1.03 for ciprofloxacin and norfloxacin respectively), strong adsorption of

these compounds to soils and sediments has been reported [Vasudevan et al. 2009]. The

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favorable interactions of antibacterial agents with soils and sediment point to the

potentially significant role in the environmental fate of these compounds. Currently, little

information is available on the transformation and fate of antibacterial agents at the

mineral-water interfaces and a systematic investigation is highly needed. As FQs are

ubiquitous in nature there fate and degradation is need to be analyzed further in order to

access their environmental impact.

1.3.1: Fluoroquinolones as microcontaminants in aquatic environment

In most countries antibiotics including the sub-groups of penicillins, cephalosporins and,

as a marginal fraction, carbapenems, make up the largest share of human-use antibiotics.

They account for approximately 50–70% of total antibiotic use in human medicine. In

most countries sulfonamides, macrolides, and fluoroquinolones follow in order of

decreasing use [Goossens et al. 2005].

Image 1. Distribution of pharmaceuticals used in human medicine in the environment.

Wise [Wise, 2002] estimated antibiotic consumption worldwide to lie between 100,000

and 200,000 tones per year. Ingested antibiotics reach enter into the environment through

individual human activity and as residues from manufacturing, veterinary use, hospital

and community use (Image 1).

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1.3.1.1: FQ in Hospital waste water

Hospital run-offs are one of the most important sources of anti-infectives in the aquatic

environment [Gómez et al. 2006]. Watkinson et al. also showed that the presence of

antibiotics in hospital effluent depended on the volume of antibiotic prescription

[Watkinson et al. 2009]. The amoxicillin concentration measured in the wastewater of a

large German hospital was between 28 and 82.7 'g L–1

[Kümmerer, 2001]. Färber

[Färber, 2002; Hartmann et al. 1998] demonstrated the presence of penicillins,

macrolides, sulfonamides, fluoroquinolones, and tetracyclines in concentrations of up to

15 'g L–1

(sum of the compounds detected) in a hospital wastewater and in

concentrations of up to 1 'g L–1

in the influent of the sewage treatment plant to which the

hospital wastewater was discharged. Hartmann et al. found ciprofloxacin in hospital

effluent in concentrations between 3 and 89 'g L–1

and ciprofloxacin in native hospital

wastewater in the range of 3 to 87 'g/L [Hartmann et al. 1998]. In Michigan, USA

ofloxacin was found at concentrations of 204 and 100ng/l in secondary and final effluents

of a wastewater treatment plant respectively [Haruhiko et al. 2005]. Jarnheimer et al.

found low levels of ciprofloxacin and ofloxacin in hospital waste water but high

concentrations in sediment [Jarnheimer et al. 2004]. In a study in Hanoi, Vietnam the

concentrations of the FQs, ciprofloxacin (CIP) and norfloxacin (NOR) in six hospital

wastewaters ranged from 1.1 to 44 and from 0.9 to 17 ng l-1

, respectively. Total FQ loads

to the city sewage system varied from 0.3 to 14 g l-1

[Duong et al. 2008]. Hiroyuki

Takasu et al. found FQs concentrations were greater Thailand (avg. 5130, max 46100 ng

L-1

) than in Vietnam (avg. 235, max 1130 ng L-1

) [Hiroyuki et al. 2011]. However, the

concentration of FQs in hospital effluents may depend upon community, prevailing

season and few area-wise factors.

1.3.1.2: FQ in ground, surface and waste water

A variety of antibiotics have been detected in surface water. In an important study FQs

are found to sorbed in sediments [Hektoen et al. 1995]. In a study on surface waters from

Hangzhou, China four typical fluoroquinolone antibiotics (ofloxacin, norfloxacin,

ciprofloxacin, and ernofloxacin)) were found in the wastewater and surface water. The

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residual contents of the four typical fluoroquinolone antibiotics in influent, effluent and

surface water samples were 108-1405, 54-429, and 7.0-51.6 ng/L, respectively [Tong et

al. 2011]. The concentrations of some widely used pharmaceuticals, namely

fluoroquinolones (ciprofloxacin , norfloxacin and ofloxacin ) were determined in urban

sewage sludge utilized for making compost with the highest pharmaceutical

concentration of ciprofloxacin in sewage sludge, 426 'g/kg was detected [Lillenberg et

al. 2010]. A study on concentration of four fluoroquinolones in tap water in Guangzhou

and Macao found that antibiotic concentration in tap water tends to reduce at the

beginning of rainy season [Yiruhan et al. 2010]. Two FQs, ciprofloxacin and norfloxacin,

were found in primary and tertiary waste-water effluents at concentrations between 249

and 405 ng/L and from 45 to 120 ng/L, respectively [Golet et al. 2001]. Study by Tamtam

Fabien et.al showed large inputs of norfloxacin, ofloxacin, trimethoprim and

sulfamethoxazole from wastewater treatment plants, with concentration of norfloxacin

and sulfamethoxazole reaching 155 ng L− 1 in the river downstream from a wastewater

outlet [Fatima Tamtam, 2008]. Among 31 antibiotics from the groups of tetracyclines,

macrolides, sulfonamides and fluoroquinolones were reported in concentrations of up to

1.7 and 1.9 'g/l [Kolpin et al. 2002]. In a recent study, fluoroquinolone levels up to 0.12

'g L-1

were detected in various streams throughout the United States [Kolpin et al. 2002].

1.3.2: Oxidation of Fluoroquinolones

The presence of FQs in the aquatic environment is a matter of great concern. Effective

removal of FQs is important to minimize possible antibiotic resistance development and

other health risks. Research is ongoing for effective removal or transformation of FQs

into less hazards species. Transformation by oxidation of fluoroquinone is an effective

process for the purpose. Wang(2010) in his study of oxidation of FQs by ClO2

investigated that FQs with piperazine groups are more reactive to ClO2 while quinolone

ring remain mostly intact [Wang et al. 2010]. In a study seven FQs were examined for

adsorptive and oxidative interactions with MnO2 under environmental conditions and

exhibited reactivity in the order of ciprofloxacin ( enrofloxacin ( norfloxacin ( ofloxacin

> lomefloxacin > pipemidic acid >> flumequin. This study investigated that piperazine

moiety is the predominant adsorptive and oxidative reaction site [Zhang et al. 2005].

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Elena Guinea et al. degraded enrofloxacin by electrochemical advanced oxidation

processes based on hydrogen peroxide electrogeneration and almost total

decontamination of enrofloxacin solutions was achieved [Elena et al. 2010]. Study on the

photocatalytic transformation of fluoroquinolone antibacterial agents (ciprofloxacin,

enrofloxacin, norfloxacin, and flumequine) in aqueous titanium dioxide (TiO2)

suspensions irradiated with UV/Vis light showed oxidation occurs by electron transfer

with TiO2 resulting in stable organic products [Paul et al. 2007]. The cyclic voltammetry

and electrogenerated chemiluminescent (ECL) reactions of a series of quinolone and

fluoroquinolone antibiotics were investigated in a flow injection analysis (FIA) system.

The study investigated that fluoroquinolone antibiotics were found to participate as a

coreactant in an oxidative-reductive ECL mechanism with tris(2,2)-bipyridyl)

ruthenium(II) (Ru(bpy)32+

) as the luminescent reagent [Matthew et al. 2008]. Kiran et al.

showed that oxidative transformation by permanganate is result of dealkylation at the

piperazine moiety of ciprofloxacin [Thabaj et al. 2007]. A novel study on oxidation in

ozone environment of CIP investigated that pH 10 is optimum for process [Witte et al.

2009]. Voltammetric determination of ciprofloxacin based on the enhancement effect of

CTAB at carbon paste electrode showed that oxidation peak increases remarkably in

presence of even low concentrations of CTAB [Hongchao & Chunya]. Nanda et al.

studied kinetic and mechanistic studies on the oxidation of norfloxacin by cloramine-B

and N-Chlorobenzotriazole in acidic medium [Nanda et al. 1999].

1.3.3: Environmental impact of Fluoroquinolones

The possible effects of FQs on the environment are of particular interest because of their

properties as bio-active chemicals. Due to complex chemical structure, their behavior in

the environment is not always easy to assess. There is major concern that antibiotics

emitted into the aquatic environment can reach drinking water, or that they may affect

non-target organisms in the environment. In contrast to the properties and effects desired

from their therapeutic application, these same properties are often disadvantageous for

target and non-target organisms in the environment. Antibiotics are by definition active

against bacteria. As a consequence, bacteria have developed mechanisms for resisting

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them. Fluoroquinolone resistance was first reported in the late 1980s, but since 1990, the

incidence of resistance has increased. For example, in the Netherlands, resistance went

from 11% in 1990, to 30% in 1991 [Piddock, 1995]. Bacterial resistance promoted by the

input of antibiotics into the environment is also under discussion [Kümmerer, 2004]. For

years it was believed that giving low-dose antibiotics via feed to promote growth in cows,

swine, chickens and the use of antibiotics in fish farming had no negative consequences.

Today, there is overwhelming evidence that non-therapeutic use of antibiotics contributes

to antibiotic resistance, even if we do not understand all the mechanisms in the genetic

transmission chain. The transfer, as well as the new combination of resistance genes, will

preferably happen in compartments with high bacterial density. Some microbiologists

believe that if antibiotic concentrations are higher than the minimum inhibitory

concentrations (MICs) of a species of pathogenic bacteria, a selective pressure would be

exerted and, as a result, antibiotic resistance would be selectively promoted [Segura et al.

2005]. The scope of human exposure to pharmaceuticals and personal care products from

the environment is a complex function of many factors. These factors include the

concentrations, types, and distribution of pharmaceuticals in the environment; the

pharmacokinetics of each drug; the structural transformation of the chemical compounds

either through metabolism or natural degradation processes; and the potential

bioaccumulation of the drugs [Daughton, 2008]. Robinson, et al. studied toxicity of

different FQs to aquatic environment. The study finds that concentrations of

ciprofloxacin, levofloxacin, and ofloxacin treatments in fish dry weights were

significantly higher than in control fish. The hazard of adverse effects in the tested

organisms in the environment was quantified by using hazard quotients. An estimated

environmental concentration of 1 'g/L was harmful [Robinson et al. 2005]. Study by

Perreten et al. claimed that resistance is transferred to human thorough food from animal

products [Perreten et al. 1997]. Biodegradation is one of the the most crucial process of

elimination of pharmaceuticals from waste water but paracetamol (acetaminophen)

yields products that are 58 and 25 times more toxic than itself following biodegradation

[Bedner & MacCrehan, 2006]. Fluoroquinolone resistance has been reported in S. typhi in

developed countries [Scuderi et al. 2000] In Austria, 50% of Campylobacter isolates from

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poultry were resistant to ciprofloxacin [Hein et al. 2003].An Indian context study was

done in Ujjain (MP) by Vishal Diwan et al. found that There was a positive correlation

between the quantity of antibiotics prescribed in the hospital and antibiotic residue levels

in the hospital wastewater. Wastewater samples collected in the afternoon contained both

a higher number and higher levels of antibiotics compared to samples collected in the

morning hours. No amikacin was found in the wastewater, but E.coli isolates from all

wastewater samples were resistant to amikacin. Although ciprofloxacin was the most

prevalent antibiotic detected in the wastewater, E.coli was not resistant to it. Vishal

Diwan et al. isolated quinolone resistance genes in Escherichia coli isolates from hospital

wastewater from central India [Diwan et al. 2012]. In a remarkable study Dae-Wi Kim et

al. reported that Microbacterium sp. Strain Isolated from a Wastewater Treatment Plant

defluorinated and hydroxylated FQs and suggested that the results suggest that some

bacteria may degrade fluoroquinolones in wastewater to metabolites with less

antibacterial activity that could be subject to further degradation by other microorganisms

[Kim et al. 2012]. More in-depth studies are needed to assess the correlation between the

quantity of antibiotics prescribed and both the levels of antibiotic residues in hospital

effluent and the effects on the development of bacterial resistance in the environment.

SECTION 1.4

CHLORAMINE-T AND POTASSIUM PERMANGANATE AS

OXIDANTS

Chloramine-T

Aromatic N-halosulfonamides, a group of mild oxidizing agents, have been extensively

used for the oxidation of a variety of organic compounds, including aldehydes, amines,

and amino acids. The mechanistic aspects of many of its reactions have been well

documented [Singh et al. 2011, 2009; Vinod et al. 2009]. The diverse nature of the

chemistry of N-metello Narylhalosulfonamides (organic haloamines) is attributed to their

ability to act as sources of halonium cations, hypohalite species, and N-anions, which act

as both bases and nucleophiles. These oxidants contain strongly polarized n-linked

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halogens which are in +1 state. They undergo two electron changes to form prominent

member of this class of oxidants that is N-chloro-p-toluene sulfonamide (chloramines-T,

abbreviated as CAT or RNClNa) [Prasantha et al. 2012].

Chloramine-T acts as an oxidizing agent in both acidic and alkaline media. The redox

potential of chloramine–T/sulfonamide system is pH dependent (1.139, 0.778 and 0.614

V at pH 0.65, 7.0 and 9.7, respectively) and decreasing with increase in pH of the

medium. The existence of similar equilibria in acid and alkaline solutions of CAT has

been reported by many workers. Aqueous solution of chloramine-T (TsNClNa) behaves

as a strong electrolyte [Bishop & Jennings, 1958] and depending on the pH, it furnishes

different types of reactive species. The possible oxidizing species in acidified CAT

solutions are the conjugate free acid (TsNHCl), dichloramine-T (TsNCl2), hypochlorous

acid (HOCl) and possibly H2OCl+, and in alkaline solutions TsNHCl, HOCl, TsNCl- and

OCl- [Vinod et al. 2009].

Potassium permanganate

It is a salt consisting of K+ and MnO4

− ions. Formerly known as permanganate of potash

or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely

purple solutions. Potassium permanganate is highly reactive under conditions found in

the water industry. It oxidizes a wide variety of inorganic and organic substances.

Potassium permanganate (Mn7+

) is reduced to manganese dioxide (MnO2) (Mn4+

) which

precipitates out of solution [Hazen and Sawyer, 1992]. Nafisur Rahman determine

Labetalol hydrochloride using potassium permanganate as Oxidant [Rahman et al. 2011].

Other cited examples include determination of Piroxicam and Tenoxicam [Amin et al.

2010] and Riboflavin [Li et al. 1997].

The kinetics of the oxidative degradation of dipeptide glycyl–glycine (Gly-Gly) by water-

soluble colloidal MnO2 in acidic medium has been studied [Akram et al. 2011]. Perez-

Benito et al. [Benito & Arias, 1992] has reported for the first time a method for the

preparation of water-soluble colloidal MnO2. They studied the oxidation of organic acids

[Benito et al. 2011] and Mn(II) [Benito, 2003] by colloidal MnO2. The reduction of

Mn(IV) oxide by organic compounds has also been studied in micellar media by Tuncay

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et al. [Tuncay et al. 1999] and Kabir-ud-Din et al. [Kabir-ud-Din et al. 2004; 2005J. Colloid

Interface Sci..; 2005

Colloid Polym. Sci.; Akram et al. 2007; Altaf et al. 2009]. Reactions between

colloidal MnO2 and organic reductants, which play a key role in the redox cycling of

manganese in the environment, can be accelerated, or inhibited, by photoxidation [Ulrich

& Stone, 1989; Xyla et al. 1992]. The kinetics of phenylalanine oxidation by

permanganate has been investigated in absence and presence of CTAB using

conventional spectrophotometric technique [Andres et al. 1988]. Zahoor Andrabi et al.

postulated involvement of manganese (IV) in the oxidation of D-fructose by

permanganate in cationic micelles of CTAB. According to their investigation, redox

reaction proceeds through the formation of water soluble colloidal MnO2 as an

intermediate in less acidic medium [Andrabi et al. 2007]. The kinetics and degradation

pathways of oxidation of ciprofloxacin by permanganate in alkaline medium at constant

ionic strength of 0.04 mol-3

has been studied which reveal that the piperazine moiety of

ciprofloxacin is the predominant oxidative site to KMnO4 [Thabaj et al. 2007]. The study

done by Zhang et al. demonstrated that phenolic, FQ and aromatic N-oxide antibacterials

are highly susceptible to oxidative transformation by Mn-oxides under environmentally

relevant conditions. New results in this and other studies show that tetracycline (TC)

antibiotics are also highly susceptible to oxidation by MnO2 [Zhang et al. 2008].