To collect a series of IR spectra of sugarsolutions at different concentrations anautomated setup was chosen consistingof a 5mL syringe pump, an injection valve,and an ATR flow-through cell in theBRUKER 80v infrared spectrometer. Theinjected sample plug diffused into the H Ocarrier stream to create a sugarconcentration gradient by the time itreached the flow through cell.The abrupt change of the refractive indexof water from n=1.49 at 3160cm ton=1.11 at 3590cm [1] leads incombination with ATR crystals with arefractive index close to that of water (e.g.diamond, n=2.4) to a perceived shift of thewater band (anistropic dispersion). Tocounteract this effect, a Germanium ATR(n=4) was used.With this setup 200g/L solutions oftrehalose, maltose and sucrose wereanalyzed, approximately 400 spectraper run were aquired.

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Experimental Setup

In this work we investigate the impact of the concentration of sugars in aqueous solutions on the strong and bands of water throughGe-ATR-FTIR spectroscopy using an automated setup.2DCoS was used to study the changes in the andThe investigated sugars were trehalose, maltose and sucrose. Trehalose is of importance in biophysics due its role as cryoprotectant ininsects and bacteria.

ν ν

ν ν bands of water caused by changes of the sugar concentration.

1 3

1 3

Influence of sugars on theinfrared spectrum of water

Georg Ramer, Christoph Wagner, Bernhard LendlIntitute of Chemical Technologies and Analytics, Vienna University of TechnologyA-1060 Vienna, Austria http://cta.tuwien.ac.at/cavs

Due to long measurement times, all spectra were affected by anoticeable baseline drift. This could easily be corrected for bysubtracting the last collected spectrum of each series multiplied by acorrection factor from all the other spectra in the series. wascalculated via a method of least squares fit of the last spectrum to theother spectra in the peakless 1850-1950cm region.Only the spectra between the concentration maximum and the end ofeach run were used for the calculation of 2DCoS plots. The integral ofthe strong sugar bands between 1400-800cm (directly proportional tothe concentration of the sugar) was used as perturbation [2].

α α

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Typical Datasetand Data Treatment

b. after background correction

Sugars cause a shift of waterbands ( , , )

Strong, clear peaks in the asynchonous 2DCoS spectrum of the sugarsolutions show, that the changes in the spectra are not simply causedby the displacement of water. At least one additional process is atwork.

The sequence of these processes is dependent on the sugar used(see asynchronous plots). This is likely caused by the influence ofsugars on H-bond network of water [3].

ν ν ν1 2 3

Results

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Sucrose Maltose Trehalose

[1]°

[2][3] ù ;

Bertie, J. E. & Lan, Z. (1996), 'Infrared intensities of liquids XX: the intensity of the OH stretching band of liquid water revisited, and the best current values ofthe optical constants of H2O(l) at 25 C between 15,000 and 1 cm-1.', Appl. Spectrosc. 50, 1047-1057.

Noda, I. & Ozaki, Y. (2004), Two-dimensional Correlation Spectroscopy - Applications in Vibrational and OpticalSpectroscopy, John Wiley & Sons Ltd.Magaz , S. Migliardo, F. & Telling, M. (2008), 'Structural and dynamical properties of water in sugar mixtures', Food Chemistry 106(4), 1460 - 1466.

Ins t i t u te o f Chemica lTechnologies and Analytics

Trehalose

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Do you know what causes this difference?

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Financial support from Carinthian Tech Research AG and the COMET Competence Center Program of the Austrian Government is gratefully acknowledged.