Water, water: Aqueous perturbations

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  • Published: Jan 15, 2013
  • Author: David Bradley
  • Channels: Chemometrics & Informatics
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Aqueous curve resolution

Aquaphotomics, a new discipline, together with multivariate curve resolution-alternating least squares have being used to characterise the hydrogen bond perturbations in aqueous systems.

Aquaphotomics, a new discipline, together with multivariate curve resolution-alternating least squares have being used to characterise the hydrogen bond perturbations in aqueous systems.

Aoife Gowen of University College Dublin, Ireland (funded by the EU Marie Curie postdoctoral fellowship scheme), Jose Amigo of the University of Copenhagen, Denmark (funded by the Japanese Society for the Promotion of Science) and Roumiana Tsenkova of Kobe University, Japan, explain how aquaphotomics, a new discipline in science, provides researchers with a framework for the understanding of changes that occur in the structure of water when it is exposed to different perturbations, such as changes in temperature or the addition of solutes. The discipline uses near infrared spectroscopy (NIRS) as its investigative tool of choice, the team adds.

A primary aim of aquaphotomics is to reveal bands in the spectra that emerge through perturbations, the absorbance patterns of which could be used as biomarkers in the study of water's behaviour and effects in biological systems. The team points out in the journal Analytica Chimica Acta this month how despite its omnipresence in biology, the fundamental nature of life's solvent, water, remains less than fully understood, particularly with regard to its structure arising from hydrogen bonding interactions. Moreover, there is no consensus on the nature of water's hydrogen bond networks. Are they mixtures of ever-changing clusters of hydrogen bonds or do they exist as a continuum? The answer to that question might emerge from aquaphotomics and could have implications for studies of protein folding, enzyme activity, cell membrane behaviour and many other aspects of biology particularly where hydrophobic and hydrophilic molecules and salts interact with water.

Spectroscopic studies

Various spectroscopic studies have lent support to both the multi-component mixture view of water and to the continuum model. One thing that scientists do agree on, however, is that hydrogen bonds are affected by temperature changes and by the presence of salts in the water.

NIRS has, of course, been used for many years in studies of the structure of water. Now, the international team has used multivariate curve resolution-alternating least squares (MCR-ALS) to investigate how perturbations - solutes and temperature - affect the NIR spectra of water in terms of hydrogen bonding. To this end, they recorded NIR spectra over the temperature range 28 to 45 Celsius with the addition of four solutions of different ionic strength and Lewis acidity (sodium, potassium, magnesium and aluminium chloride), at concentrations from 0.2 to 1 molar.

"We have found that three distinct components with varying temperature dependence are present in water perturbed by temperature. The salt solutions studied exhibited similar trends with respect to the temperature perturbation, while the peak locations of their MCR-ALS pure components varied according to the ionic strength of the salt used," the team reports.

Watery interpretation

The team adds that their chemometric approach was successful in interpreting the changing forms of water as temperature and salt concentration were changed. In particular, they have demonstrated the existence of three distinct components in water at biologically relevant temperatures of 30 to 45 Celsius. The salts reveal themselves to be, as predicted, makers or breakers of structure within water in the locale of the salt ions. "This research has significance for understanding the structure of water in idealised systems and is also a step forward towards understanding the aquaphotomics of real biological systems," the team concludes.

Related Links

Anal Chim Acta, 2013, 759, 8-20: "Characterisation of hydrogen bond perturbations in aqueous systems using aquaphotomics and multivariate curve resolution-alternating least squares"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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