Structure of Water and Its Dynamic Hydrogen Bond Network

Structure of Water and Its Dynamic Hydrogen Bond webIntroductionWater is essential to life as it is main constituent of cell in living organism. All biological macro pinchs be al close to placid in its structural stability and functioning in absence of irrigate.Water-Role in LifeWater is key compound for our existence on this planet imputable to its ubiquitous presence on the earth and in living organisms. It is involved in all chemical, biological and geological processes. Due to its anomalous behavior it named as matrix of life, solvent of life. It plays a vital mathematical function from molecule and cell to tissues and organisms.1-4 In past several decades urine has attr performanceed the most scientific attention among the liquid due to its anomalous properties. It shows peculiar properties such as negative volume of melting, density maximum at 277 K, high melting and boiling point, high dielectric constant, minimum in the isobaric heat capacity and isothermal compressibi lity at 308 K and 319 K, respectively, high mobility transport for H+ and OH ions. The density of most liquids increases as it give upze but in case of weewee it expands about 11% due to which ice floats on pee. It is the solvent of life and plays an important role in protein interactions and stabilization of protein twist. The work of Kauzmann gives the importance of urine in protein folding and its interactions with wet.5Structure of Liquid WaterThe anomalous behavior of urine is due to its unequaled ability to form a network of self associated molecules through heat content nonplusing. To hit the books the organize of urine and its dynamic hydrogen bond network stupendous number of studies has been carried out.1-12 Still many aspects of water are not fully understand at molecular level. Dyke and co-workers first reported existence of H- hold fast in vapor phase experimentally and measured the H-bond length as 2.98 in water dimer using molecular beam resonance techn ique which is higher than water in solid (for ice H-bond strength 2.74 ) and liquid (2.85 ) indicates the H-bond strength is wateryer in Gas phase.13From X-ray diffraction study of Bernal and Fowler and Morgan and Warren it is revealed that water is tetrahedrally coordinated through hydrogen bonds similar to the structure of ice I (Figure 1.1). 14-15The number of theories for the water structure has been proposed based on different techniques such as X-ray, neutron diffraction, dielectric relaxation and Raman spectroscopy. 16-22. These theories are generally classified into two poses as a) Continuum stick and b) Mixture model.Figure 1.1 Crystal structure of ice I at low pressureContinuum modelIn continuum model it is assumed that almost on the whole hydrogen bonded water molecules in a continuous network. Pople described the continuum model which is agreement with the observed alteration of X-ray radial distribution function with temperature. 23According to Pople In continuous bonded network of the water bond turn and deformations occurs instead of bond water. Recently, Rice and Sceats 24proposed Random net Model (RNM), which explains the continuum model and it is further developed by Henn and Kauzmann. 25This model is apply for determining the heat capacity contribution due to water-water interactions.b) Mixture modelIn mixture model water consists of differently H-bonded species with zero, one or both hydrogens are engaged in hydrogen bonding. Franks and Wen 26 gives the Flickering thumping model in which cooperative H-bonding is observed in water molecules. The co-operativity involves the hydrogen bond formation of one bonding site of water molecule contributes the delocalization button to the molecule, which is involved in hydrogen bonding with another water molecule. According to Franks and Wen the clusters of the water molecules (bulk water) and free monomer molecules (dense water) are in equilibrium with each other. Samoilov 27 proposed the in terstitial model in which water molecules are present in the cavities of ice lattice. Nemethy and Scheraga 28 used statistical thermodynamic model to calculate the Helmholtz free energy, internal energy and entropy as a function of temperature. Also the water hydrate model proposed by Pauling. 29 Now a days, divinatory techniques such as Monto Carlo, molecular dynamic simulation are used to study structural behavior of water. It provides most promising approach for the study of water at molecular level. Jorgensen 30 has developed transferable intermolecular potential functions (TIPS) suitable for use in liquid simulations for water. This potential has been used by Jorgensen and Madura 31 in MC simulation on liquid water to study the effect of temperature on vaporization, hydrogen bonding, density, isothermal compressibility and radial distribution functions. morsel of water models such as SPC, TIP3P, TIP4P, TIP5P are developed for the molecular simulation of large biomolecular sys tems. Figure 1.2 Frank-Wen Flickering Cluster Model of Liquid Water1.2 aquaphobic Hydration and Hydrophobic InteractionsThe weak non-covalent interactions like van der Waals forces, H-bonding, ion-dipole, hydrophobic interactions are responsible for change in the structure of water around the solute molecule. The hydrophobic interaction is the giving factor in the solvation of apolar or non-polar molecule. When a non-polar solute is dissolve in water there is large negative change in entropy. The disruption in the customary H-bonded structure is occurred and new H-bonded cage-like structure is formed around the solute molecule. So the structure formed is more ordered than the ordinary water. The term hydrophobic hydration is used when non-polar solute solvated by the cage of the solvent molecule around it. The short lived aggregates are formed around the solute molecule. The formation of polymeric aggregates strengthens the hydrogen bonding which gives negative contribution to H0. 10The hydrophobic interactions are important in a field of biochemistry for the purpose of conformational stability of biological macromolecules, protein folding, aggregation, ion transport, drug delivery as well as in industry. Usually hydrophobic hydration occurs in non-polar compounds such as alcohols, ethers, and amines. The tetraalkylammonium (TAA) salts with larger cation also shows the hydrophobic hydration effect. Kustov gives the effect of size of cation on the hydrophobic hydration. He study the proper(postnominal) heat of solution for the higher size cation TAA salts and observed that as the size of cation in salt increases the particular(prenominal) heat of solution and hydration increases upto the tetrapentylammonium salts and then decreases. As the specific heat of solution increases the hydrophobic hydration increases. For the hexyl and heptyltetraalkylammonium salts the C0p decreases so the hydrophobic hydration weakens. Thus hydrophobic hydration depends on the size of cation of TAA. The hydrophobic interaction is best explained by Goring et al. by studying the interaction of non-electrolytes in aqueous solutions by dilatometrically. They compared the apparent specific volume (2) relative to apparent specific volume at 0 C as function of temperature for non-electrolytes and showed that 1-butanol be cast offs like hydrophobic compound and acts as structure maker in aqueous solution while glycerol with polar groups disrupts the structure of water. The hydrophobic compound shows the slope d2/dT is less than the corresponding thermal expansions of pure compound while it greater for the hydrophilic compounds. Madan and Sharp explained that non-polar solutes have large capacity heat of hydration Cp while for polar solutes it is small negative. The large change in heat capacity at high temperature is due to hostile enthalpic interacions and not due to entropy change. The effect of salt on the hydrophobic hydration was carried out by Talukdar and Kundu and observed that hydrophobic cation induce more hydrophobic hydration in aqueous NaNO3 solution than in pure water. Rossky et al. with the help of computer simulation studied the hydration properties of the interfaces between the water and the hydrophobic surfaces for the active peptide melittin in its monomeric and dimeric form and cogitate that hydrophobic hydration is depends on the surface topography of biomolecule.1.3 Spectroscopic study of waterDue to its various anomalous properties and great importance in the several field water is the most studied compound. To study the structure of water, number of spectroscopic techniques such as IR, Raman, neutron diffraction, X-ray scattering, NMR spectroscopy etc. have been used distillery today. The spectroscopy and scattering studies provides the structural information of water at molecular level. Bernal and Fowler analyzed the X-ray diffraction of water and investigated water as distorted quartz-like. The hydrogen bond net work in water is found to be tetrahedral in nature and each water molecule can be bound with another intravenous feeding water molecules i.e. each water molecule is double proton donor and double proton acceptor. While recently, Wernet et al. studied the structure of water by soft X-ray denseness spectroscopy and X-ray Raman scattering and investigate that hydrogen bond network in the water consists of only two strong hydrogen bonds and one act as proton door and another as proton acceptor. This controversial result of structure of water from earlier study makes the scientist to study the water structure more interesting. In this context, number of scientists have been studied the water structure by X-ray absorption spectroscopy.Infrared and Raman techniques are also the important sources of the information of hydrogen bonding in water. Above the absolute temperature all the atoms in the molecules are in continuously vibrating motion with respect to each other. Any molecule absorb s the radiation when frequence of a specific vibration is equal to frequency of the IR radiation directed on the molecule. Each atom has three degrees of freedom, corresponding to motions of the three Cartesian coordinate axes (x, y, z). Total no of coordinate values is 3N for a molecule containing N atoms. Thus, Water has 9 degrees of freedom with C2v symmetry. It shows the two stretching vibrations (symmetric and asymmetric), one bending vibration, three hindered rotations (librations), and three hindered translations. Earlier, number of research papers has been published on the study of the structure of water in solid, liquid as well as in vapor phase by IR and Raman technique. The fundamental IR frequencies for the H2O and heavy water is as shown in TableTable cardinal vibrations of liquid ordinary water and heavy waterVibration(s)liquid H2O (25 C)liquid D2O (25 C)liquid T2Ov, cm-1, M-1cm-1v, cm-1, M-1cm-1v, cm-1v21643.521.651209.417.101024 confederacy ofv2+ libration2127.53.4 61555.01.88v1,v3, and overtone ofv23404.0100.612504.069.682200http//www1.lsbu.ac.uk/water/water_vibrational_spectrum.htmlWalrafen investigated the structure of water by Raman spectroscopy in the intermolecular as well as intramolecular vibrational region. From Raman scattering it is observed that for liquid H2O and D2O a broad weak hydrogen bending isthmus at 60 cm-1 and it is observed to be decreases as temperature rise, the lot near 170 cm-1 is produced by the stretching motion of O-H band in water molecule. This is also decreases as increases in temperature which indicates the structural breakdown of water units. These vibrations are the intermolecular vibrations of water which are observed in the restricted translational region. The intramolecular vibrations of water occurs in the range of 2000-4000 cm-1.Walrafen studied the Raman spectra of 50 mole % solution of H2O and D2O in the intramolecular region in which normal contribution of HDO vibrations are studied. The two maxi ma at 34155 cm-1 and 24955 cm-1 are referred due to OH and OD stretching vibrations of HDO, and of H2O and D2O. Also the weak band at 2860 10 cm-1 arises from the overtone of the fundamental intramolecular bending vibration of HDO near 1450 cm-1. When H2O, D2O mixture studied at 32.2 to 93 C, the isosbestic point observed at 25705 cm-1 indicates the equilibrium exists between hydrogen bonded and nonhydrogen bonded OD stretching vibrations. Senior and Verrall observed same results when studied the HDO stretching at temperature 29 to 87 C by infrared spectroscopy. Bakker et al. studied the lifetime of the OH-stretching vibration in the water as a function of temperature by using femtosecond mid-infrared pump-probe spectroscopy and observed that it increases from 26018 (at 298 K) to 32018 (at 358 K)Recently, molecular dynamic simulation is becomes the fast method for the structural detection at molecular level. Xantheas et al. used the ab initio method to obtain the vibrational frequen cies as well as zero point energy for the water clusters and its isomers with the help of second-order MllerPlesset perturbation level of theory (MP2) with the augmented correlation consistent footing set of double zeta quality (aug-cc-pVDZ).1.3.1 Near-Infrared spectral study of water and aqueous solutionsNear-Infrared consists of the region 800-2500 nm (12500-4000 cm1) in the electromagnetic spectrum. In this region molecule have energy sufficient to excite first (2), second (3), and higher overtones (n) vibrations. The overtones observed in the molecule when the intermolecular vibrations of the molecules do not obey the displumes law. The band is more intense when the greater the anharmonicity. The combination bands are also observed in the same region.Near infrared spectroscopy is the underlying tool to study the hydrogen bonding in molecule. Earlier, the scientist Luck studied water and alcohol in the NIR region and observed that the strength of cooperativity of H-bond in wat er is about 250 % stronger than H-bond in a monomeric water. Different species of water present in the cooperative H-bond such as H-non bonded, H-bond strong and H-bond weaker. Ozaki et al. studied the structure of water by using two analytical techniques such as two dimensional correlation spectroscopy and principal component analysis in which they showed the two-state water model by measurements of the water at different temperatures from 6 to 80 C. Two bands are observed at 1412 and 1491 nm due to two different species of water i.e. weak H-bond and strong H-bond respectively. The species observed at 1438 nm which has no much effect of temperature which suggested may be due to distorted two-state model of water. The water at high temperature and pressure remarkably exhibits different properties than at ambient temperature. It becomes good solvent for hydrophobic substance such as benzene and hydrocarbons which are non-polar gets completely miscible at certain temperature and press ure. The effect of high temperature as well as pressure has been given by Ikawa et al. in the range of 5500 to 7800 cm-1. They observed the band at 7000 cm-1 gradually shifts to higher wavenumber is due to free OH vibrations and at 673 K and 400 bar pressure the absorption band retain the rotational features i.e. water molecule quite rotate freely though there is collision with other molecules.Recently, Near-Infrared spectroscopy has been used extensively for chemical analysis and characterization. The applications of NIR spectroscopy in various fields have attracted the scientific community. It is also used in the determination of moisture content in food samples. It can be used to probe the hydration effects in aqueous solutions of salt. Wu et al. have studied the effect of ethanol on the structural organization of aqueous solutions of BmimBF4 and AmimCl using one-dimensional and 2D correlation NIR spectroscopy. They showed that hydrogen bonding between water and ILs gets reduced in presence of high concentration of ethanol32 and can be used to remove water as an impurity in hygroscopic ILs. They also used this technique to study aggregation behavior of ILs in water. NIR spectroscopy has been used previously for the study of hydration by McCabe and Fisher in which they have studied the hydration of perchlorate and alkali halides in aqueous solutions by using excluded volume. Koga et al. have given the excess molar absorption factor in the range of 4600-5500 cm-1 i.e. (2+3) combination band of water for the Na halides and concluded that the Br and I form the hydrogen bond directly with the water network which is different than the Cl ion. Bonner and Woolsey have obtained the hydration number for some alkali halides by using the 958 nm (21+3) combination band of water. By applying their method, Hollenberg et al. reckon the hydration number for amino acids and carbohydratesThe new concept introduced by Noda in 1993 i.e. two dimensional correlation spectroscopy has attracted many scientist to study effect of solutes on the structure of water by IR as well as NIR spectroscopy. This technique becomes powerful tool for the elucidation of spectral changes induced by temperature, time and concentration. Noda et al. studied the structural and crystallization dynamics of poly(L-lactide) during isothermal cold crystallization by two dimensional correlation spectroscopy.An interpretation of the evolution with temperature of the 2+3 combination band in water V. Forns and J. Chaussidon, J. Chem. Phys. 68, 4667-4671 (1978)Near-infrared spectroscopic study of water at high temperatures and pressures Yusuke Jin and Shun-ichi Ikawa J. Chem. Phys., 119(23), 12432-12438, 2003.The importance of cooperativity for the properties of liquid water W.A.P. Luck Journal of molecular Structure, 448 (1998) 131 142.Studies on the Structure of Water Using Two-Dimensional Near-Infrared Correlation Spectroscopy and Principal Component Analysis V. H. Segtnan, S. Sasic, T. Isaksson, Y. Ozaki Anal. Chem. 2001, 73, 3153-3161