Biological water protein hydration layer

Here A//adS is the enthalpy of adsorption, T is the temperature, and AAads is the entropy change associated with the adsorption of the protein onto the surface. Protein adsorption will take place if AGads < 0. Considering a complex system, where proteins are dissolved in an aqueous environment, and are brought into contact with an artificial interface, there are a vast number of parameters that impact AGads due to their small size (i.e., large diffusion coefficient), water molecules are the first to reach the surface when a solid substrate is placed in an aqueous biological environment. Hence, a hydrate layer is formed. With some delay, proteins diffuse to the interface and competition for a suitable spot for adsorption starts. This competition... 

It is very difficult to directly observe water molecules in vivo at the surfaces of proteins or lipid bilayers or in the grooves of DNA. X-ray studies of protein crystals cannot provide full information as only a fi action of water molecules remain on the surface and even then in restricted positions. Also, the hydration layer is mobile in solution. One would like to know about the structural and dynamical characteristics of these water molecules in the active state, ideally within biological cells. Such detailed information is still not available in most cases. Much of our current understanding of water in biological systems has come from study of proteins and DNA in aqueous solution. 

R. Pethig, Protein-water interactions determined by dielectric methods. Anna. Rev. Phys. Chem., 43 (1992), 177-205 E.H. Grant, Nature, 196 (1962), 1194 N. Nandi, K. Bhattacharyya, and B. Bagchi, Dielectric relaxation and solvation dynamics of water in complex chemical and biological systems. Chem. Rev., 100 (2000), 2013 B. Bagchi, Water dynamics in the hydration layer around proteins and micelles. Chem. Rev., 105 (2005), 3197. 

Understanding the relationship between the properties of proteins [4] and their associated water [5-7] is an ongoing challenge. Many biological functions [3] can be understood only if we know the structure and function of the first hydration layer. When a protein is in solution, there are two categories of water molecule in close proximity to it, (i) internal bound molecules and (ii) hydration water molecules. The internal bound molecules, located in cavities of the protein, play a structural role in protein folding. 

It is commonly stated that the first readily observable event at the interface between a material and a biological Quid is protein or macromolecule adsorption. Clearly other interactions precede protein adsorption water adsorption and possibly absorption (hydration effects), ion bonding and electrical double layer formation, and the adsorption and absorption of low molecular weight solutes — such as amino acids. The protein adsorption event must result in major perturbation of the interfacial boundary layer which initially consists of water, ions, and other solutes. 

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