Relaxation protein-water systems

The temperature dependence of the MRD profile for the protein-water systems where the protein is magnetically a solid, is remarkably weak. The relaxation rate is proportional to IjT, which is consistent with Eq. (4) that was derived on the assumption that the relaxation process is a direct spin-phonon coupling rather than an indirect or Raman process. If it were a Raman process, there would be no magnetic field dependence of the relaxation rate therefore, the temperature dependence provides good evidence in support of the theoretical foundations of Eq. (6). 

The most powerful technique for studying molecular motions in protein-water systems below 0°C is magnetic resonance. Dielectric relaxation measurements can be used, but these measurements are more suitable at higher temperatures in homogenous solutions (13). Recently, the frequency dependence of the mehcanical properties of biopolymers has been shown to yield considerable kinetic information (14). I will limit discussion to the salient results attainable from these techniques. 

Molecular dynamics simulations of proteins often begin with a known structure (such as an X-ray diffraction structure) that you want to maintain during equilibration. Since the solvent may contain high energy hot spots, equilibration of the protein and solvent at the same time can change the protein conformation. To avoid this, select only the water molecules and run a molecular dynamics equilibration. This relaxes the water while fixing the protein structure. Then deselect the water and equilibrate the whole system. 

Picullel L, Halle B (1986) Water spin relaxation in colloidal systems. Part 2., 70 and 2H relaxation in protein solutions. J Chem Soc Faraday Trans I 82 401-414... 

Interest in water at protein surfaces and other surfaces arises from a desire to understand structural, functional, and dynamic factors as well as their interrelationships. Nuclear magnetic resonance (NMR) spectroscopy provides both structural and dynamic information. This presentation will focus on dynamical aspects of the water-protein Interaction. In particular, the phenomenon of cross relaxation between the water and protein proton systems will be discussed and new evidence will be reported. Failure to recognize the importance of cross relaxation effects leads to incorrect conclusions about the dynamics of water at protein surfaces. 

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. 

Other studies included the investigation of the stabilizing effect of sorbitol on hen egg white lysozyme and the use of the self-diffusion coefficient, D, to follow the solution and aggregative properties of lysozyme at different pH, temperature, and protein and salt concentrations. The properties of frozen ovalbumin solutions were studied by NMR relaxation spectroscopy. It is known that the functional properties of muscle proteins are affected by protein interactions with ions, and NMR was used to assess protein/water, protein/salt, and protein/protein interactions in myofibrillar protein solutions. Previous X-ray and NMR studies on collagen and peptides were reviewed by Mayo and, more recently, such types of system were characterized by high-resolution H and C NMR. °0 The structure, hydration state, and nature of the interactions between water and gelatin were determined by time domain NMR. ... 

To further probe the role of hydration water in the high-T crossover, we measure the NMR proton spin-lattice relaxation time constant Ti of the lysozyme-water system with h = 0.3 in the interval 275K < T < 355K (Fig. 3b). Figure 3b also shows T for pure bulk water. Note that the hydration water Ti is characterized by two contributions, one coming from the hydration water protons (on the order of seconds, as in bulk water, Tih) and the other from the protein protons (on the order of 10 ms Tip). Figure 3b also shows that, as T increases, the bulk water Ti follows the VFT law across the entire temperature range, but the Tn, exhibits two... 

NMR spectroscopy is one of the most widely used analytical tools for the study of molecular structure and dynamics. Spin relaxation and diffusion have been used to characterize protein dynamics [1, 2], polymer systems[3, 4], porous media [5-8], and heterogeneous fluids such as crude oils [9-12]. There has been a growing body of work to extend NMR to other areas of applications, such as material science [13] and the petroleum industry [11, 14—16]. NMR and MRI have been used extensively for research in food science and in production quality control [17-20]. For example, NMR is used to determine moisture content and solid fat fraction [20]. Multi-component analysis techniques, such as chemometrics as used by Brown et al. [21], are often employed to distinguish the components, e.g., oil and water. 

The relaxivity enhancement associated with exchangeable protons in the second-coordination sphere of a Gd(III) complex is quite important in the supramolecular adducts of Gd(III)-based systems with proteins. For example, it has been reported that, besides water protons in the second-coordination... 

Many natural materials are porous but also proton-rich such as wood or other plant products. Relaxation of liquids in these materials has features in common with both inorganic matrices and the protein systems discussed above. The class of porous polysaccharide materials used for size exclusion chromatography provides an example one commercial product is Sephadex. The material swells on solvation to form a controlled pore gel. The main application involves excess liquid, generally water, which flows through the gel bed carrying solutes of various size. The large solutes are excluded from the pore interior and elute rapidly while the smaller ones equilibrate with the pore interior and elute later. The solvent generally samples the pore interior as well as the bulk phase. 

Water exchange reaction mechanism 332 Water NMRD in diamagnetic systems 33-9 Water protein relaxation rate 149 Wigner rotation matrices 65, 67 Wild type azurin 122... 

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