Solvent perturbation spectroscopy

Heme accessibility for free cyt f and cyt f in the PC-cyt f adduct was determined by solvent perturbation spectroscopy using 20% ethylene glycol as the perturbant. Cytochrome c was also examined as a control. The results are presented in Table 1. 

Conventional UV difference spectroscopy and solvent perturbation difference spectroscopy have been used in a wide variety of protein stud-... 

The biochemical applications of UV and visible spectroscopy are determination of concentrations, interactions of ligands with biomaaomolecules and conformational changes caused by experimental perturbations. The sensitivity of UV and visible spectra to the solvent environment of the chromophore leads to shifts in the absorption maximum and the absorption intensity, and it is the basis of solvent perturbation spectra in the structural studies of biomacromolecules (Donovan, 1969). The ideahzed development of environmental (solvent) contribution to the extinction coefficient of a chromophore is described by... 

We then designed model studies by adsorbing cinchonidine from CCU solution onto a polycrystalline platinum disk, and then rinsing the platinum surface with a solvent. The fate of the adsorbed cinchonidine was monitored by reflection-absorption infrared spectroscopy (RAIRS) that probes the adsorbed cinchonidine on the surface. By trying 54 different solvents, we are able to identify two broad trends (Figure 17) [66]. For the first trend, the cinchonidine initially adsorbed at the CCR-Pt interface is not easily removed by the second solvent such as cyclohexane, n-pentane, n-hexane, carbon tetrachloride, carbon disulfide, toluene, benzene, ethyl ether, chlorobenzene, and formamide. For the second trend, the initially established adsorption-desorption equilibrium at the CCR-Pt interface is obviously perturbed by flushing the system with another solvent such as dichloromethane, ethyl acetate, methanol, ethanol, and acetic acid. These trends can already explain the above-mentioned observations made by catalysis researchers, in the sense that the perturbation of initially established adsorption-desorption equilibrium is related to the nature of the solvent. 

Permeability changes in full-thickness skin have been associated with temperature or solvent pretreatment. The molecular basis of these permeability changes has been attributed to lipid melting or protein conformational changes. The current studies have probed the role of lipid fluidity in the permeability of lipophilic solutes, and examined the effects of temperature on the physical nature of the stratum corneum by differential scanning calorimetry and thermal perturbation infrared spectroscopy. Combining molecular level studies that probe the physical nature of the stratum corneum with permeability results, a correlation between flux of lipophilic solutes and nature of the stratum corneum barrier emerges. 

The proton spin-lattice relaxation times for solvent water are strongly perturbed if the water is in rapid exchange with a paramagnet. In particular, Mn is a strong relaxer for water protons and thus nuclear magnetic resonance (NMR) spectroscopy provides a sensitive probe for the presence of exchangeable water molecules bound to Mn in Mn proteins. 

Nuclei that are typically analyzed with this technique include those of 13C, 31P, 1SN, 2SMg, and 23Na. Different crystal structures of a compound can result in perturbation of the chemical environment of each nucleus, resulting in a unique spectrum for each form. Once resonances have been assigned to specific atoms of the molecule, information on the nature of the polymorphic variations can be obtained. This can be useful early in drug development, when the single-crystal structure may not be available. Long data acquisition times are common with solid-state NMR, so it is often not considered for routine analysis of samples. However, it is usually a very sensitive technique, and sample preparation is minimal. NMR spectroscopy can be used either qualitatively or quantitatively, and can provide structural data, such as the identity of solvents bound in a crystal. 

Gas phase experiments are ideally suited for this since the perturbations induced by the local environment are completely eliminated, providing an ideal tool for exact measurements. Studies of coherent proton transfer of isolated molecules in the gas phase are able to yield absolute numbers on proton transfer tunneling without being influenced by solvent effects or the interaction of a crystal surrounding. Moreover, high resolution spectroscopy can yield state specific tunneling frequencies. These studies allow direct comparison with the results of ab initio studies and will therefore provide a sensitive test for recently developed theoretical methods. 

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