Hydrophobic stability

Stabilization of a P-hairpin structure can be achieved in two ways, promoting a stable (or restricted) turn structure (as done with mimetics) or linking the two arms either chemically, or, more naturally, by hydrophobic interactions. In an approach to utilizing both methods, a D-Pro-Gly linkage was used to stabilize a left-handed turn (type I or II ) and various charged and hydrophobic residues were used to stabilize the molecule and enhance the interaction between arms. I252"254 Examples of these peptides studied in nonaqueous solution by IR, VCD and NMR spectroscopy exhibit characteristics of well-formed hairpins. 255 Alternatively, in aqueous solution, IR, VCD, and ECD results for related peptides agree with the NMR interpretation of conformations characterized as hairpins stabilized at the turn and frayed at the ends. 256 These latter results also have a qualitative match with theoretical simulations. Recently, examples of hydrophobically stabilized hairpins studied by NMR spectroscopy have avoided use of a nonnatural amino acid. 257,258 ... 

Hydrophobic Stabilization in T4 Lysozyme Determined Directly by Multiple Substitutions of lie 3. 

Matsumura, M., Becktel, W. J., and Matthews, B. W. (1988). Hydrophobic stabilization in T4 lysozyme determined directly by multiple substitutions of He 3. Nature London) 334, 406-410. 

In spite of this interest of physical and biochemists, prior to the work of Hansch and Fujita there appears to have been no eifort to devise a scale of hydrophobicity analogous to the Hammett scale for electronic effects, or the Taft scale for steric effects. Part of this reluctance was due to the selection of the relevant solvent system for such a scale. In addition, biochemists who were interested in hydrophobic stabilization of protein structures needed only to consider the few hydrophobic amino acid side chains. 

Hydrophobic stability domains In globular protein structures -... 

Buurma, N.J., Pastorello, L., Blandamer, M.J. and Engberts, J.B.E.N., Kinetic evidence for hydrophobically stabilized encounter complexes formed by hydrophobic esters in aqueous solutions containing monohydric alcohols, /. Am. Chem. Soc., 2001,123,11848—11853. 

This important consequence of the hydrophobic effect is referred to as the hydrophobic interaction, which, according to Israelachvili, describes "the unusually strong attraction between hydrophobic molecules and surfaces in water... often stronger than their attraction in free space." This concept is perfectly illustrated by the energy of interaction between two methane molecules in vacuo and in water (respectively, -2.5 x 10 and -14 X 10 J, or a 5.6-fold increase in affinity in water compared with free space). Intuitively, one can consider that water molecules exert a pressure on methane molecules, just like cold weather forces the sheep of a herd to get closer than they would do at higher temperatures. In other words, water really helps lipids to self-aggregate into hydrophobically stabilized clusters. 

Papisov et al. [36] used sedimentation studies to analyze the distribution of oligomers of PEG and PNVP present in non-stoichiometric amounts in complexes with PMAA and PAA templates. Here, an excess of the polyacid was used. In water and in a 30% methanol/water mixture, complexes of PEG and PMAA exhibited two distinct sedimentation fractions, in a 60% methanol/water mixture, only one fraction was observed. Papisov et al. concluded that PMAA matrices are filled in an "all or nothing" manner in aqueous environments. That is, available oligomers complex with and completely fill PMAA chains until PEG oligomers are exhausted, leaving the remaining PMAA chains complex free. Thus, complexation of oligomeric PEG or PNVP with PMAA seems to promote further complexation with the same PMAA chain, perhaps due to establishment of a favorable thermodynamic microenvironment for hydrophobic stabilization of further complexes. 

Basic polymer poly(vinyl pyridine) (PVP) and a hydrophobic stabilizer PTFE, PVDF, PVDF-HFP, PS, PBD, PVDC, PMMA, PVAI, PVAc, PPE, PEEK, PET, PBT PC, PBI, PDMS, PANI... 

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