Hydrophobic interactions stability

Membranes are composed of lipids and proteins in varying combinations particular to each species, cell type, and organelle. The fluid mosaic model describes features common to all biological membranes. The lipid bilayer is the basic structural unit. Fatty acyl chains of phospholipids and the steroid nucleus of sterols are oriented toward the interior of the bilayer their hydrophobic interactions stabilize the bilayer but give it flexibility. 

Since the major driving force of inclusion is hydrophobic interaction, stabilities of ICs depend strongly on the polarity of the polymer. The more hydrophobic the polymer is, the higher is the affinity of CDs towards it. On the other hand, solubility in water decreases with increasing hydrophobicity of the polymer. Since affinity and solubility have to be compromised, an optimum of polarity of the polymer should exist for complexation by CDs. It is difficult to quantify the binding free energies of CD channel inclusion compounds, since they are insoluble in water. Stabilities of these polymeric ICs can be qualitatively compared by competition experiments. For example, PLLA and PCL were competitively included in a-CD. The IC of PCL was... 

Figure 17.15 Schematic diagrams of the main-chain conformations of the second zinc finger domain of Zif 268 (red) and the designed peptide FSD-1 (blue). The zinc finger domain is stabilized by a zinc atom whereas FSD-1 is stabilized by hydrophobic interactions between the p strands and the a helix. (Adapted from B.I. Dahiyat and S.L. Mayo, Science 278 82-87, 1997.)...

Kellis, J.T., et al. Contribution of hydrophobic interactions to protein stability. Nature 333 784-786, 1988. 

Superdex is stable to the same conditions as cross-linked Sepharose media (see earlier). The chemical stability in acidic and basic solutions, as well as ionic and hydrophobic interactions of various molecules, has been studied... 

Several different kinds of noncovalent interactions are of vital importance in protein structure. Hydrogen bonds, hydrophobic interactions, electrostatic bonds, and van der Waals forces are all noncovalent in nature, yet are extremely important influences on protein conformations. The stabilization free energies afforded by each of these interactions may be highly dependent on the local environment within the protein, but certain generalizations can still be made. 

Fig. 7. Besides direct interactions between functional groups of the biopolymer molecule itself there are also various kinds of interactions with water molecules. These hydrophilic and hydrophobic interactions are essential for stabilizing the native conformation of biopolymers. In the last few years some progress was made in elucidating the hydration of these molecules.

Upon formulating these relationships, phenols with branched alkyl substituents were not included in the data of a-cyclodextrin systems, though they were included in (3-cyclodextrin systems. In all the above equations, the n term was statistically significant at the 99.5 % level of confidence, indicating that the hydrophobic interaction plays a decisive role in the complexation of cyclodextrin with phenols. The Ibrnch term was statistically significant at the 99.5% level of confidence for (3-cyclo-dextrin complexes with m- and p-substituted phenols. The stability of the complexes increases with an increasing number of branches in substituents. This was ascribed to the attractive van der Waals interaction due to the close fitness of the branched substituents to the (3-cyclodextrin cavity. The steric effect of substituents was also observed for a-cyclodextrin complexes with p-substituted phenols (Eq. 22). In this case, the B parameter was used in place of Ibmch, since no phenol with a branched... 

Macrocyclic tetraammonium compounds VIII and IX 611 form stable 1 1 inclusion complexes with anionic molecules in aqueous solutions 62). The anions are halides, carbonate, phosphate, AMP, ATP etc. The stability of the inclusion complexes hepends on electrostatic as well as hydrophobic interactions. Whereas the complexes of VIII are dominated by the electfostatic component, the hydrophobic interaction plays the main part in complexes of IX. 

Soluble tetrameric form (G4) Composed of four identical monomers and stabilized by hydrophobic interactions of hydrophobic amino acids at the C terminus of monomers. Abundant for brain AChE and BChE in mammalian body fluids and in the soluble fraction of tissue homogenates. 

In a first step towards the design of / -peptides tyligomers (oligomers that fold into predictable tertiary structures [8]), carefully controlled interhelical hydrophobic interactions have been utilized to stabilize a / -peptide two-helix bundle (92) [179] (Fig. 2.17). 

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