Tryptophane molecular surface

Polymeric collagen peptides should be somewhat substantive to hair because they contain multiple ionic and polar sites for bonding, in addition to offering large molecular surfaces with many sites for Van der Waals bonding. Methionine, tyrosine [46], and tryptophan [47] are monomeric species of proteins, and they have been shown to sorb onto hair from aqueous solution. Collagen-derived polypeptides, or polymers of amino acids, have also been shown to have an affinity for hair [48-50], and one would predict that they should be more substantive to hair than their monomers. 

The combination of molecular surfaces with the standard visualization techniques of molecular models leads to new insights into physicochemical interactions. By displaying the surface in a transparency modus, the interior of the molecular structure can be seen., In Figure 13(d) the tryptophane molecule is shown with a transparent Connolly surface. The interior of a surface could also be displayed by a method called clipping (see Figure 16). A part of the surface cut by the clipping plane is not displayed to show the underlying molecular structure or even other surfaces, e.g., different contour levels of electronic density surfaces. 

Figure 33 Molecular surface of the tryptophane molecule color coded with respect to the electrostatic potential of a unit charge and repre.sentation of the electric field surrounding the molecule. The field vectors are represented as field lines (left) and as small cones positioned on the points of a Cartesian grid (right). The sizes of the cones are scaled according to the magnitude of the field, their orientations indicate the field direction...

Figure 17 shows the 11/A isotherms of racemic and enantiomeric films of the methyl esters of 7V-stearoyl-serine, -alanine, -tryptophan, and -tyrosine on clean water at 25°C. Although there appears to be little difference between the racemic and enantiomeric forms of the alanine surfactants, the N-stearoyl-tyrosine, -serine, and -tryptophan surfactants show clear enantiomeric discrimination in their WjA curves. This chiral molecular recognition is first evidenced in the lift-off areas of the curves for the racemic versus enantiomeric forms of the films (Table 2). As discussed previously, the lift-off area is the average molecular area at which a surface pressure above 0.1 dyn cm -1 is first registered. The packing order differences in these films, and hence their stereochemical differentiation, are apparently maintained throughout the compression/expansion cycles. 

The crystal structure of the extracellular domain of P0 has also been determined [41]. The arrangement of molecules in the crystal indicates that P0 may exist on the membrane surface as a tetramer (Fig. 7-7) that can link to other tetramers from the opposing membrane to form an adhesive lattice, like a molecular Velcro . The structure also suggests that P0 mediates adhesion through the direct interaction of apically directed tryptophan side chains with the opposing membrane [42], in addition to homo-philic protein-protein interaction. 

Electron beam damage effects followed the general rule that molecular groups in intimate contact with the metal substrate and aromatic groups appear relatively stable. Thus in the monolayer, alanine, with a methyl group likely sticking out from the surface, was the only molecule found to be unstable. In multilayer films, only tryptophan with the aromatic indole group to stabilize the molecule was found to yield multilayers stable under electron beam irradiation. 

The experiments demonstrate that femtosecond laser pulses offer new opportunities for multiple-photon ionization of bioorganic molecules on surface. The fast femtosecond excitation makes it possible to produce molecular and fragmentation ions directly on the surface being irradiated. The two-photon excitation with an intense femtosecond pulse allows the selectivity of ionization of the chromophore (tryptophan in our case) in large molecules... 

Melittin, which is an amphipathic peptide from honeybee venom, consists of 26 amino acid residues and adopts different conformations from a random coil, to an a-helix, and to a self-assembled tetramer under certain aqueous environments see Fig. 9. We have carried out our systematic studies of the hydration dynamics in these three conformations using a single intrinsic tryptophan ( W19) as a molecular probe. The folded a-helix melittin was formed with lipid interactions to mimic physiological membrane-bound conditions. The self-assembled tetramer was prepared under high-salt concentration (NaCl = 2 M). The tryptophan emission of three structures under three different aqueous environments is 348.5 nm, 341 nm, and 333.5 nm, which represents different exposures of aqueous solution from complete in random-coil, to locating at the lipid surface of a nanochannel (50 A in diameter) in a-helix and to partially buried in tetramer. Figure 10 shows... 

Water-soluble globular proteins usually have an interior composed almost entirely of nonpolar, hydrophobic amino acids such as phenylalanine, tryptophan, valine and leucine with polar and charged amino acids such as lysine and arginine located on the surface of the molecule. This packing of hydrophobic residues is a consequence of the hydrophobic effect, which is the most important factor that contributes to protein stability. The molecular basis for the hydrophobic effect continues to be the subject of some debate but is generally considered to be entropic in origin. Moreover, it is the entropy change of the solvent that is... 

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