Peptides peptide-acid hydrogen bond

Pentynoic acid, 5 34t People. See also Personnel investment in, 21 624 organizational ties to, 21 627-628 People s Republic of China. See also China demand for oil in, 23 530 oil recovery program in, 23 534 Pepper, pipeline levels in, 23 159 Peptide antibiotics, 18 252-253. See also Antimicrobial peptides Peptide backbone hydrogen bonds, in proteins, 20 826 Peptide mapping, 3 840-841 Peptide nucleic acids, 17 631-634... 

P2j Z = 2 DX = 1.43 R = 0.067 for 1269 intensities. The uracil residue is in the anti (63.4°) disposition. The conformation of the D-ribosyl group is 2T3 (176.8°, 37.5°). The orientation about the exocyclic, C-4 -C-5 bond is t (—174.2°). The phenyl and uracil ringsofthe same molecule lie in almost parallel planes, 120 pm apart. The phenyl group is disordered. The uracil ring is sandwiched by the phenyl rings, and vice versa. The 0-1 and N-a atoms of the peptide backbone are hydrogen-bonded to 0-4 and N-3 of atranslationally related uracil to form cyclic dimers. Such interactions serve as models for nucleic acid-protein interactions. [Coordinate errors H(02 ) x should be —1574, instead of —1474 H(Na)2 z should be —145 instead of— 645.]... 

When N -deprotection reactions and amino acid coupling steps do not go to completion or proceed in low yields, repeated or prolonged reaction times should overcome these problems. Nevertheless, this is not always sufficient. The cause of this failure is thought to be self-association of the peptide chain by hydrogen bond formation leading to aggregation. This aggregation results in incomplete... 

The a-Helix (a-Screw). In pleated-sheet structures or peptide grids hydrogen bonds link the individual chains. But a structure in which the hydrogen bonds are all satisfied within a single chain should be favored. Such a preferred structure is achieved by winding the peptide chain around an imaginary cylinder in a way that from one turn to the next, CO and HN face one another with the proper distance. Several models of this concept are possible. The one that is found widely distributed in nature is the a-helix with 3.7 amino acid residues per turn and mth an identity period of about 5.44 A. 

Ammo acids with polar but nonwmzed side chains Among ammo acids with polar side chains serine is the smallest it is not much larger than alanine With a —CH2OH side chain serine participates well m hydrogen bonding and often occurs m regions of a peptide that are exposed to water... 

Fig. 3. (a) Chemical stmcture of a synthetic cycHc peptide composed of an alternating sequence of D- and L-amino acids. The side chains of the amino acids have been chosen such that the peripheral functional groups of the dat rings are hydrophobic and allow insertion into Hpid bilayers, (b) Proposed stmcture of a self-assembled transmembrane pore comprised of hydrogen bonded cycHc peptides. The channel is stabilized by hydrogen bonds between the peptide backbones of the individual molecules. These synthetic pores have been demonstrated to form ion channels in Hpid bilayers (71). 

Proline is the only amino acid in Table 27.1 that is a secondary amine, and its presence in a peptide chain introduces an amide nitrogen that has no hydrogen available for hydrogen bonding. This disrupts the network of hydrogen bonds and divides the peptide into two separate regions of a helix. The presence of proline is often associated with a bend in the peptide chain. 

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