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When proline is bound as an amide in a peptide bond, its nitrogen is not bound to any hydrogen, meaning it cannot act as a hydrogen bond donor, but can be a hydrogen bond acceptor. Peptide bond formation with incoming Pro-tRNA Pro in the ribosome is considerably slower than with any other tRNAs, which is a general feature of N -alkylamino acids ...
This modification of the proline residue increases the stability of the collagen triple helix. It was initially proposed that the stabilization was due to water molecules forming a hydrogen bonding network linking the prolyl hydroxyl groups and the main-chain carbonyl groups. [6]
The Agami mechanism (1984) has an enamine intermediate with two proline units involved in the transition state (based on experimental reaction kinetics) [17] and according to a mechanism by Houk (2001) [18] [19] a single proline unit suffices with a cyclic transition state and with the proline carboxyl group involved in hydrogen bonding.
Hydroxylation improves water‐solubility, as well as affecting their structure and function. The most frequently hydroxylated amino acid residue in human proteins is proline. This is because collagen makes up about 25–35% of the protein in our bodies and contains a hydroxyproline at almost every 3rd residue in its amino acid sequence.
The hydrogen bond donors are the peptide NH groups of glycine residues. The hydrogen bond acceptors are the CO groups of residues on the other chains. The OH group of hydroxyproline does not participate in hydrogen bonding but stabilises the trans isomer of proline by stereoelectronic effects, therefore stabilizing the entire triple helix.
In this context, simple organic acids have been used as catalyst for the modification of cellulose in water on multi-ton scale. [9] When the organocatalyst is chiral an avenue is opened to asymmetric catalysis; for example, the use of proline in aldol reactions is an example of chirality and green chemistry. [10]
The C-H bond is nonpolar and totally non-acidic. The C-S bond is basically nonpolar. But the S-H bond can weakly hydrogen bond (much weaker than water's of course) -- but the high boiling point of ethanethiol (35C! that's higher than HF!) means the S-H bond must be decently polar -- and afterall, thiols have a lower pKa than water.
Proline organocatalysis is the use of proline as an organocatalyst in organic chemistry. This theme is often considered the starting point for the area of organocatalysis, even though early discoveries went unappreciated. [ 1 ]
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