Amino acid enantiomers energies

Steric hindrance cannot be directly calculated, but a lower MI energy value indicates lower steric hindrance in a complex. This phenomenon ean be observed in enantiomer recognition and protein-ligand interactions, with the latter also being known as affinity. Such phenomena can be studied via amino acid enantiomer complexes. The optimized energy values of (I )- and (S)-alanine are the same, as summarized in Table 2.4. 

The calculated energy values of the amino acid enantiomers derivatized with (+)-l-(9-fluorenyl)ethyl chloroformate using the MM2 program are listed Tables 8.12 and 8.13 with chromatographic data measured in reversed-phase from ref. 18. The energy values of individual complexes between the model phase and an enantiomer are listed Table 8.13. 

The influence of the weak interaction on chemical reactions can be calculated since it favours left-handedness, it has an effect on the energy content of molecules and thus on their stability. In the case of the amino acids, the L-form would be more stable than the corresponding D-form to a very small extent. Theoretical calculations (using ab initio methods), in particular by Mason and Tranter (1983), indicated that the energy difference between two enantiomers due to the parity violation is close to 10 14J/mol (Buschmann et al., 2000). More recent evidence suggests that the... 

Tranter, G. E. 1985a. The Parity Violating Energy Differences Between the Enantiomers of a-amino Acids. Mol. Phys. 56, 825-838. 

The rates of reaction of both enantiomers of amino-acid esters in the presence of (S)-[324] are the same, but with (S)-[323] they are in most cases different. The reactions of L-amino acid esters in the presence of (S)-[323] are faster than those in the presence of (R)-[323] by factors of 9.2 (R = i-Pr), 8.2 (R = C6H5CH2) and 6.0 (R = i-Bu). No difference in rates is observed for L-alanine p-nitrophenyl ester. The results were explained in terms of the formation of diastereomeric tetrahedral intermediates [325] and [326]. The bulk of the group R will determine how much the complex stability of the (D)-complex decreases relative to that of the (L)-complex, which difference is reflected in the activation energy of the rate-determining step. 

Despite the theoretical difficulties outlined above, some small PVED between enantiomers does exist, on the order of 10 18 3 times the average thermal energy (feT) at room temperature per light-atom molecule. In a mole of a racemic mixture of amino acids, for example, this energy difference leads to an excess of approximately a million molecules of the more energetically stable enantiomer. Thus, we are led to search experimentally for how such minuscule excesses could be translated into a macroscale preference. As yet, another challenge, the measurement of the energy differences associated with the different enantiomers (PVEDs) so far eludes our detection abilities. 

Later, a commercially available TAG CSP was tested in the enantioseparation of 10 secondary a-amino acids, by using RP mobile mode systems [154]. The chromatographic results, compared with those obtained on a native teicoplanin CSP, were given as the retention, separation, and resolution factors, together with the enanti-oselective free energy difference corresponding to the separation of the investigated enantiomers. 

A careful analysis of conformational energy maps (Ramachandran plots) revealed that both enantiomers of P-tetralin amino acids were compatible with the right handed a-helical conformation.109 This was an important prerequisite for the development of N- and C-caps since the ( -configuration of the P-tetralin amino acid is needed for N-terminal helix induction, whereas the (R)-enantiomer was used in the C-cap series. The fact that both configurations were compatible with a-helical conformations made these amino acids our first choice as building blocks for... 

Deterministic and stochastic processes should be taken into account. The deterministic scenario invokes transfer of the intrinsic chirality of the universe to the biopolymers of life [6,7]. Ab initio theoretical estimates that take into account the chiral electroweak forces indicate that the L-amino acids and the D-sugars are more stable than their corresponding enantiomers [8,9]. The minute energy differences between these enantiomeric pairs, under Darwinian reaction kinetics in a flow reactor, were invoked to account for the biomolecular handedness that arose when fife began [7]. Several reports describing deterministic mechanisms that could have induced mirror sym-... 

A remarkably simple one-step synthesis of a peptide receptor in 13% yield has been reported by Yoon and Still (Figure 69) [94], This molecule was shown to bind y-acylated amino acids and dipeptide amides with high enantioselectivity. For example, L- and D-enantiomers of N-Boc-Gly-Val-NHMe (Boc=t-butoxycarbonyl, Val = valine) showed complexation free energies of... 

Amino acids are the basic building blocks of peptides and proteins and are simpler in structure than ribonucleotides. They are the major constituents for building up cells and serve as energy storage, too. Peptides and proteins mainly occur as l-enantiomers in nature. Almost each enantiomer of any amino acid can act as a specific enzyme in aldol condensations. 

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