Chiroptical Properties of Amino Acids: A Density Functional Theory Study

Density functional theory study to functionalization of BC2N nanotubes with cysteine amino acid

The density functional theory (DFT) was used to study the interaction of cysteine amino acid with (8, 0) zigzag single-walled BC₂N nanotubes (BC₂NNTs) both in gas and solvent phases. The interaction between cysteine amino acid and BC₂NNTs is found to be energetically favorable in both phases. Based on the calculations of solvation energy, it can be seen that the dissolution of BC₂NNT/amino acid complex in water is spontaneous. During the functionalization process, the quantum molecular descriptor and the energy of adsorption changed significantly. Findings suggest that the cysteine amino acid can be considerably adsorbed chemically onto the surface of BC₂NNTs. Based on the E_g values obtained, the cysteine molecule caused a reduction in the E_g value, which also increased the reactivity and conductivity of functionalized BC₂NNTs. According to the findings of chemical hardness, the kinetic stability of the functionalized nanotubes was better than pure nanotubes. As a result of this approach, E_g values are indicative of high propensity reaction and electron transfer. Our findings have shown that BC₂NNTs can function as an appropriate drug delivery system for cysteine amino acid within biological systems for the adsorption of the drug and controlled drug release.

Gas-Phase Conformational Map of the Amino Acid Isovaline

Four conformers of the non-proteinogenic α-amino acid isovaline, vaporized by laser ablation, are characterized by Fourier-transform microwave techniques in a supersonic expansion. The comparison between the experimental rotational and ¹⁴ N nuclear quadrupole coupling constants and the ab initio calculated ones provides conclusive evidence for the identification of the conformers. The most stable species is stabilized by an N-H⋅⋅⋅O =C intramolecular hydrogen bond and a cis-COOH interaction, whereas the higher-energy conformers exhibit an N⋅⋅⋅H-O intramolecular hydrogen bond and trans-COOH, as in other aliphatic amino acids. The spectroscopic data herein reported can be used for the astrophysical purpose in a possible detection of isovaline in space.

Role of ionic liquids on the selectivity and the rate of organic reactions: A computational approach

In the last years, ionic liquids have been used as substitutes to common solvents since they combine good solubility properties with small vapor pressures. Herein, the Diels-Alder reactions of cyclopentadiene (CP) with acrolein, methyl acrylate and acrylonitrile in ionic liquids ([Emim][N(Tf)₂]), ([Hbim][N(Tf)₂]) and ([Bmim][OTf]) have been modeled with density functional theory to explore the effect of ionic liquids on the endo selectivity in the adducts. Besides the hydogen bonding interactions between the cation and the diene in all the structures, endo transition structures are slightly better stabilized than exo transition structures because of the favorable interactions between the H's of the CP ring and the O's of the [N(Tf)₂]^- and [OTf]^- anions of the IL's. In this study, B3LYP/6-31 + G* and M06-2X/6-31 + G* calculations have demonstrated that endo selectivity in the Diels-Alder reactions can be achieved in the presence of ionic liquids in agreement with experiments.

Absolute configuration of remisporines A & B

The absolute configuration of remisporine B was determined based on a comparison of experimental and calculated electronic circular dichorism (ECD) spectra.

Photochirogenesis: photochemical models on the absolute asymmetric formation of amino acids in interstellar space

Proteins of all living organisms including plants, animals, and humans are made up of amino acid monomers that show identical stereochemical L-configuration. Hypotheses for the origin of this symmetry breaking in biomolecules include the absolute asymmetric photochemistry model by which interstellar ultraviolet (UV) circularly polarized light (CPL) induces an enantiomeric excess in chiral organic molecules in the interstellar/circumstellar media. This scenario is supported by a) the detection of amino acids in the organic residues of UV-photo-processed interstellar ice analogues, b) the occurrence of L-enantiomer-enriched amino acids in carbonaceous meteorites, and c) the observation of CPL of the same helicity over large distance scales in the massive star-forming region of Orion. These topics are of high importance in topical biophysical research and will be discussed in this review. Further evidence that amino acids and other molecules of prebiotic interest are asymmetrically formed in space comes from studies on the enantioselective photolysis of amino acids by UV-CPL. Also, experiments have been performed on the absolute asymmetric photochemical synthesis of enantiomer-enriched amino acids from mixtures of astrophysically relevant achiral precursor molecules using UV-circularly polarized photons. Both approaches are based on circular dichroic transitions of amino acids that will be highlighted here as well. These results have strong implications on our current understanding of how life's precursor molecules were possibly built and how life selected the left-handed form of proteinogenic amino acids.