L-phenylalanine (Phe), an essential amino acid, is necessary for the synthesis of proteins such as catecholamine and melanin, also precursor acid L-tyrosine (Tyr). In this paper, optimized structures Phe, were calculated by using semi-empirical models AM1, PM3 MNDO; Density Functional (DFT) at B3LYP Hartreefock methods (HF) with 6-311++G (d,p) level. The energies geometric parameters Kaempferol...

the ability of the present semiempirical quantum mechanics methods are surveyed for reproducing the transannular interaction in the bifunctional n-phenyl-5-azocanones. the am1 method is the best with the order of reliability being am1, pm3, mndo and mindo/3. am1 calculations were then carried out for quantification of transannular interaction. the n(o) ionization potential has been used for thi...

The transition structures of the thione-to-thiol rearrangement of O-(2-dimethylaminoethyl and 2-methylthio-) S-methyl xanthates in several solvents were located by semiempirical molecular orbital method (PM3) using the conductor-like screening model (COSMO) approach. Each transition state transforms into the ion-pair intermediate with a three-membered ring structure (aziridinium or thiiranium),...

Anti-leukemia screening of previously prepared isothiouronium and quaternary salts was performed, and some salts exhibited promising activity as anticancer agents. Quantum chemical calculations were utilized to explore the electronic structure and stability of these compounds. Computational studies have been carried out at the PM3 semiempirical molecular orbitals level, to establish the HOMO-LU...

Molecular dynamics simulation techniques, together with semiempirical PM3 calculations, have been used to investigate the effect of photoisomerization of the 4-hydroxy-cinnamic acid chromophore on the structural properties of the photoactive yellow protein (PYP) from Ectothiorodospira halophila. In this bacteria, exposure to blue light leads to a negative photoactic response. The calculations s...

In the mol-ecule of title compound, C15H20O6, also known as cynarinin A, the cyclo-pentane ring having twist conformation and a γ-lactone ring assuming an envelope conformation are trans- and cis-fused, respectively, to a cyclo-heptane ring adopting a twist-chair conformation. In the crystal, O-H⋯O hydrogen bonds link neighbouring mol-ecules, forming a three-dimensional network. Theoretical cal...

The asymmetric unit of the title compound, C20H34O2, contains two crystallographically independent mol-ecules (1 and 2) with similar conformations. In both mol-ecules, the cyclo-hexane rings adopt a chair conformation, while the oxane rings are also puckered. In the crystal, O-H⋯O hydrogen bonds connect adjacent mol-ecules, forming C(6) helical chains located around a 21 screw axis and running ...