Size dependence of optical activities in helical polymers.

Chiroptical properties of helical polymers do not always align with the sum of the local contributions of their unit cells. This study investigates the discrepancy in optical rotatory strength between local and global structures using a right-handed helical polyacetylene model. The chirality is examined through density functional theory (DFT) calculations. The analysis reveals that, at higher degrees of polymerization, the contribution of chirality from the helical strand generally surpasses the partial chirality from the local structure. The ratio of local contribution to total contribution is deduced within the framework of crystal orbital theory, and a numerical method using Wannier functions is presented for evaluation.

Some structural aspects of ammeline - Keto preference and dimerization.

Subtle tautomerism in ammeline is clarified by means of IR- and UV-spectroscopic measurements and DFT calculations. While the enol form is narrowly preferred as an isolated molecule, dimerization of the keto form is plausible in solid phase due to double hydrogen bonds. In aqueous solutions, the keto form is proved to be more stable than the enol form due to the large electric dipole moment of the peptide group. The keto preference is also consistent with the acidity and basicity of the related heterocycles.

Optical activities of steroid ketones - Elucidation of the octant rule.

Theoretical calculations of optical activities in steroid ketones are presented by using modern semi-empirical PM7 wavefunctions. Both circular dichroism (CD) and specific rotation, which is proportional to optical rotation dispersion (ORD), are well simulated, and signs of the Cotton effect at the most long-wavelength region are fully in accordance with the experimental results. The good accordance is related to the octant rule, which is deduced within the framework of the perturbation theory. Our treatment is promising to predict the signs of the Cotton effect of large molecules, and thus, the absolute configurations can also be grasped without demanding procedures.

Puckering Energetics and Optical Activities of [7]Circulene Conformers.

The structural preference of [7]circulene is analyzed by taking into account vibronic interactions. DFT calculations reveal that pseudo-Jahn-Teller effects cause the D7h-symmetry structure to relax to C2- and Cs-symmetry structures, which are both ca. 9 kcal/mol lower in energy than the D7h structure. In energy terms, the C2-symmetry structure is 0.05 kcal/mol lower than that of the Cs-symmetry. The active vibrations are attributed to low-frequency puckering modes that are coupled with π-σ excitation states. The optical activities of the C2-symmetry structure were simulated by configuration interaction calculations, and the simulated CD/ORD spectra were reasonable and consistent with the experimental data. The optical rotatory strengths obeyed the helix rule; that is, the left-handed helix shows negative Cotton effects through the antisymmetric excited states. The calculated spectra will serve as a foundation for further investigation of optical activities of negatively curved structures.

Role of topological charge stabilization in protomeric tautomerism.

Protomeric tautomerism is analyzed in view of the topological charge stabilization rules. Based on Hückel molecular orbital considerations and modern DFT calculations, it was found that the branching of amino or hydroxyl groups significantly contributes to the stability of major species through the first- and second-order perturbations with respect to the isoelectronic hydrocarbon. While amino-imino tautomerism is almost completely dominated by topological charge stabilization, hydroxyl-oxo tautomerism is affected by changes in the resonance integral of C-O/C═O bonds. Nevertheless, apart from side effects such as hydrogen bonds or solvent effects, a quantitative preference rule for the prediction of the tautomeric stability can be developed using topological π-electron energetics. As well as the analyses of simple bases, applications to complex or extended systems are exemplified analyzing purine bases, polyguanide, and polyuret. The present approach can be useful in conjunction with chemical intuition that comes from conventional valence bond theory.

The fixed structure of Licochalcone A by alpha, beta-unsaturated ketone is necessary for anti-inflammatory activity through the inhibition of NF-kappaB activation.

Glycyrrhiza inflata has been used as a traditional medicine with anti-inflammatory activity. Previously, we reported that a major component, Licochalcone A, potently inhibited TNFalpha-induced NF-kappaB activation by inhibiting IKKbeta activation. In this study, we investigated whether the fixed structure of Licochalcone A by alpha, beta-unsaturated ketone is required for its inhibitory effect of NF-kappaB activation. Interestingly, reduced Licochalcone A, which lacks a double bond, failed to inhibit TNFalpha-induced NF-kappaB activation. Whereas Licochalcone A potently inhibited TNFalpha-induced IKK activation, IkappaBalpha degradation, nuclear localization of NF-kappaB and its DNA binding activity, no inhibitory effect was observed by reduced Licochalcone A. In addition, TNFalpha-induced expression of inflammatory cytokines, CCL2/MCP-1 and CXCL1/KC, was clearly inhibited by Licochalcone A but not reduced Licochalcone A. As a result, culture media pretreated with Licochalcone A but not reduced Licochalcone A following TNFalpha stimulation significantly inhibited the chemotactic activity of neutrophils. Furthermore, acute carrageenan-induced paw edema in mice was markedly inhibited by administration of Licochalcone A but not reduced Licochalcone A. Taken together, it is suggested that Licochalcone A is a promising anti-inflammatory drug in vivo and its fixed structure is critical for anti-inflammatory activity.

2,2'-Pyridoin derivatives protect HL-60 cells against oxidative stress.

Focusing on 2,2'-pyridoin (1, 1,2-di(2-pyridyl)-1,2-ethenediol) and its synthetic derivatives as the lead compound of the potent antioxidative enediol, their protective effect against oxidative stress was evaluated on the HL-60 cell system. 2,2'-Pyridoins showed no remarkable cytotoxic effect on HL-60 cells. The derivatives 1, 2, 3, 5, and 6 inhibited H(2)O(2)-induced cell death and intracellular oxidative stress more significantly than ascorbic acid. Since 2,2'-pyridoins are oxidized to the diketones, 2,2'-pyridils, in a protic solvent, the antioxidant activity of 2,2'-pyridils was also investigated. 2,2'-Pyridils showed antioxidant activity in the cell; however, the activity was lower than that of 2,2'-pyridoins. These results suggested that 2,2'-pyrdoin derivatives can be good cytoprotective agents against oxidative stress.

Preparation and antioxidant activity of alpha-pyridoin and its derivatives.

Focusing on alpha-pyridoin (1, 1,2-di(2-pyridyl)-1,2-ethenediol) as the lead compound of the novel antioxidative enediol, we synthesized 5,5'- or 6,6'-bis-substituted derivatives of 1 from disubstituted pyridines. The antioxidant activity of 1 and its synthetic derivatives 2-7 was evaluated by DPPH (1,1-diphenyl-2-picrylhydrazyl radical) scavenging assay and inhibition of lipid peroxidation. In the DPPH assay, 1 exhibited an activity stronger than that of ascorbic acid, and 5,5'-dimethyl-(5) or 5,5'-dimethoxy-substituted derivatives (6) exhibited more potent activity than 1. The DPPH scavenging activities of alpha-pyridoins were correlated with their oxidation potential and thus the electron density of enediol. 5 and 6 effectively inhibited lipid peroxidation in the rat liver microsome/tert-butyl hydroperoxide system. Therefore, 5 and 6 serve as good candidates for a pharmacologically useful enediol antioxidant.