关于内结合环的注记（英）

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Solvatochromism, prototropism and complexation of para-aminobenzoic acid

Effect of solvents, buffer solutions of different pH and β-cyclodextrin (β-CD) on the absorption and fluorescence spectra of p-aminobenzoic acid (pABA) have been investigated. The inclusion complex of pABA with β-CD is investigated by UV-visible, fluorimetry, semiempirical quantum calculations (AM1), ¹H NMR and Scanning Electron Microscope (SEM). The thermodynamic parameters (ΔH, ΔG and ΔS) of the inclusion process are also determined. The experimental results indicated that the inclusion processes is an exothermic and spontaneous. The large Stokes shift emission in solvents with pABA are correlated with different solvent polarity scales. The increase in the excited dipole moment values suggest that pABA molecule is more polar in the S₁ state. Solvent and β-CD studies indicates intramolecular charge transfer in pABA is less than ortho and meta isomers. Acidity constants for different prototropic equilibria of pABA in the S₀ and S₁ states are calculated. β-Cyclodextrin studies shows that pABA forms a 1:1 inclusion complex with β-CD. A mechanism is proposed to explain the inclusion process.     

Structure–Activity relationships in auxins

Of the various theories proposed for auxin activity, the conformational change theory and the charge separation theory have received considerable attention. However, no conclusive theory collating molecular structure with hormonal activity has yet been established. We have studied the structural requirements for hormonal activity in plants through single crystal x-ray studies, as well as through conformational and charge density calculations on a series of plant hormones. We find that the existing theories are inadequate in explaining the activity of several auxins. We propose that the size of the auxin molecule in conjunction with the charge separation serves as a possible mechanism of action in plant hormones.     

Ethyl 6‐acetylamino‐6,7‐dihydro‐5H‐dibenzo[a,c]cycloheptene‐6‐carboxylate

The title compound, C₂₀H₂₁NO₃, is a derivative of Aib (α‐­aminoisobutyric acid) and is cyclized at the C^α position by bi­phenyl rings. The seven‐membered ring possesses C2 symmetry. The C^α cyclization causes the backbone to assume a helical conformation in the crystal structure. The packing of the mol­ecules is stabilized by intermolecular C—H?O, C—H?π and N—H?O hydrogen bonds.     

Molecular structure and activity of Vicolides isolated fromVicoa indica

Vicolide A to D, sesquiterpenoid lactones, were isolated from Vicoa indica and crystal structure of A and D were established by X-ray analysis. The structures were solved by direct methods and refined to an R index of 0.09. Vicolide B and D are reported to have anti-fertility activity while A and C are devoid of this activity. Conformational features of B and C are similar but differ from those of A and C.DCB Contribution No. 805.     

Higgs bosons inE 6 and intermediate mass scales

Considering the importance ofE ₆ as the grand unification group in superstring theories, several breakdown patterns ofE ₆ through maximal subgroups are studied. The Higgs which break the low energy group and give masses to the fermions are determined in each case. At each scale we consider minimal Higgs and apply extended survival hypothesis to determine the limits on the mass scales. The combination of intermediate mass scales that give rise to acceptable electroweak mixing angle and unification mass is determined. Proton decay rate is found to be acceptable in all cases except one.