RP-HPLC analysis of methanol extract of Viscum articulatum.

BACKGROUND: Viscum articulatum Burm. (Family: Loranthaceae) is commonly known as mistletoe. In ayurveda, the plant parts are used in "Kapha", "Vata", diseases of the blood, ulcer, and epilepsy. The plant parts are also used in urinary tract infection and wound infection. The plant contains five triterpenoids such as α-amyrin, lupeol, betulin, betulinic acid and oleanolic acid, exhibiting several pharmacological activities including antimicrobial, anti-HIV, antitumor, antiviral activity. OBJECTIVE: To ensure the content of uniformity of oleanolic acid, a RP-HPLC method has been developed for estimation of oleanolic acid in V. articulatum aerial part. MATERIAL AND METHODS: The RP-HPLC method was carried out in reverse phase C18 column, using methanol and water as mobile phase in the ratio of 95:5 (v/v), at the flow rate of 1 mL/min. The pH of aqueous phase was adjusted 3.2 with 1% (v/v) glacial acetic acid. The λmax was set at 210 nm. RESULTS: The retention time of oleanolic acid was found at 21.5 ± 0.05 min. The linearity of the response was found to be 10-800 µg/mL. The coefficient of determinants of oleanolic acid was found to be (r2) 0.995 and equation Y = 19462X + 16,172. The LOD and LOQ were found to be for oleanolic acid (1.96% w/w) 0.197 ± 0.63 and 0.623 ± 0.87 µg/mL, respectively. The developed method was accurate, specific, precise and reproducible. CONCLUSION: This RP-HPLC may be useful for quantitative estimation of the chemical constituents present in the plant extract as well as the quality assessment of the herbal product.

Conformational analysis of N,N,N-Trimethyl-(3,3-dimethylbutyl)ammonium iodide by NMR spectroscopy: a sterically hindered trans-standard.

A predominantly trans-1,2-disubstituted ethane system - N,N,N-trimethyl-(3,3-dimethylbutyl)ammonium iodide - is of particular interest for conformational analysis, because it contains both an organic and a highly polar substituent, making it soluble and thus applicable to study in a large variety of solvents. The fraction of the trans conformer of this molecule in a wide range of protic and aprotic solvents was determined by the nuclear magnetic resonance proton couplings to be approximately 90%, in contrast to the previously assumed 100%. The consistently strong preference of the trans conformation should establish N,N,N-trimethyl-(3,3-dimethylbutyl)ammonium iodide as a possibly useful 'trans-standard' in conformational analysis, much more so than 1,2-ditert-butylethane, which has a poor solubility in many solvents.

Conformational preferences of trans-1,2- and cis-1,3-cyclohexanedicarboxylic acids in water and dimethyl sulfoxide as a function of the ionization state as determined from NMR spectroscopy and density functional theory quantum mechanical calculations.

The populations of diaxial (aa) and diequatorial (ee) conformers of trans-1,2- and cis-1,3-cyclohexanedicarboxylic acids (CDCAs; 1 and 2, respectively) and their salts were determined in water and dimethyl sulfoxide (DMSO) solutions from vicinal proton-proton NMR J couplings ((3)J(HH)). Optimized geometries and free energies for these compounds were obtained at the M06-2X/cc-pVTZ(-f)++ level. Although carboxylic acid groups in cyclohexane rings are generally believed to be far more stable (~2 kcal/mol) in equatorial than axial positions, this investigation demonstrated that an aa conformation (normally assumed to be completely insignificant for these compounds) can be favored depending on the medium and ionization state: strong ee preferences (>90%) were observed in water and DMSO for both diacids and their salts, except for the dianion of 1 in DMSO, which was found to be substantially aa (~57%). The possibility of intramolecular hydrogen bonding (H-bonding) was also investigated; the ratios of the ionization constants (K(1)/K(2)) indicated an absence of intramolecular H-bonding because K(1)/K(2) ≪ 10(4) (a standard criterion for non-H-bonding in dicarboxylic acids) for both 1 and 2 in water and also for 2 in DMSO. For 1, K(1)/K(2) increased drastically in DMSO (K(1)/K(2) = 4 × 10(6)), where (3)J(HH) and the ratio K(1)/K(E) = 10, K(E) being the acidity constant of the monomethyl ester of 1, indicated the formation of an intramolecular H-bond for the monoanion in this solvent. An explanation for the observation of compact dianions in solution in terms of the generalized Born equation is also provided.

Theoretical calculations on the tetramethyldisilene rearrangement: a new approach to an old mechanistic problem.

Roark and Peddle first observed that, when not trapped, Me(2)Si=SiMe(2) underwent a series of rearrangements to give two major isomeric products: 1,1-dimethyl-1,3-disilacyclobutane and 1,3-dimethyl-1,3-disilacyclobutane. The widely accepted mechanism for this rearrangement was proposed by Barton and co-workers. However, little is known about the thermodynamic or kinetic properties of this reaction, because the relevant data are limited to the product ratios of the two isomers. Our calculations predict that the product ratio is driven by kinetic control rather than thermodynamic control. We also show that new DFT functionals, such as MPW1K and M052X, produce thermochemical results comparable with CCSD(T) calculations.

Photochemistry of substituted dibenzothiophene oxides: the effect of trapping groups.

[reaction: see text] Photolyses of dibenzothiophene sulfoxides (DBTOs) with intramolecular trapping functionalities attached in the 4-position show higher quantum yields of deoxygenation. Deoxygenation quantum yields are also less solvent dependent for the substituted DBTOs. Product analysis shows a detectable amount of intramolecular O-trapped products and suggests that solvent effects observed in previous studies of DBTO derive at least mainly from the reactivity between the oxidizing species that is released, presumably O((3)P), and the solvent, rather than from other macroscopic solvent parameters.

Photochemistry and photophysics of halogen-substituted dibenzothiophene oxides.

Dibenzothiophene-5-oxide (DBTO) cleanly produces dibenzothiophene (DBT) on direct photolysis, but with very low quantum yield. A proposed mechanism involves scission of the S-O bond which is coupled to an intersystem crossing step, thus producing the sulfide and O((3)P) via a unimolecular pathway. To test this hypothesis, heavy atom substituted DBTOs were prepared and photolyzed. Iodo-, bromo-, and chloro-substituted DBTOs show higher quantum yields for deoxygenation than does the parent molecule, in the order consistent with an intersystem crossing-related heavy atom effect. 2-Iododibenzothiophene also undergoes photochemical deiodination. Phosphorescence data are consistent with heavy-atom assisted intersystem crossing.