Complete spectroscopic structural characterization of novobiocin,isonovobiocin, decarbamylnovobiocin, 2″-(o-Carbamyl)novobiocin,and novobiocin-2″,3″-carbonate

The rigorous structural characterization of novobiocin, is reported using mass spectrometric, infrared and nmr spectroscopic analysis. Complete nmr assignments are reported. Previous reports in the literature had left some quaternary carbon resonances unassigned. Isonovobiocin and decarbamylnovobiocin, although known in the literature for a number of years, have never been completely characterized. Mass spectrometric fragmentation pathways and complete ¹H and ¹³C nmr assignments are reported for these congeners for the first time. The mass spectral fragmentation pathway and nmr assignments are also reported for 2″-(O-carbamyl)novobiocin although the nmr assignments at lower field were reported previously. The structural characterization of novobiocin-2″,3″-carbonate observed in the Test Assay procedure used for Novobiocin is reported for the first time.     

Controlled Synthesis of 2‐Acetyl‐6‐carbethoxypyridine and 2,6‐Diacetylpyridine from 2,6‐Dimethylpyridine

The controlled syntheses of mono‐ and bis‐acetylpyridine from the same starting material (2,6‐dimethylpyridine) are reported, including the asymmetrical compound 2‐acetyl‐6‐carbethoxypyridine, which has not before been reported. The influences of the amount of catalyst EtONa and the reaction conditions to the final products are also explored. A modification of the reported preparation for the 2,6‐dipicolinic acid, 2,6‐dicarbethoxypyridine and 2,6‐diacetylpyridine with higher purity and improved yields is provided here, and the physical and spectral properties of these products are identical to those reported in the literature.     

The isomers of HF-HCN formed in helium nanodroplets: Infrared spectroscopy and ab initio calculations

Binary complexes containing hydrogen cyanide and hydrogen fluoride are formed in helium nanodroplets, and studied using high-resolution infrared laser spectroscopy. Rotationally resolved spectra are reported for the H-F and C-H stretches of the linear HCN-HF complex, a system that has been thoroughly studied in the gas phase. We report the high-resolution spectra of the higher energy, bent HF-HCN isomer, which is also formed in helium. Stark spectra are reported for both isomers, providing dipole moments of these complexes. The experimental results are compared with ab initio calculations, also reported here. Spectra are reported for several ternary complexes, including (HCN)2-HF, HCN-(HF)2, HF-(HCN)2, and HF-HCN-HF.     

General synthesis for chiral 4-alkyl-4-hydroxycyclohexenones

[reaction: see text] Some selective transformations of resorcinol-derived cyclohexadienone are reported. Efforts led to a structure reported to display anticancer properties. On the basis of the results, the structures for natural products reported to contain a 4,6-dihydroxy-4-alkyl-cyclohexenone nucleus are corrected.     

SOME PHOTOPHYSICAL PROPERTIES OF 3-CARBETHOXYPSORALEN, 8-METHOXYPSORALEN and 5-METHOXYPSORALEN TRIPLET STATES

Abstract Triplet absorption spectra, extinction coefficients (ɛ_T), decay rates ( K ₁), oxygen quenching rates (k_q) and intersystem crossing yields (φ_T) for 3-carbethoxypsoralen (3-CPs). 8-methoxypsoralcn (8-MOP) and 5-methoxypsoralen (5-MOP) in methanol are reported. For 8-MOP and 3-CPs corresponding values are also reported with water as the solvent. Some photophysical data are also reported for 5-MOP in water, but ɛ_T and φ_T were not obtained.
The phosphorescence spectra for these furocoumarin derivatives in ethanol at 77 K are reported together with the corresponding lowest triplet energy and lifetime. The values of the various photophysical properties obtained are compared with values reported by previous workers.     

Conformational study of protonated,neutral, and deprotonated formamide

Neutral, protonated, and deprotonated formamide isomers were studied at the 3-21G SCF level with complete geometry optimization. Ten stable structures, ten first-order saddle points, and three second-order saddle points (conformational maxima) are reported. [Total energies are reported in hartrees (1 hartree = 627.51 kcal/mol = 2625.5 kJ/mol) and energy differences are reported in kJ/mol (1 kJ/mol = 0.239 kcal/mol).] Rotational barriers and proton affinities are discussed and compared to isoelectronic amidine species.     

Two-photon absorption in “double molecules”

The two-photon excited fluorescence excitation spectrum is reported for naphthalene and 2,2-binaphthyl, and for fluorene and difluorenyl. These results are compared with the previously reported results for benzene and biphenyl. The exciton approximation predicts that the two-photon spectra of such single and double molecules should resemble each other quite closely, even in cases where the one-photon spectra are quite different. However, this behaviour is not observed in the reported compounds.     

Carbon-13 resonance assignments of some friedelanes and taraxasteranes

Carbon-13 signal assignments of taraxasteryl acetate, taraxasteryl palmitate, taraxasterol and epi-friedelinyl acetate are reported. Some signal assignments of the friedelanones, reported recently by others, are inconsistent and require revision.     

Comment on “Isobaric (vapour + liquid) equilibria for the (1-propanol + 1-butanol) binary mixture at (53.3 and 91.3) kPa”

The (vapor + liquid) equilibrium values reported by Mohsen-Nia and Memarzadeh appear to be flawed. In particular, neither the reported experimental activity coefficients are consistent with the reported composition data nor the reported model parameters can be used to adequately represent their experimental data.     

“Oxidative Deoximation with Bentonite-Supported Silver Carbonate”

An oxidative deblocking procedure of ketoximes using bentonitic clay supported silver carbonate, is proposed. Reaction yields are competitive with those methods previously reported, easy of set-up and work-up was encountered, some important characteristics of the clay are reported.     

Dielectric Constants of Water,Methanol, Ethanol,Butanol and Acetone: Measurement and Computational Study

The dielectric constants (relative permittivities) of water, methanol, ethanol, butanol and acetone were measured at 91.3 kPa and (283.15 and 293.15) K and are reported here. The dielectric constants were determined by using a new setup based on a low-pass filter. The obtained dielectric constant values are compared with those reported in the literature, and are consistent with those reported in the literature. The obtained dielectric constant data were also compared with those calculated by the Kirkwood model. The comparisons indicated that Kirkwood model can be successfully used for calculation of dielectric constants of the pure fluids.     

Evaluation and characterization of a commercial zeeman-modulated tungsten-strip electrothermal atomic absorption spectrometer

The operating parameters and the quantitative of an AAZ-2 Zeeman-modulated tungsten-strip atomic absorption spectrometer are reported. The figures of merit for Ag, Au, Cd, Co, Cu, Fe, Mn, Ni, Pb, Tl, and Zn are reported. Detection limits obtained with the AAZ-2 were comparable to those obtained with other metal atomizers reported in the literature. A maximum heating rate of 12 K ms^?1 was measured for the tungsten-strip atomizer.     

Facile reactions of functionally substituted 1,3,5,7-tetrasilaadamantanes with nucleophilic reagents

The first facile nucleophilic displacement reáctions of functionally-substituted tetrasilaadamantanes are reported and are in dramatic contrast to the previously reported lack of reactivity of this system toward nucleophilic reagents.     

Observation of the A-X electronic transition of the 1-C3H7O2 and 2-C3H7O2 radicals using cavity ringdown spectroscopy

Cavity ringdown spectra of the A-X electronic transition of the 1-propyl and 2-propyl peroxy radicals are reported. Spectroscopic assignments are facilitated by implementing several production mechanisms, either isomer-specific or not. Assignments of specific spectral lines to particular conformers of a given isomer are suggested. Observations on the temporal decay of the various species are reported.     

Carbon-13 nuclear magnetic resonance studies on dichloropyridoquinolines

Carbon-13 NMR chemical shifts are reported for six angular and one linear dichloropyridoquinolines in CDCl₃. The chemical shift assignments have been made using model compounds, fully coupled spectra, selective proton decoupling and results from lanthanide shift studies. Chlorine substituent effects are compared to those reported for chloroquinolines. The effect of the heteroaromatic nitrogen atoms on ¹³C? ¹H coupling constants in these polycyclic systems are compared to those reported for pyridine systems.     

Synthesis and reactivity of new chelate-N-heterocyclic biscarbene complexes of ruthenium

The carbene-ligand precursors methylenebis(N-alkylimidazolium) iodide (alkyl = methyl, neo-pentyl) and ethylenebis(N-methylimidazolium) chloride have been used in the preparation of several new Ru(II)-p-cymene complexes where the ligand behaves as mono- and bidentate. The molecular structures of the two biscarbene-complexes are reported. From the data reported, we can conclude that steric reasons (mainly the bisimidazolium linkers, methylene/ethylene) are the main factors determining both reactivity and synthetic difficulties of the products reported.     

Luminescence characteristics of several classes of drugs affecting the central nervous system

The excitation, fluorescence and phosphorescence characteristics of 29 compounds of psychopharmacological interest have been studied in ethanol at 77 k. Phosphorescence lifetimes are reported and the low-temperature luminescence spectra discussed. Luminescence characteristics of several important 1,4-benzodiazepines in acidic, basic and neutral solution are reported.     

α-Silyl ketones: A high resolution mass spectrometric study

The mass spectrometric fragmentation modes of a series of α-silyl phenyl ketones are reported. For comparison, the fragmentation modes of the analogous silanol and α,β-epoxysilane are also reported. Migration of phenyl moieties to silicon is common throughout the ketone series.     

The osmotic and activity coefficients of some guanidinium salts at 298.15 K

Osmotic and activity coefficients are reported for aqueous solutions of six guanidinium salts at (298.15 ± 0.01) K, and these coefficients are compared with those of other uni-univalent electrolytes. The results are consistent with previously reported spectral results that indicated hydrogen bonding of guanidinium ion with chloride ion in aqueous solutions.     

Cyclization reactions of 3-hydrazino[1, 2, 4]triazino[5, 6-b]indole

The reaction of 3-hydrazino[1, 2, 4]triazino[5, 6-b]indole I with nitrous acid affords the azide III which could be cyclized with acetic anhydride to 10-acetyl-10H-tetrazolo[5′,1′:3, 4][1, 2, 4]triazino[5, 6-b]indole IIb . Cyclization reactions of I with acetic anhydride, ethyl chloroformate, carbon disulphide and aromatic aldehydes to the corresponding fused triazolo derivatives V–VIII are reported. On the other hand cyclization reactions of I with malononitrile, ethyl cyanoacetate, ethyl acetoacetate and acetylacetone to the corresponding condensed pyrazolino derivatives IX–XI are also reported. The reaction of I with α-dicarbonyl compounds to form mono and dihydrazones are reported. The structure of the compounds prepared and their cyclization mechanisms are reported.