Triplet-sensitized photolysis of alkoxycarbonyl azides in solution and matrices

Photolysis of azides 1–4 in methanol, which have a built-in intramolecular triplet sensitizer, yields mainly carbamates 5–8. Laser flash photolysis of 1–4 shows formation of their triplet-excited ketone, which decays by intramolecular energy transfer to form triplet nitrenes 1n–4n. Irradiating 1–3 in matrices yields isocyanic acid, whereas photolysis of 4 forms isocyanate 4i. The depletion rate of the azide bands between 2100 and 2200 cm^?1 is different than the rate of formation for the isocyanic acid bands at ～2265 cm^?1; thus, the formation of isocyanic acid is a stepwise process. Irradiating 1 in matrices produces an absorption band due to nitrene 1n (λ_max ～ 343 nm), which is depleted upon further irradiation, whereas the absorption due to 4-acetyl benzaldehyde (λ_max ～ 280 nm) increases with prolonged irradiation. We propose that formation of isocyanic acid in matrices must come from secondary photolysis of nitrenes 1n–3n. This mechanism is further supported by calculation, which show that the estimated transition state for 1n–4n to fall apart to yield alkoxy and cyanato radicals is only ～34 kcal/mol above the ground state of the triplet nitrenes and thus the cleavage can take place photochemically. Thus, nitrenes 1n–4n can be formed selectively, but these intermediates are highly photosensitive and undergo secondary photolysis in matrices.     

Titrimetric assay of ofloxacin in pharmaceuticals using cerium(IV) sulphate as an oxidimetric reagent

Two titrimetric methods which are simple, rapid, cost-effective and eco-riendly are described for the determination of ofloxacin (OFX) in bulk drug and in tablet formulations based on the oxidation of OFX by Ce(IV) sulphate. In direct titrimetry (method A), the acidified solution of OFX is titrated directly with Ce(IV) sulphate using ferroin as indicator, and indirect titrimetry (method B) involves the addition of known excess of Ce(IV) sulphate to an acidified solution of OFX followed by the determination of unreacted oxidant by back titration with ferrous ammonium sulphate (FAS) using the same ferroin indicator. In both the methods, the amount of Ce(IV) sulphate reacted corresponds to OFX concentration. Method A and method B permit the determination of OFX over the concentration range of 1.5?C15 mg in both the methods and the quantitation is based on a 1: 5 reaction stoichiometry (OFX: Ce (IV) sulphate). The methods were statistically evaluated by calculating percent relative error (% RE) for accuracy and percent relative standard deviation (% RSD) for precision, and were applied successfully to the determination of OFX in tablets with mean recoveries in the range of 96.50?C98.42%. No interference was observed from common additives found in pharmaceutical preparations. The accuracy and reliability of the methods were further ascertained by performing recovery tests s standard-addition technique.     

Sodium bromide catalysed one-pot synthesis of tetrahydrobenzo[b]pyrans via a three-component cyclocondensation under microwave irradiation and solvent free conditions

Sodium bromide catalysed three-component cyclocondensation of aryl aldehydes, alkyl nitriles and dimedone proceeds under microwave irradiation in solvent free conditions to give highly functionalised tetrahydrobenzo[b]pyrans in excellent yields.     

Ugi three-component coupling reaction for the synthesis of 2-(6-oxo-11-phenyl-7,8-dihydrobenzo[b]pyrrolo[1,2-d][1,4]diazocin-5(6H)-yl)-2-phenylacetamide derivatives

A three-component, four center Ugi reaction of 3-(1-(2-aminophenyl)-5-phenyl-1H-pyrrol-2-yl)propanoic acid with aromatic aldehyde and t-butyl isocyanide has been achieved to produce a novel class of N-tert-butyl-2-(6-oxo-11-phenyl-7,8-dihydrobenzo[b]pyrrolo[1,2-d][1,4]diazacine-5(6H)-yl)-2-phenylacetamides in moderate to good yields.     

Ring opening of epoxides with alcohols using Fe(Cp)2BF4 as catalyst

Fe(Cp)₂BF₄ is an efficient catalyst for the alcoholysis of aromatic, aliphatic, and cyclic epoxides giving excellent yields of the corresponding β-alkoxy alcohols under ambient conditions. The methanolysis of styrene oxide using Fe(Cp)₂BF₄ as a catalyst (5 mol %) gave excellent yield of 2-methoxy-2-phenylethanol with complete regio-selectivity. The ring opening of cyclic epoxides gave 77–97% yields of trans-β-methoxy alcohols, in 0.5–6 h. The use of 1,2-epoxyhexane and 1,2-epoxydodecane as substrates gave both regioisomers in excellent yields. The first order rate of reaction with respect to catalyst was observed for the kinetics of ring opening of 1,2-epoxyhexane with methanol.     

A simultaneous TG-DTG-DSC-quadrupole mass spectrometric study

Mechanistic aspects of the thermal decomposition of benzyl-triethyl-ammonium tetrafluoroborate (BTEATFB) employing simultaneous TG-DSC coupled with a quadrupole mass spectrometer are considered in this work. The experiments were conducted in an inert atmosphere of helium. The decomposition of BTEATFB proceeds through several competing mechanisms. While nucleophilic substitution reaction occurs through the formation of a tertiary amine and plays an important role in the initial stages of the decomposition, and the probability of Hoffman elimination also exists.     

Assessment of inhalation exposure potential of broken uranium ore piles in low-grade uranium mine

This paper presents the assessment of inhalation exposure potential of broken uranium ore piles in different stopes of Jaduguda uranium mines of India. ²²²Rn emanation coefficient of broken uranium ore was measured in laboratory by collecting air sample from airtight glass jar containing ore sample. An attempt was also made to correlate the emanation coefficient with ²²⁶Ra content of the ore. The ²²²Rn progeny doses estimated based on radon activity concentration of broken ore, occupancy period and equilibrium ratio in different stopes were well below the prescribed limit of International Commission on Radiological Protection. The maximum ²²²Rn progeny dose contribution from broken ore piles was worked out to be 0.22 mSv year^?1. This suggests that the broken ore piles are not the significant contributor of inhalation exposure under the existing ventilation condition of Jaduguda uranium mine.     

Formation of Periodic γ‐Turns in α/β‐Hybrid Peptides: DFT and NMR Experimental Evidence

Hybrid peptidic oligomers comprising natural and unnatural amino acid residues that can exhibit biomolecular folding and hydrogen‐bonding mimicry have attracted considerable interest in recent years. While a variety of hybrid peptidic helices have been reported in the literature, other secondary structural patterns such as γ‐turns and ribbons have not been well explored so far. The present work reports the design of novel periodic γ‐turns in the oligomers of 1:1 natural‐α/unnatural trans‐β‐norborenene (TNAA) amino acid residues. Through DFT, NMR, and MD studies, it is convincingly shown that, in the mixed conformational pool, the heterogeneous backbone of the hybrid peptides preferentially adopt periodic 8‐membered (pseudo γ‐turn)/7‐membered (inverse γ‐turn) hydrogen bonds in both polar and non‐polar solvent media. It is observed that the stereochemistry and local conformational preference of the β‐amino acid building blocks have a profound influence on accessing the specific secondary fold. These findings may be of significant relevance for the development of molecular scaffolds that facilitate desired positioning of functional side‐chains.     

Nonsteroidal Anti‐inflammatory Drug‐based N‐Allylidene Benzohydrazides and 1‐Acyl‐2‐pyrazolines: Their Synthesis as Potential Cytotoxic Agents In Vitro

A series of 1‐acyl‐2‐pyrazoline derivatives derived from nonsteroidal anti‐inflammatory drugs was designed as potential anticancer agents. Synthesis of these compounds was carried out via the condensation reaction of chalcones and acid hydrazides under heating. The methodology did not require the use of any costly reagents or catalysts, and the acid hydrazide reactants were readily prepared from mefenamic acid or ibuprofen. A variety of 1‐acyl‐2‐pyrazolines was prepared in good to excellent yields. An N‐allylidene benzohydrazide intermediate was isolated during the reaction optimization study, the structure of which was confirmed unambiguously by X‐ray single crystal data. A range of N‐allylidene benzohydrazides were also prepared in good yields. Some of the compounds synthesized showed promising cytotoxic activities when tested against HCT‐15 human colon cancer cell line in vitro.