BHC Residues in Milk: A Gas Chromatographic Investigation

Abstract

BHC residues were determined in milk samples of cows and buffaloes (Indore, M.P., India), α-, β- and γ-BHC were identified in samples from four different localities using gas chromatography. All samples were contaminated with BHC, with the toxic gamma isomer appearing in the largest concentration. Buffalo milk was more contaminated than cow milk, with maximum values of 17 and 12 μg/l, respectively.     

Androstane‐Type Steroidal Glycoside from the Roots of Asparagus curillus Buch.‐Ham. ex Roxb.

The novel androstane‐type steroidal glycoside 1 was isolated from the roots of Asparagus curillus Buch .‐Ham . ex Roxb . Its structure was elucidated as (2α,3β,5α,17β)‐17‐(1‐methoxyethoxy)‐17‐methylandrostane‐2,3‐diol 3‐(β‐D ‐digitoxopyranoside) by means of chemical and advanced spectral analysis.     

Electrochemical synthesis of copper nanowires in anodic alumina membrane and their impedance analysis

Copper (Cu) nanowires having 20 nm diameter were fabricated by electrodeposition within the pores of anodic alumina membrane (AAM) by using template synthesis method. The morphology and composition of nanowires was characterized by scanning electron microscope (SEM) and energy dispersive X-ray fluorescence (EDXRF). X-ray diffraction (XRD) was utilized for structural characterization. Impedance of nanowires was measured at room temperature by leaving the nanowires embedded in the insulating template membrane and small decrease in impedance was found at higher frequency above 10 kHz.     

Liquid–liquid–liquid microextraction of degradation products of nerve agents followed by liquid chromatography–tandem mass spectrometry

Alkyl alkylphosphonic acids (AAPAs) are important environmental markers of nerve agents. A simple hollow fiber-based liquid–liquid–liquid microextraction (HFLLLME) technique has been developed to enrich the AAPAs from water. AAPAs were extracted from acidified aqueous phase to organic phase present in pores of the hollow fiber, and then back extracted into the alkaline acceptor phase present in the lumen of the hollow fiber. Variables affecting the HFLLLME process were optimized using a Plackett–Burman design and a Doehlert design. Optimal experimental conditions were: organic solvent, 1-octanol; pH of acceptor phase, 14; extraction time, 60 min; pH of donor phase, 1; and NaCl concentration, 10% (w/v). Depending upon the alkyl substituent, lower limits of detection varied from 0.1 to 100 ng mL⁻¹ (S/N ≥ 5). Repeatability of the method was observed with relative standard deviation of 1.49–9.83% (n = 3). After validation, the method was applied to detect AAPAs present in the water sample provided by the Organization for Prohibition of Chemical Weapons (OPCW) during the 23rd official proficiency test. The added advantage of this method is that several successive extractions of AAPAs from the same water sample can be performed.     

A mild and convenient one-pot two-step synthesis of hydroxy- iminodihydrobenzofurans mediated by silica gel under microwave activation conditions

A convenient one-pot two-step procedure for the synthesis of hydroxyiminodihydrobenzofurans assisted by microwave irradiation in presence of silica gel is described herein. Cyclic 1,3-dicarbonyl compounds reacted smoothly with various nitroolefins to furnish hydroxyiminodihydrobenzofuran derivatives as the mixture of E and Z isomers. Clean reaction conditions, no work-up procedure, easy isolation and good yields of the products are the salient features of the methodology.     

Neutral Ni(II) complexes based on keto-enamine salicylideneanilines active for selective dimerization of ethylene

Single component organonickel(II)phosphino neutral complexes from salicylideneaniline based ligands bearing N–O chelate sites, were synthesized, which were found efficient in dimerizing ethylene selectively to various butene products.     

Energetics of Electron‐Transfer Reactions of Photoinitiated Polymerization: Dye‐Sensitized Fragmentation of N‐Alkoxypyridinium Salts

Electron transfer from excited dyes to N‐alkoxypyridinium salts leads to reductive cleavage of the N−O bond to give an alkoxy radical that can be used to initiate polymerization. Bond‐dissociation energies obtained from calculations based on density‐functional theory are in agreement with predictions from a thermochemical cycle. These data show a difference of ca. 290 – 315 kJ/mol between the BDE of the pyridinium and that of the pyridyl radical and indicate that the fragmentation of the radical is highly exothermic. The energetic requirements for the photochemical electron transfer are discussed in terms of a simplified model that shows that the initiation efficiency of the radical polymerization can be correlated with a single parameter, the reduction potential of the sensitizing dye. Dyes from many classes and with absorption bands spanning the entire visible region were found to be effective in initiating photopolymerization of acrylate monomers in this system. Doubling of the photoresponse can be achieved through coupling of the reductive cleavage of the N‐alkoxypyridinium with an oxidative cleavage of a C−B bond of an alkyltriarylborate, a process that utilizes the chemical potential stored in the oxidized dye following electron transfer to the pyridinium salt.     

A highly contorted push–pull naphthalenediimide dimer and evidence of intramolecular singlet exciton fission

Singlet fission is a process by which two molecular triplet excitons are generated subsequent to the absorption of one photon. Molecules that enable singlet fission have triplet state energy at least half of the bright singlet state energy. This stringent energy criteria have challenged chemists to device new molecular and supramolecular design principles to modulate the singlet–triplet energy gap and build singlet fission systems from a wide range of organic chromophores. Herein, we report for the first time intramolecular singlet fission in the seminal naphthalenediimide (NDI) scaffold constrained in a push–pull cyclophane architecture, while individually the NDI chromophore does not satisfy the energy criterion. The challenging synthesis of this highly contorted push–pull cyclophane is possible from the preorganized pincer-like precursor. The special architecture establishes the shortest co-facial NDI⋯NDI contacts (3.084 Å) realized to date. Using broadband femtosecond transient absorption, we find that the correlated T–T pair forms rapidly within 380 fs of photoexcitation. Electronic structure calculations at the level of state-averaged CASSCF (ne,mo)/XMCQDPT2 support the existence of the multi-excitonic T–T pair state, thereby confirming the first example of singlet exciton fission in a NDI scaffold.

We report for the first-time intramolecular singlet fission (SF) in the naphthalenediimide (NDI) scaffold constrained in a cyclophane architecture, while individually the NDI units does not satisfy the requisite energy criterion for SF.     

Synthesis and Characterization of a Magnesium Boryl and a Beryllium‐Substituted Diazaborole

Reaction of a lithium boryl, [(THF)₂Li{B(DAB)}] (DAB=[(DipNCH)₂]^2?, Dip=2,6‐diisopropylphenyl), with a dinuclear magnesium(I) compound [{(^MesNacnac)Mg}₂] (^MesNacnac=[HC(MeCNMes)₂]^?, Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, [(^MesNacnac)(THF)Mg{B(DAB)}]. Attempts to prepare the magnesium boryl via a salt metathesis reaction between the lithium boryl and a β‐diketiminato magnesium iodide compound, instead led to an intractable mixture of products. Similarly, reaction of the lithium boryl with a β‐diketiminato beryllium bromide precursor, [(^DepNacnac)BeBr] (Dep=2,6‐diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, [{(^DepNacnac)Be(4‐DAB^?H)}BBr]. For sake of comparison, the same group 2 halide precursor compounds were treated with a potassium gallyl analogue of the lithium boryl, viz. [(tmeda)K{:Ga(DAB)}] (tmeda=N,N,N’,N’‐tetramethylethylenediamine), but no reactions were observed.