Trapping H- bound to the nitrogenase FeMo-cofactor active site during H2 evolution: characterization by ENDOR spectroscopy

We here show that the iron-molybdenum (FeMo)-cofactor of the nitrogenase alpha-70(Ile) molybdenum-iron (MoFe) protein variant accumulates a novel S = (1)/(2) state that can be trapped during the reduction of protons to H(2). (1,2)H-ENDOR measurements disclose the presence of two protons/hydrides (H(+/)(-)) whose hyperfine tensors have been determined from two-dimensional field-frequency (1)H ENDOR plots. The two H(+/)(-) have large isotropic hyperfine couplings, A(iso)( )() approximately 23 MHz, which shows they are bound to the cofactor. The favored analysis for these plots indicates that the two H(+/)(-) have the same principal values, which indicates that they are chemically equivalent. The tensors are further related to each other by a permutation of the tensor components, which indicates an underlying symmetry of binding relative to the cofactor. At present, no model for the structure of the iron-molybdenum (FeMo)-cofactor in the S = (1)/(2) state trapped during the reduction of H(+) can be shown unequivocally to satisfy all of the constraints generated by the ENDOR analysis. The data disfavors any model that involves protonation of sulfides, and thus suggests that the intermediate instead contains two chemically equivalent bound hydrides; it appears unlikely that these are terminal monohydrides.     

Facile and efficient synthesis of chiral sulfoxide esters: Versatile tool in asymmetric synthesis

Facile and efficient synthesis of sulfoxide esters using menthols as chiral auxiliary is described. Phenylthio/benzylthio/naphthylthioacetic esters act as an efficient substrate for chiral sulfoxides via oxidation in one step. The structural and stereochemical aspects of target product were established on the basis of various spectroscopic studies, namely FT-IR, NMR (¹H NMR and ¹³C NMR) and elemental analysis. This method is simple, fast, convenient and very efficient.     

Human Health Risk Surveillance Through the Determination of Organochlorine Pesticides by High-Performance Liquid Chromatography in Water,Sediments, and Fish from the Chenab River,Pakistan

The current study assessed the spatiotemporal variations and human health surveillance associated with organochlorine pesticide (OCP) contamination in water, sediments, and fish from Chenab River, Pakistan. The OCP determinations were performed using high-performance liquid chromatography with a reverse-phase C18 column. The total OCP levels ranged from 13.33 to 274.59?ng/L in water, 4.63 to 239.11?ng/g in sediments, and 23.79 to 387.12?ng/g in fish species. The overall pattern of mean OCP concentrations followed the order as ΣDDTs?>?Σendosulfan?>?aldrin and OCP pollution pattern among the headworks were Khanki Barrage?>?Qadirabad Barrage?>?Trimmu Barrage?>?Marala Barrage in all three environmental matrixes during both seasons. The estimated daily intake (EDI) for ∑OCPs was found to be 22.44?ng/kg/day. The hazard ratios calculated to assess the carcinogenic risk indicated that the values for ∑DDT and aldrin at the 95th percentile concentrations were greater than one, indicating the probability of carcinogenic risk occurrence of one in million populations due to fish consumption. Therefore, these high levels of OCPs and carcinogenic risk through fish consumption highlight the needs of immediate elimination of OCPs from riverine environment of Chenab River and we recommend long-term monitoring-based freshwater ecological studies to be conducted in the study area.     

Solitaire and gemini metallocene porphyrazines.

We report the synthesis and physical characterization of a series of peripherally functionalized porphyrazines (pzs) of the forms H2[pz(A;B3)] and trans-H2[pz(A2);B2], where A is a dithiolene chelate of molybdocene or vanadocene and B is a solublizing group. The precursor pz's 8 and 9, of the form H2[pz(A;B3)], where A = (4-(butyloxycarbonyl)-S-benzyl)2 and B = di-tert-butylphenyl (8) or di-n-propyl (9), have been prepared, deprotected, and peripherally metalated with molybdocene and vanadocene to form 1(Mo(IV)) and 1(V(IV)), prepared from 8, and 2(Mo(IV)) from 9, respectively. Likewise, the protected trans-H2[pz(A2);B2)], where A = (S-benzyl)2 and B = 3,6-butyloxybenzene (12) or A = (S-benzyl)2 and B = (tert-butylphenyl)2 (13), have been prepared and peripherally metalated with molybdocene and vanadocene to give the trans dinuclear complexes, 3(Mo(IV),Mo(IV)), 3(V(IV),V(IV)) (from 12), and 4(V(IV),V(IV)) (from 13). A crystal structure of the trans vanadocene pz 4(V(IV),V(IV)) is presented; the distance between the two vanadium atoms is 14.5 A. The molybdocene-appended pz's are highly redox active and exhibit cyclic voltammograms that are more than just the sum of the metallocene and the parent pz's. Chemical oxidation with FcPF6 gives the Mo(V) species 1(Mo(V)), 2(Mo(V)), 3(Mo(V),Mo(IV)), and 3(Mo(V),Mo(V)). Their EPR spectra are indicative of extensive delocalization from the Mo(V) into the dithiolato-pz. The EPR spectrum of the mononuclear paramagnetic vanadocene pz, 1(V(IV)), shows an expected 8-line pattern for an S = 2 system with hyperfine coupling to a single 51V (I = 7/2) nucleus, but the dinuclear vanadocene pz's, 3(V(IV),V(IV)) and 4(V(IV),V(IV)), exhibit a striking 15-line pattern of the same breadth from the S = 1 state formed by exchange coupling between the S = 2 vanadium centers of a dinuclear complex. Thus, the porphyrazine macrocycle is capable of mediating magnetic exchange interactions between metal ions bound to the periphery, separated by 14.5 A.     

pH‐sensitive hemolysis by random copolymers of alkyl acrylates and acrylic acid

We have been designing and synthesizing synthetic polymers that mimic viral fusogenic peptides, which contain peptide residues having alkyl groups and carboxyl groups. We have synthesized two different types of such polymers, and their abilities to hemolyse red blood cells at pH 7.4 and 5.5 are compared here. The polymers are poly(2‐alkylacrylic acid)s such as poly(2‐propylacrylic acid), and random copolymers of poly(alkyl acrylate‐co‐acrylic acid) where the alkyl group is propyl or butyl. We have found that the poly(2‐alkylacrylic acid)s such as poly(2‐propylacrylic acid) are significantly more hemolytic at acidic pH than the random copolymers of equivalent propyl and carboxyl contents.     

1H NMR isotope shifts arising from the substitution of 12C by 13C: application to polycyclic aromatic hydrocarbon anions

Isotope shifts are a well-established tool for structural analysis by NMR. The substitution of a protium with a deuterium is the most widely studied of these effects. However, such studies call for specific deuteration that requires complex synthetic techniques owing to the low natural abundance of deuterium. ¹³C occurs at a higher natural abundance and couples strongly with its attached proton. We have developed and refined a method to reliably observe these much smaller shifts without needing to resort to chemical synthesis. We show that carbon induced isotope shifts reflect structural features. Copyright © 2001 John Wiley & Sons, Ltd.     

Low Frequency Rf Heating with a Helical Coupler in a Hot Electron Plasma

A magnetic mirror (mirror ratio 2.38:1) containing ECRH generated hydrogen plasma, with a density of 5 x 1010 cm-3 with cold electron temperature of 11 eV, was used to study propagation of an artificially launched wave varying as ej(?t + m? - kz) at approximately the ion cyclotron frequency. The wave was transmitted between two similar internally placed helically wound antennas separated by 11 wavelengths. The coupling between them was enhanced by as much as 50 times in the presence of plasma. The m = 1 left-handed component was cut off when ? > ?ci. Electron temperatures could be increased by more than 2 times with the m = 1 mode, presumably due to ion heating. Little pump-out was observed.     

On the variation of co-ordinates in subspaces

Summary Let1≦k≦n−1, 2≦n. This paper examines the vectors δ_p(L_k), where L_k is a k-dimensional subspace of an n-dimensional space, and the co-ordinates of δ_p(L_k) are given below by (1.1). For fixed k, the set of such vectors as L_k varies is determined for p=2. For general p, information is given on upper and lower bounds for the sum of the co-ordinates of δ_p(L_k). Dedicated to the sixtieth birthday of Prof. Edgar R. Lorch This research was supported in part by the Office of Naval Research under contract number Nonr 3775(09), NR 047040.     

Temperature dependence of the 1H chemical shift of tetramethylsilane in chloroform, methanol, and dimethylsulfoxide

The chemical shift of tetramethylsilane (TMS) is usually taken to be zero. However, it does vary slightly with temperature, having obvious implications for studies of temperature effects on chemical shifts. In this work, we measure the variation in the chemical shift of TMS with temperature in three solvents, CDCl3, CD3OD, and DMSO-d6, relative to the resonant frequency of 3He gas, which can be reasonably assumed to be temperature independent. In all three solvents, the average temperature coefficient over a wide temperature range is about -6 x 10(-4) ppm/degrees C, a factor of five smaller than that previously reported in the literature. Data are included for 3He resonance frequencies over a temperature range of -110 to +180 degrees C, along with new measurements of volume magnetic susceptibilities of the three solvents and estimates of their temperature dependence. A novel method is used to provide temperature measurement via 2H resonances of methanol and ethylene glycol samples, which can concurrently be used for field/frequency locking.