New chiral phosphine-phosphite ligands in the enantioselective palladium-catalyzed allylic alkylation

A series of chiral phosphine-phosphite ligands 1-6 have been synthesized and used in the enantioselective palladium-catalyzed reaction of rac-1,3-diphenyl-2-propenyl acetate with dimethyl malonate as nucleophile. Ligands 1a, 2, 3, 5a, 6a, and 6b have been synthesized starting from racemic tert-butylphenylphosphinoborane. The use of dynamically resolved Li phosphide (-)-sparteine provided the optically pure ligands. Crystals of the allylpalladium (6a) complex were obtained, suitable for X-ray crystal structure determination. The X-ray crystal structure of the allylpalladium (6a) complex revealed a longer palladium-carbon bond distance trans to the phosphine moiety indicating that the attack of the nucleophile takes place at the carbon trans to the phosphine moiety. This was confirmed by the fact that the phosphine moiety did not affect the enantioselectivity directly. Under mild reaction conditions, enantioselectivities up to 83% were obtained (25 degrees C) with ligand 1e. Systematic variation of the ligand bridge and the phosphite moiety showed that the configuration of the product is controlled by the atropisomerism of the biphenyl substituent at the phosphite moiety. The conformation of the biphenyl group, in turn, is controlled by the substituent at the chiral carbon in the bridge. Ligands with large bite angles yielded higher enantioselectivities.     

Aminosulf(ox)ides as ligands for Iridium(I)-catalyzed asymmetric transfer hydrogenation

A new class of efficient catalysts was developed for the asymmetric transfer hydrogenation of unsymmetrical ketones. A series of chiral N,S-chelates (6-22) was synthesized to serve as ligands in the iridium(I)-catalyzed reduction of ketones. Both formic acid and 2-propanol proved to be suitable as hydrogen donors. Sulfoxidation of an (R)-cysteine-based aminosulfide provided a diastereomeric ligand family containing a chiral sulfur atom. The two chiral centers of these ligands showed a clear effect of chiral cooperativity. In addition, aminosulfides containing two asymmetric carbon atoms in the backbone were synthesized. Both the sulfoxide-containing beta-amino alcohols and the aminosulfides derived from 1,2-disubstituted amino alcohols gave rise to high reaction rates and moderate to excellent enantioselectivities in the reduction of various ketones. The enantioselective outcome of the reaction was favorably affected by selecting the most appropriate hydrogen donor. Enantioselectivities of up to 97% were reached in the reduction of aryl-alkyl ketones.     

Molecularly Imprinted Supermacroporous Cryogels for Myoglobin Recognition

Myoglobin is a primary iron, and oxygen-binding protein of muscle tissues and levels can be an important diagnostic biomarker for acute myocardial infarction, myocardial necrosis, or other cardiac diseases. The establishment of myoglobin recognition systems is important because of its protein’s structural and functional values in physiology, biochemistry, and diagnostic value in some damaged muscle tissue and cardiac diseases. For this purpose, we used molecular imprinting technique for myoglobin recognition from aqueous solutions and human plasma. In the first step, myoglobin-imprinted poly(hydroxyethyl methacrylate) (PHEMA) cryogels (MGb-MIP) were prepared, and optimum myoglobin adsorption conditions were determined. Selectivity experiments have been done with the competitive proteins, and myoglobin adsorption from IgG and albumin-free human plasma was studied. The purity of the desorbed samples was determined with SDS-PAGE. The desorption efficiency and reusability of the MGb-MIP cryogels were tested, and it was shown that without any significant loss in the adsorption capacity, MGb-MIP cryogels can be used a number of times for myoglobin recognition and separation.     

Multiresidue analysis of multiclass plant growth regulators in grapes by liquid chromatography/tandem mass spectrometry

A selective and rapid multiresidue analysis method is presented for simultaneous estimation of 12 plant growth regulators (PGRs), namely, auxins (indol-3-acetic acid, indol-3-butyric acid, and naphthyl acetic acid), cytokinins (kinetin, zeatin, and 6-benzyladenine), gibberellic acid (GA3), abscisic acid, and synthetic compounds, namely, forchlorfenuron, paclobutrazole, isoprothiolane, and 2,4-dichlorophenoxy acetic acid (2,4-D) in bud sprouts and grape berries at the development stages of 2-3 and 6-8 mm diameters, which are the critical phases when exogenous application of PGRs may be necessary to achieve desired grape quality and yield. The sample preparation method involved extraction of plant material with acidified methanol (50%) by homogenization for 2 min at 15000 rpm. The pH of the extract was enhanced up to 6 by adding ammonium acetate, followed by homogenization and centrifugation. The supernatant extract was cleaned by SPE on an Oasis HLB cartridge (200 mg, 6 cc). The final extract was measured directly by LC/MS/MS with electrospray ionization in positive mode, except for 2,4-D, GA3, and abscisic acid extracts, which required analysis in negative mode. Quantification by multiple reaction monitoring (MRM) was supported with full-scan mass spectrometric confirmation using "information-dependent acquisition" triggered with MRM to "enhanced product ionization" mode of the hybrid quadrupole-ion trap mass analyzer. The LOQ of the test analytes varied between 1 and 10 ng/g with associated recoveries of 80-120% and precision RSD <25% (n = 8). Significant matrix-induced signal suppression was recorded when the responses for pre- and postextraction spikes of analytes were compared; this could be resolved by using matrix-matched calibration standards. The method could successfully be applied in analyzing incurred residue samples and would, therefore, be useful in precisely deciding the necessity and dose of exogenous applications of PGRs on the basis of measured endogenous levels.     

Mass Spectral Studies Reveal the Structure of Aβ1-16-Cu(2+) Complex Resembling ATCUN Motif

In Alzheimer's disease, copper binds to amyloid beta (Aβ) peptide and generates oxidative stress. The coordination of histidine (His) residues to Cu(2+) is still uncertain. We studied Cu(2+) binding to Aβ1-16 peptide using the diethyl pyrocarbonate (DEPC) assay and mass spectrometry. Our results show that only one His is involved in Cu(2+) coordination, which is identified as His6 using mass spectral studies. Novel nickel displacement studies have further supported the proposal that the Cu(2+) binding site of Aβ1-16 peptide resembles the ATCUN motif of human serum albumin.     

Effect of ecological factors on conjugal transfer of chromium-resistant plasmid in Escherichia coli isolated from tannery effluent

The influence of total organic carbon (TOC), pH, and mating temperature on transfer of chromium-resistant plasmid between Escherichia coli strains in terms of variation in the number of transconjugants formed and variation in transfer frequency was investigated. In vitro transfer was studied in five chromate-tolerant E. coli strains isolated from tannery effluent using E. coli K12 J62 (Nal^r Lac⁻) as a recipient. Conjugal transfer of different selection markers was observed in three strains. The study was carried out in sterile wastewater. A gradual decrease was observed both in the number of transconjugants and in transfer frequencies as the concentration of TOC in the mating medium descended from 10,095 to 1.2 mg of C/L, obtaining the maximum values with a TOC concentration of 10,095 mg of C/L. The number of transconjugants and the transfer frequency were maximum at 30°C. However, neither the transfer frequency nor the transconjugant number varied significantly in the range of pHs assayed. The strains were also found resistant to different heavy metals and antibiotics. Curing of these strains resulted in loss of one or more resistance markers indicating the plasmid-borne resistance. It is inferred that plasmid transfer by conjugation occurs in wastewater bodies within a wide range of conditions.     

A Robust, Environmentally Benign Catalyst for Highly Selective Hydroformylation

By a sol-gel process a rhodium complex containing a diphosphane with a large natural P-Rh-P bite angle is covalently anchored in a silica matrix (see picture). The immobilized catalyst is a very selective hydroformylation catalyst that is completely and conveniently separated from the product and can be reused in numerous cycles.     

Carboxymethyl chitosan‐montmorillonite nanoparticles for controlled delivery of isoniazid: evaluation of the effect of the glutaraldehyde and montmorillonite

Chitosan, a natural biopolymer, is used for drug delivery application. But its potential application is limited by its low solubility in aqueous media. The present study was designed to prepare carboxymethyl chitosan (CMC), a water soluble derivative of chitosan, and evaluate the prospective of crosslinked CMC‐Montmorillonite (MMT) nanoparticles for controlled delivery of isoniazid. The nanoparticles were characterized by Fourier Transmission Infrared Spectroscopy (FTIR), Nuclear Magnetic Resonance (NMR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Transmission emission microscopy (TEM). The effects of MMT and glutaraldehyde on nanoparticles were assessed with regard to encapsulation efficiency, percentage swelling degree, and cumulative release. Percentage swelling degree and cumulative release were studied in pH medium 1.2 and 7.4 for 6 h. The cumulative release was studied by UV‐visible spectrophotometer. Cell viability study was performed by MTT assay analysis. FTIR and NMR study indicated the successful preparation of CMC. FTIR study confirmed the interaction of MMT with CMC. The exfoliation of MMT layers and molecular level dispersion of isoniazid in CMC was examined by XRD and TEM. SEM study showed that the surface of the CMC‐MMT nanoparticles was smooth compared with those of CMC nanoparticles. Swelling and release of isoniazid from the nanoparticles increased with the decrease in the MMT and glutaraldehyde content. The percentage swelling degree and cumulative release was more in pH 1.2. Cell viability study revealed that CMC was not cytotoxic, and the nanoparticles containing MMT was less cytotoxic than those of MMT free nanoparticles. CMC‐MMT nanoparticles can be exploited as potential drug carrier for controlled release applications. Copyright © 2014 John Wiley & Sons, Ltd.     

In vitro DNA damage characterisation studies on plasmid pBR322 after exposure to γ radiation by <Superscript>60</Superscript>Co

When a biological system is either accidentally or intentionally exposed to radiation, the energy absorbed triggers a number of successive events including damage to living tissues. Major radiation damage is due to the aqueous free radicals generated by the radiolysis of water. These free radicals act as molecular marauders and in turn damage DNA, mitochondrial membrane, lipid, cellular protein, resulting in cellular dysfunction and mortality. In view of the above mentioned facts an experiment was conducted to study the genotoxic effects of γ radiation and its dose effectiveness. The present experiment was conducted on samples of plasmid pBR322 DNA as the in vitro experimental model devoid of any DNA repair and replication machinery. The samples were exposed to different doses of gamma radiations from 1 to 200 Gy. Exposure of plasmid pBR322 DNA to γ radiation resulted in production of single strand breaks as a result of which, the supercoiled (SC) form was converted to relaxed form (RL). Exposure of radiation, even at very low dose of 1 Gy, exhibited a significant damage to DNA resulting in about 70% SC form and 30% RL form of DNA. At a dose of 10 Gy the SC form was reduced to about 37% and further 5% at a dose of 50 Gy with about 88.5 and 6.5% RL and linear (L) forms of DNA respectively. Thus, the disappearance of supercoiled form of plasmid pBR322 DNA was found to be directly related to radiation dose and exhibited a radiation dose dependent pattern.