Preparation of polymandelide by reaction of α-bromophenylacetic acid and triethylamine

Polymandelide was prepared in 77% yield by reaction of α-bromophenylacetic acid and triethylamine. The product was characterized by ¹H- and ¹³C-NMR and IR spectra and isolation and identification of mandelic acid from hydrolysis of the polymer. The NMR spectra indicate the presence of tacticity at CH in the polymer. Molecular weights were determined by GPC and viscosity measurements; n values of 12–20 are comparable to those reported for polymandelides prepared by other methods. The x-ray powder diffraction pattern showed the product to be completely amorphous. Thermal decomposition was studied using DSC.     

Generalized jump-type Ornstein-Uhlenbeck processes as limits of infinite-particle systems

We prove the existence and uniquencess of the solution to the martingale problem associated with jump-type Ornstein-Uhlenbeck processes in the Schwartz space of distributions onR ^d. An example of a noninteracting infinite-particle system is given, which after rescaling has such a process as a limit. Cases when such a process has an invariant measure are identified.     

Characterization of the network properties of poly(ethylene glycol)–acrylate hydrogels prepared by variations in the ethanol–water solvent composition during crosslinking copolymerization

The characteristics of poly(ethylene glycol) (PEG)–acrylate hydrogel networks were investigated as a function of the ethanol–water solvent composition during free‐radical crosslinking copolymerization. Macromonomer (88% ω‐methoxy‐PEG–acrylate and 10% ω‐phenoxy‐PEG–acrylate) and crosslinker (2% PEG–diacrylate) concentrations were kept constant. As the copolymerization progressed, the polymer solution in 100% ethanol became increasingly turbid, indicating the development of a heterogeneous network structure. In 100% water, however, the initially turbid polymer solution became increasingly transparent as the crosslinking copolymerization progressed. All the gels were optically clear upon equilibration in water. Kinetic studies, with attenuated total reflectance‐infrared, showed a long induction period, along with a lowered reaction rate, in 100% ethanol, and a decrease in conversion with an increase in ethanol content. These results agree with the UV analysis of the sol fractions, which indicated an increase in the amounts of unreacted PEG–acrylates with an increase in the ethanol content. The gels which were formed with a high ethanol concentration exhibited lower Young's modulus and higher swelling ability, suggesting that the network structure was significantly affected by the solvent composition during free‐radical crosslinking copolymerization. From the stress–strain and swelling experiments, the Flory–Huggins interaction parameter was evaluated. The creep characteristics of the hydrogels were modeled with two Kelvin elements. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2677–2684, 2002     

Encounter at far point

This column is a place for those bits of contagious mathematics that travel from person to person in the community, because they are so elegant, suprising, or appealing that one has an urge to pass them on. Contributions are most welcome.     

A one-pot chemoselective S-alkylation and acetylation of thiohydantoins using the alkyl orthoformate-ZnCl2-Ac2O reagent system

The chemoselective S-alkylation of 2-thiohydantoins is reported. The methodology involves the use of alkyl orthoformates (trimethyl and triethyl) as alkylating agents, which in the presence of Ac₂O and ZnCl₂ chemoselectively alkylate the thio group whilst other nucleophilic groups present in the thiohydantoins are acetylated simultaneously in moderate to high yields. A plausible mechanism for this reaction is delineated.     

Ply-by-Ply Failure Analysis of Laminates Under Dynamic Loading

Ply-by-ply failure analysis of symmetric and anti-symmetric laminates under uniform sinusoidal transverse dynamic loading is performed for a specified duration. The study investigates the first ply failure load, followed by the detection of successive ply failures along with their failure modes using various failure theories. Some of the well-established failure theories, mostly used by the researchers, are considered for the failure prediction in laminates. The finite element computational model based on higher order shear deformation displacement field is used for the failure analysis and the complete methodology is computer coded using FORTRAN. The ply-discount stiffness reduction scheme is employed to modify the material properties of the failed lamina. The failure theories used in the analysis are compared according to their ability to predict failure load, failed ply, failure mode and progression of failure. The failure analysis is performed for both the cross-ply and angle-ply laminates with all edges simply supported and clamped. The significance of fibre orientation and stacking sequence in terms of the strength of a laminate and failure progression is also highlighted.     

Prebiotic Oligosaccharides: Special Focus on Fructooligosaccharides,Its Biosynthesis and Bioactivity

MicroRNAs (miRNAs) are important nonprotein-coding genes involved in almost all biological processes during biotic and abiotic stresses in plants. To investigate the miRNA-mediated plant response to drought stress, two drought-tolerant (C-306 and NI-5439) and two drought-sensitive (HUW-468 and WL-711) wheat genotypes were exposed to 25 % PEG 6000 for 1, 12 and 24 h. Temporal expression patterns of 12 drought-responsive miRNAs and their corresponding nine targets were monitored by quantitative real-time PCR (qRT-PCR). The results showed differential expression of miRNAs and their targets with varying degree of upregulation and downregulation in drought-sensitive genotypes. Likewise, in drought-tolerant wheat genotypes, maximum accumulation of miR393a and miR397a was observed at 1 h of stress. In addition, nearly perfect negative correlation was observed in four miRNA and target pairs (miR164-NAC, miR168a-AGO, miR398-SOD and miR159a-MYB) across all the temporal period studied which could be a major player during drought response in wheat. We, for the first time, validated the presence of miR529a and miR1029 in wheat. These findings gives a clue for temporal and variety-specific differential regulation of miRNAs and their targets in wheat in response to osmotic shock and could help in defining the potential roles of miRNAs in plant adaptation to osmotic stress in future.     

Photoactivated antimicrobial activity of carbon nanotube-porphyrin conjugates

We report the design of antimicrobial nanocomposite films based on conjugates of multiwalled carbon nanotubes (MWNT) and protoporphyrin IX (PPIX) that are highly effective against Staphylococcus aureus (S. aureus) upon irradiation with visible light. S. aureus infections can lead to life-threatening situations, especially when caused by antibiotic-resistant strains. While the light-activated antimicrobial activity of porphyrins against such pathogens is well-known, a facile way to incorporate porphyrins into coatings may lead to their more effective use. To that end, we decided to synthesize and characterize MWNT-PPIX conjugates which combine the biocidal capacity of porphyrins with the mechanical strength of MWNTs. The conjugates could effectively deactivate S. aureus cells in solution upon irradiation with visible light. We also designed large area nanocomposite films comprised of the MWNT-PPIX conjugates that showed potent antimicrobial activity. These MWNT-PPIX conjugates represent a facile strategy for the design of antimicrobial and antifouling coatings.     

Liquid Chromatographic Resolution of the Enantiomers of Metoprolol and Carvedilol in Pharmaceutical Formulations by use of Marfey’s Reagent and its Variants

JPC – Journal of Planar Chromatography – Modern TLC - A simple and rapid method has been established for indirect separation of the enantiomers of (R,S)-metoprolol and (R,S)-carvedilol...     

Atomic imaging of the monolayer nucleation and unpinning of a compound semiconductor surface during atomic layer deposition

The reaction of trimethyl aluminum on the group III rich reconstructions of InAs(0 0 1) and In(0.53)Ga(0.47)As(0?0?1) is observed with scanning tunneling microscopy/spectroscopy. At high coverage, a self-terminated ordered overlayer is observed that provides the monolayer nucleation density required for subnanometer thick transistor gate oxide scaling and removes the surface Fermi level pinning that is present on the clean InGaAs surface. Density functional theory simulations confirm that an adsorbate-induced reconstruction is the basis of the monolayer nucleation density and passivation.