Solvent effect on the racemization kinetics of d-2,2′-dimethoxybiphenyl-6,6′-dicarboxylic acid

The rate constants of racemization of d-2,2′-dimethoxybiphenyl-6,6′-dicarboxylic acid in different solvents can be satisfactorily described by multiparameter equations based on the linear free energy relationship. The main factors responsible for solvent effects are their polarizability and electrophilic solvation power.     

Effect of shock-wave compression up to 65 GPa on the crystal structure and superconducting properties of MgB<Subscript>2</Subscript>

The effect of steplike shock-wave compression up to 65 GPa on the crystal structure and super-conducting transition temperature of a polycrystalline MgB₂ sample is studied. X-ray diffraction demonstrates that the shock-wave compression of the MgB₂ sample does not cause any irreversible structural phase transformations in it except for the formation of lattice microstrains. These conclusions agree with the super-conducting transition temperatures of the MgB₂ sample measured before and after shock-wave compression.     

A facile one-pot synthesis of highly luminescent CdS nanoparticles using thioglycerol as capping agent

Absence of emission concentration quenching accompanied by high emission efficiency in a solid state is highly challenging though very attractive, for example, for fabrication of solid state light emitters or fluorescent organic nanoparticles (FONs). Here, formation of FONs based on novel p-phenylenediacetonitrile derivatives by re-precipitation method in aqueous solutions is demonstrated. The exceptionality of the derivatives employed is manifested by nitrile groups-induced steric hindrance effects inhibiting concentration quenching of emission. Consisting of different size and polarity end-groups, phenyl groups in one compound and hexyl-carbazolyl in another, the derivatives were examined and compared in regard to nanoparticle formation morphology, size tunability, spectral signatures, and fluorescence turn-on efficiency. The variation of solvent/non-solvent ratio allowed to achieve tuning of the FON sizes from 55?nm up to 360?nm and resulted in maximal fluorescence on/off ratio of 38. Spectrally resolved confocal fluorescence microscopy revealed somewhat different molecule arrangement in different FONs suggesting dominant amorphous-like phase, which was confirmed by small angle X-ray scattering measurements. The FONs were verified to be stable against degradation or conglomeration into larger clusters at least over a couple of months thus implying their feasibility for practical applications. Finally, potential application of the fluorescent p-phenylenediacetonitrile nanoparticles for organic vapor sensing via fluorescence on/off switching was demonstrated.     

LC–MS–MS Development and Validation for Simultaneous Quantitation of Metformin, Glimepiride and Pioglitazone in Human Plasma and Its Application to a Bioequivalence Study

A simple, precise and reproducible liquid chromatography–tandem mass spectrometry method has been developed and validated according to the Food and Drug Administration guidelines for the simultaneous quantitation of antidiabetic drugs metformin, glimiperide and pioglitazone in human plasma using glipizide as an internal standard. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique, operating in multiple reaction monitoring and positive ion mode. Inter-batch and intra-batch coefficient of variation across four validation runs for the quality control samples was less than 7%. The accuracy determined at quality control levels was within 92.81–105.13%. The method was applied to a bioequivalence study.     

Theoretical investigation of helix distortion and dielectric spectrum of antiferroelectric liquid crystals

Landau-Ginzburg equation is utilized to investigate the dielectric spectrum of an antiferroelectric liquid crystal (AFLC). Two collective modes, one associated with the in-phase motion at the low frequency side and the other related with the anti-phase motion at the high frequency side, are discussed in details utilizing the concept of bulk free energy of the material in terms of the pair interactions of two adjacent Smectic layers. The phenomenon of helix distortion related to the in-phase motion is observed theoretically based on the interlayer interactions of the AFLC system. The anti-phase mode related to the degree of the antiferroelectric ordering is also an important phenomenon depending on the layer-to-layer interactions. Finally we have theoretically obtained the critical field for helix unwinding with the model proposed by de Gennes.     

Catalyst‐free,Knoevenagel–Michael Addition Reaction of Dimedone under Microwave Irradiation: An Efficient One‐pot Synthesis of Polyhydroquinoline Derivatives

Present investigation reports a concise and efficient protocol for the synthesis of polyhydroquinoline derivatives through coupling of four different components viz. aromatic aldehydes, dimedone, ethyl acetoacetate or ethyl cyanoacetate, and ammonium acetate. The same phenomenon can be observed using arylmethylene bis(3‐hydroxy‐2‐cyclohexene‐1‐ones), ethyl acetoacetate, and ammonium acetate in one pot under microwave irradiation. The key advantages of the given protocol include short reaction time, high yields, and simple work‐up and purification procedure. The present method also allows us to synthesize highly functionalized title compounds from simple and readily available starting materials.     

Effect of time-delay on a food chain model

This paper aims to study the effect of discrete time-delay on a tritrophic food chain model with Holling type-II functional responses. Dynamical behaviours such as boundedness, stability, persistence and bifurcation of the model are studied. Our analytical findings are illustrated through computer simulation. Biological implications of our analytical findings are addressed critically.