Crystal and molecular structure of benzoyl-l-leucyl-glycine ethyl ester (l-LEUGLY)

The crystal structure of the dipeptide derivative benzoyl-l-leucylglycine ethyl ester has been determined by direct methods (Multan 78), and refined by fullmatrix least squares toR=0.092 for 1638 reflections;I>3(I), CuK radiation. The space group isP2₁2₁2₁,a=20.679(7),b=16.440(6),c=11.034(5) Å,Z=8. Disorder observed in the ethyl ester and leucyl side-chains of the two independent molecules per asymmetric unit probably accounts, at least partially, for the weak diffracting power of the crystals. Both molecules exhibit markedly coiled hydrogen-bonded conformations. An attempt was made to obtain improved hydrogen bond geometry by the use of neutron diffraction data.     

Synthesis,spectral, structural characterization and biological activity of new palladium(II) complexes containing 3‐acetyl‐8‐methoxy‐2H‐chromen‐2‐one derived Schiff bases

Four different mononuclear palladium(II) complexes of 3‐acetyl‐8‐methoxycoumarin Schiff bases were synthesized and characterized by spectrochemical techniques. Further analysis through X‐ray crystallography confirmed the structures of the complexes. Their interactive ability with Calf Thymus DNA and protein (Bovine Serum Albumin and Human Serum Albumin) were investigated by means of absorption and emission methods. The intercalative mode of binding with DNA was supported by EB displacement studies and viscosity measurements. Configurational changes that occurred in the proteins have been analysed with the help of 3D fluorescence studies. The complexes were shown to have good antimicrobial activity against the tested bacterial and fungal pathogens. In addition, antiproliferative activity of the complexes was evaluated on A549 and MCF‐7 cell lines and the complexes were comparatively more active than the standard drug cisplatin. Among the compounds, complex 3 was the most effective against MCF‐7 (IC₅₀ value of 5.20 ± 0.15 μM) and A549 (5.09 ± 0.13 μM) compared with the other complexes 1 (6.48 ± 0.17 μM; 5.98 ± 0.09 μM), 2 (5.53 ± 0.12 μM; 5.85 ± 0.11 μM), 4 (6.73 ± 0.19 μM; 6.63 ± 0.16 μM) and cisplatin (16.79 ± 0.08 μM; 15.10 ± 0.05 μM) respectively. LDH and NO release assays confirmed the cytotoxic potential of the synthesized complexes.     

Cell migration and polarity on microfabricated gradients of extracellular matrix proteins

This paper explores the effects of the surface density and concentration profiles of extra cellular matrix proteins on the migration of rat intestinal IEC-6 cells. Microfluidic devices were used to create linear, immobilized gradients of laminin. This study investigated both the impact of the steepness and local concentrations on the directedness of cell migration. The bulk concentrations of proteins in the feed streams in the mixing device determined the gradient profile and the local concentration of laminin in the device. Two sets of gradients were used to explore cell migration directedness: (i) gradients with similar change in local concentration, i.e., the same gradient steepness, and (ii) different gradients with similar local concentrations. Cells migrated up the gradients, independent of the steepness of the gradients used in this study. At the same local laminin concentration, the migration rate was independent of the gradient steepness. However, cell directedness decreased significantly at high laminin densities.     

A simple picture for the rotational enhancement of the rate for the F + HCl --> HF + Cl reaction: a dynamical study using a new ab initio potential energy surface

Quantum scattering calculations for the reaction F + HCl --> HF + Cl are performed on a new ground-state ab initio potential energy surface. The reagent rotation is found to have a dramatic effect on the reaction probability. Furthermore, the exit channel rotational thresholds leave a strong imprint on the reaction probabilities and even on the cumulative reaction probability. A very simple vibrationally adiabatic model is shown to account for most aspects of the reaction dynamics. In this model, the fast vibrational motion is adiabatically eliminated leaving the key reaction dynamics represented by a reduced atom + rotor collision. The shape of the adiabatic potential surface immediately yields to a simple and intuitive interpretation for the rotational enhancement of the rate. The rotational enhancement is shown to be an effect of the entrance channel dynamics of the atom-rotor problem.     

Retention in overloaded columns, an experimental approach

Employing a micro-bore silica capillary coated with Carbowax 20 M, the dependence of chromatographic retention upon operative variables was studied surpassing the sample capacity of the column. Solution thermodynamics in the non-linear range of the absorption isotherm of n-alkanes on poly(ethylene oxide) were analyzed interpreting the experimental data through a retention equation deduced in a preceding theoretical work. At 120 degrees C, and pressures up to 11 bar abs, deviations from the ideal-gas behavior are found to be negligible, either for the fluid dynamics of the carrier-gas, or the thermodynamics of solution of the n-alkanes. Within the experimental error, for all practical purposes the mobile phase can be treated as an ideal gas. This constraint allows studying a solute molecule placed in an environment ranging from solvent monomers only, to a mixture of varying composition of solvent and solute, avoiding effects from significant interactions in the gas phase. In the experimental conditions explored, the absorption isotherm can be represented by taking only two-terms of its power series development.     

Synthesis,properties and solid state structure of 5‐diphenylphosphino‐2‐hydroxy‐1,3‐xylyl‐18‐crown‐5

5‐Diphenylphosphino‐2‐hydroxy‐1,3‐xylyl‐18‐crown‐5 has been synthesized from 5‐bromo‐2‐hydroxy‐18‐crown‐5 by reacting it in sequence at low temperature with n‐butyl lithium and methyl diphenylphosphonite. The phosphorous donor properties of this phenol phosphine (OH derivative) and the corresponding phenoxide (O^? derivative) have been studied in the presence and absence of alkali metal ions by determining the frequencies of the A₁ ν(CO) bands of Ni(CO)₃L complexes. For the OH and O^? derivatives, the latter generated by addition of CsOH to the former, the ν(CO) bands are observed at 2067.6 and 2063.4 cm^?1, respectively, providing the trend predicted by Hammett parameters for OH and O^? substituents. Addition of Na⁺ or K⁺ to the OH derivative has little effect on this stretching frequency, but the former ion shifts the O^? derivative band to 2067.7 cm^?1 A solid state structure has been obtained of the OH derivative, and two independent molecules were found in the unit cell. Both have a single water molecule hydrogen bonded to two across‐ring oxygen atoms and the phenol hydrogen. The crown ether ring has the usual gauche and anti arrangements for the C‐C and C? O bonds.     

Multireference configuration interaction calculations for the F(2P)+HCl-->HF+Cl(2P) reaction: a correlation scaled ground state (1 2A') potential energy surface

This paper presents a new ground state (1 (2)A(')) electronic potential energy surface for the F((2)P)+HCl-->HF+Cl((2)P) reaction. The ab initio calculations are done at the multireference configuration interaction+Davidson correction (MRCI+Q) level of theory by complete basis set extrapolation of the aug-cc-pVnZ (n=2,3,4) energies. Due to low-lying charge transfer states in the transition state region, the molecular orbitals are obtained by six-state dynamically weighted multichannel self-consistent field methods. Additional perturbative refinement of the energies is achieved by implementing simple one-parameter correlation energy scaling to reproduce the experimental exothermicity (DeltaE=-33.06 kcalmol) for the reaction. Ab initio points are fitted to an analytical function based on sum of two- and three-body contributions, yielding a rms deviation of <0.3 kcalmol for all geometries below 10 kcalmol above the barrier. Of particular relevance to nonadiabatic dynamics, the calculations show significant multireference character in the transition state region, which is located 3.8 kcalmol with respect to F+HCl reactants and features a strongly bent F-H-Cl transition state geometry (theta approximately 123.5 degrees ). Finally, the surface also exhibits two conical intersection seams that are energetically accessible at low collision energies. These seams arise naturally from allowed crossings in the C(infinityv) linear configuration that become avoided in C(s) bent configurations of both the reactant and product, and should be a hallmark of all X-H-Y atom transfer reaction dynamics between ((2)P) halogen atoms.     

Theoretical aspects of retention in overloaded columns

Issues regarding the concentration dependent solute distributions in overloaded chromatographic columns are discussed. Geometric simplicity of wall-coated capillary columns is taken as a reference and the discussion is developed using the example of the absorption isotherm of a solute having more affinity for itself than for the stationary phase. A retention function is deduced solving the equation of motion for the peak maximum, making some approximations. By means of this expression, the applicability of capillary gas chromatography (GC) as a technique for obtaining information on the sorption isotherm is analyzed.