Plasma-induced graft-polymerization of polyethylene glycol acrylate on polypropylene substrates

A detailed study of argon plasma-induced graft-polymerization of polyethylene glycol acrylate (PEGA) on polypropylene (PP) substrates (membranes and films) is presented. The process consists of four steps: (a) plasma pre-activation of the PP substrates; (b) immersion in a PEGA solution; (c) argon plasma-induced graft-polymerization; (d) washing and drying of the samples. Influence of the solution and plasma parameters on the process efficiency evaluated in terms of amount of grafted polymer, coverage uniformity and substrates wettability, are investigated. The plasma-induced graft-polymerization of PEGA is then followed by sample weighting, water droplet adsorption time and contact angle measurements, attenuated total reflection infrared spectroscopy (ATR-IR), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) analyses. The stability of the obtained thin films was evaluated in water and in phosphate buffer saline (PBS) at 37 °C. Results clearly indicates that plasma-induced graft-polymerization of PEGA is a practical methodology for anti-fouling surface modification of materials.     

Dynamics of Multiple Degree Ginzburg-Landau Vortices

For the two dimensional complex parabolic Ginzburg-Landau equation we prove that, asymptotically, vortices evolve according to a simple ordinary differential equation, which is a gradient flow of the Kirchhoff-Onsager functional. This convergence holds except for a finite number of times, corresponding to vortex collisions and splittings, which we describe carefully. The only assumption is a natural energy bound on the initial data. This paper, together with [3,4], is companion to [2] where the higher dimensional case is considered.     

Analysis of vibronic intensities in the phosphorescence spectrum of dimethylbenzaldehydes in durene

An attempt is reported to explain the main intensity patterns in the phosphorescence spectra of 2,4-, 2,5- and 3,4-dimethyl-benzaldehyde-1h₁ and -1d₁, observed previously. The analysis is based on CNDO and MINDO calculations of (transition) dipole moments, spin-orbit couplings, vibronic couplings, state energies, normal coordinates and vibrational frequencies. Where possible these quantities are empirically checked and corrected. Additional information, especially about the separation of the closely spaced T₁(³ππ^*) and T₂(³nπ^*) states, is obtained from phosphorescence excitation spectra reported here for all six isomers. The phosphorescence spectra consist of two components, an “allowed” component of ³ππ^* and a “forbidden” component of ³nπ^* symmetry. It is concluded that the allowed component is partly induced by the crystal field. The forbidden component is vibronically induced by out-of-plane vibrations among which the aldehydic CH(CD)-wag mode is the most active. The observed intensity patterns for this component are ascribed to interference between two mechanisms, one involving vibronic coupling between S₀ and S₁(¹nπ^*) and spin-orbit coupling between S₁ and T₁, the other involving vibronic coupling between T₁ and T₂ and spin-orbit coupling between S₀ and T₂. Within the groups of either 1h₁ or 1d₁ isomers, the main changes in the spectrum are shown to be due to the change in T₁–T₂ energy separation. The changes observed upon deuterium substitution in the aldehyde group involve, in addition to changes in the T₁–T₂ gap, changes in vibronic coupling due to normal-coordinate mixing. All these spectral changes are reproduced by calculations based on a mixture of theoretical and empirical input parameters, derived from, or at least consistent with, other observations, including excitation spectra, dipole moments and zero-field splittings. It is concluded that the mechanisms underlying these calculations offer a satisfactory explanation of the observed intensity patterns in the phosphorescence spectra of dimethylbenzaldehydes.     

On the temperature dependence of vibrationally induced intensity

The temperature dependence of vibrationally induced transitions is investigated in the general case in which both BO and HT mechanisms are active and it is shown that this can give information about the relative strength of the two mechanisms.     

Features of the photochemically active state surfaces of azobenzene

To discuss the main features of the potential energy curves of azobenzene along the two possible isomerization paths ab initio and cofiguration-interaction (CI) computations have been performed for the cis and trans isomers and for the intermediate geometries along the rotational and the inversion isomerization paths. From the expression of the excited states, we propose a correlation diagram and potential energy curves for the ground and lowest excited states. These curves, integrated with the available experimental data, provide a basis for interpreting the photochemical and photophysical properties of azobenzene.     

Absorption and emission spectra of molecules subject to hindered internal rotation with an application to α-dicarbonyls

A simple model of a flexible molecule with one hindered rotation and one totally symmetric vibration is presented and the resulting absorption and emission spectra are discussed. The results are applied to ¹S₀-¹S₁(¹nπ*) spectra of α-dicarbonyls.     

Drug-Excipient Compatibility Studies. Search of interaction indicators

This paper is the first one of a research project aimed to find and optimize methods by which drug-excipient compatibility can be reliably and quickly assessed. A number of experimental techniques (simultaneous TG-DSC, FT-IR spectroscopy, X-ray powder diffraction, scanning electron microscopy) have been used to investigate the compatibility between a novel tricyclic β-lactam antibiotic developed by GlaxoWellcome (now GlaxoSmithKline), GV118819x, and some commonly used excipients (poly(vinylpyrrolidone), magnesium stearate and α-lactose). Binary mixtures of two different compositions have been analyzed: drug:excipient=80:20 and 20:80 (mass/mass). Both qualitative and quantitative interaction indicators have been identified. It is shown that simultaneous thermal analysis is the best suited technique in the search of interaction indicators. With a proper selection of experimental conditions it is able to reveal the thermal changes brought about by the early stages of interaction, i.e. those occurring during the measurement on physical mixtures not previously annealed under stress conditions. Such an ability is discussed, in particular, with respect to the role of the water vapour, which has been found to be a critical parameter for all our systems. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ab initio DFT study of Z–E isomerization pathways of <Emphasis Type="Italic">N</Emphasis>–benzylideneaniline

The ground state properties and absorption spectra of N-benzylideneaniline (NBA) have been studied at the density functional (DFT) and at the time-dependent density functional (TD-DFT) level of the theory. The equilibrium geometries of the E and Z isomers in the ground state and their vibrational frequencies have been computed. Furthermore, the excitation energies of the lowest excited singlet and triplet states and the potential energy curves along the torsion and the inversion isomerization coordinates were evaluated. The results are discussed in light of the available experimental data.     

Solvent effects on the vibrational activity and photodynamics of the green fluorescent protein chromophore: a quantum-chemical study

Vibrational activities in the Raman and resonance Raman spectra of the cationic, neutral, and anionic forms of 4'-hydroxybenzylidene-2,3-dimethyl-imidazolinone, a model compound for the green fluorescent protein chromophore, have been obtained from quantum-chemical calculations in vacuo and with the inclusion of solvent effects through the polarizable continuum model. It is found that inclusion of solvent effects improves slightly the agreement with experimental data for the cationic and neutral forms, whose spectra are qualitatively well-described already by calculations in vacuo. In contrast, inclusion of solvent effects is crucial to reproduce correctly the activities of the anionic form. The structural effects of solvation are remarkable both in the ground and in the lowest excited state of the anionic chromophore and influence not only the vibrational activity but also the photodynamics of the lowest excited state. CASPT2//CASSCF photoreaction paths, computed by including solvent effects at the CASSCF level, indicate a facile torsional deformation around both exocyclic CC bonds. Rotation around the exocyclic CC double bond is shown to lead to a favored radiationless decay channel, more efficient than that in gas phase, and which explains the ultrafast fluorescence decay and ground-state recovery observed in solution. Conversely, rotation around the exocyclic CC single bond accounts for the bottleneck observed in the ground-state recovery cycle. It is also speculated that the ultrafast radiationless decay channel would be hampered in protein for unfavorable electrostatic interactions and steric reasons.     

Vibronic coupling in pyrazine nπ* transitions

Vibronic coupling integrals governing the induced absorption of the first nπ* excited state have been evaluated theoretically. The calculations, based on the CNDO/S method, confirm the b_1g assignment of the 918 cm^?1 vibration, its prominent role in the intensity borrowing and its anharmonic character in the B_3u state. Furthermore they suggest that non-BO coupling and borrowing from higher electronic states cannot be neglected.