A comparative study of laser tissue interaction at 2.94 μm and 10.6 μm

Laser cutting of gelatin and tissue with Er and CO₂ lasers is explained by combined action of evaporation, ejection of liquid and elastic deformation of the region of radiation impact. It is shown that the ejection mechanism is more pronounced at 2.94 m than at 10.6 m. The use of high speed photography has revealed the influence of the temporal pulse shape. The experimental results are explained by a thermo-mechanical model.     

A short synthesis of morachalcone A

Advanced C-prenylated intermediates for three aromatase inhibitors, including morachalcone A, can be synthesized through a Claisen-Schmidt condensation followed by Florisil^®-catalyzed [1,3]-sigmatropic rearrangement of a prenyl phenyl ether.     

The influence of subinhibitory concentrations of ampicillin and vancomycin on physico-chemical surface characteristics of Enterococcus faecalis 1131

The effects of growth in the presence of sub-inhibitory concentrations of ampicillin and vancomycin on physico-chemical cell surface properties of Enterococcus faecalis 1131 have been determined. Growth in the presence of antibiotics yielded increased exposure of nitrogen and oxygen at the cell surface, proportional to the amount of antibiotic added to the growth medium, probably as a result of progressive removal of lipoteichoic acid (LTA) by ampicillin and vancomycin. Bacterial isoelectric points (IEP's), derived from particulate microelectrophoresis at different suspension pH, increased concurrently. Water contact angles on bacterial lawns only varied slightly in the presence of antibiotic during growth, whereas formamide contact angles after growth in the presence of vancomycin were significantly higher than after growth in the absence of this antibiotic, yielding a strongly electron-donating character of the cell surface. Surface thermodynamical analyses indicated favourable conditions for adhesion to hexadecane and chloroform, but more negative values of interaction free energies did not necessarily coincide with increased adhesion. Bacterial adhesion to hexadecane and chloroform increased when the pH of the bacterial suspension approached the isoelectric point of the organisms, because of the minimal electrostatic interactions.     

Monte carlo simulation of water solvent with biomolecules. Glycine and the corresponding zwitterion

Monte Carlo calculations for clusters consisting of 200 water molecules surrounding glycine in the neutral and zwitterionic forms were carried out at 300 K; all the relevant interaction potentials have been obtained by means of quantum–mechanical calculations. Water–water and amino acid–water energies were calculated, and the zwitterion was found to be strongly favored with respect to the neutral molecule, as expected. A detailed analysis of the energetic results yielded some information on the special extension of the solute-induced perturbation. The structural results were found to be in reasonable agreement with predictions that can be obtained by analyzing isoenergy contour maps, calculated for the two-body amino acid–water potential.     

Influence of DNA on the rate of ligand substitution in platinum(II) terpyridine complexes

The kinetics of substitution of pyridine or 2-methylpyridine, by iodide or thiourea, in the complexes [Pt(4'-R'terpy)(2-Rpy)](BF4)2 (R' = o-tolyl or H; R = H or CH3) has been studied, at 25 degrees C, pH 7, and various ionic strength values, in the presence of and without calf thymus DNA. The reactions occur in one observable step, and plots of kobsd against nucleophile concentration give straight lines with zero intercepts. DNA inhibits all the reactions studied without altering the rate law; the second-order rate constants k2 decrease systematically on increasing DNA concentration and are larger at higher ionic strength values. Partitioning of the ionic reactants in solution on electrostatic grounds can account for this kinetic effect in the reaction with iodide. Iodide is kept off the double helix proximity while the dicationic complexes concentrate on it. The inhibiting effect observed for the uncharged reagent thiourea can be related to the specific binding mode of the complexes to DNA. The complexes studied are effective intercalators to double helix, and this type of interaction, which prevents attack of thiourea at platinum, decreases their actual concentration in solution. The inhibiting effect is larger for [Pt(terpy)(py)]2+ that is a better intercalator. Likewise, the decrease in the rate of substitution of 2-Rpy, at a given [DNA] on decreasing ionic strength, is due to the influence of ionic strength on the complex-DNA interactions.     

Search for melanoma markers in plasma and serum samples

Fourteen blood samples from patients with melanoma and eleven blood samples from healthy subjects were analyzed by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The study was focussed on species of low molecular weight, in the range 800-5000 Da, present in plasma and sera. While for healthy subjects plasma samples lead to the production of a higher number of ionic species, for melanoma patients a high number of diagnostic ions, present with high frequency and with quite high relative abundance, are present in particular in serum samples and to a lesser extent also in plasma. Since plasma samples are obtained more easily in comparison to sera, it is possible to suggest that also plasma can be used for these studies.     

Anomeric and mesomeric effects in methoxycarbonylsulfenyl chloride, CH(3)OC(O)SCl: an experimental and theoretical study

The molecular structure and conformational properties of methoxycarbonylsulfenyl chloride, CH(3)OC(O)SCl, were determinated in the gas and solid phases by gas electron diffraction, low-temperature X-ray diffraction, and vibrational spectroscopy. Furthermore, quantum chemical calculations were performed. Experimental and theoretical methods result in structures with a planar C-O-C(O)-S-Cl skeleton. The electron diffraction intensities are reproduced best with a mixture of 72(8)% syn and 28(8)% anti conformers (S-Cl bond synperiplanar/antiperiplanar with respect to C=O bond) and the O-CH(3) bond synperiplanar with respect to the C=O bond. The syn form is the preferred form and becomes the exclusive form in the crystalline solid at low temperature. This experimental result is reproduced very well by Hartree-Fock approximation and by density functional theory at different levels of theory but not by the MP2/6-311G method, which overestimates the value of DeltaG between the syn and anti conformers. The results are discussed in terms of anomeric effects and a natural bond orbital (NBO) calculation. Photolysis of matrix-isolated CH(3)OC(O)SCl with broad-band UV-visible irradiation produces an interconversion of the conformers, and the concomitant decomposition leads to formation of OCS and CO molecules.     

Research on nitrogen containing heterocyclic compounds. XVIII. Synthesis of 9H-pyrrolo[2,1-c]-s-triazolo[4,3-a][1,4]benzodiazepine,a novel tetracyclic ring of pharmaceutical interest

Reaction of di-4-morpholinylphosphinic chloride on 5,10-dihydro-9H-pyrrolo[2,1-c][1,4]benzodiazepin-11-one 9 afforded 11-(di-4-morpholinylphosphinyloxy)-5H-pyrrolo[2,1-c][1,4]benzodiazepine 10 . Displacement of di-4-morpholinylphosphinyloxy group of 10 by formylhydrazine with concomitant intramolecular cyclization led directly to 9H-pyrrolo[2,1-c]-s-triazolo[4,3-a][1,4]benzodiazepine 7, a novel nitrogen heterocyclic ring of pharmaceutical interest. A new procedure for the synthesis of 9 is also described.     

Monoaxial drawing behaviour of isotactic polypropylene quenched at different temperatures

Quenched films of isotactic polypropylene were obtained in different quenching conditions; the films structure was analyzed in terms of phases composition and gross morphology. The mechanical behaviour, analyzed at room temperature in monoaxial drawing shows that the initial structure strongly affects the drawing behaviour. The drawing occurs by necking propagation in all the samples, but the deformation in the neck depends on the gross morphology while the drawing load depends on crystallinity. The obtianed results are discussed on the basis of the molecular and structural model of the fibers formation by drawing of crystalline polymeric films.     

High conversion free-radical suspension polymerization: End groups in poly(methyl methacrylate) and their influence on the thermal stability

Suspension free-radical polymerization of vinyl monomers, carried out in the presence of alkyl mercaptans as chain-transfer agents, is analyzed. A model which accounts for the development with conversion of the polymer weight fractions having particularly tagged end groups, namely sulfur-containing and unsaturated end groups, is presented. The best current theories for diffusion-controlled polymerizations are included in the model. The sulfur content of poly(methyl methacrylate), determined as a function of conversion by a microcoulometric method, is in good agreement with the values predicted from polymerization kinetics. The rate of weight loss of the produced polymers is then related to the content of the unsaturated end groups. By comparing experimental thermal stability indexes (from thermogravimetry and isothermal heating experiments) to calculated polymer weight fractions, it is shown that the thermal stability of poly(methyl methacrylate) produced in the presence of alkyl mercaptans approximately depends on the square of the weight fraction of the polymer chains with an unsaturated end group.