Study of the degradation of a new PLA braided biomaterial in buffer phosphate saline,basic and acid media,intended for the regeneration of tendons and ligaments

The purpose of this study was to evaluate the effects of hydrolytic degradation on the properties of a PLA hollow braid designed as a new concept of biodegradable prosthesis for the regeneration of tendons and ligaments. The main function of the braided material is to bear mechanical loads while it is being replaced by the newly-generated tissue. The kinetics of braided material degradation is thus an important factor in determining the success of the product. In order to study this mechanism, PLA braid was subjected to a 12-month degradation process at 37 °C in PBS at pH 7.4 (to simulate the human physiological medium) and to accelerated degradation for one month in pH 12 and pH 3 solutions. Degradation of the braid subjected to hydrolysis was evaluated by weight loss, molecular weight distribution, mechanical properties, and calorimetric and morphologic analyses. The weight loss in a basic medium reached 21%, versus no significant change in the other media. Average molecular weight was reduced by approximately 50% in the three media, with loss of mechanical properties in all cases. The morphological changes were more evident in the PLA degraded in the basic medium. The crystallinity of the material increased at the first stages of degradation, regardless of the medium used.     

Infrared spectroscopy of gas-phase Cr+ coordination complexes: determination of binding sites and electronic states

Infrared spectra were recorded for a series of gas-phase Cr+ complexes using infrared multiphoton dissociation (IRMPD) in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. The functionalized aromatic ligands (acetophenone, anisole, aniline, and dimethyl aniline) offer a choice of either aromatic ring-pi or n-donor-base binding sites. Use of the FELIX free electron laser light source allowed convenient, rapid scanning of the chemically informative wavelength range from approximately 500 to 1800 cm(-1), which in many cases characterized the preferred site of metal binding, as well as the electronic spin state of the complex. Mono-complex ions, Cr+(ligand), for anisole, aniline, and dimethyl aniline and bis-complex ions, Cr+(ligand)(2), for anisole, aniline, and acetophenone were produced by ligand attachment to laser-desorbed Cr+ ions in the FT-ICR cell. The photodissociation yields plotted as a function of wavelength were interpreted as approximations to the infrared absorption spectra and were compared with computed spectra of different possible geometries and spin states. Clear-cut diagnostic features in the spectra of the acetophenone, anisole, and aniline complexes showed the sites of Cr+ attachment to be the carbonyl oxygen site for acetophenone (bis-complex) and the ring-pi site for anisole and aniline (both mono- and bis-complexes). The bis-complexes of aniline and anisole are low-spin (probably doublet) states, while the mono-complexes of these same ligands are high-spin (sextet) states. The dimethyl aniline complex gave a cluttered spectrum in poor agreement with calculations, which may reflect a mixture of binding-site isomers in this case.     

Cross-linking of polyolefins: a study by thermoporosimetry with benzene derivatives as swelling solvents.

The solvents o-, m-, p-xylene, p-dichlorobenzene, 1,2,4-trichlorobenzene, and naphthalene were calibrated as condensates used in the thermoporosimetry technique. Exponential relationships were found connecting the pore radii R(p) (in nm) and the freezing-point depression of the swelling solvent deltaT (in degrees C) on the one hand and the apparent energy of crystallization W(a) (in J cm(-3)) and deltaT on the other hand: R(p) = t exp[-1/(c deltaT)]; W(a) = W0 exp(deltaT/f). Pore- or mesh-size distributions can be derived from differential scanning calorimetry results by using the following equation: dV(p)/dR(p) = k{[cY(T)deltaT2]/[W(a)R(p)]}. All the numerical parameters were determined. Polyethylene and polypropylene samples, cross-linked with high-energy electrons or gamma-rays, were submitted to thermoporosimetry study. Relative mesh-size distributions, which depend on the polymer/solvent pair, were calculated for these polyolefins with o-, m-, and p-xylene as solvent and were found to be in the same sequence as those of their degrees of swelling and the irradiation doses received.     

A pyrimidine thiolate Rh(I) complex: structure, bonding and one-dimensional interactions in solid and in solution

The reaction of [Rh(micro-Cl)(COD)]2 with 4,6-dimethyl-pyrimidinethiolate (Me2-pymt) and subsequent substitution of COD by CO yields [Rh(Me2-pymt)(CO)2]. The stacking pattern found in this compound is in contradiction with previously studied comparable square-planar complexes of type d8-[M(chelate)(monodentate)2] in which each ligand has different pi-acidic character. A theoretical study of the intermolecular interactions and conformation of the title compound has been carried out, combining semi-empirical band calculations on the real chains and ab initio(MP2 level) calculations on a model dimer. The combination of electronic and steric effects determines the rotation of the successive monomers and the deviation from linearity of the one-dimensional stacks. Its behaviour in solution is also special, developing a blue colour and forming micelles, when adding water to acetone solutions.     

Analysis of complex samples by solvating gas chromatography (supercritical fluid to gas transition)

The various forms of chromatography are primarily determined by differences in the physical state of the mobile phases. The main chromatographic categories include gas chromatography (GC), liquid chromatography, and supercritical fluid chromatography. Adjusting a temperature and pressure will change the mobile phase from liquid to supercritical fluid to gas, with concomitant changes in their physical properties. In this paper, the technique transition-phase chromatography (TPC) is described. In TPC, different mobile phase conditions exist inside the column. This phase transformation within the column results in huge differences in density, solvating power, viscosity, diffusivity, and, as a consequence, in the chromatographic properties of the mobile phase. TPC experiments using capillary columns packed in our laboratory have shown that when the mobile phase is transformed from supercritical fluid to gas, high column efficiencies can be achieved. The transition from supercritical fluid to gas (also called solvating GC), a particular case of the TPC, is evaluated for the separation of complex real samples (environmental, food, and fuels).     

Reversible colorimetric probes for mercury sensing

The selectivity and sensitivity of two colorimetric sensors based on the ruthenium complexes N719 [bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate)] and N749 [(2,2':6',2' '-terpyridine-4,4',4' '-tricarboxylate)ruthenium(II) tris(tetrabutylammonium) tris(isothiocyanate)] are described. It was found that mercury ions coordinate reversibly to the sulfur atom of the dyes' NCS groups. This interaction induces a color change in the dyes at submicromolar concentrations of mercury. Furthermore, the color change of these dyes is selective for mercury(II) when compared with other ions such as lead(II), cadmium(II), zinc(II), or iron(II). The detection limit for mercury(II) ions--using UV-vis spectroscopy--in homogeneous aqueous solutions is estimated to be approximately 20 ppb for N719 and approximately 150 ppb for N749. Moreover, the sensor molecules can be adsorbed onto high-surface-area mesoporous metal oxide films, allowing reversible heterogeneous sensing of mercury ions in aqueous solution. The results shown herein have important implications in the development of new reversible colorimetric sensors for the fast, easy, and selective detection and monitoring of mercuric ions in aqueous solutions.     

Microcalorimetric determination of the activity of supercritical extracts of wormwood (Artemisia absinthium L.) over Spodoptera littoralis

The aim of this study is to develop a method and to determine by means of isothermal microcalorimetry the activity of supercritical extracts obtained from growth-controlled wormwood (Artemisia absinthium L.) over Spodoptera littoralis L. (S. littoralis), a polyphagous pest of the Mediterranean crops. In order to achieve this goal, a three-step microcalorimetric method has been developed to insure the quality of the measurements and the validity of the results. Once optimized, different extracts of wormwood obtained by means of supercritical fluid extraction and by traditional methods have been used to investigate their effects over S. littoralis. The microcalorimetric method serves as a tool to complement other bioassays found in the literature. Several extracts from supercritical extractions with solvent density ranging from 485.5 to 819.5 kg m^?3 have been tested. The influence of an entrainer addition to the supercritical fluid has also been investigated. The traditional extracts were obtained by hydrodistillation and organic Soxhlet extraction. The supercritical extracts were more efficient against S. littoralis than the traditionally obtained extracts.     

Spectroscopic Identification of Cyclic Imide b2-Ions from Peptides Containing Gln and Asn Residues

In mass-spectrometry based peptide sequencing, formation of b- and y-type fragments by cleavage of the amide C–N bond constitutes the main dissociation pathway of protonated peptides under low-energy collision induced dissociation (CID). The structure of the b ₂ fragment ion from peptides containing glutamine (Gln) and asparagine (Asn) residues is investigated here by infrared ion spectroscopy using the free electron laser FELIX. The spectra are compared with theoretical spectra calculated using density functional theory for different possible isomeric structures as well as to experimental spectra of synthesized model systems. The spectra unambiguously show that the b₂-ions do not possess the common oxazolone structure, nor do they possess the alternative diketopiperazine structure. Instead, cyclic imide structures are formed through nucleophilic attack by the amide nitrogen atom of the Gln and Asn side chains. The alternative pathway involving nucleophilic attack from the side-chain amide oxygen atom leading to cyclic isoimide structures, which had been suggested by several authors, can clearly be excluded based on the present IR spectra. This mechanism is perhaps surprising as the amide oxygen atom is considered to be the better nucleophile; however, computations show that the products formed via attack by the amide nitrogen are considerably lower in energy. Hence, b₂-ions with Asn or Gln in the second position form structures with a five-membered succinimide or a six-membered glutarimide ring, respectively. b₂-Ions formed from peptides with Asn in the first position are spectroscopically shown to possess the classical oxazolone structure.      

TG and DSC analyses of eucalyptus black liquor as alternative methods to estimate solids content

As a consequence of the continuous increase in the production rate of pulp and paper mills around the world, a great quantity of black liquor, a by-product of the wood digestion process, is produced. This by-product has a great potential as biomass, but needs to be concentrated to higher solids content to be burned as fuel in a recovery boiler. This is necessary to make the pulping process economically feasible, incinerating black liquor to produce high pressure steam, recycling inorganic chemicals to the process. The greater the solids content in black liquor, the better the combustion process in the boiler. Nevertheless, concentration of solids in black liquor above 75 mass/%, causes scaling formation on the heat transfer surfaces of evaporators and concentrators, due to the precipitation of sodium salts, reducing the overall efficiency of this equipment. The aim of this work is to evaluate the use of thermal analyses techniques, TG and DSC, as alternative methods to estimate solids content in eucalyptus black liquor samples since this information is essential to understand scaling formation process, allowing actions to reduce this industrial problem. Traditional techniques applied to determine solids content use gravimetric methods, which are simple, fine, but take a lot of time to be executed. Thermal analyses have proved to be very accurate and have the advantage to be faster than the traditional techniques. On the other hand, the cost-benefit relationship of the traditional technique is much greater and the final decision which one should be used depends on the conditions available.     

Effect of viscosity of a liquid membrane containing oleyl alcohol on the pertraction of butyric acid

Solvent formulation is important in the optimization of the mass-transfer through supported liquid membranes (SLM) in pertraction and membrane extraction. Oleyl alcohol (OA) is frequently used as the solvent or diluent in the extraction of carboxylic acids. A disadvantage of OA is its relatively high viscosity of 28.32 mPa s at 25°C. This can be decreased by the application of a less viscous OA diluent, e.g. dodecane. The relationship between the ratio of the distribution coefficient of butyric acid (BA), D _F, and the viscosity of OA-dodecane solvents, µ, as extraction and transport characteristics, and the overall mass-transfer coefficient, K _p, through SLMs was analyzed. Dependence of the D _F/µ ratio on the OA concentration showed a maximum at the OA concentration of 15 mass % to 30 mass %. The OA concentration dependence of K _p for SLMs exhibited also a maximum at about 30 mass % and 20 mass % of OA at the BA concentration driving force of 0.12 kmol m^?3 and 0.3 kmol m^?3, respectively. Shifting of the maximum in K _p dependences towards lower OA concentrations by increasing the BA concentration driving force is in agreement with the D _F/µ ratio dependence. Using pure OA as the solvent or diluent is not preferable and a mixture of a low viscosity diluent with the OA concentration below 40 mass % should be used. The presented results show the potential of the D _F/µ ratio in the screening and formulation of solvents in extraction and SLM optimization.