Proton mobility and copper coordination in polysaccharide- and gelatin-based bioblends and polyblends

Polysaccharide- and gelatin-based bioblends and polyblends were synthesized and characterized by complex impedance spectroscopy, proton nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Higher ionic conductivities of 7.9 × 10^?5 S/cm at room temperature and 2.5 × 10^?3 S/cm at 80 °C were obtained for the agar-chitosan polyblends. For all samples, the activation energies, calculated from the Arrhenius plot of ionic conductivity and from the onset of NMR line narrowing, are in the range 0.30–0.86 and 0.38–0.57 eV, respectively. The glass transition temperatures (T _g ^NMR ) varied from 200 to 215 K, depending on the sample composition. The temperature dependence of the ¹H spin–lattice relaxation revealed two distinct proton dynamics. The EPR spectra are characteristic of Cu² ions in tetragonally distorted octahedral sites. Quantitative analysis of the EPR spin Hamiltonian g _|| and A _|| parameters revealed copper ions complexed by nitrogens and oxygens in the samples containing chitosan or gelatin and only by oxygens in agar-based ones. The in-plane π bonding is less covalent for the gelatin and chitosan blends. Results suggest that natural bioblends and polyblends are interesting systems to be used in materials science engineering.     

Uniqueness of the solution of a partial differential equation problem with a non-constant coefficient

We consider the problem , , , where is bounded below by a positive constant. The solution on the boundary is a known function and . This is an ill-posed problem in the sense that a small disturbance on the boundary specification can produce a big change in its solution, if it exists. In a previous work, we used a Wavelet Galerkin Method with the Meyer Multiresolution Analysis to generate a sequence of well-posed approximating problems to it. In the present work, by assuming that is Lipschitz, we are able to prove that the existence of a solution , for this problem, implies its uniqueness.

     

Method for Quantitative Evaluation of Kinetic Constants in Olefin Polymerizations, 3

A method for the quantitative evaluation of kinetic constants in Ziegler–Natta and metallocene olefin homopolymerizations presented previously (V. Matos, A. G. M. Neto, J. C. Pinto, J. Appl. Polym. Sci. 2001 , 79, 2076; V. Matos, A. G. M. Neto, M. Nele, J. C. Pinto, J. Appl. Polym. Sci. 2002 , 86, 3226) is extended to allow for estimation of model parameters in copolymerization reactions. The method is used to estimate kinetic parameters of ethylene/propylene copolymerization during the synthesis of high impact poly(propylene) in a train of cascade reactors. Process models were developed to describe the reaction rate profile, reactor solubles, molecular weight distribution of the total polymer, xylene solubles, and insoluble polymer. The process models and the estimated parameters were inserted into a process simulator that successfully described the industrial process.

     

Enzymatic regioselective production of chloramphenicol esters

An enzymatic study has been performed in the search for synthetic routes to produce chloramphenicol derivatives through regioselective processes using lipases. Complementary transesterification and hydrolytic reactions have been carried to synthesize chloramphenicol regioisomers. Reaction parameters, such as biocatalyst, solvent, acyl donor, and temperature have been optimised in order to obtain chloramphenicol esters with high yields through acylation processes. Scale-up of the enzymatic reactions (1 g-scale at 0.25 M) and catalyst recycling (up to 10 cycles) have been successfully achieved. Furthermore, monoacylated derivatives at the more hindered secondary position could also be obtained employing hydrolysis processes.     

The Ritter reaction of N-(hydroxymethyl)saccharin with nitriles

The development of the Ritter reaction of N-(hydroxymethyl)saccharin with nitriles for the synthesis of N-[(saccharinyl)methyl]amides is reported. The success of this reaction relies on an operationally simple procedure and on the use of inexpensive reagents. The present method enables access to a variety of saccharin scaffolds of potential interest in medicinal chemistry in moderate to high yields. Furthermore, the scalability of this reaction was demonstrated by a multigram-scale transformation, without any loss of efficiency.     

Effects of Inoculum Physiological Stage on the Growth Characteristics of Chlorella sorokiniana Cultivated Under Different CO2 Concentrations

In order to maximize microalgae biomass production and reduce its overall costs, it is important to optimize inoculum conditions based on its physical and physiological characteristics. Chlorella sorokiniana cultures inoculated with inoculum at three different physiological stages (lag, exponential, and stationary) diluted to the same optical density were cultivated for 12?days under three different CO₂ concentrations (0.038, 5, or 10?% CO₂ v/v) and growth pattern and biomass production was observed. Samples inoculated with lag phase inoculum supplied with 5?% CO₂ achieved the maximum biomass production, whereas samples supplied with 0.038?% CO₂ never reached exponential growth. The better growth of samples inoculated with lag phase inoculum was attributed to its increased number of cells compared to the other two inocula.     

Conformational and Electronic Interaction Studies of P-Substituted α-Phenoxyacetones

The v_co analysis of p-substituted α-phenoxy-acetones X-θ-O-CH₂-C(O)-Me (1-6) indicates the existence of the cislgauche rotational isomerism. The nearly constant increase in the cislgauche population ratios for the whole series, on going from carbon tetrachloride to acetonitrile, and the small sensitivity of the carbonyl frequency shifts (Δv_c) for the cis rotamer, on going from electron-attracting to electron-donating substituents, are interpreted as an interplay of the Field (F) and the Inductive (-I) Effects, which originates an almost constant carbonyl bond order, and suggests that the cis rotamers have almost the same energy in the whole series. The decrease in the cislgauche population ratios, in all solvents, and the deshielding effects on the carbonyl carbon atom, and on the methylene carbon atom in a weaker extent, observed in the ¹³C NMR spectra, on going from electron-attracting to electron-donating substituents, are discussed in terms of φ*CO/ⁿO orbital and Ar^δ+ -O^δ- — C^δ+ =O^δ- Coulombic interactions, which stabilize the gauche rotamers of the investigated compounds.     

Asymmetric chemoenzymatic synthesis of N-acetyl-α-amino esters based on lipase-catalyzed kinetic resolutions through interesterification reactions

Several phenylalanine analogs have been synthesized through a four-step route starting from easily available ethyl acetamidocyanoacetate. In a first reaction, and making use of phase transfer catalysts, this compound reacted with several alkyl halides, being benzyltributylammonium chloride identified as the best one for the production of a series of quaternary amino acids in moderate to excellent yields (52–95%). Then, the corresponding N-acetyl-phenylalanine methyl and allyl ester derivatives were obtained through acidic hydrolysis, esterification, and N-acetylation. Rhizomucor miehei lipase was found as a versatile enzyme for the resolution of these amino esters, finding the best results through interesterification reactions with butyl butyrate in acetonitrile. A great influence in the stereoselectivity was found depending on the chemical structure of the compound, achieving for the non- or para-substituted in the phenyl ring excellent stereoselectivities, being moderate for the meta-nitro derivative, while the ortho-nitro amino ester did not react.     

Wave-vector dependence of electron-optical phonon coupling in GaAs

Induced non equilibrium distribution of optical phonons allows direct measurement of electron-phonon coupling as a function of phonon wave-vector K. Results indicate that near K=0(K<20, 000 cm^?1 coupling between TO phonons and electrons is independent of K whereas LO phonons show a K^-2 dependence. Results also suggest that electron relaxation in the conduction band by multiple phonon production is quite significant.