Crystalline properties and decomposition kinetics of cellulose fibers in wood pulp obtained by two pulping processes

In this study two cellulose fibers, Eucalyptus grandis (CEG) and Pinus taeda (CPT), obtained through the kraft and sulfite pulping processes, respectively, were characterized. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were carried out. From the XRD analysis the interplanar distance, crystallite size and crystallinity index were calculated and the degradation kinetics parameters were determined by TGA at heating rates of 5, 10, 20 and 40 °C min⁻¹ using the Avrami, Flynn-Wall-Ozawa (FWO) and Criado methods. The results obtained by FTIR showed that the composition of the fibers is similar, while from the XRD analysis slight differences in the crystallinity were observed. The thermogravimetric analysis showed higher thermal stability for CPT than CEG while the values for the activation energy (E_a) were higher for CEG than CPT. The results obtained by Avrami and Criado methods showed that the degradation mechanism in the CEG samples involves a diffusion process while in the case of CPT the degradation process is a phase boundary controlled reaction. The degradation mechanisms demonstrated that the difference between thermal stability and E_a may be due to differences in the type of crystalline structure of the samples obtained through the two pulping processes.     

Solution structure and conformational dynamics of deoxyxylonucleic acids (dXNA): an orthogonal nucleic acid candidate

Orthogonal nucleic acids are chemically modified nucleic acid polymers that are unable to transfer information with natural nucleic acids and thus can be used in synthetic biology to store and transfer genetic information independently. Recently, it was proposed that xylose-DNA (dXNA) can be considered to be a potential candidate for an orthogonal system. Herein, we present the structure in solution and conformational analysis of two self-complementary, fully modified dXNA oligonucleotides, as determined by CD and NMR spectroscopy. These studies are the initial experimental proof of the structural orthogonality of dXNAs. In aqueous solution, dXNA duplexes predominantly form a linear ladderlike (type-1) structure. This is the first example of a furanose nucleic acid that adopts a ladderlike structure. In the presence of salt, an equilibrium exists between two types of duplex form. The corresponding nucleoside triphosphates (dXNTPs) were synthesized and evaluated for their ability to be incorporated into a growing DNA chain by using several natural and mutant DNA polymerases. Despite the structural orthogonality of dXNA, DNA polymerase β mutant is able to incorporate the dXNTPs, showing DNA-dependent dXNA polymerase activity.     

Stereoelectronic interactions and the one-bond C-F coupling constant in sevoflurane

The conformational preference of the widely utilized anesthetic fluoromethyl-1,1,1,3,3,3-hexafluoro-2-propyl ether (sevoflurane) has been investigated computationally and by NMR spectroscopy. Three conformational minima were located at the B3LYP/aug-cc-pVDZ level, but one is significantly more stable (by ca. 4 kcal/mol) than the other two. This is the case both for gas phase calculations and for solution NMR data. Although the main conformer is stabilized by electron delocalization (n(O) → σ*(C-F)), this type of hyperconjugation was not found to be the main driver for the conformer stabilization in the gas phase and, consequently, for the apparent anomeric effect in sevoflurane. Instead, more classical steric and electrostatic interactions appear to be responsible for the conformational energies. Also the (1)J(CF) coupling constants do not appear to be dominated by hyperconjugation; again, dipolar interactions are invoked instead.     

Numerical modeling of the thermal–hydraulic behavior of wire-on-tube condensers operating with HFC-134a using homogeneous equilibrium model: evaluation of some void fraction correlations

This study presents a numerical evaluation of the influence of some void fraction correlations over the thermal–hydraulic behavior of wire-on-tube condensers operating with HFC-134a. The numerical model is based on finite volume method considering the homogeneous equilibrium model. Empirical correlations are applied to provide closure relations. Results show that the choice of void fraction correlation influences the refrigerant charge and pressure drop calculations, while no influences the heat transfer rate.     

Reliability-Based Optimization Using Differential Evolution and Inverse Reliability Analysis for Engineering System Design

In this contribution, a new methodology based on a double-loop iteration process is proposed for the treatment of uncertainties in engineering system design. The inner optimization loop is used to find the solution associated with the highest probability value (inverse reliability analysis), and the outer loop is the regular optimization loop used to solve the considered reliability problem through differential evolution and multi-objective optimization differential evolution algorithms. The proposed methodology is applied to mathematical functions and to the design of classical engineering systems according to both mono- and multi-objective contexts. The obtained results are compared with those obtained by classical approaches and demonstrate that the proposed strategy represents an interesting alternative to reliability design of engineering systems.     

Anion effect on the conformational equilibrium of sulfamide and its N,N′‐diindolyl derivative: Insights on anion transportation

The relatively high acidity of the sulfamide hydrogens suggests a potential for the development of sulfamide derivatives as novel anion receptors. The interactions of sulfamide with F^?, Cl^?, CH₃COO^?, and H₂PO₄^? anions were spectroscopically (¹H and ¹⁹F NMR) and theoretically (density functional theory) analyzed, and the complexation through hydrogen bonds was confirmed by changes in the NMR signals and theoretical calculations. The replacement of 2 sulfamide hydrogens with indolyl groups yields the N,N′‐diindolylsulfamide ( DIS , N‐1H‐indol‐4‐yl‐N′‐1H‐indol‐7‐ylsulfuric diamide), whose bond rotations allow the interaction of 4 H(N) atoms with anions. The conformational preferences of DIS change upon the presence of anions, but they are practically insensitive to the anion type. According to the quantum theory of atoms in molecules, natural bond orbital analysis, and NMR chemical shifts, as well as to a thermodynamic cycle, the complex with fluoride is the most stable, followed by the oxoanion‐derived models.     

Synthesis and rational design of anti‐inflammatory compounds: N‐phenyl‐cyclohexenyl sulfonamide derivatives

The synthesis of (±)‐ethyl 6‐[N‐(2‐chloro‐4‐fluorophenyl)sulfamoyl]cyclohex‐1‐ene‐1‐carboxylate ( 5n ) has been reproduced from a method previously described and served as the background for the preparation of a nitro derivative, potentially useful as an anti‐inflammatory agent. Furthermore, a structure‐based QSAR analysis of a series of N‐arylsulfamoyl congeners derived a highly predictive model for the activities of novel small‐molecule inhibitors of NO and cytokine production, whose preparation may be successfully achieved according to a similar procedure as above. Copyright © 2009 John Wiley & Sons, Ltd.     

Existence and symmetry for elliptic equations in ℝn with arbitrary growth in the gradient

We define the Polish space R of non-degenerate rank-1 systems. Each non-degenerate rank-1 system can be viewed as a measure-preserving transformation of an atomless, σ-finite measure space and as a homeomorphism of a Cantor space. We completely characterize when two non-degenerate rank-1 systems are topologically isomorphic. We also analyze the complexity of the topological isomorphism relation on R, showing that it is \({F_\sigma }\) as a subset of R× R and bi-reducible to E₀. We also explicitly describe when a non-degenerate rank-1 system is topologically isomorphic to its inverse.     

The role of carbonyl and thiocarbonyl groups in the conformational isomerism of haloacetones and halothioacetones

The presumable, but not well-known parallelism between carbonyl and thiocarbonyl groups as electron acceptors in conformational analysis is reported. Our theoretical investigation was carried out for model compounds, namely mono-haloacetones and mono-halothioacetones. Furthermore, the donor ability of C–H and C–halo bonds has been evaluated on the basis of natural bond orbital (NBO) analysis and orbital levels calculations, and the conformational isomerism discussed in terms of classical and hyperconjugative interactions. It has been found that the conformational behavior of the titled compounds is strongly dependent on the π donor/acceptor behavior, which differs substantially between C=O and C=S systems, as well as on the steric/electrostatic and non-Lewis-type interactions involving the series of halogens.