Thermal, Mechanical and Microstructures Properties of Cellulose Derivatives Films: A Comparative Study

The proposal in this study was to evaluate the physical properties of different biopolymers films. The materials used were: pectin, carboxyl methylcellulose, methylcellulose, hydroxyl propylcellulose, hydroxypropyl-methylcellulose, and corn waxy starch; from these polysaccharides aqueous dispersions were prepared to 3% (w/v) for obtained films. In these biopolymer films, the thermal diffusivities (α) was evaluated by the Open Photoacoustic Cell method; also, their mechanical properties as tensile strength, elongation, and Young’s modulus were measured, their crystallinity percentage was evaluated by X-ray diffraction and microstructure through atomic force microscopy in contact mode. From the polysaccharide films, it was observed that most of them were flexible and transparent. In the case of the films, mechanical properties were found that the highest value of tensile strength and Young’s modulus corresponded to carboxyl methylcellulose with 69.17 and 1,912.20 MPa values, respectively. Also, Open Photoacoustic Cell method and X-ray diffraction measurements showed that there exist a correlation between the thermal diffusivity values and the crystallinity measured in the biopolymer films. It was also observed that α values of cellulose derived was affected by the substitution group in the molecule, reaching the highest α value, the films of carboxyl methylcellulose. Regarding the microstructural of the films, starch showed the highest roughness value (88.6 nm) whereas hydroxypropyl-methylcellulose resulted with the lowest roughness value (7.67 nm).     

Protein changes in the shoot-tips of vanilla (<Emphasis Type="Italic">Vanilla planifolia</Emphasis>) in response to osmoprotective treatments

Cryogenic storage of vanilla shoot-tips represents the safest biotechnological strategy for the long-term conservation of the vanilla germplasm, but successful cryopreservation depends on its tolerance to both dehydration stress imposed by cryoprotective treatments and thermal stress produced by immersion in liquid nitrogen. In this work, we evaluated the impact of various osmoprotective treatments on protein expression patterns in vanilla (Vanilla planifolia) shoot-tips subjected to successive dehydration steps prior to cryopreservation. Two-dimensional electrophoretic protein profiles of shoot-tips dissected from in vitro grown plants and preconditioned on semisolid media with 0.3 M sucrose for one day, and shoot-tips preconditioned, loaded with a solution of 0.4 M sucrose and 2 M glycerol, and subsequently exposed to plant vitrification solution 3 (50% (w/v) sucrose and 50% (w/v) glycerol), were compared with non-treated dissected shoot-tips. We observed an increase in the expression level of six protein spots (fold change exceeding 1.5) and a decrease (fold change not exceeding 0.6) of ten protein spots after preconditionig treatment, whereas the profiles after preconditioning, loading and exposure to vitrification solution showed an increase in the expression level of 21 protein spots and a decrease in the expression level of 13. Most proteins identified were down-regulated and belonged to groups of biosynthesis, folding, and protein degradation. Many others were related to energetic metabolism, defense, and cell structure. These preliminary results contribute to knowledge of the proteome of this species and partially clarify its sensitivity to osmotic dehydration treatments.     

Copper(II) coordination polymers derived from triethanolamine and pyromellitic acid for bioinspired mild peroxidative oxidation of cyclohexane

The new inorganic 1D coordination polymer [Cu₂(H₃tea)₂(μ₄-pma)]_n has been prepared, via self-assembly in aqueous medium, from copper(II) nitrate, triethanolamine (H₃tea), pyromellitic acid (H₄pma) and lithium hydroxide, and characterized by IR spectroscopy, elemental and single-crystal X-ray diffraction analyses. This compound and the related 2D polymer [Cu₂(μ-H₂tea)₂{μ₃-Na₂(H₂O)₄}(μ₆-pma)]_n · 10nH₂O are shown to mimic the alkane partial oxidation activity of the multicopper particulate methane monooxygenase, acting as catalysts precursors for the peroxidative oxidation of cyclohexane into cyclohexanol and cyclohexanone, by hydrogen peroxide (as green oxidant) and at room temperature in acidic MeCN/H₂O medium. An overall yield (based on cyclohexane) of 29% has been achieved.     

Asymmetric bilayers mimicking membrane rafts prepared by lipid exchange: Nanoscale characterization using AFM-Force spectroscopy

Sphingolipids-enriched rafts domains are proposed to occur in plasma membranes and to mediate important cellular functions. Notwithstanding, the asymmetric transbilayer distribution of phospholipids that exists in the membrane confers the two leaflets different potentials to form lateral domains as next to no sphingolipids are present in the inner leaflet. How the physical properties of one leaflet can influence the properties of the other and its importance on signal transduction across the membrane are questions still unresolved. In this work, we combined AFM imaging and Force spectroscopy measurements to assess domain formation and to study the nanomechanical properties of asymmetric supported lipid bilayers (SLBs) mimicking membrane rafts. Asymmetric SLBs were formed by incorporating N-palmitoyl-sphingomyelin (16:0SM) into the outer leaflet of preformed 1,2-Dioleoyl-sn-glycero-3-phosphocholine (DOPC)/Cholesterol SLBs through methyl-β-cyclodextrin–mediated lipid exchange. Lipid domains were detected after incorporation of 16:0SM though their phase state varied from gel to liquid ordered (Lo) phase if the procedure was performed at 24 or 37 °C, respectively. When comparing symmetric and asymmetric Lo domains, differences in size and morphology were observed, with asymmetric domains being smaller and more interconnected. Both types of Lo domains showed similar mechanical stability in terms of rupture forces and Young's moduli. Notably, force curves in asymmetric domains presented two rupture events that could be attributed to the sequential rupture of a liquid disordered (Ld) and a Lo phase. Interleaflet coupling in asymmetric Lo domains could also be inferred from those measurements. The experimental approach outlined here would significantly enhance the applicability of membrane models.     

Preextinction viral RNA can interfere with infectivity

When the error rate during the copying of genetic material exceeds a threshold value, the genetic information cannot be maintained. This concept is the basis of a new antiviral strategy termed lethal mutagenesis or virus entry into error catastrophe. Critical for its success is preventing survival of residual infectious virus or virus mutants that escape the transition into error catastrophe. Here we document that mutated, preextinction foot-and-mouth disease virus (FMDV) RNA can interfere with and delay viral production up to 30 h when cotransfected in BHK-21 cells with standard RNA. Interference depended on the physical integrity of preextinction RNA and was not observed with unrelated RNAs or with nonmutated, defective FMDV RNA. These results suggest that this type of interference requires large size, preextinction FMDV RNA and is mediated neither by small interfering RNAs nor by RNAs that can compete with infectious RNA for host cell factors. A model based on the aberrant expression of mutated RNA as it is expected to occur in the initial stages of the transition into error catastrophe is proposed. Interference mediated by preextinction RNA indicates an advantage of mutagenesis versus inhibition in preventing the survival of virus escape mutants during antiviral treatments.     

In vitro assembly into virus-like particles is an intrinsic quality of Pichia pastoris derived HCV core protein

Different variants of hepatitis C virus core protein (HCcAg) have proved to self-assemble in vitro into virus-like particles (VLPs). However, difficulties in obtaining purified mature HCcAg have limited these studies. In this study, a high degree of monomeric HCcAg purification was accomplished using chromatographic procedures under denaturing conditions. Size exclusion chromatography and sucrose density gradient centrifugation of renatured HCcAg (in the absence of structured RNA) under reducing conditions suggested that it assembled into empty capsids. The electron microscopy analysis of renatured HCcAg showed the presence of spherical VLPs with irregular shapes and an average diameter of 35nm. Data indicated that HCcAg monomers assembled in vitro into VLPs in the absence of structured RNA, suggesting that recombinant HCcAg used in this work contains all the information necessary for the assembly process. However, they also suggest that some cellular factors might be required for the proper in vitro assembly of capsids.     

Amber force field implementation, molecular modelling study, synthesis and MMP-1/MMP-2 inhibition profile of (R)- and (S)-N-hydroxy-2-(N-isopropoxybiphenyl-4-ylsulfonamido)-3-methylbutanamides

Ab initio calculations (B3LYP/Lanl2DZ level of theory) were performed in this study to determine all the structural and catalytic zinc parameters required in order to study MMPs and their complexes with hydroxamate inhibitors by means of the AMBER force field. The parameters thus obtained were used in order to study the docking of some known MMPi (Batimastat, CGS 27023A and Prinomastat) and our previously described inhibitor a which had shown an inhibitory activity for MMP-1, and -2, with the aim of explaining the different selectivity. On this basis the two enantiomers (R)-b and (S)-b were designed and synthesized, as more potent MMP-2 inhibitors than our previously described inhibitor a. Between these two enantiomers the eutomer (R)-b proved to be 24.7 times and 15.3 times more potent than CGS 27023A and the parent compound a on MMP-2, maintaining a higher index of MMP-2/MMP-1 selectivity compared with CGS 27023A and the more potent inhibitor Prinomastat. The hydroxamate (R)-b can be considered as a progenitor of a new class of biphenylsulfonamido-based inhibitors that differ from compound a in the presence of an alkyl side chain on the C alpha atom, and show different potency and selectivity profiles on the two MMPs considered.     

Some Characteristics of Threonine Transport Across the Blood-Brain Barrier of the Rat

Threonine entry into brain is altered by diet-induced changes in concentrations of plasma amino acids, especially the small neutrals. To study this finding further, we compared effects of various amino acids (large and small neutrals, analogues, and transport models) on transport of threonine and phenylalanine across the blood-brain barrier. Threonine transport was saturable and was usually depressed more by natural large than small neutrals. Norvaline and 2-amino-n-butyrate (AABA) were stronger competitors than norleucine. 2-Aminobicyclo[2.2.1]heptane-2-carboxylate (BCH), a model in other preparations for the large neutral (L) system, and cysteine, a proposed model for the ASC system only in certain preparations, reduced threonine transport; 2-(methylamino)isobutyrate (MeAIB; a model for the A system for small neutrals) did not. Phenylalanine transport was most depressed by cold phenylalanine and other large neutrals; threonine and other small neutrals had little effect. Norleucine, but not AABA, was a strong competitor; BCH was more competitive than cysteine or MeAIB. Absence of sodium did not affect phenylalanine transport, but decreased threonine uptake by 25% (p less than 0.001). Our results with natural, analogue, and model amino acids, and especially with sodium, suggest that threonine, but not phenylalanine, may enter the brain partly by the sodium-dependent ASC system.