Synthesis and characterization of a brush-like copolymer of polylactide grafted onto chitosan

A brush-like poly(DL)-lactide grafted onto chitosan as the backbone was investigated. The graft copolymerization was carried out with triethylaluminum as catalyst in toluene at 70 degrees C. It was found that a greater lactide content in the feeding ratio results in a higher grafting percentage. FTIR spectrometry, (1)H NMR, DSC scanning, and wide-angle X-ray scattering, respectively, are used to characterize these branch copolymers. A copolymer has a definite melting point when the molar feeding ratio of lactide to chitosan is more than 10:1, and the deltaH of the copolymers increases with the feed ratio of lactide to chitosan in feeding.     

Investigation of the solid state properties of amoxicillin trihydrate and the effect of powder pH

The purpose of this research was to investigate some physicochemical and solid-state properties of amoxicillin trihydrate (AMT) with different powder pH within the pharmacopoeia-specified range. AMT batches prepared using Dane salt method with the pH values from 4.39 to 4.97 were subjected to further characterization studies. Optical and scanning electron microscopy showed that different batches of AMT powders were similar in crystal habit, but the length of the crystals increased as the pH increased. Further solid-state investigations using powder x-ray diffraction (PXRD) demonstrated the same PXRD pattern, but the intensity of the peaks raised by the powder pH, indicated increased crystallinity. Differential scanning calorimetry (DSC) studies further confirmed that as the powder pH increased, the crystallinity and, hence, thermal stability of AMT powders increased. Searching for the possible cause of the variations in the solid state properties, HPLC analysis showed that despite possessing the requirements of the United States Pharmacopoeia (USP) for purity/impurity profile, there was a direct relationship between the increase of the powder pH and the purity of AMT, and also decrease in the impurity I (alpha-Hydroxyphenylglycine) concentration in AMT powder. Recrystallization studies confirmed that the powder pH could be controlled by adjusting the pH of the crystallization.     

High-performance polylactide/ZnO nanocomposites designed for films and fibers with special end-use properties

Metallic oxides have been successfully investigated for the recycling of polylactide (PLA) via catalyzed unzipping depolymerization allowing for the selective recovery of lactide monomer. In this contribution, a metallic oxide nanofiller, that is, ZnO, has been dispersed into PLA without detrimental polyester degradation yielding PLA/ZnO nanocomposites directly suitable for producing films and fibers. The nanocomposites were produced by melt-blending two different grades of PLA with untreated ZnO and surface-treated ZnO nanoparticles. The surface treatment by silanization proved to be necessary for avoiding the decrease in molecular weight and thermal and mechanical properties of the filled polyester matrix. Silane-treated ZnO nanoparticles yielded nanocomposites characterized by good mechanical performances (tensile strength in the interval from 55 to 65 MPa), improved thermal stability, and fine nanofiller dispersion, as evidenced by microscopy investigations. PLA/ZnO nanocomposites were further extruded in films and fibers, respectively, characterized by anti-UV and antibacterial properties.     

Transformation of lactulose trihydrate into anhydrous lactulose by fluidized bed drying and its characterization

Stable anhydrous lactulose was produced from lactulose trihydrate by stepwise heating on a fluidized bed. The processes were performed on stable powder forms. The anhydrous lactulose was characterized by an opaque white appearance, a coarse surface structure with random cracks and indentations, a high degree of crystallization, stability under humid conditions, and by X-ray powder diffraction, differential thermal analysis, and differential thermogravimetry. Those characteristics were different from those of the original trihydrate, which was transparent, had a smooth surface and a higher degree of crystallization, was stable under humid conditions and had different X-ray powder diffraction, differential thermal analysis, and thermogravimetric characteristics. The transformation was enhanced when the inlet temperature was 45-55 degrees C or when the temperature of the fluidized bed was over 40 degrees C. At these cutoff temperatures, both crystalline forms were observed.     

Optical and electrochemical properties and the calculated structure of pentacoordinate aluminum 8-hydroxyquinoline

In this study we report on the characterization of a series of pentacoordinate aluminum 8-hydroxyquinolines, AlQ₂X (X = F, Cl, Br), composed of two 8-hydroxyquinoline (8-HQ) groups and one halogen ligand. These were prepared by reacting 8-hydroxyquinoline and dialkylaluminum halide stoichiometrically. The λ_maxs of absorption and emission were in the range of 385-388 and 515-516 nm, respectively, which were similar to AlQ₃. The molar absorptivity of AlQ₂X is similar regardless of the X group but emission efficiency of AlQ₂X is 2-3 fold higher than that of AlQ₃ when X = F or Br, but not when X = Cl. This result can be attributed to decreased quenching of energy due to a less steric environment by reducing quinolinate content. The overall molecular orbital structures and the absorption spectra of AlQ₂X and AlQ₃ are very similar due to a single quinolinate unit. The value of the potential difference of AlQ₂Xs between anodic and cathodic waves (ΔE = 3.12 V) is close to the estimated HOMO-LUMO energy gap (the optical band gap, ΔE_optical ∼ 1240/λ_max), 3.19 eV. Detailed optical and electrochemical properties of AlQ₂X are discussed.     

Thermal glycosylation and degradation reactions occurring at the reducing ends of cellulose during low-temperature pyrolysis

Thermal glycosylation and degradation reactions of cellulose (Avicel PH-101) were studied in the presence or absence of alcohols (glycerol, mannitol, 1,2,6-hexanetriol, 3-phenoxy-1,2-propanediol, and 1-tetradecanol) under N₂ at 60–280 °C. In the presence of glycerol (heating time, 10 min), the reducing ends were converted into glycosides when the temperature of the glycerol was >140 °C without the addition of any catalysts. A temperature of 140 °C is close to that required for the initiation of thermal polymerization (glycosylation). Although the conversion was only around 20% in the range of 140–180 °C, the reactivity increased above 200–240 °C where the thermal expansion of cellulose crystals is reported to become significant. Finally, all reducing ends were converted into glycosides at 260 °C. Such heterogeneous reactivity likely arose from the lower reactivities of the reducing ends in the crystalline region due to their lower accessibility to glycerol, although the reactivity in the non-crystalline region was similar to that of glucose. Alcohols that have a lower OH/C ratio did not react with the reducing ends, suggesting that the hydrophilicity of the alcohol was critical for the glycosylation reaction to proceed. The glycosylated cellulose samples were found to be significantly stabilized against pyrolytic coloration. The results of neat cellulose pyrolysis indicated that two competitive reactions, thermal glycosylation and degradation, formed a dark-colored substance at the reducing ends while the internal glucose units in the cellulose were comparatively stable.     

Effect of oral aluminum and aluminum citrate on blood level and short-term tissue distribution of aluminum in the rat

Aluminum (Al) absorption seems to be very low, but many factors can enhance it in animals and humans. In the present study, we investigated the acute effect of Na citrate on Al absorption by monitoring Al levels in blood and several tissues. For this purpose, 18 Wistar male rats were divided into 3 groups: control, Al, and Al + Na citrate. After a 14-h fasting period, animals were dosed orally with deionized water, or 2 mmol Al chloride, or 2 mmol Al chloride plus 2 mmol Na citrate. Blood samples were taken before and 1, 2, 4, and 6 h after the gavage. Al concentrations in blood, liver, tibia, kidney, and intestinal wall were determined by ICP-OES. In the Al and Al + citrate groups, Al blood concentrations peaked at 1 h and 2 h with higher levels in the Al + citrate group. Al gavage resulted in an increase in Al level in intestinal wall, but not in the other investigated tissues. Simultaneous gavage of citrate with Al significantly increased its tissue levels in tibia, kidney, and in intestinal wall. Our data show clearly that Al as chloride can be absorbed, but not well retained by the organism tissues. Furthermore, the model used in the present study is appropriate for acute studies to investigate the effect of various compounds on Al absorption in the rat.     

Rapid microwave-assisted synthesis and characterization of cellulose-hydroxyapatite nanocomposites in N,N-dimethylacetamide solvent

Preparation of nanocomposites was carried out using microcrystalline cellulose, CaCl₂, and NaH₂PO₄ in N,N-dimethylacetamide (DMAc) solvent by a microwave-assisted method at 150 °C. XRD results showed that the nanocomposites consisted of cellulose and hydroxyapatite (HA). The cellulose existed as a matrix in the nanocomposites. SEM and TEM analysis showed that HA nanorods were homogeneously dispersed in the cellulose matrix. The effects of the microwave heating time on the products were investigated. This method has advantages of being simple, rapid, low-cost, and environmentally friendly.     

Genotypic variation in aluminum resistance, cellular aluminum fractions, callose and pectin formation and organic acid accumulation in roots of Populus hybrids

Soil acidity and aluminum (Al) toxicity are major factors limiting crop yield and forest productivity worldwide. Hybrid poplar (Populus spp.) was used as a model to assess genotypic variation in Al resistance and physiological stress responses to Al in a woody tree species. Eight hybrid crosses of P. trichocarpa, P. deltoides and P. nigra were exposed to Al in solution culture. Resistance to Al varied by genotype and hybrid cross, with P. trichocarpa × P. deltoides crosses being most resistant, P. trichocarpa × P. nigra being intermediate and P. deltoides × P. nigra being most sensitive to Al. Total root Al accumulation was not a good indicator of Al resistance/sensitivity. However, the partitioning of Al into apoplastic and symplastic fractions indicated that differences in sensitivity among genotypes were associated with Al uptake into the symplasm. Aluminum treatment increased callose and pectin concentrations of root tips in all genotypes, but more prominently in Al sensitive genotypes/hybrids. In Al sensitive genotypes, higher levels of symplastic Al accumulation correlated with elevated concentrations of citrate, malate, succinate or formate in root tips, whereas organic acid accumulation was not as pronounced in Al resistant genotypes. These findings suggest that exclusion of Al from the symplast is associated with Al resistance. Further screening of Al tolerant poplar genotypes could yield successful candidates to be utilized for sustainable reforestation/reclamation and carbon sequestration projects where soil acidity may limit tree growth.     

Synthesis and characterization of NaMt biocomposites with corn cob xylan in aqueous media

In this study synthesis and characterization of biopolymer/clay biocomposites was aimed using naturally occurring polysaccharide (xylan) as biopolymer and montmorillonite type clay (NaMt). Xylan was extracted from corn cobs via alkaline oxidative treatment. Maximum solubility of xylan was determined as 1% (w/v) in water at room temperature. Thus synthesis was realized following two routes; first NaMt concentration was kept constant at 2.0 × 10⁻² g/ml and xylan concentration was changed. Latter xylan concentration was kept constant at 1.0 × 10⁻² g/ml and NaMt concentration was changed. Natural xylan, NaMt and biocomposites were examined in terms of their spectral, electrokinetic, rheologic, morphologic and thermal properties. Results showed that lower amounts of xylan interacted with NaMt on the surface, however, when the xylan amount was increased also intercalation of NaMt has occurred. Biocomposites showed better thermal and rheologic behaviors with respect to the starting materials.     

Water pH and aluminum chemistry in the gill micro-environment of rainbow trout during acid and aluminum exposures

Summary Rainbow trout (Salmo gairdneri) were exposed to acidic soft water (pH_in4.2–6.3) in the presence (93 g·l^–1) or absence of Al. Fish were fitted with latex masks and opercular catheters to measure ventilation , pH changes at the gills, O₂ consumption , ammonia excretion , and Al extraction. During 2–3-h exposures, was generally higher in Al-exposed fish over the pH_in range 4.7–6.3. Alkalinization of expired water was about 0.3 pH units less in Al-exposed fish than in acid-only exposed fish at pH_in 4.5–5.2, an effect attributable to both increased and to buffering by Al. During 44-h exposures to pH_in 5.2 and 4.8 plus Al, increased greatly and expired water pH (pH_ex) decreased with time. There was a small increase in over 44 h at pH 4.4 plus Al, and no changes in pH_ex. In contrast, during 44-h exposures to pH 5.2, 4.8, and 4.4 in the absence of Al, such changes were much smaller or absent. During both short- and longerterm exposures, measured Al accumulation on the gills was only 5–18% of that calculated from cumulative Al extraction from the water, suggesting considerable sloughing of Al. In free-swimming trout, gill Al accumulation was greatest during exposure (2h) to Al at pH 5.2, lower at pH 4.8, and least at pH 4.4 and 4.0. Our results suggest that Al deposition occurs at the gills, causing respiratory and ionoregulatory toxicity, because the pH in the branchial micro-environment is raised above that in the acidic inspired soft water. Higher pH at fish gills may result in Al precipitation due to loss of solubility, or Al accumulation because of shifts in Al species to Al-hydroxide forms which more readily adsorb to the gills.Abbreviations pH _ex expired pH - pH _in inspired pH     

Thermal decomposition kinetics of wheat straw treated by Phanerochaete chrysosporium

Combining biological pretreatment with thermal processing may offer an alternative strategy for efficient conversion of lignocellulosic biomass into fuels and chemicals. The thermal decomposition kinetics of biologically pretreated wheat straw by Phanerochaete chrysosporium was investigated in this study using thermogravimetry (TG) - deconvoluted thermogravimetry (DTG) techniques and the Friedman method. This study revealed that biological pretreatment reduced the thermal degradation temperature of the biomass significantly. Relying on the thermal behavior of the biologically pretreated wheat straw, we proposed two biomass degradation phases during the biological degradation of wheat straw. The first phase of biodegradation (within 10 days of biological pretreatment) improved the efficiency of pyrolysis by reducing the temperature demand. In the second phase (after 10 days), although the efficiency of pyrolysis displayed the similar trend as the first phase, it showed a significant increase in activation energy demand. This process is greatly influenced by the residual lignin and cellulose ratios in the biomass. These experimental results will be useful in developing a biological pretreatment based thermochemical conversion process for lignocellulosic biomass.     

A model of aluminum exposure associated with lipid peroxidation in rat brain

We have developed a rat model to investigate the relationship between aluminum exposure and aluminum accumulation, and with oxidative damage in brain tissues. Intraperitoneal injections of aluminum lactate for 7 wk (the total aluminum dosage per rat was approx 100 mg) significantly increased aluminum levels in the brain. The concentration of lipid peroxidation products (thiobarbituric acid-reactive substances [TBARS]) also increased in the brain following aluminum lactate injections. No significant correlations between the concentrations of aluminum and of TBARS were found in the whole brain. Subcellular analysis revealed that aluminum lactate injections led to a significant increase in the concentration of aluminum in the mitochondrial fraction but had no significant effect on the concentration of peroxides in any subcellular fraction. These results suggest that aluminum accumulation induced by the aluminum lactate administration associates with the acceleration of lipid peroxidation in rat brain. Furthermore, these data indicate that the pro-oxidant effect of aluminum may be indirect and concentration independent. The experimental conditions used here provide an animal model of aluminum accumulation in the brain that should prove useful for further investigations of the mechanisms of aluminum neurotoxicity.     

Effects of the administration routes and chemical forms of aluminum on aluminum accumulation in rat brain

An experimental rat model of aluminum accumulation in the brain was developed to aid in determining neurotoxity of aluminum (Al). Al was administered orally, intravenously, and intraperitoneally, in the absence or presence of citric acid or maltol. Oral administration of Al hydroxide [Al (OH)₃] or aluminum chloride (AlCl₃) with citric acid for 7 wk was not found to increase brain Al levels. Similarly, a single intravenous injection of AlCl₃ in the presence or absence of either citric acid or maltol did not alter brain Al levels after 48 h. Only daily intraperitoneal injections of AlCl₃ (8 mg Al/kg body weight) and an equimolar amount of maltol over a 14-d period enhanced accumulation of Al in rat brain. No significant increases were observed for the experimental groups receiving intraperitoneal AlCl₃ alone or with citric acid. This result suggests that the chemical form of Al strongly influences its bioavailability and that intraperitoneal administration of the Al-maltol complex appears to be useful in creating subacute model of Al accumulation in brain tissue.     

Long-term persistence of vaccine-derived aluminum hydroxide is associated with chronic cognitive dysfunction

Macrophagic myofasciitis (MMF) is an emerging condition, characterized by specific muscle lesions assessing long-term persistence of aluminum hydroxide within macrophages at the site of previous immunization. Affected patients mainly complain of arthromyalgias, chronic fatigue, and cognitive difficulties. We designed a comprehensive battery of neuropsychological tests to prospectively delineate MMF-associated cognitive dysfunction (MACD). Compared to control patients with arthritis and chronic pain, MMF patients had pronounced and specific cognitive impairment. MACD mainly affected (i) both visual and verbal memory; (ii) executive functions, including attention, working memory, and planning; and (iii) left ear extinction at dichotic listening test. Cognitive deficits did not correlate with pain, fatigue, depression, or disease duration. Pathophysiological mechanisms underlying MACD remain to be determined. In conclusion, long-term persistence of vaccine-derived aluminum hydroxide within the body assessed by MMF is associated with cognitive dysfunction, not solely due to chronic pain, fatigue and depression.     

Molecular interactions of MnO2@RGO (manganese dioxide-reduced graphene oxide) nanocomposites with bovine serum albumin

Abstract

Graphene based materials have attracted global attention due to their excellent properties. GO-metal oxide nanocomposites have been conjugated with biomolecules for the development of novel materials and potentially used as biomarkers. Herein, a detailed study on the interaction of Bovine serum albumin (BSA) with MnO₂@RGO (manganese dioxide-reduced graphene oxide) nanocomposites (NC) has been carried out. MnO₂@RGO nanocomposites were prepared through a template/surfactant free hydrothermal route at 180?°C for 12?h by varying the graphene oxide (GO) concentration. Different biophysical experiments have been carried out to evaluate molecular interactions between BSA and NCs. Intrinsic fluorescence has been used to quantify the quenching efficiency of NCs and the binding association of BSA-NC complexes. NCs effectively quenched the intrinsic fluorescence of BSA via static and dynamic mechanism. Further, the results indicate that the molecular interactions of NC with BSA are dependent on the GO percentage in NC. Circular dichroism results demonstrate nominal changes in the secondary structure of BSA in presence of NCs. Also, the esterase-like activity of BSA was marginally affected after adsorption upon NCs. In addition, the FESEM micrographs reveal that the protein-NC complexes consist of nanorod and sheet-like morphologies are forming aggregates of different sizes. We hope that this study will provide a basis for the design of novel graphene based and other related nanomaterials for several biological applications.

Communicated by Ramaswamy H. Sarma     

Thermal properties and fauna on the bark of trees in two different African ecosystems

Summary The thermal properties of 26 African tree species in two different ecosystems were studied using thermocouples. In a subtropical moist forest were three bark types of trees: species with thin and smooth bark types with low values of insulation across the bark; species with a more structured bark type and medium insulation values; and species with deep-fissured or scaly bark types and high insulation values. Only these latter trees are able to survive openings in the subtropical forest and stand alone on edges of forest gaps. In the savanna all tree species showed adaptations in the structure of their bark in different forms: many tree species shade their trunks. Some have low bark insulation and these are known to be sensitive to fires. Some tree species show high bark insulation and do not shade their trunks. Tree species with white bark avoid overheating of their surface by reflection of the radiation. The arthropod community living exclusively on the bark was investigated for the first time on South African trees, on ten tree species. In the two different ecosystems this habitat is occupied by different arthropod groups. In the subtropical forest Acari, Araneae, Opiliones, Isopoda, Myriopoda, Blattodea, Psocoptera, Heteroptera, Coleoptera, Formicidae, and Nematocera (Diptera) are the main arthropod groups living exclusively on the bark of trees. In the savanna Pseudoscorpiones, Araneae, Collembola, Blattodea, Psocoptera, Coleoptera, Neuroptera, Termites, Formicidae, Hymenoptera and Brachycera (Diptera) are the main arthropod groups living exclusively on the bark of trees. Within one ecosystem on one bark type the dominant species are similar; richly structured bark types have a richer fauna. In the forest, bark arthropod diversity is related to the bark structure of the constituent trees, and the arthropod communities on the bark would reflect changes in the structure of the forest. Forests comprising tree species with different bark types would have a richer total bark arthropod fauna. Specialists on richly structured bark types would die out if tree species composition were altered by man to give stands consisting only of tree species with smooth bark types. Bark arthropods in a subtropical moist forest have different proportions of herbivorous and fungivorous compared to carnivorous species than those on the bark of trees in a savanna.     

Thermal properties of rhodopsin: insight into the molecular mechanism of dim-light vision

Rhodopsin has developed mechanisms to optimize its sensitivity to light by suppressing dark noise and enhancing quantum yield. We propose that an intramolecular hydrogen-bonding network formed by ～20 water molecules, the hydrophilic residues, and peptide backbones in the transmembrane region is essential to restrain thermal isomerization, the source of dark noise. We studied the thermal stability of rhodopsin at 55 °C with single point mutations (E181Q and S186A) that perturb the hydrogen-bonding network at the active site. We found that the rate of thermal isomerization increased by 1-2 orders of magnitude in the mutants. Our results illustrate the importance of the intact hydrogen-bonding network for dim-light detection, revealing the functional roles of water molecules in rhodopsin. We also show that thermal isomerization of 11-cis-retinal in solution can be catalyzed by wild-type opsin and that this catalytic property is not affected by the mutations. We characterize the catalytic effect and propose that it is due to steric interactions in the retinal-binding site and increases quantum yield by predetermining the trajectory of photoisomerization. Thus, our studies reveal a balancing act between dark noise and quantum yield, which have opposite effects on the thermal isomerization rate. The acquisition of the hydrogen-bonding network and the tuning of the steric interactions at the retinal-binding site are two important factors in the development of dim-light vision.     

Effects of aluminum chloride on normal and uremic adult male rats

Normal and uremic adult male rats were given a daily ip injection of 20 mg Al (Al chloride)/kg for 14 d. The results indicate that Al induces a significant decrease in food ingestion, weight gain, and total protein concentration in the plasma. Compared with control animals, very high increases in Al levels were found in plasma and hepatic homogenates (about 36 and 19 times, respectively). In the brain homogenates, the Al increases were lower (about 23%). The brain cholineacetyltransferase activity was reduced: 10.6 and 14.9% in normal and uremic rats, respectively. The nephrectomy and the food restriction did not affect the total protein concentrations in plasma and the cerebral cholineacetyltransferase activity. Both were only found to be reduced in the rats treated by Al chloride.     

Lignin as additive in polypropylene/coir composites: Thermal, mechanical and morphological properties

PP/CF composites were prepared and the effect of lignin incorporation in the presence and absence of compatibilizer (maleic anhydride grafted polypropylene, PP-g-MA) was investigated by means of mechanical, thermal and morphological properties. Lignin added to the composite was obtained by the Acetosolv process. The composites were prepared in a Haake torque rheometer and assessed by means of tensile testing, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The results showed that in the absence of PP-g-MA, incorporation of lignin did not affect tensile strength and in its presence this property was reduced. Thermal analysis revealed that incorporation of lignin in the composites resulted in increase in both the initial thermal decomposition temperatures and oxidation induction times.