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141.
Temperature-induced phase transition in water solutions of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-isopropylmethacrylamide) (PNIPMAM) have been studied by ATR FTIR and Raman spectroscopy in combination with quantum chemical calculations. The presence or absence of the α-methyl group has a strong effect on the physical structure of water solutions. Although the hydrophobic interactions for PNIPMAM and PNIPAM are very similar, PNIPMAM with additional methyl group exhibits significantly weaker intermolecular interactions between the amide groups. That effect is the cause of the higher transition temperature Tt by about 8 °C for PNIPMAM compared to PNIPAM due to the formation of larger compact structures. The presence of the methyl group is significant for the reversibility of the temperature transition during the backward cooling as the dissolution of more stable compact PNIPMAM requires overcoming of a higher energy barrier and shows a strong hysteresis. 相似文献
142.
The space of the torsion (0,3)-tensors of the linear connections on almost contact manifolds with B-metric is decomposed in 15 orthogonal and invariant subspaces with respect to the action of the structure group. Three known connections, preserving the structure, are characterized regarding this classification. 相似文献
143.
The present work shows the feasibility of preparing transparent titania coatings being doped with platinum nanoparticles by sol–gel processing. The used platinum nanoparticles are modified by two different functional thiol ligands, mercaptoethanol and mercaptopropionic acid. The functional ligands are used to create a nanoparticle network and they can also promote anchorage of titanium alkoxides as sol–gel precursors, ensuring a regular distribution of the metal nanoparticles within the coating as well as a good stability to the film. 相似文献
144.
For a minimal surface immersed into an odd-dimensional unit sphere S
2n+1 with the first (n−2) higher-order ellipses of curvature being a circle, we construct a sequence of such surfaces and investigate if some two
minimal surfaces in such a sequence can be congruent by an orientation-reversing isometry. 相似文献
145.
Armando Valenzuela Peraza David Calderón Guzmán Norma Osnaya Brizuela Maribel Ortiz Herrera Hugo Juárez Olguín Miroslava Lindoro Silva Belén Juárez Tapia Gerardo Barragán Mejía 《BMC neuroscience》2018,19(1):71
Background
Neurological disorders suggest that the excitotoxicity involves a drastic increase in intracellular Ca2+ concentrations and the formation of reactive oxygen species. The presence of these free radicals may also affect the dopaminergic system. The aim of this work was to determine if riboflavin (B2) and pyridoxine (B6) provide protection to the brain against free radicals generated by 3-nitropropionic acid (3-NPA) by measuring the levels of dopamine (DA) and selected oxidative stress markers.Methods
Male Fisher rats were grouped (n?=?6) and treated as follows: group 1, control (NaCl 0.9%); group 2, 3-NPA (20 mg/kg); group 3, B2 (10 mg/kg); group 4, B2 (10 mg/kg)?+?3-NPA (20 mg/kg); group 5, B6 (10 mg/kg) and group 6, B6?+?3-NPA. All treatments were administered every 24 h for 5 days by intraperitoneal route. After sacrifice, the brain was obtained to measure DA, GSH, and lipid peroxidation, Ca2+, Mg2+, ATPase and H2O2.Main findings
Levels of dopamine increased in cortex, striatum and cerebellum/medulla oblongata of animals that received 3-NPA alone. The lipid peroxidation increased in cortex, striatum, and cerebellum/medulla oblongata, of animals treated with B2 vitamin alone. ATPase dependent on Ca+2, Mg+2 and H2O2 increased in all regions of animals that received 3-NPA alone.Conclusion
The results confirm the capacity of 3-NPA to generate oxidative stress. Besides, the study suggests that B2 or B6 vitamins restored the levels of DA and reduced oxidative stress in brain of rats. We believe that these results would help in the study of neurodegenerative diseases.146.
A microprocessor controlled gradient elution system suitable for capillary electrochromatography has been developed and tested. It is based on a liquid handling device described previously which is capable of liquid transport with both low and high fluid dispersion. The low dispersion region formed by stainless steel needle 250 microm I.D. serves for sample injection, while the high dispersion region, created by steep extension of tube diameter, is used for continuous mobile phase gradient generation. A homologous series of seven alkylphenones was electrochromatographically separated on a monolithic polyacrylic column under gradient conditions. An S-shaped acetonitrile gradient (30-70%) was applied. A high reproducibility of retention times (RSD about 0.1%) was obtained, indicating accuracy of automated gradient operations. 相似文献
147.
Thin composite films of metal nanoparticles incorporated into a phthalocyanine matrix were prepared by simultaneous vacuum deposition of copper and phthalocyanine from two evaporation sources. Absorption spectra in both the IR and UV/VIS regions were measured in order to study changes of structure and properties with different volume fractions of copper in the films. The effective medium theory (EMT) approach was used to model optical spectra. A pronounced aging of composite layers was observed after the deposition. 相似文献
148.
Capillary electrophoresis fingerprinting and spectrophotometric determination of antioxidant potential for classification of Mentha products
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Vendula Roblová Miroslava Bittová Petr Kubáň Vlastimil Kubáň 《Journal of separation science》2016,39(14):2862-2868
In this work aqueous infusions from ten Mentha herbal samples (four different Mentha species and six hybrids of Mentha x piperita) and 20 different peppermint teas were screened by capillary electrophoresis with UV detection. The fingerprint separation was accomplished in a 25 mM borate background electrolyte with 10% methanol at pH 9.3. The total polyphenolic content in the extracts was determined spectrophotometrically at 765 nm by a Folin–Ciocalteu phenol assay. Total antioxidant activity was determined by scavenging of 2,2‐diphenyl‐1‐picrylhydrazyl radical at 515 nm. The peak areas of 12 dominant peaks from CE analysis, present in all samples, and the value of total polyphenolic content and total antioxidant activity obtained by spectrophotometry was combined into a single data matrix and principal component analysis was applied. The obtained principal component analysis model resulted in distinct clusters of Mentha and peppermint tea samples distinguishing the samples according to their potential protective antioxidant effect. Principal component analysis, using a non‐targeted approach with no need for compound identification, was found as a new promising tool for the screening of herbal tea products. 相似文献
149.
Karasová G Lehotay J Sádecká J Skacáni I Lachová M 《Journal of separation science》2005,28(18):2468-2476
Selective SPE of derivates of p-hydroxybenzoic acid (pHBA) from plant extract of Melissa officinalis is presented using a molecularly imprinted polymer (MIP) made with protocatechuic acid (PA) as template molecule. MIP was prepared with acrylamide as functional monomer, ethylene glycol dimethacrylate as crosslinking monomer and ACN as porogen. MIP was evaluated towards six phenolic acids: PA, gallic acid, pHBA, vanillic acid (VA), gentisic acid (GeA) and syringic acid (SyrA), and then steps of molecularly imprinted SPE (MISPE) procedure were optimized. The best specific binding capacity of MIP was obtained for PA in ACN (34.7 microg/g of MIP). Other tested acids were also bound on MIP if they were dissolved in this solvent. ACN was chosen as solvent for sample application. M. officinalis was extracted into methanol/water (4:1, v/v), the extract was then evaporated to dryness and dissolved in ACN before application on MIP. Water and ACN were used as washing solvents and elution of benzoic acids was performed by means of a mixture methanol/acetic acid (9:1, v/v). pHBA, GA, PA and VA were extracted with recoveries of 56.3-82.1% using this MISPE method. GeA was not determined in plant extract. 相似文献