Search results for "aqueous solution"
showing 10 items of 1610 documents
Influence of gamma-irradiation on thermally-induced mesoscopic gelation of degalactosylated xyloglucans
2014
Thermoresponsive degalactosylated xyloglucans have been already proposed as in situ gelling scaffolds for tissue engineering, due to their reversible macroscopic thermal gelation at body temperature and biodegradability. The highly branched, hydroxyl group-rich molecular structure renders xyloglucans interesting raw materials also in the form of micro/nanoparticles for application as nanoscalar drug delivery devices in cosmetic and pharmaceutical formulations. Owing to their natural source, xyloglucans show high average molecular weight, broad molecular weight distribution and poor water solubility, as large and compact aggregates usually form via inter-molecular hydrogen bonding. Co-60 gam…
Studies of network organization and dynamics of e-beam crosslinked PVPs: From macro to nano
2012
Abstract In this work the influence of poly(N-vinyl pyrrolidone) (PVP) concentration in water on the organization and dynamics of the corresponding macro-/nanogel networks has been systematically investigated. Irradiation has been performed at the same irradiation dose (within the sterilization dose range) and dose rate. In the selected irradiation conditions, the transition between macroscopic gelation and micro-/nanogels formation is observed just below the critical overlap concentration (∼1 wt%), whereas the net prevalence of intra-molecular over inter-molecular crosslinking occurs at a lower polymer concentration (below 0.25 wt%). Dynamic–mechanical spectroscopy has been applied as a cl…
Palladium-catalyzed reaction of boronic acids with chiral and racemic alpha-bromo sulfoxides.
2004
Palladium-catalyzed cross-coupling reactions of racemic alpha-bromo sulfoxides with boronic acids are carried out in either aqueous or nonaqueous medium with formation of a new C sp(3)-C sp(2) bond. The arylation of chiral alpha-bromo sulfoxides occurs without racemization. The cross-coupling reaction is general and gives high yields with arylboronic acids substituted with either donor or acceptor groups but gives poor results with heteroarylboronic acids. The best yields are obtained using degassed solvents and CsF instead of aqueous base. The use of aqueous base and the presence of oxygen favor the homocoupling side reaction.
Effects of ions on water structure: a low-field1HT1NMR relaxometry approach
2014
Aqueous salt solutions play an important role in nature because of their effects on environmental biogeochemical processes and on structural properties of biomolecules. Upon dissolution, salts split in ions that are solvated. Water in hydration shells is subjected to molecular motions that can be monitored by (1)H T1 NMR relaxometry. This technique allowed the evaluation of the nature of the interactions between water and ions via variable temperature experiments. Examination of relaxometry properties of aqueous solutions at variable salt concentrations allowed acknowledgement of the role played by ions in either structuring or destructuring water aggregates. A mathematical model has been a…
Zero- to Ultralow-Field NMR Spectroscopy of Small Biomolecules.
2021
Nuclear magnetic resonance (NMR) spectroscopy is a well-established analytical technique used to study chemicals and their transformations. However, high-field NMR spectroscopy necessitates advanced infrastructure, and even cryogen-free benchtop NMR spectrometers cannot be readily assembled from commercially available components. We demonstrate construction of a portable zero-field NMR spectrometer employing a commercially available magnetometer and investigate its applications in analytical chemistry. In particular, J-spectra of small representative biomolecules [13C]-formic acid, [1-13C]-glycine, [2,3-13C]-fumarate, and [1-13C]-d-glucose were acquired, and an approach relying on the prese…
ISOLATION OF RAT LIVER EPOXIDE HYDRATASE: PROPERTIES AND SUBSTRATE SPECIFICITY OF THE PURE ENZYME
1977
ABSTRACT The microsomal enzyme epoxide hydratase has been purified to homogeneity as judged by electrophoretical, ultracentrifugal and immunological criteria and by C- and N-terminal analysis. The preparation procedure consisted of solubilisation using the non-ionic detergent cutscum, (NH4)2SO4 precipitation, ion-exchange chromatography on DEAE-cellulose and cellulose phosphate and hydrophobic chromatography on butyl-sepharose. The product was detergent-free, had a relatively high content of hydrophobic amino acids and tended to aggregate in aqueous solutions. The protein had a minimum molecular weight of 49,000 ± 500 with a sedimentation coefficient of S20w≃ 3. Antibodies raised against th…
Unexpectedly ambivalent O-2 role in the autocatalytic photooxidation of 2-methoxybenzyl alcohol in water
2015
An unusual autocatalytic photooxidation of 2-methoxybenzyl alcohol has been observed under UV irradiation in aqueous medium. The homogeneous oxidation is catalyzed by the corresponding aldehyde that is also the main oxidation product. The trend of alcohol disappearance rate matches the typical shape of an autocatalytic process, where a crucial and ambivalent role is played by the presence of molecular oxygen. Low oxygen concentrations give rise to a zero-order reaction since the beginning of irradiation, while higher amounts of oxygen reduce the alcohol oxidation rate until the aldehyde reaches a concentration high enough to speed up the alcohol's conversion. Experiments performed by varyin…
Aqueous selective photocatalytic oxidation of salicyl alcohol by TiO2 catalysts: Influence of some physico-chemical features
2021
Abstract Partial photocatalytic oxidation of salicyl alcohol (2-hydroxybenzyl alcohol) to salicylaldehyde in water was investigated under environmental friendly conditions in the presence of home-prepared and commercial TiO2 (Merck and Aeroxide P25) samples under UVA irradiation. The photocatalysts were characterized by using BET, XRD, SEM and/or TEM techniques. The effects of crystallinity degree, pH (3–11) and presence of a hole trap (ethanol) on the photocatalytic activity and product selectivity were investigated. 4-Hydroxybenzyl alcohol was also used to study the influence of the position of the substituent group in the aromatic ring. High alcohols conversion and product selectivity va…
Kinetics of 4-Methoxybenzyl Alcohol Oxidation in Aqueous Solution in a Fixed Bed Photocatalytic Reactor
2010
WOS: 000280384800004
Interrelation between the thermodynamic and viscometric behaviour of aqueous solutions of hydrophobically modified ethyl hydroxyethyl cellulose
2000
Abstract Aqueous solutions of a commercial sample of hydrophobically modified ethyl hydroxyethyl cellulose (HC, Mw=100 kg/mol, nonylphenol substitution ca. 1.7 mol%) were studied with respect to their demixing behaviour and flow characteristics. Phase separation temperatures were measured turbidimetrically and by determining the first discernible macroscopic phase separation. In some cases demixing was also monitored viscometrically. Phase volume ratios yielded a critical polymer concentration of 1.87 wt.% HC (displaced considerably out of the minimum of the demixing curve towards higher polymer concentrations) and a lower critical solution temperature of 47°C. Model calculations of the spi…