Search results for "Aqueous solution"
showing 10 items of 1610 documents
New biodegradable hydrogels based on an acryloylated polyaspartamide cross-linked by gamma irradiation
1999
Alpha, beta-poly(N-2-hydroxyethyl)-DL-aspartamide (PHEA), a synthetic biocompatible macromolecule, was functionalized with glycidyl methacrylate (GMA) in order to introduce in its side chains residues having double bonds and ester groups. The copolymer (PHG), obtained from PHEA and GMA, had a degree of derivatization of 29 mol%. PHG aqueous solutions are cross-linked by gamma radiation at 0 degrees C either in the presence or absence of N,N'-methylenebisacrylamide (BIS) giving rise to new hydrogel systems. In both cases gelation occurs at quite low doses (0.26 and 0.4 kGy, respectively). The obtained networks were characterized by FT-IR spectrophotometry which confirmed that the cross-linki…
Biodegradable hydrogels obtained by photocrosslinking of dextran and polyaspartamide derivatives
2003
The functionalization of dextran with glycidyl methacrylate (GMA) leads to the formation of a derivative that generates hydrogels for irradiation at 365nm. The effects of various polymer concentrations and irradiation times on the yield and the properties of the obtained hydrogels are reported. The networks have been characterized by FT-IR spectra, dimensional analysis and swelling measurements carried out at different pH values. In vitro studies suggest that all samples undergo a partial chemical hydrolysis, whereas the incubation with dextranases causes a total degradation whose rate depends on the degree of crosslinking. In addition, aqueous solutions of functionalized dextran have been …
Interaction of metal ions with N-glycosylamines: isolation and characterization of the products of 4,6-O-benzylidene-N-(o-carboxyphenyl)-β-D-glucopyr…
2001
Metal-ion complexes of Li+, Na+, K+, Mg2+, Ca2+, Ba2+, Pb2+, Cd2+, Hg2+ with 4,6–O–benzylidene–N–(o–carboxyphenyl)–β–D–glucopyranosylamine were synthesized and isolated as solid products and characterized by analytical means as well as by spectral techniques, such as, 1H and 13C NMR, FTIR, absorption, FAB mass spectrometry, optical rotation and CD. While the alkali metal ions formed ML type of complexes, the other metal ions formed ML2 type complexes. Molecular weights of the complexes of Li+, Na+ and K+ were established based on the molecular-ion peaks in the FAB mass spectra. The saccharide portion remians in the β-anomeric form even after the complexation. The spectral data, as well as t…
119Sn M�ssbauer studies of bis[cysteinato(1?)-S]- and bis[penicillaminato(1?)-S]-diorganotin(IV) species in the crystalline state and in frozen aqueo…
1988
The bonding and the configuration of the tin environment in the title compounds {R2Sn[SCH2CH(NH3+)COO−]2 and R2Sn[SC(CH3)2CH(NH3+)COO−]2, indicated in the following as R2Sn(cysH)2 and R2Sn(penH)2 respectively} has been investigated through the determination of the Mossbauer-Zeeman spectra of Ph2Sn(cysH)2 and Ph2Sn(penH)2 in the solid state, and through conventional Mossbauer spectroscopy of Me2Sn(penH)2 in the solid state as well as of Me2Sn(cysH)2 and Me2Sn(penH)2 in aqueous solution (frozen). The treatment of the data by the pointcharge model approach suggested the general occurrence of a tetrahedral C2SnS2 core. In aqueous Hepes buffer, a tertiary amino nitrogen atom has been observed to…
Sustainable and cost-efficient electro-synthesis of formamidine acetate from cyanamide in aqueous acidic electrolyte
2021
Formamidine represents a versatile building block in synthetic organic chemistry. We developed a new electrochemical synthesis of formamidine acetate by cathodic reduction of cyanamide in an aqueous electrolyte and in high yield. The crude product could be used for further conversions, such as to pyrimidines without purification. Compared to established synthetic routes neither prior processing of cyanamide was necessary, nor precious transition-metal catalyst were required, nor any reagent waste was produced, and only biocompatible and sustainable solvents were employed for this process, following the requirements of green chemistry.
A119Sn Mössbauer spectroscopic study on complexes of di-and tri-organotin(IV) moieties with 2-mercaptoethanesulfonates, in the solid state and in aqu…
1988
The configuration of the bonding environment of tin in the complexes [R2Sn(SCH2CH2SO3)2]2− (R = Me, Ph) and [Me3Sn(SCH2CH2SO3)]− has been determined to be tetrahedral both in the solid state and in aqueous solution (for the methyl derivatives). The coordination number of tin increases to five in aqueous solutions for the Me2Sn(IV) complexes in Hepes buffer (N-2-hydroxyethylpiperazine-N′-2-ethanesulfonic acid; at least in fivefold excess, at pH 7.4) due to coordination by the tertiary amino nitrogen atom. No effect is detected due to the surfactant 2-hydroxypropylcellulose concerning both coordination to tin and influence on the Mossbauer parameters. The stoichiometry of mixed complex format…
Photochemical Synthesis of Water-Soluble Gold Nanorods: The Role of Silver Ions in Assisting Anisotropic Growth
2009
The role of Ag+ ions in the ultraviolet-driven photochemical synthesis of Au nanorods (NRs) in aqueous surfactant mixtures has been investigated in order to elucidate the mechanism that drives anisotropic nanoparticle growth. The samples, grown in the presence of varying amounts of Ag+ ions for scheduled irradiation times, have been characterized by ultraviolet−visible−near infrared (UV−vis−NIR) absorption spectroscopy, analytical transmission electron microscopy (ATEM), inductively coupled plasma atomic emission spectroscopy (ICP-AES), and extended X-ray absorption fine structure (EXAFS) measurements. Moreover, the time evolution of size and shape distribution has been investigated by stat…
Calorimetric investigation of the precipitation of calcium monohydrogen phosphate in water/AOT/n-heptane microemulsions
2000
Abstract The molar enthalpies of precipitation of calcium monohydrogen phosphate (CaHPO 4 ) in water/sodium bis(2-ethylhexyl) sulfosuccinate (AOT)/ n -heptane microemulsions were measured at 25°C by a calorimetric technique as a function of the molar ratio R ( R = [water]/[AOT]) at a fixed AOT concentration. Calorimetric data indicate the formation of CaHPO 4 nanoparticles encapsulated in the aqueous core of the AOT reversed micelles displaying a slow growing process with time. Their energetic state is initially different from that in bulk water approaching the value in water at longer times. The observed growing process results to be completely inhibited by the presence of small amounts o…
Synthesis, size control, and passivation of CdS nanoparticles in water/AOT/n-heptane microemulsions
2003
Abstract CdS nanoparticles have been synthesised by adding tetrabutylammonium hydrogen sulphide to water/sodium bis(2-ethylhexyl) sulfosuccinate/ n -heptane microemulsions containing CdSO 4 . Analysis of UV–Vis absorption spectra recorded at various times indicates that an initial rapid formation of CdS nanoparticles is followed by a very slow growth process which can be well described by a power law. The growth process is totally inhibited by the addition of an appropriate amount of bis(2-ethylhexyl)amine (BEA) leading to the formation of stable nanosized CdS particles coated by an oriented monolayer of chemically bonded BEA molecules. Depending on the BEA addition time, the growth inhibit…
Inclusion complexes of triphenylphosphine derivatives and peracetylated-β-cyclodextrin in supercritical carbon dioxide
2008
The supramolecular chemistry of peracetylated-β-CD (perAc-β-CD) as a host for triphenyphosphine derivatives has been studied in supercritical (scCO2) using UV absorption spectroscopy. It was found that the association constant in scCO2 at 40°C and 300 bar is 10 to 1000 times smaller compared to analogous systems in aqueous solvent. Studies of the thermodynamics of the inclusion process found an enthalpy of association of -30 kJ/mole and an entropy of -55 J/moleK. This difference with respect to water is attributed to the absence of the hydrophobic effect in scCO2 due to the much smaller polarity of scCO2 versus water. To further explore the effect of the solvent on the association constant,…