Search results for " solution"
showing 10 items of 3084 documents
Extraction of short peptides using supported liquid membranes
2002
Studies of extraction of short peptides using supported liquid membranes containing Aliquat 336 as a carrier are presented. The extractions are carried out from an aqueous donor phase with pH ≥ 10 to an acceptor phase containing salt. The mass transfer is driven by the gradient of salt concentration between these phases. The extraction efficiency is dependent on the composition of water phases, the type and concentration of counter-ion in the stagnant acceptor phase and the flow rate of the donor phase. Moreover, it is also influenced by the concentration and structure of the examined peptides.
Polyelectrolytes: Intrinsic Viscosities in the Absence and in the Presence of Salt
2008
Intrinsic viscosities were determined at 25 °C for 10 samples of narrowly distributed sodium polystyrene sulfonate (the molecular weights M ranging from 0.9 to 1000 kg/mol) in pure water and in aqueous solutions containing 0.9 wt % NaCl from the slope of ln ηrel versus polymer concentration. In the middle range of M, the [η] values are in the former case almost 2 orders of magnitude larger than in the latter case. In the absence of salt, the plot of log [η] as a function of log M exhibits a sigmoidal shape, which can be approximated within the interval 3 < M (in kg mol-1) < 30 by log[η] = −0.17 + 2.1 log M. In the presence of salt, the following relation holds true in the entire regime: lo…
Static measurements of refractive index increments at 633 nm with a modified refractive index detector
1985
A R 401 Waters Assoc. differential refractometer has been modified to obtain the variation of refractive index increments, dn/dc, of polymer solutions at 633 nm. The introduced modifications were in the sample injection system and in the light source. The performance of the modified refractometer both with aqueous and organic solutions is analyzed. In order to localize a conformational transition in lysozyme, the dependence of dn/dc on temperature for lysozyme solutions in phosphate buffer is studied. Similarly, (dn/dc)k values for the ternary n-alkane/butanone/poly(dimethyl siloxane) systems over the whole composition range of the binary solvent mixtures are evaluated.
Chromatography of metal chelates
1973
The chromatographic behavior of metal bis(ethoxyethyl)dithiocarbamate was investigated. The chelates of 14 elements (V, Cr, Co, Ni, Cu, Zn, Se, Mo, Cd, Te, Hg, Tl, Pb and Bi) could be preconcentrated from water with an on-line system and were shown to be suitable for C18-reversed-phase liquid chromatography. A quaternary solvent mixture with admixture of a surfactant was used as eluent, UV-detection was performed at 254 nm. Thermostating the column to 40° C resulted in a significant increase in chromatographic resolution and in a decrease of analysis time. The recovery of the chelates from the aqueous solutions as well as reproducibility of the results are very sensitive to pH changes.
Influence of some physicochemical factors on the viscosity of aqueous levan solutions ofZymomonas mobilis
1998
Zymomonas mobilis strain 113 “S” produces levan – an extracellular, viscous, biologically active, non-toxic fructose polymer with a unique structure and extraordinary properties. This polysaccharide was isolated at two different degrees of purity by alcohol precipitation from aqueous solutions and was characterized with respect to some rheological properties and stability of viscous solutions. The effects of temperature, pH and salt concentration on the viscosity of 1–3% levan solutions were examined. The viscosity of levan solutions was found to be quite stable and reversible at room temperature over a wide range of pH from 4 to 11. The viscosity was slightly affected by increased salt con…
Characterization of the Cyclodextrin−Surfactant Interactions by Volume and Enthalpy
2003
Volume and enthalpy of transfer of hydroxypropyl-α-cyclodextrin (HP-α-CD) and hydroxypropyl-γ-cyclodextrin (HP-γ-CD) from water to the aqueous solutions of sodium alkanoates (sodium hexanoate, sodium decanoate and sodium dodecanoate) were determined at 298 K. The cyclodextrin concentration was kept constant, and that of the surfactant was varied in order to analyze both the pre- and postmicellar regions. The experimental data in the premicellar region were consistent with the formation of 1:1 and 1:2 (1 cyclodextrin:2 surfactants) inclusion complexes, with the exception of the HP-α-CD/sodium dodecanoate system which presented only the 1:1 complexes. The mechanism of the 1:2 complexes format…
Temperature-responsive inclusion complex of cationic PNIPAAM diblock copolymer and γ-cyclodextrin
2012
Aqueous mixtures of γ-cyclodextrin (γ-CD) and the thermosensitive cationic diblock copolymer poly(N-isopropylacrylamide)-b-poly(3-acrylamidopropyl)trimethylammonium chloride (PNIPAAM24-b-PAMPTAM(+)9) or the PNIPAAM homopolymer PNIPAAM47 have been investigated using various experimental methods. Solid γ-CD–polymer inclusion complexes (pseudopolyrotaxanes) form at ambient temperatures in fairly concentrated CD solutions. The NMR measurements showed that the stoichiometry of the inclusion complexes is close to two NIPAAM units per CD molecule. The cationic block of the copolymer is not incorporated into the CD cavity. Synchrotron radiation X-ray diffraction spectra of the solid inclusion compl…
Thermodynamic Evidence of Cyclodextrin−Micelle Interactions
2002
The enthalpy of transfer (ΔHt) of hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD), and β-cyclodextrin (β-CD) from water to the aqueous C6F13CO2Na and C7F15CO2Na solutions were determined in the pre- and post-micellar regions. The behavior of the macrocycles is system specific. Generally, the magnitude of the enthalpy is influenced by several factors: (1) the alkyl chain length of the surfactant, (2) the cyclodextrin cavity and its alkylation, (3) the interactions between the free cyclodextrin and the free surfactant, (4) the host−guest equilibrium constant, (5) the host/guest stoichiometry, and (6) the micelle-cyclodextrin (free and/or complexed) interactions…
Chemical and pharmaceutical evaluation of the relationship between triazole linkers and pore size on cyclodextrin–calixarene nanosponges used as carr…
2016
Mixed cyclodextrin–calixarene nanosponges were used to prepare some composites with the well known polyphenolic bioactive compounds quercetin and silibinin. The composites were characterized by means of different techniques (UV-vis, FT-IR, microcalorimetry, thermogravimetry), in order to assess their loading and thermal stability. The kinetics of release of the bioactive molecules into aqueous solution were studied at two different pH values (1.0, 6.4), which mimic typical physiological conditions. Finally the possible antiproliferative effects in vitro were assayed towards three triple negative breast cancer cell lines (SUM 149, SUM 159 and MDA-MB-23). Our results point out the role assume…
Heat Capacity Study to Evidence the Interactions between Cyclodextrin and Surfactant in the Monomeric and Micellized States
2003
The heat capacities of transfer (ΔCpt) of hydroxypropyl-α-cyclodextrin and hydroxypropyl-γ-cyclodextrin (0.05 mol kg-1) from water to aqueous solutions of sodium hexanoate, sodium decanoate, and so...