Search results for "Solvent"
showing 10 items of 1395 documents
Photochemical Functionalization of Allyl Benzoates by C-H Insertion
2013
The photoreactivity of allyl benzoates, containing an electron-rich double bond, has been explored by irradiation at 305 nm in different solvents. Solvent addition products arising from an insertion of the alpha H–C bonds of THF, dioxane, and i-PrOH to the allylic double bond was realized. The observed reactivity depended on reaction conditions and substitution pattern of the substrate. A DFT study on this unusual reaction was performed allowing the formulation of two mechanistic pathways.
Application of the negative staining technique to both aqueous and organic solvent solutions of polymer particles
1999
Abstract Transmission electron microscopy (TEM) imaging of several different polymers in aqueous and organic solutions using the negative staining technique is demonstrated, to emphasise the possibilities of this specimen preparation technique for polymer science. Negative stains can readily be prepared in both water and organic solvents (e.g. dimethyl formamide (DMF), dimethyl sulfoxide (DMSO) and tetrahydrofurane (THF)). Polymer particle size, size distribution and shape seen in negative stain correlates well with those of unstained materials. The particle surface and smaller particles (e.g. 10–20 nm) are more clearly defined in the presence of a negative stain. The inherent problems of s…
Synthesis of bi- and tricyclic β-lactam libraries in aqueous medium
2007
Water as a solvent is not only inexpensive and environmentally benign, but may allow good reactivity. The present work focuses on the application of a modified Ugi reaction, i.e. the Ugi four-centre three-component reaction (U-4C-3CR), in aqueous medium to construct β-lactam libraries. All the attempted reactions could be successfully performed in water. The reaction conditions under which the precipitation process was effective were investigated; no further work-up or purification was necessary. In several cases when less water-soluble β-amino acids were used, the precipitated products were isolated easily by simple filtration. In other cases, evaporation of the solvent was appropriate for…
Function of biomolecules as a probe for studying the effects of organic co-solvents on their conformations
1980
Abstract Conformation changes associated with the function of biomolecules can bring out variations of the extent and specific structure of their hydrophobic areas exposed to solvent, with consequent local rearrangements of the solvent. This is one of the channels through which the solvent exerts its role in the functional equilibria of biomolecules. The function of biological macromolecules in perturbed aqueous solvent can therefore be a suitable probe for studying the response of macromolecule-solvent systems to perturbations caused by organic co-solvents. We shall discussed the effects that the presence of some monohydric alcohols and some amides in the aqueous medium have on some thermo…
Introduction to the microsymposium and on the modulation of thermodynamic parameters relative to biomolecule-solvent interactions
1980
Abstract As a result of introducing a macromolecule in a solvent, changes in the structures of both solute and solvent are generally found. In this specific meaning we refer here to ‘relaxation phenomena’. The discussion will either concern or keep in a view the case of biomolecules and to which extent these changes are involved in their thermodynamic stability or functional structure: Dr. Ben-Naim will discuss hydrophobic interactions and structural changes in the solvent; Dr. Wen will focus on thermodynamic properties of aqueous solutions on hydrophobic solutes; Dr. Cordone, Dr. Fornili and myself shall discuss results of experiments concerning solutes on several types(proteins, polynucle…
Ionic polymers based on dextran: hydrodynamic properties in aqueous solution and solvent mixtures.
2009
Hydrodynamic properties of a series of ionic polysaccharides with different charge density but the same molecular weight have been evaluated in salt-free aqueous solution and aqueous/organic solvent mixtures by means of capillary viscometry. The polyelectrolytes investigated contain quaternary ammonium salt groups, N-ethyl-N,N-dimethyl-2-hydroxypropylammonium chloride, attached to a dextran backbone. The experimental viscometric data have been plotted in terms of the Wolf method. The results show that the experimental data fit well with this model and allow the calculation of intrinsic viscosities and other hydrodynamic parameters, which provide new information about the dependence of the p…
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.
On the tautomerization process of glycine in aqueous solution
2000
The experimental activation energy for the tautomerization of glycine zwitterion neutral form has been reported to be 14.6 kcalrmol. It has been generally assumed that this energy barrier is needed for proton transfer to occur. However, previous theoretical results do not support this interpretation. In the present work, we examine this question using density functional calculations, extended basis sets and a polarizable continuum solvent model. Our results suggest that the limiting step for the tautomerization process corresponds basically to H-atom reorientation in the -COOH group. This could be a general feature in the tautomerization of amino acids. q 2000 Elsevier Science B.V. All righ…
A Facile Approach for Transferring Hydrophobic Magnetic Nanoparticles into Water-Soluble Particles
2008
A novel, easy and high-efficient method is described for transferring hydrophobic magnetic Fe 3 O 4 nanoparticles from organic to aqueous solution by wrapping a thermo-responsive and photocrosslinkable poly(N-isopropylacrylamide) (PNIPAm) terpolymer around the particles. The wrapping procedure is introduced by the co-nonsolvent transition of PNIPAm in the mixing solvent and the polymer can dissolve in water carrying Fe 3 O 4 nanoparticles by noncovalent interaction. The temperature-dependant and magnetic properties of the water-soluble particles are characterized in this paper.