Search results for "aqueous solution"
showing 10 items of 1610 documents
Viscosimetric investigation of the interaction between sodium dodecylsulfate micelles and a polymer drug carrier
1993
Abstract The viscosities of aqueous sodium dodecyl sulfate solutions with and without α,β-poly( N -hydroxyethyl)- dl -aspartamide (PHEA), at 15, 25 and 35°C are reported. The viscosities of SDS and of PHEA aqueous solutions are discussed in terms of the parameter D [D = ( η η 0 − 1)/φ] describing the non-ideal behavior of SDS micelles and of PHEA macromolecules. The viscosities of SDS plus PHEA aqueous solutions, discussed in terms of the parameter F [ F = η rel ( PHEA ) + η rel ( SDS ) − η rel ( SDS + PHEA )] M , demonstrate the occurrence of interactions between SDS micelles and the PHEA macromolecule. Both D and F are scarcely influenced by temperature variation.
Aqueous self-assembly and cation selectivity of cobaltabisdicarbollide dianionic dumbbells.
2014
The anion [3,3'-Co(C2B9H11)2](-) ([COSAN](-)) produces aggregates in water. These aggregates are interpreted to be the result of C-H⋅⋅⋅H-B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN](-) units. The approach is to join two [COSAN](-) anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K(+) selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K(+) from a mixture containing Li(+), Na(+), …
Coordination chemistry of N,N′-bis(coordinating group substituted)oxamides: a rational design of nuclearity tailored polynuclear complexes
1999
Abstract The coordinating properties of N , N ′-bis(coordinating group substituted)oxamides have been thoroughly investigated both in aqueous solution and in the solid state. The easy cis – trans isomerization equilibria that they exhibit together with the great variety of N , N ′-substituents which can be used to play on the overall charge, complexing ability and polarity, make them very suitable ligands in designing homo- and heterometallic species. The knowledge of their complex formation in aqueous solution by potentiometry and using the hydrogen ion concentration as a probe, allowed us to settle the basis of a rational design of oxamidate-containing polynuclear species whose nuclearity…
Azacoronands and Azacyclophanes
2012
Azacycloalkanes and azacyclophanes are among the first macrocyclic ligands developed in the field of supramolecular chemistry. Since they are polyamines, they show dual nature in the coordination of both metal cations, when they are in the free-base form, and anionic species, when they are protonated. As a matter of fact, they played a key role in the birth of macrocyclic chemistry of transition metal complexes and anion coordination chemistry. Furthermore, azacyclophanes fostered also the birth of apolar complexation in aqueous solution, since their aromatic units act as binding sites for apolar substrates. Keywords: azacycloalkanes; azacyclophanes; metal complexes; anion complexes; apolar…
Thermodynamics ofN,N,N-octylpentyldimethyl-ammonium chloride in water-urea mixtures
1997
Specific conductivities, densities, heat capacities, and enthalpies of dilution at 25‡C were measured forN,N,N-octylpentyldimethylammonium chloride (OPAC) in water-urea mixtures at various urea concentrations mu as functions of the surfactant concentration ms. From conductivity data, the cmc and the degree of the counterion dissociation Β of the OPAC micelles were calculated. The cmc increases linearly with increasingm u while Βvs. mu is a smooth concave curve. From the experimental thermodynamic data, the apparentY Φ and partialY 2 molar properties (volumes, heat capacities, and relative enthalpies) are derived as functions of mu andm s . The effect of urea on the dependences of the differ…
Rod-Length Dependent Aggregation in a Series of Oligo(p-benzamide)-Block-Poly(ethylene glycol) Rod-Coil Copolymers
2005
The synthesis of a series of rod-coil diblock copolymers with flexible poly(ethylene oxide) chains (M n = 5 000 g mol -1 ) and rod blocks consisting of monodisperse oligo(p-benzamide)s is described. The formation of defined supramolecular aggregates in solution as well as the solid state has been analyzed. The length of the oligo(p-benzamide)s has been systematically varied from n = 1 to 7 units. The influence of n on aggregation in chloroform and aqueous solution was investigated by GPC as well as UV-vis spectroscopy. A critical aggregation length was found for chloroform (n = 5) and water (n = 4), below which no aggregation is observed under otherwise identical experimental conditions. Ag…
Solution properties of polyelectrolytes
1993
Abstract Aqueous size-exclusion chromatography was used to analyse the elution behaviour of several standard ionic polymers, including poly( l -glutamic acid), sodium poly(styrene sulphonate) and poly(acrylic acid), different in nature and chain flexibility, as a function of the pH and ionic strength of the eluent. Two organic-based hydrophilic packings, Spherogel TSK PW4000 and Ultrahydrogel 250, were tested in order to select the optimal conditions of macromolecular separation, and the results obtained for each column were compared. A set of calibration graphs for the above polyions as a function of eluent pH and ionic strength were obtained and compared with those obtained for uncharged …
Calorimetric study on the solubilization of some primary alcohols by reversed AOT micelles
1989
A calorimetric method to evaluate, at the same time, the distribution constant and the standard enthalpy of transfer of a solute partitioned between organic phase and reversed micelles is proposed. The method was applied to the partition of methanol, 1-propanol and 1-pentanol between n-heptane and AOT reversed micelles containing water at 25°C. The results show that the distribution constant decreases as the alcohol alkyl chain length increases and that the solubilization site can change as the water content of reversed AOT micelles increases. In particular, at sufficiently high water content, methanol seems to be preferably solubilized in the aqueous pseudophase whereas 1-pentanol prefers …
Chromatographic and mass spectrometric characterization of the structures of the polypeptide antibiotics samarosporin and stilbellin and identity wit…
1983
The structural identity of the polypeptide antibiotics, samarosporin I(II) and stilbellin I(II) with emerimicin IV(III) has been established by thin-layer chromatography, quantitative amino acid analysis by ion-exchange chromatography, gas-liquid chromatography of the N-pentafluoropropionyl amino acid n-propyl esters and N,O-bis-pentafluoropropionyl phenylalaninol with quartz capillaries coated with the chiral stationary phase N-propionyl-L-valine-tert-butylamide, and determination of the relative molecular masses and sequence-specific fragments by field desorption fast atom bombardment mass spectrometry. The separation of closely related sequence analogues of the above polypeptides could b…
Influence of dissolved humic material and ionic strength on C8 extraction of pesticides from water
1995
A mixture of twelve intermediate polarity pesticides, mostly carbamate-type, have been chromatographied on an octadecyl-silica bonded-phase column using acetonitrile-water gradient mobile phase and UV detection. Pesticides were extracted from aqueous matrix by solid-phase extraction. The extraction system consisted of a glass microcolumn containing octyl-silica solidphase conditioned with methanol and water. The elution was by acetonitrile-dichloromethane (50:50). Studies of extraction factors like volume of sample, addition of 10% sodium chloride and presence of dissolved humic material are investigated.