No abstract

No abstract

The interaction of polymers with water has been extensively studied because of its scientific interest and importance in industrial applications.Poly(ethylene glycol) (PEG) has received a great deal of attention due to its unique properties pertinent to biomedical and biotechnical applications such as complete miscibility in water over a wide range of temperatures and molecular weights, very low toxicity, ability to precipitate proteins and nucleic acids and to form two-phase systems with aqueous solutions of other polymers. 1 Previous results by various techniques, such as complex permittivity, 2 partition, 3,4 potentiometric, 5 spectroscopic 6 measurements and thermal methods, 7 indicated that the physicochemical properties of water in polymer solutions are significantly changed, compared to those of pure water. Recently, Zaslavsky et al. 8 reported "polarity" of aqueous PEG solutions measured by a solvatochromic technique. 9 They measured the molar transition energy (ET) for the UV-VIS absorption band of Reichardt's betaine dye 9 in aqueous solutions of PEGs of various molecular weight (MW) at different concentrations, and observed that the polarity of aqueous PEG solutions, represented by ET, decreased with increasing the MW and concentration of PEGs. It has been suggested that the polarity decrease is due to the structuring action of PEG on water and that the observed solvatochromic effects are due to a change of solvent properties produced by the presence of polymer molecules, not due to a direct interaction of the dye with the polymer. 5,8 It is well known that ET is a composite characteristic that actually responds to changes in both a solvent's dipolarity/polarizability and a solvent's hydrogen bond (HB) donor acidity strength. 10,11 This suggests that the ET values alone can not clearly explain whether the presence of PEG molecules in water cause both of the dipolarity/polarizability and HB donor acidity of water or only one of these two properties to be altered. Water is HB basic as well as dipolar and HB acidic.11 In order to fully understand the effect of PEG on water we thought it is important to measure the HB acceptor basicity as well as the dipolarity/polarizability and HB donor acidity of the water in the presence of varying concentration of PEG.In the present work, we used the Kamlet-Taft solvatochromic comparison approach 10 to study dipolarity/polarizability (π*), HB acceptor basicity (β) and HB donor acidity (α) of aqueous PEG solutions. This method has been widely used to measure these properties of many types of solvents and solvent mixtures. [10][11][12][13][14][15][16] The π*, β and α values for neat liquid PEGs at room temperature have also been measured. Terminal hydroxyl groups of a PEG molecule can act as both an HB donor acid and an acceptor base, and oxyethylene repeating units can act as HB acceptor base. PEG molecules with these moieties are certainly dipolar. These properties of neat liquid PEG might be useful in understanding how PEG molecules affect the properties of water in...

No abstract

A,C‐Bridged (ACCX) and A,D‐bridged isopropyldimethylsilylcalix[6]arene (ADCX) dissolved in OV‐1701 were used as stationary phases in isothermal capillary gas chromatographic separation of some positional isomers. Retention factors and separation factors for the isomers were measured. The isomers investigated are well resolved on the two phases. Retention of all the solutes investigated is longer on ACCX than on ADCX. The longer retention on A,C‐bridged calix[6]arene is probably due to extra inductive interactions of the solute molecule with the carbonyl moieties in the phase. Separation factors for closely eluting isomer pairs are similar on the two phases. This seems to indicate that the carbonyl moieties do not play an appreciable role in discriminating the isomer molecules on entering the cavity of the calixarene if the solute is retained by the inclusion process.