Hydrophilic OH Groups Research Articles

Spectroscopic probes of the interactions of the dye Stains-all with deoxycholate and cholate

The biological surfactants sodium cholate (NaC) and sodium deoxycholate (NaDC) differ from the normal surfactants such as sodium dodecyl sulphate (SDS) by having hydrophilic OH groups in their hydrophobic moieties, and they failed to induce sharp blue shifted metachromasia in the common cationic dyes such as acridine orange, methylene blue, pinacyanol etc. However, both the cholates induce extremely sharp and stable blue-shifted metachromasia in the cyanine dye Stains-all (Stal), at concentrate much below the critical micellar concentrations and not disrupted by the excess of surfactants unless at above the respective critical micellar concentrations. Both chiral cholates induce very strong biphasic negative circular dichroism (CD) in Stal. At high surfactant dye both NaDC-Stal and NaC-Stal exhibit a second positive biphasic CD spectrum, indicating the formation of second species of the complexes, not immediately discernible from the respective absorption spectrum. Though the reported structures of micelles and crystals of NaDC are distinctly different from that of NaC, the induced metachromasia and circular dichroism in Stal by the two surfactants are remarkably similar. It is reasonably thought that Stal cations bound at NaC and NaDC are arranged with systematic twists in one sense, responsible for metachromasia and dichroism of the dye aggregates, the formation of NaDC-Stal and NaC-Stal are probably followed by some self organization of the complexes formed in the premicellar range of concentrations, excess surfactants added to these complexes form just part of the solvent. Only above cmc the micelles start disruption of the dye aggregates. Our results fit well with the helical model of NaDC and the Small's model of NaDC micellar aggregate with the hydrophobic surfaces oriented inside.

Chemical Characterization by FT-IR Spectrometry and Modification of the Very First Atomic Layer of A TiO2 Nanosized Powder

AbstractNanosized powders exhibit high specific surface areas resulting in enhanced reactivities. Surface tailoring by controlled adsorption of molecules can thus be conveniently performed and more easily monitored by surface-sensitive techniques. In situ and ex situ grafting procedures of hexamethyldisilazane (HMDS) on nanosized titania (n-TiO2) powder were carried out and studied by Fourier transform infrared spectrometry (FT-IR). In addition to a decrease of the hydrophilic OH groups, the vibration analysis revealed hydrophobic CH3 groups on the grafted samples. Co-adsorption of CO and H2O on the differently grafted samples showed a large reduction of water effect compared to the as-received n-TiO2 powder. Modulation of infrared transmitted energy by controlled adsorption of O2 and CO made it possible to qualitatively compare the electronic properties of the surface-tailored samples.

On the Mechanism of Dissolution Inhibition in Phenolic Resins.

Until quite recently it was believed that dissolution inhibition in phenolic resins is based on a general hydrophobic effect of the inhibitor. Honda et al. [5] have now shown that the hydrophobicity of an additive is not sufficient and that the polar functional groups of the inhibitor play an important role in the inhibition effect. They found that additives with very similar skeletal structures, and therefore with similar hydrophobicity, but which differ in their polar functional groups, have very different inhibition efficiencies in a common novolak resin. In an earlier communication [4] it was suggested that inhibition in phenolic resins comes about by the blocking of some of the hydrophilic OH-groups. Such blocking action by the inhibitor presupposes interaction between the inhibitor and the phenols of the resin. Here we investigate this interaction by determining the associated equilibrium constants in dilute solution. From these data the fraction of phenol-bound inhibitors in the casting solutions of the films can be estimated. For the group of additives investigated by Honda et al. [5] the fraction of phenol-bound inhibitors correlates quite satisfactorily with the inhibition effect.

Investigating the New Interaction Model between Cu(II) and PVA by the Proton Relaxation Method

AbstractAn aqueous PVA‐Cu2+ solution at pH = 3 is in the hydrated form and becomes green at pH ⩾ 6 with a decrease in viscosity. The structure of the copper ion is suggested to be that of a polynuclear complex at pH > 6. For the green solution the polynuclear chains of the copper complex are believed to be surrounded by the PVA chains with the hydrophobic backbones facing toward the inside and the hydrophilic OH groups oriented toward the outside facing the bulk water. The proton spin‐lattice relaxation rate 1/T1p and the spin‐spin relaxation rate 1/T2 of CH and CH2 in PVA and H2O for aqueous PVA‐Cu2+ solutions at pH = 3, can be explained by the two site exchange model in the region of the fast exchange limit. The dipolar correlation time τc is dominated by the reorientational process with a dipolar correlation time of 2.11 × 10−11 s. When the pH rises from pH=3 to pH=12.5, the variation of 1/T1p and 1/T2p of CH and CH2 in PVA with Cu2+ ion concentration in aqueous PVA‐Cu2+ solution at pH=12.5 can be explained in terms of the relaxation by an inclusive model of the polynuclear copper complex and PVA. Furthermore, the frequency (or field) dependence of 1/T1p, 1/T2p of CH in PVA for aqueous PVA‐Cu2+ solution at pH = 12.5 suggests that the dipolar relaxation is dominated by the electron‐spin relaxation with the electron spin relaxation time T1e = 1 ˜ 2 × 10−10 s. The invariance of 1/T1p and 1/T2p of H2O with the variation of the Cu2+ ion concentration in aqueous PVA‐Cu2+ solution at pH = 12.5 supports the hypothesis that the water is not directly bound to the Cu2+ ion.