1,721,013 research outputs found
Understanding the Properties of the Coagel and Gel Phases A H-2 and C-13 NMR Study of Amphiphilic Ascorbic Acid Derivatives
No full textThe coagel and gel phases formed by the D and L diastereoisomers of ascorbyl-dodecanoate (ASC12) in deuterated water were studied through solid-state NMR techniques. In particular, the dynamic properties of water and surfactant chains were investigated by 2H and 13C NMR static spectra, respectively. Two fractions of water with very different dynamics were found in the coagel phases, one solidlike and one liquidlike, assigned to water strongly bound to the surfactant polar heads and bulk water, respectively. Only one kind of “intermediate” water was instead detected in the gel phase suggesting that the merging of the two types of water in the interlayers between the surfactant lamellae occurs at the coagel-to-gel transition. Moreover, the surfactant chains, very rigid in the coagel phase, give rise to fast trans-gauche interconformational jumps in the gel phase, where almost isotropic reorientations of the whole aggregates also occur. A different dynamic behavior was found for the two diastereoisomers in particular for what concerns the surfactant molecules in the gel phase and the water molecules in the coagel presumably ascribable to different inter- and intramolecular interactions that involve the polar heads
Spectroscopic Study on the Adducts of Substituted Tetraazaporphyrins with alfa-Cyclodextrins
No full textStructuring effect of some salts on glycerol carbonate: A near-infrared spectroscopy, small- and wide-angle X-ray scattering study
No full textAlkylene carbonates such as ethylene, glycerol and propylene carbonates offer a valuable tool for the investigation of intermolecular interactions in polar non-aqueous liquids. Their physico-chemical properties suggest the presence of a strong structure that mainly depends on hydrogen bonds. The addition of salts bearing basic anions such as fluoride, carbonate and phosphate leads to the formation of free ions and ion pairs that are well accommodated in the solvent structure. In this work near infrared and attenuated total reflection Fourier-transform infrared spectroscopy, small- and wide-angle X-ray scattering were carried out on pure glycerol carbonate and on its solutions of saturated KF, K2CO3 and K3PO4 in order to probe the structure of the solvent. Linear and cyclic oligomeric clusters produced by the association of the liquid molecules are proposed. The different effectiveness of the studied anions in enhancing the internal arrangement of the liquid can be explained in terms of polarizability (i.e. of the delocalization of their charge), different basicity and hydrogen bonding (HB) accepting capacity and geometry of the anions
Hofmeister Effect in Self-Organized Chemical Systems
No full textWe studied the effect of spectator ions in the prototype of far-from-equilibrium self-organized chemical systems, the Belousov-Zhabotinsky (BZ) reaction. In particular, we investigated the specific ion effect of alkali metal cations, connoted for their kosmotropic and chaotropic properties. By means of combined experimental and numerical approaches, we could show a neat and robust evidence for the Hofmeister effect in this system. Spectator cations induce a marked increment of the induction period that preludes regular oscillations and decrease the oscillation amplitude following the sequence Li+ < Na+ ≪ K+ ∼Cs+. These ions affect the system kinetics by interfering in the interaction between the oxidized form of the catalyst and the organic substrate, responsible for resetting the BZ system to pre-autocatalytic (reduced) conditions. The specific ion effect on these key reactive steps is systematically characterized and correlated with different parameters which describe the interaction of the cations with the solvent
Incorporation of the sunscreen agent, octyl methoxycinnamate in a cellulosic fabric grafted with beta-cyclodextrin
No full textThe aim of the study was to investigate the incorporation of the sunscreen agent, octyl methoxycinnamate into cyclodextrin cavities covalently bound to cloth fibres. Tencel, a cellulosic fabric, was grafted with β-cyclodextrin molecules through reaction with monochlorotriazinyl-β-cyclodextrin (β-CDMCT). The finished and untreated textiles were soaked in water-methanol mixtures containing 2% (v/v) of sunscreen agent and subsequently subjected to several washing cycles. The unmodified and modified fabrics were characterized by UV spectrophotometry and thermogravimetric analysis. The level of octyl methoxycinnamate entrapped in the Tencel tissue was determined by high-performance liquid chromatography and was found to be much higher (0.0203%, w/w) for the textile functionalised with β-CDMCT compared to the unmodified fabric (0.0025%, w/w). In addition, spectrophotometric assessment of UV transmission through the fabric samples using the TransporeTM test showed that the in vitro sun protection factor of the textile support was markedly enhanced (3.2-fold increase) by impregnation with octyl methoxycinnamate of the β-CDMCT grafted textile. Hence, even after repeated washings, the β-CD finished fabric exhibits higher sunscreen agent retention and photoprotective properties than the unmodified textile material
Ionochromism, solvatochromism and effect of dissolved gases on the spectral properties of bromothymol blue
Full text linkThe color of the pH indicator Bromothymol blue (BTB) changes from yellow to blue with increasing pH. The effect of some electrolytes (LiCl, NaCl, KCl, CsCl, KSCN and KClO3) and of D2O on the spectral properties of dilute solutions of BTB is explored. The results are interpreted in terms of dimerization of the dye molecules and of the different hydration that D2O induces. The effects of dissolved gases on the spectral properties of BTB is studied. Complete removal of dissolved gas is achieved. Surprising effects on the UV–vis spectra emerged. After degassing solutions, gases were re-admitted via bubbling. The gases He, Ar, N2, CO2 and CH4.were studied. The effects can be explained by presence or absence of nano- and microbubbles of gas in the solution. These allow formation of dimers and multiple association via adsorption and so affect the spectral properties of the dye molecules
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