Cytoplasmic Solvent Structure of Single Barnacle Muscle Cells Studied by Electron Spin Resonance

1982

The nature of organo-phosphate and carboxylate bonding in aqueous suspensions of noncrystalline alumina, boehmite, and gibbsite has been studied using the anionic nitroxide spin probes 3-carboxy-2,2,5,5-tetramethyl-l-pyrrolidinyloxyl and 4-hydroxy-2,2,6,6-tetramethyl-piperidinooxyl dihydrogen phosphate. Analysis of the electron spin resonance (ESR) spectra of these molecules revealed that adsorption of both molecules occurred rapidly on the high surface area alumina and boehmite, whereas only the organophosphate adsorbed on gibbsite. A loss in rotational motion of the molecules accompanied adsorption, with the greater degree of motional restriction observed for the carboxylate attributed to steric restrictions to rotation about the surface-bound C -C 0 0 bond axis. The ease of displacement of adsorbed carboxylate from surface binding sites by weakly adsorbing anions (CI-, C104 ) compared to organophosphate suggests that the carboxylate adsorbed by ligand exchange of a single surface OH, whereas the organophosphate probably formed a bidentate bond. The carboxylate bound on noncrystalline alumina showed evidence of nonspecific electrostatic adsorption in addition to ligand exchange of surface OH. This weak bonding was indicated by a moderate loss in rotational motion and ease of exchangeability.

Section: Tempo-cooh On Aluminum Hydroxidesmentioning

confidence: 55%

Organic Anion Adsorption on Aluminum Hydroxides: Spin Probe Studies

1982

“…Further evidence for the exchange cation effect upon adsorbed molecular cations is found in the apparent rotational correlation times (zc) for adsorbed TEMPAMINE + (Table 1). These values are calculated from the ESR spectra by the method described by Sachs and Latorre (1974), which is only useful in the fast motion region (% < 10 -8 sec) for random tumbling. The A and z values determined for the II and I orientations for the hydrated systems ( Table 1) are indicative that the probe is tumbling more rapidly about one molecular axis than about others.…”

Section: U; mentioning

confidence: 99%

Exchangeable Cation and Solvent Effects Upon the Interlamellar Environment of Smectites: Esr Spin Probe Studies

1977

Abstract--The ESR spin probe, TEMPAMINE +, was used to study the interlamellar behavior of adsorbed organic cations on hectorites solvated with water, ethanol, and water-ethanol mixtures, and saturated with several monovalent and divalent metallic cations. The mobility and orientation of the probe was affected greatly by the solvent, and to a lesser extent by the predominant exchangeable cation on the silicate surface. Most of the effects could be interpreted in terms of the basal spacings of the hectorite. In all instances, the adsorbed probe was much less mobile than in solution despite the different interlamellar volumes available for molecular motion.

“…The 3-line spin probe spectra are used to obtain rR according to the equation (Sachs and Latorre, 1974):…”

Section: Methodsmentioning

confidence: 99%

Mobility of Small Molecules in Interlayers of Hectorite Gels: ESR Study with an Uncharged Spin Probe

1994

Abstract--Electron spin resonance (ESR) spectroscopy was used to measure the rotational mobility of an uncharged nitroxide spin probe (4-hydroxy-2,2,6,6-tetramethyl-piperidinyloxy) in hectorite gels of variable water content. Physical adsorption segregated the probe molecules into two populations: probes in the solution or a solution-like phase, and motionally restricted probes in the adsorbed phase. Although the spectra of these two populations were discrete, indicating that exchange between them was slow on the time scale relevant to ESR, their overlap prevented a straightforward determination of mobility of the adsorbed probes. Even though adsorption was weak, effects of the adsorbed population on the spectral lineshape were detectable for suspensions containing as little as 20 grams clay per liter of water. Orientation of the adsorbed probes on the fully hydrated hectorite surfaces was similar to that of a positively charged nitroxide probe, suggesting that steric factors rather than electrostatic forces control short-range organic molecule interaction with the silicate. The possibility of reaching false conclusions about probe mobility and interlamellar water viscosity when using a weakly adsorbing probe is discussed.