Low Probe Concentrations Research Articles

SORPTION BEHAVIOR OF POLYMER MATERIALS BY INVERSE GAS CHROMATOGRAPHY

The chromatographic behavior of n-dodecane, water, benzene and n-caproic and with polystyrene (PS), poly4-vinylpyridine (PVP), acrylic fiber (PAN) and cotton fiber was investigated at a wide range of temperature.For systems of PS/water, PS/benzene, PVP/water, PAN/n-caproic acid and cotton/n-caproic acid, plots of retention volume against sample size were seen to pass through a minimun, respectively, At high probe concentration, the retention volume VR was linearly related with sample size s. At low probe concentration, 1/VR was related to s through 1/VR=A/(1+B√s), where A and B were constants. Limiting retention volume, VR°, was estimated for the high and low probe concentration ranges by extrapolating the proper relations to s=0. The values of heat of adsorption obtained for the two concentratio regions were compared. The showed that at low probe concentration, probes interacted strongly with polymers.Adsorption isotherms were determined for n-dodecane and water on PS respectively, From the results, it is suggested that adsorption on the polymer surface is the main sorption mechanism below Tg and diffusion into the bulk of the polymer dominates above Tg.

Paramagnetic isoprenoid carrier lipids. 2. Dispersion and dynamics in lipid membranes.

The transbilayer diffusion rates and self-association of spin-labeled glycosyl carrier lipids and other isoprenoids have been studied in model phospholipid membranes. Transposition rates of phosphorylated species in small (300 A) or large (greater than or equal to 1000 A) diameter unilamellar phosphatidylcholine (PC) vesicles are slow (t1/2 greater than 5 h at 25 degrees C); this argues against their proposed role in the transbilayer portage of sugar units during polysaccharide and glycoprotein assembly. The same probes mix well with several host lipids, remaining monomolecularly dispersed even at high ionic strength (0.5 M NaCl) or in the presence of various polyvalent cations. This behavior persists for several degrees beneath the transition temperature (Tc) of saturated lecithins. In contrast, neutral carboxylate analogues undergo pronounced reversible self-association. Aggregation is quite dependent on the probe concentration and nature of the host but only weakly temperature dependent above the Tc. Even at low probe concentrations (less than 0.5 mol %) in fluid membranes, aggregates persist above 75 degrees C. Unsaturation in the lecithin fatty acyl chains dramatically increases isoprenoid monomer solubility. Segregation appears to involve relocation of the entire molecule in the membrane interior.

A photochemical technique for measuring lateral diffusion of spin-labeled phospholipids in membranes

A technique is described for the measurement of lateral diffusion of any spin-labeled molecule in planar phospholipid multilayers, using low probe concentrations and a photochemical reaction to generate the initial concentration gradient. Features of the technique include simplicity of data analysis, versatility, and applicability over a wide range of motional rates. Measurements have been made on dimyristoyl phosphatidylcholine and dipalmitoyl phosphatidylcholine in the fluid phase (using a phospholipid with head-group spin label), and excellent agreement is found with recent nuclear magnetic resonance spin-echo measurements, as well as with other spin-label and fluorescence photobleaching results.

Model membrane studies of spin-label probes Part I. Mixed monolayers of 12-nitroxide stearic acid and myristic acid

Pure and mixed monomolecular films of a cell membrane spin label probe, 12-nitroxide stearic acid have been studied where myristic acid was selected as the host lipid. The behavior of 12-nitroxide stearic acid at the air water interface is understood in terms of two molecular configurations: erect (with only the carboxyl group in the interface) and bent (with both the carboxyl group and the oxazolidine ring in the interface). In mixed films both of these conformations play a role at high surface pressures. At low probe concentrations, 12-nitroxide stearic acid is primarily in an erect conformation, while at high probe concentrations the reverse is true. This particular host lipid appears capable of erecting the probe molecule with only small concentrations of myristic acid. In a condensed host lipid, the probe is partially immiscible, and segregates to form a heterogeneous film from which it is readily collapsed. The probe is seen to perturb the molecular packing in this mixed system and the perturbation to be dependent on both the molecular shape and nature of the probe.