Search results for "MOLA"
showing 10 items of 1216 documents
Solubility of NH3 and apparent pK of NH4+ in human plasma, isotonic salt solutions and water at 37 degrees C.
1998
The solubility of ammonia, alphaNH3 (mM/mmHg), was determined at 37 degrees C and low ammonia partial pressure (0.02-1 mmHg) in pure water (n =24) as 46.70+/-0.40; aqueous isotonic salt solutions (n = 7) as 46.8+/-0.81; and human plasma (n = 5) as 42.0+/-0.66. The last figure increases to 45.3+/-0.63 if expressed in molal units (mmol/kg plasma water x mmHg) instead of molarity with respect to the water content of the plasma (mean from four healthy and fasting donors: 0.908+0.005 kg H2O/kg plasma; mean density at 37 degrees C: 1.020+/-0.002 kg/l). In pure water, the solubility value is the mean of three different methods: (a) extrapolation of the salting-out effect of ammonia in aqueous NaOH…
Kinetic interpretation of influence of sodium chloride concentration and temperature on xanthan gum dispersion flow model
2001
The present study derives a fixed-concentration (0.4%) xanthan gum dispersion flow model for different molar concentrations of sodium chloride (0–0.25M) and different temperatures (20–70°C). The Ostwald–de Waele model is used in all cases. A temperature rise reduces the shear-thinning characteristics of the systems, although the power law index is much less sensitive to changes in temperature when NaCl is added, even in very small amounts. The lowest consistency values correspond to the dispersions formulated in the absence of salt, the highest values are observed for molar values of ≥0.15, and there are decreases in consistency upon raising the temperature in all cases. The viscous behavio…
Precipitation of slightly soluble silver salts in reversed AOT micelles: Calorimetric investigation
1991
The enthalpies of precipitation, of AgCl, Agl, Ag2S and silver tetraphenylborate (AgTPB) in water containing reversed sodium bis(2-ethylhexyl) sulfosuccinate (AOT) micelles as a function of the molar concentration ratio R (R=[water]/[AOT]) at various concentrations of AOT and reagent salts, were measured by a calorimetric technique. The molar enthalpies of precipitation are independent of the surfactant concentration but are dependent on the concentration of the reagent salts and the R value. The molar enthalpies for the same processes in bulk water are not approached even at the highest R value. Effects due to the smallness of the microcrystals and to the interactions between ions and mice…
Rapid hyperpolarization and purification of the metabolite fumarate in aqueous solution
2020
Significance Magnetic resonance imaging is hindered by inherently low sensitivity, which limits the method for the most part to observing water molecules in the body. Hyperpolarized molecules exhibit strongly enhanced MRI signals which opens the door for imaging low-concentration species in vivo. Biomolecules can be hyperpolarized and injected into a patient allowing for metabolism to be tracked in real time, greatly expanding the information available to the radiologist. Parahydrogen-induced polarization (PHIP) is a hyperpolarization method renowned for its low cost and accessibility, but is generally limited by low polarization levels, modest molecular concentrations, and contamination by…
Phase diagrams calculated for sheared ternary polymer blends
1997
Abstract On the basis of the generalized Gibbs energy of mixing G γ (which is the sum of the Gibbs energy for zero shear and the energy the system stores in steady flow) phase diagrams were calculated as a function of shear rate γ for ternary model blends. This modelling uses simple equations for the description of the stagnant systems (Flory-Huggins) and for the contributions resulting from flow. Surface and alignment effects are neglected. A new procedure, which does not require the derivatives of G γ with respect to composition, was used to that end. Choosing typical values for the binary interaction parameters and molar masses, four classes of ternary systems were studied in greater det…
Molecular characterization of α,β-poly[( N -hydroxyethyl)- dl –aspartamide] by light scattering and viscometry studies
2000
Abstract α,β-poly[(N-hydroxyethyl)- dl -aspartamide] (PHEA) is a new synthetic polymer which is of interest in biomedical applications. In this paper, the molecular characterization of PHEA by multi-angle laser light scattering and viscometry off-line and on-line to a size exclusion chromatography system is reported. These techniques furnish an exhaustive and consistent characterization of the PHEA polymer. The fractionation of the PHEA macromolecules was relatively simple. Using an aqueous mobile phase of medium ionic strength, the elution was substantially regular and the macromolecules were not aggregate. The molar mass M of four PHEA samples approximately ranges from 46 to 53 K g/mol, t…
Fractionation of cellulose acetate for the investigation of molecular weight influences on the morphology of membranes
2003
Abstract Cellulose acetate (CA) with an apparent weight average molar mass, M w ∗ , of 150 kg/mol was fractionated with respect to M by means of the mixed solvent methyl acetate (MeAc)/2-propanol (2-POH) applying a new method that uses spinning nozzles to promote the rapid attainment of phase equilibria. Two of the fractions obtained in this manner were employed to prepare membranes from solutions in methyl acetate with 2-propanol as coagulating agent. Electron micrographs demonstrate that the molar mass of CA influences the morphology of the membranes markedly under otherwise identical conditions. For M w ∗ =128 kg/mol, one obtains considerably denser structures than for M w ∗ =263 kg/mo…
Size-Exclusion Chromatographic Determination of Polymer Molar Mass Averages Using a Fractal Calibration
2005
The characterization of polymers by size-exclusion chromatography basically consists of the determination of the weight-average molar mass (Mw), number-average molar mass (Mn), and polydispersity index (I). An accurate estimation of these magnitudes requires the use of a reliable and trusted calibration curve. Three procedures for building up a calibration curve are analyzed in this work. The first is the classical universal calibration (UC), based on the elution of tetrahydrofuran-polystyrene in a system as reference. The second is based on the proper calibration curve made with standards of the sample under study. However, two main drawbacks arise when using these methodologies: the nonfu…
Main Chain Conformation and Anomalous Elution Behavior of Cylindrical Brushes As Revealed by GPC/MALLS, Light Scattering, and SFM
1999
High molar mass polymacromonomers based on methacryloyl end-functionalized oligo methacrylates (Mn = 2410 g/mol) adopt the conformation of wormlike cylindrical brushes. Comparison of the absolute molar mass, Mw, determined by static light scattering and the contour length, Lw, of the molecules measured by SFM in the dry state revealed the length per vinylic main chain monomer of the cylindrical structure to be less than 0.1 nm, thus being much shorter than the maximum value of 0.25 nm. In solution this shrinkage could be quantified to 0.071 nm per monomer by Holtzer analysis of the scattering curves which in addition yielded the Kuhn statistical segment length lk = 120 nm. GPC MALLS investi…
Intrinsic Viscosity of Aqueous Solutions of Carboxymethyl Guar in the Presence and in the Absence of Salt
2008
Intrinsic viscosities were determined for solutions of CMG in pure water and 0.9 wt.-% aqueous NaCl. To avoid the 0/0-type extrapolation typical for Huggins plots, a new procedure was used. For CMG and pure water, this requires only two adjustable parameters: the specific hydrodynamic volume of the polymer in the limit of infinite dilution and a hydrodynamic interaction parameter. The intrinsic viscosity of CMG (no salt) at room temperature is 6 050 mL · g -1 ; approximately half as large as that of Na-PSS of comparable molar mass. The ratio of the intrinsic viscosities with and without salt is ≈7 for CMG, as compared to >100 for Na-PSS. The reasons for the different behaviors of the two ty…