Pulsed NMR Data Research Articles

Impact of semi-solid formulations on skin penetration of iron oxide nanoparticles

BackgroundThis work aimed to provide useful information on the incidence of the choice of formulation in semi-solid preparations of iron-oxide nanoparticles (IONs). The appropriate analytical methods to assess the IONs physical stability and the effect of the semi-solid preparations on IONs human skin penetration were discussed. The physical stability of IONs (Dh = 31 ± 4 nm; ζ = −65 ± 5 mV) loaded in five semi-solid preparations (0.3% w/v), namely Carbopol gel (CP), hydroxyethyl cellulose gel (HEC), carboxymethylcellulose gel (CMC), cetomacrogol cream (Cet) and cold cream was assessed by combining DLS and low-field pulsed NMR data. The in vitro penetration of IONs was studied using human epidermis or isolated stratum corneum (SC).ResultsReversible and irreversible IONs aggregates were evidenced only in HEC and CMC, respectively. IONs diffused massively through SC preferentially by an intercellular pathway, as assessed by transmission electron microscopy. The semi-solid preparations differently influenced the IONs penetration as compared to the aqueous suspension. Cet cream allowed the highest permeation and the lowest retained amount, while cold cream and CP favored the accumulation into the skin membrane.ConclusionBasic cutaneous semi-solid preparations could be used to administer IONs without affecting their permeation profile if they maintained their physical stability over time. This property is better discriminated by low-field pulsed NMR measurements than the commonly used DLS measurements.

The temperature dependence of the solubility of oxygen in sea water according to the pulsed NMR data

The temperature dependences of the solubility of oxygen in distilled and sea water were obtained over the temperature range 0–90°C on the basis of proton spin—lattice relaxation measurements in degassed and not degassed samples. The temperature dependence of O2 solubility is approximated by the sum of exponential functions according to not only relaxation measurement results but also literature data. The temperature dependence of the solubility of O2 in distilled water can be written as the sum of two exponential functions with the predominance of the first component over the low-temperature interval. The best approximation for sea water has the form of the sum of three exponential functions, the relative contributions of the second and third components being approximately equal. The conclusion was drawn from the temperature dependences obtained that the main mechanism of the solution of oxygen in water was the filling of ice-like formation voids.

Porous structure of rigid and swelling adsorbents according to pulsed NMR data on the mobility of adsorbed water and benzene molecules

Potentialities of pulsed NMR technique to estimate parameters of the porous structure of microporous adsorbents according to the data on nuclear magnetic relaxation and self-diffusion of adsorbed molecules are analyzed. Main attention was focused on the adsorbed systems studied by the adsorption and NMR techniques. Measurements of nuclear magnetic relaxation of adsorbed molecules make it possible to analyze the porous structure at the scale of pore sizes; data on self-diffusion, at the scale of different-porosity zones. Specific features of the translational mobility of water and benzene molecules with different mechanisms of adsorption in active carbons having relatively rigid structure and polymer adsorbents capable of swelling are discussed. In general, data obtained by the NMR technique agree with and supplement the results of adsorption measurements.

Towards Rapid and Unique Curve Resolution of Low-Field NMR Relaxation Data: Trilinear SLICING versus Two-Dimensional Curve Fitting

In this work an alternative method, named SLICING, for two-dimensional and noniterative T 2 decomposition of low-field pulsed NMR data (LF-NMR) is proposed and examined. The method is based on the Direct Exponential Curve Resolution Algorithm (DECRA) proposed by W. Windig and A. Antalek (1997, Chemom. Intell. Lab. Syst. 37, 241–254) and takes advantage of the fact that exponential decay functions, when translated in time, retain their characteristic relaxation times while only their relative amounts or concentrations change. By such simple translations (slicing) it is possible to create a new “pseudo” direction in the relaxation data and thus facilitate application of trilinear (multiway) data-analytical methods. For the application on LF-NMR relaxation data, the method has two basic requirements in practice: (1) two or more samples must be analyzed simultaneously and (2) all samples must contain the same qualities (i.e., identical sets of distinct T 2 values). In return, if these requirements are fulfilled, the SLICING (trilinear decomposition) method provides very fast and unique curve-resolution of multiexponential LF-NMR relaxation curves and, as a spin-off, calibrations to reference data referring to individual proton components require only scaling of the resulting unique concentrations. In this work the performance of the SLICING method (including multiple slicing schemes) is compared to a traditional two-dimensional curve fitting algorithm named MATRIXFIT through application to simulated data in a large-scale exhaustive experimental design and the results validated by application to two small real data sets. Finally a new algorithm, Principal Phase Correction (PPC) based on principal component analysis, is proposed for phase rotation of CPMG quadrature data, an important prerequisite to optimal SLICING analysis.

Wax precipitation from North Sea crude oils: 1. Crystallization and dissolution temperatures, and Newtonian and non-Newtonian flow properties

Summary and Conclusions Nearly all the oils studied were found to benefit from Energy & Fuels, Vol. 5, No. 6, 1991 907 thermal pretreatment, Le., preconditioning at 80 C, in that the pour points and viscosities in the non-Newtonian temperature range (generally below 30 C) were lowered. The pour points were in some cases lowered by as much as 30-40 C. This reflects the action of inherent pour point depressants (asphaltenes, resins) present in the oils. The exceptions to this rule were the condensates, which hardly contain any inherent pour point depressants. The pour point of thermally pretreated oil (minimum pour point) was in most cases 40-60 C lower than the WPT. On average, about 4 wt % precipitated wax (pulsed NMR data) was present at the minimum pour point. At the non-Newtonian temperature limit about 1 wt % was found to be present. Isoalkanes were the most abundant hydrocarbon class in wax fdtered from one of the oils at 40,23, and 6 C. The ratio isoalkanes/ n-alkanes

Pulsed NMR study of proton motions in uranium trioxide hydrates

Pure samples of UO 2(OH) 2·H 2O, β-UO 2(OH) 2, and “α-UO 3·0.85H 2O” have been synthesized. Pulsed NMR data from a wide temperature range have been interpreted in terms of structural features and proton motions for all three materials. Two types of water molecule reorientation have been observed in UO 2(OH) 2·H 2O and characterized in terms of activation energies and correlation times for the motions (Motion A: T c = 2.2 ± 0.5 × 10 −15 sec, E A = 29.0 ± 4 kJ mole −1; Motion B: T c = 4 ± 0.5 × 10 −13 sec, E A = 31.2 ± 4 kJ mole −1).

NMR of 89Y in normal and superconducting YBa2Cu3O9- δ

Pulsed NMR data for 89Y in the high- T c superconductor YBa 2 Cu 3 O 9- δ (δ ≈ 2.1) in both the normal and mixed states are presented. Spin-lattice relaxation exhibits a Korringa temperature dependence in the normal state, with T 1 T = (4.6 ± 0.1) × 10 3 s- K. Below T c , T 1 increases much more quickly than for a conventional superconductor. From linewidth measurements, the zero-field penetration depth is estimated to be λ ≈ 3800 Å. The Knight shift in the normal state is small, K ≈ 0.02%. Spin-spin relaxation times, determined by Y-Cu dipolar interactions, decrease below T c due to the detuning of Cu-Cu interactions by fluxoid field gradients.

An estimate of the thermal conductivity of solid T 2 from pulsed nmr data

The thermal conductivity of solid T 2 below 17 K has been estimated from pulsed nmr data to be roughly temperature independent and approximately equal to 0.7 W/mK. Results for some mixtures of T 2 with D 2 and DT are also given.

A simple and inexpensive pulsed NMR data acquisition system

The development and implementation of a simple and inexpensive pulsed NMR data acquisition system is described. Measurements of the relaxation times T 1, T 1 ϱ , and T 2 have been made on polyisobutylene (PIB) over the temperature range 130–490 K. A major advantage of this system over previous designs is that it enables values of T 2 as low as 10 μsec to be measured. The system has also been used for self-diffusion measurements in PIB and can be simply interfaced to peripheral devices such as signal averagers and calculators.

Computation of T1 from pulsed NMR data using a generalized and rapid least-squares formula

A fast least-squares method using minicomputers for determining T 1 is given, valid in all cases where the relaxation is described by a single relaxation time. It is shown that this method is relatively insensitive to the width of the rf pulses, and does not require the measurement of the magnetization of the sample in thermal equilibrium. In addition, the duration of the experiment is reduced.

Physical properties of poly(vinyl chloride) -copolyester thermoplastic elastomer mixtures

A study has been made on the compatibility, thermal behavior, and mechanical properties of the system poly(vinyl chloride) and a copolyester thermoplastic elastomer (under the trade name of Hytrel by duPont). Results from NMR, linear thermal expansion, tensile test, and dynamic mechanical measurements indicate extensive mixing of PVC and the soft segments of the thermoplastic elastomer when the mixture is rapidly cooled from around 150 °C to ambient temperature. The hard segments of the elastomer crystallize under these conditions, as revealed by the calorimetric measurements. Upon isothermal annealing at 130 °C the mixture shows signs of phase separation in dynamic mechanical measurements. These observations suggest the existence of upper critical solution temperatures for the system. The associated miscibility gap encompasses room temperature and reaches a maximum temperature somewhere between 130 and 150 °C. The phase domains in the annealed sample are extremely fine and have been estimated to be no more than 100 Å in size from the pulsed NMR data.