High pressure treatment of pharmaceutical drug delivery and related systems

Abstract

Solids like layer silicates (kaolinite and montmorillonite) as well as ZnO are in use in pharmacy. They are pressure treated and subsequently analyzed by means of ESR spectroscopy. The structural changes indicated by Fe³⁺ ions and paramagnetic defects are reponsible for the enhanced chemical activity of the pressurized systems.

Especially active Fe-O-species are formed which can react with intercacalated organic molecules. The most probable first step of such reactions will be a solid state single electron transfer. Spin probes and spin traps were used to prove this statements. The activation of the drug delivery systems by mechanical treatments is of importance for the stability of the drugs incorporated.     

Multivariate linear regression with missing values

This contribution presents and discusses an efficient algorithm for multivariate linear regression analysis of data sets with missing values. The algorithm is based on the insight that multivariate linear regression can be formulated as a set of individual univariate linear regressions. All available information is used and the calculations are explicit. The only restriction is that the independent variable matrix has to be non-singular. There is no need for imputation of interpolated or otherwise guessed values which require subsequent iterative refinement.     

Comprehensive kinetic and thermodynamic study of the reactions of CO2(aq) and HCO3(-) with monoethanolamine (MEA) in aqueous solution

The temperature dependence of the reversible reaction between CO(2)(aq) and monoethanolamine (MEA) has been investigated using stopped-flow spectrophotometry by following the pH changes during the reactions with colored acid-base indicators. Multivariate global analysis of both the forward and backward kinetic measurements for the reaction of CO(2)(aq) with MEA yielded the rate and equilibrium constants, including the protonation constant of MEA carbamate, for the temperature range of 15-45 °C. Analysis of the rate and equilibrium constants in terms of the Arrhenius, Eyring, and van't Hoff relationships gave the relevant thermodynamic parameters. In addition, the rate and equilibrium constants for the slow, reversible reaction of bicarbonate with MEA are reported at 25.0 °C. At high pH, reactions of the amine with CO(2) and with bicarbonate are significant.     

Transmission-line analysis of gravitational pulse detector response functions

Basic notations for measuring gravity waves are recalled, and a δ-pulse of areaJ ₀=10^?12 sec^?1 chosen as a convenient unit for sensitivity calculations. Pulse excitation of a long thin bar causes stress variations following trapezoidal patterns of time dependence, with a flat top duration proportional to distance from the bar's center of mass. A suitable arrangement of piezoelectric transducers (‘PX’) provides frequency-independent matching, both mechanical and electrical, allowing a straightforward and accurate calculation of electric signals. Signal shape is given explicitly for two extreme cases:

1. whole bar is piezoelectric (parabolic arcs resembling a sine wave),
2. very short PX sections (triangular or trapezoidal, depending on position along the bar).

A suitable combination ofn (=1, 3, 5, ...) transducers generates directly a triangular wave at then-th harmonic of the fundamental bar frequency, with amplitude proportional toL/n, so that the use of a long bar as a Fourier Analyser of gravity waves appears feasible. For an estimate of the sensitivity limit, preliminary results of a noise background analysis are quoted, according to which the PX-length can be optimized. A threshold energy relation \( \sim \sqrt[4]{{kT/M^2 Q_{{\text{PX}}} }}\) is obtained in the case where amplifier noise becomes important.     

The reduction of rotational ambiguity in soft-modeling by introducing hard models

Rotational ambiguity is a major problem in the application of soft-modeling analysis to a variety of multivariate mixture resolution problems and particularly important in the analysis of kinetic data. Soft-modeling analyses rely on constraints that restrict the concentration profiles and/or the spectral responses of all components. The main goal of this work is to demonstrate how a hard-modeling constraint on concentration profiles drastically decreases the extent of the rotational ambiguity. Therefore, in the present paper the discussion is focused on systems in which hard-modeling information is available. The results of simulated examples reveal that the utilized hard constraint decreases the rotational ambiguity in estimated concentration profile even components that do not take part in the explicit model. In addition, the rate constant of known reaction is determined in this method.     

Energy-Minimized Structures and Calculated and Experimental Isomer distributions in the hexaamine-cobalt(III) system [Co(L)2]3+ with the chiral facially-coordinating triamine (l = butane-1,2,4-triamine)

Butane- 1,2,4-triamine (trab) is the smallest tridentate aliphatic unsubstituted chiral triamine. With optically pure trab, there are three, with racemic trab five isomers of [Co(trab)₂]³⁺, One of the five isomers is centrosymmetrical, the others are chiral. For one of the isomers, there are four possible conformations (all combinations of chair and skew boat conformations for the chelate six ring of each ligand), for the others there exist only three independent conformers. All sixteen independent structures have been calculated by strain-energy minimization. The calculated isomer distribution, based on total strain energies corrected with statistical entropy contributions (21%:16%:16%:4%:43%, and 40%:30%:30%, for racemic and optically pure trab, respectively) are in excellent agreement with the experimental data based on HPLC and ¹³C-NMR analyses of equilibrium solutions of the hexaamine-Co(III) compounds prepared by oxygenation of aqueous solutions in presence of activated charcoal. The results are also briefly discussed in relation to possible stereoselectivity upon complexation of optically pure trab and a racemic chiral ligand to a transition-metal center.