Poly(β-malic acid) : a new polymeric drug-carrier

Summary Poly(-malic acid) is a new synthetic functional polyester of the poly(-hydroxy-acid)-type whose properties are investigated in regard to possible uses as bioresorbable polyvalent drug-carrier. Degradation of polymer chains in 0.15 N phosphate buffer at pH=7.5 is monitored by aqueous GPC on SEPHADEX gels and by enzymatic titration of ultimate degradation products. It is shown that the rate of degradation obeys first order kinetics at the begining and that poly(-malic acid) degrades to malic acid at last.Presented at the 26th IUPAC Microsymposium on Macromolecules: Polymers in Medicine and Biology, Prague, July 9–12, 1984     

Glass fiber-filled thermoplastics. I. Wall and processing effects on rheological properties

A systematic study of wall effects on the shear viscosity of short glass fiber-filled polypropylene and polystyrene is presented. The dependence of these effects on capillary radius, shear rate, temperature, and polymer matrix is examined. The “true” viscosity curves of these materials (free from wall effects) can be obtained by an extrapolation procedure. Breakage of glass fibers in the high shear-rate processes of extrusion and injection molding lead to an appreciable reduction of the viscosity of these materials and is probably the more important effect to take into account in these processes.     

Ionization of Acetylacetone in Me2SO—Water Mixtures. Reactivity—Selectivity Principle or Principle of Imperfect Synchronization?

Rate constants for the reversible deprotonation of acetylacetone were measured in carboxylate and amine buffers in water and in 50%, 90% and 95% Me₂SO at 20°C. The Brønsted plot for the carboxylate ions is curved in the Me₂SO—water mixtures, but straight in water. The curvature is in the direction predicted by the Reactivity—Selectivity Principle (RSP). However, the Brønsted plot for the reaction with primary amines is straight in all solvents. This suggests that the curvature observerd with the carboxylate ions is caused by loss of solvation of the base; this loss of solvation is ahead of bond formation in the transition state rather than being a manifestation of the RSP. (Note that all Brønsted plots are based on pK_a values measured in the respective solvents.) The intrinsic rate constant (k₀) for proton transfer increases with the addition of Me₂SO, and more so with the carboxylate buffers than with the amines. This increase in k₀ is attributed to delayed solvation of the developing enolate ion in the transition state; with the carboxylate buffers, an additional factor is the early loss of solvation of the base. The various solvation effects observed in this study can all be understood in the context of the Principle of Imperfect Synchronization (PIS).     

The xanthate method of grafting. X. Grafting of acrylamide onto very-high-yield chemithermomechanical birch and aspen pulps

Hardwood pulp (birch: Betula Papyfera Marsh, and aspen: Populus Tremolides Michx) has been copolymerizeed with acrylamide using the xanthate grafting method. Grafting has been initiated using a redox system of ferrous ion and hydrogen peroxide. The effect of operating conditions on grafting parameters was also investigated. The factors studied were initial pH, time, and concentrations of hydrogen peroxide and acrylamide. When birch was used as a substrate, grafting parameters were as follows: grafting efficiency 82%, degree of conversion 35%, and polymer loading 60%. In the case of aspen, the maximum level of grafting efficiency, i.e., 87%, was reached with a polymer loading of 60%. Nevertheless, as in the case of birch, the conversion reached a rather low-level reading, i.e., 50%. Finally, some mechanical properties of paper sheets obtained through grafted pulps (dry and wet breaking lengths, dimensional stability, modulus, and extension at break) are compared to those of standard paper sheets.     

The chemical basis of attraction of ithomiine butterflies to plants containing pyrrolizidine alkaloids

The plantHeliotropium indicum L. (Boraginaceae) contains pyrrolizidine alkaloids. When dried, it is a powerful attractant for male ithomiine and danaine butterflies, which congregate and feed at its dead shoots. The butterflies use alkaloids derived from the plants for the formation of chemicals with pheromone/allomone activity. Baiting with alkaloids and esterifying acids, which form a part of the alkaloid molecules, indicates that a volatile product derived from the esterifying acids attracts males to the plants, where intact alkaloids then act as phagostimulants.     

Electrochemical behaviour of lead chloride (PbCl2) in dimethylsulphoxide (DMSO)—II. a chronopotentiometric study

In our earlier electrode kinetic studies (chronopotentiometric) of lead chloride (PbCl₂) in dimethylsulfoxide (DMSO), the points in the plot of E, vs log (τ^1/2 ? t^1/2) were linear in the form of a wave. This situation was similar to that observed by Delahay in the chronopotentionmetric reduction of chromate ion (aqueous medium) and thought to be due to a prekinetic step. To verify the presence of a prekinetic step in our case a survey of iτ^1/2vs i for a wider range of lead chloride concentration was started. But a distortion observed in the initial part of the curve (from 4·0 mM PbCl₂) was another point of similarity with that of chromate ion. This led us to consider the polarographic and chronopotentiometric reduction behaviour of CrO^2?₄ in two different electrolytes sodium hydroxide and sodium carbonate. Such considerations justify the presence of a prekinetic step in electrochemical reduction of chromate. Such a prekinetic step, probably the dissociation of PbCl₂, is verified and Kk^1/2₂ values for this coupled chemical reaction are determined according to the transition time expressions of Delahay and Dracka.     

The synthesis of14C- and3H-labeled glycerol ethers

The racemic¹⁴C-and³H-labeled alpha and beta derivatives of octadecyl glycerol ether (batyl alcohol) and of hexadecyl glycerol ether (chimyl alcohol) of high specific activity were synthesized by treating the appropriate alkyl halides with a large excess of the potassium salts of isopropylidene or benzylidene glycerol. By use of the trifluoroacetic anhydride esterification procedure, the labeled diesters of alpha and beta octadecyl and hexadecyl glycerol ethers were prepared. The labeled monoesters of beta octadecyl and of beta hexadecyl glycerol ethers were isolated from the reaction mixtures by silicic acid column chromatography. Work done in partial fulfillment for PhD Degree, Department of Biochemistry, University of North Carolina.     

Les comportements rheologiques du mortier frais

There are two critical values of the concentration C of the dispersed solid in fresh mortars called C_i and C_d such that, for angular granulates, when C ? C_i, the behaviour is binghamian at rest and pseudoplastic when the mortar is vibrated; when C ? C_d, it is dilatant in the two cases and when C_i < C < C_d, it is unstable. For spherical granulates, these behaviours are unchanged, except under vibration when C ? C_i : in this case, the behaviour is newtonian. These changes of behaviour are explained by structural modifications in the packing of particles : dilatancy comes out with close-packing while instability appears with maximum loose-packing.     

Méthode de calcul des colonnes de distillation et d'extraction application de l'équation NRTL

The NRTL equation (non random two liquids) associated with an equation of state of the vapour phase reprensents the vapor—liquid and liquid—liquid equilibria.     

Composition and structure of triacylglycerols in brown adipose tissue of rats fed fish oil

This study examines the incorporation of highly unsaturated n−3 fatty acids (HUFA) into triacylglycerols (TAG) of brown adipose tissue (BAT), and their effect on the positional distribution of saturated (SFA) and of unsaturated (UFA) 16- or 18-carbon fatty acids. To this end, rats were fed a fish oil diet for up to four weeks. The stereospecific analysis of TAG was based on generation ofsn-1,2- andsn-2,3-acylglycerols by Grignard degradation, followed by synthesis of phosphatidic acid and specific hydrolysis with phospholipase A₂. From the end of the first week of fish oil feeding, a steady-state in the fatty acid composition of TAG in BAT was reached. HUFA concentration increased 30-fold, mainly at the expense of n−9 UFA and of SFA. The amount of SFA decreased selectively at position 3, where these fatty acids were progressively replaced by n−3 HUFA. By contrast, the amount of UFA decreased at all positions, and their positional distribution was not affected. About 60% of HUFA was incorporated at position 3. Nearly twice as much 22∶6n−3 was incorporated into TAG than had been previously observed in white adipose tissue (WAT) [Leray, C., Raclot, T., and Groscolas, R. (1993)Lipids 28, 279–284]. At the steady-state, the distribution of HUFA was characterized by high proportions of 22∶6n−3 and 20∶5n−3 in position 3. Moreover, in each position of TAG, a steady level was reached rapidly (within 1 wk). It is concluded that, during fish-oil feeding, fatty acids in TAG of BAT show characteristic time-course changes that lead to a characteristic composition and a tissue-specific positional distribution. This suggests that adipose tissue has its own specificity in controlling the build-up of TAG stores, which is likely to be regulated by the specificity of acylating enzymes as well as molecular rearrangements.