Mats Sundell

Improved stability and release control of levodopa and metaraminol using ion-exchange fibers and transdermal iontophoresis

Achievement of controlled drug delivery and stability of drugs during storage is a problem also in transdermal drug delivery. The objective of this study was to determine, whether an easily oxidized drug, levodopa, could be stabilized during storage using pH-adjustment and ion-exchange fibers. Controlled transdermal delivery of the zwitterionic levodopa was attempted by iontophoresis and ion-exchange fiber. Ion-exchange kinetics and transdermal permeation of a cationic (presumably more stable) model drug, metaraminol, were compared to the corresponding data of levodopa. Levodopa was rapidly oxidized in the presence of water, especially at basic pH-values. At acidic pH-values the stability was improved significantly. Ion-exchange group and the pH had a clear effect on the release of both the levodopa and metaraminol from the ion-exchange fiber. The adsorption/release kinetics of metaraminol were more easily controllable than the corresponding rate and extent of levodopa adsorption/release. Iontophoretic enhancement of drug permeation across the skin was clearly more significant with the positively charged metaraminol than with the zwitterionic levodopa. Ion-exchange fibers provide a promising alternative to control drug delivery and to store drugs that are degraded easily.

Hydrogenation of Citral Over a Polymer Fibre Catalyst

A polymer-supported Pd catalyst was investigated in hydrogenation of citral (3,7-dimethyl-2,6-octadienal), which is a stereoisomer with an isolated and a conjugated double bond as well as a carbonyl group. The catalyst was a fibrous polymer-supported catalyst modified with functional groups and immobilized metals. A comparison of the polymer-supported catalyst with conventional catalysts was made.

A Cheap One-Pot Approach to Tetraethyl Methylenediphosphonate

Abstract A cheap procedure for the preparation of tetraethyl methylene-diphosphonate is described.

Preparation of poly[ethylene-g-(vinylbenzyl chloride)] and functionalization with bis(phosphonic acid) derivatives

Abstract Poly[ethylene- g -(vinylbenzyl chloride)] ( 1 ) film was prepared and used as an intermediate for the synthesis of polymer supported bis(phosphonic acid) derivatives. ( 1 ) was synthesized by preirradiation grafting of vinylbenzyl chloride (VBC) on polyethylene film. A reaction time of 29 h gave ( 1 ) with a chlorine capacity of 4.7 mmol Cl/g. As shown by energy dispersive X-ray analysis, the depth of the graft modification can be varied from surface to bulk modification by controlling the reaction time. The gel content of the film was found to increase with increased extent of grafting. A 28% VBC grafted film was found to have a gel content of 91%. The swelling of the Poly[ethylene- g -(vinylbenzyl chloride)] ( 1 ) film in toluene or THF was rapid A 145% VBC grafted film swells 260 area % within 2 min in refluxing toluene. Tetraisopropyl methylene-bisphosphonate ( 2 ) or tetraethyl ethane-1,1-bisphosphonate ( 3 ) were reacted with NaH and used for nucleophilic substitution of chlorine in the poly[ethylene- g -(vinylbenzyl chloride)] film. Forty-six percent of the chlorine groups were substituted within 24 h using the sodium salt of tetraisopropyl methylenebisphosphonate ( 2 ) in a 10-fold excess in refluxing toluene. Under the same reaction conditions, using the sodium salt of tetraethyl ethane-1,1-bisphosphonate ( 3 ) gave 50% substitution. Energy dispersive X-ray analysis showed that the substitution reaction proceeds throughout the film at the same rate, which implies that the reaction is not mass-transfer controlled. Hydrolysis of the polymer supported bisphosphonate in hydrochloric acid to yield the bis(phosphonic acid) form gave a film which swells 60 area % in water at room temperature and 100 area % at 100°C.