Walkiria Schlindwein

Pharmaceutical cocrystals: An overview

Pharmaceutical cocrystals are emerging as a new class of solid drugs with improved physicochemical properties, which has attracted increased interests from both industrial and academic researchers. In this paper a brief and systematic overview of pharmaceutical cocrystals is provided, with particular focus on cocrystal design strategies, formation methods, physicochemical property studies, characterisation techniques, and recent theoretical developments in cocrystal screening and mechanisms of cocrystal formations. Examples of pharmaceutical cocrystals are also summarised in this paper.

Polymer electrolytes based on modified natural rubber

Abstract Modified natural rubber polymer hosts having low transition glass temperatures have been investigated for use in polymer electrolytes. Two types of modified natural rubber, namely 25% epoxidised natural rubber (ENR-25) and 50% epoxidised natural rubber (ENR-50) were employed in conjunction with poly(ethylene oxide), PEO. Results are reported for ionic conductivity and thermal properties for both unplasticized and plasticized polymer electrolyte systems with lithium triflate. The samples were in the form of free standing films with the thickness 0.2–0.5 mm and mixtures of ethylene carbonate (EC) and propylene carbonate (PC) were used as plasticizers. Unplasticized modified natural rubber-based systems exhibit ionic conductivities in the range 10−6 to 10−5 S cm−1 at ambient temperatures. Incorporating 100% of EC/PC by weight fraction of polymer (ENR/PEO) to the systems yielded mechanically stable films and ionic conductivities in the range of 10−4 S cm−1 at ambient temperature.

Conducting polymer‐based electrochemical redox supercapacitors using proton and lithium ion conducting polymer electrolytes

Polypyrrole-based solid-state redox supercapacitors have been constructed using proton and lithium ion conducting polymer electrolytes: poly(vinyl alcohol) (PVA)–H3PO4, and poly(ethylene oxide) (PEO)–LiCF3SO3 plasticized with poly(ethylene glycol) (PEG). The capacitors have been characterized using a.c. impedance, cyclic linear sweep voltammetry and galvanostatic charge–discharge methods. Redox capacitors based on polypyrrole show large values of capacitance (about 1·5–5·0 mFcm-2) (equivalent to a single electrode capacitance of 40–84 Fg-1 of polypyrrole) for both the electrolytes. The values of capacitance have been found to be stable up to 1000 charge–discharge cycles between 0 and 1·0 V.

In situ monitoring of carbamazepine–nicotinamide cocrystal intrinsic dissolution behaviour

Cocrystals have shown huge potential to improve the dissolution rate and absorption of a poorly water soluble drug. However, solution mediated phase transformation of cocrystals could greatly reduce the enhancement of its apparent solubility and dissolution rate. The aim of this study is to gain a deep understanding of the phase transition behaviour of cocrystals during dissolution and to investigate the improvement of dissolution rate. Dissolution and transformation behaviour of carbamazepine-nicotinamide (CBZ-NIC) cocrystal, physical mixture and different forms of carbamazepine: form I (CBZ I), form III (CBZ III) and dihydrate (CBZ DH) were studied by different in situ techniques of UV imaging and Raman spectroscopy. It has been found that compared with CBZ III and I, the rate of intrinsic dissolution rate (IDR) of CBZ-NIC cocrystal decreases slowly during dissolution, indicating the rate of crystallisation of CBZ DH from the solution is slow. In situ solid-state characterisation has shown the evolution of conversion of CBZ-NIC cocrystal and polymorphs to its dihydrate form. The study has shown that in situ UV imaging and Raman spectroscopy with a complementary technique of SEM can provide an in depth understanding during dissolution of cocrystals.

Studies on all solid state electric double layer capacitors using proton and lithium ion conducting polymer electrolytes

Proton and lithium ion conducting polymer electrolytes, based on poly(vinyl alcohol)–H3PO4 and poly(ethylene oxide)–LiCF3SO3 plasticised with poly(ethylene glycol), have been used in the construction of electric double layer capacitors with both high density graphite sheet and activated carbon fabric electrodes. The polymer electrolytes have room temperature ionic conductivities (ca. 10−4–10−3 S cm−1) that make them suitable for use in thin-film form in devices. The performance characteristics of the capacitors have been studied using impedance analysis, linear-sweep voltammetry and charge–discharge methods. The supercapacitors based on the activated carbon fabric have characteristically large values of overall capacitance of 360–470 mF cm−2 [equivalent to single electrode capacitance 70–90 F (g carbon)−1] with the proton conducting electrolyte. Systems based on lithium ion conducting polymer electrolytes, however, have a much lower capacitance of ca. 20 mF cm−2 (equivalent to a single electrode capacitance of ca. 4 F g−1).

Supercapacitor devices using porous silicon electrodes

Electrical double layer (EDL) supercapacitors have been constructed using gold coated porous silicon (PSi) electrodes in a 0.25 M TEABF4/PC solution. As a comparison with the PSi, graphite paper, carbon cloth and ITO on glass electrodes have also been tested using the same electrolyte. The capacitors have been characterised using a.c. impedance spectroscopy and cyclic voltammetry (normal staircase mode). Devices using PSi electrodes showed a capacitance of approximately 0.2 mF cm−2 (equivalent to 5 mF g−1). In comparison, devices based on ITO on glass electrodes had a capacitance of 0.76 mF cm−2. Those based on graphite-paper electrodes gave 10 mF cm−2 (equivalent to 131 mF g−1) and those using carbon cloth gave 600 mF cm−2 (equivalent to 35 F g−1).

Supercapacitors using polymer electrolytes based on poly(urethane)

Abstract Electrical double layer supercapacitors have been constructed from a poly(urethane) electrolyte, [Poly(urethane):ethylene carbonate:propylene carbonate:lithium perchlorate in the ratio of 1:2:2:0.1 based on the mass of the polymer as the electrolyte], using both the high surface area carbon cloth and carbon composite electrodes. The cells have been characterised using the AC impedance spectroscopy, galvanostatic charge–discharge experiments, and cyclic voltammetry. Capacitance values of up to 35 and 5.5 F g −1 for the composite and carbon cloth electrodes were respectively attained. The supercapacitor cells showed a good stability up to 1000 charge–discharge cycles, retaining 80% of their original capacity at 1000 cycles.

Polymer electrolyte based solid state redox supercapacitors with poly (3-methyl thiophene) and polypyrrole conducting polymer electrodes

Types I and II solid state redox supercapacitors have been constructed using polypyrrole (pPy) and poly (3-methyl thiophene) (pMeT) conducting polymer electrodes with lithium ion conducting polymer electrolyte poly(ethylene oxide) (PEO)-LiCF3SO3 plasticised with poly (ethylene glycol) (PEG). The performance of the capacitors has been characterised by a.c. impedance, linear sweep voltammetry, galvanostatic charge-discharge methods and long term cycling tests. The asymmetric type II capacitors with p-doped pPy and pMeT electrodes give a capacitance value ∼ 2 mF cm−2 (equivalent to 18 Fg−1 of the total mass of the electrodes) and can be charged up to the voltage of 1.7 V. The symmetric type 1 capacitors of the configuration pPy | polymer electrolyte | pPy and pMeT | polymer electrolyte | pMeT show comparable values of capacitance but they are limited to the working voltage of <1.0 V.

Using the Box–Behnken experimental design to optimise operating parameters in pulsed spray fluidised bed granulation

In this work, the influence factors of pulsed frequency, binder spray rate and atomisation pressure of a top-spray fluidised bed granulation process were studied using the Box-Behnken experimental design method. Different mathematical models were developed to predict the mean size of granules, yield, relative width of granule distribution, Hausner ratio and final granule moisture content. The study has supported the theory that the granule size can be controlled through the liquid feed pulsing. However, care has to be taken when the pulsed frequency is chosen for controlling the granule size due to the nonlinear quadratic relation in the regression model. The design space of the ranges of operating parameters has been determined based on constraints of the mean size of granules and granule yield. High degree of prediction obtained from validation experiments has shown the reliability and effectiveness of using the Box-Behnken experimental design method to study a fluidised bed granulation process.

Cation-oxygen geometry in polymer electrolytes: interpretation of EXAFS results

Two issues are of current interest in the field of ionically conducting polymers (polymer electrolytes): these are ion pairing and possible interference of the polymer-cation interaction by water. EXAFS was chosen as a suitable technique to probe local structure surrounding the cations. The systems studied were PEOn:ZnX2, where n= 6–15 and X = Cl, Br or I. They were chosen in order to ascertain the reliability of information pertaining to oxygen neighbours when the system under investigation contains heavy counterions. The results reveal, as expected, that the information about numbers of oxygen nearest neighbours is qualitative rather than quantitative, and firmer conclusions can be drawn for the lighter counterions. Cations and anions were found to be in close proximity, thus confirming ion pairing in PEO-zinc polymer electrolytes; this is in accord with recent observations of zinc diffusion.