The conductivity of single crystals of 9-methyladenine

The conductivity of single crystals of 9-methyladenine(6-amino-9-methyl-purine) has been determined using proton-injecting solution electrodes. The conductivities parallel and perpendicular to the (100) plane are 2.5 ± 1.9 × 10^?13/ohm-cm and 7.0 ± 2.9 × 10^?15/ohm-cm, respectively, at 295°K. The H-bonded pathways lie in the (100) planes. The conductivity is ohmic over the range of applied fields. The temperature dependence of the conductivity was determined parallel and perpendicular to the (100) planes.     

The conductivity of single crystals of 1-methylthymine

The conductivity of single crystals of 1-methylthymine (2,4-dihydroxy-1,5-dimethylpyrimidine) has been determined using proton-injecting solution electrodes. The conductivities parallel and perpendicular to the H-bonded, (102) planes are 2.4 × 10^?10 ± 1.9 × 10^?10 and 1.0 × 10^?14 ± 0.4 × 10^?14/ohm cm, respectively (298°K). The conductivity is ohmic over the range of fields employed for either crystallographic direction. The energy of activation for conduction parallel to the (102) plane is 43 ± 10 kJ/mole.     

Thermodynamics of hydrogen trapping in intermetallic compounds: Application to LaNi5H

It has been observed for several intermetallic compound/H systems that deviations from Sieverts' law of ideal solubility occur which are in the opposite direction from the deviations from ideality which occur in pure metal/H systems. The principal source of nonideality on both types of interstitial solutions arises from the changes of the relative partial molar enthalpy of H₂ solution, ΔH_H, with H content. The variations of ΔH_H with H content are, however, in the opposite directions for intermetallic/H and pure metal/H interstitial solutions. Relative partial molar entropies for solution of H₂ in the α-phase of the $\text{LaNi}{}_5\text{H}$ system are given at 298.2 K. These have been determined from calorimetric determinations of ΔH_H and measurements of . The partial entropies show unusual extrema as a function of H content. A model based on trapping of H atoms is proposed which explains the variations of ΔH_H and ΔS_H. Since the deviations from ideality arising from an increase of ΔH_H with H content seem to be limited to solids with at least two different ordered metal components, e.g., intermetallic compounds, it seems reasonable to assign the trapping sites to interstices which result from an interchange of metal atoms. This interchange may create interstices rich in those nearest-neighbor metal atoms which have the greatest affinity for H.     

High performance liquid chromatographic measurement of lignocaine in tissue samples following transabdominal placental biopsy

A method is described for the measurement of lignocaine in small samples of fetal and placental tissue. Tissue samples (ca 100 mg) are digested using a preteolytic enzyme. Lignocaine and an internal standard are extracted into methyl tert-butyl ether and analysed by high-performance liquid chromatography with electrochemical detection (+1.0 V vs Ag/AgCl). The limit of accurate measurement is better than 0.1 mg/kg wet weight for a 100 mg sample. This method has been used to assess fetal exposure to the drug when used as a local anaesthetic during transabdominal placental biopsy (chorionic villus sampling). The range of lignocaine concentrations found in the tissue samples was large (from less than 0.04 mg/kg wet weight to 15.4 mg/kg wet weight) although most samples contained less than 1.0 mg lignocaine/kg wet weight.     

Dipyrrinato-Iridium(III) Complexes for Application in Photodynamic Therapy and Antimicrobial Photodynamic Inactivation

The generation of bio-targetable photosensitizers is of utmost importance to the emerging field of photodynamic therapy and antimicrobial (photo-)therapy. A synthetic strategy is presented in which chelating dipyrrin moieties are used to enhance the known photoactivity of iridium(III) metal complexes. Formed complexes can thus be functionalized in a facile manner with a range of targeting groups at their chemically active reaction sites. Dipyrrins with N- and O-substituents afforded (dipy)iridium(III) complexes via complexation with the respective Cp*-iridium(III) and ppy-iridium(III) precursors (dipy=dipyrrinato, Cp*=pentamethyl-η⁵-cyclopentadienyl, ppy=2-phenylpyridyl). Similarly, electron-deficient [Ir^III(dipy)(ppy)₂] complexes could be used for post-functionalization, forming alkenyl, alkynyl and glyco-appended iridium(III) complexes. The phototoxic activity of these complexes has been assessed in cellular and bacterial assays with and without light; the [Ir^III(Cl)(Cp*)(dipy)] complexes and the glyco-substituted iridium(III) complexes showing particular promise as photomedicine candidates. Representative crystal structures of the complexes are also presented.     

Observations on the Stereochemical Outcome of the UGI Four-Component Condensation

Investigations were carried out to explain the unexpected distribution of cis and trans products from the Ugi four-component condensation involving a cyclic imine. The nature of the transition state complex was deemed to be a determining factor. The influence of solvent polarity on the isomeric ratio of the products was also examined.     

Micro-extraction techniques in analytical toxicology: short review

This paper discusses new developments in plasma micro-extraction techniques in the context of established micro-extraction and protein precipitation methodology. Simple liquid-liquid solvent extraction (LLE) of plasma with direct GC or HPLC analysis of the resulting extract has been used for many years. Butyl acetate and methyl t-butyl ether (MTBE) give efficient extraction of many drugs and metabolites from small volumes of plasma or whole blood at an appropriate pH, and form the upper layer, thus simplifying extract removal. Butyl acetate does not interfere with NPD, ECD or MS in GC, whilst MTBE has a relatively low UV cutoff (220 nm). Thus, HPLC eluents that use a high proportion of an organic component allow MTBE extracts to be analysed directly. 'Salting-out' and extractive derivatization using acetic anhydride or phenylboronic acid can be used with appropriate analytes. As regards protein precipitation, an important consideration is lowering the pH, although this is not feasible with acid-labile analytes. More recent developments include sold-phase micro-extraction (SPME) and liquid-phase micro-extraction (LPME). This latter technique especially may prove invaluable as analytes that cannot easily be extracted with LLE can be isolated simply at low cost with a minimum of apparatus.     

Polymorphism of N-(2,6-dioxo-3-piperidyl)pthalimide (thalidomide): Structural characterization of a second monoclinic racemic modification

The X-ray crystal structure of the drug N-(2,6-dioxo-3-piperidyl)pthalimide (thalidomide), C₁₃H₁₀N₂O₄, obtained from 11 dimethyformamide-ethanol solution, is reported. This species is monoclinic, space groupC2/c, witha=20.679(5),b=8.042(2),c=14.162(5) , =102.86(3)°,Z=8,R=0.051 for 1674 unique reflections. crystal packing is determined by intermolecular N–H... O hydrogen bonding which is more extensive than that reported in the literature for a racemate of thalidomide crystallizing in space groupP2₁/n. Comparison of the melting behavior and X-ray powder diffractograms of the two racemic polymorphs shows that they are distinctly different, allowing easy identification of these species. By comparing experimental X-ray powder patterns with those calculated from single crystal data, it was concluded that neither of these polymorphs undergoes a phase change on trituration.