Construction and Evaluation of a Promazinium Cation-Selective Electrode

 The construction of a plasticised PVC matrix-type promazinium cation-selective membrane electrode and its use in the potentiometric determination of promazine hydrochloride in pharmaceutical preparations are described. It is based on the use of the ion-associate species, formed by promazinium cation and tetraphenylborate (TPB) counter ion. The basic electrode performance characteristics are evaluated according to IUPAC recommendations. It exhibited a linear response for 1 × 10⁻²−1 × 10⁻⁵ M of promazine hydrochloride solutions with a cationic Nernstian slope over the pH range 2–6. Common organic and inorganic cations showed negligible interference. Direct potentiometric determination of 1 × 10⁻²−1 × 10⁻⁵ M aqueous promazine hydrochloride using this membrane electrode system showed an average recovery of 99.5% with a mean standard deviation of 1.5%. This electrode was successfully used for monitoring the titration of promazine hydrochloride with sodium tetraphenyl borate and for determining promazine hydrochloride in ampoules. Received June 15, 2001 Revision November 6, 2001     

Thermal decomposition and hydrolysis of polyacrylamide-co-tert-butyl acrylate

Hydrolysis and thermal decomposition of polyacrylamide tert-butyl acrylate (PAtBA) copolymer were investigated. Carbon-13 nuclear magnetic resonance (¹³C NMR) spectroscopy was used to monitor the structural changes of the PAtBA. Hydrolysis of the amide groups occurred only after the complete conversion of tBA. Activation energy for the amide groups of the PAtBA was found to be 86.4 kJ/mol. Gas chromatography was used to identify gas products of the thermal decomposition of PAtBA. Gas analysis showed conclusively the formation of isobutene and carbon dioxide from the tBA groups of the copolymer. Tertiary butanol was found to be the hydrolysis product in the aqueous phase at temperatures from 60 to 130 °C. Kinetics governing the contribution of tBA and amide groups to the total degree of hydrolysis of the PAtBA is presented. An nth order equation was used to check for the hydrolysis reaction order of both the amide and the tBA groups. Analysis of ¹³C NMR spectra revealed that tBA groups were randomly distributed on the PAtBA copolymer chain.     

Voltammetric determination of meclizine HCL and its application in pharmaceuticals and biological fluid using CNTS/ZnO nano-carbon modified electrode

In this article, we report a methodology for the voltammetric behavior of meclizine hydrochloride at different nano modified electrodes e.g., Glassy carbon (GCE), pencil graphite (PGE), Carbon Nano tubes-carbon paste (CNTS-CPE) and Carbon Nano tubes-zinc oxide carbon paste (CNTS/ZnO-CPE) using cyclic and square wave voltammetry and the highest performance of them was CPE/CNTs/ZnO electrode and therefore was used as working electrode. The oxidation reaction mechanism of meclizine hydrochloride (MEC-HCL) is proposed to be one electron system. The results obtained with a square wave were linear over the concentration ranges 19.5–102.4 ng mL^?1 with a correlation coefficient 0.998. The square wave technique showed a low of detectable (LOD) of 6.444 ng/mL and a limit of quantification (LOQ) of 19.530 ng/mL at CNTS/ZnO-CPE. Based on these findings, a simple and not time-consuming method was used for the analysis of MEC-HCL in pharmaceutics and biological fluids. The method showed a minimum detectability (LOD) of 0.02, 0.008 and 0.14 lg/mL and a limit of quantitation (LOQ) of 0.06, 0.02 and 0.42 lg/mL at PGE, CPE and GCE, respectively. The method was validated and compared with the reference valid method. It revealed good accuracy and reproducible results. The anticipated voltammetric procedure has the advantage of being simple, precise, inexpensive and highly sensitive.     

Analysis of toxic trace elements in sea food samples by neutron activation

The aim of this study is to investigate the contents of toxic and essential trace element such as As, Hg, Se and Zn by neutron activation analysis in coastal fishes consumed by the general population of Malaysia. The mean values of the elements analysed expressed in mg/kg fresh weight ranged 1.42–5.61, 0.06–0.42, 4.2–20.6, 0.41–1.28 for As, Hg, Zn and Se, respectively. The maximum permissible limit for As in food was set at 1.0 mg/kg under the Malaysian Food Regulations. Our results showed that consumption of coastal fishes is not permitted under the regulations, while the levels of Hg, Se and Zn were within the permissible limits. The daily dietary intake of As and Hg at 400 g and 30g respectively are still within the tolerance levels.     

Synthesis of 3,4‐Fused γ‐Lactone‐γ‐Lactam Bicyclic Moieties as Multifunctional Synthons for Bioactive Molecules

A short approach for the synthesis of 3,4‐fused γ‐lactone‐γ‐lactam bicyclic systems ( 1 ) in diastereomeric mixtures from chiral D ‐alanine methyl ester hydrochloride is described. The key step towards lactonisation is the reduction of the carbonyl ketone of the 5R‐configured 3,5‐dimethylpyrrolidine‐2,4‐dione diastereomers ( 8 ) via sodium borohydride in the presence of hydrochloric acid. With the presence of ethyl acetyl functionality at C3‐position, ester hydrolysis of 8 occurred concomitantly with keto reduction leading to lactonisation and eventually affording the anticipated (3S,4S,5R), (3R,4R,5R), (3R,4S,5R) and (3S,4R,5R) bicyclic moieties. The formation of the fused systems was confirmed by mass spectroscopy (MS) and nuclear magnetic resonance (NMR) analyses.     

Effect of Sn additions on the microstructure,mechanical properties,corrosion and bioactivity behaviour of biomedical Ti–Ta shape memory alloys

Ti–Ta and Ti–Ta–xSn shape memory alloys (SMAs) were produced successfully by microwave sintering. Tin element was added to Ti–Ta SMA with three different atomic percentages (0.37, 0.745 and 2.26 at.%). The influences of Sn addition on microstructure, transformation temperatures, mechanical properties, shape memory behaviours, corrosion resistance and bioactivity were investigated. It was found that the morphologies of the modified and unmodified Ti–Ta alloys contain a plate-like and needle-like structure, where the former structure is related to the β phase and the latter related to the α phase. The transformation temperatures of M _s to M _f with and without Sn additions were observed to be in the range of 389.65 to 355 K, while the transformation temperatures of A _s to A _f were found to be in the range of 250.42 to 365.8 K. By increasing the proportion of Sn, the compressive fracture strength and shape memory behaviour were enhanced; however, the corrosion resistance tended to be decreased. Based on the bioactivity results, antibacterial activity was improved with the addition of Sn. In conclusion, the existent results indicate that Ti–30 at.% Ta SMAs may be a convenient alternative to Ni–Ti for certain biomedical applications.

     

Constraints on heterotic M-theory from s-cobordism

We interpret heterotic M-theory in terms of h-cobordism, that is the eleven-manifold is a product of the ten-manifold times an interval is translated into a statement that the former is a cobordism of the latter which is a homotopy equivalence. In the non-simply connected case, which is important for model building, the interpretation is then in terms of s-cobordism, so that the cobordism is a simple-homotopy equivalence. This gives constraints on the possible cobordisms depending on the fundamental groups and hence provides a characterization of possible compactification manifolds using the Whitehead group - a quotient of algebraic K-theory of the integral group ring of the fundamental group - and a distinguished element, the Whitehead torsion. We also consider the effect on the dynamics via diffeomorphisms and general dimensional reduction, and comment on the effect on F-theory compactifications.     

1,1‐Di(9‐fluorenyl)­ethyl acetate,a by‐­product from the acetyl­ation of 9‐fluorenyl­lithium

The preparation of sp‐9‐acetyl­fluorene from the reaction of 9‐­fluorenyl­lithium with acetyl chloride also provided 9‐(1‐acetoxy­ethyl­idene)­fluorene (`di­acetyl­fluorene') and 1,1‐di(9‐fluorenyl)­ethanol, (II), as by‐products recently characterized by X‐ray analysis. A third by‐product, 1,1‐di(9‐fluorenyl)­ethyl acetate, (III), C₃₀H₂₄O₂, has now been unequivocally identified for the first time, and emanates from the acetyl­ation of the oxy­anion of (II). In the asymmetric unit, compound (III) exists as two almost identical structures which differ slightly, but significantly, in conformation. Neither possesses the significant fluorene‐ring bowing or the perpendicularity of the two ring planes exhibited by (II). The angle between the least‐squares planes of the two fluorene rings of (III) is 58.45 (9) and 60.95 (10)°, respectively, for the two conformations, and their corresponding bonding parameters also differ slightly in a number of instances.     

Thermodynamics of Amino Acid Methyl Ester Hydrochlorides—Crown Ether Complexes in Methanol at 25°C

Stability constants, free energies, and enthalpies and entropies of the complexation of L-alanine methyl ester hydrochloride (L-Ala-HCl), L-phenylalanine methyl ester hydrochloride (L-Phe-HCl), and valine methyl ester hydrochloride (L-Val-HCl) with 15-crown-5 (15C5), benzo-15-crown-5 (B15C5), 18-crown-6 (18C6), benzo-18-crown-6 (B18C6), dicyclohexano-18-crown-6 (DC18C6), and dicyclohexano-24-crown-8 (DC24C8) in methanol are reported for 20°C. No significant variation in the stability constants and free energies of complexation is observed, indicating that the various crown ethers are poorly selective in binding the amino acids. However, the nature of the crown ether and the amino acid and their pattern of substitution cause a remarkable variation in the enthalpies and entropies of complexation. This indicates a strong enthalpy–entropy compensation effect. The enthalpy–entropy compensation effect for the crown ether complexes of the amino acid methyl ester hydrochlorides reported herein is compared with that of the crown ethers complexes of the amino alcohols and the free amino acid. It is found that the enthalpy–entropy compensation effect holds equally for the three classes of complexes.