A Validated Quantification of Benzocaine in Lozenges Using TLC and a Flatbed Scanner

We present a video-densitometric quantification method for benzocaine in lozenges. The quantification is based on a derivatisation reaction with 4-dimethylaminobenzaldehyde. Measurements were carried out using a 16-bit flatbed scanner. Benzocaine was separated to a distance of 50 mm in a vertical developing chamber without vapour saturation. We present an RP-18 phase separation on a cyanopropyl plate (Merck, Darmstadt, Germany) using water, CH₃CN, dioxane, ethanol, and NH₃ (25 %) (8 + 2 + 1 + 1 + 0.05, v/v) as the mobile phase. We also separated benzocaine in a normal phase system on silica gel 60 LiChrospere^® plates (Merck, Darmstadt, Germany) with the mobile phase MTBE/cyclohexane (1 + 1, v/v). The calibration functions for benzocaine in both separations were linear in the range from 1 to 1,000 ng per spot. The range of linearity covers two magnitudes of power because the Kubelka–Munk expression was used for data transformation. In the cyanopropyl-system, the benzocaine amount was quantified as 242.5 ± 18.2 ng in a spot or 6.86 ± 0.52 mg in a single lozenge. The amount of 7.0 mg benzocaine per lozenge was labelled. The combined uncertainty of sample and calibration measurements was statistically calculated using a significance level of α = 0.05 to a total relative uncertainty of 7.49 %. The separation method is inexpensive, fast and reliable.     

Capillary Electrophoretic Determination of Disodium Ethylene Bisdithiocarbamate (NABAM) and Sodium Diethyldithiocarbamate (NADDC)

Abstract

A simple and sensitive capillary elecrophoretic method has been developed for the separation and determination of Nabam and NaDDC in boric acid buffer by direct UV absorbance detection at 254 nm. The separation is dependent on pH and nature of the buffer. In this method the detection limits (S/N = 3) are 1.56 × 10^?6 mol/L and 2.48 × 10^?6 mol/L and the linear calibration range is three orders of magnitude for Nabam and NaDDC, respectively. The method has been successfully applied for the analysis of wheat samples spiked with Nabam.     

Some Applications of Computerized GC-MS to the Determination of Biogenic and Anthropogenic Organic Matter in the Environmentt

Abstract

This is an overview of the application of organic mass spectrometry and ancillary techniques to the analysis of organic matter in environmental research. Such organic matter is usually analyzed in terms of gas, bitumen (lipids), and “kerogen”, with asphaltenes and humic substances for some samples. This approach is illustrated with some examples and the origin, the environmental history and the nature of secondary products of this organic matter can be evaluated by using the data derived from both specific molecular and bulk chemical (also physical) analyses. Evaluations of production and fluxes and cross-correlations can thus be made by the application of the same separation and analytical procedures to samples from different environmental compartments (eg., biota, atmosphere, hydrosphere, lithosphere, etc.).     

Determination of oxalate in urine by zone electrophoresis on a chip with conductivity detection

The use of a poly(methylmethacrylate) capillary electrophoresis chip, provided with a high sample load capacity separation system (a 8500 nL separation channel coupled to a 500 nL sample injection channel) and a pair of on-chip conductivity detectors, for zone electrophoresis (ZE) determination of oxalate in urine was studied. Hydrodynamic and electroosmotic flows of the solution in the separation compartment of the chip were suppressed and electrophoresis was a dominant transport process in the separations performed on the chip. A low pH of the carrier electrolyte (4.0) provided an adequate selectivity in the separation of oxalate from anionic urine constituents and, at the same time, also a sufficient sensitivity in its conductivity detection. Under our working conditions, this anion could be detected at a 8 x 10(-8) mol/L concentration also in samples containing chloride (a major anionic constituent of urine) at 3.5 x 10(-3) mol/L concentrations. Such a favorable analyte/matrix concentration ratio (in part, attributable to a transient isotachophoresis stacking in the initial phase of the separation) made possible accurate and reproducible (typically, 2-5% relative standard deviation (RSD) values of the peak areas of the analyte in dependence on its concentration in the sample) determination of oxalate in 500 nL volumes of 20-100-fold diluted urine samples. Short analysis times (about 280 s), no sample pretreatment (not considering urine dilution) and reproducible migration times of this analyte (0.5-1.0% RSD values) were characteristic for ZE on the chip. This work indicates general potentialities of the present chip design in rapid ZE analysis of samples containing the analyte(s) at high ionic matrix/analyte concentration ratios.     

Theoretical and experimental studies of biotin analogues that bind almost as tightly to streptavidin as biotin

We have used a newly developed qualitative computational approach, PROFEC (Pictorial Representation of Free Energy Changes), to visualize the areas of the ligand biotin where modifications of its structure might lead to tighter binding to the protein streptavidin. The PROFEC analysis, which includes protein flexibility and ligand solvation/desolvation, led to the suggestion that the pro-9R hydrogen atom of biotin, which is in alpha-position to the CO(2)(-) group, might be changed to a larger group and lead to better binding with streptavidin and avidin. Free energy calculations supported this suggestion and predicted that the methyl analogue should bind approximately 3 kcal/mol more tightly to streptavidin, with this difference coming exclusively from the relative desolvation free energy of the ligand. The PROFEC analysis further suggested little or no improvement for changing the pro-9S hydrogen atom to a methyl group, and great reduction in changing the ureido N-H groups to N-CH(3). Stimulated by these results, we synthesized 9R-methylbiotin and 9S-methylbiotin, and their binding free energies and enthalpies were measured for interaction with streptavidin and avidin, respectively. In contrast to the calculated results, experiments found both 9-methylbiotin isomers to bind more weakly to streptavidin than biotin. The calculated preference for the binding of the 9R- over the 9S-stereoisomer was observed. In addition, 9-methylbiotin is considerably less soluble in water than biotin, as predicted by the calculation, and the 9R isomer is, to our knowledge, thus far the tightest binding analogue of biotin to streptavidin. Subsequently, X-ray structures of the complexes between streptavidin and both 9R- and 9S-methylbiotin were determined, and the structures were consistent with those used in the free energy calculations. Thus, the reason for the discrepancy between the calculated and experimental binding free energy does not lie in unusual binding modes for the 9-methylbiotins.     

Platinum(II) and Palladium(II) Halides and Pseudohalides with the Ligand Tri(1‐cyclohepta‐2, 4, 6‐trienyl)phosphane. X‐Ray Structural Analysis of [P(C7H7)2(η2‐C7H7)]PtI2

Tri(1‐cyclohepta‐2, 4, 6‐trienyl)phosphane, P(C₇H₇)₃ ( 1 ) ([P] when coordinated to a metal) stabilizes platinum(II) ( 2 ) and palladium(II) dihalides ( 3 ) as [P]MX₂ with X = Cl ( a ), Br ( b ) and I ( c ). The phosphane coordinates to the metal as a chelate ligand via both phosphorus and the central η²‐C=C bond of one of the cyclohepta‐2, 4, 6‐trienyl rings. The complexes were prepared by various routes, mainly by the reaction of (cod)MCl₂ (cod = cycloocta‐1, 5‐diene) with 1 to give the chlorides 2a and 3a , which then could be converted into the bromides 2b , 3b or the iodides 2c , 3c by reaction with NaBr or NaI, respectively. The molecular structure of 2c was determined by X‐ray analysis. Treatment of 2a and 3a with sodium or potassium salts of several pseudohalides afforded the complexes [P]MX₂ 2d (NCO/NCO), 2e₁ (NCS/SCN), 2e₁' (SCN/NCS), 2f₂ (SeCN/SeCN), 3f₁ (NCSe/SeCN), 2g and 3g (X = N₃). Attempts failed to synthesize the cyanides 2h and 3h by the same route. By using an excess of trimethylsilyl cyanide in the reaction with 2a in THF solution, the complex trans‐{[(C₇H₇)₃P]₂Pt(CN)₂} ( 4h ) was obtained instead of 2h . The analogous complexes trans‐{[(C₇H₇)₃P]₂MX₂} with M = Pt ( 4 ) and Pd ( 5 ) for X = Cl ( a ), Br ( b ), I ( c ) could be prepared from the reaction of the corresponding tetrahalogenometallates and 1 (in the case of 5c from PdI₂ and 1 ). In contrast to 4h , the complexes 4a‐c and 5a‐c were found to be labile in solution with respect to partial loss of the phosphane 1 and rearrangement into 2a‐c and 3a‐c , respectively. All compounds were characterized by IR spectroscopy and by multinuclear magnetic resonance spectroscopy (¹H, ¹³C, ³¹P, ⁷⁷Se and ¹⁹⁵Pt NMR). The ligand [P] in 2 and 3 is fluxional with regard to coordination of the C₇H₇ rings to the metal.     

β‐Ketoesters as Mono‐ or Bisnucleophiles: A Concise Enantioselective Total Synthesis of (−)‐Englerin A and B

A short enantioselective total synthesis of englerin A, a guaiane sesquiterpene with significant in vitro antitumor activity, is reported. Key features of this total synthesis are an organocatalytic asymmetric decarboxylative aldol reaction, a neighboring‐group‐participating [4+3] cycloaddition, a novel one‐pot Heck coupling/regioselective 1,4‐hydrosilylation/Tamao–Fleming oxidation cascade, and a kinetic CBS reduction, generating the optically pure natural product in 6.7 % overall yield over twelve steps starting from methylglyoxal. Selective saponification of the more reactive glycolic ester moiety of englerin A also gave (?)‐englerin B.