A study of the intermolecular interactions of tolmetin/N-acetyl-l-tyrosine ethyl ester complex

The formation of tolmetin/N-acetyl-l-tyrosine ethyl ester (ATEE) complex has been reported by means of both theoretical and experimental studies, including quantum mechanical calculations as well as UV–vis absorption, fluorescence and time-resolved spectroscopy measurements. It has been found that the fluorescence of ATEE is quenched due to the formation of a non-fluorescent complex between ATEE and tolmetin in the ground state. The geometrical parameters of ATEE/tolmetin complex have been determined with the use of the DFT method applying the B3LYP correlation-exchange functional and 6-31G(d) basis set. The results of experiments indicated the static ATEE quenching by tolmetin. Additionally, the experimental and theoretically predicted Gibbs free energy of complexation has been calculated.     

Adsorptive stripping voltammetric determination of the anti-inflammatory drug tolmetin in bulk form, pharmaceutical formulation and human serum

The electro-reduction of tolmetin at the hanging mercury drop electrode was studied in different supporting electrolytes using cyclic voltammetry and square-wave stripping voltammetry techniques. Voltammograms of tolmetin exhibited a single well-defined 2-electron irreversible cathodic peak in media of pH < 4, which may be attributed to reduction of the >C=O double bond of the analyte molecule. Adsorption of tolmetin onto the surface of the hanging mercury electrode was identified and each adsorbed tolmetin molecule was found to occupy an area of 0.23 nm². A square-wave adsorptive cathodic stripping voltammetric procedure was described for the direct determination of tolmetin in bulk form and pharmaceutical formulation (Rumatol® capsules) with a limit of quantitation of 2 × 10^?9 M and a mean percentage recovery of 98.35 ± 1.21% to 99.57 ± 1.23. Moreover, the described procedure was successfully applied for the direct assay of tolmetin in spiked human serum without pretreatment or extraction prior to the analysis while a quantitation limit of 5 × 10^?9 M tolmetin was achieved.      

Photolysis of NSAIDs. IV. Photoproducts of zomepirac determined by LC-ESI-MS

A sample of 10 mm zomepirac in methanol was photo-irradiated with a Hanovia 200 W high-pressure quartz Hg lamp for 14 days. In total, four photoproducts were observed from the HPLC chromatogram. The preparative HPLC included an YMC-Pack Pro C18 column (250 x 20 mm i.d.), a mobile phase of CH3CN-CH3OH-1%HOAc (10:60:30, v/v/v), and UV detection at 254 nm. The most probable structures of the four photoproducts were determined by LC-MS. Two major photoproducts were separated, and their structures were further confirmed by the spectroscopic methods. A reaction scheme of zomepirac was proposed that the photochemical reaction routes occur mainly via bond fission between carbonyl-pyrrolyl groups (alpha-cleavage of a ketone), and decarboxylation followed by oxidation with singlet oxygen to produce an aldehyde.     

双表白术内酯的结构鉴定

白术(ArtactylodesmacrocephalaKoidz)为有多种生物活性的传统常用中药。从中分得4个已知化合物,另外一个物质的MS,1D和2DNMR表明是类型较为罕见的完全对称的双倍半萜新化合物,命名为双表白术内酯(biepiasterolid)。     

Identification of flurbiprofen and its photoproducts in methanol by gas chromatography-mass spectrometry

A sample of 10 mM flurbiprofen in methanol (or ethanol) was photoirradiated with sixteen 8 W low-pressure quartz mercury lamps irradiated at 306 nm in a Panchum PR-2000 photochemical reactor. In total, four major photoproducts derived from each sample were observed from the HPLC chromatogram. The photoproducts were separated and their structures elucidated by various spectroscopic methods. Alternatively, using GC-MS, 11 major photoproducts were observed. A reaction scheme of flurbiprofen in methanol is proposed: the photochemical reaction routes occur mainly via esterification and decarboxylation, followed by oxidation with singlet oxygen to produce a ketone, alcohols and other derivatives.     

Photolysis of polymers using the medium pressure mercury lamp: Part 3—Photolysis of poly(2-ethylhexyl acrylate), alone and in presence of benzoin

The photolysis of poly(2-ethylhexyl acrylate) (P2EHA) has been studied using techniques recently devised for the use of polymer films on metal supports. Condensable volatile products have been identified and measured quantitatively for various times of irradiation and the development of crosslinking has been followed by sorption measurements using a radioactive solvent and a non-solvent medium. The effect of a low concentration of benzoin on the photolysis reaction has also been examined.The photolysis products are as expected from the general scheme of polyacrylate photolysis given by Fox et al., comprising carbon dioxide, alkane, alkene, alcohol, aldehyde and formate. No additional materials have been observed. Crosslinking occurs much more slowly in the case of P2EHA than for PMA photolysis: this is attributed to the effect of the bulky branched side group in hindering macroradical combination. A greater proportion of short chain fragments is observed. Benzoin retards crosslinking and the production of volatiles.     

Structural elucidation of disinfection by-products in treated drinking water

Two unusual disinfection by-products have been detected periodically in the gas chromatography/mass spectrometry (GC/MS) characterization analyses of semi-volatile organics in treated drinking water. The electron ionization (EI) mass spectra contained mono-chlorinated and mono-brominated ions at m/z 107/109 and 151/153, respectively. Library searching techniques suggested mono-halogenated butanol structures but no matches could be found. Positive ion chemical ionization (CI) spectra contained mono-chlorinated and mono-brominated ions at m/z 105/107 and 149/151, respectively. No [M + H]+ ions were initially observed. Accurate mass measurements confirmed the empirical formulae for the significant ions in the EI spectra and the mono-halogenated butanol structures. Further CI experiments with other reagent gases and instruments revealed possible molecular weights of 139 and 183 Da, respectively. Tandem mass spectrometry (MS/MS) experiments in EI and CI were used to elucidate the fragmentation schemes. The two compounds have been tentatively identified as 1-aminoxy-1-chlorobutan-2-ol and 1-aminoxy-1-bromobutan-2-ol, respectively.     

Structure elucidation of triglycerides by chromatographic techniques. Part 1: Capillary GC of ozonized triglycerides

Structure determination of triglycerides according to their number of unsaturated fatty acids (N.U.F.A.) is more easily achieved after ozonolysis of their mixtures (fats and oils) than by capillary gas chromatographic analysis of the mixture as such. Analyses performed before and after ozonolysis of cocoa buttel, hazelnut oil, and a mixture of both fats illustrate the potential of this approach to the structure elucidation of triglycerides by chromatographic techniques.     

Structural elucidation of propargylated products of 3-substituted-1,2,4-triazole-5-thiols by NMR techniques

Propargylation of 3-substituted-1,2,4-triazole-5-thiols, which predominantly exist as their thione tautomers, was carried out with the view to synthesize different heterocycles and study their biological activity. Three different products namely, a mono S-propargyl and two S,N-dipropargyl regioisomers, arising from N1/N2 substitution, were isolated and characterized. Unambiguous structural elucidation of the regioisomers of S,N-dipropargyl derivatives was achieved by means of (13)C-(1)H HMBC technique. The proportion of the regioisomers was found to vary with the substituent on the 1,2,4-triazole thiols. No product corresponding to N4 substitution was isolated from any of the reactions carried out.     

Photolysis of 3-nitrophenyl azide: Trapping the reactive intermediates

Irradiation of 3-nitrophenyl azide gives four trappable intermediates; the singlet nitrene, two isomeric dehydroazepines, and the triplet nitrene.     

Vapor pressures of non-aqueous electrolyte solutions. Part 1. Alkali metal salts in methanol

Precise vapor pressure data for solutions of NaCl, NaBr, NaI, NaClO₄, KBr, KI, RbI, and CsI in methanol at 25°C in the concentration range 0.02m (mol-kg^–1)0.7 are communicated and discussed. Measurements were carried out by procedures and equipment known to produce data of high precision. Polynomials of fourth degree in molalities are given for the vapor pressure of methanol solutions which can be used for calculating precise reference values as needed in indirect methods. Osmotic coefficients were calculated by taking into account the second virial coefficient of methanol vapor. Discussion of the data is based on the chemical model of electrolyte solutions taking into account short range interactions. Ion-pair association constants are compared to those of conductance measurements.     

Structural elucidation of hyaluronic acid gels after heat sterilisation

The influence of heat sterilisation and hyaluronic acid (HA) concentration on the micro- and macrostructure of HA hydrogels was investigated. HA hydrogels of different concentrations were prepared and heat sterilised. The microstructures of the polymer gels were characterised by positron annihilation lifetime spectroscopy (PALS) based on their ortho-positronium lifetime values and distributions, while their macrostructures were characterised by rheological measurements. As expected, the heat sterilisation modified both the micro- and macrostructures of the gels. The HA concentration was also observed to influence the hydrogel structure. At a concentration of 7.5 mg/ml HA, the thermal treatment did not cause significant microstructural changes, and the viscoelastic properties of the treated gels were similar to those of the untreated samples.     

Structure elucidation of triglycerides by chromatographic techniques. Part 2: RP HPLC of triglycerides and brominated triglycerides

The structure determination of triglycerides by RP HPLC is discussed, and the importance of temperature and mobile phase composition demonstrated. The formation of brominated triglycerides followed by RP HPLC analysis allows rapid determination of cocoa butter equivalents (CBE ) in cocoa butter and chocolate products.     

Photolysis of some unsymmetrical phosphinic azides in methanol: Relative migratory aptitudes of alkyl groups and phenyl in the curtius-like rearrangement

When an alkylphenylphosphinic acid PRhP(O)N₃ (R = Me, Et, Prⁱ, or Bu^t) is photolysed in MeOH either the alkyl or phenyl group can migrate from P to N in the Curtius-like rearrangement. The composition of the product shows that migration of the alkyl group R is preferred. However, the preference is not great and decreases as R changes Bu^t→Prⁱ→Et→Me (approx. migratory aptitudes relative to Ph: 2.1, 1.7, 1.3 and 1.2 respectively), probably because the PhP bond is better able to assume the correct conformation for Ph migration when R is less bulky. For t-butylmethylphosphic azide there is very little preference for migration of Bu^t relative to Me. Small amounts of unrearranged products such as Bu^tPhP(O)NHOMe and Bu^tPhP(O)NH₂ are generally produced in the photolyses, together with the methyl phosphinates RPhP(O)OMe (major product when R = Me) resulting from (non-photochemical) solvolysis of the azide.     

Automatic polarographic elucidation of electrode mechanisms by means of a knowledge-based system : Part 1. Sampled d.c. polarography

A knowledge-based system has been developed for the automatic elucidation of electrochemical mechanisms. The system is based on sampled direct current (or Tast) polarography at a dropping mercury electrode as a technique for collecting experimental information and consists of a general expert system shell for the reasoning process, the specific set of rules and experimental modules. The set of rules allows the elucidation of eight relatively simple electrode reaction mechanisms fully atomatically. The computer system has been validated with chemical systems the electrochemical behaviour of which is well established. All parts of the program are written in FORTH language for Apple II microcomputers. This expert system has an open character and new rules can be added to extend the set of mechanisms that can be determined.