Qualitative gas chromatographic analysis of bacterial amines as their Schiff bases and other derivatives

Summary Columns of SE-30 and OV-17 on Chromosorb W, Apiezon N on Chromosorb G and Tenax-GC porous polymer were compared for their ability to separate bacterial amines converted to carbethoxy, dinitrophenyl, trimethylsilyl, Schiff base and fluorinated Schiff base derivatives.Tenax-GC performed less well than the other packings with respect to the number of plates and peak resolution. Dinitrophenyl and trimethylsilyl derivatives were both unsatisfactory for analysis of bacterial amines. Schiff bases and their fluorinated derivatives were found to be the most suitable. However, the former were preferred as the use of fluorinated Schiff bases confered little advantage when a flame ionization detector was employed. A maximum of 16 amines was separated, using columns of OV17 on Chromosorb W programmed from 110 °C to 280 °C at 5.5 °C min^–1 after an initial holding time of 6 min. The application of the method to analysis of cultures ofProteus mirabilis yielded two amines tentatively identified asiso-butylamine andiso-amylamine.     

Analysis of naturally occurring α-acetotriacylglycerides by gas chromatography — chemical ionization mass spectrometry

The seed oils of three Maytenus species have been examined by high temperature GLC using SOP-50 (methoxy-terminated) and OV-225-OH (OH-terminated) glasscapillary columns. The main compounds (71–76%) could be identified as α-mono-acetotriacylglycerols by a combination of high temperature GLC-MS in negative chemical ionization mode with a CH₄/N₂O mixture as reactant gas and other spectroscopical methods (infrared, ¹H- and ¹³C-nuclear magnetic resonance spectroscopy). The OV-225-OH phase demonstrated better separation properties that the SOP-50 phase for this substance class and up to eight species of α-monoacetotriacylglycerols could be separated. The content of usual triacyclglycerols was below 1%. The results of the analysis of the individual fatty acids as their methyl esters by GC and GC-MS are also presented.     

Deactivation of silica surfaces with a silanol-terminated polysiloxane; structural sharacterization by inverse gas chromatography and solid-state NMR

Retention gape deactivated with Silicone OV-1701-OH show good chromatographic performance and remarkable stability against water induced stationary phase degradrdation. In an attempt to better understand the findamentals off the deactivation process using silanol terminated polysiloxanes, a fumed silica was deactivated with Silicon OV-1701-OH. In contrast to fused silic capillaries, fumed silica (Aerosil A-200) can be studied by ²⁹Si cross-polarization magic-angle-spinning (CPMAS) NMR, thus serving as a model substrate for fused silica. Retention data from inverse gas chromatography at infinite dilurion and ²⁹Si CP MAS NMR data of five Aerosil phases, differing in residual silanol surface concentration, are correlated with the aim of validating this approach for stationary phase characterization. A comparatively detailed model of the deactivating polymer layer that explains the observed absorption activities is deduced. Surface silanols are shown to play a key role in the polymer layer, the structure of which is of primary importance for the absorption behavior after deactivation. Contrary to common belief, the absolute silanol surface concentration after deativation is only of secondary importance for the overall absorption activity. High silanol surface concentrations enhance degradation of the polysiloxane chains into small cyclic fragments as well as subsequent absorption and immobolization to the silica substrate surface. The mobility of linear polysiloxane chains in the kHz regime (as determined bby NMR cross-polarization dynamics) appears to determine the extent which the residual silanols are accessible for analytes. It is therefore anticipated that there is an optimum silanol surface concentration of fused silica surfaces to be deactivated with silanol terminated polysiloxanes; it should be lazrge enough to adsord polymer fragments, but not large to avoid excessive residual silanol activity.     

Hydrolytic vs. Nonhydrolytic Sol-Gel in Preparation of Mixed Oxide Silica–Alumina Catalysts for Esterification

The development of green and sustainable materials for use as heterogeneous catalysts is a growing area of research in chemistry. In this paper, mesoporous SiO₂-Al₂O₃ mixed oxide catalysts with different Si/Al ratios were prepared via hydrolytic (HSG) and nonhydrolytic sol-gel (NHSG) processes. The HSG route was explored in acidic and basic media, while NHSG was investigated in the presence of diisopropylether as an oxygen donor. The obtained materials were characterized using EDX, N₂-physisorption, powder XRD, ²⁹Si, ²⁷Al MAS-NMR, and NH₃-TPD. This approach offered good control of composition and the Si/Al ratio was found to influence both the texture and the acidity of the mesoporous materials. According to ²⁷Al and ²⁹Si MAS NMR analyses, silicon and aluminum were more regularly distributed in NHSG samples that were also more acidic. Silica–alumina catalysts prepared via NHSG were more active in esterification of acetic acid with n-BuOH.     

Quantitative LAMMA analysis of biological specimens I. Standards. II. Isotope labeling

Summary Besides a remarkably high sensitivity for light elements, laser microprobe mass spectroscopy offers two main advantages for microprobe analysis: 1) the possibility to obtain data of relatively high precision and 2) the ability to discriminate isotopes. This opens the possibility to use cold isotopes as atomic labels to study cellular or subcellular kinetics of ions or labelled organic compounds. In this study photoreceptor cells were labelled with ⁴⁴Ca²⁺ prior to LAMMA analysis to monitor Ca²⁺ uptake and/or Ca²⁺ accumulation from extracellular sources into intracellular compartments such as the various pigment granula present in these photoreceptors.As in other microprobe techniques also LAMMA analysis requires internal standards for quantitative work. For this purpose thin films of inorganic material were shown to be useful standards when deposited (in vacuum) directly onto the specimen to be analyzed. Some metals and dielectrica have been tested for their possible suitability for standardisation procedures. Even though metals like Pt, Ag, Au, Al are excellent for thin film production, they seem to be less useful for the present purpose because their threshold for laser induced perforation and ion production is rather different from that of the specimen material. However, thin film deposits of some dielectric materials such as MgF₂ turned out to be more suitable to serve as an internal standard for plastic embedded biological material in LAMMA analysis.

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Quantitative LAMMA-Analyse biologischer Proben. I. Standards. II. Isotopenmarkierung

     

Histochemical and Phytochemical Analysis of Lamium album subsp. album L. Corolla: Essential Oil,Triterpenes, and Iridoids

The aim of this study was to conduct a histochemical analysis to localize lipids, terpenes, essential oil, and iridoids in the trichomes of the L. album subsp. album corolla. Morphometric examinations of individual trichome types were performed. Light and scanning electron microscopy techniques were used to show the micromorphology and localization of lipophilic compounds and iridoids in secretory trichomes with the use of histochemical tests. Additionally, the content of essential oil and its components were determined using gas chromatography-mass spectrometry (GC-MS). Qualitative analyses of triterpenes carried out using high-performance thin-layer chromatography (HPTLC) coupled with densitometric detection, and the iridoid content expressed as aucubin was examined with spectrophotometric techniques. We showed the presence of iridoids and different lipophilic compounds in papillae and glandular and non-glandular trichomes. On average, the flowers of L. album subsp. album yielded 0.04 mL/kg of essential oil, which was dominated by aldehydes, sesquiterpenes, and alkanes. The extract of the L. album subsp. album corolla contained 1.5 × 10⁻³ ± 4.3 × 10⁻⁴ mg/mL of iridoid aucubin and three triterpenes: oleanolic acid, β-amyrin, and β-amyrin acetate. Aucubin and β-amyrin acetate were detected for the first time. We suggest the use of L. album subsp. album flowers as supplements in human nutrition.     

Chromatographic properties of various polysiloxane stationary phases for separation of 2,3,7,8–chloro-substituted dibenzo-p-dioxin and dibenzofuran isomers–a systematic comparison

Glass capillaries coated with four crosslinked and surface-bonded OH-terminated polysiloxanes [PS 347.5, OV-17-OH, OV-225-OH, and OV-240-OH] were compared with commonly used methyl-terminated SP-2330-coated columns with respect to their selectivity for the separation of 2,3,7,8-chloro-substituted dibenzo-p-dioxins and dibenzofurans. The methyl- and phenyl-substituted phases [PS 347.5 and OV-17-OH] exhibit only moderate isomer selectivity which limits their applicability in this field. The examined 3-cyanopropyl-substituted phases [OV-225-OH, OV-240-OH, and SP-2330] allow complete separation of all 2,3,7,8-chlorosubstituted PCDDs and PCDFs. With SP-2330 longer columns are required (50 m) for baseline separation of critical groups of isomers. OV-225-OH was found to be the most suitable phase as to isomer selectivity. In comparison to SP-2330, the analysis times can be reduced by a factor of two.     

Two Key Amino Acids Variant of α-l-arabinofuranosidase from Bacillus subtilis Str. 168 with Altered Activity for Selective Conversion Ginsenoside Rc to Rd

α-l-arabinofuranosidase is a subfamily of glycosidases involved in the hydrolysis of l-arabinofuranosidic bonds, especially in those of the terminal non-reducing arabinofuranosyl residues of glycosides, from which efficient glycoside hydrolases can be screened for the transformation of ginsenosides. In this study, the ginsenoside Rc-hydrolyzing α-l-arabinofuranosidase gene, BsAbfA, was cloned from Bacilus subtilis, and its codons were optimized for efficient expression in E. coli BL21 (DE3). The recombinant protein BsAbfA fused with an N-terminal His-tag was overexpressed and purified, and then subjected to enzymatic characterization. Site-directed mutagenesis of BsAbfA was performed to verify the catalytic site, and the molecular mechanism of BsAbfA catalyzing ginsenoside Rc was analyzed by molecular docking, using the homology model of sequence alignment with other β-glycosidases. The results show that the purified BsAbfA had a specific activity of 32.6 U/mg. Under optimal conditions (pH 5, 40 °C), the kinetic parameters K_m of BsAbfA for pNP-α-Araf and ginsenoside Rc were 0.6 mM and 0.4 mM, while the K_cat/K_m were 181.5 s⁻¹ mM⁻¹ and 197.8 s⁻¹ mM⁻¹, respectively. More than 90% of ginsenoside Rc could be transformed by 12 U/mL purified BsAbfA at 40 °C and pH 5 in 24 h. The results of molecular docking and site-directed mutagenesis suggested that the E173 and E292 variants for BsAbfA are important in recognizing ginsenoside Rc effectively, and to make it enter the active pocket to hydrolyze the outer arabinofuranosyl moieties at C₂₀ position. These remarkable properties and the catalytic mechanism of BsAbfA provide a good alternative for the effective biotransformation of the major ginsenoside Rc into Rd.     

Ethidium Binding to Salmonella enterica ser. Typhimurium Cells and Salmon Sperm DNA

Bacterial resistance to antibiotics due to increased efficiency of the efflux is a serious problem in clinics of infectious diseases. Knowledge of the factors affecting the activity of efflux pumps would help to find the solution. For this, fast and trustful methods for efflux analysis are needed. Here, we analyzed how the assay conditions affect the accumulation of efflux indicators ethidium (Et⁺) and tetraphenylphosphonium in Salmonella enterica ser. Typhimurium cells. An inhibitor phenylalanyl-arginyl-β-naphtylamide was applied to evaluate the input of RND family pumps into the total efflux. In parallel to spectrofluorimetric analysis, we used an electrochemical assessment of Et⁺ concentration. The results of our experiments indicated that Et⁺ fluorescence increases immediately after the penetration of this indicator into the cells. However, when cells bind a high amount of Et⁺, the intensity of the fluorescence reaches the saturation level and stops reacting to the accumulated amount of this indicator. For this reason, electrochemical measurements provide more trustful information about the efficiency of efflux when cells accumulate high amounts of Et⁺. Measurements of Et⁺ interaction with the purified DNA demonstrated that the affinity of this lipophilic cation to DNA depends on the medium composition. The capacity of DNA to bind Et⁺ considerably decreases in the presence of Mg²⁺, Polymyxin B or when DNA is incubated in high ionic strength media.     

Terpyridine-Functionalized Calixarenes: Synthesis,Characterization and Anion Sensing Applications

Lanthanide complexes have been developed and are reported herein. These complexes were derived from a terpyridine-functionalized calix[4]arene ligand, chelated with Tb³⁺ and Eu³⁺. Synthesis of these complexes was achieved in two steps from a calix[4]arene derivative: (1) amide coupling of a calix[4]arene bearing carboxylic acid functionalities and (2) metallation with a lanthanide triflate salt. The ligand and its complexes were characterized by NMR (¹H and ¹³C), fluorescence and UV-vis spectroscopy as well as MS. The photophysical properties of these complexes were studied; high molar absorptivity values, modest quantum yields and luminescence lifetimes on the ms timescale were obtained. Anion binding results in a change in the photophysical properties of the complexes. The anion sensing ability of the Tb(III) complex was evaluated via visual detection, UV-vis and fluorescence studies. The sensor was found to be responsive towards a variety of anions, and large binding constants were obtained for the coordination of anions to the sensor.     

Chelate von Chinolin-8-ol — Derivaten. XI. Eigenschaften und Struktur von Nickelchelaten alkyl-substituierter Chinolin-8-ole bzw. Chinolin-8-thiole

Reactions of 1,1,3,3-Tetrakis(dimethylamino)-1λ⁵,3λ⁵-diphosphete with N? H and P? H Acidic Compounds 1,1,3,3-Tetrakis(dimethylamino)-1λ⁵,3λ⁵-diphosphete, 1 , reacts with aniline to give by opening of the ring 2,2,4,4-tetrakis(dimethylamino)-1-phenyl-1,2λ⁵,4λ⁵-azadiphosphapenta-1,3-diene, 2 , with p-CN? C₆F₄? NH₂ the product is 1-(4-cyano-2,3,5,6-tetrafluorophenyl)-2,2,4,4-tetrakis(dimethylamino)-1,2λ⁵,4λ⁵-azadiphosphapenta-1,3-diene, 3 . t-Butylamine or diethylamine do not react with 1 . Mesitylphosphane opens the ring system 1 forming by reduction of one phosphorus atom {[bis(dimethylamino)phosphanyl]methylidene}bis(dimethylamino)methylphosphorane, 4 . The same product 4 is obtained by reaction with phenylphosphane. The reaction products 2–4 are characterized by their nmr, mass, and ir spectra. Their way of formation is discussed. In 4 a ⁵J(PH), in 3 a ⁷J(CF) long range coupling constant could be identified.     

Combined liquid chromatography-coulometric detection and microextraction by packed sorbent for the plasma analysis of long acting opioids in heroin addicted patients

The sublingual combination of buprenorphine and naloxone (Suboxone^®) and Methadone Maintenance Therapy have been found effective in treating heroin addiction. A new analytical method suitable for the simultaneous determination of buprenorphine, norbuprenorphine, methadone and naloxone in human plasma by means of liquid chromatography with coulometric detection has been developed. The chromatographic separation was achieved with a phosphate buffer–acetonitrile mixture as the mobile phase on a cyano column. The monitoring cell of the coulometric detector was set at an oxidation potential of +0.600 V. A rapid clean-up procedure of the biological samples using a microextraction by packed sorbent technique has been implemented, employing a C8 sorbent inserted into a syringe needle. The extraction yield values were satisfactory for all analytes (>85%). The calibration curves were linear over a range of 0.25–20.0 ng mL⁻¹ for buprenorphine and norbuprenorphine, 3.0–1000.0 ng mL⁻¹ for methadone and 0.13–10.0 ng mL⁻¹ for naloxone. The sensitivity was also high with limits of detection of 0.08 ng mL⁻¹ for both buprenorphine and norbuprenorphine, 0.9 ng mL⁻¹ for methadone and 0.04 ng mL⁻¹ for naloxone. The intraday and interday precision data were always satisfactory.The method was successfully applied to plasma samples obtained from former heroin addicts treated with opioid replacement therapy.     

The use of a gold-containing membrane for ion-sensitive electrodes and their application in analysing systems. I

Summary Pellets of a material, resulting from the precipitation of silver salts (AgCl, AgBr, AgI and Ag₂S) onto finely divided gold (particle size less than 3 m) showed a selective ion-sensitive behaviour for halogens, silver and sulphide, resp. Silver iodide on gold turned out to be sensitive for cyanide as well.Electrodes with this type of membrane combined a low redox sensitivity with good mechanical strength and chemical resistance and with a low membrane impedance (1–500 kOhm mm^–1 as a maximum). Settling times vary in the range of 0.1–10 sec. A linear Nernstian response was shown in the ranges 10^–1×10^–5 M (chloride), 10^–1 –10^–6 M (bromide, iodide, cyanide) and 10^–1–10^–7 M (silver, sulphide). In order to obtain good cleaning facilities for heavy duty applications (e. g. measurements in slurries) the membrane pellet was mounted in the electrode body in a way that its cylindrical side contacted the solution to be measured or monitored.

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Verwendung einer goldhaltigen Membran für ionensensitive Elektroden und ihre Anwendung in analytischen Systemen. IHerstellung und Charakteristik ionensensitiver Elektroden

Zusammenfassung Tabletten eines Materials, das durch Fällung von Silbersalzen (AgCl, AgBr, AgJ und Ag₂S) auf fein-pulverisiertem Gold (Teilchengröße weniger als 3 m) entstand, wurden zur Fertigung selektiver ionen-sensitiver Elektroden für Halogene, Silber und Sulfid eingesetzt. Silberjodid auf Gold war auch für Cyanid empfindlich. Diese Elektroden vereinigen eine niedrige Redox-Empfindlichkeit mit einer guten mechanischen und chemischen Stabilität sowie einer niedrigen Elektrodenimpedanz (Höchstwert: 1–500 kOhm mm^–1). Der Signalwert bildet sich in 0,1–10 sec. Das Elektrodensignal ist proportional der Ionenaktivität gemäß dem Nernstschen Gesetz im Bereich von 10^–1–3·10^–5 M (Chlorid), 10^–1–10^–6 M (Bromid, Jodid, Cyanid) und 10^–1–10^–7 M (Silber, Sulfid). Die Tablette ist im Elektrodengehäuse so montiert, daß nur die cylindrische Außenseite von der zu messenden Flüssigkeit berührt wird. Die Reinigung der Elektrode im anspruchsvollen Dauerbetrieb (z. B. kontinuierliche Messungen in Festkörper enthaltenden Abwässern) wird durch diese Anordnung erheblich vereinfacht.

     

High performance liquid chromatography with electrochemical detection. 1: Separation of Cannabis constituents and quantitation of Δ9 tetrahydrocannabinol

A simple, isocratic high performance liquid chromatography system (HPLC) with electrochemical detection (EC) was used to study Cannabis constituents. Several Cannabis extracts and reference standards were examined. A total of eleven constituents were separated, and three major cannabinoids; Δ⁸, Δ⁹ tetrahydrocannabinol (THC) and cannabidiol (CBD) were identified. A linear relationship was established for the quantitation of the halucinogenic constituent Δ⁹ THC. Minor contaminants in Δ⁹ THC reference standard, which were not detected by gas chromatography (GC) were detected for the first time. The detection limits of Δ⁹ THC and related cannabinoids were in the low nanogram range (2–20 ng).     

Tantalum(v) oxoalkoxides. Synthesis and structure

Anodic oxidation of tantalum in isopropyl alcohol or prolonged reflux of an alcohol solution of Ta(OPrⁱ)₅ afford crystalline oxoisopropoxide Ta₂O(OPrⁱ)₈ · PrⁱOH (1). In its molecule, two octahedra about Ta atoms are linkedvia the shared edge [(OPrⁱ)O]. Compound1 is the first example of oxoalkoxide containing such a small number of metal atoms. Unlike the known polynuclear molecules M _n O _m (OR) _p , oxoalkoxide1 is stable in solutions; on transition to the gas phase, this compound is desolvated to form a very stable molecule Ta₂O(OPrⁱ)₈ (apparently, consisting of two octahedra with a shared edge). According to the data of mass spectrometry, analogous molecules exist in the gas phase over Ta(OAlk)₅ (Alk = Me, Et, Prⁱ, or Bu¹¹). When compound1 is heated invacuo (10^–2–10^–3 Torr), Ta(OPrⁱ)₅ is sublimated. Crystals of Ta₇O₉(OPrⁱ)₁₇ (2) were formed upon prolonged storage of solutions of1 in PrⁱOH. Heptanuclear molecule2 consists of two [Ta₄] tetrahedra with a shared vertex. These tetrahedra are additionally linked togethervia one ₃-oxo and two ₂-OPrⁱ groups. Complex2 is a representative of heptameric oxoalkoxides of a new structural type.Deceased in I995.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–131, January, 1996.     

Spectrophotometric Determination of Molybdenum(VI) as a Ternary Complex with 4-Nitrocatechol and Benzalkonium Chloride

A new liquid—liquid extraction system for molybdenum(VI) was studied. It contains 4-nitrocatechol (4NC) as a complexing chromogenic reagent and benzalkonium chloride (BZC) as a source of heavy cations (BZ⁺), which are prone to form chloroform-extractable ion-association complexes. The optimum conditions for the determination of trace molybdenum(VI) were found: concentrations of 4NC and BZC (7.5 × 10⁻⁴ mol dm⁻³ and 1.9 × 10⁻⁴ mol dm⁻³, respectively), acidity (3.75 × 10⁻² mol dm⁻³ H₂SO₄), extraction time (3 min), and wavelength (439 nm). The molar absorptivity, limit of detection, and linear working range were 5.5 × 10⁴ dm³ mol⁻¹ cm⁻¹, 5.6 ng cm⁻³, and 18.6–3100 μg cm⁻³, respectively. The effect of foreign ions was examined, and the developed procedure was applied to the analysis of synthetic mixtures and real samples (potable waters and steels). The composition of the extracted complex was 1:1:2 (Mo:4NC:BZ). Three possible structures of its anionic part [Mo^VI(4NC)O₂(OH)₂]²⁻ were discussed based on optimizations at the B3LYP/3-21G level of theory, and simulated UV/Vis absorption spectra were obtained with the TD Hamiltonian.     

Stereoisomeric Tris-BINOL-Menthol Bulky Monophosphites: Synthesis,Characterisation and Application in Rhodium-Catalysed Hydroformylation

Four stereoisomeric monoether derivatives, based on axially chiral (R)- or (S)-BINOL bearing a chiral (+)- or (−)-neomenthyloxy group were synthesised and fully characterised by NMR spectroscopy and X-ray crystallography. The respective tris-monophosphites were thereof prepared and fully characterised. The coordination ability of the new bulky phosphites with Rh(CO)₂(acac), was attested by ³¹P NMR, which presented a doublet in the range of δ = 120 ppm, with a ¹J(¹⁰³Rh-³¹P) coupling constant of 290 Hz. The new tris-binaphthyl phosphite ligands were further characterised by DFT computational methods, which allowed us to calculate an electronic (CEP) parameter of 2083.2 cm⁻¹ and an extremely large cone angle of 345°, decreasing to 265° upon coordination with a metal atom. Furthermore, the monophosphites were applied as ligands in rhodium-catalysed hydroformylation of styrene, leading to complete conversions in 4 h, 100% chemoselectivity for aldehydes and up to 98% iso-regioselectivity. The Rh(I)/phosphite catalytic system was also highly active and selective in the hydroformylation of disubstituted olefins, including (E)-prop-1-en-1-ylbenzene and prop-1-en-2-ylbenzene.     

A Novel Enzyme Membrane Electrode for Oxalate Determination in Foodstuffs

Abstract

An enzyme membrane electrode usable for the assay of oxalate in foodstuffs is described. A commercially available preactivated polyamide membrane was used for the immobilization of oxalate oxidase. The bioactive disk thus obtained was associated with an amperometric transducer. The resulting self-contained enzyme electrode wich allows oxalate determination in various materials with minimal pretreatment exhibits a linear calibration ranging from 10–7 M and 10–4 M in the cell. The response-time was comprised between 20 seconds and 1 minute, depending on the oxalate content in the sample. The electrode-response was very stable for at least 4 months, a period during which more than 150 assays were performed.

The results obtained with several food materials were in good agreement with those obtained with the conventional spectrophotometric method. Assays were also performed with a microprocessor-based analyzer normally used for glucose measurements with a glucose oxidase electrode When the analyzer is equipped with an oxalate oxidase membrane, without further setting, oxalate can be determined in the range 5 10^?3 M-10^?1 M in the sample.     

Metallkomplexe von Farbstoffen. VI. Phosphan-Nickel-, Palladium- und Platin-Komplexe sowie Pentamethyl-cyclopentadienyl-Rhodium- und Iridium-Komplexe von Bis(2-hydroxyaryl)azo-Farbstoffen

Metal Complexes of Dyes. Phosphine-Nickel, Palladium, Platinum Complexes and Pentamethylcyclopentadienyl Rhodium and Iridium Complexes of 2,2′-Dihydroxyazoarenes The terdentate dianions of 2,2′-dihydroxyazobenzene (L¹H), 1-(2-hydroxy-4-nitrophenylazo)-2-naphthol (L²H), 1-(2-hydroxy-5-nitrophenylazo)-2-naphthol (L³H) and 1-phenyl-3-methyl-4-(2-hydroxy-5-nitrophenylazo)-5-pyrazolone (L⁴H) form with chloro bridged complexes [(R₃P)MCl₂]₂ (M = Pd, Pt; R = Ph, nBu), [(n⁵-C₅Me₅)MCl₂]₂ (M = Rh, Ir) and with (nBu₃P)₂NiCl₂ the metal dye complexes (R₃P)ML (M = Ni, Pd, Pt) and (C₅Me₅)ML (M = Rh, Ir). The structures of (Ph₃P)PtL¹ and (nBu₃P)PdL³ have been determined by X-ray diffraction. For the complexes (n⁵-C₅Me₅)ML (M = Rh, Ir) with asymmetric metal centers two diastereoisomers are detected by nmr spectroscopy which points to the ?hydrazone”? form of the azo ligand with a pyramidalized N-atom.     

Integrated 3D-QSAR,molecular docking,and molecular dynamics simulation studies on 1,2,3-triazole based derivatives for designing new acetylcholinesterase inhibitors

Alzheimer’s disease (AD) is a multifactorial and polygenic disease. It is the most prevalent reason for dementia in the aging population. A dataset of twenty-six 1,2,3-triazole-based derivatives previously synthetized and evaluated for acetylcholinesterase inhibitory activity were subjected to the three-dimensional quantitative structure-activity relationship (3D-QSAR) study. Good predictability was achieved for comparative molecular field analysis (CoMFA) (Q² = 0.604, R² = 0.863, r_ext² = 0.701) and comparative molecular similarity indices analysis (CoMSIA) (Q² = 0.606, R² = 0.854, r_ext² = 0.647). The molecular features characteristics provided by the 3D-QSAR contour plots were quite useful for designing and improving the activity of acetylcholinesterase of this class. Based on these findings, a new series of 1,2,3-triazole based derivatives were designed, among which compound A1 with the highest predictive activity was subjected to detailed molecular docking and compared to the most active compound. The selected compounds were further subjected to 20 ns molecular dynamics (MD) simulations to study the comparative conformation dynamics of the protein after ligand binding, revealing promising results for the designed molecule. Therefore, this study could provide worthy guidance for further experimental analysis of highly effective acetylcholinesterase inhibitors.