Tetramethylammonium fluorochromate(VI): a new and efficient oxidant for organic substrates

Tetramethylammonium fluorochromate(VI), (CH₃)₄N⁺CrO₃F⁻ (TMAFC), was prepared and used for quantitative oxidation of several organic substrates. This new compound is more efficient and has certain advantages over similar oxidizing agents in terms of the amount of oxidant and solvent required, short reaction times and high yields.     

Synthesis of (S)-isoprenoid thiodiphosphates as substrates and inhibitors

Thiolo thiophosphate analogues of isopentenyl diphosphate (IPP), dimethylallyl diphosphate (DMAPP), geranyl diphosphate (GPP), farnesyl diphosphate (FPP), and geranylgeranyl diphosphate (GGPP) were synthesized. Inorganic thiopyrophosphate (SPP(i)) was prepared from trimethyl phosphate in four steps. The tris(tetra-n-butylammonium) salt was then used to convert isopentenyl tosylate to (S)-isopentenyl thiodiphosphate (ISPP). (S)-Dimethylallyl (DMASPP), (S)-geranyl (GSPP), (S)-farnesyl (FSPP), and (S)-geranylgeranyl thiodiphosphate (GGSPP) were prepared from the corresponding bromides in a similar manner. ISPP and GSPP were substrates for avian farnesyl diphosphate synthase (FPPase). Incubation of the enzyme with ISPP and GPP gave FSPP, whereas incubation with IPP and GSPP gave FPP. GSPP was a substantially less reactive than GPP in the chain elongation reaction and was an excellent competitive inhibitor, K(I)(GSPP) = 24.8 microM, of the enzyme. Thus, when ISPP and DMAPP were incubated with FPPase, GSPP accumulated and was only slowly converted to FSPP.     

Dibutyltin-3-hydroxyflavone titrates a dissociable component (cofactor) of mitochondrial ATP synthase: An energy-transfer component linked to the ubiquinone pool

Dibutyltin-3-hydroxyflavone, Bu₂Sn(of), is a new fluorescence probe inhibitor of F₁F₀-ATPase and oxidative phosphorylation which inhibits by titration of an unidentified component of F₀. Its site of action is closely related to that of the trialkyltins and of venturicidin. This F₀ component is part of a pool of this component which is present in the heart mitochondrial inner membrane at levels of 5–7 nmol (mg protein)^?1 [18 ± 3 Bu₂Sn(of) sites per mol F₁F₀-ATPase]. However, ATPase activity in submitochondrial particles is near maximally inhibited by titration of approx. three Bu₂Sn(of) sites per mol F₁F₀-ATPase. Over 60% (60–80%) of the Bu₂Sn(of) interaction sites can be lost during the purification of F₁F₀-ATPase from submitochondrial particles. The number of Bu₂Sn(of) interaction sites in various F₁F₀-ATPase preparations is variable. The high numbers of Bu₂Sn(of) sites per mol F₁F₀-ATPase for heart mitochondria (18–21) and submitochondrial particles (15–19.5) decline in ATP synthase (11–15) to the low values obtained in Complex V (7–10.5) and the minimal values observed in highly purified F₁F₀?ATPase (3.5–5.6), thus indicating a variable dissociable component or cofactor of ATP synthase. The Bu₂Sn(of) interaction site, a component of ATP synthase, is responsive to the redox status of the respiratory chain and the interaction with Bu₂Sn(of) is with the reduced form of this component. Fluorescence titration studies show that this component is in redox equilibrium with the ubiquinone pool of the respiratory chain. It is proposed that this redox component serves as an inhibitor titratable cofactor pool which cycles through an F₀ interaction site (or sites) via a system which serves as an energy-transfer link between the respiratory chain and ATP synthase.     

Screen-printed poly(3,4-ethylenedioxythiophene) (PEDOT): A new electrochemical mediator for acetylcholinesterase-based biosensors

This work describes the use of a PEDOT:PSS-based conductive polymer for designing AChE-based biosensors. The transducers were obtained directly by screen-printing a PEDOT:PSS suspension on the surface of thick film carbon electrodes. The obtained working electrodes showed a high conductivity when compared with electrodes modified with conventional mediators like cobalt phthalocyanine or tetracyanoquinodimethane. The PEDOT:PSS polymer was shown to be suitable for thiocholine oxidation, allowing the measurement of AChE activity at 100 mV vs Ag/AgCl. The high conductivity of PEDOT:PSS allowed the accurate detection of the organophosphate insecticide chlorpyrifos-oxon at concentrations as low as 4 × 10⁻⁹ M, corresponding to an inhibition ratio of 5%.     

Insight into technetium amidoxime complex: oxo technetium(V) complex of N-substituted benzamidoxime as new basic structure for molecular imaging

In search of benzamidoxime (BHam) derivatives that provide a single (99m)Tc-labeled compound of high in vivo stability, we synthesized three N-alkyl compounds of benzamidoxime (BHam) ligand. They provided a single (99m)Tc-labeled compound by ligand exchange reaction of (99m)Tc-glucoheptonate in high radiochemical yields (over 95% at MBHam concentration of 1 × 10(-5) M). (99m)Tc-N-methyl benzamidoxime ((99m)Tc-MBHam) showed higher stability than the parental (99m)Tc-BHam. The complex of this compound with (99g)TcO(3+) ion was prepared, isolated, and characterized by FT-IR and NMR spectra as well as X-ray diffraction. (99g)Tc-MBHam crystallized in an orthorhombic space group Pna2(1) with a = 13.4823(5), b = 15.5410(7), c = 7.7907(3) ?, V = 1632.39(11) ?(3), and Z = 4. The (99g)Tc complex possessed square base pyramid coordination geometry. The equatorial plane was formed by two-amine nitrogen and two-oxime oxygen atoms in trans position, while the oxo core of the technetium(V) occupied the apical position. The (99g)Tc-MBHam proved to be identical with the (99m)Tc-MBHam prepared at the no-carrier-added level by comparison of their HPLC profiles.     

Liquid crystal-gold nanoparticle composite-modified indium tin oxide (ITO) substrates and their electrochemical characterisation

A simple efficient strategy for the simultaneous synthesis and anchoring of liquid crystal (LC)-stabilised gold nanoparticles (NPs) on indium tin oxide (ITO) substrate is described. A monolayer of 3-mercaptopropyltrimethoxy silane (MPS) compound was formed on ITO and quality of the monolayer was assessed using electrochemical techniques namely cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Gold NP preparation was carried out on this monolayer-modified substrate (and on bare ITO), in a single-step reaction, simply by drop-casting a solution containing an appropriate amount of chloroauric acid and a LC compound possessing a terminal amino group, on the MPS monolayer-modified substrate and heating (70degree) for 2-3 min.. The LC compound served as a reducing agent as well as a capping ligand. LC-capped NPs were chemically anchored onto the ITO substrate through bonding to thiol moiety of the MPS. The CV and EIS analysis of the MPS monolayer showed a complete blocking behaviour for the electron transfer across the electrode/electrolyte interface confirming the formation of a high-quality dense compact monolayer. On the other hand, upon immobilisation of LC-gold NP composite on self-assembled monolayer-modified ITO substrates, both CV and impedance studies showed a small current indicating the gold NP-mediated electron transfer, thus confirming the successful immobilisation of NPs.     

(Me3Si)3SiSH: a new radical-based reducing agent

Tris(trimethylsilyl)silanethiol is an effective and useful reducing agent for some organic substrates. The reduction involves free-radical chain reactions.     

"Inject-mix-react-separate-and-quantitate" (IMReSQ) method for screening enzyme inhibitors

Many regulatory enzymes are considered attractive therapeutic targets, and their inhibitors are potential drug candidates. Screening combinatorial libraries for enzyme inhibitors is pivotal to identifying hit compounds for the development of drugs targeting regulatory enzymes. Here, we introduce the first inhibitor screening method that consumes only nanoliters of the reactant solutions and is applicable to regulatory enzymes. The method is termed inject-mix-react-separate-and-quantitate (IMReSQ) and includes five steps. First, nanoliter volumes of substrate, candidate inhibitor, and enzyme solutions are injected by pressure into a capillary as separate plugs. Second, the plugs are mixed inside this capillary microreactor by transverse diffusion of laminar flow profiles. Third, the reaction mixture is incubated to form the enzymatic product. Fourth, the product is separated from the substrate inside the capillary by electrophoresis. Fifth, the amounts of the product and substrate are quantitated. In this proof-of-principle work, we applied IMReSQ to study inhibition of recently cloned protein farnesyltransferase from parasite Entamoeba histolytica. This enzyme is a potential therapeutic target for antiparasitic drugs. We identified three previously unknown inhibitors of this enzyme and proved that IMReSQ could be used for quantitatively ranking the potencies of inhibitors.     

A new sensitive reagent for identifying and determining Cu(2+)

The synthesis of the new long-chain saturated fatty hydrocarbon substituting group compound, N-undecyl-N'-(sodium p-aminobenzenesulfonate)-thiourea (UPT) is described. According to the studies on its analytical performance, it is found that this reagent can be used to identify Cu(2+)(PD 6.3) and determine microamounts of copper (epsilon(300.4 nm)=2.39x10(5) l mol(-1)cm(-1)) in aqueous solution. Both of their sensitivities and selectivity's are better than other common methods [1-3].These new methods are simple and convenient and can provide satisfactory results on samples.     

A facile and one-pot electrochemical method for the synthesis of a new anthraquinonethioether

The reaction of electrochemically generated anthradiquinone as a Michael acceptor with 2-mercaptobenzothiazole and 2- mercaptobenzoxazole,as nucleophiles in ethanol/water mixtures has been studied by means of cyclic voltammetry.Our voltammetric data indicate that produced anthradiquinone participates in Michael addition reaction with nucleophiles and via an ECEC mechanism converts to the new anthraquinonethioether derivatives.Based on an EC mechanism,the observed homogeneous rate constant of the Michael reaction of anthradiquinone with nucleophiles were estimated by comparing the experimental cyclic voltammograms with the digital simulated results.     

A new way for synthesis of phenoxazine and diphenoxazine derivatives via electrochemical method

Electrochemical oxidation of hydroquinone (1a) and 2,3-dimethylhydroquinone (1b) have been studied in the presence of 2-aminophenol (3a) and 2-amino-4-chlorophenol (3b), as nucleophiles in phosphate buffer solution (pH 7.2) using cyclic voltammetry and controlled potential coulometry. We proposed different mechanisms for the electrode process. The products were derived with good yield and purity using controlled-potential electrochemical oxidation of 1a, b in the presence of 3a and 3b at the graphite electrode in an undivided cell.     

An electrochemical reactivation method for solid electrodes used in electrochemical detectors for high-performance liquid chromatography and flow injection analysis

An electrochemical reactivation method for solid electrodes used in electrochemical detectors is optimized for glassy carbon electrodes. Application of a voltage pulse train for 5 min is effective in restoring the response of the electrode after deactivation by organic compounds. Potassium hexacyanoferrate(II) and dl-synephrine were used to test the reactivation of electrodes; 2,6-dihydroxybenzoic acid and urine served to deactivate them. The effects of the amplitude, d.c. level, and frequency of the applied voltage pulse train, as well as the mode of termination, are discussed.     

An efficient method for synthesising unsymmetrical silaketals: substrates for ring-closing, including macrocycle-closing, metathesis

Diisopropylsilyl ethers were activated with N-bromosuccinimide, and reacted with a fluorous-tagged alcohol, to yield tethered substrates for ring-closing metathesis reactions.     

A new sensitive reagent for identifying Ag(+) and Hg(2+)

This paper describes the synthesis of a new reagent: N,N′-difuroyl thiourea for the purpose of improving coordination capacity of thiourea compounds. It has been characterized by IR, UV, MS and ¹H-NMR as well as elemental analytical data. According to the studies on its analytical performance, it is found that this reagent can be used to identify Ag⁺ and Hg²⁺. Both of their sensitivities and selectivities are the best in all methods for the time being. The new methods are simple and convenient, and can provide satisfactory results on synthetic and standard samples.     

Determination of total antioxidant capacity by a new spectrophotometric method based on Ce(IV) reducing capacity measurement

Dietary antioxidants widely found in fruits and vegetables may serve the task of reducing oxidative damage in humans induced by free radicals and reactive oxygen species under ‘oxidative stress’ conditions. The aim of this work is to develop a simple, low-cost, sensitive, and diversely applicable indirect spectrophotometric method for the determination of total antioxidant capacity of several plants. The method is based on the oxidation of antioxidants with cerium(IV) sulfate in dilute sulfuric acid at room temperature. The Ce(IV) reducing capacity of the sample is measured under carefully adjusted conditions of oxidant concentration and pH such that only antioxidants and not other organic compounds would be oxidized. The spectrophotometric determination of the remaining Ce(IV) was performed after completion of reaction with antioxidants. Quercetin and gallic acid were used as standards for flavonoids and phenolic acids, respectively, and results of antioxidant measurements were reported as trolox equivalents. The developed procedure was successfully applied to the assay of total antioxidant capacity due to simple compounds such as trolox, quercetin, gallic acid, ascorbic acid, catechin, naringin, naringenin, caffeic acid, chlorogenic acid, ferulic acid, and p-coumaric acid, and due to phenolic acids and flavonoids in the arieal parts of nettle (Urtica Dioica L.). Blank correction of significantly absorbing plant extracts at 320 nm could be made with the aid of spectrophotometric titration. Plant selection was made in respect to high antioxidant content, and extraction was made with water. The proposed method was reproducible, and the trolox equivalent antioxidant capacities (TEAC coefficients) of the tested antioxidant compounds were correlated to those found by reference methods such as ABTS and CUPRAC. Since the TEAC coefficients found with the proposed method of naringin-naringenin and rutin-catechin pairs were close to each other, this Ce(IV)-based assay probably caused the simultaneous hydrolysis of flavonoid glycosides to the corresponding aglycones and their subsequent oxidation such that the hydrolysis products exhibed antioxidant capacities roughly proportional the number of -OH groups contained in a molecule.     

Vinyl tris(trimethylsilyl)silanes: substrates for Hiyama coupling

The oxidative treatment of vinyl tris(trimethylsilyl)silanes with hydrogen peroxide in aqueous sodium hydroxide in tetrahydrofuran generates reactive silanol or siloxane species that undergo Pd-catalyzed cross-couplings with aryl, heterocyclic, and alkenyl halides in the presence of Pd(PPh₃)₄ and tetrabutylammonium fluoride. Hydrogen peroxide and base are necessary for the coupling to occur while activation of the silanes with fluoride is not required. The conjugated and unconjugated tris(trimethylsilyl)silanes serve as good cross-coupling substrates. The (E)-silanes undergo coupling with retention of stereochemistry while coupling of (Z)-silanes occurred with lower stereoselectivity to produce an E/Z mixture of products.     

An enzyme biosensor based on beta-galactosidase inhibition for electrochemical detection of cadmium (II) and chromium (VI)

The focus of this article is the development and optimisation of a simple, sensitive, selective biosensor for the detection of heavy metals, through inhibition of β-galactosidase (β-gal) from Aspergillus oryzae after its immobilisation on an electrochemical transducer by cross-linking with glutaraldehyde. The inhibition of β-gal by Cd(II) and Cr(VI) was demonstrated by the decrease of β-gal activity monitored by the conductometric signal. Under optimal conditions, the developed voltammetric and impedimetric biosensor, based on the specific interaction of metallic ions with beta-galactosidase that increases the electron transfer of the redox probe, presented a wide range of linearity. Detection limits of 3.12 × 10^–10 M (91.7 ng/L) were obtained, using both techniques, for Cr(VI). For Cd(II) detection limits were 2.85 × 10^–8 M (6.95 µg/L) using EIS and 3.22 × 10^–11 M (7.61 ng/L) using square wave voltammetry (SWV).     

Pharmacophore modeling and in silico screening for new P450 19 (aromatase) inhibitors

Cytochrome P450 19 (P450 19, aromatase) constitutes a successful target for the treatment of breast cancer. This study analyzes chemical features common to P450 19 inhibitors to develop ligand-based, selective pharmacophore models for this enzyme. The HipHop and HypoRefine algorithms implemented in the Catalyst software package were employed to create both common feature and quantitative models. The common feature model for P450 19 includes two ring aromatic features in its core and two hydrogen bond acceptors at the ends. The models were used as database search queries to identify active compounds from the NCI database.     

Synthesis and electrochemical studies of ferrocene-dithiafulvalenes (Fc-DTF) and 1,1′-bis(dithiafulvalenyl)ferrocene (DTF-Fc-DTF). An approach towards new conducting organic materials

Novel π-conjugated donor compounds based on the strong electron-donating ferrocene moiety and dithiafulvalene donors exhibited increased electron donor ability. The ferrocenylketones 4a,b, 5, 8 and 9 were synthesized via described methods, and allowed to react with 2-dimethoxyphosphinyl-1,3-benzodithiole (13) in the presence of n-BuLi at −78°C in dry THF to afford the corresponding ferrocene-dithiafulvalenes 14a,b, 18, 19 and 1,1′-bis(benzo-1,3-dithiol-2-ylidene)ethyl]ferrocene (15). Electrochemical properties of these new donor compounds were studied using cyclic voltammetry (CV) and UV-Vis spectra. CV and absorption spectra of the new compounds were studied in comparison with ferrocene (6) and dibenzo-tetrathiafulvalene DB-TTF 3. Two-electron and three-electron redox behaviors were observed as two waves. The absorption spectra showed a red-shift with a slight increase in the absorption intensities.