Phenyl Borate Research Articles

L‐Tryptophan methyl ester Evokes Endothelium‐, Serotonin‐Independent Biphasic Vasoconstrictor and Vasodilator Responses in Rat Mesenteric Arterioles

The vascular effects of L‐tryptophan (L‐W) are unknown. The in vitro responses to L‐W and its cell permeant analog, L‐W methyl ester (L‐Wme), were compared in third order branches of mesenteric arterioles of 12 week old male Sprague Dawley rats. While L‐W had no effect, L‐Wme evoked concentration‐dependent vasoconstriction (10 – 160 μM) followed by vasodilatation (300 μM – 2.5 mM) in both endothelium‐intact and endothelium‐denuded vessels. While 5‐HT antagonist, ketanserin (50 nM), shifted the responses to 5‐HT (EC50 Control 107 ± 10 nM vs. Treatment 32 ± 6 μM; p<0.001), it failed to affect the responses to L‐Wme. The inclusion of transient receptor potential channel (TRPC) blocker, 2‐aminoethoxy phenyl borate (10 μM) or the voltage‐gated Ca2+ channel blocker, verapamil (10 μM), abolished the bipahsic responses to L‐Wme. L‐Wme evoked (1 μM ‐ 2.5 mM) vasodilatation was more sensitive in potassium chloride depolarized (IC50 330 ± 19 μM; Imax 95%) than in phenylephrine constricted vessels (IC50 767 ± 23 μM; Imax 96%). These data suggest that the cell permeant amino acid, L‐Wme, exerts endothelium‐/serotonin‐independent responses that could be due to activation and blockade of Ca2+ influx occurring through either the TRPC and/or the voltage‐gated Ca2+ channels present on vascular smooth muscle cells of resistance type vessel. This confirms a direct role for L‐W analogs in the regulation of vascular smooth muscle tone.

A New Ritodrine Selective Electrode and its Pharmaceutical Application

A novel ritodrine hydrochloride ion‐selective PVC membrane electrode based on ion‐pair complex of ritodrine‐tetra phenyl borate was prepared with di-n‐butyl phosphate as a plasticizer. The influences of membrane composition, temperature, pH of the test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a wide ritodrine concentration range (1×10−5‐ 1×10−2 M) with a slope of 59.33 mV decade−1 and was found to be very selective, precise and usable within the pH range 3‐7.5. The standard electrode potentials, E°, were determined at different temperatures and used to calculate the isothermal temperature coefficient (dE°/dT) of the electrode, which was 0.00075. The electrode was successfully used for potentiometric determination of ritodrine hydrochloride both in pure solutions and in pharmaceutical preparations.

Ion selective electrode for cesium based on 5-(4′-nitrophenylazo)25,27-bis(2-propyloxy)26,28-dihydroxycalix[4]arene

A polyvinylchloride (PVC) based liquid membrane ion selective electrode (ISE) for cesium was fabricated with 5-(4'-nitrophenylazo)25,27-bis(2-propyloxy)26,28-dihydroxycalix[4]arene as ionophore. Different membrane constituents were investigated to realise optimum performance of the ISE developed. Of the four plasticizers and two ion additives studied, the best response was observed with membrane having 2-nitro phenyl octyl ether (oNPOE) as plasticizer and potassium tetrakis (perchloro phenyl) borate (KTpClPB) as ion additive. Linear response over concentration range of 10(-5)-10(-1)M CsCl was obtained. The Nernstian slope of the response was 56 mV per decade for Cs with a response time less than 20s. Matched potential method has been applied to find out the selectivity for Cs over several ions like Rb(+), K(+), Na(+), NH(4)(+), Sr(2+), Ba(2+), Ca(2+), Mg(2+), Cu(2+), Pb(2+), Zn(2+), Ni(2+) and Ce(3+). The response of ISE for Cs(+) was fairly constant over the pH range of 3-11. The lifetime of the electrode is 9 months which is the longest life for any membrane-based Cs-ISE so far developed. The concentration of cesium in two simulated high level active waste streams was determined and results agreed well with those obtained independently employing atomic absorption spectrometry.

Comparative studies of ONNO-based ligands as ionophores for palladium ion-selective membrane sensors

Palladium sensors based on two neutral ionophores, N, N′-bis(acetylacetone) cyclohexanediamine ( L 1 ) and N, N′-bis( o-hydroxyacetophenone)-1,2-cyclohexanediamine ( L 2 ) for quantification of palladium ions are described. Effect of various plasticizers ( o-NPOE, DBP, DEP, DOP, TBP, and CN) and anion excluder, sodium tetra phenyl borate (NaTPB) has been studied. The best performance is obtained with a membrane composition of PVC: o-NPOE:ionophore ( L 1 ):NaTPB of 150:300:5:5 (%, w/w). The sensor exhibits significantly enhanced selectivity towards palladium ion over the concentration range 1.0 × 10 −8 to 1.0 × 10 −1 M with a lower detection limit of 4.0 × 10 −9 M and a Nernstian compliance (29.1 ± 0.3 mV decade −1 of activity) within pH range 2.0–6.0 and fast response time of 10 s. Influence of the membrane composition and possible interfering ions has also been investigated on the response properties of the electrode. Fast and stable response, good reproducibility and long-term stability of the sensor are demonstrated. The sensor has been found to work satisfactorily in partially non-aqueous media up to 20% (v/v) content of methanol, ethanol and acetonitrile and could be used for a period of 4 months. Selectivity coefficients determined with fixed interference method (FIM) indicate high selectivity for palladium. The proposed electrode shows fairly good discrimination of palladium from other cations. The application of prepared sensor has been demonstrated in determination of palladium ions in spiked water sample.

A New Scorpionate Ligand: Tris(4,4-dimethyl-2-oxazolinyl)borate and Its Zirconium(IV) Complexes

The first example of a new class of oxazoline-based scorpionate ligand, tris(4,4-dimethyl-2-oxazolinyl)phenyl borate, [ToM]−, is prepared by reaction of 2-lithio-4,4-dimethyl-2-oxazolide and 0.3 equiv of dichlorophenylborane. The steric bulk of this ligand is greater than that of tris(3,5-Me2-pyrazolyl)borate (Tp*), as quantified by comparison of solid angles of crystallographically characterized zirconium(IV) complexes.

Pharmacological Characterization and Molecular Determinants of the Activation of Transient Receptor Potential V2 Channel Orthologs by 2-Aminoethoxydiphenyl Borate

Despite its expression in different cell types, transient receptor potential V2 (TRPV2) is still the most cryptic members of the TRPV channel family. 2-Aminoethoxydiphenyl borate (2APB) has been shown to be a common activator of TRPV1, TRPV2, and TRPV3, but 2APB-triggered TRPV2 activation remains to be thoroughly characterized. In this study, we have developed an assay based on cell lines stably expressing mouse TRPV2 channels and intracellular calcium measurements to perform a pharmacological profiling of the channel. Phenyl borate derivatives were found to activate mouse TRPV2 with similar potencies and thus were used to screen a panel of channel blockers. Besides the classic TRP inhibitors ruthenium red (RR) and 1-(beta-[3-(4-methoxyphenyl) propoxy]-4-methoxyphenethyl)-1H-imidazole hydrochloride (SKF96365), two potassium channel blockers, tetraethylammonium (TEA) and 4-aminopyridine, and an inhibitor of capacitative calcium entry, 1-(2-(trifluoromethyl) phenyl) imidazole (TRIM), were found to inhibit TRPV2 activation by 100 microM 2APB. Activation by 300 microM 2APB, however, could only be inhibited by RR and TRIM. Electrophysiological recordings demonstrated that TEA inhibition was use-dependent, suggesting that high concentrations of 2APB might induce a progressive conformational change of the channel. Comparison of TRPV2 orthologs revealed that the human channel was insensitive to 2APB. Analysis of chimeric constructs of mouse and human TRPV2 channels showed that the molecular determinants of 2APB sensitivity could be localized to the intracellular amino and carboxyl domains. Finally, using lentiviral-driven expression, we demonstrate that hTRPV2 exerts a dominant-negative effect on 2APB activation of native rodent TRPV2 channels and thus may provide an interesting tool to investigate cellular functions of TRPV2 channels.

Study of ion–solvent interactions and activation energy of LiBr in DMSO, H2O and DMSO–H2O mixtures at various temperatures

The Jones–Dole B coefficients of the electrolyte Lithium bromide (LiBr), reference salts tetra butyl ammonium tetra phenyl borate (BU4NBPh4), tetra butyl ammonium bromide (BU4NBr), and potassium chloride (KCl) in dimethylsulfoxide (DMSO), water, and DMSO–water mixtures were obtained at different temperatures range from 25 to 45 °C For this, the relative viscosities were measured for Lithium bromide (LiBr) and reference salts in DMSO, water, and DMSO–water mixtures at above-mentioned temperatures. The B coefficients of these electrolytes were behaved as structure makers in DMSO, while in H2O and DMSO–H2O mixtures, the B-coefficient values were less positive showing the weak structure-making effect. Ionic viscosity B coefficients allow us to assess the behavior of ions in the solvent mixtures. In this study it was observed that all the values of ionic B coefficient of (Li+) were positive and small showing the weak structure-making effects. It was also observed that Br− ions maintain negative B coefficient values in all DMSO–H2O mixtures, except in 60% DMSO mole fraction. From this it can be concluded that Br− ion behaved as a structure breaker in water and in all DMSO–H2O mixtures except in 60% DMSO mole fraction mixtures. The low B ± values of alkali metal ions and Br− ions in water are due to the breakdown of the tetrahedral structural of water and the formation of strongly structured solvated ion. It is also observed that the values of the energy of activation of the flow for LiBr are greater in DMSO–water mixtures and in pure water than in DMSO. This may be due the presence of a network of hydrogen bonds which cause the hindrance in the flow of the solution of LiBr in DMSO–water mixtures and in pure water than in DMSO.

Development of Nalbuphine‐Selective Membrane Electrode and Its Applications in Pharmaceutical Analysis

A nalbuphine ion‐selective PVC membrane electrode based on ion‐pair complex of nalbuphine with tetra phenyl borate was prepared with di‐butyl sebacate as a plasticizer. The electrode exhibits a linear response with a Nernstain slope 59.6 mV decate−1 at 25°C with the concentration range of 1×10−6−1×10−2 M nalbuphine. The electrode response was not sensitive to pH changes from 3.5–7 and not affected by possible interfering species such as common inorganic cations, sugars and amino‐acids. The electrode shows good stability, reproducibility and fast response. These characteristics of the electrode enable it to be used successfully for the determination of nalbuphine hydrochloride in pure form and in pharmaceutical preparations.

Approaches to analytical and synthetic electrochemistry in fluorous solvent-containing media

The implementation of voltammetry in highly fluorous media has been demonstrated. Two strategies were utilized in order to overcome the major impediments to electrochemistry imposed by the low polarity of fluorous solvents. First, benzotrifluoride was used as a cosolvent with perfluoromethylcyclohexane in a 1-to-1 ratio to afford a fluorous mixture with a modest dielectric constant. Second, a fluorophilic supporting electrolyte was synthesized. The electrolyte consists of an imidazolium cation with a fluorous ponytail and the lipophilic tetrakis(3,5-trifluoromethyl)phenyl borate anion. The electrolyte medium allows for the routine electroanalysis of substrates using millimeter-sized electrodes. The electrochemical properties of ferrocene and a fluorous-ponytail analogue in the fluorous medium are given, and the ability to perform bulk electrolysis in the solvent mixture is demonstrated. The thermally regulated miscibility of fluorous and organic solvents is a particularly interesting phenomenon at present, and its applicability towards electrolysis-product purification is discussed.

A Novel Holmium(III) Membrane Sensor Based on N‐(1‐Thien‐2‐Ylmethylene)‐1,3‐Benzothiazol‐2‐Amine

A novel plasticized membrane sensor for Ho(III) ions based on N‐(1‐thien‐2‐ylmethylene)‐1,3‐benzothiazol‐2‐amine (TBA) as a neutral carrier was prepared. The best performance was obtained with a membrane composition of 31% PVC, 61% benzyle acetate, 2% sodium tetra phenyl borate and 6% carrier. The electrode exhibits a Nernstian response for Ho(III) ions over a particular concentration range (1.0×10−5−1.0×10−2 M) with a slope of 19.7±0.2 mV decade−1. The limit of the detection is 7.0×10−6 M. The sensor has a response time of <15 s and a useful working pH range of 4.0–9.5. The proposed sensor discriminates relatively well towards Ho(III) ions with regard to common alkali, alkaline earth, and specially lanthanide ions. It was successfully applied as an indicator electrode in a potentiometric titration of Ho(III) ions with EDTA. It was also applied in determination of fluoride ions in a mouth wash preparation. The proposed sensor was applied for the determination of Ho(III) ion concentration in binary mixtures.

Polymerization of Methyl Methacrylate with Chloro Zirconocene Enolates

AbstractSummary: The polymerization of methyl methacrylate (MMA) in the presence of the neutral chloro zirconocene enolates, Cp2ZrCl[OC(OMe)CMe2] (1), Me4C2(Cp)2ZrCl[OC(OMe)CMe2] (2), and Me2C(Cp)2ZrCl[OC(OMe)CMe2] (3), was investigated. None of these compounds is catalytically active on its own. They could be activated by adding Ph3CB(C6F5)4 (4); however, only if the initial concentration of enolate is higher than that of the perfluorated phenyl borate. Polymers were produced with a number average molar mass of up to 100 000 g/mol and a dispersion index of 1.1–1.3 with mixtures comprising 1 and 4 or 2 and 4. The degree of polymerization depends only on the quantity of excess enolate and not on the absolute concentration of the initiator components. In contrast, a mixture of 3 and 4 was not very active. Kinetic modeling of the systems as well as NMR spectroscopic investigations indicate that a bimetallic mechanism can describe chain growth. The activity of these catalytic systems depends on the structure of the ligand. The two zirconocenes with bridged cyclopentadienyl ligands, (2) and (3), convert MMA considerably slower. In addition to the methyl zirconocene enolates with unbridged cyclopentadienyl ligands, the corresponding chloro zirconocene enolates are also suitable for the polymerization of MMA. The latter compounds offer the advantage that preparations for the production of the initiators are comparatively simple.Structures of investigated initiators.magnified imageStructures of investigated initiators.

A Porphyrin Based Potentiometric Sensor for Zn2+ Determination

PVC based membranes of disodium salt of porphyrin 3,7,12,17-tetramethyl-8, 13-divinyl 2,18-porphine dipropionic acid (I) as ionophore with sodium tetra phenyl borate (NaTPB) as anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butyl phosphonate (DBBP), tris(2- ethyl hexyl)phosphate (TEP), tri-n-butylphosphate (TBP) and 1- chloronaphthalene (CN) as plasticizing solvent mediators were prepared and constructed for determination of Zn(II). The PVC based membrane of (I) with DBBP as plasticizer and having anion excluder, NaTPB in the ratio PVC: I: NaTPB: DBBP (150: 10: 2: 200) gave the best results in terms of working concentration range (1.3×10-5-1.0 ×10-1M) with a Nernstian slope (30.0 mV/decade of activity). The useful pH range of the sensor is 3.0 –7.4, beyond which a drift in potential was observed. The response time of the sensor is 10s and the lifetime was about 2 months during which it could be used without any measurable divergence. It had good stability and reproducibility. The membrane worked satisfactorily in non-aqueous medium up to 40% (v/v) non-aqueous content. The selectivity coefficient values indicate that the electrode is highly selective for Zn2+ over a number of other cations except Na+ and Cd2+. Although Na+ and Cd2+ are likely to cause some interference, they would not interfere if present at the concentrations &lt; 1 ×10-5 and &lt; 5 ×10-5 M, respectively. The electrode has been used as an indicator electrode to determine the end point in the potentiometric titration of Zn2+ with EDTA.

Novel Beryllium Membrane Sensor Based on 2,4-Dinitrophenylhydrazinebenzo-9- crown -3 Coated Graphite

A novel sensor based on 2,4-dinitrophenylhydrazinebenzo-9-crown-3 (NPHC) for selective determination of ultra trace amount of beryllium is reported. The plasticized PVC membrane containing 30% PVC, 58% ortho-nitrophenyloctyl ether (NPOE), 3% sodium tetra phenyl borate (NaTPB) and 9% NPHC was directly coated on a graphite electrode works well over a wide range of concentration (1.0 × 10−1 to 4.0 × 10−7 M) with a Nernstian slope of 29.5 mV per decade. The electrode shows a fast response time of 10 s and operates in the pH range 3.0–9.0. The sensor can be used for more than five months without any divergence in the potential. The selectivity of the electrode was studied and it was found that the electrode exhibits very good selectivity for beryllium ion over alkali, alkaline earth, heavy, and transition metal ions. The beryllium ion-selective electrode was used as an indicator electrode for the potentiometric titration of beryllium ion in solution using a standard solution of EDTA, a sharp potential change occurs at the end-point. The applicability of the sensor to Be(II) ion measurement in water samples spiked with beryllium chloride is illustrated.

Membranes of 5,10,15,20-Tetrakis(4-Methoxyphenyl) Porphyrinatocobalt (TMOPP-Co) (I) as MoO42- - Selective Sensors

Polyvinyl chloride (PVC) membrane electrodes based on porphyrin 5,10,15,20-tetrakis(4methoxyphenyl)porphyrinatocobalt (TMOPP-Co) (I) incorporating sodium tetra phenyl borate (NaTPB) as anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butyl phosphonate (DBBP), tri-n-butyl phosphate (TBP), and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and tested for selective detection of molybdate ions. The membrane having anion excluder, NaTPB and DBP as plasticizer (membrane no. 2) proved to be best in terms of working concentration range 5.0×10-5 – 1.0×10-1M with a near – Nernstian slope of 32.0±1.0 mV/decade of activity over the pH range 5.4- 10.5. The response time of this sensor is 18s with a lifetime of about 4 months. The sensor can be used in non-aqueous medium with no significant change in the value of slope or working concentration range for the estimation of MoO42- in solutions having up to 25% (v/v) non-aqueous fraction.

1,1´,3,3´-Tetramethyl-2,2´-diimidazolium dication: Its bromide salt and the tetraphenylborates of its ketone adducts

The crystal structures of several 1,1´,3,3´-tetramethyl-2,2´-diimidazolium dication salts were determined at low temperatures. The dihedral angles between the planes of the two five-membered rings vary between 64° in the bromide salt and up to 80° in the ketone adduct tetraphenylborates, indicating some conformational flexibility around the central C–C bond of the 1,1´,3,3´-tetramethyl-2,2´-diimidazolium dication. Semiempirical calculations predict the conformation with a dihedral angle of 90° to be most favourable and the conformations within the crystal structures to be results of packing effects. In tetra phenyl borate salts of ketone and diketone adducts, the oxygen centers coordinate to the dication from above as well as below the defined molecular least squares plane and form chains of alternating dications and ketones. Since this packing motif is found in tetraphenylborate salts with different ketones, it might prove to be a robust supramolecular synthone in crystal engineering.

All-Solid-State Sodium-Selective Electrodes Based on Room Temperature Vulcanizing-Type Silicone Rubber Matrix.

Sodium-selective membranes based on room temperature vulcanizing-type silicone rubber (RTV-type SR) matrix and tert-butyl calix[4]arene-tetraacetic acid tetraethyl ester (1.0 wt %) have been developed for all-solid-state-type electrodes. It was observed that the potentiometric response, stability and lifetime of these SR membrane-based all-solid-state electrodes critically depend on the type of lipophilic salts employed. Among the several phenyl borate derivative-based additives examined, the SR membranes prepared with 0.5 wt % tetrakis[3,5-bis(trifluoromethyl)phenyl]borate salt (TFPB) exhibited low impedance, resulting in electrochemical performance comparable to that of the PVC-based membranes mounted in conventional electrodes. The lifetime of all-solid-state electrodes with SR/TPFB/ tert-butyl calix[4]arene tetraethyl ester was longer than 230 days.

Ice nucleating activity of Pseudomonas syringae and Erwinia herbicola.

Chemical and biological properties of the ice nucleating sites of Pseudomonas syringae, strain C-9, and Erwinia herbicola have been characterized. The ice nucleating activity (INA) for both bacteria was unchanged in buffers ranging from pH 5.0 to 9.2, suggesting that there were no essential groups for which a change in charge in this range was critical. The INA of both bacteria was also unaffected by the addition of metal chelating compounds. Borate compounds and certain lectins markedly inhibited the INA of both types of bacterial cells. Butyl borate was not an inhibitor, but borate, phenyl borate, and m-nitrophenyl borate were, in order, increasingly potent inhibitors. These compounds have a similar order of affinity for cis hydroxyls, particularly for those found on sugars. Lentil lectin and fava bean lectin, which have binding sites for mannose or glucose, inhibited the INA of both bacteria. All other lectins examined had no effect. The inhibition of INA by these two types of reagents indicate that sugar-like groups are at or near the ice nucleating site. Sulfhydryl reagents were potent inhibitors of the INA of both bacteria. When treated with N-ethylmaleimide, p-hydroxymercuribenzoate, or iodoacetamide, the INA was irreversibly inhibited by 99%. The kinetics of inactivation with N-ethylmaleimide suggested that E. herbicola cells have at least two separate ice nucleating sites, whereas P. syringae cells have possibly four or more separate sites. The effect of infection with a virulent phage (Erh 1) on the INA of E. herbicola was examined. After multiple infection of a bacterial culture the INA was unchanged until 40 to 45 min, which was midway through the 95-min latent period. At that time, the INA activity began falling and 99% of the INA was lost by 55 min after infection, well before any cells had lysed. This decrease in INA before lysis is attributed to phage-induced changes in the cell wall.

Rearrangements of organometallic compounds: XI. Duality of mechanism for 1,2-aryl migrations in the oxidation of tetraarylborate salts

Individual oxidative couplings of potassium phenyl(tri- m-tolyl)borate and potassium phenyl(tri- p-tolyl)borate with transition metal ions, organic oxidants and halogen sources revealed a duality of mechanism, namely electron-transfer and electrophilic pathways. Not only the ratios of the respective bitolyls and methylbiphenyls obtained, but also the behavior of potassium bis( o, o′-biphenylene)-borate, showed that bridging of the migrating group is important for iodine oxidations, but not for Ce IV oxidations.

Synthesis of N-trialkylborazines from phenyl borate, aluminum, hydrogen, and primary amines

Synthesis of N-trialkylborazines from phenyl borate, aluminum, hydrogen, and primary amines

Reactions of complex metal hydrides with borate esters

The reaction of sodium borohydride, sodium aluminum hydride and lithium aluminum hydride with methyl borate and phenyl borate is reported. Sodium borohydride does not react with methyl borate or phenyl borate in ether solvents up to 200°; however, in tertiary amine solvent sodium borohydride does react with phenyl borate at elevated temperatures. Triethylamine-borane and dimethylaniline-borane have been prepared in this manner. In amine solvents, under the same conditions, methyl borate does not react. Lithium aluminum hydride and sodium aluminum hydride, on the other hand, react rapidly with both methyl borate and phenyl borate at room temperature in both ether and amine solvent. Diborane and lithium tetraphenoxyaluminate [LiAl(OC 6H 5 4] are formed as the major products from lithium aluminum hydride reaction with phenyl borate. If the mode of addition is reversed (borate added to hydride), no diborane is formed and lithium borohydride is the major product from normal addition. In triethylamine solvent, triethylamine-borane is formed in good yield from either methyl borate or phenyl borate reaction with lithium aluminum hydride. When an olefin is used as the solvent in conjunction with diethyl ether, the corresponding trialkyl-borane is formed. Similar reactions with sodium aluminum hydride are also discussed.