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At least 253 records · Page 14Linked to original sources
PubMed1998

[Physico-chemical properties of borate derivatives of DOPA, dopamine, and their liposome forms].

To increase the solubility of L-3,4-dihydroxyphenylalanine (DOPA) and dopamine (DA) incorporated in liposomes, it was suggested to convert them into ammonium and 1-adamantylammonium borate complexes. The structure of these complexes was studied by 11B and 1H NMR, IR, and mass spectrometry and conductometry. The liposomic form of the complexes is characterized by a high active compound/lipid molar ratio (0.5). Catechols in the form of complex salts are retained better within the inner volume of liposomes.

Amantadine↗
PubMed1975

Skin dose with cones and diaphragms in 137Cs teletherapy - a study using lithium borate thermoluminescent dosimeters.

Beam definition in 137Cs teletherapy is done either by use of cones for specified SSDs or by means of adjustable diaphragms. Using lithium borate thermoluminescent dosimeters, the skin dose was studied for conditions of the bare cone without any electron filter, the cone with an affixed perspex cup for cutting off the electrons, the cone with an affixed copper plate filter at its face. It was observed that of the above three arrangements, the case employing the copper filter gave the minimum skin dose. Similar skin dose measurements made for a diaphragm type collimator are discussed in comparison with the values for cones.

Borates↗
PubMed1978

Studies on the mode of action of phenylmercuric borate on Escherichia coli. I. Structural localization and kinetics of incorporation.

Phenylmercuric borate (PHB) is very rapidly incorporated into the cells of Escherichia coli, and binds directly to its sites of fixation. The rapid incorporation of PHB probably results from the lipophilic character of the [phenylmercuric]+ cation. The distribution of PHB in the cell is fairly uniform if one compares with that of the proteins. This shows the low specificity of PHB with regard to proteins, all of which appear to be potential sites for fixation. However, from the structural point of view, PHB is more differentiated in its distribution. The cell wall of E. coli and the soluble cytoplasmic fraction do not constitute important sites of fixation. On the contrary, the cytoplasmic membrane appears to be a preferential site of fixation. Moreover, it is very probable that the distribution of PHB in vivo should be even more likely at the cytoplasmic membrane since the process of homogenization of the cells solubilizes a large part of the proteins associated to the membrane. On the membrane, an important part of PHB seems to be associated with the ribosomes and particularly to the ribosomal proteins.

Bacterial Proteins↗
PubMed1978

Studies on the mode of action of phenylmercuric borate on Escherichia coli. II. Biochemical localization and inhibition of some metabolic activities.

The biochemical localization of phenylmercuric borate (PHB) on Escherichia coli shows that this disinfectant associates essentially with proteins. Protein electrophoresis demonstrates that each protein contains PHB, and that SH groups play a very important role in its fixation. The quantity of PHB able to associate with proteins is so large that many other electron donor groups must react with it. Moreover, it appears that concentration of PHB on cytoplasmic membrane results rather from the privileged position of this structure than from special physicochemical properties. The great reactivity of PHB towards proteins leads to numerous inhibitions and confers upon this antibacterial drug a very complex mode of action. Four important metabolic activities have been tested in the presence of PHB, namely: respiration, protein-synthesis, RNA synthesis and DNA synthesis. These four metabolic functions are rapidly and totally inhibited at low concentrations of PHB. The complexity of the mode of action of PHB makes the adaptation of bacteria to this disinfectant more difficult. In addition, in the case of plasmid dependent resistence, PHB, with its complexe mode of action, does not favour such a selection in opposition to the antibiotics which generally have a more specific mode of action.

Bacterial Proteins↗
PubMed1999

Stabilization of a Discrete Lanthanide(II) Hydrido Complex by a Bulky Hydrotris(pyrazolyl)borate Ligand.

Divalent and solvent-free: the ytterbium hydrido complex 1 was obtained by the hydrogenolysis of [(Tp(tBu,Me))Yb(CH(2)SiMe(3))(thf)]. The steric demand of the bulky hydrotris(3-tert-butyl-5-methylpyrazolyl)borate ligand, Tp(tBu,Me), is sufficient to stabilize the dimer, yet facile room-temperature reactions with amines, alkynes, diynes, and CO indicate a rich chemistry of 1.

Journal Article↗
PubMed2000

Denticity Changes of Hydrotris(pyrazolyl)borate Ligands in Rh(I) and Rh(III) Compounds: From kappa(3)- to Ionic "kappa(0)"-Tp'

Isolated hydrotris(pyrazolyl)borate anions Tp' were obtained as salts of metal complex cations (see picture) by the displacement of Rh-coordinated kappa(3)-N,N',N"-Tp' by PMe(3) (Tp'=Tp and Tp(Me2)). With [(kappa(3)-Tp(Me2))Rh(C(2)H(4))(2)], stepwise diplacement of the Tp(Me2) ligand allowed the isolation of complexes exhibiting the kappa(2)- Tp(Me2) and kappa(1)-Tp(Me2) coordination modes.

Journal Article↗
PubMed2001

Step-by-step uncoordination of the pyrazolyl rings of hydrotris(pyrazolyl)borate ligands in comlexes of Rh and RhIII.

Compounds of rhodium(I) and rhodium(III) that contain ancillary hydrotris(pyrazolyl)borate ligands (Tp') react with monodentate and bidentate tertiary phosphanes in a step-wise manner, with incorporation of P-donor atoms and concomitant replacement of the Tp' pyrazolyl rings. Accordingly, [Rh(kappa3-TpMe2)(C2H4)(PMe3)] (1b), converts initially into [Rh(kappa2-TpMe2)-(PMe3)2] (3), and then into [Rh(kappa1-TpMe2)-(PMe3)3] (2) upon interaction with PMe3 at room temperature, in a process which can be readily reversed under appropriate experimental conditions. Full disengagement of the Tp' ligand is feasible to give Tp' salts of rhodium(I) complex cations, for example, [Rh(CO)(dppp)2]-[TpMe2,4-Cl] (5; dppp = Ph2P(CH2)3PPh2), or [Rh(dppp)2][TpMe2,4-Cl] (6). Bis(hydride) derivatives of rhodium(III) exhibit similar substitution chemistry, for instance, the neutral complex [Rh(Tp)-(H)2(PMe3)] reacts at 20 degrees C with an excess of PMe3 to give [Rh(H)2-(PMe3)4][Tp] (9b). Single-crystal X-ray studies of 9b, conducted at 143 K, demonstrate the absence of bonding interactions between the [Rh(H)2(PMe3)4]+ and Tp ions, the closest Rh...N contact being at 4.627 A.

Journal Article↗
PubMed2001

Structural characterization and intramolecular aliphatic C-H oxidation ability of M(III)(mu-O)2M(III) complexes of Ni and Co with the hydrotris-(3,5-dialkyl-4-X-pyrazolyl)borate ligands TpMe2,X (X = Me, H, Br) and TpiPr2.

Reaction of the dinuclear M(II)-bis(mu-hydroxo) complexes of nickel and cobalt, [(M(II)(TpR)]2(mu-OH)2] (M = Ni; 3Ni M = Co: 3Co), with one equivalent of H2O2 yields the corresponding M(III)-bis(mu-oxo) complexes, [[M(III)(TpR)]2-(mu-O)2] (M=Ni; 2Ni, M=Co: 2Co). The employment of a series of TpMe2,X (TpMe2,X = hydrotris(3,5-dimethyl-4-X-1-pyrazolyl)borate; X = Me, H, Br) as a metal supporting ligand makes it possible to isolate and structurally characterize the thermally unstable M(III)-bis-(mu-oxo) complexes 2Ni and 2Co. Both the starting (3Ni and 3Co) and resulting complexes (2Ni and 2Co) contain five-coordinate metal centers with a slightly distorted square-pyramidal geometry. Characteristic features of the nickel complexes 2Ni, such as the two intense absorptions around 400 and 300 nm in the UV-visible spectra and the apparent diamagnetism, are very similar to those of the previously reported bis(mu-oxo) species of Cu(III) and Ni(III) with ligands other than TpR, whereas the spectroscopic properties of the cobalt complexes 2Co (i.e., paramagnetically shifted NMR signals and a single intense absorption appearing at 350 nm) are clearly distinct from those of the isostructural nickel compounds 2Ni. Thermal decomposition of 2Ni and 2Co results in oxidation of the inner saturated hydrocarbyl substituents of the TpR ligand. Large kH/kD values obtained from the first-order decomposition rates of the TpMe3 and Tp(CD3)2,Me derivatives of 2 evidently indicate that the rate-determining step is an hydrogen abstraction from the primary C-H bond of the methyl substituents. mediated by the M(III)2-(mu-O)2 species. The nickel complex 2Ni shows reactivity about 10(3) times greater than that of the cobalt analogue 2Co. The oxidation ability of the M(III)(mu-O)2M(III) core should be affected by the hindered TpR ligand system, which can stabilize the +2 oxidation state of the metal centers.

Cobalt↗
PubMed2006

Reaction of azole heterocycles with tris(dimethylamino)borane, a new method for the construction of tripodal borate-centred ligands.

Reaction of 2-mercapto-1-methylimidazole (methimazole) with tris(dimethylamino)borane, B(NMe2)3, provides the tetrahedral dimethylamine adduct of tris(methimazolyl)borane, [(Me2HN)B(methimazolyl)3]. By contrast, imidazole, 2-methylimidazole, 2-chloroimidazole and benzimidazole provide the homoleptic tetra-azolyl systems H[B(azolyl)4], and the same product is obtained even when a substoichiometric quantity of the heterocyle is employed. The change in reaction outcome is correlated with the variation of basic pKa for the heterocycles. A simple acid-base reaction with elimination of HNMe2 is proposed for the reaction with the weakly basic, but more strongly acidic, methimazole. However, for the more strongly basic imidazoles, initial coordination of the heterocycle imine nitrogen to the weakly Lewis acidic boron centre in B(NMe2)3 to form the tetrahedral adduct [(azole)B(NMe2)3] is proposed. The greater availability of the NMe2 lone pairs in this species results in increased basicity and a rapid reaction with further heterocycle to provide the observed H[B(azolyl)4] products. For 2-nitroimidazole, the low basicity (and increased N-H acidity) results in the formation of [(HNMe2)B(2-nitroimidazolyl)3] on reaction with B(NMe2)3, analogous to the product formed with methimazole. Both [(HNMe2)B(methimazolyl)3] and H[B(benzimidazolyl)4] have been structurally characterised by single crystal X-ray crystallography. This chemistry has been exploited to provide a new synthesis of borate-centred tripod ligands, whereby N-methylimidazole is used to activate B(NMe2)3 to reaction with methimazole to form the new ligand [(N-methylimidazole)B(methimazolyl)3] in good yield and a complex of this ligand with Ru(II) has been structurally characterised.

Journal Article↗
PubMed1998

Apparent pore size of polyacrylamide gels: comparison of gels cast and run in Tris-acetate-EDTA and Tris-borate-EDTA buffers.

The electrophoretic mobilities of DNA molecules in three different molecular weight ladders were measured in polyacrylamide gels containing different acrylamide concentrations (%T) and cross-linker ratios (%C), cast and run in Trisacetate-EDTA (TAE) buffer. The apparent pore radius of each gel was estimated from Ferguson plots of the relative mobilities of each of the DNA molecules, using the mobility of the monomer fragment in each molecular weight ladder as the reference mobility. The effective size of each of the DNA molecules was estimated from its radius of gyration. The apparent gel pore radii calculated in this manner ranged from 21 nm in gels containing 10.5%T, 5%C to 200 nm in gels with 4.6%T, 2%C, similar to the values observed for polyacrylamide gels cast and run in Tris-borate-EDTA (TBE) buffer (Holmes and Stellwagen, Electrophoresis 1991, 12, 612-619). Hence, the effective pore size of polyacrylamide gels is essentially independent of whether the gels are cast and run in TAE or TBE buffer.

Acetates↗
PubMed2005

Charge donation to and dearomatization of benzene attending complexation: DFT estimates of binding energies of TpMXO(L) with benzene, for Tp = hydridotris(pyrazolyl) borate, MXO = MoNO, ReCO, and WNO, and L = ammonia, N-methylimidazole, pyridine, phosphine, methyl isocyanide, and carbon monoxide.

By density functional methods we characterize the bonding and charge distribution in complexes of benzene with dearomatizing agents tpReCO(L), tpMoNO(L), and tpWNO(L), where tp = hydrido Tris (pyrazolyl)borate), for a range of ligands L. Our LSDA and B3LYP density functional calculations use the Spartan LACVP+ basis and pseudopotential on Re, Mo, and W and 6-31G* on light atoms. The binding energy is strongly dependent on the nature of the ligand L, being greatest for L = ammonia and N-methylimidazole and weakest for CH3NC and CO. We find a correlation between strength of binding and electron transfer from the dearomatizing agents toward benzene. For the most strongly bound systems we find substantial (up to 500 millielectrons) charge transfer towards benzene, while for the most weakly bound systems charge is withdrawn from benzene. Structural details illustrate the ability of Re, Mo, and W species to dearomatize complexed benzene, which is extensive for all but the most weakly bound species with L = MeNC and CO. Re and W dearomatizing agents, which are computed and observed to form stable complexes with benzene, may be economic alternatives to osmium dearomatizing agents.

Journal Article↗
PubMed1999

The effects of 2-aminoethoxydiphenyl borate, a novel inositol 1,4, 5-trisphosphate receptor modulator on myometrial contractions.

These studies were performed to evaluate the effect of 2-aminoethoxydiphenyl borate (2-APB), a novel membrane-permeable inositol 1,4,5-trisphosphate-receptor inhibitor on agonist-induced, spontaneous, and KCl-stimulated in vitro myometrial contractions. 2-APB significantly inhibited spontaneous myometrial contractions as well as phasic contractions induced by various uterotonic agonists. Confiriming its effects on intracellular calcium release, 2-APB inhibited phasic contractions in the absence of extracellular calcium. 2-APB had little effect on the tonic response to KCl stimulation, implicating its insignificant effect on voltage-gated calcium channels. The inhibitory effect of 2-APB on phasic contractions was completely reversed by washout. In summary, 2-APB effectively penetrated uterine tissue and significantly inhibited myometrial events previously shown to be mediated through activation of the PI-signaling pathway.

Animals↗
PubMed2007

2-Aminoethoxydiphenyl borate as a common activator of TRPV1, TRPV2, and TRPV3 channels.

2-Aminoethoxydiphenyl borate (2APB) had been depicted as a universal blocker of transient receptor potential (TRP) channels. While evidence has accumulated showing that some TRP channels are indeed inhibited by 2APB, especially in heterologous expression systems, there are other TRP channels that are unaffected or affected very little by this compound. More interestingly, the thermosensitive TRPV1, TRPV2, and TRPV3 channels are activated by 2APB. This has been demonstrated both in heterologous systems and in native tissues that express these channels. A number of 2APB analogs have been examined for their effects on native store-operated channels and heterologously expressed TRPV3. These studies revealed a complex mechanism of action for 2APB and its analogs on ion channels. In this review, we have summarized the current results on 2APB-induced activation of TRPV1-3 and discussed the potential mechanisms by which 2APB may regulate TRP channels.

Animals↗
PubMed2002

Slow depletion of endoplasmic reticulum Ca(2+) stores and block of store-operated Ca(2+) channels by 2-aminoethoxydiphenyl borate in mouse pancreatic acinar cells.

The compound 2-aminoethoxydiphenyl borate (2-APB) has been used as either a specific membrane-permeable inhibitor for InsP(3) receptors or a store-operated Ca(2+) channel blocker in some cells. In this study, we have investigated actions of 2-APB on Ca(2+) signalling in mouse pancreatic acinar cells by measuring Ca(2+) concentration in the cytosol ([Ca(2+)]c) and in the endoplasmic reticulum (ER). Although 2-APB (50 microM) inhibited or modulated [Ca(2+)]c oscillations generated by a low dose of ACh, it did not block InsP(3)-mediated Ca(2+) release from the ER elicited by high doses of acetylcholine (ACh). 2-APB alone more than 70 microM tended to increase [Ca(2+)]c. When we directly measured Ca(2+) concentration in the lumen of the ER with a low affinity Ca(2+) dye, Mag-fluo-4, 2-APB itself slowly lowered ER Ca(2+) concentration and ACh could further release Ca(2+) from the ER in the presence of 2-APB, suggesting its lack of potency to block InsP(3) receptors. When store-operated Ca(2+) entry was evoked by addition of external Ca(2+) (5 mM) after depletion of Ca(2+) stores, 2-APB (50 microM) substantially blocked the Ca(2+) influx in a reversible manner. We conclude that (a) 2-APB is a good blocker for store-operated Ca(2+) channels, (b) 2-APB could not effectively block InsP(3) receptors, and (c) low doses of 2-APB lower Ca(2+) concentration in the lumen of the ER without a significant elevation of [Ca(2+)]c.

Animals↗
PubMed2002

2-Aminoethoxydiphenyl borate causes dissociation between membrane electrical and mechanical activity in guinea-pig urinary bladder smooth muscle.

Physiological functions of urinary bladder profoundly reflect smooth muscle mechanical activity. Urinary bladder smooth muscle itself produces myogenic rhythmic contraction, and this spontaneous mechanical event could be the fundamental determinant of urinary bladder functions. The spontaneous contraction of urinary bladder smooth muscle is thought to be triggered primarily by the action potential generated in this smooth muscle cell. Modulators of ion channels contributing to the configuration of action potential also affect urinary bladder smooth muscle mechanical activity as expected exactly from the effects on the electrical event. In the present study, we show that the frequency of action potential recorded in intact strip of guinea-pig urinary bladder smooth muscle is dramatically increased by 2-aminoethoxydiphenyl borate (2-APB; 30 microM) from 0.2 Hz to 1 Hz (approximately 500% increments). In contrast to an increasing effect expected from the membrane electrical alterations, mechanical activity (both contraction amplitude and frequency) of this smooth muscle is unexpectedly reduced by the same concentration of 2-APB to approximately 35% of the control. The present results firstly show an apparent dissociation of electrical-mechanical coupling in urinary bladder smooth muscle. The alteration of membrane electrical activity might not be the exclusive trigger mechanism responsible for the generation of spontaneous rhythmic contraction of this smooth muscle.

Action Potentials↗