Computational chemistry calculations of stability for bismuth nanotubes, fullerene-like structures and hydrogen-containing nanostructures

Using molecular mechanics (MM+), semi-empirical (PM6) and density functional theory (DFT) (B3LYP) methods we characterized bismuth nanotubes. In addition, we predicted the bismuth clusters {Bi(20)(C(5V)), Bi(24)(C(6v)), Bi(28)(C(1)), B(32)(D(3H)), Bi(60)(C(I))} and calculated their conductor properties.     

Nanoplated bismuth titanate sub-microspheres for protein immobilization and their corresponding direct electrochemistry and electrocatalysis

A layered inorganic perovskite sub-micrometer-scale material, nanoplated bismuth titanate (Bi₄Ti₃O₁₂) sub-microspheres (NBTSMs) constructed with tens of Bi₄Ti₃O₁₂ nanoplates, was for the first time synthesized by a facile hydrothermal synthesis strategy. The NBTSMs were employed as a supporting matrix to explore a novel immobilization and biosensing platform of redox proteins through a combined hydrogen bond and electrostatic assembly process. Biocompatibility, stability, reproducibility, and electrochemical and electrocatalytic properties of the resulting NBTSMs-based composite were studied by UV–vis absorption, FTIR, and electrochemical methods. The research results revealed that the NBTSMs-based composite was a satisfying matrix for proteins to effectively retain their native structure and bioactivity. With advantages of the Bi₄Ti₃O₁₂ layered material, facilitated direct electron transfer of the metalloenzymes with an apparent heterogeneous electron transfer rate constant (k_s) of 20.0 ± 3.8 s⁻¹ was acquired on the NBTSMs-based enzyme electrode. The NBTSMs-based biosensor demonstrated significant electrocatalytic activity for the reduction of hydrogen peroxide with an apparent Michaelis–Menten constant (204 μM), wide linear range (2–430 μM), and low detection limit (0.46 μM, S/N = 3). These indicated that the nanoplate-constructed Bi₄Ti₃O₁₂ sub-microspheres were one of ideal candidate materials for direct electrochemistry of redox proteins and the construction of the related enzyme biosensors, and may find potential applications in biomedical, food, and environmental analysis and detection.     

Comparisons of platinum, gold, palladium and glassy carbon as electrode materials in the design of biosensors for glutamate

Four electrode materials: Pt, Au, Pd and glassy carbon (GC), were studied to investigate their suitability as substrates in the development of two different classes of glutamate biosensor. Glutamate oxidase cross-linked onto poly(o-phenylenediamine) was chosen as the type 1 biosensor (PPD/GluOx), incorporating PPD as the permselective element to detect H(2)O(2) directly on the electrode surface at relatively high applied potentials. GluOx and horseradish peroxidase/redox polymer modified electrodes (Os(2+)PVP/HRP/GluOx) that relied on enzyme-catalysed H(2)O(2) detection at lower applied potentials were used as type 2 biosensors. The voltammetric and amperometric responses to the enzyme signal transduction molecule, H(2)O(2), and the archetypal interference species in biological applications, ascorbic acid, were determined on the bare and PPD/GluOx-modified surfaces. The amperometric responses of these electrodes were stable over several days of continuous recording in phosphate buffered saline (pH 7.4). The sensitivity of the type 1 biosensors to H(2)O(2) and glutamate showed parallel trends with low limits of detection and good linearity at low concentrations: Pt>Au approximately Pd>GC. Type 2 biosensors out-performed the type 1 design for all electrode substrates, except Pt. However, the presence of the permselective PPD membrane in the type 1 biosensors, not feasible in the type 2 design, suggests that Pt/PPD/GluOx might have the best all-round characteristics for glutamate detection in biological media containing interference species such as ascorbic acid. Other points affecting a final choice of substrate should include factors such as mass production issues.     

Interactions of bismuth complexes with metallothionein(II).

Bismuth complexes are widely used as anti-ulcer drugs and can significantly reduce the side effects of platinum anti-cancer drugs. Bismuth is known to induce the synthesis of metallothionein (MT) in the kidney, but there are few chemical studies on the interactions of bismuth complexes with metallothionein. Here we show that Bi(3+) binds strongly to metallothionein with a stoichiometry bismuth:MT = 7:1 (Bi(7)MT) and can readily displace Zn(2+) and Cd(2+). Bismuth is still bound to the protein even in strongly acidic solutions (pH 1). Reactions of bismuth citrate with MT are faster than those of [Bi(EDTA)](-), and both exhibit biphasic kinetics. (1)H NMR data show that Zn(2+) is displaced faster than Cd(2+), and that both Zn(2+) and Cd(2+) in the beta-domain (three metal cluster) of MT are displaced by Bi(3+) much faster than from the alpha-domain (four metal cluster). The extended x-ray absorption fine structure spectrum of Bi(7)MT is very similar to that for the glutathione and N-acetyl-L-cysteine complexes [Bi(GS)(3)] and [Bi(NAC)(3)] with an inner coordination sphere of three sulfur atoms and average Bi-S distances of 2.55 A. Some sites appear to contain additional short Bi-O bonds of 2.2 A and longer Bi-S bonds of 3.1 A. The Bi(3+) sites in Bi(7)MT are therefore highly distorted in comparison with those of Zn(2+) and Cd(2+).     

Ratiometric fluorescence imaging of dual bio-molecular events in single living cells using a new FRET pair mVenus/mKOκ-based biosensor and a single fluorescent protein biosensor

Genetically coded fluorescent protein (FP)-based biosensors are powerful tools for the non-invasive tracking of molecular events in living cells. Although a variety of FP biosensors are available, the simultaneous imaging of multiple biosensors (multi-parameter imaging) in single living cells remains a challenge and is far from routinely used to elucidate the intricate networks of molecular events. In this study, we established a novel combination of FP biosensors for dual-parameter ratiometric imaging, consisting of a new fluorescence resonance energy transfer (FRET) pair mVenus (yellow FP)/mKOκ (orange FP)-based (abbreviated as YO) biosensor and a single FP-based biosensor Grx1-roGFP2. Under our imaging condition, 1.4±0.05% of Grx1-roGFP2 signal contributes to the mVenus channel and 5.2±0.12% of the mVenus signal contributes to the Grx1-roGFP2 channel. We demonstrate that such low degree of cross-talk causes negligible distortion of the ratiometric signal of the YO-based FRET biosensor and Grx1-roGFP2. By using this dual-parameter ratiometric imaging approach, we achieved simultaneous imaging of Src/Ca(2+) signaling and glutathione (GSH) redox potential in a single cell, which was previously unattainable. Furthermore, we provided direct evidence that epidermal growth factor (EGF)-induced Src signaling was negatively regulated by H(2)O(2) via its effect on GSH-based redox system, demonstrating the power of this dual-parameter imaging approach for elucidating new connections between different molecular events that occur in a single cell. More importantly, the dual-parameter imaging approach described in this study is highly extendable.     

Gold nanoparticles modified electrode via simple electrografting of in situ generated mercaptophenyl diazonium cations for development of DNA electrochemical biosensor

A novel protocol for development of DNA electrochemical biosensor based on gold nanoparticles (AuNPs) modified glassy carbon electrode (GCE) was proposed, which was carried out by the self-assembly of AuNPs on the mercaptophenyl film (MPF) via simple electrografting of in situ generated mercaptophenyl diazonium cations. The resulting MPF was covalently immobilized on GCE surface via C-C bond with high stability, which was desirable in fabrication of excellent performance biosensors. Probe DNA was self-assembled on AuNPs through the well-known Au-thiol binding. The recognition of fabricated DNA electrochemical biosensor toward complementary single-stranded DNA was determined by differential pulse voltammetry with the use of Co(phen)(3)(3+) as the electrochemical indicator. Taking advantage of amplification effects of AuNPs and stability of MPF, the developed biosensor could detect target DNA with the detection limit of 7.2×10(-11) M, which also exhibits good selectivity, stability and regeneration ability for DNA detection.     

High-performance electrochemical biosensor for the detection of total cholesterol

We report on a highly sensitive electrochemical biosensor for the determination of total cholesterol. The novel biosensor was fabricated by co-immobilizing three enzymes, cholesterol oxidase (ChO(x)), cholesterol esterase (ChE) and horseradish peroxidase (HRP), on nanoporous gold networks directly grown on a titanium substrate (Ti/NPAu/ChO(x)-HRP-ChE). The morphology and composition of the fabricated nanoporous gold were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction spectroscopy (XRD). The electrochemical behaviour of the Ti/NPAu/ChO(x)-HRP-ChE biosensor was studied using cyclic voltammetry (CV), showing that the developed biosensor possessed high selectivity and high sensitivity (29.33 μA mM?1 cm?2). The apparent Michaelis-Menten constant, K(M)(app) of this biosensor was very low (0.64 mM), originating from the effective immobilization process and the nanoporous structure of the substrate. The biosensor exhibited a wide linear range up to 300 mg dL?1 in a physiological condition (pH 7.4), which makes it very promising for the clinical determination of cholesterol. The fabricated biosensor was further tested using real food samples margarine, butter and fish oil, showing that the biosensor has the potential to be used as a facile cholesterol detection tool in food and supplement quality control.     

Growth, structure and spectroscopic characterization of Nd3+-doped KBaGd(WO4)3 crystal with a disordered structure

The undoped and the Nd(3+):KBaGd(WO(4))(3) crystals were grown by the top seeded solution growth (TSSG) method from a flux of K(2)W(2)O(7). The structure of the pure crystal was determined by the single-crystal X-ray diffraction method. It crystallizes in the monoclinic symmetry with space group C2/c. In the structure, K(+) and Ba(2+) ions share the same 8f site with occupancy of 0.464 and 0.536, respectively. The investigation of spectral properties of Nd(3+):KBaGd(WO(4))(3) crystal indicates that it exhibits broad absorption and emission bands, which are attributed to locally disordered environments around the Nd(3+) centers. The broad absorption band is suitable for diode laser pumping.     

Highly ordered mesoporous carbons as electrode material for the construction of electrochemical dehydrogenase- and oxidase-based biosensors

In this work, the excellent catalytic activity of highly ordered mesoporous carbons (OMCs) to the electrooxidation of nicotinamide adenine dinucleotide (NADH) and hydrogen peroxide (H(2)O(2)) was described for the construction of electrochemical alcohol dehydrogenase (ADH) and glucose oxidase (GOD)-based biosensors. The high density of edge-plane-like defective sites and high specific surface area of OMCs could be responsible for the electrocatalytic behavior at OMCs modified glassy carbon electrode (OMCs/GE), which induced a substantial decrease in the overpotential of NADH and H(2)O(2) oxidation reaction compared to carbon nanotubes modified glassy carbon electrode (CNTs/GE). Such ability of OMCs permits effective low-potential amperometric biosensing of ethanol and glucose, respectively, at Nafion/ADH-OMCs/GE and Nafion/GOD-OMCs/GE. Especially, as an amperometric glucose biosensor, Nafion/GOD-OMCs/GE showed large determination range (500-15,000mumoll(-1)), high sensitivity (0.053nAmumol(-1)), fast (9+/-1s) and stable response (amperometric response retained 90% of the initial activity after 10h stirring of 2mmoll(-1) glucose solution) to glucose as well as the effective discrimination to the possible interferences, which may make it to readily satisfy the need for the routine clinical diagnosis of diabetes. By comparing the electrochemical performance of OMCs with that of CNTs as electrode material for the construction of ADH- and GOD-biosensors in this work, we reveal that OMCs could be a favorable and promising carbon electrode material for constructing other electrochemical dehydrogenase- and oxidase-based biosensors, which may have wide potential applications in biocatalysis, bioelectronics and biofuel cells.     

Indirect electrocatalytic determination of choline by monitoring hydrogen peroxide at the choline oxidase-prussian blue modified iron phosphate nanostructures

Choline, as a marker of cholinergic activity in brain tissue, is very important in biological and clinical analysis, especially in the clinical detection of the neurodegenerative disorders disease. This work presents an electrochemical approach for the detection of choline based on prussian blue modified iron phosphate nanostructures (PB-FePO(4)). The obtained nanostructures showed a good catalysis toward the electroreduction of H(2)O(2), and an amperometric choline biosensor was developed by immobilizing choline oxidase on the PB-FePO(4) nanostructures. The biosensor exhibited a rapid response (ca. 2s), low detection limit (0.4±0.05 μM), wide linear range (2 μM to 3.2 mM), high sensitivity (~75.2 μAm M(-1) cm(-2)), as well as good stability and repeatability. In addition, the common interfering species, such as ascorbic acid, uric acid and 4-acetamidophenol did not cause obvious interference due to the low detection potential (-0.05 V versus saturated calomel electrode). This nanostructure could be used as a promise platform for the construction of other oxidase-based biosensors.     

Comparison of amperometric biosensors fabricated by palladium sputtering, palladium electrodeposition and Nafion/carbon nanotube casting on screen-printed carbon electrodes

Different strategies, including palladium electrodeposition (Pd(CV)), Pd sputtering (Pd(S)) and Nafion-solubilized carbon nanotube casting (Nafion/CNT), were used to modify screen-printed carbon electrodes (SPCEs) for the fabrication of amperometric enzyme biosensors. The electrochemical properties of the bare and modified SPCEs and the optimal conditions for surface modification were determined. The electrochemical response of the bare SPCE to H(2)O(2) under the potential of 0.3 V could be improved about 100-fold by Pd modification by electrodeposition or sputtering. By contrast, the electrochemical response of the bare SPCE was enhanced by only about 11-fold by Nafion/CNT casting. Moreover, the Pd(CV)-SPCEs exhibited better reproducibility of electrochemical response (a relative standard deviation (R.S.D.)<6.0%) than freshly prepared Pd(S)-SPCEs (R.S.D.>10%). The glucose biosensor fabricated from Pd-modified electrodes could be stored for up to 108 days without loosing significant activity. The Pd(CV)-SPCE also showed very reliable signal characteristics upon 50 consecutively repeated measurements of ascorbic acid. The electrocatalytic detection of the Pd-SPCE was combined with additional advantages of resistance to surface fouling and hence good stability. In conclusion, this study demonstrated that deposition of Pd thin film on SPCEs by electrodeposition or sputtering provided superior enhancement of electrochemical properties compared to Nafion/CNT-SPCEs. Despite their high electrochemical response, Pd(S)-SPCEs required an activation process to improve stability and Pd(CV)-SPCEs suffered from poor between electrode reproducibility.     

Studies on the interaction mechanism between hexakis(imidazole) manganese(II) terephthalate and DNA and preparation of DNA electrochemical sensor

The interaction between hexakis(imidazole) manganese(II) terephthalate ([Mn(Im)(6)](teph).4H(2)O) and salmon sperm DNA in 0.2M pH 2.30 Britton-Robinson buffer solution was studied by fluorescence spectroscopy and cyclic voltammetry. Increasing fluorescence was observed for [Mn(Im)(6)](2+) with DNA addition, while quenching fluorescence phenomenon appeared for EB-DNA system when [Mn(Im)(6)](2+) was added. There were a couple quasi-reversible redox peaks of [Mn(Im)(6)](2+) from the cyclic voltammogram on the glassy carbon electrode. The peak current of [Mn(Im)(6)](2+) decreased with positive shift of the formal potential in the presence of DNA compared with that in the absence of DNA. All the experimental results indicate that [Mn(Im)(6)](2+) can bind to DNA mainly by intercalative binding mode. The binding ratio of the DNA-[Mn(Im)(6)](2+) association complex is calculated to be 1:1 and the binding constant is 4.44x10(3) M(-1). By using [Mn(Im)(6)](teph).4H(2)O as the electrochemical hybridization indicator, the DNA electrochemical sensor was prepared by covalent interaction and the selectivity of ssDNA modified electrode were described. The results demonstrate the use of electrochemical DNA biosensor in the determination of complementary ssDNA.     

Au nanospheres and nanorods for enzyme-free electrochemical biosensor applications

Au nanocrystals with different morphologies were prepared and used for enzyme-free electrochemical biosensor applications. To investigate the electrocatalytic properties of Au nanocrystals as a function on their morphologies, Au nanocrystals, Au nanospheres (NSs) on silica, Au NSs, and Au nanorods (NRs) with aspect ratios of 1:3 and 1:5, were coated on the screen printed electrodes and further measure the amperometric responses to hydrogen peroxide via three-electrode system. The electrodes modified with Au nanocrystals showed biosensing properties without any enzyme being attached or immobilized at their surface. The hydrogen peroxide detection limits of the biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) were 6.48, 8.65, and 9.38 μM (S/N = 3), respectively. The biosensors with Au NSs, Au NRs (1:3), and Au NRs (1:5) showed the sensitivities of 11.13, 54.53, and 58.51 μA/mM, respectively. These results indicate that morphologies of Au nanocrystals significantly influence the sensitivity of the biosensors. In addition, the enzyme-free biosensors with Au nanocrystals were stable for 2 months. Au nanocrystal-based enzyme-free system, which is proposed in this study, can be used as a platform for various electrochemical biosensors.     

Invertase inhibition based electrochemical sensor for the detection of heavy metal ions in aqueous system: Application of ultra-microelectrode to enhance sucrose biosensor's sensitivity

We are reporting fabrication and characterization of electrochemical sucrose biosensor using ultra-microelectrode (UME) for the detection of heavy metal ions (Hg(II), Ag(I), Pb(II) and Cd(II)). The working UME, with 25 microm diameter, was modified with invertase (INV, EC: 3.2.1.26) and glucose oxidase (GOD, EC: 1.1.3.4) entrapped in agarose-guar gum. The hydrophilic character of the agarose-guar gum composite matrix was checked by water contact angle measurement. The atomic force microscopy (AFM) images of the membranes showed proper confinement of both the enzymes during co-immobilization. The dynamic range for sucrose biosensor was achieved in the range of 1 x 10(-10) to 1 x 10(-7)M with lower detection limit 1 x 10(-10)M at pH 5.5 with 9 cycles of reuse. The spectrophotometric and electrochemical studies showed linear relationship between concentration of heavy metal ions and degree of inhibition of invertase. The toxicity sequence for invertase using both methods was observed as Hg(2+)>Pb(2+)>Ag(+)>Cd(2+). The dynamic linear range for mercury using electrochemical biosensor was observed in the range of 5 x 10(-10) to 12.5 x 10(-10)M for sucrose. The lower detection limit for the fabricated biosensor was found to be 5 x 10(-10)M. The reliability of the electrochemical biosensor was conformed by testing the spike samples and the results were comparable with the conventional photometric DNSA method.     

A novel L-lactate-selective biosensor based on flavocytochrome b2 from methylotrophic yeast Hansenula polymorpha

A novel amperometric biosensor highly selective to L-lactate has been developed using L-lactate-cytochrome c oxidoreductase (flavocytochrome b2) isolated for the first time from thermotolerant methylotrophic yeast Hansenula polymorpha as biorecognition element. Different immobilization methods and low-molecular free-diffusing redox mediators have been tested for optimising the electrochemical communication between the immobilized enzyme and the electrode surface. Moreover, the possibility of direct electron transfer from the reduced form of FCb2 to carbon electrodes has been evaluated. The bioanalytical properties of FCb2-based biosensors, such as signal rise time, dynamic range, dependence of the sensor output on the pH value, the temperature and the storage stability were investigated, and the proposed biosensor demonstrated a very fast response and a high sensitivity and selectivity for L-lactate determination.     

Reagentless biosensors based on self-deposited redox polyelectrolyte-oxidoreductases architectures

Reagentless fructose and alcohol biosensors have been produced with a versatile enzyme immobilisation technique which mimics natural interactions and flexibility of living systems. The electrode architecture is built up on electrostatic interactions by the sequential adsorption of redox polyelectrolytes and redox enzymes giving rise to the efficient transformation of substrate fluxes into electrocatalytic currents. All investigated multilayer structures were self-deposited on 3-mercapto-1-propanesulfonic acid monolayers self-assembled on gold electrodes. Fructose dehydrogenase, horseradish peroxidase (HRP) and the couple HRP-alcohol oxidase were electrochemically connected with a cationic poly[(vinylpyridine)Os(bpy)2Cl] redox polymer (RP) interface in a layer-by-layer self-deposited architecture. The dependence of the distance on the electrochemical response of this interface was also studied showing a clear decrease in the Faradaic current when the distance to the electrode surface was increased. The sensitivities obtained for each biosensor were 19.3, 58.1 and 10.6 mA M(-1) cm(-1) for fructose, H2O2 and methanol, respectively. The sensitivity values can be easily controlled by a rational deposition and manipulation of the charge in the catalytic layers. The electrostatic assembly of the electrochemical interface and the catalytic layers resulted in integrated biochemical systems in which mass transfer diffusion and heterogeneous catalytic and electron transfer steps are efficiently coupled and can be easily manipulated.     

Simultaneous use of electrochemistry and chemiluminescence to detect reactive oxygen species produced by human neutrophils

A novel approach for the simultaneous optical and electrochemical detection of biologically produced reactive oxygen species has been developed and applied. The set-up consists of a luminol-dependent chemiluminescence assay combined with two amperometric biosensors sensitive to superoxide anion radicals (O(2)(-)) and hydrogen peroxide (H(2)O(2)), respectively. The method permits direct, real-time in vitro determination of both extra- and intracellular O(2)(-) and H(2)O(2) produced by human neutrophil granulocytes. The rate of O(2)(-) production by stimulated neutrophils was calculated to about 10(-17)mol s(-1) per single cell. With inhibited NADPH oxidase, a distinct extracellular release of H(2)O(2) instead of O(2)(-) was obtained from stimulated neutrophils with the rate of about 3 x 10(-18)mol s(-1) per single cell. When the H(2)O(2) release was discontinued, fast H(2)O(2) utilisation was observed. Direct interaction with and possibly attachment of neutrophils to redox protein-modified gold electrodes, resulted in a spontaneous respiratory burst in the population of cells closely associated to the electrode surface. Hence, further stimulation of human neutrophils with a potent receptor agonist (fMLF) did not significantly increase the O(2)(-) sensitive amperometric response. By contrast, the H(2)O(2) sensitive biosensor, based on an HRP-modified graphite electrode, was able to reflect the bulk concentration of H(2)O(2), produced by stimulated neutrophils and would be very useful in modestly equipped biomedical research laboratories. In summary, the system would also be appropriate for assessment of several other metabolites in different cell types, and tissues of varying complexity, with only minor electrode modifications.     

Strategies to develop malic acid biosensors based on malate quinone oxidoreductase (MQO)

An amperometric biosensor based on malate quinone oxidoreductase (MQO) was developed for monitoring of the malolactic fermentation of wines. Screen-printed electrodes coupled with appropriate mediators were used as transducers for this novel biosensor. MQO was immobilized by physical entrapment in a photo-cross-linkable poly(vinyl alcohol) polymer (PVA-SbQ) on the surface of the working electrode. Several electrochemical mediators were studied in order to lower the applied potential and minimise the matrix effects. Among them, 2,6-dichlorophenol indophenol (DPIP) and phenazine methosulfate (PMS) were chosen for further development. The working conditions (mediator concentration, applied potential and pH) were optimised for both DPIP and PMS. Detection limits for both types of biosensors were of 5 μM malic acid. Sensitivities obtained for the linear part of the calibration curve were 0.85 and 1.7 mA/M for the biosensors based on DPIP and PMS, respectively. Interferences due to non-specific oxidations were shown to be negligible when using PMS as mediator.     

Syntheses, crystal structures and antimicrobial activities of monomeric 8-coordinate, and dimeric and monomeric 7-coordinate bismuth(III) complexes with tridentate and pentadentate thiosemicarbazones and pentadentate semicarbazone ligands

Novel bismuth(III) complexes 1-4 with the tridentate thiosemicarbazone ligand of 2N1S donor atoms [Hmtsc (L1); 2-acetylpyridine (4N-morpholyl thiosemicarbazone)], the pentadentate double-armed thiosemicarbazone ligand of 3N2S donor atoms [H2dmtsc (L3); 2,6-diacetylpyridine bis(4N-morpholyl thiosemicarbazone)] and the pentadentate double-armed semicarbazone ligand of 3N2O donor atoms [H2dasc (L4b); 2,6-diacetylpyridine bis(semicarbazone)], were prepared by reactions of bismuth(III) nitrate or bismuth(III) chloride and characterized by elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), FTIR and NMR (1H and 13C) spectroscopy. The crystal and molecular structures of complexes 1, 2a, 2b and 4b, and the "free" ligand L1 were determined by single-crystal X-ray structure analysis. The dimeric 7-coordinate bismuth(III) complex [Bi(dmtsc)(NO3)]2, 1, and the monomeric 7-coordinate complexes [Bi(Hdasc)(H2O)](NO3)2.H2O (major product), 2a, and [Bi(dasc)(H2O)]NO3.H2O (minor product), 2b, all with pentagonal bipyramidal bismuth(III) centers, are depicted with one electron pair (6s2) of the bismuth(III) atom, deprotonated forms of multidentate thiosemicarbazone or semicarbazone ligands, and monodentate NO3 or H2O ligands, respectively. These complexes are related to the positional isomers of one electron pair of the bismuth(III) atom; 1 has an electron pair positioned in the pentagonal plane (basal position), while 2a and 2b have an electron pair in the apical position. The monomeric 8-coordinate complex [Bi(mtsc)2(NO3)], 4b, which was obtained by slow evaporation in MeOH of the 1.5 hydrates 4a, was depicted with one electron pair of the bismuth(III) atom, two deprotonated mtsc- ligand and one nitrate ion. On the other hand, crystals of the complex "[Bi(mtsc)Cl2]", 3, prepared by a reaction of BiCl3 with L1 showed several polymorphs (3a, 3b, 3c and 3d) due to coordination and/or solvation of dimethyl sulfoxide (DMSO) used in the crystallization. Bismuth(III) complexes 1 and 4a showed selective and effective antibacterial activities against Gram-positive bacteria. The structure-activity relationship was discussed.     

A histidine-rich and cysteine-rich metal-binding domain at the C terminus of heat shock protein A from Helicobacter pylori: implication for nickel homeostasis and bismuth susceptibility

HspA, a member of the GroES chaperonin family, is a small protein found in Helicobacter pylori with a unique histidine- and cysteine-rich domain at the C terminus. In this work, we overexpressed, purified, and characterized this protein both in vitro and in vivo. The apo form of the protein binds 2.10 +/- 0.07 Ni(2+) or 1.98 +/- 0.08 Bi(3+) ions/monomer with a dissociation constant (K(d)) of 1.1 or 5.9 x 10(-19) microm, respectively. Importantly, Ni(2+) can reversibly bind to the protein, as the bound nickel can be released either in the presence of a chelating ligand, e.g. EDTA, or at an acidic pH (pH((1/2)) 3.8 +/- 0.2). In contrast, Bi(3+) binds almost irreversibly to the protein. Both gel filtration chromatography and native electrophoresis demonstrated that apo-HspA exists as a heptamer in solution. Unexpectedly, binding of Bi(3+) to the protein altered its quaternary structure from a heptamer to a dimer, indicating that bismuth may interfere with the biological functions of HspA. When cultured in Ni(2+)-supplemented M9 minimal medium, Escherichia coli BL21(DE3) cells expressing wild-type HspA or the C-terminal deletion mutant clearly indicated that the C terminus might protect cells from high concentrations of external Ni(2+). However, an opposite phenomenon was observed when the same E. coli hosts were grown in Bi(3+)-supplemented medium. HspA may therefore play a dual role: to facilitate nickel acquisition by donating Ni(2+) to appropriate proteins in a nickel-deficient environment and to carry out detoxification via sequestration of excess nickel. Meanwhile, HspA can be a potential target of the bismuth antiulcer drug against H. pylori.