Surface Microstructure and Component Changes of Chromium-resistant Enterobacter Cloacae CYS-25 Strain

Enterobacter cloacae CYS-25 strain was isolated from a chromate plant. This bacterium was capable of resisting high hexavalent chromium concentration and reducing Cr（VI） under aerobic condition. CrO4^2- stimulated the increase of bacterial size and production of compact convex paths containing chromium on the bacterial surface. The increase of bacterial size was caused by integrative growth but not extracellular polymeric substance hyperplasia. IR and SDS-PAGE analyses showed the extracellular polymeric substance （EPS） components were mainly proteins and had no obvious changes whether the strains were induced by Cr（VI） or not. The EPS was amorphous and contained trivalent chromium. Under CrO4^2- growth condition, the extracellular substance of Enterobacter cloacae CYS-25 strains and Cr（VI） had redox reaction. The products were Cr^3＊-protein complexes which formed a piece of compact convex paths on the surface of bacteria and prevented Cr（VI） from entering into cells.     

铬酸钠碳氨转化过程的相图分析

研究了铬酸钠碳氨转化过程中Na＋, NH4+// CrO42－, HCO3－-H2O体系的溶解度和相图.根据溶解度和相图对铬酸钠的氨水溶液碳氨转化过程固相析出行为进行分析.结果表明: 相图中存在NaNH4CrO4·2H2O复盐结晶区,浓度较高的铬酸钠氨水溶液转化过程中NaC(HO)3、(NH4)2CrO4和NaNH4CrO4·2H2O结晶可能同时析出,形成混晶.为避免同时析出铬酸铵、碳酸氢钠结晶,铬酸钠氨水初始溶液浓度应稍低于相图中P2(P2′)对应的组成,即为1 g H2O中Na2CrO4 0.8633～1.1377 g,氨0.0611～0.0986 g.     

原子吸收光谱法间接测定萤石中的全硫

基于SO42-和BaCrO4溶液反应生成BaSO4沉淀, 置换出定量的CrO42-, 通过原子吸收法测定Cr, 建立了间接测定萤石中硫的原子吸收光谱法. 方法的工作曲线范围0.05～20 μg/mL SO42-, 检出限为0.017 μg/mL S, 适用于硫质量分数在0.01%～3%范围内萤石样品的测定.     

Al2O3自电解质溶液中吸附CrO4^2^-的特性研究

本文特别延长了pH范围(2-10),详细研究pH、温度、外加正负离子对CrO4^2^-吸附量的影响,说明这种吸附主要是以离子交换方式进行的,并认为表面活性点是产生这类吸附的重要原因.     

Layered double hydroxides as potential chromate scavengers

The LDH of Ni with Fe, having the formula Ni(1-x)Fe(x)(OH)2(A(n-))(x/n)yH2O (A = NO3-, Cl-; x = 0.25, 0.33), scavenges CrO4(2-) ions from solution throughout the concentration range examined (0.00625-0.25 N). The CrO4(2-) uptake capacity is independent of the anion in the starting LDH but is higher when x = 0.25 (3.60 meq g(-1)) as compared to x = 0.33 (2.40 meq g(-1)). These values are higher than those observed for control compounds beta-Ni(OH)2 (1.86 meq g(-1)) and FeO(OH) (1.26 meq g(-1)), which do not have any interlayer chemistry, showing that chromate uptake takes place by its incorporation in the interlayer region by a stoichiometric anion-exchange reaction, rather than by adsorption. Nevertheless, the interaction between the LDH and the chromate ions is weak. The weak interaction is due to the mismatch between the symmetry of the chromate ions and the symmetry of the interlayer site, which introduces turbostratic disorder in the chromate-intercalated LDHs. The chromate ions can be completely leached out by soaking the LDH in a sodium carbonate solution.     

Solvent extraction of the ion-pairs of chromium(VI) and molybdenum(VI) with trioctylmethylammonium chloride and benzyldimethylcetylammonium chloride

The number of capriquat molecules per chromium(VI) atom in the chromate-capriquat ion-association complex has been found to be between one and two. The distribution ratio in the extraction of chromium(VI) with capriquat is dependent on the dielectric constant of the organic solvent, with a minimum at a dielectric constant of about 8. The absorption spectra of the ion-pair extracted into cyclohexane, carbon tetrachloride, benzene and n-butanol are very similar to that of chromate in aqueous solution. The absorption spectra of the chromium(VI)-capriquat extracts in these organic solvents gradually change to an absorption spectrum similar to that of HCrO(4)(-) in aqueous solution. Chromium(VI)-capriquat extracted into chloroform and 1,2-dichloroethane gives absorption spectra similar to that of HCrO(4)(-)in aqueous medium. The chromium(VI)-capriquat species extracted into 1,2-dichloroethane may be (Q(+))(2).CrO(4)(2-)(H(2)O)(n). In contrast, chromium(VI) is extracted with capriquat into the other organic solvents from ammoniacal medium as a mixture of (Q(+))(2).CrO(4)(2-)(H(2)O)(n) and Q(+).NH(4)(+).CrO(4)(2-)(H(2)O)(n). The spectral change is ascribed to the change of the extracted species from (Q(+))(2).CrO(4)(2-)(H(2)O)(n) and Q(+)NH(4)(+).CrO(4)(-)(H(2)O)(n) to Q(+).HCrO(4)(2-)(H(2)O)(n-1). The chromium(VI)-zephiramine species extracted is formulated as (Q(+), NH(4)(+))(2)CrO(4)(2-)(H(2)O)(n).(Q(+).Cl(-))(m). Molybdenum(VI) is extracted with capriquat into the same organic solvents as a mixture of (Q(+))(2).MoO(4)(2-)(H(2)O)(n) and Q(+).NH(4)(+).MoO(4)(2-).(H(2)O)(n).     

聚离子液体水凝胶用于中性水中Cr(VI)的去除

随着经济的快速发展,水污染已成为全球关注的紧迫问题。其中,Cr（VI）在废水中含量较高且毒性较强,可引起多种严重疾病。而大多数污染地表水和地下水的pH往往是接近中性的。因此,开发具有近中性pH值下有效去除Cr（VI）的吸附剂对生态系统和公众健康至关重要。本文设计并制备了具有不同结构的三氮唑鎓聚离子液体水凝胶,并将其应用于CrO42-的吸附和释放。该水凝胶可在中性条件下实现水中CrO42-的100%去除,最大吸附量高达356 mg/g。等温吸附结果表明,在较低浓度下CrO42-在聚离子液体水凝胶中为单层吸附。此外,可进一步通过离子交换将吸附于水凝胶中的CrO42-释放出来,实现吸附剂的再生。     

Vibrational anharmonicity and vibrational Stark effect of sulfate ions trapped in potassium, rubidium and cesium chromate

Room and low temperature (approximately 100 K) FT-IR and Raman spectra of the sulfate doped K2CrO4, Rb2CrO4 and Cs2CrO4 were recorded. The positions of the nu1, nu3, and nu4 fundamental mode components of the dopant anions were measured. Nine (out of possible ten) second-order stretch-stretch vibrational transitions of the dopant anions were detected. On the basis of these data, the anharmonicity constants and the corresponding harmonic eigenvalues were calculated for several vibrational transitions using second-order perturbation theory expressions. The anharmonicity of the studied second-order transitions of the type nu1 + nu3i increases in the order (SO4/K2CrO4) < (SO4/Rb2CrO4) < (SO4/Cs2CrO4), while for those of the type nu3j + nu3i it basically follows the trend: (SO4/K2CrO4) > (SO4/Rb2CrO4) < (SO4/Cs2CrO4). The measured relative Stark splittings of the nu3 and nu4 mode components of the dopant SO4(2-) anions, as well as the average X13i/3i3j values decrease in the order (SO4/K2CrO4) > (SO4/Rb2CrO4) > (SO4/Cs2CrO4). In all cases, the splitting is larger for nu3 than for nu4 modes, indicating a smaller angular than the bond length distortion. The theory of vibrational Stark effect suggests that the observed frequency shifts of the nu1, nu3 and nu4 mode components may be attributed to the increase of the field strength at the doped anion site going from K2CrO4 to Cs2CrO4. The Stark splitting of these modes, on the other hand, implies that the internal crystalline field vector is almost parallel to the (hypothetical) C2 axis of the slightly distorted dopant tetrahedral anions.     

Speciation of aqueous chromium(VI) solutions with the aid of Q-mode factor analysis followed by oblique projection

The identities of the species of chromium(VI) that are present in aqueous solution, their spectra and their equilibria, continue to be a subject of discussion in the literature. In this paper, the composition of the Cr(VI) equilibria was estimated from the UV-vis spectra of dilute potassium dichromate solutions, without any prior knowledge of the quantities of pure components, with the aid of Imbrie Q-mode factor analysis (Q-mode FA) followed by Varimax rotation and Imbrie oblique projection. Combining these results with the k-matrix method, it was possible to obtain the spectra of the individual Cr(VI) species. Sets of 3.3x10(-4) and 3.3x10(-5) mol l(-1) Cr(VI) solutions were studied. In the pH range from 1 to 12, two factors were identified, which were related to the two species, chromate ion (CrO(4)(2-)) and bichromate ion (HCrO(4)(-)). When the analysis was extended to concentrated acid media, another factor appeared, which was related to chromic acid (H(2)CrO(4)). No evidence for the dichromate ion (Cr(2)O(7)(2-)) was seen at the Cr(VI) concentrations used. The spectra of the pure components were obtained and pK values for the first and second chromic acid dissociations were estimated as -0.54 and 5.8, respectively.     

Crystallographic evidence for oxygen acceptor directionality in oxyanion hydrogen bonds.

A survey of 2632 D-H...O-A hydrogen bonds in crystal structures (where D is any atom and A is the central atom of a trigonal planar (A = C, N) or tetrahedral (A = P, S, Cl, As, Se, Cr, Mo) oxyanion, has established the existence of a distinct directionalities at the oxygen atom acceptors. The directionality depends primarily on the geometry of the oxyanion. With the trigonal planar oxyanions NO3-, HCO3-, and CO32-, the average H...O-A angle is 115 +/- 12 degrees and there is a clear preference for the hydrogen to lie within the plane of the anion. With the tetrahedral oxyanions H2PO4-, HPO42-, HSO4-, SO42-, ClO4-, H2AsO4-, HAsO42-, AsO43-, HSeO4-, SeO42-, CrO42-, and MoO42-, the average H...O-A angle is 122 +/- 12 degrees , and there is a weak preference for eclipsed H...O-X-O dihedral angles. The observed directionality closely coincides with minima on electrostatic potential surfaces calculated for the anions.     

Interactions of nucleosides with CrO(4) (2-) and Cr(3+) as studied by electrospray ionization mass spectrometry

The interactions of CrO(4) (2-) and Cr(3+) with nucleosides studied by electrospray ionization mass spectrometry (ESI-MS) are reported. In water, the nucleosides which do not contain the NH(2) group form the unstable [M+HCrO(4)](-) anion. In the presence of a reducing agent, namely methanol, chromate anion forms stable complexes with nucleosides, [M+CH(3)CrO(4)](-) anions. The fragmentation of [M+CH(3)CrO(4)](-) anions involve elimination of the methanol molecule. Chromium cation-nucleoside complexes were not observed in water. In methanol solutions, adenosine and cytidine form [(M-H)+CrOCH(3)](+) and [(M-H)(2)+Cr](+) ions. Most probably, deprotonated imine tautomers form complexes in which a metal cation is simultaneously coordinated by two nitrogen atoms. Complexes containing chloride anions and a few methanol molecules were observed for other nucleosides. Guanosine and inosine form doubly charged ions of the type [M(2)+CrOCH(3)](2+) that probably contain a bond between the oxygen atom and the chromium cation, (HN(1)--C(6)==O)(2) (....)Cr(3+)).     

Using ratchets and sorters to fractionate motile cells of Escherichia coli by length

This paper describes the fabrication of a composite agar/PDMS device for enriching short cells in a population of motile Escherichia coli. The device incorporated ratcheting microchannels, which directed the motion of swimming cells of E. coli through the device, and three sorting junctions, which isolated successively shorter populations of bacteria. The ratcheting microchannels guided cells through the device with an average rate of displacement of (32 +/- 9) microm s(-1). Within the device, the average length of the cells decreased from 3.8 microm (Coefficient of Variation, CV: 21%) at the entrance, to 3.4 microm (CV: 16%) after the first sorting junction, to 3.2 mum (CV: 19%) after the second sorting junction, to 3.0 mum (CV: 19%) after the third sorting junction.     

Interaction of chromium with resistant strain Aspergillus versicolor: investigation with atomic force microscopy and other physical studies

The interaction of chromium and a chromate resistant Aspergillus versicolor strain has been studied by atomic force (AFM) and transmission electron (TEM) microscopies. The nanomechanical properties such as cell wall rigidity and elasticity were measured by force spectroscopy and found to be 0.61 +/- 0.08 N/m, and 20.5 +/- 2.1 MPa, respectively. On chromium binding, ultrastuctural changes of the cell wall along with the formation of layered structures on the cell wall were observed. TEM and AFM micrographs demonstrate the accumulation of chromium on the cell wall, which were rough and irregular compared with the smooth pristine mycelia. The surface roughness, cell wall rigidity and elasticity increased to 35.5 +/- 3.5 nm, 0.88 +/- 0.05 N/m, and 62.5 +/- 3.5 MPa, respectively, from the corresponding values of 5.2 +/- 0.68 nm, 0.61 +/- 0.02 N/m, and 20.5 +/- 2.1 MPa for the pristine mycelia. X-ray photoelectron spectroscopy and Fourier transform infrared studies suggest that bound chromium was reduced to its trivalent state by the cell wall components. The reduced chromium species on the cell surface further electrostatically bind chromate ions forming layered structure on the cell wall.     

Anisotropic Brownian diffusion near a nanostructured surface

The Brownian diffusion of sub-micrometer-sized particles (diameter 0.52 microm) in the vicinity of a nanostructured surface was experimentally characterized. The surface consisted of a repeating pattern of rectangular grooves with depth 35 nm and pitch 400 nm. It was found that the one-dimensional particle diffusivity parallel to the nanogrooves was significantly higher than the diffusivity perpendicular to the grooves (1.518+/-0.274 (S.E.) microm2/s compared to 0.704+/-0.090 microm2/s). No such anisotropy in the one-dimensional Brownian diffusivity was found for particles near a flat surface.     

A solid-state 53Cr NMR study of chromate and dichromate salts

Solid-state (53)Cr NMR spectra of a series of chromate (CrO4(2-)) and dichromate (Cr2O7(2-)) salts have been examined by employing the stepped-frequency quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) experiment and high applied magnetic field strengths, 11.75 and 18.8 T. Cr-53 nuclear quadrupolar coupling constants, CQ(53Cr), ranging from 1.23 to 5.01 MHz for the Cr(4(2-) salts and 7.25 to 8.14 MHz for the Cr2O7(2-) salts have been measured. For the dichromate salts, this corresponds to central transition 53Cr NMR lineshapes of 200-250 kHz at 18.8 T. The use of hyperbolic secant (HS) pulses in combination with the Hahn-echo (HE) or QCPMG experiment results in significant sensitivity enhancements when acquiring 53Cr NMR spectra of magic-angle spinning (MAS) samples, provided the MAS rate is fast with respect to the second-order quadrupolar interaction. For the CrO4(2-) and Cr2O7(2-) salts, the anisotropic chromium magnetic shielding interaction is generally negligible compared to the second-order 53Cr nuclear quadrupolar interaction. No simple correlation between the structure of the CrO4(2-) and Cr2O7(2-) anions and the observed CQ(53Cr) values has been found.     

The fractal nature of Escherichia coli biological flocs

The fractal structures of Escherichia coli biological flocs were characterised in terms of fractal dimension, which is a measurement of how the bacteria in the flocs occupy space. The dimensional analysis methods, based on power law correlations between floc perimeter, projected area and maximum length, were used to determine the one- and two-dimensional fractal dimensions (D(1) and D(2)) of E. coli flocs formed by flocculation in chitosan solution with a concentration of 10.0 mg chitosan per g dry cell weight (DCW), giving D(1)=1.07+/-0.06 and D(2)=1.70+/-0.08 (+/-S.D.). The three-dimensional fractal dimension (D(3)) of the E. coli flocs was determined by the two-slopes method, using cumulative size distributions of floc length and solid volume, to be 1.99+/-0.08 (+/-S.D.), which is close to the value of D(3)=2.14+/-0.04 (+/-S.D.) measured by the small angle light scattering method. The results demonstrate that E. coli flocs flocculated with chitosan have a fractal nature, as their fractal dimensions D(1), D(2) and D(3) differ from the values of 1, 2 and 3 expected for the spherical Euclidean object, respectively.     

Removing UV-A and UV-C radiation from UV-B fluorescent lamp emissions. Differences in the inhibition of photosynthesis in the marine alga Dunaliella tertiolecta using chromate versus cellulose acetate-polyester filters

Ultraviolet-B (UV-B; 280-320 nm)-emitting lamps unavoidably emit ultraviolet-A (UV-A; 320-400 nm) and ultraviolet-C (UV-C; <280 nm) radiation. Short-wavelength-blocking filters are generally used to limit the wave bands of UV under investigation. The widespread use of such filters means that all exposures to UV-B radiation will have a significant UV-A component. Therefore, the physiological effects unique to UV-B exposure are difficult to clearly isolate. This study presents a method to remove the UV-A and UV-C "contamination" using a liquid potassium chromate (K(2)CrO(4)) filter, thus allowing more direct assessment of the effects of UV-B exposure. Cultures of the green marine alga Dunaliella tertiolecta were grown in the absence of UV radiation. Sunlamps supplied the UV radiation for a 24 h exposure (solar radiation was not used in this study). The UV radiation was filtered either by the standard method (i.e. cellulose acetate (CA) with polyester = Mylar controls) or by a liquid filter of potassium chromate. Photosynthetic responses were compared. Major decreases in the ratio of variable to maximal fluorescence in dark-adapted cells and photosynthetic capacity were observed in CA-filtered cultures, whereas no change was observed in cells exposed to the same UV-B flux with the UV-A removed by K(2)CrO(4). The use of a CA filter with a Mylar control does not link results unequivocally to UV-B radiation. Such results should be interpreted with caution.     

Free-energy landscape of alcohol driven coacervation transition in aqueous gelatin solutions

Liquid-liquid phase separation of a homogeneous polyampholyte (gelatin) solution into a dense polymer-rich coacervate and the dilute supernatant phase is discussed through free-energy landscape formalism. We have evaluated the free energy and entropy of the system as it undergoes the phenomenon of simple coacervation, driven by the addition of a nonsolvent. Electrophoretic mobility (mu) and turbidity measurements were performed on 0.01% and 0.05% (w/v) aqueous gelatin solutions that were driven towards coacervation by the addition of ethanol. The mobility of the polyampholyte molecules, which was typically mu approximately 0.38+/-0.02 microm/s cm/V in water, gradually reduced for the soluble intermolecular complexes to a plateau value of mu approximately 0.11+/-0.01 microm/s cm/V as the ethanol volume fraction equaled phi(ns) approximately 0.47+/-0.03, which coincided with the first appearance of coacervate droplets (coacervation transition) observed from turbidity measurements, a behavior found to be invariant of gelatin concentration. These results were used as input to the theoretical model to explicitly construct the free-energy landscape for a single gelatin chain and the global system comprising the polymer-rich coacervate and the dilute supernatant phase.     

A novel 58-nuclei silver nanowheel encapsulating a subvalent Ag64+ kernel

The combination of CrO_4~(2-)anion and N,N′-dimethylformamide(DMF)-containing solvent helps to stabilize an atom-precise ultrasmall Ag_6 kernel into a 52-nuclei silver shell, giving a core-shell Ag_6@Ag_(52) wheel-like structure(SD/Ag58b). The solution behavior and photocurrent response property were investigated in details.     

Lipid diffusion from single molecules of a labeled protein undergoing dynamic association with giant unilamellar vesicles and supported bilayers

It is demonstrated that single-molecule tracking of a fluorescently labeled protein undergoing transient binding to model membranes presents a useful method of obtaining fluid properties. The labeled ACBP protein was tracked during its binding to free-standing giant unilamellar vesicles (GUVs) and supported bilayers prepared from the GUVs in the same environment. The analysis of images that are blurred as a result of fast probe diffusion was discussed. An examination of the lateral diffusion trajectories revealed a homogeneous diffusion on the top segments of the GUVs with D = 6.9 +/- 0.3 microm(2)/s. The supported bilayer experiments revealed two diffusion processes, one with Df = 3.1 +/- 0.4 microm(2)/s and the other with Ds = 0.078 +/- 0.001 microm(2)/s. The 2-fold difference in the lipid bilayer mobility for the free-standing and fast components in the supported bilayers is attributed to the known effect of frictional coupling with the solid support. The slow mobile fraction in the bilayer is suggested to be associated with the migration of pore-like structures, originating from the interaction of the membrane with the glass support.