Biosynthesis, purification and characterization of silver nanoparticles using Escherichia coli

The application of nanoscale materials and structures, usually ranging from 1 to 100 nanometers (nm), is an emerging area of nanoscience and nanotechnology. Nanomaterials may provide solutions to technological and environmental challenges in the areas of solar energy conversion, catalysis, medicine, and water-treatment. The development of techniques for the controlled synthesis of nanoparticles of well-defined size, shape and composition, to be used in the biomedical field and areas such as optics and electronics, has become a big challenge. Development of reliable and eco-friendly processes for synthesis of metallic nanoparticles is an important step in the field of application of nanotechnology. One of the options to achieve this objective is to use ‘natural factories’ such as biological systems. This study reports the optimal conditions for maximum synthesis of silver nanoparticles (AgNPs) through reduction of Ag⁺ ions by the culture supernatant of Escherichia coli. The synthesized silver nanoparticles were purified by using sucrose density gradient centrifugation. The purified sample was further characterized by UV–vis spectra, fluorescence spectroscopy and TEM. The purified solution yielded the maximum absorbance peak at 420 nm and the TEM characterization showed a uniform distribution of nanoparticles, with an average size of 50 nm. X-ray diffraction (XRD) spectrum of the silver nanoparticles exhibited 2θ values corresponding to the silver nanocrystal. The size-distribution of nanoparticles was determined using a particle-size analyzer and the average particle size was found to be 50 nm. This study also demonstrates that particle size could be controlled by varying the parameters such as temperature, pH and concentration of AgNO₃.     

Reduction of Escherichia coli 0157:H7 in shredded iceberg lettuce by chlorination and gamma irradiation

Lettuce was inoculated with a six-strain cocktail of acid-adapted Escherichia coli 0157:H7 at a level of 1×10⁷ CFU/g. Following chlorination at 200 μg/ml, the lettuce was irradiated at 0.15, 0.38, or 0.55 kGy using a ⁶⁰Co source. Survival of E. coli 0157:H7, aerobic mesophiles and yeast and molds were measured over a period of 10 days. For quality analysis, chlorinated lettuce was subjected to irradiation at 0.33 and 0.53 kGy and stored at 1.0°C, 4.0°C or 7.0°C. Changes in texture and color were determined by instrumental means and changes in flavor, odor, and visual quality were determined by sensory testing.

Chlorination plus irradiation at 0.55 kGy produced a 5.4−log reduction in E. coli 0157:H7 levels. Chlorination alone reduced the E. coli 0157:H7 counts by 1–2 logs. Irradiation at 0.55 kGy was also effective in reducing standard plate counts and yeast and mold counts. Irradiation at this level did not cause softening of lettuce and sensory attributes were not adversely affected. In general, appearance and flavor were affected more by the length of storage than by temperature conditions. The 5+log reduction in E. coli counts and lack of adverse effects on sensory attributes indicate that low-dose irradiation can improve the safety and shelf-life of fresh-cut iceberg lettuce for retail sale or food service.     

Ab Initio Study of Conformational Properties of ( Z, Z)-, ( E, Z)-, and ( E, E)-Cyclonona-1,5-dienes

Summary. Ab initio calculations at the HF/6-31G^* level of theory for geometry optimization and MP2/6-31G^*//HF/6-31G^* for a single point total energy calculation are reported for the important energy-minimum conformations and transition-state geometries of (Z,Z)-, (E,Z)-, and (E,E)-cyclonona-1,5-dienes. The C₂ symmetric chair conformation of (Z,Z)-cyclonona-1,5-diene is calculated to be the most stable form; the calculated energy barrier for ring inversion of the chair conformation via the C_s symmetric boat-chair geometry is 58.3kJmol^–1. Interconversion between chair and twist-boat-chair (C₁) conformations takes place via the twist (C₁) as intermediate. The unsymmetrical twist conformation of (E,Z)-cyclonona-1,5-diene is the most stable form. Ring inversion of this conformation takes place via the unsymmetrical chair and boat-chair geometries. The calculated strain energy for this process is 63.5kJmol^–1. The interconversion between twist and the boat-chair conformations can take place by swiveling of the trans double bond with respect to the cis double bond and requires 115.6kJmol^–1. The most stable conformation of (E,E)-cyclonona-1,5-diene is the C₂ symmetric twist-boat conformation of the crossed family, which is 5.3kJmol^–1 more stable than the C_s symmetric chair–chair geometry of the parallel family. Interconversion of the crossed and parallel families can take place by swiveling of one of the double bonds and requires 142.0kJmol^–1.     

Determination of peptidoglycan-associated protein in Escherichia coli NCIB 8545 by capillary zone electrophoresis

An efficient reliable and sensitive capillary zone electrophoresis assay for the six major bacterial peptidoglycan-associated proteins of Escherichia coli NCIB 8545 is described. The method provides the facility to determine quantitatively the effect of antibacterials on bacterial peptidoglycan-associated protein synthesis and thus to further elucidate the mechanism of antibacterial action of such drugs as the antifolates which recently have been shown to adversely affect peptidoglycan synthesis.     

Adhesion of Escherichia coli onto quartz, hematite and corundum: Extended DLVO theory and flotation behavior

The adhesion of Escherichia coli onto quartz, hematite and corundum was experimentally investigated. A strain of E. coli was used that had the genes for expressing protein for silica precipitation. The maximum cell adhesion was observed at pH <4.3 for quartz and at pH 4.5–8.5 for corundum. For hematite, cell adhesion remained low at all pH values. The microbe–mineral adhesion was assessed by the extended DLVO theory approach. The essential parameters for calculation of microbe–mineral interaction energy (Hamaker constants and acid–base components) were experimentally determined. The extended DLVO approach could be used to explain the results of the adhesion experiments. The effect of E. coli on the floatability of three oxide minerals was determined and the results showed that E. coli can act as a selective collector for quartz at acidic pH values, with 90% of the quartz floated at 1.5 × 10⁹ cells/ml. However, only 9% hematite and 30% corundum could be floated under similar conditions. By using E. coli and no reagents, it was possible to separate quartz from a hematite–quartz mixture with Newton's efficiency of 0.70. Removal of quartz from the corundum mixture was achieved by E. coli with Newton's efficiency of 0.62.     

A MO-theoretical study of the hydrogen bond in (HCOOH)2, (HCONH2)2 and (B(OH)3)2

The energy decomposition scheme is used with the ab initio MO of the STO-3G minimal basis to elucidate the nature of hydrogen-bondings in (HCOOH)₂, (HCONH₂)₂ and (B(OH)₃)₂. The comparison of the interaction energy and its five components, together with that of the difference density map, reveals the similarity or the difference of these three systems. Each component of the global difference density represents the characteristic role of the corresponding interaction. While the effect of the exchange and charge-transfer interaction is limited to the hydrogen-bonded region, that of the polarization and the coupling terms is spread over the intramolecular bonds of each monomer. The analysis of some orbital interactions is made with respect to (HCOOH)₂ and the importance of the particular charge-transfer interaction is demonstrated.     

Phototransformation of monovinyl and divinyl protochlorophyllide by NADPH:Protochlorophyllide oxidoreductase of barley expressed in Escherichia coli

The chlorophyll precursors monovinyl protochlorophyllide (MV-PChlide) and divinyl protochlorophyllide (DV-PChlide) were extracted from mutant C-2A' of the unicellular green alga Scenedesmus obliquus which accumulates both protochlorophyllide derivatives in the dark. The two pigments were characterized by absorption and fluorescence spectroscopy and by plasma desorption mass spectrometry. The molecular masses of MV-PChlide and DV-PChlide were determined as 612 and 610 atomic mass units (amu) respectively. Both MV-PChlide and DV-PChlide were accepted as substrates and photoconverted to chlorophyllides in vitro by NADPH:protochlorophyllide oxidoreductase of barley expressed in Escherichia coli.     

Influence of the medium electrolyte concentration on the electric polarizability of bacteria Escherichia coli in presence of ethanol

The electric polarizability is an important parameter of bacteria, giving information about the electric properties of the cells. In our previous works [A.M. Zhivkov, A.Y. Gyurova, Colloids Surf. B: Biointerfaces 66 (2008) 201; A.Y. Gyurova, A.M. Zhivkov, Biophys. Chem., 139 (2009) 8; A.M. Zhivkov, A.Y. Gyurova, J. Phys. Chem. B, 113 (2009) 8375] we have applied an experimental approach to distinguish the contribution of the components of the two types of interface electric polarizability—surface charge dependent (ChD) and Maxwell–Wagner (MW) polarizability. It is based on electro-optical study of the separate influence of the outer and inner medium electrolyte concentration, which changes the external ChD and internal MW components of polarizability; the last effect is reached by the membrane permeability increase in low ethanol concentration. In the present work we investigate the behavior of electric polarizability of Escherichia coli K12 at increasing the outer KCl concentration in presence of 10 vol.% ethanol in order to check if the polarizability components change independently from one another. The conclusion is that the outer electrolyte concentration influence indirectly the internal MW component by the trans-membrane concentration gradient, but the polarizability components themselves change independently.     

Comparison of the effects of visible femtosecond laser pulses and continuous wave laser radiation of low average intensity on the clonogenicity of Escherichia coli

To evaluate the contribution of local pulsed heating of light-absorbing microregions to biochemical activity, irradiation of Escherichia coli was carried out using femtosecond laser pulses (λ = 620 nm, τ_p=3 × 10⁻¹³ s, f_p = 0.5 Hz, E_p = 1.1 × 10⁻³J cm⁻², I_av = 5.5 × 10⁻⁴ W cm⁻², I_p = 10⁹ W cm⁻²) and continuous wave (CW) laser radiation (λ = 632.8 nm, I = 1.3 W cm⁻²). The irradiation dose required to produce a similar biological effect (a 160%–190% increase in the clonogenic activity of the irradiated cells compared with the non-irradiated controls) is a factor of about 10³ lower for pulsed radiation than for CW radiation (3.3 × 10⁻¹ and 7.8 × 10² J cm⁻² respectively). The minimum size of the microregions transiently heated on irradiation with femtosecond laser pulses is estimated to be about 10 Å, which corresponds to the size of the chromophores of hypothetical primary photoacceptors—respiratory chain components.     

Induction of phr gene expression in E. coli strain KY706/pPL-1 by He–Ne laser (632.8 nm) irradiation

We have observed that He–Ne laser irradiation of E. coli strain KY706/pPL-1 leads to induction of photolyase gene, phr. The magnitude of induction was found to depend on the He–Ne laser fluence, fluence rate and post-irradiation incubation period in the nutrient medium. The optimum values for fluence and fluence rate were 7×10³ J/m² and 100 W/m², respectively, and the induction of phr gene was observed to saturate beyond an incubation period of 2 h. Experiments carried out with singlet oxygen quenchers and with D₂O suggest that the effect is mediated via singlet oxygen. Photoreactivation studies carried out after UVC exposure of both the He–Ne laser-exposed as well as unexposed cells showed a larger surviving fraction in the He–Ne laser pre-irradiated cells. This can be attributed to He–Ne laser irradiation-induced induction of phr expression. However, since even without photoreactivating light He–Ne laser pre-irradiated cells show higher survival against UVC radiation it appears that He–Ne laser irradiation induces both light-dependent as well as dark DNA repair processes.     

(R)-4-menthen-3-one in the synthesis of (3S)-methylundecand (2S)-methyldec-1-ylbromides, key synthons for (S,S,S)-diprionylacetate

New capabilities for the synthetic use of (R)-4-menthen-3-one were demonstrated using as examples (3S)-methylundec- and (2S)-methyldec-1-ylbromides, key synthons for (S,S,S)-diprionylacetate (sex pheromone of pine sawflies of genera Diprion and Neodiprion).     

Spin Crossover Properties of the [Fe( PM - BiA )2(NCS)2] Complex – Phases I and II

Summary.  In the present review, we reexamine the photomagnetic properties of the [Fe(PM-BiA)₂(NCS)₂], cis-bis(thiocyanato)-bis[(N-2′-pyridylmethylene)-4-(aminobiphenyl)]iron(II), compound which exhibits, depending on the synthetic method, an exceptionally abrupt spin transition (phase I) with a very narrow hysteresis (T _1/2↓ = 168 K and T _1/2↑ = 173 K) or a gradual spin conversion (phase II) occurring at 190 K. In both cases, light irradiation in the tail of the ¹MLCT-LS absorption band, at 830 nm, results in the population of the high-spin state according to the light-induced excited spin-state trapping (LIESST) effect. The capacity of a compound to retain the light-induced HS information, estimated through the T(LIESST) experiment, is determined for both phases. Interestingly, the shape of the T(LIESST) curve is more gradual for the phase II than for the phase I and the T(LIESST) value is found considerably lower in the case of the phase II. The kinetics parameters involved in the photoinduced high-spin→low-spin relaxation process are estimated for both phases. From these data, the experimental T(LIESST) curves are simulated and the particular influence of the cooperativity as well as of the parameters involved in the thermally activated and tunneling regions are discussed. The Light-Induced Thermal Hysteresis (LITH), originally described for the strongly cooperative phase I, is also reinvestigated. The quasi-static LITH loop is determined by recording the photostationary points in the warming and cooling branches. Corresponding authors. E-mail: letard@icmcb.u-bordeaux.fr Received August 26, 2002; accepted August 30, 2002     

The Stannides YNi x Sn2 ( x = 0, 0.14, 0.21, 1) – Syntheses, Structure, and 119Sn M?ssbauer Spectroscopy

Summary. The stannides YNi _x Sn₂ (x = 0, 0.14, 0.21, 1) were prepared by arc-melting of the pure elements. They were characterized through X-ray powder and single crystal data: ZrSi₂ type, space group Cmcm, a = 438.09(6), b = 1629.6(4), c = 430.34(7) pm, wR2 = 0.0607, 386 F ² values, 14 variables for YSn₂, CeNiSi₂ type, Cmcm, a = 440.6(1), b = 1640.3(1), c = 433.0(1) pm, wR2 = 0.0632, 416 F ² values, 19 variables for YNi_0.142(7)Sn₂, a = 441.0(1), b = 1646.3(1), c = 434.6(1) pm, wR2 = 0.0491, 287 F ² values, 19 variables for YNi_0.207(7)Sn₂, and LuNiSn₂ type, space group Pnma, a = 1599.3(3), b = 440.89(5), c = 1456.9(2) pm, wR2 = 0.0375, 1538 F ² values, 74 variables for YNiSn₂. The YSn₂ structure contains Sn1–Sn1 zig-zag chains (297 pm) and planar Sn2 networks (307 pm). The stannides YNi_0.142(7)Sn₂ and YNi_0.207(7)Sn₂ are nickel filled versions of YSn₂. The nickel atoms have a distorted pyramidal tin coordination with Ni–Sn distances ranging from 220 to 239 pm. New stannide YNiSn₂ adopts the LuNiSn₂ type. The nickel and tin atoms build up a complex three-dimensional [NiSn₂] network in which the yttrium atoms fill distorted pentagonal and hexagonal channels. Within the network all nickel atoms have a distorted square pyramidal tin coordination with Ni–Sn distances ranging from 247 to 276 pm. Except the Sn4 atoms which are located in a tricapped trigonal Y₆ prism, all tin atoms have between 4 and 5 tin neighbors between 297 and 350 pm. ¹¹⁹Sn M?ssbauer spectroscopic data of YNi _x Sn₂ show a decreasing isomer shift (from 2.26 to 2.11 mm/s) from YSn₂ to YNiSn₂, indicating decrease of the s electron density at the tin nuclei.     

High-valent first-row transition-metal complexes of tetraamido (4N) and diamidodialkoxido or diamidophenolato (2N/2O) ligands: Synthesis, structure, and magnetochemistry

Introduced approximately two decades ago, macrocyclic deprotonated tetraamido (4N) and, nearly a decade earlier, acyclic diamidodialkoxido or diamidophenolato (2N/2O) ligand systems have been used, among other things, for the synthesis of a wide variety of high-valent complexes of iron, manganese, cobalt, vanadium, nickel, chromium, and copper. Structural, magnetic, and catalytic properties of these mononuclear, dinuclear, and polynuclear complexes created by the Collins group are reviewed. The present account continues an overview of complexes of this type published recently and devoted to iron species exclusively [Chanda et al., J. Inorg. Biochem., 100 (2006) 606], which provide the first highly effective small molecule mimics of peroxidase enzymes, called TAML activators. The story of the reviewed first-row complexes does not include the diverse and instructive chemistry discovered for osmium, but like the osmium chemistry, it derives its greatest significance from the fact that key members of the various species mark the steps along the design pathway that led to iron-TAML activators. Consideration is given to recent questioning in the literature of the innocence of a TAML system that was designed to be innocent. The reasons underlying the now 15-year old refocusing of our research program on oxidation catalysis and green chemistry with the associated termination of research into designed molecule-based magnetic materials are explained. Our closing contributions from the mid-1990s to the design of molecule-based magnetic materials are reviewed. Previously reported data are discussed in conjunction with newly obtained information on the complexes using density functional theory.     

Preparation, crystal structure and magnetic properties of Ni2(dpa)2(pyz)(H2O)4

A Ni(II)-based dimer structure, Ni₂(dpa)₂(pyz)(H₂O)₄ (dpa = 2,6-pyridine dicarboxylic acid dianion, pyz: pyrazine), has been prepared using hydrothermal synthesis and the solid-state magnetic properties have been evaluated. In the dimeric structure, the planar tridentate 2,6-pyridine dicarboxylic acid dianion coordinates to a Ni(II) ion in a meridional fashion and defines the equatorial plane of the complex. The fourth equatorial coordination site is then occupied by a pyrazine molecule that functions as a linear bidentate ligand bridging two Ni(II) complexes to form a dimer. The axial positions of each Ni(II) complex are occupied by two water molecules to form a distorted octahedral geometry. Susceptibility and magnetization measurements show that both intra-dimer and inter-dimer exchange interactions are weakly antiferromagnetic. The fitting of the magnetic data also indicates the existence of a large axial zero-field splitting term that contributes to the small magnetization even under high fields.     

Solubility of Lanthanide Chlorides ( Ln Cl3) in Alkali Metal Chlorides ( M Cl): Thermodynamics and Electrical Conductivity of the M 3 Ln Cl6 Compounds

Summary.  Several compounds may exist in LnCl₃–MCl mixtures. Those corresponding to the M ₂ LnCl₅ and MLn ₂Cl₇ stoichiometries are formed in a few systems only, with diverse stability strongly dependent on both the corresponding lanthanide and alkali metal. On the other hand, M ₃ LnCl₆ that occur in most systems have a far larger stability range and melt congruently. These latter compounds were investigated in the present work by differential scanning calorimetry and electrical conductivity measurements. The thermodynamic and transport properties were correlated to structural features and related to the mechanism of compound formation. Corresponding author. E-mail: Marcelle.Gaune-Escard@polytech.univ-mrs.fr Received October 2, 2002; accepted November 6, 2002 Published online April 24, 2003 RID="a" ID="a" This paper is dedicated to Professor H. Gamsj?ger on the occasion of his birthday     

Mechanochemical Synthesis of LaOX (X=Cl, Br) and Their Solid State Solutions

A mixture of lanthanum oxide (La₂O₃), chloride (LaCl₃), and bromide (LaBr₃) was ground in air by a planetary ball mill to investigate synthesis of lanthanum oxychloride (LaOCl), oxybromide (LaOBr), and their solid solutions, LaOCl_1−xBr_x (0≤x≤1, Δx=0.25). The synthesizing reactions proceed with an increase in grinding time. Unit cell dimensions, a, c, and lattice volume of the solutions evolve linearly with an increase in x in the LaOCl_1−xBr_x series. Comparing unit cell dimensions of LaOX synthesized by mechanochemical reaction to those of LaOX synthesized by solid-state reaction at high temperature, there is no difference in the length of c, while a is shortened slightly. This may be attributed to the complex cation layer of (LaO)ⁿ⁺_n, with a close relationship to a of the cell dimensions, being affected by the intensive grinding.     

Reactions of organotin chlorides R2SnCl2 (R = Et, But, or Ph) with lithium 4,6-di( tert -butyl)- N -(2,6-diisopropylphenyl)- o -amidophenolate. Synthesis and structures of tin( IV ) o -iminoquinone complexes

The exchange reactions of tin diorganohalides R₂SnCl₂ (R = Et, Bu^t, or Ph) with lithium amidophenolate APLi₂ (AP is the 4,6-di(tert-butyl)-N-(2,6-diisopropylphenyl)-o-iminobenzo-quinone dianion) in tetrahydrofuran produced the new five-coordinate (Et₂SnAP(THF) (3)) and four-coordinate (R₂SnAP (R = Bu^t, Ph)) tin(IV) complexes. The reaction of Ph₂SnCl₂ with APLi₂ in a nonpolar solvent (hexane or toluene) is accompanied by the additional redox process giving rise to the paramagnetic complex Ph₂Sn(ImSQ)Cl (6) (ImSQ is the 4,6-di(tert-butyl)-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone radical anion). The molecular structures of complexes 3 and 6 were established by X-ray diffraction. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 253–258, February, 2007.     

New Pyrrolo[1,2-a]azepine Type Alkaloids from Stemona and Stichoneuron (Stemonaceae)

Summary. Three new pyrroloazepine type alkaloids, stichoneurines A and B and 6-hydroxycroomine were isolated from the lipophilic root extracts of Stichoneuron caudatum and Stemona tuberosa collected in Thailand together with the already known croomine, tuberostemonine, and tuberostemonine A. The structures were elucidated by spectroscopic methods including H/H-COSY, HMQC, and HMBC. Information on the relative stereochemistries and conformational behaviour was obtained by analysis of the NOESY spectra. The formation of pyrroloazepine alkaloids in the genus Stichoneuron is reported for the first time and supports its affiliation to the family Stemonaceae. The occurrence of two different types of alkaloids, of the tuberostemonine and croomine series, in different geographical provenances of Stemona tuberosa is of special chemosystematic interest and may contribute to a more natural species delimitation within that complex group.