Transformations of mercury species in the presence of Elbe river bacteria

The influence of Elbe river bacteria isolated from suspended particulate matter (SPM) on dynamic species transformation of mercury was investigated. Experiments were carried out in the presence of bacteria (batch cultures) and in sterile tapwater as a control. For the methylation of inorganic mercury ions by bacteria several cofactors are under discussion. In this work, methylcobalamin, methyl iodide and S-adenosylmethionine were tested as biogenic methyl donors and trimethyl-lead chloride, trimethyltin chloride and dimethylarsenic acid as abiotic methyl donors. Transmethylation reactions as examples of abiotic methyl transfers have higher effectiveness in the formation of methylmercury (CH₃Hg⁺) than methylation with biogenic compounds. This result was observed in batch cultures as well as in sterile water. SPM-bacteria inhibit methyl transfer to mercury(II) ions. This is not only due to passive adsorption processes of mercury(II) to bacterial cell walls; methylmercury is also decomposed very rapidly by SPM-bacteria and is immobilized as mercury(II) by the cells.     

Highly sensitive and selective pre-column derivatization high-performance liquid chromatography approach for rapid determination of triterpenes oleanolic and ursolic acids and application to Swertia species: optimization of triterpenic acids extraction and pre-column derivatization using response surface methodology

Oleanolic acid (OA) and ursolic acid (UA) are the ubiquitous triterpenic acids in plant kingdom and have multiple biological effects. In the present study, a highly sensitive and selective method using a dual-sensitive probe 2-(5-benzoacridine)ethyl-p-toluenesulfonate (BAETS) as pre-column labeling reagent has been developed for rapid determination of the triterpenes OA and UA by HPLC with fluorescence detection (FLD) and online mass spectrometry identification. Response surface methodology as an efficient tool was employed to optimize the ultrasonic-assisted extraction of triterpenic acids from Swertia plants and the pre-column derivatization reaction, respectively, which ensured the highest triterpenic acids recoveries within the shortest extraction time and the sufficient labeling of the analyzed components. Fast separation of the isomers OA and UA could be achieved on a Hypersil BDS C8 column within 7 min. Both of OA and UA gave the good correlation coefficients of 0.9999. This developed method offered the satisfactory detection limits of 1.10 and 1.30 ng mL⁻¹ for UA and OA, respectively. When applied to Swertia species, it showed good reproducibility.     

Application of the interference standard method for the determination of sulfur, manganese and iron in foods by inductively coupled plasma mass spectrometry

The interference standard method (IFS) is evaluated to improve the accuracy of the determination of S, Mn and Fe in meat and grain samples by inductively coupled plasma quadrupole mass spectrometry (ICP-QMS). Due to ICP-QMS relatively low resolution, polyatomic interferences caused by ¹⁶O₂⁺, (¹⁶OH)₂⁺, ⁴⁰Ar¹⁴NH⁺, and ⁴⁰Ar¹⁶O⁺, for example, can compromise determinations at m/z 32, 34, 55, and 56, respectively. In IFS, differently from traditional internal standard methods, plasma naturally occurring species are used to correct for variations in the interference signal rather than the analyte signal. The method is based on the hypothesis that the interfering ion and the IFS probe present similar behaviors in the plasma, and that by using the analytical (analyte plus interference)/IFS signal ratio one could reduce variations due to interference and, consequently, improve accuracy. In this work, this strategy is evaluated in real sample applications and significant improvements on accuracy are observed for ³²S, ³⁴S, ⁵⁵Mn, and ⁵⁶Fe determinations. Recoveries ranging from 72% for Mn to 105% for Fe in two different standard reference materials are obtained using the ³⁸Ar probe. These analytes are successfully determined in meat and grain samples with concentrations ranging from 4.42 μg g⁻¹ for Mn in corn to 7270 μg g⁻¹ for S in chicken liver. The method is compared with other strategies such as internal standardization and mathematical correction. No instrumental modification or introduction of foreign gases is required, which is especially attractive for routine applications.     

Reexamination of the π-bond strengths within H2C=XHn systems: a theoretical study

The accurate determination of π-bond energies, D(π), in doubly-bonded species has been an important issue in theoretical chemistry. The procedure using the divalent state stabilization energy defined by Walsh has been suggested, and the procedure seems to be conceptually reasonable and applicable to all kinds of doubly-bonded species. Therefore, the aim of this study was to examine whether the procedure could be a reliable methodology for estimating the D(π) values for a variety of H(2)C=XH(n) species. To achieve a higher accuracy, the D(π) values were estimated at QCISD(T)/6-311++G(3df,2p) level of theory combined with isogyric correction. The D(π) values estimated in this work were in excellent agreement with the extant literature values. On the other hand, in determining accurate D(π) values for doubly bonded species, especially in species with lone-pair electrons such as H(2)C=O, it has been found that consideration of highly sophisticated electron correlation effects could be important. However, sufficiently accurate D(π) values have been obtainable at QCISD(T) or CCSD(T) levels with a 6-311++G(3df,2p) basis set on geometries at relatively inferior correlated levels such as MP2 and B3LYP levels with a 6-31+G(d) basis set.     

Evaluation of cadmium species lability using ion-pair reversed phase HPLC coupled on-line with inductively coupled plasma mass spectrometry

Inductively coupled plasma mass spectrometry (ICP-MS) coupled on-line with an ion-pair reversed phase HPLC (IP-RP HPLC) was developed for determining the lability of Cd species. The IP-RP HPLC-ICP-MS system measures chromatographic behaviors of Cd species in the presence of different model complexing agents (L) with stability constants (log K_CdL) from 3.8 to 19.0. Cd species with log K_CdL higher than 16, between 8 and 16, and smaller than 8 was then classified into inert, moderately labile, and labile species, respectively. The conditional stability constants and dissociation rate constants were also estimated from their corresponding chromatographic behavior. This method was applied to evaluating the lability-dependent biouptake of different Cd species in Phaeodactylum tricornutum, a typical unicellular marine diatom. IP-RP HPLC-ICP-MS is a useful and promising technique for determining the lability of noncovalent-bonded metal species (such as Cd species) in the environment and for forecasting their corresponding bioavailability especially when their speciation cannot be rigorously controlled and measured.     

Solid-phase extraction (SPE) assays to ascertain the mechanisms of retention of antimony species in several stationary phases

Liquid chromatography is the most suitable technique for antimony speciation in several types of samples. However, efficiency can be poor for some of these peaks, especially Sb(III) and Me₃SbCl₂ (TMSb). Weak and strong anion exchange stationary phases are mainly used for antimony speciation in several chromatographic conditions. The present study examines the possible contribution of the interaction between antimony species (Sb(III), Sb(V) and TMSb) and stationary phase support to the overall retention mechanism in their chromatographic separation. Several SPE cartridges, selected from those mainly used as support in anion exchange columns, were assayed. Sb (V) was quantitatively eluted from the PSDVB (polystyrene divinylbenzene) and SiO₂ phases, showing the absence of interaction. Sb (III) showed some interaction with the PSDVB phase; TMSb showed strong retention with all the cartridges studied and it was only eluted from the PSDVB phase.     

Exploration of overloaded cation exchange chromatography for monoclonal antibody purification

Cation exchange chromatography using conventional resins, having either diffusive or perfusive flow paths, operated in bind-elute mode has been commonly employed in monoclonal antibody (MAb) purification processes. In this study, the performance of diffusive and perfusive cation exchange resins (SP-Sepharose FF (SPSFF) and Poros 50HS) and a convective cation exchange membrane (Mustang S) and monolith (SO(3) Monolith) were compared. All matrices were utilized in an isocratic state under typical binding conditions with an antibody load of up to 1000 g/L of chromatographic matrix. The dynamic binding capacity of the cation exchange resins is typically below 100 g/L resin, so they were loaded beyond the point of anticipated MAb break through. All of the matrices performed similarly in that they effectively retained host cell protein and DNA during the loading and wash steps, while antibody flowed through each matrix after its dynamic binding capacity was reached. The matrices differed, though, in that conventional diffusive and perfusive chromatographic resins (SPSFF and Poros 50HS) demonstrated a higher binding capacity for high molecular weight species (HMW) than convective flow matrices (membrane and monolith); Poros 50HS displayed the highest HMW binding capacity. Further exploration of the conventional chromatographic resins in an isocratic overloaded mode demonstrated that the impurity binding capacity was well maintained on Poros 50HS, but not on SPSFF, when the operating flow rate was as high as 36 column volumes per hour. Host cell protein and HMW removal by Poros 50HS was affected by altering the loading conductivity. A higher percentage of host cell protein removal was achieved at a low conductivity of 3 mS/cm. HMW binding capacity was optimized at 5 mS/cm. Our data from runs on Poros 50HS resin also showed that leached protein A and cell culture additive such as gentamicin were able to be removed under the isocratic overloaded condition. Lastly, a MAb purification process employing protein A affinity chromatography, isocratic overloaded cation exchange chromatography using Poros 50HS and anion exchange chromatography using QSFF in flow through mode was compared with the MAb's commercial manufacturing process, which consisted of protein A affinity chromatography, cation exchange chromatography using SPSFF in bind-elute mode and anion exchange chromatography using QSFF in flow through mode. Comparable step yield and impurity clearance were obtained by the two processes.     

Spectroscopic investigation on the sonodynamic damage to proteins in the presence of berberine in vitro

In this paper, bovine serum albumin (BSA) was selected as a target molecule, and the sonodynamic damage to proteins in the presence of berberine (BER) and its mechanism were studied by means of absorption and fluorescence spectra. The results of hyperchromic effect of absorption spectra, and quenching of intrinsic fluorescence spectra indicated that the ultrasound-induced BSA molecules damage was enhanced by BER. The damage degree of BSA molecules increased with the increase in ultrasonic irradiation time and BER concentration. The results of synchronous fluorescence and three-dimensional fluorescence spectra confirmed that the synergistic effects of ultrasound and BER induced the damage of BSA molecules. The results of oxidation-extraction photometry with several reactive oxygen species (ROS) scavengers indicated that the damage of BSA molecules could be mainly due to the generation of ROS, and ¹O₂ was the major mediator of the ultrasound-induced BSA molecules damage in the presence of BER.     

Enumeration of point-determining graphs

Point-determining graphs are graphs in which no two vertices have the same neighborhoods, co-point-determining graphs are those whose complements are point-determining, and bi-point-determining graphs are those both point-determining and co-point-determining. Bicolored point-determining graphs are point-determining graphs whose vertices are properly colored with white and black. We use the combinatorial theory of species to enumerate these graphs as well as the connected cases.     

Doping mode, band structure and photocatalytic mechanism of B-N-codoped TiO2

The photocatalyst B and N codoped TiO₂ (B-N-TiO₂) was prepared via the sol-gel method by using boric acid and ammonia as B and N precursors. The doping mode, band structure and photocatalytic mechanism of B-N-TiO₂ were investigated well and elucidated in detail. B-N-TiO₂ showed the narrowed band gap and thus extended the optical absorption due to interstitial N and [NOB] species in the TiO₂ crystal lattice. The coexistence of interstitial N and [NOB] species in the TiO₂ crystal lattice and surface NO_x species allowed the more efficient utilization of visible light. Simultaneously, interstitial [NOB] and N species and surface B₂O₃ and NO_x species facilitated the separation of photo generated electrons and holes and suppress their recombination effectively. Hence, B-N-TiO₂ showed a higher photocatalytic activity than pure TiO₂, N-doped TiO₂ (N-TiO₂) and B-doped TiO₂ (B-TiO₂) under both UV and visible light irradiation.