Interactions of Pb(II) with particles of a polluted river

Pb(II) interactions with the surface of suspended matter from a polluted river was studied using differential pulse anodic stripping voltammetry (DPASV) technique. Three sampling sites were selected and studies have been done with samples collected in different times of the year (winter, autumn and summer). The values have been compared with those obtained in spring in the same conditions [Sci. Total Environ. 151 (1994) 101].Particles were separated by centrifugation and suspensions of the freeze-dried particles were titrated with Pb(II), being measured the labile metal fraction by DPASV. For comparison, suspensions of river water without any separation have also been titrated.Results show that surface metal complexes are inert, within the time scale of the analytical technique and desorbed organics from surfaces, form labile Pb(II) complexes in solution. For each sample it was determined the capacity for Pb complexation of particles and desorbed organics and the differential function has been estimated. Despite the heterogeneity of ligands, the systems interpreted in a discontinuous way, present one or two kinds of dominant ligands with Pb affinity.     

Pathways of the reactions of nucleophilic addition of H2O and HF molecules to formaldehyde in the gas phase and in the complex with formic acid:ab initio calculations

The gradient pathways of the reactions of nucleophilic addition of H₂O and HF molecules to formaldehyde in the gas phase and in the XH…H₂CO…HC(O)OH complex (X=OH, F) were calculated by theab initio RHF/6-31G^**, MP2(fc)/6-31G^**, and MP2(full)/6-311++G^** methods. Both reactions proceed concertedly. The formation of H-bonded bimolecular pre-reaction complexes is the initial stage of the gas-phase reactions; at the same time, no indications of the formation of stable π-complexes were found on the potential energy surfaces of systems under study. The calculated energy barriers to the gasphase reactions exceed 40 kcal mol⁻¹, while those to reactions in the complex XH…H₂CO…HC(O)OH (X=OH, F) become more than halved. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2146–2154, November, 1998.     

Cation-crown ether complex formation in water. II. Alkali and alkaline earth cations and 12-crown-4, 15-crown-5, and 18-crown-6

The stability constants and the partial molal volume and isentropic partial molal compressibility changes of complex formation between cations and crown ethers in water at 25°C are presented. The cations involved are Na⁺, K⁺, Rb⁺, Cs⁺, Ca²⁺, and Ba²⁺, and the crown ethers are 12-crown-4, 15-crown-5, and 18-crown-6. Values of V of complex formation have been discussed in terms of two simple models, one based on the scaled particle theory, and the others on the Drude-Nernst continuum model. The results indicate that the charge of the potassium cation in 18-crown-6 is especially well screened from the water. On this basis hydration numbers of complexed cations have been calculated. This shows that the size of the cation compared to the crown ether hole is important for the contacts between complexed cations and water.     

四苯硼酸盐的热化学研究——Ⅱ.一价四苯硼酸盐的标准生成焓

本文用自行建立的精密溶解层热装(?)测定了298.15K时,NH_4BPh_4、KBPH_4、RbBPh_4、CsBPh_4、TlBPh_4、AgBPh_4和HgPh_2七种沉淀反应的反应焓,由此计算了一价四苯硼酸盐的标准生成焓、熵及吉布斯自由能.     

Gas-Chromatographic Studies of the Interaction between Water and Methanol Molecules and the Surface of Carbon Materials

The gas-chromatographic method is used to study the interaction of water and methanol molecules with active hydrophilic centres existing at the surface of thermally exfoliated graphite and graphitized thermal carbon black. The concentration of carboxyl and phenol hydroxyl groups at the surface of these sorbents is determined, and heats of adsorption of the studied molecules are shown to be and 28−25 kJ/mol, respectively. It is also shown that adsorption of water at the hydrophilic centres at lowest relative pressure values takes place with formation of clusters consisting of n = 2 water molecules.     

Agro-industrial waste enzymes: Perspectives in circular economy

According to the Food and Agriculture Organization of the United Nations, approximately 1.3 billion tons of food is wasted each year, equivalent to approximately one-third of world production. Agri-food wastes are the source of proteins, carbohydrates, lipids, and other essential minerals that have been exploited for value-added products by the development of biorefineries and sustainable business as important elements of circular economies. The innovation and materialization of these types of processes, including the use of disruptive technologies on microbial bioconversion and enzyme technology, such as nanotechnology, metabolic engineering, and multi-omics platforms, increase the perspectives on the waste valorization process. Lignocellulolytic enzymes, pectinases, and proteases are mainly used as catalyzers on agri-food waste treatment, and their production in house might be the trend in near future for agro-industrial countries. Another way to transform the agri-food wastes is via aerobic or anaerobic microbial process from fungal or bacterial cultures; these processes are the key to produce waste enzymes.     

Traceability of (values carried by) reference materials

 Traceability is a property of the result of a measurement. Since values carried by (reference) materials must also have been obtained, of necessity, by measurement, the definition of traceability also applies to reference materials. It is extremely helpful to give the traceability (of the origin) of a reference material a separate name, i.e. 'trackability'. An analysis of the function of values carried by reference materials, shows that they can fulfill different functions, depending on the intended use. One of the functions located outside the traceability chain – and hence not very relevant for establishing traceability – is evaluating the approximate size of the uncertainty of the measurement of an unknown sample by performing a similar measurement on a reference material, used as a 'simulated sample'. Another function is located inside the traceability chain, where the reference material is used as an added 'internal standard'. Then, the value carried by the reference material is essential for establishing the traceability of the measured value of an unknown sample. In the latter application, the reference material acts as an 'amount standard' (the certified value for amount is used). Received: 11 November 1999 / Accepted: 24 February 2000     

Erratum: Separability between valence and conduction bands in transition metal clusters

Density Functional Theory (DFT) and direct ab initio molecular dynamics (MD) calculations were applied to the hydrogen molecule trapped in a water cluster composed of 12 water molecules (H₂O)₁₂. The static DFT calculation showed that the H₂ molecule is trapped in the center of mass of (H₂O)₁₂. The vibrational frequency of the H–H stretching mode of the H₂ molecule trapped in the water cluster was blueshifted from that in vacuo. On the other hand, the vibrational frequency of H₂ in water‐hydrogen 1:1 complex (H₂O–H₂) was redshifted. A direct ab initio MD calculation of H₂(H₂O)₁₂ at 50 K indicated that the H₂ molecule is rotated freely around the center of mass of the water cluster. The origin of the spectral shift of H₂ in water ice is discussed on the basis of the theoretical results. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

诱导效应指数与含硫含氮的低碳直链有机化合物的标准汽化热

本文利用诱导效应指数建立了含硫含氮的低碳直链有机物的标准汽化热的简单估算方法，我们利用此法计算了一些含硫含氮的直链有机物的标准汽化热，４１个可比较值的相对误差均在５％以内。     

标准气体在检测可燃气体报警器中的重要性

介绍可燃气体报警器的检测现状，分析可燃气体报警器检测元件中毒的原因，强调了检测可燃气体报警器时使用标准气体的重要性，以及标准气体的正确使用。