Optimised method of coal digestion for trace metal determination by atomic absorption spectroscopy

Understanding the transport of trace elements through a coal-fired power plant requires reliable analytical methods for these elements in all the ingoing and outgoing mass streams. Coal and different kinds of ashes comprise the most abundant mass streams in such a plant. As a continuation of our previous work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissolution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO₃ (conc.) and HF (conc.) in the volume ratio of 50 : 1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO₃ alone was used as the digestion acid. Received: 18 June 1998 / Revised: 23 September 1998 / Accepted: 24 September 1998     

Optimised method of coal digestion for trace metal determination by atomic absorption spectroscopy

Understanding the transport of trace elements through a coal-fired power plant requires reliable analytical methods for these elements in all the ingoing and outgoing mass streams. Coal and different kinds of ashes comprise the most abundant mass streams in such a plant. As a continuation of our previous work, we have optimised a digestion method for the AAS determination of heavy metals in coal samples. It has become evident that complete dissolution of metals in coal samples and accurate results in subsequent analysis can be obtained by means of applying pressurised digestion under microwave heating. The combination of HNO₃ (conc.) and HF (conc.) in the volume ratio of 50?:?1 attacked the sample well enough, and good recoveries for all the metals studied were obtained. Surprisingly good results were obtained also when HNO₃ alone was used as the digestion acid.     

The Crystal Structure of Hop‐17(21)‐en‐3β‐yl acetate of Pluchea pteropoda Hemsl. from Vietnam

The title compound isolated from the roots of a Vietnamese plant and being known for its activity against fever was identified by this X‐ray analysis to be a pentacyclic triterpene of hopanoide type with a C17=C21 endocyclic double bond in the five membered ring. The presence of several axially substituted methyl groups on both the α and β side causes the so called "mid‐molecule strain" having already been reported in the literature for other hopane type ring systems.     

Moisture effects on the glass transition and the low temperature relaxations in semiaromatic polyamides

The influence of moisture absorption on the primary (glass) transition (T_a or T_g) and the low temperature relaxations of semiaromatic amorphous polyamides synthesized by isomeric aliphatic diamine and metha or para oriented phthalicdiacids has been investigated by means of differential scanning calorimeter (DSC) and dynamic mechanical thermal analyser (DMTA). The glass transition of semiaromatic polyamides was lowered due to the water absorption, and the β and the γ relaxations were as well. From the observed T_g and the difference in the heat capacity, the calculated T_g depression per 1 wt % water content was 12.3 K and the result was in good agreement with the experimental data. The depression of the glass transition may be expressed by the same manner as the plasticization of nylon 6 by water. The depressed β relaxation observed in the specimen containing a few percent of moisture was splitted into two transitions due to the reduction of water content, of which one was the elevation of the T_β and another was the simultaneous appearance of the T_γ, and then the single T_γ solely was observed for the completely dried specimen. The T_γ seemed to be merged into or not to be observed by the large and broad T_β transition when the sample was governed by a few percent of water, then it was emerged from the T_β due to water desorption. Thus, the T_β is believed to arise from the intermolecular hydrogen bonding between water molecules or between water and amide groups in wet polyamides. In addition, the γ relaxation originated from the peptide groups is attributable to the inter- and intramolecular hydrogen bonding between amide groups. © 1997 John Wiley & Sons, Inc. J Polyn Sci B: Polym Phys 35: 807–815, 1997     

Synthesis and Properties of Novel Nonlinear Optical Polyester Containing Cyanovinylnitroresorcinoxy Group

Novel X-type polyester 5 containing 4-(2’-carbomethoxy-2’-cyano)vinyl-6-nitroresorcinoxy group as nonlinear optical (NLO) chromophore, which constitutes parts of the polymer backbone, was prepared and characterized. Polyester 5 is soluble in common organic solvents such as N,N-dimethylformamide and acetone. Polyester 5 shows a thermal stability up to 280°C from thermogravimetric analysis with glass-transition temperature obtained from differential scanning calorimetry of near 116°C. The second harmonic generation (SHG) coefficient (d₃₃) of poled polymer film at the 1064 nm fundamental wavelength is 4.25 × 10^?9 esu. The dipole alignment exhibits a thermal stability even at 4°C higher than glass-transition temperature (T_g), and no significant SHG decay is observed below 120°C due to the partial main-chain character of polymer structure, which is acceptable for NLO device applications.     

Postsynthetically Modified Alkoxide-Exchanged Ni2(OR)2BTDD: Synergistic Interactions of CO2 with Open Metal Sites and Functional Groups

Postsynthetic modifications (PSMs) of metal–organic frameworks (MOFs) play a crucial role in enhancing material performance through open metal site (OMS) functionalization or ligand exchange. However, a significant challenge persists in preserving open metal sites during ligand exchange, as these sites are inherently bound by incoming ligands. In this study, for the first time, we introduced alkoxides by exchanging bridging chloride in Ni₂Cl₂BTDD (BTDD=bis (1H-1,2,3,–triazolo [4,5-b],–[4′,5′-i]) dibenzo[1,4]dioxin) through PSM. Rietveld refinement of synchrotron X-ray diffraction data indicated that the alkoxide oxygen atom bridges Ni(II) centers while the OMSs of the MOF are preserved. Due to the synergy of the existing OMS and introduced functional group, the alkoxide-exchanged MOFs showed CO₂ uptakes superior to the pristine MOF. Remarkably, the tert-butoxide-substituted Ni_T exhibited a nearly threefold and twofold increase in CO₂ uptake compared to Ni₂Cl₂BTDD at 0.15 and 1 bar, respectively, as well as high water stability relative to the other exchanged frameworks. Furthermore, the Grand Canonical Monte Carlo simulations for Ni_T suggested that CO₂ interacts with the OMS and the surrounding methyl groups of tert-butoxide groups, which is responsible for the enhanced CO₂ capacity. This work provides a facile and unique synthetic strategy for realizing a desirable OMS-incorporating MOF platform through bridging ligand exchange.     

Multiparameter kinetic analysis of alkaline hydrolysis of a series of aryl diphenylphosphinothioates: models for P=S neurotoxins

Alkaline hydrolysis of a series of X‐substituted‐phenyl diphenylphosphinothioates ( 2a‐i ) in 80 mol%/20 mol% DMSO at 25.0 ± 0.1°C has been studied kinetically and assessed through a multiparameter approach. Substrates 2a to 2i are approximately 12 to 22 times less reactive than their P=O analogues 1a to 1i (ie, the thio effect). The Brønsted‐type plot for the reactions of 2a to 2i is linear with β_lg = ?0.43, consistent with a concerted mechanism. Hammett plots correlated with σ^o and σ^? constants also support a concerted mechanism; the Yukawa‐Tsuno plot results in an excellent linear correlation with ρ_X = 1.26 and r = 0.30, indicating that expulsion of the leaving group occurs in the rate‐determining step (RDS). The ΔH^? value increases from 10.5 to 11.7 and 13.9 kcal/mol as substituent X in the leaving group changes from 3,4‐(NO₂)₂ to 4‐NO₂ and H, in turn, while TΔS^? remains constant at ?6.0 kcal/mol. The strong dependence of ΔH^? on the electronic nature of substituent X also indicates that the leaving group departs in the RDS. The reaction mechanism and origin of the thio effect are discussed by comparison of the current kinetic results with those reported for the reactions of 1a to 1i . The results suggest that for useful OP neurotoxins the mechanism of abiotic hydrolysis is concerted (with varying degrees of asynchronicity) when the substrate bears good leaving groups.     

Experimental determination technique for magnetic anisotropy of individual nanowires

We present an experimental technique to determine the magnetic anisotropy of ferromagnetic nanowires. In the technique, the magnetization state is monitored by measuring the anisotropic magnetoresistance with rotating the external magnetic field. The measured magnetoresistance curves exhibit basically the same curves typically appeared in the torque magnetometric measurements, which are then readily analyzed based on the Stoner–Wohlfarth theory with a single fitting parameter – the magnetic anisotropy. By applying the present technique to Permalloy nanowires, it is shown that the shape anisotropy in real nanowires is significantly influenced by the edge roughness.     

Radioactivity in the Baltic Sea: inventories and temporal trends of <Superscript>137</Superscript>Cs and <Superscript>90</Superscript>Sr in water and sediments

The Baltic Sea is ecologically unique as one of the world’s largest brackish water basins. It was significantly contaminated by radioactivity following the Chernobyl accident in 1986, the major contaminant being long-lived ¹³⁷Cs. Due to the slow exchange of water between the Baltic Sea and the North Sea and the relatively rapid sedimentation rates, radionuclides have prolonged residence times in the Baltic Sea. ¹³⁷Cs levels are consequently still clearly higher than in other water bodies around the world. In addition to the Chernobyl accident, artificial radionuclides in the Baltic Sea originate from the global fallout following nuclear weapons testing in the 1950s and 1960s, while discharges into the Baltic Sea from nuclear power plants and other facilities are of minor importance. Here, inventories and the temporal evolution of radionuclides both in seawater and sediments of the Baltic Sea are presented and discussed.     

Nano‐Conjugate Fluorescence Probe for the Discrimination of Phosphate and Pyrophosphate

We describe a pyrophosphate (PPi) probe that is based on a fluorescent dicarboxylate‐substituted poly(para‐phenyleneethynylene) (PPE) and 10 nm cobalt–iron spinel nanoparticles (NPs) in aqueous media. The spinel NPs efficiently quench the fluorescence of the PPE at a concentration of 20–30 pmol. Addition of phosphate anions to the PPE–NP construct displaces the quenched PPE to give rise to a fluorescent response; we found that PPi and phosphate (Pi) have significantly different binding affinities for the self‐assembled materials. We can discern >40 nM PPi in the presence of 0.1 mM Pi at pH 7, which suggests that these assemblies may be useful in bio‐analytical applications. This displacement assay was used to effectively determine the ability of pyrophosphatase to hydrolyze PPi to Pi.