Dipotassium Sodium Diantimonidoindate,K2Na[InSb2], a compound with the polyanion [In2Sb2Sb4/2]6−

The novel compound K₂Na[InSb₂] was synthesized from the elements at 900 K in sealed niobium ampoules. The compound forms plate-like crystals with silver metallic luster, which are very unstable in air and moisture. The crystal structure of K₂NaInSb₂ has been determined using single-crystal X-ray diffraction methods (space group Cmca (No. 64); a = 14.032(2), b = 16.399(3), c = 7.009(1) Å; Z = 8; Pearson symbol oC48). The structure contains pairs of edge-sharing InSb₄ tetrahedra which are linked to four other pairs via common vertices and form a two-dimensional [In₂Sb₂Sb_4/2]^6? anionic partial structure. The resulting pairs of tetrahedral holes are filled by Na⁺ cations. These [In₂Sb₂Sb_4/2]^6? layers are stacked along the b-axis and are interconnected by K⁺ cations. The whole structure can be considered as an ordered derivative of the KMnP structure (PbFCl type).     

Microwave-assisted extraction and ultrasonic slurry sampling procedures for cobalt determination in geological samples by electrothermal atomic absorption spectroscopy

Slurry sampling is compared to microwave-assisted acid digestion for cobalt determination in soil/sediment samples by electrothermal atomic absorption spectrometry (ETAAS). Furnace temperature programs and appropriate amounts of three chemical modifiers were optimised in order to get the highest signals and good separations between the atomic and background signals. Using nitric acid (0.5% (v/v)) as liquid medium, no chemical modifier was needed. The detection limit, based on integrated absorbance, was 0.04 μg g⁻¹ for digests and slurries. Within-batch precision and analytical recoveries were satisfactory for both procedures. Accuracy was tested by analysing a reference soil and a sediment from IRMM. The methods were further compared employing a set of roadside soils and estuarine sediments. As no significant differences (95% confidence) were found, practical analytical properties were suggested in order to select one of them.     

A review of the main factors influencing the FT-IR-PLS abilities exemplified with petrochemical qualimetric applications

Quality control usually involves monitoring several variables directly related with industrial necessities using univariate tests. One powerful alternative is to link multivariate analytical techniques and multivariate chemometrics. In this way, Fourier Transform Infrared spectroscopy and Partial Least Squares regression are used to discuss and review several advantages and drawbacks encountered in using such combination in industrial facilities. Typical drawbacks are selection of data pretreatment, errors in reference methods, selection of calibration and validation sets and model-aging. This review is exemplified with petrochemical applications although other fields are also considered (mainly when dealing with data pretreatment).     

Substrate-assisted antibody catalysis

A new strategy in transition-state analog design is demonstrated to elicit catalytic antibodies. The strategy is based on substrate-assisted antibody catalysis and utilizes analogs designed to mimic the transition-state for intramolecular catalysis and thereby favor antibodies that can recruit catalytic groups from substrate. The hydrolysis of the benzoyl ester of cocaine provides an illustration. The benzoyl ester of cocaine is distant from the protonated nitrogen in the stable chair conformer but proximate in the strained boat form. An antibody stabilizing the boat form and approximating ester and amine could catalyze ester hydrolysis. To mimic the transition-state for the intramolecular catalysis, we synthesized a cocaine analog that replaces this ester with a methylenephenylphosphinate bridge to the tropane nitrogen. This bridged analog elicited 85 cocaine esterases out of 450 anti-analog antibodies-a performance markedly superior to that of a simple phosphonate ester-based analog with an identical tether. The correspondence of the analog to a "high energy" conformer eliminated product inhibition. For certain polyfunctional targets, substrate assistance can be an effective strategy for eliciting catalytic antibodies.     

Rapid determination of some 1,4-benzodiazepines by flow injection analysis

The rapid determination of three 1,4-benzodiazepines (lorazepam, bromazepam, and chlordiazepoxide) by spectrophotometry has been adapted to flow injection analysis. The effects of flow rate and manifold design on the determination are studied. At sampling rates of 120 samples per hour high reproducibility of measurements (relative standard deviations below 1.5% are obtained with 200-μ1 injection volumes) and low reagent consumtions were achieved. The system was applied to determination of these 1,4-benzodiazepines in pharmaceutical formulations and human urine.     

Birth and Death Chains on Finite Trees: Computing their Stationary Distribution and Hitting Times

Every birth and death chain on a finite tree can be represented as a random walk on the underlying tree endowed with appropriate conductances. We provide an algorithm that finds these conductances in linear time. Then, using the electric network approach, we find the values for the stationary distribution and for the expected hitting times between any two vertices in the tree. We show that our algorithms improve classical procedures: they do not exhibit ill-posedness and the orders of their complexities are smaller than those of traditional algorithms found in the literature.     

An eleven amino acid residue deletion expands the substrate specificity of acetyl xylan esterase II (AXE II) from <Emphasis Type="Italic">Penicillium purpurogenum</Emphasis>

The soft-rot fungus Penicillium purpurogenum secretes to the culture medium a variety of enzymes related to xylan biodegradation, among them three acetyl xylan esterases (AXE I, II and III). AXE II has 207 amino acids; it belongs to family 5 of the carbohydrate esterases and its structure has been determined by X-ray crystallography at 0.9 A resolution (PDB 1G66). The enzyme possesses the alpha/beta hydrolase fold and the catalytic triad typical of serine esterases (Ser90, His187 and Asp175). AXE II can hydrolyze esters of a large variety of alcohols, but it is restricted to short chain fatty acids. An analysis of its three-dimensional structure shows that a loop that covers the active site may be responsible for this strict specificity. Cutinase, an enzyme that hydrolyzes esters of long chain fatty acids and shows a structure similar to AXE II, lacks this loop. In order to generate an AXE II with this broader specificity, the preparation of a mutant lacking residues involving this loop (Gly104 to Ala114) was proposed. A set of molecular simulation experiments based on a comparative model of the mutant enzyme predicted a stable structure. Using site-directed mutagenesis, the loop's residues have been eliminated from the AXE II cDNA. The mutant protein has been expressed in Aspergillus nidulans A722 and Pichia pastoris, and it is active towards a range of fatty acid esters of up to at least 14 carbons. The availability of an esterase with broader specificity may have biotechnological applications for the synthesis of sugar esters.     

K3Na26In48: An Intermetallic Phase with Large Pseudo-icosahedral Clusters and a Na46 Clathrate-I Network Enveloping a Covalent [In12] Cluster Framework

K₃Na₂₆In₄₈ was synthesized from the elements in sealed niobium ampoules (melted at 873 K; annealed at 573 K). The compound forms brittle crystals with silver metallic lustre, behaves as a metallic conductor, and is very sensitive to air and moisture. The crystal structure of K₃Na₂₆In₄₈ (cubic; space group Pm3 n,No. 223; a = 16.046(2) Å; Z = 2; Pearson symbol cP154) contains two empty icosahedral In and six hexagonal antiprismatic In indium clusters per unit cell. The latter are centered by Na atoms. All In₁₂ clusters are interconnected by 12 exo-bonds forming a covalent 3 D network (In—In = 2.912—3.149 Å). The remaining Na atoms form a Na₄₆ 3 D-network of the clathrate-I type with (2 + 6) cages, enveloping the In₁₂ clusters network. This novel structure can be regarded as a filled derivative of the clathrate-I structure: . The potassium atoms link the filled [NaIn] clusters to 1 D columns, and also form (6,4) net of the NbO type with Na atoms at bridging positions. The whole structure can also be described as a bcc packing of huge condensed A₁₂₂ clusters (16 Å diameter) which have nearly icosahedral symmetry and consist of several atomic shells. The bonding as well as the structural relationships to other phases are discussed in detail.     

Microwave extraction of organochlorine pesticides from soils

The purpose of this work was to develop a rapid, reliable and sensitive method for the extraction of organochlorine pesticides from soils using microwave energy with closed vessel technology. Three oven programs were assayed with two different solvent mixtures in order to achieve adequate experimental conditions for the complete extraction of organochlorine pesticides from the matrix. The method was validated using a certified reference soil material (CRM804-050).     

An inexact scalarization proximal point method for multiobjective quasiconvex minimization

Annals of Operations Research - In this paper we present an inexact scalarization proximal point algorithm to solve unconstrained multiobjective minimization problems where the objective functions...