Algorithm of object identification in qualitative chemical analysis based on fuzzy similarity criteria

An identification algorithm in qualitative chemical analysis is proposed based on the application of fuzzy (using the fuzzy set theory) similarity criteria. Examples of algorithm application to the identification of some objects are given; the stability of conclusions about the identification/nonidentification of objects to certain drawbacks is demonstrated.     

X-Ray determination of the effective charges on sulfur and phosphorus atoms in chemical compounds

The dependencies of Kα line shifts of the P and S atoms on effective charges of the atoms, calculated by CNDO/S, CNDO/2, INDO, and MNDO methods in the minimal and extended basis sets, have been investigated for model compounds. Good linear relationships between Kα shifts and atomic charges have been obtained for all cases investigated except for CNDO/2 and INDO calculations in the extended basis set. It is found that the PS bond ionicity is a nearly constant value, whereas the P S bond ionicity increases linearly with an increase in the positive charge of the central P atom. It is shown that the P and S atom charge in sulfides and phosphines containing no substituents with a strong M-effect at the central atom depend only on inductive substituent effects. Also, the positive charge on the central atom increases with the growth of the π-donor properties of substituents in sulfides and phosphines containing substituents exerting a strong M-effect, as well as in phosphoryl and thiophosphoryl compounds and sulfones.     

Indirect polarographic microdetermination of sulphur in organic compounds

A polarographic method for the microdetermination of sulphur in organic compounds is described; it is based on oxygen-flask combustion to yield sulphate, which is then reacted with excess of barium dichromate solution in hydrochloric acid, followed by adjustment to pH 12, collection of the combined barium chromate and sulphate precipitate, and polarographic determination of the free chromate (equivalent to the sulphate originally present).     

Activation analysis: A basis for chemical similarity and classification

It is shown that activation analysis is especially suited to serve as a basis for determining the chemical similarity between samples defined by their trace element concentration patterns. The general problem of classification and identification is discussed. The nature of possible classification structures and their approriate clustering strategies is considered. A practical computer method is suggested and its application as well as the graphical representation of classification results are given. The possibility for classification using information theory is mentioned. Classification of chemical elements is discussed and practically realized after Hadamard transformation of the concerntration variation patterns in a series of samples.     

Mathematical correction for fingerprint similarity measures to improve chemical retrieval

In many modern chemoinformatics systems, molecules are represented by long binary fingerprint vectors recording the presence or absence of particular features or substructures, such as labeled paths or trees, in the molecular graphs. These long fingerprints are often compressed to much shorter fingerprints using a simple modulo operation. As the length of the fingerprints decreases, their typical density and overlap tend to increase, and so does any similarity measure based on overlap, such as the widely used Tanimoto similarity. Here we show that this correlation between shorter fingerprints and higher similarity can be thought of as a systematic error introduced by the fingerprint folding algorithm and that this systematic error can be corrected mathematically. More precisely, given two molecules and their compressed fingerprints of a given length, we show how a better estimate of their uncompressed overlap, hence of their similarity, can be derived to correct for this bias. We show how the correction can be implemented not only for the Tanimoto measure but also for all other commonly used measures. Experiments on various data sets and fingerprint sizes demonstrate how, with a negligible computational overhead, the correction noticeably improves the sensitivity and specificity of chemical retrieval.     

The chemical state plot for beryllium compounds

Herein, we report the construction of a Wagner chemical state plot for beryllium containing the following: metallic, oxide, nitride and carbide forms of beryllium by combining electron beam‐induced AES and XPS data. AES and XPS values were collected from metallic beryllium mechanically abraded in vacuum, bulk and native beryllium oxide and homogeneous secondary‐phase beryllium nitride and beryllium carbide inclusions. XPS data for beryllium nitride and carbide were obtained from the literature. Copyright © 2015 John Wiley & Sons, Ltd.     

Linear notation for benzenoid aromatic hydrocarbons. Molecular similarity based on notation similarity

Two succinct linear notation systems to encode the structure of polybenzenoid aromatic hydrocarbons are exemplified. Both notation systems use a labeled dual inner graph to represent the hydrocarbon. A molecular similarity index ranging from unity (identical molecules) to zero (completely different molecules) is defined based on a comparison of the linear notations for a pair of compounds. The similarity index procedure is applied to a correlation of the carcinogenic properties of the benzenoid hydrocarbons.     

Scientific foundations and effective chemical methods of combustion,explosion, and gas detonation control

The competition between the branching and termination of reaction chains is shown to determine all general laws of gas combustion and explosion not only at pressures much lower that atmospheric, but also at atmospheric and increased pressures upon self-heating. It is established that the role of any elementary reaction in combustion is determined primarily by its effect on the relation between the rates of chain branching and termination. Scientific foundations and effective chemical methods of combustion, explosion, and combustible gas detonation control are developed.     

Indirect polarographic microdetermination of chlorine or bromine in organic compounds

A polarographic method for the microdetermination of chlorine or bromine in organic compounds is based on oxygen-flask combustion followed by an exchange reaction of chloride or bromide with excess of solid silver chromate, and polarographic determination of the chromate liberated. The method has been applied satisfactorily to a wide range of chlorine or bromine organic compounds with a coefficient of variation not exceeding 1%.     

Recent advances in sample preparation techniques for effective bioanalytical methods

This paper reviews the recent developments in bioanalysis sample preparation techniques and gives an update on basic principles, theory, applications and possibilities for automation, and a comparative discussion on the advantages and limitation of each technique. Conventional liquid-liquid extraction (LLE), protein precipitation (PP) and solid-phase extraction (SPE) techniques are now been considered as methods of the past. The last decade has witnessed a rapid development of novel sample preparation techniques in bioanalysis. Developments in SPE techniques such as selective sorbents and in the overall approach to SPE, such as hybrid SPE and molecularly imprinted polymer SPE, have been addressed. Considerable literature has been published in the area of solid-phase micro-extraction and its different versions, e.g. stir bar sorptive extraction, and their application in the development of selective and sensitive bioanalytical methods. Techniques such as dispersive solid-phase extraction, disposable pipette extraction and micro-extraction by packed sorbent offer a variety of extraction phases and provide unique advantages to bioanalytical methods. On-line SPE utilizing column-switching techniques is rapidly gaining acceptance in bioanalytical applications. PP sample preparation techniques such as PP filter plates/tubes offer many advantages like removal of phospholipids and proteins in plasma/serum. Newer approaches to conventional LLE techniques (salting-out LLE) are also covered in this review article.