Computer modeling of standardless molecular spectral analysis of mixtures

The possibility of developing a combined IR-UV-photochemical method of the standardless spectral analysis of a mixture of isomers with similar properties is theoretically justified and a possible method of such analysis is proposed. The necessary condition of the natural design and implementation of the method is carrying out computer experiments based on the theory and methods of calculation of IR and vibronic spectra and the kinetics and quantum yields of photochemical reactions. The efficiency of the inclusion of photochemical transformations of molecules into the analytical procedure is demonstrated. By the arising time dependences of the spectra one can detect the presence of different components in the mixtures and their amounts and extract the corresponding spectral components from the total spectra. This gives a chance to use the elaborated standard methods qualitative and quantitative standardless analysis at the next following stage.     

From theory of spectra to standardless analysis of molecular objects

The authors discuss the methodology of quantitative analysis of pure substances and mixtures by optical spectra (IR, Raman, UV, etc.) without using samples of standard composition (standardless molecular spectral analysis). An algorithm of quantitative mixture analysis using the reduction of ideal spectra to real ones and computational algorithms of the determination of component concentrations in a mixture taking into account error distribution is proposed. The applicability of the method is estimated using computational experiments parsed and conclusions about the specific features of its work are drawn.     

Particular features of photochemical transformations of molecules initiated by continuous external impact

Photochemical transformations induced by long-term continuous exposure to light have been studied. Using the developed theory and methods for calculating photochemical processes, computer experiments have been performed and their results have been analyzed for a large number of model systems and particular reactions. The excitation process has been considered in an explicit form, and the population of energy levels in excited states by absorption of light quanta has been taken into account. It has been shown that continuous optical excitation qualitatively changes the situation in comparison with pulsed excitation: the quantum yield is not zero even at very low quantum beat frequencies. For fast reactions, the kinetics of the process is exponential; in the case of slow reactions, concentration oscillations (on the order of 25% or more) arise, which are clearly manifested in the stationary state of the molecular system. The choice of the optimal photoirradiation time is an important factor in experimental design aimed to obtain a desired amount of the product. Molecular modeling makes it possible to a priori evaluate this quantity.     

Thermal analysis in studies of photochemical transformations in PVC

The effects of photochemical processes in PVC in response to UV irradiation at 253.7 nm on its thermal stability were investigated. It was found that small differences in the efficiency of the photochemical processes taking place in the PVC can be recorded in the thermal measurements, and that photodehydrochlorination lowers the temperature of thermal dehydrochlorination, while photooxidation and crosslinking increase the temperature of complete decomposition of this polymer.

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Zusammenfassung Der Einfluß der durch UV-Bestrahlung bei 253,7 nm hervorgerufenen fotochemischen Prozesse auf die thermische Stabilität von PVC wurde untersucht. Mittels der thermischen Untersuchungen wurde gefunden, daß im Ergebnis der im PVC stattfindenden fotochemischen Prozesse kleine Unterschiede bestehen. Fotodehydrochlorierung vermindert die Temperatur für die thermische Dehydrochlorierung, während Fotooxidation und Vernetzung die Temperatur für die vollständige Zersetzung dieses Polymers erhöhen.

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Structural transformations of metal alloys under electrocatalytic conditions

Nanostructured alloys are efficient catalysts for mediating renewable energy storage and recovery reactions. The morphology and composition of an alloy can change during catalysis; particularly for potentials more oxidizing than the reversible hydrogen electrode. The formation of noble-metal shells covering an alloy core, or bi-continuous nanoporosity, is a common way an alloy can evolve by a corrosion mediated process. Recently, it was found that alloys can reconstruct within the bulk and form an ordered intermetallic material with different crystal structures and compositions than the starting material during corrosion. This review will discuss the different pathways alloys can be altered by electrochemistry. We will discuss the mechanisms which cover known structural changes and the more recently discovered process involving electrochemically driven incongruent phase transformations. Insights into the transformation of alloy materials are important for understanding how to prepare catalysts with improved electrochemical stability, and for synthesizing materials.     

Monitoring of molecular transformations in acid-base reactions by evolving factor analysis of Fourier transform infrared spectral data

An evolving factor analysis procedure with concentration constraints (gradient concentration window) was applied to the analysis of data sets of aqueous Fourier transform infrared (FT-IR) spectra of carboxylic acids (acetic, malonic and succinic acids) collected in experiments with varying pH. Besides the calculation of the number of acid-base systems, this procedure allowed the calculation of the FT-IR spectra of the acid-base species present in equilibrium as well as the corresponding pK(a) values.     

Iodine induced transformations of alcohols under solvent-free conditions

Iodine has been shown to be an efficient catalyst for transformations of alcohols under solvent-free conditions. In the presence of 5% of iodine, tertiary alcohols underwent dehydration forming the corresponding alkenes, while in the case of 2-phenylpropane-2-ol cyclodimerisation to 1,1,3-trimethyl-3-phenylindane took place. Secondary and primary benzyl alcohols under the same conditions gave the corresponding ethers.     

The standardization of standardless NAA

This review describes how the original `standardless' (absolute and single-comparator) NAA-calibration methods, introduced in the mid-1960s, were stepwise upgraded with respect to their accuracy and manageability, leading to the launching of the k ₀-method in the mid 1970s. Next, an account is given of the achievements in the continuous development of the k ₀-standardization of NAA up to the present. Topics highlighted are:the k 0 -data library, the development of dedicated calibration procedures, extensions and limitations, computerization and quality control/assurance. Finally, a short outline is given of the international dissemination of the k ₀-methodology.     

Synthesis of highly labile SG1-based alkoxyamines under photochemical conditions

Highly labile SG1-based alkoxyamines were synthesized using the photodecomposition of both azo compounds and dithiocarbamates. The former method was a straightforward procedure to obtain the alkoxyamines, but a high [azo]/[nitroxide] ratio is needed. The latter method required only a stoichiometric amount of dithiocarbamate and allowed the recovery of the disulfide after irradiation. This enabled combination of the two methods in a process where only 0.75 equiv of azo compound is needed and where sulfurous compounds acted only as intermediates.     

New photochemical transformations of 1-iodopropan-2-one

Photolysis of 1-iodopropan-2-one (λ = 254 nm) at 80–90°C in the absence of CCl₄ was studied. The structure of obtained polymer was studied by ¹H NMR, IR, and ESR spectroscopy.     

Regularization of methods of a standardless X-ray phase analysis

The Tikhonov regularization of the reference intensity ratio (RIR) method integrated within the information retrieval system of X-ray phase analysis together with the method of cluster phase identification is reported. The possibilities of the methods are discussed by the example of the X-ray phase analysis of test mixtures from Round Robin on QPA held by the International Union of Crystallography Commission for Powder Diffraction (CPD).     

Mass spectral analysis of N-oxides of Chemical Weapons Convention related aminoethanols under electrospray ionization conditions

N,N'-Dialkylaminoethanols are the hydrolyzed products or precursors of chemical warfare agents such as V-agents and nitrogen mustards, and they are prone to undergo oxidation in environmental matrices or during decontamination processes. Consequently, screening of the oxidized products of aminoethanols in aqueous samples is an important task in the verification of chemical weapons convention-related chemicals. Here we report the successful characterization of the N-oxides of N,N'-dialkylaminoethanols, alkyl diethanolamines, and triethanolamine using positive ion electrospray ionization mass spectrometry. The collision-induced dissociation (CID) spectra of the [M+H](+) and [M+Na](+) ions show diagnostic product ions that enable the unambiguous identification of the studied N-oxides, including those of isomeric compounds. The proposed fragmentation pathways are supported by high-resolution mass spectrometry data and product/precursor ion spectra. The CID spectra of [M+H](+) ions included [MH-CH(4)O(2)](+) as the key product ion, in addition to a distinctive alkene loss that allowed us to recognize the alkyl group attached to the nitrogen. The [M+Na](+) ions show characteristic product ions due to the loss of groups (R) attached to nitrogen either as a radical (R) or as a molecule [R+H or (R-H)] after hydrogen migration.     

Calibration of wavelength-dispersive X-ray spectrometer for standardless analysis

An experimental procedure for calibrating wavelength-dispersive X-ray spectrometer is presented. The detection efficiency was determined from the ratio of fluorescent radiation measured using the flow-proportional and the scintillation counter. The relative reflection efficiency of the analyzing crystal for various wavelengths was determined from the X-ray measurements of standard samples. The absorption correction for the atmosphere in the spectrometer chamber was also experimentally examined. All parameters (with the exception of reflection efficiency of the analyzing crystal) can be calculated from the X-ray measurements of unknown samples.