New applications of the retention index concept in gas and high performance liquid chromatography

New methods for the precalculation of GC retention indices (RIs) are discussed. The first is based on a new modification of the correlation equation log RI = a logT_b + bA + c and is recommended for low boiling compounds of the general type R-X with known boiling points (T_b) analyzed on polymer sorbent Porapack Q. The second method permits one to predict RIs of products of organic reactions A + B → C +… with the correlation ΔRI = a ΔE + b (a < 0,|ρ| > 0.9), where ΔRI = RI_C– RI_A– RI_B and ΔE = E_C– E_A– E_B– are the differences in the internal molecular energies of reagents and products of organic reactions which are estimated by molecular dynamics methods. In the final section new possibilities of the use of RIs in reversed phase HPLC, namely for the determination of the number of hydroxyl groups in phenols, are illustrated. Received: 9 November 1998 / Revised: 15 April 1999 / Accepted: 30 April 1999     

Organic chemosensors with crown-ether groups (review)

Recent advances in the chemistry of organic chemosensors containing crown-ether groups are reviewed. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1123–1151, August, 2008.     

Ambient temperature sol–gel synthesis of CeO2–SiO2 and TiO2–CeO2–SiO2 films with high efficiency of UV absorption and without destructive oxidation on heat sensitive organic substrate

Highly efficient UV absorption films of CeO₂–SiO₂ and TiO₂–CeO₂–SiO₂ were synthesized through an epoxide assisted sol–gel strategy. As proven by their UV–vis transmittance spectra, the obtained films show very strong absorption in the UV region, at the same time, keeping the high transparency in the visible range. Due to the unique chemistry of this route and the delicate selection of Ce precursor salts, the ceria in the film can be crystallized at ambient temperature, resulting in the effective UV absorption and oxidation minimization of the films. These advantages guarantee their application in the protection of heat-sensitive organic materials.     

Comparison of ascorbic and citric acid contents inRosa canina L. fruit growing in the Central Asian region

The evaluation ofRosa canina L. fruits and their products is depended in part on their organic acid contents. In this study, ascorbic and citric acid contents inRosa canina L. fruits collected from five different regions in Central Asia were investigated. Amounts of acids determined with the HPLC method were found to be 0.048–0.1143 g/100 g for ascorbic acid and 5.9–7.5 g/100 g for citric acid. Presented at the Third International Symposium on the Chemistry of Natural Products (Bukhara, Uzbekistan, October 19–22, 1998). Deceased. Published in Khimiya Prirodnykh Soedinenii, No. 6, pp. 768–771, November–December, 1998.     

Proton sponges-based (2-naphthyl)pyridylmethanol

The action of 2-, 3-, and 4-pyridinecarboxaldehydes on 1,8-bis(dimethylamino)-2-lithium-and 1,8-bis(dimethylamino)-2,7-dilithiumnaphthalenes gave secondary mono-and dicarbinols containing pyridylcarbinol groups at C-2 and C-7 of the proton sponge. Spectral and X-ray diffraction structural data were used to study the molecular structure of these products. Dedicated to Academician B. A. Trofimov, an outstanding organic chemist, who has made a major contribution to the chemistry of acetylenes and nitrogen heterocycles on the occasion of his seventieth jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1409–1417, September, 2008.     

Recent advances in application of intramolecular Suzuki cross-coupling in cyclization and heterocyclization

Abstract  

Palladium-catalyzed reactions are key steps for the formation of carbon–carbon bonds in modern synthetic chemistry and among these reactions few have influenced organic synthesis as greatly as the Suzuki–Miyaura reaction which was first reported in 1979. This review highlights recent and major developments of this approach in intramolecular cyclization and heterocyclization reactions.     

Ordinary organic crystal chemistry. Interpretation of the most probable homomolecular structures

For homomolecular organic crystals, most characteristic types of molecular arrangement corresponding to most widespread structural classes and subclasses are named and interpreted. These characteristic structural variants cover about 70% of crystal substances consisting of chemically identical molecules. Examples of crystal structures are cited to illustrate the structural laws of organic crystals; the structures are given as easily perceptible representations taken from the album “Structure of Organic Crystals.” An important structural feature of ordinary molecular crystals is coexistence of molecules with four or two different orientations (64 and 28%, respectively). Basic notions and approaches of modern organic crystal chemistry are briefly defined. M. V. Lomonosov Moscow State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 1, pp. 126–152, January–February, 1998. This work was supported by RFFR grant No. 96-03-32455.     

Phase distribution of the products of radiation and postradiation distillation of cellulose

A comparison of the postradiation dry distillation of cellulose and its distillation in the mode of electron-beam radiation heating has shown that irradiation reduces the yield of char and water. Preirradiation of cellulose at doses of 0.2–2.2 MGy stimulates a monotonic increase in the proportion of total organic products in the condensate distilled off during postradiation dry distillation, reducing the proportion of water by one third. Effective distillation of cellulose in the radiation heating mode is observed at a dose rate above ∼1 kGy/s. The condensate distilled off at 1.5–2.5 kGy/s is composed of organic compounds by ∼90% and is characterized by a high density (up to 1.33 g/cm³) and a high refractive index (up to 1.4690).     

Host-molecule-coated quantum dots as fluorescent sensors

“Host” molecules, containing a binding site that is highly specific for an analyte “guest,” are used as sensors to register analyte binding through a variety of mechanisms such as colorimetric, fluorescent, or electrochemical signals. There is increasing interest in the host–guest chemistry on the surface of quantum dots (QDs) and in the changes that it produces in the luminescent properties of QDs. The bulk of this study focuses on those QDs with bound host molecules (crown ether, cyclodextrin, calixarene, and porphyrin) and the selectivity they display toward metal ions and small organic molecules.     

Synthesis of Non-Symmetric Functionalized Polyfluoroalkyl Phosphites

Two ways for the synthesis of new representatives of non-symmetric organic phosphites with polyfluoroalkyl substituents were developed based on organic dichlorophosphites. The reaction of polyfluoroalkyl dichlorophosphites with allyl alcohol, proceeding at a temperature of –10–22°C (2 h) in the presence of triethylamine, gave diallyl polyfluoroalkyl phosphites in a yield of 75–77%. Under similar conditions (–30–22°C, 2–4 h, Et3N), alkyl (or aryl) dichlorophosphites reacted with polyfluoroalkanols to form alkyl (or aryl) bis(polyfluoroalkyl) phosphites (yield 56–67%). Unlike diallylpolyfluoroalkyl- and alkylbis(polyfluoroalkyl) phosphites, arylbis(polyfluoroalkyl) phosphites are symmetrized under storage conditions (room temperature, inert atmosphere), forming the corresponding triaryl- and tris(polyfluoroalkyl) phosphites.     

The “supercompressed” state of matter as an investigation object in high-pressure chemistry

The prospects of a new line of research in high-pressure chemistry are discussed, which is associated with investigations of chemical reactions accompanied by large volume effects at ambient pressure and, hence, resulting in greater compressibilities of the reaction products. The compounds formed by intercalation of alkali metals in graphite and intermetallic compounds formed between alkali metals and silver or Group V metals (Sb, Bi), which crystallize with the BiF₃ structural type, are considered as examples of “chemical compression”. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1442–1447, August, 1999.     

Studies on the Distribution of Phenoxyacetic Acid in Two-Phase Systems: n -Aliphatic Hydrocarbon – Water

Phenoxyacetic acid distribution in two-phase systems n-aliphatic hydrocarbon (C₅–C₈) – water and its dimerization in organic phase were investigated. The values of distribution coefficient (D _HR), distribution constant (K _D), and dimerization constant (K _dim) of acid were obtained. The empirical correlations of these quantities with Hildebrand solubility parameter of organic solvents were established. The influence of pH of the aqueous phase as well as the polarity of the applied organic solvents on phenoxyacetic acid physical chemistry in the two-phase systems was described.     

Degradation of an ether–alcohol (3-ethoxypropan-1-ol) by photo-Fenton-generated <Superscript>•</Superscript>OH radicals: products analysis and formation pathways; relevance to atmospheric water-phase chemistry

We have chosen 3-ethoxypropan-1-ol (EtOPrOH) as a typical short-carbon-chain ether–alcohol used as industrial solvent and have analyzed the degradation products resulting from its attack by ^•OH radicals generated by the photo-Fenton reaction. The laboratory conditions were representative of those found in tropospheric water droplets. Twelve products have been identified by use of GC–MS analysis, either directly or after extraction by SPME fibers, and by HPLC–UV analysis with a special column for carboxylic acids and after reaction of carbonyl groups with 2,4-dinitrophenylhydrazine. These products contain one to three carbon atoms (instead of five in EtOPrOH), among which one or two are oxidized. According to the reaction pathways proposed, seven products—including methanal—can result from attack by one ^•OH only, three products imply attack by a second ^•OH, as expected from their higher oxidation number, and it is suggested that reaction between two organic radicals is needed for formation of only two products. The relevance of this investigation to the fate of EtOPrOH and similar ether–alcohols in the troposphere is briefly discussed.     

Effect of coke formation on the transformations of butylenes on a high-silica zeolite catalyst

The transformations of butylenes on a high-silica zeolite catalyst (HHSZC) at 423–773 K were studied. Liquid reaction products formed above 443 K. The liquid phase of the reaction products mainly consisted of aliphatic hydrocarbons at 448–523 K and aromatic hydrocarbons at 623–723 K. The catalyst activity in the formation of liquid products did not show itself until 4–6% consolidation products (CPs) accumulated on its surface. DTA and gravimetric studies showed that CPs were nonuniform in composition. Some of the CPs were removed by decomposition under nitrogen, while others by oxidation with oxygen. It was inferred from ammonia adsorption data that the accumulation of CPs on the surface of HHSZC led to a decrease in the number of acid centers.     

Half-century history of clathrate chemistry

This paper is devoted to the history of a new field of knowledge — clathrate chemistry, whose 50th anniversary is being celebrated. The Historical Dates section contains data on clathrates from the first observations of these compounds (late 18th century) to the pioneering works (1947–1948) of the English crystallographer Herbert Marcus Powell explaining their nature. Major trends of research into clathrate chemistry since Powell’s works are discussed. Translated fromZhurnal Strukturnoi Khimii, Vol. 40, No. 5, pp. 797–808, September–October, 1999     

Hydrogen physisorption in metal–organic frameworks: concepts and quantum chemical calculations

Storage of hydrogen by physisorption in metal–organic frameworks is reviewed from the perspective of quantum chemistry. Concepts regarding the interaction of hydrogen with metals are revised and the specific features of metal–organic frameworks are explained. The influence of the type of inorganic cluster and hydrogen loading and its relation to hydrogen storage are analysed. Heats of hydrogen adsorption in previous studies are critically discussed and estimations are made regarding the adsorption strength needed for storage applications and how to approach commercial targets.     

Fluorescent organic nanocrystal confined in sol–gel matrix for bio-imaging

The sol–gel chemistry combined to a spray-drying process allowed us to control the formation of original hybrid core–shell nanoparticles constituted by molecular nanocrystals of rubrene embedded in biocompatible silicate spheres. With a good management of all the physical (gas flows, temperatures) and chemical (dye, solvent and alkoxide natures, concentrations, and hydrolysis and condensation conditions) parameters, we optimized a one-step and self-assembly process allowing to obtain nanoparticles exhibiting promising optical properties such as highly fluorescent labels (two-photon excitation) for medical imaging. Moreover, the presence of Si–OH functions on the silicate shell surface make easy to functionalize these fluorescent nanoparticles by grafting biomolecules for targeting properties. The confined nucleation and growth of rubrene nanocrystals in sol–gel silicate spheres during their drying in the air laminar flows, prevents any phase segregation or particle coalescence and stabilizes mechanically and chemically the organic cores. The first particle sizes obtained in these first experiments are ranging between 80 and 600 nm, but lower diameters will be easily prepared by increasing the solvent amount. Transmission electron microscopy was used to characterize the rubrene organic cores. The electron diffraction patterns performed at 100 K, under low-dose illumination to avoid amorphization of the samples during electron irradiation, have shown the good crystallinity of the NP rubrene cores that seem to be constituted by single rubrene nanocrystals. Finally, optical confocal microscopy, used in reflection and fluorescence modes, showed that all the core–shell particles are strongly fluorescent. This high fluorescence intensity arises from the high molecule numbers of rubrene nanocrystals, which enhance the absorption and emission cross sections.     

New tools: Uncertainty-based data evaluation

 The principles of uncertainty-based data evaluation are explained. Based on a brief review of recent publications on the topic, examples for application to standard procedures in analytical chemistry – calibration, method validation, standard addition etc., – are given. The performance and the advantages of uncertainty-based data evaluation are discussed. Received: 4 July 1998 · Accepted: 6 July 1998     

Thermo-kinetics study of orange peel in air

Thermal degradation of orange peel was studied in dynamic air atmosphere by means of simultaneous TG-DSC and TG-FTIR analysis. According to the obtained thermal profiles, the orange peel degradation occurred in at least three steps associated with its three main components (hemicellulose, cellulose and lignin). The volatiles compounds evolved out at 150–400 °C and the gas products were mainly CO₂, CO, and CH₄. A mixture of acids, aldehydes or ketones C=O, alkanes C–C, ethers C–O–C and H₂O was also detected. The E _α on α dependence reveled the existence of different and simultaneous processes suggesting that the combustion reaction is controlled by oxygen accessibility, motivated by the high evolution low-molecular-mass gases and volatile organic compounds. These results could explain the non-autocatalytic character of the reactions during the decomposition process.     

Exploring the structural and electronic properties of nitrogen-containing exohydrogenated carbon nanotubes: a quantum chemistry study

Saturated nanotubes consisting of 2–10 and 20 layers of cyclic units of six-membered rings, each one having a pyrimidine-like framework (i.e., –C–C–C–N–C–N–), were studied by quantum chemistry methods using Density Functional Theory (DFT) at the B3LYP/6-31G* level of theory. Four different nanotube (NT) configurations were theoretically studied in this work. They were formed by covalently arranging each layer over the other, with uniform relative rotations of 0°, 60°, 120°, and 180° with respect to each of the layers. Different structures can be created by modulating the relative rotation as layers are added to the main nanostructure. NTs with a relative rotation of 60° showed both greater stabilities and highest potential for catalytic activity. All of them showed band gaps of around 0.2 eV. Charges and other properties can be controlled by appropriate layer arrangement. The studied families of NTs have a very small diameter and could find potential applications in chemistry, physics, and medicine.