Experimental and computational studies of molecules with close,non-bonded hydrogen–hydrogen contacts: common computational methods grossly overestimate some ‘through-space’ NMR scalar coupling constants

The NMR spin–spin scalar coupling constants (J_HH's) of closely contacting, but non-bonded hydrogen atoms in a series of highly strained molecules (including a new in,in-cyclophane made specifically for this study) have been examined both experimentally and computationally. The experimental J_HH's are invariably quite small (0.1–0.6 Hz), but common DFT methods with modest basis sets nearly always overestimate these values, by factors of 10–30, and even with quite large basis sets (up to cc-pVQZ) the J_HH's of two of the molecules are overestimated by a factor of 10 or more. Possible reasons for these discrepancies are discussed.     

Aryl-ONN-azoxy-α,α-dinitroalkanes and some of their derivatives

Previously unknownN-dinitroalkyl-NNO-azoxybenzenes have been prepared (by nitration ofN-(-hydroximino) alkyl-NNO-azoxybenzenes) and transformed to some derivatives.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1972–1975, November, 1994     

Thick-film electrodes for measurement of superoxide and hydrogen peroxide based on direct protein–electrode contacts

Cytochrome c was immobilized on screen-printed thick-film gold electrodes by a self-assembly approach using mixed monolayers of mercaptoundecanoic acid and mercaptoundecanol. Cyclic voltammetry revealed quasi-reversible electrochemical behavior of the covalently fixed protein with a formal potential of +10 mV vs. Ag/AgCl. Polarized at +150 mV vs. Ag/AgCl the electrode was found to be sensitive to superoxide radicals in the range 300–1200 nmol L^–1. Compared with metal needle electrodes sensitivity and reproducibility could be improved and combined with the easiness of preparation. This allows the fabrication of disposable sensors for nanomolar superoxide concentrations. By changing the electrode potential the sensor can be switched from response to superoxide radicals to hydrogen peroxide—another reactive oxygen species. H₂O₂ sensitivity can be provided in the range 10–1000 mol L^–1 which makes the electrode suitable for oxidative stress studies.     

ω,ω′-imino dicarboxylic acids and some of their derivatives

Summary Starting from the corresponding-chloro carboxylic acids we prepared, -imino dicarboxylic acids and their N- and O- derivatives; the products had the following structures:     

On-line solid phase extraction fast liquid chromatography–tandem mass spectrometry for the analysis of bisphenol A and its chlorinated derivatives in water samples

In this study an on-line column-switching fast LC–MS/MS method was developed to analyze bisphenol A (BPA) and its chlorinated derivatives in water. Fast liquid chromatographic separation was performed on a C18 reversed phase column based on fused-core particle technology (2.7 μm particle size) providing analysis times shorter than 3 min and high peak efficiencies. The main benefit of this LC system is that it can easily be hyphenated to a conventional on-line preconcentration device allowing the direct analysis of water samples without any pretreatment at concentrations levels down to 60 ng L⁻¹ and preventing contaminations frequently reported in the analysis of BPA. This on-line SPE fast LC system was coupled to a triple quadrupole mass spectrometer operating in enhanced mass resolution mode (Q1 FWHM = 0.7 Th, Q3 FWHM = 0.1 Th) in order to minimize interferences and chemical noise. This highly sensitive and selective method was successfully employed to analyze BPA and its chlorinated derivatives in water samples.     

Electronic absorption study on acid–base equilibria for some pyrimidine derivatives containing semi- and thiosemicarbazone moiety

The UV–vis spectra of recently synthesized 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-one, (I), and 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-thione, (II) were studied in aqueous methanol (5%, v/v methanol). The nature of the electronic transitions and the roles of carbonyl oxygen of I and thiocarbonyl sulfur of II on the behavior of UV–vis spectra were discussed.Acid–base equilibria of the compounds against varying pH and pK_a values related equilibria were determined at an ionic strength of 0.10 M by using the Henderson–Haselbalch equation. The mean acidity constants for the protonated forms of the compounds were determined as pK_a1 = 5.121, pK_a2 = 7.929 and pK_a3 = 11.130 for I and pK_a1 = 4.684, pK_a2 = 7.245 and pK_a3 = 10.630 for II. The preferred dissociation mechanisms were discussed based on UV–vis data and a mechanism was proposed for each compound.     

Nano CuO–Ag-catalyzed synthesis of some novel pyrano[2,3-d] pyrimidine derivatives and evaluation of their bioactivity

A simple, highly efficient, and green method is developed for the synthesis of pyrano[2,3-d] pyrimidine derivatives via Knoevenagel and Michael addition in the presence of nano CuO–Ag as a catalyst. The structures of synthesized target compounds 5a–l were confirmed by spectral and elemental analysis and were screened for their antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH), H₂O₂, and NO methods. Their antibacterial activity against Gram-negative bacteria Pseudomonas aeruginosa and Escherichia coli, against Gram-positive bacteria such as Bacillus subtilis and Staphylococcus aureus, and antifungal activity against Candida albicans and Candida glabrata was also evaluated. The compounds showed higher bacterial activity than the standard used. Compounds 5b , 5d , 5g , 5h , and 5i exhibited higher free radical scavenging activity than the standard butylated hydroxy toluene (BHT). Compounds 5b , 5d , and 5h showed higher activity on Gram-positive bacteria, and compounds 5b , 5d , 5h , and 5i showed higher activity on Gram-negative bacteria than that of standard tetracycline. Compounds 5b , 5j , and 5l showed much higher antifungal activity against Candida globrata and C. albicans than that of standard Griseofulvin.     

UHPLC–MS/MS method for the determination of bisphenol A and its chlorinated derivatives,bisphenol S,parabens, and benzophenones in human urine samples

In the present work, a new method based on a sample treatment by dispersive liquid–liquid microextraction (DLLME) for the extraction of six bisphenols (bisphenol A, bisphenol S, and monochloro-, dichloro-, trichloro-, and tetrachlorobisphenol A), four parabens (methyl-, ethyl-, propyl-, and butylparaben), and six benzophenones (benzophenone-1, benzophenone-2, benzophenone-3, benzophenone-6, benzophenone-8, and 4-hydroxybenzophenone) in human urine samples, followed by ultrahigh-performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) analysis, is validated. An enzymatic treatment allows determining the total content of the target EDCs. The extraction parameters were accurately optimized using multivariate optimization strategies. Ethylparaben ring-¹³C₆, benzophenone-d₁₀, and bisphenol A-d₁₆ were used as surrogates. Limits of quantification ranging from 0.1 to 0.6 ng mL^?1 and interday variabilities (evaluated as relative standard deviations) from 2.0 to 13.8 % were obtained. The method was validated using matrix-matched standard calibration followed by a recovery assay with spiked samples. Recovery rates ranged from 94 to 106 %. A good linearity, for concentrations up to 300 ng mL^?1 for parabens and 40 ng mL^?1 for benzophenones and bisphenols, was also obtained. The method was satisfactorily applied for the determination of target compounds in human urine samples from 20 randomly selected individuals.     

Cyclodextrin and some its derivatives inclusion compounds with “Ibuprofen” remedy substrate

The practical pathways are proposed for the synthesis of cyclodextrins and some of their derivatives inclusion compounds with the “Ibuprofen“ remedy substrate. The effect of the cavity size, nature of the solvent and character and number of substituents at the cyclodextrin carcass on the possibility of isolation of the inclusion compounds that are of pharmacological significance, are elucidated.     

Synthesis and specific nootropic activity of (–)-cytisine derivatives with carbamide and thiocarbamide moieties in their structure

N-(methylcytisinyl)-N′-substituted ureas, N-substituted cytisine-12-carbamides, and cytisine-12-thiocarbamide were prepared by reaction of (–)-cytisine with urea and thiourea and of (–)-cytisine and its 12-N-methyl-3-amino derivative with isocyanates. Their specific nootropic activity was studied in vivo. The therapeutic index was determined for the lead compound. Promising candidates for further pharmacological testing were found.     

An expeditious protocol for synthesis of Baylis–Hillman derived piperazine derivatives and evaluation of their AChE inhibition

Research on Chemical Intermediates - The highly efficient and eco-economical “on water” method has been developed for the rapid construction of highly functionalized...     

What is necessary for next‐generation atmospheric environmental standards? Recent research trends for PM2.5‐bound polycyclic aromatic hydrocarbons and their derivatives

The air pollution associated with PM_2.5 kills 7 million people every year in the world, especially threatening the health of children in developing countries. However, the current air quality standards depend mainly on particle size. PM_2.5 contains many carcinogenic/mutagenic polycyclic aromatic hydrocarbons (PAHs) and their derivatives such as nitropolycyclic aromatic hydrocarbons and oxygenated PAHs. Among them, environmental standards and guidelines have been set for benzo[a]pyrene by few countries and international organizations. Recent research reports showed that these pollutants are linked to diseases other than lungs, and new methods have been developed for determining trace levels of not only PAHs but also their derivatives. It is time to think about the next‐generation environmental standards. This article aims to (a) describe recent studies on the health effects of PAHs and their derivatives other than cancer, (b) describe new analytical methods for PAH derivatives, and (c) discuss the targets for the next‐generation standards.     

Identification of endogenous and anthropogenic hydrocarbons in bottom deposits of peat lakes and evaluation of their contribution to the “hydrocarbon index”

Gas chromatography with mass spectrometric detection was used to analyze bitumens isolated from bottom sediments of peat lakes contaminated with petroleum products. Endogenous hydrocarbons are characterized by the presence of n-alkanes with an odd number of carbon atoms in the molecule in the characteristic region of C₂₃–C₃₃, the absence of a “hump” characteristic of oil products in the chromatogram, and the presence of light hydrocarbons, eluting in the initial part of the chromatogram (light hydrocarbons are usually lost when the sample is dried). The distribution profile of odd n-alkanes is used to assess the contribution of endogenous hydrocarbons to the “hydrocarbon index” with the help of the pattern recognition method. The concentration of light hydrocarbons is from 50 and 300–400 to 3500–5000 mg/kg for a number of samples and even up to 26000 mg/kg in some samples. The concentration of petroleum hydrocarbons and heteroatomic compounds varies from the lowest values of 30–80 mg/kg up to 20000 mg/kg and higher.     

Prospects of application of Mo–V-phosphoric heteropolyacid solutions as bifunctional catalysts for syntheses of anthraquinones and their substituted derivatives

The acid-catalyzed condensation of 1,3-butadienes with p-quinones and oxidation of the obtained adducts can be carried out as one-pot process in the presence of aqueous solutions of Mo–V–P-heteropolyacids (HPA) of the general composition H_aP_zMo_yV_xO_b. These solutions act as bifunctional catalysts, since they simultaneously behave as strong Brönsted acids and fairly strong reversible oxidants. The condensation of 1,4-naphthoquinone (NQ) with 1,3-butadiene in solutions of high-vanadium HPA of the empirical compositions H₁₅P₄Mo₁₈V₇O₈₉ and H₁₇P₃Mo₁₆V₁₀O₈₉ in the presence of water-miscible organic solvents (acetone, 1,4-dioxane) affords 9,10-anthraquinone in a yield of ~70% and purity up to 97% at a complete conversion of NQ. Under similar conditions, the reactions of NQ and substituted 1,3-butadienes afford substituted anthraquinones in the yields up to 90% and purity up to 99%. The catalysts are regenerated with oxygen in an individual step and can be reused.     

“Increased-valence” structures and the bonding for some cyclic sulphur-nitrogen compounds

For the following (mostly cyclic) thiazyl compounds, attention is given to the construction and examination of “increased-valence” structures when sulphur 3d-orbitals are omitted from the bonding schemes: S₄N₄ and its adducts, Ar₂S₄N₃⁺, S₄N₃⁺, S₄N₄O₂, S₄N₄²⁺, S₅N₅⁺, S₄N₅⁻, S₄N₅O⁻, S₅N₆, S₃N₂⁺, S₆N₄²⁺, and S₃N₂X (with X  Cl⁺, NSO₂F, NCOCF₃, and NP₃N₃F₅). Lewis-Langmuir octet structures are written down, and then some of the non-bonding electrons for these structures are delocalized into bonding SN orbitals. The resulting “increased-valence” structures have one-electron-bonds and fractional electron-pair bonds, as well as normal electron-pair bonds. The hypothesis that fractional electron-pair bonds are shorter than one-electron bonds leads to deductions concerning the relative lengths of the SN bonds that are mostly in general agreement with the experimental values.The nearest-neighbour SS bonds for each of S₄N₄, S₄N₅⁻, S₅N₆ S₄N₃⁺, S₃N₂⁺ and derivatives, and S₆N₄²⁺ are longer than the standard SS single-bond length of ∼ 2.06Å. These lengthenings are due either to less-than-unity values for the SS σ-bond numbers in the “increased-valence” structures, or to the straining of the SS σ-bonds as a consequence of local planarity requirements.The results of simple Hückel molecular orbital calculations of bond lengths are also reported for some of the planar systems. The calculations support the hypothesis that expanded valence-shell linkages (such as

and

for 2-and 3-coordinate sulphur) are not required in the valence structures for the systems considered in this paper.     

Ranking and similarity for quantitative structure–retention relationship models in predicting Lee retention indices of polycyclic aromatic hydrocarbons

Quantitative structure–(chromatographic) retention relationship (QSRR) models for prediction of Lee retention indices for polycyclic aromatic hydrocarbons (PAHs) were gathered from the literature and the predictive performances of models were compared. Numerous Lee retention indices (46) were served as a reliable basis for ranking by a recently developed novel method of ordering based on the sum of ranking differences (SRD) [TrAC, Trends Anal. Chem. 29 (2010) 101–109], by which the best model can be selected easily. Two kinds of references for ranking were accepted, average (consensus) and the experimental retention indices. Leave-many-out cross validation of the SRD procedure provides an easy way to group similar models. Significant differences among models can be revealed by using Wilcoxon's matched pair test.     

Ultrasound-assisted extraction and on-line LC–GC–MS for determination of polycyclic aromatic hydrocarbons (PAH) in urban dust and diesel particulate matter

A method has been developed for determination of polycyclic aromatic hydrocarbons (PAH) in particulate matter from ambient air and diesel exhaust emissions. It is reproducible and accurate and, compared with similar methods for analysis of individual PAH components in complex matrices, it is relatively fast and simple. Single PAH components can be determined in samples of particulate matter from ambient air and diesel exhaust emissions with LOD of approximately 1 pg/sample. Further, sample throughput is high, because more than 20 samples can be extracted and prepared for analysis in one working (8-h) day. The particulate matter is subjected to ultrasound-assisted extraction, a technique that is shown to extract PAH from particulate material with efficiencies fully comparable with those of Soxhlet extraction. An aliphatic/PAH-enriched fraction is obtained by solid-phase extraction before isolation, separation, and identification/quantification of PAH by on-line liquid chromatography–gas chromatography–mass spectrometry. The method was validated by analysis of US National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) 1649a, Urban Dust, and 2975, Diesel Particulate Matter. Results from the method are in good agreement with the NIST-certified PAH concentrations and with NIST reference PAH concentrations.