Electron localization and radiation chemistry of amides

Alkylamides (such as N,N'-dimethylformamide, N,N'-diethylformamide, and N,N'-dimethylacetamide) are aprotic solvents that are widely used in organic synthesis. These polar molecules have no electron affinity, and it is believed that irradiated liquid and solid amides stabilize excess electrons as cavity-type species analogous to hydrated and ammoniated electrons. In this study, we use isotope substitution and EPR spectroscopy to demonstrate that, in frozen amides, the suspected "cavity electron" is, in fact, a solvent-stabilized monomer anion. Our observations call into question other attributions of such features in the literature, both in low temperature solids and room temperature liquids. We also provide a general scheme describing amide radiolysis, as the related amides are used as metal ion extracting agents in nuclear separations.     

Formation of long-lived fluorofullerene trianions in collisions with Na

The first experimental observation of long-lived triply charged fluorofullerene anions in the gas phase obtained from C60F48 is reported. The existence of a Coloumb barrier trapping the third electron in the trianion is supposed to be responsible for detection of the species which is estimated to have negative third electron affinity.     

N‐phosphorylated 3,5‐bis(arylidene)4‐piperidones: Synthesis,X‐ray structure,and evaluation of antitumor activity

In a search for cytotoxic fluorescent materials, a series of N‐phosphorylated compounds 2a–c were prepared by phosphorylation of 3,5‐bis(4‐N,N‐dimethylbenzylidene)‐4‐piperidone 1 . According to X‐ray investigations, molecule 2a is E,E‐isomer with axial position of the P(O)(OCH₂CF₃)₂ substituent. Fluorescence of compounds 2a–c was found to be similar to fluorescence of nonphosphorylated compound 1 . The cytotoxicity of the compounds 2a–c was estimated on several human tumor cell lines (H9, K562, and MCF7). © 2005 Wiley Periodicals, Inc. Heteroatom Chem 16:497–502, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20147     

Electronic Communication between S=1/2 Spins in Negatively‐charged Double‐caged Fullerene C60 Derivative Bonded by Two Single Bonds and Pyrrolizidine Bridge

Radical anion salt {cryptand[2.2.2] (K⁺)}₂(bispheroid)^2??3.5C₆H₄Cl₂ ( 1 ) of the double‐caged fullerene C₆₀ derivative, in which fullerene cages are linked by a cyclobutane bridging cycle and additionally by a pyrrolizidine moiety, was obtained. Each fullerene cage in this derivative accepts one electron on reduction, thus forming the (bispheroid)^2? dianions with two interacting S=1/2 spins on the neighboring cages. Low‐temperature magnetic measurements reveal a singlet ground state of the bispheroid dianions whereas triplet contributions prevail at increased temperature. An estimated exchange interaction between two spins J/k_B=?78 K in 1 indicates strong magnetic coupling between them, nearly two times higher than that (J/k_B=?44.7 K) in previously studied (C₆₀^?)₂ dimers linked via a cyclobutane bridge only. The enhancement of magnetic coupling in 1 can be explained by a shorter distance between the fullerene cages and, possibly, an additional channel for the magnetic exchange provided by a pyrrolizidine bridge. Quantum‐chemical calculations of the lowest electronic state of the dianions by means of multi‐configuration quasi‐degenerate perturbation theory support the experimental findings.     

[6,6]‐Open and [6,6]‐Closed Isomers of C70(CF2): Synthesis,Electrochemical and Quantum Chemical Investigation

Novel difluoromethylenated [70]fullerene derivatives, C₇₀(CF₂)_n (n=1–3), were obtained by the reaction of C₇₀ with sodium difluorochloroacetate. Two major products, isomeric C₇₀(CF₂) mono‐adducts with [6,6]‐open and [6,6]‐closed configurations, were isolated and their homofullerene and methanofullerene structures were reliably determined by a variety of methods that included X‐ray analysis and high‐level spectroscopic techniques. The [6,6]‐open isomer of C₇₀(CF₂) constitutes the first homofullerene example of a non‐hetero [70]fullerene derivative in which functionalisation involves the most reactive bond in the polar region of the cage. Voltammetric estimation of the electron affinity of the C₇₀(CF₂) isomers showed that it is substantially higher for the [6,6]‐open isomer (the 70‐electron π‐conjugated system is retained) than the [6,6]‐closed form, the latter being similar to the electron affinity of pristine C₇₀. In situ ESR spectroelectrochemical investigation of the C₇₀(CF₂) radical anions and DFT calculations of the hyperfine coupling constants provide evidence for the first example of an inter‐conversion between the [6,6]‐closed and [6,6]‐open forms of a cage‐modified fullerene driven by an electrochemical one‐electron transfer. Thus, [6,6]‐closed C₇₀(CF₂) constitutes an interesting example of a redox‐switchable fullerene derivative.     

Reflections on spontaneous asymmetric synthesis by amplifying autocatalysis

Spontaneous generation of chirality was observed in the course of studying the mechanism of asymmetric autocatalysis by NMR in ZnR2 alkylation of pyrimidin-5-aldehydes. A systematic study was carried out in order to discover its origins. Even in clean fresh non-glass reaction vessels spontaneous ee was clearly observed, and was not dependent on any single reaction parameter. For comparison it was demonstrated that enantiomerically pure Zn alkoxide catalyst could control the configuration of the reaction product even when present at below micromolar concentrations. The high propensity of the Soai reaction system to produce an enantiomerically enriched product without initial bias is suggested to result from stochastic effects. These are especially important in autocatalysis because all the final products can be derived by breeding from a small number of initial events. The statistical excess of one enantiomer in that set is sufficient to generate a measurable ee in the product. The process is aided by the requirement for dimerisation before the product is an active catalyst. An enumeration that rationalises these observations is provided.     

Are there reliable DFT approaches for 13C NMR chemical shift predictions of fullerene C60 derivatives?

The relationships between experimental and theoretical ¹³C NMR chemical shifts of a pristine fullerene C₆₀, monoadducts from [2 + n] cycloaddition (n = 1–3), and one [2 + 1] bis‐adduct are systematically analyzed for the first time by using diverse quantum‐chemical levels of theory. These levels involved B3LYP, B3PW91, B97‐2, mPW1PW91, PBE1PBE, and X3LYP hybrid functionals combined with 3‐21G, 6‐31G, 6‐31G(d), 6‐31G(d,p), 6‐31G(d,2p), LanL2DZ, and SDDAll basis sets. X3LYP/6‐31G approach is determined to have the lowest deviations from the ¹³C NMR experimental data compared to the other methods for all the fullerene compounds (mean absolute error value is 0.856 ppm and root mean squared error value is 1.197 ppm). The highest deviations are characteristic for α (sp² C2/C5/C8/C10) and β (sp² C6/C7/C11/C12) carbon atoms relative to a functionalization site and for those (sp³ C1/C9) directly attached with a side fragment in the [2 + n] monoadducts (n = 1–3). A probable reason of such deviation is that the approaches do not take into account a contribution of paramagnetic ring currents to ¹³C NMR chemical shifts. The results will be useful in design of novel fullerene derivatives and in performing unambiguous ¹³C NMR chemical shift assignments with modern quantum chemistry calculations.     

A Novel Streptavidin–luciferase Fusion Protein: Preparation,Properties and Application in Hybridization Analysis of DNA

A streptavidin–luciferase fusion protein comprising the thermostable mutant form of firefly luciferase Luciola mingrelica and minimal core streptavidin was constructed. The streptavidin–luciferase fusion was mainly produced in a tetrameric form with high luciferase and biotin‐binding activities. It was shown that fusion has the same K_m values for ATP and luciferin and the bioluminescence spectra as initial luciferase. The linear dependence of the bioluminescence signal on the content of the fusion was observed within the range of 10^?18–10^?13 mol per well. Successful application of obtained fusion in a biospecific bioluminescence assay based on biotin–streptavidin interactions was demonstrated by the example of a specific DNA hybridization analysis. A DNA hybridization analysis for Escherichia coli cells identification was developed using unique for these cells gadB fragment encoding glutamate decarboxylase. The amplified biotinylated GadB fragments were hybridized with the immobilized oligonucleotide probes; then, the biotin in the DNA duplexes was detected using the streptavidin–luciferase fusion protein. To reach the high sensitivity of the assay, we optimized the conditions of the assay. It was shown that the use of Pluronic for plate modification resulted in a significant reduction in the DNA detection limit which finally was 0.4 ng per well.     

The Development of a Multiparametric Immunochromatographic Test System for the Analysis of Cardiomarkers

Moscow University Chemistry Bulletin - Abstract—An immunochromatographic test system for the combined analysis of two cardiomarkers, such as fatty acid binding protein (FABP) and troponin I...