bluuebunny/crossref_metadata_2025 huggingface dataset:
Atomic properties of selected biomolecules. Part 1. The interpretation of atomic integration errors
Authors: Aicken Fiona M , Popelier Paul LA
Published: April 2011

Reliable atomic properties can be obtained via the theory of "Atoms in Molecules" (AIM) via integration over a finite volume. These integrations are challenging because of the variety and complexity of the shape of the AIM atoms. In practice the integration of a large number of atoms (100-1000, sampled from many molecules) yields integration errors L(Ω) of varying magnitude. We prove that it is impossible to predict the size of an angular Gauss-Legendre grid (outside the β sphere) that guarantees a pre-set error. Hence it is incorrect to assume that a large grid (~23 000 angular grid points) will automatically yield a low L(Ω) value. The erratic relationship between the integration error and the grid size prompts a statistical interpretation of atomic integration, at a purely practical level. More importantly we have investigated the relationship between L(Ω) and seven atomic properties which include volume, energy, and the magnitudes of five electrostatic multipole moments. The electronic population (N(Ω)) and the volume (v(Ω)) of carbon is linearly correlated with L(Ω), enabling the interpolation or extrapolation of N(Ω) and v(Ω). Other properties of carbon and other atoms (N, O, and S) yield low correlation coefficients but occasionally trends can be observed. For example, we find that some properties are systematically underestimated if L(Ω) is negative. This work has led to an estimate of safe error bars of atomic properties for atoms occurring in biological molecules with reasonably sized integration grids. The most stable properties were found to be the energy and the population. Finally, we have observed that the influence of the grid orientation is less if L(Ω) is small, and that population and energy are the least affected.Key words: electron density, topology, atoms in molecules, atomic properties, amino acids.
Metal ion-biomolecule interactions. Part 22.1Cr(III)-catalyzed isotopic hydrogen exchange in methylimidazoles
Authors: Clement Omoshile , Onyido Ikenna , Buncel Erwin
Published: April 2011

The detritiation kinetics of the Cr(III) complexes 1 and 3-6 have been studied in aqueous buffers at 35°C, using the liquid scintillation counting technique. Results for 5 and 6 provide benchmark kinetic data for N-T/N-H exchange under the experimental conditions of the study and have aided in the delineation of N-T/N-H from C-T/C-H exchange in the parallel reactions observed experimentally. Curved first-order plots obtained for 1, 3, and 4 were treated to yield rate constants for two parallel exchange reactions kobsA  and kobsB  for the "fast" and "slow" processes, respectively. The "fast" process has been assigned to C(2)-H exchange in 1, competing N-H and C(2)-H exchange in 3, and N-H exchange in 4. In all cases, the "slow" process is associated with C(4,5)-H exchange. Identification of exchange sites in 1, 3, and 4 was made possible by the consideration of the results of an IR spectroscopic study of hydrogen-deuterium exchange, comparison of the extent of3H incorporatation in different complexes in the tritiation experiments, and a careful analysis of the exchange kinetic data. Analysis of the rate data indicates that Cr(III) significantly enhances C(2)-H exchange in 1 and 3, while C(4,5)-H exchange, hitherto reported in the literature only under drastic reaction conditions, was observed for 1, 3, and 4 under the mild conditions of the present study. Quantitation of the effect of Cr(III) coordination on3H exchange in imidazole-type nuclei was achieved fully in 1; giving kM+values of 6 × 103and 7 × 102M-1s-1for C(2)-H and C(4,5)-H exchange, respectively. Using the literature value for kH+, the second-order rate constant for C(2)-H exchange under H+catalysis, 2.9 × 102M-1s-1, it follows that Cr(III) is ca. 20 times better as a catalyst for C(2)-H exchange in 1-methylimidazole than H+, providing the first example of a metal ion being more effective than a proton in these processes. Comparison of the results obtained with 1 with literature results for 2 shows a very large (ca. 3 × 105-fold) difference in the catalytic activities of Cr(III) and Co(III), favouring the former. The dichotomy in the effectiveness of the two metal ions in catalyzing3H exchange in the imidazole nucleus has been ascribed to differences in (i) extent of Mn+N bond polarization (and the consequent effect on ligand C-H acidity); (ii) electronic configuration; (iii) crystal field stabilization and activation energies; and (iv) importance of metal-ligand π back-bonding. The study highlights the diversity of factors and complexity of interactions involved in determining the role of metal ions in biological systems, especially where such processes involve complex formation between metal ions and heterocyclic fragments of biomolecules.Key words: metal ion-biomolecule interactions, methylimidazole, isotopic hydrogen exchange, catalysis by chromium.
Formation of organosilicon compounds 117:1 C-brominated 1,3,5-trisilacyclohexanes and their reactions with BuLi
Authors: Fritz G , Keuthen M , Kirschner F , Matern E , Goesmann H , Peters K , Peters E -M , Schnering H G von
Published: April 2011

The photobromination of 1,1,3,3,5,5-hexamethyl-1,3,5-trisilacyclohexane (1) almost exclusively attacks CH2 groups and results in 2,2-dibromo-trisilacyclohexane (2) as well as 2,2,4,4-tetrabromo-trisilacyclohexane (3) in high yields. Starting from a mixture of C-brominated trisilacyclohexanes the isomeric 2,2,9-tribromo-1,3,3,5,5,8,8,10,10,13,13-undecamethyl-1,3,5,8,10,13-hexasilabicyclo[7.2.2]tridec-6-yne (6) had been obtained in very low yield in an attempt to establish a preparative route to adamantanes with a C4Si6 skeleton, i.e., with C bridgeheads and SiR2 bridges. By ICl-cleavage of a Simethyl bond in 2 and subsequent substitution with Br3CLi, the trisilacyclohexane 4 with functional groups in opposite positions of the ring can be obtained. Linking the step-by-step synthesized Cl-Me2Si-C=C-SiMe2-CH2-SiMe2-Ph to the CBr3 group of 4 results after HBr-cleavage of the SiPh bond in (ω-bromo-octynyl)-trisilacyclohexane (12). A ring closure of 12 would result in an isomeric hexasila bicyclo[7.2.2]tridec-6-yne. The compounds were characterized by 1H, 13C, and 29Si NMR spectra. Additionally, the molecular structures of 4 and 6 were confirmed by X-ray single crystal investigations.Key words: 1,1,3,3,5,5-hexamethyl-1,3,5-trisilacyclohexane, bromination, 2,2,9-tribromo-1,3,3,5,5,8,8,10,10,13,13-undecamethyl-1,3,5,8,10,13-hexasilabicyclo[7.2.2]tridec-6-yne, carbosilane synthesis, NMR data, crystal structure investigation.
Dissolution of organic solvents from painted surfaces into water
Authors: Wren J C , Jobe D J , Sanipelli G G , Ball J M
Published: April 2011

The presence of volatile iodine in containment buildings is one of the major safety concerns in the potential event of nuclear reactor accidents. Organic impurities in containment water, originating from various painted structural surfaces and organic materials, could have a significant impact on iodine volatility following an accident. To determine the source and magnitude of organic impurities and their effects on time-dependent iodine volatility, the dissolution for organic constituents from paints used in reactor buildings has been studied under postulated accident conditions. The studies of the organic dissolution from carbon steel coupons coated with zinc-primed vinyl, epoxy-primed polyurethane or epoxy paints over the temperature range 25-90°C are reported. Relatively large activation energies were measured for the release of the principal organic compounds from painted surfaces, suggesting it is the release of the solvents from the paint matrix rather than their diffusion through the solution that is the rate determining step for the dissolution mechanism. The similarities in the values of activation energies for the dissolution of different organic compounds from the paints suggest the release rate is independent of the nature of the painted surface or the type of organic being released from the surface. These two observations indicate that it may be possible to write a generalized rate expression for the release of organic compounds from painted surfaces in containment following an accident. The possible implications of these results for predicting iodine volatility in containment are also discussed.Key words: dissolution kinetics, organic solvents, painted surfaces, reactor accidents.
Reactions of the stable bis(amino)silylene Si[{N(CH2tBu)}2C6H4-1,2] with group 3 or lanthanide metal organic compounds. Crystal structures of [Ln(η5-C5H5)3Si{[N(CH2tBu)]2C6H4-1,2}]·C7H8 (Ln = Y or Yb)
Authors: Cai Xiaoping , Gehrhus Barbara , Hitchcock Peter B , Lappert Michael F
Published: April 2011

Treatment of the thermally stable aminosilylene Si[{N(CH2tBu)}2C6H4-1,2] [= Si(NN)] with a tris(cyclopentadienyl)- group 3 or -lanthanide metal compound LnCp3 (Cp = η5-C5H5 and Ln = Y or Yb) in toluene at ambient temperature afforded the first earliest transition or f-block metal-silylene complexes [LnCp3{Si(NN)}]·C7H8 (Ln = Y (1) or Yb (2)), characterized by NMR spectroscopy and X-ray crystallography: complex 1 (monoclinic, space group P21/c (no. 14), a = 15.641(5), b = 15.895(7), c = 14.876(5) Å, β = 112.93(3), Z = 4, R1 = 0.067 for 6194 observed data), and2 (monoclinic, space group P21/c (no. 14), a = 15.635(3), b = 15.795(2), c = 14.842(2) Å, β = 112.87(2), Z = 4, R1 = 0.044 for 9829 observed data). The Ln atom in each of the isoleptic complexes 1 and 2 has distorted trigonal monopyramidal geometry, with the approximately trigonal silicon atom in the apical position. The Ln-Si bond length is 3.038(2) (1) or 2.984(2) Å (2). Variable temperature 29Si{1H} NMR spectra in toluene-d8 show that each complex readily dissociates (Y > Yb) into its factors; at 188 K, the 29Si{1H} signal for (1) was a doublet centred at δ 119.5, 1J(29Si-89Y) = 59 Hz.Key words: crystallography, NMR, silylene, yttrium, ytterbium, organometallic complexes.
Diphenylboron complexes of the enol tautomers of arylpyruvic acids. Crystal and molecular structure of triethylammonium (2-nitrophenyl)pyruvato-diphenylboron(1-)
Authors: Kliegel Wolfgang , Pokriefke Jens O , Rettig Steven J , Trotter James
Published: April 2011

Synthesis has been carried out of 15 examples of anionic diphenylboron complexes of arylpyruvic acids, and the structures of the compounds have been determined from spectroscopic data and from X-ray analysis of one of the compounds. Crystals of5j are monoclinic, P21/n,a = 9.5566(10), b = 15.961(3), c = 16.6382(6) Å, beta = 99.3239(10)°, and Z = 4, at 180 K. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R(F2) = 0.056 for 6662 CCD data. 5j contains a triethylammonium cation and an anion containing a planar five-membered OBOCC ring, with cation and anion linked by an N-H···O hydrogen bond. Spectroscopic data and bond distances establish that the pyruvate ligand is the enol-tautomeric state.
Superamidines 2. Synthesis of the bulky ligand N,N'-bis-(2,6-diisopropylphenyl)-trifluoroacetamidine and its molybdenum carbonyl complex
Authors: Boeré René T , Klassen Vicki , Wolmershäuser Gotthelf
Published: April 2011

N,N'-bis-(2,6-diisopropylphenyl)trifluoroacetamidine has been prepared for the first time from 2,6-diisopropylaniline and the trifluoroacylation reagent TFAP via the imidoylchloride. The crystal structure of the amidine was determined, indicating that it crystallizes in the Z-anti tautomer, in contrast to the nonfluorinated analogue, which is E-anti in the solid state. In solution, as indicated by NMR spectroscopy, it exists in two isomeric forms. The amidine reacts with Mo(CO)6 to produce a coordination complex with Mo(CO)3 in which the ligand is also in the Z-anti geometry, the metal is η6-coordinated to the imino-2,6-diisopropylphenyl ring, and the amino N-H unit is directed towards the metal, as determined by a single-crystal X-ray structure. Unlike the analogous nonfluorinated acetamidine, there is no indication of an intermediate in which the neutral amidine is coordinated in a monodentate fashion to an Mo(CO)5 unit, which we now attribute to the predominant geometry of the ligand, both in the solid state and in solution, being Z-anti. The high steric bulk of this superamidine ligand apparently prevents the formation of a metal-metal bonded Mo2(amidinate)4 as observed previously in a redox reaction between N,N'-diphenylbenzamidine and Mo(CO)6 under similar thermal reaction conditions.Key words: trifluoromethyl, superamidine, amidine, molybdenum, carbonyl, coordination.
Diastereoselective double ring closing metathesis reactions as an approach to symmetrical bicyclodienes
Authors: Lautens Mark , Hughes Gregory , Zunic Valentin
Published: April 2011

A new class of bicyclic dienes which contain a σ plane of symmetry are efficiently prepared in a diastereoselective fashion using ring closing metathesis reactions. These molecules have potential as starting materials for a wide range of organic targets.Key words: metathesis, catalysis, stereoselective, decalin, desymmetrization.
Straightforward synthesis of new tetrahydroquinoline derivatives
Authors: Fabio Romano Di , Alvaro Giuseppe , Bertani Barbara , Giacobbe Simone
Published: April 2011

To identify novel classes of glycine antagonists, compounds potentially useful as neuroprotective after stroke, novel substituted tetrahydroquinoline derivatives, satisfying the key pharmacophoric requirements for glycine antagonists, were designed. To explore the SAR of these compounds an efficient synthetic route was set up exploiting the outstanding reactivity of suitable N-aryl imine derivatives. In particular an allylmetalation reaction or the addition of bis(trimethyldisilyl)ketene acetals allowed the preparation of versatile intermediates which were smoothly transformed into the desired bicycle tetrahydroquinoline derivatives by a Heck-type cyclization reaction.Key words: glycine antagonists, neuroprotection, tetrahydroquinolines, synthesis, allylmetalation.
Conformational effects in the diastereoselective protonation of chiral enolates derived from 2,4-dimethyl-1-tetralone using carbonyl chelating proton donors
Authors: Coumbarides Gregory S , Eames Jason , Weerasooriya Neluka
Published: April 2011

The synthesis of syn-2,4-dimethyl-1-tetralone 6 via a reprotonation strategy using chelating proton donors is discussed. We comment on the comformational effects associated with these acids, and discuss the differences between direct protonation and deprotonation-reprotonation of chiral enolates in the presence of diisopropylamine and LiBr.Key words: conformation, chelating proton donors, deprotonation-reprotonation strategy, diastereoselective protonation and solvent effects.
Synthesis, characterization, and reactivity of scandium chloro, alkyl, aryl, and borohydride complexes, Sc(η5-C5H5)R[N(SiMe2CH2PiPr2)2] (R = Cl, Me, Ph, and BH4)
Authors: Fryzuk Michael D , Giesbrecht Garth R , Rettig Steven J
Published: April 2011

Reaction of ScCl2(THF)[N(SiMe2CH2PiPr2)2] with NaCp(DME) leads to Sc(η5-C5H5)Cl[N(SiMe2CH2PiPr2)2] (1). The X-ray crystal structure shows the scandium centre to reside in a square pyramidal environment with the [N(SiMe2CH2PiPr2)2] - ligand bound in a pseudo-meridional fashion. The 1H NMR spectrum is consistent with a Cs symmetric structure in solution. Metathesis of the chloride ligand with RLi (R = Me, Ph, BH4) yields the five-coordinate species Sc(η5-C5H5)R[N(SiMe2CH2PiPr2)2]. Phenyl 3 and borohydride 4 are isolated as crystalline solids, while methyl 2 resisted crystallization. 2-4 exhibit 1H NMR spectra consistent with Cs symmetric solution structures. Sc(η5-C5H5)Ph[N(SiMe2CH2PiPr2)2] (3) was characterized in the solid state and found to have a similar geometry to that of the parent chloride. Reaction of Sc(η5-C5H5)Me[N(SiMe2CH2PiPr2)2] (2) with NH2R (R = Ph, tBu) yields the amides Sc(η5-C5H5)NHPh[N(SiMe2CH2PiPr2)2] (5) and Sc(η5-C5H5)NHtBu [N(SiMe2CH2PiPr2)2] (6) via σ-bond metathesis routes; these reactions are accompanied by a competing reaction at the scandium-amide bond to produce the protonated ligand, HN(SiMe2CH2PiPr2)2. 5 and 6 are also produced by salt-elimination from the chloride 1 and LiNHR (R = Ph, tBu). Sc(η5-C5H5)(BH4)[N(SiMe2CH2PiPr2)2] (4) reacts with PMe3 to produce the putative hydride, Sc(η5-C5H5)H[N(SiMe2CH2PiPr2)2] (7); this species was identified in solution. An equilibrium between 4, PMe3, 7, and PMe3·BH3 exists which greatly favors the starting scandium-borohydride. Crystals of Sc(η5-C5H5)Cl[N(SiMe2CH2PiPr2)2] (1) are monoclinic, a = 17.409(2), b = 10.0803(7), c = 17.688(2) Å, β = 94.606(8)°, Z = 4, space group P21/c; and those of Sc(η5-C5H5)Ph[N(SiMe2CH2PiPr2)2] (3) are triclinic, a = 10.5129(15), b = 19.124(2), c = 9.114(2) Å, α = 95.582(13), β = 107.047(12), γ = 90.042(11)°, Z = 2, space group P. The structures were solved by Patterson (1) and direct (3) methods and refined by full-matrix least-squares procedures to R = 0.047 and 0.054 (Rw = 0.042 and 0.049) for 2414 and 2844 reflections with I [Formula: see text] 3σ(I), respectively.Key words: scandium, σ-bond metathesis, borohydride.
The Suzuki, the Heck, and the Stille reaction - three versatile methods for the introduction of new C-C bonds on solid support
Authors: Franzén Robert
Published: April 2011

Metal-catalyzed coupling reactions are very efficient and reliable methods for the introduction of new carbon-carbon bonds onto molecules attached to a solid support. This review summarizes recent advances in utilizing the three most used methods, the Suzuki reaction, the Heck reaction, and the Stille reaction, in the field of solid phase organic synthesis resulting in small organic molecule libraries.Key words: metal-catalyzed coupling reactions, carbon-carbon bonds, solid phase synthesis, combinatorial chemistry, drug discovery.
Preparation and characterization of organic-inorganic hybrid materials incorporating diphosphino moieties. Study of the accessibility of the phosphorus atoms included into the material
Authors: Bezombes Jean-Philippe , Chuit Claude , Corriu Robert JP , Reyé Catherine
Published: April 2011

The hydrolysis-polycondensation by the sol-gel process of the aromatic diphosphines (X3SiC6H4)2PC6H4P(C6H4SiX3)2, which are rigid molecules bearing four hydrolysable SiX3 groups (X = OiPr, H), leads to new organic-inorganic hybrid materials, characterized by solid state 13C, 29Si, and 31P NMR spectroscopies. The accessibility of the phosphorus centres incorporated into the xerogel obtained from the diphosphine with X = OiPr has been studied. All the phosphorus atoms reacted quantitatively with H2O2, S8, and CH3I but only 20% with the more bulky reagent W(CO)5·THF. This result is explained by the rigidity of the inorganic network resulting from the high number of hydrolysable Si-OiPr groups in the precursor.Key words : Diphosphines, sol-gel process, xerogels, solid 31P NMR.
Ab initio analysis of C-H and C-C stretching intensities in Raman spectra of hydrocarbons
Authors: Gough Kathleen M , Dwyer Jason R , Dawes Richard
Published: April 2011

Molecular polarizability and changes in the polarizability associated with the stretch of CC and CH bonds have been calculated for thirty-four saturated hydrocarbons, including the series of n-alkanes to C15, as well as several cyclo- and bicycloalkanes, propellanes, prismanes, and hedranes. The ab initio results (HF/D95(d,p)) are compared to experimental Raman trace scattering intensities where such information is available. Possible factors governing trends in the magnitude of the derivatives are considered. For the CC stretches, chain length and position along the chain are the most important factors for the n-alkanes, whereas strain appears to be significant for the ring and caged structures. For the CH stretches, the most significant factors are the same as those found in our earlier work: location, type, and orientation relative to the carbon skeleton.Key words: hydrocarbons, Raman scattering intensities, molecular polarizability, polarizability derivatives, theory of atoms in molecules.
Hydrogen bonding interaction of diphenylbarbituric acid and 9-ethyladenine. Crystal structure of a 1:1 complex
Authors: Camerman Arthur , Mastropaolo Donald , Hempel Andrew , Camerman Norman
Published: April 2011

There are several different types of adenosine receptors found in the brain and molecules capable of interacting with the adenine ring system may have an effect on brain activity. Phenobarbital and diphenylhydantoin, two commonly used antiepileptic drugs have been shown to form hydrogen bonded complexes with adenine derivatives. Although 5,5-diphenylbarbituric acid has anticonvulsant properties equivalent to phenobarbital, neither its structure nor possible interactions with adenine have been investigated. 5,5-Diphenylbarbituric acid and 9-ethyladenine were, therefore, cocrystallized and the three-dimensional 1:1 hydrogen bonded complex was determined by X-ray diffraction. The crystals are monoclinic, C2/c, a = 28.457(9), b = 10.633(3), c = 13.995(4) Å, β = 100.20(2)°, Z = 8, R = 0.067 for 1680 reflections with I > 3σ(I). The molecules propagate along the b crystallographic axis in an alternating fashion in which adjacent adenine and barbiturate molecules interact through a pair of hydrogen bonds. Two-fold symmetry related barbiturate carbonyl groups in neighboring planes of hydrogen bonded ribbons are involved in dipoledipole attractive interactions. This hydrogen bonding pattern is compared to patterns found in other barbiturateadenine complexes.Key words: hydrogen bonding, crystal structure, barbiturates, adenine, anticonvulsants.
The insertion of germylene into the HH bond; rate constant limits and thermochemistry. Ab initio and DFT calculations on the reactions of GeH2 and SiH2 with H2
Authors: Becerra Rosa , Boganov Sergey E , Egorov Mikhail P , Faustov Valery I , Nefedov Oleg M , Walsh Robin
Published: April 2011

The technique of laser flash photolysis in the gas-phase has been used to set limits on the rate constants for the bimolecular reaction of germylene (GeH2) with deuterium (D2) at both ambient and elevated temperatures (585 K). These limits show that the activation energy for the insertion of GeH2 into the HH bond is at least 19 (±6) kJ mol1. Thermochemical arguments place the activation energy approximately in the range 6384 kJ mol1. DFT B3LYP/6-311++G(3df,2pd) and ab initio QCISD(T)/6-311G++(3df,2pd)//QCISD/6-311G(d,p) calculations have been carried out on the potential energy surfaces of reactions ZH2 + H2 [Formula: see text] ZH4 (Z= Ge, Si). Both methods predict the same mechanisms for germylene and silylene insertion which include formation of loose prereaction complexes and transition states of similar structure. The prereaction complex is only about half as strong in the case of germylene (ΔH (298 K) = 9 (11) kJ mol1) as in the case of silylene (ΔH (298 K) = 16 (21) kJ mol1) (QCISD values cited with B3LYP values in parentheses). The differences in activation energies are even more significant. Germylene insertion has a very high barrier of 58 (56) kJ mol1 compared to that of silylene 13 (6) kJ mol1. Calculated activation parameters for both reactions are in reasonable consistency with experimental results. Reasons for the enhanced HH insertion barrier for germylene compared with silylene are discussed.Key words: laser flash photolysis, germylene, silylene, deuterium, activation energy, thermochemistry, ab initio calculation, DFT B3LYP calculation.
Coefficient d'activité de l'acide sulfurique déterminé par titrage infrarouge
Authors: Ménichelli Christophe , Max Jean-Joseph , Chapados Camille
Published: April 2011

The titration of sulphuric acid by infrared spectroscopy using the attenuated total reflection (ATR) technique was made in the 0 to 14 pH range for solutions ranging from 1.89 to 0.01 M. The subtraction of the water spectrum was made using acidic, neutral, and basic waters which exhibit different spectra. The results gave the spectra of mixtures of the HSO4 and SO24 ionic species in solutions. For each concentration, factor analysis (FA) sorted the spectra of the pure ionic species and gave through the multiplying factors (MF) the distribution of the species as a function of pH. This distribution is the same as that obtained from the equilibrium equations. The IR measurements gave directly the ratios of the activity coefficients of HSO4 and SO24 ions. This ratio varies with the total concentration of both ions but is independent of the relative concentration. The fitting of the experimental and theoretical volumetric titration curves in the high and low pH regions gave the mean activity coefficients of the other species present in the solutions. The values obtained are comparable to those obtained by electrochemical measurements. These results show that it is possible to use IR spectroscopy to study aqueous solutions of inorganic acids from low to high concentrations.Key words : IR spectroscopy, sulfuric acid, aqueous solutions, factor analysis, ATR, principal spectra, solvation, activity coefficients, IR titration.
Synthesis of nanocrystalline Cu2  xSe at room temperature by γ-irradiation
Authors: Qiao Zhengping , Xie Yi , Xu Jianguang , Liu Xianming , Zhu Yingjie , Qian Yitai
Published: April 2011

Ten nm nonstoichiometric compound Cu2  xSe was firstly synthesized at room temperature by γ-irradiation, using sodium selenosulfate as the selenium source. The influence of the coordination of copper ions and the pH value of the solutions on the formation of Cu2  xSe has been studied. The Cu2  xSe was prepared here for x = 0.13.Key words: copper selenide, nanocrystalline, γ-irradiation.
Acidity constants and reactivities of the benzidine andN,N-dimethylbenzidine dications, the two electron oxidation intermediates of benzidine carcinogens
Authors: McClelland Robert A , Ren Daniel , D'Sa Raechelle , Ahmed Abid R
Published: April 2011

This paper describes the behavior in aqueous solutions of the two electron oxidation products of the carcinogens benzidine and N,N-dimethylbenzidine. In biological systems there is evidence that these diamines are oxidized by peroxidases, and that a product of this oxidation may be partly responsible for carcinogenicity. Entry into the oxidation products in the present study was provided through the bis-perchlorate salts of dications obtained upon chemical oxidation and through the irradiation of 4'-amino and 4'-N,N-dimethylamino-4-azidobiphenyls. The benzidine oxidation product exists in three conjugate acid-base forms, a dication, a monocation and neutral bisimine, with pKa(1) = 5.0 and pKa(2) = 9.0. These values stand in marked contrast to ones previously obtained for the two electron oxidation product of p-phenylenediamine, pKa(1) < 1.5 and pKa(2) = 5.75. The dimethylamino derivative, blocked from forming the neutral form, exists as a dication and monocation, with pKa= 5.0. Both systems are quite long-lived in aqueous solution, but they do decay on the minutes-to-hours time scale. The kinetics can be explained by reactions of both the dication and the monocation with water, with a reaction of hydroxide and the monocation becoming important around pH 10. One surprising result is that the monocations are two orders of magnitude more reactive than the dications. Thus, at neutral pH the form that exists in both systems is the monocation, and this is the species that is the most reactive towards the solvent. One of the resonance contributors in the monocation is a 4-biphenylylnitrenium ion. Comparison with other 4'-substituted-4-biphenylylnitrenium ions studied by laser flash photolysis shows that the 4'-amino- and 4'-dimethylamino substituents are highly kinetically stabilizing. These cations, for example, are a billion-fold longer-lived in aqueous solution than the parent 4-biphenylylnitrenium ion.Key words: quinone bisimine, nitrenium, aryl azide.
Co(II) and Mn(II) complexes of 2,2'-thiodiethanol: [CoII(2,2'-thiodiethanol)2Cl2] and [Mn(2,2'-thiodiethanol)Cl2]n
Authors: Zhang Yousheng , Wang Suning , Bridges Craig , Greedan John E
Published: April 2011

[Co(2,2'-thiodiethanol)2Cl2] (1) and [Mn(2,2'-thiodiethanol)Cl2]n (2), have been synthesized and characterized structurally. Compound 1 is a six-coordinate, mononuclear Co(II) complex. The mononuclear units in the crystal lattice of 1 are linked together through intermolecular hydrogen bonds between hydroxy and chloride groups to form a three-dimensional array. Compound 2 consists of six-coordinate Mn(II) units that are linked by covalently bound 2,2'-thiodiethanol and chloride ligands to form an alternating one-dimensional chain, which is further linked together by inter-chain hydrogen bonds to form a two-dimensional sheet. Antiferromagnetic exchange is present in compound 2.Key words: cobalt, manganese, 2,2'-thiodiethanol, structure, magnetism.
New syntheses of dillapiol [4,5-dimethoxy-6-(2-propenyl)-1,3-benzodioxole], its 4-methylthio and other analogs
Authors: Majerus Sherry L , Alibhai Najma , Tripathy Sasmita , Durst Tony
Published: April 2011

Three syntheses of the natural synergist dillapiol from the natural, commercially available sesamol as starting material, are described. A major difference between these is the order of introduction of the additional methoxy and allyl substituents. In one of the syntheses, a formyl group is introduced at C4 via an electrophilic aromatic substitution reaction and then converted into the methoxy group using a Baeyer-Villiger reaction and subsequent methylation; in the other two, a directed ortho-metalation, Baeyer-Villiger, methylation sequence was employed. Various intermediates along the synthetic route were used to generate more than 30 analogs, including the 4-thiomethyldillapiol, to investigate the structure activity relationships of the pesticide synergism of these compounds. Radio-labeled dillapiol, bearing 14C at the C4 methoxy group was also prepared. Initial screening with mosquito larvae showed that most of the derivatives prepared in this study had signifacant synergistic activities in combination with the phototoxic larvicide α-therthiophene.Key words: dillapiol, insecticide synergists, dillapiol analogs, 4-methylthiodillapiol.
Interactions of 6-aminopurine (adenine) in water and aqueous urea solutions
Authors: Pandey J D , Haroon S , Dubey Krishna K , Upadhyaya Madhulika , Dey Ranjan , Misra K
Published: April 2011

Density (ρ), ultrasonic velocity (U), viscosity (η), and absorbance (A) of adenine in water, 1 M, 3 M, and 6 M aqueous urea solutions have been measured in the presence (and absence) of different concentrations of salts, i.e., NaCl, KCl, and CaCl2. From these measured values, the apparent molar volume (ϕv), experimental slope (Sv), apparent molar compressibility (ϕK), viscosity coefficients A and B of JonesDole equation, specific acoustic impedance (Z), hydration number (Sn), internal pressure (Pi), molar absorptivity (ε), hypochromicity (h), and oscillator strength (f) have been calculated at 298.15 K. The increasing and (or) decreasing trends of all these parameters indicate a strong interaction of urea in moderate concentration (1 M and 3 M) with adenine especially at the hydrophilic/polar and ionic sites, particularly by hydrogen bonding. However, the interaction at hydrophobic sites are relatively weaker. Higher concentrations of urea (6 M) have more denaturation effect. The ππ interactions (stacking) in adenine are more prominent in concentrated solutions and are also strengthened by the presence of cations up to an optimum concentration of salts (cut-off point). The self-association of urea and adenine is more significant in concentrated aqueous solutions and becomes negligible on dilution.Key words: interaction, adenine, urea, density, viscosity, and ultrasonic velocity.
Determination of the acidity constant of isothiocyanic acid in aqueous solution
Authors: Chiang Y , Kresge A J
Published: April 2011

Changes in absorbance of the thiocyanate ion (SCN) at λ = 220 nm, measured in concentrated aqueous perchloric acid solution, were analyzed using a titration curve expression containing the Xo excess acidity function; this provided the acidity constant Ka = 19.2 ± 1.1 M, pKa = 1.28 ± 0.03, for isothiocyanic acid (SCNH).Key words: isothiocyanic acid (acidity of), thiocyanate ion (basicity of), acidbase titration in concentrated aqueous acids, Xo excess acidity function, CoxYates method.
Theoretical study on the influence of H2O for the 1,2-hydrogen shift from hydrogen peroxide (H2O2) to water oxide (O-OH2)
Authors: Okajima Toshiya
Published: April 2011

Theoretical calculation was performed to study the solvent effect for the 1,2-hydrogen shift from hydrogen peroxide (H2O2) (1) to water oxide (O-OH2) (2). Stationary points including transition structures (TSs) were optimized with no geometrical constraint at Becke3LYP/6-311++G** level. All stationary points were tested by frequency analysis and IRC calculation. The activation energies (ΔE[Formula: see text]) and heats of reaction (ΔH0) were evaluated at Becke3LYP/6-311++G**//Becke3LYP/6-311++G** level of theory. The following points were clarified: (i) inclusion of polarization function (*) and diffusion function (+) for calculation hardly affected the energetic of the reaction; (ii) judging from the change of ΔE[Formula: see text] and ΔH0 values, the reaction is predicted to be accelerated by the increase of involving H2O; (iii) proton-relaying mechanism considerably reduced ΔE[Formula: see text] values; (iv) the endothermicity became monotonically small as the number of solvating H2O molecules increased. The calculation suggests that the formation of water oxide (O-OH2) (2) from H2O2 (1) is promoted by a proton-relaying pathway in protic media (such as H2O).Key words: theoretical calculation, ab initio, transition structure, 1,2-hydrogen shift, water oxide.
Synthesis, characterization, and protonation of octaethylporphyrin osmium nitrosyl complexes containing axial thiolate ligands - X-ray structures of an alkyl thionitrite (RSNO) and its (OEP)Os(NO)(SR) addition product
Authors: Lee Jonghyuk , Yi Geun-Bae , Powell Douglas R , Khan Masood A , Richter-Addo George B
Published: April 2011

The (OEP)Os(NO)(SR) compounds (R = Me, Et, i-Pr, t-Bu) have been prepared in 33-48% isolated yields by the formal trans-addition of the precursor alkyl thionitrites (RSNO) across the metal center in (OEP)Os(CO). The nitrosyl thiolate compounds have been characterized by IR,1H NMR, and UV-vis spectroscopy, and by FAB mass spectrometry. Their IR spectra display bands in the 1751-1755 cm-1(KBr) range, which is indicative of terminal N-bound NO ligands in this class of compounds. The thiolate-thiol (OEP)Os(NO)(SCH2CH2SH) complex has been prepared in 70% isolated yield from the reaction of (OEP)Os(NO)(O-i-C5H11) with ethane-1,2-dithiol. Nitrosation of the free -SH group in (OEP)Os(NO)(SCH2CH2SH) with t-BuONO, followed by reaction with (TTP)Ru(CO) gave [(OEP)Os(NO)](µ-SCH2CH2S-S,S')[Ru(NO)(TTP)] in 70% yield by1H NMR spectroscopy. The (OEP)Os(NO)(SCR'2CH2NHC(O)Me) compounds have also been prepared either by an alkoxide-thiolate exchange reaction (for R' = H) or by RSNO addition to (OEP)Os(CO) (for R' = Me). The solid-state molecular structures of the precursor RSNO thionitrite (for R' = Me) and the metalloderivative have been determined by single-crystal X-ray crystallography. Protonation of these (OEP)Os(NO)(SCR'2CH2NHC(O)Me) complexes gave the amide-bound [(OEP)Os(NO)(O=C(Me)NHCH2CR'2SH)]BF4derivatives. The latter cationic compounds were also obtained by the sequential reaction of (OEP)Os(CO) with nitrosonium tetrafluoroborate, followed by addition of the amide-thiol reagent. Key words: thionitrite, nitrosothiol, porphyrin, X-ray structure, nitric oxide, osmium.
Homobinuclear Ru-Ru and heterobinuclear Ru-Rh complexes with alkynyl and vinylidene ligands as molecular units
Authors: Werner Helmut , Bachmann Petra , Martin Marta
Published: April 2011

The chelate complex [RuCl2{κ2(P,O)-i-Pr2PCH2CH2OMe}2] (1) reacted, in the presence of CF3SO3Ag, with 1 equiv of C6H4(CºCH)2-p (4) to afford the mononuclear vinylidene compound [RuCl(C=CHC6H4-p-CºCH){κ2(P,O)-i-Pr2PCH2CH2OMe}2](CF3SO3) (3). From 1 and 0.5 equiv of 4, the binuclear bis(vinylidene) complex [RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2(C=CHC6H4-p-CH=C)RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2](CF3SO3)2 (6) was obtained. The related compound [RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2(C=CHC6H4-m-CH=C)RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2](CF3SO3)2 (7) was prepared from 1, 0.5 equiv of C6H4(CºCH)2-m (5), and silver triflate. The reaction of 2 or 3 with [RhCl(P-i-Pr3)2]2 (8) in the molar ratio of 2:1 yields, by addition of the 14-electron fragment [RhCl(P-i-Pr3)2] to the uncoordinated CC triple bond, the heterobinuclear complexes [RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2(C=CHC6H4-m/p-CºCH)RhCl(P-i-Pr3)2](CF3SO3) (9, 10) which slowly rearrange at room temperature to give the bis(vinylidene) isomers [RuCl{κ2(P,O)-i-Pr2PCH2CH2OMe}2(C=CHC6H4-m/p-CH=C)RhCl(P-i-Pr3)2](CF3SO3) (11, 12).Key words: ruthenium, rhodium, vinylidene complexes, alkyne complexes, phosphine complexes.
Photochemical preparation of cyclopropanes from cyclobutanones
Authors: Ramnauth Jailall , Lee-Ruff Edward
Published: April 2011

A general method for the preparation of cyclopropanes is reported. Triplet-photosensitized reactions of a series of cyclobutanones give cyclopropanes as the major product. Part 1 describes the synthesis of substituted cyclobutanones used in this study. In Part 2, the photo-reactions of cyclobutanones are reported. Triplet-sensitized reactions of cyclobutanones using acetone as a sensitizer give cyclopropanes as the major non-polar products. The extent of photodecarbonylation seems to be dependent on α-substitution. Electron-donating groups promote decarbonylation while electron-withdrawing groups favour cycloelimination.Key words: photodecarbonylation, cyclobutanones, cyclopropanes, triplet-sensitization.
Excess electrons in aqueous glasses and crystalline ice
Authors: Gillis Hugh A , Quickenden Terence I
Published: April 2011

Experimental studies of excess electrons in aqueous glasses and crystalline ice are reviewed. Emphasis is placed on studies of the two main optical absorption bands, the well known visible band, which is similar to that of the solvated electron in water, and the IR band which has λmax [Formula: see text] 2950 nm. Under some circumstances partial conversion of the IR-absorbing species to the visible-absorbing species has been observed. Evidence indicates that the two species are due to electrons trapped in distinctly different physical environments. Two mechanisms have been proposed for the formation of the visible-absorbing electron in crystalline ice, one involving naturally occurring vacancies and the other radiation produced vacancies. Studies of the UV and visible luminescence emitted when ice at low temperature is irradiated are summarized, and the mechanisms suggested for its production are discussed briefly. The studies on excess electrons in aqueous solids seem to the authors to be highly relevant to the more recent studies of electron solvation in water which are done on a much shorter time-scale. These latter studies are reviewed briefly with the aim of elucidating the relevance.Key words: visible-absorbing electrons, IR-absorbing electrons, irradiation of aqueous glasses, irradiation of crystalline ice, electron solvation in water.
Proton- and lanthanide-coordinating properties of the tetraaza macrocycle (EDDA-KA)2 in aqueous solution
Authors: Song Bin , Kurokawa Glen S , Liu Shuang , Orvig Chris
Published: April 2011

The new potentially multidentate ligand (EDDA-KA)2 has been prepared and its acid-base properties determined. Its coordination properties with three lanthanide ions (La3+, Gd3+, and Lu3+) and Fe3+ have been studied in aqueous solution (I = 0.16 M NaCl, 25°C) by potentiometric pH, spectrophotometric, and 1H NMR titrations. In total, eight pKa values could be determined by these diverse methods. From the 1H NMR titrations, all the deprotonation steps could be determined and assigned (in groups). Strong hydrogen bonding among two nitrogen atoms and one oxygen atom on the pyrone ring was observed, and the corresponding pKa values were estimated to be 13.2 and 14.0. By comparison with similar systems, an equilibrium constant for the formation of the hydrogen bond was estimated, KI = 104.4. Eight stability constants in total were determined for various protonation states of the La3+ and Gd3+ complexes, but for Lu3+ only the last four constants were obtained. The species distribution diagram showed that [M(EDDA-KA)2-4H]2- predominated in the range 5 [Formula: see text] pH [Formula: see text] 9 and [M(EDDA-KA)2-6H]4- predominated in the region 9 [Formula: see text] pH [Formula: see text] 11. In the former complex, two strong hydrogen bonds anchored the macrocycle and Ln3+ was coordinated with the four carboxylate groups; in the latter, the two hydrogen bonding protons were absent and the metal ion might also bind to the nitrogens on the macrocycle. The stability of Gd3+-(EDDA-KA)2 is lower than the analogous Gd3+ complexes of DOTA, DTPA, and DTPA-BMA.Key words: acidity constants, stability constants, La3+, Gd3+, Lu3+, Fe3+, amino carboxylate chelator.
Polymerization of 1-hexene catalyzed by Cp*TiMe3-B(C6F5)3; a mechanistic and structural study
Authors: Murray Michael C , Baird Michael C
Published: April 2011

Solutions of the ZieglerNatta system Cp*TiMe3  B(C6F5)3 in toluene catalyze the polymerization of 1-hexene to mixtures of atactic poly-1-hexenes and complex oligomeric materials, which were characterized by 1H and 13C{1H} NMR spectroscopy and gel permeation chromatography (GPC). The polymer molecular weights and the relative proportions of polymers and oligomers vary with temperature, monomer:catalyst ratios, and degree of dilution and may generally be rationalized in terms of a conventional ZieglerNatta mechanism. The 13C{1H} NMR spectra of the polymers exhibit resonances suggesting significant degrees of 2,1-insertions during propagation, while experiments utilizing Cp*Ti(13CH3)3 verify that initiation in toluene involves predominantly via 1,2-insertion of the first monomer unit but that 2,1-insertions occur up to 1520% of the time in CH2Cl2. NMR experiments involving Cp*Ti(13CH3)3 demonstrate that both methyl groups in the presumed active species Cp*TiMe+2 are incorporated into polymerKey words: titanium, polymers, polymerization, ZieglerNatta
Study of the hydroformylation of 2,5-dihydrofuran catalyzed by rhodium diphosphine complexes
Authors: Río Inmaculada del , van Leeuwen Piet WNM , Claver Carmen
Published: April 2011

Rhodium diphosphine systems, including chiral ones, were used as catalyst precursors for the hydroformylation of 2,5-dihydrofuran. The effect of the reaction conditions and the bite angle on the activity and selectivity of the reaction were studied. The solution structures of the species present have been investigated spectroscopically through HP-NMR experiments during the hydroformylation reaction.Key words: hydroformylation, dihydrofuran, rhodium complexes, diphosphines, HP-NMR.
Evaluation of ruthenium-based complexes for the controlled radical polymerization of vinyl monomers
Authors: Simal François , Jan Dominique , Delaude Lionel , Demonceau Albert , Spirlet Marie-Rose , Noels Alfred F
Published: April 2011

New complexes of the type RuCl2(p-cymene)L where the ligand L is either a phosphine or a stable triazolinylidene carbene have been tested and compared to the Grubbs' benzylidene complex RuCl2(=CHPh)(PCy3)2 as catalyst precursors for the controlled atom transfer radical polymerization (ATRP) of methyl methacrylate and of various para-substituted styrenes. Kinetic data and Hammett ρ constants are reported, as well as the X-ray structure of the ortho-metallated triazolinylidene-ruthenium(II) complex RuCl(p-cymene)[1,2-phenylene[3,4-diphenyl-1H-1,2,4-triazol-1-yl-5(4H)-ylidene]].Key words: ruthenium, carbene, chelate complex, homogeneous catalysis, atom transfer radical polymerization.
Novel polyfluoroalkylated pyrazoles from 2-polyfluoroacylcycloalkanones and hydrazines: syntheses and unequivocal molecular structure assignment
Authors: Sevenard D V , Khomutov O G , Kodess M I , Pashkevich K I , Loop I , Lork E , Röschenthaler G -V
Published: April 2011

The reaction between 2-trifluoroacetylcycloalkanones and methylhydrazine or phenylhydrazine exclusively yields 3-CF3-pyrazoles. When the chain length of the polyfluorinated substituent in RFC(O) group increases, 5-RF-pyrazoles are isolated. The reaction of 2-trifluoroacetylcyclohexanone with 2-hydrazinopyradine gives 5-hydroxypyrazoline, an intermediate in the formation of 5-CF3-pyrazoles. The regiochemistry of the condensation is probably controlled by the nucleophilicity of the terminal nitrogen in the mono substituted hydrazines and by the steric requirements of the RF group in the 1,3-diketones. Polymethylene chain containing pyrazoles obtained from the 1,3-diketones in question and hydrazine prefer the 3-RF tautomeric form, irrespective of carbocyclic ring size and polyfluoroalkyl group chain length.Key words: polyfluorinated 1,3-diketones, hydrazines, isomeric pyrazoles, molecular structure.
Possible structures for H-Cu-CH3 molecules
Authors: Symons Martyn CR , March Raymond E
Published: April 2011

EPR spectra for H-Cu-CH3 molecules in glasses at 77 K show 63Cu hyperfine splitting that accords with a d1x2  y2 orbital for the semi-occupied molecular orbital (SOMO) rather than a d1z2 SOMO. The g-values also strongly imply a d1x2  y2 configuration. The estimated spin densities on the H- and -CH3 ligands are small. It is argued that the molecule must be strongly bent in order to favour this SOMO and that this bending may be induced by weak solvation.Key words : H-Cu-CH3, EPR spectra, molecular structure, hyperfine splitting.
Chelated fluoroboron cations. III. Spectroscopic evidence for ring size and steric limitations to chelate formation by amine chelating donors
Authors: Hartman J Stephen , Shoemaker James AW
Published: April 2011

Factors affecting the ability of potentially chelating amine ligands to form chelated fluoroboron cations are explored by19F and11B NMR spectroscopy and fast atom bombardment mass spectrometry (FAB-MS). Five-membered chelate rings form much more readily than six-membered. Some potentially chelating ligands give rise to additional fluoroboron species by various redistribution and decomposition reactions.Key words: chelated fluoroboron cations,19F NMR,11B NMR; FAB-MS, N,N,N',N'-tetraethylethylenediamine.