bluuebunny/crossref_metadata_2025 huggingface dataset:
Specific intramolecular interactions C-H···N in heteroaryl vinyl ethers and heteroaryl vinyl sulfides studied by 1H, 13C, and 15N NMR spectroscopies and by ab initio calculations on molecular structures as well as on nuclear shieldings
Authors: Afonin Andrei V , Vashchenko Alexander V , Takagi Tatsuya , Kimura Atsuomi , Fujiwara Hideaki
Published: April 2011

1H,13C, and 15N NMR spectra have been measured for a series of isostructural aryl (heteroaryl) vinyl sulfides and compared with analogues of vinyl ethers. It was found that "intramolecular interaction" of the α-hydrogen of the vinyl group with endocyclic nitrogen takes place in 2-vinylthiopyridines. This is in common with the findings for 2-vinyloxypyridine and the intramolecular interaction is shown to have a profile characteristic of hydrogen bonding. Also, the NMR spectral data show that this type of interaction is more intense (~1.5 times) in 2-vinyloxypyridine than in 2-vinylthiopyridine. This is probably due to the greater electronegative effect of oxygen compared to that of sulfur. To discuss these findings further in detail, ab initio calculations have been made, and the conformational energy map and the NMR chemical shifts have been discussed. The ab initio calculations, which were carried out on the D95++(d,p) basis set at the B3LYP level, confirm the planar structure of 2-vinyloxy- and 2-vinylthiopyridines, while other analogues of these ethers and sulfides were essentially nonplanar. Gauge-Independent Atomic Orbital (GIAO) calculations of the shielding constants, based on the same basis set, support the extraordinary low-field shift of the α-hydrogen in the vinyl group when it is situated close to endocyclic nitrogen. All these calculations support our proposal that the vinyl proton is involved in intramolecular hydrogen bonding in 2-vinyloxy- and 2-vinylthiopyridines.Key words: NMR, intramolecular hydrogen bonding, ab initio calculation, GIAO.
Organic reaction in water. Part 21: Michael addition in water without phase transfer agents
Authors: da Silva Flavia Martins , Gomes Adriana Kniaseff , Jones, Jr. Joel
Published: April 2011

The Michael additions of dicarbonyl compounds, nitroalkanes, and thiols to 2-cyclohexen-1-one can be accomplished in water without phase transfer agents. The reaction is extremely sensitive to the pH of the reaction media, and therefore, the methodology can be optimized with the control of this variable. The best pH depends on the used nucleophile.Key words: Michael addition, aqueous media, water, 2-cyclohexen-1-one, ketone.
The role of the medium in solvent isotope effects on serine protease action
Authors: Tian Jiaher , Tan Jue , Schowen K Barbara , Schowen Richard L
Published: April 2011

The hydrolysis of N-carbobenzyloxyaminoacyl-O-p-nitrophenyl esters derived from L-leucine, L-phenylalanine, and L-tryptophan, with catalysis by bovine pancreatic α-chymotrypsin at pH 7.00 at 25.00°C in water containing acetonitrile from 15.0% to 60% (v/v), exhibits values of kcat/Km that decrease as the 34th to 36th power of the activity of water and values of kcat that are essentially constant. Solvent isotope effects kcat(H2O)/ kcat(D2O) range from 2.1 to 3.0 with proton inventories (dependences of kcat(n) on n, the atom fraction of deuterium in the water component of the solvent) that are linear, regardless of the amount of acetonitrile in the medium. The isotope effect on kcat thus appears to arise from a single transition-state site and to be little affected by the medium. Contributions from the medium to solvent isotope effects on enzymic reactions clearly exist but appear not to be detectable in the deacylation reactions of acyl chymotrypsins.Key words: solvent isotope effects, proton inventories, medium effects, enzyme catalysis, alpha-chymotrypsin.
15N nuclear polarization in the reactions of diallyl ether with nitrogen dioxide
Authors: Claridge Robert P , Millar Ross W , Ridd John H
Published: April 2011

The reaction of diallyl ether with nitrogen dioxide in organic solvents yields a mixture of cis and trans 2,3-bis(nitromethyl)tetrahydrofurans, cis and trans 2-nitratomethyl-3-nitromethyltetrahydrofurans and a number of straight-chain compounds with one to four nitro groups. Under the conditions used, the cyclic compounds form the main products when the solution of nitrogen dioxide is slowly added to the solution of diallyl ether but not when the reverse mode of addition is used. When 15N-nitrogen dioxide is used, the products show strong 15N nuclear polarization: the 2,3-di(nitromethyl)tetrahydrofurans give an emission signal, and one straight-chain product with two nonequivalent nitro groups shows both an emission signal and an enhanced absorption signal. For both the cyclic and straight-chain products, the nuclear polarization is consistent with the successive reactions of diallyl ether with two nitrogen dioxide radicals with uncorrelated spins.Key words: diallyl ether, nitrogen dioxide, 15N nuclear polarization, CIDNP.
Ab initio test of the usefulness of the Redlich–Teller product rule in computing kinetic isotope effects
Authors: Schaad L J , Bytautas Laimutis , Houk K N
Published: April 2011

It has been known since the early work of Bigeleisen that incorporating the Redlich-Teller product rule into isotope-effect equations minimizes the importance of low-frequency vibrations. Similar analysis suggests that errors in low frequencies especially are minimized by the use of the Redlich-Teller rule, though its use improves accuracy at all frequencies. However, in the computation of isotope effects, cancellation between isotopomers caused this advantage to vanish exactly in the case of diatomic reactants or products. It does not do so for all polyatomics, and computational experiments again show use of the Redlich-Teller rule to be preferred.Key words: isotope effect, Bigeleisen equation, Redlich-Teller product rule, formamide, Z-1,3-pentadiene.
A structural investigation of the singly layered silicates, silinaite and makatite, by vibrational spectroscopy
Authors: Huang Yining , Jiang Zhimei , Schwieger Wilhelm
Published: April 2011

The IR and Raman spectra of two singly layered silicates, silinaite and makatite, have been investigated. The vibrational spectra were assigned based on previous studies of various silicates. The correlation between vibrational modes and the structural properties of silicates under investigation has been made. The IR and Raman spectra of silinaite are in good agreement with the known structure. However, the observed vibrational data of makatite are not completely consistent with those predicted by a factor group analysis based on the published single-crystal data.Key words: layered silicates, silinaite, makatite, vibrational spectroscopy.
Studies of the photophysics and spectroscopy of alloxazine and related compounds in solution and in the solid state
Authors: Sikorski M , Sikorska E , Wilkinson F , Steer R P
Published: April 2011

The absorption and emission spectra and the fluorescence lifetimes and quantum yields of alloxazine and several of its N- and C- methyl-substituted derivatives, including two isoalloxazines, have been measured in a nonpolar solvent (1,2-dichloroethane), a polar aprotic solvent (acetonitrile), and a polar protic solvent (ethanol). The excited state decays are all single exponential, suggesting that only one emitting species is present in all cases. The spectroscopic data show that the emitting species is the π,π* electronic excited state corresponding to the ground state of the absorbing molecule; there is no evidence of excited state proton transfer for any of these solutes in any of the three solvents. The longer lifetimes and larger fluorescence quantum yields of the isoalloxazines compared with the alloxazines can be attributed exclusively to significantly slower rates of radiationless relaxation in the excited isoalloxazines. The remission and emission spectra of these same compounds adsorbed on cellulose are similar to the corresponding absorption and emission spectra in homogeneous solution, suggesting that the emitting species are the same in the adsorbed state as they are in homogeneous solution. However, the adsorbed excited species exhibit non-exponential temporal decay, attributed to inhomogeneities in the binding of the chromophore to cellulose. The emission spectra of polycrystalline samples of alloxazine and lumichrome suggest the possible occurrence of double intermolecular excited state proton transfer, but this interpretation is not supported by the further photophysical data obtained here.Key words: photophysics, spectroscopy, alloxazine, lumiflavin, cellulose.
Étude expérimentale et modélisation des réactions d’oxydation du néopentane et de l’isopentane
Authors: Taconnet S , Simon Y , Scacchi G , Baronnet F
Published: April 2011

The different behaviour of hydrocarbons with respect to autoignition phenomena is, at present, not yet fully explained. We have therefore investigated the oxidation of two alkanes that have different octane numbers: neopentane (85.5) and isopentane (92.3), to obtain a better understanding of their reaction mechanisms, in particular, those reactions that are responsible for the onset of knock in spark ignition engines. The experimental study was performed at 873 K in a jet-stirred flow reaction vessel. The oxidation mechanisms were simplified by using the CHEMKIN programme of simulation of reaction mechanisms. These mechanisms were compared to those accounting for the oxidation of n-pentane, cyclopentane, n-heptane, and isooctane that we have previously studied. This comparison shows that the different behaviour of these hydrocarbons can be explained, at least in part, by the presence, in the reaction medium, of resonance-stabilized radicals.Key words: oxidation, neopentane, isopentane, autoignition, modelling.
Multiple changes in rate-determining step in the acid and base catalyzed cyclizations of ethyl N-(p-nitrophenyl)hydantoates caused by methyl substitution
Authors: Blagoeva Iva B , Kirby Anthony J , Koedjikov Asen H , Pojarlieff Ivan G
Published: April 2011

The slopes of the pH-rate profiles for the cyclization of 2-methyl- and 2,3-dimethyl hydantoates 1-NPU and 2-NPU between pH 1 and 7 change from 1 to 0 and then back to 1. A reaction first order in H+ was observed with the latter compound. The 2,2,3-trimethyl derivative 3-NPU showed only one reaction first order in OH-, but complex acid catalysis is described by slopes 0, -1, 0, and finally -1 again. The cyclizations were general base catalyzed, with Brønsted β values of 0.5-0.6. The OH- catalysis at higher pH for 1-NPU and 2-NPU showed inverse solvent kinetic isotope effects and deviated from the Brønsted relationships, while that for 3-NPU showed a normal effect and complied with the Brønsted relationship. The accelerations due to the gem-dimethyl effect were lost with the OH- and general base-catalyzed reactions of 3-NPU. This behaviour is due to a change from the rate-determining formation of the tetrahedral intermediate with 1-NPU and 2-NPU to the rate-determining breakdown with 3-NPU, due to steric hindrance to protonation of the leaving ethoxy group. The OH- reaction at higher pH involves attack of the ureide anion with 1-NPU and 2- NPU, becoming concerted with deprotonation when catalyzed by general bases and changing to acid inhibition of the anion of the tetrahedral intermediate at low pH. With 3-NPU at higher pH, T- is in equilibrium and the conjugate acids of the general bases accelerate its breakdown by protonating the ethoxy group. Acid catalysis of the cyclization of 3-NPU at higher pH is also protonation of the leaving group from T0 changing to the rate-determining formation of T at lower pH. The latter mechanism is preferred for the cyclization of 2-NPU.Key words: gem-dimethyl effect, mechanism, general base catalysis, proton transfer, steric hindrance.
Aminolysis of naphthyl acetates catalyzed by cyclodextrins
Authors: Tee Oswald S , Boyd Michael J
Published: April 2011

The effects of cyclodextrins (CDs) on the rate of nucleophilic attack on 1- and 2-naphthyl acetates (1-NA and 2-NA) in aqueous solution have been investigated. Analysis of the variation of the pseudo-first-order rate constants with [nucleophile] and [CD] affords rate constants for reaction of the nucleophiles with free ester (kN) and with ester bound to the CD (kcN). The reaction of 1-NA and 2-NA with the trifluoroethoxide anion is slowed down by β-CD as the ratios kcN/kN are 0.11 and 0.30, respectively. For reaction with the anion of 2-mercaptoethanol in the presence of α-CD, β-CD, "hydroxypropyl-β-CD" (hp-β-CD) and γ-CD, the reactivity ratios kcN/kN vary between 0.04 and 2.4, ranging from strong retardation to modest catalysis; the retardations arise with β-CD and hp-β-CD, which bind the esters strongly. By contrast, the attack of primary alkylamines is generally accelerated, and in many cases substantially so. For the aminolysis of 1-NA in the presence of β-CD, values of kcN/kN range from 7 to 460, assuming that free amine reacts with CD-bound ester. Alternatively, if the CD-catalyzed reaction involves free ester reacting with CD-bound amine, with rate constant kNc, the ratios kNc/kN vary from 43 to 140. Either way, there is appreciable catalysis of the aminolysis of 1-NA by β-CD. For the aminolysis of 2-NA, the effects are less dramatic: the ratios kcN/kN range from 0.19 to 17, and values of kNc/kN vary from 17 to 110. The reaction of 1-NA with n-hexylamine is also catalyzed by γ-CD. The variations of kinetic parameters with alkylamine chain length suggest that the CD-catalyzed aminolysis basically takes place by the attack of CD-bound amine on the free ester. However, there must be some stabilizing interactions between the aryl group of the ester and the CD during the reaction, since the transition state stabilization is different for 1-NA and 2-NA, as well for other esters.Key words: aminolysis, catalysis, cyclodextrin, ester cleavage, kinetics.
Formation of a cyclic tetrahedral intermediate by the addition of water to 2-methyl-4H- 3,1-benzoxazine followed by ring opening to 2-aminobenzyl acetate and 2-acetylaminobenzyl alcohol; pH-dependence of rate of reaction and product ratio
Authors: Dixon Wendy J , Hibbert Frank
Published: April 2011

Kinetic studies have shown that addition of water to protonated 2-methyl-4H-3,1-benzoxazine occurs to give a cyclic tetrahedral carbonyl addition intermediate. At pH <5, the intermediate is protonated and reacts to 2-aminobenzyl acetate, whereas at pH >7.5, the unprotonated intermediate collapses to give 2-acetylaminobenzyl alcohol. The former reaction is catalysed by buffer base but the latter is uncatalysed. At pH 9-12, reaction of hydroxide ion with protonated 2-methyl-4H-3,1-benzoxazine to give 2-acetylaminobenzyl alcohol becomes important, and at pH >12, the same product is formed by reaction of hydroxide ion with unprotonated 2-methyl-4H-3,1-benzoxazine.Key words: mechanism, addition, tetrahedral intermediate, hydrolysis, pH profile.
Versatility of helix–loop–helix catalysts — cooperative HisH+–His sites that span both helices
Authors: Nilsson Jonas , Broo Kerstin S , Sott Richard S , Baltzer Lars
Published: April 2011

Peptides with 42 amino acid residues have been designed to fold into helix-loop-helix motifs that dimerize to form four-helix bundles and catalyze the hydrolysis of p-nitrophenyl esters. Their reactivities depend on nucleophilic and general-acid catalysis by cooperative HisH+-His pairs. The peptide catalyst MNV with the HisH+-His pair separated by three residues within the helical segment catalyzes the hydrolysis of p-nitrophenyl fumarate with a second-order rate constant of 0.034 M-1 s-1 at pH 5.1 and 290 K. This i, i+3 site is a factor of three more efficient than the corresponding i, i+4 site. Helix-loop-helix peptides having histidines situated at opposing helices were designed and exhibited cooperative HisH+-His catalytic pairs. The peptide H11,34K hydrolyzed p-nitrophenyl acetate and p-nitrophenyl valerate with second-order rate constants of 0.044 and 0.15 M-1 s-1, respectively, at pH 5.1 and 290 K, indicating that the hydrophobic substituent was recognized by the catalyst.Key words: de novo design, helix-loop-helix, four-helix bundle, histidine, catalysis.
Electrochemical reduction and oxidation of DDT
Authors: Merica Simona G , Jedral Wojceich , Lait Susan , Keech Peter , Bunce Nigel J
Published: April 2011

Electrolysis has been studied as a possible method to treat DDT wastes. In methanol, the major process was dehydrochlorination to DDE followed by further reduction. In an aqueous emulsion containing 1% heptane and 0.1% Triton SP-175®, DDT was reduced at a deposited lead electrode with sodium sulphate as the supporting electrolyte by sequential hydrodechlorination of the aliphatic chlorine atoms. An excellent material balance was achieved, but the current efficiency was poor, even at low current densities. Electrooxidation of DDT was also investigated; in aqueous solutions or emulsion, little oxidation occurred because of competing oxidation of water at the highly positive potentials needed to oxidize DDT. In acetonitrile, electrooxidation occurred with high current efficiency by way of "electrochemical combustion" of DDT and its intermediate oxidation products to CO2. We conclude that development of an electrolytic technology for destroying DDT wastes is unlikely.Key words: electroreduction, electrooxidation, voltammetry, surfactant media.
NMR conformational analysis on cyclic decapeptide template molecule
Authors: Peng Zhenghong
Published: April 2011

We report the synthesis and conformational analysis of a series of cyclic and bicyclic decapeptide templates for combinatorial chemistry. The peptides were synthesized via solid phase synthesis and followed by solution cyclization. The conformation of the peptides was studied by proton NMR spectroscopy in DMSO and in TFE-water. The structure of the peptide template was calculated with the program DIANA and followed by SA from the NMR experimental constraints. The peptide adopts a fold comprising two β-strands and two type II β-turns. The design of such a restained cyclic decapeptide template will be discussed along with Template Assembled Synthetic Proteins (TASP).Key words: solid phase peptide synthesis, cyclic decapeptide, NMR, conformational analysis, β-sheet.
Crystal structures of dihydroquercetin 3-acetate and dihydroquercetin 3,3'4',7-tetraacetate: hydrogen bonding in 5-hydroxyflavanones
Authors: Kiehlmann Eberhard , Biradha Kumar , Domasevitch Konstantin V , Zaworotko Michael J
Published: April 2011

The molecular structures of dihydroquercetin 3-acetate 3 and dihydroquercetin 3,3',4',7-tetraacetate 4 were determined by single crystal X-ray analysis. Comparison of their crystal data with those of 16 known 5-hydroxyflavanones shows intramolecular O(5)-H···O(4)=C hydrogen bonding, preference for nearly perpendicular orientation of the two aromatic rings and preferred sofa conformation of the heterocyclic ring. The major stabilizing force in the crystal packing pattern of 3 is intermolecular hydrogen bonding.Key words: crystal structure, dihydroquercetin, flavanones, hydrogen bonding.
Qualitative analysis of complex mixtures of VOCs using the inside needle capillary adsorption trap
Authors: Shojania S , McComb M E , Oleschuk R D , Perreault H , Gesser H D , Chow A
Published: April 2011

An alternative sampling technique for fingerprint analysis of complex mixtures of petroleum-based products is presented. Fingerprint chromatograms of the volatile organic compounds (VOCs) for class 0-5 accelerants can be readily obtained using the recently developed inside needle capillary adsorption trap (INCAT) device. The concentration of VOCs from the static headspace of these complex mixtures, onto the adsorbing carbon coating of the INCAT device, avoids some problems associated with conventional headspace gas chromatography (HS-GC). The INCAT sampling method is a solventless extraction technique in which the analytes adsorbed inside the device are thermally desorbed inside the heated injection port of a gas chromatograph (GC), or a gas chromatograph coupled with a mass spectrometer (GC-MS). The presented method of active sampling with the INCAT device was used to obtain fingerprint chromatograms of the headspace of various gasolines, paint thinners, and lighter fluids. The static headspace chromatograms, from active sampling with the INCAT device, were compared with direct liquid injection of the samples. The INCAT chromatograms showed preferential adsorption of aromatic compounds over lighter, more volatile, but less polar compounds. Each class of the accelerant can be positively identified from the fingerprint chromatogram using only a few characteristic peaks. In addition, the ability to detect these volatile components of gasoline in aqueous samples at environmentally significant levels was also investigated.Key words: VOC, fingerprinting, INCAT, petroleum, headspace GC.
Determination of proton exchange rates in aqueous solution using TOCSY
Authors: McClung RED , Nakashima T T , Yamamoto H , Kotovych G
Published: April 2011

A product operator description of the nuclei in an ensemble of molecules undergoing intermolecular exchange during the spin-lock period of TOCSY is presented. Experimental measurements of the transfer of magnetization from the CH2 protons in N-acetylglycine to the solvent water protons, via exchange of the NH proton with water protons during the spin-lock period in TOCSY, are shown to be in agreement with theoretical predictions at lower pH values (7.85-9.54) where the rate constants for NH-water exchange are known. Measurements at higher pH (up to 11.03) indicate that the highest rate constant for exchange that can be determined by this technique is τA-1 ~ 4000 s-1.Key words: product operator, density matrix, intermolecular exchange, TOCSY, NMR.
Time-reversal in NMR of solids
Authors: Lacelle Serge
Published: April 2011

The behavior of multiple spin dynamics under time-reversal excitation is investigated in strongly dipolar coupled spin networks. It is demonstrated that the typical physical intuition that NMR spectroscopists have of time-reversal in such systems is erroneous. By studying the equation of motion of the spin system in an infinite one-dimensional quantum spin chain with nearest-neighbor dipolar interactions and evolving under time-reversal excitation, a more appropriate physical picture emerges. Implications of these new findings are briefly discussed in the context of error propagation and teleportation in NMR quantum information processing.Key words: time-reversal, NMR, nuclear spin dynamic, quantum information processing.
Electron self-exchange, oxidation, and reduction reactions of bis(2,9-dimethyl-4,7-diphenyl- 1,10-phenanthroline)copper(II/I) and bis(6,6'-dimethyl-2,2'-bipyridine)copper(II/I) couples in acetonitrile: gated ET for the reduction, oxidation, and self-exchange processes
Authors: Koshino Nobuyoshi , Kuchiyama Yoshio , Funahashi Shigenobu , Takagi Hideo D
Published: April 2011

The electron self-exchange rate constant for the Cu(dmbp)22+/+couple (dmbp = 6,6'-dimethyl-2,2'-bipyridine) was measured in acetonitrile by the NMR method (kex= 5.5 × 103kg mol-1s-1, ΔH* = 35.0 ± 0.3 kJ mol-1and ΔS* = -56 ± 1 J mol-1K-1). Reduction reactions of Cu(bcp)22+(bcp = 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline) and Cu(dmbp)22+with Co(bipy)32+(bipy = 2,2'-bipyridine) and ferrocene (Fe(Cp)2= bis(cyclopentadienyl)iron(II)), and oxidation reactions of Cu(bcp)2+and Cu(dmbp)2+by Ni(tacn)23+(tacn = 1,4,7-triazacyclononane) and Mn(bipyO2)33+(bipyO2= N,N'-dioxo-2,2'-bipyridine) were also studied in acetonitrile. The electron self-exchange rate constants, kex, estimated for the Cu(bcp)22+/+and Cu(dmbp)22+/+couples from the oxidation reactions of Cu(bcp)2+and Cu(dmbp)2+by Ni(tacn)23+and Mn(bipyO2)33+were consistent with the directly measured values by NMR, while kexestimated from the reduction reactions of Cu(bcp)22+and Cu(dmbp)22+by Co(bipy)32+([Cu(bcp)22+]0, [Cu(dmbp)22+]0>> [Co(bipy)32+]0) were 103times smaller than those directly measured by the NMR method. The pseudo-first-order rate constant for the reduction reaction of Cu(bcp)22+and Cu(dmbp)22+by Fe(Cp)2was not linear against the concentration of excess amounts of Fe(Cp)2. Analyses of the reactions revealed that the reductions of Cu(bcp)22+and Cu(dmbp)22+involve slow paths related to the deformation of Cu(II)N4center from tetragonal to tetrahedral coordination. The energetic preference for the deformation of Cu(II) species rather than that of Cu(I) was discussed on the basis of the ligand field activation energy (LFAE).Key words: electron transfer, copper(II) and copper(I) complexes, gated behavior.
Synthesis and X-ray structural characterization of the ruthenium β-diketonato complexes: Ru(hfac)3, cis-Ru(hfac)2(MeCN)2, and cis-Ru(hfac)(acac)(MeCN)2
Authors: Baird Ian R , Rettig Steven J , James Brian R , Skov Kirsten A
Published: April 2011

Ru(hfac)3 (2) was synthesized via peroxide oxidation of the Ru(II) species [Na][Ru(hfac)3] (1) (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonate). Treatment of either 1 or 2 with CF3SO3H in MeCN generated cis-Ru(hfac)2(MeCN)2 (3). Ru(acac)2(hfac) (4) (acac = acetylacetonate) was generated by addition of hfac to an EtOH solution of cis-[Ru(acac)2(MeCN)2][CF3SO3]. Subsequent treatment of 4 with CF3SO3H in MeCN yielded cis-Ru(acac)(hfac)(MeCN)2 (7). Syntheses of [Na][Ru(hfac)2(acac)] (5) and Ru(hfac)2(acac) (6) are also reported. The complexes were characterized generally by elemental analysis, cyclic voltammetry, UV-vis, NMR, and IR spectroscopies. The structures of 2, 3, and 7 were established by X-ray crystallographic analyses. Crystals of 2 are monoclinic with a = 8.7781(4), b = 13.0760(11), c = 19.1857(5) Å, β = 92.2275(5)°, Z = 4, and space group P21/n; those of 3 are monoclinic with a = 25.731(4), b = 8.8332(13), c = 18.1955(4) Å, β = 93.3395(6)°, Z = 8, and space group C2/c; and those of 7 are triclinic with a = 7.6812(9), b = 10.680(2), c = 12.578(2) Å, α = 88.062(6)°, β = 83.874(3)°, γ = 69.5898(15)°, Z = 2, and space group Pbar over 1. The structures were solved by Patterson methods and refined by full-matrix least-squares procedures to R(F) = 0.036, 0.035, and 0.068 (Rw(F2) = 0.061,Rw(F) = 0.052, and Rw(F) = 0.089), respectively.Key words: ruthenium, β-diketonato complexes, acetylacetonate, 1,1,1,5,5,5-hexafluoroacetylacetonate, acetonitrile complexes.
New “molecular metals” based on symmetrically tetrasubstituted copper phthalocyanine complexes
Authors: Achar B N , Jayasree P K
Published: April 2011

Pure copper(II) tetrasubstituted phthalocyanine complexes, CuPTX (where X = -NO2, -NH2, -SO3H, and -OH) were synthesized. The electrical conductivity properties of these complexes were investigated both before and after iodine doping for the first time. Elemental, electronic, IR, magnetic susceptibility measurements, ESR, X-ray diffraction, and TGA analytical techniques were used to characterize and study the effect of substituents as well as iodine doping. Variation in the electrical conductivity of the copper phthalocyanine derivatives depends on the nature of the substituents and were found to show ~105 times improved electrical conductivity in comparison to parent unsubstituted copper phthalocyanine. Interestingly, these substituted complexes after iodine doping showed remarkably increased electrical conductivity nearly 1012 times that of unsubstituted copper phthalocyanine. This may be accounted for by the decrease in the metal-metal bond distance, increase in the approach of the ideal eclipsed system, or due to the combined effects of the above factors.Key words: copper phthalocyanine, iodine doping, electrical conductivity.
Solid-state nuclear magnetic resonance studies of triphenylsilyl-, triphenyltin-, and triphenyllead(pentacarbonyl)manganese(I) complexes
Authors: Christendat Dharamdat , Butler Ian S , Gilson Denis FR , Morin Frederick G
Published: April 2011

The solid-state CP MAS (29Si, 119Sn, and 207Pb) NMR spectra of the triphenylsilyl-, triphenyltin-, and triphenyllead(pentacarbonyl)manganese(I) complexes, (Ph3E)Mn(CO)5 (E = Si, Sn, Pb), have been analyzed to give the chemical shifts, one-bond spin-spin coupling constants, 1JE-Mn, the "effective-dipolar" coupling constants (D - ΔJ/3), the chemical shift tensors, and the spin-spin anisotropy (ΔJ), where the analysis permits. For the tin and lead compounds, three and four sets of chemical shifts, respectively, were observed, and two different polymorphs occur for the lead complex, depending on the solvent used for recrystallization. The average values of the reduced coupling constants, 1KMn-Si (2.64 × 1020 T2 J-1), 1KSn-Mn (1.25 × 1020 T2 J-1), and 1KPb-Mn (4.18 × 1020 T2 J-1) showed a linear correlation with the s-electron densities at the respective metal nuclei. The principal components of the chemical shift tensors have been determined for the tin and lead compounds.Key words: manganese-group-14 compounds, solid-state 29Si, 119Sn, and 207Pb CP MAS NMR, spin-spin coupling, chemical shift anisotropy, quadrupole coupling.
Solid-state phosphorus-31 NMR study of phosphine- and phosphite-substituted cobaloximes
Authors: Schurko Robert W , Wasylishen Roderick E , Moore Scott J , Marzilli Luigi G , Nelson John H
Published: April 2011

Solid-state 31P NMR spectra of two phosphite- and 17 phosphine-substituted cobaloximes have been acquired under conditions of magic-angle spinning (MAS) and cross polarization (CP) at two applied magnetic fields. In the majority of cases, eight-peak multiplets are observed in the 31P CPMAS NMR spectra, arising from one-bond indirect spin-spin coupling to cobalt (spin S = 7/2). The spacings between adjacent peaks gradually increase or decrease from low to high frequency, due to the presence of residual dipolar coupling between the cobalt and phosphorus nuclei. Values of 1J(59Co,31P) were estimated from the spacing between the central peaks of the eight-peak multiplets. For the phosphine-substituted cobaloximes, values of 1J(59Co,31P) range from 225 to 372 Hz, while in the phosphite derivatives this coupling is considerably larger, from 420 to 615 Hz. From comparison with cobaloximes for which the cobalt nuclear quadrupole coupling interaction is fully characterized, the residual dipolar shift, d, and sense of the 31P NMR spectrum can be utilized to infer the electric field gradient (EFG) orientations at the cobalt nucleus in cobaloximes for which such data are unavailable. The magnitudes of 1J(59Co,31P) and d, as well as the sense of the spectra, are shown to be dependent upon the nature of the axially-substituted ligands. Phosphorus-31 CPMAS NMR spectra of several cobaloximes exhibit broad peak shapes at room temperature. Variable-temperature 31P NMR experiments reveal that the cobalt nucleus is effectively self-decoupled at room temperature; however, splittings due to 1J(59Co,31P) were observed in spectra acquired at low temperatures.Key words: solid-state 31P NMR, 59Co-31P spin-spin coupling constants, 59Co electric field gradient tensors, cobaloximes.
Solvent dependence of rotational energetics and formyl-proton long-range spin-spin coupling behavior of 2,6-dichloro- and 2,6-dinitrobenzaldehydes using dipolar couplings and temperature dependence of long-range couplings
Authors: Lounila Juhani , Hiltunen Yrjö , Tuppurainen Kari , Pulkkinen Anja , Laatikainen Reino
Published: April 2011

The formyl rotational energetics, solvent effects on the energetics and formyl-proton spin-spin coupling behavior of 2,6-dichlorobenzaldehyde were studied by using dipolar couplings analysis and the temperature dependence of the spin-spin couplings. The general form of the rotational potential was taken from molecular mechanics and the conjugative sin2 Θ-type component (where Θ is the formyl-ring dihedral angle) was then optimized using the dipolar couplings obtained by analyzing 1H NMR and 13C proton satellite spectra in a liquid crystal solvent. The optimization based on the dipolar couplings gave the following rotational free energy potential: V(Θ) = 4.5 cos6 Θ + 10.7 (± 2.0) sin2 Θ, in kJ/mol. The analysis based on the temperature dependence of 6J data allowed estimation of solvent effects on the potential. For example, the potentials in acetone and in acetonitrile differ by a 1.0 sin2 2Θ (in kJ/mol). The chloroform solvent effect can be described by term of -1.0 cos6 Θ. When the formyl-proton six-bond coupling data was fit, assuming it obeyed the expression 6J(Θ) = 6J90 sin2 Θ + 6J0 and assuming 6J0 = 0.015 Hz, the analysis yielded 6J90 of -0.48 (± 0.03) Hz. The scalar coupling temperature dependence method was applied also to the conformational analysis of 2,6-dinitrobenzaldehyde.Key words: spin-spin coupling, dipolar coupling, solvent effect, rotational barrier, benzaldehyde.
A short synthesis of both enantiomers of enterolactone
Authors: Sibi Mukund P , Liu Pingrong , Johnson Michael D
Published: April 2011

A short and efficient synthesis of both enantiomers of enterolactone, a mammalian lignan, is described. The overall yield for the natural enterolactone, over seven steps, was 19% and for its enantiomer 27%. Key words: enterolactone, 4-diphenylmethyl-2-oxazolidinone, succinate, enantioselective synthesis.
Structure of 8-[4'-(3''-nitrobenzamido) benzamido]naphthalene-1,3,6-trisulfonate (NF-033), and molecular basis of its cellular toxicity
Authors: Camerman Arthur , Mastropaolo Donald , Nickel Peter , Hempel Andrew , Camerman Norman
Published: April 2011

The title compound is one of a large number of compounds related to the drug suramin which have been found to have anti-HIV properties. However, its toxicity to uninfected cells is high. We crystallized the compound, determined its structure, and investigated the molecular basis for its high toxicity. The crystals are monoclinic, C2/c, a = 28.614(1), b = 10.031(0), c = 24.051(1) Å, β = 98.36(2)°, Z = 8, convergence at R = 0.066 for 4264 reflections with I > 2σ(I). The oxygen atoms of one of the sulfonate groups are disordered, as are several water molecules. Stereochemical comparisons with a segment of B-DNA have yielded a plausible explanation for the molecule's toxicity.

Key words: crystal structure, cellular toxicity, stereochemistry, NF-033.
Pyrolysis gas chromatography - mass spectrometry of humic substances extracted from Canadian lake sediments
Authors: Joly Helen A , Li Hongbo , Belzile Nelson
Published: April 2011

Humic substances (HS) were extracted with the aid of 0.1 M Na4P2O7 and 0.5 M NaOH solutions from the sediments of four lakes located in the Sudbury area in Ontario, Canada, namely, Tilton, Clearwater, Silver and Ramsey Lake. The humic acid (HA) and fulvic acid (FA) extracts, purified and characterized using classical methods i.e., elemental analysis, FTIR spectroscopy, and CPMAS 13C NMR (see N. Belzile, H.A. Joly, and H. Li. (1997)), were submitted to pyrolysis - gas chromatography - mass spectrometry (Py-GC-MS). The pyrolysates of the HA and FA extracts were found to be complex mixtures of at least 200 compounds. Results based on statistical analysis of the abundances of pyrolysis products (of known origin) revealed trends similar to those obtained from the classical bulk characterization techniques. The Py-GC-MS technique supported the observation, obtained from classical methods, that the chemical composition of HA extracts varied less significantly among the four lake sediments than for the FA extracts. The abundances of lignin and carbohydrate pyrolysates showed the highest variation among the FA extracts. Pyrolysis products originating from lignin, carbohydrates, proteins, and fatty acids were identified. Key words: humic substances, humic acid, fulvic acid, pyrolysis, pyrolysis  gas chromatography  mass spectrometry, lake sediments.
Construction of bicyclic tetrahydroisoquinolinones by combination of an IMDAF-ring cleavage reaction of N-allyl-2-furan-2-yl-acetamides
Authors: Padwa Albert , Reger Thomas S
Published: April 2011

The intramolecular Diels-Alder reaction of furanyl amides derived from 2-furylacetic acid has been examined. Substrates containing either an imide or tertiary amide linkage between the furan and the dienophile underwent smooth cycloaddition upon thermolysis. By varying the reaction conditions, either the primary cycloadduct or the ring-opened and acetylated product could be isolated in excellent yield. The stereochemical outcome of the IMDAF cycloaddition has the side arm of the tethered alkenyl group oriented syn with respect to the oxygen bridge. Semi-empirical AM1 calculations show that the exo-cycloadduct is 11 kcal lower in energy than the corresponding endo adduct and, presumably, some of this energy difference is reflected in the transition state for the cycloaddition. The IMDAF reaction of N-allyl-[2-(3,4-dimethoxyphenethyl)]-2-furanyl-2-yl-acetamide proceeded in 90% yield upon heating in xylene. The 4+2-cycloadduct undergoes ring-opening on treatment with base and the resulting alcohol was converted into the corresponding benzyl ether. Raney nickel reduction followed by Bischler-Napieralski cyclization furnished the tetracyclic skeleton of the berberine alkaloids.Key words: intramolecular, cycloaddition, Diels-Alder, furanylamide, heterocycle.
Reduction of conjugate double bonds with trichlorosilane
Authors: Chauhan Moni , Boudjouk Philip
Published: April 2011

A variety of α,β-unsaturated esters and cyclic ketones underwent smooth reduction of the carboncarbon double bond with a combination of inexpensive and readily available trichlorosilane and CoCl2. The reactions are performed under very mild conditions and products are obtained in high yields.Key words: reduction, carbonyl compounds, trichlorosilane, ketones, chemoselectivity.
Two novel Diels-Alder adducts from Hippocratea celastroides roots and their insecticidal activity
Authors: Jiménez-Estrada M , Reyes-Chilpa R , Hernández-Ortega S , Cristobal-Telésforo E , Torres-Colín L , Jankowski C K , Aumelas A , Van Calsteren M R
Published: April 2011

Two novel compounds, celastroidine A (1) and B (2), were isolated from the roots of Hippocratea celastroides K. Their structures were elucidated by spectroscopical and X-ray diffraction studies. Celastroidine A (1) (C50H74O5) was identified as a Diels-Alder adduct of a triterpene plus a diterpene and celastroidine B (2) as a beyerane, a type of dimer of two diterpene (C40H60O4). Both compounds could be formed in vivo by a Diels-Alder reaction. Celastroidine A showed some antifeeding activity against the stored grain insect Sitophyllus zeamays.Key words: Hippocratea celastroides, Hippocrataceae, roots, Diels-Alder adducts, diterpenoids, triterpenoids, x-ray diffraction, insect antifeedants, stored grain insects, Sitophyllus zeamays, insecticidal plants, Diels-Alderase.
Alkoxides of o-silyl benzyl alcohols in cleavage reactions: approaches to benzyl and silyl anion equivalents
Authors: Hudrlik Paul F , Arango Jose O , Hijji Yousef M , Okoro Cosmas O , Hudrlik Anne M
Published: April 2011

The alkoxides of o-silyl benzyl alcohols 4 undergo cleavage reactions under mild conditions allowing transfer of a benzyl or silyl group to an electrophile. Reactions 3a [Formula: see text] 8, and 3c or 4c [Formula: see text] 11 illustrate their potential as benzyl and silyl anion equivalents.Key words: silyl migration, benzyl anion equivalent, silyl anion equivalent, β-silyl ketone, γ-hydroxysilane.
Enantioselective synthesis of syringolide 2 from D-arabinose
Authors: Chênevert Robert , Dasser Mohammed
Published: April 2011

Syringolide 2, a bacterial signal molecule which elicits active defence in resistant plants, has been synthesized in 9 steps from 2,3:4,5-di-O-isopropylidene-D-arabinose, a known derivative of D-arabinose.Key words: syringolide, arabinose, synthesis.
Enhancement of lignin degradation and laccase activity in Pleurotus ostreatus by cotton stalk extract
Authors: Ardon Orly , Kerem Zohar , Hadar Yitzhak
Published: April 2011

The white rot fungus Pleurotus ostreatus was grown in a chemically defined solid state fermentation system amended with cotton stalk extract (CSE).Treated cultures exhibited increased laccase activity as well as enhanced lignin mineralization. Mineralization of [14C]lignin initialized 4 days earlier in CSE-supplemented cultures than in control cultures. Total mineralization in the first 16 days was 15% in the CSE-treated cultures, compared with only 7% in the controls. Cotton stalk extract also contained compounds that serve as substrates for laccase purified from P. ostreatus as shown by oxygen consumption, as well as changes in the UVvisible spectrum.Key words: cotton, Pleurotusostreatus, white rot, laccase, lignin biodegradation.
The enzymatic activity of phosphoglycerate mutase from gram-positive endospore-forming bacteria requires Mn2+ and is pH sensitive
Authors: Chander Monica , Setlow Barbara , Setlow Peter
Published: April 2011

The enzymatic activity of phosphoglycerate mutase (Pgm) from three gram-positive endospore-forming bacteria (Bacillus subtilis, Clostridium perfringens, and Sporosarcina ureae) requires Mn2+ and is very sensitive to pH; at low concentrations of Mn2+, a pH change from 8 to 6 resulted in greater than 30- to 200-fold decreases in the activity of these Pgms. However, Pgm deactivation at pH 6 was reversed by shifting the enzyme to pH 7 or 8. Free Mn2+ was not directly involved in Pgm catalysis, although enzyme-bound Mn2+ may be involved. The rate of catalysis by Mn2+-containing Pgm was also slightly pH dependent, although the Km for 3-phosphoglyceric acid appeared to be the same at pH 6, 7, and 8. These findings suggest that Mn2+ binds to catalytically inactive Pgm and converts it to a catalytically competent form, and further, that pH influences the efficiency with which the enzyme binds Mn2+. The extreme pH sensitivity of the Mn2+-dependent Pgms supports a model in which this enzyme is inhibited during sporulation by acidification of the forespore, thus allowing accumulation of the spore's large depot of 3-phospho-glyceric acid. The activity of Pgm from two closely related gram-positive bacteria that do not form spores (Planococcus citreus and Staphylococcus saprophyticus) also requires Mn2+ and is pH sensitive. In contrast, the Pgm activities from two more distantly related non-endospore-forming gram-positive bacteria (Micrococcus luteus and Streptomyces coelicolor) are neither dependent on metal ions nor particularly sensitive to pH.Key words: Bacillus, Clostridium, Mn2+, phosphoglycerate mutase, sporulation.
Regulation in the rpoS regulon of Escherichia coli
Authors: Loewen Peter C , Hu Bei , Strutinsky Jeanna , Sparling Richard
Published: April 2011

In Escherichia coli, the transcription factor sigmaS, encoded by rpoS, controls the expression of a large number of genes involved in cellular responses to a diverse number of stresses, including starvation, osmotic stress, acid shock, cold shock, heat shock, oxidative DNA damage, and transition to stationary phase. A list of over 50 genes under the control of rpoS has been compiled. The transcription factor sigmaS acts predominantly as a positive effector, but it does have a negative effect on some genes. The synthesis and accumulation of sigmaS are controlled by mechanisms affecting transcription, translation, proteolysis, and the formation of the holoenzyme complex. Transcriptional control of rpoS involves guanosine 3',5'-bispyrophosphate (ppGpp) and polyphosphate as positive regulators and the cAMP receptor protein - cAMP complex (CRP-cAMP) as a negative regulator. Translation of rpoS mRNA is controlled by a cascade of interacting factors, including Hfq, H-NS, dsrA RNA, LeuO, and oxyS RNA that seem to modulate the stability of a region of secondary structure in the ribosome-binding region of the gene's mRNA. The transcription factor sigmaS is sensitive to proteolysis by ClpPX in a reaction that is promoted by RssB and inhibited by the chaperone DnaK. Despite the demonstrated involvement of so many factors, arguments have been presented suggesting that sensitivity to proteolysis may be the single most important modulator of sigmaS levels. The activity of sigmaS may also be modulated by trehalose and glutamate, which activate holoenzyme formation and promote holoenzyme binding to certain promoters. Key words: transcription, translation, regulation, sigma factor, starvation.
Differences in the microbial communities associated with the roots of different cultivars of canola and wheat
Authors: Siciliano S D , Theoret C M , de Freitas J R , Hucl P J , Germida J J
Published: April 2011

Plant characteristics are known to alter endophytic and rhizosphere microbial communities; however, the effect of crop breeding programs on the microbial endophytic and rhizosphere communities is not clear. The purpose of this study was to determine if root-associated microbial communities differed between three cultivars of canola (Brassica spp.) and wheat (Triticum spp.). BiologTM analysis was used to characterize the microbial communities associated with the root interior and rhizosphere soil of field grown canola (Parkland, Excel, and Quest cultivars) as well as wheat (PI 167549, Red Fife, and CDC Teal cultivars). Fatty acid methyl ester (FAME) profiles of roots and rhizosphere soil of the cultivars were also compared. These crop cultivars represent a continuum from older to the most recent crop cultivars, with Quest being a transgenic canola variety tolerant of the herbicide glyphosate. To the best of our knowledge, Quest is not directly related to Parkland or Excel. The endophytic community of Quest used the BiologTM polymer, carbohydrate, amino acid, and miscellaneous functional guilds at a slower rate than the endophytic community of Excel or Parkland. Furthermore, there were lower levels of the microbial FAMEs, 18:0, 18:3 w6c (6,9,12), 16:0 2OH, and 15:0 2OH in the roots of Quest compared with Excel or Parkland. In contrast, there were no differences in the utilization rate of BiologTM functional guilds or the microbial FAMEs in the roots of the three wheat cultivars studied. The correlation between the ability of endophytic and rhizosphere communities to utilize BiologTM substrates was lower in Quest and CDC Teal compared with earlier crop cultivars. Our results indicate that endophytic and rhizosphere microbial communities of the transgenic cultivar Quest were different from nontransgenic cultivars grown at the same field site.Key words: Brassica spp., Triticum spp., rhizosphere, endophytes, FAME, BiologTM, transgenic.
Comparison of metabolites produced in vitro and in vivo by Photorhabdus luminescens, a bacterial symbiont of the entomopathogenic nematode Heterorhabditis megidis
Authors: Hu Kaiji , Li Jianxiong , Wang Wenjie , Wu Houming , Lin Hai , Webster John M
Published: April 2011

The types of metabolites produced by Photorhabdus luminescens C9 when it is introduced by Heterorhabditis megidis 90 into Galleria mellonella larvae are different from those produced in tryptic soy broth. Only 3,5-dihydroxy-4-isopropylstilbene 1 was identified from the organic extracts of P. luminescens culture broth, but both 3,5-dihydroxy-4-isopropylstilbene 1 and 3,5-dihydroxy-4-ethylstilbene 3 were isolated from the organic extracts of nematode-bacterium infected G. mellonella larvae. In addition to two pigments, both of which had been previously reported from P. luminescens C9 culture broth, three pigments, 1,8-dihydroxy-3-methoxy-9,10-anthraquinone 2, 1-hydroxy-2,6,8-trimethoxy-9,10-anthraquinone 6, and 1,4-dihydroxy-2,5-dimethoxy-9,10-anthraquinone 7 were isolated from the organic extracts of G. mellonella larvae infected by the nematode-bacterium complex. Among these, compounds 6 and 7 are novel and isolated from a natural source for the first time.Key words: Photorhabdus luminescens, Heterorhabditis megidis, 1-hydroxy-2,6,8-trimethoxy-9,10-anthraquinone, 1,4-dihydroxy-2,5-dimethoxy-9,10-anthraquinone, pigment.