bluuebunny/crossref_metadata_2025_split huggingface dataset:
Revealing new electronic behaviours in the Raman spectra of chirality‐enriched carbon nanotube ensembles
Authors: Duque Juan G. , Chen Hang , Swan Anna K. , Hároz Erik H. , Kono Junichiro , Tu Xiaomin , Zheng Ming , Doorn Stephen K. 
Published: September 2010

AbstractWe present Raman spectroscopy of single‐walled carbon nanotubes (SWNTs) that are enriched in metallic species by density gradient ultracentrifugation (DGU) and enriched in single semiconducting chiralities through DNA‐based separations. Radial breathing mode (RBM) spectra demonstrate that DGU samples are highly enriched in armchair chiralities. The enrichment allows acquisition of pure G‐band spectra of the armchair SWNTs and reveals that the LO mode is absent in these structures. Raman excitation profiles for the G‐band in nearly pure (10,2) samples reveals a strong asymmetry in the intensities of the resonance coupling to incident and scattered photons. The experimental data may be fit using a four‐level molecular model for Raman scattering and the strong asymmetry can be understood as a consequence of the presence of non‐Condon effects. The result requires a reassessment of the assumption that the incident and scattered resonances are equivalent. The consequences of such non‐Condon effects on other SWNT electronic and optical processes will be an important topic for future study.
Effects of Hypericum perforatum extract on diabetes‐induced learning and memory impairment in rats
Authors: Hasanein Parisa , Shahidi Siamak 
Published: September 2010

AbstractCognitive impairment occurs in diabetes mellitus. Hypericum perforatum has been used in folk medicine to improve mental performance. Here it is hypothesized that chronic treatment with an extract of Hypericum perforatum (6, 12 and 25 mg/kg, p.o.) would have effects on passive avoidance learning (PAL) and memory in control and streptozotocin‐induced diabetic rats. Treatments were begun at the onset of hyperglycaemia. PAL was assessed 30 days later. A retention test was done 24 h after training. At the end, the animals were weighed and blood samples were drawn for plasma glucose measurement. Diabetes caused impairment in acquisition and retrieval processes of PAL and memory. Hypericum treatment (12 and 25 mg/kg) improved learning and memory in control rats and reversed learning and memory deficits in diabetic rats. A dose of 6 mg/kg did not affect cognitive function. Hypericum administration did not alter the body weight and plasma glucose levels. Antioxidant properties and cholinergic facilitatory effects of Hypericum may be involved in its nootropic effects. These results show that Hypericum perforatum prevented the deleterious effects of diabetes on PAL and memory. As Hypericum would be free of major side effects compared with other nootropic medications, it may provide a new potential alternative for demented diabetic patients. Copyright © 2010 John Wiley & Sons, Ltd.
Rhodium(I)‐centered cyclotriveratrylene
Authors: Coolen H. K. A. C. , Reek J. N. H. , Ernsting J. M. , van Leeuwen P. W. N. M. , Nolte R. J. M. 
Published: September 2010

AbstractThe rigid bowl‐shaped molecule cyclotriveratrylene (CTV,1) was provided with short and long spacer arms terminating in triphenyl phosphite functions. These CTV ligands were used to immobilize a rhodium(I)‐carbonyl‐hydride complex. The ligand with short spacers gave a rigid, strained complex with a trigonal‐coordination sphere around the rhodium. The ligand with long flexible spacers allowed the formation of a large cavity after the complexation to the rhodium center. This cavity, however, is filled up by the spacer arms, as was indicated by NMR studies. Variable‐temperature NMR experiments suggested that the H‐Rh‐CO dipole in the rhodium‐ CTV complex can adopt two orientations: one with the hydride group pointing away from the CTV cavity (low‐temperature conformation) and one in which this orientation is inverted (high‐temperature conformation).
The influence of substituents on the geometry of the cyclopropane ring VIII. The molecular and crystal structures of azocyclopropane N,N′‐dioxide and 1,1′‐dimethylazocyclopropane N,N′‐dioxide
Authors: de Boer J. S. A. M. , Schenk H. 
Published: September 2010

AbstractCrystals of azocyclopropane N,N′‐dioxide, (C3H5NO)2, (1) are monoclinic, space group C2/c, a = 8.708(2), b = 8.321(1), c = 9.836(2) Å, β = 95.437(3)° (243K). Z = 4. The final R for 479 independent observed reflections is 0.035. The molecules are centrosymmetric and have the bisecting (s‐cis) conformation for the NO group.Crystals of 1,1′‐dimethylazocyclopropane N,N′‐dioxide, (C4H7NO)2, (2) are monoclinic, space group P21/n, a = 10.727(5), b = 7.181(3), c = 5.969(2) Å, β = 90.52 (2)° (223K), Z = 2. The final R for 773 independent observed reflections is 0.046. The molecules are also centrosymmetric but steric interference by the methyl group at C1 prevents them from assuming the bisecting conformation. The effect of the N(O)N(R) group on the geometry of the cyclopropane ring is small to negligeable.
Complex formation of Ca2+ ions with 1‐O‐n‐octyl‐β‐D‐mannofuranoside
Authors: Kooreman Peter A. , Engberts Jan B. F. N. 
Published: September 2010

AbstractThis paper describes the first example of complex formation of an alkylglycoside with calcium ions. Qualitative evidence for complex formation is obtained by titration microcalorimetry.
Effect of the nitrogen heteroatom on the photophysics and photochemistry of trans‐1‐styrylnaphthalene and trans‐9‐styrylphenanthrene in different solvents
Authors: Bartocci Giampiero , Mazzucato Ugo , Spalletti Anna 
Published: September 2010

AbstractThe effect of the nitrogen heteroatom on the excited state properties of trans‐1‐styryl‐naphthalene (1‐StN) and trans‐9‐styrylphenanthrene (9‐StPh) has been investigated by fluorimetric and photochemical techniques. The relaxation processes of two aza analogues of each of these diarylethylenes, bearing the nitrogen atom in the mono‐ and polycyclic aryl group, respectively, were studied in different solvents and over a large temperature range. The aza derivatives have smaller radiative and large reactive decay yields compared with the parent hydrocarbons. The polar solvent reduces the torsional energy barrier and favours the trans → cis photoisomerization while intramolecular hydrogen bonding may slow down the rate of the reactive deactivation.
The influence of the chiral environment in the photosynthesis of enantiomerically enriched hexahelicene. A sudden change in the chirality of hexahelicene by a change in the temperature of a chiral crystalline medium
Authors: Prinsen W. J. C. , Laarhoven W. H. 
Published: September 2010

AbstractThe enrichment of one of the enantiomers (P or M) of hexahelicene (3) synthesized by the photochemical cyclodehydrogenation of 2‐styryl‐benzo[c]phenanthrene (1) in chiral media has been (re)investigated. Four different chiral solvents, two cholesteric liquid crystals, two chiral crystals, all at several temperatures, and two chiral polymers were used as media. To avoid erroneous values from circular‐dichroism (CD) measurements due to contributions of chiral side‐products, the enantiomeric excess (ee) was determined by HPLC analysis.In general the observed ee is small (< 7%). In chiral solvents the ee increases with decreasing temperatures. In the liquid crystals the macroscopic helix of the cholesteric phase has a small but distinct effect on the ee, probably due to the preferred fitting of one enantiomer of Z‐1 to the helix of the ‘solvent’. In chiral crystals the ee is relatively larger. A peculiar effect is observed when 1 is irradiated in ethyl (S)‐(+)‐O‐(4‐phenylbenzoyl)lactate. Below −19°C the M enantiomer and above −14°C the P enantiomer of 3 is the preferred photoproduct. In the polymer triacetylcellulose, M‐hexahelicene is formed in 4.5% excess; in β‐cyclodextrine only a very small amount of 3 is formed, due to the preferred photo‐isomerization into E‐1.
Synthesis and photochemistry of 2‐styrylpyrroles. Intermolecular photoaddition of pyrroles to a double bond
Authors: Šindler‐Kulyk Marija , Tomšić Slavica , Marinić ŽEljko , Metelko Biserka 
Published: September 2010

AbstractIrradiation of the 2‐styrylpyrroles 3 and 5 resulted in intermolecular addition of the pyrrole derivative to the double bond of a second molecule in a regiospecific way to give the dimeric products 6 and 7 as the main products. The N‐methyl‐substituted derivative 4 did not show the same reaction, but reacts as the corresponding furan derivative.
Factors influencing the reaction‐mode selectivity and regiochemistry of intermolecular photocycloaddition reactions of ethenes to polysubstituted benzenes
Authors: Al‐Qaradawi S. , Gilbert A. , Jones D. T. 
Published: September 2010

AbstractThe photoreactions of the methylbenzonitriles; 2,3‐, 2,4‐, 2,6‐, 3,4‐, and 3,5‐ benzonitriles; and 2′‐ and 4′‐ methoxyacetophenones with cyclopentene and ethyl vinyl ether have been investigated. Meta photocycloaddition is the major process for the benzonitriles with cyclopentene, and regiochemical features reflect the influence of polar factors along the reaction pathway. The enol ether yields ortho cycloadducts exclusively from all the benzenoid derivatives. The thermal ring opening of the primary photoadduct and the photolability of the cycloocta‐1,3,5‐triene isomer depend markedly on the position of the substituents.
[2 + 2] Photoaddition of 2‐aminopropenenitriles to diarylethanediones. A product study
Authors: Döpp Dietrich , Fischer Michael‐Alexander 
Published: September 2010

AbstractA selection of symmetrical (1a‐f) and unsymmetrical (4a,b) diarylethanediones, starting from their 3(n, π*) states, undergoes smooth head‐to‐head [2 + 2] photoaddition of various 2‐aminopropenenitriles 2A‐F to form oxetanes 3, 5 and 6 in moderate to good yields. Only one diastereomer out of two a‐priori possible regioisomers is formed in each case. The connectivity and the preferred geometry of the products is rationalized in terms of the geometry of the most easily accessible and most stabilized (including captodative stabilization) 1,4‐biradical intermediate. Whereas 2‐naphthyl‐substituted diones 1f and 4b form oxetanes, 1,1′‐naphthil and 1‐(1‐naphthyl)‐2‐phenylethanedione are ineffective.
Photoinduced energy‐ and electron‐transfer processes in dinuclear ruthenium(II) and/or osmium(II) complexes connected by a linear rigid bis‐chelating bridge
Authors: de Cola Luisa , Balzani Vincenzo , Barigelletti Francesco , Flamigni Lucia , Belser Peter , Bernhard Stefan 
Published: September 2010

AbstractA rigid and linear bridging ligand containing two 4,5‐diazafluorene chelating units separated by an adamantane spacer (diazf‐a‐diazf) has been synthesized and its dinuclear complexes [(bpy)2Ru(diazf‐a‐diazf)Ru(bpy)2]4+ (RuII · FAF · RuII), [(bpy)2Os(diazf‐a‐diazf)Os(bpy)2]4+ (OsII · FAF · OsII), and [(bpy)2Ru(diazf‐a‐diazf)Os(bpy)2]4+ (RuII · FAF · OsII) have been prepared as PF−6 salts. In these novel compounds, each Ru‐based and Os‐based unit displays its own absorption spectrum and electrochemical properties, regardless of the presence of a second metal‐based unit. The luminescence properties have also been investigated and it has been shown that electronic energy transfer takes place in the mixed‐metal RuII · FAF · OsII species at 77K from the Ru‐based to the Os‐based unit with rate constant 2.6 · 108 s−1. At room temperature the intrinsic decay of the Ru‐based unit is too fast (3.3 · 109 s−1) to allow the occurrence of energy transfer. Partial oxidation of the binuclear compounds RuII · FAF · OsII and OsII · FAF · OsII by CeIV in acetonitrile‐water solutions leads to the mixed‐valence RuII · FAF · OsIII and OsII · FAF · OsIII species where the oxidized metal‐based unit quenches, by electron transfer, the luminescent excited state of the unit that is not oxidized. At room temperature, the rate constants for the excited state * RuII · FAF · OsIII · RuIII · FAF · OsII and * OsII FAF · OsIII · OsIII · FAF · OsII processes are 8.3 · 108 s−1 and 3.9 · 108 s−1, respectively, and the rate constant for the back‐electron‐transfer process RuIII · FAF · OsII · RuII · FAF · OsIII is 2.9 · 107 s−1.
Volume changes associated with intramolecular electron transfer during MLCT state formation. Time‐resolved optoacoustic studies of ruthenium cyano complexes
Authors: Jiwan Jean‐Louis Habib , Wegewijs Bas , Indelli Maria T. , Scandola Franco , Braslavsky Silvia E. 
Published: September 2010

AbstractVolume changes associated with the intramolecular photooxidation of RuIIin bipyridine cyano complexes in aqueous solutions were determined by temperature‐dependent laser‐induced optoacoustics. The values obtained are attributed mainly to photoinduced changes in the specific interactions between the complexes and the water molecules of the first solvation shell. In particular, the values determined for the formation of the MLCT state in the homologous series Ru(bpy)(CN)2−4, Ru(bpy)(CN)3(CNCH3)−; and Ru(bpy)(CN)2(CNCH3)2, which are expansions for the two first compounds(i.e., ΔVR= 15, 10, andca.0 ml/mol, respectively), correlate directly with the number of cyanide ligands available for donor‐acceptor interactions with water. A parallel correlation with the number of cyanide ligands is found for the solvent effect on the MLCT energy of the complexes, as measured from the slope of plots of emission energyusthe solvent acceptor number. This correlation supports the concept of solvent (water in this case) reorganization around the MLCT state being responsible for the volume changes observed.
Medium effects on the photophysical properties of porphyrazine‐metal(II) complexes in micellar solutions
Authors: Dürr Heinz , Hayo Rudolf , David Elke , Willner Itamar , Zahavy Eran 
Published: September 2010

AbstractThe solubility of different phthalocyanine and porphyrazine metal(II) complexes 1–6 is described in cationic, neutral and anionic surfactants under various conditions. Optimal conditions were evaluated and photophysical properties of the dyes were measured. Various possibilities which have a direct effect on the aggregation phenomena were tested and dimerization constants and extinction coefficients are derived for the optimal monomer conditions. Each study was carried out in cationic, neutral and anionic micelles. With light‐scattering experiments micellar shapes were measured and compared with theoretical models. Triplet‐absorption spectra of the porphyrazine 2–4 were recorded and showed similar maxima to phthalocyanine 1. In steady‐state experiments photoinduced electron transfer reactions of 1, 2, 5 and 6 were investigated for several electron acceptors and hydrogen was evolved from 1, 3, 5 and 6 in a four‐component sacrificial system in order to check the photocatalytic properties of hydrophobic porphyrazines dissolved in surfactants.
Synthesis of a novel tetrapyrrolic macrolactam and its activity towards Uro'gen III synthase
Authors: Pichon Clotilde , Scott A. Ian 
Published: September 2010

AbstractA novel macrocyclic tetrapyrrolelactam 8, analog of a putative intermediate, has been synthesized. Its very low inhibitory effect on Uro'gen III synthase renders it unlikely to be a low‐energy transition‐state analog.
Screening of arylboronic acids to search for a strong inhibitor for γ‐glutamyl transpeptidase (γ‐GTP)
Authors: Suenaga Hikaru , Nakashima Kazuaki , Mikami Masafumi , Yamamoto Hiromasa , James Tony D. , Sandanayake K. R. A. Samankumara , Shinkai Seiji 
Published: September 2010

AbstractIn a study of the development of a strong inhibitor for γ‐glutamyl transpeptidase (γ‐GTP), the inhibitory effect of 21 arylboronic acids was determined in the γ‐GTP‐mediated hydrolysis of N‐(L‐γ‐glutamyl)‐4‐nitroanilide. It was shown that most boronic acids can moderately inhibit the enzyme activity and, in particular, the inhibitory effects of (3‐formylphenyl)boronic acid and (3‐carboxyphenyl)boronic acid (9% and 12%, respectively) are comparable to that reported for the binary L‐serine‐plus‐borate inhibition system (7%). Furthermore, it was shown that the addition of physiologically nontoxic saccharides is very effective in regenerating the enzyme activity. This effect is attributed to the competitive binding of saccharides with the boronic acid inhibitor to pull it out into the water phase. Thus, this paper offers a novel methodology for inhibition and control of γ‐GTP activity.
Studies with plant‐cell cultures of the Chinese herbal plant, Tripterygium wilfordii. Isolation and characterization of diterpenes
Authors: Kutney James P. , Han Kang 
Published: September 2010

AbstractA detailed analysis of the established cell‐culture line (coded as TRP4a) of the important Chinese herbal plant, Tripterygium wilfordii, in terms of diterpene production, is presented. In this study, 28 diterpenes have been isolated and characterized. Of these, 26 were isolated for the first time from the TRP4a cell line, 8 were novel compounds. From an analysis of the diterpenes obtained, a biosynthetic pathway of the pharmacologically interesting triepoxide, tripdiolide 29, is proposed.
Metallation and functionalization of 1‐allenylpyrrole
Authors: Tarasova O.A. , Taherirastgar F. , Verkruijsse H.D. , Mal'kina A.G. , Brandsma L. , Trofimov B.A. 
Published: September 2010

Abstract1‐Allenylpyrrole is lithiated at the α‐carbon atom of the allenyl group by n‐butyllithium in mixtures of diethyl‐ether/hexane or tetrahydrofuran/hexane. Whereas functionalization with trimethylchlorosilane, butyl iodide and dimethyl disulfide gives only allenic derivatives, addition of carbonyl compounds generally leads to mixtures of allenic and acetylenic derivatives. Upon heating its solutions in ether or tetrahydrofuran, Li‐allenylpyrrole is slowly transformed into the lithium derivative of 1‐(propyn‐2‐yl)pyrrole.
Reductive O‐ and N‐alkylations. Alternative catalytic methods to nucleophilic substitution
Authors: Fache Fabienne , Bethmont Valérie , Jacquot Laurent , Lemaire Marc 
Published: September 2010

AbstractDifferent amides have been selectively mono‐N‐alkylated using catalytic heterogeneous palladium and carbonyl compounds as alkylating agents. The same salt free method has been applied to the synthesis of ethers from alcohols. Reaction parameters have been studied in detail and a mechanism is proposed.
“Green” MMA; an environmentally benign and economically attractive process for the production of methyl methacrylate
Authors: Keijsper J. , Arnoldy P. , Doyle M.J. , Drent E. 
Published: September 2010

AbstractOver the last seven years Shell has developed a novel, economically attractive, and environmentally benign process for the production of methyl methacrylate (MMA). The process is based on the highly efficient Palladium‐catalysed methoxycarbonylation of propyne (methyl‐acetylene or MA) under mild, non‐corrosive reaction conditions (temperature ca. 50°C, CO pressure ca. 10 bar) according to the equation:MeOH + CO + HC ≡ C − Me(MA) → H2C = C(Me) − C(O)OMe(MMA)The activity (> 20000 mol‐MMA/mol‐Pd.h) and selectivity (> 99%mol) of the homogeneous Pd catalyst are very high making a once‐through process with minimal waste possible.The MA feedstock for the process, together with propadiene (PD), is separated from a steam‐cracker C3 stream by extractive distillation with DMF. Subsequently, PD is removed from this MA + PD/DMF mixture and isomerized over a heterogeneous K2O/Al2O3 catalyst to yield additional MA.Crude MMA obtained from the methoxycarbonylation of MA can easily be purified by a ‘topping and tailing’ procedure to yield MMA of very high purity (> 99.99 w%).This article describes some of the R&D work carried out at the ‘Koninklijke/Shell‐Laboratorium, Amsterdam’ which has enabled the design of a plant, based on this novel technology.
The use of dialkyl carbonates for safe and highly selective alkylations of methylene‐active compounds. A process without waste production
Authors: Bomben Andrea , Selva Maurizio , Tundo Pietro 
Published: September 2010

AbstractThe non‐toxic compound dimethyl carbonate (DMC) can be used as a methylating and a methoxycarbonylating agent in place of methyl chloride and phosgene, respectively. We report here that DMC and other dialkyl carbonates (DAlkCs: dimethyl, diethyl and dibenzyl carbonates) allow very selective alkylations of a variety of CH2‐acidic compounds. Both arylacetonitriles and alkyl arylacetates react with DAlkCs to yield the mono‐C‐alkylated derivatives (α‐alkyl‐α‐arylacetonitriles and alkyl α‐alkyl‐α‐arylacetates) with a selectivity of up to 99%, at complete conversion. Likewise, the mono‐C‐methylation by DMC proceeds selectively also on (aryloxy)acetonitriles and methyl (aryloxy)acetates. The reactions are carried out at temperature of 180‐220°C in the presence of weak bases (usually K2CO3); under such conditions, DAlkCs efficiently replace the common and very toxic alkylating agents (dialkyl sulfates and alkyl halides). In addition to the high selectivity obtained and the intrinsic safety of the dialkyl carbonates, the reported reactions give rise to neither organic nor inorganic waste products.
Palladium arenethiolates with intramolecularly coordinating nitrogen lewis bases
Authors: Janssen Maurits D. , Grove David M. , van Koten Gerard , Spek Anthony L. 
Published: September 2010

AbstractThe reaction of [PdCl2(MeCN)2] with one or two equivalents of Me3SiSC6H4NMe2‐2 in toluene affords the mono(arenethiolate) complex [PdCl(SC6H4NMe2‐2)] (1) or the bis(arenethiolate) complex [Pd(SC6H4NMe2‐2)2] (2), respectively, in high yields. [PdCl(SC6H4NMe2‐2)] (1) exists as a tetramer in the solid state (X‐ray) while [Pd(SC6H4NMe2‐2)2] (2) is a monomer both in the solid state and in solution (cryoscopy, NMR). The X‐ray structure determination of tetrameric 1 shows arenethiolate ligands bridging between PdCl units to form a unique eight‐membered U‐shaped Pd4S4 ring. Crystals of 1 are tetragonal, space group magnified image, with a = b = 12.0495(10) Å, c = 16.672(1) Å, V= 2420.6(3) Å3, Z = 2, and final R = 0.029, wR = 0.034 and S = 1.42 for 1174 reflections with I > 2.5 σ(I) and 111 variables. The X‐ray structure determination of 2 shows it to be monomeric in the solid state. The palladium has a square‐planar geometry that results from coordination by two S,N‐chelating arenethiolate ligands with a trans S and trans N arrangement of the donor atoms. Crystals of 2 are triclinic, space group magnified image, with a = 8.9923(5) Å, b = 9.2472(5) Å, c = 11.5933(6) Å, V = 825.93(9) Å3, Z = 2, and final R = 0.025, wR = 0.047 and S = 0.53 for 3603 reflections with I > 2.5 σ(I) and 226 variables.
Sulfonation oftrans‐10b,10c‐dimethyl‐10b,10c‐dihydropyrene and its 2,7‐di‐tert‐butyl derivative with sulfur trioxide
Authors: Cerfontain Hans , Koeberg‐Telder Ankie , Mitchell Reginald H. , Khalifa Nasr , Tashiro Masashi 
Published: September 2010

AbstractThe sulfodeprotonation oftrans‐10b,10c‐dimethyl‐10b,10c‐dihydropyrene (1) with sulfur trioxide has been studied in dioxane as solvent, as well as in dichloromethane, using 4.0–5.0 equivalents of dioxane relative to the amount of SO3as reactivity moderator. Reaction of1with 0.6 mol‐equiv. of SO3in dioxane at 22°C yields initially only the 2‐ and 4‐sulfonic acid in a 84/16 ratio. Using 3.0‐6.0 mol‐equiv. of SO3in dichloromethane with the temperature increasing from −78 up to 22°C the initially very rapid formation of the 1‐, 2‐ and 4‐sulfonic acid (formed in a ratio of 11/82/7) is followed by a much slower conversion into a mixture of 1,7‐, 2,4‐, 2,5‐ and 2,7‐disulfonic acid. These four acids are subsequently converted even more slowly into a mixture of the 1,4,7‐, 2,4,7‐ and 2,5,9‐trisulfonic acids to yield in part the 1,4,7,9‐, 2,4,7,9‐ and 2,4,7,10‐tetrasulfonic acids.trans‐2,7‐Di‐tert‐butyl‐10b, 10c‐dimethyl‐10b, 10c‐dihydropyrene (2) with 0.8–2.0 equiv. of SO3in dioxane as solvent gives the 4‐sulfonic acid which is slowly converted into a 16/84 mixture of the 4,9‐ and 4,10‐disulfonic acids.The observed distributions of sulfonic acid isomers are discussed in terms of the directing effects of the “ideal” ‐ almost planar ‐ [14] annulene and the sulfo and/ortert‐butyl substituent(s) already present.