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Ligand Effects on the Pd-Catalyzed Cross-Coupling Reaction of 3-Iodoalk-2-enoates with Propargyl/1,2-Allenylic Metallic Species: An Efficient Regiodivergent Synthesis of 2,4,5-Trienoates.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19921717 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 17, 2009 Category: Chemistry Authors: Zhao J, Yu Y, Ma S Tags: Chemistry Source Type: journals

A Convenient Domino Access to Substituted Alkyl 1,2-Dihydropyridine-3-carboxylates from Propargyl Enol Ethers and Primary Amines.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19921718 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 17, 2009 Category: Chemistry Authors: Tejedor D, Méndez-Abt G, García-Tellado F Tags: Chemistry Source Type: journals

Byproduct-Catalyzed Four-Component Reactions of Aldehydes with Hexamethyldisilazane, Chloroformates, and Nucleophiles in Acetonitrile Leading to Protected Primary Amines, beta-Amino Esters, and beta-Amino Ketones.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Multicomponent reactions are a very powerful tool for the construction of complex organic molecules by using readily available starting materials. While most of the multicomponent reactions discovered so far consist of three components, the reactions with four or more components remain sparse. We have successfully developed several four-component reactions using a catalytic amount of water as a hydrolyzing agent to decompose byproduct chlorotrimethylsilane (TMSCl) to yield secondary byproduct HCl that serves as a catalyst. In the presence of 40 mol % of water, the four-component reaction of aldehydes with hexamethyldis...
Source: Chemistry - November 17, 2009 Category: Chemistry Authors: Yang BL, Weng ZT, Yang SJ, Tian SK Tags: Chemistry Source Type: journals

Enzymatic Synthesis of Organic-Polymer-Grafted DNA.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
To create bioorganic hybrid materials, interdisciplinary work in the fields of chemistry, biology and materials science is conducted. DNA block copolymers are promising hybrid materials due to the combination of properties intrinsic to both the polymer and the nucleic acid blocks. Until now, the coupling of DNA and organic polymers has been exercised post-synthetically in solution or on solid support. Herein, we report the first enzyme-catalysed synthesis of DNA-organic polymer chimeras. For this purpose, four novel 2'-deoxyuridine triphosphates carrying polymer-like moieties linked to the nucleobase were synthesised. ...
Source: Chemistry - November 17, 2009 Category: Chemistry Authors: Baccaro A, Marx A Tags: Chemistry Source Type: journals

How to Distinguish Isodesmic from Cooperative Supramolecular Polymerisation.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In this report, both methods are evaluated to determine their effectiveness in identifying and quantifying the self-assembly mechanism for isodesmic and cooperative self-assembling systems. It was found that for a rapid and unambiguous determination of the self-assembly mechanism and its thermodynamic parameters, temperature-dependent measurements are more appropriate. These studies allow the acquisition of a large data set leading to an accurate determination of the self-assembly mechanism and quantification of the different thermodynamic parameters that describe the supramolecular polymerisation. For a comprehensive char...
Source: Chemistry - November 17, 2009 Category: Chemistry Authors: Smulders MM, Nieuwenhuizen MM, de Greef TF, van der Schoot P, Schenning AP, Meijer EW Tags: Chemistry Source Type: journals

Analysis of the Detailed Configuration of Hydrated Lanthanoid(III) Ions in Aqueous Solution and Crystalline Salts by Using K- and L(3)-Edge XANES Spectroscopy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The structural properties of the hydrated lanthanoid(III) ions in aqueous solution and in the isostructural trifluoromethanesulfonate salts have been investigated by a quantitative analysis of the X-ray absorption near-edge structure (XANES) spectra at the K- and L(3)-edges. The XANES analysis has provided a clear description of the variation of lanthanoid(III) hydration properties across the series. It was found that all of the lanthanoid(III) hydration complexes retain a tricapped trigonal prism (TTP) geometry, and along the series two of the capping water molecules become less and less strongly bound, before finally...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: D'Angelo P, Zitolo A, Migliorati V, Persson I Tags: Chemistry Source Type: journals

One-Step Preparation of Multifunctional Chitosan Microspheres by a Simple Sonochemical Method.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications due to its biocompatibility, high charge density, nontoxicity, and mucoadhesion properties. Processing techniques for the preparation of chitosan microspheres have been extensively developed since the 1980s. The present paper describes for the first time a fast and one-step process for the preparation of stable chitosan microspheres by a simple sonochemical method. The microspheres were characterized by their particle size, surface morphology, stability, and drug-entrapment efficiency. The average size of the microspheres w...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Skirtenko N, Tzanov T, Gedanken A, Rahimipour S Tags: Chemistry Source Type: journals

Design and Synthesis of a Highly Sensitive Off-On Fluorescent Chemosensor for Zinc Ions Utilizing Internal Charge Transfer.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Fluorescence imaging is a powerful tool for the visualization of biological molecules in living cells, tissue slices, and whole bodies, and is important for elucidating biological phenomena. Furthermore, zinc (Zn(2+)) is the second most abundant heavy metal ion in the human body after iron, and detection of chelatable Zn(2+) in biological studies has attracted much attention. Herein, we present a novel, highly sensitive off-on fluorescent chemosensor for Zn(2+) by using the internal charge transfer (ICT) mechanism. The rationale of our approach to highly sensitive sensor molecules is as follows. If fluorescence can be ...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Hanaoka K, Muramatsu Y, Urano Y, Terai T, Nagano T Tags: Chemistry Source Type: journals

Syntheses, Optical Properties, and Theoretical Investigation of Silafluorenes and Spirobisilafluorenes Bearing Electron-Donating Aminostyryl Arms around a Silafluorene Core.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
pi-Extended silafluorenes and spirobisilafluorenes bearing electron-donating aminostyryl substituents at the 2,7- or 3,6-positions were synthesized by a Horner-Wadsworth-Emmons reaction. The electronic influence of spirocyclic structure and substitution mode of the aminostyryl substituents was investigated by UV/Vis spectroscopy, which indicated the existence of a spiroconjugation effect in the 3,6-substituted spirobisilafluorene. They exhibited moderate to strong fluorescence emission, and the fluorescence properties were compatible with the UV/Vis absorption characteristics, except for the 3,6-substituted spirobisila...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Agou T, Hossain MD, Kawashima T Tags: Chemistry Source Type: journals

Effect of CO on the Oxidative Addition of Arene C--H Bonds by Cationic Rhodium Complexes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Sequential addition of CO molecules to cationic aryl-hydrido Rh(III) complexes of phosphine-based (PCP) pincer ligands was found to lead first to C--H reductive elimination and then to C--H oxidative addition, thereby demonstrating a dual role of CO. DFT calculations indicate that the oxidative addition reaction is directly promoted by CO, in contrast to the commonly accepted view that CO hinders such reactions. This intriguing effect was traced to repulsive pi interactions along the aryl-Rh-CO axis, which are augmented by the initially added CO ligand (due to antibonding interactions between occupied Rh d(pi) orbitals...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Montag M, Efremenko I, Cohen R, Shimon LJ, Leitus G, Diskin-Posner Y, Ben-David Y, Salem H, Martin JM, Milstein D Tags: Chemistry Source Type: journals

Correlation of the Catalytic Activity for Oxidation Taking Place on Various TiO(2) Surfaces with Surface OH Groups and Surface Oxygen Vacancies.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Three catalytic oxidation reactions have been studied: The ultraviolet (UV) light induced photocatalytic decomposition of the synthetic dye sulforhodamine B (SRB) in the presence of TiO(2) nanostructures in water, together with two reactions employing Au/TiO(2) nanostructure catalysts, namely, CO oxidation in air and the decomposition of formaldehyde under visible light irradiation. Four kinds of TiO(2) nanotubes and nanorods with different phases and compositions were prepared for this study, and gold nanoparticle (Au-NP) catalysts were supported on some of these TiO(2) nanostructures (to form Au/TiO(2) catalysts). FT...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Zheng Z, Teo J, Chen X, Liu H, Yuan Y, Waclawik ER, Zhong Z, Zhu H Tags: Chemistry Source Type: journals

Alkane Activation over Acidic Zeolites: The First Step.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The heterogeneous acid-catalyzed activation step of alkanes leading to the reaction intermediates (carbocationic or alkoxy species) was up to now the matter of a longstanding controversy. Gas chromatography and online mass spectroscopy measurements show that H(2) and methane are formed over H-zeolites, whereas HD and CH(3)D are formed over D-zeolites as the primary products in the reaction with isobutane. These results indicate that sigma-bond protolysis by strong acid sites is the first step for hydrocarbon activation on these catalysts at mild temperatures (473 K), in analogy to the activation path occurring in liqui...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Louis B, Pereira MM, Santos FM, Esteves PM, Sommer J Tags: Chemistry Source Type: journals

Reactivity of ortho-Substituted Aryl-Palladium Complexes towards Carbodiimides, Isothiocyanates, Nitriles, and Cyanamides.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Complexes [Pd(C(6)H(3)XH-2-R'-5)Y(N;N)] (X=O, NH; Y=Br, I; R'=H, NO(2); N;N=N,N,N',N'-tetramethylethylenediamine (tmeda), 2,2'-bipyridine (bpy), 4,4'-di-tert-butyl-2,2'-bipyridine (dtbbpy)) react with RN==C==E (E=NR, S) or RC identical withN (R=alkyl, aryl, NR''(2)) and TlOTf (OTf=CF(3)SO(3)) to give, respectively, 1) products of the insertion of the C==E group into the C--Pd bond, protonation of the N atom, and coordination of X to Pd, [Pd{kappa(2)-X,E-(XC(6)H(3){EC(NHR)}-2-R'-4)}(N;N)]OTf or [Pd(kappa(2)-X,N-{ZC(6)H(3)(NH==CR)-2-R'-4})(N;N)]OTf, or products of the coordination of carbodiimides and OH addition, [Pd{ka...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Vicente J, Abad JA, López-Sáez MJ, Jones PG, Bautista D Tags: Chemistry Source Type: journals

Bisthienylethenes Containing a Benzothiadiazole Unit as a Bridge: Photochromic Performance Dependence on Substitution Position.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A conveniently synthesized photochromic compound, BTB-1, containing an unprecedented six-membered 2,1,3-benzothiadiazole unit as the center ethene bridge, possesses good photochromic performance, with a high cyclization quantum yield and moderate fatigue resistance in solution or an organogel system. The fluorescence of BTB-1 can be modulated by solvato- and photochromism. However, the analogue BTB-2, in which the dimethylthiophene substituents are relocated to the 5,6-positions of benzothiadiazole, does not show any detectable photochromism. To the best of our knowledge, this is the first example of six-membered bridg...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Zhu W, Meng X, Yang Y, Zhang Q, Xie Y, Tian H Tags: Chemistry Source Type: journals

Synthesis of Highly Efficient Ag@AgCl Plasmonic Photocatalysts with Various Structures.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
By means of a simple ion-exchange process (using different precursors) and a light-induced chemical reduction reaction, highly efficient Ag@AgCl plasmonic photocatalysts with various self-assembled structures-including microrods, irregular balls, and hollow spheres-have been fabricated. All the obtained Ag@AgCl catalysts were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and UV-visible diffuse reflectance spectroscopy. The effect of the different morphologies on the properties of the photocatalysts was studied. The average content of elemental Ag in Ag@AgCl...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Wang P, Huang B, Lou Z, Zhang X, Qin X, Dai Y, Zheng Z, Wang X Tags: Chemistry Source Type: journals

Difluorophosphoryl Nitrene F(2)P(O)N: Matrix Isolation and Unexpected Rearrangement to F(2)PNO.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Triplet difluorophosphoryl nitrene F(2)P(O)N (X(3)A'') was generated on ArF excimer laser irradiation (lambda=193 nm) of F(2)P(O)N(3) in solid argon matrix at 16 K, and characterized by its matrix IR, UV/Vis, and EPR spectra, in combination with DFT and CBS-QB3 calculations. On visible light irradiation (lambda>420 nm) at 16 K F(2)P(O)N reacts with molecular nitrogen and some of the azide is regenerated. UV irradiation (lambda=255 nm) of F(2)P(O)N (X(3)A'') induced a Curtius-type rearrangement, but instead of a 1,3-fluorine shift, nitrogen migration to give F(2)PON is proposed to be the first step of the photoisomer...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Zeng X, Beckers H, Willner H, Neuhaus P, Grote D, Sander W Tags: Chemistry Source Type: journals

First Titanium-Catalyzed 1,4-Hydrophosphination of 1,3-Dienes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19918817 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Perrier A, Comte V, Moïse C, Le Gendre P Tags: Chemistry Source Type: journals

Hydroxypyridinechromene and Pyridinechalcone: Two Coupled Photochromic Systems.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Substitution of the phenyl group in 2-hydroxychalcones by a 4-pyridine unit dramatically changes the network of chemical reactions of this compound: trans-chalcone-type (Ct), cis-chalcone-type (Cc), and a hemiketal (hydroxy-4-pyridinechromene) (B) and their protonated forms are formed, but the presence of a flavylium-type cation could not be detected even at very acidic pH values. Moreover, whereas in 2-phenyl-2-benzopyrylium compounds B and Cc are generally elusive species whose kinetic processes in aqueous solutions occur on the sub-second timescale, in the present compound these species equilibrate on a timescale fo...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Leydet Y, Parola AJ, Pina F Tags: Chemistry Source Type: journals

Controlling Helical Chirality in Atrane Structures: Solvent-Dependent Chirality Sense in Hemicryptophane-Oxidovanadium(V) Complexes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The diastereomeric hemicryptophane oxidovanadium(V) complexes (P)-(S,S,S)-3 and (M)-(S,S,S)-4 have been synthesized. (1)H and (51)V NMR spectra in solution are consistent with the formation of Lambda and Delta forms of the propeller-like vanatrane moiety, leading to two diastereomeric conformers for each complex: that is, (P)-(S,S,S-Lambda)-3/(P)-(S,S,S-Delta)-3 and (M)-(S,S,S-Lambda)-4/(M)-(S,S,S-Delta)-4. The Lambda/Delta ratio is rather temperature-insensitive but strongly dependent on the solvent (the de of (M)-(S,S,S)-4 changes from 0 in benzene to 92 % in DMSO). The solvent therefore controls the preferential clo...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Martinez A, Robert V, Gornitzka H, Dutasta JP Tags: Chemistry Source Type: journals

An Interpenetrated Framework Material with Hysteretic CO(2) Uptake.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A new, twofold interpenetrated metal-organic framework (MOF) material has been synthesized that demonstrates dramatic steps in the adsorption and hysteresis in the desorption of CO(2). Measurement of the structure by powder X-ray diffraction (PXRD) and pair distribution function (PDF) analysis indicates that structural changes upon CO(2) sorption most likely involve the interpenetrated frameworks moving with respect to each other. PMID: 19918820 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Mulfort KL, Farha OK, Malliakas CD, Kanatzidis MG, Hupp JT Tags: Chemistry Source Type: journals

Evaporation-Induced Ordered Honeycomb Structures of Gold Nanoparticles at the Air/Water Interface.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The breath figure method was used to prepare dodecanethiol-capped gold nanoparticle macroporous structures with pore diameters from 1.7 to 3.5 mum on an air/water interface. A two-step procedure is proposed for the fabrication of these macroporous structures, by forming a surfactant monolayer on water, and drop-casting a gold nanoparticle dispersion in chloroform onto the surfactant monolayer. The self-assembled films are easily transferred from the water surface onto different substrates and were characterized by TEM, SEM, and AFM. Ordered honeycomb structures with different pore arrays (perforated monolayer films, he...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Ma H, Hao J Tags: Chemistry Source Type: journals

Dispersion Oriented Soft Interaction in a Frustrated Lewis Pair and the Entropic Encouragement Effect in its Formation.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The origin of the stability of a frustrated Lewis pair (FLP) tBu(3)P:B(C(6)F(5))(3) is investigated computationally to demonstrate the importance of the dispersion interaction. To this end, the interaction between alkyl-substituted phosphines (Me(3)P and tBu(3)P) and hexafluorobenzene (C(6)F(6)) is first investigated. Driven by the lone-pair to pi-orbital interaction, the binding energy is found to be even larger than usual pi-pi interaction energies between small aromatic compounds. This character, which is inherited to fluorophenyl-substituted B(C(6)F(5))(3) in the FLP, induces large flexibility in the FLP over the m...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Kim HW, Rhee YM Tags: Chemistry Source Type: journals

Enantioselective Michael Addition to alpha,beta-Unsaturated Aldehydes: Combinatorial Catalyst Preparation and Screening, Reaction Optimization, and Mechanistic Studies.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19918823 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Fleischer I, Pfaltz A Tags: Chemistry Source Type: journals

Tuning Hydrogen Sorption Properties of Metal-Organic Frameworks by Postsynthetic Covalent Modification.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Postsynthetic modification is presented as a means to tune the hydrogen adsorption properties of a series of metal-organic frameworks (MOFs). IRMOF-3 (isoreticular metal-organic framework), UMCM-1-NH(2) (University of Michigan crystalline material), and DMOF-1-NH(2) (DABCO metal-organic framework) have been covalently modified with a series of anhydrides or isocyanates and the hydrogen sorption properties have been studied. Both the storage capacities and isosteric heats of adsorption clearly show that covalent postsynthetic modification can significantly enhance the sorption affinity of MOFs with hydrogen and in some ...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Wang Z, Tanabe KK, Cohen SM Tags: Chemistry Source Type: journals

Tungsten(VI) and Tungsten(V) Fluoride Complexes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
WF(6) reacts with phosphines R(3)P forming 1:1 compounds. With R=P(CH(3))(3) the coordination around the tungsten atom is capped trigonal prismatic, with R=P(CH(3))(2)C(6)H(5) the coordination is capped octahedral, as established by single-crystal structure determinations: [(CH(3))(3)P--WF(6)]: a=752.5(21), b=945.7(24), c=629.8(18) pm. beta=110.36(13) degrees , space group Cm, Z=2; [(CH(3))(2)(C(6)H(5))P--WF(6)]: a=762.2(2), b=1123.5(2), c=2647.5(6) pm, space group Pbca, Z=8. [(CF(3)CH(2))(2)N--WF(5)] reacts smoothly with P(C(6)H(5))(3) forming known P(C(6)H(5))(3)(F)(2) and [(CF(3)CH(2))(2)N--WF(4)--P(C(6)H(5))(3)], a...
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: El-Kurdi S, Al-Terkawi AA, Schmidt BM, Dimitrov A, Seppelt K Tags: Chemistry Source Type: journals

Noncovalent Isotope Effect for Guest Encapsulation in Self-Assembled Molecular Capsules.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19918826 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 13, 2009 Category: Chemistry Authors: Haino T, Fukuta K, Iwamoto H, Iwata S Tags: Chemistry Source Type: journals

A New Zincate-Mediated Rearrangement Reaction of 2-(1-Hydroxyalkyl)-1-alkylcyclopropanol.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A novel rearrangement of 2-(1-hydroxyalkyl)-1-alkylcyclopropanol has been found. It proceeds in the presence of a catalytic amount of organozinc ate complex to give vic-diols. The rearrangement can be applied to various types of 2-(1-hydroxyalkyl)-1-alkylcyclopropanol, which can be easily prepared from the corresponding alpha,beta-epoxyketones and bis(iodozincio)methane. When bicyclo[13.1.0]pentadecane-1,15-diol was treated with the organozinc ate complex, the corresponding 14-membered cyclic vic-diol was obtained. Thus, this rearrangement is also useful for changing the ring size of cyclic substrates. PMID: 199082...
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Nomura K, Matsubara S Tags: Chemistry Source Type: journals

Chiral Primary-Secondary Diamines Catalyzed Michael-Aldol-Dehydration Reaction between Benzoylacetates and alpha,beta-Unsaturated Ketones: Highly Enantioselective Synthesis of Functionalized Chiral Cyclohexenones.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19908264 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Yang YQ, Chai Z, Wang HF, Chen MX, Cui HF, Zheng CW, Xiao H, Li P, Zhao G Tags: Chemistry Source Type: journals

Understanding the Signatures of Secondary-Structure Elements in Proteins with Raman Optical Activity Spectroscopy.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A prerequisite for the understanding of functional molecules like proteins is the elucidation of their structure under reaction conditions. Chiral vibrational spectroscopy is one option for this purpose, but provides only indirect access to this structural information. By first-principles calculations, we investigate how Raman optical activity (ROA) signals in proteins are generated and how signatures of specific secondary-structure elements arise. As a first target we focus on helical motifs and consider polypeptides consisting of twenty alanine residues to represent alpha-helical and 3(10)-helical secondary-structure...
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Jacob CR, Luber S, Reiher M Tags: Chemistry Source Type: journals

Ion Pairs and C(60): Simultaneous Guests in Supramolecular Nanotubes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19908266 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Tamanini E, Pantoş GD, Sanders JK Tags: Chemistry Source Type: journals

A Combined Theoretical and Experimental Investigation on the Enantioselective Oxidation of Aryl Benzyl Sulfides in the Presence of a Chiral Titanium Catalyst.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An experimental investigation of the enantioselective oxidation of aryl benzyl sulfides by tert-butyl hydroperoxide in the presence of a titanium/hydrobenzoin catalyst has shown that these sulfides are ideal substrates for this catalytic system, with negligible interference by the substituents on the aryl groups. A reaction mechanism based on DFT computations has been proposed. The DFT MPWB1K functional was used in the theoretical investigation to account for weak hydrogen-bonding and pi interactions. The computed reaction profile explains the experimentally observed enantioselectivity, which is determined by the therm...
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Naso F, Capozzi MA, Bottoni A, Calvaresi M, Bertolasi V, Capitelli F, Cardellicchio C Tags: Chemistry Source Type: journals

Surfactant-Encapsulated Polyoxometalates as Immobilized Supramolecular Catalysts for Highly Efficient and Selective Oxidation Reactions.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A type of interesting immobilized supramolecular catalysts based on surfactant-encapsulated polyoxometalates has been developed for oxidation reactions. Through a sol-gel process with tetraethyl orthosilicate, hydroxyl-terminated surfactant-encapsulated polyoxometalate complexes have been covalently and uniformly bound to a silica matrix with unchanged complex structure. The formed hybrid catalysts possess a defined hydrophobic nano-environment surrounding the inorganic clusters, which is conducive to compatibility between the polyoxometalate catalytic centres and organic substrates. The supramolecular synergy between ...
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Qi W, Wang Y, Li W, Wu L Tags: Chemistry Source Type: journals

Chirality in Dynamic Supramolecular Nanotubes Induced by a Chiral Solvent.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Amplification of chirality has been reported in polymeric systems. It has also been shown that related effects can occur in polymer-like dynamic supramolecular aggregates, if a subtle balance between noncovalent interactions allows the coupling between a chiral information and a cooperative aggregation process. In this context, we report a strong majority-rules effect in the formation of chiral dynamic nanotubes from chiral bisurea monomers. Furthermore, similar helical nanotubes (with the same circular dichroism signature) can be obtained from racemic monomers in a chiral solvent. Competition experiments reveal the re...
Source: Chemistry - November 11, 2009 Category: Chemistry Authors: Isare B, Linares M, Zargarian L, Fermandjian S, Miura M, Motohashi S, Vanthuyne N, Lazzaroni R, Bouteiller L Tags: Chemistry Source Type: journals

Spotlights on our sister journals: Chem. Eur. J. 45/2009.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Authors: PMID: 19902559 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 10, 2009 Category: Chemistry Tags: Chemistry Source Type: journals

Preview: Chem. Eur. J. 46/2009.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Authors: PMID: 19902560 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 10, 2009 Category: Chemistry Tags: Chemistry Source Type: journals

A Bifunctional Pd/MgO Solid Catalyst for the One-Pot Selective N-Monoalkylation of Amines with Alcohols.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
It has been found that a bifunctional metal Pd/base (MgO) catalyst performs the selective monoalkylation of amines with alcohols. The reaction goes through a series of consecutive steps in a cascade mode that involves: 1) the abstraction of hydrogen from the alcohol that produces the metal hydride and the carbonyl compound; 2) condensation of the carbonyl with the amine to give an imine, and 3) hydrogenation of the imine with the surface hydrogen atoms from the metal hydride. Based on isotopic and spectroscopic studies and on the rate of each elementary step, a global reaction mechanism has been proposed. The controlli...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Corma A, Ródenas T, Sabater MJ Tags: Chemistry Source Type: journals

Mechanistic Insights into the Substrate-Controlled Stereochemistry of Glycals in One-Pot Rhodium-Catalyzed Aziridination and Aziridine Ring Opening.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
We carried out a principle study on the reaction mechanism of rhodium-catalyzed intramolecular aziridination and aziridine ring opening at a sugar template. A sulfamate ester group was introduced at different positions of glycal to act as a nitrene source and, moreover, to allow the study of the relative reactivity of the nitrene transfer from different sites of the glycal molecule. The structural optimization of each intermediate along the reaction pathway was extensively done by using BPW91 functional. The crucial step in the reaction is the Rh-catalyzed nitrene transfer to the double bond of the glycal. We found tha...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Lorpitthaya R, Xie ZZ, Sophy KB, Kuo JL, Liu XW Tags: Chemistry Source Type: journals

Palladium-Catalyzed Hydroalkynylation of Alkylidenecyclopropanes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19904776 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Villarino L, López F, Castedo L, Mascareñas JL Tags: Chemistry Source Type: journals

The Palladium-Catalyzed Aerobic Kinetic Resolution of Secondary Alcohols: Reaction Development, Scope, and Applications.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The first palladium-catalyzed enantioselective oxidation of secondary alcohols has been developed, utilizing the readily available diamine (-)-sparteine as a chiral ligand and molecular oxygen as the stoichiometric oxidant. Mechanistic insights regarding the role of the base and hydrogen-bond donors have resulted in several improvements to the original system. Namely, addition of cesium carbonate and tert-butyl alcohol greatly enhances reaction rates, promoting rapid resolutions. The use of chloroform as solvent allows the use of ambient air as the terminal oxidant at 23 degrees C, resulting in enhanced catalyst select...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Ebner DC, Bagdanoff JT, Ferreira EM, McFadden RM, Caspi DD, Trend RM, Stoltz BM Tags: Chemistry Source Type: journals

Stereoselective Control by Face-to-Face Versus Edge-to-Face Aromatic Interactions: The Case of C(3)-Ti(IV) Amino Trialkolate Sulfoxidation Catalysts.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The stereoselective oxidation of differently functionalised benzyl phenyl sulfides has been examined by using enantiopure Ti(IV) trialkanolamine complexes. These complexes efficiently catalyse the sulfoxidation with good stereoselectivities. The data highlight the contribution to the stereoselectivity of steric effects and non-covalent pi-pi interactions between the aromatic rings of the Ti(IV) complex and those pertaining to the substrates. Enantiomeric excesses have been correlated with the electrostatic potential surfaces (EPS) of the reacting sulfides. The overall study leads to a mechanistic interpretation that ex...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Santoni G, Mba M, Bonchio M, Nugent WA, Zonta C, Licini G Tags: Chemistry Source Type: journals

Structure-Reactivity Relationships in Negishi Cross-Coupling Reactions.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Competition experiments have been performed to determine the relative reactivities of substituted bromobenzenes and of different arylzinc reagents in the [Pd(PPh(3))(4)]-catalyzed Negishi cross-coupling reaction in THF at 25 degrees C. The cross-coupling reactions are accelerated by electron acceptors in the bromobenzenes, the effect of which increases in the order ortho <meta <para. On the other hand, electron acceptors in the arylzinc halides diminish the reaction rates. Hammett correlations show that substituent variations in the bromobenzenes (rho=+2.5) have a larger effect than substituent variations in the ...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Dong ZB, Manolikakes G, Shi L, Knochel P, Mayr H Tags: Chemistry Source Type: journals

Kinetic Resolution of the Racemic 2-Hydroxyalkanoates Using the Enantioselective Mixed-Anhydride Method with Pivalic Anhydride and a Chiral Acyl-Transfer Catalyst.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A variety of optically active 2-hydroxyalkanoates and the corresponding 2-acyloxyalkanoates are produced by the kinetic resolution of racemic 2-hydroxyalkanoates by using achiral 2,2-diarylacetic acid with hindered carboxylic anhydrides as the coupling reagents. The combined use of diphenylacetic acid, pivalic anhydride, and (+)-(R)-benzotetramisole ((R)-BTM) effectively produces (S)-2-hydroxyalkanoates and (R)-2-acyloxyalkanoates from the racemic 2-hydroxyalkanoates (s-values=47-202). This protocol directly provides the desired chiral 2-hydroxyalkanoate derivatives from achiral diarylacetic acid and racemic secondary ...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Shiina I, Nakata K, Ono K, Sugimoto M, Sekiguchi A Tags: Chemistry Source Type: journals

Protecting-Group-Free Total Synthesis of Isoquinoline Alkaloids by Nickel-Catalyzed Annulation of o-Halobenzaldimine with an Alkyne as the Key Step.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
An efficient short total synthesis of benzo[c]phenanthridine alkaloids including oxyavicine, oxynitidine, and oxysanguinarine is described. Thus, N-methyl-o-bromobenzaldimines 1 b-d undergo regioselective cyclization with 4-(benzo[d][1,3]dioxol-5-yl)but-3-yn-1-ol (2 b) in the presence of [Ni(cod)(2)] (cod=1,5-cyclooctadiene). In situ oxidation of the resultant isoquinolinium salts gives isoquinolinone derivatives 5 b-d with benzo[d][1,3]dioxol-5-yl substitution at the C(3) atom and a (CH(2))(2)OH group at the C(4) atom. Later, oxidation of the alcohol group in 5 b-d to the aldehyde moiety followed by acid-catalyzed cyc...
Source: Chemistry - November 10, 2009 Category: Chemistry Authors: Korivi RP, Cheng CH Tags: Chemistry Source Type: journals

Ionic Liquid-Based Routes to Conversion or Reuse of Recycled Ammonium Perchlorate.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
New, potentially green, and efficient synthetic routes for the remediation and/or re-use of perchlorate-based energetic materials have been developed. Four simple organic imidazolium- and phosphonium-based perchlorate salts/ionic liquids have been synthesized by simple, inexpensive, and nonhazardous methods, using ammonium perchlorate as the perchlorate source. By appropriate choice of the cation, perchlorate can be incorporated into an ionic liquid which serves as its own electrolyte for the electrochemical reduction of the perchlorate anion, allowing for the regeneration of the chloride-based parent ionic liquid. The...
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Cordes DB, Smiglak M, Hines CC, Bridges NJ, Dilip M, Srinivasan G, Metlen A, Rogers RD Tags: Chemistry Source Type: journals

Hydration of Sugars in the Gas Phase: Regioselectivity and Conformational Choice in N-Acetyl Glucosamine and Glucose.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
The influence of an acetamido group in directing the preferred choice of hydration sites in glucosamine and a consequent extension of the working rules governing regioselective hydration and conformational choice, have been revealed through comparisons between the conformations and structures of "free" and multiply hydrated phenyl N-acetyl-beta-D-glucosamine (betapGlcNAc) and phenyl beta-D-glucopyranoside (betapGlc), isolated in the gas phase at low temperatures. The structures have been assigned through infrared ion depletion spectroscopy conducted in a supersonic jet expansion, coupled with computational methods. The...
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Cocinero EJ, Stanca-Kaposta EC, Dethlefsen M, Liu B, Gamblin DP, Davis BG, Simons JP Tags: Chemistry Source Type: journals

Order Versus Disorder in Chiral Tetrathiafulvalene-Oxazoline Radical-Cation Salts: Structural and Theoretical Investigations and Physical Properties.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
Electrocrystallization experiments with the chiral ethylenedithio-tetrathiafulvalene-methyl-oxazoline (EDT-TTF-OX) donors (R)-, (S)-, and (rac)-1 have provided two series of mixed-valence salts with the PF(6) (-) and [Au(CN)(2)](-) anions. Within each series the cell parameters are the same for the three R, S, and rac compounds, except for the space group, which is centrosymmetric triclinic P1 for the racemic forms and noncentrosymmetric P1 for the enantiopure salts. In the racemic salt [(rac)-1](2)PF(6) the two enantiomers crystallize disordered on the same crystallographic site with a site occupational factor of 0.6:...
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Madalan AM, Réthoré C, Fourmigué M, Canadell E, Lopes EB, Almeida M, Auban-Senzier P, Avarvari N Tags: Chemistry Source Type: journals

Noncovalent Synthesis of Hierarchical Zinc Phosphates from a Single Zn(4)O(12)P(4) Double-Four-Ring Building Block: Dimensionality Control through the Choice of Auxiliary Ligands.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
In contrast to the well-known reaction of phosphonic acids RP(O)(OH)(2) with divalent transition-metal ions that yields layered metal phosphonates [RPO(3)M(H(2)O)](n), the 2,6-diisopropylphenyl ester of phosphoric acid, dippH(2), reacts with zinc acetate in methanol under ambient conditions to afford tetrameric zinc phosphate [(ArO)PO(3)Zn(MeOH)](4) (1). The coordinated methanol in 1 can be readily exchanged by stronger Lewis basic ligands at room temperature. This strategy opens up a new avenue for building double-four-ring (D4R) cubane-based supramolecular assemblies through strong intercubane hydrogen-bonding intera...
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Murugavel R, Kuppuswamy S, Gogoi N, Boomishankar R, Steiner A Tags: Chemistry Source Type: journals

Metallocyclo- and Polyphosphazenes Containing Gold Or Silver: Thermolytic Transformation into Nanostructured Materials.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
A cyclotriphosphazene bearing two 4-oxypyridine groups on the same phosphorus atom, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4)(2)] (I), and its analogous polymer [{NP(O(2)C(12)H(8))}(0.7){NP(OC(5)H(4)N-4)(2)}(0.3)](n) (II), have been used to prepare gold or silver, cyclic and polymeric, metallophosphazenes. The following complexes, gem-[N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{ML})(2)] (ML=Au(C(6)F(5)) (1) or Au(C(6)F(5))(3) (2)), [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AuPPh(3)})(2)][NO(3)](2) (3), and [N(3)P(3)(O(2)C(12)H(8))(2)(OC(5)H(4)N-4{AgPPh(2)R})(2)][SO(3)CF(3)](2) (R=Ph (4) or Me (5)) have been obtained. C...
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Jiménez J, Laguna A, Benouazzane M, Sanz JA, Díaz C, Valenzuela ML, Jones PG Tags: Chemistry Source Type: journals

A 3D Copper(II) Coordination Framework Showing Different Kinetic and Thermodynamic Crystal Transformations through Removal of Guest Water Cubes.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19902440 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Chen XD, Zhao XH, Chen M, Du M Tags: Chemistry Source Type: journals

Heparin-Coated Gold Nanoparticles for Liver-Specific CT Imaging.Email this article to a colleague. Save this article to My Clippings. Discuss or comment on this article.
PMID: 19902441 [PubMed - as supplied by publisher] (Source: Chemistry)
Source: Chemistry - November 9, 2009 Category: Chemistry Authors: Sun IC, Eun DK, Na JH, Lee S, Kim IJ, Youn IC, Ko CY, Kim HS, Lim D, Choi K, Messersmith PB, Park TG, Kim SY, Kwon IC, Kim K, Ahn CH Tags: Chemistry Source Type: journals