bluuebunny/crossref_metadata_2025 huggingface dataset:
Selective biotransformation reactions on (±)-aryl alkyl ketones, (±)-benzoxazines, and d-arabino- and d-threo-hydroxyalkyltriazoles
Authors: Raunak  , Prasad Ashok K. , Shakil Najam A. , Himanshu  , Parmar Virinder S.
Published: October 2007

The capabilities of porcine pancreatic lipase (PPL), Candida antarctica lipase (CAL), and Candida rugosa lipase (CRL) were evaluated for enantio- and/or regioselective acetylation/deacetylation of (±)-2,4-diacetoxyphenyl alkyl ketones, (±)-4-alkyl-3,4-dihydro-3-hydroxyalkyl-2H-1,3-benzoxazines, and d-arabino and d-threo-polyhydroxyalkyltriazoles in organic solvents. PPL in tetrahydrofuran (THF) exhibited high to moderate enantioselectivity during the deacetylation of (±)-2,4-diacetoxyaryl alkyl ketones and acetylation of (±)-3-hydroxyalkyl-2H-1,3-benzoxazines. Together with enantioselectivity, PPL in THF also showed exclusive regioselectivity for the deacetylation of para-acetoxy over the ortho-acetoxy function, with respect to the nuclear carbonyl group in 2,4-diacetoxyphenyl alkyl ketones. CAL in diisopropyl ether (DIPE) and PPL in THF exhibited exclusive selectivity for the acetylation of primary hydroxyl over secondary hydroxyl group(s) of d-arabino- and d-threo-polyhydroxyalkyltriazoles.
Applications of green chemistry in the manufacture of oligonucleotide drugs
Authors: Sanghvi Yogesh S. , Ravikumar V. T. , Scozzari Anthony N. , Cole Douglas L.
Published: October 2007

We have modified the current phosphoramidite-based, solid-phase synthesis of antisense oligonucleotides to accommodate principles of green chemistry. In this article, we summarize key accomplishments that reduce or eliminate the use or generation of toxic materials, solvents, and reagents. Also discussed are methodologies that allow reuse of valuable materials such as amidites, solid-support, and protecting groups, thus improving the atom economy and cost-efficiency of oligonucleotide manufacture. Approaches to accident prevention and the use of safer reagents during oligonucleotide synthesis are also covered.
Design, synthesis, and application of chelating polymers for separation and determination of trace and toxic metal ions. A green analytical method
Authors: Sharma Rakesh K.
Published: October 2007

A green analytical method was developed for separation and preconcentration of trace amounts of copper from aqueous samples using aurin tricarboxylic acid-immobilized silica gel (ATA-SG). This was done by determining chemical speciation and stability constant of Cu-ATA complex. The pH-metric studies indicate strong complexation of Cu with ATA (log bCu2ATA = 19.56). Species distribution curve for Cu-ATA complex indicates almost 100% complexation of copper, with ATA forming Cu2ATA as the predominant species. Considering the selectivity and strong interaction of ATA toward copper, ATA was immobilized on the polymeric matrix of silica gel, and the conditions were optimized for the uptake of copper from the aqueous solutions. The uptake of Cu ions by ATA-SG was studied both by batch and column methods. The method was developed for the estimation of trace amounts of copper in various samples. Molecular modeling studies were also performed on ATA-immobilized silica gel for gaining an insight into the active structure of ATA on the silica surface.
Recent progress in the chemistry of multicomponent reactions
Authors: Ugi Ivar
Published: October 2007

The chemistry of multicomponent reactions (MCRs) and isocyanides belongs to three periods: In the century 1859­1958, isocyanide chemistry was moderately active and was separate from the classical name reactions of the MCRs. In the next period, isocyanides became well available, and MCRs of isocyanides became the most variable way of forming chemical compounds. The year 1993 began a new era of the formation and investigation of the products and the libraries of the Ugi reaction (U-4CR) and higher MCRs of the isocyanides. This chemistry is primarily accomplished in the industrial search and preparation of new pharmaceutical and plant-protecting products.
Solvent-free accelerated organic syntheses using microwaves
Authors: Varma Rajender S.
Published: October 2007

A solvent-free approach for organic synthesis is described which involves microwave (MW) exposure of neat reactants (undiluted) either in the presence of a catalyst or catalyzed by the surfaces of inexpensive and recyclable mineral supports such as alumina, silica, clay, or "doped" surfaces, namely, Fe(NO3)3-clay (clayfen), Cu(NO3)2-clay (claycop), NH2OH-clay, PhI(OAc)2-alumina, NaIO4-silica, MnO2-silica, and NaBH4-clay. A variety of deprotection, condensation, cyclization, oxidation, and reduction reactions are presented including the efficient one-pot assembly of heterocyclic molecules from in situ generated intermediates such as enamines and a-tosyloxyketones. The application of this solvent-free MW approach to multicomponent reactions is highlighted that can be adapted for high-speed parallel synthesis of the library of dihydropyrimidine-2(1H)-ones and imidazo [1,2-a]annulated pyridines, pyrazines, and pyrimidines.
Green twist to an old theme. An eco-friendly approach
Authors: Yadav J. S. , Meshram H. M.
Published: October 2007

Owing to present environmental awareness, attempts are being made toward the evolution of environmentally benign processes using solid-supported reagents and microwave-assisted reactions. A newly developed, nonmetallic oxidative reagent, "clayan", has been exploited for various reactions such as deprotection, oxidation, oxidative coupling, and nitration and bromination of activated and deactivated arenes. In another green chemistry endeavor, reactions such as reduction and cyclization have been successfully carried out in dry media under microwave irradiation. The nonsolvent reaction, experimental simplicity, and enhanced selectivity are the main attractive features of the approach.
Organometallic chemistry. Past, present, and future
Authors: Yamamoto Akio
Published: October 2007

Development of organometallic chemistry in the past half century is reviewed from the author's personal viewpoint with focus on the establishment of fundamental concepts relevant to catalysis. Further development in the coming century is expected in view of the diversity of transition-metal complexes and their unique properties.
Cooperative bimetallic oxidative addition reactions
Authors: Qin C. Jin , Gavrilova Anna , Bosnich and B.
Published: October 2007

The factors that control the oxidation of metals in bimetallic complexes are investigated in relation to the possibility of developing one-site addition two-metal oxidation reactions such as those that occur in the respiratory protein,hemerythrin. It is shown that the behavior of bimetallic complexes is not represented by the sum of the analogous monometallic parts because of metal and ligand interactions.
Asymmetric hydrogenation via architectural and functional molecular engineering
Authors: Noyori Ryoji , Koizumi Masatoshi , Ishii Dai , Ohkuma Takeshi
Published: October 2007

RuCl2 (phosphine) 2 (1,2-diamine) complexes, coupled with an alkaline base in 2-propanol, allows for preferential hydrogenation of a C=O function over coexisting conjugated or nonconjugated C=C linkages, a nitro group, halogen atoms, and various heterocycles. The functional group selectivity is based on the novel metal-ligand bifunctional mechanism. The use of appropriate chiral diphosphines and diamines results in rapid and productive asymmetric hydrogenation of a range of aromatic, hetero-aromatic, and olefinic ketones. The versatility of this method is manifested by the asymmetric synthesis of various biologically significant chiral compounds.
Some newer aspects of organozirconium chemistry of relevance to organic synthesis. Zr-Catalyzed enantioselective carbometallation
Authors: Negishi Ei-ichi
Published: October 2007

The reaction of terminal alkenes with trialkylalanes in the presence of chiral (NMI) 2ZrCl2 has been shown to be 70-75% ee for methylalumination and 90-95% ee for ethyl- and higher alkylalumination. It must involve an acyclic bimetallic process. Its scope, limitations, and applications to some natural products syntheses are discussed.
Rational design of polymers for optoelectronic interests
Authors: Luh Tien-Yau , Chen Ruey-Min , Hwu Tsyr-Yuan , Basu Sourav , Shiau Chung-Wai , Lin Wei-Yu , Jin Bih-Yaw , Hsu Chia-Chen
Published: October 2007

Using organometallic catalysts, two types of polymers containing conjugated moiety and insulating linker are synthesized. The investigations on the photophysical properties of these polymers (photoluminescence, electroluminescence and nonlinear optical properties) are briefly summarized. These polymers represent a new class of materials for optoelectronic interests.
Effect of ligands on the divalent palladium- catalyzed carbon-carbon coupling reactions. Highly enantioselective synthesis of optically active g-butyrolactones
Authors: Lu Xiyan , Zhang Qinghai
Published: October 2007

In the palladium (II) -catalyzed enyne coupling reactions, the nitrogen-containing ligand plays the same role as the halide ion to inhibit the β-hydride elimination. Employing the pymox or bisoxazoline as ligands, the catalytic asymmetric cyclization of (Z) -4'-acetoxy-2'-butenyl 2-alkynoates initiated by acetoxypalladation was established with high efficiency (up to 92% ee) to afford the optically active γ-butyrolactones.
Chemical nitrogen fixation by using molybdenum and tungsten complexes
Authors: Hidai Masanobu , Mizobe Yasushi
Published: October 2007

Dinitrogen complex cis-[W (N2) 2 (PMe2Ph) 4] reacts with an excess of acidic dihydrogen complexes such as trans-[RuCl (h2-H2) (dppe) 2]BF4 (dppe = 1,2-bis (diphenylphosphino) ethane) at 55 °C under 1 atm of H2 to form ammonia in moderate yield. The reaction is presumed to proceed through nucleophilic attack of the remote nitrogen of the coordinated dinitrogen on the dihydrogen ligand. The coordinated dinitrogen is also protonated by treatment with hydrosulfido-bridged dinuclear complexes such as [Cp*Ir (m-SH) 3IrCp*]Cl (Cp* = h5-C5Me5) to afford ammonia. On the other hand, the synthetic cycle for the formation of pyrrole and N-aminopyrrole from dinitrogen and 2,5-dimethoxytetrahydrofuran has been established starting from dinitrogen complexes of the type trans-[M (N2) 2 (dppe) 2 ] (M = Mo, W).
Synthesis of oxygen heterocycles via alkynyltungsten compounds
Authors: Liu Rai-Shung
Published: October 2007

This short review article covers some useful applications of alkynyltungsten compounds to the syntheses of complex lactones. Two types of cyclizations will be emphasized: (1) cycloalkenylation of tungsten-alkynol compounds with aldehydes to give a-alkylidene oxacarbeniums, further leading to a-alkylidene lactones and (2) intramolecular [3+2]-cycloaddition of epoxides to give bicyclic lactones. The new methodologies can provide a short synthesis of enantiopure lactones such as (-) -epilitsenolide C2, (+) -listenolide C1, (+) -isodihydromahubanolide A, (+) -blastmycinone, and (-) -epi-blastmycinone.
Selective preparation of benzene derivatives from three different alkynes and pyridine derivatives from two different alkynes and a nitrile
Authors: Takahashi Tamotsu
Published: October 2007

Selective preparation of benzene derivatives from three different alkynes and pyridine derivatives from different alkynes and a nitrile were developed.
Fullerenes covalently linked to transition metals with organic ligands
Authors: Sokolov Viatcheslav I. , Nefedova Marina N. , Potolokova Tatiana V. , Bashilov Vasily V.
Published: October 2007

Synthesis of molecules combining both fullerene and metallocene moieties separated by some spacer is discussed in connection with the possible intramolecular charge transfer. Two new kinds of spacers, =CH-CO- and -Pd-P-, have been introduced by using the corresponding reactions. Reaction of diazoacetyl ferrocene and cymantrene with C60 has been studied in detail and products characterized. 1,1'-Bis (diazoacetyl) ferrocene gave with C60 1:1 adduct to which the ansa-structure has been assigned on the basis of 1H and 13C NMR spectra. Palladium-h2-C60 complex with a bidentate ferrocenyl diphosphine as a ligand has been also prepared.
Lewis-acidic organometallic compounds of the lanthanides and the alkaline earth metals as catalysts for the activation of carbonyl groups
Authors: Schumann Herbert , Glanz Mario , Gottfriedsen Jochen , Dechert Sebastian , Wolff Dietmar
Published: October 2007

1,3-dialkyl-4,5-dimethylimidazol-2-ylidenes form adducts with various bis (alkylcyclopentadienyl) complexes of magnesium, calcium, strontium, barium, samarium, and ytterbium. The X-ray structures of selected metallocenes and carbene adducts are discussed. Liquid-crystalline homo- and block copolymers with a narrow molecular mass distribution index were obtained in high yields by living polymerization of mesogenic methacrylates with organosamarium complexes. Depending on the structure of the catalyst and the polarity of the solvent used, different, partially competitive reaction mechanisms are observed.
Asymmetric synthesis by stereocontrol
Authors: Kim Yong Hae , Kim Sam Min , Youn So Won
Published: October 2007

Diels-Alder cycloadditions of S-indoline chiral acrylamides with cyclopentadiene in the presence of Lewis acids proceed with high diastereofacial selectivity, giving either endo-R or endo-S products depending on Lewis acid and the structures of chiral dienophiles. Diastereo- and enantioselective pinacol coupling reactions of chiral α-ketoamides mediated by samarium diiodide afforded extremely high diastereoselectivities. Enantiopure (S,S) - or (R,R) -2,3-dialkyltartaric acid and derivatives can be synthesized. Furthermore, it was demonstrated that α,β-unsaturated amides coupled with SmI2 to dimerized products containing two chiral carbons which were first obtained as the adjacent chiral carbons.
New methods for the synthesis of transition-metal fullerene complexes
Authors: Thompson David M. , McLeod Jason , Baird Michael C.
Published: October 2007

Buckminsterfullerene, C60, is readily reduced on exposure to solutions of strongly reducing transition-metal carbonylate anions to give the radical anion fulleride C60
- and the corresponding highly reactive, 17-electron neutral compounds. Three secondary reaction paths have been identified, depending on the nature of the reactants and the reaction conditions. (1) With Na+ and PPN+ salts of [Mn (CO) 5]-, thermal substitution of a CO on the metal radical by the C60-results in formation of the anionic, h2-fullerene complex [Mn (C60) (CO) 4]- . (2) With salts of [Co (CO) 4]-, the thermal reaction results in formation of a novel transition-metal fulleride NaCoC60 while (3) with Na[CpFe (CO) 2] and [CpM (CO) 3]- (M = Mo, W) , the 17-electron intermediates couple to form the 18-electron dimers, [CpFe (CO) 2]2 and [CpM (CO) 3]2. In contrast, photochemical reactions of C60 with salts of [Mn (CO) 5]-, [Co (CO) 4]-, and [CpM (CO) 3]- result in excellent yields of the complexes [Mn (C60) (CO) 4]- , [Co (C60) (CO) 3]- and [CpM (C60) (CO) 2]- , respectively; analogous complexes of C70 may be made similarly. The new complexes have been characterized crystallographically, by IR, 13C NMR, and/or Raman spectroscopy and by electrospray mass spectrometry.
Novel polymerization and copolymerization of ethylene, styrene, and/or butadiene by new organolanthanide-based catalysts
Authors: Hou Zhaomin , Kaita Shojiro , Wakatsuki Yasuo
Published: October 2007

Replacement of one of the two C5Me5 ligands in the samarocene (II) complex (C5Me5) 2Sm (THF) 2 with a monodentate anionic ligand (e. g. , OAr, SAr, or NR1R2) gives a unique catalytic system, which can not only polymerize styrene and ethylene, but also copolymerize them into block styrene-ethylene copolymers under the presence of both monomers. On the other hand, addition of an appropriate cocatalyst such as MMAO or AlR3/[Ph3C][B (C6F 5) 4] to the samarocene complex (C5Me5) 2Sm (THF) 2 or (C5Me5) 2Sm (m-Me) 2AlMe2 affords a novel catalytic system for stereospecific 1,4-cis living polymerization of butadiene and copolymerization of butadiene with styrene.
Isolobal displacement methodology for the synthesis of transition-metal cluster complexes containing various biscyclopentadienyl ligands
Authors: Song Li-Cheng , Guo Dian-Shun
Published: October 2007

The isolobal displacement methodology for the synthesis of biscyclopentadienyl-bridged transition-metal cluster complexes has been developed. This methodology involves various isolobal displacement reactions between tetrahedral cluster substrates and Mo/W-containing isolobal reagents, leading to a series of linear biscyclopentadienyl-bridged cluster complexes and cyclic biscyclopentadienyl-bridged cluster crown ethers, respectively.
Alkane activation on a multimetallic site
Authors: Suzuki Hiroharu , Inagaki Akiko , Matsubara Kouki , Takemori Toshifumi
Published: October 2007

Trinuclear polyhydrido complex of ruthenium effectively activates alkanes to cleave C-H bonds in a selective manner due to cooperative action of the metal centers. The reaction of (Cp´Ru) 3 (m-H) 3 (m3 -H) 2 (1) (Cp´ = h5-C5Me5) with n-alkane at 170 °C leads to the formation of a trinuclear closo-ruthenacyclopentadiene complex as a result of a successive cleavage of six C-H bonds. Introduction of a m3-sulfido ligand into the Ru3 core of the trirutheniumpolyhydrido cluster significantly modifies the regioselectivity of the alkane C-H activation. Heating of a solution of (Cp´Ru) 3 (m3-S) (m-H) 3 (4) in alkane exclusively gives a trinuclear m3-alkylidyne complex via a selective C-H bond cleavage at the less-hindered terminus of alkane molecule.
New developments in transition metal-catalyzed synthetic reactions via C-H bond activation
Authors: Fujiwara Yuzo , Jia Chengguo
Published: October 2007

Several novel and useful reactions involving transition metal-catalyzed C-H bond activation discovered in our laboratory have been summarized here, which includes olefin arylation, hydroarylation of alkynes, carboxylation of arenes and alkanes, and acetoxylation and aminomethylation of alkanes. Possible mechanisms of these reactions have been suggested.
Interplay of synthesis and mechanism in asymmetric homogeneous catalysis
Authors: Adams Nicholas J. , Bargon Joachim , Brown John M. , Farrington Edward J. , Galardon Erwan , Giernoth Ralf , Heinrich Hanjo , John Benjamin D. , Maeda Kenji
Published: October 2007

Asymmetric homogeneous catalysis forms one of the main planks of modern organic synthesis. It has developed rapidly and largely through the application of novel ligands, whose design is very much based on insight and intuition. At the same time, a better understanding of catalytic reaction mechanisms can contribute to further progress, since it can identify the intimate relationship between ligand structure and successful applications. The presentation will concentrate on the author's research with complexes of the late transition metals and include the search for superior methodologies in hydroboration, as well as ventures into the chemistry of reactive intermediates. The latter will be exemplified from work with rhodium and palladium catalysts.
Chemistry of η5-fullerene metal complexes
Authors: Nakamura Eiichi , Sawamura Masaya
Published: October 2007

Treatment of [60]fullerene with an organocopper reagent converts one of the pentagons of the fullerene into cyclopentadienyl anion through addition of five organic groups on every peripheral carbon atom surrounding the pentagon. Similar treatment of [70]fullerene afforded indenyl anion through regioselective tri-addition of the organic group. These anionic moieties strongly interact with the remainder of the fullerene p-system, and provide unique opportunity for exploration of organometallic chemistry of a new class of metal cyclopentadienides.
New class of metallacarboranes incorporating the η7-carboranyl ligand
Authors: Xie Zuowei
Published: October 2007

This article provides an overview of our work on the synthesis, molecular structure, and bonding of a novel class of 13-vertex closo-metallacarboranes incorporating the h7-carboranyl ligand. This bonding mode can only be observed in the d0/fn transition-metal ions with the proper size.
New metallocenes of early transition metals with functional groups in organic ligands. Red-ox transformations
Authors: Krut'ko Dmitrii P. , Borzov Maxim V. , Veksler Edward N. , Kirsanov Roman S. , Churakov Andrej V. , Lemenovskii Dmitri A.
Published: October 2007

The reduction behavior of the novel zirconocene dichlorides, (h5-C5Me5) (h5-C 5Me4CH2CH2ER 2) ZrCl2 (ER2 = NMe2, PMe2, PPh2) , (h5-C5Me4CH2 CH2PMe2) 2ZrCl 2, and (h5-C5Me4CH2 CH2PPh2) (h5-C 5Me4CH2CH2PMe 2) ZrCl2, together with the new types of intramolecular activation of inert C-H and C-heteroatom bonds are presented and discussed. A remarkably thermally stable zirconocene alkylhydryde type framework complex (h5-C5Me5) [h5 ,s-C5Me4CH2CH 2N (Me) CH2-]ZrH, zirconocene arylhydryde complex (h5-C5Me5) [h5 ,s-C5Me4CH2CH 2P (Ph) -o-C6H4-]ZrH, tetramethylfulvene hydride-type complexes (h5-C5Me5) [h6 :h1- (CH2C5Me3 ) CH2CH2PR2]ZrH (R = Me, Ph) and (h5-C5Me4CH2 CH2PPh2) [h6:h 1- (CH2C5Me3) CH 2CH2PMe2]ZrH are reported. The first unusually thermally stable zirconocene (h5,h1-C5Me4 CH2CH2PMe2) 2 Zr with the Zr (II) center stabilized by intramolecular coordination of two Me2P-groups is described.
Dynamic solvatochromism in solvent mixtures
Authors: Wetzler Diana E. , Chesta Carlos , Fernández-Prini Roberto , Aramendía Pedro F.
Published: October 2007

Solvatochromism and thermochromism of 4-aminophthalimide and 4-amino-N-methylphthalimide were studied by absorption and steady-state and time-resolved emission spectroscopy in solvent mixtures of toluene­ethanol and toluene­acetonitrile at different temperatures. Emission spectra shift to the red upon addition of a polar solvent (PS) to toluene. Solvent mixtures show a much greater thermochromic shift to the blue in emission than the neat solvents. This is explained by the decrease in temperature of the exothermic association of the polar solvent to the excited state. Emission spectra are time dependent in solvent mixtures in the ns timescale. The time evolution of this emission is interpreted on the basis of the different solvation of the ground state and the emitting excited state. Stern­Volmer plots are obtained for the dependence of the spectral-shift characteristic time with [PS].
Tryptophan rotamers that report the conformational dynamics of proteins
Authors: Fidy Judit , Laberge Monique , Ullrich Beata , Polgar Laszlo , Szeltner Zoltan , Gallay Jacques , Vincent Michel
Published: October 2007

The binding of acetyl­pepstatin to the Q7K/L33I/L63I mutant of HIV-1 protease was studied by fluorescence, phosphorescence, and 500-ps molecular dynamics. The protease is a homodimer with two tryptophans per monomer. Maximum entropy method (MEM) analysis and acrylamide quenching results show two tryptophyl, tryptophan (Trp) populations in the apoenzyme that merge into one in the complex. These results are in agreement with molecular dynamics simulations indicative of Trp asymmetry in the apoenzyme as revealed by the occurrence of nonequivalent Trp42 indole rotamer interconversions, not observed for the complex. Analysis of the local Trp42B environments of the apoenzyme with respect to possible quencher groups shows that the c2 interconversions do not influence the lifetime, while the c1 interconversions do. Upon binding the inhibitor, Trp42B acquires a single conformation with the same lifetime and orientation as that of Trp42, and also with less quenching accessibility. Thus, protein conformational dynamics become constrained with inhibitor binding. This conclusion is supported by red-edge effect experiments and phosphorescence lifetime measurements. The low temperature tp (~5.8 s) is quenched to ~200 ms as protein motions become activated around the glass transition temperature. In the case of the complex, the phosphorescence lifetime data show a more cooperative activation of the quenching mechanisms.
Charge separation and energy transfer in multicomponent porphyrinic arrays
Authors: Flamigni Lucia
Published: October 2007

An overview of the recent activity of the laboratory in the determination of the photophysical properties of porphyrinic arrays, with emphasis on the theme of photoinduced charge separation, is presented.
Conjugated polymers. New materials for optoelectronic devices
Authors: Friend R. H.
Published: October 2007

Conjugated polymers now provide a class of processible, film-forming semiconductors and metals. We have worked on the development of the semiconductor physics of these materials by using them as the active components in a range of semiconductor devices. Polymer light-emitting diodes show particular promise, and recent developments in color range (red, green, and blue), efficiency (above 20 lumen/W for green emitters), and operating lifetime are discussed. Progress on their application to displays, with integration with active-matrix TFT drive, and with patterned deposition using inkjet printing techniques is also reviewed. The role played by interfaces between electrode and semiconducting polymer is also discussed.
Microscopy and optical manipulation of dendrimer-built vesicles
Authors: Gensch T. , Tsuda K. , Dol G. C. , Latterini L. , Weener J. W. , Schenning A. P. H. J. , Hofkens J. , Meijer E. W. , De Schryver F. C.
Published: October 2007

A fifth-generation poly(propylene imine) dendrimer decorated with palmitoyl- and azobenzene-containing alkyl groups forms giant vesicles in aqueous solutions with diameters from 50 nm up to 20 mm and a multilaminar onion-like structure. Dense and ordered arrangement of the azobenzene chromophores in the bilayer structure leads to fluorescence with lmax= 600 nm. The fluorescence intensity can be increased by irradiation with blue light, and at low pH a distinctive blue shift of the spectrum is observed. With the aid of a single-beam optical tweezers it is possible to trap vesicles and direct them in a billiard-like fashion against each other using forces in the range of several pN. In collision experiments, the vesicles behave like hard spheres, and merging is not observed.
Organometallic alkane and noble-gas complexes in conventional and supercritical fluids
Authors: Childs Gavin I. , Grills David C. , Sun Xue Z. , George Michael W.
Published: October 2007

Fast time-resolved infrared (TRIR) spectroscopy has been used to study a wide range of organometallic alkane and noble-gas complexes at ambient temperature. We have shown that the reactivity of the n-heptane complexes decreases both across and down Groups V, VI, and VII, and that the corresponding xenon complexes have similar reactivities.
Long-distance charge transport through DNA. An extended hopping model
Authors: Giese Bernd , Spichty Martin , Wessely Stefan
Published: October 2007

Long-distance transfer of a positive charge through DNA can be described by a hopping model. In double strands where the (A:T)n bridges between the guanines are short (n 3), the charge hops only between guanines, and each hopping step depends strongly upon the guanine to guanine distances. In strands where the (A:T)n sequences between the guanines are rather long (n 4), also the adenines act as charge carriers. To predict the yields of the H2O-trapping products one has to take into account not only the charge-transfer rates but also the rates of H2O-trapping reactions.
New approach to silver halide photography using radical cation chemistry
Authors: Gould I. R. , Lenhard J. R. , Muenter A. A. , Godleski S. A. , Farid S. Y.
Published: October 2007

A new mechanism for spectral sensitization of silver halide is described, which can potentially double the sensitivity of photographic emulsions. The photooxidized sensitizing dye is trapped using an organic donor molecule, which fragments to form a cation and a reducing radical, which injects an electron into the conduction band of the silver halide. In this way, two conduction-band electrons can be produced for each absorbed photon.
Electron-transfer dyads suitable for novel self-assembled light-harvesting antenna/electron-transfer devices
Authors: Holzwarth Alfred R. , Katterle Martin , Müller Marc G. , Ma Ying-Zong , Prokhorenko Valentin
Published: October 2007

The synthesis and photophysical and photochemical characterization of four novel bacterio-chlorin-fullerene dyads with fullerene C60 coupled at various positions and by various bridges to the chlorin ring are described. All dyads undergo rapid charge separation in the sub-picosecond to picosecond time range as characterized by time-resolved fluorescence and transient absorption spectroscopy.
Vital role of entropy in photochirogenesis
Authors: Inoue Yoshihisa , Sugahara Norimitsu , Wada Takehiko
Published: October 2007

The effects of temperature, pressure, solvent, and substrate concentration upon several enantio- and diastereodifferentiating photochemical reactions have been investigated and discussed in detail. These entropy-related external factors, which manipulate the weak electronic and steric interactions in the excited state, dynamically control the stereochemical outcome of asymmetric photochemical reactions, and even switch the product chirality. A global view on the "entropy chemistry" and its potential applications are also discussed.
Photosensitization by drugs
Authors: Miranda Miguel A.
Published: October 2007

Certain drugs are known to elicit photosensitivity side effects. A satisfactory understanding of the involved mechanistic aspects is necessary to anticipate the photosensitizing potential. We have used tiaprofenic acid (TPA), a photosensitizing nonsteroidal antiinflammatory drug, to illustrate the methodology followed to address this problem. After studying the photophysical and photochemical properties of TPA, the attention has been directed towards the reactivity of its lowest lying p-p* triplet with biomolecules. Photosensitized lipid peroxidation occurs by a mixed type I (radicals) and type II (singlet oxygen) mechanism. In the case of proteins, the photosensitized reactions include Tyr, Trp, and His photodegradation, protein­protein photocrosslinking and drug­protein photobinding. This involves direct quenching of the drug triplet by the amino acid residues (Tyr and Trp) or by oxygen, followed by singlet oxygen oxidation (His and Trp). With DNA, the studies have included comet assay, induction of single-strand breaks in supercoiled DNA, and reaction with 2'-deoxyguanosine and thymidine. Product studies, together with time-resolved measurements, have shown that the fastest reaction occurs with purine bases, by a mechanism involving both radical and singlet oxygen processes. The employed methodology can be of general use to investigate the mechanistic aspects of photosensitization by drugs.
New polymeric photosensitizers
Authors: Nowakowska Maria , Kepczynski Mariusz , Szczubialka Krzysztof
Published: October 2007

Novel polymeric photosensitizers for singlet oxygen production in water are described. The polymers contain rose bengal (4,5,6,7-tetrachloro-2',4',5',7'­tetraiodo-fluorescein) chromophores covalently attached to the polymer chain. The quantum yields of singlet oxygen formation and photooxidation of phenol in water have been determined. The methods of separation of photosensitizer from the reactants after completion of reaction have been established.
Luminescent sensors and photonic switches
Authors: de Silva A. Prasanna , Fox David B. , Moody Thomas S. , Weir Sheenagh M.
Published: October 2007

The principles of photochemistry continue to fuel progress in luminescent sensors and photonic switches. Examples of sensors based on photoinduced electron transfer (PET) are discussed, including those which form the basis of successful systems used in physiology and medicine. More complex formats usually involve multiple receptors. One progression takes us to lanthanide complexes enabled with sensory capabilities. Another path takes us to molecular-scale implementation of logic gates such as AND and INHIBIT. Such luminescent switches can be enriched by combination with nonluminescent cousins. The latter are based on internal charge-transfer excited states (ICT). An example of rudimentary arithmetic at the molecular scale is presented by running a luminescent AND gate in parallel with a nonluminescent XOR gate. Thus, small molecules can process small numbers for the first time outside of our brains.
Quinone methide intermediates in organic photochemistry
Authors: Wan Peter , Brousmiche Darryl W. , Chen Christy Z. , Cole John , Lukeman Matthew , Xu Musheng
Published: October 2007

Quinone methides are widely encountered reactive intermediates in the chemistry of phenols and related compounds. This paper summarizes our recent progress in uncovering new and general photochemical methods for forming quinone methides of various structural types in aqueous solution. Their mechanism of formation and subsequent chemistry are also discussed. New examples of excited-state intramolecular proton transfer (ESIPT) have been uncovered in these studies. We have also discovered that appropriately designed biphenyls and terphenyls display photochemistry that is best rationalized by highly polarized and planar excited states of these ring systems, which can efficiently lead to the corresponding extended quinone methides.
Molecular design of luminescent metal-based materials
Authors: Yam Vivian Wing-Wah
Published: October 2007

A series of soluble di- and polynuclear transition-metal acetylides with rich luminescence behavior have been designed and successfully isolated. The photophysical and photochemical properties have been studied. Luminescent polynuclear metal complexes have also been obtained based on the metal chalcogenide building block. These high-nuclearity transition-metal chalcogenide complexes have been structurally characterized and shown to display rich luminescence behavior. Various approaches and strategies to design and synthesize luminescent polynuclear metal complexes that may find potential applications as chemosensors and luminescence signalling devices will also be described.
Bioactive natural products as a potential source of new pharmacophores. A theory of memory
Authors: Atta-ur-Rahman  , Choudhary M. Iqbal
Published: October 2007

The plant kingdom offers a rich source of structural biodiversity in the form of a variety of natural products. Our work on new bioactive compounds from medicinal plants has led to the isolation and structure elucidation of a number of exciting new pharmacophores. Bioassay-guided fractionation has recently led to the discovery of a series of new acetylcholinesterase, urease and a-glucosidase inhibitors, antioxidants and other classes of bioactive compounds, which will be presented. A theory based on hydrogen bonding on the chemical basis of memory storage in the brain is presented.
Gains achieved by molecular approaches in the area of lignification
Authors: Boudet Alain-M. , Chabannes Matthieu
Published: October 2007

In this article we highlight the contribution of molecular biology and lignin genetic engineering toward a better understanding of lignin biosynthesis and spatio-temporal deposition of lignin. Specific examples from the literature and from our laboratory will serve to underline the chemical flexibility of lignins, the complexity of the regulatory circuits involved in their synthesis, and the specific behavior of different cell types within the xylem. We will also focus on strategies aiming to reduce the lignin content or to modify the lignin composition of plants and present their impact on plant development. We will show that the ectopic expression of a specific transgene may have a different impact, depending on the genetic background, and that plants with a severe reduction in lignin content may undergo normal development. Lignification is currently benefiting enormously from recent developments in molecular biology and transgenesis, and the progress made opens the way for future developments to study how the walls of lignified plant cells are built and organized.
Natural products from around the world
Authors: Connolly J. D.
Published: October 2007

The structures of a range of natural products from Africa, Nepal, and Chile will be discussed.
Efficient stereoselective syntheses of piperidine, pyrrolidine, and indolizidine alkaloids
Authors: Enders Dieter , Thiebes Christoph
Published: October 2007

Recent advances in the diastereo- and enantioselective synthesis of piperidine, pyrrolidine, and indolizidine alkaloids, based on the highly stereoselective 1,2-addition to the CN double bond of chiral aldehyde-SAMP/RAMP hydrazones, are described. The enantioselective syntheses of the pyrrolidine alkaloids bgugaine and (2S,12¢R)-2-(12¢-aminotridecyl)-pyrrolidine, a defense alkaloid of the Mexican bean beetle are reported. Furthermore, the SAMP/RAMP-hydrazone method was applied to the syntheses of two 5,8-disubstituted indolizidine alkaloids that have been extracted from neotropical poison-dart frogs. The a-alkylation of aldehyde-SAMP/RAMP hydrazones has been used in the enantioselective synthesis of two epimers of stenusine, a 3-substituted piperidine alkaloid and spreading reagent of the beetle Stenus comma.
Chemistry and biotransformations in the Scrophulariaceae family
Authors: Garbarino J. A. , Fraga B. M. , Hernandez M. G. , Chamy M. C. , Piovano M.
Published: October 2007

One of our research lines has been the chemical studies among Calceolaria species (Scrophulariaceae), from which have been isolated 77 new diterpenes of various skeleton types (labdanes, pimaranes, stemaranes, and stemodanes), all coming from a common bicyclic intermediate, having H-9 and C-20 as a cis relationship and C-11 becomes trans with respect to C-20. Another line of research is bringing out chemical changes on diterpenes obtained from this family, using biological systems as the fungus Giberella fujikuroi and Mucor plumbeus.
Quantitative chemobiology
Authors: Gottlieb Otto R. , de M. B. Borin Maria Renata , de Brito Nei Regis S.
Published: October 2007

One of the mysteries of man's contact with nature concerns the question why shamanism and science so often lead to consistent results in the search for useful natural products. To find clues toward an answer via a coherent chemobiological language, structural and functional information is taken into account. The functional information, given by ethnobotanical codes based on traditional knowledge (via number of useful dicotyledon species), is confronted with the structural information, given by metabolic codes based on micromolecular diversification (via number of occurrences in dicotyledons). The challenge to integrate these databases implies in the development of qualitative (via dahlgrenograms) and quantitative (via Sporne indices) models into an evolutionary framework. The follow-up of ethnobotanical qualifications reveals systematic and evolutionary patterns, susceptible to juxtaposition into a phytochemical background based on gallates (GAL) and caffeates (CAF), regulators of intermediate metabolism. Comparison of the two models of information suggests that the "spectral" features of the GAL and CAF-models are coincident with the ethnobotany-guided food- and medicine-plants respectively. Hence, the complementary nature of food and medicine species can be rationalized by oscillations between GAL/CAF. Analyses of these indicators of toxicity would allow advances in the understanding of mechanisms regulating the production of bioactive products.
Bioactive compounds from coral reef invertebrates
Authors: Higa Tatsuo , Tanaka Junichi , Ohtani Ikuko I. , Musman Musri , Roy Michael C. , Kuroda Ikuma
Published: October 2007

Manzamine A (1) known as a cytotoxin exhibited potent antimalarial activity with 40% recovery 60 days after single intraperitoneal (i.p.) injection against mice infected with the malaria parasite Plasmodium berghei. Pachastrisamine (6), a simple derivative of a sphingosine, isolated from a sponge, Pachastrissa sp. showed a high level of cytotoxicity. New sesquiterpene carbonimidic dichlorides and related aldehydes (8­12) have been isolated as cytotoxic constituents of the sponge Stylotella aurantium and shown to have moderate cytotoxicity. Cyclic undecapeptides, barangamides A­D (13­16), have been isolated from the sponge Theonella swinhoei. Their structures were established by spectroscopic analysis and chemical reaction.
Biodiversity conservation and drug discovery in Suriname. Explorations in nature's combinatorial library
Authors: Kingston David G. I.
Published: October 2007

The preservation of tropical rain forests is an important goal both for the intrinsic value of their cultural and biological diversity and for the well-being of the forest peoples who make these forests their home. In addition, tropical forests are potential sources of new pharmaceutical products which can only be found by chemical prospecting in nature's genetically encoded combinatorial library. A collaborative program to discover potential pharmaceuticals in the rain forest of Suriname is described as part of an effort to integrate biodiversity conservation and drug discovery with economic development. Progress on this project will be reported, including results obtained on the isolation of bioactive diterpenoids, quinones, alkaloids, and polyketides, and the benefits of this general approach to biodiversity and drug discovery will be discussed.
Recent results in the synthesis of ecologically important bioregulators
Authors: Mori Kenji
Published: October 2007

Absolute configuration was established for the following semiochemicals: (S)-polyzonimine (1), (S)-9-methylgermacrene-B (2) and (1S,3S,7R)-3-methyl-a-himachalene (3). The stereoisomers of 2,6-dimethylheptane-1,7-diol monotetrahydropyranyl ether served as useful building blocks for the synthesis of syn- or anti-1,5-dimethylated aliphatic pheromones such as 4 and 5. Synthesis of analogs of the Israeli pine bast scale pheromone 6, which exhibits both pheromonal and kairomonal activities, enabled us to find a strong pheromone mimic 7 without any kairomonal activity.
Molecules and macromolecules involved in chemical communication of scarab beetles
Authors: Leal Walter Soares
Published: October 2007

Chemical communication involves the production and release of specific chemicals (pheromones and other semiochemicals) by the emitter, and the detection and olfactory processing of these signals leading to appropriate behavioral responses in the receiver. In contrast to most of the scarab species investigated to date, the Japanese and Osaka beetles have the ability to detect the allospecific pheromone, which plays a pivotal role in the isolation mechanism between these two species. Each species produces a single enantiomer of japonilure [(Z)-5-(dec1-enyl)oxacyclopentan-2-one], but they have evolved the ability to detect both enantiomers, one as an attractant and the other as a behavioral antagonist (stop signal). There is growing evidence in the literature that the inordinate sensitivity and selectivity of the insect olfactory system is achieved by a combination of various olfactory-specific proteins, namely, odorant-binding proteins (OBPs), odorant receptors (ORs), and odorant-degrading enzymes. The relationship between the pheromone structures and the primary sequences of the proteins suggest that OBPs play a part in the selectivity of the olfactory system in scarab beetles by "filtering" chemical signals during the early olfactory processing (perireceptor events). Nevertheless, it is unlikely that pheromone-binding proteins are "chiral filters" as the Japanese and Osaka beetles each possess only one single binding protein. Upon interaction with negatively charged membranes, OBPs undergo conformational changes that may lead to the release of the ligands.
Strategies for the isolation and identification of trypanocidal compounds from the Rutales
Authors: Vieira Paulo C. , Mafezoli Jair , Pupo Mônica T. , Fernandes João B. , da Silva M. Fátima das G. F. , de Albuquerque Sérgio , Oliva Glaucius , Pavão Fernando
Published: October 2007

Crude extracts of Rutales species were tested in vitro against the trypomastigote form of Trypanosoma cruzi at 4 mg/mL, and 20% of them showed significant activity (80%). Their inhibitory activity against the glycolytic enzyme GAPDH from T. cruzi has also been evaluated at the concentrations of 100 and 200 mg/mL. Additionally, the inhibitory activity of 13 purified coumarins were also assayed against T. cruzi-GAPDH. Chalepin was the most active substance with IC50 = 64 mM. The 3D structure of the complex chalepin-enzyme was elucidated by X-ray crystallography, revealing the architecture of the interactions between the inhibitor and the enzyme active site.
Studies directed toward the preparation of key intermediates for the synthesis of trisporic acids and cassiol
Authors: Colombo María I. , Zinczuk Juan , Mischne Mirta P. , Rúveda Edmundo A.
Published: October 2007

An enantioselective synthesis and resolution of the key White intermediate (3) for the synthesis of trisporic acids are described. Attempts to develop a synthetic route toward the antiulcerogenic compound cassiol (2) by an olefination reaction of 3 and an alternative sequence involving a Michael addition followed by an aldol condensation of an open substrate, are also reported.
Figures-of-merit for the technical development and application of advanced oxidation technologies for both electric- and solar-driven systems (IUPAC Technical Report)
Authors: Bolton James R. , Bircher Keith G. , Tumas William , Tolman Chadwick A.
Published: October 2007

Advanced oxidation technologies (AOTs), which involve the in situ generation of highly potent chemical oxidants, such as the hydroxyl radical (áOH), have emerged as an important class of technologies for accelerating the oxidation (and hence removal) of a wide range of organic contaminants in polluted water and air. In this report, standard figures-of-merit are proposed for the comparison and evaluation of these waste treatment technologies. These figures-of-merit are based on electric-energy consumption (for electric-energy-driven systems) or collector area (for solar-energy-driven systems). They fit within two phenomenological kinetic order regimes: 1) for high contaminant concentrations (electric energy per mass, E
EM, or collector area per mass, A
CM) and 2) for low concentrations (electric energy per order of magnitude, E
EO, or collector area per order of magnitude, A
CO). Furthermore, a simple understanding of the overall kinetic behavior of organic contaminant removal in a waste stream (i.e., whether zero- or first-order) is shown to be necessary for the description of meaningful electric- or solar-energy efficiencies. These standard figures-of-merit provide a direct link to the electric- or solar-energy efficiency (lower values mean higher efficiency) of an advanced oxidation technology, independent of the nature of the system, and therefore allow for direct comparison of widely disparate AOTs. These figures-of-merit are also shown to be inversely proportional to fundamental efficiency factors, such as the lamp efficiency (for electrical systems), the fraction of the emitted light that is absorbed in the aqueous solution, and the quantum yield of generation of active radicals.
Organic photochromism (IUPAC Technical Report)
Authors: Bouas-Laurent Henri , Dürr Heinz
Published: October 2007

This technical report is a general introduction to organic photochromism. The definition of photochromism (PC) is given together with that of words with the ending "chromism", such as thermo-, electro-, piezo-, and tribochromism. Important concepts such as two-photon, gated, dual-mode PC and chirochromism are illustrated. The concept of fatigue (chemical degradation) and the determination of the main photochromic parameters (number of cycles, cyclability, half-life), and the spectrokinetic and mechanistic aspects are discussed. The main families of PC (organic compounds and biological receptors) are illustrated with chemical formulae, and the different types of reactions involved in the photochromic processes (pericyclic reactions, E/Z isomerization, group transfer, etc.) are listed. Some examples of applications to "optical power limiting" substances, photoresponsive materials, and photoswitchable biomaterials are considered.