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Atomically precise bottom-up synthesized graphene nanoribbons (GNRs) are promising candidates for next-generation electronic materials. The incorporation of these highly tunable semiconductors into complex device architectures requires the development of synthetic tools that provide control over the absolute length, the sequence, and the end groups of GNRs. Here, we report the living chain-growth synthesis of chevron-type GNRs (cGNRs) templated by a poly-(arylene ethynylene) precursor prepared through ring-opening alkyne metathesis polymerization (ROAMP). The strained triple bonds of a macrocyclic monomer serve both as the site of polymerization and the reaction center for an annulation reaction that laterally extends the conjugated backbone to give cGNRs with predetermined lengths and end groups. The structural control provided by a living polymer-templated synthesis of GNRs paves the way for their future integration into hierarchical assemblies, sequence-defined heterojunctions, and well-defined single-GNR transistors via block copolymer templates.

Reengineering or the rational redesigning of the binding pocket of the Cellular Retinoic Acid Binding Protein II ( CRABPII) can easily copy the binding found in rhodopsin protein, hence giving rise to a mutant that can bind retinal as a protonated Schiff base. The all-trans-retinal bound to CRABPII triple mutant are found to have a high-resolution crystal structure, which then proves the formation of an imine between the retinal and the protein.

A comprehensive report of parahydrogen/orthohydrogen (p-10-H(sub 2)) nuclear spin isomerization, catalyzed by various paramagnetic species studied by the use of HNMR spectroscopy is discussed. The rate constants in terms of variations in magnetic moments and radii were analyzed by Wigner's theory.

A series of rhenium(V) complexes are prepared to explore electronic effects on the C-S cleavage reaction that occurs upon reaction with PAr(sub 3) at ambient temperatures. The scope and selectivity of the C--S activation are examined.

The two molecules, 14 pi bis enol triflate ester and the 3,7-diisopropylsilyl substituted 14 pi cross-linked annulene, belonging to the family of dicyclopenta[a,e]pentalenes are synthesized and studied spectroscopically and by X-ray structural analysis. The new allenic tandem Pauson-Khand reaction mediated by Mo(CO)6 was employed as the key reaction to build up the core of the tetracycles.

The structure of Streptococcus suis serotype type 2 dTDP-D-glucose 4,6-dehydratase (RmlB) is determined to 1.5 A resolution with its nicotinamide coenzyme and substrate analogue dTDP-xylose bound in and abortive complex. Results indicate the ability of dehydratase enzymes to fine-tune the redox potential of NADH through conformational changes in the nicotinamide ring.

The temperature-dependent excited-state lifetime measurements on [Ru(bpy)2dppz](super 2+) in both protic and aprotic solvents are reported. It is found that the bright state is localized on one of the two bpy ligands and the dark state is associated with the dppz ligand.

Research into a compound made up of three molecular templates and a peptide strand that emulates a three-stranded protein beta-sheet is presented. The triply templated artificial beta-sheet is more tightly folded than its smaller doubly stranded homologue.

A new approach to the investigation of the conformational and motional properties of the oligosaccharide methyl 3,6-di-O-(alpha-D-mannopyranosyl)-alpha-D-mannopyranoside is presented. This technique uses an order matrix analysis of residual dipolar couplings in the solution state.

The formation of (+)-narciclasine and (+)-pancratistatin by an enantioselective process is presented. The significance of the photocyclization to synthesize these antitumor alkaloids is described.

A study developed a total synthesis of enantiomerically pure (+)-estradiol where the higher order cycloaddition Ramberg-Backlund protocol served as the key strategy level formation. The experiment revealed several significant characteristics of thiepin dioxide as a 6pi participant in the Cr(O)-promoted higher-order cycloaddition process. Structurally elaborate dienes react with good efficiency, and high levels of regiocontrol are often derived, when sterically hindered substituents are present on the triene.

Research was conducted to examine the kinetics and mechanism of the oxidation of 10-methyl-9,10-dihydroacridine by chromium(VI,V,IV). The anaerobic reaction swiftly takes place requiring methods for fast reactions. In contrast, O2 is a strong inhibitor that slows down the reaction by some 2 orders of magnitude. A combination of these effects signals a chain mechanism in which O2 acts in a chain-breaking capacity.

Research was conducted to examine the effects of pyridine and its derivatives on the equilibria and kinetics pertaining to epoxidation reactions catalyzed by methyltrioxorhenium (MTO). The steady-state concentration of MTO is decreased by coordinating a pyridine derivative which stabilizes the MTO/H2O2 system against irreversible decomposition. The Bronsted basicity of pyridine lowers the activity of hydronium ion in the long term and reduces the rate of epoxide ring opening.

a study was conducted on tetraanionic molecular squares, macrocycles that contain for pentacoordinate siliconate groups, to investigate their molecular structure and solution conformation. An ion exchange synthesis resulted in an ion pair consisting of tetraanionic siliconate macrocycle and cyclobis(paraquat-p-phenylene) tetracation. An analysis of the novel tetraanion-tetracation ion pair reveals that the cyclic bisparaquat selectively intercalates around the phenyl ring of the tetraanion's C2 face, which is then engulfed by the interior of the tetraanion.

The core structure of the Amaryllidaceae alkaloid tazettine, [2]benzopyrano[3,4-c]hydroindole, was synthesized from piperonyl alcohol in 11% overall yield. The synthesis of tazettine was started with the assembly of a key AC ring fragment. The key bond construction served as an insertion of a carbonyl 1,1-dipole equivalent between the responsive termini of a functionalized beta-aryl vinyl isocyanate. The incorporation of a [4+1] cycloaddition between the beta-aryl vinyl isocyanate and dimethoxycarbene allowed the faster assembly of tazettine's core structure.

It has been established that phosphotyrosine-containing peptides bind to the SH2 domain of pp60c-src (Src), a nonreceptor tyrosine kinase, with micromolar affinity. Researchers have been able to design a de novo series of small molecule ligands that bind with affinity comparable to the parent phosphopeptide. The unusual binding at the P-site may be used as a basis for designing new phosphate mimetics that are more conducive to cell penetration and higher levels of bioavailability.

The catalytic efficiency of methylrhenium trioxide (MTO) for Diels-Alder (DA) reactions in water was analyzed during reactions involving alpha, beta-unsaturated ketones or aldehydes as dienophiles. DA cycloaddition reactions between aldehydes or alpha, beta-unsaturated ketones with six representative dienes were accelerated by MTO. Furthermore, MTO-catalyzed reactions proceeded with high stereoselectivity and produced a single isomer.

Optically active (R)-1,1,3,4,4,5,5,5-octadeutero-1-pentene (1) was produced and employed for studying the stereoselectivity of Y-H and Y-n-pentyl additions for the optically pure C2-symmetric (R,S)-(BnBp)Y-R/(S,R)-(BnBp)Y-R and racemic (+/-)-(BnBp)Y-R isospecific polypropylene catalysts (BnBp = ((OC10H6C10H6O)Si(C5H2-2-SiMe3-4-CMe3)2)). Deuteration and deuterodimerization of 1 mediated by (R,S)-, (S,R)-, and (+/-)-(BnBp)Y-D produce alkanes whose 1H NMR spectra indicate the sense and magnitude of olefin facial selectivity for insertions into metal-hydride and metal-n-pentyl bonds.

A cyclic species containing Re, O, and CHCO2Et in a three-membered ring is proposed as an intermediate in the reactions of ethyl diazoacetate (EDA) catalyzed by methylrhenium trioxide (MTO). MTO-catalyzed cycloaddition reactions take place between EDA and aromatic imines, olefins and carbonyl compounds. These form the three-membered ring products of aziridines, cyclopropanes and epoxides, respectively. These favor the formation of trans products and offer a convenient route for the preparation of aziridines. Carbenoid and nitrenoid species are proposed as intermediates.

Methylrhenium trioxide, (MTO), and hydrogenperoxide give catalytically active peroxorhenium complexes, CH3ReO2(eta2-O2), (A) and CH3Re(O)(eta2-O2)2(H2O), (B). The complex decomposes to methanol and perrhenate ions in the presence of hydrogen peroxide. The attack by hydroxide on A or by HO2 on MTO explains the pH dependence of the complex. B decomposes slowly to give O2 and CH3ReO3, which is stable only in acidic medium. Variable temperature 1H-NMR reveals a labile coordinated water molecule in B and an anhydride form of A.

A four-atom spin system composed of three 13C sites and one 15N site in a synthetically produced lactam analog of ganglioside GM4 is investigated using liquid crystal nuclear magnetic resonance spectroscopy. The system resembles the natural membrane-bound state in which the system's molecules move about. Results give a reasonable picture of the GM4 lactam headgroup orientation in a membrane environment.

The triplet state reactivities of bromophenyl ketones were investigated to determine the effect of triplet configuration and energy on the rate of constants for cleavage of C-X bonds. Steady-state and time-resolve analyses showed that m- and p-bromophenyl alkyl ketone triplets undergo C-Br bond homolysis with 25 degrees C rates constants of 2 x 10(super 8) and 1 x 10(super 8) s-1, respectively. The activation parameters for triplet state cleavage were obtained by flash kinetic measurements of the temperature dependence of the triplet decay.

A kinetic study on the acidic CH3CN/H2O solutions determined the reactivities of mono-peroxide, CH3Re(O)2(O2) and the bis-peroxide, CH3Re(O)(O2)2 along with the other features of the mechanisms. The rate constants for different stages are reported. The results indicated that methylrhenium trioxide, CH3ReO3, catalyzes the oxidation of styrenes by hydrogen peroxide. The mechanism of the reaction is discussed.

UV Raman resonance and transient absorption data indicates the formation of an eta-superoxochromium(III) complex when Cr2+ and O2 react. The Cr-O2 bond is photolabile at wavelengths near 290-nm LMCT transition. Cr2+ and O2 undergo thermal recombination with reduction of unphotolyzed CrO22+by Cr2+, to form Cr(III) complexes. The cyclam ligands lower the Cr-O2 and O-O stretching frequencies.

Dipolar interactions between C-C and C-H pairs were measured using nuclear magnetic resonance spectroscopy to determine conformation of uniformly C-labeled monogalactosyldiacylglycerol (MGDG) of chloroplast membranes in the lipid matrix and in solution. Analysis of potential energy maps revealed a set of low-energy conformations from the galactose headgroup to the membrane surface, while MGDG dissolved in CD3OD revealed a mixture of low-energy conformers and higher motional averaging. This suggests that conformation of MGDG favors the membrane environment.

Methylrhenium trioxide, CH3ReO3, catalyzes the oxidation of tertiary phosphines by hydrogen peroxide. Kinetic studies of the interactions between CH3ReO3 and H2O2 to form CH3Re(eta2-O2)(O)2(OH2) and CH3Re(eta2-O2)2(O)(OH2) suggest a mechanism wherein the nucleophile attacks the substrate at the rhenium peroxides. The nucleophilicity of phosphine and its cone angles can be varied upon introduction of changes in the substituents on phosphorus.

A water-soluble organometallic oxide, Ch3ReO3, catalyzed the reaction between bromide ions and hydrogen peroxide in aqueous acidic solutions. This rhenium catalyst exhibited similar catalytic activities to the enzyme vanadium bromoperoxidase. Peroxide activation included the binding of bromide ions to the rhenium compound during its nucleophilic attack on peroxide ions.

New NMR methods that help perceive the correlations with water proton resistance and aid the classification of the origin of reactions were examined. Pulsed field gradients for diffusion editing, isotope editing for selective detection and restricting solvents and selective excitation for acquisition efficacy, were utilized in these methods. Protons which exchange physically between water and amide regions have a variety of exchange lifetimes.

A study conducted to examine experimental findings on tetramethylenebenzene (TMB) revealed that electron spin resonance (ESR) and UV-vis spectrum assigned to TMB do not actually come from a common species. A singlet state of TMB is the carrier of the UV-vis spectrum. These findings strengthen the disjoint hypothesis and put an end to the dispute between theory and practice in the matter of TMB.

NMR studies of (6Li)- and (6Li,15N)-labeled lithium hexamethyldisilazide (LiHMDS) show that LiHMDS exists as a mixture of monomer and cyclic dimer in THF and as a mixture of oligomers in hydrocarbons. Stepwise addition of hexamethylphosphoramide results in serial solvation of the monomer and dimer and in the formation and serial solvation of triple ions but has no effect on the aggregation state. Comparisons with lithium tetramethylpiperidide reveals parallel solvation behavior. The empirical results are supported by MNDO calculations.

A study was done on the reactions of the 17-electron radicals CpW(CO)3, (C5H4COOCH3)W(CO)3 and CpMo(CO)3 with organic halides and halocobalt(III) complexes. Results showed trends in absolute and relative reactivity, steric and electronic properties of the substrate, solvent effect and effect of Lewis bases. The fate of the substrate was also examined as well as the rates and mechanisms of the reactions of CpW(CO)3 with O2, ROOH and (n-Bu)3SnH.

The stereochemistry and regioselectivity of higher order (6pi + 4pi) cycloaddition reactions of transition metals are presented. Findings indicate that group 6 metals can activate a number of such reactions using a combination of stoichiometric amounts of cyclic triene chromium tricarbonyl complexes and 4pi reactants. The mechanisms involved in the activation of these cycloaddition reactions, their implications and applications to organic synthesis are discussed.

Voltammetry, coulometry, optical spectroelectrochemistry and electron spin resonance spectroscopy are used to study the redox properties of the 30-e triple-decker complexes. The results indicate the presence of a specific electron-transfer series and electronic spectra within the 300-2,000 nm range is also obtained using an optically transparent thin-layer electrolysis cell. The presence of group III and V atoms in the bridge is also observed in all reasonably stable odd-electron triple deckers.

The laser flash photolysis study of thiyl radical reactions reveals that thiyl radicals oxidize reduced transition-metal complexes. Inner-sphere reagents react with ethylthiyl radicals to form metal-sulfur bonds. Outer-sphere reagents yield thiolate ions and oxidized metal complexes upon reaction with ethylthiyl radicals.

A structural examination of a group of alkyl monoglycosides has revealed no differences between the headgroup orientation at the bilayer membrane. The headgroup orientation for each glycoside was explored using diapolar coupling data from C NMR spectra. Various 13C-labeled glycosides such as beta-dodecyl galactopyranoside and alpha-tetradecyl 2-deoxyglucopyranoside were prepared and dissolved in lipid bilayer membranes.