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The structural and electronic characterization of trans-polyacetylene (PA) and polyyne (PY) is presented. The findings from the comparison provide evidence for the high-quality theoretical prediction that could be obtained from the Coulomb-attenuated CAM-B3LYP functional.

Recent studies on a bacterial virulence factor, YopJ of Yersinia, have led to the realization that the acetylation of serine and threonine residues could be an important form of post-translational modification in eukaryotes. Although the identification of the machinery used for the addition and removal of acetyl groups on serine or threonine residues is in its infancy, the enzymes thus-far studied provide early insight into the mechanism of this newly discovered post-translational modification, and hint at its potential importance. For example, acetylation can compete with phosphorylation targeted to the same residues and could, therefore, alter the course of signaling pathways. What are the implications for signal transduction in eukaryotes and how widespread could acetylation of serine and threonine prove to be?

The way the beta-hairpin region of the C2H2-type zinc finger peptides contributes to the DNA binding properties is investigated. The results strongly indicate that the beta-hairpin region appears to function as a scaffold and has an important effect on the DNA binding properties of the C(sub 2)H(sub 2) type zinc finger peptides.

The study investigated some novel properties of organized molecular films of 10,12-tricosadiynoic acid (TDA), which were modulated by transition metal ions. It concluded that metal ions such as Cu(super 2+), Zn(super 2+), Ni(super 2+), Cd(super 2+), and Ag(super +) in the subphase can greatly affect the monolayer formation of TDA and the properties of the subsequently deposited Langmuir-Blodgett (LB) films, particularly in the case of Ag(super +), Zn(super 2+), and Cu(super 2+) ions.

The study on the reactions of transition metal dioxides with acetylene molecules using matrix isolation absorption spectroscopy is presented. These acetylene and transition metal dioxide reactions may serve as a simple model for understanding the interactions of transition metal oxides with other more complicated organic substrates.

The population relaxation rate of the first excited state of the acetylenic C-H stretch is compared for a series of isolated and solvated terminal acetylenes. It is observed that two factors together explain the large increase in the isolated molecule rate when the molecular-beam intramolecular vibrational-energy redistribution (IVR) rate is compared to the solution-phase relaxation rate of the room-temperature sample.

The pathway for vibrational-energy flow is examined following the excitation of the first excited state of the acetylenic C-H stretch which is investigated for a series of 10 terminal acetylenes in room-temperature gases and dilute solution using transient absorption picosecond infrared spectroscopy. The main effects of the solvent are to increase the extent of population relaxation for the first stage of IVR (intramolecular vibrational-energy redistribution) and to cool vibrational excitation rapidly in the low-frequency acetylene wag normal-mode vibrations produced by the IVR dynamics.

The population relaxation rate is examined of the first excited state of the acetylenic C-H stretch that is compared for room-temperature gas-phase and solution-phase samples of 10 terminal acetylenes. It is observed that a single solvent relaxation contribution to the total relaxation rate describes the solution dynamics for all terminal acetylenes which is consistent with the idea that solvent-induced energy relaxation pathways are dominated by the vibrational motions that are in close proximity to the excited state.

The matrix isolation technique, combined with ab initio computations is used to characterize the 'one is to one ratio' complexes of formic acid and acetylene. Ab initio calculations are done based on the Gaussian 98 program suite.

The laser-induced fluorescence (LIF) and H-atom action spectra of the A~-X~ transition of acetylene in a supersonic jet were observed in the excitation-energy range of 47000-50600 cm(super -1). It was found that the predissociation mechanism is not dependent on the vibrational parity but is attributed to the anharmonic coupling between the v(sub 3') and v(sub 4')/ v(sub 6') vibrational modes.

The feasibility of molecular electrostatic potential measurements at atomic sites as reactivity descriptor for the mechanism of hydrogen bonding is evaluated for a range of complexes consisting of acetylene and diacetylene derivatives as proton donors and ammonia as an acceptor. A distinct linear relation between the molecular electrostatic potential with the energy of hydrogen-bond formation is observed.

The quenching of the locally excited state that occurs with 4-(demethylamino)phenylacetylene in p-dioxane/water mixtures is studied. It is concluded that this quenching does not lead to the appearance of an emission from an intramolecular charge-transfer state.

Research has been conducted on alpha,beta-acetylenic ketones that serve as intermediates for the heterocyclic compounds preparation. The method developed to converse alkynes to alpha,beta-acetylenic ketones with high conversion and selectivity is discussed.

Research into the C2D2 reduction stereospecificity of altered MoFe proteins with amino acid substitutions within the active site FeMo-cofactor environment is presented. The electron flux through nitrogenase was seen to substantially influence the ratio of cis- to trans-1,2-C2H2D2 formed.

Presented here are the gas-phase measurements of the 13C and 1H magnetic shielding and spin-spin coupling coupling of 1,2-C13-enriched acetylene in the gas phase.

Ab initio investigations of structures of (HCCH)2 have produced energetics and separation distances that were represented by model potentials with three options for representing acetylene's permanent charge field. Similar surfaces could be obtained from the different ab initio starting points.

Amorphous nitrogenated carbon (a-CN(sub x)) films are prepared from a mixture of acetylene and nitrogen gas in electron cyclotron resonance plasma and characterized by electron energy-loss spectroscopy (EELS), spectroscopic ellipsometry (SE), Fourier transformed infrared (FTIR) spectroscopy. The results show that the incorporation of nitrogen does not increase the graphitization of the nitrogenated carbon films prepared from acetylene, unlike that seen from methane-based films.

Thee protophysical characteristics of a series of phenylacetylene dendrimers are investigated, using steady-state and time-resolved fluorescence data.

Research has been conducted on the Azotobacter vinelandii Mo-nitrogenase's altered MoFe proteins. The use of these proteins in interaction probing among C (sub)2 H (sub)2, C (sub)2 H (sub)4, CO and H (sub)2 is discussed.

An investigation of the impact of a range of theoretical methods and basis sets on the calculated geometry and dimerization energy of the acetylene-ammonia dimer HCCH...NH3 is presented.

A supramolecular self-assembly showing visible and rapid color changes in the presence of specific cations, is described.

A new flame method of atomic absorption spectrometry is described. The liquid sample to be analyzed is transported as a high-speed liquid jet into a heated tube which is positioned in an air/acetylene flame. The jet is generated by means of an HPLC pump which feeds a smooth jet nozzle having a diameter of 50 (mu)m or smaller. After traveling a distance of 10 cm, the liquid jet enters a small sample introduction hole, impacts onto the opposite inner wall of the tube furnace, and immediately vaporizes (jet impact vaporization, JIV). Both the complete introduction of the entire sample and the extended residence time inside the absorption volume result in an improvement in power of detection from 6- to 202-fold for 17 elements (Ag, As, Au, Bi, Cd, Cu, Hg, In, K, Pb, Pd, Rb, Sb, Se, Te, Tl, Zn). A standard deviation of 1.7-4.0% (n = 12, 50 (mu)L) was achieved. Sample volumes between 10 (mu)L and 1 mL have been investigated. For 50 (mu)L sample volumes, the sampling frequency is 4/min. The new method can also be considered a simple, effective interface between HPLC and flame AAS.

A study of 2-alkoxycarbonylpyridinium N-aminide behavior toward acetylenic compounds is presented. Results demonstrate that they yield conjugated mesomeric betaines.

In this research, two Hartree-Fock methods are used to investigate acetylene adsorption on the perfect (0001) hexagonal ice surface. A comparison is made of the success in the interpretation of the observed spectra by the periodic model to the failure of previous research using the dimer H2O-C2H2 model.

Dimer cations of cyanoacetylene were produced in a selected-ion flow tube in helium buffer.

The oxygen atom addition to dimethylacetylene (DMA) and the oxygen molecule and ozone molecule reactions with DMA are reported.

Research was conducted to examine the 13C NMR shieldings for acetylene, allene and some higher cumulenes which were measured at the MPW1PW91/6-311+G(2d,p) level using both the GIAO and IGAIM methods. The tensor components of the shielding for both allene and acetylene as well as the remarkably large difference in the components about the long axes of the molecules were efficiently reproduced by the calculations. The large difference in isotropic shielding may have resulted from the differences in p-orbital coefficients among the occupied orbitals and the virtual orbitals with which they couple in the presence of a magnetic field.

A study on the hydrocarbon acetylene investigated the photoinduced isomerization of an acetylene radical anion generated in a frozen, polar and rigid 2-MTHF glassy matrix at 77 K. This radical anion generated in a metal-free system was confirmed to have a trans-bent structure based on the comparison of the ESR spectroscopic results with the theoretical calculations particularly on anisotropic 1H hyperfine and g tensor components. Experimental methods and findings are presented.

A study on the pyrolysis of acetylene investigated the kinetics and the chemistry, particularly the potential energy surface, of a NO-C2H2 system in its electronic doublet ground state using electronic structure and rate theory calculations. On the doublet potential energy state, five intermediates were found to be involved in the formation of the most favorable dissociation product, HCO + HCN. Other experimental results are discussed.

Charge reversal (CR) of cations to anions has proven to be the superior method for a structural characterization of the C8H6+ isomers formed upon loss of acetylene from ionized naphthalene, despite its poor sensitivity. The method gives rise to some structurally indicative fragmentations for the different hydrocarbon isomers, while the other methods yield much less pronounced fragmentations. Comparison of the CR spectra of the C8H6+ cations belies the formation of ionized phenylacetylene and 2,4,6-octatriyne upon loss of acetylene from napthalene ion, as does the formation of ionized cycloocta-1,3,5-triene-7-yne. Results are in agreement with the formation of ionized benzocyclobutadiene upon loss of acetylene from napthalene ion.

The microwave spectrum and structure of four isotopomers of the HCCH-OCS van der Waals dimer are probed with the aid of a Fourier transform microwave spectrometer. The rotational constants for the normal isotopomer are calculated at A = 5839.1071(20) MHz, B = 2055.4388(13) MHz and C = 1514.9785(12) MHz, all of which are consistent with an almost parallel arrangement of the monomer subunits with a calculated R(sub CM) distance of 3.6062(13) Angstroms.

A novel system that is based on hydrazide derivatives of single-chain diacetylene lipids is presented. The lipids were examined using different spectroscopic methods in organic solution, solid films and vesicles to explore the specific role of the hydrazide headgroup interactions. Results provide detailed insight into the mechanism of colorimetric transitions in polydiacetylenes upon changes in the layer packing.

Different fluorescence behaviors were exhibited by the carbazolyldiacetylenes depending on how the carbazolyl (Cz) moiety was connected to the diacetylenic backbone. Fluorescence properties were observed which were closely related to those of the fluorescent Cz group when Cz was attached to the backbone through one or more CH2 spacers. When Cz was directly attached to the backbone, almost no fluorescence was observed. The phenomena were then studied quantum chemically to provide an explanation for the observations.

Three new 'lower molar ratio' double salts of silver acetylide with silver nitrate were synthesized and their crystal structures determined. These are Ag2C2*5.5AgNO3*0.5H2O, Ag2C2*5AgNO3 and Ag2C2*AgNO3, wherein the acetylide dianion is located inside a silver cage shaped like a monocapped pctahedron, a monocapped trigonal prism and an octahedron, respectively. This series of related complexes adopted different structural alternatives, which indicate that a higher molar composition of silver acetylide in a double salt prefers the formation of a network of edge- and vertex-sharing silver polyhedra that closely resemble the structure of neat silver acetylide.

The resonant two-photon ionization (R2PI) spectra for several primary reaction products of metastable diacetylene (C4H2*) reaction with alkynes, alkenes, ethylene and propene were investigated using ultraviolet photochemistry. The R2PI spectrum of the C7H6 product from the C4H2* + propene reaction was found to be closely similar to that of the C6H4 product 1-hexene-3,5-diyne.

Research was conducted to examine the inactivation of toluene 2-monooxygenase in Burkholderia cepacia G4 by alkynes. Results demonstrate that different alkynes serve as potent inhibitors of the toluene-dependent growth of B. cepacia. Findings also reveal that toluene 2-monooxygenase activity is specifically inactivated by the compounds. Therefore, alkynes represent a general class of mechanism-based inactivators for toluene 2-monooxygenase activity in B. cepacia G4.

The energy barrier and transition structure of the concerted 1,3-dipolar cycloaddition of fulminic acid to acetylene were investigated using molecular orbital and density functional theory calculations. The aim was to compute the accurate energetics and find an economical but reliable method for treating larger substituted systems. It was found that the activation energy is highly dependent on the treatment of dynamical electron correlation but not particularly sensitive to the geometries employed.

A study was conducted to analyze the trimerization of acetylene to benzene on a Cu(100) surface. The study was carried out in a stainless steel chamber supporting four-grid LEED apparatus, a quadrupole mass spectrometer and an Auger spectrometer. Results indicated that the mass 26 signal imitated the trimerization rate at high coverages. Findings also showed that increases in the reaction yield correlated with increases in the initial acetylene coverage.

Most textbooks perpetuate the erroneous proposition of free alkyl carbocation intermediates in solvolysis. Research with acetylene has shown reaction mechanism problems with intermediate cations will no longer exist if the two-step model is abandoned. This leaves two reaction types, one of which is irreversible and requires an aggressive nucleophile, the other being largely reversible with an active nucleofuge.