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Four siiicon-containing acrylacetylene resins were synthesized by polycondensation of Grignard reagent of m-diethynylbenzene with methylethyldichlorosilane, dimethyldichlorosilane, methylphenyldichlorosilane, and diphenyldichlorosilane, respectively. The structures of the resins were verified by nuclear magnetic resonance spectroscopy and Fourier transform infrared (FTIR) spectroscopy. The solubility, crystallinity, and rheological character of the resins were characterized. The curing behavior was traced by differential scanning calorimetry (DSC) and FTIR analyses. The effect of the side groups on the silicon atom on the properties was investigated. The results show that the resins with asymmetrical side groups display better processability (wide processing window) as compared with those with symmetrical side groups. The resin with side phenyl groups shows higher flexural strength but lower thermal stability as compared with those without side phenyl groups. Meanwhile, the side phenyl groups also enhance the temperature at which secondary relaxation occurs. KEYWORDS effect of side groups, high-performance resins, siiicon-containing arylacetylene resin, structure-properties relationships, 1 | INTRODUCTION Siiicon-containing arylacetylene resins are a kind of highperformance polymers with excellent heat resistance and low dielectric constant, which has already shown highly potential applications as ceramic precursors, [...]

Abstract: Density functional theory (DFT) calculation was used to investigate the mechanism of [Au.sub.3] clusters, separately supported on pure graphene ([Au.sub.3]/graphene) and one graphitic N-doped graphene ([Au.sub.3]/N-graphene). These supported [Au.sub.3] [...]

For the last four decades, the role of polyynes such as diacetylene (HCCCCH) and triacetylene (HCCCCCCH) in the chemical evolution of the atmosphere of Saturn's moon Titan has been a subject of vigorous research. These polyacetylenes are thought to serve as an UV radiation shield in planetary environments; thus, acting as prebiotic ozone, and are considered as important constituents of the visible haze layers on Titan. However, the underlying chemical processes that initiate the formation and control the growth of polyynes have been the least understood to date. Here, we present a combined experimental, theoretical, and modeling study on the synthesis of the polyyne triacetylene (HCCCCCCH) via the bimolecular gas phase reaction of the ethynyl radical (CCH) with diacetylene (HCCCCH). This elementary reaction is rapid, has no entrance barrier, and yields the triacetylene molecule via indirect scattering dynamics through complex formation in a single collision event. Photochemical models of Titan's atmosphere imply that triacetylene may serve as a building block to synthesize even more complex polyynes such as tetraacetylene (HCCCCCCCCH). electronic structure calculations | planetary chemistry | crossed molecular beams | photochemical model

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.

The vibrational dynamics of molecular complexes, acetylene-HCN and cyanoacetylene-HCN, solvated in helium naodroplets were examined by infrared-infrared double resonance spectroscopy. It was found that vibrational excitation of acetylene-HCN complex results in a population transfer to the other isomer, however, no population transfer was observed for the cyanoacetylene-HCN complex.

The kinetics and H atom yields at both 298 and 195 K were determined for reactions of CN radicals with [C.sub.2][H.sub.2], [C.sub.2][H.sub.4], [C.sub.3][H.sub.6], trans-2-[C.sub.4][H.sub.8] and iso- [C.sub.4][H.sub.8]. The results extended the upper limit of the temperature range of study from 886 to 14010 K and indicate a non-Arrhenius behavior of the rate coefficient.

An initio calculations of the potential energy surface for the reaction of the tricarbon with acetylene were performed at the RCCSD(T)/cc-pVQZ/B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p) level. The results show that this reaction starts from the formation of the 30(didehydrovinylidene)cyclopropene intermediate i1 or the five-member ring structure i7.

The synthesis, spectroscopic, electrochemical, as well as p[b.sup.2+]-binding properties of a series of different tetarthiafulvalence (TTF) acetylene derivatives, exhibiting a strong donor-acceptor interaction are studied. The analysis clearly demonstrates that the extent of the intermolecular charge transfer interactions through the [pi]-conjugated triple bond is smaller than that through the double bond.

The static second hyperpolarizabilities ([gamma]) of the singlet diradical systems with intermediate diradical character involving phenalenyl radicals connected by acetylene and vinylene [pi]-conjugated linkers were investigated. The results provided the possibility of developing a novel control scheme of [gamma] for phenalenyl radical systems involving [pi]-conjugated linkers.

[pi]-Electrons of acetylene and [sigma]-electrons of molecular hydrogen are examined as Lewis bases in different complexes and high level ab initio calculations are performed. The results have shown that some of interactions contain characteristics typical for covalent bonds or at least the partial covalency.

The ground-state carbon atom was analyzed for the multichannel reaction with acetylene and cyclic tricarbon isomers. The chemical kinetic studies and electronic structure calculations show that the cyclic isomer has lower energy than the linear isomer.

An indium catalyzed addition of a 1,3-dicarbonyl compound to a terminal alkyne has provided an efficient synthetic route to 2-alkenyl-1,3-dicarbonyl compounds. The results have suggested that the reaction proceeds via a concerted carbometalation reaction of an indium(III) enolate with the acetylene, where indium-acetylene interaction is important.

Topographical analysis of the molecular electrostatic potential (MESP) along a reaction path is used to bring out the sequential electronic reorganizations for 1,3-dipolar cycloadditions of ethyne to fulminic acid as well as diazomethane. The MESP topography at each point on the reaction path is associated with classical electronic structure, thereby providing a clear picture of the electronic reorganization along the reaction path.

Supramolecular helical assembly of an achiral cyanine dye in an induced helical amphiphilic poly(phenylacetylene) interior in water was studied. It was shown that a water-soluble neutral poly(phenylacetylene) can specifically trap an achiral cyanine dye in its cavity inside the polymer in water.

The chemical kinetic behavior of CH and [C.sub.2] is examined by monitoring their ground-state concentrations along with those of OH and H in a series of well-defined and characterized fuel-rich acetylene flames. CH and [C.sub.2] are formed and destroyed on a sub-microsecond time scale so that their flame profiles are the reflection of complex kinetically dynamic systems.

Treatment of the hydrazone of 2H-perfluoro-2-methyl-3-pentanone with trietylamine at increased temperature has yielded a methylenecyclobutene via degradation to acetylene followed by dimerization. The finding suggests that the acidity and the conformational dynamics of the methylenecyclobutene are influenced by buttressing effects in this crowed molecule.

The tungsten-iron-sulfur enzyme acetylene hydratase stands out from its class because it catalyzes a nonredox reaction, the hydration of acetylene to acetaldehyde. Sequence comparisons group the protein into the dimethyl sulfoxide reductase family, and it contains a bis-molybdopterin guanine dinucleotide-ligated tungsten atom and a cubane-type [4Fe:4S] cluster. The crystal structure of acetylene hydratase at 1.26 [Angstrom] now shows that the tungsten center binds a water molecule that is activated by an adjacent aspartate residue, enabling it to attack acetylene bound in a distinct, hydrophobic pocket. This mechanism requires a strong shift of p[K.sub.a] of the aspartate, caused by a nearby low-potential [4Fe:4S] cluster. To access this previously unrecognized W--Asp active site, the protein evolved a new substrate channel distant from where it is found in other molybdenum and tungsten enzymes. acetylene reduction | metalloproteins | tungsten enzymes

The syntheses and characterization of a series of 22[pi] samaragdyrins with diverse meso substitutes ranging from simple hydrogen to phenylacetylene and ferrocene are described. A simple oxidative coupling methodology with the appropriate precursor is applied for the synthesis and it is shown that the optical, emission, and electrochemical properties depend on the nature of the substituents, the linking group, and the spacer length.

Stark and Fourier transform microwave spectroscopy is used to study Z-3-Amino-2-propenenitrile, [H.sub.2]NCH=CHCN, a compound of astrochemical and astrobiological interest, along with eight of its isotopologues. Quantum-chemical calculations are performed to help in the assignment procedure, to predict an accurate equilibrium structure, dipole moment, and quadrupole coupling constants, and to model the gas-phase reaction between ammonia and cyanoacetylene forming 3-aminopropenenitrile.

A study on direct adsorption of phenylacetylene on clean silicon surface Si(100)-2 x 1 is conducted in ultrahigh vacuum (UHV). Scanning tunnel microscopy (STM) images of weakly covered surfaces provide evidence of two very distinct adsorption geometries for phenylacetylene, with slightly different initial sticking probabilities.

The synthesis, crystal structure and fluorescence behavior of acetylene-bridged pentiptycene dimer, trimer, and tetramer are described and phenylene-pentiptycene-phenylene three-ring system is investigated. The results have shown that twisting of the [pi]-conjugated peak maxima for acetylene-bridged pentiptycene dimer, trimer, and tetramer in the solid state resemble those in dilute solutions, but the reabsorption effects determine the relative intensity of the fluorescence vibrionic bands.

An environment friendly and reliable synthesis of difluorohomopropargyl alcohols utilizing indium and a catalytic amount of Eu[(OTf).sub.3] was carried out. 3,3-Difluoror-1,7-diene, prepared in two steps form [beta],[beta]-difluorohomopropargyl alcohol, reacted with monosubstituted acetylenes in the presence of RhCl[(P[Ph.sub.3]).sub.3] to produce 4,4-difluoroisochromans in moderate to god yields and regioselectivities.

The objective of the study is to determine the nature of interaction between acetylated lysines with aromatic rings and its potential role in protein structure and function as the effect of lysine acetylation on the interaction of acelylated lysines with tryptophan is examined within the context of a [beta]-hairpin peptide. Acetylation of Lys results in the replacement of a cation-[pi] interaction with an amide-[pi] interaction.

'Naked eye' color detection of proteins is achieved by embedding calixarene receptors within vesicles comprising phospholipids and the chromatic polymer polydiacetylene. Fluorescence and circular dichroism experiments confirmed the relationship between the coloimetric phenomena and protein docking on the surface of the chromatic vesicles.

The synthesis of the pentadeuterated (Z)-11-hexadecenoic acids regiospecifically deuterated at each vinyl position and bearing a tetradeuterium tag distant from the site of desaturation is described. The findings provided experimental evidence that the transformation of (Z)-11-hexadecenoic acid into 11-hexadecynoic acid by the [[DELTA].sup.11] acetylenase takes place by stepwise mechanism, in which a significant perturbation of the strong vinyl C11-H bond occurs prior to a fast elimination of the vinyl hydrogen at C-12.

The synthesis and characterization of two novel fluorophosphazene derived from cobaltocyclopentadienylmetallacycles is reported and a hitherto unknown synthetic route for making aryl bridged fluorinated cyclophosphazenes by the reaction of the metallacycles with substituted acetylenes is provided. These cobaltametallocycles are possible precursors for making novel acetylene-trimerized aryl compounds as well as [[eta].sup.5]-Cp]Co[[[eta].sup.4]-R4C4] metallocenes.

Fluorescence energy transfer and scanning force microscopy were used to explore the influence of the salt concentration, linker histon H1, and histone acetylation on the structure of trinucleosomes reconstituted on a 608 bp DNA containing one centered nucleosome positioning signal. The effect of acetylation of all histones is found to lead to decomposition, measured as an increased distance between the DNA ends, and also increased the internucleosomal distances.

Laboratory experiments involving ultraviolet (UV) irradiation of dicyanoacetylene ([C.sub.4][N.sub.2]) trapped in water ice at 10 K are conducted and monitored by infrared spectroscopy (FTIR). These experiments have shown that the irradiation of a DCA/[H.sub.2]O ice mixture at lambda greater than 230 nm is the possible source of N[H.sub.4.sup.+]HC[O.sub.3.sup.-] (ammonium bicarbonate) and N[H.sub.3.sup.+]HCO[O.sup.-] (ammonium formate).

The synthesis of 1,4-cyclohexadiene-based acetylenic macrocyles in excellent isolated yields and material balance on a preparative scale is reported. The tetrameric macrocycle showed a tub-shaped conformation and encapsulated a molecule of ethyl acetate within the tub.

Facile C-C bond cleaving fragmentation reactions induced by the addition of nucleophiles to cyclic vinylogous acyl triflates is developed to produce acyclic acetylenic compounds. The respective reactions produce ketones, 1,3-diketones and their analogues, alcohols, and amides.

A detailed study on ligand preparation and their applications to the amination reactions of unactivated aryl chlorides and Suzuki-Miyaura coupling reactions of different substrates including ortho-substituted aryl chlorides to form hindered biaryls is discussed. A cache model for the Pd/7i complex shows that the likelihood of a Pd-arene interaction might be a rationale for its high catalytic activity.

Reaction of (2E)-2,3-difluoro-3-iodoacrylic acid with a variety of terminal acetylenes under cocatalysis of PdCl2(PPh3)2 and CuI gave difluorinated 2-pyrones as the product in good yields. Cyclization of enyes with I2 afforded 5-iodo-6-substituted 2-pyrones, which could be further utilized to synthesize more functionalized fluorinated 2-pyrones.

A new synthetic route leading to a PdH precatalyst in one step from a stable NHC salt and the commercially available Pd(acac)2 is described. The resulting complex, (IPr)-Pd(acac)Cl has shown excellent catalytic activity in the Buchwald Hartwig and the alpha-ketone arylation reactions using aryl chlorides under milk reaction conditions.

Full-dimensional ab initio calculations of vibrational energies of trans-C2H2(A) are reported using the code MULTIMODE and with a full-dimensional potential energy surface obtained by fitting singles and doubles coupled-cluster equations-of-motion (EOM-CCSD) energies, with the code ACES II, using a [3s 2p 1d] atomic natural orbital basis. The properties of the potential surface are compared to previous calculations at the trans minimum and the vibrational energies are compared to experimental values.

One nanosized oxadiazole bridging ligand, bis(3-acetylenylphenyl-(4-cyanophenyl))oxadiazole (L11), is designed and synthesized by the reaction of bis(3-iodophenyl)oxadiazole with 4-cyanophenylacetylene through a Sonogashira-Hagihara cross-coupling reaction. Eight silver(I)-L11 coordination polymers with one-, two-, or three-dimensional structures are also successfully prepared by the reaction of L11 with various silver(I) salts in solution.

Carboxy-terminated polydiacetylene vesicles are known to undergo dramatic color transitions in response to exposure to external stimuli such as pH, temperature, and receptor--ligand binding. FTIR spectroscopy was used to identify the breakdown in the interfacial hydrogen-bonding interactions of the carboxylic acid headgroups of polymerized 10,12-tricosadiynoic acid (TRCDA) vesicles in aqueous solution during pH chromic transition. The headgroup structure was monitored as the chromic transition takes place and the dissociation dependence of the p[k.sub.a] was determined. Due to the attenuated acidity of the interfacially confined carboxy groups, which exhibit p[K.sub.a] values in the range 9.5-9.9, it was found that the deprotonation-triggered blue--red chromic transition occurred in the pH range 9.0-10.1 and that the mechanism of the transition required interaction with the surface carboxyl group, which is of importance in the design of a biochromic mechanism using PDA assemblies. Transmission electron microscopy and FTIR spectroscopy revealed that the surface ionization and the pH-induced chromogenic transition was also accompanied by a dramatic vesicleplanar morphological transition alongside subtle changes to the alkyl chain conformation and packing. A two-step mechanism was implicated as causing the chromic transition that first involves surface deprotonation and then specific cation binding, which can aid the design of sensitive surface--ligand chemistry for new PDA structures.

New 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives were synthesized as an 'off-on' fluorescent chemosensor and fluorescent chemodosimeter for Cu(super 2+) and Pb(super 2+). It is concluded that new fluorescent sensor displayed selective large chelation enhanced fluorescence effects with Pb(super 2+) and Cu(super 2+).

An effective method is described for the production of ultrasharp vertically oriented silicon nanocones with tip radii as small as 5 nm via an acetylene and ammonia dc plasma process. The mechanism for the formation of these structures is reactive ion etching of the silicon substrate facilitated by copper seed particles and it is shown that by patterning the seed and etch barrier materials the location of the nanocones can be predetermined.

The reaction of the stereoselective addition of aryl- and alkylacetylene derivatives to imines is catalyzed by coper complexes of enantiomerically pure bisimines. The extremely convenient methodology and the possibility of a modular approach for developing more efficient bisimine-based chiral ligands make the methodology very attractive.

A modular approach towards polymer-supported, metalated, salen catalysts is reported. This strategy is based on the synthesis of monofunctionalized Mn- and Co-salen complexes attached to a norbornene monomer via a stable phenylene-acetylene linker.

Quantum chemical methods, based on a second-order perturbation treatment of electron correlation, are used to investigate the cycloaddition reactions of 18 1,3-dipolar molecules to ethylene and acetylene. It is found that the new perturbative B2-PLYP density functional provide accurate reaction barriers and outperforms MP2 and standard density functionals like B3-LYP, also suggesting that properly polarized triple-zeta AO basis sets represent good accuracy and computational speed.

Ab initio calculations of the potential energy surface (PES) for the C(sub 2)(X(super 1)sigma(sub g)(super(+)+CH(sub 3)CCH(X(super 1)A(super 1)) reaction are carried at the G2M level of theory. The calculations also indicate the that C(sub 2)((X(super 1)sigma(sub g)(super(+)+CH(sub 3)CCH(X(super 1)A(super 1)) reaction can proceed by direct H-abstraction of a methyl hydrogen to form C3H3+C2H almost without a barrier.

The reactivity of intermolecular complexes cyanoacetylene:acetylene and dicyanoacetylene:acetylene, trapped in solid argon matrixes at 10K and irradiated with vacuum UV is studied. FTIR measurements, together with (super 2)H, (super 15)N, (super 13)C labeling experiments and with density functional theory (DFT) calculations pointed to the formation of cyanodiacetylene HC(super 5)N (cyanobutadiyne).

A pulsed Laval nozzle apparatus is used for examining the reaction of the C2H radical with benzene at low temperature. Rate coefficients over a temperature range between 105 and 298 K are observed.

A general and practical large-scale synthesis of hydroxyl acids that possess alkenyl and alkynyl appendages are reported. No variation are induced by substitution of only one ethyl group with a vinyl one, although the substitution of both ethyl groups with vinyl or acetylene appendages has the greatest effect on the molecular structure and results in different hydrogen-bonding motifs.

The electronic excited states of the Si(100) surface and acetylene, 9,10-phenanthrenequinone and benzene adsorbed on Si(100) is studied with time-dependent density functional theory. The results show that on clean Si(100), the low-lying excitation corresponds to transitions between the pi orbitals of the silicon-silicon dimers.

The assignment of the pure rotational spectrum of the lowest energy enolic species Enol I of AcAc and all of its singly substituted (super 13)C-isotopologues are presented. It provides strong evidence in support of C(sub 2V) symmetry for the shape of the lowest energy enolic tautomer.

Reduced-dimensionality quantum reactive scattering calculations for the C((super 3)P) + C(sub 2)H(sub 2) reaction are carried out to understand the product branching dynamics of cyclic-C(sub 3)H and linear-C(sub 3)H. The results show that cyclic-C(sub 3)H is preferentially formed through the cyclic-C(sub 3)H(sub 2) intermediate produced by insertion of C((super 3)P) into the CC bond.

A detailed theoretical study is carried out for the unknown HCO/HOC + C(sub 2)H(sub 2) reactions at the CCSD(T)/6-311G(2d,p)//B3LYP/6-311G(d,p)+ZPVE, Gaussian-3//B3LYP/6-31G(d), and Gaussian-3//MP2(full)/6-31G(d) levels. For the HCO/HOC + C(sub 2)H(sub 2) reaction, both the most feasible C-addition channel and the slightly less competitive H-donation channel lead to P(sub 1) C(sub 2)H(sub 3) +CO.