Aromatic End Research Articles

A pseudo-cage complex of silver(I) with tripodal tetraamine having benzyl end groups, [tris[2-(benzylamino)ethyl]amine-kappa 4N]silver(I) perchlorate.

The synthesis and crystal structure of [tris[2-(benzylamino)ethyl]amine-kappa(4)N]silver(I) perchlorate, [Ag(C(27)H(36)N(4))]ClO(4) or [Ag(bz(3)tren)]ClO(4) [bz(3)tren is tris[2-(benzylamino)ethyl]amine or N,N',N''-tribenzyltris(2-aminoethyl)amine] are reported. The Ag atom is coordinated to four N atoms of the tren unit and is located 0.604 (3) A out of the trigonal plane described by the three secondary amine N atoms, away from the bridgehead N atom. Edge-to-face pi-pi interactions between the aromatic end groups, and weak interactions between Ag and arene, allow the formation of a pseudo-cage complex.

The lubricant migration rate on the hard disk surface

The optical surface analyzer (OSA) was found to be an excellent tool to examine the lubricant migration rate on thin film disks. Using the OSA it was found that the rate of lubricant migration increased as molecular weight decreased. An AM type perfluoropolyether with an aromatic end group and Z-Dol were also observed to have different migration rates for the same molecular weight. The migration rate of AM lubricant was increased significantly by the presence of X-1P as an additive in the lubricant system.

Thermally Curing Aryl−Ethynyl End-Capped Imide Oligomers: Study of New Aromatic End Caps

Two new aryl−ethynyl end-cap model compounds, N-phenyl-4-(1-naphthylethynyl)phthalimide (1) and N-phenyl-4-(2-naphthylethynyl)phthalimide (3), were synthesized and characterized. The single-crystal molecular structure of 1 reveals an alternating “head to tail” packing mode whereas the “heads and tails” of 2 are aligned and not alternating. The thermal cure kinetics of 1 and 3 were analyzed using NMR and FT-IR spectroscopy, respectively, and compared to N-phenyl-4-phenylethynylphthalimide (2). In both cases the naphthyl−ethynyl model compounds reacted faster than the phenyl−ethynyl derivative. The end-capped imide oligomers analogues of 1 and 2, NETI-5 and PETI-5, respectively, were synthesized and their thermal cure kinetics were analyzed by DSC. The thermal cure kinetics of 1 and 2 best fit a first-order rate law. Compound 1 cures at faster rates than 2, although the calculated Ea values of 1 and 2 are statistically indistinguishable. The thermal cure kinetics of 2 and 3 also fit a first-order rate law a...

Cyclic diperoxides as sources of radicals for the initiation of the radical polymerization of methyl methacrylate

Thermolysis of cyclic diperoxides gave radicals. When solution polymerization of MMA was initiated by acetone cyclic diperoxide transfer to solvent was the dominant feature of the initiation process. However, transfer in the bulk polymerization of MMA was not a significant feature. Initiation of polymerization of MMA in solution by dibenzyl ketone cyclic diperoxide occurred at lower temperatures, and also aromatic end groups, derived from initiation by benzyl radicals, could be detected by 1H NMR.

Elucidating the Mode of Action of a Corrosion Inhibitor for Iron

Two polymetallic iron(III) complexes 1 and 2 have been synthesised from the known corrosion inhibitor 3-(4-methylbenzoyl)-propionic acid HL1 and their crystal structures determined. Coordination geometries extracted from these structures have been used as the basis for molecular modelling onto idealised iron(III) oxide surfaces as an aid to understanding the efficacy of inhibitors of the 4-keto acid type. The proposed mode of action involves 1,3-bridging didentate coordination of the carboxylate function of L1 to two FeIII ions, hydrogen-bond formation between the 4-keto group of L1 and a bridging surface hydroxy group, as well as close packing of the aromatic end groups, which should generate a hydrophobic barrier on the surface. Adsorption isotherm experiments have been used to compare the strengths of binding of related carboxylic acids onto iron(III) oxide surfaces and indicate that the presence of the 4-keto function leads to the formation of significantly more stable surface complexes.

Elucidating the mode of action of a corrosion inhibitor for iron

Two polymetallic iron(III) complexes 1 and 2 have been synthesised from the known corrosion inhibitor 3-(4-methylbenzoyl)-propionic acid HL1 and their crystal structures determined. Coordination geometries extracted from these structures have been used as the basis for molecular modelling onto idealised iron(III) oxide surfaces as an aid to understanding the efficacy of inhibitors of the 4-keto acid type. The proposed mode of action involves 1,3-bridging didentate coordination of the carboxylate function of L1 to two FeIII ions, hydrogen-bond formation between the 4-keto group of L1 and a bridging surface hydroxy group, as well as close packing of the aromatic end groups, which should generate a hydrophobic barrier on the surface. Adsorption isotherm experiments have been used to compare the strengths of binding of related carboxylic acids onto iron(III) oxide surfaces and indicate that the presence of the 4-keto function leads to the formation of significantly more stable surface complexes.

Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2‐dichloroethane

Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2‐dichloroethane

Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2-dichloroethane

Synthesis of podands bearing aromatic end groups and complex formation with tropylium tetrafluoroborate in 1,2-dichloroethane

Functional analysis of genes from Streptomyces griseus involved in the synthesis of isorenieratene, a carotenoid with aromatic end groups, revealed a novel type of carotenoid desaturase

The biosynthesis of the aromatic carotene isorenieratene is restricted to green photosynthetic bacteria and a few actinomycetes. Among them Streptomyces griseus has been used to study the genes involved in this pathway. Five genes out of seven of two adjacent operons in one cluster could be identified to be sufficient for the synthesis of isorenieratene. Stepwise deletions of these genes demonstrated their participation in phytoene synthesis, phytoene desaturation and lycopene cyclization. The novel gene crtU was assigned to encode a unique desaturase responsible for the conversion of β-carotene via β-isorenieratene to isorenieratene by a desaturation/methyltransferation mechanism. Sequence analysis of crtU revealed two conserved regions, one at the N-terminus and the other at the C-terminus of the protein which is universal to different types of carotene desaturases. In addition, the sequence comprises a motif typically found in methyltransferases. The deletion of the two remaining genes of the cluster left the carotenoid biosynthetic pathway unaffected.

Silver(I)-selective membrane electrodes based on sulfur-containing podands

Some podands, acyclic polyethers, were utilized as membrane active components to prepare Ag +-selective polymeric membrane electrodes. The thiapodand-based electrodes exhibited considerable selectivity toward Ag + over other heavy metal ions including Cd 2+, Pb 2+, Cu 2+ and Hg 2+. Also, good selectivity over alkali and alkali earth metal ions were observed. Response slopes, pH effects, response time, and signal baseline return of the sensor systems were studied in static mode and/or in a flow-injection system. The Ag +-selectivity was explained by the soft-soft interaction of the Ag + ion with the sulfur donor atoms as well as the stacking interaction between aromatic end groups of the host molecule on complexation.

Structure of Styrene and Acrylate Block Copolymers

Abstract Using UV light as the energy source and polystyrene- (PS-) or polymethyl methacrylate- (PMMA-) macroinitiators with active aromatic or aliphatic thiyl end groups, PS-PMMA and PMMA-PEA (poly-ethyl acrylate) block copolymers were synthesized. The molecular weights of both block copolymers increased with increasing reaction time. The reactivity of macroinitiators depended on the type of thiyl groups and monomer and not on the length of the polymer chain. The most reactive were macroinitiators containing resonance stabilized non-substituted or substituted aromatic end groups. The decomposition of the macroinitiators took place over the formation of the thiyl radical and macroradical. The bond length, the bond dissociation energy, and the bond order of macroradical end groups were calculated. The most reactive monomer was ethyl acrylate; the less reactive was styrene. The structure, the molecular weight, and the T g of the styrene-acrylate block copolymers were determined. The PMMA/PEA block copolymer had two of block's T g s, the first at 105°C, the second at −24°C, and a third at 16°C which probably represents contacting segments.

Structural Investigation of a Self-Assembled Monolayer of a p-Nitroanilino-Terminated Thiol

Monolayers of an end-group-modified thiol, 4-(12-mercaptododecyl)aminonitrobenzene (p-NO2−C6H4−NH(CH2)12SH) formed by self-assembly on Au substrates, were investigated by grazing-incidence reflection absorption infrared spectroscopy (IRRAS), X-ray photoelectron spectroscopy (XPS), near-edge X-ray absorption fine structure spectroscopy (NEXAFS), and contact angle measurements. The monolayer exhibits a packing of the alkyl chains which is 10−20% less dense compared to a monolayer of docosanethiol. The orientation of the aromatic end group was determined completely by a combination of IRRAS and NEXAFS. The 1,4-axis of the benzene ring is inclined to 52° with respect to the surface normal, and the plane of the benzene ring is rotated by 58° away from the plane defined by the 1,4-axis and the surface normal. No hydrogen bonding between the p-nitroaniline moieties is detected. The hydrocarbon chains do not show a preferred orientation. The film is described by a layered structure consisting of a layer of alkane...

Synthetic Modification of the Escherichia coli Chromosome: Enhancing the Biocatalytic Conversion of Glucose into Aromatic Chemicals

The yield of l-phenylalanine, racemic phenyllactic acid, and prephenic acid synthesized from glucose has been doubled and contamination of these aromatic end products by biosynthetic intermediates drastically reduced. These improvements resulted from increasing the in vivo catalytic activity of specific enzymes in the common pathway of aromatic amino acid biosynthesis by chromosomal modification of Escherichia coli. The centerpiece of these changes was the synthesis of a multigene cassette carrying aroA (encoding EPSP synthase), aroC (encoding chorismate synthase), and aroB (encoding DHQ synthase). Chromosomal insertion of the synthesized multigene cassette into E. coli KAD29B, a strain having a mutation in the tyrR locus which relieves transcriptional repression of aroL (encoding shikimate kinase), resulted in biocatalysts KAD1D and KAD11D. Improved catalytic activities of individual common pathway enzymes have previously been accomplished with extrachromosomal plasmids encoding the appropriate loci. By ...

Conformational analysis of dolastatin 10: An nmr and theoretical approach

A solution conformational analysis of dolastatin 10, a powerful antineoplastic agent, has been carried out by means of nmr techniques and theoretical calculations. 1H mono- and bidimensional nmr experiments, as well as 1H-13C heterocorrelated spectra, have been performed on CD2Cl2 solutions. The most interesting nmr data is a huge shielding of the aCH(25) proton of the Dov residue, suggesting the presence of an interaction between the N-terminal and the aromatic C-terminal ends of the molecule. The possibility of a head-to-tail intermolecular association having been discarded, the presence of a series of preferred folded conformation has been hypothesized. Conformational theoretical analysis supports the nmr hypothesis of a folded peptide-like molecule, and a series of possible conformers in good agreement with the experimental data have been analyzed.

Synthesis and characterization of aromatic amine functional semicrystalline aryl ether ketone macromers

AbstractFrom earlier experiments it was observed that the reactions of aryl fluoride functional aryl ether ketone oligomers (PEK) with m‐aminophenol lead to poor levels of amine incorporation because of side‐reactions. In this article, a method is presented to protect the m‐aminophenol by converting it into a triarylimine group. This protected m‐aminophenol was used together with 4‐fluoro,4′‐hydroxybenzophenone in a typical poly(aryl ether) synthesis. PEKs of different molecular weights were synthesized with number average molecular weights \documentclass{article}\pagestyle{empty}\begin{document}$\overline {M}_n$\end{document}) of 2600, 4500, and 5400 g/mol. The deprotection of the triarylimine chain end was carried out by an acid treatment to afford a monofunctional aromatic amine end group, amenable towards copolymerization. © 1995 John Wiley & Sons, Inc.

Aromatic amino acid biosynthesis in the yeast Saccharomyces cerevisiae: a model system for the regulation of a eukaryotic biosynthetic pathway

This review focuses on the gene-enzyme relationships and the regulation of different levels of the aromatic amino acid biosynthetic pathway in a simple eukaryotic system, the unicellular yeast Saccharomyces cerevisiae. Most reactions of this branched pathway are common to all organisms which are able to synthesize tryptophan, phenylalanine, and tyrosine. The current knowledge about the two main control mechanisms of the yeast aromatic amino acid biosynthesis is reviewed. (i) At the transcriptional level, most structural genes are regulated by the transcriptional activator GCN4, the regulator of the general amino acid control network, which couples transcriptional derepression to amino acid starvation of numerous structural genes in multiple amino acid biosynthetic pathways. (ii) At the enzyme level, the carbon flow is controlled mainly by modulating the enzyme activities at the first step of the pathway and at the branch points by feedback action of the three aromatic amino acid end products. Implications of these findings for the relationship of S. cerevisiae to prokaryotic as well as to higher eukaryotic organisms and for general regulatory mechanisms occurring in a living cell such as initiation of transcription, enzyme regulation, and the regulation of a metabolic branch point are discussed.

Aromatic amino acid biosynthesis in the yeast Saccharomyces cerevisiae: a model system for the regulation of a eukaryotic biosynthetic pathway.

This review focuses on the gene-enzyme relationships and the regulation of different levels of the aromatic amino acid biosynthetic pathway in a simple eukaryotic system, the unicellular yeast Saccharomyces cerevisiae. Most reactions of this branched pathway are common to all organisms which are able to synthesize tryptophan, phenylalanine, and tyrosine. The current knowledge about the two main control mechanisms of the yeast aromatic amino acid biosynthesis is reviewed. (i) At the transcriptional level, most structural genes are regulated by the transcriptional activator GCN4, the regulator of the general amino acid control network, which couples transcriptional derepression to amino acid starvation of numerous structural genes in multiple amino acid biosynthetic pathways. (ii) At the enzyme level, the carbon flow is controlled mainly by modulating the enzyme activities at the first step of the pathway and at the branch points by feedback action of the three aromatic amino acid end products. Implications of these findings for the relationship of S. cerevisiae to prokaryotic as well as to higher eukaryotic organisms and for general regulatory mechanisms occurring in a living cell such as initiation of transcription, enzyme regulation, and the regulation of a metabolic branch point are discussed.

End Groups of Poly(methyl methacrylate) as a Function of Molecular Weight Determined by Pyrolysis-Gas Chromatography

Abstract End groups of poly(methyl methacrylate) (PMMA) radically polymerized with benzoyl peroxide (initiator) in toluene solution were investigated by pyrolysis gas chromatography as a function of molecular weight. The number-average molecular weights (\barMn) of fractionated PMMA samples were estimated from the relative peak intensities of characteristic pyrolysis products and were compared with those determined by size exclusion chromatography. The observed result suggested that the chain transfer reactions to the monomer might yield relatively smaller PMMA molecules. Furthermore, the relative peak intensities among aromatic products which reflect three kinds of aromatic chain ends were correlated to the (\barMn) of the fractionated PMMAs. The result suggested that the chain transfer reaction to the solvent also tended to yield relatively smaller PMMA molecules whereas the polymerization initiated by the phenyl radical from the initiator yielded relatively larger PMMA molecules under given polymerization conditions.

Effects of cyclodextrins on the fluorescence of Europium ion-diketone complexes

The thermodynamics of the complexation of cyclodextrins (CDs) to naphthyl, phenyl and thienyl subtituted 1,3-diketones, used as sensitizers in time-resolved fluorescence analysis of lanthanides, was studied by gel chromatography. The complexation occurs predominantly at the aromatic end of the diketones with a strength comparable to related aromatic compounds. The effects of CDs on the fluorescence of an europium (III) ion with diketones in an aqueous solution were tested for their applicability in time-resolved fluorescence analysis.

13C relaxation studies of the structure and flexibility of the carboxylic ionophore lasalocid A

Carbon-13 spin lattice relaxation times (T1) were determined for all the protonated carbon atoms of the carboxylic ionophore lasalocid A in non-hydroxylic (CDCl3) and hydroxylic (CD3OD) media. In CDCl3, the motions of the protonated backbone carbon atoms C-4 to C-24 (inclusive) are all equally restricted. The correlation time for overall molecular reorientation, τeff, calculated from an average NT1 value of 565 ms, is 8.6 × 10–11 s, where N is the number of attached protons. The carbon atoms in the side chains are more mobile than those in the backbone. The carbon backbone in CD3OD is characterized by segmental motion at the aromatic end, as evidenced by increased NT1, values for C-4, C-5, C-7, and C-8. The reminder of the backbone appears to be rigid and to have a τeff virtually identical with that observed for the entire backbone in CDCl3. These results are discussed in terms of the mechanism that has been proposed for ion complexation and transport by carboxylic ionophores in biomembranes.