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At least 649 records · Page 36Linked to original sources
PubMed2000

Tuning of photo- and electroluminescence of new soluble, PPV-analogous short-chain compounds with naphthalene moieties

A series of oligomers analogous to poly(p-phenylenevinylene) (PPV), combining naphthalene and benzene as aromatic units, have been synthesized by a Knoevenagel reaction. By measuring UV/Vis spectra, photoluminescence (PL) and electroluminescence (EL), we studied the influence of the position of the naphthalene unit as well as the steric and electronic influences of cyano and alkyloxy substituents on the luminescent properties of these compounds.

Journal Article↗
PubMed2001

Direct measurements of the enthalpy of solution of solid solute in supercritical fluids: study on the CO2-naphthalene system.

A setup for a calorimeter for simultaneously measuring the solubility and the solution enthalpy of solid solutes in supercritical fluids (SCFs) has been established. The enthalpy of solution of naphthalene in supercritical CO2 was measured at 308.15 K in the pressure range from 8.0-11.0 MPa. It was found that the enthalpy of solution (deltaH) was negative in the pressure range from 8.0 to 9.5 MPa, and the absolute value decreased with increasing pressure. In this pressure range, the dissolution of the solute was enthalpy driven. However, the deltaH became positive at pressures higher than 9.5 MPa, and the dissolution was entropy driven. Monte Carlo simulation was performed to analyze the local structural environment of the solvated naphthalene molecules in supercritical CO2 under the experimental conditions for the calorimetric measurements. By combining the enthalpy data and the simulation results, it can be deduced that the energy level of CO2 in the high compressible region is higher than that at higher pressures, which results in the large negative enthalpy of solution and the larger degree of solvent-solute clustering in the high compressible region.

Journal Article↗
PubMed2002

1,8-bis(tetramethylguanidino)naphthalene (TMGN): a new, superbasic and kinetically active "proton sponge".

1,8-Bis(tetramethylguanidino)naphthalene (TMGN, 1) is a new, readily accessible, and stable "proton sponge" with an experimental pK(BH(+)) value of 25.1 in MeCN, which is nearly seven orders of magnitude higher in basicity than the classical proton sponge 1,8-bis(dimethylamino)-naphthalene (DMAN). Because of the sterically less crowded character of the proton-accepting sp(2)-nitrogen atoms, TMGN also has a higher kinetic basicity than DMAN, which is shown by time-resolved proton self-exchange reactions. TMGN is more resistant to hydrolysis and is a weaker nucleophile towards the alkylating agent EtI in comparison to the commercially available guanidine 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene (MTBD). Crystal structures of the free base, of the mono- and bisprotonated base were determined. The dynamic behavior of all three species in solution was investigated by variable-temperature (1)H NMR experiments. DeltaG (++) values obtained by spectra simulation reveal a concerted mechanism of rotation about the C-N bonds of the protonated forms of TMGN.

Journal Article↗
PubMed2002

Core-substituted naphthalene bisimides: new fluorophors with tunable emission wavelength for FRET studies.

Highly colored and photoluminescent naphthalene bisimide dyes have been synthesized from 2,6-dichloronaphthalene bisanhydride 1 by means of a stepwise nucleophilic displacement of the two chlorine atoms by alkoxides and/or alkyl amines. The alkoxy-substituted derivatives are yellow dyes with green emission and low photoluminescence quantum yields, whereas the amine-substituted derivatives exhibit a color range from red to blue with strong photoluminescence up to 76%. Structure-property relationships for this class of two-dimensional chromophores were evaluated based on a single-crystal X-ray analysis for dye 5a, the observed solvatochromism, and quantum-chemical calculations. Owing to the simple tuning of the absorption properties over the whole visible range by the respective substituents, the pronounced brilliancy, and the intense photoluminescence, this class of dyes is considered to be highly suited for numerous applications such as fluorescent labeling of biomacromolecules and light-harvesting in supramolecular assemblies. As an important step towards such applications efficient FRET (fluorescence resonance energy transfer) has been demonstrated for a covalently tethered bichromophoric compound that contains a red and a blue naphthalene bisimide dye.

Journal Article↗
PubMed2003

Cyclization triggered by deprotonation: the gas-phase acidity of 1,8-chalcogen-bridged naphthalenes.

High-level density functional theory computations have been used to estimate the gas-phase (intrinsic) acidities of the complete series of 1,8-chalcogen-bridged naphthalene derivatives. The existence of a chalcogen-chalcogen bond in chalcogen-bridged naphthalene derivatives plays a crucial role in the intrinsic acidity of the system. For 1,8-naphthalenedilylbis(oxy), where this bond does not exist, the para C-H group is the most acidic site, whereas for the remaining compounds, deprotonation of the ortho CH groups is the most favorable process. Deprotonation of the aromatic rings has a large effect on the strength of the bonds of the five-membered ring. These effects depend on the nature of the heteroatoms forming the X-Y bridge, and modulate the acidity of the molecule. Also importantly, when one of the heteroatoms is oxygen, ortho and para deprotonation lead to cleavage of the X-Y bridge. This bond fission favors the formation of a CYC (Y = S, Se, Te) three-membered ring that enhances the stability of the anion and, therefore, increases the acidity of these compounds. We have shown that, whereas this cyclization process is energetically favorable for oxygen-containing compounds, it is not favorable for the remaining derivatives.

Journal Article↗
PubMed2004

Genes similar to naphthalene dioxygenase genes in trifluralin-degrading bacteria.

Trifluralin (alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) is a dinitroaniline compound which was first produced in the 1960s and has been used extensively as an agricultural herbicide. There are a few publications on the biodegradation of this xenobiotic compound, but to our knowledge nothing has been documented on the genetic aspects of its catabolism. In this article, we report the analysis of DNA isolated from bacteria previously shown to degrade trifluralin, using as probes the catabolic genes ndoB, todC, xyIX, catA and xyIE which encode the enzymes naphthalene 1,2-dioxygenase, toluene dioxygenase, toluate 1,2-dioxygenase, catechol 1,2-dioxygenase and catechol 2,3-dioxygenase respectively. Using PCR and hybridization analysis, the strong hybridization of the ndoB gene with DNA extracted from four trifluralin-degrading isolates was demonstrated, although none of them was able to degrade naphthalene, as indicated by the 'clear zone' test. The results indicated the presence in these bacteria of a dioxygenase gene, whose product could act on trifluralin as its principal substrate, or fortuitously, by cometabolism. This is the first publication on genes in trifluralin-degrading bacteria.

Bacillus megaterium↗
PubMed2001

Micellar Effects on S(N)2 Reactions of Alkyl Naphthalene-2-sulfonates:The Role of Hydrophobic Substituents.

Reactivities of methyl naphthalene-2-sulfonate, MeONs, and its 6-alkyl derivatives, alkyl=Me, n-C(6)H(13) and n-C(12)H(25), 6-Me-MeONs, 6-Hex-MeONs, and 6-Do-MeONs, respectively, are compared for reactions in cetyl trialkylammonium bromide micelles, n-C(16)H(33)NR(3)Br, R=Me, Et, n-Pr, n-Bu, CTABr, CTEABr, CTPABr, CTBABr, respectively. Similar experiments were made on reactions of Br(-) with n-butyl and n-decyl naphthalene-2-sulfonates, BuONs, and DeONs, respectively. Reactions with OH(-) were followed in cetyl trialkylammonium hydroxide, alkyl=Me, Et, n-Pr, CTAOH, CTEAOH, and CTPAOH, solubility permitting. Some reactions with OH(-) or Br(-) were also followed in mixed-ion systems of CTAOMs or CTPAOMs (OMs=MeSO(3)). Micellar rate effects were analyzed by using pseudophase treatments including interionic competition in mixed-ion systems. Second-order rate constants in the micellar pseudophase increase systematically with increases in substrate hydrophobicity and for reactions with Br(-), but not OH(-), they also increase with bulk of the cationic head group. Copyright 2001 Academic Press.

Journal Article↗
PubMed1996

Choice of microbial host for the naphthalene dioxygenase bioconversion.

The use of whole cell biotransformations for single and multistep enzyme conversions is gaining widespread application. In this study the naphthalene dioxygenase nah A gene was transferred into Pseudomonas aeruginosa PAC 1R, Escherichia coli JM107 and Pseudomonas putida PpG 277. The effect of ethanol on these genetically engineered Gram-negative bacteria was studied by measurement of enzyme activity, stability and cell integrity. Ethanol has been used in biotransformations as a co-substrate carbon source for co-factor recycling and as a co-solvent increasing dissolved substrate and product levels. Ethanol increased the dissolved substrate (naphthalene) concentration slightly and dissolved product ((+)-cis-(1R,2S)-dihydroxy-1,2-dihydronaphthalene) by approximately 30% at 4% (w/v) ethanol. Both P. aeruginosa PAC 1R and P. putida PpG 277 showed decreased activity with increasing ethanol concentration whilst E. coli enzyme activity increased with increasing ethanol concentration being comparable to that when glucose was used as a carbon source. This project highlighted the many factors involved in the selection of microbial hosts for whole cell biotransformation processes.

Biotransformation↗
PubMed2005

Column preconcentration of gold by adsorbing AuCl4- onto methyltrioctyl ammonium chloride-naphthalene and subsequent atomic absorption spectrometric determination.

A sensitive, selective and simple preconcentration method for ultra-trace gold determination has been developed that uses naphthalene-methyltrioctyl ammonium chloride (Aliquat 336s) as an adsorbent. Gold, in the form of AuCl4-, was retained by the adsorbent in the column at a flow rate of 1 ml min(-1). After filtration, the solid mass consisting of the gold complex and naphthalene was dissolved out of the column with 5 ml of N,N-dimethylformamide (DMF), and the metal was then determined by atomic absorption spectrometry. In the initial solution, the calibration graph of absorbance versus gold concentration was found to be linear in the range 0.5-150 ng ml(-1) Au(III) with r=0.997 (n=9), and the 3 s detection limit was 0.428 ng ml(-1). The relative standard deviation for eight replicate measurements of 20 microg of gold was 2.14%. Preconcentration factors of 390 and 650 were achieved using 5 ml and 3 ml of DMF, respectively. The proposed method was successfully applied to the determination of gold in wastewater, processed pool water, slurry pool water, and raw well-water from the Moteh gold mine, and synthetic samples.

Journal Article↗
PubMed1997

Distribution of Polychlorinated Naphthalene Congeners inEnvironmental and Source-Related Samples

Polychlorinated naphthalene (CN) congener profiles inenvironmental and source related samples were compared graphically and byprincipal component analysis. Samples investigated included biological,sediment, water, and air samples, technical polychlorinated biphenyl (PCB)and polychlorinated naphthalene (PCN) formulations, as well as municipalwaste incineration (MWI) fly ash and graphite electrode sludge. Biologicalsamples showed a preferential enrichment of planar, 1,3,5,7-substitutedtetra-, penta-, and hexachlorinated congeners and most of these samplesshowed profiles that displayed some similarity to those found in thetechnical PCB formulations. Sediment samples representing diffuse pollution,i.e., sediment samples from remote sites, showed an elevatedabundance of the planar hexa- and heptaCN congeners(1,2,3,4,6,7-/1,2,3,5,6,7- and 1,2,3,4,5,6,7-). The CN congener profile foundin these sediment samples and the two air samples were more similar to thetechnical PCB formulations than to the investigated MWI and graphite sludgesamples. Samples from three PCB contaminated lakes displayed similar congenerprofiles as Aroclor 1242, 1254 and Clophen A40. Two sediment samples and apike sample collected from the vicinity of a chloroalkali plant showedprofiles that were closely related to the investigated graphite electrodesludge sample. None of the environmental samples displayed profiles similarto low or medium chlorinated technical PCN (Halowax 1099, 1013, and 1014).

Journal Article↗
PubMed2003

Naphtho[1,2- b]thiophene degradation by Pseudomonas sp. HKT554: involvement of naphthalene dioxygenase.

Pseudomonas sp. strain HKT554 degrades naphtho[1,2- b]thiophene and two other isomers, naphtho[2,1- b]thiophene and naphtho[2,3- b]thiophene, by cometabolism, in the absence of any specific inducer, at similar degradation rates. A mutant of strain HKT554, deficient in dibenzothiophene degradation, was generated by using a recently developed transposition system. Sequence analysis of the mutant revealed that the knocked out gene was almost identical to naphthalene dioxygenase (EC 1.14.12.12). The mutant, HKT554M, degraded neither the naphthothiophene isomers nor dibenzothiophene, suggesting that the naphthalene dioxygenase is responsible for the initial catabolic reactions onto naphthothiophenes and dibenzothiophene.

Biodegradation, Environmental↗
PubMed1993

Sequences of genes encoding naphthalene dioxygenase in Pseudomonas putida strains G7 and NCIB 9816-4.

The multicomponent enzyme, naphthalene dioxygenase, initiates the metabolism of naphthalene by Pseudomonas putida strains G7 (PpG7) and NCIB 9816-4 (Pp9816-4). The genes involved (nahAaAbAcAd) are encoded by the NAH7 and pDTG1 plasmids, respectively, and form part of the nah operon. The locations of the structural genes were determined on previously cloned fragments of DNA. The nucleotide (nt) sequences were determined for nahAaAb from Pp9816-4 and for nahAaAbAcAd from PpG7. The appropriate open reading frames were identified using N-terminal amino acid sequences determined from the purified proteins. The two nt sequences showed 93% homology, with the least homology seen upstream from the promoter region.

Amino Acid Sequence↗
PubMed1994

Recombinant Escherichia coli strains synthesize active forms of naphthalene dioxygenase and its individual alpha and beta subunits.

Pseudomonas sp. strain NCIB 9816-4 utilizes naphthalene dioxygenase (NDO), a multicomponent enzyme system, to initiate naphthalene degradation. The terminal component of NDO is an iron-sulfur protein (ISPNAP) with an alpha 2 beta 2 subunit composition. The structural genes encoding the alpha (nahAc) and beta (nahAd) subunits were cloned separately and together into expression vectors where transcription is under the control of the T7 promoter. The recombinant plasmids were transformed into Escherichia coli JM109[pGP1-2] and the synthesis of ISPNAP and its alpha and beta subunits was determined by SDS-PAGE. Low expression of nahAd was shown to be due to inefficient initiation of translation, but a sixfold increase in the amount of beta subunit synthesized was achieved in a coupled translation system. Inclusion bodies were found in all recombinants. Increased levels of soluble active proteins were obtained when E. coli JM109(DE3), used as the host strain for recombinant plasmid, was grown at 25 degrees C. ISPNAP from JM109(DE3)[pDTG121] was purified to homogeneity and shown to have the same properties as those determined for the enzyme purified from NCIB 9816-4. Active ISPNAP was also obtained by mixing cell extracts from separate strains that synthesized the alpha and beta subunits. The availability of large amounts of purified ISPNAP and its alpha and beta subunits will facilitate future studies on the mechanism of oxygen fixation by NDO.

Bacterial Proteins↗
PubMed2004

Identification of [(naphthalene-1-carbonyl)-amino]-acetic acid derivatives as nonnucleoside inhibitors of HCV NS5B RNA dependent RNA polymerase.

A novel series of HCV NS5B RNA dependent RNA polymerase inhibitors containing a naphthalene carboxamide scaffold were identified by high throughput screening. Optimization of substituents by parallel synthesis and the iterative design towards understanding structure-activity relationship to improve potency are described. Tetra substituted naphthalene 31 displayed potent activity with IC(50) of 120 nM against HCV NS5B enzyme and was selective over a panel of polymerases.

Acetates↗
PubMed2005

Polychlorinated naphthalenes in air and snow in the Norwegian Arctic: a local source or an Eastern Arctic phenomenon?

PCNs were measured in air and snow during separate field campaigns at Ny-Alesund (April 2001) and Tromsø (February/March 2003) in the Norwegian Arctic. Air concentrations ranged from 27 to 48 and 9 to 47 pg sigmaPCN m(-3) for Ny-Alesund (n=6) and Tromsø (n=10), respectively. These concentrations (including the tri-chlorinated naphthalenes) greatly exceeded concentrations previously measured in the Canadian Arctic, but did fall within the upper range of concentrations observed over the eastern Arctic Ocean and regional seas. Local sources appear to be affecting concentrations observed at both sites, with the presence of several hexa-chlorinated naphthalenes at Tromsø probably attributed to local/regional sources. Use of air mass back trajectories at Tromsø revealed that background air concentrations in the Norwegian Arctic are likely to range between <9 and 20 pg sigmaPCN m(-3) and that contemporary concentrations derived close to potential sources (i.e. arctic towns) may equal or exceed those of PCBs. The mean concentration in surface snow was 350 and 240 pg sigmaPCN L(-1) (meltwater) (or 0.014 and 0.01 pg g(-1) (snow)) at Ny-Alesund and Tromsø, respectively. The wide variation in concentrations observed between fresh snowfalls could be explained by different snow densities (as a surrogate of snow surface area), rather than attributed to varying air concentrations. A statistically significant inverse relationship was found between snow density and concentrations of tri- to penta-chlorinated homologues and compliments similar findings for the polychlorinated biphenyls (PCBs). This suggests that the vapour-sorbed quantity changes rapidly with snow ageing/compaction; with implications for the fate of these chemicals in the Arctic.

Journal Article↗
PubMed1998

Nature of interaction between basic fibroblast growth factor and the antiangiogenic drug 7,7-(Carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino] )bis-(1, 3-naphthalene disulfonate).

PNU145156E (7,7-(carbonyl-bis[imino-N-methyl-4, 2-pyrrolecarbonylimino[N-methyl-4,2-pyrrole]-carbonylimino]) -bis-(1, 3-naphthalene disulfonate)) is a naphthalene sulfonic distamycin A derivative that interacts with heparin-binding growth factors. Because PNU145156E inhibits tumor angiogenesis, it was selected for clinical development. Picosecond time-resolved fluorescence emission and anisotropy were used to characterize the binding of PNU145156E to the basic fibroblast growth factor (a protein associated with tumor angiogenesis). A decrease in PNU145156E fluorescence lifetime was observed as a function of human basic fibroblast growth factor (bFGF) concentration. Nonlinear least-squares fitting of the binding isotherm yielded Kd = 145 nM for a single class of binding sites. Time-resolved anisotropy gave Kd = 174 nM. Kd = 150 nM was independently verified by quantitative high-performance affinity chromatography. The displaced volume of the complex, calculated from its rotational correlation time, fitted a sphere of 1:1 stoichiometry. These results account for the formation of a tight yet reversible PNU145156E:bFGF complex. An evaluation of PNU145156E fluorescence lifetimes in various solvents has highlighted the forces involved in stabilizing the complex. These are mostly electrostatic-hydrophobic in nature, with a relatively low contribution from hydrogen bonding. Both polar and nonpolar groups are involved on the protein-binding site within a largely hydrophobic cleft. A potential binding trajectory, based on a combination of these results with site-directed chemical modification and known bFGF x-ray structure, is suggested.

Binding Sites↗
PubMed1998

Self-association of 8-anilino-1-naphthalene-sulfonate molecules: spectroscopic characterization and application to the investigation of protein folding.

It was suggested long ago that the reason for the considerable increase of 8-anilino-1-naphthalene-sulfonate (8-ANS) fluorescence intensity upon the transition from aqueous to organic solvents is the dissociation of 8-ANS associates. To clarify this point the dependence of spectral properties of the dye on concentration and solvent composition was investigated by means of steady-state and time-resolved fluorescence spectroscopy. It was shown that the increase of 8-ANS concentration leads to the changes in the shape of absorption and fluorescence spectra of the dye, accompanied by the decrease in its fluorescence decay time values. Such changes were observed in aqueous and organic solvents for Mg2+- and NH+4-salts of 8-anilino-1-naphthalene-sulfonateic acid and reflect the existence of self-association of the dye molecules in both media. However, the decrease in fluorescence intensity induced by the self-association of the probe molecules is too small to explain weak fluorescence of 8-ANS in water. At the same time, it expounds the difference between the decay times of protein-embedded 8-ANS molecules upon interaction of this probe with native and molten globule proteins.

Anilino Naphthalenesulfonates↗
PubMed2002

Conformationally restrained analogues of sympathomimetic catecholamines. Synthesis and adrenergic activity of 5,6- and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1(2H)-2',5'-morpholines].

The 5,6- (10a) and 6,7-dihydroxy-3,4-dihydrospiro[naphthalen-1(2H)-)-2',5'-morpholine](11a) and their N-isopropyl derivatives (10b and 11b) (DDSNMs), which can be viewed as the result of the combination of the structure of the 2-(3,4-dihydroxyphenyl)morpholine 5a or 5b (DPMs) with the structure of the corresponding 1-(aminomethyl)-5,6-dihydroxy- (8a or 8b) or 1-(aminomethyl)-6,7-dihydroxy-1,2,3,4-tetrahydro-1-naphthalen-ol (9a or 9b) (1-AMDTNs) were synthesised. The new compounds DDSNMs 10a,b and 11a,b were assayed for their alpha- and beta-adrenergic properties by means of binding experiments and functional tests and the results were compared with those obtained for catecholamines 1a, b and the previously described morpholine (5) and tetrahydronaphthalene (8, 9) derivatives. The affinity and activity indices thus obtained indicate in general a low ability of the new compounds 10 and 11 to interact with the alpha- and beta-adrenoceptors, which, in all cases, was lower than that of the corresponding morpholine (5) and tetrahydronaphthalene (8, 9) analogues.

Adrenergic Agonists↗