Oxygen Analog Research Articles

Synthesis, structural, electrochemical, and photophysical properties of 4,2′‐thiopyrylogens – a novel class of sensitizers for photoinduced electron transfer reactions

AbstractThe first three examples of the thioanalog of the 4,2′‐pyrylogen ring system are reported. The influence of the sulfur atom on the structural, electrochemical, and photophysical behavior of this ring system is discussed. In addition, these 4,2′‐thiopyrylogens are compared to their previously reported 4,4′‐isomers and their 4,4′‐ and 4,2′‐oxygen analogs. Copyright © 2010 John Wiley & Sons, Ltd.

OBSERVATIONS OF THE [HNCS]/[HSCN] RATIO IN Sgr B2 AND TMC-1: EVIDENCE FOR LOW-TEMPERATURE GAS-PHASE CHEMISTRY

Millimeter observations of isothiocyanic acid (HNCS) and its higher energy isomer, thiocyanic acid (HSCN), have been carried out toward Sgr?B2 and TMC-1 using the 12?m telescope of the Arizona Radio Observatory. For both species, the JKa,Kc ?= 80,8?? 70,7 and 90,9?? 80,8 transitions near 91-93?GHz and 103-106?GHz were mapped across a 6'?? 3' region, centered near Sgr?B2(M). Comparative mapping observations were also done for the JKa,Kc ?= 40,4?? 30,3 line of HNCO and HOCN near 84-87?GHz. In addition, the JKa,Kc ?= 70,7?? 60,6 and 80,8?? 70,7 transitions of both HNCS and HSCN were detected in TMC-1, the first identification of either molecule in a cold, dark cloud. Emission from HNCS and HSCN was found to be extended over the Sgr?B2 cloud, with a single velocity component and a linewidth of ~20-25?km?s?1. Column densities derived for HSCN in Sgr?B2 are typically N tot ~ (0.2-1)?? 1013?cm?2, with N tot ~ (0.8-5)?? 1013?cm?2 for the more stable isomer, HNCS. In TMC-1, these species have similar column densities of (6-8)?? 1010?cm?2. The [HNCS]/[HSCN] abundance ratio ranges from 2 to 7 in Sgr?B2, with a value of ~1 in TMC-1. In contrast, the [HNCO]/[HOCN] ratio in Sgr?B2 is ~110-250. Gas-grain chemical models do not reproduce the observed abundances of the sulfur isomers in either source. Given the energy difference of over 3200?K between HNCS and HSCN, these observations suggest that both molecules are produced from gas-phase, ion-molecule chemistry with a common precursor, HNCSH+. The oxygen analogs, in contrast, probably have a more complex chemical network, perhaps involving the H2NCO+ precursor, which preferentially leads to HNCO.

Surface‐enhanced Raman spectra of dimethoate and omethoate

AbstractSurface‐enhanced Raman scattering (SERS) spectra are presented and analyzed for two important organophosphate pesticides, dimethoate (DMT) and omethoate (OMT). Very detailed SERS spectra were obtained by aggregated Ag hydrosols, both in aqueous suspension and dried on a glass substrate. The SERS and ordinary Raman spectra of DMT do not resemble each other, suggesting that a chemical reaction immediately occurs when DMT is adsorbed onto the metal surface. We propose that the reaction product is OMT, which is the oxygen analog of DMT, on the basis of the Raman and SERS spectra of OMT. Further support is derived from the calculated Raman spectra of DMT and OMT. Minor wavenumber and intensity differences that are observed between the SERS spectra of DMT reaction product and those of OMT could be related to different metal/adsorbate interaction modes. The results can be useful in the development of new analytical methods for the determination of pesticide residues in food. Copyright © 2010 John Wiley & Sons, Ltd.

Nickel(II) and copper(II) complexes of Schiff base ligands containing N 4O 2 and N 4S 2 donors with pyrrole terminal binding groups: Synthesis, characterization, X-ray structures, DFT and electrochemical studies

A series of hexadentate ligands, H 2L m ( m = 1−4), [1 H-pyrrol-2-ylmethylene]{2-[2-(2-{[1 H-pyrrol-2-ylmethylene]amino}phenoxy)ethoxy]phenyl}amine (H 2L 1), [1 H-pyrrol-2-ylmethylene]{2-[4-(2-{[1 H-pyrrol-2-ylmethylene]amino}phenoxy)butoxy]phenyl}amine (H 2L 2), [1 H-pyrrol-2-ylmethylene][2-({2-[(2-{[1 H-pyrrol-2-ylmethylene]amino}phenyl)thio]ethyl}thio)phenyl]amine (H 2L 3) and [1 H-pyrrol-2-ylmethylene][2-({4-[(2-{[1 H-pyrrol-2-lmethylene]amino}phenyl)thio]butyl}thio) phenyl]amine (H 2L 4) were prepared by condensation reaction of pyrrol-2-carboxaldehyde with {2-[2-(2-aminophenoxy)ethoxy]phenyl}amine, {2-[4-(2-aminophenoxy)butoxy]phenyl}amine, [2-({2-[(2-aminophenyl)thio]ethyl}thio)phenyl]amine and [2-({4-[(2-aminophenyl)thio]butyl}thio)phenyl]amine respectively. Reaction of these ligands with nickel(II) and copper(II) acetate gave complexes of the form ML m ( m = 1−4), and the synthesized ligands and their complexes have been characterized by a variety of physico-chemical techniques. The solid and solution states investigations show that the complexes are neutral. The molecular structures of NiL 3 and CuL 2, which have been determined by single crystal X-ray diffraction, indicate that the NiL 3 complex has a distorted octahedral coordination environment around the metal while the CuL 2 complex has a seesaw coordination geometry. DFT calculations were used to analyse the electronic structure and simulation of the electronic absorption spectrum of the CuL 2 complex using TDDFT gives results that are consistent with the measured spectroscopic behavior of the complex. Cyclic voltammetry indicates that all copper complexes are electrochemically inactive but the nickel complexes with softer thioethers are more easily oxidized than their oxygen analogs.

Discovery, Structure, and Anticancer Activity of an Iridium Complex of Diselenobenzoquinone

Caught in the act: The first stable η4-diseleno-p-benzoquinone complex, [Cp*lr(η4-C6H4Se2)], has been isolated. The X-ray structure confirms the coordination of the elusive diselenobenzoquinone intermediate. The anticancer activity of this complex was compared to related oxygen and sulfur analogs; only the diseleno complex was cytotoxic, having a comparable activity to cisplatin.

Theoretical Study of Bond-Switching in 1,6-Dihydro-6a-thia-1,6-diazapentalene (10-S-3) Systems Compared with Corresponding Oxygen Analogues

Abstract Theoretical study of the mechanism of bond-switching of 5-(1-aminoethylimino)-3-methyl-1,2,4-thiadiazole and 5-(2-aminovinyl)isothiazole was carried out by using simplified models of 1,6-dihydro-6a-thia-1,6-diazapentalene (10-S-3) systems and corresponding oxygen analogs. Geometries and energetics were examined along unimolecular and bimolecular reaction paths by hybrid density functional theory (DFT) calculations with triple-zeta class basis sets by taking into account solvent effects which is estimated by the polarizable continuum model. It was clarified that the unimolecular reactions cannot proceed due to the high energy barriers around 70 kcal mol−1. On the other hand, the bimolecular processes in neutral and acidic conditions can be accomplished for the sulfur compounds, not for the oxygen ones. The differences of the reactivities between the sulfur and oxygen compounds were found to be due to the difference of the stability of the symmetric intermediates with the hypervalent three-center four-electron bonds.

Assessing the Role of Poly(ethylene glycol-bl-propylene sulfide) (PEG-PPS) Block Copolymers in the Preparation of Carbon Nanotube Biocompatible Dispersions

Amphiphilic block copolymers based on hydrophobic polysulfides (poly(propylene sulfide), PPS) and hydrophilic polyethers (poly(ethylene glycol), PEG) have been used to solubilize and disperse single-walled carbon nanotubes (SWNTs). The obtained highly concentrated aqueous dispersions are stable for months. The factors that affect the dispersant activity of the studied block copolymers have been characterized, and comparisons with the much more investigated oxygen analogues (Pluronics) are reported. The biocompatibility and the stability after dilution of the most representative suspensions have been investigated as prospective drug carriers.

1,7-dithioxo-substituted systems. Synthesis, structure, and photoconductivity of bis(5,5-dimethyl-3-hydrazonocyclohex-1-enyl) sulfide

Bis(5,5-dimethyl-3-hydrazonocyclohex-1-enyl) sulfide was synthesized by the reaction of bis(5,5-dimethyl-3-thioxocyclohex-1-enyl) sulfide or its oxygen analog with hydrazine. Conformational lability of the molecule of dihydrazone was studied by the DFT(B3LYP) method using expanded basis sets 6–311G and 6–11G(d,p). Analysis of vibration IR and Raman spectra of the most stable conformers of the isolated molecule of dihydrazone was performed at the harmonic approximation. Using the Onsager SCRF solvation model the absence of solvent effect on the relative stability of the conformers was shown. The photoconductivity of dihydrazone was studied. Low value of the ratio of photocurrent to dark current (Jp/Jd = 2.5–3.5) for dyhydrazone was assigned to the lability of its stereoelectronic structure, which was in line with the data of 1H, 13C, and 15N NMR spectra.

Analysis of oxidation byproducts of dyfonate in various oxidant systems using high performance liquid chromatography coupled with quadrupole ion trap mass spectrometry

Dyfonate is a dithiophosphonate pesticide used to control lepidopterous insects in corn, potatoes, and peanuts. It may be transferred to the surface water and underground water system and can be degraded by free chlorine and other oxidants, which are used by water treatment plants during the disinfection process, to produce oxidation byproducts. These byproducts may be more toxic than their parent compounds. Therefore, it is crucially important to identify these byproducts during the water treatment for full scale removal of them. In this article, a high pressure liquid chromatography/mass spectrometry (HPLC/MS) method was developed to investigate the oxidation byproducts of dyfonate by free chlorine (Cl2), hydrogen peroxide (H2O2), monochloroamine (MCA), chlorine dioxide (ClO2), Ozone (O3), and permanganate in an aqueous buffer (pH 7). Thin layer chromatography (TLC) and nuclear magnetic resonance (NMR) were also used for structure confirmation of the byproduct that was identified through HPLC/MS. One byproduct, dyfonate oxygen analog (phosphonothioic acid) was identified as the primary oxidation byproduct for free chlorine, ozone, MCA, and the H2O2 system, while no oxidation byproduct was detected in the ClO2 and permanganate system. The results of this study can serve as a valuable reference for water treatment plants.

Modeling the overall persistence and environmental mobility of sulfur-containing polychlorinated organic compounds

Experimental data on partition coefficients and environmental half-lives of sulfur analogs of polychlorinated organic compounds are scarce. Consequently, little is known about their overall persistence and long-range transport potential, which are the most vital measures in the environmental exposure assessment. We performed Multimedia Modeling of environmental fate and transport to complement this paucity of scientific data. The main aim of our study was to investigate whether the sulfur analogs of polychlorinated dibenzo-p-dioxins, -dibenzofurans, and -diphenylethers are as environmentally persistent and/or mobile as their oxygen counterparts and to propose the environmental exposure-related classification of the examined sulfur compounds. Our study included all possible congeners of the sulfur analogs generated in a combinatorial approach. We predicted (1) lacking data on partition coefficients (log K OW, log K OA and log K AW) for oxygen and sulfur analogs using Quantitative Structure-Property Relationship (QSPR) modeling and (2) their half-lives in air, water, and soil using US EPA tool 'The PBT Profiler, v. 1.203 2006'. Subsequently, we introduced these results into multimedia mass balance model 'The OECD POV and LRTP Screening Tool, v. 2.2'. Our study revealed that log K OW and log K OA are increasing by constant values of 0.60 and 1.07, respectively, and the values of log K AW are decreasing by 0.90, whenever one oxygen atom in the carbon skeleton is replaced by sulfur. The persistence ranking performed by the PBT Profiler showed that PCDDs, PCDFs, PCDEs, and their sulfur analogs belong to one half-life class. The Multimedia Modeling by the means of 'The OECD POV and LRTP Screening Tool, v. 2.2' suggested that the long-range transport potential depends on the presence/absence of oxygen/sulfur atoms in particular molecules, their substitution pattern and the parent carbon skeleton. Sulfur analogs are generally less mobile than their oxygen analogs, but have similar overall persistence and much higher bioaccumulation potential. Thus, according to the classification of chemicals proposed by Klasmeier et al. (Environ Sci Technol 40:53-60, 2006), some of them show POP-like POV and LRTP characteristics while the rest shows POP-like P OV characteristics. The sulfur analogs of PCDDs, PCDFs, or PCDEs bring environmental mobility comparable with the risk related to the oxygen ones; they belong to the pollutants of 'highest' or 'intermediate' priority. Further studies that would verify the necessity to include the studied sulfur molecules in the international lists of high-priority environmental pollutants are recommended.

Conformational energetics and low-frequency vibrations of cyclohexene and its oxygen analogs

Ab initio and DFT calculations with MP2/cc-pVTZ and B3LYP/cc-pVTZ basis sets have been carried out for cyclohexene and four of its oxygen analogs. All of the molecules possess a twisted structure while the bent forms represent saddle points in two-dimensional surfaces. The structures, relative energies, and frequencies for the lowest energy vibrations of the twisted, bent, and planar forms were calculated and compared to experimental results. The calculated results agree very well with the microwave data but the computed barriers are somewhat less than those based on low-frequency infrared data.

Hg 2+-selective fluorogenic chemodosimeter based on naphthoflavone

A new Hg 2+-selective chemodosimeter based on α-naphthoflavone was investigated. The chemodosimetric behavior is based on the Hg 2+-triggered desulfurization of flavothione into its oxygen analogue flavone. The signaling was effective in aqueous environment and the selective signaling was not affected in the presence of common physiologically and environmentally important metal ions.

Diphenylmethylene hydroxamic acids as selective class IIa histone deacetylase inhibitors

We have identified a series of diphenylmethylene hydroxamic acids as novel and selective HDAC class IIa inhibitors. The original hit, N-hydroxy-2,2-diphenylacetamide ( 6), has sub-micromolar class IIa HDAC inhibitory activity, while the rigidified oxygen analogue, N-hydroxy-9 H-xanthene-9-carboxamide ( 13), is slightly more selective for HDAC7 with an IC 50 of 0.05 μM. Substitution of 6 allows for the modulation of selectivity and potency amongst the class IIa HDAC isotypes.

Inhibition of nitric oxide synthase by cobalamins and cobinamides

Cobalamins are important cofactors for methionine synthase and methylmalonyl-CoA mutase. Certain corrins also bind nitric oxide (NO), quenching its bioactivity. To determine if corrins would inhibit NO synthase (NOS), we measured their effects on - l-[ 14C]arginine-to- l-[ 14C]citrulline conversion by NOS1, NOS2, and NOS3. Hydroxocobalamin (OH-Cbl), cobinamide, and dicyanocobinamide (CN 2-Cbi) potently inhibited all isoforms, whereas cyanocobalamin, methylcobalamin, and adenosylcobalamin had much less effect. OH-Cbl and CN 2-Cbi prevented binding of the oxygen analog carbon monoxide (CO) to the reduced NOS1 and NOS2 heme active site. CN 2-Cbi did not react directly with NO or CO. Spectral perturbation analysis showed that CN 2-Cbi interacted directly with the purified NOS1 oxygenase domain. NOS inhibition by corrins was rapid and not reversed by dialysis with l-arginine or tetrahydrobiopterin. Molecular modeling indicated that corrins could access the unusually large heme- and substrate-binding pocket of NOS. Best fits were obtained in the “base-off” conformation of the lower axial dimethylbenzimidazole ligand. CN 2-Cbi inhibited interferon-γ-activated Raw264.7 mouse macrophage NO production. We show for the first time that certain corrins directly inhibit NOS, suggesting that these agents (or their derivatives) may have pharmacological utility. Endogenous cobalamins and cobinamides might play important roles in regulating NOS activity under normal and pathological conditions.

Demonstration That CobG, the Monooxygenase Associated with the Ring Contraction Process of the Aerobic Cobalamin (Vitamin B12) Biosynthetic Pathway, Contains an Fe-S Center and a Mononuclear Non-heme Iron Center

The ring contraction process that occurs during cobalamin (vitamin B(12)) biosynthesis is mediated via the action of two enzymes, CobG and CobJ. The first of these generates a tertiary alcohol at the C-20 position of precorrin-3A by functioning as a monooxygenase, a reaction that also forms a gamma lactone with the acetic acid side chain on ring A. The product, precorrin-3B, is then acted upon by CobJ, which methylates at the C-17 position and promotes ring contraction of the macrocycle by catalyzing a masked pinacol rearrangement. Here, we report the characterization of CobG enzymes from Pseudomonas denitrificans and Brucella melitensis. We show that both contain a [4Fe-4S] center as well as a mononuclear non-heme iron. Although both enzymes are active in vivo, the P. denitrificans enzyme was found to be inactive in vitro. Further analysis of this enzyme revealed that the mononuclear non-heme iron was not reducible, and it was concluded that it is rapidly inactivated once it is released from the bacterial cell. In contrast, the B. melitensis enzyme was found to be fully active in vitro and the mononuclear non-heme iron was reducible by dithionite. The reduced mononuclear non-heme was able to react with the oxygen analogue NO, but only in the presence of the substrate precorrin-3A. The cysteine residues responsible for binding the Fe-S center were identified by site-directed mutagenesis. A mechanism for CobG is presented.

Arylation of 3-heterylmethylene-5-arylfuran-2(3H)-thiones

The behaviour of 3-heterylmethylene-5-arylfuran-2(3 H)-thiones towards the Lewis acid AlCl3 under Friedel–Crafts reaction conditions compared with their oxygen analogues, the furan-2(3 H)-ones is studied. Although the later are known to undergo alkyl/oxygen ring cleavage to give resonance stabilised carbocations which can exhibit either intra- or intermolecular alkylations, furanthiones gave 1, 4-adducts with the furan ring remaining intact. This difference in behaviour is explained in terms of both electronic and steric effects.

THE DETECTION OF POLYCYCLIC AROMATIC COMPOUNDS IN AIR SAMPLES BY GC×GC-TOFMS

Multidimensional Gas Chromatography-Time of Flight Mass Spectrometry is a relatively new, highly versatile and productive technique that is ideally suited for the detection of PACs in environmental samples. Air samples collected in Slocan Park in Vancouver and in Langley, BC (a semi-rural site) during the PACIFIC 2001 field study and aerosol samples from St. Anicet in Quebec (a rural site) collected in 2006 were analyzed for their PAC content. In addition to the parent PAH, many alkylated-PAH, oxygen, sulphur and nitrogen heterocyclic analogues of the parent PAH were detected. Many of the PAHs observed at these sites were also found in diesel exhaust.

Synthesis and evaluation of dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones—targeting pilus biogenesis in uropathogenic bacteria

Dihydrothiazolo ring-fused 2-pyridones have previously been shown to inhibit pilus assembly in uropathogenic Escherichia coli. Methods have now been developed to synthesize both dihydroimidazolo and dihydrooxazolo ring-fused 2-pyridones. To obtain the nitrogen analogs, Cbz-protected imidazolines were reacted with an acyl-Meldrum's acid derivative under acidic conditions. To prepare the oxygen analogs, a one-pot procedure was developed that allowed synthesis of dihydrooxazolo ring-fused 2-pyridones starting from acylated serine derivatives. After hydrolysis to their corresponding carboxylic acids and lithium carboxylates, biological evaluation revealed that the sulfur could be replaced by an oxygen atom and still maintains the ability to inhibit pilus assembly in uropathogenic E. coli. However, introducing a secondary amine instead of oxygen resulted in a substantial decrease in biological activity.

Ruthenium Tris(bipyridine) Complexes with Sulfur Substituents: Model Studies for PEG Coupling

Ruthenium polypyridyl complexes are incorporated into polymers for sensing and light emitting materials applications. Coupling reactions between metal complexes and polymers are one route to polymeric metal complexes. In an effort to increase conjugation efficiency, tune materials properties, and introduce a responsive crosslink, ruthenium tris(bipyridine) derivatives with sulfur substituents were synthesized and compared to oxygen analogues. Difunctional thiols, thioesters, thioethers, and disulfides, as well as hexafunctional nonpolymeric model systems, were explored. Upon exposure to oxygen, the thiol derivative was readily oxidized. These studies guided Ru(bpy)3 PEG coupling reactions with disulfide and thioether linkages, which proceeded to approximately 80% and approximately 60% yield, respectively. The luminescence properties of the Ru PEG derivatives and model systems were investigated. The emission spectra and lifetimes for all complexes in CH3CN under an inert atmosphere are comparable to [Ru(bpy)3]Cl2. Lifetime data for nonpolymeric analogues fit to a single exponential decay indicating heterogeneity, suggesting sample homogeneity, whereas data for polymers fit to a multiexponential decay. In contrast to certain [Ru(bpy)3](2+)/thiol mixtures, no intramolecular quenching by the sulfide is observed for [Ru(bpy)2{bpy(CH2SH)2}](PF6)2. Emission spectra red shift and multiexponential decay are noted for the oxidized Ru thiol product. The rates of oxygen quenching are slower for Ru PEG derivatives than those for nonpolymeric analogues, which may be attributed to shielding effects of the polymer chain.

The effects of sulfur substitution for the nucleophile and bridging oxygen atoms in reactions of hydroxyalkyl phosphate esters.

The effects of sulfur substitution on the reactions of hydroxyalkyl phosphate esters are examined. These compounds are models for the intramolecular phosphoryl transfer reaction involved in the cleavage of the internucleotide bond in RNA. The models studied here lack the ribose ring and their conformational flexibility results in greater stability and the availability of different reaction pathways. Sulfur in the nucleophilic position shows no nucleophilic reaction at phosphorus, instead rapidly attacking at the beta carbon atom, forming thiirane with departure of a phosphomonoester. Sulfur substitution at either of the two bridging positions leads to cleavage of the diester via formation of a cyclic intermediate, but with significant rate acceleration when compared to the oxygen analogues. The bridge-substituted models react substantially slower than the analogous ribose compounds with sulfur substitution at comparable positions. Kinetic isotope effects reveal significant differences in the transition state depending on which bridging position sulfur occupies. When sulfur is in the scissile bridging position, a highly associative transition state is indicated, with a largely formed bond to the nucleophile and the scissile P-S bond is little changed. When sulfur occupies the other bridging position, the isotope effects imply a very early transition state in a concerted reaction.