Inter And Intramolecular Interactions Of Porphyrins With 5,5′-Dithiobis(2-Nitrobenzoic Acid)

meso-Tetraphenylporphyrin and its metal [zinc(II) and copper(II)] derivatives form both inter and intramolecular complexes with 5,5′-dithiobis(2-nitrobenzoic acid) (DTNB). The nature of interaction is predominantly charge transfer (CT) in origin, with the porphyrin functioning as a II-donor and DTNB as an acceptor. Among the covalently linked intramolecular systems, the magnitude of CT interaction varies with the position (of one of the aryl groups of the porphyrin) to which DTNB is attached as ortho meta > para. Steady-state and time-resolved fluorescence studies revealed electron transfer to be the dominant pathway for the fluorescence quenching in these systems. Steady-state photolysis experiments probed using EPR and optical absorption studies have shown that electron transfer (from the excited singlet state of the porphyrin) to DTNB results in the formation of thiyl radical and production of free thiolate anion. It is found that the products of electrochemical reduction of covalently linked porphyrin-DTNB systems are different from those observed for the photochemical studies.

Synthesis and matrix isolated photolysis of 2,3-dimethylbicyclo [2.2.0]hexa-2,5-diene-1,4-dicarboxylic acid anhydride: a potential percursor to 2,3-dimethyl-1,4-dehydrobenzene

The synthesis of the first member of a new class of Dewar benzenes has been achieved. The synthesis of 2,3- dimethylbicyclo[2.2.0]hexa-2,5-diene-1, 4-dicarboxylic acid and its anhydride are described. Dibromomaleic anhydride and dichloroethylene were found to add efficiently in a photochemical [2+2] cycloaddition to produce 1,2-dibromo- 3,4-dichlorocyclobutane-1,2-dicarboxylic acid. Removal of the bromines with tin/copper couple yielded dichloro- cyclobutenes which added to 2-butyne under photochemical conditions to yield 5,6-dichloro-2,3-dimethylbicyclo [2.2.0] hex-2-ene dicarboxylic acids. One of the three possible isomers yielded a stable anhydride which could be dechlorinated using triphenyltin radicals generated by the photolysis of hexaphenylditin.

Photolysis of argon matrix isolated 2,3-dimethylbicyclo [2.2.0]hexa-2, 5-diene-1,4-dicarboxylic acid anhydride produced traces whose strongest bands in the infrared were at 3350 and 600 cm^(-1). This suggested the formation of terminal acetylenes. The spectra of argon matrix isolated E- and Z- 3,4-dimethylhexa-1,5-diyne-3-ene and cis-and trans-octa- 2,6-diyne-4-ene were compared with the spectrum of the photolysis products. Possibly all four diethynylethylenes were present in the anhydride photolysis products. Gas chromatograph-mass spectral analysis of the volatiles from the anhydride photolysis again suggested, but did not confirm, the presence of the diethynylethylenes.

A family of simple benzene 1,3,5-tricarboxamide (BTA) aromatic carboxylic acid hydrogels.

We present the characterisation of a hydrogel forming family of benzene 1,3,5-tricarboxamide (BTA) aromatic carboxylic acid derivatives. The simple, easy to synthesise compounds presented here exhibit consistent gel formation at low concentrations through the use of a pH trigger.

Effect of acid strength distribution on conversion of FCC gasoline over a ZSM-5 zeolite catalyst

Acid strength distribution and the distribution of aromatics formed in the FCC gasoline conversion reaction on a ZSM-5 zeolite with different Na contents have been studied. With increasing Na content in the ZSM-5 zeolite, the acid sites determined by NH3-TPD technique, especially the strong acid sites, clearly decrease. When used as catalyst for the aromatization reaction, the transformation of olefins in the FCC gasoline into aromatics is governed directly by the strong acid sites on the ZSM-5 catalyst. Only under the conditions that a ZSM-5 catalyst possesses suitable strong acid sites is reaction temperature favorable for the aromatics formed.

Characterization of the acid sites in dealuminated nanosized HZSM-5 zeolite with the probe molecule trimethylphosphine

The acid sites in dealuminated HZSM-5 zeolite with crystal sizes down to the nanoscale were firstly characterized by the probe molecule trimethylphosphine (TMP). As evidenced by the combination of P-31 CP/MAS NMR, Al-27 MAS and H-1 --> Al-27 CP/MAS NMR measurements, the Bronsted acid sites of both microsized and nanosized HZSM-5 could be decreased upon the dealumination of zeolitic framework after hydrothermal treatment. At the same time, the appearance of Lewis acid sites was observed. The dealuminated nanosized HZSM-5 is easier to form Lewis acid sites than microsized HZSM-5, and the type of Lewis acid sites in nanosized HSM-5 is more than one. In addition, the origin of Lewis acid sites is mainly associated with the aluminum at ca. 30 ppm, in the Al-27 MAS NMR spectra, and only a part of which in the dealuminated HZSM-5 zeolite acts as Lewis acid sites. (C) 2002 Elsevier Science B.V. All rights reserved.

Solvent extraction of rare earths from chloride medium with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and sec-octylphenoxyacetic acid

The extraction of rare earth elements from chloride medium by mixtures of sec-nonylphenoxy acetic acid (CA100) with bis(2,4,4-trimethylpentyl) dithiophosphinic acid (Cyanex301) or bis(2,4,4-trimethylpentyl) monothiophosphinic acid (Cyanex302) in n-heptane has been studied. The synergistic enhancement of the extraction of lanthanum (III) by mixtures of CA100 with Cyanex301 has been investigated using the methods of slope analysis and constant mole. The extracted complex of lanthanum (III) is determined. The logarithm of the equilibrium constant is calculated as - 1.41. The formation constants and the thermodynamic functions, Delta H, Delta G, and Delta S have also been determined.

Assembly of 12-tungstosilicic acid and 4-aminobenzo-15-crown-5 ether based on the electrostatic attraction through bridging of oxonium ions on different substrates

Based on the electrostatic attraction Keggin-type polyoxometalate H4SiW12O40 (SiW12) and small molecule 4-aminobenzo-15-crown-5 ether (4-AB15C5) were alternately deposited on poly (allylamine hydrochloride) (PAH)-derived indium tin oxide (ITO) substrate through a layer-by-layer (LBL) self-assembly, forming a supramolecular multilayer film (film-A). SiW12 was also deposited on a glassy carbon electrode (GCE) derived by 4-AB15C5 via covalent bonding in 0.1 M NaCl aqueous solution and formed a composite monolayer film (film-B). UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy measurements demonstrated that the interactions between SiW12 and 4-AB15C5 in both two film electrodes were the same and caused by the bridging action of oxonium ions. But, the nanostructure in the two film electrodes was different. 4-AB15C5 in film-A was oriented horizontally to ITO substrate, however, that in film-B was oriented vertically to GCE. Namely film-A corresponded to a layer structure, and film-B corresponded to an intercalation structure.

THERMODYNAMICS OF AMINO-ACID DISSOCIATION IN MIXED-SOLVENTS .3. GLYCINE IN AQUEOUS GLUCOSE SOLUTIONS FROM 5-DEGREES-C TO 45-DEGREES-C

The first thermodynamic dissociation constants of glycine in 5, 15 mass % glucose + water mixed solvents at five temperatures from 5 to 45-degrees-C have been determined from precise emf measurements of a cell without liquid junction using hydrogen and Ag-AgCl electrodes and a new method of polynomial approximation proposed on the basis of Pitzer's electrolytic solution theory in our previous paper. The results obtained from both methods agree within experimental error. The standard free energy of transfer for HCl from water to aqueous mixed solvent have been calculated and the results are discussed.

Effect of variations in acid properties of HZSM-5 on the coking behavior and reaction stability in butene aromatization

In order to investigate the effect of acid properties on the coke behavior and stability of butene aromatization, we prepared the AHZSM-5 samples with various acid properties by the methods of hydrothernial treatment and K addition. The reaction of butene aromatization was carried out at 350 degrees C and 0.5 MPa in a continuous flow fixed bed. The characterization of the fresh/coked catalysts with NH3-TPD, N-2 adsorption-desorption measurement, and TG techniques has shown that a large amount of acid sites (high acid density) of the AHZMS-5 catalyst can cause a large quantity of coke deposit and serious channel blockage, and so result in a rapid loss of aromatization activity. On the contrary, after a great reduction in strong acid sites of AHZSM-5 catalyst resulting from some K-modification, the presence of only many weak acid sites also could not lessen the formation of coke nor improve the reaction stability of butene aromatization. Interestingly, the simultaneous reduction in the strong and weak acid sites to a desirable level by hydrothermal treating the AHZSM-5 catalyst at a proper temperature can effectively suppress the coke formation and channel blockage, and thus improve its olefin aromatization stability. (c) 2005 Elsevier B.V. All rights reserved.

Methane dehydroaromatization over Mo/HZSM-5 catalysts: The reactivity of MoCx species formed from MoOx associated and non-associated with Bronsted acid sites

The catalytic performances of methane dehydroaromatization (MDA) under non-oxidative conditions over 6 wt.% Mo/HZSM-5 catalysts calcined for different durations of time at 773 K have been investigated in combination with ex situ H-1 MAS NMR characterization. Prolongation of the calcination time at 773 K is in favor of the diffusion of the Mo species on the external surface and the migration of Mo species into the channels, resulting in a further decrease in the number of Bronsted acid sites, while causing only a slight change in the Mo contents of the bulk and in the framework structure of the HZSM-5 zeolite. The MoQ(x) species associated and non-associated with the Bronsted acid sites can be estimated quantitatively based on the 1H MAS NMR measurements as well as on the assumption of a stoichiometry ratio of 1: 1 between the Mo species and the Bronsted acid sites. Calcining the 6 wt.% Mo/HZSM-5 catalyst at 773 K for 18 h can cause the MoOx species to associate with the Bronsted acid sites, while a 6 Wt-% MO/SiO2 sample can be taken as a catalyst in which all MoOx species are non-associated with the Bronsted acid sites. The TOF data at different times on stream on the 6 wt.% Mo/HZSM-5 catalyst calcined at 773 K for 18 h and on the 6 Wt-% MO/SiO2 catalyst reveal that the MoCx species formed from MoOx associated with the Bronsted acid sites are more active and stable than those formed from MoOx non-associated with the Bronsted acid sites. An analysis of the TPO profiles recorded on the used 6 wt.% Mo/HZSM-5 catalysts calcined for different durations of time combined with the TGA measurements also reveals that the more of the MoCx species formed from MoOx species associated with the Br6nsted acid sites, the lower the amount of coke that will be deposited on it. The decrease of the coke amount is mainly due to a decrease in the coke burnt-off at high temperature. (c) 2005 Elsevier B.V. All rights reserved.

Nutrient- and hypotonicity-induced insulin secretion: effects of cyclic AMP analogs, IBMX, tenidap and 5-nitro-2-(3-phenylpropylamino)benzoic acid

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