Chloroform Medium Research Articles

Role of TiO 2 nanoparticles on the photoinduced intramolecular electron-transfer reaction within a novel synthesized donor–acceptor system

Steady-state, FT-IR and time-resolved spectroscopic measurements were carried out on the two novel synthesized π-conjugated rigid naphthothiophene compounds, 7-methoxynaphtho[1,2- b]thiophene (7MNT) and 7-methoxynaphtho[1,2- b]thiophene-2-carboxylic acid (7MTCA) in chloroform (CHCl 3) medium as well as in presence of TiO 2 nanoparticles. 7MTCA multichromophoric system contains both electron donor (–OCH 3) and acceptor functionalities (–COOH) at the two different ends of the rigid naphthothiophene moiety whereas in 7MNT only the electron donor functional group, –OCH 3, is present. Thus 7MNT looks like the donor part of 7MTCA where –COOH group overlaps, due to its free rotation, with the electron rich site 7MNT part. The experimental findings observed from steady-state absorption, fluorescence and time-resolved spectroscopic (fluorescence lifetime and transient absorption) measurements demonstrate that the survival duration of charge-separated species formed within 7MTCA due to intramolecular photoinduced electron-transfer (PET) reactions between the donor –OCH 3 and acceptor –COOH functional groups, attached at the two different ends of this compound, could be enhanced by inhibiting the energy wasting charge recombination process through complexation of the carboxylate group (–COOH) with TiO 2 nanoparticles. Thus, in the present investigation TiO 2 appears not to act as an acceptor but its presence helps to survive or protect the charge-separated species formed within 7MTCA. The possibility of designing of low-cost artificial (model) solar energy conversion devices by linking the organic donor–acceptor (DA) systems like 7MTCA with TiO 2 core is hinted.

Organophosphorus and carbamate pesticide analysis using an inhibition tyrosinase organic phase enzyme sensor; comparison by butyrylcholinesterase + choline oxidase opee and application to natural waters

Recent research performed in our laboratory (using a butyrylcholinesterase + choline oxidase enzyme electrode) suggested the validity of the biosensor approach using enzyme inhibition OPEEs (i.e. enzyme electrodes working in organic phase) in the case of organophosphorus and carbamate pesticides, which are poorly soluble in aqueous solutions. Since these pesticides are generally much more soluble in chloroform than in water, the present research aimed at analysing this class of pesticides using a tyrosinase inhibition OPEE operating in water-saturated chloroform medium. The tyrosinase biosensor was assembled using an oxygen amperometric transducer coupled to the tyrosinase enzyme, immobilized in kappa-carrageenan gel. Lastly a detailed comparison between the inhibition monoenzymatic tyrosinase and inhibition bienzymatic (butyrylcholinesterase + choline oxidase) OPEEs was performed and discussed in this work.

UV–vis, IR spectra and thermal studies of charge transfer complex formed between poly(amidoamine) dendrimers and iodine

The intermolecular charge-transfer (CT) complexes formed between two poly(amidoamine) dendrimers (PAMAM) from zero (D1) and second generation (D2) as donor and iodine as σ-acceptor have been studied spectrophotometrically in the chloroform medium. The suggested structures of the solid iodine charge-transfer complexes investigated by several techniques using elemental analysis, mid infrared spectra, and thermal analysis (TGA and DTG) of the solid CT-complexes along with the photometric titration curves for the reactions. The results indicate the formation of two CT-complexes [(D1)]–I 2 and [(D2)]–2I 2 with acceptor:donor molar ratios of 1:1 and 1:2, respectively. The kinetic parameters (non-isothermal method) for their decomposition have been evaluated by graphical methods using the equations of Horowitz–Metzger (HM) and Coats–Redfern (CR).

NMR Determination of the Bioactive Conformation of Peloruside A Bound To Microtubules

We report here on the determination of the conformation of Peloruside A bound to biochemically stabilized microtubules, by using TR-NOESY NMR experiments. As a previous step, the conformation of the free molecule in water solution has also been deduced. Despite the large size of the ring, Peloruside A mainly adopts two conformations in water solution. A conformational selection process takes place, and the microtubules-bound conformer is one of those present in the water solution, different than that existing in chloroform medium. A model of the binding mode to tubulin has also been proposed, by docking the bioactive conformation of peloruside, which involves the alpha-tubulin monomer, in contrast with taxol, which binds to the beta-monomer.

Kinetics and mechanism of the defluorination of 8-fluoropurine nucleosides in basic and acidic media

For investigating the stability of C(8)–fluorine bond in 8-fluoropurine nucleosides some protected 8-fluoroguanosine, 8-fluoroinosine and 8-fluoroadenosine derivatives were prepared by direct fluorination of acetyl-protected purine nucleosides with elemental fluorine in solvents such as chloroform, acetonitrile and nitromethane. Fluorination reactions conducted in chloroform medium gave better yields of 8-fluoropurines. The fluorination yields were slightly lower when acetonitrile or nitromethane was used as solvent, but the product purification was found to be much easier. When the synthesized, protected fluoronucleosides were subjected to standard basic (NH 3 in methanol or 2-propanol) and acidic (HCl in methanol) deprotection conditions relevant to nucleoside chemistry, an efficient defluorination reaction took place. The kinetics of these defluorination reactions were conveniently followed, under pseudo-first-order reaction conditions, using 19F NMR spectroscopy. 1H NMR, LC–MS and mass spectroscopy identified the products of the kinetic reaction mixtures. The defluorination reaction rate constants ( k obs) in basic media depended upon the electron density at C(8) while the k obs data in acidic medium were determined by the p K a of N 7. An addition–elimination based mechanism (S NAr) has been proposed for the defluorination reactions of these 8-fluoropurine nucleosides.

Synthesis and application of PLGA labeled with 125I

Abstract The weight loss in vivo degradation of poly (lactide-co-glycolide) (PLGA) radiolabeled with 125I was investigated. PLGA with molecular weight ( M w) of 84000(LA/GA = 85/15) were labeled with 125I in the chloroform media by circularly heating and round films of about 15 mm in diameter were formed. The composition and M w of the 125I-PLGA were characterized by 1H-NMR and viscosimeter. The weight loss of this copolymer in vitro and in vivo degradation was quantified by determining radioactivity of materials. The results indicated that PLGA exhibited significantly faster degradation in vivo than that of in vitro conditions.

Synthesis and antifungal activity of novel 3-anilino-6-ethylthio-4,5-dihydro-1,2,4,5- tetrazines

Synthesis of some novel 4,5-dihydro-l,2,4,5-tetrazines have been achieved by the interaction of S-ethyl-thiocarbohydrazide and N-arylisocyanodichlorides in chloroform medium. A comparative antifungal study has also been carried out on the fungus Fusarium udum.

Tyrosinase inhibition organic phase biosensor for triazinic and benzotriazinic pesticide analysis (part two)

Several triazine pesticides, such as atrazine, are much more soluble in several organic solvents, such as chloroform, than in water. Our recent research was aimed at analyzing this class of pesticides using tyrosinase OPEE (organic phase enzyme electrodes), exploiting their inhibiting action on the tyrosinase enzyme when operating in water-saturated chloroform medium. In this work we studied the response of a tyrosinase inhibition enzyme sensor to several triazinic (simazine, propazine, terbuthylazine) and benzotriazinic (azinphos-ethyl and azinphos-methyl) pesticides (LOD=0.5x10(-9) mol l(-1)). Recovery trials were also performed in vegetal matrixes (corn, barley, lentils). Lastly, the effect of the solvent (chloroform or water) on the inhibition process was investigated via Hill's equation and the diffusion of analyte from the solvent to the enzyme membrane.

Study of electron donor–acceptor complexes of tri- n-octyl amine with [60]- and [70]fullerenes and some other electron acceptors by absorption spectrophotometric method

Electron donor–acceptor (EDA) complexes of tri- n-octylamine (TOA) with [60]- and [70]fullerenes and some other electron acceptors have been studied in chloroform medium by absorption spectrophotometric technique. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potential of TOA was determined utilizing CT transition energy. Oscillator strengths, transition dipole strengths and resonance energies for all the complexes have been calculated. [60]Fullerene/TOA and [70]fullerene/TOA complexes are found to decay slowly with time. Kinetics of these reactions have been studied and activation energies for such processes have been estimated. Ab initio calculations suggest that complexation of [70]fullerene with TOA is enthalpy favoured.

Absorption spectroscopic study of synergistic extraction of praseodymium with benzoyl acetone in presence of crown ether

The extraction behaviour of Pr(III) from aqueous nitric acid medium employing benzoylacetone has been studied in presence of two crown ethers, viz., 15-crown-5 and benzo-15-crown-5 in chloroform medium using UV–vis absorption spectroscopy. The binary equilibrium constant (log k ex) for the complex [Pr(benzoylacetonate)( N O 3 − ) 2(H 2O)] in organic phase was found to be 1.170. The overall equilibrium constants (log K) for the ternary species [Pr(benzoylacetonate)(crown ether)( N O 3 − ) 2] were estimated to be 4.01 and 4.41 for 15-crown-5 and benzo-15-crown-5, respectively. The trend in the equilibrium constant values were very much in accordance with the nature of substitution of the donor moiety. The extraction of Pr(III) by the benzoylacetone–crown ether combination was maximum at pH 3.0 and extraction decreases with increase in pH. It has been found that the extent of extraction of Pr(III) in organic phase as the binary as well as ternary complex [Pr(benzoylacetonate)( N O 3 − ) 2(H 2O)] and [Pr(benzoylacetonate)(crown ether)( N O 3 − ) 2], increases with increase in concentration of the ligand. Similar trend is observed in the extraction by only donors. Enthalpies and entropies of formation for the ternary extraction process have been estimated. In addition, the effect of NaNO 3 as foreign salt was also studied and it was observed that with increase in ionic strength, percentage extraction increases.

Complexation of a Macrocycle Containing Thiopyrimidine and Uracil Moieties with Dicarboxylic and Amino Acids in Various Organic and Aqueous Organic Solutions

The complexation of a macrocycle containing thiopyrimidine and uracil moieties (M) with amino acids and some dicarboxylic acids was studied by pH-metric, UV-VIS, 1H NMR spectroscopy methods in chloroform, methanol, aqueous 1,4-dioxane, and biphasic water–chloroform media. The complexation of M with acids is too weak to solubilize them from the solid state into chloroform solutions containing M. The 1H NMR spectra and pH-metric data of aqueous 1,4-dioxane (80 vol.%) reveal the pH-dependent 1:1 binding between M and the acids studied. The protonation of M is not a prerequisite for binding of fumaric, succinic, o-phtalic acids and the series of amino acids, whereas binding of maleic acid requires the protonation of both thiopyrimidine moieties of M. Therefore,M·(H+)2 exhibits strong selectivity towards maleic acid in aqueous 1,4-dioxane and in biphasic water–chloroform media.

Association Behavior of 4-Acylpyrazolone Derivative and Tertiary Amine of High Molecular Weight in Antagonistic Synergistic Extraction of Palladium

To find an effective extraction and removal method for palladium(II), which is one of the main fission products from an acidic nuclear spent fuel solution, the extraction behavior of palladium(II) from a nitric acid medium by an acidic chelating extractant, 1-phenyl-3-methyl-4-trifluoroacetylpyrazolone-5-one (HPMTP) and a tertiary amine of high molecular weight, tri-n-octylamine (TOA), has been studied by spectrophotometry. A noticeable antagonistic extraction effect was observed in the extraction system under the given conditions. To understand this phenomenon, a preliminary investigation was performed to explain the mechanism of this reaction. According to the theory of corresponding solutions (TCS), the association reaction between HPMTP and TOA is proposed in the organic phase. An associated species, HPMTP·TOA, formed through hydrogen bonding in a chloroform medium might be the main reason why an antagonistic extraction effect occurred. The association constant between HPMTP and TOA was calculated to be 2.86±0.05.

Monte Carlo simulation of 2-ethoxyethanol in continuum configurational biased procedure: conformational analysis and association in aqueous and non-aqueous media

Monte Carlo simulations have been carried out for 2-ethoxyethanol (C2E1) in isothermal-isobaric ensemble (NPT) at different temperatures and 1 atm pressure with a continuum configurational biased procedure in water and chloroform media. Hydrogen bond bridges were formed between adjacent oxygen atoms in C2E1 (CH3CH2OCH2CH2OH) through water molecules. We also found that the stable conformers of C2E1 in water and CHCl3 are different and the effect of temperature on solute-solvent interaction energies is considerable. The self-association of C2E1 in aqueous and nonaqueous media has been studied by statistical perturbation theory, and the relative free energy has been obtained at different reaction coordinates by double-wide sampling method. Two minima were found in water solvent in the potential of mean force (PMF), corresponding to the contact and solvent-separated pairs, but only one minimum was found in CHCl3 solvent corresponding to a contact pair complex.

STUDY OF THE ANTAGONISTIC EXTRACTION OF PALLADIUM(II) WITH 1-PHENYL-3-METHYL-4-PROPIONYLPYRAZOLONE-5-ONE AND AN ORGANIC AMINE

The extraction mechanism of palladium (II) with the acidic chelating extractant 1-phenyl-3-methyl-4-propionylpyrazolone-5-one (HPMPP) and the tertiary amine (R1R2R3N) has been studied by spectrophotometry. A noticeable antagonistic extraction effect was observed in the extraction system under the given conditions. To understand this phenomenon, a preliminary work was performed to explain the mechanism of this reaction. According to the theory of the corresponding solutions (TCS), the association reaction between HPHBP and R1R2R3N was represented and discussed in the organic phase. An associated species HPMPP · NR1R2R3 formed through hydrogen bonding in chloroform medium might be the main reason why an antagonistic extraction effect occurs. The association constant between HPMPP and R1R2R3N was calculated to be 2.2 ± 0.1.

Dual fluorescence of 4-dimethylaminopyridine and its derivatives: Effects of methyl substitution at the pyridine ring

Electronic absorption and emission spectra of 4-(dimethylamino)pyridine (DMAP), 3-methyl-4-(dimethylamino)pyridine (MDMAP), and 3,5-dimethyl-4-(dimethylamino)pyridine (TMAP=tetramethylaminopyridine) were measured in cyclohexane (nonpolar), chloroform (medium polar), and acetonitrile (highly polar) solutions. Intense charge transfer emission of DMAP was observed only in acetonitrile, while that of MDMAP and TMAP was observed in all the three solvents. Dynamics of excited electronic states of these molecules is discussed on the basis of steric hindrance between methyl groups at 3- and 5-positions of pyridine ring and dimethylamino groups.

Absolute partition coefficients for organic solutes by using Monte Carlo simulations in chloroform/water system

Absolute chloroform/water partition coefficients for organic solutes were calculated by using a linear response method for determining the free energy of solvation and Monte Carlo simulations. In the used linear equations, in addition to the Coulombic and van der Waals components of the solute–solvent interaction energy, the cavity terms such as molecular surface area, molecular volume and ovality have also been used. For most solutes, the calculated log P values and predicted free energy of solvation in both water and chloroform are in good agreement with available experimental values and other theoretical methods. However, including ovality produces better results. The trend of ΔG solvation in water and chloroform media were matched with their polarities.

Extraction chemistry of palladium I. Study on the mechanism of synergistic extraction of palladium (II) with 1-phenyl-3-methyl-4-dichloroacetopyrazolone-5-one and diphenyl sulfoxide

ABSTRACT l-Phenyl-3-methyl-4-dichloroacetopyrazolone-5-one (HPMDCP), which is an acidic chelating β-diketone extractant, was synthesized by acylation reaction in dioxane medium. The behavior of synergistic extraction of palladium (II) with HPMDCP and diphenyl sulfoxide (DPSO) has been studied. The results show that an antagonistic effect was observed under the given conditions. To understand this phenomenon, a preliminary work was performed to explain the mechanism of this reaction. According to the theory of the corresponding solutions (TCS), the association reaction between HPMDCP and DPSO in the organic phase was discussed. The results show that the associate species HPMDCP.DPSO formed in chloroform medium is the main reason why an antagonistic extraction effect occurs. The association constant between HPMDCP and DPSO in the extraction process was calculated to be 4.2.

Biocatalysis of tyrosinase in chloroform medium, using selected phenolic substrates

The biocatalysis of mushroom tyrosinase was optimized in chloroform medium using as substrates selected phenolic compounds, including chlorogenic acid (CA), p-aminophenol (pAP) and hydroquinone (HQ). The specific activity of tyrosinase was found to be much higher in the chloroform medium than that obtained in the aqueous one. The optimal pH and temperature as well as other kinetic parameters for tyrosinase biocatalysis was also determined. The presence of catechol in the chloroform medium resulted in an increase in tyrosinase activity when CA was used as substrate; however, no activatory effect was found with pAP or HQ. The presence of ethylenediamine tetraacetic acid in the chloroform medium showed different effects on tyrosinase activity depending on the nature of the substrate. FT-IR analyses confirmed the bioconversion of selected phenolic substrates into o-quinones by tyrosinase activity in the chloroform medium. © 2000 Society of Chemical Industry

Palladium(II)-induced Alkali Metal Ion Incorporation of 2,6-Disubstituted Pyridines with Bis(alkoxyethyl) Malonate Subunits

Abstract A series of 2,6-bis(2,2′-dicarbalkoxyethyl)pyridine ligands were prepared. A couple of the ligands linked by a trans-PdCl2 unit extracted alkali metal ions from an aqueous media into a chloroform media, while a single pyridine ligand did not work as an extractive reagent.

Transformation of rhodium carbonyl complexes in hydroformylation of 1-hexene studied fromin situ IR spectroscopic data

Rhodium carbonyl complexes that formed from RhCl3·4H2O and RhCl3·4H2O modified by poly-N,N-dimethyl-N,N-diallylammonium chloride in a methanol—chloroform medium in the hydroformylation of 1-hexene were studied byin situ IR spectroscopy. Along with the rhodium hydrocarbonyl complexes, anionic complexes of the [Rh(CO)2Cl2]− type, whose concentrations and rates of formation in an acidic medium are much higher than those in a basic medium, were shown to be the active centers of hydroformylation. The function of the polycation is the stabilization of the catalytically active mononuclear rhodium complexes.