Study of Molecular Complex Formation of Coal-Derived Asphaltene with TCNQ in Homogeneous and Heterogeneous Media by UV-Vis and Fluorescence Spectroscopic Studies

Coal-derived asphaltene (CDA) has been shown to form electron donor–acceptor-type molecular complexes with electron acceptor such as 2,5-cyclohexadiene-1,4-diylidene also known as tetracyanoquinodimethane (TCNQ) in homogeneous medium of carbon tetrachloride and heterogeneous medium of aqueous SDS. This has been investigated both by UV-Vis and fluorescence spectrophotometric method. The Charge transfer (CT) absorption peaks have been detected by difference spectral method and the wavelengths of the CT peaks are close in both the medium. The formation constants (K) have been determined using the Benesi–Hildebrand equation. The magnitudes of K are in the order of 10³ L mol^?1 that are comparable to some supramolecular or inclusion complexes. The study reveals the presence of π-donor (i.e., aromatic) type of compounds in CDA molecule. It also supports the view that CDA molecules exist in solution forming micellar aggregate, in the cavities of which the TCNQ molecules are included. The remarkable increase (three fold) in the formation constant in the SDS medium compared to CCl₄ further indicates that the CDA aggregate in SDS undergoes some preorganization to further facilitate inclusion.     

Study of Electron Donor–Acceptor Complex Formation of o-Chloranil With a Series of Phosphine Oxides and Tri- n-butyl Phosphate by the Absorption Spectrometric Method

Electron donor–acceptor (EDA) complex formation of o-chloranil with six different phosphine oxides and tri-n-butyl phosphate (TBP) has been studied in CCl ₄ solution by the UV-VIS absorption spectrophotometric technique. An absorption band due to a charge–transfer (CT) transition is observed in the visible region. Utilizing the CT transition energy, the electron affinity of o-chloranil in solution has been calculated. Degrees of charge transfer, and oscillator and transition dipole strengths have also been calculated for all of the investigated EDA complexes. Except for TBP, other phosphine oxides, viz., tri-n-octyl phosphine oxide, tri-n-butyl phosphine oxide, triphenyl phosphine, octyl(phenyl)-N,N-diisobutylcarbamoylphosphine oxide, octyl(phenyl)-N,N-dicyclohexylcarbamoylmethylphosphine oxide and octyl(phenyl)-N,N-diisopropylcarbamoylmethylphosphine oxide have been shown to form stable 1:1 EDA complexes with o-chloranil. The complex of TBP with o-chloranil decays slowly into a secondary product. Formation constants of the EDA complexes have been determined.     

Spectroscopic Investigation of Asphaltene Aggregation in Carbon Tetrachloride Medium Containing Microquantities of Water

By fluorescence spectroscopy it has been established that coal derived asphaltene (CDA) forms aggregates in CCl₄ medium. The new feature of this compound is that even before aggregate formation it can incorporate water molecules and the critical aggregation concentration (CAC) in nonaqueous medium increases with increase in ω (= water:CDA mole ratio). The fluorescence spectroscopic determination of the equilibrium constant (K) of the molecular complex of [60] fullerenes with CDA in carbon tetrachloride medium has revealed that K increases on addition of microquantities of water. This observation has been rationalized by assuming that the nitrogenatoms at one end of CDA molecules attach themselves to the water micropool and thus producing a different conformation with a wider distance at the other end. This pre-organization further facilitates inclusion. By utilizing fluorescence variation of [60]fullerene/CDA complex in CCl₄ as continuous medium with change in ω a critical ω (=5) has been found. The formation of CDA/[60]fullerene complex has also been established by NMR spectroscopy.     

Studies on labile chargetransfer complexes between o-chloranil and a series of phenols

The electron donor–acceptor (EDA) interactions between o-chloranil and a series of phenols have been studied in dioxan medium. Except for resorcinol, the EDA complexes are formed instantaneously on mixing the donor and the acceptor solutions and then they decay slowly into secondary products. In case of resorcinol, formation and decay of the EDA complex are slow and simultaneous. The kinetics of all these reactions have been studied spectrophotometrically and the formation constants of EDA complexes have been determined from kinetic data. The hν_CT values change systematically as the number and position of the –OH groups change in the aromatic ring of the phenol moiety. From the trends in the hν_CT values, the Hückel parameters (h_Ö and k_C–Ö) for the –OH group, required for a PMO calculation on phenols, have been obtained in a straightforward way and the values so obtained, viz., 1.8 and 1.0 respectively, are close to the ones (1.8 and 0.8) recommended by Streitwieser on the basis of other evidences.     

Spectral properties and inclusion of 3-(4'-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one in organized media of micellar solutions, beta-cyclodextrin and viscous medium

On the line of a previous work on the spectral properties of some of heteroaryl chalcone, the absorption and fluorescence emission spectral properties of 3-(4'-dimethylaminophenyl)-1-(2-furanyl)prop-2-en-1-one (DMAFP), have been investigated in organized media of aqueous micellar and beta-cyclodextrin (beta-CD) solutions. While the absorption spectra are less sensitive to the nature of the added surfactant or beta-CD, the characteristics of the intramolecular charge transfer (ICT) fluorescence are highly sensitive to the properties of the medium. The ICT maximum is strongly blue-shifted with a great enhancement in the fluorescence quantum yield on adding micellar or beta-CD. This indicates the solubilization of DMAFP in the micellar core and formation of an inclusion complex with beta-CD. The critical micelle concentrations (CMC) as well as the polarity of the micellar core of SDS, CTAB and TX-100 have been determined. The CMC values are in good agreement with the reported values while the polarity is lower indicating that DMAFP molecules are incorporated in the micellar core not at the micellar interface. The inclusion constants of binding of DMAFP in micellar or beta-CD have been also determined. The thermodynamic parameters of formation of DMAFP:CD inclusion complex have been calculated from the temperature dependence of the fluorescence spectra of the formed complex. The highly negative value of formation entropy (DeltaS=-98.0Jmol(-1)K(-1)) reflects the high restrictions imposed on the movement of both the host and included guest molecules which is consistent with the increase of the fluorescence yield and blue shift of the fluorescence maximum.     

Interaction of pyrimethamine and sulfadiazine with ionic and neutral micelles: Electronic absorption and fluorescence studies

The binding of two antitoxoplasmosis drugs, pyrimethamine (PYR) and sulfadiazine (SDZ) to cationic cetyltrimethylammonium chloride (CTAC), anionic sodium dodecylsulfate (SDS), zwiterionic N-hexadecyl-N,N-dimethyl-2-ammonium-1-propanesulfonate (HPS) and neutral polyoxyethylene-dodecyl-ether (Brij-35^®) micelles was studied using absorption and fluorescence spectroscopic methods. The pK_a of PYR changed in the presence of charged anionic, cationic and zwiterionic micelles, indicating that interaction is influenced by the micellar charge. For SDZ, pK_a changes were lower than 1 for all micelles, suggesting the occurrence of low binding constants in addition to a reasonable influence of the micellar charge. The values of binding constants K_b, obtained from fluorescence measurements, for PYR to CTAC micelles were very low at pH 4.0, where the drug is in a complete protonated state, increasing at pH 9.0 to long-chained CTAC and HPS micelles since this factor also favors accomodation of the neutral drug in the hydrophobic compartments. For SDZ the binding constants were determined from optical absorption measurements. Low binding constants were observed to charged surfactant micelles, with influence of micellar charge. It must be stated however that those values can be underestimated due to the relatively low sensitivity of the method based on absorption measurements.     

A 13C n.m.r. study of the charge-transfer complexes between o-chloranil and some aromatic electron donors

The ¹³C n.m.r. spectra of complexes between o-chloranil and aromatic electron donors were studied. Complexation leads to a general diamagnetic shift of the ¹³C n.m.r. signals for the acceptor (o-chloranil), but for signals from the ¹³C nuclei in the donors both diamagnetic and paramagnetic shifts are found. These phenomena are thought to be the result of competing anisotropy and charge-migration effects. Charge migration in o-chloranil complexes appears to be more important than in corresponding 1,3,5-trinitrobenzene complexes.     

Fluorescence resonance energy transfer from tryptophan in human serum albumin to a bioactive indoloquinolizine system

The interaction between a bioactive molecule, 3-acetyl-4-oxo-6,7-dihydro-12H indolo-[2,3-a] quinolizine (AODIQ), with human serum albumin (HSA) has been studied using steady-state absorption and fluorescence techniques. A 1:1 complex formation has been established and the binding constant (K) and free energy change for the process have been reported. The AODIQ-HSA complex results in fluorescence resonance energy transfer (FRET) from the tryptophan moiety of HSA to the probe. The critical energy-transfer distance (R ₀) for FRET and the Stern-Volmer constant (K _sv) for the fluorescence quenching of the donor in the presence of the acceptor have been determined. Importantly, K _SV has been shown to be equal to the binding constant itself, implying that the fluorescence quenching arises only from the FRET process. The study suggests that the donor and the acceptor are bound to the same protein at different locations but within the quenching distance.     

Charge transfer interactions in some poly[[o-(trimethylsilyl)phenyl] acetylene]-acceptor complexes

Charge transfer (CT) interactions between poly[[o-(trimethylsilyl)phenyl]acetylene] or poly(o-Me₃SiPA) and some electron acceptors were studied by ultraviolet-visible and infrared absorption spectroscopy and by x-ray photoelectron spectroscopy, (XPS). The electron acceptors used included iodine, bromine, o-chloranil, o-bromanil, 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), and tetracyanoethylene (TCNE). Varying degrees of CT interactions were observed in all of the polymer/acceptor complexes studied. The electrical conductivities σ of the organic acceptor complexes exhibited a strong acceptor concentration dependence at low acceptor levels, with the DDQ complex exhibiting the highest σ. The extent of CT and the redistribution of charges resulting from the CT in all the complexes were revealed by XPS. The poly (o-Me₃SiPA)/I₂ complex film lost iodine spontaneously while more than half of the bromine in the poly (o-Me₃SiPA)/Br₂ complex existed as covalently bonded bromine, even at low halogen loading.     

A mononuclear nickel(II) complex based on polypyridyl ligand: synthesis,characterization, and biological activity

[Ni(acac)₂(o-NPIP)](CH₃OH)₃ (acac = acetylacetonate), based on the polypyridyl ligand 2-(2-nitrophenyl)imidazo[4,5-f]1,10-phenanthroline) (o-NPIP), has been synthesized and characterized by single-crystal analysis, IR and electronic spectra. In the structure of Ni(II) complex, the coordination sphere around Ni(II) is distorted octahedral with one o-NPIP and two acetylacetonates. DNA binding and human serum albumin (HSA) interactions with the Ni(II) complex have been investigated by electronic absorption and fluorescence measurements, revealing that the Ni(II) complex binds with DNA via intercalative binding. The quenching constants verified a dynamic quenching mechanism between HSA and the Ni complex by fluorescence quenching. ΔG, ΔH, and ΔS at different temperatures (288, 298, and 310 K) indicated that hydrophobic interactions play a major role. Synchronous fluorescence spectral experiments revealed that the Ni(II) complex affected the microenvironment around the tryptophan residue of HSA.     

Effect of cationic and anionic surfactants on the addition–elimination-type interaction between o-toluidine and d-glucose

The kinetics of the o-toluidine–d-glucose reaction has been studied as a function of [o-toluidine], [d-glucose], [acetic acid], and temperature by UV–visible spectrophotometry at 630 nm in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulfate (SDS). The reaction follows second-order kinetics, being unity in each of the reactants in both media. The effect of added surfactants has also been investigated. The model of micellar catalysis, such as the Menger–Portony model modified by Bunton, is applied to explain the catalytic role of CTAB and SDS micelles. The association/incorporation constants (K _s and K _n), the rate constant in micellar media (k _m), and the activation parameters of this system have been calculated and discussed. The value of the rate constant is found to be higher in SDS than in CTAB. Hydrophobic and electrostatic interactions are responsible for higher reaction rates in SDS. From all observed facts, a reaction mechanism involving a nucleophilic addition–elimination path has been suggested.     

Energies of Charge Transfer for the Supramolecular Complexes of [60]- and [70]Fullerenes with a Series of meso-Tetraphenylporphyrins in the Solution State

Supramolecular complexes of [60]- and [70]fullerenes with various meso-tetraphenylporphyrins in toluene solutions have been studied by electronic absorption spectroscopy. Charge transfer (CT) absorption bands are observed in the visible region. Vertical ionization potentials (I _D ^V) of the meso-tetraphenylporphyrins are reported from a study of EDA interaction of these porphyrins with a number of electron acceptors like o-chloranil, p-chloranil, 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) and vitamin K. The dependence of the CT transition energy on the donor ionization potential has been utilized to estimate the vertical electron affinities (E _A ^V) of [60]- and [70]fullerenes in solution. The value of E _A ^V for [60]fullerene is found to be 0.10 eV lower in magnitude than that of [70]fullerene. We have extracted degrees of CT, and oscillator and transition dipole strengths of the fullerenes/meso-tetraphenylporphyrins complexes. The experimental results show that the CT complexes studied here have a neutral character in their ground states. Electronic coupling elements have been determined for fullerene/meso-tetraphenylporphyrin complexes. Values of the solvent reorganization energy indicate that the electron transfer process takes place at a faster rate in the case of [70]fullerene/meso-tetraphenylporphyrin complexes.     

Micellar effects of cation-active surfactants on the reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate

The reaction of (o-aminomethyl)phenols with ethylp-nitrophenyl chloromethylphosphonate in aqueous micellar solutions of cation-active surfactants has been studied. The effect of the structure of the surfactant and the nucleophile, pH of the medium, and temperature on the reaction rate in the micellar phase has been investigated. The rate constants in micelles are much higher than those in water.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2065–2068, December, 1993.     

Dual Fluorescence and Photoprototropic Characteristics of 2-Aminodiphenylsulphone-β-Cyclodextrin Inclusion Complex

The absorption and fluorescence spectral characteristics of 2-aminodiphenylsulphone (2ADPS) have been investigated in the presence of β-cyclodextrin (β-CDx) in water. Dual emission is observed upon the complexation of 2ADPS in β-CDx. The stoichiometry of the host:guest inclusion complex is found to be 2:1. Steady state and time-resolved fluorescence spectral analysis support the formation of 2:1 complex between β-CDx and 2ADPS. The large enhancement in fluorescence intensity of twisted intramolecular charge transfer (TICT) band in aqueous β-CDx solution is due to the decrease in non-radiative processes. The ground and the excited state pK_a values for the monocation-neutral equilibrium of 2ADPS in β-CDx are found to be different from the pK_a values in aqueous solution. In the presence of β-CDx, 2ADPS is found to be less basic in the ground and the excited states.     

Spectrofluorimetric Study of an Inclusion Complex of 2-Hydroxypropyl-β-Cyclodextrin with the Antitumour 11-Methyl Benzophenothiazine. Analytical Application to Urine

The electronic absorption and fluorescence spectral properties of 11-methyl-12H-benzo[a]phenothiazine (11-MeBPHT) were investigated in various media (water, ethanol, β-cyclodextrin (β-CD) and 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) aqueous solutions). Fluorescence quantum yields were respectively about 20 and 2 times larger in HP-β-CD and β-CD than in water. The formation of a 1:1 stoichiometry inclusion complex between 11-MeBPHT and HP-β-CD (association constant K _f=118±3 M⁻¹ at 20 °C) was studied in aqueous medium by fluorescence spectroscopy. Analytical figures of merit were satisfactory for 11-MeBPHT with linear dynamic ranges over at least two orders of magnitude and limits of detection (LODs) between 0.2 and 1 ng/ml according to the medium. An analytical application to the determination of 11-MeBPHT in human urine samples by the standard addition procedure led to satisfactory recovery percentages (91–108%).     

Spectral and fluorescent study of the interaction of cyanine dyes Cyan 2 and Cyan 45 with DNA

The noncovalent interaction of the cyanine dyes Cyan 2 and Cyan 45 with DNA (in a pH 7 phosphate buffer) was studied by spectral and fluorescent methods. Upon titration of dye solutions with a concentrated DNA solution, a drop in the absorption band of the initial dye, a long-wavelength shift, and a rise of the absorption of the dye bound to DNA occur. Simultaneously, a growth of dye fluorescence is observed. Mathematical modeling of the fluorescence growth has been performed on the basis of the formation of one or two types of dye complexes with DNA. The experimental results are adequately described by the model involving one type of the dye-DNA complex. It is shown that Cyan 2 binds to DNA probably as the cis-isomer, whereas Cyan 45 as the trans-isomer.     

Spectral,kinetic, and redox properties of basic fuchsin in homogeneous aqueous and sodium dodecyl sulfate micellar media

Effect of anionic surfactant on the optical absorption spectra and redox reaction of basic fuchsin, a cationic dye, has been studied. Increase in the absorbance of the dye band at 546 nm with sodium dodecyl sulfate (SDS) is assigned to the incorporation of the dye in the surfactant micelles with critical micellar concentration (CMC) of 7.3 × 10^?3 mol dm^?3. At low surfactant concentration (<5 × 10^?3 mol dm^?3) decrease in the absorbance of the dye band at 546 nm is attributed to the formation of a dye–surfactant complex (1:1). The environment, in terms of dielectric constant, experienced by basic fuchsin inside the surfactant micelles has been estimated. The association constant (K_A) for the formation of dye–SDS complex and the binding constant (K_B) for the micellization of dye are determined. Stopped‐flow studies, in the premicellar region, indicated simultaneous depletion of dye absorption and formation of new band at 490 nm with a distinct isosbestic point at 520 nm and the rate constant for this region increased with increasing SDS concentration. The reaction of hydrated electron with the dye and the decay of the semireduced dye are observed to be slowed down in the presence of SDS. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 629–636, 2003     

Synthesis,structure and spectroscopic studies on DNA binding,BSA interaction of a nickel(II) complex containing l–methionine Schiff base and 1,10-phenanthroline

A new nickel(II) complex, [Ni(o-van-L-met)(phen)(CH₃OH)] (o-van-L-met = Schiff base derived from o-vanillin and l-methionine, phen = 1,10–phenanthroline), has been synthesized and characterized by elemental analyses, IR spectra, and single-crystal X-ray diffraction. The crystal structure shows nickel is six-coordinate in a distorted octahedral geometry. In this crystal, molecules form a 2-D plane structure via hydrogen bonds and π–π interactions. The interaction of the complex with calf thymus DNA (CT-DNA) was investigated by absorption, fluorescence, circular dichroism (CD), spectroscopies, and viscosity measurement. The complex binds to CT-DNA in an intercalative mode with a binding constant of (4.7 ± 0.5) × 10⁴ M^?1. The interaction of the complex with bovine serum albumin (BSA) was also studied by the multispectroscopic methods. Results illustrated that the nickel(II) complex can effectively quench the intrinsic fluorescence of BSA via a static quenching mechanism and cause conformational changes. The binding constant K_b was (6.3 ± 1.6) × 10⁴ M^?1 and the binding site number n was 0.96 ± 0.04; its bind site was located within subunit IIA of BSA.     

Photodynamic activity of a nickel diimine complex and its interaction with DNA

Employing 1,3-diphenylisobenzofuran as a probe, the photodynamic activity of a nickel diimine complex, bis(o-diiminobenzosemiquinonato)nickel(II), in red light has been studied by fluorescence spectra. These results show that the nickel complex can generate singlet oxygen efficiently after irradiation in red light. The interaction of the metal complex with DNA has also been studied by electronic absorption spectra, fluorescence spectra and viscosity measurements. The electronic spectra of the metal complex exhibit dramatic hypochromism on interaction with DNA. Scatchard plot analyses indicate that the metal complex can competitively inhibit the binding between DNA and ethidium bromide. Viscosity experiments show that the binding of the metal complex increases the relative viscosity of DNA. These results suggest that the photoactive nickel diimine complex may interact with DNA by intercalation binding mode. Potential applications of the complex in photodynamic therapy are discussed.     

Complexation of Al(III) by 8-Hydroxyquinoline and Drastic Fluorescence Enhancement in Reverse Micelles

Complexation of Al^IIIby 8-hydroxyquinoline and fluorescence behavior of the quinolinate(s) were studied in reverse micellar systems at low water content, and compared to aqueous media. Two surfactants were used: one was cationic (CTAC: cetyltrimethylammonium chloride) and the other was anionic (AOT: sodium bis(2-ethylhexyl)sulfosuccinate). The results obtained in the CTAC/dichloromethane system (W= [H₂O]/[surfactant] = 0.9) showed that complexation occurred very likely in the oil phase and no micellar effect was observed. On the contrary, in the presence of AOT, specific micellar effects were observed due to the presence of the anionic polar heads: stabilization of the positively charged 1:1 and 1:2 chelates, at the expense of the neutral water-insoluble 1:3 chelate which is formed in aqueous solutions under similar conditions;drastic fluorescence enhancement factorsof 120 and 100 in AOT/heptane (W= 1.5) and AOT/dichloromethane (W= 1.6), respectively. Such factors have never been reported so far in either hydroorganic or direct micellar systems. In return, the length of time for the production of the complex(es) is increased because of the microheterogeneity of the medium and the small sizes of the water pools.