Spectrophotometric study of charge transfer complex between 2,6-diaminopyridine and 2,5-dihydroxy-p-benzoquinone

Charge transfer (CT) complex formation between 2,6-diaminopyridine (2,6-DAP) as the electron donor with 2,5-dihydroxy-p-benzoquinone (DHBQ) as the electron acceptor has been studied spectrophotometrically in different polar solvents at room temperature. A new absorption band due to CT complex formation was observed near 490?nm. The stoichiometric ratio of the complex has been identified by Job's, photometric and conductometric titration methods to be 1?:?1. Benesi–Hildebrand equation has been applied to estimate the formation constant (K _CT) and molecular extinction coefficient (ε). They recorded high values confirming high stability of the formed complex. The physical parameters, oscillator strength (f), transition dipole moment (μ), ionisation potential (I _D), resonance energy (R_N ) and standard free energy change (ΔG°) of the formed complex were determined and evaluated in the different solvents. The solid complex between 2,6-DAP and DHBQ has been isolated and characterised using elemental analysis, FT-IR and ¹H-NMR measurements.     

Solvation and temperature effect on the charge-transfer complex between 2-amino-4-picoline with 2,5-dihydroxy-p-benzoquinone

The charge-transfer (CT) complex between the donor 2-amino-4-picoline (2A4P) and the acceptor 2,5-dihydroxy-p-benzoquinone (DHBQ) was studied spectrophotometrically in different polar and non-polar solvents. The molecular composition of the complex, in all solvents, was determined by Job's method of continuous variation and photometric titrations to be 1:1. Benesi–Hildebrand equation has been applied to estimate the formation constant (K _CT) and molecular extinction coefficient (ε) of the formed complex. The variation in K _CT was rationalised based on Taft–Kamlet and electric permittivity parameters of the used solvents. Thermodynamic parameters ΔH°, ΔG° and ΔS° were estimated, they were all negative so the studied complex is reasonably stable and exothermic in nature. In addition, the thermodynamic properties were observed to be sensitive to the nature of the solvent. Moreover, the solid 1:1 CT complex between 2A4P and DHBQ was isolated and characterised using elemental analysis, FTIR and ¹H NMR measurements.     

Spectrophotometric study on the charge transfer reaction between 2-amino-4-methylpyridine with chloranilic acid in polar solvents

Charge transfer (CT) complexes formed between 2-amino-4-methylpyridine as electron donor, chloranilic acid as electron acceptor was investigated spectrophotometrically in acetonitrile (AN), methanol (MeOH) and binary mixture of acetonitrile 50% + methanol 50% (MeOH-AN). Minimum–maximum absorbance method has been used for estimating the formation constants of the CT reactions (K_CT). Job’s method of continuous variation and photometric titration studies were used to detect the stoichiometric ratios of the formed complexes, and they showed that 1:1 complexes were produced. The molar extinction coefficient (e), oscillator strength (f), dipole moment (l), CT energy (E_CT), ionisation potential (I_P) and the dissociation energy (W) of the formed complexes were estimated; they reached acceptable values suggesting the stability of the formed CT complexes. The solid CT complexes were synthesised and characterised by elemental analyses, ¹H NMR and FTIR spectroscopies where the formed complexes included proton and electron transfer.     

UVRR spectroscopic studies of valinomycin complex formation in different solvents

We investigated the complexation of valinomycin (VM) in different solvent environments with the aid of the UVRR spectroscopy. By probing the 206.5 and 229 nm excited Raman spectra, we showed that new bands are observed around 1700 and 1290 cm(-1). We assigned the 1700 cm(-1) band to the hydrogen bonded ester carbonyl stretching vibration. In a polar solvent, VM-K(+) complexation shows significant intensity changes in amide and ester carbonyl stretching region. Because of the small amount of conformational interconversion, complexation has a negligible effect on other band intensities including, the amide III, C(alpha)H, and amide II. We also showed the effects of the solvent polarity on the solution conformation of VM.     

Synthesis and spectroscopic studies of the charge transfer complexes of 2- and 3-aminopyridine

The interactions of the electron donors 2-aminopyridine (2APY) and 3-aminopyridine (3APY) with the π-acceptors tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), 2-chloro-1,3,5-trinitrobenzene (picryl chloride, PC), and 2,3,5,6-tetrachloro-1,4-benzoquinone (chloranil) were studied spectrophotometrically in chloroform at room temperature. The electronic and infrared spectra of the formed molecular charge transfer (CT) complexes were recorded. Photometric titration showed that the stoichiometries of the reactions were fixed and depended on the nature of both the donor and the acceptor. The molecular structures of the CT-complexes were, however, independent of the position of the amino group on the pyridine ring and were formulated as [(APY)(TCNE)], [(APY)(DDQ)], [(APY)(PC)], and [(APY) (chloranil)]. The formation constants (K_CT), charge transfer energy (E_CT) and molar extinction coefficients (_CT) of the formed CT-complexes were obtained.     

Spectrophotometric and spectroscopic studies of charge transfer complexes of p-toluidine as an electron donor with picric acid as an electron acceptor in different solvents

The charge transfer complexes of the donor p-toluidine with π-acceptor picric acid have been studied spectrophotometrically in various solvents such as carbon tetrachloride, chloroform, dichloromethane acetone, ethanol, and methanol at room temperature using absorption spectrophotometer. The results indicate that formation of CTC in non-polar solvent is high. The stoichiometry of the complex was found to be 1:1 ratio by straight-line method between donor and acceptor with maximum absorption bands. The data are discussed in terms of formation constant (K_CT), molar extinction coefficient (?_CT), standard free energy (ΔG^o), oscillator strength (f), transition dipole moment (μ_EN), resonance energy (R_N) and ionization potential (I_D). The results indicate that the formation constant (K_CT) for the complex was shown to be dependent upon the nature of electron acceptor, donor and polarity of solvents that were used.     

X-ray photoelectron spectroscopic studies of charge transfer interactions in electroactive polyaniline

Four modes of charge transfer interactions in polyaniline (PAN), viz. acid protonation, self-doping, charge transfer interactions with organic acceptors, and charge transfer interactions with surface grafted functional polymers have been studied by X-ray photoelectron spectroscopy (XPS). In the case of acid protonation, the protonation behavior of volatile and non-volatile acid differs. The structures of sulfonated leucomeraldine (LM) and nigraniline (NA) are similar to those of sulfonated and self-protonated emeraldine (EM). A substantially higher degree of charge transfer interaction with the organic acceptors is observed for EM film that has been subjected to one cycle of acid/base treatment. The charge transfer interactions with the organic acceptors have proceeded further than the pure formation of molecular complexes. Both pristine and Ar plasma or O₃ pretreated EM films are susceptible to surface modifications by graft copolymerization. The protonic acid functional groups of the graft readily give rise to a self-protonated EM surface.     

Spectroscopic,thermal studies and molecular modelling of charge transfer complexation between 5-amino-2-methoxypyridine with chloranilic acid in different polar solvents

Charge transfer (CT) interaction between 5-amino-2-methoxypyridine (5AMPy), as electron donor (proton acceptor), with 3,6-dichloro-2,5-dihydroxy-p-benzoquinone (chloranilic acid, H₂CA), as electron acceptor (proton donor), has been investigated spectrophotometrically in the polar protic solvents ethanol (EtOH) and methanol (MeOH) and the aprotic one acetonitrile (AN). Pink-coloured solution is formed instantaneously upon mixing 5AMPy with H₂CA solutions in all solvents, which is the hallmark evidence of CT complex formation. Based on Job’s method of continuous variations, as well as spectrophotometric titrations, the stoichiometry of the complex was found to be 1:1 [(5AMPy) (H₂CA)] in all solvents. Benesi–Hildebrand equation has been applied to estimate the formation constant of the produced CT complex (K_CT) and its molar absorptivity (ε), they reached high values, confirming the complex high stability. Solid CT complex has been synthesised and analysed by elemental analyses and FTIR, ¹H NMR spectroscopies, where 2:1 [(5AMPy)₂ (H₂CA)] CT complex was obtained.     

Applications of chemometric methods to spectroscopic studies of aggregate formation and twisted intramolecular charge transfer in the gas phase and in non-polar solvents

Principal component analysis—self-modelling and non-linear least-squares spectral resolution methods were applied to quantitative fluorescence studies of the aggregate formation and the twisted intramolecular charge transfer (TICT) state emission of p-(N,N-diethylamino)ethylbenzoate (DEAEB) in the gas phase and in low-density supercritical ethane. A broad Gaussian-like fluorescence band at approximately 400 nm was obtained and assigned to the emission of DEAEB microcrystals or microsolids. It is shown that the red-shifted band can essentially be eliminated by keeping the sample undisturbed for a period of time and by selecting appropriate excitation wavelengths. The results support the conclusion that even in the gas phase the contribution of DEAEB TICT state emission is still significant. It is also demonstrated that a quantitative characterization of the excited state equilibium between the locality excited and TICT states of DEAEB in non-polar solvents can be accomplished by application of a spectral resolution method.     

2,5-二溴-4-硝基咪唑的合成

以咪唑为原料,经硝化和溴化反应合成了抗炎药物中间体——2,5-二溴-4-硝基咪唑,总收率80.3%,其结构经1H NMR和IR确认。     

Synthesis, characterization, spectroscopic and thermodynamic studies of charge transfer interaction of a new water-soluble cobalt(II) Schiff base complex with imidazole derivatives

The water-soluble cobalt(II) tetradentate Schiff base complex [Co(II)L](ClO4)(2), L: (N,N'-bis(5-[(triphenylphosphonium)-methyl]salicylidine)-o-phenylenediamineperchlorate has been synthesized and characterized. This complex forms charge transfer (CT) complexes with imidazole and 1-methylimidazole. The formation constant, molar absorptivity (epsilon'), and thermodynamic parameters for charge transfer complexes formation of cobalt(II) Schiff base complexes with imidazole derivatives were determined by using UV-vis spectrophotometric method in aqueous solutions at constant ionic strength (I=0.2mol dm(-3) KNO3) at pH 6.0 and various temperatures between 292 and 315K.     

Photodecomposition and charge transfer complexes of acetylferrocene in binary solvents

Photoreactions of acetylferrocene in equimolar binary solvents: CCl₄ — cyclohexane and C₂Cl₄ — cyclohexane were investigated. Photoproducts were identified and the relations between the quantity of photoproducts, their quantum yield, the amount of decomposed acetylferrocene and exposure time and wavelength were determined. Equilibrium constantsK and molar extinction coefficients _c of the CT complexes formed between acetylferrocene and halogen derivative were determined.

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Photochemische Zersetzung und Charge-Transfer-Komplexe von Acetylferrocen in binären Lösungsmitteln

Zusammenfassung Die Photoreaktionen von Acetylferrocen in binären (äquimolaren) Lösungsmittelgemischen — CCl₄/Cyclohexan und C₂Cl₄/Cyclohexan — wurden untersucht. Die Photoprodukte wurden identifiziert und die Abhängigkeit ihrer Menge, der Quantenausbeute und der Menge des zersetzten Acetylferrocens von der Belichtungszeit und der Wellenlänge bestimmt. Die Gleichgewichtskonstanten und die molaren Extinktionskoeffizienten der Charge-Transfer-Komplexe zwischen Acetylferrocen und den Halogenverbindungen wurden ermittelt.

     

Utilization of 2-ylidene-4-thiazolidinones in the synthesis of heterocyclic compounds. Part I: Synthesis of pyrazoles

2-Ylidene and 2,5-diylidene-4-thiazolidinones 2a–d were synthesized and converted into pyrazole derivatives 4a–d by reaction with hydrazine hydrate. A mechanism of this novel conversion is suggested.     

氨基酸-多金属氧酸盐电荷转移配合物的固相法合成及表征

多金属氧酸盐是一类纳米级金属-氧多核配合物,可通过变换抗衡阳离子、杂原子、配原子等方法从原子、分子水平上进行物理或化学修饰,与不同的有机分子结合后可以获得具有特定功能和性质的化合物.     

Spectroscopic analysis of charge transfer complex formation between neuroleptics and iodine

Molecular interactions between iodine and various neuroleptics were investigated by UV/Vis spectroscopy. Iodine was found to form charge transfer complexes in a 1:1 stoichiometry and of n-sigma type with these molecules. The values of the formation constants Kc of these iodinated complexes indicate a strong donor-acceptor interaction. These drugs can therefore be expected to interfere with thyroid metabolism.     

Synthesis and spectroscopic studies of trans-bis-(3,5-dimethyl-4-nitrosopyrazole) dimer

Bis-(3,5-dimethyl-4-nitrosopyrazole) dimer was prepared by reaction of acetyl acetone with nitrous acid and condensation with hydrazine. Spectroscopic techniques, including IR, UV, ¹H NMR, and ¹³C NMR, and CHN analysis were used to identify the product.     

Spectroscopic studies of charge transfer complexes of meso‐tetra‐p‐tolylporphyrin and its zinc complex with some aromatic nitro acceptors in different organic solvents

The charge transfer complex (CTC) formation of 5,10,15,20‐tetra(p‐tolyl)porphyrin (TTP) and zinc 5,10,15,20‐tetra(p‐tolyl)porphyrin with some aromatic nitro acceptors such as 2,4,6‐trinitrophenol (picric acid), 3,5‐dinitrosalicylic acid, 3,5‐dinitrobenzoic acid (DNB) and 2,4‐dinitrophenol (DNP) was studied spectrophotometrically in different organic solvents at different temperatures. The spectrophotometric titration, Job's and straight line methods indicated the formation of 1:1 CTCs. The values of the equilibrium constant (K_CT) and molar extinction coefficient (ε_CT) were calculated for each complex. The ionization potential of the donors and the dissociation energy of the charge transfer excited state for the CTC in different solvents was also determined and was found to be constant. The spectroscopic and thermodynamic properties were observed to be sensitive to the electron affinity of the acceptors and the nature of the solvent. No CT band was observed between Zn‐TTP as donor and DNP or DNB as acceptors in various organic solvents at different temperature. Bimolecular reactions between singlet excited TTP (¹TTP*) and the acceptors were investigated in solvents with various polarities. A new emission band was observed. The fluorescence intensity of the donor band decreased with increasing the concentration of the acceptor accompanied by an increase in the intensity of the new emission. The new emission of the CTCs can be interpreted as a CT excited complex (exciplex). Copyright © 2007 John Wiley & Sons, Ltd.     

In situ synthesis, photometric and spectroscopic studies of chelating system during the 1,4,7,10,13,16-hexaoxacyclooctadecane charge transfer reaction with different acceptors

Electron donor acceptor complexes (EDA) of the 1,4,7,10,13,16-hexaoxacyclooctadecane (18-crown-6) as a rich donor were spectrophotometrically discussed and synthesized in solid form according the interactions with different nine of usual π-acceptors like 2,3,5,6-tetrachlorocyclohexa-2,5-diene-1,4-dione (p-chloranil; p-CHL), tetrachloro-1,2-benzoquinone (o-chloranil; o-CHL), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), tetracyanoquinodimethane (TCNQ), 2,6-dichloroquinone-4-chloroimide (DCQ), 2,6-dibromoquinone-4-chloroimide (DBQ), 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid; CLA), N-bromosuccinimide (NBS), 2,4,6-trinitrophenol (picric acid; PA). Spectroscopic and physical data such as formation constant (K(CT)), molar extinction coefficient (?(CT)), standard free energy (ΔG°), oscillator strength (f), transition dipole moment (μ), resonance energy (R(N)) and ionization potential (I(p)) were estimated in chloroform or methanol at 25°C. Based on the elemental analysis and photometric titrations the CT-complexes were formed indicated the formation of 1:1 charge-transfer complexes for the o-CHL, TCNQ, DCQ, DBQ and NBS acceptors but 1:3 ratio for p-CHL, DDQ, CLA and PA, respectively. The charge-transfer interactions were interpretative according to the formation of dative ion pairs [18C6(?+), A(?-)], where A is acceptor. All of the resulting charge transfer complexes were isolated in amorphous form and the complexes formations on IR and (1)H NMR spectra were discussed.     

A spectrophotometric study of the charge transfer complexes of [60]fullerene with different tert-butylcalix[4]crowns

Formation of the charge-transfer complexes between various calix[4]crowns (1-4) and [60]fullerene were studied in toluene solution using UV-vis spectrophotometry. The stability constants and the thermodynamic data of the resulting 1:1 complexes were determined and were found to decrease with increasing the size of the crown moiety of the calixcrown. Except the complex of 3, all the complexes were found to be enthalpy stabilized but disfavored in terms of entropy.     

Ultraviolet and nuclear magnetic resonance studies of the fumaric nitrile-benzene charge transfer complex

The fumaric nitrile-benzene charge transfer complex has been investigated. The equilibrium constant K has been determined by both ultraviolet and nuclear magnetic resonance spectroscopy, following the method of Benesi-Hildebrand. The experimental result k_NMR > K_UV is associated with the structure of the complex.