N. Rajendiran

Dual Fluorescence of Fast Blue RR and Fast Violet B: Effects of Solvents and Cyclodextrin Complexation

Absorption and steady-state and time-resolved fluorescence spectra of fast blue RR (FBRR) and fast violet B (FVB) were studied in solvents with different polarities and in the presence of α- and β-cyclodextrins (CDs). Dual emission observed in nonpolar solvents suggested that the energy of the intramolecular charge transfer (ICT) state is lower than that of the locally excited state. The normal Stokes-shifted band originated from the locally excited state, and the large Stokes-shifted band was due to the emission from a planar intramolecular charge transfer (PICT) state. The ratio of the PICT emission to the normal emission increased with β-CD concentration, whereas it was constant upon addition of α-CD. This behavior is in accordance with CD-dependent decay times of PICT and normal emissions, indicating the formation of different 1:1 FBRR/CD inclusion complexes. The rise time for the PICT emission increased with β-CD concentration, whereas no rise time was observed in the case of the α-CD complex. The size of the dimethoxyaniline ring suggested that the orientation of FBRR in the β-CD complex was different from that in the α-CD complex. The benzamido moiety of FBRR is deeply encapsulated in the CD cavity, whereas the aniline ring is exposed to the hydrophilic part. Semiempirical quantum-mechanical (ΔE, ΔG, ΔH, ΔS, and HOMO-LUMO) calculations were also carried out to assign the encapsulation of FBRR and FVB.

Inclusion complex of sulfadimethoxine with cyclodextrins: preparation and characterization.

The inclusion complexation behavior, characterization and binding ability of sulfadimethoxine (SDMO) with α-cyclodextrin (α-CD) and β-cyclodextrin (β-CD) have been investigated both in solution and solid state by means of absorption, fluorescence, time-resolved fluorescence, (1)H NMR, FT-IR, DSC, SEM, TEM, XRD and molecular modeling methods. The spectral shifts revealed that the part of pyrimidine and aniline rings of SDMO are entrapped in the CD cavity. The stoichiometric ratio and association constant were determined by Benesi-Hildebrand plots and spectroscopic studies respectively. FT-IR spectroscopy was used to compare inclusion systems with physical mixtures, and demonstrated the complex formation in the solid state. The morphology and size of the nanoparticles of SDMO/CD complexes in aqueous solution were observed by TEM. The DSC analysis showed that the thermal stability of SDMO was enhanced in the presence of CD. Investigations of energetic and thermodynamic properties by PM3 method confirmed the stability of the inclusion complexes.

Solvatochromism and prototropism of diaminodiphenyl sulphones and 2-aminodiphenyl sulphone: a comparative study by electronic spectra

Abstract A comparative study of absorption and fluorescence maxima of 4,4′-diaminodiphenyl sulphone (4DADPS), 3,3′-diaminodiphenyl sulphone (3DADPS) and 2-aminodiphenyl sulphone (2ADPS) in different solvents reveals that (i) solvatochromic shifts are found to be mainly due to interaction of solvents with amino group, (ii) in any one solvent the net solvatochromic shifts of two amino groups are less than that of one amino group, (iii) fluorescence shift from cyclohexane to water is a maximum for 4DADPS and a minimum for 2ADPS and (iv) 4DADPS and 3DADPS possess more twisted intramolecular charge transfer character than 2ADPS. The excited-state acidity constants, determined by fluorimetric titration and Forster cycle methods, have been reported and discussed.

Excimer formation in inclusion complexes of β-cyclodextrin with salbutamol, sotalol and atenolol: Spectral and molecular modeling studies

The inclusion complexation behavior of salbutamol, sotalol and atenolol drugs with β-cyclodextrin (β-CD) were investigated by UV-visible, fluorometry, time resolved fluorescence, FT-IR, (1)H NMR, SEM and PM3 methods. The above drugs gave a single emission maximum in water where as dual emission in β-CD. In β-CD solutions the shorter wavelength fluorescence intensity was regularly decreased and longer wavelength fluorescence intensity increased. Addition of β-CD to aqueous solutions of drugs resulted into excimer emission. The excimer emission is concluded to be due to a 1:2 inclusion complex between β-CD and drug. Nanosecond time-resolved studies indicated that all drugs exhibited biexponential decay in solvents and triexponential decay in CD. Investigations of thermodynamic and electronic properties confirmed the stability of the inclusion complex.

Intramolecular Proton Transfer Effects on 2,6-diaminopyridine

The photophysical behaviour of 2,6-diaminopyridine (DAP) has been studied in solvents of different polarity, pH, β-cyclodextrin (β-CD) and compared with 2-amino pyridine (2AP). The inclusion complex of both molecules with β-CD are analysed by UV-visible, fluorimetry, FT-IR, 1H NMR, SEM and AM1 methods. The solvent studies shows i) DAP gives more red shifted absorption and emission maxima than 2AP molecule and ii) addition of amino group in 2AP effectively increase the resonance interaction in the pyridine ring. A regular red shift observed in acidic pH solutions suggests intramolecular proton transfer (IPT) present in both molecules. β-CD studies indicates i) in pH  ~ 7, a regular red shifted absorption and emission maxima observed in AP molecules suggests pyridine ring encapsulated in to the β-CD cavity (1:1 inclusion complex formed) and ii) in pH ~ 1, a blue shifted absorption maxima noticed in 2AP, is due to protonated amino group deeply encapsulated in to the hydrophobic part of the β-CD cavity.

Unusual spectral shifts on fast violet-B and benzanilide: Effect of solvents, pH and β-cyclodextin

The absorption and fluorescence spectra of fast violet-B (FVB) and benzanilide (BA) have been analysed in different solvents, pH and beta-cyclodextrin. The inclusion complex of FVB with beta-CD is investigated by UV-visible, fluorimetry, AM 1, FTIR and SEM. The absorption maximum of FVB (anilino substitution) is red shifted than that of BA, but the benzoyl substitution hardly changed the ground state structure of BA. Compared to BA, the emission maxima of FVB largely blue shifted in cyclohexane and aprotic solvents, but red shifted in protic solvents and the longer wavelength maxima in FVB is due to the intramolecular charge transfer (TICT). In BA, the normal emission originates from a locally excited state and the longer wavelength band due to intramolecular proton transfer in non-polar/aprotic solvents and in protic solvents it is due to TICT state. beta-CD studies reveal that, FVB forms 1:2 complex from 1:1 complex and BA forms 1:2 complex with beta-CD.

Azonium-Ammonium Tautomerism and Inclusion Complexation of 1-(2,4-diamino phenylazo) Naphthalene and 4-aminoazobenzene

Spectral characteristics of 1-(2,4-diamino phenylazo) naphthalene (FBRR, fat brown RR) and 4-aminoazobenzene (AAB) have been studied in various solvents, varying hydrogen ion concentrations and in β-cyclodextrin (β-CD). The inclusion complex of FBRR and AAB with β-CD were analysed by UV-visible, fluorometry and CAche-DFT methods. Solvent study reveals that only azo tautomer is present in both compounds and the large red shifted absorption and emission maxima of FBRR indicate naphthalene ring effectively increases the π-π* transition. Unusual red shift is observed in acid solutions suggests azonium-ammonium tautomer is present in both molecules. In β-CD solutions, the large hypsochromic shift is observed in S0 and S1 states indicates ortho amino group of FBRR molecule is entrapped in the β-CD cavity and the large bathochromic shift for AAB in the S1 state indicates 1:1 inclusion complex is formed.

Spectral characteristics of sulphadiazine, sulphisomidine: effect of solvents, pH and β-cyclodextrin

The absorption and fluorescence spectra of sulphadiazine (SDA), sulphisomidine (SFM) and sulphanilamide (SAM) have been analysed in different solvents, pH and β-cyclodextin. The inclusion complexes of the above sulphonamides with β-CD were investigated by UV–Vis, fluorometry, DFT, FT–IR and 1H-NMR. The solvent study shows that the absorption and emission maxima of the SDA and SFM are more red-shifted than SAM molecule. In non-aqueous solvents, a single fluorescence band (340 nm) is observed, whereas in water and β-CD solutions, dual emission (at 340 and 430 nm) is noticed for SDA and SFM molecules. The dual emission is due to twisted intramolecular charge transfer band (TICT). Studies on β-CD solutions reveal that (1) sulphonamides form 1 : 1 inclusion complex with β-CD; and (2) the red-shift and the presence of TICT in the β-CD medium confirm that the heterocyclic ring is encapsulated in the hydrophobic part and aniline ring is present in the hydrophilic part of the β-CD cavity.

LUMINESCENCE CHARACTERISTICS OF 4,4'-DIAMINODIPHENYL METHANE IN DIFFERENT SOLVENTS AND AT VARIOUS PH

Abstract The effects of solvents and pH on absorption and fluorescence spectra of 4,4′-diaminodiphenyl methane (DADPM) have been investigated. The solvatochromic shifts reveal that in the ground state the CH 2 group isolates two phenyl rings whereas in the excited singlet state (S 1 ) there is a resonance interaction between the rings. The dual luminescence of the monocation of DADPM in polar and nonpolar solvents is explained by the formation of twisted intramolecular charge transfer state. An unusual equilibrium between the dication and the neutral form is observed in the ground state.

Inclusion complexes of sulphanilamide drugs and β-cyclodextrin: a theoretical approach

PM3 theoretical methodology was used to access and compare the relative stability of inclusion complexes formed by sulphadiazene, sulphisomidine, sulphamethazine and sulphanilamide with β-cyclodextrin (β-CD). The study predicted that (i) the heterocyclic ring is encapsulated in the hydrophobic part and aniline ring is present in the hydrophilic part of the β-CD cavity and (ii) intermolecular hydrogen bonds were formed between host and guest molecules. The negative free energy and enthalpy changes indicated that all the four inclusion complexation processes were spontaneous and enthalpy driven process. HOMO and LUMO orbital investigation confirmed that the stability increased in the inclusion complexes and also proved no significant change in the electronic structure of the guest and host molecules after complexation.