G. Venkatesh

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.

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.

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.

Azo-hydrazo Tautomerism and Inclusion Complexation of 1-phenylazo-2-naphthols with Various Solvents and β-cyclodextrin

Spectral characteristics of sudan I (SDI), sudan II (SDII) and mordant violet-5 (MV5) have been studied in various solvents and β-cyclodextrin (β-CD). The inclusion complex of the above molecules with β-CD was analyzed by UV-visible, fluorometry, and DFT methods. The solvent study shows that azo-hydrazo tautomer is present in these molecules. The increase in the fluorescence intensity and a large bathochromic shift in the S1 state indicate these molecules forms 1:1 inclusion complex with β-CD.

Investigation of inclusion complexes of sulfamerazine with α- and β-cyclodextrins: an experimental and theoretical study.

Inclusion complexation behavior and binding ability of sulfamerazine (SMRZ) with α- and β-cyclodextrins (α-CD and β-CD) were investigated. The formation of inclusion complexes are studied by UV-visible, fluorescence, time-resolved fluorescence, (1)H NMR, FT-IR, DSC, XRD, SEM, TEM and molecular modeling methods. Both experimental and PM3 results indicated that the SMRZ is partially encapsulated in the CD cavity. The different spectral shifts observed in both the CDs indicate that different types of inclusion complexes are formed. Nanosecond time-resolved fluorescence studies demonstrated that SMRZ exhibit biexponential decay in water and triexponential decay in CD solutions. The resonance of the aromatic protons of SMRZ showed remarkably upfield shift in the complexes suggested that the aniline ring deeply encapsulated in the CD cavity. The amino and amido stretching vibrations at 3483 cm(-1) and 3379 cm(-1) respectively are strongly affected in the inclusion complexes. DSC curves for the inclusion complexes exhibited a broad endothermic effect from 106.4 °C, 123.8 °C and 234.5 6 °C for α-CD and 118.2 °C and 231.4 °C for β-CD. TEM images of both inclusion complexes are forms a nanochain like agglomerated structures with a width ranging from 40 nm to 100 nm. Thermodynamic parameters and binding affinity of the inclusion complex formation were determined and discussed.

Fabrication of 2D nanosheet through self assembly behavior of sulfamethoxypyridazine inclusion complexes with α- and β-cyclodextrins

A 2D nanosheet was fabricated through the supramolecular self assembly of sulfamethoxypyridazine (SMP) and β-cyclodextrin (β-CD) inclusion complexes. HRTEM image exhibited 2D nanosheet morphology with a length of 1200mm and the sheet thickness of 60mm. It is noted that the nanosheet did not form a single layer aggregation but a bulk aggregation of SMP/β-CD inclusion complex. The formation of this multilayer 2D nanosheet based on the self assembly of SMP/β-CD inclusion complexes is proposed by the topological transformation as well as molecular modeling calculations. But, nanorods are formed in SMP/α-CD inclusion complex indicated that the nature of the CD determined the shape of the self assembled supramolecular architecture. The formation of nanomaterial was characterized by using FT-IR, DSC, PXRD, (1)H NMR, absorption, fluorescence and lifetime measurements.

Absorption and fluorescence spectral characteristics of norepinephrine, epinephrine, isoprenaline, methyl dopa, terbutaline and orciprenaline drugs

The absorption and fluorescence spectral characteristics of norepinephrine, epinephrine, isoprenaline, methyl dopa, orciprenaline and terbutaline have been investigated for levels of different pH and β-cyclodextrin (β-CD). The inclusion processes are discussed based on absorption, emission and semiempirical quantum mechanical calculations (CAChe – DFT). The pH study reveals that, deprotonation takes place in the CHOH group and the longer wavelength emission at 450 nm is due to intramolecular proton transfer. The β-CD study shows that the above-mentioned drugs form 1:1 inclusion complexes. Single-emission maximum in water (∼316 nm) and dual emission (316 nm, 450 nm) in β-CD is noticed for drugs. In the β-CD solutions, the shorter wavelength fluorescence intensity is regularly decreased and longer wavelength fluorescence intensity is increased. The alkyl chain and the hydroxyl group are present in the interior and hydrophilic parts of the β-CD cavity, respectively.

Supramolecular aggregates formed by sulfadiazine and sulfisomidine inclusion complexes with α- and β-cyclodextrins.

Sulfadiazine (SDA) and sulfisomidine (SFM) inclusion complexes with two cyclodextrins (α-CD and β-CD) are studied in aqueous as well as in solid state. The inclusion complexes are characterized by UV-visible, fluorescence, time correlated single photon counting, FTIR, DSC, PXRD and (1)H NMR techniques. The self assembled SDA/CD and SFM/CD inclusion complexes form different types of nano and microstructures. The self assembled nanoparticle morphologies are studied using SEM and TEM techniques. SDA/α-CD complex is formed hierarchal morphology, SDA/β-CD and SFM/β-CD complexes form the nanosheet self assembly. However, SFM/α-CD complex forms nanoporous sheet self assembly. van der Waals, hydrophobic and hydrogen bonding interaction play a vital role in the self assembling process.

Unusual spectral shifts of imipramine and carbamazepine drugs.

The absorption and fluorescence spectra of imipramine and carbamazepine have been recorded in solvents of different polarity and β-cyclodextrin (β-CD). The inclusion complexes for both drugs are investigated by UV-visible, fluorimetry and DFT. Solvents study shows isotropic polarizability structure is present in imipramine while the amide group inhibits the above structure in carbamazepine. The band width half a maximum of carbamazepine decreased in polar solvents suggest that different species present in non-polar solvents and among that one of this species is affected in protic solvents. Both drugs form two different 1:2 inclusion complexes with β-CD. The structured longer wavelength emission in β-CD solution suggests viscosity plays major roles in the inclusion complex. This study also confirms van der Waals forces and hydrophobic interactions are the driving forces in imipramine and hydrogen bonding interactions play major roles in carbamazepine.