A. Ram Reddy

Absorption and fluorescence spectra of 7-aminocoumarin derivatives

Abstract The absorption and fluorescence spectra of twelve 7-aminocoumarin derivatives have been studied with methanol and chloroform as solvents. Electronic transitions to nπ * states have been traced. The effect of different substituents on the nitrogen was easily observed in the fluorescence spectra. Fluorescence quantum yields and oscillator strengths were evaluated. The role of hydrogen bonding on emission maxima, quantum yields and photolytic dissociation were discussed.

2-Hexylaminoethylamidonaphthalimide as Cu2+ sensor

New fluorescent hexylaminoalkylamidonaphthalimides were synthesized and their fluorescence was investigated in different solvents. The fluorescence intensity of hexylaminoalkylamidonaphthalimides is directly related to the number of carbons in the intervening chain between the naphthalimide and n-hexylamine. Among the hexylaminoalkylamidonaphthalimides, 2-hexylaminoethylamidonaphthalimide was developed into a new fluorogenic probe. The bidentate 2-hexylaminoethylamidonaphthalimide acted as fluorescent chemosensor with a high selectivity and suitable affinity towards Cu(2+) in aqueous medium (pH 7.4). This technique of detection of Cu(2+) is highly sensitive and can detect 0.1 μM range.

Synthesis of a few cyclothiadiazanones and aminosulfonyl benzamides from saccharin

Saccharin is hydrolyzed with two different acids to yield 1,2-di-acid. The di-acid, on chlorination with phosphorous pentachloride, gave 2-chlorosulfonylbenzoyl chloride. The 2-chlorosulfonylbenzoyl chloride on hydrazinolysis gave benzothiadiazinetrione, while with phenyl hydrazine it selectively yielded 2-phenylbenzothiadiazinetrione. 2-chlorosulfonoylbenzoyl chloride with different aromatic 1,2-diamines resulted in dibenzothiadiazocine derivatives. Electron-donating groups in the diamine facilitate while the electron-withdrawing groups retard the cyclization. However, aliphatic diamines, aniline and substituted anilines readily gave acyclic aminosulfonyl carboxybenzamides on condensation with 2-chlorosulfonylbenzoyl chloride. The di-acid and anhydride did not react with either hydrazine/phenyl hydrazine or amines to give the above products. However, when its ester derivative, isopropyl-2-chlorosulfonylbenzoate, condensed with hydrazine, it gave benzothiadiazinetrione. But the ester failed to react with phenyl hydrazine. All the condensation reactions were carried out at room temperature.Saccharin is hydrolyzed with two different acids to yield 1,2-di-acid. The di-acid, on chlorination with phosphorous pentachloride, gave 2-chlorosulfonylbenzoyl chloride. The 2-chlorosulfonylbenzoyl chloride on hydrazinolysis gave benzothiadiazinetrione, while with phenyl hydrazine it selectively yielded 2-phenylbenzothiadiazinetrione. 2-chlorosulfonoylbenzoyl chloride with different aromatic 1,2-diamines resulted in dibenzothiadiazocine derivatives. Electron-donating groups in the diamine facilitate while the electron-withdrawing groups retard the cyclization. However, aliphatic diamines, aniline and substituted anilines readily gave acyclic aminosulfonyl carboxybenzamides on condensation with 2-chlorosulfonylbenzoyl chloride. The di-acid and anhydride did not react with either hydrazine/phenyl hydrazine or amines to give the above products. However, when its ester derivative, isopropyl-2-chlorosulfonylbenzoate, condensed with hydrazine, it gave benzothiadiazinetrione. But the ester failed to react with ...

Synthesis of 1,4-dihydropyridines under solvent free conditions and investigation of their photo physical properties.

Synthesis of five 4-aryl substituted 1,4-dihydropyridines was developed following condensation of multi component reaction strategy using yttrium triflate as a catalyst. The absorption and fluorescence properties of structurally related 4-aryl 1,4-dihydropyridines in different solvents of varied polarities was investigated. The absorption maxima of these compounds follow no order of solvent polarity and nature of substitution. The spectral characteristics are solvent and compound specific. Fluorophores with electron withdrawing group have larger fluorescence quantum yields and greater solvatochromism than the compounds with electron donating groups. Protic solvents yielded higher fluorescence quantum efficiency. The chemical shift of the proton attached to C-4 and the carbonyl stretching frequency of bis acetyl groups at 3 and 5-positions exhibited a linear relationship with Hammetts para substituent constants while no such relationship exists between the latter and electronic absorption maxima, fluorescence emission maxima, fluorescence quantum efficiency and Stokes shift.

Structure dependent prototropy in 4-hydroxy-3-formylideneamino-1-methyl/phenylquinolin-2-ones

The electronic absorption spectra of 4-hydroxy-3-formyl quinolin-2-ones and their Schiff bases were investigated in various solvents of varying polarity. The three aromatic transitions of napthalene in quinolin-2-one are shifted to longer wavelength on their transformation to anils. Electron-donating group in the anils lead to enolimine form, while electron-withdrawing group leads to an equilibrium mixture of enolimine and ketoamine forms and the Schiff base derived from alkyl amine exist in ketoamine form. The prototropic interconversion of enolimine and ketoimine forms in the anils with the electron-withdrawing substituted anils is further supported by proton NMR studies. The spectral shifts are solvent dependent. Dipolar aprotic solvents bring bathochromic shift while polar protic solvents cause blue shift in the longer wavelength absorption maxima. In the case of Schiff bases substituted by electron-donating group the bathochromic shift is directly related to the polarity of the solvents.

Efficient Procedure for the Preparation of Oligomer-Free Nα-Fmoc Amino Acids

Abstract A two-step method is presented for the peptide-free, high-purity, and high-yield synthesis of Nα-Fmoc amino acids. The first step involves the preparation of stable dicyclohexylammonium–amino acid ionic adduct in acetone. Subsequently, the ionic adducts, on reaction with Fmoc-Nosu under mild alkaline conditions, give dipeptide-free Nα-Fmoc amino acids. The positive charge of the dicyclohexylammonium counterion in the ionic salt has a longer radius, moderating the nucleophilicity of the carboxylate ion of the amino acid and preventing by-products by arresting the formation of mixed anhydrides, the precursors of oligopeptide impurities.

Synthesis and photophysical properties of 1, 4-disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazole

AbstractRegioselective synthesis of a series of 1,4-disubstituted of naphthoxymethyl-N-alkyl naphthalimide-1,2,3-triazoles employing click reaction is presented. Highly selective and efficient copper(I)-catalysed 1,3-dipolar cyclo addition between 1-naphthylpropargylic ether and azido alkyl naphthalimides yielded the title compounds in 74% to 94%. The structure of all the new 1,2,3-triazoles was characterized by 1HNMR, 13C NMR, IR and Mass. The electronic absorption and emission studies revealed that the light absorbing and emitting chromophore is the naphthoxy moiety. There is no extensive delocalization of aromatic π-electrons in the active chromophore which exhibited lower quantum yields and lower Stokes shifts. Graphical AbstractSynthesis and photophysical properties of 1,4-disubstituted naphthyloxymethyl-N-alkyl naphthimido-1,2,3-triazole are presented.

Synthesis and fluorescence study of Naphthalimide-Coumarin, Naphthalimide-Luminol conjugates

Fluorescent naphthalimide-coumarin and naphthalimide-luminol conjugates were prepared by nucleophilic substitution reaction. The synthesized conjugates were characterized by 1H-NMR, 13C-NMR, mass and IR spectra. The absorption and fluorescence of these conjugates revealed that naphthalimide-luminol conjugates are more fluorescent than the naphthalimide-coumarin conjugates. In proton accepting DMSO solvent the fluorescence of the conjugates was quenched, while in proton donating ethanol solvent enhanced fluorescence was noticed. Based on the excitation maxima and fluorescence maxima it was found that in naphthalimide-coumarin conjugates coumarin acting as donor and naphthalimide acting as acceptor where as in naphthalimide-luminol conjugates naphthalimide acts as donor and luminol acts as acceptor.Fluorescent naphthalimide-coumarin and naphthalimide-luminol conjugates were prepared by nucleophilic substitution reaction. The synthesized conjugates were characterized by 1H-NMR, 13C-NMR, mass and IR spectra. The absorption and fluorescence of these conjugates revealed that naphthalimide-luminol conjugates are more fluorescent than the naphthalimide-coumarin conjugates. In proton accepting DMSO solvent the fluorescence of the conjugates was quenched, while in proton donating ethanol solvent enhanced fluorescence was noticed. Based on the excitation maxima and fluorescence maxima it was found that in naphthalimide-coumarin conjugates coumarin acting as donor and naphthalimide acting as acceptor where as in naphthalimide-luminol conjugates naphthalimide acts as donor and luminol acts as acceptor.

Potential benefits of triethylamine as n-electron donor in the estimation of forskolin by electronic absorption and emission spectroscopy

Diterpenoid forskolin was isolated from Coleus forskolii. The electronic absorption and emission studies of forskolin were investigated in various solvents with an aim to improve its detection limits. The two chromophores present in the diterpenoid are not conjugated leading to the poor absorption and emission of UV light. The absorption and fluorescence spectra were solvent specific. In the presence of a monodentate ligand, triethylamine the detection of forskolin is improved by 3.63 times in ethanol with the fluorescence method and 3.36 times in DMSO by the absorption spectral method. The longer wavelength absorption maximum is blue shifted while the lower energy fluorescence maximum is red shifted in the presence of triethylamine. From the wavelength of fluorescence maxima of the exciplex formed between excited forskolin and triethylamine it is concluded that the order of reactivity of hydroxyl groups in the excited state forskolin is in the reverse order to that of the order of the reactivity of hydroxyl groups in its ground state.

Exciplex formation in 2-propanol solutions of imidazo[4,5-f]quinolines

Abstract The association of the excited state derived from four imidazo[4,5- f ]-quinolines with 2-propanol in cyclohexane has been studied. The unusual bathochromic shift and bandwidth of the fluorescence spectra of these heterocyclic compounds in 2-propanol—cyclohexane solutions compared with those obtained in cyclohexane solutions have been attributed to the association of the excited state imidazoquinolines with the 2-propanol molecules. Hydrogen bonding between the imidazole NH moiety of the excited state imidazoquinolines and the 2-propanol is shown to be responsible for the association.