Spectrofluorometric studies on the binding interaction of bioactive imidazole with bovine serum albumin: a DFT based ESIPT process

Protein interactions, molecular docking, antimicrobial and antifungal studies of terpyridine ligands

Resistance to antibiotics/antibacterials/antifungals in pathogenic microbes has been developing over the past few decades and has recently become a commonplace public-health peril. Thus, alternative nontoxic potent antibiotic agents are covertly needed to control antibiotic-resistant outbreaks. In an effort to combat the challenges posed by the co-occurrence of multidrug resistance, two terpyridine ligands 4'-(4-N,N'-dimethylaminophenyl)-2,2':6',2″-terpyridine (L1) and 4'-(4-tolyl)-2,2':6',2″-terpyridine (L2) have been designed, prepared and confirmed their structure by spectral studies. Thereafter, antimicrobial assay was performed against gram positive and negative bacterial strains along with fungal strains. Both compounds L1 and L2 exhibited remarkable inhibitory activities against bacteria, Escherichia coli and Staphylococcus aureus at MIC values 6.25 and 3.125 µg/ml, respectively. In addition, in silico molecular docking studies were ascertained with bacterial DNA gyrase and fungal demethylase. Furthermore, both L1 and L2 could bind Bovine Serum Albumin (BSA) protein and binding interaction has been studied with the help of UV-Visible and fluorescence spectroscopy. While fluorescence of BSA unperturbed in the presence of L2, an addition of L1 to the solution of BSA resulted significant quenching. The binding constant calculations at different temperature confirmed that the fluorescence quenching between BSA and L1 is predominantly static in nature. The toxicity of L1 and L2 was checked using Drosophila melanogaster. The toxicity analysis suggest both the dyes are non-cytotoxic in nature.Communicated by Ramaswamy H. Sarma.

A nitro-capped tetraaniline derivative with AIE features for BSA detection and the selective imaging of Gram-positive bacteria

A nitro-capped tetraaniline derivative (NO2-B3-Ani4-NO2) with AIE feature was synthesized and characterized, which presented an ultrasensitive turn-on response towards bovine serum albumin and selective imaging of Gram-positive bacteria based on AIE mechanism.

Deciphering the binding behaviours of BSA using ionic AIE-active fluorescent probes

The binding behaviours of a transport protein, bovine serum albumin (BSA), in its native, unfolding and refolding states have been probed by monitoring the emission changes of two exogenous AIE-active fluorescent probes, M2 and M3, which are designed to be anionic and cationic, respectively. Due to their AIE properties, both M2 and M3 display emission enhancement when bound to the hydrophobic cavity of BSA. The binding site of M2 and M3 is found to be subdomain IIA. Then, the BSA + M2 and BSA + M3 systems are utilized to fluorescently signal the conformation changes of BSA caused by various external stimuli, including thermally or chemically induced denaturation. The data confirmed the multi-step unfolding process and the existence of a molten-globule intermediate state. The unfolding process consists of the rearrangement of subdomain IIA, the exposure of a negatively charged binding site in domain I that prefers interacting with cationic species, and the transformation of the molten-globule intermediate into the final random coil. The anionic and cationic modifications of the probes enable us to observe that electrostatic interactions play a role in the folding and unfolding of BSA.

Single molecule laser spectroscopy

In this article, we discussed some single molecule spectroscopy techniques and methods. We have chosen the simplicity in this survey based on our laboratory experience in this field. We concentrated on the imaging by both techniques the wide field and the scanning microscopes. Other imaging enhancements on the technique like extended resolution wide field, the total internal reflection imaging, and its derivatives are also reviewed. In addition to the imaging techniques, some diffusion techniques also are discussed like fluorescence correlation spectroscopy. The related methods like Forester resonance transfer, photo-induced electron transfer and anisotropy (steady state and time decay) are also discussed. In addition, we elucidated some simple details about the theory behind the FCS and its resulting curve fitting. This review is preceded by general introduction and ended with the conclusion.

Sensitive and selective PET-based π-expanded phenanthrimidazole luminophore for Zn2+ ion

The novel photoinduced electron transfer (PET) chemosensor, 1-(1-(4-methoxyphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [MPPN] and its zinc complex were synthesised and characterized by electronic spectral and Frontier molecular orbital energy analysis. MPPN becomes efficient fluorescent chemosensor upon binding with metal ions and shows a strong preference toward Zn(2+) ion. Density Functional theory (DFT) calculations reveal that luminescence of free MPPN originates from its orbital structure in which two π-orbitals (HOMO and HOMO-1) of the imidazole ring are situated between two π-orbitals (HOMO-2 and LUMO) of the naphthyl fragment. Therefore the absorption and emission processes occur between the two π- orbitals (HOMO-2 and LUMO). The two higher energy imidazole orbitals (HOMO and HOMO-1) serve as quenchers for the excited state of the molecule through nonradiative processes. Upon binding with Zn(2+) ion, MPPN becomes a highly luminescent with λemi - 421 nm. The significant enhancement of luminescence upon binding with Zn(2+) ion is attributed to the stabilization of HOMO-2 and HOMO-1 π-orbitals of imidazole ring upon their engagement in new bonds with Zn(2+) ion. The affinity of MPPN to zinc ion is found to be very high [K = 6 × 10(6) M(-1)] when compared with other metals ions. The nonlinear absorption coefficient γ for MPPN is 1.9 × 10(-12) m/W and 3.9 × 10(-11) m/W for MPPN-Zn complex.

Dynamics of Solvent Controlled ESIPT of π-Expanded Imidazole Derivatives - pH Effect

A set of π-expanded imidazole derivatives employing excited state intramolecular proton transfer (ESIPT) was designed and synthesized. The relationship between the structure and photophysical properties were thoroughly elucidated by comparing with the analogue blocked with ESIPT functionality. The compound possessing an acidic NH function as part of an intramolecular hydrogen bond system has much higher fluorescence quantum yield and Stokes shift and the π-expansion strongly influences the optical properties. The occurrence of ESIPT for imidazole tosylamide derivatives were less affected by the hydrogen-bonding ability of the solvents compared to the unprotected amine. The low pKa values for the monocation ⇌ neutral equilibrium indicate the presence of intramolecular hydrogen bonding between the amino proton and tertiary nitrogen atom.

Intramolecular excited proton transfer of 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol--a combined experimental and quantum chemical studies

Synthesis of the 1-(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)naphthalen-2-ol [PPIN] is reported, spectral and fluorescent properties of the title compound are investigated. The feasibility of excited state intramolecular proton transfer (ESIPT) has been argued from the changeover of relative stability of the enol and the keto forms on photoexcitation from the S0-PES to the S1-PES. Critical evaluation on the modulations of geometrical parameters other than the proton transfer reaction coordinate has also been undertaken. The intramolecular hydrogen bonding (IMHB) interaction in PPIN has been explored by calculation of the hyperconjugative charge transfer interaction from the lone electron pair of ring nitrogen atom to the σ(∗) orbital of O-H bond, under the provision of Natural Bond Orbital (NBO) analysis. However, DFT calculations together with the experimental results reveal that the excited species with the intramolecular N⋯HO hydrogen bond type undergoes rapid radiationless deactivation. This leads to a conclusion that the low-intensity dual-band fluorescence of the title compound in solution originates from the traces of the conformation with the -OH bond to azomethine nitrogen atom (ESIPT).

Synthesis, spectral studies and solvatochromism of some novel benzimidazole derivatives--ESIPT process

Some novel benzimidazole derivatives were synthesized and characterized by (1)H, (13)C NMR mass and elemental analysis. XRD analysis was carried out for 1-(4-methylbenzyl)-2-p-tolyl-1H-benzo[d]imidazole. The solvent effect on the absorption and fluorescence bands has been analyzed. The energetic analysis of the potential energy surface (PES), HOMO and LUMO levels [DFT/B3LYP/6-31G(d,p)] evidenced the existence of excited state intramolecular proton transfer (ESIPT) in hydroxy benzimidazole derivative.

Physico-chemical studies on some fluorescence sensors: DFT based ESIPT process

A group of novel heterocyclic Schiff base derivatives were synthesized and characterized by NMR spectra, mass and CHN analysis. Excited state intramolecular proton transfer (ESIPT) processes in o-hydroxy Schiff base have been studied using electronic spectral studies. Experimental and FT studies support that trans enol form predominates over the cis enol form. The fluorescence of Schiff bases quenched markedly with the gradual addition of Cu(2+). DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivatives were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state. The charge distribution has been calculated from the atomic charges by non-linear optical (NLO) and natural bond orbital (NBO) analysis. The energies of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and the molecular electrostatic potential (MEP) energy surface studies evidenced the existence of intramolecular charge transfer (ICT) within the molecule.

Physico-chemical studies of new luminescent chemosensor for Cu2+

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-phenylpropanoic acid (HBDPPA) has been studied in a series of different solvents. As revealed by absorbance, and emission results, the molecule undergoes fast excited-state intramolecular proton transfer (ESIPT) to yield emission of the corresponding tautomeric species. A large energy barrier for interconversion of the keto-enol rotamers in the ground and excited state have been predicted on the basis of DFT calculations and also supported by HOMO-LUMO energies, PES calculation, NLO and NBO analysis. Hyperpolarizability and octupolar and dipolar components ratio confirmed that HBDPPA can be used as optoelectronic materials. The ground state equilibrium and ESIPT process of HBDPPA are essentially unaffected by the nature of the solvent. Measurements of absorption solvatochromism have been interpreted with Marcus and Reichardt-Dimroth solvent functions to estimate the transition dipoles. Good correlation exists between absorption as well as fluorescence wavenumbers obtained by the multi-component linear regression employing the Taft and Catalan solvent parameters with the experimental values. The prepared Schiff base HBDPPA can be used as a new fluorescent sensor to detect the quantity of Cu(2+) ion in any sample solution depending on the relative intensity change.

DFT based ESIPT process of luminescent chemosensor: Taft and Catalan solvatochromism

Amino acid containing o-hydroxy Schiff base derivative was synthesized and an excited state intramolecular proton transfer (ESIPT) process in o-hydroxy Schiff base (HBMBA) has been studied using solution spectral studies. It was detected that the two distinct ground state isomers I and II are responsible for the emission. By comparing the emission wavelength in hydrocarbon solvent, it was predicted that the trans enol form predominates over the cis enol form. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the Schiff base derivative were performed and discussed. PES calculation indicates that the energy barrier for the interconversion of two rotamers is too high in the excited state than in the ground state. The fluorescence of HBMBA quenched with the gradual addition of Cu(2+). Therefore the prepared Schiff base HBMBA can be used as a new fluorescent sensor to detect the quantity of Cu(2+) ions in any sample solution depending on the relative intensity change. Measurements of absorption solvatochromism have been interpreted with Marcus and Reichardt-Dimroth solvent functions to estimate the transition dipoles. Good correlation exists between absorption as well as fluorescence wavenumbers obtained by the multi-component linear regression employing the Taft and Catalan solvent parameters with the experimental values.

Potential fluorescent chemosensor based on L-tryptophan derivative: DFT based ESIPT process

The spectroscopic properties of (E)-2-(2-hydroxybenzylideneamino)-3-(1H-indol-3-yl) propanoic acid (HBDIPPA) has been studied in a series of different solvents. An excited state intramolecular proton transfer (ESIPT) process in hydroxy Schiff base has been studied using emission spectroscopy. DFT calculations on energy, HOMO-LUMO energies, MEP, dipole moment, charge distribution of the Schiff base derivative have been performed and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state is shown by PES calculation. Positive values of laplacian ▿(2)ρ((rc)) (2.81) and electron density ρ((rc)) (0.22) are indicative of hydrogen bonds interactions. Absorption as well as fluorescence wavenumbers are correlated with Marcus and Reichardt-Dimroth solvent functions and also with Taft and Catalan solvent parameters. Schiff base HBDIPPA can be used as a new fluorescent sensor.

Studies on interaction between an imidazole derivative and bovine serum by spectral methods

The interaction between a trifluoromethyl substituted imidazole derivative 2-(4-(trifluoromethyl)phenyl)-1-phenyl-1H-imidazo[4,5-f] [1,10] phenanthroline (tfmppip) and bovine serum albumin (BSA) was investigated by solution spectral studies. The observed experimental result shows that the imidazole derivative has strong ability to quench the fluorescence of BSA by forming complex which is stabilized by electrostatic interactions. The effective quenching constants (k(sv)) were 2.79 × 10(4), 2.51 × 10(4), and 2.32 × 10(4) at 301, 310 and 318K respectively. The Stern-Volmer quenching constant (K(sv)), binding site number (n), apparent binding constant (K(A)) and corresponding thermodynamic parameters (ΔG, ΔH and ΔS) were calculated. The distance between the donor (BSA) and acceptor (tfmppip) was obtained according to fluorescence resonance energy transfer (FRET). Conformational changes of BSA were observed from synchronous fluorescence technique. The effect of metal ions such as Cu(2+), Zn(2+), Ca(2+), Mg(2+), Ni(2+), Co(2+) and Fe(2+) on the binding constants between the imidazole derivative and BSA were also studied.

Binding interaction of 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole with bovine serum albumin

A promising benzimidazole derivative 1-(4-methybenzyl)-2-p-tolyl-1H-benzo[d]imidazole (MBTBI) has been synthesized and characterized by single crystal XRD, NMR, mass and IR spectral techniques. The mutual interaction of this benzimidazole derivative (MBTBI) with bovine serum albumin (BSA) was investigated using solution spectral studies. The fluorescence quenching mechanism of BSA by MBTBI was analyzed and the binding constant has been calculated. The binding distance between these two was obtained based on the theory of Forester's non-radiation energy transfer (FRET). The effect of some common ions on the binding constant was also examined.

Physicochemical studies of chemosensor imidazole derivatives: DFT based ESIPT process

A series of substituted imidazoles have been synthesized in very good yield under a solvent free condition using molecular iodine as the catalyst. An excited state intramolecular proton transfer (ESIPT) process in hydroxy imidazole has been studied using emission spectroscopy. DFT calculations on energy, dipole moment, charge distribution of the rotamers in the ground and excited states of the imidazole derivatives have been performed and discussed. DFT analysis about HOMO, HOMO-1, LUMO and LUMO+1 has been carried out and discussed. The energy barrier for the interconversion of two rotamers is too high in the excited state than the ground state that is shown by PES calculation. The molecular electrostatic potential surface (MEP) has also been employed to show the higher electron density at N(3) nitrogen. Fluorescence enhancement has been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n-π* state in the chemosensors.

Synthesis, spectral studies and solvatochromic analysis of novel imidazole derivatives

Bioactive imidazole derivatives were synthesized and characterized by spectral techniques. The photophysical properties of imidazole derivatives were studied in several solvents. The observed spectral shift is attributed to a loss of planarity in the excited state provided by the non-co-planarity of the aryl rings attached to C(2) and N(1) atoms of the imidazole ring. The observed solvatochromic shifts were analyzed in detail by Kamlet-Taft and Catalan parameters. The interaction between bioactive imidazole derivative and bovine serum albumin (BSA) was also investigated.

Optical properties of organic nonlinear optical crystal--a combined experimental and theoretical study

The optical properties of the synthesized imidazole derivative, 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole, has been studied both experimentally and theoretically. Fluorescence enhancement have been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n-π* state in the chemosensors. Quantum chemical calculations of heat of formation, optimized geometry, NLO, HOMO-LUMO, MEP and NBO analysis of 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole (mpdsi) have been carried out by using density functional theory (DFT/B3LYP) method with 6-31G(d,p) as basis set. This chromophore possess more appropriate ratio of off-diagonal versus diagonal β tensorial component (r=β(xyy)/β(xxx)=-0.002) which reflects the inplane non-linearity anisotropy. Since they have largest μβ(0) value, the reported imidazole can be used as potential NLO material. The solvent effect on the absorption and fluorescence has been analyzed simultaneously.

Physicochemical studies of some novel Y-shaped imidazole derivatives--a sensitive chemisensor

Some novel Y-shaped imidazole derivatives were developed for highly sensitive chemisensors for transition metal ions. A prominent fluorescence enhancement was found in the presence of transition metal ions such as Hg(2+), Pb(2+) and Cu(2+) and it is due to the suppression of radiationless transitions from the n-π* state in the chemisensors. The HOMO-LUMO energies, electric dipole moment (μ) and the first-hyperpolarizability (β) values of the investigated molecule have been studied theoretically which reveal that the synthesized molecules have microscopic non-linear optical (NLO) behaviour with non-zero values.