The excited-state intramolecular proton transfer (ESIPT) reaction of l-hydroxy-2-naphthaldehyde (HN12) has been studied within the interior of the supramolecular assemblies of α-, β-, and γ-cyclodextrins (CD) and biomimicking environments of ionic (SDS) and non-ionic (TW-20) micelles. Fluorescence measurements are used to investigate the effect of various supramolecular assemblies on the ESIPT reaction by monitoring the large Stokes-shifted tautomer emission of HN12. Enhanced tautomer emission in the microencapsulated state predicts favorable ESIPT reaction in the supramoleuclar assemblies. Benesi-Hildebrand plots have been employed to ascertain that the stoichiometric ratios of the complexes formed between HN12 and CDs are 1:2, 1:1, and 1:1 for α-, β-, and γ-CD, respectively. The binding constants (K1) and free-energy change (ΔG) for inclusion complexation are also determined from the linearized Benesi-Hildebrand plots. Steady-state fluorescence anisotropy, REES, excitation anisotropy, and fluorescence lifetime measurements are in line with other experimental findings. Differential action of urea on SDS and TW-20-bound probe has also been investigated. © 2009 American Chemical Society.

NIKHIL GUCHHAIT

Chemistry

B K PAUL

A SAMANTA

University of Calcutta (informally known as Calcutta University or CU) is a collegiate public state university located in Kolkata, West Bengal, India.&nbsp;Within India it is recognized as a &quot;Five-Star University&quot; and accredited &quot;A&quot; Grade by National Assessment and Accreditation Council.

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The University of Calcutta has secured the Fifth position among the Universities of India in the prestigious &quot;Indian University Ranking 2019&quot; list, released by the NIRF of the Ministry of Human Resource Development, Government of India.

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It was established on 24 January 1857, and was one of the first institutions in Asia to be established as a multidisciplinary and Western-style university. Its alumni and faculty include several heads of state, heads of government, social reformers, prominent artists, only academy award winner and Dirac medal winner in India, many Fellows of the Royal Society and five Nobel laureates as of 2019 which is highest in South Asia.

University Of Calcutta

Langmuir

This article describes a detailed characterization of the binding interaction of a pharmaceutically important isoindole fused imidazole derivative, namely 1-(2-hydroxy-5-methyl-phenyl)-3,5-dioxo-1H-imidazo-[3,4-b] isoindole (ADII) with biomimetic micellar assemblies of varying surface charge using steady state absorption, emission and time resolved emission spectroscopy. The studied molecule ADII is known to exhibit an intramolecular proton transfer process through a four member hydrogen bonding system resulting in a lactim lactam isomerisation process. Upon interaction with the micellar environment, a significant change in the absorption and emission profiles of ADII is observed due to differential modulation of inherent proton transfer in the three studied ionic and non-ionic micellar environments. The micropolarity measurement and fluorescence quenching experiments have been performed to evaluate the binding location of the probe (ADII) in the three micellar assemblies. The differential binding affinity of the probe with the micelles also results in different rotational relaxational motion of the probe within the encapsulated microheterogeneous environments. This journal is © the Partner Organisations 2014.

RSC Advances

Differential modulation of lactim-lactam tautomerism process of an isoindole fused imidazole system in three different micellar assemblies of varying surface charge: A spectroscopic approach to various photophysical properties

Photophysical properties of a potent intramolecular charge transfer probe viz.; 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid methyl ester (DPDAME) have been investigated in aqueous micellar environments using spectroscopic techniques. The intramolecular charge transfer (ICT) fluorescence of DPDAME is found to display remarkable hypsochromic shift coupled with intensity enhancement within the microheterogeneous micellar environments. This is also associated with discernible increase in fluorescence anisotropy whereby indicating the impartation of considerable motional restrictions on the fluorophore within the micellar systems. The fluorescence anisotropy results are also processed to delve into an estimate of the microviscosity of the probe environment at the binding site on the micellar aggregates. Quantitative evaluation of the probe-micelle binding strength has been achieved from fluorescence data in terms of binding constant and free energy change of the interaction process. The extensive polarity-sensitive fluorescence behavior of DPDAME has been exploited to cast light on assessing the micropolarity at the interaction site of the probe within the micelles. This information has in turn been efficiently employed as the actuating avenue to argue on complex issues like probable location, distribution and orientation of the probe within the micellar aggregates. The pattern of variation of emission intensity of DPDAME as a function of surfactant concentrations is found to reveal the existence of multiple critical micellar concentration (CMC). Overall, the present results have been argued to reflect the commendable efficiency of DPDAME to function as a prospective molecular reporter for complex microheterogeneous micellar environments. © 2014 Elsevier B.V.

Journal of Molecular Liquids

Explicit spectral response of an intramolecular charge transfer molecule within microheterogeneous micellar environments

The present work demonstrates the effect of biological confinement on the photophysics of a proton transfer phototautomer viz.; 2-hydroxy-1-naphthaldehyde (HN21). HN21 is a potential candidate exhibiting excited-state intramolecular proton transfer (ESIPT) reaction and thereby generating the phototautomer (i.e.; proton transferred keto form) in the excited-state. The ESIPT photophysics of the probe (HN21) is found to be remarkably modified within the confined bio-environment of a model transport protein Bovine Serum Albumin (BSA). Such considerable modification of the ESIPT photophysics of the probe has been exploited to determine the probe-protein binding strength (binding constant, K(±10%)=1.23×104 M-1). The probe-protein binding process is found to be thermodynamically feasible (ΔG=-24.25 kJ mol-1). The present work also delves into evaluation of the probable binding location of the probe (HN21) within the biomacromolecular assembly of the protein by blind docking simulation technique, which reveals that HN21 favorably binds to the hydrophobic subdomain IIIA of BSA. Circular dichroism (CD) spectroscopy delineates the effect of probe binding on the protein secondary structure in terms of decrease of α-helical content of BSA with increasing probe concentration. Apart from this, excitation-emission matrix fluorescence technique is found to hint at the effect on protein tertiary structure upon binding to the probe. The modulated dynamics of the proton transfer phototautomer of HN21 within the biological confinement is investigated in this context by time-resolved fluorescence decay measurements. The present work also accentuates the mutually corroborating data found from experimental and computational studies. © 2014 Elsevier B.V.

Journal of Luminescence

Photophysics of a proton transfer phototautomer within biological confinement of a protein: Spectroscopic and molecular docking studies

Density functional theory based computational study has been performed to characterize intramolecular hydrogen bonding (IMHB) interaction in a series of salicylic acid derivatives varying in chlorine substitution on the benzene ring. The molecular systems studied are salicylic acid, 5-chlorosalicylic acid, 3,5-dichlorosalicylic acid and 3,5,6-tricholorosalicylic acid. Major emphasis is rendered on the analysis of IMHB interaction by calculation of electron density ρ(r) and Laplacian ∇2ρ(r) at the bond critical point using atoms-in-molecule theory. Topological features, energy densities based on ρ(r) through perturbing the intramolecular H-bond distances suggest that at equilibrium geometry the IMHB interaction develops certain characteristics typical of covalent interaction. The interplay between aromaticity and resonance-assisted hydrogen bonding (RAHB) is discussed using both geometrical and magnetic criteria as the descriptors of aromaticity. The optimized geometry features, molecular electrostatic potential map analysis are also found to produce a consensus view in relation with the formation of RAHB in these systems. © 2012 Elsevier B.V. All rights reserved.

Chemical Physics

Geometrical criteria versus quantum chemical criteria for assessment of intramolecular hydrogen bond (IMHB) interaction: A computational comparison into the effect of chlorine substitution on IMHB of salicylic acid in its lowest energy ground state confor

The present contribution demonstrates the photophysics of a prospective cancer cell photosensitizer Harmane (HM) belonging to the family of β-carboline in mixed microheterogeneous environments of β-cyclodextrin (β-CD) and surfactants having varying surface charges using steady-state and time-resolved fluorescence spectroscopic techniques. The remarkable modulations in prototropic activities of the micelle-bound drug in the presence of β-CD evinces for disruption of the micellar structural integrity by β-CD. The results are meticulously discussed in relevance to the effect of a potential drug delivery vehicle (CD) on the membrane-mimetic micellar system. Further, application of an extrinsic fluorescence probe for monitoring such interactions is fraught by the possibilities of no less than three equilibria that can operate simultaneously viz., (i) surfactant-cyclodextrin, (ii) surfactant-fluorophore and (iii) cyclodextrin-fluorophore. This aspect highlights the enormous importance of the issue of suitability of the fluorescence probe to study such complicated systems and interaction phenomena. Also the varying interaction scenario of β-CD with the nature of the surfactant highlights the importance of precise knowledge of the strength and locus of drug binding in delineating such complex interactions. The results of the present investigation advocate for the potential applicability of the drug (HM) itself as a fluorescence reporter in study of such complex microheterogeneous interactions. © 2013 Elsevier Inc.

Journal of Colloid and Interface Science

Modulation in prototropism of the photosensitizer harmane by host: Guest interactions between Î²-cyclodextrin and surfactants

The ground and excited state properties of 1-hydroxy-2-naphthaldehyde (HN12) towards proton transfer reaction have been elaborately investigated on the basis of steady state absorption and emission, time-resolved fluorescence spectroscopy and quantum chemical calculations by ab initio (Hartree-Fock) and density functional theory (DFT) methods. The molecule HN12 exists as closed (intramolecular hydrogen bonded) and open conformer and their anions, and the hydrogen bonded solvated cluster in the ground state. The closed conformer on excitation undergoes photo-induced keto-enol tautomerism across the pre-existing intramolecular hydrogen bond (IMHB) and shows a red shifted emission band for the keto tautomer. Theoretically a significant change of some structural parameters such as Od-H1 bond length, Od⋯H1⋯Oa bond angle and charge distribution at the proton translocation site in the excited state favours intramolecular proton transfer process. Calculated potential energy curves along the proton transfer coordinate at the pre-existing hydrogen bonding site by DFT level account well for the feasibility of a barrierless ultrafast excited state intramolecular proton transfer reaction in HN12 molecule. © 2006 Elsevier B.V. All rights reserved.

Photo-physical properties of 1-hydroxy-2-naphthaldehyde: A combined fluorescence spectroscopy and quantum chemical calculations

Proceedings of the National Academy of Sciences

PNAS Plus Significance Statements

The Journal of Physical Chemistry B

Effect of Cyclodextrin Nanocavity Confinement on the Photophysics of a β-Carboline Analogue:  A Spectroscopic Study

Photophysical Study of 3-Acetyl-4-oxo-6,7-dihydro-12H-indolo[2,3-a]quinolizine in Biomimetic Reverse Micellar Nanocavities:  A Spectroscopic Approach

Chemical Physics Letters

“Dynamics of twisted intramolecular charge transfer process of 4-N, N-dimethylaminocinnamic acid in α-cyclodextrin environment” [Chem. Phys. Lett. 336 (2001) 57–62]

Journal	Langmuir
Publisher	AMER CHEMICAL SOC
ISSN	0743-7463
Open Access	No