Himank Kumar

Design, synthesis, physicochemical studies, solvation, and DNA damage of quinoline-appended chalcone derivative: comprehensive spectroscopic approach toward drug discovery.

The present study epitomizes the design, synthesis, photophysics, solvation, and interaction with calf-thymus DNA of a potential antitumor, anticancer quinoline-appended chalcone derivative, (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ) using steady state absorption and fluorescence spectroscopy, molecular modeling, molecular docking, Fourier-transform infrared spectroscopy (FTIR), molecular dynamics (MD) simulation, and gel electrophoresis studies. ADMQ shows an unusual photophysical behavior in a variety of solvents of different polarity. The dual emission has been observed along with the formation of twisted intramolecular charge transfer (TICT) excited state. The radiationless deactivation of the TICT state is found to be promoted strongly by hydrogen bonding. Quantum mechanical (DFT, TDDFT, and ZINDO-CI) calculations show that the ADMQ is sort of molecular rotor which undergoes intramolecular twist followed by a complete charge transfer in the optimized excited state. FTIR studies reveals that ADMQ undergoes important structural change from its native structure to a β-hydroxy keto form in water at physiological pH. The concentration-dependent DNA cleavage has been identified in agarose gel DNA electrophoresis experiment and has been further supported by MD simulation. ADMQ forms hydrogen bond with the deoxyribose sugar attached with the nucleobase adenine DA-17 (chain A) and result in significant structural changes which potentially cleave DNA double helix. The compound does not exhibit any deleterious effect or toxicity to the E. coli strain in cytotoxicity studies. The consolidated spectroscopic research described herein can provide enormous information to open up new avenues for designing and synthesizing chalcone derivatives with low systematic toxicity for medicinal chemistry research.

Antihypertensive activity of a quinoline appended chalcone derivative and its site specific binding interaction with a relevant target carrier protein

Inhibition of Angiotensin Converting Enzyme (ACE) is identified as a main therapeutic target in controlling hypertension. The principal intent of this work is to investigate the ACE inhibitory property of a quinoline appended chalcone derivative (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ), and its binding mechanism with model transport protein BSA by employing steady state and time resolved fluorescence, Circular Dichroism (CD), in silico molecular docking, Induced Fit Docking (IFD) and Molecular Dynamics (MD) simulation. Incubation of ADMQ with kidney cortex plasma membrane shows considerable antihypertensive effect by the inhibition of ACE. ADMQ undergoes strong interaction with ACE both in the absence and presence of BSA. Comparable ACE inhibitory mechanistic profile of ADMQ with standard drug captopril has been identified in terms of the ligand interaction pattern, changes in secondary structural elements and protein RMSF. The steady state emission of BSA undergoes a remarkable decrement via ground state complex formation upon addition of ADMQ in an aqueous buffer solution of BSA at a physiological pH of 7.4 contrary to the time resolved and FRET measurement where both the static and energy transfer mechanism co-exists. The rotationally restricted ADMQ molecule shows strong binding affinity towards subdomain IIA of site I with a close proximity (2.45 nm) to the Trp 213 residue. The minor decrease of α-helical content as calculated from CD spectral measurement and 1–3 A change in protein RMSD during MD simulation clearly indicate that the polypeptide chain is partially destabilized due to the above site specific accommodation of the host (ADMQ). A slight diminution in the ACE inhibitory profile is observed in the presence of BSA; however BSA shows lesser binding towards ADMQ in the presence of the target enzyme. The spectroscopic research described herein may provide enormously important information for ACE inhibition of the chalcone derivative and its detailed binding interaction with a carrier protein for chalcone based drug designing in medicinal chemistry research.

Groove binding mediated structural modulation and DNA cleavage by quinoline appended chalcone derivative

The present study embodies the detail DNA binding interaction of a potential bioactive quinoline appended chalcone derivative (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ) with calf thymus DNA (ctDNA) and its consequences by UV-Vis absorption, steady state fluorescence spectroscopy, fluorescence anisotropy, circular dichromism, helix melting, agarose gel electrophoresis, molecular docking, Induced Fit Docking (IFD) and molecular dynamics (MD) simulation. The UV-Vis absorption and fluorescence study reveal that the molecule undergoes considerable interaction with the nucleic acid. The control KI quenching experiment shows the lesser accessibility of ADMQ molecule to the ionic quencher (I(-)) in presence of ctDNA as compared to the bulk aqueous phase. Insignificant change in helix melting temperature as well as in circular dichromism (CD) spectra points toward non-covalent groove binding interaction. The moderate rotational confinement of this chalcone derivative (anisotropy=0.106) trapped in the nucleic acid environment, the comparative displacement assay with well-known minor groove binder Hoechst 33258 and intercalator Ethidium Bromide establishes the minor groove binding interactions of the probe molecule. Molecular docking, IFD and MD simulation reveal that the DNA undergoes prominent morphological changes in terms of helix unwinding and bending to accommodate ADMQ in a crescent shape at an angle of 110° in a sequence specific manner. During interaction, ADMQ rigidifies and bends the sugar phosphate backbone of the nucleic acid and thereby shortens its overall length by 3.02Å. Agarose gel electrophoresis experiment with plasmid pBR 322 reveals that the groove binded ADMQ result in a concentration dependent cleavage of plasmid DNA into its supercoiled and nicked circular form. The consolidated spectroscopic research described herein provides quantitative insight into the interaction of a heterocyclic chalcone derivative with relevant target nucleic acid, which may be useful for the future research on chalcone based therapeutic agents.

Surfactant induced aggregation–disaggregation of photodynamic active chlorin e6 and its relevant interaction with DNA alkylating quinone in a biomimic micellar microenvironment

The present paper epitomizes the detailed physicochemical behaviour of photodynamic active chlorin e6 (Ce6) and its interaction with the DNA alkylating quinone; 2,5-dichloro diaziridinyl-1,4-benzoquinone (AZDCIQ) in different bio-mimicking micellar microenvironments using steady state absorption, fluorescence, time resolved fluorescence and fluorescence anisotropy studies. Dramatic modulation in the photophysics of Ce6 has been observed in two types of surfactant assemblies namely premicellar and postmicellar assemblies of cationic CTAB, anionic SDS and nonionic TX-100. In water at pH 7.4, Ce6 exists as monomeric (73%, 4.91 ns) and dimeric (27%, 2.49 ns) forms, but with increasing concentration of CTAB in the premicellar region, the absorption and emission intensity decreases significantly due to the formation of surfactant induced higher aggregates. Interestingly further addition of CTAB (at critical micellar concentration and above) leads to disaggregation of those higher aggregates into its subsequent monomeric and dimeric form. In the case of TX-100 and SDS, the dye does not form higher aggregates in the premicellar region, rather it remains as monomeric–dimeric forms throughout the concentration range until the critical micellar concentration (CMC). After micellization, the percentage of Ce6 monomer increases in the case of TX-100, whereas the reverse case is observed in SDS, which may be explained by the forced dimerisation caused by repulsive interactions between anionic Ce6 and SDS micelles. The copper induced fluorescence quenching, solvation dynamics, and fluorescence anisotropy shows that the dye is localised in the Stern layer of CTAB, in the palisade layer of TX-100 and in the outer Gouy–Chapman layer or in aqueous bulk phase in the case of SDS micelles. The interaction of fully micellized PDT active Ce6 with DNA alkylating AZDCIQ is found to be more in CTAB as compared to TX-100 and water. The solvation dynamics of Ce6 in the presence of the quinone reveals the dynamic nature of the interaction between these two partners. The spectroscopic research described herein may provide numerous effective information for the use of chlorin(s) and alkylating quinones together to overcome the limitation of PDT, especially in the hypoxic environment of solid tumors.

Conformation controlled turn on–turn off phosphorescence in a metal-free biluminophore: thriving the paradox that exists for organic compounds

The legacy of phosphorescence from expensive organometallic compounds has inspired researchers to develop efficient metal-free organic phosphors. Although organic phosphors offer a cheaper alternative, the long-lived triplets of organic phosphors that are primarily consumed by vibrational dissipation need to be adequately suppressed, and this provides an opportunity to design new organic entities, at par with the organometallic compounds, based on conformational control and incorporation of useful functional groups to alter their emissive properties, especially phosphorescence. Here, we have achieved a proficient dual state emission, underlining the key design rule of conformational control in an organic molecular platform for 2-(6-chlorobenzo[d]thiazol-2-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (CBIQD). In contrast to other known naphthalimides, the system limiting access to non-radiative triplet states is achieved by steric encumbrance which exhibits strong phosphorescence. Here, in addition to strong fluorescence (from planar conformer), phosphorescence is unlocked by suppression of non-radiative channels from the non-planar conformer in glassy solvents (77 K) and when embedded in a polymer matrix of poly(methyl methacrylate) (PMMA) at RT. The spectroscopic delineation of adopted geometry and optical property relationship is sought by a steric approach, extent of intramolecular charge transfer (ICT), presence of carbonyl groups, directed heavy atom effect and the spin-orbit coupling (SOC) invoked by -S- and -Cl atoms. Time dependent density functional theory (TD-DFT) is used to explain the favourable mechanistic path for the decay of excited states (ESs) leading to phosphorescence from a non-planar conformer and fluorescence from a planar conformer. The spectacular access to the radiative singlet and triplet states suggests that there is less scope for loss channels. The phosphorescence of the CBIQD-PMMA system may find use in other biomedical applications due to the biocompatibility of each component.

Development of multifunctional heterocyclic Schiff base as a potential metal chelator: a comprehensive spectroscopic approach towards drug discovery.

Amyloid-β peptides and their metal-associated aggregated states have been implicated in the pathogenesis of Alzheimer’s disease. The present paper epitomises the design and synthesis of a small, neutral, lipophilic benzothiazole Schiff base (E)-2-((6-chlorobenzo[d]thiazol-2-ylimino)methyl)-5-diethylamino)phenol (CBMDP), and explores its multifunctionalty as a potential metal chelator/fluorophore using UV–visible absorption, steady-state fluorescence, single molecule fluorescence correlation spectroscopic (FCS) techniques which is further corroborated by in silico studies. Some pharmaceutically relevant properties of the synthesized compound have also been calculated theoretically. Steady-state fluorescence and single molecule FCS reveal that the synthesized CBMDP not only recognizes oligomeric Aβ40, but could also be used as an amyloid-specific extrinsic fluorophore as it shows tremendous increase in its emission intensity in the presence of Aβ40. Molecular docking exercise and MD simulation reveal that CBMDP localizes itself in the crucial amyloidogenic and copper-binding region of Aβ40 and undergoes a strong binding interaction via H-bonding and π–π stacking. It stabilizes the solitary α-helical Aβ40 monomer by retaining the initial conformation of the Aβ central helix and mostly interacts with the hydrophilic N-terminus and the α-helical region spanning from Ala-2 to Val-24. CBMDP exhibits strong copper as well as zinc chelation ability and retards the rapid copper-induced aggregation of amyloid peptide. In addition, CBMDP shows radical scavenging activity which enriches its functionality. Overall, the consolidated in vitro and in silico results obtained for the synthesized molecule could provide a rational template for developing new multifunctional agents.

Is the Sudlow site I of human serum albumin more generous to adopt prospective anti-cancer bioorganic compound than that of bovine: A combined spectroscopic and docking simulation approach

A comparative biophysical study on the individual conformational adaptation embraced by two homologous serum albumins (SA) (bovine and human) towards a potential anticancer bioorganic compound 2-(6-chlorobenzo[d] thiazol-2-yl)-1H-benzo[de] isoquinoline-1,3(2H)- dione (CBIQD) is apparent from the discrimination in binding behavior and the ensuing consequences accomplished by combined in vitro optical spectroscopy, in silico molecular docking and molecular dynamics (MD) simulation. The Sudlow site I of HSA although anion receptive, harbors neutral CBIQD in Sudlow site I (subdomain IIA, close to Trp) of HSA, while in BSA its prefers to snugly fit into Sudlow site II (subdomain IIIA, close to Tyr). Based on discernable diminution of HSA mean fluorescence lifetime as a function of biluminophore concentration, facile occurrence of fluorescence resonance energy transfer (FRET) is substantiated as the probable quenching mechanism accompanied by structural deformations in the protein ensemble. CBIQD establishes itself within HSA close to Trp214, and consequently reduces the micropolarity of the cybotactic environment that is predominantly constituted by hydrophobic amino acid residues. The stronger association of CBIQD with HSA encourages an allosteric modulation leading to slight deformation in its secondary structure whereas for BSA the association is comparatively weaker. Sudlow site I of HSA is capable to embrace a favorable conformation like malleable gold to provide room for incoming CBIQD, whereas for BSA it behaves more like rigid cast-iron which does not admit any change thus forcing CBIQD to occupy an altogether different binding location i.e. the Sudlow site II. The anticancer CBIQD is found to be stable within the HSA scaffold as vindicated by root mean square deviation (RMSD) and root mean square fluctuation (RMSF) obtained by MD simulation. A competitively inhibited esterase-like activity of HSA upon CBIQD binding to Lys199 and Arg257 residues, plausibly envisions that similar naphthalimide based prodrugs, bearing ester functionality, can be particularly activated by Sudlow site I of HSA. The consolidated spectroscopic research described herein may encourage design of naphthalimide based pro-drugs for effective in vivo biodistribution using HSA-based drug delivery systems.

A Chalcone-Based Potential Therapeutic Small Molecule That Binds to Subdomain IIA in HSA Precisely Controls the Rotamerization of Trp-214

The principal intent of this work is to explore whether the site-specific binding of a newly synthesized quinoline-appended anthracenyl chalcone, (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ), with an extracellular protein of the human circulatory system, human serum albumin (HSA), can control the rotamerization of its sole tryptophan residue, Trp-214. With this aim, we have systematically studied the binding affinity, interactions, and localization pattern of the title compound inside the specific binding domain of the transport protein and any conformation alteration caused therein. Multiple spectroscopic experiments substantiated by an in silico molecular modeling exercise provide evidence for the binding of the guest ADMQ in the hydrophobic domain of HSA, which is primarily constituted by residues Trp-214, Arg-218, Arg-222, Asp-451, and Tyr-452. Rotationally restricted ADMQ prefers to reside in Sudlow site I (subdomain IIA) of HSA in close proximity (2.45 nm) to the intrinsic fluorophore Trp-214 and is interestingly found to control its vital rotamerization process. The driving force for this rotational interconversion is predominantly found to be governed by the direct interaction of ADMQ with Trp-214. However, the role of induced conformational perturbation in the biomacromolecule itself upon ADMQ adoption cannot be ruled out completely, as indicated by circular dichroism, 3D fluorescence, root-mean-square deviation, root-mean-square fluctuation, and secondary structure element observations. The comprehensive spectroscopic study outlined herein provides important information on the biophysical interaction of a chalcone-based potential therapeutic candidate with a carrier protein, exemplifying its utility in having a regulatory effect on the microconformations of Trp-214.

Aggregation–disaggregation pattern of photodynamically active ZnPcS4 and its interaction with DNA alkylating quinone: effect of micellar compactness and central metal ion

The hypoxic nature of solid tumours and the aggregation of photosensitizers in physiological environments are two governing limiting factors in photodynamic therapy (PDT). This article describes the effect of sensitivity to polarity and the central metal ion on the aggregation–disaggregation pattern of the PDT-active metallophthalocyanine ZnPcS4 and its relevant interaction with a DNA alkylating quinone in an aqueous medium, as well as in a biomimicking micellar microenvironment, under hypoxic conditions to overcome the limitations of PDT. Steady-state absorption and emission, time-resolved fluorescence (TRF), fluorescence anisotropy and dynamic light scattering (DLS) techniques were employed for this purpose. Similarly to AlPcS4, the spectral behaviour of ZnPcS4 remains immune to anionic SDS and also displays a significant interaction with the positively charged head group of cationic surfactants (DTAB, TTAB, and CTAB). In the premicellar region, surfactant-induced aggregation of the probe molecules is dominant. Above the critical micellar concentration (CMC), AlPcS4 fully disaggregates into monomers but the tendency of ZnPcS4 to undergo monomerization increases with a decline in the compactness of cationic micelles. The increase in the fluorescence anisotropy of ZnPcS4 in a fully micellized system upon reducing the compactness of the micelles confirms deeper penetration of the dye inside the micelles, a behaviour which is the reverse of that of AlPcS4. The latter remained resistant in neutral micelles, whereas ZnPcS4 substantially monomerized on an increase in the TX-100 concentration and distributed itself at the shear surface and in the deeper hydrophobic core of a fully micellized system. Dye-induced formation of micellar clusters was identified by DLS measurements, especially in cationic micelles. The interaction of PDT-active ZnPcS4 with DNA alkylating 2,5-dichlorodiaziridinyl-1,4-benzoquinone (AZDCIQ) was studied in an aqueous medium, as well as in all the micellar microenvironments under study, and found to be more prominent in cationic micelles compared with the other systems. However, the association constants (Ka) thus obtained in the cationic micelles were found to be greater for ZnPcS4 than for AlPcS4. Our findings may prove instrumental in expanding the effectiveness and applicability of metallophthalocyanines in terms of understanding their aggregation pattern and interaction with DNA alkylating quinones in a hypoxic micellar microenvironment.