Ground and Singlet Excited State Pyridinic Protonation of N9-Methylbetacarboline in Water-N,N-Dimethylformamide Mixtures

Photophysical and thermodynamic landscape of interaction of a styryl-based dye with DNA duplex: effect of medium ionic strength and live cell imaging

A red-emitting excited-state intramolecular charge transfer pyridinium dye, [4-((1E,3E)-4-(4-(dimethylamino)phenyl)buta-1,3-dien-1-yl)-1-methylpyridin-1-ium] (DAPBMP), was synthesized and characterized using NMR and ESIMS studies. Binding interaction between dye DAPBMP and genomic DNA were investigated using steady-state and time-resolved spectroscopic methods. The thermodynamics of the interaction process were characterized using isothermal titration calorimetry (ITC) which reveals the key role of the hydrophobic effect and electrostatic interaction between the positive charged dye and the negatively charged polyphosphate of DNA backbone. The binding of dye to the minor groove of the DNA double helix is confirmed by circular dichroism spectroscopy and molecular docking simulation study. The binding interaction is found to be strongly dependent on the ionic strength of the medium as demonstrated by a systematic study in the presence of various concentrations of NaCl. A detailed calorimetric study shows that polyelectrolytic contribution, ΔGpe, (a measure of the role of electrostatic force) to the total free energy change (ΔG) of interaction progressively decreases with increasing ionic strength of the medium due to weakening of the DAPBMP:DNA binding by screening of the electrostatic charges. The fluorescence of DAPBMP exhibits a remarkable emission enhancement of almost 15 times when the viscosity of the water-propylene glycol system increases. Fluorescent microscopy was performed with C2C12 mouse skeletal myoblast and A549 lung cancer cells in the presence of DAPBMP dye. The dye passed through the C2C12 cell membrane and binds the negatively charged nucleic acids, essentially double-stranded DNA which made the nuclear puncta along with perinuclear located mitochondria.

A versatile sensor capable of ratiometric fluorescence detection of trace water and turn-on detection of Cu2+ modulating the binding interaction of a Cu(II) complex with BSA and DNA complemented by docking studies

A fluorescent molecule, pyridine-coupled bis-anthracene (PBA), has been developed for the selective fluorescence turn-on detection of Cu2+. Interestingly, the ligand PBA also exhibited a red-shifted ratiometric fluorescence response in the presence of water. Thus, a ratiometric water sensor has been utilized as a selective fluorescence turn-on sensor for Cu2+, achieving a 10-fold enhancement in the fluorescence and quantum yield at 446 nm, with a lower detection limit of 0.358 μM and a binding constant of 1.3 × 106 M-1. For practical applications, sensor PBA can be used to detect Cu2+ in various types of soils like clay soil, field soil and sand. The interaction of the PBA-Cu(II) complex with transport proteins like bovine serum albumin (BSA) and ct-DNA has been investigated through fluorescence titration experiments. Additionally, the structural optimization of PBA and the PBA-Cu(II) complex has been demonstrated by DFT, and the interaction of the PBA-Cu(II) complex with BSA and ct-DNA has been analyzed using theoretical docking studies.

Experimental and theoretical investigation on the nonlinear optical properties of LDS 821 dye in different solvents and DNA

Linear and nonlinear optical properties of near-infrared laser grade dye LDS 821 in different solvents and Salmon Deoxyribonucleic acid (DNA) were studied using spectroscopic and Z-scan techniques. UV-Vis absorption spectrum of the dye shows a bathochromic shift with a decrease in the solvent polarity parameter, and in DNA, the dye exhibits a hypochromic shift. The fluorescence spectrum of the dye does not show any notable correlation with the solvent polarity parameter, but in DNA, the fluorescence intensity of the dye decreases with the incremental addition of DNA. Molecular docking studies reveal that the dye intercalates on the major grooves of DNA. Nonlinear optical properties of the dye in different solvents and phosphate buffer solution with varying DNA concentrations were studied using the Z-scan technique using a Q-switched Nd: YAG laser operating at fundamental and second harmonics. A closed and open aperture Z-scan of dye in different solvents was carried out to estimate the nonlinear refractive index, excited-state absorption cross-section, and two-photon absorption coefficient (TPA). The variation in nonlinear optical properties of the dye in different solvents was due to solvent-induced structural modifications. Theoretical investigation on nonlinear optical properties of the dye in different solvents was carried out using density function theory. The theoretical first and second-order hyperpolarizability was calculated using B3LYP functional. The predicated nonlinear optical parameters of the dye in different solvents does not show any direct correlation with solvent polarity. Nonlinear absorption of the dye in phosphate buffer solution (PBS) and DNA were estimated. The nonlinear absorption of the dye in PBS decreases with the addition of DNA. Molecular docking studies were carried out to determine the structural changes induced in dye due to the intercalation with DNA.

Colorimetric and ratiometric fluorescence sensing of water based on 9-methyl pyrido[3,4-b]indole-boron trifluoride complex

In this work, 9-methyl pyrido[3,4-b]indole-boron trifluoride complex, 9-MP-BF3, was designed and developed as a colorimetric and ratiometric fluorescent sensor for the detection of water in the low- and high-water-content regions in solvents. In the low-water-content region, a new photoabsorption band at around 360 nm and a fluorescence band at around 370 nm gradually appeared due to the dissociation of 9-MP-BF3 into 9-methyl pyrido[3,4-b]indole (9-MP) by water molecules with a simultaneous decrease in the photoabsorption band at around 390 nm and the fluorescence band at around 460 nm originating from 9-MP-BF3. In the moderate-water-content region, the photoabsorption band at around 360 nm and the fluorescence band at around 370 nm gradually shifted to a longer wavelength region with an increase in the fluorescence intensity, which could be ascribed to the formation of a hydrogen-bonded complex (9-MP-H2O) with water molecules. Furthermore, in the high-water-content region, two photoabsorption bands at around 305 nm and 390 nm and one fluorescence band at around 460 nm gradually reappeared with simultaneous decrease in the photoabsorption band at around 290 nm and the fluorescence band at around 370 nm, which was attributed to the formation of a hydrogen-bonded proton transfer complex (9-MP-H+) with water molecules. Thus, this work revealed the mechanism of a colorimetric and ratiometric fluorescent sensor based on pyrido[3,4-b]indole-boron trifluoride complex for the detection of water over a wide range from low water content to high water content in solvents.

Development of an intramolecular charge transfer-type colorimetric and fluorescence sensor for water by fusion with a juloidine structure and complexation with boron trifluoride

An intramolecular charge transfer-type optical sensor fused with a juloidine structure and complexed with boron trifluoride can detect and determine water over a wide concentration range.

Synthesis and optical and electrochemical properties of julolidine-structured pyrido[3,4-b]indole dye

The julolidine-structured pyrido[3,4-b]indole dye ET-1 possesses the ability to act as a calorimetric and fluorescent sensor for Brønsted and Lewis acids.

Supramolecular interaction of a cancer cell photosensitizer in the nanocavity of cucurbit[7]uril: A spectroscopic and calorimetric study

The interaction of small biologically active molecules in the nanocavity of supramolecular host is very interesting and thriving research area. In the presence of supramolecular host the absorption and emission properties of small biologically active molecules were modulated several folds compared to bulk solution. In this study we have investigated the supramolecular interaction of a cancer cell photosensitizer molecule harmane in the presence of cucurbit[7]uril (CB7) as host in aqueous buffer solution (pH∼7.2). We have used steady state absorption, emission and time resolved fluorescence spectroscopy techniques. The thermodynamics of the binding between harmane in the nanochannel of CB7 were studied by using isothermal titration calorimetry (ITC) method. The emission properties of harmane are modulated several fold in the presence of CB7. ITC study indicates that the complexation between harmane and CB7 are enthalpically favourable.

Photoactive assemblies of organic compounds and biomolecules: drug–protein supramolecular systems

Modification of the drug excited state properties within proteins provides information on binding and may result in a different photoreactivity.

Spectral and photophysical properties of α-carboline (1-azacarbazole) in aqueous solutions

The absorption and fluorescence spectra of α-carboline, 9H-pyrido[2,3-b]indole, AC, in organic aprotic solvents containing different water proportions and in acid/base aqueous solutions inside and outside the pH range have been examined. In the organic aprotic solvents, the addition of increasing concentrations of water sequentially quenches and shifts to the red the fluorescence spectra of AC. These spectral changes have been rationalized assuming the formation, at the lower water concentrations, of a discrete ground state non-cyclic weakly fluorescent AC hydrate emitting at 376 nm that, upon increasing the water concentrations, evolves to a higher order AC poly hydrate emitting at 397 nm. The changes of the AC absorption spectra in aqueous acid/basic solutions indicate the existence of three ground state prototropic species; the pyridinic protonated cation, C (pK(a) = 4.10 ± 0.05), the neutral, N (pK(a) = 14.5 ± 0.2), and the pyrrolic deprotonated anion, A. Conversely, the changes of the AC fluorescence spectra in these media indicate the existence of four excited state species emitting at 376 nm, 397 nm, 460 nm and 465 nm. Since the emissions at 376 nm and 397 nm satisfactorily match those of the hydrates observed in the organic-water mixtures, they were consistently assigned to two differently hydrated ground state N species. The remaining emissions at 460 nm and 465 nm have been assigned without ambiguity, on the basis of their excitation spectra, to the C and A species, respectively. The excited-state pK(a)s of the prototropic species of AC have been estimated by using the Förster-Weller cycle.

Exploring the strength, mode, dynamics, and kinetics of binding interaction of a cationic biological photosensitizer with DNA: implication on dissociation of the drug-DNA complex via detergent sequestration

The present study aims at exploring a detailed characterization of the binding interaction of a promising cancer cell photosensitizer, harmane (HM), with DNA extracted from herring sperm. The polarity-sensitive prototropic transformation of HM, a naturally occurring, fluorescent, drug-binding alkaloid, β-carboline, is remarkably modified upon interaction with DNA and is manifested through significant modulations on the absorption and emission profiles of HM. From the series of studies undertaken in the present program, for example, absorption; steady-state emission; the effect of chaotrope (urea); iodide ion-induced steady-state fluorescence quenching; circular dichroism (CD); and helix melting from absorption spectroscopy; the mode of binding of HM into the DNA helix has been substantiated to be principally intercalative. Concomitantly, a discernible dependence of the photophysics of the DNA-bound drug on the medium ionic strength indicates that electrostatic attraction should not be ignored in the interaction. Efforts have also been delivered to delineate the dynamical aspects of the interaction, such as modulation in time-resolved fluorescence decay and rotational relaxation dynamics of the drug within the DNA environment. In view of the prospective biological applications of HM, the issue of facile dissociation of intercalated HM from the DNA helix also comprises a crucial prerequisite for the functioning as an effective therapeutic agent. In this context, our results imply that the concept of detergent-sequestered dissociation of the drug from the drug-DNA complex can be a prospective strategy through an appropriate choice of the detergent molecule. The utility of the present work resides in exploring the potential applicability of the fluorescence property of HM for studying its interactions with a relevant biological target, for example, DNA. In addition, the methods and techniques used in the present work can also be exploited to study the interaction of HM with other biological, biomimicking assemblies and drug delivery vehicles, and so forth.