Novel Bifunctional Viologen-Linked Pyrene Conjugates: Synthesis and Study of Their Interactions with Nucleosides and DNA

Antiglycation potential of plant based TiO2 nanoparticle in D-ribose glycated BSA in vitro

Biosynthetic procedure is one of the best alternatives, inexpensive and ecologically sound for the synthesis of titanium dioxide (TiO₂ ) nanoparticles using a methanolic extract of medicinal plant. The main prospect of this study was to investigate the antiglycation activity of the TiO₂ nanoparticles (TNP) prepared by ethanolic leaf extract of the Coleus scutellarioides. In this study, biosynthesized TNP characterized with UV-Visible spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscope. These TNP were further investigated with respect to their antiglycation property and it was checked in the mixture of d-ribose glycated bovine serum albumin (BSA) by measuring ketoamine, carbonyl content, Advanced glycation end products (AGEs) and aggregation of protein instigated by glycation process. The inhibitory effect of TNP to restore the structure of BSA in presence of d-ribose were also characterize by biophysical techniques mentioned above. Therefore, the findings of this study suggest repurposing of TNP for its antiglycation property that could be helpful in prevention of glycation instigated AGEs formation and structural loss of proteins.

Efficient Photoinduced Electron Transfer from Pyrene-o-Carborane Heterojunction to Selenoviologen for Enhanced Photocatalytic Hydrogen Evolution and Reduction of Alkynes

A series of pyrene or pyrene-o-carborane-appendant selenoviologens (Py-SeV²⁺ , Py-Cb-SeV²⁺ ) for enhanced photocatalytic hydrogen evolution reaction (HER) and reduction of alkynes is reported. The efficient photoinduced electron transfer (PET) from electron-rich pyrene-o-carborane heterojunction (Py-Cb) with intramolecular charge transfer (ICT) characteristic to electron-deficient selenoviologen (SeV²⁺ ) (k_ET = 1.2 × 10¹⁰ s^-1 ) endows the accelerating the generation of selenoviologen radical cation (SeV^+• ) compared with Py-SeV²⁺ and other derivatives. The electrochromic/electrofluorochromic devices' (ECD and EFCD) measurements and supramolecular assembly/disassembly processes of SeV²⁺ and cucurbit[8]uril (CB[8]) results show that the PET process can be finely tuned by electrochemical and host-guest chemistry methods. By combination with Pt-NPs catalyst, the Py-Cb-SeV²⁺ -based system shows high-efficiency visible-light-driven HER and highly selective phenylacetylene reduction due to the efficient PET process.

Anti-Sandwich Structured Photo-Electronic Wound Dressing for Highly Efficient Bacterial Infection Therapy

Photo-electronic devices based on reactive oxygen species (ROS) generation suffer a crucial limitation in wound treatment due to their sandwich structure, which prevents the contact of ROS with wound tissue. In this work, the first anti-sandwich structured visible-light/electricity dual-responsive wound dressing is constructed for treatment of methicillin-resistant Staphylococcus aureus (MRSA), based on selenoviologen-appendant polythiophene (SeV²⁺ -PT)-containing polyacrylamide hydrogels. The new wound dressing is named an anti-sandwich structured photo-electronic wound dressing (PEWD). The unique structure of PEWD enables its use in synergistic electrodynamic and photodynamic therapy (EDT and PDT), providing rapid, on-demand, and sustained generation of ROS in situ via short-time light irradiation and/or wireless-controlled electrification. The PEWD possesses good flexibility, excellent biocompatibility, and fast response, as well as sustained ROS generation in a physiological environment. Animal experiments demonstrate effective ROS generation in 6 s under irradiation and electrification, inhibiting infection at an early stage, and substantially shortening the healing time of bacterial infection (to within 7 days). This proof-of-concept research holds great promise in developing new flexible PEWD, and novel strategies to improve wound treatment.

Photophysical Properties of an Azine-Linked Pyrene-Cinnamaldehyde Hybrid: Evidence of Solvent-Dependent Charge-Transfer-Coupled Excimer Emission

We report the photophysical properties of a synthetic asymmetric azine-based compound (17Z,18E)-4'-((E)-3-phenylallylidene)-1'-(dimethylamino)-1-((pyren-8-yl)methylene)hydrazine (PYNC). The molecule PYNC shows an appreciable red shift in the emission maximum in a wide range of solvents. In water, PYNC shows the characteristic feature of excimer formation exclusively. However, in all other solvents, the excimer band is present alongside the charge transfer emission band. The assignment of charge transfer and excimer bands has been established by various steady-state emission spectral data. PYNC, owing to this novel excimer-coupled charge transfer phenomenon, can be a potential probe for studying various supramolecular assemblies of biological interest.

Strong ion pair charge transfer interaction of 1,8-naphthalimide–bipyridinium conjugates with basic anions – towards the development of a new type of turn-on fluorescent anion sensors

Fluoride, acetate and benzoate anions reduce naphthalimide–viologen dyads into radicals, which is indicated by a strong fluorescence enhancement.

Photolysis of a bola-type supra-amphiphile promoted by water-soluble pillar[5]arene-induced assembly

A novel monolayer supramolecular vesicle assembled from a pillararene-based bola-type supra-amphiphile was successfully constructed, which showed excellent photodegradable properties and might have potential applications in phototherapy.

Naphthalene Imide Conjugates: Formation of Supramolecular Assemblies, and the Encapsulation and Release of Dyes through DNA-Mediated Disassembly

We report the synthesis of two new amphiphilic conjugates 1 and 2 based on naphthalene di- and monoimide chromophores and the investigation of their photophysical, self-assembly and DNA-binding properties. These conjugates showed aqueous good solubility and exhibited strong interactions with DNA and polynucleotides such as poly(dG⋅dC)-poly(dG⋅dC) and poly(dA⋅dT)-poly(dA⋅dT). The interaction of these conjugates with DNA was evaluated by photo- and biophysical techniques. These studies revealed that the conjugates interact with DNA through intercalation with association constants in the order of 5-8×10(4)  M(-1) . Of these two conjugates, bolaamphiphile 1 exhibited a supramolecular assembly that formed vesicles with an approximate diameter of 220 nm in the aqueous medium at a critical aggregation concentration of 0.4 mM, which was confirmed by SEM and TEM. These vesicular structures showed a strong affinity for hydrophobic molecules such as Nile red through encapsulation. Uniquely, when exposed to DNA the vesicles disassembled, and therefore this transformation could be utilised for the encapsulation and release of hydrophobic molecules by employing DNA as a stimulus.

Effective Amyloid Defibrillation by Polyhydroxyl-Substituted Squaraine Dyes

With an objective to develop β-amyloid destabilizing agents, we have investigated the interactions of a few water-soluble near-infrared (NIR)-absorbing squaraine dyes 1-3 with lysozyme and its amyloid aggregates through photophysical and biophysical techniques. These dyes exhibited strong interactions with lysozyme and β-amyloids in addition to serum albumins as evidenced by the absorption and emission changes. The interactions were found to be spontaneous with association constant values in the range of approximately 10(4)-10(5)  m(-1), as confirmed through half-reciprocal analysis and isothermal calorimetric measurements. Uniquely, such effective interactions of the dyes have led to the complete disassembly of the β-amyloid fibrillar structures to form spherical particles approximately 350 nm in size, as confirmed through photophysical, thioflavin assay, circular dichroism (CD), atomic force microscopy (AFM), TEM, and selected-area electron diffraction (SAED) techniques. These results demonstrate that the squaraine dyes 1-3 under investigation act as effective protein-labelling and destabilizing agents of the protein amyloidogenesis.

Fluorescence reporting of G-quadruplex structures and modulating their DNAzyme activity using polyethylenimine-pyrene conjugate

Four-stranded G-quadruplex structure is one of the most important non-canonical secondary structures of DNA formed by guanine (G)-rich sequences. G-rich DNA sequences are known to occur in the human genome, especially in the telomere 3' end and in oncogene promoters such as c-MYC and c-KIT. In this context, we designed pyrene-conjugated polyethylenimine (PEI-Py) as a fluorescence reporter for the recognition and detection of G-quadruplex structures of G-rich deoxyoligonucleotides and human telomere and gene promoter sequences, under ambient conditions. PEI-Py exhibited prominent pyrene excimer emission in the presence of G-quadruplex structures of G-rich deoxyoligonucleotides and biologically relevant DNA sequences. PEI-Py further displayed the modulation of DNAzyme activity of various G-quadruplex structures in the presence of hemin and hydrogen peroxide.

Physicochemical analysis of mixed micelles of a viologen surfactant: extended to water-in-oil (w/o) microemulsion and cucurbit[8]uril-assisted vesicle formation

A systematic study of the self-assembly process of a viologen-containing surfactant in aqueous medium is reported. Dodecyl-ethyl-viologendibromide (DDEV) is mixed in different proportions with dodecyltrimethylammonium bromide (DTAB), and the physicochemical properties of micellization are evaluated in order to find a suitable combination which does not interfere with the micellar properties of DTAB but introduces the characteristic properties of viologen. In this process, 1% doping of DDEV with DTAB was found to be the most appropriate, as negligible changes were observed in the physicochemical behavior of this system with respect to that of pure DTAB. The 1% DDEV-doped DTAB mixed micellar system showed the characteristic two-step reduction process for the viologen units at the interface as revealed by CV experiments. 1% mixing of DDEV with DTAB also allowed us to prepare stable w/o microemulsions containing viologen units at the interface which is otherwise unattainable with pure viologen surfactants. The charge-transfer capability of the viologen unit to the electron-rich 2,6-dihydroxynaphthalene (DHN) moiety inside the macrocyclic host, cucurbit[8]uril (CB[8]) is also evaluated for this system, and surprisingly even at this very low concentration, the ternary complex of DDEV-DHN@CB[8] transformed the micellar assembly to uniform vesicles. All of these properties have been further extended to other tetraalkylammonium surfactants, and similar effects were observed.

Molecular packing, crystal to crystal transformation, electron transfer behaviour, and photochromic and fluorescent properties of three hydrogen-bonded supramolecular complexes containing benzenecarboxylate donors and viologen acceptors

Structures of three D–A supramolecular systems and their photoresponsive characteristics are investigated.

Interaction of DNA and a series of aromatic donor-viologen acceptor molecules with and without the presence of CB[8]

A series of 1-ethyl-1'-arylmethyl-4,4'-bipyridinium compounds is synthesized, where the aryl is phenyl (BEV), 2-naphthyl (NEV), 2-anthracenyl (AEV) or 1-pyrenyl (PEV). Among them, PEV and AEV can bind with calf thymus DNA mainly through intercalation and groove-binding modes, and both of them can be observed to photocleave plasmid pBR 322 DNA significantly under irradiation with a xenon arc lamp. After inclusion of cucurbit[8]uril (CB[8]), all of the aromatic donor-viologen acceptor compounds exhibit efficient DNA photocleavage ability. The reason is that CB[8] can inhibit the intramolecular backwards electron transfer in the aromatic donor-viologen acceptor molecule, prolonging the lifetime of the charge separated excited state to some extent. These studies bring a new subject in DNA photocleavage research and a potential application of the host-guest supramolecular system.

Functional cyclophanes: promising hosts for optical biomolecular recognition

Cyclophanes possess a defined cavity size and are efficient in encapsulating and stabilising guest molecules inside the cavity through various non-covalent interactions. This unique property of the cyclophanes has been widely exploited for the development of selective probes for a variety of guest molecules. The present tutorial review highlights the use of various interesting functionalised cyclophane architectures for the sensitive and selective optical recognition of important biomolecules.

Encapsulation of Electron Donor−Acceptor Dyads in β-Cyclodextrin Cavity: Unusual Planarization and Enhancement in Rate of Electron-Transfer Reaction

Interaction of beta-cyclodextrin (beta-CD) with a few novel electron donor acceptor dyads 1a-c and 2a-c, having aryl and flexible methylene spacer groups, has been investigated through photophysical, chiroptical, electrochemical, NMR, and microscopic techniques. Dyads 1a and 1c, with p-tolyl and biphenyl spacer groups, respectively, exhibited significantly decreased fluorescence quantum yields and lifetimes in the presence of beta-CD, while negligible changes were observed for dyad 1b with an o-tolyl spacer. In contrast, spacer-length-dependent significant enhancement in fluorescence quantum yields and lifetimes was observed for dyads 2a-c, with flexible polymethylene (n = 1, 3, 11) spacer groups. Association constants of beta-CD encapsulated complexes have been determined and the contrast behavior observed in these systems is explained through an electron transfer (kET) mechanism based on calculated favorable change in free energy (DeltaGET = -1.27 eV) and the redox species characterized through laser flash photolysis studies. Rates of kET have been estimated and are found to increase ca. 2-fold in the case of dyads 1a and 1c when encapsulated in beta-CD, while significantly decreased kET values were observed for the dyads 2a-c with flexible spacer (ca. 9-fold for 2c). As characterized through cyclic voltammetry, 2D NMR [correlated (COSY) and nuclear Overhauser enhancement (NOESY) spectroscopy], and laser flash photolysis studies, the beta-CD encapsulation of dyads with aliphatic spacer groups leads to the conformational unfolding of a sandwich type of structure, whereas dyads with rigid aryl spacer groups undergo unusual planarization as compared to the uncomplexed dyads, resulting in enhanced electron-transfer reaction between the donor and acceptor moieties.

Synthesis, characterization, and use of asymmetric pyrenyl-gemini surfactants as emissive components in DNA-lipoplex systems

Gemini surfactants are potential candidates as synthetic vectors for the delivery of genes into cells to induce protein expression. With the ultimate objective of obtaining a better understanding of the mechanism of DNA transfection, two new asymmetric gemini surfactants (py-3-12 and py-6-12) have been synthesized as fluorescence probes. The physicochemical properties and morphologies of the self-assembled aggregates formed in aqueous solution have been studied using surface tension, specific conductance, dynamic light scattering (DLS), isothermal titration calorimetry (ITC), and fluorescence techniques. The interaction between pyrene-based gemini surfactants and DNA was investigated by using UV-vis and fluorescence spectroscopy. Binding constants for the DNA (salmon sperm)-gemini lipoplexes were measured. Fluorescence studies show that excimer emission occurs upon complexation with DNA.

Photochromic Dibenzobarrlenes: Long-Lived Triplet Biradical Intermediates

Upon exposure to UV light, the disubstituted dibenzobarrelene derivative 1a turns green in the solid phase and reverts back to its original pale-yellow color within several hours in the dark. The lifetime of the colored species in degassed benzene at room temperature is 37 +/- 2 s (Ea for decoloration is 14.5 +/- 0.7 kcal mol-1 and log A is 8.92 +/- 0.5 s-1) and highly sensitive to molecular oxygen; the Stern-Volmer quenching constant is 6.9 +/- 0.2 x 108 M-1 s-1. Similarly, the disubstituted dibenzobarrelenes 1b and 1c exhibited pink coloration when exposed to UV light in the solid phase. On the basis of combined experimental and theoretical evidence, it is proposed that upon photoexcitation the excited singlet state of 1a undergoes rapid intersystem crossing to its triplet state, followed by intramolecular delta-H abstraction, to yield the triplet biradical intermediate (3)2. Upon prolonged irradiation, 2 undergoes cyclization to the alcohol 3, which affords the enone 4 as the final photoproduct. The delta-H abstraction on the triplet-state potential energy surface, calculated at the B3LYP/6-31G* level of density functional theory (DFT), has an activation energy of 18.5 kcal/mol. Further, the absorption spectrum of the triplet biradical (3)2, obtained from time-dependent DFT calculations, displays an intense absorption maximum at 670 nm, which is in good agreement with the observed absorption peak at 700 nm. The molecular-orbital analysis of the triplet diradical (3)2 suggests that its long-wavelength absorption involves the transition of the unpaired electron from the comparatively localized benzyl-type HOMO to the extensively conjugated benzoyl-type LUMO. The present experimental and theoretical results strongly support the intervention of a long-lived triplet biradical (3)2 in the photochromism of appropriately substituted dibenzobarrelenes.

Chiral Supramolecular Assemblies of a Squaraine Dye in Solution and Thin Films: Concentration-, Temperature-, and Solvent-Induced Chirality Inversion

We prepared novel cholesterol-appended squaraine dye 1 and model squaraine dye 2 and investigated their aggregation behavior in solution and thin films using photophysical, chiroptical, and microscopic techniques. Investigations on the dependence of aggregation on solvent composition (good/poor, CHCl3/CH3CN) demonstrated that squaraine dye 1 forms two novel H-type chiral supramolecular assemblies with opposite chirality at different good/poor solvent compositions. Model compound 2 formed J-type achiral assemblies under similar conditions. The supramolecular assembly of 1 observed at lower fractions of the poor solvent could be assigned to the thermodynamically stable form, while a kinetically controlled assembly is formed at higher fractions of the poor solvent. This assignment is evidenced by temperature- and concentration-dependent experiments. With increasing temperature, the chirality of the kinetically controlled aggregate was lost and, on cooling, the aggregate with the opposite chirality was formed. On further heating and cooling the aggregates thus formed resulted in no significant changes in chirality, that is they are thermodynamically stable. Similarly, at lower concentrations, the thermodynamically stable form exists, but at higher concentration aggregation was found to proceed with kinetic control. Based on these observations it can be assumed that formation of the kinetically controlled assembly might be largely dependent on the presence of the nonpolar cholesterol moiety as well as the amount of poor solvent present. However, under solvent-free conditions, structurally different aggregates were observed when drop cast from solutions containing monomer, whereas a left-handed CD signal corresponding to the thermodynamically controlled assemblies was observed from pre-aggregated solutions.

Selective Interactions of a Few Acridinium Derivatives with Single Strand DNA: Study of Photophysical and DNA Binding Interactions

Novel acridinium derivatives 1-3, wherein steric factors have been varied systematically through substitution at the ninth position of the acridinium ring, were synthesized and their interactions with single strand and double strand DNA have been investigated through photophysical, biophysical, and microscopic techniques. The acridinium derivative 1 exhibited quantitative fluorescence yields (phi f approximately =1) and high lifetime of 35 ns, while significantly lower fluorescence yields of 0.11 and 0.02 and lifetimes of 3.5 and 1.2 ns were observed for 2 and 3, respectively. The derivatives 1 and 2 having 2-methylphenyl and 2,4-dimethylphenyl substituents at the ninth position of the acridinium ring showed selective interactions with single strand DNA (ssDNA) with association constants of KssDNA = 6.3-6.6 x 10(4) M(-1), while negligible interactions were observed with double strand DNA (dsDNA). In contrast, the derivative 3 with 2,6-dimethylphenyl substitution showed negligible interactions with both ssDNA and dsDNA. Studies with a series of 19-mer oligonucleotides indicate that these derivatives exhibit significant selectivity for the sequences rich in guanosine (ca. 3-fold) as compared to the cytosine-rich sequences. These derivatives with high water solubility and the ability to distinguish between ssDNA and dsDNA through changes in fluorescence emission can be used as fluorescent probes for understanding the role of ssDNA in various biological processes and to study various DNA-ligand interactions.

Selective Recognition of Tryptophan through Inhibition of Intramolecular Charge-Transfer Interactions in an Aqueous Medium

[reaction: see text] A novel donor-acceptor conjugate 1 was synthesized, and its interactions with various amino acids have been investigated as compared to the model system 2. The conjugate 1 unusually forms an intramolecular charge-transfer complex in the aqueous medium and undergoes selective binding interactions with tryptophan. The uniqueness of this system is that it selectively recognizes tryptophan among all other amino acids and involves synergistic effects of pi-stacking, electrostatic, and donor-acceptor interactions.