G-Quadruplex selectivity and cytotoxicity of a guanidine-encapsulated porphyrin-cyclodextrin conjugate.

G-Quadruplex DNAs represent out-of-the-way nucleic acid conformations, frequently formed by guanine-rich sequences. They have emanated as cancer-associated targets for designed small molecules. The variation in the binding affinity of the synthesized compounds to duplex and quadruplex structures is an intriguing quest, solved by spectroscopic analysis.

An overview from simple host-guest systems to progressively complex supramolecular assemblies.

Supramolecular chemistry involving macrocyclic hosts is a highly interdisciplinary and fast-growing research field in chemistry, biochemistry, and materials science. Host-guest based supramolecular assemblies, as constructed through non-covalent interactions, are highly dynamic in nature, and can be tuned easily using their responses to various external stimuli, providing a convenient approach to achieve excellent functional materials. Macrocyclic hosts, particularly cyclodextrins, cucurbit[]urils, and calix[]arenes, which have unique features like possessing hydrophobic cavities of different sizes, along with hydrophilic external surfaces, which are also amenable towards easy derivatizations, are versatile cavitands or host molecules to encapsulate diverse guest molecules to form stable host-guest complexes with many unique structures and properties.

Multimode binding and stimuli responsive displacement of acridine orange dye complexed with p-sulfonatocalix[4/6]arene macrocycles.

Interaction of acridine orange (AOH+) dye with water soluble anionic p-sulfonatocalix[n]arene (SCXn) hosts, SCX4 and SCX6, having different cavity dimensions, has been investigated using multispectroscopic techniques. Intriguing modulation in the photophysical properties of AOH+ upon interaction with SCXn hosts indicate the formation of different host-guest complexes at different regions of the host concentrations. At lower host concentrations, AOH+ undergoes SCXn assisted aggregation, causing a drastic reduction in fluorescence intensity.

Complexation induced aggregation and deaggregation of acridine orange with sulfobutylether-β-cyclodextrin.

The present study reports a contrasting interaction behaviour of a biologically important dye, acridine orange (AOH), with a highly water soluble anionic host, based on a β-cyclodextrin (βCD) scaffold, i.e. sulfobutylether-β-cyclodextrin (SBEβCD), in comparison to native βCD.

Unraveling multiple binding modes of acridine orange to DNA using a multispectroscopic approach.

The interaction of acridine orange (AOH(+)) with calf thymus DNA (ct-DNA) under different dye-DNA conditions has been investigated in detail using multispectroscopic techniques, unraveling a number of hitherto unexplored intricacies of dye-DNA binding. The observed results intriguingly show contrasting binding features when low (2.4 μM) and significantly high (23 μM) dye concentrations are used.

pH-Assisted control over the binding and relocation of an acridine guest between a macrocyclic nanocarrier and natural DNA.

The differential binding affinity of the hydroxypropyl-β-cyclodextrin (HPβCD) macrocycle, a drug delivery vehicle, towards the protonated and deprotonated forms of the well-known DNA binder and model anticancer drug acridine has been exploited as a strategy for dye-drug transportation and pH-responsive delivery to a natural DNA target. From pH-sensitive changes in the ground state absorption and steady-state fluorescence characteristics of the studied acridine dye-HPβCD-DNA ternary system and strongly supported by fluorescence lifetime, fluorescence anisotropy, Job's plots, (1)H NMR and circular dichroism results, it is revealed that in a moderately alkaline solution (pH ∼ 8.5), the dye can be predominantly bound to the HPβCD macrocycle and when the pH is lowered to a moderately acidic region (pH ∼ 4), the dye efficiently detaches from the HPβCD cavity and almost exclusively binds to DNA.

Photophysical and quantum chemical studies on the interactions of oxazine-1 dye with cucurbituril macrocycles.

Supramolecular host-guest interaction of cationic oxazine-1 (OX1) dye with two cucurbit[n]uril (CBn) hosts, namely, CB7 and CB8, has been investigated using photophysical and quantum chemical studies. Both CB7 and CB8 display much stronger binding affinities for OX1 dye compared to conventional cyclodextrin (CD) hosts, which arises due to strong ion-dipole interaction in stabilizing the dye-host inclusion complexes in the present systems. From photophysical studies supported by (1)H NMR results and quantum chemical calculations, it is inferred that 1:1 inclusion complexes are mainly formed in the present systems, though a small percentage of 1:2 (dye·host2) complexes are also indicated from time-resolved (TR) fluorescence studies.

Triple emission from p-dimethylaminobenzonitrile-cucurbit[8]uril triggers the elusive excimer emission.

The intriguing dual-emission behavior of p- dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule- specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water-soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation.

Observation of the Marcus inverted region for bimolecular photoinduced electron-transfer reactions in viscous media.

The general observation of Marcus inverted region (MIR) for bimolecular electron-transfer (ET) reactions in different viscous media, e.g., micelles, reverse micelles, vesicles, ionic liquids, DNA scaffold, etc.

Atypical energetic and kinetic course of excited-state intramolecular proton transfer (ESIPT) in room-temperature protic ionic liquids.

The excited-state intramolecular proton-transfer (ESIPT) process in 1,8-dihydroxyanthraquinone (18DHAQ) dye has been investigated in protic ionic liquid (PIL) solvents using photochemical measurements. The results demonstrate noteworthy modulations in both steady-state and time-resolved emission characteristics of excited normal (N*) and tautomeric (T*) forms of the dye. That the emission of T* increases unexpectedly upon increasing solvent viscosity indicates that subsequent to the initial forward ESIPT, there is also a relatively slower back ESIPT process involved for the excited dye.