Cyclodextrin Cavity Size Effect on the Complexation and Rotational Dynamics of the Laser Dye 2,5-Diphenyl-1,3,4-oxadiazole: From Singly Occupied Complexes to Their Nanotubular Self-Assemblies

Host assisted molecular recognition by human serum albumin: Study of molecular recognition controlled protein/drug mimic binding in a microfluidic channel

Human serum albumin (HSA) plays a pivotal role in drug release from its delivery vehicles such as cyclodextrins (CDs) by binding to the drugs. Here molecular recognition and binding of a drug mimic (CD1) to HSA have been explored in a microfluidic channel when CD1 is encapsulated in β-cyclodextrin (βCD) and heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (TRIMEB), respectively, to investigate whether change of the host vehicle modulate the rate of drug binding to the serum protein. Molecular recognition of βCD encapsulated CD1 by HSA occurs by the conformational selection fit mechanism leading to rapid binding of CD1 to HSA (k₁ ~ 700 s^-11) when the βCD/CD1 complex interacts with HSA. In contrary, HSA recognizes CD1 encapsulated in TRIMEB by an induced fit mechanism leading to a significantly slower binding rate (k₁ ~ 20.8 s^-1) of the drug mimic to the protein. Thus molecular recognition controls the rate of HSA binding by CD1 which in turn modulates the rate of delivery of the drug mimic from its macrocyclic hosts. The remarkable change in the molecular recognition pathway of CD1 by HSA, upon change of the host from βCD to TRIMEB, originates from significantly different conformational flexibility of the host/drug mimic complexes.

Fluorescent pseudorotaxanes of a quinodicarbocyanine dye with gamma cyclodextrin

Spectrophotometric titration of buffered solutions of gamma cyclodextrin (γCD) and 1,1'-diethyl,2,2'-dicarbocyanine (DDI) demonstrates extension of the known 1:2 host:guest complex to form a previously unreported 2:2 complex near the γCD solubility limit. Though DDI is predominantly hosted as a non-fluorescent H-aggregate, both complexes exist in respective equilibria with two secondary complexes hosting unaggregated DDI as 1:1 and 2:1 complexes. The 2:1 complex exhibits significant fluorescence emission, with a quantum yield six times that of DDI in organic solvents, but ten times lower than that of an analogous indodicarbocyanine. Fragment Molecular Orbital calculations suggest that the 2:1 complex has the tail-to-tail conformation, and that solvent access to the dye strongly favors photoisomerization. In the host-guest complex, γCD limits solvent access to the dye and hinders rotation of the quinolyl terminal groups, but nevertheless pairwise rotation of methine carbons within the γCD cavity likely remains as a significant nonradiative relaxation pathway for the excited state.

CdII/ZnIIdiscrimination using 2,5-diphenyl[1,3,4]oxadiazole based fluorescent chemosensors

Two ditopic PPD based ligands are able to discriminate Cd^IIover Zn^IIin aqueous solution based on the difference in their ionic radii, acting as OFF–ON fluorescent probes.

Carbohydrate-Based Host-Guest Complexation of Hydrophobic Antibiotics for the Enhancement of Antibacterial Activity

Host-guest complexation with various hydrophobic drugs has been used to enhance the solubility, permeability, and stability of guest drugs. Physical changes in hydrophobic drugs by complexation have been related to corresponding increases in the bioavailability of these drugs. Carbohydrates, including various derivatives of cyclodextrins, cyclosophoraoses, and some linear oligosaccharides, are generally used as host complexation agents in drug delivery systems. Many antibiotics with low bioavailability have some limitations to their clinical use due to their intrinsically poor aqueous solubility. Bioavailability enhancement is therefore an important step to achieve the desired concentration of antibiotics in the treatment of bacterial infections. Antibiotics encapsulated in a complexation-based drug delivery system will display improved antibacterial activity making it possible to reduce dosages and overcome the serious global problem of antibiotic resistance. Here, we review the present research trends in carbohydrate-based host-guest complexation of various hydrophobic antibiotics as an efficient delivery system to improve solubility, permeability, stability, and controlled release.

Tuning the constrained photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline inside the cyclodextrin nanocavities: A detailed insight via experimental and theoretical approach

The modulation in the photophysics of a pyrazoline dye 3-naphthyl-1-phenyl-5-(4-carboxyphenyl)-2-pyrazoline (NPCP), when it drifts from bulk water into the nanocages of aqueous cyclodextrin solutions was investigated. The intramolecular charge transfer (ICT) fluorescence band intensity was found to increase with a blue shift in the presence of cyclodextrins. The results from ¹H NMR and ¹HH COSY NMR spectral analysis clearly points out the position of pyrazoline ring inside the cavity and its role in complexation process. A quantitative assessment of the emission intensity data on Benesi-Hildebrand (B-H) equation along with ESI-MS spectra reveals the probable stoichiometry of NPCP-CD complexes. Molecular docking and molecular dynamics studies were conducted for β/γ cyclodextrin associated inclusion complexes of NPCP. The results obtained by computational studies are in good relation with the data obtained through experimental methods and both ascertain the encapsulation of NPCP into cyclodextrins.

Trimethyl-β-cyclodextrin-encapsulated monolithic capillary columns: Preparation, characterization and chiral nano-LC application

Trimethylated-β-cyclodextrin (TM-β-CD) was encapsulated within several polymer monolithic capillary columns for reversed-phase chiral nano-liquid chromatography (nano-LC). The monolithic phases were prepared using the one-pot in situ copolymerization of ethylene glycol dimethacrylate (EDMA), glycidyl methacrylate (GMA) monomers and 1-propanol, 1,4-butanediol as progenic solvents in presence of TM-β-CD solution within fused silica capillaries (150µm I.D.). The obtained chiral monolithic stationery phases were characterized by scanning electron microscopy (SEM), N₂ adsorption/desorption isotherms, wide angle x-ray diffraction (WAXRD), thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The materials characterization demonstrated that monolithic phases with higher concentration of TM-β-CD have relatively larger surface area, smaller pore size and larger total pore volume compared to those with lower concentration TM-β-CD. The prepared columns were tested for their enantioseparation efficiency of a range of racemic pharmaceuticals. The screening results demonstrated the potential of functionalizing polymer monolithic stationary phases with TM-β-CD using the in situ encapsulation approach.

A pH-driven molecular shuttle based on rotaxane-bridged periodic mesoporous organosilicas with responsive release of guests

A pH-driven molecular shuttle was immobilized into the framework of the PMOs in which the β-CDs could shuttle mechanically.

Supramolecular aggregates formed by sulfadiazine and sulfisomidine inclusion complexes with α- and β-cyclodextrins

Sulfadiazine (SDA) and sulfisomidine (SFM) inclusion complexes with two cyclodextrins (α-CD and β-CD) are studied in aqueous as well as in solid state. The inclusion complexes are characterized by UV-visible, fluorescence, time correlated single photon counting, FTIR, DSC, PXRD and (1)H NMR techniques. The self assembled SDA/CD and SFM/CD inclusion complexes form different types of nano and microstructures. The self assembled nanoparticle morphologies are studied using SEM and TEM techniques. SDA/α-CD complex is formed hierarchal morphology, SDA/β-CD and SFM/β-CD complexes form the nanosheet self assembly. However, SFM/α-CD complex forms nanoporous sheet self assembly. van der Waals, hydrophobic and hydrogen bonding interaction play a vital role in the self assembling process.

Controlling the stereospecificity of a volume-conserving adiabatic photoisomerization within a nanotubular self-assembled cage: a reversible light-heat torque converter

We present herein a host-guest supramolecular system by which we were able to obtain precise control of the stereospecificity of a new and unusual adiabatic photoisomerization reaction capable of restoring reversibly the original configuration. The host-guest system is composed of (a) a naphthalene ring linked centrosymmetrically-via sp(2) hybridized oxygen atoms-with methoxytriethyleneglycol chains (1) and (b) a nanotubular cage formed by four self-assembled face-to-face β-cyclodextrins threaded onto the long "axle" of 1. The compound 1 can exist in distinct cis,cis, cis,trans, and trans,trans conformations that are spectrally distinguishable (see Scheme 1 ). Spectroscopic and kinetic manifestations of the torsional isomerization of 1 in the lowest excited singlet state both in solution and within the tubular cage were investigated. The results provide clear evidence that the compact cavity completely blocks the photoisomerization pathway manifested in common solution (cis,cis* → cis,trans*), allowing observation of stereospecific, volume-conserving turning of the naphthalene ring about the two "quasidouble" bonds C(Naph)-O by φ ≈ 180° (cis,cis* → trans,trans*). The photoisomerization is purely adiabatic, and the encaged molecule restores its original configuration by generating torque thermally, when relaxing to the ground state.