Solubilization and Photostabilization in a Sodium Deoxycholate Hydrogel of a Neutral Conjugated Thiophene Oligomer and Polymer.

Oligo(3-hexylthiophene--1,4-phenylene) and poly(3-hexylthiophene) were solubilized in sodium deoxycholate self-assemblies in water solutions and hydrogels, with the goal of solubilizing sufficient material in a hydrogel for fluorescence applications. The neutral conjugated oligomer and polymer were incorporated as monomers into the self-assemblies with sodium deoxycholate aggregates, leading to the photoprotection of these neutral conjugated and water-insoluble molecules. Dynamic light scattering, rheology, and fluorescence experiments established that the deoxycholate aggregation and gel formation properties were not altered with the incorporation of the oligomer or polymer into the deoxycholate self-assemblies, showing that this adaptable host system with some molecular recognition elements is a viable strategy to incorporate into hydrogels neutral conjugated molecules as isolated monomers.

Dynamics of small molecules within the F127 PEO-PPO-PEO triblock copolymer gel and sol phases studied at the molecular scale.

Triplet excited states of guest molecules with different hydrophobicities were used to probe the association and dissociation dynamics of these guests with F127 micelles in the gel and sol phases. The dynamics probed was on a longer length scale than amenable with fluorescence techniques, but at a shorter length scale than probed in translational diffusion studies. The mobility of the guests at the molecular scale showed that subtle changes in the guest's structure affect the guest's release time from the micelles, where the structural features of the guest are more important than the phase, gel sol, of the system.

Mechanism of a Disassembly-Driven Sensing System Studied by Stopped-Flow Kinetics.

We carried out steady-state and stopped-flow photophysical measurements to determine the kinetics of a discrete disassembly driven turn-on fluorescent system. On and off rates for both DimerDye1 assembly and nicotine binding were determined. Relative rates for these competing processes provide insight on how this system can be optimized for sensing applications.

Nonlinear Dependence on Na Ions for the Binding Dynamics of Cucurbit[6]uril with the -1-Methyl-4-(4-hydroxystyryl)pyridinium Cation.

The binding dynamics of the -1-methyl-4-(4-hydroxystyryl)pyridinium cation (HSP) to cucurbit[6]uril (CB[6]) in the presence of Na cations were studied to establish the effect of the relative concentrations of the system's components (HSP, CB[6], and Na) on these dynamics. The formation of the HSP@CB[6] complex was temporally uncoupled from the photoisomerization of -HSP, while a nonlinear effect of the Na cation concentration on the HSP@CB[6] dynamics was observed. This nonlinearity is a consequence of Na having the opposite effect on the association and dissociation rate constants for the HSP@CB[6] complex, creating a conceptual framework for using such nonlinearities to control multistep reactions in cucurbit[]uril chemistry.

Labeling of Proteins by BODIPY-Quinone Methides Utilizing Anti-Kasha Photochemistry.

A novel approach for the photolabeling of proteins by a BODIPY fluorophore is reported that is based on an anti-Kasha photochemical reaction from an upper singlet excited state () leading to the deamination of the BODIPY quinone methide precursor. On the other hand, the high photochemical stability of the dye upon excitation by visible light to allows for the selective fluorescence detection from the dye or dye-protein adduct, without concomitant bleaching or hydrolysis of the protein-dye adduct. Therefore, photolabeling and fluorescence monitoring can be uncoupled by using different excitation wavelengths.

Probing the Microenvironments in a Polymer-Wrapped Core-Shell Nanoassembly Using Pyrene Chromophores.

The local environments within an amphiphilic polymer shell wrapped around lanthanide-doped upconverting nanoparticles were probed using steady-state and time-resolved fluorescence spectroscopy techniques. Emission lifetime measurements of pyrene chromophores trapped within the polymer shell reveal that there are at least two environments, where the organic pyrene molecules are encapsulated in hydrophobic environments that have lower polarity than in water. The migration of pyrene chromophores from their initial location to another location was also observed, demonstrating that the polymeric shell provides both hydrophobicity and mobility for entrapped molecules.

Photoelimination of nitrogen from adamantane and pentacycloundecane (PCU) diazirines: a spectroscopic study and supramolecular control.

Photochemical reactivity of pentacycloundecane (PCU) and adamantane diazirines was investigated by preparative irradiation in different solvents, laser flash photolysis (LFP) and quantum chemical computations. In addition, formation of inclusion complexes for diazirines with cucurbit[7]uril, β- and γ-cyclodextrin (β- and γ-CD) was investigated by 1H NMR spectroscopy, isothermal microcalorimetry and circular dichroism spectroscopy, followed by the investigation of photochemical reactivity of the formed complexes. Diazirines undergo efficient photochemical elimination of nitrogen (ΦR > 0.

Noninnocent Role of Na Ions in the Binding of the N-Phenyl-2-naphthylammonium Cation as a Ditopic Guest with Cucurbit[7]uril.

Na ions influence the mechanism for the binding of the ditopic guest N-phenyl-2-naphthylammonium cation (Ph-AH-Np) to cucurbit[7]uril (CB[7]) by facilitating, at increased Na concentrations, the formation of a higher-order complex. Binding of the larger naphthyl moiety of Ph-AH-Np forms the Ph-AH-Np@CB[7] 1:1 complex (where "@" represents an inclusion complex) at low Na ion concentrations (≤5 mM), whereas the inclusion of the smaller phenyl moiety in CB[7] (CB[7]@Ph-AH-Np) is transient. Ph-AH-Np@CB[7] is formed by reactions with free CB[7] and CB[7]·Na (where "·" represents an exclusion complex) with displacement of the Na cation.

Highly fluorescent hybrid pigments from anthocyanin- and red wine pyranoanthocyanin-analogs adsorbed on sepiolite clay.

Flavylium cations serve as models for the chemical and photochemical reactivity of anthocyanins, the natural plant pigment responsible for many of the red, blue and purple colors of fruits and flowers. Likewise, pyranoflavylium cations serve as models of the fundamental chromophoric moiety of pyranoanthocyanins, molecules that can form from reactions of grape anthocyanins in red wines during their maturation. In the present work, hybrid pigments are prepared by the adsorption of a series of five synthetic flavylium cations (FL) and five synthetic pyranoflavylium cations (PFL) on sepiolite clay (SEP).

Photodeamination to quinone methides in cucurbit[n]urils: potential application in drug delivery.

We demonstrate a proof of principle for a new approach in the development of a drug delivery system. A positively charged prodrug (phenol) can form a stable inclusion complex with CB[7], which enables more efficient delivery of the prodrug. After photochemical transformation (photoactivation) inside the complex, an active drug quinone methide (QM) is formed and released from the complex, since it is a neutral molecule and forms a less stable complex with CB[7].

Steric Demand and Rate-determining Step for Photoenolization of Di-ortho-substituted Acetophenone Derivatives.

Laser flash photolysis of ketone 1 in argon-saturated methanol yields triplet biradical 1BR (τ = 63 ns) that intersystem crosses to form photoenols Z-1P (λ = 350 nm, τ ~ 10 μs) and E-1P (λ = 350 nm, τ > 6 ms). The activation barrier for Z-1P re-forming ketone 1 through a 1,5-H shift was determined as 7.7 ± 0.

Triplet Excited States and Singlet Oxygen Production by Analogs of Red Wine Pyranoanthocyanins.

During the maturation of red wines, the anthocyanins of grapes are transformed into pyranoanthocyanins, which possess a pyranoflavylium cation as their basic chromophore. Photophysical properties of the singlet and triplet excited states of a series of synthetic pyranoflavylium cations were determined at room temperature in acetonitrile solution acidified with 0.10 mol dm trifluoroacetic acid (TFA, to inhibit competitive excited state proton transfer) and at 77 K in a rigid TFA-acidified isopropanol glass.

Protein capped nanosilver free radical oxidation: role of biomolecule capping on nanoparticle colloidal stability and protein oxidation.

We studied the effect of human serum albumin protein capped spherical nanosilver on the nanoparticle stability upon peroxyl radical oxidation. The nanoparticle-protein composite is less prone to oxidation compared to the individual components. However, higher concentrations of hydrogen peroxide were formed in the nanoparticle-protein system.

Hydroxymethylaniline Photocages for Carboxylic Acids and Alcohols.

ortho-, meta- and para-Hydroxymethylaniline methyl ethers 3-5-OMe and acetyl derivatives 3-5-OAc were investigated as potential photocages for alcohols and carboxylic acids, respectively. The measurements of photohydrolysis efficiency showed that the decaging from ortho- and meta-derivatives takes place efficiently in aqueous solution, but not for the para-derivatives. Contrary to previous reports, we show that the meta-derivatives are better photocages for alcohols, whereas ortho-derivatives are better protective groups for carboxylic acids.

Tuning the Binding Dynamics of a Guest-Octaacid Capsule through Noncovalent Anchoring.

Hydrophobic or hydrophilic substituents have different effects on the binding dynamics of pyrene derivatives with a 2:1 capsule formed from two octaacid cavitands, showing a subtle interplay of different kinetic factors. Anchoring of the methyl group of 1-methylpyrene within one cavitand slowed the association and dissociation dynamics of the 1:1 complex by at least 1000 times when compared to the 1:1 complex for pyrene. This slow down for the transient formation of the 1:1 complex is responsible for the overall increase in stability of the 2:1 complex without affecting the overall capsule dissociation.

Photochemical Formation of Anthracene Quinone Methide Derivatives.

Anthrols 2-7 were synthesized and their photochemical reactivity investigated by irradiations in aq CHOH. Upon excitation with visible light (λ > 400 nm) in methanolic solutions, they undergo photodehydration or photodeamination and deliver methyl ethers, most probably via quinone methides (QMs), with methanolysis quantum efficiencies Φ = 0.02-0.

Photochemical behavior of biosupramolecular assemblies of photosensitizers, cucurbit[n]urils and albumins.

Biosupramolecular assemblies combining cucurbit[n]urils (CB[n]s) and proteins for the targeted delivery of drugs have the potential to improve the photoactivity of photosensitizers used in the photodynamic therapy of cancer. Understanding the complexity of these systems and how it affects the properties of photosensitizers is the focus of this work. We used acridine orange (AO) as a model photosensitizer and compared it with methylene blue (MB) and a cationic porphyrin (TMPyP).

Hydroxybenzo[b]quinolizinium Ions: Water-Soluble and Solvatochromic Photoacids.

It is shown by photometric and fluorimetric analysis, along with supporting theoretical calculations, that hydroxy-substituted benzo[b]quinolizinium derivatives display the characteristic features of organic photoacids. Specifically, the experimental and theoretical results confirm the strong acidity of these compounds in the excited state (pK* < 0). The combination of the prototropic properties of 8- and 9-hydroxybenzo[b]quinolizinium with the particular solvent-solute interactions of the excited acid and its conjugate base leads to a pronounced fluorosolvatochromism, hence the emission maxima shift from 468 nm (8-hydroxybenzo[b]quinolizinium) or 460 nm (9-hydroxybenzo[b]quinolizinium) in CHCN to 507 and 553 nm in DMF, respectively.

Electrostatically promoted dynamic hybridization of glucans with cationic polythiophene.

Hybridizing natural macromolecules with synthetic polymers is an efficient general method for constructing sophisticated supramolecular architectures. To comprehensively elucidate the controversial hybridization mechanism of glucans with synthetic polymers, the hybridization behaviors of triple-stranded curdlan (Cur) and schizophyllan (SPG) with cationic polythiophene (PyPT) were investigated in aqueous DMSO solutions by using UV-vis, circular dichroism (CD), fluorescence, fluorescence excitation, and NMR spectroscopy methods, as well as theoretical calculations, dynamic light scattering, and zeta potential measurements. Upon mixing with glucan, a hetero-triplex formed, which was dynamic and greatly accelerated by heating and by adding a base or a salt.

Correction: Cucurbit[7]uril inclusion complexation as a supramolecular strategy for color stabilization of anthocyanin model compounds.

Correction for 'Cucurbit[7]uril inclusion complexation as a supramolecular strategy for color stabilization of anthocyanin model compounds' by Barbara Held, et al., Photochem. Photobiol.

Cucurbit[7]uril inclusion complexation as a supramolecular strategy for color stabilization of anthocyanin model compounds.

Host-guest complexation with cucurbit[7]uril of anthocyanin model compounds in which acid-base equilibria are blocked resulted in essentially complete stabilization of their color. The color protection is a thermodynamic effect and establishes a strategy to stabilize these colored compounds at pH values of interest for practical applications.