Dynamics of Guest Binding to Supramolecular Assemblies

Bohne, Cornelia

doi:10.1002/9781118095300.ch1

Cited by 7 publications

(6 citation statements)

References 126 publications

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“…In addition to [2 + 2] photocycloaddition discussed here, a number of other reactions have been investigated in a variety of confined media listed in Figure . Numerous reviews on these topics have appeared, and readers are directed to consult those to familiarize themselves with the value of organized and constrained media in controlling photoreactions. ,,,− ,,,,,− Many of the photoreactions such as decarbonylation, cis–trans isomerization, and hydrogen abstraction described in these reviews are likely to be of interest to synthetic chemists. Due to space constraints we limited the discussion to a single photoreaction, namely, [2 + 2] addition.…”

Section: Conclusion and Outlookmentioning

confidence: 99%

Supramolecular Photochemistry as a Potential Synthetic Tool: Photocycloaddition

2016

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Photochemistry, bearing significant applications in natural and man-made events such as photosynthesis, vision, photolithography, photodynamic therapy, etc., is yet to become a common tool during the synthesis of small molecules in a laboratory. Among other rationale, the inability to influence photochemical reactions with temperature, solvent, additives, etc., dissuades chemists from employing light-initiated reactions as a routine synthetic tool. This review highlights how diverse, highly organized structures such as solvent-free crystals and water-soluble host-guest assemblies can be employed to control and manipulate photoreactions and thereby serve as an efficient tool for chemists, including those interested in synthesis. The efficacy of the media in modifying the excited-state behavior of organic molecules is illustrated with photocycloaddition in general and [2 + 2] photocycloaddition in particular, reactions widely employed in the synthesis of complex natural products as well as highly constrained molecules, as exemplars. The reaction media, highly pertinent in the context of green sustainable chemistry, include solvent-free crystals and solids such as silica, clay, and zeolite and water-soluble hosts that can solubilize and preorganize hydrophobic reactants in water. Since no other reagent would be more sustainable than light and no other medium greener than water, we believe that the supramolecular photochemistry expounded here has a momentous role as a synthetic tool in the future.

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Section: Conclusion and Outlookmentioning

confidence: 99%

Supramolecular Photochemistry as a Potential Synthetic Tool: Photocycloaddition

2016

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“…Bile salts, the most widely studied naturally occurring amphiphilic compounds, are of great interest to the research communities of chemistry and biology because of their unique roles in a wide variety of biological processes such as solubilization of fats and other fat-soluble substances in living organisms. − Understanding the binding dynamics of guest molecules confined within the nanocavities of various chemically and biologically active supramolecular host systems has been the subject of active scientific research for the past several years. − In this time, the importance of host–guest inclusion complexes has been demonstrated for a variety of chemical, biological, and industrial applications, including the development of drug-delivery systems, energy-storage materials and devices, photonic devices, and nanometer-sized electronic devices . Bile salt aggregates are potential supramolecular host systems that can carry both hydrophobic and hydrophilic guest molecules of suitable size and shape because of the presence of both types of binding sites under varying experimental conditions, such as concentration, pH, and ionic strength of the surrounding medium. − The self-assemblies of bile salts are of particular interest from the biological point of view because of their unique ability to solubilize various biologically active organic guests including many sparingly water-soluble drug molecules. − Moreover, the formation of inclusion complexes in such aggregates helps to control the selectivity of various chemical reactions such as photoinduced reactions, enzymatic reactions, and complexation reactions. , Unlike common surfactant molecules, bile salts have a nonplanar steroidal skeleton with a convex surface of hydrophobic groups and a concave surface of hydrophilic groups.…”

Section: Introductionmentioning

confidence: 99%

Modulation of Photophysics and Photodynamics of 1′-Hydroxy-2′-acetonaphthone (HAN) in Bile Salt Aggregates: A Study of Polarity and Nanoconfinement Effects

et al. 2012

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The modulation of the photophysical properties of 1'-hydroxy-2'-acetonaphthone (HAN) upon encapsulation into the hydrophobic nanocavities of different bile salt aggregates has been investigated for the first time using steady-state and time-resolved fluorescence spectroscopy. Because HAN is very sensitive to the polarity of the microenvironment in which it is confined, we performed a comparative study on the excited-state binding dynamics of HAN using three different bile salts of varying hydrophobicity. The encapsulation of HAN into the bile salt aggregates led to an enhanced fluorescence intensity along with a significant blue shift in the emission maxima that was highly sensitive to the confined microenvironment. Using HAN as a sensitive fluorophore to probe the nanocavities of bile salt aggregates in aqueous solution, we found different mechanisms of probe encapsulation depending on the degree of hydrophobicity of the nanocavities, which results in a difference in the alteration of the spectral behavior. A sharp increase in the fluorescence quantum yield near the cmc was observed, followed by saturation for all three bile salt aggregates. However, maximum fluorescence quantum yield in NaDC aggregates can be rationalized by maximum partitioning of HAN into the more hydrophobic and rigid environment provided by NaDC aggregates. Moreover, the alteration of the spectral behavior with increasing concentration of bile salts strikingly differs from that observed previously in the presence of conventional surfactants. Time-resolved fluorescence measurements further elucidated how the probe molecules interact with the aggregates. Longer fluorescence lifetime and anisotropy values clearly indicate the caging of the tautomers of HAN into the hydrophobic nanocavities of bile salt aggregates. This work further demonstrates the changes in the fluorescence properties of HAN with structural changes of bile salt aggregates induced by the addition of salt and organic cosolvent.

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“…Bile salt aggregates are interesting host systems in which guests can be included in different environments within the aggregate. − The incorporation of guests into bile salt aggregates alters the selectivity and kinetics for the photoreactivity of the bound guests. , Studies on the binding dynamics of guests with bile salt aggregates and on the accessibility of quenchers to the excited state of guests bound to the aggregates led to a proposal for the presence of two different binding sites. − The size and shape of the guests incorporated into the primary aggregates affect both the accessibility of quenchers to the bound guest and the residence time of the guest inside the aggregate. ,, The trends for the residence time and the protection efficiencies from quenching with changes in the structure of the guests are not the same, suggesting that the mechanisms for the entry of anions into the aggregate and the exit of the guest are different. Finally, there is no correlation between the residence time of the guests and their hydrophobicity, as is observed for conventional micelles such as those formed with sodium dodecyl sulfate.…”

Section: Introductionmentioning

confidence: 99%

Effect of the Structure of Bile Salt Aggregates on the Binding of Aromatic Guests and the Accessibility of Anions

Carpentier

Newell

et al. 2009

Langmuir

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The binding of naphthalene (Np), 1-ethylnaphthalene (EtNp), acenaphthene (AcN), and 1-naphthyl-1-ethanol (NpOH) as guests to the aggregates of sodium cholate (NaCh), taurocholate (NaTC), deoxycholate (NaDC), and deoxytaurocholate (NaTDC) was studied with the objective of determining how the structure of the bile salts affects the binding dynamics of guests and quenchers with the bile salt aggregates. Time-resolved and steady-state fluorescence experiments were used to determine the binding efficiency of the guests with the aggregates and were also employed to investigate the quenching of the singlet excited state of the guests by iodide anions. Quenching studies of the triplet excited states using laser flash photolysis were employed to determine the accessibility to the aggregate of nitrite anions, used as quenchers, and the dissociation rate constants of the guests from the bile salt aggregates. The binding efficiency of the guests to NaDC and NaTDC is higher than for NaCh and NaTC, and the protection efficiency is also higher for NaDC and NaTDC, in line with the larger aggregates formed for the latter bile salts. The formation of aggregates is in part driven by the structure of the guest, where an increased protection efficiency and residence time can be achieved by the introduction of short alkyl substituents (AcN or EtNp vs Np). NpOH was shown to be located in a very different environment in all four bile salts when compared to AcN, EtNp, and Np, suggesting that hydrogen bonding plays an important role in the formation of the aggregate around NpOH.

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Dynamics of Guest Binding to Supramolecular Assemblies

Cited by 7 publications

References 126 publications

Supramolecular Photochemistry as a Potential Synthetic Tool: Photocycloaddition

Supramolecular Photochemistry as a Potential Synthetic Tool: Photocycloaddition

Modulation of Photophysics and Photodynamics of 1′-Hydroxy-2′-acetonaphthone (HAN) in Bile Salt Aggregates: A Study of Polarity and Nanoconfinement Effects

Effect of the Structure of Bile Salt Aggregates on the Binding of Aromatic Guests and the Accessibility of Anions

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