Nonpolar Guest Molecules Research Articles

Self-Healing and Thermoresponsive Dual-Cross-Linked Alginate Hydrogels Based on Supramolecular Inclusion Complexes.

β-Cyclodextrin (β-CD), with a lipophilic inner cavity and hydrophilic outer surface, interacts with a large variety of nonpolar guest molecules to form noncovalent inclusion complexes. Conjugation of β-CD onto biomacromolecules can form physically cross-linked hydrogel networks upon mixing with a guest molecule. Herein, the development and characterization of self-healing, thermoresponsive hydrogels, based on host-guest inclusion complexes between alginate-graft-β-CD and Pluronic F108 (poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol)), are described. The mechanics, flow characteristics, and thermal response were contingent on the polymer concentration and the host-guest molar ratio. Transient and reversible physical cross-linking between host and guest polymers governed self-assembly, allowing flow to occur under shear stress and facilitating complete recovery of the material's properties within a few seconds of unloading. The mechanical properties of the dual-cross-linked, multi-stimuli-responsive hydrogels were tuned as high as 30 kPa at body temperature and are advantageous for biomedical applications such as drug delivery and cell transplantation.

Nonfouling tunable βCD dextran polymer films for protein applications.

Polymeric β-cyclodextrin (βCD) films tunable with respect to thickness and βCD content were prepared in order to develop a suitable platform, allowing for inclusion of nonpolar guest molecules in the βCD cavity, while suppressing nonspecific protein adsorption. The βCD films were synthesized from linear βCD dextran polymers, and grafted onto silicon oxide surfaces by "click" chemistry. Topographic and morphological characteristics are controllable by reaction conditions and polymer type, with average film heights from 2.5 to 12.5 nm. Reversible introduction of electrostatic charges in the βCD dextran by complex formation with 1-adamantanecarboxylic acid prior to surface grafting resulted in a thinner and denser film, presumably by decompaction of the polymers. Total internal reflection fluorescence spectroscopy (TIRF) was employed to evaluate the accessibility of βCD cavities to the fluorescent probe 2-anilinonaphthalene-6-sulfonic acid. Only a minor fraction of the βCD cavities was accessible in the thicker and less dense films; however, accessibility was largely improved with increased ionic strength using NaCl up to 1 M. Antifouling properties of the βCD dextran polymer films were assessed by TIRF real-time monitoring, using bovine serum albumin as a model protein, and showed a 5- to 10-fold reduction in nonspecific adsorption as compared to a bare quartz surface with the degree of reduction reflecting film thickness and interfacial polymer density.

Stepwise Assembly of Pd6(RuL3)8 Nanoscale Rhombododecahedral Metal–Organic Cages via Metalloligand Strategy for Guest Trapping and Protection

Stepwise synthesis of nanosized Pd-Ru heteronuclear metal-organic cages from predesigned redox- and photo-active Ru(II)-metalloligand and naked Pd(II) ion is described. The resulting cage shows rhombododecahedral shape and contains a 5350 Å(3) cavity and 12 open windows, facilitating effective trapping of both polar and nonpolar guest molecules. Protection of photosensitive guests against UV radiation is studied.

Hydrogen Bonding Effects in Adsorption of Water−Alcohol Mixtures in Zeolites and the Consequences for the Characteristics of the Maxwell−Stefan Diffusivities

This work highlights a variety of peculiar characteristics of adsorption and diffusion of polar molecules such as water, methanol and ethanol in zeolites. These peculiarities are investigated with the aid of configurational-bias Monte Carlo (CBMC) simulations of adsorption isotherms, and molecular dynamics (MD) simulations of diffusivities in FAU, MFI, DDR, and LTA zeolites. Because of strong hydrogen bonding, significant clustering of the guest molecules occurs in all investigated structures. Because of molecular clustering, the inverse thermodynamic factor 1/Gamma(i) identical with (d[ln c(i)])/(d[ln f(i)]) exceeds unity for a range molar concentrations c(i) within the micropores. The degree of clustering is lowered as the temperature is increased. For the concentration ranges for which 1/Gamma(i) > 1, the Fick diffusivity, D(i), for unary diffusion is often lower than both the Maxwell-Stefan, D(i), and the self-diffusivity, D(i,self). For water-alcohol mixtures, the hydrogen bonding between water and alcohol molecules is much more predominant than for water-water, and alcohol-alcohol molecule pairs. Consequently, the adsorption of water-alcohol mixtures shows significant deviations from the predictions of the ideal adsorbed solution theory (IAST). The water-alcohol bonding also leaves its imprint on the mixture diffusion characteristics. The Maxwell-Stefan diffusivity, D(i), of either component in water-alcohol mixtures is lower than the corresponding values of the pure components; this behavior is distinctly different from that for mixtures of nonpolar guest molecules. The binary exchange coefficient D(12) for water-alcohol mixtures is also significantly lower than either self-exchange coefficients D(11) and D(22) of the constituent species. This implies that correlation effects are significantly stronger in water-alcohol mixtures than for the constituent species. Correlation effects are found to be significant for water-alcohol mixture diffusion in DDR and LTA zeolites, even though such effects are negligible for the pure constituents. The major conclusion to emerge from this investigation is that, unlike mixtures of nonpolar molecules, it is not possible to estimate water-alcohol mixture adsorption and diffusion characteristics on the basis of pure component data.

Proton disorder and the dielectric constant of type II clathrate hydrates

Computational studies are presented examining the degree of proton disorder in argon and molecular hydrogen sII clathrate hydrates. Results are presented using a variety of model potentials for the dielectric constant, the proton order parameter, and the molecular volume for the clathrate systems. The dielectric constant for the clathrate systems is found to be lower than the dielectric constant of ice in all models. The ratio of the clathrate to ice dielectric constant correlates well with the ratio of the densities, which is not the case for comparisons to the liquid, so that differences in the dielectric constants between ice and the clathrates are most likely due to differences in densities. Although the computed dielectric constant is a strong function of the model potential used, the ratio of the dielectric constant of ice to that of the clathrates is insensitive to the model potential. For the nonpolar guest molecules used in the current study, the degree proton of disorder is found to depend weakly on the identity of the guest but the dielectric constant does not appear to be sensitive to pressure or the type of guest.

Dendritic Polyglycerol Core-Double-Shell Architectures: Synthesis and Transport Properties

Dendritic core-double-shell architectures consisting of a hyperbranched polyglycerol core, a long aliphatic hydrophobic inner shell, and hyperbranched polyglycerol-based hydrophilic outer shell have been synthesized and characterized. They have been prepared from simple building blocks by applying an anionic ring-opening polymerization protocol. The obtained, well-defined, globular, nanometer-sized architectures possess the ability to host polar and nonpolar guest molecules in water. The polymer−guest molecule complexes were characterized by UV and DLS measurements. Unimolecular transport behavior was observed for nonpolar guest molecules with transport capacities of 1.5 guest molecules per nanocarrier and particle sizes of 7−10 nm. However, for polar guest molecules, the formation of uniform aggregates with a diameter of 70 nm and transport capacities up to 10 guests per nanocarrier was detected.

Highly Efficient Synthesis and Inclusion Properties of Star-Shaped Amphiphilic Derivatives of Cholic Acid

New star-shaped cholic acid derivatives with different functional groups have been synthesized by the use of Cu I -catalyzed [2+3] cyclization (click chemistry) and Curtius rearrangement of acyl azide intermediate in good yields. We have also studied the -solution properties of these star-shaped amphiphilic compounds as host molecules to interact with nonpolar guest molecules by the use of fluorescent probes.

Supramolecular Aggregates of Dendritic Multishell Architectures as Universal Nanocarriers

Chemical chameleons: Highly stable supramolecular aggregates built from dendritic multishell architectures show a universal transport ability for both polar and nonpolar guest molecules and can adapt to various solvent environments, ranging from toluene to water.

Structure of a Cyclodextrin Functionalized Anionic Clay: XRD Analysis, Spectroscopy, and Computer Simulations

Carboxy-methyl beta-cyclodextrin (CMCD) cavities have been intercalated within the galleries of anionic clay, Mg-Al layered double hydroxide (LDH). The cyclodextrin functionalized LDH has been reported to adsorb neutral and nonpolar guest molecules. X-ray diffraction, IR, and Raman vibrational spectroscopy and (13)C CPMAS NMR have been used to characterize the confined CMCD molecules, whereas molecular dynamics simulations have been used to probe the interlayer arrangement and orientation of the intercalated species. Spectroscopic measurements as well as MD simulations show that there is no significant change in the geometry of the CMCD cavity on intercalation. Within the galleries of the anionic clay, the CMCD anions are arranged as bilayers with the carboxy methyl substituents, located at the narrower opening of the bucket-like cyclodextrin toroid, anchored to the LDH sheet. This arrangement leaves the wider opening of the CMCD anion facing away from the layers allowing the interior of the cyclodextrin cavity to be accessible to guest molecules. Finally, the hydrophobicity of the anchored cyclodextrin cavity has been characterized using fluorescence from pyrene included within it.

Undesirable Reaction of Aqueous Cyclodextrin Solutions with Polypropylene

Cyclodextrins are cyclic sugars that have extensive applications in the pharmaceutical, food, biomedical, and other industries. Although cyclodextrins are water-soluble sugars, they have hydrophobic central cavities that are capable of accommodating nonpolar molecules of the right dimensions. This inclusion complexation property, which is key to its utilization in solubilization and stabilization of nonpolar guest molecules, can also lead to undesirable reactions. The present investigation demonstrates the ability of aqueous cyclodextrin solutions to extract plastic additives when stored in polypropylene tubes that are commonly used in biological research. Storage of α- and γ-cyclodextrin solutions in polypropylene microcentrifuge tubes led to the extraction of 2,6-di- tert-butyl- p-cresol, or BHT, a common additive used as an antioxidant and for polymer stabilization. γ-Cyclodextrin solutions also formed an insoluble complex with an unidentified substance. These results suggest the potential of cyclodextrin solutions stored in plastic containers to be contaminated with additives. In many cases, the additives added by plastic manufacturers may be trade secrets and difficult to identify. One should be cautious in using aqueous cyclodextrin solutions stored in plastic containers for biological or biomedical research and applications.

Polarization Reversal in AlPO4-5 Crystals Containing Polar or Nonpolar Organic Molecules: A Scanning Pyroelectric Microscopy Study

Large AlPO4-5 crystals containing different polar or nonpolar guest molecules have been studied with scanning pyroelectric microscopy. Calcined crystals are pyroelectric with a polar structure that...