Thermally-Induced Acid Generation from 18-Molybdodiphosphate and 18-Tungstodiphosphate within Poly(2-Hydroxyethyl Methacrylate) Films

The thermally induced acid generation by two Dawson-type polyoxometalates (POMs), namely, the ammonium 18-molybdodiphosphate, (NH4)6P2Mo18O62, (Mo186−) and the ammonium 18-tungstodiphosphate, (NH4)6P2W18O62, (W186−) within poly(2-hydroxyethyl methacrylate) (PHEMA) films is reported. The acid is generated by the simultaneous thermal reduction of POMs and oxidation of a small percentage of PHEMA hydroxyl groups, and it subsequently catalyzes the cross-linking of the polymer. The generated protons are detected by introducing a known acid indicator (methylene blue, MB) within the films and monitoring the indicator’s protonation with UV spectroscopy. The acid-catalyzed cross-linking of PHEMA is studied by dissolution studies supported with FTIR and NMR spectroscopy. From the combination of those two spectroscopic studies it is concluded that PHEMA cross-linking within POM-PHEMA films is an acid-catalyzed reaction involving elimination of hydroxyl groups (possibly transesterification) accompanied by the side reaction of acid-catalyzed dehydration of PHEMA that leads to the formation of soluble products. Both POMs investigated can be completely removed, if desired, from the thermally cross-linked PHEMA films at the end of the process, by incubation in an aqueous solution of base, allowing therefore the use of POMs as acid generating agents in applications where the removal of the acid generator from the polymer films is beneficial

Synthesis of 6-Mono-6-deoxy-β<i>-</i>cyclodextrins Substituted with Isomeric Aminobenzoic Acids. Structural Characterization, Conformational Preferences, and Self-inclusion as Studied by NMR Spectroscopy in Aqueous Solution and by X-ray Crystallography in the Solid State

The synthesis, purification, and characterization of mono-6-modified-β-cyclodextrins bearing N-attached o-, m-, and p-aminobenzoic acids (2, 3, and 4, respectively) are presented. The structures in aqueous solution were investigated using one- and two-dimensional NMR spectroscopy. Detailed assignment of the spectra together with intramolecular NOE correlations revealed the way each of the isomeric appendages is positioned relative to the macrocyclic cavity. No self-inclusion is observed. The o-isomer 2 turns inward over the top of the primary side and interacts with specific protons of the substituted glucopyranose unit A and those of a neighboring unit. The m-isomer 3 displays two conformations, where the substituent resides above the primary side in a tilted manner and interacts either with the previous or the next unit. We propose that the carboxyl groups in both 2 and 3 are localized through H-bonding with one or two, respectively, primary hydroxyl groups of the neighboring glucopyranose units. In a similar positioning of the aromatic ring of the p-isomer 4, the hydrophilic carboxyl end is fully exposed to the aqueous environment. The X-ray structure of 4 shows that the solution conformation has evolved such that in the crystalline state, the aromatic moiety is inserted through its carboxyl part inside another CD where it establishes intermolecular H-bonds with inward-turned primary OH groups. Besides this stabilization, 4 forms parallel and antiparallel supramolecular chains in the crystal that are additionally stabilized by direct H-bonds

NMR Detection of Simultaneous Formation of [2]- and [3]Pseudorotaxanes in Aqueous Solution between α-Cyclodextrin and Linear Aliphatic α,ω-Amino acids, an α,ω-Diamine and an α,ω-Diacid of Similar Length, and Comparison with the Solid-State Structures

The interactions of 11-aminoundecanoic acid (1), 12-aminododecanoic acid (2), 1,12-diaminododecane (3), and 1,13-tridecanoic diacid (4) with α-cyclodextrin (αCD) were studied in aqueous solution by NMR spectroscopy. The association modes were established with titration and continuous variation plots, variable temperature NMR spectra, and dipolar interactions as recorded in 2D ROESY spectra. The studies were carried out at pH 7.3 and 13.6. These long, linear bifunctional molecules were found to form simultaneously [2]- and [3]pseudorotaxanes with αCD in the aqueous solution. At the higher pH the 1:1 adducts were present at concentrations higher than at the neutral pH. The longer guests formed complexes enriched in the 2:1 constituent at both pH values. There were clear indications that the [2]pseudorotaxanes are present in two isomeric forms. The presence of isomers also in the [3]pseudorotaxanes was not ruled out. Various exchange rate regimes were observed; clearly in neutral solutions the formation of the 1:1 complexes was fast in the NMR time scale, whereas the threading of a second αCD ring was a slower process. In the solid state, the adduct of αCD/2 had the structure of a [3]pseudorotaxane, in accordance with previously solved crystal structures of αCD/3 and βCD/4. The species in solution, in contrast with those present in the solid state, are therefore of varying nature, and thus the frequently and conveniently assumed 1:1 stoichiometry in similar systems is an oversimplification of the real situation

Encapsulation of Olive Leaf Extract in β-Cyclodextrin

Olive leaf extract, rich in oleuropein, formed an inclusion complex with β-cyclodextrin (β-CD) upon mixing of the components in aqueous media and subsequent freeze-drying. Inclusion complex formation was confirmed by differential scanning calorimetry (DSC). DSC thermograms indicated that the endothermic peaks of both the olive leaf extract and the physical mixture of olive leaf extract with β-CD, attributed to the melting of crystals of the extract, were absent in DSC thermogram of inclusion complex. Moreover, DSC studies under oxidative conditions indicated that the complex of olive leaf extract with β-CD was protected against oxidation, since it remained intact at temperatures where the free olive leaf extract was oxidized. Phase solubility studies afforded AL type diagrams, 1:1 complex stoichiometry, a moderate binding constant (∼300 M−1), and an increase of the aqueous solubility by ∼50%. The formation of the inclusion complex was also confirmed by nuclear magnetic resonance (NMR) studies of β-CD solutions in the presence of both pure oleuropein and olive leaf extract. The NMR data have established the formation of a 1:1 complex with β-CD that involves deep insertion of the dihydroxyphenethyl moiety inside the cavity from its secondary side

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 sp2 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 ). 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 CNaph–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

Partially Fluorinated, Polyhedral Oligomeric Silsesquioxane-Functionalized (Meth)Acrylate Resists for 193 nm Bilayer Lithography

The influence of partial fluorination on the lithographic performance of photoresists based on (meth)acrylate terpolymers containing polyhedral oligomeric silsesquioxane (POSS) pendant groups is investigated in bilayer schemes for 193 nm lithography. For the first time the capability of POSS-functionalized resists for standard lithographic processing, including use of standard developer (0.26 N tetramethylammonium hydroxide) and industrial processing equipment is demonstrated. The optimized resists formulated exhibited high sensitivity (2) and potential for resolution performance comparable to mature 193 nm materials. The role of the fluorinated acid as a component in the terpolymer composition was crucial to the homogeneity of the resist material and its lithographic performance. Also, a photoacid generator (PAG) study revealed that the use of a highly hydrophobic PAG containing organic anion with a long fluorinated chain in the resist formulation improved further the homogeneity of the material and its lithographic performance. The adhesion of the highly fluorinated materials to the substrate is influenced by the type of polymeric underlayer used, whereas best results were obtained on a hard baked novolac polymer

Efficient “green” encapsulation of a highly hydrophilic anticancer drug in metal–organic framework nanoparticles

<div><p></p><p>Metal–organic frameworks (MOFs) are coordination polymers of interest for biomedical applications. Of particular importance, nanoparticles made of iron(III) trimesate (MIL-100, MIL standing for Material Institut Lavoisier) (nanoMOFs) can be conveniently synthesised under mild and green conditions. They were shown to be biodegradable, biocompatible and efficient to encapsulate a variety of active molecules. We have addressed here the challenges to encapsulate a highly hydrophilic anticancer prodrug, phosphated gemcitabin (Gem-MP) known for its instability and inability to bypass cell membranes. MIL-100 nanoMOFs acted as efficient “nanosponges”, soaking Gem-MP from its aqueous solution with almost perfect efficiency (>98%). Maximal loadings reached ∼30 wt% reflecting the strong interaction between the drug and the iron trimesate matrices. Neither degradation nor loss of crystalline structure was observed after the loading process. Storage of the loaded nanoMOFs in water did not result in drug release over three days. However, Gem-MP was released in media containing phosphates, as a consequence to particle degradation. Drug-loaded nanoMOFs were effective against pancreatic PANC-1 cells, in contrast to free drug and empty nanoMOFs. However, an efflux phenomenon could contribute to reduce the efficacy of the nanocarriers. Size optimization and surface modification of the nanoMOFs are expected to further improve these findings.</p></div

NMR and EPR Structural Analysis and Stability Study of Inverse Vulcanized Sulfur Copolymers

Sulfur copolymers with high sulfur content find a broad range of applications from Li–S batteries to catalytic processes, self-healing materials, and the synthesis of nanoparticles. Synthesis of sulfur-containing polymers via the inverse vulcanization technique gained a lot of attention due to the feasibility of the reaction to produce copolymers with high sulfur content (up to 90 wt %). However, the interplay between the cross-linker and the structure of the copolymers has not yet been fully explored. In the present work, the effect of the amount of 1,3-diisopropenyl benzene (DIB) cross-linker on the structural stability of the copolymer was thoroughly investigated. Combining X-ray diffraction and differential scanning calorimetry, we demonstrated the partial depolymerization of sulfur in the copolymer containing low amount of cross-linker (<30 wt % DIB). On the other hand, by applying NMR and electron paramagnetic resonance techniques, we have shown that increasing the cross-linker content above 50 wt % leads to the formation of radicals, which may severely degrade the structural stability of the copolymer. Thus, an optimum amount of cross-linker is essential to obtain a stable copolymer. Moreover, we were able to detect the release of H₂S gas during the cross-linking reaction as predicted based on the abstraction of hydrogen by the sulfur radicals and therefore we emphasize the need to take appropriate precautions while implementing the inverse vulcanization reaction

Design and Synthesis of Porphyrin–Nitrilotriacetic Acid Dyads with Potential Applications in Peptide Labeling through Metallochelate Coupling

The need to detect and monitor biomolecules, especially within cells, has led to the emerging growth of fluorescent probes. One of the most commonly used labeling techniques for this purpose is reversible metallochelate coupling via a nitrilotriacetic acid (NTA) moiety. In this study, we focus on the synthesis and characterization of three new porphyrin–NTA dyads, TPP-Lys-NTA, TPP-CC-Lys-NTA, and Py3P-Lys-NTA composed of a porphyrin derivative covalently connected with a modified nitrilotriacetic acid chelate ligand (NTA), for possible metallochelate coupling with Ni2+ ions and histidine sequences. Emission spectroscopy studies revealed that all of the probes are able to coordinate with Ni2+ ions and consequently can be applied as fluorophores in protein/peptide labeling applications. Using two different histidine-containing peptides as His6-tag mimic, we demonstrated that the porphyrin–NTA hybrids are able to coordinate efficiently with the peptides through the metallochelate coupling process. Moving one step forward, we examined the ability of these porphyrin–peptide complexes to penetrate and accumulate in cancer cells, exploring the potential utilization of our system as anticancer agents