Temporal Control over Transient Chemical Systems using Structurally Diverse Chemical Fuels

The next generation of adaptive, intelligent chemical systems will rely on a continuous supply of energy to maintain the functional state. Such systems will require chemical methodology that provides precise control over the energy dissipation process, and thus, the lifetime of the transiently activated function. This manuscript reports on the use of structurally diverse chemical fuels to control the lifetime of two different systems under dissipative conditions: transient signal generation and the transient formation of self-assembled aggregates. The energy stored in the fuels is dissipated at different rates by an enzyme, which in-stalls a dependence of the lifetime of the active system on the chemical structure of the fuel. In the case of transient signal generation, it is shown that different chemical fuels can be used to generate a vast range of signal profiles, allowing temporal control over two orders of magnitude. Regarding self-assembly under dissipative conditions, the ability to control the lifetime using different fuels turns out to be particularly important as stable aggregates are formed only at well-defined surfactant/fuel ratios, meaning that temporal control cannot be achieved by simply changing the fuel concentration

Polymer network hole transport layers based on photochemically cross-linkable N′N′-diallyl amide tri-N-substituted triazatruxene monomers

Novel phtotpolymerisable hole-transport layers based on novel triazatruxenes incorporating six non-conjugated dienes as photo cross-linkable end-groups attached to flexible, aliphatic spacers have been synthesised using simple one-step substitution reactions. Hole-only test devices, fabricated using a combination of solution-deposition, spin-coating and initiator-free photochemical cross-linking of these photopolymerisable triazatruxenes, exhibit almost identical current density vs. voltage profiles before and after cross-linking, and as such, represent a promising new class of hole-transport layer for plastic electronic devices

Welcoming natural isotopic abundance in solid-state NMR: probing π-stacking and supramolecular structure of organic nanoassemblies using DNP

The self-assembly of small organic molecules is an intriguing phenomenon, which provides nanoscale structures for applications in numerous fields from medicine to molecular electronics. Detailed knowledge of their structure, in particular on the supramolecular level, is a prerequisite for the rational design of improved self-assembled systems. In this work, we prove the feasibility of a novel concept of NMR-based 3D structure determination of such assemblies in the solid state. The key point of this concept is the deliberate use of samples that contain 13C at its natural isotopic abundance (NA, 1.1%), while exploiting magic-angle spinning dynamic nuclear polarization (MAS-DNP) to compensate for the reduced sensitivity. Since dipolar truncation effects are suppressed to a large extent in NA samples, unique and highly informative spectra can be recorded which are impossible to obtain on an isotopically labeled system. On the self-assembled cyclic diphenylalanine peptide, we demonstrate the detection of long-range internuclear distances up to ∼7 Å, allowing us to observe π-stacking through 13C–13C correlation spectra, providing a powerful tool for the analysis of one of the most important non-covalent interactions. Furthermore, experimental polarization transfer curves are in remarkable agreement with numerical simulations based on the crystallographic structure, and can be fully rationalized as the superposition of intra- and intermolecular contributions. This new approach to NMR crystallography provides access to rich and precise structural information, opening up a new avenue to de novo crystal structure determination by NMR

Self-Assembly of G-Rich Oligonucleotides Incorporating a 3′-3′ Inversion of Polarity Site: A New Route Towards G-Wire DNA Nanostructures

Obtaining DNA nanostructures with potential applications in drug discovery, diagnostics, and electronics in a simple and affordable way represents one of the hottest topics in nanotechnological and medical sciences. Herein, we report a novel strategy to obtain structurally homogeneous DNA G-wire nanostructures of known length, starting from the short unmodified G-rich oligonucleotide d(5′-CGGT-3′–3′-GGC-5′) (1) incorporating a 3’–3′ inversion of polarity site. The reported approach allowed us to obtain long G-wire assemblies through 5′–5′ π–π stacking interactions in between the tetramolecular G-quadruplex building blocks that form when 1 is annealed in the presence of potassium ions. Our results expand the repertoire of synthetic methodologies to obtain new tailored DNA G-wire nanostructures

Control over the Self-Assembly Modes of Pt^II Complexes by Alkyl Chain Variation: From Slipped to Parallel π-Stacks

We report the self-assembly of a new family of hydrophobic, bis(pyridyl) PtII complexes featuring an extended oligophenyleneethynylene-derived π-surface appended with six long (dodecyloxy (2)) or short (methoxy (3)) side groups. Complex 2, containing dodecyloxy chains, forms fibrous assemblies with a slipped arrangement of the monomer units (dPt⋯Pt≈14 Å) in both nonpolar solvents and the solid state. Dispersion-corrected PM6 calculations suggest that this organization is driven by cooperative π-π, C-H⋯Cl and π-Pt interactions, which is supported by EXAFS and 2D NMR spectroscopic analysis. In contrast, nearly parallel π-stacks (dPt⋯Pt≈4.4 Å) stabilized by multiple π-π and C-H⋯Cl contacts are obtained in the crystalline state for 3 lacking long side chains, as shown by X-ray analysis and PM6 calculations. Our results reveal not only the key role of alkyl chain length in controlling self-assembly modes but also show the relevance of Pt-bound chlorine ligands as new supramolecular synthons. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Consequences of conformational flexibility in hydrogen-bond-driven self-assembly processes

We report the synthesis and self-assembly of chiral, conformationally flexible C3-symmetrical trisamides. A strong Cotton effect is observed for the supramolecular polymers in linear alkanes but not in cyclic alkanes. MD simulations suggest 2:1 conformations of the amides within the aggregates in both types of solvents, but a chiral bias in only linear alkanes.JAB, MGI, RPAG, EWM and ARAP would like to thank the Gravity program 024.001.035, NWO TOP-PUNT 718.014.003 for financial support and Anneloes Oude Vrielink for TEM imaging. FDM and ML acknowledge the Swedish e-Research Center (SeRC) for financial support, the Swedish Research Council (Grant No. 621-2014-4646), SNIC (Swedish National Infrastructure for Computing) and Dr Julien Idé for providing the code for exciton coupling calculations

Photoactive bile salts with critical micellar concentration in the micromolar range

The aggregation behavior of bile salts is strongly dependent on the number of hydroxyl groups. Thus, cholic acid (CA), with three hydroxyls, starts forming aggregates at 15 mM, while deoxycholic, chenodeoxycholic or ursodeoxycholic acids, with two hydroxyls, start aggregating at 5-10 mM; for lithocholic acid, with only one hydroxyl group, aggregation is observed at lower concentration (2-3 mM). Here, the singular self-assembling properties of dansyl and naproxen derivatives of CA (3 beta-Dns-CA and 3 beta-NPX-CA, respectively) have been demonstrated on the basis of their photoactive properties. Thus, the emission spectra of 3 beta-Dns-CA registered at increasing concentrations (25-140 mu M) showed a remarkable non-linear enhancement in the emission intensity accompanied by a hypsochromic shift of the maximum and up to a three-fold increase in the singlet lifetime. The inflection point at around 50-70 mu M pointed to the formation of unprecedented assemblies at such low concentrations. In the case of 3 beta-NPX-CA, when the NPX relative triplet lifetime was plotted against concentration, a marked increase (up to two-fold) was observed at 40-70 mu M, indicating the formation of new 3 beta-NPX-CA assemblies at ca. 50 mu M. Additional evidence supporting the formation of new 3 beta-Dns-CA or 3 beta-NPX-CA assemblies at 40-70 mu M was obtained from singlet excited state quenching experiments using iodide. Moreover, to address the potential formation of hybrid assemblies, 1 : 1 mixtures of 3 beta-Dns-CA and 3 beta-NPX-CA (2-60 mu M, total concentration) were subjected to steady-state fluorescence experiments, and their behavior was compared to that of the pure photoactive derivatives. A lower increase in the emission was observed for 3 beta-NPX-CA in the mixture, while a huge increase was experienced by 3 beta-Dns-CA in the same concentration range (up to 60 mu M total). A partial intermolecular energy transfer from NPX to Dns, consistent with their reported singlet energies, was revealed, pointing to the formation of extremely fluorescent hybrid assemblies at 5-10 mu M (total concentration). The morphology of the entities was investigated by means of confocal microscopy. At 90 mu M, 3 beta-Dns-CA showed disperse assemblies in the mu m range.Financial support from the Spanish Government (Grants SEV-2012-0267 and CTQ2012-38754-C03-03) and the Generalitat Valenciana (Prometeo Program) is gratefully acknowledged.Gómez Mendoza, M.; Marín García, ML.; Miranda Alonso, MÁ. (2016). Photoactive bile salts with critical micellar concentration in the micromolar range. Physical Chemistry Chemical Physics. 18(18):12976-12982. https://doi.org/10.1039/c6cp00813eS1297612982181

pH-dependent binding of guests in the cavity of a polyhedral coordination cage : reversible uptake and release of drug molecules

A range of organic molecules with acidic or basic groups exhibit strong pH-dependent binding inside the cavity of a polyhedral coordination cage. Guest binding in aqueous solution is dominated by a hydrophobic contribution which is compensated by stronger solvation when the guests become cationic (by protonation) or anionic (by deprotonation). The Parkinson's drug 1-amino-adamantane (‘amantadine’) binds with an association constant of 104 M−1 in the neutral form (pH greater than 11), but the stability of the complex is reduced by three orders of magnitude when the guest is protonated at lower pH. Monitoring the uptake of the guests into the cage cavity was facilitated by the large upfield shift for the 1H NMR signals of bound guests due to the paramagnetism of the host. Although the association constants are generally lower, guests of biological significance such as aspirin and nicotine show similar behaviour, with a substantial difference between neutral (strongly binding) and charged (weakly binding) forms, irrespective of the sign of the charged species. pH-dependent binding was observed for a range of guests with different functional groups (primary and tertiary amines, pyridine, imidazole and carboxylic acids), so that the pH-swing can be tuned anywhere in the range of 3.5–11. The structure of the adamantane-1-carboxylic acid complex was determined by X-ray crystallography: the oxygen atoms of the guest form CH[cdots, three dots, centered]O hydrogen bonds with one of two equivalent pockets on the internal surface of the host. Reversible uptake and release of guests as a function of pH offers interesting possibilities in any application where controlled release of a molecule following an external stimulus is required

Application of built-in adjuvants for epitope-based vaccines

Several studies have shown that epitope vaccines exhibit substantial advantages over conventional vaccines. However, epitope vaccines are associated with limited immunity, which can be overcome by conjugating antigenic epitopes with built-in adjuvants (e.g., some carrier proteins or new biomaterials) with special properties, including immunologic specificity, good biosecurity and biocompatibility, and the ability to vastly improve the immune response of epitope vaccines. When designing epitope vaccines, the following types of built-in adjuvants are typically considered: (1) pattern recognition receptor ligands (i.e., toll-like receptors); (2) virus-like particle carrier platforms; (3) bacterial toxin proteins; and (4) novel potential delivery systems (e.g., self-assembled peptide nanoparticles, lipid core peptides, and polymeric or inorganic nanoparticles). This review primarily discusses the current and prospective applications of these built-in adjuvants (i.e., biological carriers) to provide some references for the future design of epitope-based vaccines