Revisiting Homochiral Heterochiral Interactions through a Long Detective Story of a Useful Azobis-Nitrile and Puzzling Racemate.

This paper documents and reinvestigates the solid-state and crystal structures of 4,4'-azobis-4-cyanopentanoic acid (ACPA), a water-soluble azobis-nitrile of immense utility as a radical initiator in living polymerizations and a labile mechanophore that can be embedded within long polymer chains to undergo selective scission under mechanical activation. Surprisingly, for such applications, both the commercially available reagent and their derivatives are used as "single initiators" when this azonitrile is actually a mixture of stereoisomers. Although the racemate and compounds were identified more than half a century ago and their enantiomers were separated by classical resolution, there have been confusing narratives dealing with their characterization, the existence of a conglomeratic phase, and fractional crystallization.

Defect-engineered surfaces to investigate the formation of self-assembled molecular networks.

Herein we report the impact of covalent modification (grafting), inducing lateral nanoconfinement conditions, on the self-assembly of a quinonoid zwitterion derivative into self-assembled molecular networks at the liquid/solid interface. At low concentrations where the compound does not show self-assembly behaviour on bare highly oriented pyrolytic graphite (HOPG), close-packed self-assembled structures are visualized by scanning tunneling microscopy on covalently modified HOPG. The size of the self-assembled domains decreases with increasing the density of grafted molecules, the molecules covalently bound to the surface.

On the Origin of Sugar Handedness: Facts, Hypotheses and Missing Links-A Review.

By paraphrasing one of Kipling's most amazing short stories (How the Leopard Got His Spots), this article could be entitled "How Sugars Became Homochiral". Obviously, we have no answer to this still unsolved mystery, and this perspective simply brings recent models, experiments and hypotheses into the homochiral homogeneity of sugars on earth. We shall revisit the past and current understanding of sugar chirality in the context of prebiotic chemistry, with attention to recent developments and insights.

A new class of anionic metallohelicates based on salicylic and terephthalic acid units, accessible in solution and by mechanochemistry.

We present a new class of anionic metallohelicates based on an abundant, industrially relevant salicylic acid derivative, leading to discrete double and triple-stranded architectures based on divalent and trivalent metals (Cu, Fe, respectively). The ability to assemble the metallohelicates in a solvent-free environment presents the opportunity to develop an inexpensive and environmentally-friendly design of helicate materials.

Electrospun Upconverting Nanofibrous Hybrids with Smart NIR-Light-Controlled Drug Release for Wound Dressing.

Chronic wounds present a high risk of infection due to delayed and incomplete healing, leading to increased health risks and financial burden to health-care systems. Numerous approaches to promote wound healing have been extensively explored, especially the development of effective wound dressing materials embedded with therapeutic drug molecules. Despite advances made in this area, a remaining challenge to be addressed is the controlled, on-demand release of therapeutic molecules using noncytotoxic stimulus, for example, near-infrared (NIR) excitation.

Pasteur made simple - mechanochemical transformation of racemic amino acid crystals into racemic conglomerate crystals.

Conglomerate crystallization is required for many deracemization or enantioenrichment protocols. Here, we report the metal-mediated mechanochemical transformation of racemic compounds of some proteinogenic amino acids - valine, leucine and isoleucine - into their corresponding conglomerates. Specifically, ZnO has the ability to promote and stabilize the conglomerate phase of these amino acids to an extent where the racemic compound is not observed.

Structural organization and phase behaviour of meta-substituted dioctadecylaminobenzoquinones at the air/water interface.

The structural organization and phase behaviour of an amphiphilic zwitterionic quinonemonoimine at the air/water interface are presented. Brewster angle microscopy reveals multiple co-existing phases are observed over the entire isotherm while grazing incidence X-ray diffraction (GIXD) shows that these comprise both tilted, untilted and multilayer structures with crystalline headgroups. Despite the heterogeneity, the phase transitions are highly reversible over multiple cycles.

Alkyl chain length effects on double-deck assembly at a liquid/solid interface.

Controlled double-deck packing is an appealing means to expand upon conventional 2D self-assembly which is critical in crystal engineering, yet it is rare and poorly understood. Herein, we report the first systematic study of double-deck assembly in a series of alkylated aminoquinone derivatives at the liquid-solid interface. The competition between the fraction of alkyl chains adsorbed on the surface and the optimal conformation of the alkyl chains near the head group leads to a stepwise structural transformation ranging from complete double-deck packing to complete monolayer packing.

Directing the Viedma ripening of ethylenediammonium sulfate using "Tailor-made" chiral additives.

Both enantiomers of trans-cyclohexane-1,2-diammonium sulfate and trans-1,2-diphenylethylenediammonium sulfate were used as "tailor-made" additives to direct the mirror-symmetry breaking in the attrition-enhanced deracemization (i.e. Viedma ripening) of conglomerate crystals of ethylenediammonium sulfate (EDS).

Oriented attachment by enantioselective facet recognition in millimeter-sized gypsum crystals.

Crystal growth by oriented attachment involves the spontaneous self-assembly of adjoining crystals with common crystallographic orientations. Herein, we report the oriented attachment of gypsum crystals on agitation to form stereoselective mesoscale aggregates.

Mirror symmetry breaking and chiral amplification in foldamer-based supramolecular helical aggregates.

Spontaneous asymmetric generation of supramolecular chiral fibers was observed in the folding induced self-assembly of a lock-washer shaped foldamer. A secondary nucleation growth mechanism is proposed to explain the observed chiral amplification or deracemization of these supramolecular fibers.

Charge-assisted hydrogen bond-directed self-assembly of an amphiphilic zwitterionic quinonemonoimine at the liquid-solid interface.

Charge-assisted hydrogen bond-directed self-assembly of a zwitterionic quinonemonoimine was investigated at the liquid/solid interface using scanning tunnelling microscopy. Factors governing morphology, chirality and multilayer formation are discussed, presenting an important foundation for understanding the properties of a large family of related molecules with interesting potential in supramolecular design.

Single molecule atomic force microscopy and force spectroscopy of chitosan.

Atomic force microscopy (AFM) and AFM-based force spectroscopy was used to study the desorption of individual chitosan polymer chains from substrates with varying chemical composition. AFM images of chitosan adsorbed onto a flat mica substrate show elongated single strands or aggregated bundles. The aggregated state of the polymer is consistent with the high level of flexibility and mobility expected for a highly positively charged polymer strand.

Perfluorophenyl azide immobilization chemistry for single molecule force spectroscopy of the concanavalin A/mannose interaction.

The versatility of perfluorophenyl azide (PFPA) derivatives makes them useful for attaching a wide variety of biomolecules and polymers to surfaces. Herein, a single molecule force spectroscopy (SMFS) study of the concanavalin A/mannose interaction was carried out using PFPA immobilization chemistry. SMFS of the concanavalin A/mannose interaction yielded an average unbinding force of 70-80 pN for loading rates between 8000 and 40,000 pN/s for mannose surfaces on aminated glass, and an unbinding force of 57 ± 20 pN at 6960 pN/s for mannose surfaces on gold-coated glass.

Design and synthesis of urea-linked aromatic oligomers--a route towards convoluted foldamers.

Herein we report the design and synthesis of crescent-shaped and helical urea-based foldamers, the curvature of which is controlled by varying the constituent building blocks and their connectivity. These oligomers are comprised of two, three or five alternating aromatic heterocycles (pyridazine, pyrimidine or pyrazine) and methyl-substituted aromatic carbocycles (tolyl, o-xylyl or m-xylyl) connected together through urea linkages. A crescent-shaped conformational preference is encoded within these pi-conjugated urea-linked oligomers based on intramolecular hydrogen bonding and steric interactions; the degree of curvature is tuned by the urea connectivity to the heterocycles and the aryl groups.

Amino acid directed mirror symmetry breaking and chiral amplification of ethylenediammonium sulfate crystals.

Directed chiral symmetry breaking and asymmetric amplification of ethylenediammonium sulfate in the presence of chiral amino acids was achieved using an abrasion/grinding method.

Naphthyridine-based helical foldamers and macrocycles: synthesis, cation binding, and supramolecular assemblies.

Unraveling the factors that control the conformation of molecular chains is of great interest both for understanding the shape of biological molecular strands and for designing artificial ones that adopt desired forms. Thus, a variety of artificial folding codons have been identified that enforce the formation, among others, of helices, strands, and loops, the major emphasis being on the shape of the foldamer. We report herein the synthesis and study of a family of foldamers and macrocycles based on the 1,8-naphthyridine and pyrimidine units, whose internal cavity is large enough to accommodate ionic substrates, and focus on the impact of guest binding within a cylindrical environment.

Complete asymmetric amplification of ethylenediammonium sulfate using an abrasion/grinding technique.

Complete asymmetric amplification of ethylenediammonium sulfate was achieved under continuous dissolution/crystallization conditions using an abrasion/grinding method.

Synthesis of colloidal upconverting NaYF4: Er3+/Yb3+ and Tm3+/Yb3+ monodisperse nanocrystals.

The synthesis, characterization, and spectroscopy of upconverting lanthanide-doped NaYF4 nanocrystals (NCs) is presented. The monodisperse cubic NaYF4 NCs were synthesized via a thermal decomposition reaction of trifluoroacetate precusors in a mixture of technical grade chemicals, octadecene and the coordinating ligand oleic acid. In this straightforward method, the dissolved precursors are added slowly to the reaction solution through a stainless-steel canula resulting in highly luminescent nanocrystals with an almost monodisperse particle size distribution.

Synthesis of colloidal upconverting NaYF4 nanocrystals doped with Er3+, Yb3+ and Tm3+, Yb3+ via thermal decomposition of lanthanide trifluoroacetate precursors.

Upconverting lanthanide-doped nanocrystals were synthesized via the thermal decomposition of trifluoroacetate precursors in a mixture of oleic acid and octadecene. This method provides highly luminescent nanoparticles through a simple one-pot technique with only one preparatory step. The Er3+, Yb3+ and Tm3+, Yb3+ doped cubic NaYF4 nanocrystals are colloidally stable in nonpolar organic solvents and exhibit green/red and blue upconversion luminescence, respectively, under 977 nm laser excitation with low power densities.

Hydrogen bond directed synthesis of pyridazine and naphthyridine containing macrocycles.

This work describes a high-yielding, one-step synthesis of pyrizadine and naphthyridine containing macrocycles directed by intramolecular H-bonding.

Imaging the selective binding of synapsin to anionic membrane domains.

Synapsins are membrane-associated proteins that cover the surface of synaptic vesicles and are responsible for maintaining a pool of neurotransmitter-loaded vesicles for use during neuronal activity. We have used atomic force microscopy (AFM) to study the interaction of synapsin I with negatively charged lipid domains in phase-separated supported lipid bilayers prepared from mixtures of phosphatidylcholines (PCs) and phosphatidylserines (PSs). The results indicate a mixture of electrostatic binding to anionic PS-rich domains as well as some nonspecific binding to the PC phase.

Interaction of synapsin I with membranes.

The synapsins (I, II, and III) comprise a family of peripheral membrane proteins that are involved in both regulation of neurotransmitter release and synaptogenesis. Synapsins are concentrated at presynaptic nerve terminals and are associated with the cytoplasmic surface of synaptic vesicles. Membrane-binding of synapsins involves interaction with both protein and lipid components of synaptic vesicles.

Helical self-organization and hierarchical self-assembly of an oligoheterocyclic pyridine-pyridazine strand into extended supramolecular fibers.

The synthesis and characterization of an alternating pyridine-pyridazine strand comprising thirteen heterocycles are described. Spontaneous folding into a helical secondary structure is based on a general molecular self-organization process enforced by the conformational information encoded within the primary structure of the molecular strand itself. Conformational control based on heterocyclic "helicity codons" illustrates a strategy for designing folding properties into synthetic oligomers (foldamers).