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1.
Cryst Growth Des ; 23(8): 5719-5733, 2023 Aug 02.
Article in English | MEDLINE | ID: mdl-37547876

ABSTRACT

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 meso 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. Our results report on the X-ray crystal structures of all stereoisomers for the first time, along with further details on enantiodiscrimination and the always intriguing arguments accounting for the stability of homochiral versus heterochiral crystal aggregates. To this end, metadynamic (MTD) simulations on stereoisomer molecular aggregates were performed to capture the incipient nucleation events at the picosecond time scale. This analysis sheds light on the driving homochiral aggregation of ACPA enantiomers.

2.
Orig Life Evol Biosph ; 52(1-3): 21-56, 2022 Sep.
Article in English | MEDLINE | ID: mdl-35796896

ABSTRACT

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. Different scenarios and pathways will be discussed, from the widely known formose-type processes to less familiar ones, often viewed as unorthodox chemical routes. In particular, problems associated with the spontaneous generation of enantiomeric imbalances and the transfer of chirality will be tackled. As carbohydrates are essential components of all cellular systems, astrochemical and terrestrial observations suggest that saccharides originated from environmentally available feedstocks. Such substances would have been capable of sustaining autotrophic and heterotrophic mechanisms integrating nutrients, metabolism and the genome after compartmentalization. Recent findings likewise indicate that sugars' enantiomeric bias may have emerged by a transfer of chirality mechanisms, rather than by deracemization of sugar backbones, yet providing an evolutionary advantage that fueled the cellular machinery.


Subject(s)
Functional Laterality , Sugars , Carbohydrates/chemistry , Earth, Planet , Stereoisomerism
3.
Chem Commun (Camb) ; 57(42): 5143-5146, 2021 May 25.
Article in English | MEDLINE | ID: mdl-33899844

ABSTRACT

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 (Cu2+, Fe3+, 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.

4.
Chem Commun (Camb) ; 56(33): 4547-4550, 2020 Apr 28.
Article in English | MEDLINE | ID: mdl-32202285

ABSTRACT

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.

5.
ACS Appl Bio Mater ; 3(10): 7219-7227, 2020 Oct 19.
Article in English | MEDLINE | ID: mdl-35019380

ABSTRACT

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. Here, we report a platform that allows for the development of electrospun poly(vinyl alcohol) (PVA) fibrous hybrids embedded with upconverting nanoparticles (UCNPs) and UV-cleavable levofloxacin conjugates for wound dressings. Upon irradiation with NIR light, the excited UCNPs emit UV light around 365 nm, which can cleave the o-nitrobenzyl (ONB) linkage of the levofloxacin conjugates in the PVA fiber, leading to controlled drug release. The release was observed to be triggered only under NIR and UV irradiation, with no effect in the dark. Furthermore, the antibacterial effect against Escherichia coli and Staphylococcus aureus was successfully demonstrated, highlighting the versatility of the electrospun upconverting fiber platform. The development of antibacterial fibrous meshes with on-demand release of encapsulated drugs is imperative for precise treatment of wound infections.

6.
Phys Chem Chem Phys ; 21(5): 2345-2350, 2019 Jan 30.
Article in English | MEDLINE | ID: mdl-30657501

ABSTRACT

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.

7.
Nanoscale ; 10(31): 14993-15002, 2018 Aug 09.
Article in English | MEDLINE | ID: mdl-30052249

ABSTRACT

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. Alkyl chains on the bottom or top layer of the double-deck assemblies were selectively visualized by carefully tuning the scanning tunneling microscopy settings. A method to easily identify mirror image domains was discovered based on the coincidence of domain boundaries with a graphite main axis. The effect of molecular symmetry and metal complexation on the formation of the double-deck assembly was also explored. Based on 2D crystal engineering principles, this bottom-up double-deck assembly can potentially provide an essential toehold for constructing precise 3D hierarchical structures.

8.
Chem Commun (Camb) ; 52(85): 12626-12629, 2016 Oct 18.
Article in English | MEDLINE | ID: mdl-27722259

ABSTRACT

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). Isothermal titration calorimetry (ITC) shows chiral recognition of (1R,2R)- and (1S,2S)-1,2-diphenylethylenediamine to EDS crystals where the enthalpy of adsorption of the (1R,2R)-isomer on l-EDS crystals is higher in comparison to that on d-EDS crystals. These results are consistent with a "rule of reversal" mechanism driving the chiral outcome of the Viedma ripening of EDS.

9.
Chem Commun (Camb) ; 52(78): 11673-11676, 2016 Sep 22.
Article in English | MEDLINE | ID: mdl-27722508

ABSTRACT

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.

10.
Chem Commun (Camb) ; 48(17): 2292-4, 2012 Feb 25.
Article in English | MEDLINE | ID: mdl-22266606

ABSTRACT

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.

11.
Chem Commun (Camb) ; 47(40): 11255-7, 2011 Oct 28.
Article in English | MEDLINE | ID: mdl-21927761

ABSTRACT

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.


Subject(s)
Benzoquinones/chemistry , Hydrophobic and Hydrophilic Interactions , Imines/chemistry , Hydrogen Bonding , Microscopy, Scanning Tunneling , Models, Molecular , Molecular Conformation , Surface Properties
12.
Colloids Surf B Biointerfaces ; 82(2): 470-6, 2011 Feb 01.
Article in English | MEDLINE | ID: mdl-21071189

ABSTRACT

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. Conversely, the visualization of elongated strands indicated the presence of stabilizing interactions with the substrate. Surfaces with varying chemical composition (glass, self-assembled monolayer of mercaptoundecanoic acid/decanethiol and polytetrafluoroethylene (PTFE)) were probed with chitosan modified AFM tips and the corresponding desorption energies, calculated from plateau-like features, were attributed to the desorption of individual polymer strands. Desorption energies of 2.0±0.3×10(-20)J, 1.8±0.3×10(-20)J and 3.5±0.3×10(-20)J were obtained for glass, SAM of mercaptoundecanoic/dodecanethiol and PTFE, respectively. These single molecule level results can be used as a basis for investigating chitosan and chitosan-based materials for biomaterial applications.


Subject(s)
Chitosan/chemistry , Fatty Acids/chemistry , Microscopy, Atomic Force/methods , Polymers/chemistry , Polytetrafluoroethylene/chemistry , Spectrum Analysis/methods , Sulfhydryl Compounds/chemistry , Adsorption , Biocompatible Materials/chemistry , Glass , Materials Testing , Models, Chemical
13.
Langmuir ; 26(22): 16677-80, 2010 Nov 16.
Article in English | MEDLINE | ID: mdl-20964389

ABSTRACT

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. Dynamic force spectroscopy was used to determine the dissociation rate constant, k(off), for this interaction to be 0.16 s(-1).


Subject(s)
Azides/chemistry , Concanavalin A/metabolism , Hydrocarbons, Fluorinated/chemistry , Mannose/chemistry , Mannose/metabolism , Microscopy, Atomic Force , Photochemical Processes , Protein Binding , Surface Properties
14.
Chemistry ; 15(39): 10030-8, 2009 Oct 05.
Article in English | MEDLINE | ID: mdl-19746470

ABSTRACT

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. NMR characterization of these foldamers confirms the intramolecular hydrogen-bonded conformation expected (Z,E configuration of the urea bond) in both the pyridazyl and pyrimidyl foldamers in solution. An X-ray crystal structure of the N(3),N(6)-diisobutylpyridazine-4,6-diamine-o-tolyl urea-linked foldamer (4) confirms the presence of N-H...N hydrogen bonds between the heterocyclic nitrogen atom and the free hydrogen of the urea linkage. Additionally, the tolyl methyl group interacts unfavourably with the urea carbonyl oxygen, thus destabilising the alternate planar conformation.


Subject(s)
Heterocyclic Compounds/chemical synthesis , Macromolecular Substances/chemical synthesis , Urea/chemistry , Urea/chemical synthesis , Crystallography, X-Ray , Heterocyclic Compounds/chemistry , Hydrogen Bonding , Macromolecular Substances/chemistry , Molecular Structure
15.
Chem Commun (Camb) ; (11): 1337-8, 2009 Mar 21.
Article in English | MEDLINE | ID: mdl-19259579

ABSTRACT

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


Subject(s)
Amino Acids/chemistry , Quaternary Ammonium Compounds/chemistry , Crystallization , Models, Molecular , Stereoisomerism
16.
J Org Chem ; 73(7): 2481-95, 2008 Apr 04.
Article in English | MEDLINE | ID: mdl-18315005

ABSTRACT

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. Interestingly, the binding event within these large oligomers is translated to the outside of the receptors and affects the interaction of the overall complexes with the outside world. For instance, alkali cations bind to the one-turn helices and macrocycles to promote fibril formation and aggregation. Also, polyammonium substrates are able to tune the length of the overall helix assemblies and the rigidity of long oligomers. The reported data on one-turn, two-turn helices and macrocycles not only allows one to devise a model for the ion-controlled supramolecular assembly of such systems but also provides evidence that such controlled scaffolds bear promise in the design of complex systems.


Subject(s)
Macrocyclic Compounds/chemistry , Macrocyclic Compounds/chemical synthesis , Naphthyridines/chemistry , Naphthyridines/chemical synthesis , Pyrimidines/chemistry , Pyrimidines/chemical synthesis , Binding Sites , Cations/chemistry , Circular Dichroism/methods , Macromolecular Substances/chemical synthesis , Macromolecular Substances/chemistry , Magnetic Resonance Spectroscopy/methods , Magnetic Resonance Spectroscopy/standards , Models, Molecular , Molecular Structure , Particle Size , Powder Diffraction , Reference Standards , Stereoisomerism
18.
Nano Lett ; 7(3): 847-52, 2007 Mar.
Article in English | MEDLINE | ID: mdl-17302461

ABSTRACT

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. The NCs were characterized through the use of transmission electron microscopy, selected area electron diffraction, 1H NMR, powder X-ray diffraction, and high-resolution luminescence spectroscopy. The NaYF4 NCs are capable of being of dispersed in nonpolar organic solvents thus forming colloidally stable solutions. The colloids of the Er3+, Yb3+ and Tm3+, Yb3+ doped NCs exhibit green/red and blue upconversion luminescence, respectively, under 980 nm laser diode excitation with low power densities.

19.
J Am Chem Soc ; 128(23): 7444-5, 2006 Jun 14.
Article in English | MEDLINE | ID: mdl-16756290

ABSTRACT

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.


Subject(s)
Colloids/chemistry , Lanthanoid Series Elements/chemistry , Luminescence , Nanostructures/chemistry , Sodium Fluoride/chemical synthesis , Trifluoroacetic Acid/chemistry , Yttrium/chemistry , Cations , Crystallization , Erbium/chemistry , Hot Temperature , Luminescent Measurements , Microscopy, Electron, Transmission , Nanostructures/ultrastructure , Sodium Fluoride/analogs & derivatives , Thulium/chemistry , Ytterbium/chemistry
20.
Chem Commun (Camb) ; (46): 5751-3, 2005 Dec 14.
Article in English | MEDLINE | ID: mdl-16307134

ABSTRACT

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


Subject(s)
Macrocyclic Compounds/chemistry , Naphthyridines/chemistry , Pyridazines/chemistry , Crystallography, X-Ray , Hydrogen Bonding , Macrocyclic Compounds/chemical synthesis , Microscopy, Scanning Tunneling , Molecular Structure
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