‘Frustrated’ hydrogen bond mediated amphiphile self-assembly – a solid state study

Herein, we present the synthesis of ten structurally related ‘frustrated’ amphiphiles, from which were obtained eleven single crystal X-ray structures, allowing observation of the hydrogen bonding modes present in the solid state. We previously reported the synthesis of a novel amphiphilic salt which contains both hydrogen bond donating (HBD) and hydrogen bond accepting (HBA) functionalities. This amphiphilic salt was shown to self-associate in the solution state, aided by the formation of hydrogen bonds. The exact nature of the hydrogen bonding modes involved in this self-association process remains unclear due to the combination of HBD and HBA groups present in the amphiphile structure. This results in a ‘frustrated’ system with access to a variety of possible hydrogen bonding modes

Pressure effect investigations on spin-crossover coordination compounds

The piezochromic properties of spin-crossover complexes have been recognized for a long time, with increasing pressure favouring the low spin state due to its smaller volume and therefore shifting the spin equilibrium towards higher temperatures and accelerating the relaxation at a given temperature. However, the interpretation and quantification of pressure-induced changes have been several times compromised by the relatively poor and incomplete spectral and structural information provided by the detection methods or due to the experimental difficulties related to the need for hydrostatic conditions at low temperatures. The present review is therefore primarily focused on these experimental aspects of high-pressure spin crossover research providing an overview of methods of pressure generation and associated detection methods as well as on selected recent result

Supramolecular Self-associating Amphiphiles (SSAs) as enhancers of antimicrobial agents towards Escherichia coli (E. coli)

Supramolecular self-associating amphiphiles (SSAs) are a class of amphiphilic salt which have demonstrated antimicrobial activity against both Gram-positive and Gram-negative bacteria. Herein, we show that SSAs are also able to increase the efficacy of a range of currently used antimicrobial/therapeutic agents with a range of different chemical structures and modes of antimicrobial action against Gram-negative Escherichia coli, which include: octenidine (an antiseptic); ampicillin (an antibiotic); and cisplatin (a DNA chelating agent). Additionally, we show these effects to be dependent on the order of agent addition. Finally, through completion of a range of 1[thin space (1/6-em)]:[thin space (1/6-em)]1 SSA[thin space (1/6-em)]:[thin space (1/6-em)] antimicrobial/therapeutic agent physicochemical studies we gain an understanding as to how the self-association events and resultant SSA aggregate structure are effected by the presence of these secondary molecular species

Exploring the reactivity of donor-stabilised phosphenium cations: Lewis acid catalysed reduction of chlorophosphanes by silanes

Phosphane-stabilised phosphenium cations react with silanes to effect either reduction to primary or secondary phosphanes, or formation of P-P bonded species depending upon counter-anion. This operates for in situ generated phosphenium cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence studies have allowed insight into the competing mechanisms involved

Supramolecular Tuning of Spin Crossover Properties in Isostructural Cocrystal Solvates

In order to improve strategies for the design of spin-crossover materials, it is necessary to develop and understand structure–property relationships, and this is best achieved by obtaining isostructural materials. In this work we synthesized a series of four isostructural cocrystal solvates using the [Fe­(3-bpp)2]­[A]2 complex and the 2,2-dipyridyl disulfide coformer in methanol and ethanol (A = BF4 – or PF6 –). The spin-crossover properties of the materials were determined by variable temperature single-crystal X-ray diffraction. They show the same SCO behavior but with shifted spin-crossover temperatures, which has been related to the hydrogen bond basicity, pK BHX of the anions, and solvents present. This relationship between hydrogen bond basicity and the spin-crossover transition temperature offers a design strategy for the supramolecular tuning of spin-crossover properties in specific isostructural materials

Supramolecular Behaviour and Fluorescence of Rhodamine-Functionalised ROMP Polymers

Inherently fluorescent polymers are of interest in materials and medicine. We report a ring-opening metathesis polymerisation (ROMP) platform for creation of amphiphilic block copolymers in which one block is formed from rhodamine B-containing monomers. The polymers self-assemble into well-defined micelles which are able to sequester molecular dyes and further interact with them by energy transfer. Despite incorporating a cationic dye known to bind DNA, the polymer micelles do not interact with DNA, indicating that they are potentially safe for use in bioanalytical applications

Supramolecular Self-Assembly of Engineered Polyproline Helices

The ability to rationally design biomaterials to form desired supramolecular constructs presents an ever-growing research field, with many burgeoning works within recent years providing exciting results; however, there exists a broad expanse of promising avenues of research yet to be investigated. As such we have set out to make use of the polyproline helix as a rigid, tunable, and chiral ligand for the rational design and synthesis of supramolecular constructs. In this investigation, we show how an oligoproline tetramer can be specifically designed and functionalized, allowing predictable tuning of supramolecular interactions, to engineer the formation of supramolecular peptide frameworks with varying properties and, consequently, laying the groundwork for further studies utilizing the polyproline helix, with the ability to design desired supramolecular structures containing these peptide building blocks, having tunable structural features and functionalities

'Frustrated' hydrogen bonded self-associated systems as templates towards DNA incorporated nanostructure formation

Herein, we present the synthesis of a thymine nucleobase appended ‘frustrated’ monomer, which exhibits self-association in DMSO solutions through the formation of hydrogen bonds. This self-association process has been explored in both competitive DMSO solutions and the solid state, using a combination of NMR and single crystal X-ray diffraction techniques. The self-associative equilibria within the solution state are balanced in such a way that the hydrogen bond donating (HBD) and accepting (HBA) thymine residue present within the monomeric structure is free to coordinate further guest species such as the complimentary DNA base adenine. The adenine simulants, 2-aminopyridine and 2,6-diaminopyridine have been used to explore the potential of these self-associated structures towards the coordination of complimentary DNA base pairs

Sterol Uptake by an Alkali-β-Cyclodextrin Metal–Organic Framework

β-Cyclodextrin is well-known in cellular biology for its ability to moderate cholesterol levels in lipid bilayer membranes. Its use in extended network solids remains elusive due to the low symmetry of this macrocyclic system. Self-assembly of two different β-cyclodextrin metal–organic frameworks (MOFs) with extended nanotube structures is achieved by crystallization with excess potassium hydroxide, one in the presence of cholesterol. We then further demonstrate the proclivity of one of these MOFs to absorb cholesterol and two other sterols from solution using NMR and confocal microscopy techniques. This work demonstrates that these network solids show great potential in both substrate delivery and/or extraction

An Iodine-Vapor-Induced Cyclization in a Crystalline Molecular Flask

A vapor‐induced cyclization has been observed in the host environment of a crystalline molecular flask (CMF), within which 1,8‐bis(2‐phenylethynyl)naphthalene (bpen), a diarenynyl system primed for cyclization, was exposed to iodine vapor to yield the corresponding indeno[2,1‐α]phenalene species. The cyclization process, unique in its vapor‐induced, solvent‐free nature, was followed spectroscopically, and found to occur concurrently with the displacement of lattice solvent for molecular iodine in CMF⋅0.75 bpen⋅2.25 CHCl3⋅H2O. The cyclization occurred under mild conditions and without the need to suspend the crystals in solvent. The ability of CMFs to host purely gas‐induced reactions is further highlighted by the subsequent sequential oxidation reaction of cyclized 7‐iodo‐12‐phenylindeno[2,1‐α]phenalene (ipp) with molecular oxygen derived from air, yielding 12‐hydroxy‐7‐iodo‐2‐phenylindeno[2,1‐α]phenalen‐1(12H)‐one (hipp)