Sporopollenin Capsules as Biomimetic Templates for the Synthesis of Hydroxyapatite and ß-TCP.

Pollen grains, with their resilient sporopollenin exine and defined morphologies, have been explored as bio-templates for the synthesis of calcium phosphate minerals, particularly hydroxyapatite (HAp) and ß-tricalcium phosphate (TCP). Various pollen morphologies from different plant species (black alder, dandelion, lamb's quarters, ragweed, and stargazer lily) were evaluated. Pollen grains underwent acid washing to remove allergenic material and facilitate subsequent calcification. Ragweed and lamb's quarter pollen grains were chosen as templates for calcium phosphate salts deposition due to their distinct morphologies. The calcification process yielded well-defined spherical hollow particles. The washing step, intended to reduce the protein content, did not significantly affect the final product; thus, justifying the removal of this low-yield step from the synthesis process. Characterisation techniques, including X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and thermal gravimetric analysis, confirmed the successful calcification of pollen-derived materials, revealing that calcified grains were principally composed of calcium deficient HAp. After calcination, biphasic calcium phosphate composed of HAp and TPC was obtained. This study demonstrated the feasibility of using pollen grains as green and sustainable bio-templates for synthesizing biomaterials with controlled morphology, showcasing their potential in biomedical applications such as drug delivery and bone regeneration.

Functionalisation of gold nanoparticles with ruthenium(II) polypyridyl complexes for their application in cellular imaging.

Two new dinuclear Ru(ii) polypyridyl complexes containing an alkyl disulphide functionalised bipyridine-based ligand and either 1,10-phenanthroline (phen) or 1,4,5,8-tetraazaphenanthrene (TAP) as ancillary ligands have been synthesised and characterised. Their attachment onto the surface of gold nanoparticles (AuNPs, average diameter of ca. 2.5 nm) resulted in the formation of two new water-soluble Ru(ii)-AuNP conjugates that combine the advantageous properties of both moieties. Both free complexes show the attractive photophysical properties of Ru(ii) polypyridyl complexes and a rapid cellular uptake in HeLa cervical cancer cells. However, their corresponding gold conjugates displayed lower quantum yields than those determined for the free complexes presumed to be due to an energy transfer quenching of the Ru(ii) luminescence by interaction with the gold surface. Despite their diminished luminescence, confocal fluorescence microscopy studies revealed that the Ru(ii)-AuNP conjugates are successfully internalised into HeLa cells and better tolerated than their free complex counterparts after 24 h incubation, which makes them potential luminescent nanomaterials for bioimaging applications.

Balancing connectivity with function in silver(i) networks of pyridyltriazole (tzpa) ligands results in the formation of a metallogel.

A new flexible and divergent 1,2,3-triazol-4-yl-picolinamide (tzpa) ligand 2 and the half-equivalent model ligand 1, both functionalised with pendant 3-pyridyl groups, are reported and their coordination behaviour with silver(i) ions is explored, both in the crystalline phase and through the formation of a supramolecular metallogel. The self-assembly of tzpa ligand 1 with AgCF3SO3 resulted in the formation of a 1D coordination polymer, binding in a bidentate fashion through the pyridyl and triazole nitrogen atoms of the tzpa binding site and a pendant pyridyl nitrogen atom of an adjacent ligand. Doubling the number of metal binding sites in ligand 2, while retaining the same metal binding domain, gives rise to the formation of a supramolecular metallogel on reaction with AgBF4 at 5 wt% in MeCN, possessing self-healing properties.

Unexpected linkage isomerism in chiral tetranuclear bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) grids.

The synthesis of a chiral bis-tridentate (1,2,3-triazol-4-yl)-picolinamide (tzpa) ligand is described and its coordination chemistry with Cu(NO3)2 and [Cu(MeCN)4]PF6 is explored in the crystalline phase as well as in solution. Chiral [2 × 2] tetranuclear square grid complexes [Cu4(H21)4](NO3)8 and [Cu4(H1)4](PF6)4 were observed, and crystallographically analysed, these being linkage isomers with N4O2 and N5O coordination spheres, respectively. These come about by an unusual in situ amide deprotonation and coordination, which accompanies a CuI → CuII oxidation process.

Exploring the reversible host-guest chemistry of a crystalline octanuclear Ag(i) metallosupramolecular macrocycle formed from a simple pyrazinylpyridine ligand.

Here we report the synthesis of two new 2-(2'-pyrazinyl)pyridine ligands, and explore their coordination chemistry with Cu(ii) and Ag(i) ions, leading to the discovery of metallosupramolecular architectures of surprising complexity. Differing only in the substitution pattern of a nitrophenyl substituent attached to the 4-pyridyl position, ligands L1 and L2 both form sulfate-bridged dinuclear complexes on reaction with copper sulfate, without coordination of the nitrogen atom at the pyrazine 4-position. However, on reaction with Ag(i), both ligands adopt bridging coordination modes which lead to dramatically different outcomes. Ligand L2 reacts with AgCF3SO3 to give a densely packed coordination polymer 3 of unusually low symmetry (Z' = 7), while the structural isomer L1 instead gives an octanuclear macrocycle 4 in the crystalline state. Macrocycle 4, containing crystallographically-defined solvent molecules within its central cavity as well as in the interstitial spaces, readily undergoes solvent exchange in a single-crystal-to-single-crystal transformation. This allows a direct comparison of guest solvent affinity from single component and mixed-component exchange solutions using a combination of X-ray diffraction, NMR and TGA techniques, revealing the fully reversible uptake and exchange preferences of this material.

Synthesis, structural characterisation and antiproliferative activity of a new fluorescent 4-amino-1,8-naphthalimide Tröger's base-Ru(ii)-curcumin organometallic conjugate.

The synthesis, photophysics and biological investigation of fluorescent 4-amino-1,8-naphthalimide Tröger's bases (TB-1-TB-3) and a new Tröger's base p-cymene-Ru(ii)-curcumin organometallic conjugate (TB-Ru-Cur) are described; these compounds showed fast cellular uptake and displayed good luminescence and cytotoxicity against cervical cancer cells.