Cyclometalated iridium(III) complexes for life science

Photoluminescent cyclometalated iridium(III) complexes are now a well established class of organometallic compounds with advantageous potential applications in biology and life science. While these complexes, along with other luminescent transition metals and lanthanoid complexes, were initially proposed as alternative markers to organic fluorophores in the staining of cells, it is now evident that their specific biological behavior makes this class of compounds useful in broader areas of life science such as imaging, sensing and therapy. The critical factors for the effective design of cyclometalated iridium(III) complexes with specific biological properties are still rather difficult to rationalize, and often mainly rely of aspects such as the intrinsic charge of the complex, its lipophilicity and its aqueous solubility. This review overviews the area of cyclometalated iridium(III) complexes in biology, with an emphasis on comparing the various conditions that these compounds have been assessed for their biological potential, such as the specific tested cells lines, concentration of internalization, incubation time, and mechanism of cellular entrance

Properties and prospects for rhenium(i) tricarbonyl N-heterocyclic carbene complexes

Re(i) complexes bound to p-conjugated bidentate N-heterocyclic carbene ligands with formulation Re(CO)3(N^NHC)L (where N^NHC represents an imidazole or benzimidazole carbene ligand conjugated to a N-based heterocycle such as pyridine, pyrimidine, quinoline or quinoxaline) are a relatively new class of complexes belonging to the archetypal family of well known luminescent Re(CO)3(diim)X species (where diim is a conjugated diimine ligand and X is a halogen anion). The complexes Re(CO)3(N^NHC)L are characterised by blue-shifted emission compared to Re(CO)3(diim)X, but with shorter excited state lifetime decays and lower quantum yields, in contrast to trends expected by the energy gap law. Detailed investigations elucidated that these complexes are photochemically active and undergo ligand exchange reactions when excited to their lowest metal-to-ligand charge transfer excited states. This mechanism is entirely different from previously known mechanisms of photoactivated ligand substitution reactions in Re(i) tricarbonyl complexes. Therefore, the species Re(CO)3(N^NHC)L represent a new and unique class of photoactive Re(i) complexes. This feature article illustrates the research effort dedicated to the design and synthesis of Re(CO)3(N^NHC)L complexes and the elucidation of their photophysical and photochemical behaviour by means of a variety of spectroscopic techniques. Furthermore, for their unique characteristics, these new complexes have demonstrated potential value in several applications including catalysis, diagnosis and therapy. These studies will also be illustrated herein

Tetrazoles: calcium oxalate crystal growth modifiers

Molecules containing tetrazole substituents have become of interest due to their being bioisosteres of carboxylic acids and like their carboxylate counterparts, tetrazolate anions have been able to affect the crystal growth of barium sulphate and calcium carbonate. In this proof of principle study, we show that this behaviour also extends to calcium oxalate and therefore opens the possibility of using tetrazole-based additives for investigating mineralization processes of human pathological relevance

Lanthanoid tetrazole coordination complexes

While tetrazole derivatives are well established as anionic ligands for d-block elements, there is a growing interest in lanthanoid complexes of these compounds. Diverse structural chemistry results from the presence of four potential donor N atoms, and the conjugated nature of the heterocycle can impact on the photophysical properties of the complexes. This review examines the range of structurally characterised lanthanoid–tetrazolato complexes, focussing on the structural features of the ligand that impact on the tendency to interact with the first or second coordination spheres

Calcium oxalate crystal growth modification; investigations with confocal Raman microscopy

Confocal Raman Microscopy (CRM) in combination with a photophysical investigation has been employed to give insight into the interaction between calcium oxalate monohydrate (COM) and a series of tetrazole containing crystal growth modifier's (CGM's), in conjunction with characterisation of morphological changes using scanning electron and optical microscopy. The tetrazole CGM's were found to interact by surface adsorption with minimal morphological changes to the COM crystals however, significant interactions via chemisorption were observed; it was discovered that the chemisorption is sufficiently strong for aggregation of the tetrazole species to occur within the crystal during crystallisation

Structural characterisation and photophysical properties of lanthanoid complexes of a tetra-amide functionalised calix[4]arene

Lanthanoid complexes of a tetra-amide substituted calix[4]arene in the cone conformation are characterised by single crystal X-ray structure determination. The structural analysis shows that the metal ions are coordinated to the calixarene through the eight O donor atoms, along with one aqua ligand which is located within the cavity of the calixarene. The calixarene ligand was covalently incorporated into a polymethylmethacrylate monolith through p-allyl functional groups, followed by loading with a range of lanthanoid cations giving rise to light-emitting materials. The emission from the hydrid materials was found to be comparable to the solution phase emission

Tetrazoles: a new class of compound for crystallization modification

Tetrazoles are a class of organic compound often used as carboxylic acid analogues. This analogous behaviour is shown to extend to crystallization modification, that is, tetrazoles are also able to influence crystal growth and morphology although in a different manner to their carboxylate counterparts. All the tetrazoles investigated thus far are shown to impact on barium sulfate and calcium carbonate crystallization to varying degrees. Thus, the tetrazoles represent a new class of crystal modifier

Afferent Neural Branching at Human Acupuncture Points: Do Needles Stimulate or Inhibit?

Background: Acupuncture has previously been considered to be stimulatory to the nervous system; however, the specific mechanism for this remains unknown, with the few published studies of acupuncture-point histology showing reduced numbers of nerves and neural receptors at acupuncture-point sites. Objective: This study was undertaken to visualize the neuroanatomic features of acupuncture points in humans. Materials and Methods: Light microscopy was performed on silver-stained sections of a human cadaver at P 6, and confocal microscopy was performed on PgP9.5 and P2X3 immunostained sections of 2 points (GB 20 and SP 6) from a live human volunteer. Results: At each point, but not at control sites, a single nerve bundle extending to the dermal–epidermal junction was identified where it branched into two parts, with each branch running perpendicularly, parallel to the dermal–epidermal junction. Conclusions: Acupuncture may incise afferent unmyelinated axonal branch points, disrupting both neural transmission to the spinal cord and crosstalk along meridians, while simultaneously stimulating larger, myelinated afferents, thus explaining both the immediate and long-lasting effects of acupuncture

Defining the Anti-Cancer Activity of Tricarbonyl Rhenium Complexes: Induction of G2/M Cell Cycle Arrest and Blockade of Aurora-A Kinase Phosphorylation

Rhenium and ruthenium complexes containing N-heterocylic carbene (NHC) ligands and conjugated to indomethacin were prepared. The anticancer properties were probed against pancreatic cell lines, revealing a remarkable activity of the rhenium fragment as anticancer agent. The ruthenium complexes were found to be inactive against the same pancreatic cancer cell lines, either alone or in conjugation with indomethacin. An in-depth biological study revealed the origin of the anticancer properties of the rhenium tricarbonyl fragment, of which a complete elucidation had yet to be achieved. It was found that the rhenium complexes induce cell cycle arrest at the G2/M phase by inhibiting the phosphorylation of Aurora-A kinase. A preliminary study on the structure-activity relationship on a large family of these complexes revealed that the anticancer properties are mainly associated with the lability of the ancillary ligand, with inert complexes showing limited to no anticancer properties

Luminescent lanthanoid complexes of a tetrazole-functionalised calix[4]arene

p-t-Butylcalix[4]arene functionalised at the lower rim with two tetrazole moieties is found to be a useful receptor for lanthanoid cations. The luminescence of the resulting complexes can be controlled by addition of base, with emission achieved in the visible and infrared regions