Aggregation-Induced Emission Probe for Light-Up and in Situ Detection of Calcium Ions at High Concentration

The fluorescent probe for the detection of calcium ions is an indispensable tool in the biomedical field. The millimolar order of Ca(II) ions is associated with many physiological processes and diseases, such as hypercalcemia, soft tissue calcification, and bone microcracks. However, the conventional fluorescent probes are only suitable for imaging Ca(II) ions in the nanomolar to micromolar range, which can be because of their high affinities toward Ca(II) ions and aggregation-caused quenching drawbacks. To tackle this challenge, we herein develop an aggregation-induced emission (AIE) probe SA-4CO₂Na for selective and light-up detection of Ca(II) ions in the millimolar range (0.6-3.0 mM), which can efficiently distinguish between hypercalcemic (1.4-3.0 mM) and normal (1.0-1.4 mM) Ca²⁺ ion levels. The formation of fibrillar aggregates between SA-4CO₂Na and Ca(II) ions was clearly verified by fluorescence, scanning electron microscopy, and transmission electron analysis. Moreover, this AIE-active probe can be used for wash-free and light-up imaging of a high concentration of Ca(II) ions even in the solid analytes, including calcium deposits in psammomatous meningioma slice, microcracks on bovine bone surface, and microdefects on hydroxyapatite-based scaffold. It is thus expected that this AIE-active probe would have broad biomedical applications through light-up imaging and sensing of Ca(II) ions at the millimolar level.

The btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] binding motif: a new versatile terdentate ligand for supramolecular and coordination chemistry

Ligands containing the btp [2,6-bis(1,2,3-triazol-4-yl)pyridine] motif have appeared with increasing regularity over the last decade. This class of ligands, formed in a one pot ‘click’ reaction, has been studied for various purposes, such as for generating d and f metal coordination complexes and supramolecular self-assemblies, and in the formation of dendritic and polymeric networks, etc. This review article introduces btp as a novel and highly versatile terdentate building block with huge potential in inorganic supramolecular chemistry. We will focus on the coordination chemistry of btp ligands with a wide range of metals, and how it compares with other classical pyridyl and polypyridyl based ligands, and then present a selection of applications including use in catalysis, enzyme inhibition, photochemistry, molecular logic and materials, e.g. polymers, dendrimers and gels. The photovoltaic potential of triazolium derivatives of btp and its interactions with anions will also be discussed.

Nanoscale examination of microdamage in sheep cortical bone using synchrotron radiation transmission x-ray microscopy

Microdamage occurs in bone through repeated and excessive loading. Accumulation of microdamage weakens bone, leading to a loss of strength, stiffness and energy dissipation in the tissue. Imaging techniques used to examine microdamage have typically been limited to the microscale. In the current study microdamage was examined at the nanoscale using transmission x-ray microscopy with an x-ray negative stain, lead-uranyl acetate. Microdamage was generated in notched and unnotched beams of sheep cortical bone (2×2×20 mm), with monotonic and fatigue loading. Bulk sections were removed from beams and stained with lead-uranyl acetate to identify microdamage. Samples were sectioned to 50 microns and imaged using transmission x-ray microscopy producing projection images of microdamage with nanoscale resolution. Staining indicated microdamage occurred in both the tensile and compressive regions. A comparison between monotonic and fatigue loading indicated a statistically significant greater amount of stain present in fatigue loaded sections. Microdamage occurred in three forms: staining to existing bone structures, cross hatch damage and a single crack extending from the notch tip. Comparison to microcomputed tomography demonstrated differences in damage morphology and total damage between the microscale and nanoscale. This method has future applications for understanding the underlying mechanisms for microdamage formation as well as three-dimensional nanoscale examination of microdamage.

Recent Highlights in the use of Lanthanide-directed Synthesis of Novel Supramolecular (Luminescent) Self-assembly Structures such as Coordination Bundles, Helicates and Sensors

In this short review, we focus on the recent developments within the field of coordination chemistry where mono- or multimetallic supramolecular self-assemblies are formed by employing structurally defined organic ligands, taking advantage of the high coordination requirements of the lanthanides. Such synthesis results in the formation of both structurally complex and beautiful self-assemblies. Moreover, as the lanthanide ions possess both unique magnetic (e.g. GdIII and DyIII) and luminescent properties, either in the visible (EuIII, SmIII and TbIII) or near-infrared regions (YbIII, NdIII, ErIII), these physical features are usually transferred to the self-assemblies themselves, allowing the formation of highly functional structures, such as coordination networks, as well as molecular bundles and helicates. Hence, examples of the use of lanthanide-directed synthesis of luminescent sensors, some of which are formed on solid surfaces such as gold (flat surface or nanoparticles), and imaging agents are presented. Moreover, we demonstrate that by using chiral organic ligands, lanthanide-directed synthesis can also give rise to the formation of enantiomerically pure self-assemblies, the structure of which can be probed using circularly polarized luminescence.