ABSTRACT
Metal ions (Ag+, Cd2+, Eu3+, Sm3+) and protons can, through coordination and protonation, modulate in three specific ways the structural information contained in the pyrazine-based heterocyclic strand L (obtained from 2,5-bis(methylhydrazino)pyrazine and 2 equivalents of 2-pyridinecarboxaldehyde), thus generating two linear rod-like conformations and a bent one. This conformational diversity is associated with a structural one that consists of two diprotonated forms (H2L(PF6)2 and H2L(CF3SO3)2), a polymeric architecture [AgL]n(CF3SO3)n, two rack-like complexes ([Eu2H2L3(CF3SO3)6](PF6)2 and [Sm2H2L3(CF3SO3)6](PF6)2) and a grid-like structure ([Cd4L4](CF3SO3)8).
Subject(s)
Hydrazones , Pyrazines , Cadmium , Crystallography, X-Ray , Ligands , Models, Molecular , Protons , Pyridines/chemistryABSTRACT
The encapsulation and/or surface modification can stabilize and protect the phosphorescence bio-probes but impede their intravenous delivery across biological barriers. Here, a new class of biocompatible rhenium (ReI ) diimine carbonyl complexes is developed, which can efficaciously permeate normal vessel walls and then functionalize the extravascular collagen matrixes as in situ oxygen sensor. Without protective agents, ReI -diimine complex already exhibits excellent emission yield (34%, λem = 583 nm) and large two-photon absorption cross-sections (σ2 = 300 GM @ 800 nm) in water (pH 7.4). After extravasation, remarkably, the collagen-bound probes further enhanced their excitation efficiency by increasing the deoxygenated lifetime from 4.0 to 7.5 µs, paving a way to visualize tumor hypoxia and tissue ischemia in vivo. The post-extravasation functionalization of extracellular matrixes demonstrates a new methodology for biomaterial-empowered phosphorescence sensing and imaging.