Metal coordination
with organic ligands often produce crystalline
metal–organic frameworks and sometimes amorphous nanoparticles.
In this work, we explore a different type of material from the same
chemistry: hydrogels. Lanthanides are chosen as the metal component
because of their important technological applications and continuously
tunable properties. Adenosine monophosphate (AMP) and lanthanides
form two types of coordination materials: the lighter lanthanides
from La3+ to Tb3+ form nanoparticles, whereas
the rest heavier ones initially form nanoparticles but later spontaneously
transform to hydrogels. This slow sol-to-gel transition is accompanied
by heat release, as indicated by isothermal titration calorimetry.
The transition is also accompanied by a morphology change from nanoparticles
to nanofibers, as indicated by transmission electron microscopy. These
gels are insensitive to ionic strength or temperature with excellent
stability. Gelation is unique to AMP because other nucleotides or
other adenine derivatives only yield nanoparticles or soluble products.
Entrapment of guest molecules such as glucose oxidase is also explored,
where the hydrogels allow a better enzyme activity and stability compared
to nanoparticles. Further applications of lanthanide coordinated hydrogels
might include biosensors, imaging agents, and drug delivery.
Biocompatible transition metal complexes dyes emitting in the near-infrared (NIR) region, are highly desirable in fluorescence imaging techniques. However, a high-performance mitochondria-specific labeling NIR probe with high photostability is still lacking. Herein we reported two NIR-emitting cationic iridium(iii) complexes [Ir(pbq-g)(N^N)]Cl (pbq-g = phenylbenzo[g]-quinoline; N^N = 2-(1-benzyl-1H-pyrazol-3-yl) pyridine (Ir1) and 2-(1-(naphthalen-1-ylmethyl)-1H-pyrazol-3-yl) pyridine (Ir2)). These two novel Ir(iii) complexes with different N^N ligands exhibited similar NIR emission with λ at 751 nm for Ir1 and 750 nm for Ir2 in PBS solution, with luminescence quantum yields of around 0.62 for Ir1 and 0.85 for Ir2. These two complexes showed high mitochondrial specificity, superior photostability, high resistance to the loss of the mitochondrial membrane potential and appreciable tolerance to environmental changes, allowing NIR imaging of mitochondrial morphological changes over long periods of time. These excellent photophysical and imaging properties made them promising NIR luminescent tags for applications in bioimaging.
Cu–graphite–Cu sandwich heat spreaders with high thermal conductance and low density present outstanding ability of heat dissipation, which have potential application in smart and wearable electronics cooling.
Metal–organic coordination polymers (CPs) have
attracted great research interest because they are easy to prepare,
porous, flexible in composition, and designable in structure. Their
applications in biosensor development, drug delivery, and catalysis
have been explored. Lanthanides and nucleotides can form interesting
CPs, although most previous works have focused on a single type of
metal ligand. In this work, we explored mixed nucleotides and studied
their DNA adsorption properties using fluorescently labeled oligonucleotides.
Adenosine monophosphate (AMP) and guanosine monophosphate (GMP) formed
negatively charged CP nanoparticles with most lanthanides, and thus
a salt was required to adsorb negatively charged DNA. DNA adsorption
was faster and reached a higher capacity with lighter lanthanides.
Desorption of pre-adsorbed DNA by inorganic phosphates, urea, proteins,
surfactants, and competing DNA was successively carried out. The results
suggested the importance of the DNA phosphate backbone, although hydrogen
bonding and DNA bases also contributed to adsorption. The AMP CPs
adsorbed DNA more strongly than the GMP ones, and using mixtures of
AMP and GMP, continuous tuning of DNA adsorption affinity was achieved.
Such CPs were also used as a sensor for DNA detection based on the
different affinities of single- and double-stranded DNA, and a detection
limit of 0.9 nM target DNA was achieved. Instead of tuning DNA adsorption
by varying the length and sequence of DNA, the composition of CPs
can also be controlled to achieve this goal.
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