A library of neutral, hydrophobic reagents was synthesized for use as derivatizing agents in order to increase the ion abundance of N-linked glycans in electrospray ionization mass spectrometry (ESI MS). The glycans are derivatized via hydrazone formation and are shown to increase the ion abundance of a glycan standard more than 4-fold. Additionally, the data show that the systematic addition of hydrophobic surface area to the reagent increases the glycan ion abundance, a property that can be further exploited in the analysis of glycans. The results of this study will direct the future synthesis of hydrophobic reagents for glycan analysis using the correlation between hydrophobicity and theoretical non-polar surface area calculation to facilitate the development of an optimum tag for glycan derivatization. The compatibility and advantages of this method are demonstrated by cleaving and derivatizing N-linked glycans from human plasma proteins. The ESI-MS signal for the tagged glycans are shown to be significantly more abundant, and the detection of negatively charged sialylated glycans is enhanced.

The ability to track labeled cancer cells in vivo would allow researchers to study their distribution, growth, and metastatic potential within the intact organism. Magnetic resonance (MR) imaging is invaluable for tracking cancer cells in vivo as it benefits from high spatial resolution and the absence of ionizing radiation. However, many MR contrast agents (CAs) required to label cells either do not significantly accumulate in cells or are not biologically compatible for translational studies. We have developed carbon-based nanodiamond–gadolinium(III) aggregates (NDG) for MR imaging that demonstrated remarkable properties for cell tracking in vivo. First, NDG had high relaxivity independent of field strength, a finding unprecedented for gadolinium(III) [Gd(III)]–nanoparticle conjugates. Second, NDG demonstrated a 300-fold increase in the cellular delivery of Gd(III) compared to that of clinical Gd(III) chelates without sacrificing biocompatibility. Further, we were able to monitor the tumor growth of NDG-labeled flank tumors by T1- and T2-weighted MR imaging for 26 days in vivo, longer than was reported for other MR CAs or nuclear agents. Finally, by utilizing quantitative maps of relaxation times, we were able to describe tumor morphology and heterogeneity (corroborated by histological analysis), which would not be possible with competing molecular imaging modalities.

A homologous series of [2]rotaxanes, in which cyclobis(paraquat-p-phenylene) (CBPQT(4+)) serves as the ring component, while the dumbbell components all contain single 4,4'-bipyridinium (BIPY(2+)) units centrally located in the midst of oligomethylene chains of varying lengths, have been synthesized by taking advantage of radical templation and copper-free azide-alkyne 1,3-dipolar cycloadditions in the formation of their stoppers. Cyclic voltammetry, UV/vis spectroscopy, and mass spectrometry reveal that the BIPY(•+) radical cations in this series of [2]rotaxanes are stabilized against oxidation, both electrochemically and by atmospheric oxygen. The enforced proximity between the BIPY(2+) units in the ring and dumbbell components gives rise to enhanced Coulombic repulsion, destabilizing the ground-state co-conformations of the fully oxidized forms of these [2]rotaxanes. The smallest [2]rotaxane, with only three methylene groups on each side of its dumbbell component, is found to exist under ambient conditions in a monoradical state, a situation which does not persist in acetonitrile solution, at least in the case of its longer analogues. (1)H NMR spectroscopy reveals that the activation energy barriers to the shuttling of the CBPQT(4+) rings over the BIPY(2+) units in the dumbbells increase linearly with increasing oligomethylene chain lengths across the series of [2]rotaxanes. These findings provide a new way of producing highly stabilized BIPY(•+) radical cations and open up more opportunities to use stable organic radicals as building blocks for the construction of paramagnetic materials and conductive molecular electronic devices.

Actinium-225 (225Ac) is an excellent candidate for targeted radiotherapeutic applications for treating cancer, because of its 10-day half-life and emission of four high-energy α2+ particles. To harness and direct the energetic potential of actinium, strongly binding chelators that remain stable in vivo during biological targeting must be developed. Unfortunately, controlling chelation for actinium remains challenging. Actinium is the largest +3 cation on the periodic table and has a 6d05f0 electronic configuration, and its chemistry is relatively unexplored. Herein, we present theoretical work focused on improving the understanding of actinium bonding with macrocyclic chelating agents as a function of (1) macrocycle ring size, (2) the number and identity of metal binding functional groups, and (3) the length of the tether linking the metal binding functional group to the macrocyclic backbone. Actinium binding by these chelators is presented within the context of complexation with DOTA4–, the most relevant Ac3+ binding agent for contemporary radiopharmaceutical applications. The results enabled us to develop a new strategy for actinium chelator design. The approach is rooted in our identification that Ac3+–chelation chemistry is dominated by ionic bonding interactions and relies on (1) maximizing electrostatic interactions between the metal binding functional group and the Ac3+ cation and (2) minimizing electronic repulsion between negatively charged actinium binding functional groups. This insight will provide a foundation for future innovation in developing the next generation of multifunctional actinium chelators.

Our lab has developed a new series of self‐immolative MR agents for the rapid detection of enzyme activity in mouse models expressing β‐galactosidase (β‐gal). We investigated two molecular architectures to create agents that detect β‐gal activity by modulating the coordination of water to GdIII. The first is an intermolecular approach, wherein we designed several structural isomers to maximize coordination of endogenous carbonate ions. The second involves an intramolecular mechanism for q modulation. We incorporated a pendant coordinating carboxylate ligand with a 2, 4, 6, or 8 carbon linker to saturate ligand coordination to the GdIII ion. This renders the agent ineffective. We show that one agent in particular (6‐C pendant carboxylate) is an extremely effective MR reporter for the detection of enzyme activity in a mouse model expressing β‐gal.