Functional Grading Between Soft-Magnetic Fe-Co/Fe-Ni Alloys and the Effect on Magnetic and Microstructural Properties.

Producing soft magnetic alloys by additive manufacturing has the potential to overcome cracking and brittle fracture issues associated with conventional thermomechanical processing. Fe-Co alloys exhibit high magnetic saturation but low ductility that makes them difficult to process by commercial methods. Ni-Fe alloys have good ductility and high permeability in comparison to Fe-Co, but they suffer from low magnetic saturation. Functional grading between Fe-Co and Ni-Fe alloys through blown powder directed energy deposition can produce soft magnetic materials that combine and enhance properties beyond the strengths of the individual magnetic materials. This work focuses on the microstructure, crystal structure, and magnetic properties of functionally graded Fe49Co49V2/Ni80Fe16Mo4 coupons. The grading between the two materials is found to refine the microstructure, thereby improving the mechanical hardness without the use of a nonmagnetic element. Postbuild thermal treatments are found to recrystallize the microstructure and increase the grain size, leading to improved magnetic properties. Analysis of crystal structures provides an understanding of the solubility limits and phase equilibria between the BCC (Fe-Co) and FCC (Ni-Fe) structures. Success in functional grading of soft magnets may provide a pathway toward improving energy conversion efficiency through strategic combinations of high saturation and high strength materials.

Programmable Photoluminescence via Intrinsic and DNA-Fluorophore Association in a Mixed Cluster Heterometallic MOF.

A rapid and facile design strategy to create a highly complex optical tag with programmable, multimodal photoluminescent properties is described. This was achieved via intrinsic and DNA-fluorophore hidden signatures. As a first covert feature of the tag, an intricate novel heterometallic near-infrared (NIR)-emitting mesoporous metal-organic framework (MOF) was designed and synthesized. The material is constructed from two chemically distinct, homometallic hexanuclear clusters based on Nd and Yb. Uniquely, the Nd-based cluster is observed here for the first time in a MOF and consists of two staggered Nd µ3-oxo trimers. To generate controlled, multimodal, and tailorable emission with difficult to counterfeit features, the NIR-emissive MOF was post-synthetically modified via a fluorescent DNA oligo labeling design strategy. The surface attachment of several distinct fluorophores, including the simultaneous attachment of up to three distinct fluorescently labeled oligos was achieved, with excitation and emission properties across the visible spectrum (480-800 nm). The DNA inclusion as a secondary covert element in the tag was demonstrated via the detection of SYBR Gold dye association. Importantly, the approach implemented here serves as a rapid and tailorable way to encrypt distinct information in a facile and modular fashion and provides an innovative technology in the quest toward complex optical tags.

Encoding Multilayer Complexity in Anti-Counterfeiting Heterometallic MOF-Based Optical Tags.

Optical tags provide a way to quickly and unambiguously identify valuable assets. Current tag fluorophore options lack the tunability to allow combined methods of encoding in a single material. Herein we report a design strategy to encode multilayer complexity in a family of heterometallic rare-earth metal-organic frameworks based on highly connected nonanuclear clusters. To impart both intricacy and security, a synergistic approach was implemented resulting in both overt (visible) and covert (near-infrared, NIR) properties, with concomitant multi-emissive spectra and tunable luminescence lifetimes. Tag authentication is validated with a variety of orthogonal detection methodologies. Importantly, the effect induced by subtle compositional changes on intermetallic energy transfer, and thus on the resulting photophysical properties, is demonstrated. This strategy can be widely implemented to create a large library of highly complex, difficult-to-counterfeit optical tags.

Antibody Targeted Metal-Organic Frameworks for Bioimaging Applications.

We report on the availability and chemical utility of primary amines within metal-organic frameworks (MOFs) for cell targeting. Primary amine groups represent one of the most versatile chemical moieties for conjugation to biologically relevant molecules, including antibodies and enzymes. Specifically, we used two different chemical conjugations schemes, utilizing the amino functionality on the organic linker: first, carbodiimide chemistry was used to link the primary amine to available carboxyl groups on the protein neutravidin; second, sulfhydryl cross-linking chemistry was used via Traut's reagent scheme. Importantly, this is the first report that documents this methodology implemented with MOF systems. Finally, the ability of the EpCAM antibody targeted MOFs to bind to a human epithelial cell line (A549), a common target for imaging studies, was confirmed with confocal microscopy.

Insights into the solvent-assisted degradation of organophosphorus compounds by a Zr-based metal-organic framework.

The degradation of a chemical warfare agent simulant using a catalytically active Zr-based metal-organic framework (MOF) as a function of different solvent systems was investigated. Complementary molecular modelling studies indicate that the differences in the degradation rates are related to the increasing size in the nucleophile, which hinders the rotation of the product molecule during degradation. Methanol was identified as an appropriate solvent for non-aqueous degradation applications and demonstrated to support the MOF-based destruction of both sarin and soman.

Antibacterial Countermeasures via Metal-Organic Framework-Supported Sustained Therapeutic Release.

Long-term antimicrobial therapies are necessary to treat infections caused by virulent intracellular pathogens, including biothreat agents. Current treatment plans include injectable therapeutics given multiple times daily over a period for up to 8 weeks. Here, we present a metal-organic framework (MOF), zeolitic imidazolate framework-8 (ZIF-8), as a robust platform to support the sustained release of ceftazidime, an important antimicrobial agent for many critical bacterial infections. Detailed material characterization confirms the successful encapsulation of ceftazidime within the ZIF-8 matrix, indicating sustained drug release for up to a week. The antibacterial properties of ceftazidime@ZIF-8 particles were confirmed against Escherichia coli, chosen here as a representative of Gram-negative bacteria infection model in a proof-of-concept study. Further, we showed that this material system is compatible with macrophage and lung epithelial cell lines, relevant targets for antibacterial therapy for pulmonary and intracellular infections. A promising methodology to enhance the treatment of intracellular infections is to deliver the antibiotic cargo intracellularly. Importantly, this is the first study to unequivocally demonstrate direct MOF particle internalization using confocal microscopy via 3D reconstructions of z-stacks, taking advantage of the intrinsic emission properties of ZIF-8. This is an important development as it circumvents the need to use any staining dyes and addresses current methodology limitations concerning false impression of cargo uptake in the event of the carrier particle breakdown within biological media.

Self-Assembled Array of Tethered Manganese Oxide Nanoparticles for the Next Generation of Energy Storage.

Many challenges must be overcome in order to create reliable electrochemical energy storage devices with not only high energy but also high power densities. Gaps exist in both battery and supercapacitor technologies, with neither one satisfying the need for both large power and energy densities in a single device. To begin addressing these challenges (and others), we report a process to create a self-assembled array of electrochemically active nanoparticles bound directly to a current collector using extremely short (2 nm or less) conductive tethers. The tethered array of nanoparticles, MnO in this case, bound directly to a gold current collector via short conducting linkages eliminates the need for fillers, resulting in a material which achieves 99.9% active material by mass (excluding the current collector). This strategy is expected to be both scalable as well as effective for alternative tethers and metal oxide nanoparticles.

Infrared signature of micro-hydration in the organophosphate Sarin: an ab initio study.

The infrared (IR) spectra of micro-hydrated Sarin•(H2O)n clusters containing between one and four explicit waters have been studied using ab initio density functional theory (DFT) methods. The phosphate group P=O bond vibration region (∼1270 to 1290 cm(-1)) revealed the largest frequency variation with hydration, with a frequency red shift reflecting the direct hydrogen bond formation between the P=O of Sarin and water. Small variations to the P-F stretch (∼810 to 815 cm(-1)) and the C-O-P vibrational modes (∼995 to 1004 cm(-1)) showed that the water interactions with these functional groups were minor, and that the structures of Sarin were not extensively perturbed in the hydrated complexes. Increasing the number of explicit hydration waters produced only small vibrational changes in the lowest free energy complexes. These minor changes were consistent with a single water-phosphate hydrogen bond being the dominant structure, though a second water-phosphate hydrogen bond was observed in some complexes and was identified by an additional red shift of the P=O bond vibration. The H2O•H2O vibrational modes (∼3450 to 3660 cm(-1)) increased in complexity with higher hydration levels and reflect the extended hydrogen bonding networks formed between the explicit waters in the hydrated Sarin clusters. Graphical Abstract Ab initio studies of the infrared signature for micro-hydrated Sarin.