Daniel R. Talham

Persistent Photoinduced Magnetism in Heterostructures of Prussian Blue Analogues

Heterostructured ABA thin films consisting of two different Prussian blue analogues, where A is a ferromagnet and B is a photoinducible ferrimagnet, have been fabricated for the first time. This novel arrangement allows the magnetization to be decreased by irradiation with white light and significantly increases the ordering temperature of the photoinduced magnetism from 18 to 75 K.

Bimetallic cyanide-bridged coordination polymers as lithium ion cathode materials: core@shell nanoparticles with enhanced cyclability.

Prussian blue analogues (PBAs) have recently been proposed as electrode materials for low-cost, long-cycle-life, and high-power batteries. However, high-capacity bimetallic examples show poor cycle stability due to surface instabilities of the reduced states. The present work demonstrates that, relative to single-component materials, higher capacity and longer cycle stability are achieved when using Prussian blue analogue core@shell particle heterostructures as the cathode material for Li-ion storage. Particle heterostructures with a size dispersion centered at 210 nm composed of a high-capacity K(0.1)Cu[Fe(CN)(6)](0.7)·3.8H(2)O (CuFe-PBA) core and lower capacity but highly stable shell of K(0.1)Ni[Fe(CN)(6)](0.7)·4.1H(2)O have been prepared and characterized. The heterostructures lead to the coexistence of both high capacity and long cycle stability because the shell protects the otherwise reactive surface of the highly reduced state of the CuFe-PBA core. Furthermore, interfacial coupling to the shell suppresses a known structural phase transition in the CuFe-PBA core, providing further evidence of synergy between the core and shell. The structure and chemical state of the heterostructure during electrochemical cycling have been monitored with ex situ X-ray diffraction and X-ray absorption experiments and compared to the behavior of the individual components.

Magnetic Spin Ladder (C5H12N)2CuBr4: High Field Magnetization and Scaling Near Quantum Criticality

The magnetization, M(H< or =30 T,0.7< or =T< or =300 K), of (C5H12N)2CuBr4 has been used to identify this system as an S = 1/2 Heisenberg two-leg ladder in the strong-coupling limit, J( perpendicular) = 13.3 K and J( parallel) = 3.8 K, with H(c1) = 6.6 T and H(c2) = 14.6 T. An inflection point in M(H,T = 0.7 K) at half saturation, M(s)/2, is described by an effective XXZ chain. The data exhibit universal scaling behavior in the vicinity of H(c1) and H(c2), indicating that the system is near a quantum critical point.

Photoinduced Magnetism in Core/Shell Prussian Blue Analogue Heterostructures of KjNik[Cr(CN)6]l·nH2O with RbaCob[Fe(CN)6]c·mH2O

Core/shell and core/shell/shell particles comprised of the Prussian blue analogues K(j)Ni(k)[Cr(CN)(6)](l)·nH(2)O (A) and Rb(a)Co(b)[Fe(CN)(6)](c)·mH(2)O (B) have been prepared for the purpose of studying persistent photoinduced magnetization in the heterostructures. Synthetic procedures have been refined to allow controlled growth of relatively thick (50-100 nm) consecutive layers of the Prussian blue analogues while minimizing the mixing of materials at the interfaces. Through changes in the order in which the two components are added, particles with AB, ABA, BA, and BAB sequences have been prepared. The two Prussian blue analogues were chosen because B is photoswitchable, and A is ferromagnetic with a relatively high magnetic ordering temperature, ~70 K, although it is not known to exhibit photoinduced changes in its magnetic properties. Magnetization measurements on the heterostructured particles performed prior to irradiation show behavior characteristic of the individual components. On the other hand, after irradiation with visible light, the heterostructures undergo persistent photoinduced changes in magnetization associated with both the B and A analogues. The results suggest that structural changes in the photoactive B component distort the normally photoinactive A component, leading to a change in its magnetization.

Towards Zirconium Phosphonate-Based Microarrays for Probing DNA−Protein Interactions: Critical Influence of the Location of the Probe Anchoring Groups

Terminal phosphate groups on double-stranded DNA probes bind strongly to glass substrates coated with a zirconium phosphonate monolayer, and probes immobilized in this way as microarrays can be used to detect protein targets. The sensitivity of the microarray was shown to be enhanced by the use of a polyguanine segment ((G)n , n > or = 5) as a spacer between the phosphate linker and the protein interaction domain. More importantly, the presence of phosphate linkers on both ends of the dsDNA probes leads to significant enhancement of target capture. The relevant characteristics of the different probes when bound to the surface were determined, by the original use of a combination of surface characterization techniques (XPS, AFM, and Sarfus). In this context, the location of the phosphate linkers in the duplex probes was found to result in different probe surface coverage and presentation on the surface, which affect subsequent interactions with the target protein.

Lipids and Membranes in the Organic Matrix of Urinary Calcific Crystals and Stones

Abstract. The ultrastructure of the organic matrix of demineralized urinary stones was examined by standard transmission and scanning electron microscopy as well as after malachite green-glutaraldehyde fixation. Crystal ghosts of both calcium oxalate and calcium phosphate were made of amorphous material and were dispersed in a matrix containing amorphous, fibrillar, and membranous substances. Malachite green positive material was seen to be associated with the ghosts, as well as with the membranous and fibrillar components of the organic matrix. Calcium oxalate and calcium-phosphate crystals, induced in human urine in vitro were also found to be associated with an organic matrix containing lipids and proteins. It is suggested that the intimate association between crystals and lipids is a result of the involvement of cellular membranes in the nucleation of these crystals.

Assembly of Double-Hydrophilic Block Copolymers Triggered by Gadolinium Ions: New Colloidal MRI Contrast Agents.

Mixing double-hydrophilic block copolymers containing a poly(acrylic acid) block with gadolinium ions in water leads to the spontaneous formation of polymeric nanoparticles. With an average diameter near 20 nm, the nanoparticles are exceptionally stable, even after dilution and over a large range of pH and ionic strength. High magnetic relaxivities were measured in vitro for these biocompatible colloids, and in vivo magnetic resonance imaging on rats demonstrates the potential utility of such polymeric assemblies.

Size dependence of the photoinduced magnetism and long-range ordering in Prussian blue analogue nanoparticles of rubidium cobalt hexacyanoferrate

Nanoparticles of rubidium cobalt hexacyanoferrate (RbjCok[Fe(CN)6]l?nH2O) were synthesized using different concentrations of polyvinylpyrrolidone (PVP) to produce four different batches of particles with characteristic diameters ranging from 3 to 13?nm. Upon illumination with white light at 5?K, the magnetization of these particles increases. The long-range ferrimagnetic ordering temperatures and the coercive fields evolve with nanoparticle size. At 2?K, particles with diameters less than approximately 10?nm provide a Curie-like magnetic signal.

Bisphosphonate adaptors for specific protein binding on zirconium phosphonate-based microarrays.

Two bisphosphonate adaptors were designed to immobilize histidine-tagged proteins onto glass substrates coated with a zirconium phosphonate monolayer, allowing efficient and oriented immobilization of capture proteins, affitins directed to lysozyme, on a microarray format. These bifunctional adaptors contain two phosphonic acid anchors at one extremity and either one nitrilotriacetic acid (NTA) or two NTA groups at the other. The phosphonate groups provide a stable bond to the zirconium interface by multipoint attachment and allow high density of surface coverage of the linkers as revealed by X-ray photoelectron spectroscopy (XPS). Reversible high-density capture of histidine-tagged proteins is shown by real-time surface plasmon resonance enhanced ellipsometry and in a microarray format using fluorescence detection of AlexaFluor 647-labeled target protein. The detection sensitivity of the microarray for the target protein was below 1 nM, despite the monolayer arrangement of the probes, due to very low background staining, which allows high fluorescent signal-to-noise ratio. The performance of these Ni-NTA-modified zirconium phosphonate coated slides compared favorably to other types of microarray substrates, including slides with a nitrocellulose-based matrix, epoxide slides, and epoxide slides functionalized with Ni-NTA groups. This immobilization strategy has a large potential to fix any histidine-tagged proteins on zirconium or titanium ion surfaces.

Growth of calcium oxalate monohydrate at phospholipid Langmuir monolayers

Abstract Calcium oxalate monohydrate crystals have been nucleated from metastable solutions at Langmuir monolayers of the phospholipids dipalmitoylphosphatidylglycerol (DPPG), dipalmitoylphosphatidylserine and dipalmitoylphosphatidylcholine and the fatty acid arachidic acid. The phospholipid monolayers were used as model systems for domains of pure lipid in cellular media as part of investigations of their potential role in the nucleation of calcium oxalate in the urinary tract. Crystal formation was monitored at the air/water interface using Brewster angle microscopy and in transferred films using SEM and TEM. For each Langmuir monolayer, it was observed that nucleation is heterogeneous and is selective with respect to the orientation and morphology of the precipitated crystals with up to 90% of crystals growing with the ( 1 0 1 ) face oriented towards the monolayer interface. The selectivity is attributed to calcium binding at the lipid monolayer favoring formation of the calcium-rich ( 1 0 1 ) face. The behavior at each monolayer was similar, although a higher rate of crystal formation was observed at the anionic DPPG interface.