Controlled Delivery and Photopatterning of Mechanical Properties in Polysaccharide Hydrogels Using Vanadium Coordination and Photochemistry.

Incorporation of the transition metal ion V(V) into hydrogels has been used to impart photoresponsive behavior, which was used to tune materials properties during light irradiation. The photoreaction in QHE-cellulose/agarose hydrogels coordinated with vanadium was evidenced by a clear color change of yellow to blue through a green intermediate. This color change was attributed to the reduction of V(V) to V(IV) as described in our previous work.

Harnessing Fe(III)-Carboxylate Photochemistry for Radical-Initiated Polymerization in Hydrogels.

Coordination of Fe(III) to carboxylates in polyuronic acid hydrogels was used to impart photochemical reactivity to polysaccharide-based hydrogels. This photochemical reaction was then used for light-initiated polymerization to create hydrogels with advanced mechanical and conductive properties by capturing the photogenerated radical with a monomer, either acrylamide, methyl methacrylate, or aniline. The photopolymerization of acrylamide using the Fe(III)-polyuronic acid was quantified in solution and the polymerization efficiency was determined under different conditions.

Photoactive siderophores: Structure, function and biology.

It is well known that bacteria and fungi have evolved sophisticated systems for acquiring the abundant but biologically inaccessible trace element iron. These systems are based on high affinity Fe(III)-specific binding compounds called siderophores which function to acquire, transport, and process this essential metal ion. Many hundreds of siderophores are now known and their numbers continue to grow.

Synthesis and crystal structure of -poly[[tetra-μ-acetato-copper(II)]-μ-6-eth-oxy- , -bis-[2-(pyridin-2-yl)eth-yl]-1,3,5-triazine-2,4-di-amine].

The title compound, [Cu(CHNO)(CHO)] , was obtained reaction of copper(II) acetate with the coordinating ligand, 6-eth-oxy- , -bis-[2-(pyridin-2-yl)eth-yl]-1,3,5-triazine-2,4-di-amine. The crystallized product adopts the monoclinic 2/ space group. The metal core exhibits a paddle-wheel structure typical for dicopper tetra-acetate units, with triazine and pyridyl nitro-gen atoms from different ligands coordinating to the two axial positions of the paddle wheel in an asymmetric manner.

Fe(III)-polyuronic acid photochemistry: radical chemistry in natural polysaccharide.

The photochemistry of Fe(III) coordinated to natural uronate-containing polysaccharides has been investigated quantitatively in aqueous solution. It is demonstrated that the photoreduction of the coordinated Fe(III) to Fe(II) and oxidative decarboxylation occurs in a variety of uronate-containing polysaccharides. The photochemistry of the Fe(III)-polyuronic acid system generated a radical species during the reaction which was studied using the spin trapping technique.

Nutrient Capture from Aqueous Waste and Photocontrolled Fertilizer Delivery to Tomato Plants Using Fe(III)-Polysaccharide Hydrogels.

Inexpensive and sustainable methods are needed to reclaim nutrients from agricultural waste solutions for use as a fertilizer while decreasing nutrient runoff. Fe(III)-polysaccharide hydrogels are able to flocculate solids and absorb nutrients in liquid animal waste from Confined Animal Feeding Operations (CAFOs). Fe(III)-alginate beads absorbed 0.

Reclaiming Phosphate from Waste Solutions with Fe(III)-Polysaccharide Hydrogel Beads for Photo-Controlled-Release Fertilizer.

Photoresponsive hydrogels from polysaccharides and Fe(III) were used as a new system to capture and release PO from waste solutions. Uptake of 0.6-1.

Generating Photonastic Work from Irradiated Dyes in Electrospun Nanofibrous Polymer Mats.

For solar-driven macroscopic motions, we assert that there is a local heating that facilitates large-scale deformations in anisotropic morphologic materials caused by thermal gradients. This report specifically identifies the fate of heat generation in photonastic materials and demonstrates how heat can perform work following excitation of a nonisomerizing dye. Utilizing the electrospinning technique, we have created a series of anisotropic nanofibrous polymer mats that comprise nonisomerizing dyes.

Restricted Photoinduced Conformational Change in the Cu(I) Complex for Sensing Mechanical Properties.

When designing photoresponsive materials, the impact of a polymer host matrix on the photophysical and photochemical properties of chromophores can be dramatic and advantageous for correlating macromolecular properties. Some compounds possess changes in their photophysical response with variation in the surrounding media (e.g.

Mössbauer Spectroscopic Characterization of Iron(III)-Polysaccharide Coordination Complexes: Photochemistry, Biological, and Photoresponsive Materials Implications.

While polycarboxylates and hydroxyl-acid complexes have long been known to be photoactive, simple carboxylate complexes which lack a significant LMCT band are not typically strongly photoactive. Hence, it was somewhat surprising that a series of reports demonstrated that materials synthesized from iron(III) and polysaccharides such as alginate (poly[guluronan-co-mannuronan]) or pectate (poly[galacturonan]) formed photoresponsive materials that convert from hydrogels to sols under the influence of visible light. These materials have numerous potential applications in areas such as photopatternable materials, materials for controlled drug delivery, and tissue engineering.

Photoresponsive Polysaccharide-Based Hydrogels with Tunable Mechanical Properties for Cartilage Tissue Engineering.

Photoresponsive hydrogels were obtained by coordination of alginate-acrylamide hybrid gels (AlgAam) with ferric ions. The photochemistry of Fe(III)-alginate was used to tune the chemical composition, mechanical properties, and microstructure of the materials upon visible light irradiation. The photochemical treatment also induced changes in the swelling properties and transport mechanism in the gels due to the changes in material composition and microstructure.

Changing Mechanical Strength in Cr(III)- Metallosupramolecular Polymers with Ligand Groups and Light Irradiation.

We have demonstrated the ability to control the mechanical properties of metallosupramolecular materials via choice of ligand binding group, as well as with external light irradiation. These photoresponsive Cr(III)-based materials were prepared from a series of modified hydrogenated poly(ethylene-co-butylene) polymers linked through metal-ligand interactions between a Cr(III) metal center and pyridyl ligand termini of the polymers. The introduction of these Cr(III)-pyridine bonds gave rise to new mechanical and optical properties of the polymer materials.

Light-controlled release of nitric oxide from solid polymer composite materials using visible and near infra-red light.

Photochemical Nitric oxide releasing composite materials (Photo-NORMs) were prepared using biocompatible polymers and the photochemical nitric oxide donor complex (CrONO). We have demonstrated nitric oxide (NO) release from the solid composites for extended (>30 hours) and controlled (20-100 pmoles s(-1)) durations after visible light irradiation. Quantitation of the efficiency of NO release from the composites shows that polymer gas permeability most dramatically affects the overall efficiency (QY) of photochemical NO release, where polymers with higher gas permeability have a higher QY of nitric oxide release.

Light-responsive iron(III)-polysaccharide coordination hydrogels for controlled delivery.

Visible-light responsive gels were prepared from two plant-origin polyuronic acids (PUAs), alginate and pectate, coordinated to Fe(III) ions. Comparative quantitative studies of the photochemistry of these systems revealed unexpected differences in the photoreactivity of the materials, depending on the polysaccharide and its composition. The roles that different functional groups play on the photochemistry of these biomolecules were also examined.

Plasmonic nanocrystal solar cells utilizing strongly confined radiation.

The ability of metal nanoparticles to concentrate light via the plasmon resonance represents a unique opportunity for funneling the solar energy in photovoltaic devices. The absorption enhancement in plasmonic solar cells is predicted to be particularly prominent when the size of metal features falls below 20 nm, causing the strong confinement of radiation modes. Unfortunately, the ultrashort lifetime of such near-field radiation makes harvesting the plasmon energy in small-diameter nanoparticles a challenging task.

Engineering bright sub-10-nm upconverting nanocrystals for single-molecule imaging.

Imaging at the single-molecule level reveals heterogeneities that are lost in ensemble imaging experiments, but an ongoing challenge is the development of luminescent probes with the photostability, brightness and continuous emission necessary for single-molecule microscopy. Lanthanide-doped upconverting nanoparticles overcome problems of photostability and continuous emission and their upconverted emission can be excited with near-infrared light at powers orders of magnitude lower than those required for conventional multiphoton probes. However, the brightness of upconverting nanoparticles has been limited by open questions about energy transfer and relaxation within individual nanocrystals and unavoidable tradeoffs between brightness and size.

Liposome encapsulation of a photochemical NO precursor for controlled nitric oxide release and simultaneous fluorescence imaging.

Described are photochemical studies of the nitric oxide precursors, trans-Cr(L)(ONO)(2)(+) (L = cyclam = 1,4,8,11-tetraazacyclotetradecane, CrONO, or L = mac = 5,7-dimethyl-6-anthracenylcyclam, mac-CrONO) encapsulated in phosphatidylcholine liposomes. The liposomes provide a means to maintain a localized high concentration of NO releasing complexes and are easily modified for in vivo targeting through self-assembly. Steady, controlled release of NO is seen after photolysis of the liposome-encapsulated CrONO as compared to the burst of NO release seen by the unencapsulated complex in oxygenated solutions.

Quantum dot photoluminescence quenching by Cr(III) complexes. Photosensitized reactions and evidence for a FRET mechanism.

Reported are quantitative studies of the energy transfer from water-soluble CdSe/ZnS and CdSeS/ZnS core/shell quantum dots (QDs) to the Cr(III) complexes trans-Cr(N(4))(X)(2)(+) (N(4) is a tetraazamacrocycle ligand, X(-) is CN(-), Cl(-), or ONO(-)) in aqueous solution. Variation of N(4), of X(-), and of the QD size and composition allows one to probe the relationship between the emission/absorption overlap integral parameter and the efficiency of the quenching of the QD photoluminescence (PL) by the chromium(III) complexes. Steady-state studies of the QD PL in the presence of different concentrations of trans-Cr(N(4))(X)(2)(+) indicate a clear correlation between quenching efficiency and the overlap integral largely consistent with the predicted behavior of a Förster resonance energy transfer (FRET)-type mechanism.

Combinatorial discovery of lanthanide-doped nanocrystals with spectrally pure upconverted emission.

Nanoparticles doped with lanthanide ions exhibit stable and visible luminescence under near-infrared excitation via a process known as upconversion, enabling long-duration, low-background biological imaging. However, the complex, overlapping emission spectra of lanthanide ions can hinder the quantitative imaging of samples labeled with multiple upconverting probes. Here, we use combinatorial screening of multiply doped NaYF(4) nanocrystals to identify a series of doubly and triply doped upconverting nanoparticles that exhibit narrow, spectrally pure emission spectra at various visible wavelengths.

Controlled synthesis and single-particle imaging of bright, sub-10 nm lanthanide-doped upconverting nanocrystals.

Phosphorescent nanocrystals that upconvert near-infrared light to emit at higher energies in the visible have shown promise as photostable, nonblinking, and background-free probes for biological imaging. However, synthetic control over upconverting nanocrystal size has been difficult, particularly for the brightest system, Yb(3+)- and Er(3+)-doped β-phase NaYF(4), for which there have been no reports of methods capable of producing sub-10 nm nanocrystals. Here we describe conditions for the controlled synthesis of protein-sized β-phase NaYF(4): 20% Yb(3+), 2% Er(3+) nanocrystals, from 4.

Photochemistry of trans-Cr(cyclam)(ONO)2+, a nitric oxide precursor.

Experimental and density functional theory (DFT) studies are described that are focused on outlining the reactivity of the known photochemical nitric oxide precursor trans-Cr(cyclam)(ONO)(2)(+) ("CrONO", cyclam = 1,4,8,11-tetrazacycltetradecane). Studies in both aerated and deaerated aqueous media are described as are the roles of both the oxidant O(2) and a reductant such as glutathione in trapping the apparent Cr(IV) photoreaction intermediate trans-Cr(cyclam)(O)(ONO)(+). Also reported and characterized structurally is the Cr(V) product of long-term photolysis in the absence of reducing agents, the trans-dioxo species [trans-Cr(cyclam)(O)(2)](ClO(4)).

Metal complexes as photochemical nitric oxide precursors: potential applications in the treatment of tumors.

The bioregulatory molecule NO plays key roles in cancer biology and has been implicated in both tumor growth and suppression. Furthermore, it is a gamma-radiation sensitizer that may enhance selective killing of neoplastic tissues. For these reasons, there is considerable interest in developing methods for NO delivery to specific physiological targets.

Nitric oxide photogeneration from trans-Cr(cyclam)(ONO)(2)(+) in a reducing environment. activation of soluble guanylyl cyclase and arterial vasorelaxation.

The chromium(III) nitrito complex trans-Cr(cyclam)(ONO)(2)(+) (1) is a very promising photochemical precursor for nitric oxide delivery to physiological targets. Here, we demonstrate that visible wavelength excitation of 1 in solutions containing thiol reductants such as the biological antioxidant glutathione (GSH) leads to permanent reaction even under anaerobic conditions, resulting in high quantum yield NO release. The nitric oxide formed under such conditions is sufficient, even at muM concentrations of 1 and using a low-intensity light source, to activate the enzyme soluble guanylyl cyclase (sGC).

Nanotoxicology: characterizing the scientific literature, 2000-2007.

Understanding the toxicity of nanomaterials and nano-enabled products is important for human and environmental health and safety as well as public acceptance. Assessing the state of knowledge about nanotoxicology is an important step in promoting comprehensive understanding of the health and environmental implications of these new materials. To this end, we employed bibliometric techniques to characterize the prevalence and distribution of the current scientific literature.