Laboratory Evolution of Metalloid Reductase Substrate Recognition and Nanoparticle Product Size.

Glutathione reductase-like metalloid reductase (GRLMR) is an enzyme that reduces selenodiglutathione (GS-Se-SG), forming zerovalent Se nanoparticles (SeNPs). Error-prone polymerase chain reaction was used to create a library of ∼10,000 GRLMR variants. The library was expressed in BL21 in liquid culture with 50 mM of SeO present, under the hypothesis that the enzyme variants with improved GS-Se-SG reduction kinetics would emerge.

Chiral and Achiral Crystal Structures of Au (PET) Reveal Effects of Ligand Rotational Isomerization on Optoelectronic Properties.

The crystal structures of 4 ligand-rotational isomers of Au (PET) are presented. Two new ligand-rotational isomers are revealed, and two higher-quality structures (allowing complete solution of the ligand shell) of previously solved Au (PET) clusters are also presented. One of the structures lacks an inversion center, making it the first chiral Au (SR) structure solved.

Coherent Vibrational Dynamics of Au(SCH) Nanoclusters.

The coherent vibrational dynamics of Au(SCH), obtained from femtosecond time-resolved transient absorption spectroscopy, are described. Two acoustic modes were identified and assigned, including 2.0 THz breathing and 0.

Cloneable inorganic nanoparticles.

When a defined protein/peptide (or combinations thereof) control and define the synthesis of an inorganic nanoparticle, the result is a cloneable NanoParticle (cNP). This is because the protein sequence/structure/function is encoded in DNA, and therefore the physicochemical properties of the nanoparticle are also encoded in DNA. Thus the cloneable nanoparticle paradigm can be considered as an extension of the central dogma of molecular biology ( DNA → mRNA → protein → cNP); modifications to the DNA encoding a cNP can modify the resulting properties of the cNP.

The Evolution from Superatom- to Plasmon-Mediated Magnetic Circular Dichroism in Colloidal Metal Nanoparticles Spanning the Nonmetallic to Metallic Limits.

The magneto-optical absorption properties of colloidal metal nanoclusters spanning nonmetallic to metallic regimes were examined using variable-temperature variable-field magnetic circular dichroism (VTVH-MCD) spectroscopy. Charge neutral Au(SCH) exhibited MCD spectra dominated by Faraday C-terms, consistent with expectations for a nonmetallic paramagnetic nanocluster. This response is reconciled by the open-shell superatom configuration of Au(SCH).

An ultrastable thiolate/diglyme ligated cluster: Au(PET)(DG).

The synthesis and characterization of an Au(PET)(DG) (PET = phenylethane thiol; DG = diglyme) cluster is reported. Mass spectrometry reveals this as the first diglyme ligated cluster where diglyme ligands survive ionization into the gas phase. Thermal analysis shows the cluster degrades at 156 °C, whereas the similar Au(PET) cluster degrades at 125 °C, representing markedly increased thermal stability.

Size-Scalable Near-Infrared Photoluminescence in Gold Monolayer Protected Clusters.

Near-infrared photoluminescence of a series of three gold monolayer protected clusters (MPCs) with volumes spanning 50-200 Å was studied by using variable-temperature photoluminescence (VT-PL) spectroscopy. The three MPCs, which included Au(SCH)-diglyme, Au(SCH), and Au(SCH), all exhibited temperature-dependent intensities that reflected a few-millielectronvolt energy gap that separated bright emissive and dark nonradiative electronic states. All clusters showed increased PL intensities upon raising the sample temperature from 4.

Radiofrequency remote control of thermolysin activity.

The majority of biological processes are regulated by enzymes, precise control over specific enzymes could create the potential for controlling cellular processes remotely. We show that the thermophilic enzyme thermolysin can be remotely activated in 17.76 MHz radiofrequency (RF) fields when covalently attached to 6.

Identification of a TeO32- reductase/mycothione reductase from Rhodococcus erythropolis PR4.

A Rhodococcus erythropolis bacterium that tolerates normally lethal concentrations of Fe(II), Cu(II), AsO32-, SeO32-, TeO32-, Cd(II) and Zn(II) was identified from an environmental isolate. In characterizing the molecular basis for metal tolerance, a mycothione reductase (Mtr) with remarkable selectivity for TeO32- reduction over SeO32- was identified. In equimolar concentrations of TeO32- and SeO32-, the enzymatic product contains a 7-fold excess of Te.

Observable but Not Isolable: The RhAu (PET) Nanocluster.

The synthesis and characterization of RhAu (PET) (PET = 2-phenylethanethiol) is described. The cluster is cosynthesized with Au (PET) and rhodium thiolates in a coreduction of RhCl , HAuCl , and PET. Rapid decomposition of RhAu (PET) occurs when purified from the other reaction products, precluding the study of isolated cluster.

Metalloid Reductase Activity Modified by a Fused Se Binding Peptide.

A selenium nanoparticle binding peptide was isolated from a phage display library and genetically fused to a metalloid reductase that reduces selenite (SeO) to a Se nanoparticle (SeNP) form. The fusion of the Se binding peptide to the metalloid reductase regulates the size of the resulting SeNP to ∼35 nm average diameter, where without the peptide, SeNPs grow to micron sized polydisperse precipitates. The SeNP product remains associated with the enzyme/peptide fusion.

Acetylide-for-thiolate and thiolate-for-acetylide exchange on gold nanoclusters.

Acetylide-protected gold nanoclusters represent a recently described class of nanocluster compounds that are computationally predicted to be more stable than well-studied thiolate-protected clusters. Ligand exchange of thiolates-for-acetylides on these clusters as well as the reverse reaction are so-far unknown. Such reactions can inform a practical understanding of stability and other differences between thiolate- and acetylide-protected gold clusters.

Superatom Paramagnetism in Au(SR) Oxidation States.

Gold nanoclusters show distinctive magnetic properties and electronic structure. Nanoclusters of sufficiently small size restructure geometrically to stabilize electronically (e.g.

Cluster-mining: an approach for determining core structures of metallic nanoparticles from atomic pair distribution function data.

A novel approach for finding and evaluating structural models of small metallic nanoparticles is presented. Rather than fitting a single model with many degrees of freedom, libraries of clusters from multiple structural motifs are built algorithmically and individually refined against experimental pair distribution functions. Each cluster fit is highly constrained.

Enzyme-Catalyzed Synthesis of Temporally and Spatially Distinct CdSe Quantum Dots in Biological Backgrounds.

The cellular machinery of metal metabolism is capable of making a wide range of inorganic nanoparticles and quantum dots. Individual enzymes from these metabolic pathways are being identified with metal reducing activity, and some have been isolated for particle formation and labeling. We previously identified a glutathione reductase like metalloid reductase (GRLMR) from stanleyae with a high affinity for the bioavailable selenium thiolate selenodiglutatione, and exhibiting NADPH-dependent reduction of selenodiglutathione to Se(0); initiating the growth of pure selenium metal nanoparticles.

Superatom spin-state dynamics of structurally precise metal monolayer-protected clusters (MPCs).

Electronic spin-state dynamics were studied for a series of Au(SCH) and AuPd(SCH) monolayer-protected clusters (MPCs) prepared in a series of oxidation states, q, including q = -1, 0, +1. These clusters were chosen for study because Au(SCH) is a closed-shell superatomic cluster, but Au(SCH) is an open-shell (7-electron) system; Au(SCH) and PdAu(SCH) are isoelectronic (6-electron) closed-shell systems. Carrier dynamics for electronic fine structure spin states were isolated using femtosecond time-resolved circularly polarized transient-absorption spectroscopy (fs-CPTA).

Low-Temperature Magnetism in Nanoscale Gold Revealed through Variable-Temperature Magnetic Circular Dichroism Spectroscopy.

The low-temperature (0.35-4.2 K) steady-state electronic absorption of the monolayer-protected cluster (MPC) Au( pMBA) was studied using magnetic circular dichroism (MCD) spectroscopy to investigate previously reported low-temperature (<50 K) magnetism in d nanogold systems.

Metalloid Reductase of Stanleyae Conveys Nanoparticle Mediated Metalloid Tolerance.

A glutathione reductase (GSHR)-like enzyme in stanleyae was previously implicated as underlying the bacterium's remarkable SeO tolerance. Herein, this enzyme is sequenced, recombinantly expressed, and fully characterized. The enzyme is highly adapted for selenodiglutathione substrates ( = 336 μM) compared to oxidized glutathione ( = 8.

Regiochemistry of Thiolate for Selenolate Ligand Exchange on Gold Clusters.

Ligand exchange is a fundamental reaction of metal nanoparticles. Multiple symmetry and kinetic exchange environments are observed for thiolate protected gold nanoparticles, but the correlation between these is unclear. Structural study of ligand exchange on chalcogenide passivated gold clusters has so-far revealed the locations of 10% or fewer of incoming ligands.

Electrophoretic Mechanism of Au(SR) Heating in Radiofrequency Fields.

Gold nanoparticles in radiofrequency (RF) fields have been observed to heat. There is some debate over the mechanism of heating. Au(SR) in RF is studied for the mechanistic insights obtainable from precise synthetic control over exact charge, size, and spin for this nanoparticle.

Adsorption-Coupled Diffusion of Gold Nanoclusters within a Large-Pore Protein Crystal Scaffold.

Large-pore protein crystals (LPCs) are ordered biologically derived nanoporous materials exhibiting pore diameters greater than 8 nm. These substantial pores distinguish LPCs from typical nanoporous scaffolds, enabling engineered LPC materials to readily uptake, immobilize, and release macromolecular guests. In this study, macromolecular transport within an LPC environment was experimentally and computationally investigated by studying adsorption-coupled diffusion of Au(glutathione) nanoclusters within a cross-linked LPC scaffold via time-lapse confocal microscopy, bulk equilibrium adsorption, and hindered diffusion simulation.

Composition-dependent electronic energy relaxation dynamics of metal domains as revealed by bimetallic AuAg(SCH) monolayer-protected clusters.

We examined the electronic relaxation dynamics for mono and bimetallic AuAg(SCH) monolayer-protected clusters (MPCs) using femtosecond time-resolved transient extinction spectroscopy. MPCs provide compositionally well-defined model systems for structure-specific determination of nanoscale electronic properties. Based on pulse-energy-dependent transient extinction data, we quantified electron-phonon coupling constants for three distinct AuAg(SCH) MPC samples, where x = 0, 0 < x < 30, and x ∼ 30, as G = (1.

Polymorphism in magic-sized Au144(SR)60 clusters.

Ultra-small, magic-sized metal nanoclusters represent an important new class of materials with properties between molecules and particles. However, their small size challenges the conventional methods for structure characterization. Here we present the structure of ultra-stable Au144(SR)60 magic-sized nanoclusters obtained from atomic pair distribution function analysis of X-ray powder diffraction data.

Gold nanoparticle capture within protein crystal scaffolds.

DNA assemblies have been used to organize inorganic nanoparticles into 3D arrays, with emergent properties arising as a result of nanoparticle spacing and geometry. We report here the use of engineered protein crystals as an alternative approach to biologically mediated assembly of inorganic nanoparticles. The protein crystal's 13 nm diameter pores result in an 80% solvent content and display hexahistidine sequences on their interior.