Nuwan Kothalawala

Ag44(SR)304−: a silver–thiolate superatom complex

Intensely and broadly absorbing nanoparticles (IBANs) of silver protected by arylthiolates were recently synthesized and showed unique optical properties, yet question of their dispersity and their molecular formulas remained. Here IBANs are identified as a superatom complex with a molecular formula of Ag(44)(SR)(30)(4-) and an electron count of 18. This molecular character is shared by IBANs protected by 4-fluorothiophenol or 2-naphthalenethiol. The molecular formula and purity is determined by mass spectrometry and confirmed by sedimentation velocity-analytical ultracentrifugation. The data also give preliminary indications of a unique structure and environment for Ag(44)(SR)(30)(4-).

Neat and Complete: Thiolate-Ligand Exchange on a Silver Molecular Nanoparticle

Atomically precise thiolate-protected noble metal molecular nanoparticles are a promising class of model nanomaterials for catalysis, optoelectronics, and the bottom-up assembly of true molecular crystals. However, these applications have not fully materialized due to a lack of ligand exchange strategies that add functionality, but preserve the properties of these remarkable particles. Here we present a method for the rapid (<30 s) and complete thiolate-for-thiolate exchange of the highly sought after silver molecular nanoparticle [Ag44(SR)30](-4). Only by using this method were we able to preserve the precise nature of the particles and simultaneously replace the native ligands with ligands containing a variety of functional groups. Crucially, as a result of our method we were able to process the particles into smooth thin films, paving the way for their integration into solution-processed devices.

A scalable synthesis of highly stable and water dispersible Ag44(SR)30 nanoclusters

We report the synthesis of atomically monodisperse thiol-protected silver nanoclusters [Ag44(SR)30 ]m, (SR = 5-mercapto-2-nitrobenzoic acid) in which the product nanocluster is highly stable in contrast to previous preparation methods. The method is one-pot, scalable, and produces nanoclusters that are stable in aqueous solution for at least 9 months at room temperature under ambient conditions, with very little degradation to their unique UV-Vis optical absorption spectrum. The composition, size, and monodispersity were determined by electrospray ionization mass spectrometry and analytical ultracentrifugation. The produced nanoclusters are likely to be in a superatom charge-state of m = 4−, due to the fact that their optical absorption spectrum shares most of the unique features of the intense and broadly absorbing nanoparticles identified as [Ag44(SR)30]4− by Harkness et al. (Nanoscale, 2012, 4, 4269). A protocol to transfer the nanoclusters to organic solvents is also described. Using the disperse nanoclusters in organic media, we fabricated solid-state films of [Ag44(SR)30]m that retained all the distinct features of the optical absorption spectrum of the nanoclusters in solution. The films were studied by X-ray diffraction and photoelectron spectroscopy in order to investigate their crystallinity, atomic composition and valence band structure. The stability, scalability, and the film fabrication method demonstrated in this work pave the way towards the crystallization of [Ag44(SR)30]m and its full structural determination by single crystal X-ray diffraction. Moreover, due to their unique and attractive optical properties with multiple optical transitions, we anticipate these clusters to find practical applications in light-harvesting, such as photovoltaics and photocatalysis, which have been hindered so far by the instability of previous generations of the cluster.

Au(144-x)Pd(x)(SR)60 nanomolecules.

Au144-xPdx(SR)60 alloy nanomolecules were synthesized and characterized by ESI mass spectrometry to atomic precision. The number of Pd atoms can be varied by changing the incoming metal ratio and plateaus at 7 Pd atoms. Based on the proposed 3-shell structure of Au144(SR)60, we hypothesize that the Pd atoms are selectively incorporated into the central Au12 icosahedral core.

Temperature-responsive properties of poly(N-vinylcaprolactam) multilayer hydrogels in the presence of Hofmeister anions

We report on the effect of Hofmeister anions on the temperature-induced volume transitions and optical responses of ultrathin hydrogels of poly(N-vinylcaprolactam) (PVCL). The hydrogels were produced by glutaraldehyde-assisted cross-linking of hydrogen-bonded multilayers of poly(N-vinylcaprolactam)-co-(aminopropyl)methacrylamide) and poly(methacrylic acid). We found that swelling and temperature-induced shrinkage of PVCL hydrogels were suppressed in the order SO42?? >?H2PO4?? >?Cl?, following the Hofmeister series. In contrast, I? increased hydrogel swelling but suppressed thermal response. A layer of glutathione?stabilized gold nanoparticles was introduced within the PVCL hydrogel to initiate an optical response in the presence of anions. We found the signal intensity of (PVCL)81-Au hydrogels and the plasmon band position to be largely controlled by ion type and concentration when the temperature reversibly changed from 20 ?C to 50 ?C. The band consistently shifted to lower wavelengths with an increase in chloride concentration. In contrast, a red shift was observed in the iodide solutions with increasing salt concentration; an exception to this was for the 0.1 M solution which resulted in a blue shift. We believe that our findings provide new prospects for understanding the effect of Hofmeister anions on ultrathin non-ionic polymer networks. In addition, the (PVCL)81-Au hybrid hydrogels afford a clear and fast optical monitoring of hydrogel temperature-triggered response at varied ion concentrations.

Enhanced single molecule mass spectrometry via charged metallic clusters.

Nanopore sensing is a label-free method for characterizing water-soluble molecules. The ability to accurately identify and characterize an analyte depends on the residence time of the molecule within the pore. It is shown here that when a Au25(SG)18 metallic cluster is bound to an α-hemolysin (αHL) nanopore, the mean residence time of polyethylene glycol (PEG) within the pore is increased by over 1 order of magnitude. This leads to an increase in the range of detectable PEG sizes and improves the peak resolution within the PEG-induced current blockade distribution. A model describing the relationship between the analyte residence time and the width of the peaks in the current blockade distribution is included. Finally, evidence is presented that shows the Coulombic interaction between the charged analyte and cluster plays an important role in the residence time enhancement, which suggests the cluster-based approach could be used to increase the residence time of a wide variety of charged analyte molecules.

An analysis of the sponge Acanthostrongylophora igens' microbiome yields an actinomycete that produces the natural product manzamine A

Sponges have generated significant interest as a source of bioactive and elaborate secondary metabolites that hold promise for the development of novel therapeutics for the control of an array of human diseases. However, research and development of marine natural products can often be hampered by the difficulty associated with obtaining a stable and sustainable production source. Herein we report the first successful characterization and utilization of the microbiome of a marine invertebrate to identify a sustainable production source for an important natural product scaffold. Through molecular-microbial community analysis, optimization of fermentation conditions and MALDI-MS imaging, we provide the first report of a sponge-associated bacterium (Micromonospora sp.) that produces the manzamine class of antimalarials from the Indo-Pacific sponge Acanthostrongylophora ingens (Thiele, 1899) (Class Demospongiae, Order Haplosclerida, Family Petrosiidae). These findings suggest that a general strategy of analysis of the macroorganisms microbiome could significantly transform the field of natural products drug discovery by gaining access to not only novel drug leads, but the potential for sustainable production sources and biosynthetic genes at the same time.

Single Molecule Nanopore Spectrometry for Peptide Detection

Sensing and characterization of water-soluble peptides is of critical importance in a wide variety of bioapplications. Single molecule nanopore spectrometry (SMNS) is based on the idea that one can use biological protein nanopores to resolve different sized molecules down to limits set by the blockade duration and noise. Previous work has shown that this enables discrimination between polyethylene glycol (PEG) molecules that differ by a single monomer unit. This paper describes efforts to extend SMNS to a variety of biologically relevant, water-soluble peptides. We describe the use of Au25(SG)18 clusters, previously shown to improve PEG detection, to increase the on- and off-rate of peptides to the pore. In addition, we study the role that fluctuations play in the single molecule nanopore spectrometry (SMNS) methodology and show that modifying solution conditions to increase peptide flexibility (via pH or chaotropic salt) leads to a nearly 2-fold reduction in the current blockade fluctuations and a corresponding narrowing of the peaks in the blockade distributions. Finally, a model is presented that connects the current blockade depths to the mass of the peptides, which shows that our enhanced SMNS detection improves the mass resolution of the nanopore sensor more than 2-fold for the largest cationic peptides studied.