Simulation of Early Earth Hydrothermal Chimneys in a Thermal Gradient Environment.

Deep sea hydrothermal vents are self-organizing precipitates generated from geochemical disequilibria and have been proposed as a possible setting for the emergence of life. The growth of hydrothermal chimneys in a thermal gradient environment within an early Earth vent system was successfully simulated by using different hydrothermal simulants, such as sodium sulfide, which were injected into an early Earth ocean simulant containing dissolved ferrous iron. Moreover, an apparatus was developed to sufficiently cool the ocean simulant to near 0 °C in a condenser vessel immersed in a cold water bath while injecting a sulfide solution at hot to room temperatures, effectively creating an artificial chimney structure in a temperature gradient environment over a period of a few hours. Such experiments with different chemistries and variable temperature gradients resulted in a variety of morphologies in the chimney structure. The use of ocean and hydrothermal fluid simulants at room temperature resulted in vertical chimneys, whereas the combination of a hot hydrothermal fluid and cold ocean simulant inhibited the formation of robust chimney structures. The customizable 3D printed condenser created for this study acts as a jacketed reaction vessel that can be easily modified and used by different researchers. It will allow the careful control of injection rate and chemical composition of vent and ocean simulants, which should help accurately simulate prebiotic reactions in chimney systems with thermal gradients similar to those of natural systems.

U.S. Food and Drug Administration-Certified Food Dyes as Organocatalysts in the Visible Light-Promoted Chlorination of Aromatics and Heteroaromatics.

Seven FDA-certified food dyes have been investigated as organocatalysts. As a result, Fast Green FCF and Brilliant Blue FCF have been discovered as catalysts for the chlorination of a wide range of arenes and heteroarenes in moderate to excellent yields and high regioselectivity. Mechanistic investigations of the separate systems indicate that different modes of activation are in operation, with Fast Green FCF being a light-promoted photoredox catalyst that is facilitating a one-electron oxidation of N-chlorosuccinimide (NCS) and Brilliant Blue FCF serving as a chlorine-transfer catalyst in its sulfonphthalein form with 1,3-dichloro-5,5-dimethylhydantoin (DCDMH) as stoichiometric chlorine source. Dearomatization of naphthol and indole substrates was observed in some examples using the Brilliant Blue/DCDMH system.

Electrolysis Activation of Fused-Filament-Fabrication 3D-Printed Electrodes for Electrochemical and Spectroelectrochemical Analysis.

Following the expiration of the patents on fused-filament-fabrication (FFF), the availability and uses of this 3D-printing technology have exploded. Several recent reports describe how conductive composites can be used with FFF printers to generate 3D-printed electrodes (3DEs) for energy storage and electrochemical analysis. As printed materials, these electrodes have very high impedance values because of the high content of insulating thermoplastic required for FFF printers. To overcome this challenge, deposition of metals or activation with harsh chemicals has previously been employed. Here, a benign postprinting process was developed using the electrolysis of water to selectively remove the insulating thermoplastic (polylactic acid) via saponification. Optimization of the hydroxide-treatment process was found to reduce the impedance of 3DEs by 3 orders of magnitude in filaments from two manufacturers. This electrolysis-activation strategy offers a safe, accessible, and affordable means for improving the electrochemical performance of 3DEs. Here, the ability of these modified 3DEs to be used for electrochemical analysis and integrated into complex electrochemical cells is demonstrated.

Organic Dye-Catalyzed, Visible-Light Photoredox Bromination of Arenes and Heteroarenes Using N-Bromosuccinimide.

A variety of arenes and heteroarenes are brominated in good to excellent yields using N-bromosuccinimide (NBS) under mild and practical conditions. According to mechanistic investigations described within, the reaction is speculated to proceed via activation of NBS through a visible-light photoredox pathway utilizing erythrosine B as a photocatalyst. A photo-oxidative approach effectively amplifies the positive polarization on the bromine atom of the NBS reagent. This increase in the electrophilic nature of NBS results in drastically reduced reaction times and diversion from competing light-promoted reactive pathways.

3D Printed UV-Visible Cuvette Adapter for Low-Cost and Versatile Spectroscopic Experiments.

Ultraviolet-visible (UV-vis) spectroscopy represents one of the most popular analytical techniques in chemical research labs. A variety of vendors provide instruments that are suited for the analysis of liquid samples at moderate concentrations. However, to accommodate more specialized experiments, expensive accessories are required and often do not fit the specific needs of experimental scientists. In this work, we present a generalized adapter that can be 3D printed and used with existing spectrometers to enable a wide array of experiments to be performed. In the case of liquid samples, we provide a method for dramatically reducing the price of a quartz cuvette with minimal impact on performance. Through simple modification of the design, cuvettes with various path lengths can be prepared. Additionally, we illustrate the ability to turn any sample container into a working cuvette to simplify experimental protocols, prevent contamination risks, and further reduce costs. This strategy also enables gaseous and solid samples to be evaluated easily and reproducibly. Furthermore, we demonstrate how this concept can be extended to interface additional instrumentation with a commercial UV-vis spectrometer. All of the digital designs are provided under a creative commons license to enable other researchers to modify and adapt the designs for their unique experimental requirements.

Electrochemically Induced Transformations of Vanadium Dioxide Nanocrystals.

Vanadium dioxide (VO2) undergoes significant optical, electronic, and structural changes as it transforms between the low-temperature monoclinic and high-temperature rutile phases. Recently, alternative stimuli have been utilized to trigger insulator-to-metal transformations in VO2, including electrochemical gating. Here, we prepare and electrochemically reduce mesoporous films of VO2 nanocrystals, prepared from colloidally synthesized V2O3 nanocrystals that have been oxidatively annealed, in a three-electrode electrochemical cell. We observe a reversible transition between infrared transparent insulating phases and a darkened metallic phase by in situ visible-near-infrared spectroelectrochemistry and correlate these observations with structural and electronic changes monitored by X-ray absorption spectroscopy, X-ray diffraction, Raman spectroscopy, and conductivity measurements. An unexpected reversible transition from conductive, reduced monoclinic VO2 to an infrared-transparent insulating phase upon progressive electrochemical reduction is observed. This insulator-metal-insulator transition has not been reported in previous studies of electrochemically gated epitaxial VO2 films and is attributed to improved oxygen vacancy formation kinetics and diffusion due to the mesoporous nanocrystal film structure.

Construction of a Semiconductor-Biological Interface for Solar Energy Conversion: p-Doped Silicon/Photosystem I/Zinc Oxide.

The interface between photoactive biological materials with two distinct semiconducting electrodes is challenging both to develop and analyze. Building off of our previous work using films of photosystem I (PSI) on p-doped silicon, we have deposited a crystalline zinc oxide (ZnO) anode using confined-plume chemical deposition (CPCD). We demonstrate the ability of CPCD to deposit crystalline ZnO without damage to the PSI biomaterial. Using electrochemical techniques, we were able to probe this complex semiconductor-biological interface. Finally, as a proof of concept, a solid-state photovoltaic device consisting of p-doped silicon, PSI, ZnO, and ITO was constructed and evaluated.

Nanocomposite Architecture for Rapid, Spectrally-Selective Electrochromic Modulation of Solar Transmittance.

Two active electrochromic materials, vacancy-doped tungsten oxide (WO(3-x)) nanocrystals and amorphous niobium oxide (NbOx) glass are arranged into a mesostructured architecture. In a strategy applicable across electrochemical applications, the critical dimensions and interfacial connections in the nanocomposite are designed to optimize pathways for electrochemical charging and discharging. The result is an unprecedented optical range for modulation of visible and near-infrared solar radiation with rapid switching kinetics that indicate the WO(3-x) nanocrystal framework effectively pumps charge out of the normally sluggish NbOx glass. The material is durable for at least 2000 electrochemical cycles.

Electrochemical preparation of Photosystem I-polyaniline composite films for biohybrid solar energy conversion.

In this work, we report for the first time the entrapment of the biomolecular supercomplex Photosystem I (PSI) within a conductive polymer network of polyaniline via electrochemical copolymerization. Composite polymer-protein films were prepared on gold electrodes through potentiostatic electropolymerization from a single aqueous solution containing both aniline and PSI. This study demonstrates the controllable integration of large membrane proteins into rapidly prepared composite films, the entrapment of such proteins was observed through photoelectrochemical analysis. PSI's unique function as a highly efficient biomolecular photodiode generated a significant enhancement in photocurrent generation for the PSI-loaded polyaniline films, compared to pristine polyaniline films, and dropcast PSI films. A comprehensive study was then performed to separately evaluate film thickness and PSI concentration in the initial polymerization solution and their effects on the net photocurrent of this novel material. The best performing composite films were prepared with 0.1 µM PSI in the polymerization solution and deposited to a film thickness of 185 nm, resulting in an average photocurrent density of 5.7 µA cm(-2) with an efficiency of 0.005%. This photocurrent output represents an enhancement greater than 2-fold over bare polyaniline films and 200-fold over a traditional PSI multilayer film of comparable thickness.

Photoactive films of photosystem I on transparent reduced graphene oxide electrodes.

Photosystem I (PSI) is a photoactive electron-transport protein found in plants that participates in the process of photosynthesis. Because of PSI's abundance in nature and its efficiency with charge transfer and separation, there is a great interest in applying the protein in photoactive electrodes. Here, we developed a completely organic, transparent, conductive electrode using reduced graphene oxide (RGO) on which a multilayer of PSI could be deposited. The resulting photoactive electrode demonstrated current densities comparable to that of a gold electrode modified with a multilayer film of PSI and significantly higher than that of a graphene electrode modified with a monolayer film of PSI. The relatively large photocurrents produced by integrating PSI with RGO and using an opaque, organic mediator can be applied to the facile production of more economic solar energy conversion devices.

Photosystem I protein films at electrode surfaces for solar energy conversion.

Over the course of a few billion years, nature has developed extraordinary nanomaterials for the efficient conversion of solar energy into chemical energy. One of these materials, photosystem I (PSI), functions as a photodiode capable of generating a charge separation with nearly perfect quantum efficiency. Because of the favorable properties and natural abundance of PSI, researchers around the world have begun to study how this protein complex can be integrated into modern solar energy conversion devices. This feature article describes some of the recent materials and methods that have led to dramatic improvements (over several orders of magnitude) in the photocurrents and photovoltages of biohybrid electrodes based on PSI, with an emphasis on the research activities in our laboratory.

Photosystem I on graphene as a highly transparent, photoactive electrode.

We report the fabrication of a hybrid light-harvesting electrode consisting of photosystem I (PSI) proteins extracted from spinach and adsorbed as a monolayer onto electrically contacted, large-area graphene. The transparency of graphene supports the choice of an opaque mediator at elevated concentrations. For example, we report a photocurrent of 550 nA/cm(2) from a monolayer of PSI on graphene in the presence of 20 mM methylene blue, which yields an opaque blue solution. The PSI-modified graphene electrode has a total thickness of less than 10 nm and demonstrates photoactivity that is an order of magnitude larger than that for unmodified graphene, establishing the feasibility of conjoining these nanomaterials as potential constructs in next-generation photovoltaic devices.

Enhanced photocurrents of photosystem I films on p-doped silicon.

Tuning the Fermi energy of silicon through doping leads to alignment of silicon bands with the redox active sites of photosystem I. Integrating photosystem I films with p-doped silicon results in the highest reported photocurrent enhancement for a biohybrid electrode based on photosystem I.

Photoreduction of catalytic platinum particles using immobilized multilayers of Photosystem I.

Using the abundance of available electrons generated by immobilized multilayers of the photoactive protein complex Photosystem I (PSI), we have photoreduced platinum particles that are catalytically active for the H(2)/H(+) redox couple. The resulting platinized PSI films were optimized using electrochemical measurements and then characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and scanning electrochemical microscopy (SECM). These results demonstrate a novel method for generating immobilized platinum catalysts that are readily available on the surface of a photoactive PSI multilayer.

Microwave synthesis of mixed ligand diimine-thiosemicarbazone complexes of ruthenium(II): biophysical reactivity and cytotoxicity.

A novel microwave-assisted synthetic method has been used to synthesise a series of mixed ligand ruthenium(II) compounds containing diimine as well as bidentate thiosemicarbazone ligands. The compounds contain the diimine 1,10-phenanthroline (phen) or 2,2'-bipyridine (bpy) and the thiosemicarbazone is derived from 9-anthraldehyde. Based on elemental analyses and spectroscopic data, the compounds are best formulated as [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) and [(phen)(2)Ru(thiosemicarbazone)](PF(6))(2) where thiosemicarbazone = 9-anthraldehydethiosemicarbazone, 9-anthraldehyde-N(4)-methylthiosemicarbazone, and 9-anthraldehyde-N(4)-ethylthiosemicarbazone. Fluorescence competition studies with ethidium bromide, along with viscometric measurements suggests that the complexes bind calf thymus DNA (CTDNA) relatively strongly via an intercalative mode possibly involving the aromatic rings of the diimine ligands. The complexes show good cytotoxic profiles against MCF-7 and MDA-MB-231 (breast adenocarcinoma) as well as HCT 116 and HT-29 (colorectal carcinoma) cell lines.

Organometallic ruthenium complexes with thiosemicarbazone ligands: Synthesis, structure and cytotoxicity of [(eta-p-cymene)Ru(NS)Cl] (NS = 9-anthraldehyde thiosemicarbazones).

A series of half-sandwich arene-ruthenium complexes of the type [(eta(6)-p-cymene) Ru(thiosemicarbazone)Cl](+) have been synthesized and their biological activity investigated. The first structurally characterized arene-ruthenium half-sandwich complex with a thiosemicarbazone ligand is reported.