Synthesis of Chiral 1,2-Amino Alcohol-Containing Compounds Utilizing Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Unprotected α-Ketoamines

Herein, we disclose a facile synthetic strategy to access an important class of drug molecules that contain chiral 1,2-amino alcohol functionality utilizing highly effective ruthenium-catalyzed asymmetric transfer hydrogenation of unprotected α-ketoamines. Recently, the COVID-19 pandemic has caused a crisis of shortage of many important drugs, especially norepinephrine and epinephrine, for the treatment of anaphylaxis and hypotension because of the increased demand. Unfortunately, the existing technologies are not fulfilling the worldwide requirement due to the existing lengthy synthetic protocols that require additional protection and deprotection steps. We identified a facile synthetic protocol via a highly enantioselective one-step process for epinephrine and a two-step process for norepinephrine starting from unprotected α-ketoamines 1b and 1a, respectively. This newly developed enantioselective ruthenium-catalyzed asymmetric transfer hydrogenation was extended to the synthesis of many 1,2-amino alcohol-containing drug molecules such as phenylephrine, denopamine, norbudrine, and levisoprenaline, with enantioselectivities of >99% ee and high isolated yields.

Design and Discovery of Water-Soluble Benzooxaphosphole-Based Ligands for Hindered Suzuki-Miyaura Coupling Reactions with Low Catalyst Load

We report a new class of highly effective, benzooxaphosphole-based, water-soluble ligands in the application of Suzuki-Miyaura cross-coupling reactions for sterically hindered substrates in aqueous media. The catalytic activities of the coupling reactions were greatly enhanced by the addition of catalytic amounts of organic phase transfer reagents, such as tetraglyme and tetrabutylammonium bromide. The optimized general protocol can be conducted with a low catalyst load, thereby providing a practical solution for these reactions. The viability of this new Suzuki-Miyaura protocol was demonstrated with various substrates to generate important building blocks, including heterocycles, for the synthesis of biologically active compounds.

Electrochemical Gelation of Metal Chalcogenide Quantum Dots: Applications in Gas Sensing and Photocatalysis

ConspectusMetal chalcogenide quantum dots (QDs) are prized for their unique and functional properties, associated with both intrinsic (quantum confinement) and extrinsic (high surface area) effects, as dictated by their size, shape, and surface characteristics. Thus, they have considerable promise for diverse applications, including energy conversion (thermoelectrics and photovoltaics), photocatalysis, and sensing. QD gels are macroscopic porous structures consisting of interconnected QDs and pore networks in which the pores may be filled with solvent (i.e., wet gels) or air (i.e., aerogels). QD gels are unique because they can be prepared as macroscale objects while fully retaining the size-specific quantum-confined properties of the initial QD building blocks. The extensive porosity of the gels also ensures that each QD in the gel network is accessible to the ambient, leading to high performance in applications that require high surface areas, such as (photo)catalysis and sensing.Metal chalcogenide QD gels are conventionally prepared by chemical approaches. We recently expanded the toolbox for QD gel synthesis by developing electrochemical gelation methods. Relative to conventional chemical oxidation approaches, electrochemical assembly of QDs (1) enables the use of two additional levers for tuning the QD assembly process and gel structure: electrode material and potential, and (2) allows direct gel formation on device substrates to simplify device fabrication and improve reproducibility. We have discovered two distinct electrochemical gelation methods, each of which enables the direct writing of gels on an active electrode surface or the formation of free-standing monoliths. Oxidative electrogelation of QDs leads to assemblies bridged by dichalcogenide (covalent) linkers, whereas metal-mediated electrogelation proceeds via electrodissolution of active metal electrodes to produce free ions that link QDs by binding to pendant carboxylate functionalities on surface ligands (non-covalent linkers). We further demonstrated that the electrogel composition produced from the covalent assembly could be modified by controlled ion exchange to form single-ion decorated bimetallic QD gels, a new category of materials. The QD gels exhibit unprecedented performance for NO₂ gas sensing and unique photocatalytic reactivities (e.g., the "cyano dance" isomerization and the reductive ring-opening arylation). The chemistry unveiled during the development of electrochemical gelation pathways for QDs and their post-modification has broad implications for guiding the design of new nanoparticle assembly strategies and QD gel-based gas sensors and catalysts.

Photoexcited NO2 Enables Accelerated Response and Recovery Kinetics in Light-Activated NO2 Gas Sensing

Slow response and recovery kinetics is a major challenge for practical room-temperature NO₂ gas sensing. Here, we report the use of visible light illumination to significantly shorten the response and recovery times of a PbSe quantum dot (QD) gel sensor by 21% (to 27 s) and 63% (to 102 s), respectively. When combined with its high response (0.04%/ppb) and ultralow limit of detection (3 ppb), the reduction in response and recovery time makes the PbSe QD gel sensor among the best p-type room-temperature NO₂ sensors reported to date. A combined experimental and theoretical investigation reveals that the accelerated response and recovery time is primarily due to photoexcitation of NO₂ gaseous molecules and adsorbed NO₂ on the gel surface, rather than the excitation of the semiconductor sensing material, as suggested by the currently prevailing light-activated gas-sensing theory. Furthermore, we find that the extent of improvement attained in the recovery speed also depends on the distribution of excited electrons in the adsorbed NO₂/QD gel system. This work suggests that the design of light-activated sensor platforms may benefit from a careful assessment of the photophysics of the analyte in the gas phase and when adsorbed onto the semiconductor surface.

Electrochemical gelation of quantum dots using non-noble metal electrodes at high oxidation potentials

Relative to conventional chemical approaches, electrochemical assembly of metal chalcogenide nanoparticles enables the use of two additional levers for tuning the assembly process: electrode material and potential. In our prior work, oxidative and metal-mediated pathways for electrochemical assembly of metal chalcogenide quantum dots (QDs) into three-dimensional gel architectures were investigated independently by employing a noble-metal (Pt) electrode at relatively high potentials and a non-noble metal electrode at relatively low potentials, respectively. In the present work, we reveal competition between the two electrogelation pathways under the condition of high oxidation potentials and non-noble metal electrodes (including Ni, Co, Zn, and Ag), where both pathways are active. We found that the electrogel structure formed under this condition is electrode material-dependent. For Ni, the major phase is oxidative electrogel, not a potential-dependent mixture of oxidative and metal-mediated electrogel that one would expect. A mechanistic study reveals that the metal-mediated electrogelation is suppressed by dithiolates, a side product from the oxidative electrogelation, which block the Ni electrode surface and terminate metal ion release. In contrast, for Co, Ag, and Zn, the electrode surface blockage by dithiolates is less effective than for Ni, such that metal-mediated electrogelation is the primary gelation pathway.

Atomically dispersed Pb ionic sites in PbCdSe quantum dot gels enhance room-temperature NO2 sensing

Atmospheric NO2 is of great concern due to its adverse effects on human health and the environment, motivating research on NO2 detection and remediation. Existing low-cost room-temperature NO2 sensors often suffer from low sensitivity at the ppb level or long recovery times, reflecting the trade-off between sensor response and recovery time. Here, we report an atomically dispersed metal ion strategy to address it. We discover that bimetallic PbCdSe quantum dot (QD) gels containing atomically dispersed Pb ionic sites achieve the optimal combination of strong sensor response and fast recovery, leading to a high-performance room-temperature p-type semiconductor NO2 sensor as characterized by a combination of ultra-low limit of detection, high sensitivity and stability, fast response and recovery. With the help of theoretical calculations, we reveal the high performance of the PbCdSe QD gel arises from the unique tuning effects of Pb ionic sites on NO2 binding at their neighboring Cd sites.

Electrochemical Quantification of Corrosion Mitigation on Iron Surfaces with Gallium(III) and Zinc(II) Metallosurfactants

We have recently described a new potential use for Langmuir-Blodgett films of surfactants containing redox-inert metal ions in the inhibition of corrosion and have shown good qualitative results for both iron and aluminum surfaces. In this study we proceed to quantify electrochemically the viability of gallium(III)- and zinc(II)-containing metallosurfactants [Ga^III(L^N2O3)] (1) and [Zn^II(L^N2O2)H₂O] (2) as mitigators for iron corrosion in saline and acidic media. We evaluate their charge transfer suppression and then focus on potentiodynamic polarization and impedance spectroscopy studies, including detailed SEM data to interrogate their metal dissolution/oxygen reduction rate mitigation abilities. Both complexes show some degree of mitigation, with a more pronounced activity in saline than in acidic medium.

Evaluation of the Long-Term Storage Stability of the Cyanide Antidote: Dimethyl Trisulfide and Degradation Product Identification

This study reports the long-term storage stability of a formulation of the cyanide (CN) antidote dimethyl trisulfide (DMTS). The F3-formulated DMTS was stored in glass ampules at 4, 22, and 37 °C. Over a period of one year, nine ampules (n = 3 at each temperature) were analyzed by high-performance liquid chromatography (HPLC)-UV/vis at daily time intervals in the first week, weekly time intervals in the first month, and monthly thereafter for a period of one year to determine the DMTS content. No measurable loss of DMTS was found at 4 and 22 °C, and good stability was noted up to five months for samples stored at 37 °C. At 37 °C, a 10% (M/M) decrease of DMTS was discovered at the sixth month and only 30% (M/M) of DMTS remained by the end of the study; discoloration of the formulation and the growth of new peaks in the HPLC chromatogram were also observed. To identify the unknown peaks at 37 °C, controlled oxidation studies were performed on DMTS using two strong oxidizing agents: meta-chloroperoxybenzoic acid (mCPBA) and hydrogen peroxide (H₂O₂). Dimethyl tetrasulfide and dimethyl pentasulfide were observed as products using both of the oxidizing agents. Dimethyl disulfide was also observed as a product of degradation, which was further oxidized to S-methyl methanethiosulfonate only when mCPBA was used. HPLC-UV/vis and gas chromatography-mass spectrometry/solid phase microextraction analysis revealed good agreement between the degradation products of the stability study at 37 °C and those of disproportionation reactions. Furthermore, at 4 and 22 °C, chromatograms were remarkably stable over the one-year study period, indicating that the F3-formulated DMTS shows excellent long-term storage stability at T ≤ 22 °C.

Reversible Electrochemical Gelation of Metal Chalcogenide Quantum Dots

The ability to dictate the assembly of quantum dots (QDs) is critical for their integration into solid-state electronic and optoelectronic devices. However, assembly methods that enable efficient electronic communication between QDs, facilitate access to the reactive surface, and retain the native quantum confinement characteristics of the QD are lacking. Here we introduce a universal and facile electrochemical gelation method for assembling metal chalcogenide QDs (as demonstrated for CdS, ZnS, and CdSe) into macroscale 3-D connected pore-matter nanoarchitectures that remain quantum confined and in which each QD is accessible to the ambient. Because of the redox-active nature of the bonding between QD building blocks in the gel network, the electrogelation process is reversible. We further demonstrate the application of this electrogelation method for a one-step fabrication of CdS gel gas sensors, producing devices with exceptional performance for NO₂ gas sensing at room temperature, thereby enabling the development of low-cost, sensitive, and reliable devices for air quality monitoring.

A Molecular Approach for Mitigation of Aluminum Pitting based on Films of Zinc(II) and Gallium(III) Metallosurfactants

The use of metallosurfactants to prevent pitting corrosion of aluminum surfaces is discussed based on the behavior of the metallosurfactants [Zn^II (L^N2O2 )H₂ O] (1) and [Ga^III (L^N2O3 )] (2). These species were deposited as multilayer Langmuir-Blodgett films and characterized by IR reflection absorption spectroscopy and UV/Vis spectroscopy. Scanning electron microscopy images, potentiodynamic polarization experiments, and electrochemical impedance spectroscopy were used to assess corrosion mitigation. Both metallosurfactants demonstrate superior anticorrosion activity due to the presence of redox-inactive 3d¹⁰ metal ions that enhance the structural resistance of the ordered molecular films and limit chloride mobility and electron transfer.