Chilling out: a cool aqueous environment promotes the formation of gas-surface complexes

Infrared Spectroscopy of Stepwise Hydration Motifs of Sulfur Dioxide

Experimental characterization of microscopic events and behaviors of SO₂-H₂O interactions is crucial to understanding SO₂ atmospheric chemistry but has been proven to be very challenging due to the difficulty in size selection. Here, size-dependent development of SO₂ hydrate structure and cluster growth in the SO₂(H₂O)_n (n = 1-16) complexes was probed by infrared spectroscopy based on threshold photoionization using a tunable vacuum ultraviolet free electron laser. Spectral changes with cluster size demonstrate that the sandwich structure initially formed at n = 1 develops into cycle structures with the sulfur and oxygen atoms in a two-dimensional plane (n = 2 and 3) and then into three-dimensional cage structures (n ≥ 4). SO₂ is favorably bound to the surface of larger water clusters. These stepwise features of SO₂ hydration on various sized water clusters contribute to understanding the reactive sites and electrophilicity of SO₂ on cloud droplets, which may have important atmospheric implications for studying the SO₂-containing aerosol systems.

Controlled Disassembly of Elemental Sulfur: An Approach to the Precise Synthesis of Polydisulfides

The usage of elemental sulfur (S₈ ) for constructing sulfur-containing polymers is of great significance in terms of sulfur resource utilization or fabrication of high-performance polymers. Currently, the random disassembly of S₈ hinders its direct use in the precise synthesis of sulfur-containing polymers. Herein, we provide an effective strategy for controlling the dismantlement of S₈ to synthesize polydisulfides, a promising category of dynamic bonds containing polymers. In this strategy, the completely alternating copolymerization of one sulfur atom, which is orderly derived from S₈ , with episulfides is achieved with MTBD (7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) as catalyst and [PPN]SbF₆ ([PPN]⁺ is bis(triphenylphosphine)iminium) as cocatalyst. Delightedly, the living- polymerization feature, and the good monomer compatibility allows for the access to diverse polydisulfides. Furthermore, the density functional theory (DFT) was employed to elaborate the copolymerization process.

Catalytic effect of (H2O)n (n = 1–3) clusters on the HO2 + SO2 → HOSO + 3O2 reaction under tropospheric conditions

The HO₂ + SO₂ → HOSO + ³O₂ reaction without and with (H₂O)n (n = 1–3) have been investigated using CCSD(T)/CBS//M06-2X/aug-cc-pVTZ methods, and canonical variational transition state theory with small curvature tunneling.

Simultaneous Observation of the Orientation and Activity of Surface-Immobilized Enzymes

Surface immobilized enzymes have been widely used in many applications such as biosensors, biochips, biofuel production, and biofuel cell construction. Many factors dictate how enzymes' structure, activity, and stability may change when immobilized, including surface functionalization, immobilization chemistry, nature of the solid support, and enzyme surface density. To better understand how immobilization affects enzyme structure and activity, we have developed a method to measure both surface-sensitive protein vibrational spectra and enzymatic activity simultaneously. To accomplish this, an optical/fluorescence microscope was incorporated into a sum frequency generation (SFG) spectrometer. Using β-glucosidase (β-Glu) as a model system, enzymes were covalently tethered to a self-assembled monolayer surface using cysteine-maleimide chemistry. Their orientations were determined by SFG spectroscopy, with a single native cysteine residue oriented toward the functionalized surface, and activity measured simultaneously using a fluorogenic substrate resorufin β-d-glucopyranoside, with a loss of activity of 53% as compared to comparable solution measurements. Measuring β-Glu activity and orientation simultaneously provides more accurate information for designing and further improving enzymatic activity of surface-bound enzymes.

Room Temperature One-Step Conversion from Elemental Sulfur to Functional Polythioureas through Catalyst-Free Multicomponent Polymerizations

The utilization of sulfur is a global concern, considering the abundant and cheap source of sulfur from nature and petroleum industry, its limited consumption, and the safety/environmental problems caused during storage. The economic and efficient transformation of sulfur remains to be a great challenge for both academia and industry. Herein, a room temperature conversion from sulfur to functional polythioureas was reported through a catalyst-free multicomponent polymerization of sulfur, aliphatic diamines, and diisocyanides in air with 100% atom economy. The polymerization enjoys quick reaction and wide monomer scope, which affords 16 polythioureas with well-defined structures, high molecular weights ( M_ws up to 242 500 g/mol), and excellent yields (up to 95%). The polythioureas can be utilized to detect mercury pollution with high sensitivity ( K_sv = 224 900 L/mol) and high selectivity, clean Hg²⁺ with high removal efficiency (>99.99%) to achieve drinking water standard, and monitor the real-time removal process by fluorescence.

Trimethylamine N-oxide stabilizes proteins via a distinct mechanism compared with betaine and glycine

We report experimental and computational studies investigating the effects of three osmolytes, trimethylamine N-oxide (TMAO), betaine, and glycine, on the hydrophobic collapse of an elastin-like polypeptide (ELP). All three osmolytes stabilize collapsed conformations of the ELP and reduce the lower critical solution temperature (LSCT) linearly with osmolyte concentration. As expected from conventional preferential solvation arguments, betaine and glycine both increase the surface tension at the air-water interface. TMAO, however, reduces the surface tension. Atomically detailed molecular dynamics (MD) simulations suggest that TMAO also slightly accumulates at the polymer-water interface, whereas glycine and betaine are strongly depleted. To investigate alternative mechanisms for osmolyte effects, we performed FTIR experiments that characterized the impact of each cosolvent on the bulk water structure. These experiments showed that TMAO red-shifts the OH stretch of the IR spectrum via a mechanism that was very sensitive to the protonation state of the NO moiety. Glycine also caused a red shift in the OH stretch region, whereas betaine minimally impacted this region. Thus, the effects of osmolytes on the OH spectrum appear uncorrelated with their effects upon hydrophobic collapse. Similarly, MD simulations suggested that TMAO disrupts the water structure to the least extent, whereas glycine exerts the greatest influence on the water structure. These results suggest that TMAO stabilizes collapsed conformations via a mechanism that is distinct from glycine and betaine. In particular, we propose that TMAO stabilizes proteins by acting as a surfactant for the heterogeneous surfaces of folded proteins.

Chemistry and Composition of Atmospheric Aerosol Particles

For more than two decades a cadre of physical chemists has focused on understanding the formation processes, chemical composition, and chemical kinetics of atmospheric aerosol particles and droplets with diameters ranging from a few nanometers to ∼10,000 nm. They have adapted or invented a range of fundamental experimental and theoretical tools to investigate the thermochemistry, mass transport, and chemical kinetics of processes occurring at nanoscale gas-liquid and gas-solid interfaces for a wide range of nonideal, real-world substances. State-of-the-art laboratory methods devised to study molecular spectroscopy, chemical kinetics, and molecular dynamics also have been incorporated into field measurement instruments that are deployed routinely on research aircraft, ships, and mobile laboratories as well as at field sites from megacities to the most remote jungle, desert, and polar locations. These instruments can now provide real-time, size-resolved aerosol particle physical property and chemical composition data anywhere in Earth's troposphere and lower stratosphere.