Visible‐Light‐Driven CO2 Reduction by Mesoporous Carbon Nitride Modified with Polymeric Cobalt Phthalocyanine

The integration of molecular catalysts with low‐cost, solid light absorbers presents a promising strategy to construct catalysts for the generation of solar fuels. Here, we report a photocatalyst for CO₂ reduction that consists of a polymeric cobalt phthalocyanine catalyst (CoPPc) coupled with mesoporous carbon nitride (mpg‐CN_x) as the photosensitizer. This precious‐metal‐free hybrid catalyst selectively converts CO₂ to CO in organic solvents under UV/Vis light (AM 1.5G, 100 mW cm^?2, λ>300 nm) with a cobalt‐based turnover number of 90 for CO after 60 h. Notably, the photocatalyst retains 60 % CO evolution activity under visible light irradiation (λ>400 nm) and displays moderate water tolerance. The in situ polymerization of the phthalocyanine allows control of catalyst loading and is key for achieving photocatalytic CO₂ conversion.     

Shock structure in bubbly liquids: comparison of direct numerical simulations and model equations

Shock wave structure in a bubbly mixture composed of a cluster of gas bubbles in a quiescent liquid with initial void fractions around 10% inside a 3D rectangular domain excited by a sudden increase in the pressure at one boundary is investigated using the front tracking/finite volume method. The effects of bubble/bubble interactions and bubble deformations are, therefore, investigated for further modeling. The liquid is taken to be incompressible while the bubbles are assumed to be compressible. The gas pressure inside the bubbles is taken uniform and is assumed to vary isothermally. Results obtained for the pressure distribution at different locations along the direction of propagation show the characteristics of one-dimensional unsteady shock propagation evolving towards steady-state. The steady-state shock structures obtained by the present direct numerical simulations, which show a transition from A-type to C-type steady-state shock structures, are compared with those obtained by the classical Rayleigh–Plesset equation and by a modified Rayleigh–Plesset equation accounting for bubble/bubble interactions in the mean-field theory.      

Numerical Simulation of Dendritic Solidification with Convection: Two-Dimensional Geometry

A front tracking method is presented for simulations of dendritic growth of pure substances in the presence of flow. The liquid–solid interface is explicitly tracked and the latent heat released during solidification is calculated using the normal temperature gradient near the interface. A projection method is used to solve the Navier–Stokes equations. The no-slip condition on the interface is enforced by setting the velocities in the solid phase to zero. The method is validated through a comparison with an exact solution for a Stefan problem, a grid refinement test, and a comparison with a solution obtained by a boundary integral method. Three sets of two-dimensional simulations are presented: a comparison with the simulations of Beckermann et al. (J. Comput. Phys.154, 468, 1999); a study of the effect of different flow velocities; and a study of the effect of the Prandtl number on the growth of a group of dendrites growing together. The simulations show that on the upstream side the dendrite tip velocity is increased due to the increase in the temperature gradient and the formation of side branches is promoted. The flow has the opposite effect on the downstream side. The results are in good qualitative agreement with published experimental results, even though only the two-dimensional aspects are examined here.     

Developing photoactive affinity probes for proteomic profiling: hydroxamate-based probes for metalloproteases

The denaturing aspect of current activity-based protein profiling strategies limits the classes of chemical probes to those which irreversibly and covalently modify their targeting enzymes. Herein, we present a complimentary, affinity-based labeling approach to profile enzymes which do not possess covalently bound substrate intermediates. Using a variety of enzymes belonging to the class of metalloproteases, the feasibility of the approach was successfully demonstrated in several proof-of-concept experiments. The design template of affinity-based probes targeting metalloproteases consists of a peptidyl hydroxamate zinc-binding group (ZBG), a fluorescent reporter tag, and a photolabile diazirine group. Photolysis of the photolabile unit in the probe effectively generates a covalent, irreversible linkage between the probe and the target enzyme, rendering the enzyme distinguishable from unlabeled proteins upon separation on a SDS-PAGE gel. A variety of labeling studies were carried out to confirm that the affinity-based approach selectively labeled metalloproteases in the presence of a large excess of other proteins and that the success of the labeling reaction depends intimately upon the catalytic activity of the enzyme. Addition of competitive inhibitors proportionally diminished the extent of enzyme labeling, making the approach useful for potential in situ screening of metalloprotease inhibitors. Using different probes with varying P(1) amino acids, we were able to generate unique "fingerprint" profiles of enzymes which may be used to determine their substrate specificities. Finally, by testing against a panel of yeast metalloproteases, we demonstrated that the affinity-based approach may be used for the large-scale profiling of metalloproteases in future proteomic experiments.     

Water-soluble nanoparticles from random copolymer and oppositely charged surfactant, 3a. Nanoparticles of poly(ethylene glycol)-based cationic random copolymer and fatty acid salts

In this report, we investigate the nanoparticle formation between random copolymers (RCPs) of methoxy-poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride (MAPTAC) and oppositely charged natural surfactants, sodium oleate and sodium laurate, using turbidimetric titration, steady-state fluorescence, dynamic light scattering, and electron microscopy. Though sodium oleate and sodium laurate are sparingly soluble in water, the nanoparticle complexes formed between the RCPs and these surfactants are soluble in the entire range of compositions studied here, including the stoichiometric electronetural complexes. The spherical nature of these nanoparticle complexes is revealed by electron microscopic (EM) analysis. Dynamic light scattering (DLS) showed that the average diameters of the nanoparticles are in the range 50 to 150 nm, which is supported by EM analysis. Pyrene fluorescence experiments suggested that these soluble nanoparticles have hydrophobic cores, which may solubilize hydrophobic drug molecules. The polarity index (I(1)/I(3)) obtained from the pyrene fluorescence spectra and the conductometric measurements showed that the critical concentration of fatty acid salts needed to obtain nanoparticles are in the order of 10(-4) M. Further, the complexation of such poorly water-soluble amphiphilic surfactants with polymers offers a useful method for the immobilization of hydrophobic compounds towards water-soluble drug carrier formulations. The formation of water-soluble nanoparticles by the self-assembly of fatty acid salts upon interacting with oppositely charged poly(ethylene glycol)-based polyions.     

Controlled synthesis of organic two-dimensional nanostructures via reaction-driven,cooperative supramolecular polymerization

The bottom-up approach of supramolecular polymerization is an effective synthetic method for functional organic nanostructures. However, the uncontrolled growth and polydisperse structural outcome often lead to low functional efficiency. Thus, precise control over the structural characteristics of supramolecular polymers is the current scientific hurdle. Research so far has tended to focus on systems with inherent kinetic control by the presence of metastable state monomers either through conformational molecular design or by exploring pathway complexity. The need of the hour is to create generic strategies for dormant states of monomers that can be extended to different molecules and various structural organizations and dimensions. Here we venture to demonstrate chemical reaction-driven cooperative supramolecular polymerization as an alternative strategy for the controlled synthesis of organic two-dimensional nanostructures. In our approach, the dynamic imine bond is exploited to convert a non-assembling dormant monomer to an activated amphiphilic structure in a kinetically controlled manner. The chemical reaction governed retarded nucleation–elongation growth provides control over dispersity and size.

We report the kinetically controlled supramolecular polymerization of organic two-dimensional charge-transfer nanostructures via a chemical reaction (imine)-driven approach.     

Synthetic Origin of Tramadol in the Environment

The presence of tramadol in roots of Sarcocephalus latifolius trees in Northern Cameroon was recently attributed to point contamination with the synthetic compound. The synthetic origin of tramadol in the environment has now been unambiguously confirmed. Tramadol samples isolated from tramadol pills bought at a street market in downtown Maroua and highly contaminated soil at Houdouvou were analyzed by high‐precision ¹⁴C measurements by accelerator mass spectrometry (¹⁴C AMS): Tramadol from the pills did not contain any radiocarbon, thus indicating that it had been synthesized from ¹⁴C‐free petroleum‐derived precursors. Crucially, tramadol isolated from the soil was also radiocarbon‐free. As all biosynthetic plant compounds must contain radiocarbon levels close to that of the contemporary environment, these results thus confirm that tramadol isolated from the soil cannot be plant‐derived. Analyses of S. latifolius seeds, in vitro grown plants, plants from different origins, and stable‐isotope labeling experiments further confirmed that synthetic tramadol contaminates the environment.     

Particle on a torus knot: Constrained dynamics and semi-classical quantization in a magnetic field

Kinematics and dynamics of a particle moving on a torus knot poses an interesting problem as a constrained system. In the first part of the paper we have derived the modified symplectic structure or Dirac brackets of the above model in Dirac’s Hamiltonian framework, both in toroidal and Cartesian coordinate systems. This algebra has been used to study the dynamics, in particular small fluctuations in motion around a specific torus. The spatial symmetries of the system have also been studied.     

Reduction of Sulfur Dioxide to Sulfur Monoxide by Ferrous Porphyrin**

The reduction of SO₂ to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO₂ to H₂S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO₂ to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO₂ by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that Fe^IITPP reduces SO₂ by 2e⁻/2H⁺ to form an intermediate [Fe^III−SO]⁺ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO₂ could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.