Highly Active and Selective Photocatalytic Oxidation of Organosilanes to Silanols

Silanols are ubiquitous building blocks for organic synthesis and material fabrication. To date, a number of stoichiometric and catalytic methods have been developed for the direct oxidation of Si–H to Si–OH bonds. A common challenge in the oxidation of silanes is to combine both catalytic activity and selectivity. Herein, we report a highly active and selective photocatalytic approach for the oxidation of organosilanes to silanols. Using plasmonic Au-TiO2 as a photocatalyst for dimethylphenylsilane oxidation enables complete conversion (>99% yield) and high selectivity (98.3%) with catalytic activity up to 121.8 g g–1. The observed activity substantially exceeds those of most reported homogeneous and heterogeneous catalysts. Silanol synthesis could be achieved under mild conditions in either aqueous or solvent-free conditions and allows the oxidation of a broad scope of sterically hindered hydrosilanes in excellent yield and selectivity. The general concept of photocatalytic synthesis of valuable silanols is further demonstrated by five photocatalysts

Prototropic Exchange Governs <i>T</i>₁ and <i>T</i>₂ Relaxivities of a Potential MRI Contrast Agent Nanozeolite Gd−LTL with a High pH Responsiveness

Aqueous suspensions of lanthanide exchanged zeolite LTL have been investigated by ¹H, ¹⁷O NMR, and EPR relaxivity studies. Both the longitudinal and the transverse relaxivity of these Gd³⁺ loaded materials are strongly pH dependent and therefore, they have great potential as pH responsive contrast agents. For example, LTL-nanocrystals loaded with 3.5 wt % Gd show a dramatic decrease in the longitudinal relaxivity from 32 to 7 s^–1 mM^–1 (7.5 T and 25 °C) when going from pH 4 to 9. ¹H and ¹⁷O NMR show that this phenomenon can be rationalized by a decrease in proton mobility between the zeolite interior and the exterior due to a change from a fast prototropic exchange to a 3 orders of magnitude slower water exchange mechanism. The same material also has a high transverse relaxivity (98 s^–1 mM^–1 at 7.5 T, 25 °C, and pH 5 as measured with the CPMG pulse sequence), which is governed by proton exchange too, while water diffusion plays a minor role. The high relaxivities and pH dependence render Gd-loaded LTL materials promising pH responsive contrast agents. Since the <i>r</i>₂/<i>r</i>₁ ratio of the designed probe strongly increases with the magnetic field strength, these materials are expected to be applicable for both <i>T</i>₁ and <i>T</i>₂ weighted imaging at low and high fields, respectively

Characterization of Pt/g‑C₃N₄‑Catalyzed Methanol Oxidation to Drive Peroxygenase-Catalyzed Oxyfunctionalization of Hydrocarbons

The photobiocatalysis combining photocatalysts and enzymes provides new strategies for organic synthesis and energy conversion. However, the available photocatalysts used in photobiocatalysis are still limited. Herein, highly dispersed Pt nanoparticles supported on graphitic carbon nitride (Pt/g-C3N4) were designed and applied for the light-driven in situ generation of H2O2, which was subsequently supplied to peroxygenase for selective oxyfunctionalization of C–H bonds. Substrates with activated and non-activated C–H bonds were hydroxylated into the corresponding alcohols with an enantiomeric excess of up to 99% and a turnover number of 133,000, which was about four times higher than that of unsupported g-C3N4 catalysts. Further mechanistic study by UV–vis, static photoluminescence spectroscopy, and DFT calculations revealed that the effective absorption of visible light by Pt nanoparticles on the surface of g-C3N4 and the strong interaction between O2 and the g-C3N4 surface were advantageous to improve the performance of photobiocatalysis. This research provides new insights into the fabrication of efficient photocatalysts compatible with peroxyzymes, paving the way for synergistic photobiocatalysis for selective oxyfunctionalization of hydrocarbons

Fate of Organic Functionalities Conjugated to Theranostic Nanoparticles upon Their Activation

Neutron activation is widely applied for the preparation of radioactive isotopes to be used in imaging and/or therapy. The type of diagnostic/therapeutic agents varies from small chelates coordinating radioactive metal ions to complex nanoparticulate systems. Design of these agents often relies on conjugation of certain organic functionalities that determine their pharmacokinetics, biodistribution, targeting, and cell-penetrating abilities, or simply on tagging them with an optical label. The conjugation chemistry at the surface of nanoparticles and their final purification often require laborious procedures that become even more troublesome when radioactive materials are involved. This study represents a thorough investigation on the effects of neutron activation on the organic moieties of functionalized nanoparticles, with special focus on ¹⁶⁶Ho₂O₃ particles conjugated with PEG-fluorescein and PEG-polyarginine motives. Spectroscopic and thermogravimetric analyses demonstrate only a limited degradation of PEG-fluorescein upon irradiation of the particles up to 10 h using a thermal neutron flux of 5 × 10¹⁶ m^–2 s^–1. Cell experiments show that the polyarginine-based mechanisms of membrane penetration remain unaltered after exposure of the functionalized particles to the mixed field of neutrons and gammas present during activation. This confirms that radiation damage on the PEG-polyarginines is minimal. Intrinsic radiations from ¹⁶⁶Ho do not seem to affect the integrity of conjugated organic material. These findings open up a new perspective to simplify the procedures for the preparation of functionalized metal-based nanosystems that need to be activated by neutron irradiation in order to be applied for diagnostic and/or therapeutic purposes

Experimental, Figures S1-S4 and Tables S1-S10 from Immobilization protects enzymes from plasma-mediated inactivation

Non-thermal plasmas are used in various applications to inactivate biological agents or biomolecules. A complex cocktail of reactive species, (V)UV radiation and in some cases exposure to an electric field together cause the detrimental effects. In contrast to this disruptive property of technical plasmas, we have shown previously that it is possible to use non-thermal plasma-generated species such as H2O2 as cosubstrates in biocatalytic reactions. One of the main limitations in plasma-driven biocatalysis is the relatively short enzyme lifetime under plasma-operating conditions. This challenge could be overcome by immobilizing the enzyme on inert carrier materials. Here, we tested whether immobilization is suited to protect proteins from inactivation by plasma. To this end, using a dielectric barrier discharge device (PlasmaDerm), plasma stability was tested for five enzymes immobilized on ten different carrier materials. A comparative analysis of the treatment times needed to reduce enzyme activity of immobilized and free enzyme by 30% showed a maximum increase by a factor of 44. Covalent immobilization on a partly hydrophobic carrier surface proved most effective. We conclude from the study, that immobilization universally protects enzymes under plasma-operating conditions, paving the way for new emerging applications

Additional file 1 of Deciphering cell wall sensors enabling the construction of robust P. pastoris for single-cell protein production

Additional file 1. Identification of significantly differentially expressed genes by RNA-seq in response to changes of methanol stress

Chemoenzymatic Hunsdiecker-Type Decarboxylative Bromination of Cinnamic Acids

In this contribution, we report chemoenzymatic bromodecarboxylation (Hunsdiecker-type) of α,ß-unsaturated carboxylic acids. The extraordinarily robust chloroperoxidase from Curvularia inaequalis (CiVCPO) generated hypobromite from H2O2 and bromide, which then spontaneously reacted with a broad range of unsaturated carboxylic acids and yielded the corresponding vinyl bromide products. Selectivity issues arising from the (here undesired) addition of water to the intermediate bromonium ion could be solved by reaction medium engineering. The vinyl bromides so obtained could be used as starting materials for a range of cross-coupling and pericyclic reactions

On the Versatility of Nanozeolite Linde Type L for Biomedical Applications: Zirconium-89 Radiolabeling and In Vivo Positron Emission Tomography Study

Porous materials, such as zeolites, have great potential for biomedical applications, thanks to their ability to accommodate positively charged metal-ions and their facile surface functionalization. Although the latter aspect is important to endow the nanoparticles with chemical/colloidal stability and desired biological properties, the possibility for simple ion-exchange enables easy switching between imaging modalities and/or combination with therapy, depending on the envisioned application. In this study, the nanozeolite Linde type L (LTL) with already confirmed magnetic resonance imaging properties, generated by the paramagnetic gadolinium (GdIII) in the inner cavities, was successfully radiolabeled with a positron emission tomography (PET)-tracer zirconium-89 (89Zr). Thereby, exploiting 89Zr-chloride resulted in a slightly higher radiolabeling in the inner cavities compared to the commonly used 89Zr-oxalate, which apparently remained on the surface of LTL. Intravenous injection of PEGylated 89Zr/GdIII-LTL in healthy mice allowed for PET–computed tomography evaluation, revealing initial lung uptake followed by gradual migration of LTL to the liver and spleen. Ex vivo biodistribution confirmed the in vivo stability and integrity of the proposed multimodal probe by demonstrating the original metal/Si ratio being preserved in the organs. These findings reveal beneficial biological behavior of the nanozeolite LTL and hence open the door for follow-up theranostic studies by exploiting the immense variety of metal-based radioisotopes

Vanadium-Containing Chloroperoxidase-Catalyzed Versatile Valorization of Phenols and Phenolic Acids

The downstream product transformation of lignin depolymerization is of great interest in the production of high-value aromatic chemicals. However, this transformation is often impeded by chemical oxidation under harsh reaction conditions. In this study, we demonstrate that hypohalites generated in situ by the vanadium-containing chloroperoxidase from Curvularia inaequalis (CiVCPO) can halogenate various electron-rich and electron-poor phenol and phenolic acid substrates. Specifically, CiVCPO enabled decarboxylative halogenation, deformylative halogenation, halogenation, and direct oxidation reactions. The versatile transformation routes for the valorization of phenolic compounds showed up to 99% conversion and 99% selectivity, with a turnover number of 60,700 and a turnover frequency of 60 s–1 for CiVCPO. This study potentially expands the biocatalytic toolbox for lignin valorization

A Biocatalytic Platform for the Synthesis of Enantiopure Propargylic Alcohols and Amines

Propargylic alcohols and amines are versatile building blocks in organic synthesis. We demonstrate a straightforward enzymatic cascade to synthesize enantiomerically pure propargylic alcohols and amines from readily available racemic starting materials. In the first step, the peroxygenase from Agrocybe aegerita converted the racemic propargylic alcohols into the corresponding ketones, which then were converted into the enantiomerically pure alcohols using the (R)-selective alcohol dehydrogenase from Lactobacillus kefir or the (S)-selective alcohol dehydrogenase from Thermoanaerobacter brokii. Moreover, an enzymatic Mitsunobu-type conversion of the racemic alcohols into enantiomerically enriched propargylic amines using (R)-selective amine transaminase from Aspergillus terreus or (S)-selective amine transaminase from Chromobacterium violaceum was established. The one-pot two-step cascade reaction yielded a broad range of enantioenriched alcohol and amine products in 70–99% yield