Synthesis and Properties of a Sterically Unencumbered δ-Silanediol Amino Acid

Visible Light-Mediated Organoboron-Catalyzed Metal-Free Synthesis of Silanols from Silanes

Herein, a four-coordinated organoboron compound, aminoquinoline diarylboron (AQDAB), is utilized as the photocatalyst in the oxidation of silane to silanol. This strategy effectively oxidizes Si-H bonds, affording Si-O bonds. Generally, the corresponding silanols can be obtained in moderate to good yields at room temperature under oxygen atmospheres, representing a green protocol to complement the existing preparation methods for silanols.

Antunes I, Dömling A, H. Elsinga P. Arginase as a Potential Biomarker of Disease Progression: A Molecular Imaging Perspective

Arginase is a widely known enzyme of the urea cycle that catalyzes the hydrolysis of L-arginine to L-ornithine and urea. The action of arginase goes beyond the boundaries of hepatic ureogenic function, being widespread through most tissues. Two arginase isoforms coexist, the type I (Arg1) predominantly expressed in the liver and the type II (Arg2) expressed throughout extrahepatic tissues. By producing L-ornithine while competing with nitric oxide synthase (NOS) for the same substrate (L-arginine), arginase can influence the endogenous levels of polyamines, proline, and NO•. Several pathophysiological processes may deregulate arginase/NOS balance, disturbing the homeostasis and functionality of the organism. Upregulated arginase expression is associated with several pathological processes that can range from cardiovascular, immune-mediated, and tumorigenic conditions to neurodegenerative disorders. Thus, arginase is a potential biomarker of disease progression and severity and has recently been the subject of research studies regarding the therapeutic efficacy of arginase inhibitors. This review gives a comprehensive overview of the pathophysiological role of arginase and the current state of development of arginase inhibitors, discussing the potential of arginase as a molecular imaging biomarker and stimulating the development of novel specific and high-affinity arginase imaging probes.

Silanediol versus chlorosilanol: hydrolyses and hydrogen-bonding catalyses with fenchole-based silanes

Biphenyl-2,2’-bisfenchyloxydichlorosilane (7, BIFOXSiCl₂) is synthesized and employed as precursor for the new silanols biphenyl-2,2’-bisfenchyloxychlorosilanol (8, BIFOXSiCl(OH)) and biphenyl-2,2’-bisfenchyloxysilanediol (9, BIFOXSi(OH)₂). BIFOXSiCl₂ (7) shows a remarkable stability against hydrolysis, yielding silanediol 9 under enforced conditions. A kinetic study for the hydrolysis of dichlorosilane 7 shows a 263 times slower reaction compared to reference bis-(2,4,6-tri-tert-butylphenoxy)dichlorosilane (14), known for its low hydrolytic reactivity. Computational analyses explain the slow hydrolyses of BIFOXSiCl₂ (7) to BIFOXSiCl(OH) (8, E_a = 32.6 kcal mol⁻¹) and BIFOXSiCl(OH) (8) to BIFOXSi(OH)₂ (9, E_a = 31.4 kcal mol⁻¹) with high activation barriers, enforced by endo fenchone units. Crystal structure analyses of silanediol 9 with acetone show shorter hydrogen bonds between the Si–OH groups and the oxygen of the bound acetone (OH···O 1.88(3)–2.05(2) Å) than with chlorosilanol 8 (OH···2.16(0) Å). Due to its two hydroxy units, the silanediol 9 shows higher catalytic activity as hydrogen bond donor than chlorosilanol 8, e.g., C–C coupling N-acyl Mannich reaction of silyl ketene acetals 11 with N-acylisoquinolinium ions (up to 85% yield and 12% ee), reaction of 1-chloroisochroman (18) and silyl ketene acetals 11 (up to 85% yield and 5% ee), reaction of chromen-4-one (20) and silyl ketene acetals 11 (up to 98% yield and 4% ee).

A bentonite–gold nanohybrid as a heterogeneous green catalyst for selective oxidation of silanes

A highly efficient, green and recyclable heterogeneous bentonite–gold nanohybrid catalyst was developed for the selective oxidation of silanes.

Hydrophobization of inorganic oxide surfaces using dimethylsilanediol

Dimethylsilanediol is a stable crystalline solid that was described in 1953. As the monomer of an important class of commercial products (poly(dimethylsiloxanes)-silicones, PDMS) and as a simple molecule in its own right (the silicon analog of acetone hydrate), it has been neglected by several fields of fundamental and applied research including the hydrophobization of inorganic oxide surfaces. We report that dimethylsilanediol is a useful reagent for the surface modification (hydrophobization) of oxidized silicon and other oxidized metal surfaces and compare the wetting properties of modified solids with those of conventionally modified surfaces. That water is the only byproduct of this modification reaction suggests that this and likely other silanediols are useful surface-modification agents, particularly when substrate corrosion or the competitive adsorption of byproducts is an issue. We note that dimethylsilanediol is volatile with a significant vapor pressure at room temperature. Vapor-phase surface modifications are also reported.