Helvetica Chimica Acta最新文献

Amines, crucial components in various industries, play a pivotal role in the synthesis of pharmaceuticals, agrochemicals, and specialty chemicals. Recognizing the environmental impact of conventional methods for their preparation, our study centers on the utilization of abundantly available natural molecules, specifically amino acids, as precursors for short chain amine synthesis. This paper focuses on the biocatalyst, L-valine decarboxylase from Streptomyces viridifaciens (VlmD), delving into the substrate scope, catalytic activity, and cost-effective scalability of an enzymatic process for amine synthesis. Additionally, we investigate the feasibility of immobilizing VlmD, aiming to pave the way for its effective use in industrial applications. Our study exploits the SpinChem system and provides a comprehensive understanding of the potential and limitations of this biocatalyst. Notably, our yields for key amines (8.42 g ⋅ d⁻¹ for isobutylamine, 5.23 g ⋅ d⁻¹ for isoamylamine, 5.16 g ⋅ d⁻¹ for (S)-2-methylbutylamine, 3.78 g ⋅ d⁻¹ for 3-(methylthio)propylamine, and 10.52 g ⋅ d⁻¹ for (R)-1-amino-2-propanol) demonstrate the process efficiency and potential for industrial scalability.

A novel, industrially viable synthetic route to (+)-biotin has been developed starting from L-cysteine via the known key thiolactone intermediate. The route takes advantage of the in-built stereochemistry of the cysteine starting material and the best features of the two current industrialized processes. The key transformations are the conversion of L-cysteine into a hydantoin avoiding racemization followed by catalytic cyanation and thiolactonization to form the required thiolactone intermediate. This known intermediate can be readily further transformed into (+)-biotin.

Colloidal solutions of gallia-alumina (Ga,Al)₂O_3(x:y) solid-solution nanoparticles with nominal atomic Ga : Al (x:y) ratios of 1 : 6, 1 : 3, 3 : 1, and 1:0 were used to prepare silica-supported catalysts for propane dehydrogenation (PDH). A comparison of the unsupported and silica-supported catalysts reveals that the dispersion on silica increases the Ga-normalized PDH rates for all catalysts, albeit with a notably lower propene selectivity for (Ga,Al)₂O_3(1:6)/SiO₂. Fourier transform infrared (FTIR) spectroscopy allows contrasting the H₂ dissociation sites in the calcined and H₂-treated (Ga,Al)₂O_3(x:y)/SiO₂, indicating a transformation of Ga³⁺ surface sites with Al (mainly) and Ga atoms in the second coordination sphere (Ga_(Al/Ga) sites) in the calcined (Ga,Al)₂O_3(1:6)/SiO₂ to predominantly Ga_(Ga/Si) surface sites in the H₂-treated material. The resulting sites are similarly unselective as in amorphous gallia on silica. H₂ produced during the PDH reaction can cause a similar transformation as H₂ pretreatment in (Ga,Al)₂O_3(1:6)/SiO₂, rapidly resulting in a notably lowered selectivity. The stable and selective Ga_(Al/Ga) surface sites in (Ga,Al)₂O_3(1:3)/SiO₂ yield a Ga−H band at ca. 1990 cm⁻¹ under H₂ dissociation conditions while the less selective surface sites, observed for the other Ga : Al ratios, give Ga−H bands at ca. 2040 and 2060 cm⁻¹.

Elastomers based on cross-linked bottlebrush polymers combine an extreme softness at low strains with a strain-stiffening effect, which makes them attractive as active components in dielectric elastomer actuators (DEA). Their main disadvantage concerns the small relative permittivity, which is about 3.5, requiring relatively high driving voltage in actuators. We synthesized a bottlebrush polymer elastomer with polar brushes, which exhibit an enhanced dielectric permittivity of 4.4. Anionic ring-opening polymerization of a polar cyclosiloxane gave telechelic polar brushes, while ring-opening polymerization of a norbornene macromonomer gave a bottlebrush polymer which was cross-linked to elastomers by a thiol-ene reaction. Elastomers with a small elastic modulus below 100 kPa, strain at break exceeding 100 %, attractive elasticity, and small mechanical loss factors (tanδ) were achieved. Temperature-dependent impedance measurements revealed a transition temperature of −95 °C and an interfacial polarization. The multigram scale synthesis demonstrates the potential for scaling up, which opens the door to broader applications of these materials beyond actuators, such as capacitive sensors, batteries, and electroluminescent devices. Notably, these devices operate at extremely low voltages where the dielectric breakdown does not limit their functionality, but still, the softness and the increased dielectric permittivity are a plus.

Ni-catalyzed activation of C(sp²)−H bond remains an elusive challenge. Herein, we realized a Ni-catalyzed selective activation of C(sp²)−H bond of formamides, which underwent addition reaction with internal alkynes to provide α,β-unsaturated amide compounds in high yields. The protocol was featured by the cheap and nontoxic catalyst system. Preliminary mechanistic studies shed light on the reaction pathways.

While organoelement compounds of lithium, sodium and potassium have been much studied for decades and consequently have found forests of applications, those of the heavier alkali metals, rubidium and caesium would barely manage to fill a tree. However, recently the literature has seen some little growth spurts with these metals, hinting at a possible fertile future in areas such as homogeneous catalysis provided more work is put into their fundamental development. Here we report the synthesis and crystal structures of lithium, rubidium and caesium derivatives of the ureaphosphane Ph₂PCH₂CH₂NHC(=O)NHPh, chosen because it offers O, N, P, and π-coordination sites. Though one may expect such alkali metal compounds to be essentially similar, the caesium complex has novel features where Cs⁺ engages in a side-on coordination to the C=O bond and in a weak bond to the P centre, both of which are absent in the Rb structure. Less surprisingly, the lithium derivative is tetrameric in contrast to the infinite networks of the rubidium and caesium structures. All alkali metal derivatives were made with deprotonating the ureaphosphane by a suitable base, including the sodium and potassium complexes though these two complexes could not be obtained in a crystalline form.

Alkyne tags have been widely used for the enrichment of labeled proteins to enable their profiling at a proteome-wide scale by mass spectrometry. The key component in the enrichment process is an azido-terminated cleavable linker for capturing the labeled proteins/peptides via click reaction. Herein, we report a new efficient click linker (APA biotin) featuring an acid-cleavable acetal linkage end-caped with a highly reactive picolyl azido head and a biotin handle for anchoring onto streptavidin-coated supports. Using an amine-reactive probe to profile the proteome structural changes in living S. cerevisiae cells within 5 minutes of heat shock, we demonstrated that the linker allowed identification of >9400 labeled sites, among which 457–1656 with significantly altered reactivity upon heat shock. This study represented the first chemical labeling mass spectrometry (CL–MS)-based profiling of proteome structural changes in living cells in response to external stimuli. Data are available via ProteomeXchange with identifier PXD051279.

When developing fluorescent membrane probes, we naturally tend to focus on the fluorophore itself. In this study, we show that sometimes it can be beneficial to shift attention from the center to the periphery, to maximize multiple interfacing with complex changing environments. Palmitylation for hydrophobic interfacing and glutamate dendrons for hydrophilic interfacing are combined to improve the performance of fluorescent flipper probes. We show that to increase performance in membranes, solubility in water is important, and to increase solubility in water, we increase the hydrophobicity of the flipper probe. These seemingly paradoxical measures are taken to satisfy the Israelachvili rules. They state that only inverted cone amphiphiles form soluble micelles in water, while inverted micelles from cone shaped amphiphiles precipitate into hexagonal 1 supramolecular polymers, and the intermediate cylindrical amphiphiles show intermediate behavior dominated by bilayers and lamellar precipitates. The normal micelles obtained from inverted cone flipper amphiphiles prevent precipitation and prepare for efficient transfer into the lipid bilayer membranes. The results are flippers that break all records set by the 2016 original with regard to effective brightness, responsiveness to membrane order, anchoring in disordered membranes, partitioning into membranes of high order, and stable labeling of membranes of interest. The lessons learned confirm the obvious: The Israelachvili rules apply also to fluorescent membrane probes. They promise literally bright perspectives for fluorescent membrane probes.