The specific targeting of covalent bonds in a local, anisotropic fashion using mechanical methods offers useful opportunities to direct chemical reactivity down otherwise prohibitive pathways. Here, ...we report that embedding the highly inert 1,2,3-triazole moiety (which is often prepared using the canonical "click" coupling of azides and alkynes) within a poly(methyl acrylate) chain renders it susceptible to ultrasound-induced cycloreversion, as confirmed by comprehensive spectroscopic and chemical analyses. Such reactivity offers the opportunity to develop triazoles as mechanically labile protecting groups or for use in readily accessible materials that respond to mechanical force.
Glucose is a ubiquitous energy source for most living organisms. Its uptake activity closely reflects cellular metabolic demand in various physiopathological conditions. Extensive efforts have been ...made to specifically image glucose uptake, such as with positron emission tomography, magnetic resonance imaging, and fluorescence microscopy, but all have limitations. A new platform to visualize glucose uptake activity in live cells and tissues is presented that involves performing stimulated Raman scattering on a novel glucose analogue labeled with a small alkyne moiety. Cancer cells with differing metabolic activities can be distinguished. Heterogeneous uptake patterns are observed with clear cell–cell variations in tumor xenograft tissues, neuronal culture, and mouse brain tissues. By offering the distinct advantage of optical resolution but without the undesirable influence of fluorophores, this method will facilitate the study of energy demands of living systems with subcellular resolution.
Eine Schwingungssonde wurde entwickelt, um mit subzellulärer Auflösung die Glucoseaufnahme‐Aktivität in lebenden Zellen und Geweben durch Mikroskopie auf Basis stimulierter Raman‐Streuung (SRS) zu visualisieren. In neuronalen Kulturen und Tumorgeweben wurden heterogene Aufnahmemuster beobachtet, was interessante Perspektiven für das Studium des Energiebedarfs im Gehirn und in Tumoren eröffnet.
Penelitian ini bertujuan memberikan informasi yang detail tentang proses validitas isi, validitas butir, dan reliabilitas instrumen evaluasi berbasis model Alkin sebagai alat evaluasi pelaksanaan ...blended learning mata kuliah Matematika Diskrit di STIKOM Bali. Penelitian ini menggunakan pendekatan penelitian pengembangan instrumen, dengan tahapan-tahapan yaitu: pendefinisian variabel, penjabaran variabel menjadi indikator, penyusunan butir-butir instrumen, uji coba instrumen, serta analisis validitas dan reliabilitas instrumen. Subjek dalam penelitian ini adalah seorang pakar pendidikan informatika dan seorang pakar evaluasi pendidikan yang menguji validitas isi instrumen, sedangkan sebanyak 50 orang mahasiswa dilibatkansebagai responden dalam penentuan validitas dan reliabilitas butir instrumen. Alat pengumpulan data berupa kuesioner dan foto dokumentasi. Analisis validitas isi instrumen dilakukan melalui perhitungan Gregory, analisis validitas butir instrumen melalui perhitungan korelasi pearson–product moment, dan analisis reliabilitas instrumen melalui perhitungan koefisien Cronbach Alpha. Hasil penelitian ini menampilkan validitas isi dan reliabilitas instrumen yang tergolong dalam kriteria sangat baik.
Copper-based catalysts derived from activation of the Cu–Al hydrotalcite precursor display remarkable performance in the partial hydrogenation of propyne owing to the attainment of a high metal ...loading and a high copper dispersion. The reaction mechanism and product distribution present marked differences in comparison with nickel-based analogues.
The partial hydrogenation of propyne was studied over copper-based catalysts derived from Cu–Al hydrotalcite and malachite precursors and compared with supported systems (Cu/Al
2O
3 and Cu/SiO
2). The as-synthesized samples and the materials derived from calcination and reduction were characterized by XRF, XRD, TGA, TEM, N
2 adsorption, H
2-TPR, XPS, and N
2O pulse chemisorption. Catalytic tests were carried out in a continuous flow-reactor at ambient pressure and 423–523
K using H
2:C
3H
4 ratios of 1–12 and were complemented by
operando DRIFTS experiments. The propyne conversion and propene selectivity correlated with the copper dispersion, which varied with the type of precursor or support and the calcination and reduction temperatures. The highest exposed copper surface was attained on hydrotalcite-derived catalysts, which displayed C
3H
6 selectivity up to 80% at full C
3H
4 conversion and stable performance in long-run tests at
T
⩾
473
K. Both activated Cu–Al hydrotalcites (this work) and Ni–Al hydrotalcites S. Abelló, D. Verboekend, B. Bridier, J. Pérez-Ramírez, J. Catal. 259 (2008) 85 exhibited a relatively high alkene selectivity under optimal operation conditions, but they present a markedly distinctive catalytic behavior with respect to temperature and hydrogen-to-alkyne ratio. The product distribution was assigned through Density Functional Theory (DFT) simulations to the different stability of subsurface phases (carbides, hydrides) and the energies and barriers for the competing reaction mechanisms. The behavior of Cu in partial alkyne hydrogenation resembles that of Au nanoparticles, while Ni is closer to Pd.
•Amphiphilic Urea-cyclodextrin derivatives bind amino acids.•Amino acid binding is 1000-fold stronger in comparison to unsubstituted cyclodextrins.•Side chains attached to the cyclodextrins cause ...formation of nano-sized aggregates.
Water soluble amphiphilic anion receptors based on urea-substituted β-cyclodextrin were synthesized via a copper(I) mediated azide-alkyne coupling reaction. The synthetic route was designed to minimize the number of operations of cyclodextrins. Stable products were obtained in 90% yield. They were successfully tested as amino acid receptors, showing excellent affinity constants (103–104M−1) in a highly competitive environment (pH 8 phosphate-buffered water solution). Isothermal titration calorimetry indicated that complex formation strongly depends on the hydrophobic nature of the guest and that the urea moiety of the receptor is necessary to efficiently bind amino acids.
The successful encapsulation of reactive components for the azide/alkyne‐“click”‐reaction is reported featuring for the first time the use of a liquid polymer as reactive component. A liquid, ...azido‐telechelic three‐arm star poly(isobutylene) ($\overline {M} _{{\rm n}} $ = 3900 g · mol−1) as well as trivalent alkynes were encapsulated into micron‐sized capsules and embedded into a polymer‐matrix (high‐molecular weight poly(isobutylene), $\overline {M} _{{\rm n}} $ = 250 000 g · mol−1). Using (CuIBr(PPh3)3) as catalyst for the azide/alkyne‐“click”‐reaction, crosslinking of the two components at 40 °C is observed within 380 min and as fast as 10 min at 80 °C. Significant recovery of the tensile storage modulus was observed in a material containing 10 wt.‐% and accordingly 5 wt.‐% capsules including the reactive components within 5 d at room temperature, thus proving a new concept for materials with self‐healing properties.
The successful encapsulation of a liquid polymer (azido‐telechelic three‐arm star poly(isobutylene) ($\overline {M} _{{\rm n}} $=3900 g·mol−1)) together with a liquid alkyne for the azide/alkyne‐“click”‐reaction is reported. Using (CuIBr(PPh3)3) as catalyst for the azide/alkyne‐“click”‐reaction, crosslinking of the two components at 40°C is observed within 380min thus demonstrating a concept for self healing materials.
Iron nanoparticles (Fe‐NP) supported on chemically‐derived graphene (CDG) were prepared and identified as an effective catalyst for the hydrogenation of alkenes and alkynes. The catalyst can easily ...be separated by magnetic decantation.
Biofunctionalization of silicon substrates is important to the development of silicon-based biosensors and devices. Compared to conventional organosiloxane films on silicon oxide intermediate layers, ...organic monolayers directly bound to the nonoxidized silicon substrates via Si−C bonds enhance the sensitivity of detection and the stability against hydrolytic cleavage. Such monolayers presenting a high density of terminal alkynyl groups for bioconjugation via copper-catalyzed azide−alkyne 1,3-dipolar cycloaddition (CuAAC, a “click” reaction) were reported. However, yields of the CuAAC reactions on these monolayer platforms were low. Also, the nonspecific adsorption of proteins on the resultant surfaces remained a major obstacle for many potential biological applications. Herein, we report a new type of “clickable” monolayers grown by selective, photoactivated surface hydrosilylation of α,ω-alkenynes, where the alkynyl terminal is protected with a trimethylgermanyl (TMG) group, on hydrogen-terminated silicon substrates. The TMG groups on the film are readily removed in aqueous solutions in the presence of Cu(I). Significantly, the degermanylation and the subsequent CuAAC reaction with various azides could be combined into a single step in good yields. Thus, oligo(ethylene glycol) (OEG) with an azido tag was attached to the TMG−alkyne surfaces, leading to OEG-terminated surfaces that reduced the nonspecific adsorption of protein (fibrinogen) by >98%. The CuAAC reaction could be performed in microarray format to generate arrays of mannose and biotin with varied densities on the protein-resistant OEG background. We also demonstrated that the monolayer platform could be functionalized with mannose for highly specific capturing of living targets (Escherichia coli expressing fimbriae) onto the silicon substrates.
A concise synthesis of the putative structure assigned to the highly cytotoxic marine macrolide mandelalide A (1) is disclosed. Specifically, an iridium‐catalyzed two‐directional Krische allylation ...and a cobalt‐catalyzed carbonylative epoxide opening served as convenient entry points for the preparation of the major building blocks. The final stages feature the first implementation of terminal‐acetylene metathesis into natural product synthesis, which is remarkable as this class of substrates was beyond reach until very recently; key to success was the use of the highly selective molybdenum alkylidyne complex 42 as the catalyst. Although the constitution and stereochemistry of the synthetic samples are unambiguous, the spectra of 1 as well as of 11‐epi‐1 deviate from those of the natural product, which implies a subtle but deep‐seated error in the original structure assignment.
Bitter und süß: Die Synthese der vorgeschlagenen Struktur des zytotoxischen Makrolids Mandelalid A bekräftigt, dass die Strukturaufklärung von komplexen Naturstoffen nicht immer verlässlich ist. Aus chemischer Perspektive belegt der gewählte Syntheseweg den Nutzen von (Übergangs)Metallen als Katalysatoren in der stereoselektiven Synthese. Besonders bemerkenswert ist die erste Anwendung einer Metathese von terminalen Alkinen in der Naturstoffsynthese.
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