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1.
Geometriae Dedicata - We study the speed of convergence to the asymptotic cone for a finitely generated nilpotent group endowed with a word metric. The first result on this theme is given by Burago... 相似文献
2.
Kätchen K. Lachmayr Prof. Lawrence R. Sita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(9):3591-3595
Incorporation of small amounts of α-tocopherol (vitamin E) in blends with the cellobiose–triazole-linked atactic poly(4-methyl-1-pentene) (CB-aPMP) sugar–polyolefin conjugate can be used to exert external control over thermotropic phase behavior and provide access to non-canonical soft matter Frank–Kasper A15 and σ phases. These results establish a paradigm that can be used for the further design and development of scalable quantities of soft matter FK phases of increased structural complexity and functional capability. 相似文献
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Prof. Dr. Jevgenij A. Raskatov Dr. Scott Virgil Dr. Hsiau-Wei Lee Dr. Lawrence M. Henling Ka Chan Ariel J. Kuhn Alejandro R. Foley 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(20):4467-4470
Methionine (Met) oxidation is an important biological redox node, with hundreds if not thousands of protein targets. The process yields methionine oxide (MetO). It renders the sulfur chiral, producing two distinct, diastereomerically related products. Despite the biological significance of Met oxidation, a reliable protocol to separate the resultant MetO diastereomers is currently lacking. This hampers our ability to make peptides and proteins that contain stereochemically defined MetO to then study their structural and functional properties. We have developed a facile method that uses supercritical CO2 chromatography and allows obtaining both diastereomers in purities exceeding 99 %. 1H NMR spectra were correlated with X-ray structural information. The stereochemical interconversion barrier at sulfur was calculated as 45.2 kcal mol−1, highlighting the remarkable stereochemical stability of MetO sulfur chirality. Our protocol should open the road to synthesis and study of a wide variety of stereochemically defined MetO-containing proteins and peptides. 相似文献
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Kätchen K. Lachmayr Charlotte M. Wentz Prof. Lawrence R. Sita 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2020,132(4):1537-1542
“One-component” soft material Frank–Kasper (FK) phases are an intriguing structural form of matter that possess periodically ordered structures arising from the self-reconfiguration and close packing of an initial assembly of identical “deformable” spheres into two or more size- or shape-distinct sets of particles. Significant challenges that must still be addressed to advance the field of soft matter FK phases further, however, include their rare and unpredictable occurrence, uncertain mechanisms of solid-state assembly, and low thermodynamic stability. Here we show that a readily-accessible sugar–polyolefin conjugate quantitatively produces an exceptionally stable solid-state FK A15 phase through a rapid and irreversible thermotropic order–order transition, which contrary to other prevailing proposed mechanisms, does not require mass transfer between particles or large structural reorganization in the bulk to establish unit cell non-equivalency. Our results provide the basis for a realistic strategy for obtaining practical and scalable quantities of a diverse range of sugar–polyolefin FK A15 phases with unique intrinsic physical properties and chemical reactivities not previously seen in such systems. 相似文献
7.
Saikat Banerjee Waqas Rasheed Ruixi Fan Dr. Apparao Draksharapu Dr. Williamson N. Oloo Prof. Dr. Yisong Guo Prof. Dr. Lawrence Que Jr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(41):9608-9613
The [FeIV(O)(Me3NTB)]2+ (Me3NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, 1H NMR spectroscopy was used to determine that 1 does not have C3-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme FeIV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 FeIV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the FeIV=O center to rationalize nonheme oxoiron(IV) reactivity. 相似文献
8.
Mohammad Rostampour David J. Lawrence Jr Zaaferah Hamid Jade Darensbourg Percy Calvo-Marzal Karin Y. Chumbimuni-Torres 《Electroanalysis》2023,35(3):e202200121
It is well known that potentiometric sensors provide a versatile, cost-effective, and efficient platform for wearable applications. Unfortunately, mass production and commercialization of such devices is often constrained by the requirement of a calibration step, which is due to the poor sensor-to-sensor reproducibility and the need of conditioning the electrodes in the analyte before use. Herein, we fabricated calibration-free flexible sensors including ion-selective electrode and reference electrode by integrating single-walled carbon nanotubes (SWCNTs) with poly(3-octylthiophene) (POT) and applying on polyethylene terephthalate (PET) substrate. The developed sodium and potassium ion-selective electrodes (ISEs) display excellent repeatability, selectivity, stability as well as high sensor-to-sensor reproducibility, with a standard deviation of as low as 1.0 mV in artificial sweat microliter samples volume. 相似文献
9.
Willi R. Berg Dr. Jonathan F. Berengut Changzhuang Bai Dr. Laura Wimberger Prof. Lawrence K. Lee Dr. Felix J. Rizzuto 《Angewandte Chemie (International ed. in English)》2023,62(51):e202314458
Hierarchical DNA nanostructures offer programmable functions at scale, but making these structures dynamic, while keeping individual components intact, is challenging. Here we show that the DNA A-motif—protonated, self-complementary poly(adenine) sequences—can propagate DNA origami into one-dimensional, micron-length fibrils. When coupled to a small molecule pH regulator, visible light can activate the hierarchical assembly of our DNA origami into dissipative fibrils. This system is recyclable and does not require DNA modification. By employing a modular and waste-free strategy to assemble and disassemble hierarchical structures built from DNA origami, we offer a facile and accessible route to developing well-defined, dynamic, and large DNA assemblies with temporal control. As a general tool, we envision that coupling the A-motif to cycles of dissipative protonation will allow the transient construction of diverse DNA nanostructures, finding broad applications in dynamic and non-equilibrium nanotechnology. 相似文献
10.
Neel Sisodia Monica Miranda Kay L. McGuinness Jay D. Wadhawan Nathan S. Lawrence 《Electroanalysis》2021,33(3):559-562
This work presents the electrochemical response of a 2-(methylthio)phenol glassy carbon based electrode for a promising voltammetric pH sensor in both buffered and low-buffered solutions. Electropolymerization of the redox species was performed with the resulting polymer presenting a Nernstian response in buffered media, with a sensitivity of 51 mV/pH unit. The effectiveness of the sulfhydryl bond to facilitate proton transfer from the bulk solution to the phenol molecules has been confirmed, providing an accurate pH measurement of 8.28 in sea water media, compared to that measured with a calibrated glass pH probe of 8.30. 相似文献