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排序方式: 共有650条查询结果,搜索用时 500 毫秒
1.
Serguei Foss Takis Konstantopoulos Stan Zachary 《Journal of Theoretical Probability》2007,20(3):581-612
We consider a modulated process S which, conditional on a background process X, has independent increments. Assuming that S drifts to −∞ and that its increments (jumps) are heavy-tailed (in a sense made precise in the paper), we exhibit natural
conditions under which the asymptotics of the tail distribution of the overall maximum of S can be computed. We present results in discrete and in continuous time. In particular, in the absence of modulation, the
process S in continuous time reduces to a Lévy process with heavy-tailed Lévy measure. A central point of the paper is that we make
full use of the so-called “principle of a single big jump” in order to obtain both upper and lower bounds. Thus, the proofs
are entirely probabilistic. The paper is motivated by queueing and Lévy stochastic networks. 相似文献
2.
The trans reduction of all types of alkynes to give (E)-olefins is achieved through a two-stage trans hydrosilylation and protodesilylation. Reaction of an alkyne and a silane with the ruthenium catalyst [Cp*Ru(MeCN)3]PF6 results in clean hydrosilylation to give only the (Z)-trans addition product at ambient temperature with catalyst loadings of 1-5 mol %. The crude vinylsilane products are then protodesilylated by the action of cuprous iodide and TBAF at rt-35 degrees C. The reaction is compatible with many sensitive functional groups and provides a general trans-alkyne reduction not possible by other means. 相似文献
3.
Robert M. Smith Ping Yuan David P. Weiner Caryn R. Dutton David E. Hansen 《Applied biochemistry and biotechnology》1994,47(2-3):329-343
We describe here a novel strategy for the isolation of antibodies with sequence-specific protease activity: the synthesis
of dipeptide haptens in which the targeted peptide bond has been replaced by a ring-strained or torsionally strained hydroxyethylene
transition-state analog. Thus, the analogs mimic both a peptide bond in a distorted, reactive conformation and the transition
state for peptide bond hydrolysis. In order to obtain sequence-specific antibody proteases, these analogs have been flanked
with additional amino acid residues in preparation for immunization. In particular, we have synthesized peptides containing
analogs such as 2-cis-amino-3-cis-hydroxycyclobutane carboxylic acid andendo-(3-amino-2-hydroxy)bicyclo[2.2.1]heptane-7-anti-carboxylic acid. We have also prepared a series of peptide derivatives containing
analogs, such as 2-[3-amino-2-oxo-1-azetidinyl]-3-methylbutanoic acid, in which the targeted peptide bond has been incorporated
into a β-lactam ring. Since the “peptide bond” has been left intact, these species mimic only a distorted ground state. At
present, antibodies are being elicited against a number of the above peptide derivatives. 相似文献
4.
Zachary M. Schulte Yeon Hye Kwon Yi Han Chong Liu Lin Li Yahui Yang Austin Gamble Jarvi Sunil Saxena Gtz Veser J. Karl Johnson Nathaniel L. Rosi 《Chemical science》2020,11(47):12807
Metal–organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn–Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H2/CO2 separation ability of bMOF-200. We examine the H2/CO2 separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H2/CO2 separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H2 and CO2 and a significantly improved H2/CO2 separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H2/CO2 separations.Tailorable multicomponent MOFs and MOF membranes for efficient H2/CO2 separation. 相似文献
5.
Dai QH Tommos C Fuentes EJ Blomberg MR Dutton PL Wand AJ 《Journal of the American Chemical Society》2002,124(37):10952-10953
The use of side chains as catalytic cofactors for protein mediated redox chemistry raises significant mechanistic issues as to how these amino acids are activated toward radical chemistry in a controlled manner. De novo protein design has been used to examine the structural basis for the creation and maintenance of a tryptophanyl radical in a three-helix bundle protein maquette. Here we report the detailed structural analysis of the protein by multidimensional NMR methods. An interesting feature of the structure is an apparent pi-cation interaction involving the sole tryptophan and a lysine side chain. Hybrid density functional calculations support the notion that this interaction raises the reduction potential of the W degrees /WH redox pair and helps explain the redox characteristics of the protein. This model protein system therefore provides a powerful model for exploring the structural basis for controlled radical chemistry in protein. 相似文献
6.
Nanda V Rosenblatt MM Osyczka A Kono H Getahun Z Dutton PL Saven JG Degrado WF 《Journal of the American Chemical Society》2005,127(16):5804-5805
Metal-binding sites in metalloproteins frequently occur at the interfaces of elements of secondary structure, which has enabled the retrostructural analysis of natural proteins and the de novo design of helical bundles that bind metal ion cofactors. However, the design of metalloproteins containing beta-structure is less well developed, despite the frequent occurrence of beta-conformations in natural metalloproteins. Here, we describe the design and construction of a beta-protein, RM1, that forms a stable, redox-active 4-Cys thiolate Fe(II/III) site analogous to the active site of rubredoxin. The protein folds into a beta-structure in the presence and absence of metal ions and binds Fe(II/III) to form a redox-active site that is stable to repeated cycles of oxidation and reduction, even in an aerobic environment. 相似文献
7.
Several upper bounds are given for the maximum number of edgese possible in a graph depending upon its orderp, girthg and, in certain cases, minimum degree. In particular, one upper bound has an asymptotic order ofp
1+2/(g–1) wheng is odd. A corollary of our final result is that
whenk = e/p 2. Asymptotic and numerical comparisons are also presented. 相似文献
8.
Amber L. H. Gray Aleksandra Antevska Benjamin A. Link Bryan Bogin Susan J. Burke Samuel D. Dupuy J. Jason Collier Zachary A. Levine Michael D. Karlstad Thanh D. Do 《Chemical science》2021,12(16):5853
Despite being relatively benign and not an indicative signature of toxicity, fibril formation and fibrillar structures continue to be key factors in assessing the structure–function relationship in protein aggregation diseases. The inability to capture molecular cross-talk among key players at the tissue level before fibril formation greatly accounts for the missing link toward the development of an efficacious therapeutic intervention for Type II diabetes mellitus (T2DM). We show that human α-calcitonin gene-related peptide (α-CGRP) remodeled amylin fibrillization. Furthermore, while CGRP and/or amylin monomers reduce the secretion of both mouse Ins1 and Ins2 proteins, CGRP oligomers have a reverse effect on Ins1. Genetically reduced Ins2, the orthologous version of human insulin, has been shown to enhance insulin sensitivity and extend the life-span in old female mice. Beyond the mechanistic insights, our data suggest that CGRP regulates insulin secretion and lowers the risk of T2DM. Our result rationalizes how migraine might be protective against T2DM. We envision the new paradigm of CGRP : amylin interactions as a pivotal aspect for T2DM diagnostics and therapeutics. Maintaining a low level of amylin while increasing the level of CGRP could become a viable approach toward T2DM prevention and treatment.CGRP concentration is elevated in migraine conditions. The protective effect of migraine against type 2 diabetes is attributed to the ability of CGRP to remodel human amylin aggregation and to suppress the secretion of mouse insulin 2 (the orthologue of human insulin). 相似文献
9.
10.
It is well-known that matrix effects in high performance liquid chromatography coupled to electrospray ionization mass spectrometry (HPLC-ESI-MS) can seriously compromise quantitative analysis and affect method reproducibility. Paired ion electrospray ionization (PIESI) mass spectrometry is an approach for analyzing ultra-low levels of anions in the positive ion mode. This approach uses a structurally optimized ion pairing reagent to post-column associate with the anionic analyte, subsequently forming positively charged complexes. These newly formed complex ions are often more surface-active as compared to either the native anion or the ion pairing reagent. No studies have examined whether or not the PIESI approach mitigates matrix effects. Consequently, a controlled study was done using five analytes in highly controlled and reproducible synthetic groundwater and urine matrices. In addition, two different mass spectrometers (linear ion trap and triple quadrupole) were used. Compared to the negative ion mode, the PIESI-MS approach was less susceptible to matrix effects when performed on two different MS platforms. Using PIESI-MS, less dilution of the sample is needed to eliminate ionization suppression which, in turn, permits lower limits of detection and quantitation. 相似文献