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121.
122.
图G的L(2,1)-标号是一个从顶点集V(G)到非负整数集的函数f(x),使得若d(z,y)=1则|f(x)-f(y)|≥2;若d(x,y)=2,则|f(x)-f(y)|≥1。图G的L(2,1)-标号数是λ(G)使得G有的max|f(v):v∈V(G)|=κ的L(2,1)-标号中的最小数κ。本将L(2,1)-标号问题推广到更一般的情形即L(3,2,1)标号问题,并得到了平面三角剖分图、立体四面体剖分图的λ3(G)的上界。 相似文献
123.
124.
O. M. Kostenko S. Y. Dmitrieva O. I. Tolmachev S. M. Yarmoluk 《Journal of fluorescence》2002,12(2):173-175
New approach for fluorescent peptide labeling with cyanine dyes utilizing the reaction of pyrylium salts with aliphatic aminogroup is proposed. The reaction of two pyrylium cyanines dye acids was investigated. Lysocyme was used as a model peptide for conjugation. The proposed method can be used as a simple and convenient alternative for the known procedures because it does not require preparation of the unstable amino-reactive intermediates from a carboxyl- or sulfo-derivative of cyanine dyes. 相似文献
125.
Dalibor Froncek 《Graphs and Combinatorics》2007,23(2):145-163
An orthogonal double cover (ODC) of the complete graph Kn by a graph G is a collection = {Gi|i = 1,2, . . . ,n} of spanning subgraphs of Kn, all isomorphic to G, with the property that every edge of Kn belongs to exactly two members of and any two distinct members of share exactly one edge.
A caterpillar of diameter five is a tree arising from a path with six vertices by attaching pendant vertices to some or each
of its vertices of degree two. We show that for any caterpillar of diameter five there exists an ODC of the complete graph
Kn. 相似文献
126.
Highly Efficient Solid‐Phase Labeling of Saccharides within Boronic Acid Functionalized Mesoporous Silica Nanoparticles
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Xianghua Pan Yang Chen Peixuan Zhao Daojin Li Dr. Zhen Liu 《Angewandte Chemie (International ed. in English)》2015,54(21):6173-6176
Labeling is critical for the detection, quantitation, and structural identification of saccharides. However, conventional liquid‐phase labeling suffers from apparent disadvantages, such as time‐consuming, the presence of excessive labeling reagent, and high applicable saccharide concentration. A solid‐phase approach is presented for highly efficient labeling of saccharides, using boronic acid functionalized mesoporous silica nanoparticles (MSNs) as a selective extraction sorbent and nanoscale reactor. The solid‐phase labeling approach exhibited several significant advantages, including: much faster reaction speed (taking only 2 min), high product purity, and much lower applicable saccharide concentration (four orders of magnitude lower than that of liquid‐phase labeling). Thus, this labeling approach opens up new avenues to the facile and efficient labeling of saccharides. 相似文献
127.
Structural Revision and Elucidation of the Biosynthesis of Hypodoratoxide by 13C,13C COSY NMR Spectroscopy
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Lena Barra Dr. Kerstin Ibrom Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2015,54(22):6637-6640
Feeding of (2,3,4,5,6‐13C5)mevalonolactone to the fungus Hypomyces odoratus resulted in a completely labeled sesquiterpene ether. The connectivity of the carbon atoms was easily deduced from a 13C,13C COSY spectrum, revealing a structure that was different from the previously reported structure of hypodoratoxide, even though the reported 13C NMR data matched. A structural revision of hypodoratoxide is thus presented. Its absolute configuration was tentatively assigned from its co‐metabolite cis‐dihydroagarofuran. Its biosynthesis was investigated by feeding of (3‐13C)‐ and (4,6‐13C2)mevalonolactone, which gave insights into the complex rearrangement of the carbon skeleton during terpene cyclization by analysis of the 13C,13C couplings. 相似文献
128.
Nicholle G. A. Bell Adam A. L. Michalchuk John W. T. Blackburn Dr. Margaret C. Graham Dr. Dušan Uhrín 《Angewandte Chemie (International ed. in English)》2015,54(29):8382-8385
Humic substances, the main component of soil organic matter, could form an integral part of green and sustainable solutions to the soil fertility problem. However, their global‐scale application is hindered from both scientific and regulatory perspectives by the lack of understanding of the molecular make‐up of these chromatographically inseparable mixtures containing thousands of molecules. Here we show how multidimensional NMR spectroscopy of isotopically tagged molecules enables structure characterization of humic compounds. We illustrate this approach by identifying major substitution patterns of phenolic aromatic moieties of a peat soil fulvic acid, an operational fraction of humic substances. Our methodology represents a paradigm shift in the use of NMR active tags in structure determination of small molecules in complex mixtures. Unlike previous tagging methodologies that focused on the signals of the tags, we utilize tags to directly probe the identity of the molecules they are attached to. 相似文献
129.
Dr. Ramona Riclea Prof. Dr. Jeroen S. Dickschat 《Angewandte Chemie (International ed. in English)》2015,54(41):12167-12170
The sesquiterpenoid 7‐epi‐neopetasone was synthesized via the Wieland–Miescher ketone. The compound was identical to a previously tentatively identified headspace constituent of Penicillium roqueforti. Feeding experiments with 13C‐labeled mevalonolactone isotopomers demonstrated that oxidation at C12 and an isomerization of the C11?C12 to a C7?C11 double bond must occur independently and not via a C7‐C11‐C12 allyl radical in one step. Feeding with (11,12,13‐13C3)‐7‐epi‐neopetasone resulted in labelling of the PR toxin, thus establishing this compound as a newly identified pathway intermediate. 相似文献
130.
Hydroxylation of lysine, one of posttranslational modifications of proteins, generates 5‐hydroxylysine (Koh) and plays a crucial role in regulating protein functions in cellular activity. We have developed a chemical labeling method of Koh. The 1,2‐aminoalcohol moiety of Koh in synthetic peptide sequences was trapped by an alkyne‐containing benzimidate to form a 2‐oxazoline ring. An additional ammonia treatment process removed the undesirable amidine residue formed between benzimidate and lysine. During the ammonia treatment, the oxazoline residue formed at Koh mainly remained intact, and the ring opening to the amide form was observed for only part of oxazoline, indicating that the chemical labeling is amino acid selective. Azide‐substituted biotin or fluorescent dye was attached to the peptide through Huisgen cycloaddition at Koh and converted into an alkyne‐labeled oxazoline form. The Koh‐labeling assay could provide a platform to enhance proteomic research of lysine hydroxylation. 相似文献