The binding sites of Zn(2+), Cd(2+), and Hg(2+) in complexes with 2-(alpha-hydroxybenzyl)thiamine monophosphate chloride, (LH)(+)Cl(-), have been investigated in the solid state [2-(alpha-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N(1)' is denoted as (LH)(+)Cl(-); therefore, the ligand monoprotonated at the phosphate group and deprotonated at N(1)' is L]. Complexes of formulae MLCl(2), M(LH)Cl(3), and (MCl(4))(2)(-)(LH)(2)(+) (M = Zn(2+), Cd(2+), and Hg(2+)) were isolated in aqueous and methanolic solutions, depending on pH. The crystal structure of the complex of formula HgL(2)Cl(2) was solved, together with that of the free ligand (LH)(+)Cl(-), by X-ray crystallography. HgL(2)Cl(2) crystallizes in C2/c, with a = 32.968(6) ?, b = 7.477(2) ?, c = 21.471(4) ?, beta = 118.19(1) degrees, V = 4665(2) ?(3), and Z = 4. (LH)(+)Cl(-) crystallizes in Cc, with a = 10.951(3) ?, b = 17.579(4) ?, c = 13.373(3) ?, beta = 105.36(2) degrees, V = 2482.4(10) ?(3), and Z = 4. Mercury(II) binds to the N(1') of the pyrimidine ring. Both ligands are in the S conformation [Phi(T) = -98.1(9) degrees and Phi(P) = 176.1(10) degrees for HgL(2)Cl(2) and Phi(T) = 104.1(5) degrees and Phi(P) = 171.9(6) degrees for (LH)(+)Cl(-)]. (31)P and (13)C NMR spectra, together with vibrational spectra (IR/Raman), are used to deduce the binding sites of the metal and the protonation states of the ligand at various pH values. It is found that solid-state (31)P NMR spectroscopy is particularly useful in characterizing these complexes as the (31)P shielding tensors are sensitive to the state of the phosphate group. On the other hand, the (31)P NMR spectra indicate that direct bonding between Zn(2+) and Cd(2+) to the phosphate can occur under certain preparation conditions. Solid-state (13)C NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques. 相似文献
CE-MS and HPLC-MS methods were developed and compared for the analysis of insoluble proteins in an avian eggshell matrix. The eggshell was gradually decalcified to obtain four distinct layers (cuticle, two palisade and a mammillary layer). The insoluble proteinaceous films from these layers were chemically and/or enzymatically splitted with CNBr/trypsin and proteinase K. The generated peptides were separated by CE and HPLC on-line coupled to MS detection. Capillary electrophoresis (CE) was coupled to an ion-trap electrospray ionization mass spectrometer (Agilent LC-MSD Trap XCT-Ultra) using a grounded needle carrying a flow of sheath liquid (5 mM ammonium acetate/2-propanol, 1:1, at flow-rate 3 μL min−1). Five main proteins were identified: ovocleidin-116, ovocalyxin-32, ovocalyxin-36, ovocleidin-17 and ovalbumin. The distribution of these proteins in the eggshell was found to be dependent on the location/layer. In the outermost layer (the cuticle layer) the dominant protein is ovocalyxin-32; ovocleidin-116 is distributed throughout all layers while ovalbumin is present only in the internal mammillary layer. The CE-MS peptide maps of eggshell proteins were compared to the HPLC-MS ones, and a different mechanism of separation (migration/elution order) was demonstrated for both methods.
In this paper, we prove that the harmonious coloring problem is NP-complete for connected interval and permutation graphs. Given a simple graph G, a harmonious coloring of G is a proper vertex coloring such that each pair of colors appears together on at most one edge. The harmonious chromatic number is the least integer k for which G admits a harmonious coloring with k colors. Extending previous work on the NP-completeness of the harmonious coloring problem when restricted to the class of disconnected graphs which are simultaneously cographs and interval graphs, we prove that the problem is also NP-complete for connected interval and permutation graphs. 相似文献
A systematic investigation of the reactions of Cu(ClO4)2 · 6H2O with maleamic acid (H2L) in the presence of 2,2′-bipyridine (bpy) has been carried out. The chemical and structural identity of the products depends on the solvent, the absence or presence of external hydroxides in the reaction mixture and the molar ratio of the reactants. Various reaction schemes have led to the isolation of the complexes [Cu2(HL)2(bpy)2(H2O)2](ClO4)2 (1), [Cu2(HL)2(bpy)2(H2O)2](ClO4)2 · 2H2O (1 · 2H2O), [Cu(L′′)(bpy)]n · 2nH2O (2 · 2nH2O), [Cu2(L′′)(bpy)2(H2O)2]n(ClO4)2n · 0.5nH2O (3 · 0.5nH2O), [Cu2(L′′)2(bpy)2] · 2MeOH (5 · 2MeOH), [Cu2(L′)2(bpy)2(ClO4)2] (6) and [Cu(ClO4)2(bpy)(MeCN)2] (7b), where L′′2? and L′? are the maleate(?2) and monomethyl maleate(?1) ligands, respectively. The HL? ion has been transformed to L′′2? and L′? in the known compounds 2 · 2nH2O and 6, respectively, via metal ion-assisted processes involving hydrolysis (2 · 2nH2O) and methanolysis (6) of the primary amide group. The reaction that leads to 6 takes place through the formation of the mononuclear complex [Cu(ClO4)2(bpy)(MeOH)2] (7a), whose structure was assigned on the basis of its spectral similarity with the structurally characterized complex 7b. The structures of the cations in 1 and 1 · 2H2O consists of two CuII atoms bridged by the carboxylate groups of the two HL? ligands, each exhibiting the less common η2 coordination mode; a chelating bpy molecule and a H2O ligand complete square pyramidal coordination at each metal centre. The structure of the dinuclear repeating unit in the 1D coordination polymer 3 · 0.5nH2O consists of two CuII atoms bridged by two syn,synη1:η1:μ2 carboxylate groups belonging to two L′′2? ions; each ligand bridged two neighboring [CuII,II2] units thus promoting the formation of a helical chain. The structure of the dinuclear molecule of complex 5 · 2MeOH consists of two CuII atoms bridged by two η2 carboxylate groups from two L′′2? ligands; the second carboxylate group of each maleate(?2) ligand is monodentately coordinated to CuII, creating a remarkable seven-membered chelating ring. The L′? ion behaves as a carboxylate-type ligand in 6, with the carboxylate group being in the familiar syn,synη1:η1:μ2 coordination mode; a chelating bpy molecule and a coordinated ClO4? complete five-coordination at each CuII centre. The crystal structures of the complexes are stabilized by various H-bonding patterns. Characteristic IR bands of the complexes are discussed in terms of the known structures and the coordination modes of the ligands. 相似文献
Synchronization, a basic nonlinear phenomenon, is widely observed in diverse complex systems studied in physical, biological and other natural sciences, as well as in social sciences, economy and finance. While studying such complex systems, it is important not only to detect synchronized states, but also to identify causal relationships (i.e. who drives whom) between concerned (sub) systems. The knowledge of information-theoretic measures (i.e. mutual information, conditional entropy) is essential for the analysis of information flow between two systems or between constituent subsystems of a complex system. However, the estimation of these measures from a set of finite samples is not trivial. The current extensive literatures on entropy and mutual information estimation provides a wide variety of approaches, from approximation-statistical, studying rate of convergence or consistency of an estimator for a general distribution, over learning algorithms operating on partitioned data space to heuristical approaches. The aim of this paper is to provide a detailed overview of information theoretic approaches for measuring causal influence in multivariate time series and to focus on diverse approaches to the entropy and mutual information estimation. 相似文献
Head-space solid-phase microextraction (HS-SPME)-based procedure, coupled to comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOF-MS), was employed for fast characterisation of honey volatiles. In total, 374 samples were collected over two production seasons in Corsica (n = 219) and other European countries (n = 155) with the emphasis to confirm the authenticity of the honeys labelled as “Corsica” (protected denomination of origin region). For the chemometric analysis, artificial neural networks with multilayer perceptrons (ANN-MLP) were tested. The best prediction (94.5%) and classification (96.5%) abilities of the ANN-MLP model were obtained when the data from two honey harvests were aggregated in order to improve the model performance compared to separate year harvests. 相似文献
A damage-based cohesive model is developed for simulating crack growth due to fatigue loading. The cohesive model follows a linear damage-dependent traction–separation relation coupled with a damage evolution equation. The rate of damage evolution is characterized by three material parameters corresponding to common features of fatigue behavior captured by the model, namely, damage accumulation, crack retardation and stress threshold. Good agreement is obtained between finite element solutions using the model and fatigue test results for an aluminum alloy under different load ratios and for the overload effect on ductile 316 L steel. 相似文献
The stabilization of peptide secondary structure via stapling is a ubiquitous goal for creating new probes, imaging agents, and drugs. Inspired by indole‐derived crosslinks found in natural peptide toxins, we employed ortho‐phthalaldehydes to create isoindole staples, thus transforming inactive linear and monocyclic precursors into bioactive monocyclic and bicyclic products. Mild, metal‐free conditions give an array of macrocyclic α‐melanocyte‐stimulating hormone (α‐MSH) derivatives, of which several isoindole‐stapled α‐MSH analogues (Ki≈1 nm ) are found to be as potent as α‐MSH. Analogously, late‐stage intra‐annular isoindole stapling furnished a bicyclic peptide mimic of α‐amanitin that is cytotoxic to CHO cells (IC50=70 μm ). Given its user‐friendliness, we have termed this approach FlICk (fluorescent isoindole crosslink) chemistry. 相似文献