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Selected AbstractsEvaluation of gastric toxicity of indomethacin acid, salt form and complexed forms with hydroxypropyl-,-cyclodextrin on Wistar rats: histopathologic analysisFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 6 2009A.C. Ribeiro-Rama Abstract Indomethacin (IM) is a non-steroidal anti-inflammatory drug which inhibits prostaglandin biosynthesis. It is practically insoluble in water and has the capacity to induce gastric injury. Hydroxypropyl-,-cyclodextrin (HP-,-CD) is an alkylated derivative of ,-CD with the capacity to form inclusion complexes with suitable molecules. IM is considered to form partial inclusion complexes with HP-,-CD by enclosure of the p -chlorobenzoic part of the molecule in the cyclodextrin channel, reducing the adverse effects. The aim of this paper is to evaluate the gastric damage induced by the IM inclusion complex prepared by freeze-drying and spray-drying. A total of 135 Wistar rats weighing 224.4 ± 62.5 g were put into 10 groups. They were allowed free access to water but were maintained fasted for 18 h before the first administration until the end of the experiment. IM acid-form, IM trihydrated-sodium-salt and IM-HP-,-CD spray and freeze-dried, at normal and toxic doses, were administered through gastric cannula once/day for 3 days. Seventy-two hours after the first administration, the animals were sacrificed and the stomachs collected and prepared for morphological study by using the haematoxylin-eosin technique. Lesion indexes (rated 0/4) were developed and the type of injury was scored according to the severity of damage and the incidence of microscopic evidence of harm. Microscopic assessment demonstrated levels of injury with index one on 10,25%. The type of complexation method had different incidence but the same degree. The results show that IM inclusion complexation protects against gastric injury, reducing the incidence and the maximum degree of severity from 4 to 1, with a better performance of the spray-dried complex. [source] The role of policy instruments for promoting combined heat and power production with low CO2 emissions in district heating systemsINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2005Ĺ. Marbe Abstract Policy instruments clearly influence the choice of production technologies and fuels in large energy systems, including district heating networks. Current Swedish policy instruments aim at promoting the use of biofuel in district heating systems, and at promoting electric power generation from renewable energy sources. However, there is increasing pressure to harmonize energy policy instruments within the EU. In addition, natural gas based combined cycle technology has emerged as the technology of choice in the power generation sector in the EU. This study aims at exploring the role of policy instruments for promoting the use of low CO2 emissions fuels in high performance combined heat and power systems in the district heating sector. The paper presents the results of a case study for a Swedish district heating network where new large size natural gas combined cycle (NGCC) combined heat and power (CHP) is being built. Given the aim of current Swedish energy policy, it is assumed that it could be of interest in the future to integrate a biofuel gasifier to the CHP plant and co-fire the gasified biofuel in the gas turbine unit, thereby reducing usage of fossil fuel. The goals of the study are to evaluate which policy instruments promote construction of the planned NGCC CHP unit, the technical performance of an integrated biofuelled pressurized gasifier with or without dryer on plant site, and which combination of policy instruments promote integration of a biofuel gasifier to the planned CHP unit. The power plant simulation program GateCycle was used for plant performance evaluation. The results show that current Swedish energy policy instruments favour investing in the NGCC CHP unit. The corresponding cost of electricity (COE) from the NGCC CHP unit is estimated at 253 SEK MWh,1, which is lower than the reference power price of 284 SEK MWh,1. Investing in the NGCC CHP unit is also shown to be attractive if a CO2 trading system is implemented. If the value of tradable emission permits (TEP) in such as system is 250 SEK tonne,1, COE is 353 SEK MWh,1 compared to the reference power price of 384 SEK MWh,1. It is possible to integrate a pressurized biofuel gasifier to the NGCC CHP plant without any major re-design of the combined cycle provided that the maximum degree of co-firing is limited to 27,38% (energy basis) product gas, depending on the design of the gasifier system. There are many parameters that affect the economic performance of an integrated biofuel gasifier for product gas co-firing of a NGCC CHP plant. The premium value of the co-generated renewable electricity and the value of TEPs are very important parameters. Assuming a future CO2 trading system with a TEP value of 250 SEK tonne,1 and a premium value of renewable electricity of 200 SEK MWh,1 COE from a CHP plant with an integrated biofuelled gasifier could be 336 SEK MWh,1, which is lower than both the reference market electric power price and COE for the plant operating on natural gas alone. Copyright © 2005 John Wiley & Sons, Ltd. [source] Preparation and Characterization of Hydrolyzed Proteins from Defibrinated Bovine PlasmaJOURNAL OF FOOD SCIENCE, Issue 2 2002P.K.J.P.D. Wanasundara ABSTRACT: Proteins from defibrinated bovine blood plasma were enzymatically hydrolyzed with food-grade microbial proteases Alcalase 2.4 L® and Flavourzyme L&TM;, and a substrate consisting of small peptides and free amino acids was obtained. Hydrolysis of the plasma proteins with Flavourzyme resulted in a maximum degree of hydrolysis of 43% at an enzyme concentration of 110 LAPU/g protein after 15.5 h of hydrolysis. Among the free amino acids in the hydrolysate, hydrophobic amino acids were predominant. The major plasma proteins were degraded due to hydrolysis; peptides of less than 1.04 kDa were dominant in the product when a high degree of hydrolysis was employed. [source] d -Regular graphs of acyclic chromatic index at least d+2JOURNAL OF GRAPH THEORY, Issue 3 2010Manu Basavaraju Abstract An acyclic edge coloring of a graph is a proper edge coloring such that there are no bichromatic cycles. The acyclic chromatic index of a graph is the minimum number k such that there is an acyclic edge coloring using k colors and is denoted by a,(G). It was conjectured by Alon, Sudakov and Zaks (and earlier by Fiamcik) that a,(G),,+2, where ,=,(G) denotes the maximum degree of the graph. Alon et al. also raised the question whether the complete graphs of even order are the only regular graphs which require ,+2 colors to be acyclically edge colored. In this article, using a simple counting argument we observe not only that this is not true, but in fact all d -regular graphs with 2n vertices and d>n, requires at least d+ 2 colors. We also show that a,(Kn, n),n+ 2, when n is odd using a more non-trivial argument. (Here Kn, n denotes the complete bipartite graph with n vertices on each side.) This lower bound for Kn, n can be shown to be tight for some families of complete bipartite graphs and for small values of n. We also infer that for every d, n such that d,5, n,2d+ 3 and dn even, there exist d -regular graphs which require at least d+2-colors to be acyclically edge colored. © 2009 Wiley Periodicals, Inc. J Graph Theory 63: 226,230, 2010 [source] The size of edge chromatic critical graphs with maximum degree 6JOURNAL OF GRAPH THEORY, Issue 2 2009Rong Luo Abstract In 1968, Vizing [Uaspekhi Mat Nauk 23 (1968) 117,134; Russian Math Surveys 23 (1968), 125,142] conjectured that for any edge chromatic critical graph with maximum degree , . This conjecture has been verified for . In this article, by applying the discharging method, we prove the conjecture for . © 2008 Wiley Periodicals, Inc. J Graph Theory 60: 149,171, 2009 [source] On a conjecture about edge irregular total labelingsJOURNAL OF GRAPH THEORY, Issue 4 2008Stephan Brandt Abstract As our main result, we prove that for every multigraph G,=,(V, E) which has no loops and is of order n, size m, and maximum degree there is a mapping such that for every with . Functions with this property were recently introduced and studied by Ba,a et al. and were called edge irregular total labelings. Our result confirms a recent conjecture of Ivan,o and Jendrol, about such labelings for dense graphs, for graphs where the maximum and minimum degree are not too different in terms of the order, and also for large graphs of bounded maximum degree. © 2008 Wiley Periodicals, Inc. J Graph Theory 57: 333,343, 2008 [source] Rank-width is less than or equal to branch-widthJOURNAL OF GRAPH THEORY, Issue 3 2008Sang-il Oum Abstract We prove that the rank-width of the incidence graph of a graph G is either equal to or exactly one less than the branch-width of G, unless the maximum degree of G is 0 or 1. This implies that rank-width of a graph is less than or equal to branch-width of the graph unless the branch-width is 0. Moreover, this inequality is tight. © 2007 Wiley Periodicals, Inc. J Graph Theory 57: 239,244, 2008 [source] On k -detour subgraphs of hypercubesJOURNAL OF GRAPH THEORY, Issue 1 2008Nana Arizumi Abstract A spanning subgraph G of a graph H is a k - detour subgraph of H if for each pair of vertices , the distance, , between x and y in G exceeds that in H by at most k. Such subgraphs sometimes also are called additive spanners. In this article, we study k -detour subgraphs of the n -dimensional cube, , with few edges or with moderate maximum degree. Let denote the minimum possible maximum degree of a k -detour subgraph of . The main result is that for every and On the other hand, for each fixed even and large n, there exists a k -detour subgraph of with average degree at most . © 2007 Wiley Periodicals, Inc. J Graph Theory 57: 55,64, 2008 [source] Mechanochemical copolymerization of poly(vinyl chloride) with methyl methylacrylate in an open mill machineJOURNAL OF VINYL & ADDITIVE TECHNOLOGY, Issue 2 2006Peixin He Mechanical degradation of poly(vinyl chloride) (PVC) and mechanochemical copolymerization in poly(vinyl chloride)/methyl methylacrylate (PVC/MMA) systems were studied in an open mill machine. The effects of the mastication temperature, mastication time, and additives (oxygen, THF, or hydroquinone) on the mechanical degradation of PVC were investigated. The molecular weight of PVC decreased with increasing mastication time, and the efficiency of the mechanodegradation of PVC was lowered with increasing mastication temperature. The effects of the ratio of PVC to MMA, thin-passage time, and initiator on mechanochemical copolymerization also were studied. The experimental results indicated that the degree of copolymerization increased with increasing thin-passage times up to 45 times and then remained constant. There was a maximum degree of copolymerization at a ratio of 0.22 g/mL (PVC/MMA), and the efficiency of copolymerization always decreased with increasing time. The maximum degree and efficiency of copolymerization were 5.8 and 89%, respectively. The poly(vinyl chloride- co -methyl methylacrylate) copolymer can further improve the interfacial adhesion of PVC and PMMA. Thus it improves the mechanical properties of the PVC/CPE blend more effectively than pure PMMA. J. VINYL. ADDIT. TECHNOL. 12:42,48, 2006. © 2006 Society of Plastics Engineers. [source] The proof of a conjecture of Bouabdallah and SotteauNETWORKS: AN INTERNATIONAL JOURNAL, Issue 4 2004Min Xu Abstract Let G be a connected graph of order n. A routing in G is a set of n(n , 1) fixed paths for all ordered pairs of vertices of G. The edge-forwarding index of G, ,(G), is the minimum of the maximum number of paths specified by a routing passing through any edge of G taken over all routings in G, and ,,,n is the minimum of ,(G) taken over all graphs of order n with maximum degree at most ,. To determine ,n,2p,1,n for 4p + 2,p/3, + 1 , n , 6p, A. Bouabdallah and D. Sotteau proposed the following conjecture in [On the edge forwarding index problem for small graphs, Networks 23 (1993), 249,255]. The set 3 × {1, 2, , , ,(4p)/3,} can be partitioned into 2p pairs plus singletons such that the set of differences of the pairs is the set 2 × {1, 2, , , p}. This article gives a proof of this conjecture and determines that ,n,2p,1,n is equal to 5 if 4p + 2,p/3, + 1 , n , 6p and to 8 if 3p + ,p/3, + 1 , n , 3p + ,(3p)/5, for any p , 2. © 2004 Wiley Periodicals, Inc. NETWORKS, Vol. 44(4), 292,296 2004 [source] Minimum linear gossip graphs and maximal linear (,, k)-gossip graphs ,NETWORKS: AN INTERNATIONAL JOURNAL, Issue 3 2001Pierre Fraigniaud Abstract Gossiping is an information dissemination problem in which each node of a communication network has a unique piece of information that must be transmitted to all other nodes using two-way communications between pairs of nodes along the communication links of the network. In this paper, we study gossiping using a linear-cost model of communication which includes a start-up time and a propagation time which is proportional to the amount of information transmitted. A minimum linear gossip graph is a graph (modeling a network), with the minimum possible number of links, in which gossiping can be completed in minimum time under the linear-cost model. For networks with an even number of nodes, we prove that the structure of minimum linear gossip graphs is independent of the relative values of the start-up and unit propagation times. We prove that this is not true when the number of nodes is odd. We present four infinite families of minimum linear gossip graphs. We also present minimum linear gossip graphs for all even numbers of nodes n , 32 except n = 22. A linear (,, k)- gossip graph is a graph with maximum degree , in which gossiping can be completed in k rounds with minimum propagation time. We present three infinite families of maximal linear (,, k)- gossip graphs, that is, linear (,, k)-gossip graphs with a maximum number of nodes. We show that not all minimum broadcast graphs are maximal linear (,, k)-gossip graphs. © 2001 John Wiley & Sons, Inc. [source] Studies of cure kinetics of polyisoimide by differential scanning calorimetry in the solid statePOLYMER INTERNATIONAL, Issue 5 2002Young Jun Kim Abstract Detailed kinetic studies of the thermal imidization of polyisoimide based upon 4,4,-oxydianiline and 4,4,-oxydiphthalic anhydride by differential scanning calorimetry are described. Both isothermal and dynamic methods have been used to obtain kinetic parameters and a phenomenological rate equation for estimating the degree of imidization as a function of time. The thermal imidization of polyisoimides in the solid state showed a maximum degree of imidization that can be achieved at a given isothermal temperature, probably due to the diffusion controlled characteristics of reactions near vitrification. That the reaction stopped near to the point of vitrification was considered when developing a phenomenological rate equation for thermal imidization of polyisoimide in the solid state. The thermal imidization is well described by modified first order kinetics with an activation energy of 170,181,kJ,mol,1 and a pre-exponential factor of 4.1,×,1013,s,1. © 2002 Society of Chemical Industry [source] Beyond Gorilla and Pongo: Alternative models for evaluating variation and sexual dimorphism in fossil hominoid samplesAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 2 2009Jeremiah E. Scott Abstract Sexual size dimorphism in the postcanine dentition of the late Miocene hominoid Lufengpithecus lufengensis exceeds that in Pongo pygmaeus, demonstrating that the maximum degree of molar size dimorphism in apes is not represented among the extant Hominoidea. It has not been established, however, that the molars of Pongo are more dimorphic than those of any other living primate. In this study, we used resampling-based methods to compare molar dimorphism in Gorilla, Pongo, and Lufengpithecus to that in the papionin Mandrillus leucophaeus to test two hypotheses: (1) Pongo possesses the most size-dimorphic molars among living primates and (2) molar size dimorphism in Lufengpithecus is greater than that in the most dimorphic living primates. Our results show that M. leucophaeus exceeds great apes in its overall level of dimorphism and that L. lufengensis is more dimorphic than the extant species. Using these samples, we also evaluated molar dimorphism and taxonomic composition in two other Miocene ape samples,Ouranopithecus macedoniensis from Greece, specimens of which can be sexed based on associated canines and P3s, and the Sivapithecus sample from Haritalyangar, India. Ouranopithecus is more dimorphic than the extant taxa but is similar to Lufengpithecus, demonstrating that the level of molar dimorphism required for the Greek fossil sample under the single-species taxonomy is not unprecedented when the comparative framework is expanded to include extinct primates. In contrast, the Haritalyangar Sivapithecus sample, if itrepresents a single species, exhibits substantially greater molar dimorphism than does Lufengpithecus. Given these results, the taxonomic status of this sample remains equivocal. Am J Phys Anthropol, 2009. © 2009 Wiley-Liss, Inc. [source] Rapid mixing of Gibbs sampling on graphs that are sparse on averageRANDOM STRUCTURES AND ALGORITHMS, Issue 2 2009Elchanan Mossel Abstract Gibbs sampling also known as Glauber dynamics is a popular technique for sampling high dimensional distributions defined on graphs. Of special interest is the behavior of Gibbs sampling on the Erd,s-Rényi random graph G(n,d/n), where each edge is chosen independently with probability d/n and d is fixed. While the average degree in G(n,d/n) is d(1 - o(1)), it contains many nodes of degree of order log n/log log n. The existence of nodes of almost logarithmic degrees implies that for many natural distributions defined on G(n,p) such as uniform coloring (with a constant number of colors) or the Ising model at any fixed inverse temperature ,, the mixing time of Gibbs sampling is at least n1+,(1/log log n). Recall that the Ising model with inverse temperature , defined on a graph G = (V,E) is the distribution over {±}Vgiven by . High degree nodes pose a technical challenge in proving polynomial time mixing of the dynamics for many models including the Ising model and coloring. Almost all known sufficient conditions in terms of , or number of colors needed for rapid mixing of Gibbs samplers are stated in terms of the maximum degree of the underlying graph. In this work, we show that for every d < , and the Ising model defined on G (n, d/n), there exists a ,d > 0, such that for all , < ,d with probability going to 1 as n ,,, the mixing time of the dynamics on G (n, d/n) is polynomial in n. Our results are the first polynomial time mixing results proven for a natural model on G (n, d/n) for d > 1 where the parameters of the model do not depend on n. They also provide a rare example where one can prove a polynomial time mixing of Gibbs sampler in a situation where the actual mixing time is slower than npolylog(n). Our proof exploits in novel ways the local tree like structure of Erd,s-Rényi random graphs, comparison and block dynamics arguments and a recent result of Weitz. Our results extend to much more general families of graphs which are sparse in some average sense and to much more general interactions. In particular, they apply to any graph for which every vertex v of the graph has a neighborhood N(v) of radius O(log n) in which the induced sub-graph is a tree union at most O(log n) edges and where for each simple path in N(v) the sum of the vertex degrees along the path is O(log n). Moreover, our result apply also in the case of arbitrary external fields and provide the first FPRAS for sampling the Ising distribution in this case. We finally present a non Markov Chain algorithm for sampling the distribution which is effective for a wider range of parameters. In particular, for G(n, d/n) it applies for all external fields and , < ,d, where d tanh(,d) = 1 is the critical point for decay of correlation for the Ising model on G(n, d/n). © 2009 Wiley Periodicals, Inc. Random Struct. Alg., 2009 [source] Properly colored subgraphs and rainbow subgraphs in edge-colorings with local constraintsRANDOM STRUCTURES AND ALGORITHMS, Issue 4 2003Noga Alon We consider a canonical Ramsey type problem. An edge-coloring of a graph is called m-good if each color appears at most m times at each vertex. Fixing a graph G and a positive integer m, let f(m, G) denote the smallest n such that every m -good edge-coloring of Kn yields a properly edge-colored copy of G, and let g(m, G) denote the smallest n such that every m -good edge-coloring of Kn yields a rainbow copy of G. We give bounds on f(m, G) and g(m, G). For complete graphs G = Kt, we have c1mt2/ln t , f(m, Kt) , c2mt2, and cmt3/ln t , g(m, Kt) , cmt3/ln t, where c1, c2, c, c are absolute constants. We also give bounds on f(m, G) and g(m, G) for general graphs G in terms of degrees in G. In particular, we show that for fixed m and d, and all sufficiently large n compared to m and d, f(m, G) = n for all graphs G with n vertices and maximum degree at most d. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 2003 [source] Randomly coloring graphs with lower bounds on girth and maximum degreeRANDOM STRUCTURES AND ALGORITHMS, Issue 2 2003Martin Dyer We consider the problem of generating a random q -coloring of a graph G = (V, E). We consider the simple Glauber Dynamics chain. We show that if the maximum degree , > c1ln n and the girth g > c2ln , (n = |V|) for sufficiently large c1, c2, then this chain mixes rapidly provided q/, > ,, where , , 1.763 is the root of , = e1/,. For this class of graphs, this beats the 11,/6 bound of Vigoda E. Vigoda, Improved bounds for sampling colorings, Proc 40th Annu IEEE Symp Foundations of Computer Science, 1999, pp. 51,59 for general graphs. We extend the result to random graphs. © 2003 Wiley Periodicals, Inc. Random Struct. Alg., 23: 167,179, 2003 [source] Vertex-distinguishing edge colorings of random graphsRANDOM STRUCTURES AND ALGORITHMS, Issue 1 2002P. N. Balister A proper edge coloring of a simple graph G is called vertex-distinguishing if no two distinct vertices are incident to the same set of colors. We prove that the minimum number of colors required for a vertex-distinguishing coloring of a random graph of order n is almost always equal to the maximum degree ,(G) of the graph. © 2002 John Wiley & Sons, Inc. Random Struct. Alg., 20, 89,97, 2002 [source] Polymorphism of CaTeO3 and solid solutions CaxSr1,,,xTeO3ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2009Berthold Stöger Single crystals and microcrystalline samples of the calcium tellurate(IV) phases ,-, ,-, ,,- and ,-CaTeO3 as well as of two solid solutions CaxSr1,,,xTeO3 (x = 0.55 and 0.77) have been synthesized and characterized by X-ray diffraction and thermal analysis. A comparative description of the structures and the relations between the polymorphs is given. The main building units of the hitherto unknown structures are isolated [TeIVO3]2, units and [(Ca,Sr)Ox] (x = 6,8) polyhedra. All structures exhibit channels in which the TeIV electron lone pairs protrude. The low-temperature phase ,-CaTeO3 is stable up to 1168,K. It exhibits nearly cylindrical channels (diameter ,,4,Ĺ) and differs structurally from the other phases, whereas the metastable high-temperature phases are closely related to each other. They feature oval channels (shortest and longest diameter ,,2 and 8,Ĺ). ,-CaTeO3 can be described as an order,disorder (OD) structure of two non-polar layers with layer groups p121/m1 and p1211. The ,-CaTeO3 crystal under investigation consists of two polytypes with a maximum degree of order. The two phases CaxSr1,,,xTeO3 (x = 0.55 and 0.77) are isostructural to the MDO1 polytype of ,-CaTeO3. ,-CaTeO3 shows a distinct reversible phase transition at ,,293,K. The low-temperature modification ,,-CaTeO3 as well as its high-temperature modification ,-CaTeO3 can be considered as threefold superstructures along [100] based on the MDO1 polytype of ,-CaTeO3. [source] Order,disorder twinning model and stacking faults in ,-NTOACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2006Dieter Schwarzenbach Crystals of the recently published [Bolotina, Kirschbaum & Pinkerton (2005). Acta Cryst. B61, 577,584] triclinic (P) structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (,-NTO) occur as fourfold twins. There are Z, = 4 independent molecules per asymmetric unit. We show that the structure contains layers with 2-periodic layer-group symmetry p21/b 1 (1). This symmetry is lost through the stacking of the layers, which is a possible explanation for Z, = 4. A layer can assume four different but equivalent positions with respect to its nearest neighbor. Twinning arises through stacking faults and is an instructive example of the application of order,disorder theory using local symmetry operations. The near-neighbor relations between molecules remain unchanged through all twin boundaries. The four structures with maximum degree of order, one of which is the observed one, and the family reflections common to all domains are identified. Rods of weak diffuse scattering confirm the stacking model. [source] The structure of orange HgI2.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002The metastable orange crystals of HgI comprise three different crystal structures, all of which are built from corner-linked HgI supertetrahedra. Two of them are end members with the maximum degree of order (MDO) of a polytypic layer structure; the third shows a three-dimensional linkage. This paper presents the determination from X-ray diffraction data of the tetragonal polytypic structures and their stacking disorder. Diffraction patterns show sharp Bragg reflections and rods of diffuse intensity with pronounced maxima. In a first step, the diffuse intensity was neglected and all maxima were treated as Bragg reflections. The crystal was supposed to be a conglomerate of the two MDO structures diffracting independently, and their parameters and volume ratio were refined against the single data set. The geometries and anisotropic displacement parameters of the layers in the two structures are shown to be nearly identical. Layer contacts in the two stacking modes are identical. The structures are fractal complications of the stable red form of HgI. In a second step, the stacking disorder has been quantitatively analyzed with a Markov chain model. Two probabilities describing next-nearest-layer interactions were visually adjusted to observed intensity profiles extracted from image-plate detector data. Results consistently show that the crystal comprises nearly equal volumes of MDO structures with an average domain thickness of about 5 layers or 30,Ĺ. [source] The structure of orange HgI2.ACTA CRYSTALLOGRAPHICA SECTION B, Issue 6 2002The metastable orange crystals of HgI comprise three different crystal structures all of which are built from corner-linked HgI supertetrahedra. Two of the structures are end members with the maximum degree of order (MDO) of a polytypic layer structure. In this paper, the third structure (D) determined from X-ray diffraction, a crystal chemical discussion of the four known tetrahedral HgI structures, and a twinning model are presented. All the various diffraction results published during the past 70 years are now explained. The HgI supertetrahedra of the tetragonal structure D are corner-linked into two interpenetrating diamond-type networks. The stable red form and the three orange structures show the same cubic densest packing of I atoms and differ only in the distribution of Hg atoms in the tetrahedral voids. Transformations between the structures may involve only movements of Hg atoms, as implied by larger thermal displacement parameters of Hg than of I. A multiply twinned conglomerate of MDO1, MDO2 and D, each structure occurring in three orientations, results in metrically cubic crystals whose Bragg reflections are very close to reciprocal lattice points. [source] Regulation of ,-Chymotrypsin Catalysis by Ferric Porphyrins and CyclodextrinsCHEMISTRY - AN ASIAN JOURNAL, Issue 4 2008Koji Kano Prof. Abstract Positively charged ,-chymotrypsin (ChT) formed a 1:1 complex with negatively charged 5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrinato iron(III) (FeTPPS) in phosphate buffer at pH,7.4 through electrostatic interaction. In spite of the large binding constant (K=4.8×105,M,1), FeTPPS could not completely inhibit the catalysis of ChT in the hydrolysis of the model substrate, N -succinyl- L -phenylalanine p -nitroanilide (SPNA). The degree of inhibition (60,%) was saturated at 1.6,equivalents of FeTPPS, which indicates that covering of the active site of ChT by FeTPPS was insufficient. The enzymatic activity lowered by FeTPPS was entirely recovered for the freshly prepared sample when the porphyrin on the protein surface was detached by per- O -methylated ,-cyclodextrin (TMe-,-CD), which formed a stable 1:2 inclusion complex with FeTPPS (K1=1.26×106,M,1, K2=6.3×104,M,1). FeTPPS gradually induced irreversible denaturation of ChT, and the denatured ChT further lost its catalytic ability. No repairing effect of TMe-,-CD was observed with irreversibly denatured ChT. A new reversible inhibitor, 5,10,15,20-tetrakis[4-(3,5-dicarboxyphenylmethoxy)phenyl]porphyrinato iron(III) (FeP8M), was then designed, and its inhibitory behavior was examined. FeP8M formed very stable 1:1 and 1:2 FeP8M/ChT complexes with ChT, the K1 and K2 values being 2.0×108 and 1.0×106,M,1, respectively. FeP8M effectively inhibited the ChT-catalyzed hydrolysis of SPNA (maximum degree of inhibition=85,%), and the activity of ChT was recovered by per- O -methylated ,-cyclodextrin. No irreversible denaturation of ChT occurred upon binding with FeP8M. The kinetic data support the observation that, for nonincubated samples, both inhibitors did not cause significant conformational change in ChT and inhibited the ChT activity by covering the active site of the enzyme. [source] | |||||||||||||||||||