Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “complex structure”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed2002

Crystal structures of the sugar complexes of Streptomyces olivaceoviridis E-86 xylanase: sugar binding structure of the family 13 carbohydrate binding module.

The family 10 xylanase from Streptomyces olivaceoviridis E-86 contains a (beta/alpha)(8)-barrel as a catalytic domain, a family 13 carbohydrate binding module (CBM) as a xylan binding domain (XBD) and a Gly/Pro-rich linker between them. The crystal structure of this enzyme showed that XBD has three similar subdomains, as indicated by the presence of a triple-repeated sequence, forming a galactose binding lectin fold similar to that found in the ricin toxin B-chain. Comparison with the structure of ricin/lactose complex suggests three potential sugar binding sites in XBD. In order to understand how XBD binds to the xylan chain, we analyzed the sugar-complex structure by the soaking experiment method using the xylooligosaccharides and other sugars. In the catalytic cleft, bound sugars were observed in the xylobiose and xylotriose complex structures. In the XBD, bound sugars were identified in subdomains alpha and gamma in all of the complexes with xylose, xylobiose, xylotriose, glucose, galactose and lactose. XBD binds xylose or xylooligosaccharides at the same sugar binding sites as in the case of the ricin/lactose complex but its binding manner for xylose and xylooligosaccharides is different from the galactose binding mode in ricin, even though XBD binds galactose in the same manner as in the ricin/galactose complex. These different binding modes are utilized efficiently and differently to bind the long substrate to xylanase and ricin-type lectin. XBD can bind any xylose in the xylan backbone, whereas ricin-type lectin recognizes the terminal galactose to sandwich the large sugar chain, even though the two domains have the same family 13 CBM structure. Family 13 CBM has rather loose and broad sugar specificities and is used by some kinds of proteins to bind their target sugars. In such enzyme, XBD binds xylan, and the catalytic domain may assume a flexible position with respect to the XBD/xylan complex, inasmuch as the linker region is unstructured.

Binding Sites↗
PubMedDate not supplied

Layer-by-layer microfluidics for biomimetic three-dimensional structures.

Due to the complex structures of living systems, with size scales spanning from the micron to millimeter range, the use of microtechnology to recreate in vivo-like architecture has exciting potential applications. However, most microscale systems are two-dimensional, and few three-dimensional (3-D) systems are being explored. We have developed a versatile technique, combining surface engineering with layer-by-layer microfluidics technology, to create a 3-D microscale hierarchical tissue-like structure. The process involves immobilization of a cell-matrix assembly, cell-matrix contraction, and pressure-driven microfluidic delivery. An aminopropyltriethoxysilane-glutaraldehyde activated chip is used to effectively immobilize the cell-matrix assemblies while maintaining cell viability. Pressure-driven microfluidics is applied to transport cells-matrices with controlled flow rates, determined from dynamic flow imaging. By taking advantage of the contraction of the biopolymer matrices by cells, layer-by-layer microfluidics can be used to build multilayers of cell-matrix inside a microchannel and the thickness of each layer can be controlled down to microscale dimensions. Confocal and electron microscopy images of the final structure show a hierarchical layered cellular configuration composed of heterogeneous biomimetic materials. For a model system, a biomimetic arterial structure is formed using three types of vascular cells to mimic the 3-tunic structure found in vivo. This approach provides solutions to fabricate hierarchical "neotissues" with controlled microarchitectures and 3-D configurations of multiple cell types.

Biomimetic Materials↗
PubMed1993

Stability, structure and complexity of yeast chromosome III.

The complete sequence of yeast chromosome III provides a model for studies relating DNA sequence and structure at different levels of organisation in eukaryotic chromosomes. DNA helical stability, intrinsic curvature and sequence complexity have been calculated for the complete chromosome. These features are compartmentalised at different levels of organisation. Compartmentalisation of thermal stability is observed from the level delineating coding/non-coding sequences, to higher levels of organisation which correspond to regions varying in G + C content. The three-dimensional path reveals a symmetrical structure for the chromosome, with a densely packed central region and more diffuse and linear subtelomeric regions. This interspersion of regions of high and low curvature is reflected at lower levels of organisation. Complexity of n-tuplets (n = 1 to 6) also reveals compartmentalisation of the chromosome at different levels of organisation, in many cases corresponding to the structural features. DNA stability, conformation and complexity delineate telomeres, centromere, autonomous replication sequences (ARS), transposition hotspots, recombination hotspots and the mating-type loci.

Amino Acid Sequence↗
PubMed2006

Cationic, linear Au(I) N-heterocyclic carbene complexes: synthesis, structure and anti-mitochondrial activity.

Six linear, two-coordinate cationic Au(I) N-heterocyclic carbene complexes of the form [(R2Im)2Au]+ (R = Me 1, Me, Et 2, i-Pr 3, n-Bu 4, t-Bu 5 and Cy 6) have been prepared by the reaction of two equivalents of the appropriate dialkylimidazol-2-ylidene (R2Im) with (Me2S)AuCl in dmf. Single crystal structural studies for 1.PF6, 2.PF6), 3.Cl and 4-6.PF6 show that for all six complexes the gold(I) centres have quasi-linear C-Au-C coordination, with quasi-parallel pairs of aromatic imidazole planes, except in 5.PF6 where they are quasi-normal; in the latter, Au-C are 2.038(3), 2.033(3) A, cf. (e.g.) 2.027(2) A. Inter-cation Au...Au are close at 3.487(2), 3.525(2) A in 1PF6 and 2.PF6. The structural studies and low temperature NMR experiments provide no supportive evidence for the presence of pi back-bonding within this series of complexes. The lipophilicities of the six compounds, as estimated from the logarithm of the n-octanol-water partition coefficients (log P), varied across the series within the range -1.09 to 1.73. To investigate their potential as possible anti-mitochondrial anti-tumour agents, five of the compounds have been evaluated for their propensities to induce mitochondrial membrane permeabilization (MMP) in isolated rat liver mitochondria. At concentrations between 1-10 microM compounds 1.Br and 3-6.Cl induced dose-dependent, Ca2+-sensitive mitochondrial swelling at rates that increased with the lipophilicities of the complexes, with the most lipophilic compounds inducing the most rapid onset of swelling. The swelling was completely inhibited by cyclosporin A, the specific inhibitor of the mitochondrial permeability transition pore.

Animals↗
PubMed1995

Structural analysis of affinity maturation: the three-dimensional structures of complexes of an anti-nitrophenol antibody.

Affinity maturation of the immune response to nitrophenol-containing antigens has been extensively investigated. Significant strides made during the past several years with the advent of PCR technology have provided a wealth of biochemical knowledge. Structural investigations of the phenomena have however been limited. We have determined the three-dimensional structure of the Fab fragment of 88C6/12, an anti-4-hydroxy-3-nitrophenyl acetic acid antibody complexed with the immunizing hapten and with a heteroclitic iodinated hapten. The crystallographic structure of the complexes reveals that the binding is stabilized by a number of hydrogen bonds and extensive van der Waals interactions between the hapten and the antibody. In addition, the Fab binding pocket contains a region of positive electrostatic potential well suited for interaction with the predominant resonance form of the nitrophenyl ring system. The observed heteroclicity towards the iodinated hapten is not a direct result of iodine-protein interactions, but results from the enhanced stability in the iodinated ring of the resonance form that binds the antibody. In addition this investigation provides a rationale for the strong preference for the substitution in the heavy chain from the germ-line gene encoded Trp 33 to Leu 33 in the mature anti-nitrophenol response.

Amino Acid Sequence↗
PubMed2000

Oligomeric proanthocyanidin complexes: history, structure, and phytopharmaceutical applications.

Considerable recent research has explored therapeutic applications of oligomeric proanthocyanidin complexes (OPCs), naturally occurring plant metabolites widely available in fruits, vegetables, nuts, seeds, flowers, and bark. OPCs are primarily known for their antioxidant activity. However, these compounds have also been reported to demonstrate antibacterial, antiviral, anticarcinogenic, anti-inflammatory, anti-allergic, and vasodilatory actions. In addition, they have been found to inhibit lipid peroxidation, platelet aggregation, capillary permeability and fragility, and to affect enzyme systems including phospholipase A2, cyclooxygenase, and lipoxygenase. Based on these reported findings, OPCs may be a useful component in the treatment of a number of conditions.

Anthocyanins↗
PubMed2004

Synthesis, structure, and complexation of a large 28-mer macrocycle containing two binding sites for either anions or metal ions.

The "one-pot" synthesis and characterization of a large 28-mer macrocycle (H(4)L(2)) with oxamido units capable of complexing guest ions through oxygen or nitrogen donor atoms is reported. Single-crystal structure determination of H(8)L(2)(NO(3))(4) and (Cu(2)[H(2)L(2)](H(2)O)(2))(NO(3))(2) demonstrated that the macrocycle contains two sites capable of complexing two nitrate anions or two copper(II) ions, involving a large structural reorganization in the conformation of the macrocyclic framework on coordination of the copper(II) ions when compared to the nitrate. Electrochemical and magnetic susceptibility measurements on the dinuclear Cu(II) complex and the related mononuclear and trinuclear Cu(II) complexes derived from the related 14-mer macrocycle were carried out and illustrate the role of the oxamido groups in mediating metal-metal interaction and delocalization.

Journal Article↗
PubMed2005

Dynamics and structure in complex liquids under shear explored by neutron scattering.

It is well established that the structural order of macromolecules can be affected by the application of shear. For example, triblock copolymers in aqueous solutions are known to aggregate for high concentrations. For increasing temperature the polymer micelles crystallize and offer a model system for the investigation of percolation and crystallization. The crystalline phases rearrange under shear. We correlate the structural assemblages of polymer micelles to the microscopic dynamics of the polymer monomers as well as to the solvent molecules at rest and under shear. We find the monomer dynamics affected by the different arrangements of the polymer micelles in aqueous solutions. For pronounced structural ordering we report on the monomer diffusion to become anisotropic under shear, with the diffusive mode in the direction of the shear gradient being slowed down with respect to that in the direction of the flow.

Journal Article↗
PubMedDate not supplied

[The hierarchy of complexes and compact structures of trivaline with nucleic acids. III. Complexes of trivaline with trinucleotides forms a rod-like structure with length of about 1000 A in solution].

We demonstrated the ability of trivaline in the course of interaction with certain trinucleotides in solution to form extended fibre-like structures with lengths of up to several thousand angstroms. Such structures were observed for complexes of trivaline with both deoxyribo- and ribonucleotides with homopurine, homopyrimidine, or random sequences, with or without terminal 5'-phosphate. A model of organization of such structures is proposed. It is based on tetramer complex of trivaline with short nucleotides, two structural units of which, consisting of trivaline tetramer and two trinucleotides, form the octamer complex. It has three perpendicular axes of symmetry of the second order. The spatial location of bases in this structure is additionally fixed by nucleopeptide interactions. The latter create favourable conditions for arranging hydrogen bonds between trinucleotides belonging to different tetramer complexes and stacking interactions between the bases of each nucleotide. Octamer complexes are able to form regular aggregates in the form of a "stack", consisting of dozens of elementary units. These aggregates can be electron microscopically visualized as extended fibre-like structures.

Microscopy, Electron↗
PubMed2005

Polymorphism of bulged-out residues in HIV-1 RNA DIS kissing complex and structure comparison with solution studies.

All retroviruses encapsidate their genome as a dimer of homologous single-stranded RNAs. The dimerization initiation site (DIS) of human immunodeficiency virus type 1 (HIV-1) is located in the 5'-untranslated region of the viral genome and consists of a hairpin with a 6 nt self-complementary loop sequence. Genomic RNA dimerization, a crucial step for virion infectivity, is promoted by the formation of a loop-loop complex (or kissing complex) between two DIS hairpins. Crystal structures for the subtypes A, B and F of the HIV-1 DIS kissing complex have now been solved at 2.3 A, 1.9 A and 1.6 A, respectively. They revealed a polymorphism of bulged-out residues showing clearly that their conformation is not a mere consequence of crystal packing. They also provide more insights into ion binding, hydration, and RNA conformation and flexibility. In particular, we observed the binding of spermine to the loop-loop helix, which displaced a magnesium cation important for subtype A DIS dimerization. The excellent agreement between X-ray structures and the results of chemical probing and interference data on larger viral RNA fragments shows that the crystal structures are relevant for the DIS kissing complex present in solution and in viral particles. Accordingly, these structures will be helpful for designing new drugs derived from aminoglycoside antibiotics and targeted against the RNA dimerization step of the viral life-cycle.

5' Untranslated Regions↗
PubMed2004

Chalcogens as terminal ligands to iron: synthesis and structure of complexes with Fe(III)-S and Fe(III)-Se motifs.

Metal complexes with terminal chalcogenido ligands are known for the early transition-metal complexes, yet for the heavier congeners (e.g., sulfido and selenido), there are no analogous examples for the late 3d metal ions. Reported herein is the isolation and characterization of monomeric iron(III) complexes containing sulfido and selenido ligands; isolation was accomplished using the tripodal ligand tris[(N'-tert-butylureaylato)-N-ethylene]aminato ([H3buea]3-). The FeIII-E (E = S2-, Se2-) complexes were prepared from the iron(II) precursor, [FeII(H3buea)]2-, and the elemental forms of the chalogen. The formulation of [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2- as monomeric complexes with Fe-E units is supported by spectroscopic, analytical, and X-ray diffraction studies. For instance, X-band EPR spectra contain well-resolved axial signals, which are consistent with each complex having S = 5/2 ground states. The solid-state molecular structures reveal FeIII-E bond lengths of 2.211(1) and 2.355(1) A for [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2-, respectively. The primary coordination sphere for each complex also contains three deprotonated urea nitrogen atoms from [H3buea]3-; the apical amine nitrogen atom weakly interacts with the iron centers at distances of greater than 2.6 A. The terminal chalcogenido ligands appear to weakly hydrogen-bond with the urea NH groups of the [H3buea]3-; however, open H-bond cavities are observed for [FeIIIH3buea(S)]2- and [FeIIIH3buea(Se)]2-, which may contribute to their observed long-term instability.

Ferric Compounds↗
PubMed1997

Na(5)Sn(13): A New Zintl Phase with a Complex Network Structure Constructed from Tin Pentagons.

The compound Na(5)Sn(13) forms in the sodium-tin system in high yield following prolonged reaction of a quenched mixture at 280 degrees C in a Ta container. The compound exhibits a complex three-dimensional structure (29 independent atoms) built mainly of 4-bonded tin atoms in interbonded pentagons (orthorhombic, space group Cmcm (No. 63); a = 8.979(1) Å, b = 19.448(6) Å, c = 50.43(2) Å, Z = 16). According to Zintl-Klemm electron-counting formalisms, the compound has a closed-shell electronic configuration with the number of 3-bonded Sn(-) equal to the number of sodium cations. Property measurements show that the compound is diamagnetic.

Journal Article↗
PubMed2001

Alkynethiolato and alkyneselenolato ruthenium half-sandwich complexes: synthesis, structures, and reactions with (eta(5)-C(5)H(5))(2)Zr.

Alkynethiolato and alkyneselenolato complexes of ruthenium, CpRu(PPh(3))(2)(EC(triple bond)CR) (Cp = eta(5)-C(5)H(5); E = S, R = Ph (1a), SiMe(3) (1b), (t)Bu (1c); E = Se, R = Ph (2a), SiMe(3) (2b)), were synthesized by the reactions of CpRuCl(PPh(3))(2) with corresponding lithium alkynechalcogenolates in THF. An analogous reaction of Cp*RuCl(PEt(3))(2) (Cp* = eta(5)-C(5)Me(5)) with LiSC(triple bond)CPh produced Cp*Ru(PEt(3))(2)(SC(triple bond)CPh) (3). Complexes 1a and 2a were allowed to react in THF with "Cp(2)Zr", generated in situ from Cp(2)ZrCl(2) and 2 equiv of n-BuLi, from which the S-bridged Ru-Zr dinuclear complexes CpRu(PPh(3))(C(triple bond)CPh)(mu-S)ZrCp(2) (4a) and CpRu(PPh(3))(C(triple bond)CPh)(mu-Se)ZrCp(2) (4b) were isolated, respectively. In these complexes, C-S(Se) bond cleavage of the alkynechalcogenolate ligands was promoted by "Cp(2)Zr", and the Zr atom was oxidized from II to IV. Treatment of 4a and 4b in THF under 1 atm CO gave rise to CpRu(CO)(C(triple bond)CPh)(mu-E)ZrCp(2) (E = S (5a), Se (5b)), while addition of tert-butyl isocyanide to a THF solution of 4b afforded CpRu(CN(t)()Bu)(C(triple bond)CPh)(mu-Se)ZrCp(2) (6). The crystal structures of 1a, 1c, 2a, 2b, 3, 4a, 4b, and 5b were determined by X-ray diffraction analysis.

Journal Article↗
PubMed2003

Group 4 octahedral benzamidinate complexes: syntheses, structures, and catalytic activities in the polymerization of propylene modulated by pressure.

The synthesis and structural X-ray diffraction studies for some benzamidinate ligations and several group 4 benzamidinate complexes are presented. The use of the cis-octahedral C(2)-symmetry compounds was studied to shed light on the conceptual applicability of these complexes as potential catalysts for the stereoregular polymerization of propylene. We demonstrate that the stereoregular polymerization of propylene catalyzed by early-transition metal octahedral benzamidinate complexes, activated with either MAO or B(C(6)F(5))(3) as cocatalysts, can be modulated by pressure (from atactic to isotactic through elastomers). The different effects in the polymerization process such as the nature of solvent or cocatalyst, temperature, pressure, molar ratio catalyst:cocatalyst, and the relationship between the symmetry of the complex and the polymer microstructure have been investigated. When the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (9) was activated with MAO, it was found to be a good catalyst for the polymerization of propylene, at atmospheric pressure, producing an oily polymer resembling an atactic polypropylene. Being activated with B(C(6)F(5))(3), complex 9 produces a highly isotactic (mmmm = 98%) product. Likewise, when the polymerization of propylene was performed with complex 9 and MAO at high pressure (liquid propylene), a highly stereoregular polymer was also obtained. Larger activities and stereoregularities were achieved by performing the reaction in CH(2)Cl(2) as compared to toluene. Contrary to complex 9, at atmospheric pressure the complex [4-CH(3)-C(6)H(4)C(NTMS)(2)](2)TiMe(2) (10) is not active either in CH(2)Cl(2) or in toluene. At high pressure, complex 10 produces elastomeric polypropylene. Activities of the isolobal complexes [C(6)H(4)C(NTMS)(2)](2)ZrMe(2) (11) and [C(6)H(4)C(NTMS)(2)](2)TiMe(2) (12) were found to be larger than those of complexes 9 and 10, respectively. Contrary to the structures of the elastomeric polypropylenes described in the literature, the obtained elastomers are characterized by frequent alternation of the isotactic domains with stereodefects. The stereoregular errors are formed by the intramolecular epimerization of the growing chain at the last inserted unit. The epimerization reaction was corroborated through the isomerization of alkenes.

Journal Article↗
PubMed2006

Photoluminescence of europium(III) dithiocarbamate complexes: electronic structure, charge transfer and energy transfer.

For the first time, we observed photoluminescence in Eu(III) dithiocarbamate complexes at room temperature -- more specifically in [Eu(Et(2)NCS(2))(3)phen], [Eu(Et(2)NCS(2))(3)bpy] and the novel [Eu(Ph(2)NCS(2))(3)phen], where phen stands for 1,10-phenanthroline and bpy for 2,2'-bipyridine. Correlations between the electronic structure of the dithiocarbamate ligands on one hand, and covalency, intensity, and ligand field spectroscopic parameters on the other, could be established. Moreover, the relative values of the emission quantum efficiencies obtained for these complexes, as well as their dependence with temperature, could be satisfactorily described by a theoretical methodology recently developed.

Journal Article↗
PubMed2003

Catalytic mechanism of Escherichia coli isopentenyl diphosphate isomerase involves Cys-67, Glu-116, and Tyr-104 as suggested by crystal structures of complexes with transition state analogues and irreversible inhibitors.

Isopentenyl diphosphate (IPP):dimethylallyl diphosphate (DMAPP) isomerase is a key enzyme in the biosynthesis of isoprenoids. The reaction involves protonation and deprotonation of the isoprenoid unit and proceeds through a carbocationic transition state. Analysis of the crystal structures (2 A) of complexes of Escherichia coli IPP.DMAPPs isomerase with a transition state analogue (N,N-dimethyl-2-amino-1-ethyl diphosphate) and a covalently attached irreversible inhibitor (3,4-epoxy-3-methyl-1-butyl diphosphate) indicates that Glu-116, Tyr-104, and Cys-67 are involved in the antarafacial addition/elimination of protons during isomerization. This work provides a new perspective about the mechanism of the reaction.

Carbon-Carbon Double Bond Isomerases↗
PubMed1998

Macrocyclic Heterodinuclear Zn(II)Pb(II) Complexes: Synthesis, Structures, and Hydrolytic Function toward Tris(p-nitrophenyl) Phosphate.

A heterodinuclear Zn(II)Pb(II) complex ZnPb(L)(ClO(4))(2).2H(2)O (1) has been obtained where (L)(2)(-) is an unsymmetric macrocycle derived from the 2:1:1 condensation of 2,6-diformyl-4-methylphenol, ethylenediamine and diethylenetriamine and has the "salen"- and "saldien"-like metal-binding sites sharing the phenolic moiety. Its DMF adduct, ZnPb(L)(ClO(4))(2).MeOH.2DMF (1'), crystallizes in the triclinic space group P&onemacr; with a = 14.457(4) Å, b = 14.795(6) Å, c = 10.307(9) Å, alpha = 109.04(5) degrees, beta = 96.24(5) degrees, gamma = 102.56(3) degrees, V = 1995(2) Å(3), and Z = 2. The refinement converges with R = 0.058 and R(w) = 0.060 for 3532 reflections with |F(0)| > 3sigma(|F(0)|). It has a discrete heterodinuclear core with the Zn(II) in the "salen" site and the Pb(II) in the "saldien" site of the macrocycle (L)(2)(-). The Zn has a square-pyramidal geometry together with a methanol oxygen, and the Pb has a seven-coordinate geometry together with one DMF oxygen and one perchlorate oxygen. The complex 1 is converted into [ZnPb(L)(OH)ClO(4)]H(2)O (2) under a weak alkaline condition. Its anhydrous form, [ZnPb(L)(OH)]ClO(4) (2), crystallizes in the monoclinic space group C2/c with a = 25.835(4) Å, b = 13.190(6) Å, c = 16.553 Å, beta = 106.31(2) degrees, V = 5413(2) Å(3), and Z = 8. The refinement converges with R = 0.038 and R(w) = 0.029 for 3944 reflections with |F(0)| > 3sigma(|F(0)|). It has a dimer structure of a dinuclear {ZnPb(L)(OH)}(+) unit having the Zn(II) in the "salen" site and the Pb(II) in the "saldien" site of the macrocycle. The hydroxide is bound to the Zn(II) to afford a square-pyramidal geometry about the metal. The dimeric core [ZnPb(L)(OH)](2)(2+) is formed by the bridge of the hydroxide oxygen to the Pb of the adjacent molecule and vice versa. The geometry about the Pb in the dimer structure is a pentagonal pyramid showing a distortion to "umbrella-like" structure, with the bridging hydroxide oxygen at the apex. In a DMSO solution, an equilibrium exists between the dimeric and monomeric species: [{ZnPb(L)(OH)}(2)](2+) right harpoon over left harpoon 2[ZnPb(L)(OH)](+). On the basis of (31)P NMR and visible spectra, 2 is shown to hydrolyze tris(p-nitorophenyl) phosphate (TNP) into bis(p-nitrophenyl) phosphate (BNP) in DMSO. 1 also exhibits a low activity to hydrolyze TNP into BNP due to the equilibrium [ZnPb(L)(H(2)O)](2+) right harpoon over left harpoon [ZnPb(L)(OH)](+) + H(+). From the reaction mixture with 2, a BNP complex [ZnPb(L)(BNP)]ClO(4) (3) has been isolated. 3 crystallizes in the triclinic space group P&onemacr; with a = 13.494(9) Å, b = 13.88(1) Å, c = 12.765(8) Å, alpha = 94.71(6) degrees, beta = 97.02(6) degrees, gamma = 61.68(5) degrees, V = 2088(2) Å(3), Z = 2. The refinement converges with R = 0.044 and R(w) = 0.056 for 6070 reflections with |F(0)| > 3sigma(|F(0)|). The BNP(-) group bridges the pair of metal ions through its two oxygens, together with two phenolic oxygens of (L)(2)(-). On the basis of the above findings, a mechanistic scheme for the TNP hydrolysis by 2 is proposed; a TNP molecule is bound to the Pb center, and the hydroxide on the adjacent Zn ion attacks the phosphorus nucleus of TNP, leading to the formation of the BNP complex 3.

Journal Article↗
PubMed2006

Quantifying degeneration of white matter in normal aging using fractal dimension.

Although degeneration of brain white matter (WM) in aging is a well-recognized problem, its quantification has mainly relied on volumetric measurements, which lack detail in describing the degenerative adaptation. In this study, WM structural complexity was evaluated in healthy old and young adults by analyzing the three-dimensional fractal dimension (FD) of WM segmented from magnetic resonance images of brain. FDs detected in the old were significantly smaller than in the young subjects. Specifically, WM interior structure complexity degenerated in the left hemisphere in old men but in the right hemisphere in old women. Men showed more complex WM patterns than women. An asymmetrical (right-greater-than-left-hemisphere) complexity pattern was observed in the interior and general structures of WM, yet the surface complexity was symmetrical across WM structures of the two hemispheres. WM volumes were also measured, but no significant decline was found with aging. These results suggest that the deterioration of WM complexity is not uniformly distributed between the genders and across brain hemispheres.

Adolescent↗