DERMATOLOGIC SURGERY, Issue 6 2005
Mohammed Alhaddab MD
Background. The maximum number of hair grafts that can be safely implanted in 1 cm2 is still debatable. To our knowledge, no previous report has addressed this issue in three dimensions, taking into account the size, the angle of the graft, and the intergraft distance. Objectives. To study the effect of the size and angle of the graft and the intergraft distance on dense packing. Methods. Using a mathematical formula (the maximum number of hair grafts in 1 cm2 = 33 * cosine), the volume of the recipient area and the volume of the hair graft are calculated, assuming that the surface area of the recipient area is 1 cm2, the diameter of the hair graft is 1 mm, and the intergraft distance is 1.5 mm laterally and 1 mm anteriorly and posteriorly. Results. The maximum number of hair grafts that could be implanted in 1 cm2 at a 90 angle in relation to the skin surface is 33 grafts, at a 60 angle is 28 grafts, and at a 30 angle is 16 grafts. Conclusion. The maximum number of hair grafts that can be implanted in any given recipient area depends on the graft size, the angle or direction of these grafts, and the intergraft distance. Where more space is allowed between the grafts, and the more acute the angle, the fewer hair grafts that can be implanted. [source]

Substituent Effects on Crosslike Packing of 2,,7,-Diaryl- spiro(cyclopropane-1,9,-fluorene) Derivatives: Synthesis and Crystallographic, Optical, and Thermal Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007
Z. Wang
Abstract A series of 2,,7,-diarylspiro(cyclopropane-1,9,-fluorene) derivatives are efficiently synthesized and characterized to determine the reason for the "green-light" emission of these compounds. These compounds exhibit bright-violet to blue photoluminescence (PL) (,PLmax,=,353,419,nm) with excellent PL quantum efficiencies (,PL,=,83,100,%) in solution and show high thermal stabilities (Td,=,267,474,°C). The variation of the optical properties of these molecules in the solid state depends on the different stacking modes of these compounds containing different substituents, which are revealed by crystallographic analysis. CH,, hydrogen bonds instead of intermolecular ,,, interactions act as the driving force between adjacent fluorenes, even though a very small dialkyl group (cyclopropane) is introduced at the C-9 position of fluorene. The crosslike molecular stacking efficiently reduces the energy transfer between the herring-like aggregates and therefore results in the absence of a "green-light" emission tail. In order to determine the cause of the "green-light" emission tails, the fluorescence spectra of the films annealed in N2 or in air are recorded. Broad green-light emission tails were observed for the films annealed in air, which might be caused by fluorenone defects generated during processing or during the course of the photophysical analysis by reaction with residual oxygen. [source]

Molecular Tectonics at the Solid/Liquid Interface: Controlling the Nanoscale Geometry, Directionality, and Packing of 1D Coordination Networks on Graphite Surfaces

ADVANCED MATERIALS, Issue 10-11 2009
Artur Ciesielski
Supramolecular arrays composed of 1-D coordination networks on surfaces, with nanoscale control over both the geometry and the directionality, are achieved through the design and combination of organic tectons with metal complexes (CoCl2) or metal centers (Pd(BF4)2). Scanning tunneling microscope at the solid/liquid interface allows the visualization of long and shape-persistent arrays, with either linear or zig-zag geometries. [source]

Pyridinium Cross-Links in Bone of Patients with Osteogenesis Imperfecta: Evidence of a Normal Intrafibrillar Collagen Packing

JOURNAL OF BONE AND MINERAL RESEARCH, Issue 7 2000
Ruud A. Bank Ph.D.
Abstract The brittleness of bone in patients with osteogenesis imperfecta (OI) has been attributed to an aberrant collagen network. However, the role of collagen in the loss of tissue integrity has not been well established. To gain an insight into the biochemistry and structure of the collagen network, the cross-links hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) and the level of triple helical hydroxylysine (Hyl) were determined in bone of OI patients (types I, III, and IV) as well as controls. The amount of triple helical Hyl was increased in all patients. LP levels in OI were not significantly different; in contrast, the amount of HP (and as a consequence the HP/LP ratio and the total pyridinoline level) was significantly increased. There was no relationship between the sum of pyridinolines and the amount of triple helical Hyl, indicating that lysyl hydroxylation of the triple helix and the telopeptides are under separate control. Cross-linking is the result of a specific three-dimensional arrangement of collagens within the fibril; only molecules that are correctly aligned are able to form cross-links. Inasmuch as the total amount of pyridinoline cross-links in OI bone is similar to control bone, the packing geometry of intrafibrillar collagen molecules is not disturbed in OI. Consequently, the brittleness of bone is not caused by a disorganized intrafibrillar collagen packing and/or loss of cross-links. This is an unexpected finding, because mutant collagen molecules with a random distribution within the fibril are expected to result in disruptions of the alignment of neighboring collagen molecules. Pepsin digestion of OI bone revealed that collagen located at the surface of the fibril had lower cross-link levels compared with collagen located at the inside of the fibril, indicating that mutant molecules are not distributed randomly within the fibril but are located preferentially at the surface of the fibril. [source]

Temperature and Pressure Effects on Local Structure and Chain Packing in cis -1,4-Polybutadiene from Detailed Molecular Dynamics Simulations

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006
Georgia Tsolou
Abstract Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis -1,4-polybutadiene (cis -1,4-PB) from detailed molecular dynamics (MD) simulations with a united-atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C128cis -1,4-PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, Cn; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Qmax, in the S(q) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S(q) vs. q plot representing intramolecular contributions in a fully deuterated cis -1,4-PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Å,1) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity. 3D view of the simulation box containing 32 chains of C128cis -1,4-polybutadiene at density ,,=,0.849 g,·,cm,3 and the conformation of a single C128cis -1,4-PB chain fully unwrapped in space. [source]

Structure and conformational analysis of a bidentate pro-ligand, C21H34N2S2, from powder synchrotron diffraction data and solid-state DFTB calculations

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 5 2009
Edward E. Ávila
The molecular and crystalline structure of ethyl 1,,2,,3,,4,,4a,,5,,6,,7,-octahydrodispiro[cyclohexane-1,2,-quinazoline-4,,1,,-cyclohexane]-8,-carbodithioate (I) was solved and refined from powder synchrotron X-ray diffraction data. The initial model for the structural solution in direct space using the simulated annealing algorithm implemented in DASH [David et al. (2006). J. Appl. Cryst.39, 910,915] was obtained performing a conformational study on the fused six-membered rings of the octahydroquinazoline system and the two spiran cyclohexane rings of (I). The best model was chosen using experimental evidence from 1H and 13C NMR [Contreras et al. (2001). J. Heterocycl. Chem.38, 1223,1225] in combination with semi-empirical AM1 calculations. In the refined structure the two spiran rings have the chair conformation, while both of the fused rings in the octahydroquinazoline system have half-chair conformations compared with in-vacuum density-functional theory (DFT) B3LYP/6-311G*, DFTB (density-functional tight-binding) theoretical calculations in the solid state and other related structures from X-ray diffraction data. Compound (I) presents weak intramolecular hydrogen bonds of the type N,H...S and C,H...S, which produce delocalization of the electron density in the generated rings described by graph symbols S(6) and S(5). Packing of the molecules is dominated by van der Waals interactions. [source]

Detection and Analysis of Chimeric Tertiary Structures by Backbone Thioester Exchange: Packing of an ,,Helix against an ,/,-Peptide Helix,

ANGEWANDTE CHEMIE, Issue 2 2010
Joshua
Über den Austausch von Rückgratthioestern wurde ein Basistyp des Protein-Foldamer-Packungsmotivs untersucht, die Assoziation einer ,-Helix und einer ,/,-Peptidfoldamer-Helix. Er ist analog zu einer antiparallelen Doppelwendel-Tertiärstruktur in einem reinen ,-Reste-Rückgrat. Die Seitenkettenpackungspräferenzen an dieser chimären Grenzfläche ähneln denen, die die Paarungstendenzen zwischen antiparallelen ,-Helices bestimmen. [source]

A structural systematic study of four isomers of difluoro- N -(3-pyridyl)benzamide

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2009
Joyce McMahon
The four isomers 2,4-, (I), 2,5-, (II), 3,4-, (III), and 3,5-difluoro- N -(3-pyridyl)benzamide, (IV), all with formula C12H8F2N2O, display molecular similarity, with interplanar angles between the C6/C5N rings ranging from 2.94,(11)° in (IV) to 4.48,(18)° in (I), although the amide group is twisted from either plane by 18.0,(2),27.3,(3)°. Compounds (I) and (II) are isostructural but are not isomorphous. Intermolecular N,H...O=C interactions form one-dimensional C(4) chains along [010]. The only other significant interaction is C,H...F. The pyridyl (py) N atom does not participate in hydrogen bonding; the closest H...Npy contact is 2.71,Å in (I) and 2.69,Å in (II). Packing of pairs of one-dimensional chains in a herring-bone fashion occurs via,-stacking interactions. Compounds (III) and (IV) are essentially isomorphous (their a and b unit-cell lengths differ by 9%, due mainly to 3,4-F2 and 3,5-F2 substitution patterns in the arene ring) and are quasi-isostructural. In (III), benzene rotational disorder is present, with the meta F atom occupying both 3- and 5-F positions with site occupancies of 0.809,(4) and 0.191,(4), respectively. The N,H...Npy intermolecular interactions dominate as C(5) chains in tandem with C,H...Npy interactions. C,H...O=C interactions form R22(8) rings about inversion centres, and there are ,,, stacks about inversion centres, all combining to form a three-dimensional network. By contrast, (IV) has no strong hydrogen bonds; the N,H...Npy interaction is 0.3,Å longer than in (III). The carbonyl O atom participates only in weak interactions and is surrounded in a square-pyramidal contact geometry with two intramolecular and three intermolecular C,H...O=C interactions. Compounds (III) and (IV) are interesting examples of two isomers with similar unit-cell parameters and gross packing but which display quite different intermolecular interactions at the primary level due to subtle packing differences at the atom/group/ring level arising from differences in the peripheral ring-substitution patterns. [source]

Packing of ruthenium sensitizer molecules on mostly exposed faces of nanocrystalline TiO2: crystal structure of (NBu4+)2[Ru(H2tctterpy)(NCS)3]2,·0.5,DMSO

APPLIED ORGANOMETALLIC CHEMISTRY, Issue 11 2002
V. Shklover
Abstract An X-ray crystal study of the new ,black dye' sensitizer tri(thiocyanato)(4,4,,4,-tricarboxy-2,2,:6,,2,-terpyridine)ruthenium(II) is reported. In the crystal, strong hydrogen bonds form chains of ruthenium complex dianions with the O···O distances of 2.48,2.54,Å. From the molecular geometry of the dianions, structural models of their close packing on the (101) and (001) crystal surfaces of TiO2 (anatase) have been built. The maximum possible density of molecular packing noticeably exceeds the experimental value. The hydrogen bonding between the anions in monolayers, located on the TiO2 surface, is discussed. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Routine Packing of Simple Cutaneous Abscesses Is Painful and Probably Unnecessary

ACADEMIC EMERGENCY MEDICINE, Issue 5 2009
Gerald F. O'Malley DO
Abstract Objectives:, The objective was to determine whether the routine packing of simple cutaneous abscesses after incision and drainage (I&D) confers any benefit over I&D alone. Methods:, In a prospective, randomized, single-blinded trial, subjects with simple cutaneous abscesses (less than 5 cm largest diameter) underwent incision, drainage, irrigation, and standard abscess preparation in the usual manner. Subjects were then randomized to either packing or no-packing. Visual analog scales (VAS; 100 mm) of pain were recorded in the emergency department (ED). All patients received trimethoprim-sulfamethoxazole (TMP-SMX), ibuprofen, and narcotic prescriptions, recorded twice daily VAS pain scores, and returned in 48 hours at which time dressings and packing, if present, were removed and a physician blinded to the randomization and not part of the initial visit repeated measurements and determined the need for further intervention. Results:, Forty-eight subjects were included in the final analysis. There were no significant differences in age, sex, abscess location, or initial pain scores between the two groups. There was no significant difference in need for a second intervention at the 48-hour follow-up between the packed (4 of 23 subjects) and nonpacked (5 of 25 subjects) groups (p = 0.72; relative risk = 1.3, 95% confidence interval [CI] = 0.4 to 4.2). Patients in the group that received packing reported higher pain scores immediately postprocedure (mean difference = 23.8 mm; p = 0.014, 95% CI = 5 to 42 mm) and at 48 hours postprocedure (mean difference = 16.4 mm; p = 0.03, 95% CI = 1.6 to 31.2 mm), as well as greater use of ibuprofen (mean difference = 0.32; p = 0.12, 95% CI = ,1.4 to 2.0) and oxycodone/acetaminophen (mean difference = 2.19; p = 0.03, 95% CI = 0.2 to 4.1). Conclusion:, In this pilot study, not packing simple cutaneous abscesses did not result in any increased morbidity, and patients reported less pain and used fewer pain medications than packed patients. [source]

A Cruciform 6,6,-Dipentacenyl: Synthesis, Solid-State Packing and Applications in Thin-Film Transistors

CHEMISTRY - A EUROPEAN JOURNAL, Issue 11 2010
Xiaojie Zhang Dr.
No abstract is available for this article. [source]

Synthesis and Liquid Crystalline Properties of Mono-, Di- and Tri- O -alkyl Pentaerythritol Derivatives Bearing Tri-, Di- or Monogalactosyl Heads: The Effects of Curvature of Molecular Packing on Mesophase Formation

CHEMISTRY - A EUROPEAN JOURNAL, Issue 19 2007
Fabienne Dumoulin Dr.
Abstract Self-organisation and self-assembly are critical to the stability of synthetic and biological membranes. Of particular importance is consideration of the packing arrangements of the various molecular species. Both phospho- and glycolipids can pack in ways in which curvature can be introduced into self-organised or self-assembled systems. For instance, it is known that the degree of curvature can affect the structures of any condensed phases that are formed. In this article we report on a systematic study in which we have varied the shapes of glycolipids and examined the condensed phases that they form. In doing so, we have also unified the shape dependency of lyotropic liquid crystals with those of thermotropic liquid crystals. In order to undertake this systematic study a range of different pentaerythritol derivatives was synthesized, which covers combinations of one to three alkyl chains of different lengths (6,7,9,10,11,12,14,16 carbon atoms) and three to one galactosyl heads. Mono- and di- O -galactosyl derivatives were prepared directly by glycosylation of the corresponding alcohols using 2,3,4,6-tetra- O -benzoyl or acetyl - ,- D - galactopyranosyl trichloroacetimidate or bromide as the donors; the tri- O -galactosyl derivatives were synthesized from O -alkyl- O -benzyl di- O -galactosyl pentaerythritol intermediates, followed by de- O -benzylation and glycosylation steps. All of the fully deprotected products were obtained by standard methods, and their self-organising and self-assembling properties examined. [source]

Molecular Conformation and Packing of Peptide , Hairpins in the Solid State: Structures of Two Synthetic Octapeptides Containing 1-Aminocycloalkane-1-Carboxylic Acid Residues at the i+2 Position of the , Turn

CHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2005
Veldore Vidya Harini
Abstract Peptide ,-hairpin formation is facilitated by centrally positioned D -Pro-Xxx segments. The synthetic peptides Boc-Leu-Phe-Val- D -Pro-Ac6c-Leu-Phe-Val-OMe (1) and Boc-Leu-Phe-Val- D -Pro-Ac8c-Leu-Phe-Val-OMe (2) were synthesized in order to explore the role of bulky 1-aminocycloalkane-1-carboxylic acid residues (Acnc, where n is the number of carbon atoms in the ring), at the i+2 position of the nucleating , turn in peptide , hairpins. Peptides 1 and 2 crystallize in the monoclinic space group P21 with two molecules in the asymmetric unit. The crystal structures of 1 and 2 provide conformational parameters for four peptide hairpin molecules. In all cases, the central segments adopts a type II, ,-turn conformation, and three of the four possible cross-strand hydrogen bonds are observed. Fraying of the hairpins at the termini is accompanied by the observation of NH,,,, interaction between the Leu(1)NH group and Phe(7) aromatic group. Cross strand stabilizing interactions between the facing residues Phe(2) and Phe(7) are suggested by the observed orientation of aromatic rings. Anomalous far-UV CD spectra observed in solution suggest that close proximity of the Phe rings is maintained even in isolated molecules. In both peptides 1 and 2, the asymmetric unit consists of approximately orthogonal hairpins, precluding the formation of a planar ,-sheet arrangement in the solid state. Solvent molecules, one dioxane and one water in 1, three water molecules in 2, mediate peptide association. A comparison of molecular conformation and packing motifs in available ,-hairpin structures permits delineation of common features. The crystal structures of ,-hairpin peptides provide a means of visualizing different modes of ,-sheet packing, which may be relevant in developing models for aggregates of polypeptides implicated in disease situations. [source]

Portraying the Countercurrent Flow on Packings by Three-Dimensional Computational Fluid Dynamics Simulations

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 10 2008
Y. Y. Xu
Abstract The design of packed columns requires the detailed description of the hydrodynamics on the surface of the packings. To analyze the local flow behavior of the liquid phase, a three-dimensional Computational Fluid Dynamics (CFD) model was developed that applies to the two-phase countercurrent flow on an inclined and flat plate. This model, based on the volume-of-fluid (VOF) method, considers the gravity, the surface tension and the drag force between the two phases. The development of such a model allows investigation of the influences of the liquid and gas flow rates on the flow behavior such as the film flow and the rivulet flow. A validation of the model was performed using data from the literature and from experiments conducted in this work. Simulation and experimental results demonstrate that the specific wetted area on the plate decreases with decreasing liquid load. Moreover, CFD simulations reveal that the presence of the countercurrent gas phase tends to increase the fluctuation and the thickness of the film flow, which is in accordance with experimental data. It also affects the flow behavior of the rivulet flow and changes the velocity profiles for both film and rivulet flow behavior. On the other hand, the simulation results indicate that CFD is a potent tool for analyzing and investigating the flow phenomena in chemical engineering. [source]

A Study on Modern High Effective Random Packings for Ethanol-Water Rectification

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2008
S. Darakchiev
Abstract Raschig Super-Ring is a modern and high-efficient packing used for intensification of absorption and distillation processes. The aim of this work is to characterize the efficiency of this packing applied to rectification of an important industrial system, ethanol-water, and to compare its efficiency to that of some random packings of the third generation as well as to the structured packing, HOLPACK, which is used in the ethanol production industry. The experiments were carried out in a column installation, 0.213,m in diameter with a packing height of 2.8,m. The column is heated by a number of electrical heaters (total power 45,kW), which can be switched gradually. Operation at total and partial reflux is possible. Eight types of random packings were studied: five types of Raschig Super-Ring, four metallic (with characteristic dimensions 0.5, 0.6, 0.7, and 1") and one of plastic material 0.6"; two types of packing IMTP and one plastic Ralu Flow. Some experiments were conducted at total reflux operation at vapor velocity, 0.253,0.936,m/s, and liquid superficial velocity, 4.44,·,10,4,1.63,·,10,3,m3/(m2s). Experiments at partial reflux were carried out at constant liquid superficial velocity and changeable vapor velocity as well as at constant vapor velocity and changeable liquid velocity. The results are presented as height of transfer unit, HTU, and height equivalent to a theoretical plate, HETP, as a function of the velocity of phases. [source]

Preparation of Immobilized Metal Affinity Chromatographic Packings by Immobilization of Carboxymethylated Asparate (CM-Asp) Based on Monodisperse Hydrophilic Non-porous Beads and Their Application

CHINESE JOURNAL OF CHEMISTRY, Issue 7 2010
Bolin Gong
Abstract The hydrophilic immobilized metal affinity chromatographic packing was prepared by immobilization of carboxymethylated asparate (CM-Asp) as chelating ligand and Ni2+ as center ion on the base of monodispersed, 3.0 µm non-porous monodisperse poly(glycidylmethacrylate- co -ethylenedimethacrylate) (PGMA/EDMA) particles. The retention behavior of proteins and the effect of pH on the retention in the range from 4.0 to 9.0 were investigated on both the naked and metal ion chelated columns. Four proteins were quickly separated in 2.0 min with linear gradient elution at a flow rate of 3.0 mL·min,1 by using the synthesized Ni2+ -CM-Asp-PGMA/EDMA packings. The separation time was shorter than other immobilized metal affinity chromatography reported in the literature. The Ni2+ -CM-Asp-PGMA/EDMA column was further investigated for the rapid separation and purification of copper-zinc superoxide dismutase (Cu,Zn-SOD) from the blood of pig in 3.0 min with only one step. The results obtained were satisfactory. [source]

Preparation of Immobilized Metal Affinity Chromatographic Packings Based on Monodisperse Hydrophilic Non-porous Beads and Their Application

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2008
Chun-Miao BO
Abstract Three hydrophilic immobilized metal affinity chromatographic packings for HPLC have been synthesized by chemical modification of 3.0 µm monodisperse non-porous poly(glycidyl methacrylate- co -ethylenedimethacrylate) (PGMA/EDMA) beads. The retention behavior of proteins on the metal ion chelated columns loaded with copper(II), nickel(II) and zin(II) ion was studied. The effect of pH on the protein retention was investigated on both the naked and metal ion chelated columns in the range from 4.0 to 9.0. Four proteins were quickly separated in 3.0 min with linear gradient elution at a flow rate of 3.0 mL/min by using the synthesized Ni2+ -IDA (iminodiacetic acid) packings. The separation time was shorter than other immobilized metal affinity chromatography reported in the literature. Purification of lysozyme from egg white and trypsin on the commercially available trypsin was performed on the naked-IDA and Cu2+ -IDA columns, respectively. The purities of the purified trypsin and lysozyme were more than 92% and 95%, respectively. [source]

Synthesis and crystal structure determination of two dispiro compounds from laboratory x-ray powder diffraction data

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 2 2008
A. M. Moustafa
Abstract The crystal structures of the dispiro compounds 1,3,4,8,10,11-Hexaphenyl-13-methyl-1,2,8,9,13-pentaazadispiro[4.1.4.3]tetradeca-2,9-dien-6-one (3a) and 4,11-Bis(4-methoxyphenyl)-13-methyl-1,3,8,10-tetraphenyl-1,2,8,9,13-pentaazadispiro-[4.1.4.3]tetradeca-2,9-dien-6-one (3b) have been determined at room temperature from X-ray powder diffraction data using the method of simulated annealing as implemented in the programs DASH and TOPAS. Subsequent Rietveld refinements using the data collected to 1.5 Å resolution yielded R-Bragg values of 2.2% for (3a) and 3.7% for (3b). It was found, that both compounds crystallize in the monoclinc space group P 21/n with lattice parameters of a = 17.1656(5) Å, b =13.8128(3) Å, c = 16.1016(5) Å, and , = 103.7330(2)° for (3a) and a = 17.2529(8) Å, b = 13.8729(5) Å, c =16.1287(10) Å, and , = 103.6910(3)° for (3b). Both compounds exhibit a distorted hexagonal close type of packing (hcp) of the molecular centers of gravity. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The deaf mouse mutant whirler suggests a role for whirlin in actin filament dynamics and stereocilia development

CYTOSKELETON, Issue 7 2007
Mette M. Mogensen
Abstract Stereocilia, finger-like projections forming the hair bundle on the apical surface of sensory hair cells in the cochlea, are responsible for mechanosensation and ultimately the perception of sound. The actin cytoskeleton of the stereocilia contains hundreds of tightly cross-linked parallel actin filaments in a paracrystalline array and it is vital for their function. Although several genes have been identified and associated with stereocilia development, the molecular mechanisms responsible for stereocilia growth, maintenance and organisation of the hair bundle have not been fully resolved. Here we provide further characterisation of the stereocilia of the whirler mouse mutant. We found that a lack of whirlin protein in whirler mutants results in short stereocilia with larger diameters without a corresponding increase in the number of actin filaments in inner hair cells. However, a decrease in the actin filament packing density was evident in the whirler mutant. The electron-density at the tip of each stereocilium was markedly patchy and irregular in the whirler mutants compared with a uniform band in controls. The outer hair cell stereocilia of the whirler homozygote also showed an increase in diameter and variable heights within bundles. The number of outer hair cell stereocilia was significantly reduced and the centre-to-centre spacing between the stereocilia was greater than in the wildtype. Our findings suggest that whirlin plays an important role in actin filament packing and dynamics during postnatal stereocilium elongation. Cell Motil. Cytoskeleton 2007. © 2007 Wiley-Liss, Inc. [source]

Effect of Graft Size, Angle, and Intergraft Distance on Dense Packing in Hair Transplant

Neural agrin increases postsynaptic ACh receptor packing by elevating rapsyn protein at the mouse neuromuscular synapse

DEVELOPMENTAL NEUROBIOLOGY, Issue 9 2008
Jennifer Brockhausen
Abstract Fluorescence resonance energy transfer (FRET) experiments at neuromuscular junctions in the mouse tibialis anterior muscle show that postsynaptic acetylcholine receptors (AChRs) become more tightly packed during the first month of postnatal development. Here, we report that the packing of AChRs into postsynaptic aggregates was reduced in 4-week postnatal mice that had reduced amounts of the AChR-associated protein, rapsyn, in the postsynaptic membrane (rapsyn+/, mice). We hypothesize that nerve-derived agrin increases postsynaptic expression and targeting of rapsyn, which then drives the developmental increase in AChR packing. Neural agrin treatment elevated the expression of rapsyn in C2 myotubes by a mechanism that involved slowing of rapsyn protein degradation. Similarly, exposure of synapses in postnatal muscle to exogenous agrin increased rapsyn protein levels and elevated the intensity of anti-rapsyn immunofluorescence, relative to AChR, in the postsynaptic membrane. This increase in the rapsyn-to-AChR immunofluorescence ratio was associated with tighter postsynaptic AChR packing and slowed AChR turnover. Acute blockade of synaptic AChRs with ,-bungarotoxin lowered the rapsyn-to-AChR immunofluorescence ratio, suggesting that AChR signaling also helps regulate the assembly of extra rapsyn in the postsynaptic membrane. The results suggest that at the postnatal neuromuscular synapse agrin signaling elevates the expression and targeting of rapsyn to the postsynaptic membrane, thereby packing more AChRs into stable, functionally-important AChR aggregates. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008 [source]

Dry film microchips for miniaturised separations

ELECTROPHORESIS, Issue 24 2009
Rosanne M. Guijt
Abstract In this work microfluidic devices were made from the dry film photoresist Ordyl SY330, characterised by optical and electron microscopy and used for electrophoretic separations. A simple and fast microfabrication process was developed for the fabrication of channels that are 50,,m wide and 30,,m in height, requiring only the use of an office laminator, a hot plate, an exposure source and mask and an electric drill to make four microdevices in less than 1,h. The optical properties of the photoresist were studied and the resist showed significant absorbance below 370,nm and 570,630,nm, and had an optical transmission of 80% between 400 and 550,nm. Fluorescence emission over the region of maximum transmission was low allowing these devices to be used for fluorescence detection at 488/512,nm. Electrophoretic separation of APTS and three derivatised sugars was performed in 20,mM phosphate buffer, pH 2.5 with efficiencies of the three sugars of 40,000 plates (2,100,000,plates/m) within 30,s at a field strength of 500,V/cm. The simple fabrication process also allowed microchannels to be easily filled with chromatography particles before sealing, avoiding the challenging task of slurry packing, and the potential of these devices for liquid chromatography was demonstrated by the extraction of fluorescein onto anion exchange particles. [source]

Procedural skills quality assurance among Australasian College for Emergency Medicine fellows and trainees

EMERGENCY MEDICINE AUSTRALASIA, Issue 3 2006
David McD Taylor
Abstract Objective: Presently, no objective quality control mechanism exists for monitoring procedural skills among Australasian College for Emergency Medicine trainees. The present study examined trainee and fellow procedural experience and perceived competency, participation in accredited training courses and support for a procedural logbook. Methods: A cross-sectional mail survey of Australasian College for Emergency Medicine advanced trainees and fellows was performed. Experience and perceived competency in 23 common and important ED procedures were examined. Results: In total, 202 fellows and 264 trainees responded (overall response rate 39.0%). Overall, fellow procedural experience and perceived competency were reasonable. However, some fellows had never performed a number of procedures including some common procedures (e.g. nasal packing, fracture reduction) and there were reports of ,very poor' competency for 17 (73.9%) procedures. Trainee experience and perceived competency were less than the fellows but showed similar patterns. Perceived numbers of each procedure required to achieve competency varied considerably between the procedures and among the respondents. However, there were no significant differences in the perceived numbers reported by the trainees and the fellows (P > 0.05). Variable proportions of trainees and fellows had undertaken courses that incorporated procedural skills training. More fellows (75.7%, 95% confidence interval 69.1,81.4) than trainees (59.9%, 95% confidence interval 53.6,65.8) supported the use of a procedural logbook (P = 0.003). Conclusions: Lack of experience in some procedures among some fellows, especially commonly performed procedures, might represent a deficiency in existing quality assurance mechanisms for procedural skills training. Greater participation in skills courses, to improve experience in difficult and uncommonly encountered procedures, is recommended. Improved quality assurance mechanisms, including a procedural logbook, should be considered. [source]

Cytotoxic effects induced by hexachlorobenzene in Squilla mantis (L.) (Crustacea, Stomatopoda)

ENVIRONMENTAL TOXICOLOGY, Issue 1 2008
Antonio Dell'Anno
Abstract Contamination of marine environments by hexachlorobenzene (HCB) represents a serious concern for potential consequences on ecosystem and human health. Despite this, information on cytotoxic effects on marine organisms is still largely lacking. In this study, we investigated cytotoxic effects induced by HCB on gonads and muscular tissue of Squilla mantis by analysing Na+/K+ -ATPase activity and plasma membrane fluidity. This crustacean species was selected as a model for its habitat, trophic level, feeding behavior, and commercial exploitation for human consumption. Time course experiments revealed that low concentrations of HCB (i.e. 50 nM) determine an exponentially decrease of Na+/K+ -ATPase activity and a significant modification of cellular membrane fluidity. Significant negative relationships between Na+/K+ -ATPase activity and membrane fluidity were observed, suggesting that changes in the structure and packing of cellular membranes induced by HCB may be the primary factor affecting the activity of essential bilayer-associated enzymes. Overall these findings suggest that even small concentrations of HCB may determine important changes on cell metabolism with potential cascade effects on recruitment of this commercial species. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2008. [source]

Spatial,temporal marked point processes: a spectrum of stochastic models

ENVIRONMETRICS, Issue 3-4 2010
Eric Renshaw
Abstract Many processes that develop through space and time do so in response not only to their own individual growth mechanisms but also in response to interactive pressures induced by their neighbours. The growth of trees in a forest which compete for light and nutrient resources, for example, provides a classic illustration of this general spatial,temporal growth-interaction process. Not only has its mathematical representation proved to be a powerful tool in the study and analysis of marked point patterns since it may easily be simulated, but it has also been shown to be highly flexible in terms of its application since it is robust with respect to incorrect choice of model selection. Moreover, it is highly amenable to maximum likelihood and least squares parameter estimation techniques. Currently the algorithm comprises deterministic growth and interaction coupled with a stochastic arrival and departure mechanism. So for systems with a fixed number of particles there is an inherent lack of randomness. A variety of different stochastic approaches are therefore presented, from the exact event,time model through to the associated stochastic differential equation, taking in time-increment and Tau- and Langevin-Leaping approximations en route. The main algorithm is illustrated through application to forest management and high-intensity packing of hard particle systems, and comparisons are made with the established force biased approach. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Decomposition Cascades of Dicoordinate Copper(I) Chalcogenides

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2007
Heiko Jacobsen
Abstract Cu,E, Si,E, and Cu,P bond energies of R3PCuESiR3 and CuESiR3 complexes (E = O, S, Se) have been investigated using PBE density-functional calculations, and including empirical corrections for dispersive interactions (DFT-D). The bond energies have been used to investigate likely pathways of molecular decomposition. The energy profile for thermal decomposition is to a large degree independent of the nature of the phosphane ligands and silyl groups. Oxides, sulfides, and selenides have qualitatively the same thermal decomposition profile. Thermal decomposition is not likely to produce copper chalcogenide units CuE, but elemental copper Cu instead. Consideration of intermolecular van der Waals attraction suggests that the linear geometry of system tBu3PCuOSiPh3 as found in the crystal is most likely due to crystal packing and intermolecular forces.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Thermal Behavior of Tetrahydropyran-Intercalated VOPO4: Structural and Dynamics Study

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2007
Klára Melánová
Abstract The thermal behavior of tetrahydropyran-(THP-)intercalated VOPO4 was probed by an extensive combination of experimental methods (XRD, DSC, FTIR, solid-state NMR) and quantum chemical calculations. Two temperature-induced transitions were detected and all polymorphs exhibit a high degree of molecular order and tight packing of THP in VOPO4. The first reversible thermal transition at around 100 °C was attributed to boat/chair conformation changes of the THP molecules. Most probably, a low-temperature boat conformation of the guest molecules present in the interlayer space of VOPO4 changes to a high-temperature chair conformation. This rearrangement of the THP molecules was confirmed by variable-temperature 13C CP/MAS NMR spectroscopy. Quantum chemical calculations using a B3LYP functional and 6-31G(d) basis set also support this idea. The second change at around 140 °C is probably caused by a weakening of the donor,acceptor bond between the oxygen molecule of THP and the vanadium atom of the host and the formation of a disorder in packing of the THP molecules. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

High-Zirconium-Content Nano-Sized Bimodal Mesoporous Silicas

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006
David Ortiz de Zárate
Abstract Silica-based nanoparticulated bimodal mesoporous materials with high Zr content (43 , Si/Zr , 4) have been synthesized by a one-pot surfactant-assisted procedure from a hydroalcoholic medium using a cationic surfactant (CTMABr = cetyltrimethylammonium bromide) as structure-directing agent, and starting from molecular atrane complexes of Zr and Si as hydrolytic inorganic precursors. This preparative technique allows optimization of the dispersion of the Zr guest species in the silica walls. The bimodal mesoporous nature of the final high surface area nano-sized materials is confirmed by XRD, TEM, and N2 adsorption,desorption isotherms. The small intraparticle mesopore system (with pore sizes around 2,3 nm) is due to the supramolecular templating effect of the surfactant, while the large mesopores (around 12,24 nm) have their origin in the packing voids generated by aggregation of the primary nanometric mesoporous particles. The basicity of the reaction medium seems to be a key parameter in the definition of this last pore system. The effects induced by the progressive incorporation of Zr atoms on the mesostructure have been examined, and the local environment of the Zr sites in the framework has been investigated by UV/Vis spectroscopy. Observations based on the consequences of post-treatments of the as-synthesized materials with HCl/ethanol mixtures corroborate that the atrane method leads to Zr-rich materials showing enhanced site accessibility and high chemical homogeneity throughout the pore walls. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Structural Studies of ,-Cyclodextrin and Permethylated ,-Cyclodextrin Inclusion Compounds of Cyclopentadienyl Metal Carbonyl Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2006
Susana S. Braga
Abstract [CpM(CO)nCl] complexes with M = Fe (n = 2) and Mo (n = 3) have been immobilised in plain ,-cyclodextrin (,-CD) and permethylated ,-CD (TRIMEB) by methods tailored according to the stabilities and solubilities of the individual components. Four adducts were obtained with a 1:1 host/guest stoichiometry. The compounds were studied by powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), 13C{1H} CP/MAS NMR and FTIR spectroscopy. A comparison of the experimental powder XRD data for the TRIMEB/[CpMo(CO)3Cl] inclusion compound with reference patterns revealed that the crystal packing is very similar to that reported previously for a TRIMEB/ethyl laurate inclusion compound. The unit-cell parameters refined to a = 14.731, b = 22.476, c = 27.714 Å (volume = 9176.3 Å3), and the space group was confirmed as P212121. A hypothetical structural model of the inclusion compound was subsequently obtained by global optimisation using simulated annealing. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

An Investigation of the Reactivity of [(diimine)(dithiolato)M] Complexes Using the Fukui Functions Concept

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 3 2006
Christodoulos Makedonas
Abstract Fukui functions are widely used when investigating the reactivity of organic molecules, but rarely with metal complexes. Here, we investigate the reactivity of [(diimine)(dithiolato)M] complexes with different types of reagents and upon oxidation employing this concept. Mixed-ligand complexes of this type have a peculiar electronic description due to the mixed-metal-ligand-to-ligand charge-transfer band, which is why they are considered as very promising candidates for non-linear optical (NLO) materials and molecular photochemical devices (MPD). As a result, their reactivity is of crucial importance for their potential applications. The obtained results of f+ and f, for the neutral [(diimine)(dithiolato)M] complexes (M = Pd, Ni and Pt) not only predict that the sulfur atom is the preferable active site for electrophilic attack but also reveal the different tunability of these complexes when they are subjected to an oxidation process, in agreement with experimental results. Under the framework of the Fukui indices we also provide an alternative explanation for crystal packing that could find widespread application. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]