1D Strand Research Articles

A Methodological Framework for Assessing the Influence of Process Parameters on Strand Stability and Functional Performance in Fused Filament Fabrication.

With an ever-increasing material and design space available for Fused Filament Fabrication (FFF) technology, fabrication of complex three-dimensional structures with functional performance offers unique opportunities for product customization and performance-driven design. However, ensuring the quality and functionality of FFF-printed parts remains a significant challenge, as material-, process-, and system-level factors introduce variability and potentially hinder the translation of bulk material properties in the respective FFF counterparts. To this end, the present study presents a methodological framework for assessing the influence of process parameters on FFF strand stability and functional performance through a systematic analysis of FFF structural elements (1D stacks of FFF strands and 3D blocks), in terms of dimensional deviation from nominal geometry and resistivity, corresponding to the printability and functionality attributes, respectively. The influence of printing parameters on strand stability was investigated in terms of dimensional accuracy and surface morphology, employing optical microscopy and micro-computed tomography (mCT) for dimensional deviation analysis. In parallel, electrical resistance measurements were carried out to assess the effect of different process parameter combinations and toolpath patterns on functional performance. In low-level structural elements, strand height (H) was found to induce the greatest influence on FFF strand dimensional accuracy and resistivity, with higher H values leading to a reduction in resistivity of up to 38% in comparison with filament feedstock; however, this occurred at the cost of increased dimensional deviation. At higher structural levels, the overall effect of process parameters was found to be less pronounced, indicating that the translation of 1D strand properties to 3D blocks is subject to a trade-off due to competing mechanisms that facilitate/hinder current flow. Overall, the proposed framework enables the quantification of the influence of process parameters on the selected response variables, contributing to the development of standard operating procedures and recommendations for selecting optimal process parameters to achieve the desired process stability and functional performance in FFF.

Ionic Mechanisms of Propagated Repolarization in a One-Dimensional Strand of Human Ventricular Myocyte Model.

Although repolarization has been suggested to propagate in cardiac tissue both theoretically and experimentally, it has been challenging to estimate how and to what extent the propagation of repolarization contributes to relaxation because repolarization only occurs in the course of membrane excitation in normal hearts. We established a mathematical model of a 1D strand of 600 myocytes stabilized at an equilibrium potential near the plateau potential level by introducing a sustained component of the late sodium current (INaL). By applying a hyperpolarizing stimulus to a small part of the strand, we succeeded in inducing repolarization which propagated along the strand at a velocity of 1~2 cm/s. The ionic mechanisms responsible for repolarization at the myocyte level, i.e., the deactivation of both the INaL and the L-type calcium current (ICaL), and the activation of the rapid component of delayed rectifier potassium current (IKr) and the inward rectifier potassium channel (IK1), were found to be important for the propagation of repolarization in the myocyte strand. Using an analogy with progressive activation of the sodium current (INa) in the propagation of excitation, regenerative activation of the predominant magnitude of IK1 makes the myocytes at the wave front start repolarization in succession through the electrical coupling via gap junction channels.

Nature-Inspired Cellulose-Based Active Materials: From 2D to 4D

Multifunctional materials and devices with captivating properties can be assembled from cellulose and cellulose-based composite materials combining functionality with structural performance. Cellulose is one of the most abundant renewable materials with captivating properties, such as mechanical robustness, biocompatibility, and biodegradability. Cellulose is a low-cost and abundant biodegradable resource, CO2 neutral, with a wide variety of fibers available all over the world. Over thousands of years, nature has perfected cellulose-based materials according to their needs, such as function vs. structure. Mimicking molecular structures at the nano-, micro-, and macroscales existing in nature is a great strategy to produce synthetic cellulose-based active materials. A concise background of cellulose and its structural organization, as well as the nomenclature of cellulose nanomaterials, are first addressed. Key examples of nature-designed materials with unique characteristics, such as “eternal” coloration and water-induced movement are presented. The production of biomimetic fiber and 2D fiber-based cellulosic materials that have attracted significant attention within the scientific community are represented. Nature-inspired materials with a focus on functionality and response to an external stimulus are reported. Some examples of 3D-printed cellulosic materials bioinspired, reported recently in the literature, are addressed. Finally, printed cellulosic materials that morph from a 1D strand or 2D surface into a 3D shape, in response to an external stimulus, are reported. The purpose of this review is to discuss the most recent developments in the field of “nature-inspired” cellulose-based active materials regarding design, manufacturing, and inspirational sources that feature existing tendencies.

From a Dense Structure to Open Frameworks: The Structural Plethora of Alkali Metal Iron Fluorophosphates.

By employing the pyridinium hexafluorophosphate task-specific ionic liquids 1-butyl-4-methylpyridinium hexafluorophosphate ([C4mpyr][PF6]) and 1-ethylpyridinium hexafluorophosphate ([C2pyr][PF6]) as the reaction medium, mineralizer, structure-directing agent, and, in the case of the smaller pyridinium cation, even a structural component, it was possible to obtain five new alkali metal iron phosphates featuring interconnected FeX6 octahedra and PX4 (X = F, O, or OH) tetrahedra. NaFe(PO3F)2 (1) is a dense 3D structure, RbFe(PO3F)(PO2(OH)F)(PO2(OH)2) (2) features 1D strands, (C2pyr)LiFe(PO3F)3(PO2F2)F (3) has 2D layers, and LiFe(PO3F)(PO2F2)F (4) as well as Cs0.75Fe(PO2.75(OH)0.25F)(PO2F2)2 (5) are 3D open frameworks. While in 1–2 as well as in 4 and 5, FeX6 octahedra and PX4 (X = F, O, or OH) tetrahedra alternate, 3 features octahedra dimers, Fe2X11 (X = F, O, or OH). The magnetic behavior of all compounds is governed by antiferromagnetic interactions. Interestingly, 3 exhibits a broad maximum in the temperature dependence of the magnetic susceptibility, characteristic of a low-dimensional magnetic system consistent with the presence of Fe–Fe dimers in its crystal structure.

From 1D to 3D Graphitic Carbon Nitride (Melon): A Bottom-Up Route via Crystalline Microporous Templates.

Herein, we present a novel bottom-up preparation route for heptazine-based polymers (melon), also known as graphitic carbon nitride. The growth characteristics of isolated 1D melon strings in microporous templates are presented and studied in detail. Removal of the microporous silicate template via etching is accompanied by the self-assembly of a 1D melon to stacked 3D structures. The advantages and limitations of the bottom-up approach are shown by using microporous templates with different pore sizes (ETS-10, ZSM-5, and zeolite Y). In accordance with the molecular size of the heptazine units (0.67 nm), a 1D melon can be deposited in ETS-10 with a pore width of about 0.78 nm, whereas its formation in the smaller 0.47 nm pores of ZSM-5 is sterically impeded. The self-assembly of isolated 1D melon to stacked 3D structures offers a novel experimental perspective to the controversial debate on the polymerization degree in 2D sheets of graphitic carbon nitride as micropore sizes below 1 nm confine the condensation degree of heptazine to isolated 1D strands at a molecular level. The growth characteristics and structural features were investigated by X-ray diffraction, N2 physisorption, scanning transmission electron microscopy/energy-dispersive X-ray analysis, 13C CP-NMR spectroscopy, and attenuated total reflection–infrared spectroscopy.

Pka and CaMKII Signaling Synergistically Promotes Atrial Arrhythmia in Populations of Human Atrial Tissues

The β-adrenergic receptor (βAR)/cAMP/PKA and multifunctional Ca2+-calmodulin-dependent protein kinase II (CaMKII) signaling pathways are key mediators of cardiac excitation-contraction coupling (ECC) and share multiple downstream targets. Hyperactivation of both signaling pathways contributes to the initiation and maintenance of atrial fibrillation (AF), the world's most common arrhythmia. Using novel populations of computational models coupling atrial electrophysiology and Ca2+ handling with detailed descriptions of βAR-PKA and CaMKII pathways, we have previously shown that PKA and CaMKII effects on atrial ECC proteins synergistically promote a vicious cycle of Ca2+and membrane potential instabilities. Since both kinases are known to affect tissue-level modifiers of atrial electrophysiology, here we sought to test whether PKA and CaMKII signaling also synergize to mediate arrhythmias in tissue, and to determine the mechanisms underlying the increased vulnerability. Populations of 1D strand models revealed increased vulnerability to unidirectional block with hyperactive CaMKII, mediated by Na+ channel loss of function and cell-to-cell uncoupling, which was exacerbated by activation of βARs. Simulations of 2D heterogeneous tissues demonstrated synergistic enhancement of arrhythmia vulnerability by βAR stimulation and CaMKII hyperactivation through dysregulating conduction and modifying source-sink mismatch, as well as promoting tissue repolarization dispersion and invoking spontaneous Ca2+-overload-mediated action potentials. CaMKII inhibition substantially reduced the vulnerability. Collectively, our simulations reveal synergy in PKA and CaMKII effects on tissue-level outcomes, and depict a novel paradigm for Ca2+-CaMKII-dependent involvement in both enhanced triggered activity and conduction disturbances in AF. These findings suggest that interrupting the vicious cycle of ever-increasing CaMKII and Ca2+ (e.g., via CaMKII inhibition) may be a valuable pharmacotherapy approach to counteract both AF triggers and functional substrate.

Tweaking the affinity of aryl‐substituted diazosalicylato‐ and pyridine ligands towards Zn (II) and its neighbors in the periodic system of the elements, Cu (II) and Cd (II), and their antimicrobial activity

A series of six new Zn (II) compounds, viz., [Zn(HLASA)2(Py)2] (1), [Zn(HLMASA)2(Py)2] (2), [Zn(HLMASA)2(4‐MePy)2] (3), [Zn(HLCASA)2(4‐MePy)2] (4), [Zn(HLBASA)2(Py)2] (5), [Zn(HLBASA)2(4‐MePy)2] (6) and representative Cu (II) and Cd (II) complexes, viz., [Cu(HLASA)2(Py)2(H2O)] (7) and [Cd(HLBASA)2(Py)3] (8) [(HLXASA)− = para‐substituted 5‐[(E)‐2‐(aryl)‐1‐diazenyl]‐2‐hydroxybenzoate with X = H (ASA), Me (MASA), Cl (CASA) or Br (BASA); Py = pyridine; 4‐MePy = 4‐methylpyridine] have been synthesized and characterized by spectroscopic techniques and single‐crystal X‐ray diffraction analysis. The structural characterization of the compounds revealed distorted tetrahedral (1–6), square‐pyramidal (7) and pentagonal‐bipyramidal (8) coordination geometries around the metal atom, in which the aryl‐substituted diazosalicylate ligands are coordinated only through the oxygen atoms of carboxylate groups, either in an anisobidentate or isobidentate mode; meanwhile, the 2‐hydroxy groups of the monoanionic ligand (HLXASA)− are involved only in intramolecular O‐H···O hydrogen bonds with the carboxylate function. In the crystal structures of 1–8, the complex molecules are assembled by π‐stacking interactions giving mostly infinite 1D strands. The intermolecular binding in the solid state structures is accomplished by diverse additional non‐covalent contacts including C‐H···O, C‐H···N, C‐H···π, C‐H···Br, O···Br, Br···π and van der Waals contacts. Although the primary and secondary ligands in the Zn (II) complex series 1–6 carry different substituents at the periphery (X = H, Me, Cl, Br for (HLXASA)− and R = H, Me for 4‐Py‐R), five of the crystal structures were isostructural. Additionally, the antimicrobial activity of the pro‐ligands H2LXASA and their Zn (II), Cu (II) and Cd (II) compounds were studied in a comparative manner, showing high sensitivity (IZD ≥ 20) against Bacillus subtilis.

In silico assessment of the effects of quinidine, disopyramide and E-4031 on short QT syndrome variant 1 in the human ventricles.

AimsShort QT syndrome (SQTS) is an inherited disorder associated with abnormally abbreviated QT intervals and an increased incidence of atrial and ventricular arrhythmias. SQT1 variant (linked to the rapid delayed rectifier potassium channel current, IKr) of SQTS, results from an inactivation-attenuated, gain-of-function mutation (N588K) in the KCNH2-encoded potassium channels. Pro-arrhythmogenic effects of SQT1 have been well characterized, but less is known about the possible pharmacological antiarrhythmic treatment of SQT1. Therefore, this study aimed to assess the potential effects of E-4031, disopyramide and quinidine on SQT1 using a mathematical model of human ventricular electrophysiology.MethodsThe ten Tusscher et al. biophysically detailed model of the human ventricular action potential (AP) was modified to incorporate IKr Markov chain (MC) formulations based on experimental data of the kinetics of the N588K mutation of the KCNH2-encoded subunit of the IKr channels. The modified ventricular cell model was then integrated into one-dimensional (1D) strand, 2D regular and realistic tissues with transmural heterogeneities. The channel-blocking effect of the drugs on ion currents in healthy and SQT1 cells was modeled using half-maximal inhibitory concentration (IC50) and Hill coefficient (nH) values from literatures. Effects of drugs on cell AP duration (APD), effective refractory period (ERP) and pseudo-ECG traces were calculated. Effects of drugs on the ventricular temporal and spatial vulnerability to re-entrant excitation waves were measured. Re-entry was simulated in both 2D regular and realistic ventricular tissue.ResultsAt the single cell level, the drugs E-4031 and disopyramide had hardly noticeable effects on the ventricular cell APD at 90% repolarization (APD90), whereas quinidine caused a significant prolongation of APD90. Quinidine prolonged and decreased the maximal transmural AP heterogeneity (δV); this led to the decreased transmural heterogeneity of APD across the 1D strand. Quinidine caused QT prolongation and a decrease in the T-wave amplitude, and increased ERP and decreased temporal susceptibility of the tissue to the initiation of re-entry and increased the minimum substrate size necessary to prevent re-entry in the 2D regular model, and further terminated re-entrant waves in the 2D realistic model. Quinidine exhibited significantly better therapeutic effects on SQT1 than E-4031 and disopyramide.ConclusionsThe simulated pharmacological actions of quinidine exhibited antiarrhythmic effects on SQT1. This study substantiates a causal link between quinidine and QT interval prolongation in SQT1 and suggests that quinidine may be a potential pharmacological agent for treating SQT1 patients.

Synthesis, characterization, crystal structures and supramolecular features of bicycloazastannoxides derived from Schiff bases with L-tyrosine

Six new bicycloazastannoxides of compositions [Me2Sn(L1H)] (1), [nBu2Sn(L1H)] (2), [Ph2Sn(L1H)] (3), [Bz2Sn(L1H)] (4), [Me2Sn(L2H)(MeOH)]·MeOH (5) and [Ph2Sn(L3H)] (6), where L1H = 2-((E)-((Z)-4-hydroxypent-3-en-2-ylidene)amino)-3-(4-hydroxyphenyl)propanoate, L2H = (E)-2-((2-hydroxybenzylidene)amino)-3-(4-hydroxyphenyl)propanoate and L3H = (E)-3-(4-hydroxyphenyl)-2-((1-(2-hydroxyphenyl)ethylidene)amino)propanoate, were synthesized and spectroscopically characterized. The 1H and 13C NMR spectra of compounds 1–6 displayed two sets of signals for Sn-R2 (R = Me, nBu, Ph and Bz) indicating a diastereotopic environment according to the asymmetric nature of the ligand. The 119Sn NMR data of the compounds in CDCl3 indicate five-coordinate tin atoms, showing that the bicycloazastannoxide assemblies remain intact as observed in the solid-state structures. The crystal structures of 1–6 revealed discrete molecular structures in all cases with distorted trigonal-bipyramidal geometries for 1–4 and 6, and a strongly distorted six-fold coordination for 5 due to association of a MeOH solvent molecule. At the supramolecular level, the molecular structures in 1–4 and 6 are linked either through double-bridged O-H⋯O/C-H⋯O synthons (1 and 6) or single O-H⋯O hydrogen bonds (2–4). The resulting 1D helical strands exhibit varying Sn⋯Sn distances due to the different molecular conformations. The molecules in 5 associate to dimers through two Sn⋯O and O-H⋯O interactions, which are further connected via O-H⋯O hydrogen bonds to give 1D strands containing 22-membered macrocycles.

Arrhythmia Triggers in 1D Strands of Ventricular Myocytes

Introduction: Myocardial fibrosis increases susceptibility to ventricular tachycardia and fibrillation (VT/VF), but whether gap junction coupling between myocytes and fibroblasts actively contributes to the emergence of VT/VF is unknown. Here, we investigated this question using co-cultures of neonatal rat ventricular myocytes (NRVM) and either aged rat ventricular fibroblasts or HEK-293 cells, arranged in 1D strands of NRVM interrupted by a segment (of variable length) of fibroblasts or HEK-293 cells. Methods: We determined the frequency of arrhythmia triggers by voltage optical imaging of co-cultures at baseline and under hypokalemic (2 mmol/L) or isoproterenol (1 μmol/L) stress. The expression levels of connexin 43 and 45 (Cx43, Cx45) in fibroblasts and HEK-293 cells were measured. Results: At baseline, longer fibroblast or HEK-293 cell segments led to decay of action potential amplitude and conduction velocity or complete conduction block, but did not result in the emergence of arrhythmia triggers. Under hypokalemia or isoproterenol, however, arrhythmia triggers consistent with early and delayed afterdepolarizations (EADs, DADs) and triggered activity emerged from NRVM border zones with fibroblasts, more so than with HEK-293 cells. Western blot comparison revealed higher expression levels of Cx43 and Cx45 in fibroblasts isolated from fibrotic ventricles of aged rats compared to those in fibroblasts from younger rat ventricles or in HEK-293 cells. Conclusion: Synergistically with stress, fibroblasts are more efficient than HEK-293 cells in inducing arrhythmia triggers from NRVM border-zone regions. At the same time, fibroblasts from aged fibrotic rat ventricles also express higher levels of Cx43 and Cx45, increasing the likelihood of electrotonic coupling with neighboring NRVM via heterocellular gap junctions.

Heteronuclear, mixed-metal Ag(I)-Mn(II) coordination polymers with bridging N-pyridinylisonicotinohydrazide ligands: synthesis, crystal structures, magnetic and photoluminescence properties.

Mixed-metal dicyanoargentate-bridged coordination polymers of Ag(i)-Mn(ii) have been prepared and their structure and magnetic properties were determined. Reaction of manganese(ii) chloride and potassium dicyanoargentate(i) with (X)(pyridin-2-ylmethylene)isonicotinohydrazide ligands (HL(1) X = Ph, HL(2) X = Me, HL(3) X = H) produced the coordination polymer 2D-[Mn(μ-L(1))(Cl)(μ-NCAgCN)Mn0.5(CH3OH)]n (), 1D-{[Mn(L(2))(Cl)(μ-NCAgCN)Mn0.5(CH3OH)]CH3OH}n () and [Mn(L(3))(Cl)(μ-NCAgCN)Mn0.5(CH3OH)]n () in good yields. Trinuclear {Mn(μ-L(1))Mn(μ-L(1))Mn} and [Ag(CN)2](-) building units form a two-dimensional slab in and 1D strands in . Variable temperature magnetic susceptibility measurements showed that despite the long distance among the high spin Mn(ii) ions [10.4676(12) Å and 10.522(1) Å, for and , respectively], weak antiferromagnetic coupling takes place through the long NC-Ag-CN bridge. The best fit parameters to the model led to the magnetic coupling constant of J = -0.1 and J = -0.47 cm(-1) for and , respectively. The photoluminescence behaviour of compounds and was studied. The spectrum of compound shows a broad emission centered at about 450 nm and two excitation maxima at 270 and 310 nm.

Non-Uniform Dispersion of the Source-Sink Relationship Alters Wavefront Curvature

The distribution of cellular source-sink relationships plays an important role in cardiac propagation. It can lead to conduction slowing and block as well as wave fractionation. It is of great interest to unravel the mechanisms underlying evolution in wavefront geometry. Our goal is to investigate the role of the source-sink relationship on wavefront geometry using computer simulations. We analyzed the role of variability in the microscopic source-sink relationship in driving changes in wavefront geometry. The electrophysiological activity of a homogeneous isotropic tissue was simulated using the ten Tusscher and Panfilov 2006 action potential model and the source-sink relationship was characterized using an improved version of the Romero et al. safety factor formulation (SFm2). Our simulations reveal that non-uniform dispersion of the cellular source-sink relationship (dispersion along the wavefront) leads to alterations in curvature. To better understand the role of the source-sink relationship in the process of wave formation, the electrophysiological activity at the initiation of excitation waves in a 1D strand was examined and the source-sink relationship was characterized using the two recently updated safety factor formulations: the SFm2 and the Boyle-Vigmond (SFVB) definitions. The electrophysiological activity at the initiation of excitation waves was intimately related to the SFm2 profiles, while the SFVB led to several counterintuitive observations. Importantly, with the SFm2 characterization, a critical source-sink relationship for initiation of excitation waves was identified, which was independent of the size of the electrode of excitation, membrane excitability, or tissue conductivity. In conclusion, our work suggests that non-uniform dispersion of the source-sink relationship alters wavefront curvature and a critical source-sink relationship profile separates wave expansion from collapse. Our study reinforces the idea that the safety factor represents a powerful tool to study the mechanisms of cardiac propagation in silico, providing a better understanding of cardiac arrhythmias and their therapy.

Modeling electrical activity of myocardial cells incorporating the effects of ephaptic coupling.

Existing models of electrical activity in myocardial tissue are unable to easily capture the effects of ephaptic coupling. Homogenized models do not account for cellular geometry, while detailed spatial models are too complicated to simulate in three dimensions. Here we propose a unique model that accurately captures the geometric effects while being computationally efficient. We use this model to provide an initial study of the effects of changes in extracellular geometry, gap junctional coupling, and sodium ion channel distribution on propagation velocity in a single 1D strand of cells. In agreement with previous studies, we find that ephaptic coupling increases propagation velocity at low gap junctional conductivity while it decreases propagation at higher conductivities. We also find that conduction velocity is relatively insensitive to gap junctional coupling when sodium ion channels are located entirely on the cell ends and cleft space is small. The numerical efficiency of this model, verified by comparison with more detailed simulations, allows a thorough study in parameter variation and shows that cellular structure and geometry has a nontrivial impact on propagation velocity. This model can be relatively easily extended to higher dimensions while maintaining numerical efficiency and incorporating ephaptic effects through modeling of complex, irregular cellular geometry.

Metal Coordination Architectures of 2,3‐Bis(triazol‐1‐ylmethyl)quinoxaline: Effect of Metal Ion and Counterion on Complex Structures

AbstractA series of complexes, [ZnLCl2]2 (1), [ZnL2(NO3)2]∞ (2), [MnL2(NO3)2]∞ (3), {[ZnL2(H2O)2](ClO4)2(CH3COCH3)2}∞ (4), {[MnL2(H2O)2](ClO4)2(CH3COCH3)2}∞ (5), {[CdL2(H2O)2]‐(ClO4)2(H2O)6}∞ (6), and {[AgL](ClO4)(H2O)1.5}∞ (7), based on the flexible ligand 2,3‐bis(triazol‐1‐ylmethyl)quinoxaline (L) were synthesized and characterized by elemental analyses, IR spectroscopy, thermogravimetric analyses, and single‐crystal X‐ray diffraction. Complex 1 is a dinuclear macrocyclic molecular, which is further linked into a 1D supramolecular chain by intermolecular C–H···Cl weak interactions. The metal centers in 2 and 3 coordinate two NO3– anions, and the flexible ligand bridges M(NO3)2 [M = ZnII or MnII] units to form 1D chain structures. Complexes 4, 5, and 6 show a 2D network structure with (4,4) topology. As expected, complex 7 has a 1D strand chain structure that is different than other MII complexes (4, 5, and 6) with the same ligand. These chains are further extended into a 2D supramolecular network by O···Ag···O weak interactions. In all these complexes, the ligand bridges in a similar mode; however, the complexes have different structures ranging from a dinuclear structure to a 2D network mainly due to the differences in the coordination geometries of the metal centers and counterions. These results reveal that the coordination geometry of metal ions and the coordinating abilities of the counterions play important roles in defining the overall structure of metal–organic frameworks. In addition, the fluorescent properties of complexes 1, 2, 4, 6, 7, and ligand L and the EPR spectra of complex 5 were also investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

One-dimensional Strands of Trigonellinium Constructed by Intermolecular Strong O–H···O and Weak C–H···O Hydrogen Bonds in the Crystal of Partially Oxidized Ni(dmit)2 Salt

Abstract The trigonellinium cations in the partially oxidized Ni(dmit)2 complex salt 1 formed strong O–H···O hydrogen-bridged dimers, and the dimers are held together by the weak C(sp2 and sp3)–H···O hydrogen bond to form 1D strands. Further assembly through weak C(sp3)–H···O hydrogen bond and π···π interaction resulted in the formation of Ni(dmit)2 column structure.

The Crystal Structure of Murine Coronin-1: A Regulator of Actin Cytoskeletal Dynamics in Lymphocytes

Mammalian coronin-1 is preferentially expressed in hematopoietic cells and plays a poorly understood role in the dynamic reorganization of the actin cytoskeleton. Sequence analysis of coronin-1 revealed five WD40 repeats that were predicted to form a beta propeller. They are followed by a 130 residue extension and a 30 residue leucine zipper domain that is responsible for multimerization of the protein. Here, we present the crystal structure of murine coronin-1 without the leucine zipper at 1.75 A resolution. Coronin-1 forms a seven-bladed beta propeller composed of the five predicted WD40 repeats and two additional blades that lack any homology to the canonical WD40 motif. The C-terminal extension adopts an extended conformation, packs tightly against the bottom surface of the propeller, and is likely to be required for the structural stability of the propeller. Analysis of charged and conserved surface residues delineate possible binding sites for F-actin on the beta propeller.

From 1D strands to extended molecular assemblies in the binary compounds of dithiooxamide and dithiobiurea with crown ethers.

The hydrogen-bonding networks for seven new binary compounds of dithiooxamide, (NH2CS)2 (dtox) and dithiobiurea (NH2CSNH)2 (dtur) with crown ethers, 18-crown-6 (18C6), 15-crown-5 (15C5), 12-crown-4 (12C4), cis-syn-cis-(DCHA), and cis-anti-cis-(DCHB) isomers of dicyclohexyl-18 -crown-6 are discussed. (15C5.dtox), (18C6.dtur) and (DCHB.dtur) afford one-dimensional hydrogen-bonded polymeric arrays where the components alternate. In (DCHA.2dtox) and (DCHB.2dtox) the similar hydrogen-bonded chains are further interlinked via dtox molecules to generate layered motifs. In (15C5.2dtur) the dtur molecules are self-assembled into layers via N-H...S hydrogen bonds. 15C5 spacers link adjacent layers into a three-dimensional network. In (12C4.dtur) the dtur molecules are arranged in chains. These chains alternate with the crown molecules attached to them through N-H...O hydrogen bonds in such a way that each 12C4 appears to be linked with four dtur molecules and vice versa thus providing a three-dimensional grid.

On Variable Range Hopping near the Fermi Energy One‐Dimensional Systems

AbstractModel calculations on variable range hopping conduction in quasi‐one‐dimensional systems are presented. It is shown that the temperature behaviour of the conductivity depends strongly on the geometry of the sample consisting of 1D strands. Comparison with an analytical theory is made. Careful numerical evaluation of an integral in the latter approach is necessary to obtain reasonable agreement with the results of the model calculation.