Tubular Conformation Research Articles

Structural Evolution and Stability Trend of Small-Sized Gold Clusters Aun (n = 20-30).

Structural evolution and stability pattern of pure neutral gold clusters Aun in the small size range of n = 20-30 are examined using density functional theory (DFT) calculations. The equilibrium geometries are either confirmed or determined, and some new ground state structures are identified. The most stable configurations of Au21-Au23 sizes are formed by adding extra gold atoms to the highly stable pyramidal structure of Au20, while flat-cage shapes are the best candidates for the global minima of both Au24 and Au25. For larger sizes of n = 26-30, pyramidal motifs tend to dominate the lower-lying population rather than tubular conformations as previously reported. The energy gaps, excitation energies, and exciton binding energies are also computed to test out the performance of the computational methods employed. Accordingly, a density functional with long-range exchange effects is highly recommended to quantitatively investigate both the ground and excited states of pure gold clusters.

Tubuloids derived from human adult kidney and urine for personalized disease modeling.

Adult stem cell-derived organoids are three-dimensional epithelial structures that recapitulate fundamental aspects of their organ of origin. We describe conditions for the long-term growth of primary kidney tubular epithelial organoids, or 'tubuloids'. The cultures are established from human and mouse kidney tissue and can be expanded for at least 20 passages (>6 months) while retaining a normal number of chromosomes. In addition, cultures can be established from human urine. Human tubuloids represent proximal as well as distal nephron segments, as evidenced by gene expression, immunofluorescence and tubular functional analyses. We apply tubuloids to model infectious, malignant and hereditary kidney diseases in a personalized fashion. BK virus infection of tubuloids recapitulates in vivo phenomena. Tubuloids are established from Wilms tumors. Kidney tubuloids derived from the urine of a subject with cystic fibrosis allow ex vivo assessment of treatment efficacy. Finally, tubuloids cultured on microfluidic organ-on-a-chip plates adopt a tubular conformation and display active (trans-)epithelial transport function.

A Pentacene-based Nanotube Displaying Enriched Electrochemical and Photochemical Activities.

Unlike previously well-studied, acyclic pentacene oligomers, the first synthesis of a cyclic pentacene trimer with a fixed tubular conformation is reported. A short-step synthesis starting from common pentacenequinone yielded the target molecule with a 1.5 nanometer length and a subnanometer pore. Steady-state spectroscopic analyses revealed that the close proximity of the non-conjugated, three pentacene chromophores allows the nanotube to display stepwise electrochemical/chemical oxidation characteristics. Furthermore, time-resolved transient absorption measurements elucidated the generation of an excited triplet state of the nanotube, with high quantum yield reaching about 180 % through intramolecular singlet fission and a very long triplet lifetime.

A Pentacene‐based Nanotube Displaying Enriched Electrochemical and Photochemical Activities

AbstractUnlike previously well‐studied, acyclic pentacene oligomers, the first synthesis of a cyclic pentacene trimer with a fixed tubular conformation is reported. A short‐step synthesis starting from common pentacenequinone yielded the target molecule with a 1.5 nanometer length and a subnanometer pore. Steady‐state spectroscopic analyses revealed that the close proximity of the non‐conjugated, three pentacene chromophores allows the nanotube to display stepwise electrochemical/chemical oxidation characteristics. Furthermore, time‐resolved transient absorption measurements elucidated the generation of an excited triplet state of the nanotube, with high quantum yield reaching about 180 % through intramolecular singlet fission and a very long triplet lifetime.

Guest-Induced Arylamide Polymer Helicity: Twist-Sense Bias and Solvent-Dependent Helicity Inversion.

A benzene/naphthalene alternately incorporated amide polymer was synthesized and characterized. (1) H NMR spectroscopy, fluorescence, and circular dichroism (CD) experiments indicated that, in chloroform, the polymer could be induced by the chiral l-aspartic acid dianion or one of its derivatives to form a helical tubular conformation with twist-sense bias. CD titration studies showed that the l-aspartic acid dianion (8 equiv.) could lead to a maximum Cotton effect. It was also revealed that the twist-sense bias obeyed the majority rule, and 70 % enantiomeric excess could realize the maximum helicity bias. Adding acetonitrile to the solution of chloroform caused inversion of the guest-induced helicity bias of the polymer.

First principles study on the size evolution and stability of (AgF)n (n = 1–12) clusters

The structural evolution of (AgF)n (n=1–12) clusters has been studied by first principles global minimization technique, namely, a genetic algorithm from density functional theory geometry optimization (GA-DFT). The growth sequence and pattern for n from 1 to 12 are analyzed from the perspective of geometric structures. The average binding energy per cluster, vertical and adiabatic ionization potentials, NICS-scan curves (partial clusters) are examined. The global minimum structures are planar single-ring conformations at n=1–5, and tubular conformations when n=6, 9 and 12, where they contain triangular units. When n=7 and 11, the clusters present butterfly and helix conformations, respectively. When n=8 and 10, the clusters are separate-ring structures. One more stable structure has been found for (AgF)6 cluster in comparison with previous work, indicating the power of DFT-based genetic algorithm in finding new structures for clusters. Several magic sizes of higher stability and symmetry are discovered. In particular, we find that when n=3, 6, 9 and 12, the clusters are tubular structures with high stability and high aromaticity.

Tubular Unimolecular Transmembrane Channels: Construction Strategy and Transport Activities.

Lipid bilayer membranes separate living cells from their environment. Membrane proteins are responsible for the processing of ion and molecular inputs and exports, sensing stimuli and signals across the bilayers, which may operate in a channel or carrier mechanism. Inspired by these wide-ranging functions of membrane proteins, chemists have made great efforts in constructing synthetic mimics in order to understand the transport mechanisms, create materials for separation, and develop therapeutic agents. Since the report of an alkylated cyclodextrin for transporting Cu(2+) and Co(2+) by Tabushi and co-workers in 1982, chemists have constructed a variety of artificial transmembrane channels by making use of either the multimolecular self-assembly or unimolecular strategy. In the context of the design of unimolecular channels, important advances have been made, including, among others, the tethering of natural gramicidin A or alamethicin and the modification of various macrocycles such as crown ethers, cyclodextrins, calixarenes, and cucurbiturils. Many of these unimolecular channels exhibit high transport ability for metal ions, particularly K(+) and Na(+). Concerning the development of artificial channels based on macrocyclic frameworks, one straightforward and efficient approach is to introduce discrete chains to reinforce their capability to insert into bilayers. Currently, this approach has found the widest applications in the systems of crown ethers and calixarenes. We envisioned that for macrocycle-based unimolecular channels, control of the arrangement of the appended chains in the upward and/or downward direction would favor the insertion of the molecular systems into bilayers, while the introduction of additional interactions among the chains would further stabilize a tubular conformation. Both factors should be helpful for the formation of new efficient channels. In this Account, we discuss our efforts in designing new unimolecular artificial channels from tubular pillar[n]arenes by extending their lengths with various ester, hydrazide, and short peptide chains. We have utilized well-defined pillar[5]arene and pillar[6]arene as rigid frameworks that allow the appended chains to afford extended tubular structures. We demonstrate that the hydrazide and peptide chains form intramolecular N-H···O═C hydrogen bonds that enhance the tubular conformation of the whole molecule. The new pillar[n]arene derivatives have been successfully applied as unimolecular channels for the selective transport of protons, water, and amino acids and the voltage-gated transport of K(+). We also show that aromatic hydrazide helices and macrocycles appended with peptide chains are able to mediate the selective transport of NH4(+).

Trivial and Non-Trivial Supramolecular Assemblies Based on Nafion

We demonstrate that Nafion, a perfluorosulfonic acid ionomer, undergoes synergistic mixing with non-ionic diblock copolymers in selective solvents. A range of experimental techniques (Quartz Crystal Microbalance, Dynamic Light Scattering, optical microscopy, TEM and SEM) was employed to gain insights on the evolution of ionomer–copolymer supramolecular assemblies. Depending on the copolymer architecture and the type of the suspension medium, spherical nanoparticles, micron-long tubular conformations or vesicular structures are formed. Those morphologies are dictated by localized interactions arising from Nafion's amphiphilicity. The effect has implications on the preparation of the technologically important ion conducting membranes.

On the properties of real finite-sized planar and tubular stent-like auxetic structures

Auxetics, i.e. systems with a negative Poisson's ratio, exhibit the unexpected property of becoming wider when stretched and narrower when compressed. This property arises from the manner in which the internal geometric units within the system deform when the system is submitted to a stress and may be explained in terms of ‘geometry–deformation mechanism’ based models. This work considers realistic finite implementations of the well known rotating squares system in the form of (i) a finite planar structure and (ii) a tubular conformation, as one typically finds in stents. It shows that although the existing models of the Poisson's ratios and moduli based on periodic systems may be appropriate to model systems where the geometry/deformation mechanism operate at the micro- or nano- (molecular) level where a system may be considered as a quasi infinite system, corrections to the model may need to be made when one considers finite structures with a small number of repeat units and suggests that for finite systems, especially for the 2D systems, the moduli as predicted by the periodic model may be significantly overestimating the moduli of the real system, even sometimes by as much as 200%.

Centrosomal Protein DZIP1 Regulates Hedgehog Signaling by Promoting Cytoplasmic Retention of Transcription Factor GLI3 and Affecting Ciliogenesis

The primary cilium is required for Hedgehog signaling. So far, all known ciliogenic proteins regulate Hedgehog signaling through their role in ciliogenesis. Here we show that the mouse DZIP1 regulates Hedgehog signaling through two mechanisms. First, DZIP1 interacts with GLI3, a transcriptional regulator for Hedgehog signaling, and prevents GLI3 from entering the nucleus. Second, DZIP1 is required for ciliogenesis. We show that DZIP1 colocalizes and interacts with CEP164, a protein localizing at appendages of the mother centrioles, and IFT88, a component of the intraflagellar transport (IFT) machinery. Functionally, both CEP164 and Ninein appendage proteins fail to localize to ciliary appendages in Dzip1 mutant cells; IFT components are not recruited to the basal body of cilia. Importantly, the accumulation of GLI3 in the nucleus is independent of loss of primary cilia in Dzip1 mutant cells. Therefore, DZIP1 is the first known ciliogenic protein that regulates Hedgehog signaling through a dual mechanism and that biochemically links IFT machinery with Hedgehog pathway components.

Membrane-Mediated Aggregation of Curvature-Inducing Nematogens and Membrane Tubulation

The shapes of cell membranes are largely regulated by membrane-associated, curvature-active proteins. Herein, we use a numerical model of the membrane, recently developed by us, with elongated membrane inclusions possessing spontaneous directional curvatures that could be different along, and perpendicular to, the membrane’s long axis. We show that, due to membrane-mediated interactions, these curvature-inducing membrane-nematogens can aggregate spontaneously, even at low concentrations, and change the local shape of the membrane. We demonstrate that for a large group of such inclusions, where the two spontaneous curvatures have equal sign, the tubular conformation and sometimes the sheet conformation of the membrane are the common equilibrium shapes. We elucidate the factors necessary for the formation of these protein lattices. Furthermore, the elastic properties of the tubes, such as their compressional stiffness and persistence length, are calculated. Finally, we discuss the possible role of nematic disclination in capping and branching of the tubular membranes.

Chiral Selective Transmembrane Transport of Amino Acids through Artificial Channels

Peptide-appended pillar[n]arene (n = 5, 6) derivatives have been synthesized. (1)H NMR and IR studies revealed that the molecules adopt a tubular conformation in solution and lipid bilayer membranes. Kinetic measurements using the fluorescent labeling method with lipid vesicles revealed that these molecules can efficiently mediate the transport of amino acids across lipid membranes at a very low channel-to-lipid ratio (EC(50) = 0.002 mol %). In several cases, chiral selectivity for amino acid enantiomers was achieved, which is one of the key functions of natural amino acid channels.

Exploring the structure–composition phase space of lithium borocarbide, LixBC for x ≤ 1

Lithium borocarbide (LiBC), with a heterographite structure, has been extensively investigated in the past decades searching for possible superconductive properties. In particular, Li-vacancy creation has been regarded as the key for hole-doping at the Fermi level. In the present work, the structure–composition phase space of LixBC, for x ≤ 1, is explored via first-principles crystal structure prediction, combining cluster expansion and density functional total energy calculations. For x up to 0.5, local minima structures are found on the potential energy surface, for which the main structural changes, induced by vacancy creation, are bucklings of carbon and boron atoms from their sites on the flat (BC) layers of the stoichiometric compound. On increasing the Li-vacancy concentration, the (BC) layers bend, forming new C–C and C–B bonds and consequently tubular conformations, containing hexagonal-based boron–carbon bonding with the remaining lithium atoms trapped in. Of the ensemble of optimized structures, we report the structural data of the symmetrically non-equivalent ones, the corresponding enthalpies of formation, potential of lithium extraction, and calculated X-ray diffraction patterns.

Single-Molecular Artificial Transmembrane Water Channels

Hydrazide-appended pillar[5]arene derivatives have been synthesized. X-ray crystal structure analysis and (1)H NMR studies revealed that the molecules adopt unique tubular conformations. Inserting the molecules into the lipid membranes of vesicles leads to the transport of water through the channels produced by single molecules, as supported by dynamic light scattering and cryo-SEM experiments. The channels exhibit the transport activity at a very low channel to lipid ratio (0.027 mol %), and a water permeability of 8.6 × 10(-10) cm s(-1) is realized. In addition, like natural water channel proteins, the artificial systems also block the transport of protons.

Development of CAD/CAM Software System for Large Non-Regular Steel Constructions

Sun-valley of Expo-axis is irregular large-span steel structure building. For the complicacy and specialty of tubular joint conformation, existing domestic and oversea professional software are incapable of solving the detailing work of this structure. Characteristics, difficulties and function requirements of the engineering are analyzed; the framework, data structure kernel and implement algorithm of important functions are designed for a specialized integrated detailing/manufacture CAD/CAM information system. This software comprises the functions from 3D solid modeling to automatic output of shop drawing and NC data, and it has been successfully applied to the actual construction work of sun-valley project.

Biogenic Synthesis and Photocatalysis of Pd−PdO Nanoclusters Reinforced Hierarchical TiO2 Films with Interwoven and Tubular Conformations

Hierarchical nanocomposite films with Pd-PdO nanoparticles anchored uniformly on the inner surface of TiO2 nanotubes were achieved through a stepwise bioredox/artificial oxygenation approach by using the natural eggshell membrane (ESM) as a template. The Pd content ratio of Pd-PdO loading could be arbitrarily varied from 0 to 53 wt %, and the ESM-morphic nanocomposites Pd-PdO/TiO2 exhibited porous and multiphasic features, facilitating light transport and molecule accessibility to the active site during photocatalytic reactions. The photocatalytic activity of target nanocomposites was determined by the degradation of rhodamine B. The composites with a ratio of 10 wt % TiO2 (5 wt % Pd of Pd-PdO loading) presented a high degradation efficiency of 99.3% and showed good stability with a second run of about 95.3% and a third run of 94.6%. These composites with structural particularity and complexity are expected to find potential applications in various fields, such as photovoltaic devices, gas sensors, antistatic coating, dye-sensitized solar cells, etc.

Nefroma mesoblástico del adulto: Presentación de un caso con curso agresivo

Mesoblastic nephroma is a rare renal neoplasia mainly diagnosed in the first three months of life; there is an adult type with pathologic similarities but it has its own features. We report the case of a 71-year-old female patient with the diagnosis of adult mesoblastic nephroma, the clinical outcome of which was ominous. The presence of epithelial elements with tubular conformation surrounded by a spindle cell component is greatly useful to perform the differential diagnosis between this entity and others of greater clinical significance. Although scarce, there are cases in the bibliography similar to ours, with an aggressive behaviour that maybe require a more aggressive treatment, and not the conservative one traditionally used for these tumors.

Fabrication and gas sensitivity ofSnO2 hierarchical films with interwoven tubular conformation by a biotemplate-directed sol–geltechnique

A facile and versatile method is reported to fabricate the interwoven tubular hierarchy ofSnO2 films using a biotemplate eggshell membrane (ESM) combinedsol–gel approach. In order to promote the crystallization ofSnO2 films, calcination is necessary and can adjust the size of the building unitsin the range 2.8–26 nm. Under the direction of ESM biomacromolecules,SnO2 nanocrystallites come into being and assemble into nanotubes, and furtherpattern porous hierarchical meshworks to faithfully retain the morphologyof natural ESM. The sensor performance of as-prepared biomorphicSnO2 was measured for ethanol, liquefied petroleum gas (LPG),H2S, and gasoline. Itis found that the SnO2 hierarchical films obtained have a good selectivity for LPG with a working temperature above300 °C while forethanol below 270 °C.

The Physiological Function of von Willebrand's Factor Depends on Its Tubular Storage in Endothelial Weibel-Palade Bodies

Weibel-Palade bodies are the 1-5 microm long rod-shaped storage organelles of endothelial cells. We have investigated the determinants and functional significance of this shape. We find that the folding of the hemostatic protein von Willebrand's factor (VWF) into tubules underpins the rod-like shape of Weibel-Palade bodies. Further, while the propeptide and the N-terminal domains of mature VWF are sufficient to form tubules, their maintenance relies on a pH-dependent interaction between the two. We show that the tubular conformation of VWF is essential for a rapid unfurling of 100 microm long, platelet-catching VWF filaments when exposed to neutral pH after exocytosis in cell culture and in living blood vessels. If tubules are disassembled prior to exocytosis, then short or tangled filaments are released and platelet recruitment is reduced. Thus, a 100-fold compaction of VWF into tubules determines the unique shape of Weibel-Palade bodies and is critical to this protein's hemostatic function.

Synthesis of Nanowalled Polymer Microtubes Using Glass Fiber Templates

AbstractCovalently crosslinked flexible polymer microtubes with wall thicknesses of 1–3 nm, diameters of 2–10 μm, and lengths of 0.1–0.5 mm have been fabricated using glass wool and silica wool as templates. Fluorescent‐dye‐tagged polyamines were adsorbed onto the glass and silica templates and crosslinked by reductive amination with glutaraldehyde and sodium cyanoborohydride, then the templates were dissolved with hydrofluoric acid. Microtubes were prepared from polyallylamine (PAA), polyethyleneimine (PEI), and poly(iminohexamethylene) (PIH) labeled with sulforhodamine B. These flexible hollow structures were characterized by bright‐field and fluorescent optical microscopy and confocal laser scanning microscopy; they adopt open tubular conformations when suspended in water, and dry to give flat ribbons.