Fibrous Aggregates Research Articles

Time-Lapse Atomic Force Microscopy Observations of the Morphology, Growth Rate, and Spontaneous Alignment of Nanofibers Containing a Peptide-Amphiphile from the Hepatitis G Virus (NS3 Protein)

Time-lapse atomic force microscopy is used in this contribution to directly watch the growth of nanofibers of a lipidated peptide on a mica surface. Specifically, the studied lipopeptide is the palmitoyl derivative of the fragment 505-514 of NS3 protein from the hepatitis G virus, abbreviated as Palmitoyl-NS3 (505-514). Data on the morphology, growth rate, and orientation of these peptide-amphiphile nanofibers have been obtained. From these data, it can be concluded that this synthetic lipopeptide forms two types of fiber-like aggregates: (i) half-spherical fibrous aggregates with lengths of hundreds of nanometers and (ii) spherical fibrous aggregates with lengths of several micrometers. In addition, when a fresh lipopeptide aqueous solution is deposited onto a mica surface, the aggregates spontaneously orient parallel to each other, yielding well-aligned nanofibers on large areas of the mica surface. A significant growth in both the length and the number of the fibers was observed during the first minutes after the solution deposition. Elongation of the fibrous aggregates from one end is more frequent, though elongation from both ends also occurs, with growth rates in the 4-5 nm/s range. The effects of dilution, mechanical perturbation, and pH on the aggregation behavior of Palmitoyl-NS3 (505-514) are also detailed in this paper.

Self-Catalytic Sol−Gel Synergetic Replication of Uniform Silica Nanotubes Using an Amino Acid Amphiphile Dynamically Growing Fibers as Template

The aggregation behavior of a novel histidine derivative surfactant N-dodecanoyl-L-histidine (DHis) in aqueous solution was investigated. By mixing with cationic/anionic surfactant, an interesting phase transition over time from transparent homogeneous solution to jelly and finally to fibrous floccules was observed with aggregates growth taken place in the systems. Making use of the growing fibrous structures in the DHis/DTEAB and DHis/SDS systems as surface charge tunable dynamic template, we achieved sol-gel replication of silica and titania nanotubes in mild conditions, respectively. The possible mechanism underlying the formation of silica nanotubes was proved to be synergistically self-catalyzed hydrolysis and condensation of silica precursors depositing on the template surface. In particular, by optimizing the sol-gel process, silica nanotubes with tunable sizes in diameter and uniform wall thickness could be obtained in high yield. The large specific surface area and peculiar photoluminescence property of the silica nanomaterials indicated that the synthetic nanotubes were well-defined in both morphology and physical properties. Importantly, this fibrous aggregates could be universally used in opposite charged inorganic precursors to accomplish inorganic oxide nanotubes via sol-gel replication process, which may provide a general route for the construction of one-dimensional nanostructures in aqueous media.

The Hofmeister effect on amyloid formation using yeast prion protein

A variety of proteins are capable of converting from their soluble forms into highly ordered fibrous cross-beta aggregates (amyloids). This conversion is associated with certain pathological conditions in mammals, such as Alzheimer disease, and provides a basis for the infectious or hereditary protein isoforms (prions), causing neurodegenerative disorders in mammals and controlling heritable phenotypes in yeast. The N-proximal region of the yeast prion protein Sup35 (Sup35NM) is frequently used as a model system for amyloid conversion studies in vitro. Traditionally, amyloids are recognized by their ability to bind Congo Red dye specific to beta-sheet rich structures. However, methods for quantifying amyloid fibril formation thus far were based on measurements linking Congo Red absorbance to concentration of insulin fibrils and may not be directly applicable to other amyloid-forming proteins. Here, we present a corrected formula for measuring amyloid formation of Sup35NM by Congo Red assay. By utilizing this corrected procedure, we explore the effect of different sodium salts on the lag time and maximum rate of amyloid formation by Sup35NM. We find that increased kosmotropicity promotes amyloid polymerization in accordance with the Hofmeister series. In contrast, chaotropes inhibit polymerization, with the strength of inhibition correlating with the B-viscosity coefficient of the Jones-Dole equation, an increasingly accepted measure for the quantification of the Hofmeister series.

Tazieffite, Pb20Cd2(As,Bi)22S50Cl10, a new chloro-sulfosalt from Mutnovsky volcano, Kamchatka Peninsula, Russian Federation

Tazieffite, ideally Pb20Cd2(As,Bi)22S50Cl10, is a new mineral from the high-temperature fumaroles of the Mutnovsky volcano, Kamchatka Peninsula, Russian Federation. It occurs as tiny, slender, needle-shaped crystals, up to 400 μm long and 10 μm across, generally forming fibrous aggregates. Tazieffite is closely associated with greenockite, galena, mutnovskite, kudriavite, and Cd-rich cannizzarite. Other minerals spatially associated are pyrite, anhydrite, and cristobalite. Tazieffite is silvery-gray in color, occasionally with a magenta tint when it forms aggregates of extremely fine needles. It has a black streak and metallic luster. In plane-polarized incident light, tazieffite is weakly bireflectant and weakly pleochroic from dark gray to a blue-gray. Between crossed polars, the mineral is weakly anisotropic, without characteristic rotation tints. Reflectance percentages measured in air ( R min and R max) for a single grain are 33.9, 34.1 (471.1 nm), 32.8, 33.0 (548.3 nm), 32.4, 32.6 (586.6 nm), and 30.9, 31.1 (652.3 nm), respectively. Electron microprobe analyses yield the following ranges of concentrations: Pb 41.88–44.14 (avg. 42.90), Cd 0.87–1.16 (avg. 1.03), Sn 0.31–0.69 (avg. 0.48), Bi 20.43–22.94 (avg. 21.90), As 8.64–10.73 (avg. 9.66), S 16.10–17.48 (avg. 16.58), Se 0.82–1.28 (avg. 1.04), Cl 2.39–2.77 (avg. 2.63), Br 0.09–0.15 (avg. 0.12), I 0.27–0.58 (avg. 0.42). The empirical chemical formula, calculated on the basis of 44 cations, is Pb20.06(Cd0.89Sn0.39In0.02)∑1.30(As12.49Bi10.15)∑22.64 (S50.08Se1.28)∑51.36(Cl7.18I0.32Br0.15)∑7.65. Tazieffite is closely related to the halogen-sulfosalt vurroite, Pb20Sn2Bi22S54Cl6, both from a chemical and structural point of view. It represents the (Cd,As)-dominant of vurroite, according to the coupled heterovalent substitution Sn4+ + 2S2− → Cd2+ + 2Cl−. The crystal structure of tazieffite was refined in the space group C 2/ c to R = 0.0370 for 4271 reflections with I > 2σ( I ). Unit-cell parameters are a = 8.3520(17), b = 45.5920(92), c = 27.2610(55) A, β = 98.84(3)°, with V = 10257(4) A3, and Z = 4. The structure of tazieffite consists of lozenge-shaped composite rods made of coordination polyhedra of Pb around an octahedrally coordinated (Cd,Sn,Pb) position, interconnected into layers parallel to (010). These layers are separated by ribbons of As and Bi in distorted octahedral coordination. The ribbons form wavy, discontinuous double layers of the PbS archetype. Lone electron pairs of As and Bi are accommodated in the central portions of the PbS-like layers. The possibility that small amounts of NH4+ are incorporated in the crystal structure of tazieffite is discussed. The name of this new mineral species (IMA 2008-012) honors Haroun Tazieff (Warszawa, May 11, 1914–Paris, February 6, 1998), famous Belgian/French volcanologist, who was a pioneer in the field study of volcanoes and devoted his life to the study of volcanic gases.

Crowded Cell-like Environment Accelerates the Nucleation Step of Amyloidogenic Protein Misfolding

To understand the role of a crowded physiological environment in the pathogenesis of neurodegenerative diseases, we report the following. 1) The formation of fibrous aggregates of the human Tau fragment Tau-(244-441), when hyperphosphorylated by glycogen synthase kinase-3beta, is dramatically facilitated by the addition of crowding agents. 2) Fibril formation of nonphosphorylated Tau-(244-441) is only promoted moderately by macromolecular crowding. 3) Macromolecular crowding dramatically accelerates amyloid formation by human prion protein. A sigmoidal equation has been used to fit these kinetic data, including published data of human alpha-synuclein, yielding lag times and apparent rate constants for the growth of fibrils for these amyloidogenic proteins. These biochemical data indicate that crowded cell-like environments significantly accelerate the nucleation step of fibril formation of human Tau fragment/human prion protein/human alpha-synuclein (a significant decrease in the lag time). These results can in principle be predicted based on some known data concerning protein concentration effects on fibril formation both in vitro and in vivo. Furthermore, macromolecular crowding causes human prion protein to form short fibrils and nonfibrillar particles with lower conformational stability and higher protease resistance activity, compared with those formed in dilute solutions. Our data demonstrate that a crowded physiological environment could play an important role in the pathogenesis of neurodegenerative diseases by accelerating amyloidogenic protein misfolding and inducing human prion fibril fragmentation, which is considered to be an essential step in prion replication.

Interaction of lipidated GBV-C/HGV NS3 (513–522) and (505–514) peptides with phospholipids monolayer. An AFM study

Lipidation of a short hydrophilic peptide has the aim to make the molecule amphiphilic, which improves its insertion into lipid monolayer and at the same time, the tendency to self-assembly. These both properties of two positively charged, hepatitis G (GBV-C/HGV) related lipidated peptides—palmitic acid derivatives of the fragments: 505–514 and the 513–522 of the NS3 protein (respectively Palmitoyl-SAELSMQRRG and Palmitoyl-RGRTGRGRSG) were studied. First, using transmission electron microscope (TEM) and atomic force microscope (AFM) the tendency to self-assembly in water solution was examined. Both techniques confirmed the formation of fibrous aggregates of Palmitoyl-SAELSMQRRG in water solution. At the same conditions, any fibrous aggregates of Palmitoyl-RGRTGRGRSG were detected neither by TEM nor by AFM. Insertion of the lipidated peptides into phospholipids monolayer formed by zwitterionic 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or negatively charged 1,2-dipalmitoyl-sn-glycero-3-[phospho-rac-(1-glycerol)] (DPPG) was investigated. Monolayers prepared by Langmuir–Blodgett method were visualized by AFM. The presence of lipidated peptides in phospholipid monolayers produced changes in the monolayers and different morphologies of the monolayers were obtained for each of the lipidated peptides.

Formation of Highly Luminescent Supramolecular Architectures Possessing Columnar Order from Octupolar Oxadiazole Derivatives: Hierarchical Self‐Assembly from Nanospheres to Fibrous Gels

AbstractThe synthesis and study of the liquid crystalline, photophysical, and aggregation behavior of novel octupolar oxadiazole derivatives are reported. These molecules formed columnar mesophases at elevated temperatures which transformed into a glassy state at ambient temperatures wherein the columnar order was retained. Their spontaneous concentration dependent hierarchical self‐assembly from spheres to fibrous gels has been investigated using TEM, SEM, and XRD. Retention of the hexagonal columnar (Colh) order was also observed in the fibrous aggregates. Concentration dependent luminescence spectral studies indicated that the change in morphology from spheres to fibrous aggregates was associated with a shift in chromophore packing from predominantly H‐type to J‐type aggregates. Time resolved anisotropic investigations revealed that the columnar stacking of molecules in the aggregated state provided a pathway for excitation energy migration to the lower energy J‐traps.

Structural Characterization, Chain Conformation, and Morphology of a β-(1→3)-d-Glucan Isolated from the Fruiting Body of Dictyophora indusiata

A water-soluble glucan, namely, PD3, was isolated from the fruiting body of Dictyophora indusiata as the method reported previously. Its chemical structure was characterized by GC, FTIR, and (13)C NMR. The results indicated that PD3 is a (1-->3)-beta-D-glucan, with (1-->6)-beta-glucopyranoside side branches. The chain conformation and morphology of PD3 in aqueous solution were investigated by viscometry, rheometer, and laser light scattering (LLS) measurements, atomic force microscopy (AFM), and transmission electron microscopy (TEM), respectively. The weight-average molecular mass (M(w)), radius of gyration (R(g)), hydrodynamic radius (R(h)), and intrinsic viscosity ([eta]) of PD3 in water were determined to be 5.1 x 10(5), 141 nm, 44 nm, and 1440 cm(3) g(-1), respectively, by LLS and viscometry. The structural parameter rho (Rg/Rh) of PD3 was calculated to be 3.4, and the [eta] dependence of C(NaOH) of PD3 is similar to that of triple helical polysaccharides Scleroglucan and Lentinan, suggesting that PD3 exists as a triple helical chain in water. This conclusion was further proved by rheological measurement and AFM observation. Interestingly, the [eta] of PD3 dramatically decreased in a narrow range concentration of NaOH between 0.18 and 0.22 M, higher than that of Scleroglucan and Lentinan (both less than 0.1 M), indicating the helix-coil conformation transition of PD3 is more difficult than that of Scleroglucan and Lentinan. Moreover, with the increase of concentration, PD3 trends to self-assemble to fibrous aggregates in aqueous solution as measured by TEM.

Biosensor-based label-free assays of amyloid growth

Uncontrolled fibrous protein aggregation is implicated in a range of aberrant biological phenomena. Much effort has consequently been directed towards establishing quantitative in vitro assays of this process with the aim of probing amyloid growth in molecular detail as well as elucidating the effect of additional species on this reaction. In this paper, we discuss some recent approaches based on label-free technologies focussed on achieving these objectives. Several biosensor techniques have been developed to monitor biomolecular assembly without the requirement for fluorophore marker molecules; in particular quartz crystal microbalance and surface plasmon resonance measurements provide advantageous alternatives to traditional spectroscopic methods and are currently receiving increasing attention in the context of amyloid growth assays.

Electric Field-Assisted Alignment of Self-Assembled Fibers Composed of Hydrogen-Bonded Molecules Having Laterally Fluorinated Mesogens

Aligned fibrous aggregates of amide compounds having laterally fluorinated aromatic mesogens have been successfully obtained by the application of the alternating current electric field (1.0 V/microm, 1 kHz) in dodecylbenzene. In contrast, randomly entangled fibers are formed in the solvent without electric fields. For the analogous compounds without fluorine substituent, no aligned fibrous aggregates have been obtained under the electric fields. The electric field alignment of the fibers should be assisted by the fluorinated rod-shaped mesogens that exhibit negative dielectric anisotropy.

Luminescence of Strontianite (SrCO 3) from Strontian (Scotland, UK)

An historic Strontianite-type specimen from Strontian, Scotland, UK, was characterized to broaden our knowledge on luminescence properties of common carbonates. These fibrous aggregates are Strontianite (Sr x Ca 1− x CO 3) with circa 6% of CaO, interfacial water, hydrosilicate anions and substitutional divalent cations, e.g., Ca 2+, Mn 2+, Fe 2+ in structural Sr 2+ positions. The specimen was analyzed by X-ray Fluorescence Spectrometry (XRF), Environmental Scanning Electron Microscopy coupled with an Energy Dispersive X-ray Spectroscopy (ESEM-EDS) probe, Spatially-resolved Cathodoluminescence under the Scanning Electron Microscope (SEM-CL), Differential-Thermal Analyses (DTA), Thermogravimetry (TG), Thermoluminescence (TL), Radioluminescence (RL) and High Resolution Spectra Thermoluminescence (3DTL), to gain an overview of the spectral emissions, the defect linkages were modified by heating from room temperature (RT) up to 500 °C. Substitutional transition elements are probably responsible for the spectral emission bands from 500 nm to 800 nm and hydrous molecules from 300 nm to 400 nm. DTA–TG analyses performed on little chips, to preserve the fiber interfaces coherence, exhibit minor endothermic peaks attributed to outflow of water groups in fiber interfaces. Both, CL and RL curves show common spectral positions but UV–blue and red emission intensities are counterbalanced since electron irradiation reduces the UV–blue emissions while X-irradiation increases them. The TL curves show a top thermal limit at ∼300 °C for the 300–400 nm TL emissions which become irreversibly destroyed, whereas the longer wavelength region emits at higher temperature. The non-reversible changes observed in the 320 nm and 360 nm bands during the spectra 3DTL emission could be linked with non-bridging oxygen defects, protons and hydroxyl groups and the red emissions to the 4G ( 4T 1g)– 6S Mn 2+ ion transition. Following assignations and similar spectral CL patterns of Russian Strontianite samples, the emission-defect assignments: Dy 3+ 480 nm; Tb 3+ 540 nm; Dy 3+ 580 nm and Sm 3+ 640 nm cannot be disregarded.

Who's Afraid of the Big, Bad, Misfolded Protein?

Fatal prion diseases, such as Creutzfeldt‐Jakob disease in humans, are associated with the conversion of the normally folded mammalian PrP protein to a misfolded prion form that aggregates. Understanding how prions behave has been greatly facilitated by the study of prions in Saccharomyces cerevisiae, or baker's yeast. In yeast, the translation release factor, Sup35, misfolds to form the [PSI+] prion. Although the Sup35 protein has a significantly different primary sequence from PrP, its prion form behaves similarly to human prions. The N‐terminus of Sup35 is Q/N‐rich and responsible for prion formation. Determining the structure of this region has proven difficult since the N‐terminus forms aggregates instead of the ordered crystals required for structural studies. However, a small seven amino acid sequence (GNNQQNY) from Sup35's N‐terminus was crystallized by Nelson et al. (2005). We have constructed a 3D physical model of GNNQQNY as part of the MSOE SMART Teams program using 3D printing technology. GNNQQNY's structure suggests that multiple prion molecules assemble into strong fibrous aggregates through tightly structured interlocking parallel beta sheets called a cross‐β spine. The structure of GNNQQNY suggests a potential model of how human prions assemble, which could potentially help in developing therapies that prevent aggregation. Supported by a grant from NIH‐NCRR‐SEPA.

Polycondensation and Stabilization of Chirally Ordered Molecular Organogels Derived from Alkoxysilyl Group- Containing l-Glutamide Lipid

A lipophilic L-glutamide-derived lipid with a triethoxysilyl headgroup (Si-lipid) was newly synthesized as a self-assembling organogelator to stabilize the chirally ordered state of the aggregates. The Si-lipid formed nanofibrous network structures in various organic solvents such as benzene, cyclohexane, and dimethylformamide and entrapped them to form gels. The gels were transformed to sols by heat, and this gel-to-sol transition was thermally reversible. Polycondensation of the triethoxysilyl groups was carried out by acid-catalyzed hydrolysis and condensation in a benzene gel and confirmed by 29Si CP/MAS NMR and FT-IR measurements. After polycondensation, a gel state was maintained, and the thermal and mechanical stabilities of the aggregates increased markedly. Interestingly, polycondensation in chloroform and acetonitrile induced gelation, whereas no gelation was observed before polycondensation. Xerogel, which was prepared by freeze drying organogels, had fibrous network structures similar to those of the original gels. A strong CD signal was observed around the amide bonds in a cyclohexane gel at 20 degrees C, indicating that the gel contained chirally oriented structures based on intermolecular hydrogen bonds. An enhanced CD signal was observed even after polycondensation of the ethoxysilyl group of Si-lipid (poly(Si-lipid)) and was maintained at 70 degrees C, which is above the temperature of the gel-to-sol phase transition of the original gel. These results indicate that the formation of siloxane network structure among the fibrous aggregates stabilizes the chiral orientation of lipid aggregates.

Evidence For Metastable States Of Lysozyme Revealed By High Pressure FTIR Spectroscopy

Metastable protein conformations play an important role in the folding process because such partially disordered states can be gates for the misfolding pathway, leading sometimes to pathological structures, like fibrous aggregates. High pressure is a very useful tool in the study of metastable states, since application of the pressure is fully reversible, contrary to chemical agents. FTIR spectroscopy allows us to follow simultaneously the secondary structure, the packing (tertiary structure) and the aggregation of the protein using the amide I, amide II and the 1616 cm-1 bands respectively. We performed a systematic study on the temperature-pressure phase diagram of lysozyme and found a two-step unfolding profile both in the pressure and temperature directions. Hydrogen/deuterium exchange results show evidence for the molten globule formation at 57°C @130 MPa and 580 MPa @30°C, which are considerable lower values than those of the complete unfolding (e.g. 75°C@130MPa).Refolding of the protein after pressure unfolding is a slow process, with a time constant in the range of hours. Partially refolded structures present in this time range have different aggregation propensity. The kinetics of the aggregation has a biexponential character with a time constants of 1060 and 8600 s at 40C ambient pressure. Analyzing the time dependence of the amide I band shape we found that the strengthening of the intermolecular hydrogen bond network was accompanied by decrease of the folded secondary structure content.Moderate pressure of 300 MPa was found to be able to dissociate the aggregates, while the secondary structure is not yet unfolded. This fact together with the small temperature effect on the aggregation kinetics suggests that the rate of the aggregation of the metastable conformations is determined by the high activation volume rather than the high activation energy.

Synthesis of fibrous nanoparticle aggregates by femtosecond laser ablation in air

In this article we report the synthesis of nanoparticles using femtosecond laser ablation with MHz pulse frequency at room temperature in air. Nanoparticles agglomerate by fusion, and form interweaving fibrous structures that show certain degree of self-assembly. It is found that there is a threshold-like pulse frequency at which fibrous nanoparticle aggregates start to form. The growth mechanism can be explained by existing theories regarding nanoparticle formation through femtosecond laser ablation. The threshold pulse frequency is in good agreement with the time to start nanoparticle formation, which has been derived numerically by previous analyses.

Bi-bearing and REE-free zálesíite from the Fuka mine, Okayama Prefecture, Japan

Zalesiite is found to exist as hexagonal prismatic crystals (length: up to 1 mm; width: 10 μm) and fibrous aggregates in the alteration zone in crystalline limestone near gehlenite-spurrite skarns at the Fuka mine, Okayama Prefecture, Japan. The mineral is pale green to emerald green in color with a silky to vitreous luster. Andradite, aragonite, bornite, cahnite, chalcocite, chalcopyrite, conichalcite, johnbaumite, and an unidentified Ca-Cu arsenate mineral coexist in the abovementioned limestone. From SEM-EDS analysis, the empirical formula of zalesiite is found to be (Ca0.74Bi0.26)Σ1.00(Cu5.80Ca0.18Ni0.01Zn0.01)Σ6.00[(As2.86Si0.12P0.02)Σ3.00(O11.14OH0.86)Σ12.00](OH)6·3H2O on the basis of the following calculation: 10 (M1 + M2 + X) + 6 (OH) + 3 (H2O). Zalesiite collected from the Fuka mine contains Bi and is free of REE. The unit cell parameters of the zalesiite crystals are a = 13.656(9), c = 5.850(4) A, V = 945(1) A3, and Z = 2. It is inferred that zalesiite is formed by the reaction between crystalline limestone, cahnite, johnbaumite, Cu sulfide, and a Bi-rich hydrothermal solution.

Self-organization of dendrons with focal pyrene moiety and diacetylene-containing periphery

We have synthesized the amide dendrons with diacetylene-containing periphery and the focal pyrene moiety to investigate their self-organization behavior in aqueous phase. We investigated the effect of the assembled structure of the dendron on the polymerizability of the peripheral diacetylene moiety and the possibility of the supramolecular transformation due to host-guest interactions between the dendron and β-CD. The second generation dendron with a focal pyrene group self-assembled into the fibrous aggregates in water. We observed a low degree of polymeization of diacetylene units upon photopolymerization from the fibrous aggregates possibly due to the amorphous nature of the hydrophobic core. After addition of β-CD into the aqueous solution of dendron 7, only a fraction of pyrenes of fibrous bundles could be included in β-CDs with maintaining a fibrous structure. We are currently carrying out a comprehensive study to understand the detailed mechanism of formation of different supramolecular structures with the modified amide dendrons and their supramolecular transformation so that we can provide a clear scope of the functional nanostructures which can be derived from selfassembly of the amide dendrons.

Critical Time to Nucleation: Graphite and Silicon Nanoparticle Generation by Laser Ablation

Femtosecond laser ablation hydrodynamics has been analyzed numerically. The nucleation process of two materials (silicon and graphite) in an expanding plume produced by a femtosecond laser ablation is analyzed within the framework of the Zeldovich-Raizer theory (RZ theory). RZ theory is the most appropriate theory applicable to an expanding plume created by a femtosecond laser ablation and has been used to estimate the critical times in the evolution of nanoparticle formation. However, there is no experimental result to directly substantiate the theoretical model on a fundamental level. This paper gives an experimental approach to prove theoretical predictions of critical times to nucleation in laser-ablated graphite and silicon plumes. The critical time to nucleation deduced using the RZ theory was found to be in close agreement with pulse frequency at which fibrous nanoparticle aggregates start to form for both materials. We experimentally showed that the nanoparticle aggregates were produced consistently when the pulse frequency corresponding to the femtosecond laser time interval was shorter than the critical time to begin nucleation. Therefore the nucleation time acts as a threshold time length to begin nucleation.

Lymphangiomatous polyp of the tonsil

Lymphangiomatous polyps are non-neoplastic developmental lesions comprised of tissue elements native to the nasopharynx and categorised as hamartoma. Lyphangiomatous polyp of tonsil is a kind of hamartomatous lesion that has been described by different nomencultures such as lymphangietatic fibrous polyp, polypoid lymphangioma of the tonsil, hamartomatous tonsilar polyp, pedunculated squamous papilloma and so on. The pedunculated polyps of the palatine tonsil are relatively rare. Because of the unusual clinical and pathological features of these polyps, pathologists and clinicians alike may have difficulty in classifying them correctly. Various symptoms associated with these polypoid masses are acute tonsillitis, recurrent sore throat, blood in sputum, dysphagia, mass in throat, slowing deglutition and lump in throat. Microscopically, it is lined by squamous epithelium and its stroma is composed of variably loose or more dense collagenous tissue and adipose tissue, usually containing dilated lymphatic channels and various components of lymphoid tissue. In this report we present our experience on a case of lymphangiomatous polyp of tonsil. A 32-year-old woman was admitted to Imam Reza Hospital with a polypoid and painful oral cavity mass on the upper lobe of the right pharyngeal tonsil which had been present for 2 months. The patient underwent a right tonsillectomy. She had the following symptoms: recurrent and acute one-sided tonsillitis, recurrent sore throat, sensation of foreign body, halitosis, sleep apnea, shortness of breath and snoring. She was not a smoker with any previous history of surgery or treatment. The physical examination revealed cervical lymphadenopathy. Grossly it was a 2.8 × 2.5 × 1.8cm, firm polypoid mass that was attached to the tonsil. The cut surface was a creamy soft tissue. Histologicaly the polyp was covered by squamous epithelium with hyperkeratosis and its stroma was composed of dialated lymphatic vascular channels, varying amounts of fibrous connective tissues and aggregates of lymphoid tissues.

Growth of fibrous aggregates of silica nanoparticles: Fibre growth by mimicking the biogenic silica patterning processes

We describe the self-assembly of discrete SiO2 nanofibers via grafting of silicatein side chains to a polymer backbone. The covalent binding of silicatein to the backbone of the polymer is based on the affinity of the nitrilotriacetic acid (NTA) side chain, which serves as a ligand for the immobilization of His-tagged silicatein. The surface charge and the bulkiness of the protein moieties prevent the entropically favoured coil formation of the polymer and force it to adopt an open chain structure after hydrolysis of the silica precursors. The probes were characterized by scanning force microscopy (SFM) and optical light microscopy. Surface complexation of the resulting silica nanoparticles by the polymer-bound silicatein were analysed using high resolution tranmission electron microscopy (HRTEM).