The viscoelasticity and structure of keratin and collagen

Summary Viscoelastic properties of keratin and collagen fibres immersed in aqueous media have been measured at frequencies between 1 kc/s and 20 kc/s and at temperatures between 0‡ and 100 ‡C. Elastic and viscous moduli were derived from wave-propagation measurements which enabled fibres to be tested while they were held at different extensions. Wave velocities, generally of the order of 1,000 m/s, were readily obtained with an accuracy of about ±2%; the attenuation, and thus the viscous modulus component, could be determined only approximately. Keratin fibres held at less than 1% extension in water showed the small temperature- or rate-dependence typical of glassy or crystalline polymers. However, after a ‘setting’ treatment involving stretching in boiling water, the viscoelastic behaviour was characteristic of a crosslinked polymer with a high degree of crosslinking. Marked viscoelastic dispersion was also found when fibres were immersed in formic acid-water mixtures of different concentration, or when the mean extension in water was increased to 15%. Native collagen fibres in saline solution showed an elastic modulus component at 20 kc/s falling from 2×10¹⁰ to 1×10¹⁰ dyne/cm² as the temperature increased to the shrinkage point. After shrinking, the modulus at low extensions was approximately 2×10⁶ dyne/cm². Measurements at room temperature indicated that the curvature of the force-extension curve arises first from extension of interfibrillar material and subsequently from alignment of fibrils; plastic extension of the fibre takes place prior to breaking but the high dynamic modulus shows that the alignment of the intact part of the structure is preserved.

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Zusammenfassung Die viskoelastischen Eigenschaften von Keratin und Kollagenfasern, die in einem w?\rigen Medium eingebettet sind, wurden bei Frequenzen zwischen 1 kHz und 20 kHz und bei Temperaturen zwischen 0 und 100 ‡C gemessen. Die elastischen und viskosen Moduln wurden aus der Wellenausbreitung abgeleitet. Die Methode erlaubt, da\ die Fasern hierbei bei verschiedenen Dehnungen gehalten sind. Die Wellengeschwindigkeit, im allgemeinen von der Ordnung von 1000 m/sec, lie\en sich leicht mit einer Genauigkeit von ±2% erhalten. Die D?mpfung, und damit die viskose Komponente des Moduls, konnte nur angen?hert bestimmt werden. Keratinfasern bei weniger als 1% Dehnung zeigen im Wasser die kleine Temperatur- bzw. Geschwindigkeitsabh?ngigkeit, die typisch für den glasigen oder kristallinen Zustand Polymerer ist. Nach einer Vorbehandlung, die in einer Behandlung der gestreckten Probe in kochendem Wasser besteht (setting-Proze\), erwies sich das elastische Verhalten als charakteristisch für das eines vernetzten Polymeren mit einem hohen Grad an Vernetzungsbrücken. Merkliche viskoelastische Dispersion wurde auch gefunden, wenn die Fasern in Ameisens?ure-Wasser-Mischungen verschiedener Konzentrationen eingetaucht waren oder wenn die mittlere Dehnung in Wasser gr?\er als 15% gew?hlt wurde. Native Kollagenfasern in Salzl?sungen zeigen eine elastische Komponente bei 20 kHz, die von 2×10¹⁰ auf 1×10¹⁰ Dyn/cm abf?llt, wenn die Temperatur bis zum Schrumpfungspunkt gesteigert wird. Nach der Schrumpfung lag der Modul für kleine Dehnungen bei ungef?hr 2×10⁶ Dyn/cm². Messungen bei Raum-temperatur zeigen, da\ der Verlauf der Kraft-Dehnungskurve zuerst von der Dehnung des interfibrillaren Materials und in zweiter Linie von der Parallelisierung der Fibrillen herrührt. Plastische Dehnungen der Fasern treten kurz vor dem Bruch auf, aber der hohe dynamische Modul zeigt, da\ die Parallelisierung durch intakte Teile der Struktur gewahrt bleibt.

     

The fine structure and properties of fibrous alumina

Summary The structure and composition of Wislicenus' fibrous alumina was studied by solubility in acids, birefringence, water content, aging in water, x-ray and electron diffraction and by electron microscopy. It was found that fibrous alumina is constituted mainly of amorphous aluminum hydroxide and contains some adsorbed water and some aluminum oxide. The birefringence of the fibers was due to the existence of non-crystalline fibrils of various length and about 70–80 A. U. diameter, which were more-or-less well oriented parallel to the length of the fiber. Amorphous particles, arranged linearly, <50 A. U. in diameter were found to be the ultimate building blocks of these fibrils. These fibrils were often observed to lie together in bundles or fibers about 200–300 A. U. across. Sometimes such groupings of the fibrils did not exist but the whole macroscopic fiber seemed to be composed of an oriented bundle of fine fibrils. The binding between particulates in a fibril and between fibrils was very weak. This fact may account for the low density of the material. It has been shown that the formation of fibrous alumina is dependent on the existence of a small amount of water and a small amalgamation on distinct spots on the aluminum surface. The mechanism of the formation of fibrous alumina is suggested as similar to that of anodic films on aluminum. It was observed that strongly amalgamated aluminum or aluminum amalgam itself did not produce fibrous alumina even in air, but formed a grey powder of which the main component was mercuric oxide and aluminum.

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Zusammenfassung Die Struktur und Zusammensetzung fasriger Tonerde nach Wislicenus wurde aus L?slichkeit in S?uren, Doppelbrechung, Wassergehalt, Alterung in Wasser mit R?ntgen- und Elektronenbeugung und im Elektronenmikroskop untersucht. Es wurde festgestellt, da? Fasertonerde haupts?chlich aus amorphem Aluminium-hydroxyd besteht und etwas absorbiertes Wasser sowie etwas Aluminiumoxyd enth?lt. Die Doppelbrechung der Fasern ist dem Bestehen von nichtkristallinen Fibrillen variierender L?nge und von ungef?hr 70–80 ? Durchmesser zuzuschreiben, die mehr oder weniger gut parallel zur L?ngsrichtung der Fasern orientiert sind. Amorphe Teile linear angeordnet kleiner als 50 ? im Durchmesser bilden die letzten Bausteine dieser Fibrillen. Diese Fibrillen liegen oft zusammen in Bündeln mit 200–300 ? Querschnitt. Zuweilen bestehen solche Gruppierungen nicht, doch scheint die ganze makroskopische Faser zusammengesetzt aus einem orientierten Bündel feiner Fibrillen. Die Bindung zwischen den Teilchen in einer Fibrille und zwischen den Fibrillen ist sehr schwach. Diese Tatsache mag für die geringe Dichte des Materials verantwortlich sein. Es wurde weiter gezeigt, da? die Bildung fasriger Tonerde von der Existenz geringerer Wassermengen abh?ngt und von einer geringen Amalgamierung an ausgezeichneten Punkten der Aluminiumoberfl?che. Der Mechanismus der Bildung ist vermutlich ?hnlich der eines anodischen Films auf Aluminium. Es wurde beobachtet, da? stark amalgamiertes Aluminium oder Aluminiumamalgam selbst keine faserige Tonerde erzeugt, auch nicht in Luft, sondern da? ein graues Pulver entsteht, in dem die haupts?chlichen Komponenten Quecksilberoxyd und Aluminium sind.

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This work has been aided in part by grants from the Conselho Nacional de Pesquisas do Instituto Butantan. It was presented in part before the fourth International Congress of Crystallography in Montreal, July 1957.     

Thermal chemiluminescence of fibrous proteins

Thermal chemiluminescence (TCL) from the fibrous proteins wool and feather keratin, silk fibroin and Type I collagen is reported for the first time. The proteins all emit TCL when heated in the atmosphere of O₂ or N₂ in the range 40-220 °C. Plotting non-isothermal CL data in O₂ in Arrhenius format showed an increase in the activation energy at temperatures in the range 129-161 °C for each protein. This may indicate that a different free radical oxidation process operates when the mobility of the amorphous phase of the protein is increased above its T_g. Wool, silk and collagen exhibited a luminescence peak at 130 °C (with feather keratin at 145 °C) during non-isothermal CL experiments in N₂, similar to that observed in many synthetic polymers and characteristic of polymer hydroperoxides.     

Photo-induced chemiluminescence from fibrous polymers and proteins

A commercial thermal chemiluminescence (TCL) instrument was modified to allow in situ sample irradiation at wavelengths in the range 320-700 nm under a controlled atmosphere at constant temperature. Weak photo-induced chemiluminescence (PICL) emission was observed from commercial poly(ethylene terephthalate), polyacrylonitrile, and polyamide 6 fabrics, cotton fabric and from the fibrous proteins wool and feather keratin, silk fibroin and bovine skin collagen (Type 1) after exposure to UVA (320-400 nm) or visible light in nitrogen, followed by a change of the atmosphere to oxygen. Collagen emits PICL of similar intensity to keratin, which demonstrates that tryptophan is not essential for PICL emission from proteins. In all cases the decay of PICL with time is complex and does not follow simple first- or second-order kinetics. The effects of experimental variables, including wavelength of radiation and exposure time, sample temperature and fabric pH on the PICL intensity and decay profile are reported for wool keratin.     

The quaternary structure of proteins

Many protein molecules, particularly those with high molecular weights, consist not of a single polypeptide chain, but form a complex made up from several polypeptide chains. This structure, which can be reversibly broken down, is known as the quaternary structure. A number of metabolic phenomena can be explained on a molecular basis by invoking the quaternary structure.     

The structure of intrinsic membrane proteins

Intrinsic membrane proteins are embedded in the lipid bilayer so that the polypeptides come in contact with the non-polar region of the bilayer. There are two major types of intrinsic proteins: those with most of their mass outside the cytoplasm (Type I) and those with most of their mass inside the cytoplasm (Type II). In the latter group are the membrane transport systems. The anion exchange system of the human erythrocyte is a dimer of band 3 polypeptides. These polypeptides span the bilary, have most of their mass in the cytoplasm, and are glycosylated. About 20-25% of the polypeptide, however, is in the bilayer. Arguments are presented to support the view that the intramembrane segments of the protein are alpha-helical and that the major protein-protein interactions between the subunits are in the cytoplasmic portion of the protein.     

Superhydrophobicity of PHBV fibrous surface with bead-on-string structure

A poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) fibrous surface with various bead-on-string structures was fabricated by electrospinning. PHBV was electrospun at various concentrations and then CF4 plasma treatment was employed to further improve the hydrophobicity of the PHBV fiber surfaces. The surface morphology of the electrospun PHBV mats was observed by scanning electron microscopy (SEM). The surface properties were characterized by water contact angle (WCA) measurements and X-ray photoelectron spectroscopy (XPS). The surface morphology of the electrospun PHBV fibrous mats with the bead-son-string structure varied with the solution concentration. The WCA of all of the electrospun PHBV mats was higher than that of the PHBV film. In particular, a very rough fiber surface including porous beads was observed when PHBV was electrospun from the solution with a concentration of 26 wt%. Also, its WCA further increased from 141 degrees to 158 degrees after CF(4) plasma treatment for 150 s. PHBV can be rendered superhydrophobic by controlling the surface morphology and surface energy, which can be achieved by adjusting the electrospinning and plasma treatment conditions.     

Recovery and refining of au by gold-cyanide ion biosorption using animal fibrous proteins

Animal fibrous proteins (AFPs) such as egg-shell membrane (ESM), chicken feather (CF), wool, silk, or elastin are an intricate network of stable and water-insoluble fibers with high surface area and are abundant bioresources. Every AFP tested was found to accumulate gold-cyanide ion from aqueous solutions in high yield, depending on pH and some other parameters. Gold-cyanide ion is adsorbed by AFP at low pH range, with maximum binding observed at approx pH 2.0. Under the certain conditions, gold-cyanide ion was accumulated up to 8.6, 7.1, 9.8, 2.4, and 3.9% of dry weight on ESM, CF, wool, silk, and elastin, respectively. In the case of ESM, it was found that ESM removed gold-cyanide ion almost quantitatively and almost all the gold uptake by ESM was easily desorbed with 0.1M NaOH. ESM can be used repeatedly for the process of gold adsorption-desorption. The gold-biosorptive capacity of ESM that was chemically modified with glutaraldehyde was higher than that of control. In column procedure, ESM packed on column removed gold-cyanide ion from the dilute aqueous solution to extremely low concentrations (nondetectable concentration of below 1 ppb)     

The viscoelasticity of spinnable solutions of alkyltrimethylammonium salicylates

The viscoelasticity has been measured for aqueous solutions of tetradecyl-and hexadecyltrimethylammonium salicylates (C₁₄TASal, C₁₆TASal). The aqueous solutions of C₁₄TASal without salt displayed the gel-like behavior at 10.0×10^–2 g cm^–3, but those more dilute than 3.2×10^–2 g cm^–3 presented the viscoelasticity similar to that of a Maxwell liquid. The Maxwell-like behavior was converted to the polymer-like one on the addition of (0.1–0.2) M NaBr or (0.02–0.2) M NaSal. The gel-like viscoelasticity can be connected with the spinnability of cohesive fracture failure, and the Maxwell-like and polymer-like viscoelasticities are concerned with the spinnability of ductile failure. The gel-like and Maxwell-like viscoelasticities originate in the pseudo-network formed by the pseudo-linkages between rodlike micelles, while the polymer-like viscoelasticity is caused by the entanglement of long rodlike micelles in semidilute and concentrated solutions. The aqueous solutions of C₁₆TASal behaved very similar to those of C₁₄TASal.     

Results of investigation of the structure and physicochemical properties of fibrous dust

Results of numerical modeling of the kinetics of reaction of binding of nitrogen at mechanochemical disintegration of water solutions are illustrated. Experimental data of kinetics of more than fifty reactions which in many cases are different from Arrhenius kinetics were used in calculations. It is found that the main channel of nitrogen fixation is the formation of nitrocompounds, but in the presence of small amount of hydrogen the change to the channel of ammonia formation becomes possible.     

The viscoelasticity of polymer solutions: Comparison of theory and experiment

The theory of the preceding paper is compared with previously unpublished experimental results on the viscoelastic properties of two polystyrene fractions of molecular weight 1.9 × 10⁶ and 1.2 × 10⁶ in nitropropane, which is very nearly a theta solvent, and in toluene, a good solvent. At the concentrations used, around 1%, the theory predicts extensive departures from non-draining toward free-draining behavior; these effects are observed. The theory similarly fits experimental data of Johnson on a sample of polystyrene of molecular weight 860,000 in decalin and dioctyl phthalate in the same concentration range.     

The role of surface viscoelasticity in slide coating processes

In the slide hopper coating process for simultaneously applying multiple layers of coating liquids to a moving web, surfactants must be added to the photographic emulsion to ensure a stable position of the liquid bridge formed between the lower edge of the slide hopper and the moving web. In slide coating of gelatin solutions without an added surfactant, the liquid bridge becomes instable and begins to oscillate if critical coating conditions are reached. The addition of anionic surfactants stabilizes the liquid bridge against oscillations. The action of the added surfactants is a result of their interaction with gelatin. The degree of binding can be used as a measure of the interaction. The binding of anionic and cationic surfactants to gelatin was investigated using a surfactant-selective electrode. The binding isotherms of the surfactants to an alkali-processed bone gelatin were determined and compared with the surface dilational properties of the gelatin/surfactant adsorption layers. The comparison of surface rheological data obtained by the oscillating bubble method with the results of coating experiments demonstrates that the viscoelastic properties of gelatin/anionic surfactant adsorption layers are of essential importance to the stabilization of the liquid bridge against oscillations. Pure elastic adsorption layers are not able to stabilize the liquid bridge. The mechanism of the stabilizing action is discussed. Received: 30 October 2000/Revised: 12 February 2001/Accepted: 14 February 2001     

Study of the structure of chelate fibrous ionites by IR spectroscopy

Structure of fibrous chelate ion exchangers FIBAN X-1 and FIBAN X-2 prepared by a two-step synthesis was studied by IR Fourier spectroscopy. The first step of the ion exchanger preparation consists in the production of an aminated fiber (AF). The process can be carried out in different phases: either vapor, or aqueous. It is found that conditions of the synthesis of AF affect differently the ion exchanger structure. For the ion exchanger FIBAN X-1 it does not a matter in which phase is AF synthesized, and the FIBAN X-1 sorbent has amidoamine structure. The structure of chelate ion exchanger FIBAN X-2 depends on the conditions of the synthesis of AF. When the process is carried out in aqueous medium the FIBAN X-2 has amidoamine structure, while amination in the vapor phase leads to formation of the FIBAN X-2 ion exchanger mainly containing in its structure imidazoline rings.     

Anisotropic viscoelasticity of polymers

A director theory of solutions and melts of flexible-chain polymers that is based on a simple law of anisotropic stress relaxation is developed. A spectral approach is used to study its structure. The simplest equation for the director that describes the dependence of the orientation of anisotropic viscoelastic fluids on shear rate is presented. The most appropriate flows for determining the material properties of polymer fluids with a single preferred direction are discussed. In addition, a new classification of anisotropic fluids is proposed.     

Thermodynamic theory of viscoelasticity

The relaxation spectra in polymers arise from the existence of many possible modes for dissipating the strain energy raised by the imposed force. These modes are made up by coupling the simplest and fastest mode of relaxation involving the rotation of a conformer, typically represented by the picosecond rotation of the carbon to carbon bond. This fast relaxation process cannot take place easily in the condensed state crowded by the densely packed conformers, necessitating cooperativity among them. The domain of cooperativity grows at lower temperatures, toward the infinite size at the Kauzman zero entropy temperature. From the temperature dependence of the domain size, the well-known Vogel equation is derived, which is numerically equivalent to the empirical WLF and free volume equations. The molar volume is a crucial factor in determining the molar free volume and, therefore, in determining theT _g of a material. The molar ΔC _P is proportional to the logarithmic molar volume, and is greater for a polymer with a higherT _g, but ΔC _P per gram for it is smaller, as it is proportional to (logM) divided byM, whereM is the molecular weight of the conformer. From this theory, it is possible to predict the dependence of the characteristic relaxation time on temperature if eitherT _g or the conformer size is known, since one can be derived from the other. From the Vogel equation with all parameters thus derived, it is possible to obtain a master relaxation curve and the spectrum from one set of dynamic mechanical data taken at one frequency over a range of temperatures. Whereas the linear viscoelastic principle is limited to small strains only, a real polymer is often deformed well beyond such a limit. Above a certain limit of strain energy level, linear viscoelastic deformation is no longer possible and the plastic deformation takes over. However, because a polymer typically manifests a spectrum of relaxation times, its behavior is a combination of viscoelastic and plastic behaviors. The ratio between the two behaviors depend on the rate of deformation, and can be precisely predicted from the linear viscoelastic relaxation spectrum. The combined behavior is termed viscoplasticity, and it applies to a wide range of practically important mechanical behaviors from the flow of the melt to the yield and fracture of glassy and crystalline solids.     

Conformation and dynamics of fibrous and membrane proteins as revealed by high-resolution solid-state nuclear magnetic resonance

We examined conformation and dynamics of a variety of fibrous and membrane proteins by means of the conformation-dependent displacements of ¹³C nuclear magnetic resonance (NMR) chemical shifts and their relaxation parameters, respectively, as recorded by high-resolution solid-state ¹³C NMR. Determination of three-dimensional structure of atomic resolution is also briefly described for a simple peptide on the basis of precise measurements of interatomic distances.