197,579 research outputs found
Vibrational study on structure and bioactivity of protein fibers grafted with phosphorylated methacrylates
No full textIn the last decades, silk fibroin and wool keratin have been considered functional materials for biomedical applications. In this study, fabrics containing silk fibers from Bombyx mori and Tussah silk fibers from Antheraea pernyi, as well as wool keratin fabrics, were grafted with phosmer CL and phosmer M (commercial names, i.e., methacrylate monomers containing phosphate groups in the molecular side chain) with different weight gains. Both phosmers were recently proposed as flame retarding agents, and their chemical composition suggested a possible application in bone tissue engineering. IR and Raman spectroscopy were used to disclose the possible structural changes induced by grafting and identify the most reactive amino acids towards the phosmers. The same techniques were used to investigate the nucleation of a calcium phosphate phase on the surface of the samples (i.e., bioactivity) after ageing in simulated body fluid (SBF). The phosmers were found to polymerize onto the biopolymers efficiently, and tyrosine and serine underwent phosphorylation (monitored through the strengthening of the Raman band at 1600 cm−1 and the weakening of the Raman band at 1400 cm−1, respectively). In grafted wool keratin, cysteic acid and other oxidation products of disulphide bridges were detected together with sulphated residues. Only slight conformational changes were observed upon grafting, generally towards an enrichment in ordered domains, suggesting that the amorphous regions were more prone to react (and, sometimes, degrade). All samples were shown to be bioactive, with a weight gain of up to 8%. The most bioactive samples contained the highest phosmers amounts, i.e., the highest amounts of phosphate nucleating sites. The sulphate/sulphonate groups present in grafted wool samples appeared to increase bioactivity, as shown by the five-fold increase of the IR phosphate band at 1040 cm−1
Classification of Zeropotent Algebras of Dimension 3 over (Logic, Language, Algebraic system and Related Areas in Computer Science)
No full textThis is a summary of our results [Y. Kobayashi, K. Shirayanagi, S.-E. Takahasi and M. Tsukada, Classification of three-dimensional zeropotent algebras over an algebraically closed field, Comm. Algebra, Vol. 45 (12), 5037-5052, 2017.] and [K. Shirayanagi, S.-E. Takahasi, M. Tsukada and Y. Kobayashi, Classification of three-dimensional zeropotent algebras over the real number field, Comm. Algebra, Vol. 46 (11), 4665-4681, 2018.]
Vibrational Study on the Structure, Bioactivity, and Silver Adsorption of Silk Fibroin Fibers Grafted with Methacrylonitrile
No full textNatural fibers have received increasing attention as starting materials for innovative applications in many research fields, from biomedicine to engineering. Bombyx mori silk fibroin has become a material of choice in the development of many biomedical devices. Grafting represents a good strategy to improve the material properties according to the desired function. In the present study, Bombyx mori silk fibroin fibers were grafted with methacrylonitrile (MAN) with different weight gains. The potential interest in biomedical applications of MAN functionalization relies on the presence of the nitrile group, which is an acceptor of H bonds and can bind metals. IR and Raman spectroscopy were used to characterize the grafted samples and the possible structural changes induced by grafting. Afterward, the same techniques were used to study the bioactivity (i.e., the calcium phosphate nucleation ability) of MAN-grafted silk fibroins after ageing in simulated body fluid (SBF) for possible application in bone tissue engineering, and their interaction with Ag+ ions, for the development of biomaterials with enhanced anti-microbial properties. MAN was found to efficiently polymerize on silk fibroin through polar amino acids (i.e., serine and tryptophan), inducing an enrichment in silk fibroin-ordered domains. IR spectroscopy allowed us to detect the nucleation of a thin calcium phosphate layer and the uptake of Ag+ ions through the nitrile group, which may foster the application of these grafted materials in biomedical applications
Raman study on the structural modifications of silk and wool fibres upon grafting with methacrylamide and styrene
No full textWool keratin and silk fibroin are excellent biopolymers with outstanding properties that make them extremely valuable for biomedical and biotechnological applications. As proteins, fibroin and wool can be chemically modified at side chain groups of constituent amino acids, thus improving their properties according to the desired function. Among the chemical modifications techniques, graft copolymerization of vinyl monomers has been considered a powerful method to substantially improve some intrinsic fibre properties. Grafted fibres represent an interesting model for studying the possible structural changes induced by grafting and the interactions between the fibre matrix and the grafted polymer chains.
In this study, wool and Bombyx mori and Anthaerea pernyi (Tussah) silk fibres were grafted with methacrylamide (MAA) and styrene (St) and were analysed by Raman spectroscopy to comparatively assess the reactivity of vinyl monomers towards silk fibroins and wool and to elucidate the interactions between fibres and polymers as well as the possible conformational changes caused by grafting.
Upon grafting with both MAA and St, new bands (indicated with an asterisk, Figure 1) appeared with increasing intensity at increasing grafting yield. For B. mori and Tussah silk fibroin grafted with MAA, experimental and calculated spectra of the samples with the highest weight gains (97.6 and 71.4%, respectively) appeared different in several ranges, suggesting that silk fibroin and poly-MAA should be thermodynamically compatible rather than phase separated: intermolecular interactions seem to prevail and the changes in the niNH range indicated different H-bond interactions in the grafted samples. B. mori silk fibroin showed a conformational rearrangement towards a more disordered state. Conformational rearrangements seemed to involve poly-MAA as well, as suggested by the wavenumber shifts of some bands (indicated with a circle). Wool fibres showed less significant spectral changes, according to the lower grafting yield.
With regards to grafting with St, experimental and calculated spectra showed less significant differences than after grafting with poly-MAA. No changes were observed in the niNH stretching range, suggesting the occurrence of interactions different from those observed with poly-MAA, probably of hydrophobic nature.
The reactivity towards MAA and St was higher for B. mori and Tussah silk fibroin than for wool. Spectral changes reflected weight gain data. The spectroscopic marker that appeared the most useful to predict the MAA grafting yield was the I730/I644 intensity ratio; it was found to increase linearly with weight gain (R2 = 0.9). Analogous results were obtained for the I1602/I644 and I1002/I644 intensity ratios (St-grafting). Different interactions appeared to occur between the fibres and the two polymers
Influence of grafting with acrylate compounds on the conformational rearrangements of silk fibroin upon electrospinning and treatment with aqueous methanol
No full textSilk fabrics from Bombyx mori silkworm were grafted with 2-hydroxyethyl methacrylate (HEMA) as well as a binary system of HEMA and 4-hydroxybutyl acrylate (HBA) and then analysed by Raman and infrared (IR) spectroscopy to elucidate the interactions between the components and their possible conformational changes. The samples were then dissolved in trifluoroacetic acid and electrospun; the influence of the grafted polymers on the silk fibroin rearrangements upon these treatments was investigated by vibrational spectroscopy. Upon grafting, the fabrics underwent conformational rearrangements towards a more unordered state, although they kept their prevailing β-sheet conformation; also the polymeric component underwent hydrogen bonding and backbone rearrangements upon interaction with silk fibroin and the occurrence of strong covalent bonds cannot be excluded. By immersing the as-electrospun grafted and pure fibroin nanofibres (prevalently unordered) in aqueous methanol, they partially recovered the β-sheet content observed in the corresponding starting fabrics; the percentage of recovery decreased along the series: pure silk > HEMA-grafted silk > HEMA and HBA-grafted silk. This trend suggests that the presence of the polyHEMA grafted component hinders the silk fibroin recrystallization into β-sheet upon aqueous methanol treatment; moreover, the addition of the more sterically hindered HBA monomer in the grafting system further prevented this process. Copyright © 2016 John Wiley & Sons, Ltd
Affinity of protein fibres towards sulphation
No full textWool, Bombyx mori and Antheraea pernyi (Tussah) silk fibres were treated with chlorosulfonic acid in pyridine and investigated
by FT-IR and FT-Raman spectroscopies as well as mechanical measurements. The reactivity towards sulfation was found to
decrease along the series: wool>Bombyx mori silk fibroin>Tussah silk fibroin, in agreement with weight gain which
decreased along the same series. Accordingly, Tussah silk maintained its intrinsic tensile properties essentially unchanged
upon the treatment, while for Bombyx mori silk fibroin, the tensile performance decreased sharply especially at longer
reaction times. Sulfated wool was characterized by an increased fibre extensibility.
New IR and Raman bands attributable to various vibrations of sulfated groups were detected in sulfated wool and to a
lower extent in Bombyx mori silk fibroin fibres; all the fibres underwent conformational rearrangements upon sulfation,
independent of the sulfation yield. Wool fibres treated with chlorosulfonic acid in pyridine bound considerable amounts
of sulfate mainly through the hydroxyl groups of serine, threonine and tyrosine. Also, tryptophan and basic amino acids
were found to participate to the reaction. B. mori silk fibroin fibres appeared to bind a minor amount of sulfate groups
mainly trough the hydroxyl groups of Ser.
Weight gain, spectroscopic and mechanical data are discussed in relation to the difference in fibre morphology, structure and
crystallinity, as well as to the amount and accessibility of potentially reactive amino acids
Stability toward alkaline hydrolysis of B. mori silk fibroin grafted with methacrylamide
No full textBombyx mori silk fibroin fibers were grafted with methacrylamide (MAA) and characterized by Raman and infrared (IR) vibrational spectroscopy before and after hydrolysis in NaOH 5% to elucidate the possible interactions between the two components and the stability of the fibers toward alkaline hydrolysis. Upon grafting, the fibers underwent conformational rearrangements toward a more unordered state and lost orientation at weight gains higher than 60%. Vibrational spectroscopy disclosed the occurrence of intermolecular interactions (mainly hydrogen bonds) between B. mori silk fibroin and polyMAA in the grafted fibers, and the formation of covalent bonds has been explored. These strong interactions made the grafted fibers as a whole more stable toward alkaline hydrolysis because they prevented the solubilization of the polymer upon hydrolysis and made slower the transformation of its CONH2 groups into COOH and COO− groups. Upon hydrolysis, silk fibroin underwent an enrichment in the β-sheet crystalline domains, because of the preferential removal of the unordered domains, which were more prone to the OH− attack. IR and Raman spectroscopy proved valid techniques to investigate the degradation mechanism and kinetics of grafted silk fibroin fibers and so for designing high-performing silk-based materials. The A731/A1004 Raman intensity ratio was proposed to spectroscopically evaluate the composition of the grafted samples; its value was found to linearly increase with weight gain (R2 = 0.998), envisaging the possibility of using Raman spectroscopy as a routine analytical technique for qualitative and quantitative characterization of grafted industrial samples. Copyright © 2016 John Wiley & Sons, Ltd
Structure modifications induced in silk fibroin by enzymatic treatments. A Raman study
No full textRaman spectroscopy was used to investigate various enzyme-catalyzed reactions onto silk fibroin, i.e. the biodegradation of Tussah (Antheraea pernyi) silk fibroin films by a proteolytic enzyme, the oxidation of domestic (Bombyx mori) silk fibroin by mushroom tyrosinase and the subsequent grafting of chitosan onto oxidized silk.
The spectra of Tussah silk fibroin films exposed to a bacterial protease for different times demonstrated that the cleavage of sensitive peptide bonds in the amorphous glycine-rich domains resulted in the loss of various amino acid residues (Tyr, Trp, Asp, etc.). The bands attributed to the crystalline alanine-rich sequences increased in intensity, and the β-sheet molecular conformation was not affected by biodegradation.
Following oxidation with mushroom tyrosinase, the tyrosine bands of Bombyx mori fibroin decreased in intensity but did not disappear. The increase of the I853/I829 intensity ratio indicated that the Tyr residues not accessible to the enzyme were located in a strongly hydrophobic environment. Raman spectroscopy provided evidence that chitosan was effectively grafted onto oxidized silk, probably via the Schiff-base mechanism, as shown by the behavior of the imine band at about 1646 cm−1. Grafting chitosan onto silk fibroin resulted in a β-sheet→random coil conformational transition of the protein component in the bioconjugated product
Vibrational study on the modifications induced by chemical and grafting agents in silk and wool fibres.
No full textWool keratin and silk fibroin are excellent biopolymers with outstanding properties that make them extremely valuable for biomedical and biotechnological applications. As proteins, fibroin and wool can be chemically modified at side chain groups of constituent amino acids, thus improving their properties according to the desired function.
Among the chemical modifications techniques, graft copolymerization of vinyl monomers onto silk fibres has been considered a powerful method to substantially improve some intrinsic fibre properties. Grafted fibres represent an interesting model for studying the possible structural changes induced by grafting and the interactions between the fibre matrix and the grafted polymer chains.
On the other hand, the reaction of selected chemical agents with fibres is a particularly attractive system that can be used to obtain effective and specific modifications of the fibrous substrate. Significant changes in the physical and chemical properties of the fibres can be obtained, avoiding some of the drawbacks that arise from graft-copolymerization of vinyl monomers and from the loading of the fibre with large amounts of polymer, which is often needed to obtain the desired effects.
In the present study, IR and Raman spectroscopy has been used to comparatively analyse the reactivity of vinyl monomers (styrene, methacrylamide) and anhydrides (succinic and glutaric anhydrides) towards Bombyx mori and Antheraea pernyi silk fibroin, and wool.
Several spectroscopic ratios were identified as markers of the extent of grafting/chemical modification, due to their rough proportionality to the fibre weight gain.
Vibrational techniques have been widely recognized as valid tools for studying the secondary structure of polypeptides and proteins. The positions and relative intensities of the Amide I, II and III modes were evaluated to probe the possible occurrence of conformational rearrangements upon reaction.
In wool, the Raman SS stretching region was investigated to gain insight into the conformational changes of the CC-S-S-CC system. In silk fibroin the I850/I830 Raman intensity ratio between the two Tyr bands at 850-830 cm-1 gave information on Tyr environment.
Vibrational spectroscopy proved suitable for evaluating the reactivity of the analysed fibres towards the different agents; the observed differences can be explained in terms of the different composition of the fibres and accessibility of the amino acids potentially involvable in the reactions
Affinity towards sulphation of wool and silk fibres.
No full textWool keratin and silk fibroin are excellent biopolymers with outstanding properties that make them extremely valuable in biomedicai field. Coatings are commonly applied to the surface of materials to improve their surface properties. The biocompatibility and non-immunogenicity of silk proteins should allow their application as coatings for biomedical implants, potentially as anticoagulants, and either promoters or inhibitors of cell adhesion. Incorporation of sulphate and sulphonate groups confers anticoagulant and anti-thrombogenic properties to polymers. In view of widening the biomedicai utility of natural polymers as biomaterials, here we present a comparative vibrational study on wool, B. morì and A. pernyi silk fibroin fibres sulphated with chlorosulphonic acid in pyridine, which is known to enhance the yield of sulphation. Our aim is to prepare sulphated fibres by keeping the intrinsic fibre properties and texture unchanged, using short reaction times (i.e. 3h). The fibres were analyzed by Attenuated Total Reflectance, ATR/FT-IR and FT-Raman spectroscopy to comparatively elucidate the affinity for sulphate groups, the mechanism and the mode of linkage, the amino acid side-chains involved, and the possible conformational changes caused by sulphation. Among the analysed samples, the vibrational spectra of sulphated wool fibres showed the most pronounced changes, suggesting the highest affinity towards sulphation. New bands in the 1300-1200 and 1100-900 cm-1 ranges were assigned to the formation of alkyl and aryl sulphate salts, sulphonamides, sulphoamines and covalent aryl-alkyl sulphates. Vibrational spectra revealed the occurrence of a certain fibre degradation as well as rearrangements with consequent changes in secondary structure, conformation of disulphide bridges and tyrosine environment. The amino acid residues mainly involved in sulphation were identified as serine, threonine, tyrosine and tryptophan. Upon sulphation, the IR and Raman spectra of B. mori silk fibroin fibres showed analogous changes although less pronounced than for wool fibres. No significant changes were detected for A. pernyi silk fibroin fibres: only slight conformational rearrangements were observed. The reactivity towards sulphation was found to decrease along the series: wool > B. mori silk fibroin > A. pernyi silk fibroin, in agreement with the weight gain measurements which decreased along the same series. These results can be explained in relation to the different composition of the analysed fibres. Wool fibres were characterised by the highest content of the potentially reactive sites; evidently, these groups had also a good accessibility for the sulphating agent
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