RESUMEN

Carbon fibers (CFs) are fabricated by blending hardwood kraft lignin (HKL) and cellulose. Various compositions of HKL and cellulose in blended solutions are air-gap spun in 1-ethyl-3-methylimidazolium acetate (EMIM OAc), resulting in the production of virtually bead-free quality fibers. The synthesized HKL-cellulose fibers are thermostabilized and carbonized to achieve CFs, and consequently their electrical and mechanical properties are evaluated. Remarkably, fibers with the highest lignin content (65%) exhibited an electrical conductivity of approximately 42 S/cm, surpassing that of cellulose (approximately 15 S/cm). Moreover, the same fibers demonstrated significantly improved tensile strength (∼312 MPa), showcasing a 5-fold increase compared to pure cellulose while maintaining lower stiffness. Comprehensive analyses, including Auger electron spectroscopy and wide-angle X-ray scattering, show a heterogeneous skin-core morphology in the fibers revealing a higher degree of preferred orientation of carbon components in the skin compared to the core. The incorporation of lignin in CFs leads to increased graphitization, enhanced tensile strength, and a unique skin-core structure, where the skin's graphitized cellulose and lignin contribute stiffness, while the predominantly lignin-rich core enhances carbon content, electrical conductivity, and strength.

RESUMEN

Regenerated cellulose fibers have been considered as potential precursor fibers for carbon fibers because of their balanced cost and performance. Increased attention has been paid to blending lignin with the regenerated cellulose to generate precursor fibers which render good mechanical properties and higher carbon yield. The mechanical properties of carbon fibers have been found closely correlated to the structure of precursor fibers. However, the effects of lignin blending on molecular- and morphological structure of the precursor are still unclear. This study aims at clarifying the structural information of lignin-cellulose precursor fibers from molecular level to mesoscale by scanning X-ray microdiffraction. We present the existence of a skin-core morphology for all the precursor fibers. Increase of lignin content in precursor fiber could reduce the portion of skin and cause obvious disorder of the meso- and molecular structure. By correlating structural variations with lignin blending, 30% lignin blending has been found as a potential balance point to obtain precursor fibers maintaining structural order together with high yield rate.

Asunto(s)

Celulosa , Lignina , Lignina/química , Fibra de Carbono , Celulosa/química , Carbono/química

RESUMEN

The demand for carbon fibers (CFs) based on renewable raw materials as the reinforcing fiber in composites for lightweight applications is growing. Lignin-cellulose precursor fibers (PFs) are a promising alternative, but so far, there is limited knowledge of how to continuously convert these PFs under industrial-like conditions into CFs. Continuous conversion is vital for the industrial production of CFs. In this work, we have compared the continuous conversion of lignin-cellulose PFs (50 wt % softwood kraft lignin and 50 wt % dissolving-grade kraft pulp) with batchwise conversion. The PFs were successfully stabilized and carbonized continuously over a total time of 1.0-1.5 h, comparable to the industrial production of CFs from polyacrylonitrile. CFs derived continuously at 1000 °C with a relative stretch of -10% (fiber contraction) had a conversion yield of 29 wt %, a diameter of 12-15 µm, a Young's modulus of 46-51 GPa, and a tensile strength of 710-920 MPa. In comparison, CFs obtained at 1000 °C via batchwise conversion (12-15 µm diameter) with a relative stretch of 0% and a conversion time of 7 h (due to the low heating and cooling rates) had a higher conversion yield of 34 wt %, a higher Young's modulus (63-67 GPa) but a similar tensile strength (800-920 MPa). This suggests that the Young's modulus can be improved by the optimization of the fiber tension, residence time, and temperature profile during continuous conversion, while a higher tensile strength can be achieved by reducing the fiber diameter as it minimizes the risk of critical defects.

RESUMEN

Cellulose-lignin composite carbon fibers have shown to be a potential environmentally benign alternative to the traditional polyacrylonitrile precursor. With the associated cost reduction, cellulose-lignin carbon fibers are an attractive light-weight material for, e.g. wind power and automobile manufacturing. The carbon fiber tenacity, tensile modulus and creep resistance is in part determined by the carbon content and the molecular orientation distribution of the precursor. This work disassociates the molecular orientation of different components in cellulose-lignin composite fibers using rotor-synchronized solid-state nuclear magnetic resonance spectroscopy and X-ray scattering. Our results show that lignin is completely disordered, in a mechanically stretched cellulose-lignin composite fiber, while the cellulose is ordered. In contrast, the native spruce wood raw material displays both oriented lignin and cellulose. The current processes for fabricating a cellulose-lignin composite fiber cannot regain the oriented lignin as observed from the native wood.

Asunto(s)

Fibra de Carbono/química , Celulosa/química , Lignina/química , Espectroscopía de Resonancia Magnética/métodos , Difracción de Rayos X/métodos , Estructura Molecular , Picea/química , Solubilidad , Resistencia a la Tracción , Viscosidad , Madera/química

RESUMEN

The application range of man-made cellulosic fibers is limited by the absence of cost- and manufacturing-efficient strategies for anisotropic hierarchical functionalization. Overcoming these bottlenecks is therefore pivotal in the pursuit of a future bio-based economy. Here, we demonstrate that colloidal silica nanoparticles (NPs), which are cheap, biocompatible and easy to chemically modify, enable the control of the cross-sectional morphology and surface topography of ionic liquid-spun cellulose fibers. These properties are tailored by the silica NPs' surface chemistry and their entry point during the wet-spinning process (dope solution DSiO2 or coagulation bath CSiO2). For CSiO2-modified fibers, the coagulation mitigator dimethylsulphoxide allows for controlling the surface topography and the amalgamation of the silica NPs into the fiber matrix. For dope-modified fibers, we hypothesize that cellulose chains act as seeds for directed silica NP self-assembly. This results for DSiO2 in discrete micron-sized rods, homogeneously distributed throughout the fiber and for glycidoxy-surface modified DSiO2@GLYEO in nano-sized surface aggregates and a cross-sectional core-shell fiber morphology. Furthermore, the dope-modified fibers display outstanding strength and toughness, which are both characteristic features of biological biocomposites.

RESUMEN

Certain ionic liquids are powerful cellulose solvents, but tend to be less effective when small-molecule hydrogen bond donors are present. This is generally attributed to competition with cellulose for hydrogen bonding opportunities to the anion of the ionic liquid. We show that the solubility of cellulose in dimethyl sulfoxide solutions of tetrabutylammonium acetate is less strongly affected by water than by ethanol on a molar basis, contrary to what can be expected based on hydrogen bond stoichiometry. Molecular dynamics simulations indicate that the higher tolerance to water is due to water-cellulose interactions that improves solvation of cellulose and, thereby, marginally favors dissolution. Through Kirkwood-Buff theory we show that water, but not ethanol, improves the solvent quality of DMSO and partly compensates for the loss of acetate-cellulose hydrogen bonds.

RESUMEN

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) has been demonstrated to mediate both genomic and non-genomic responses in prostate cancer (CaP) cells. Here, we give an overview of membrane initiated 1,25(OH)2D3 signaling in prostate cancer cell progression. The presence of PDIA3 was investigated and homologous modeling of the putative PDIA3 receptor complex was conducted. Furthermore, the cellular distribution of nVDR was analyzed. We could show that both nVDR and PDIA3 are expressed in the prostate cancer cell lines investigated. The homologous modeling of PDIA3 showed that the receptor complex exists in a trimer formation, which suggests for allosteric activity. Our findings support previous reports and suggest that 1,25(OH)2D3 is an important therapeutic agent in inhibiting prostate cancer progression. Furthermore, our data show that 1,25(OH)2D3 regulate prostate cell biology via multiple pathways and targeting specific pathways for 1,25(OH)2D3 might provide more effective therapies compared to the vitamin D therapies currently clinically tested.

Asunto(s)

Neoplasias de la Próstata/metabolismo , Vitamina D/metabolismo , Sitio Alostérico , Línea Celular Tumoral , Membrana Celular/metabolismo , Progresión de la Enfermedad , Humanos , Inmunohistoquímica/métodos , Masculino , Modelos Moleculares , Modelos Teóricos , Conformación Proteica , Receptores de Calcitriol/metabolismo , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Transducción de Señal

RESUMEN

BACKGROUND: Accumulation and oxidation of LDL are believed to be important initiating factors in atherosclerosis. Oxidized LDL is recognized by the immune system, and animal studies have suggested that these immune responses have a protective effect against atherosclerosis. Aldehyde-modified peptide sequences in apolipoprotein B-100 (apoB-100) are major targets for these immune responses. METHODS AND RESULTS: Human IgG1 antibodies against 2 malondialdehyde (MDA)-modified apoB-100 peptide sequences were produced through screening of a single-chain antibody-fragment library and subsequent cloning into a pcDNA3 vector. Three weekly doses of these antibodies were injected into male apoE-/- mice. Phosphate-buffered saline and human IgG1 antibodies against fluorescein isothiocyanate were used as controls. One of the IgG1 antibodies significantly and dose-dependently reduced the extent of atherosclerosis as well as the plaque content of oxidized LDL epitopes and macrophages. In cell culture studies, human monocytes were incubated with native LDL or oxidized LDL, in the presence of antibodies. The same antibody induced an increase in monocyte binding and uptake of oxidized LDL. CONCLUSIONS: These findings suggest that antibodies are important mediators of atheroprotective immune responses directed to oxidized LDL. Thus, passive immunization against MDA-modified apoB-100 peptide sequences may represent a novel therapeutic approach for prevention and treatment of cardiovascular disease.

Asunto(s)

Apolipoproteínas B/inmunología , Arteriosclerosis/prevención & control , Inmunización Pasiva , Fragmentos de Inmunoglobulinas/uso terapéutico , Inmunoglobulina G/uso terapéutico , Región Variable de Inmunoglobulina/uso terapéutico , Lipoproteínas LDL/metabolismo , Secuencia de Aminoácidos , Animales , Apolipoproteína B-100 , Apolipoproteínas B/química , Apolipoproteínas E/deficiencia , Apolipoproteínas E/genética , Arteriosclerosis/patología , Evaluación Preclínica de Medicamentos , Humanos , Fragmentos de Inmunoglobulinas/genética , Fragmentos de Inmunoglobulinas/inmunología , Inmunoglobulina G/genética , Inmunoglobulina G/inmunología , Región Variable de Inmunoglobulina/genética , Región Variable de Inmunoglobulina/inmunología , Cadenas lambda de Inmunoglobulina/genética , Lipoproteínas LDL/farmacología , Macrófagos/patología , Masculino , Malondialdehído/química , Malondialdehído/inmunología , Ratones , Ratones Noqueados , Datos de Secuencia Molecular , Monocitos/metabolismo , Fragmentos de Péptidos/química , Fragmentos de Péptidos/inmunología , Proteínas Recombinantes de Fusión/inmunología , Proteínas Recombinantes de Fusión/uso terapéutico

RESUMEN

The Gram-positive bacterium Bacillus subtilis contains two respiratory oxidases of the haem-copper superfamily: cytochrome aa(3), which is a quinol oxidase, and cytochrome caa(3), which is a cytochrome c oxidase. Cytochrome c oxidase uniquely contains a di-copper centre, Cu(A). B. subtilis CtaG is a membrane protein encoded by the same gene cluster as that which encodes the subunits of cytochrome c oxidase. The role of B. subtilis CtaG and orthologous proteins present in many other Gram-positive bacteria has remained unexplored. The sequence of CtaG is unrelated to that of CtaG/Cox11p of proteobacteria and eukaryotic cells. This study shows that B. subtilis CtaG is essential for the formation of active cytochrome caa(3) but is not required for assembly of the core subunits I and II with haem in the membrane and it has no role in the synthesis of active cytochrome aa(3). B. subtilis YpmQ, a homologue to Sco1p of eukaryotic cells, is also a membrane-bound cytochrome c oxidase-specific assembly factor. Properties of CtaG- and YpmQ-deficient mutants were compared. Cells lacking YpmQ showed a low cytochrome c oxidase activity and this defect was suppressed by the supplementation of the growth medium with copper ions. It has previously been proposed that YpmQ/Sco1p is involved in synthesis of the Cu(A) centre. The results of this study are consistent with this proposal but the exact role of YpmQ in assembly of cytochrome c oxidase remains to be elucidated.

Asunto(s)

Bacillus subtilis/genética , Complejo IV de Transporte de Electrones/genética , Proteínas de la Membrana/metabolismo , Bacillus subtilis/enzimología , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Secuencia de Bases , Citocromos a/genética , Complejo IV de Transporte de Electrones/metabolismo , Proteínas de la Membrana/genética , Familia de Multigenes , Mutagénesis , Plásmidos , Subunidades de Proteína/genética , Mapeo Restrictivo , Espectrofotometría

RESUMEN

Heparan sulfate polymerization and modification take place in the Golgi compartment. The modification reactions are initiated by glucosaminyl N-deacetylase/N-sulfotransferase (NDST), a bifunctional enzyme that removes N-acetyl groups from selected N-acetyl-d-glucosamine units followed by N-sulfation of the generated free amino groups. Four isoforms of NDST have been identified. NDST-1 and -2 have a wide and largely overlapping tissue distribution, but it is not known if they can act on the same heparan sulfate chain. We have introduced point mutations into NDST-1 cDNA, which selectively destroy the N-deacetylase or N-sulfotransferase activity of the enzyme [Wei, Z., and Swiedler, S. J. (1999) J. Biol. Chem. 274, 1966-70 and Sueyoshi, T., et al. (1998) FEBS Lett. 433, 211-4]. Stable 293 cell lines expressing the NDST-1 mutants were then generated. Structural analyses of heparan sulfate synthesized by these cells and by cells overexpressing wild-type NDST-1 demonstrate that the N-deacetylation step is not only prerequisite but also rate-limiting, determining the degree of N-sulfation. Transfection of mutant NDST-1 lacking N-deacetylase activity had no effect on heparan sulfate sulfation, while cells expressing wild-type enzyme or NDST-1 lacking N-sulfotransferase activity both resulted in the production of oversulfated heparan sulfate. Since no increase in the amount of N-unsubstituted glucosamine residues was seen after transfection of the mutant lacking N-sulfotransferase activity, the results also suggest that two different enzyme molecules can act on the same glucosamine unit. In addition, we show that oversulfation of heparan sulfate produced by cells tranfected with wild-type NDST-1 or the mutant lacking N-sulfotranferase activity results in decreased sulfation of chondroitin sulfate.

Asunto(s)

Amidohidrolasas/química , Amidohidrolasas/genética , Heparitina Sulfato/química , Mutación Puntual , Sulfotransferasas/química , Sulfotransferasas/genética , Amidohidrolasas/biosíntesis , Amidohidrolasas/metabolismo , Animales , Sitios de Unión/genética , Línea Celular , Sulfatos de Condroitina/química , Sulfatos de Condroitina/metabolismo , Glucosamina/metabolismo , Heparitina Sulfato/biosíntesis , Heparitina Sulfato/metabolismo , Humanos , Isoenzimas/biosíntesis , Isoenzimas/química , Isoenzimas/genética , Isoenzimas/metabolismo , Ratones , Complejos Multienzimáticos/biosíntesis , Complejos Multienzimáticos/química , Complejos Multienzimáticos/genética , Complejos Multienzimáticos/metabolismo , Mutagénesis Sitio-Dirigida , Sulfotransferasas/biosíntesis , Sulfotransferasas/metabolismo , Transfección