| 1. |
- Argyropoulos, Dimitris D. S., et al.
(författare)
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Kraft Lignin: A Valuable, Sustainable Resource, Opportunities and Challenges
- 2023
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Ingår i: ChemSusChem. - : John Wiley and Sons Inc. - 1864-5631 .- 1864-564X. ; 16:23
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Forskningsöversikt (refereegranskat)abstract
- Kraft lignin, a by-product from the production of pulp, is currently incinerated in the recovery boiler during the chemical recovery cycle, generating valuable bioenergy and recycling inorganic chemicals to the pulping process operation. Removing lignin from the black liquor or its gasification lowers the recovery boiler load enabling increased pulp production. During the past ten years, lignin separation technologies have emerged and the interest of the research community to valorize this underutilized resource has been invigorated. The aim of this Review is to give (1) a dedicated overview of the kraft process with a focus on the lignin, (2) an overview of applications that are being developed, and (3) a techno-economic and life cycle asseeements of value chains from black liquor to different products. Overall, it is anticipated that this effort will inspire further work for developing and using kraft lignin as a commodity raw material for new applications undeniably promoting pivotal global sustainability concerns.
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| 2. |
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| 3. |
- Bruschi, Maurizio, et al.
(författare)
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A DFT investigation on structural and redox properties of a synthetic Fe6S6 assembly closely related to the [FeFe]-hydrogenases active site
- 2008
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Ingår i: Comptes Rendus. Chimie. - : Elsevier BV. - 1631-0748. ; 11:8, s. 834-841
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Tidskriftsartikel (refereegranskat)abstract
- In the present contribution, a density functional theory (DFT) investigation is described regarding a recently synthesized Fe6S6 complex - see C. Tard, X. Liu, S.K. Ibrahim, M. Bruschi, L. De Gioia, S.C. Davies, X. Yang, L.-S. Wang, G. Sawers, C.J. Pickett, Nature 433 (2005) 610 - that is structurally and functionally related to the [FeFe]-hydrogenases active site (the so-called H-cluster, which includes a binuclear subsite directly involved in catalysis and an Fe4S4 cubane). The analysis of relative stabilities and atomic charges of different isomers evidenced that the structural and redox properties of the synthetic assembly are significantly different from those of the enzyme active site. A comparison between the hexanuclear cluster and simpler synthetic diiron models is also described; the results of such a comparison indicated that the cubane moiety can favour the stabilization of the cluster in a structure closely resembling the H-cluster geometry when the synthetic Fe6S6 complex is in its dianionic state. However, the opposite effect is observed when the synthetic cluster is in its monoanionic form.
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| 4. |
- Bruschi, Maurizio, et al.
(författare)
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Functionally Relevant Interplay between the Fe(4)S(4) Cluster and CN(-) Ligands in the Active Site of [FeFe]-Hydrogenases.
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 132:14, s. 4992-4992
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-hydrogenases are highly efficient H(2)-evolving metalloenzymes that include cyanides and carbonyls in the active site. The latter is an Fe(6)S(6) cluster (the so-called H-cluster) that can be subdivided into a binuclear portion carrying the CO and CN(-) groups and a tetranuclear subcluster. The fundamental role of cyanide ligands in increasing the basicity of the H-cluster has been highlighted previously. Here a more subtle but crucial role played by the two CN(-) ligands in the active site of [FeFe]-hydrogenases is disclosed. In fact, QM/MM calculations on all-atom models of the enzyme from Desulfovibrio desulfuricans show that the cyanide groups fine-tune the electronic and redox properties of the active site, affecting both the protonation regiochemistry and electron transfer between the two subclusters of the H-cluster. Despite the crucial role of cyanides in the protein active site, the currently available bioinspired electrocatalysts generally lack CN(-) groups in order to avoid competition between the latter and the catalytic metal centers for proton binding. In this respect, we show that a targeted inclusion of phosphine ligands in hexanuclear biomimetic clusters may restore the electronic and redox features of the wild-type H-cluster.
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| 5. |
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| 6. |
- Gammino, Michele, et al.
(författare)
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Chemical-free Reactive Melt Processing of Biosourced Poly(butylene-succinate-adipate) for Improved Mechanical Properties and Recyclability
- 2024
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Ingår i: ACS Applied Polymer Materials. - 2637-6105. ; 6:10, s. 5866-5877
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Tidskriftsartikel (refereegranskat)abstract
- Biosourced and biodegradable polyesters like poly(butylene succinate-co-butylene adipate) (PBSA) are gaining traction as promising alternatives to oil-based thermoplastics for single-use applications. However, the mechanical and rheological properties of PBSA are affected by its thermomechanical sensitivity during its melt processing, also hindering PBSA mechanical recycling. Traditional reactive melt processing (RP) methods use chemical additives to counteract these drawbacks, compromising sustainability. This study proposes a green reactive method during melt compounding for PBSA based on a comprehensive understanding of its thermomechanical degradative behavior. Under the hypothesis that controlled degradative paths during melt processing can promote branching/recombination reactions without the addition of chemical additives, we aim to enhance PBSA rheological and mechanical performance. An in-depth investigation of the in-line rheological behavior of PBSA was conducted using an internal batch mixer, exploring parameters such as temperature, screw rotation speed, and residence time. Their influence on PBSA chain scissions, branching/recombination, and cross-linking reactions were evaluated to identify optimal conditions for effective RP. Results demonstrate that specific processing conditions, for example, twelve minutes processing time, 200 °C temperature, and 60 rpm screw rotation speed, promote the formation of the long chain branched structure in PBSA. These structural changes resulted in a notable enhancement of the reacted PBSA rheological and mechanical properties, exhibiting a 23% increase in elastic modulus, a 50% increase in yield strength, and an 80% increase in tensile strength. The RP strategy also improved PBSA mechanical recycling, thus making it a potential replacement for low-density polyethylene (LDPE). Ultimately, this study showcases how finely controlling the thermomechanical degradation during reactive melt processing can improve the material’s properties, enabling reliable mechanical recycling, which can serve as a green approach for other biodegradable polymers.
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| 7. |
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| 8. |
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| 9. |
- Giummarella, Nicola, et al.
(författare)
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A One-Pot Biomimetic Synthesis of Selectively Functionalized Lignins from Monomers: A Green Functionalization Platform
- 2018
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Ingår i: Green Chemistry. - : Royal Society of Chemistry. - 1463-9262 .- 1463-9270. ; 21:11, s. 5579-5585
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Tidskriftsartikel (refereegranskat)abstract
- Lignin is the most abundant renewable source of phenolic compound with great application potential in renewable materials, biofuels and platform chemicals. Current technology for producing cellulose-rich fibers co-produces heterogeneous lignin, which includes an untapped source of monomeric phenolics. One such monomer also happen to be the main monomer in soft wood lignin biosynthesis, namely coniferyl alcohol. Herein, we investigate the potential of coniferyl alcohol as a platform monomer for the biomimetic production of tailored functionalized oligolignols with desirable properties for material synthesis. Accordingly, a bifunctional molecule with at least one carboxyl-ended functionality is included with coniferyl alcohol in biomimetic lignin synthesis to, in one-pot, produce a functionalized lignin. The functionalization mechanism is a nucleophilic addition reaction to quinone methide intermediate of lignin polymerization. The solvent systems applied were pure water or 50% aqueous acetone. Several bi-functional molecules differing in the second functionality were successfully inserted in the lignin demonstrating the platform component of this work. Detailed characterizations were performed by a combination of NMR techniques which include 1H NMR, COSY-90, 31P NMR, 13C NMR, 13C APT, HSQC, HMBC and HSQC TOCSY. Excellent selectivity towards benzylic carbon and high functionalization degree were noted. The structure of lignin was tailored through solvent system choice, with the 50% aqeuous acetone producing a skeletal structure favorable for high functionalization degrees. Finally, material concepts are demonstrated using classical Thiol-ene- and Diels Alder- chemistries to show potential for thermoset- and thermoplastic- concepts, respectively. The functionalization concept presents unprecedentent opportunities for green production of lignin-based recyclable biomaterials.
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| 10. |
- Greco, Claudio, et al.
(författare)
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A QM/MM investigation of the activation and catalytic mechanism of Fe-only hydrogenases
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 46:15, s. 5911-5921
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Tidskriftsartikel (refereegranskat)abstract
- Fe-only hydrogenases are enzymes that catalyze dihydrogen production or oxidation, due to the presence of an unusual Fe6S6 cluster (the so-called H-cluster) in their active site, which is composed of a Fe2S2 subsite, directly involved in catalysis, and a classical Fe4S4 cubane cluster. Here, we present a hybrid quantum mechanical and molecular mechanical (QM/MM) investigation of the Fe-only hydrogenase from Desulfovibrio desulfuricans, in order to unravel key issues regarding the activation of the enzyme from its completely oxidized inactive state (H-ox(inac)) and the influence of the protein environment on the structural and catalytic properties of the H-cluster. Our results show that the Fe2S2 subcluster in the (FeFeII)-Fe-II redox statewhich is experimentally observed for the completely oxidized form of the enzymebinds a water molecule to one of its metal centers. The computed QM/MM energy values for water binding to the diferrous subsite are in fact over 70 kJ mol(-1); however, the affinity toward water decreases by 1 order of magnitude after a one-electron reduction of H-ox(inact), thus leading to the release of coordinated water from the H-cluster. The investigation of a catalytic cycle of the Fe-only hydrogenase that implies formation of a terminal hydride ion and a di(thiomethyl)amine (DTMA) molecule acting as an acid/base catalyst indicates that all steps have reasonable reaction energies and that the influence of the protein on the thermodynamic profile of H-2 production catalysis is not negligible. QM/MM results show that the interactions between the Fe2S2 subsite and the protein environment could give place to structural rearrangements of the H-cluster functional for catalysis, provided that the bidentate ligand that bridges the iron atoms in the binuclear subsite is actually a DTMA residue.
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| 11. |
- Greco, Claudio, et al.
(författare)
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Fast Generation of Broken-Symmetry States in a Large System Including Multiple Iron-Sulfur Assemblies: Investigation of QM/MM Energies, Clusters Charges, and Spin Populations
- 2011
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608. ; 111:14, s. 3949-3960
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Tidskriftsartikel (refereegranskat)abstract
- A density functional theory study is presented regarding the energetics and the Mulliken population analyses of a quantum mechanical/molecular mechanical (QM/MM) system including multiple iron-sulfur clusters in the QM region. The [FeFe]-hydrogenase from Desulfovibrio desulfuricans was studied, and both the active site (an Fe6S6 assembly generally referred to as the H-cluster) and an ancillary Fe4S4 site were treated at the BP86-RI/TZVP level. The antiferromagnetic coupling that characterizes both sites was modeled using the broken-symmetry (BS) approach. For such a QM system, 36 different BS couplings can be defined, depending on the localization of spin excess on the various spin centers. All the BS states were obtained by means of an effective and simple method for spin localization, that is here described and compared with more sophisticated approaches already available in literature. The variation of the QM/MM energy among the various geometry-optimized protein models was found to be less than 25 kJ mol(-1). This energy variation almost doubles if no geometry optimization is performed. A detailed analysis of the additive nature of these variations in QM/MM energy is reported. The Mulliken charges show very small variations among the 36 BS states, whereas the Mulliken spin populations were found to be somewhat more variable. The relevance of such variations is discussed in light of the available Mossbauer and Electron Paramagnetic Resonance (EPR) spectroscopic data for the enzyme. Finally, the influence of the basis set on the spin populations, charges, and structural parameters of the models was investigated, by means of QM/MM computations on the same system at the BP86-RI/SVP level. (C) 2010 Wiley Periodicals, Inc. Int J Quantum Chem 111: 3949-3960, 2011
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| 12. |
- Greco, Claudio, et al.
(författare)
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Isocyanide in Biochemistry? A Theoretical Investigation of the Electronic Effects and Energetics of Cyanide Ligand Protonation in [FeFe]-Hydrogenases
- 2011
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Ingår i: Chemistry: A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 17:6, s. 1954-1965
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Tidskriftsartikel (refereegranskat)abstract
- The presence of Fe-bound cyanide ligands in the active site of the proton-reducing enzymes [FeFe]-hydrogenases has led to the hypothesis that such Bronsted-Lowry bases could be protonated during the catalytic cycle, thus implying that hydrogen isocyanide (HNC) might have a relevant role in such crucial microbial metabolic paths. We present a hybrid quantum mechanical/molecular mechanical (QM/MM) study of the energetics of CN- protonation in the enzyme, and of the effects that cyanide protonation can have on [FeFe]-hydrogenase active sites. A detailed analysis of the electronic properties of the models and of the energy profile associated with H-2 evolution clearly shows that such protonation is dysfunctional for the catalytic process. However, the inclusion of the protein matrix surrounding the active site in our QM/MM models allowed us to demonstrate that the amino acid environment was finely selected through evolution, specifically to lower the Bronsted-Lowry basicity of the cyanide ligands. In fact, the conserved hydrogen-bonding network formed by these ligands and the neighboring amino acid residues is able to impede CN- protonation, as shown by the fact that the isocyanide forms of [FeFe]-hydrogenases do not correspond to stationary points on the enzyme QM/MM potential-energy surface.
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| 13. |
- Greco, Claudio, et al.
(författare)
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Magnetic Properties of [FeFe]-Hydrogenases: A Theoretical Investigation Based on Extended QM and QM/MM Models of the H-Cluster and Its Surroundings
- 2011
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Ingår i: European Journal of Inorganic Chemistry. - : Wiley. - 1099-0682 .- 1434-1948. ; :7, s. 1043-1049
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Tidskriftsartikel (refereegranskat)abstract
- In the present contribution, we report a theoretical investigation of the magnetic properties of the dihydrogen-evolving enzyme [FeFe]-hydrogenase, based on both DFT models of the active site (the H-cluster, a Fe6S6 assembly including a binuclear portion directly involved in substrates binding), and QM/MM models of the whole enzyme. Antiferromagnetic coupling within the H-cluster has been treated using the broken-symmetry approach, along with the use of different density functionals. Results of g value calculations turned out to vary as a function of the level of theory and of the extension of the model. The choice of the broken-symmetry coupling scheme also had a significant influence on the calculated g values, for both the active-ready (H-ox) and the CO-inhibited (H-ox-CO) enzyme forms. However, hyper-fine coupling-constant calculations were found to provide more consistent results. This allowed us to show that the experimentally detected delocalization of an unpaired electron at the binuclear subcluster in Desulfovibrio desulfuricans Hox is compatible with a weak interaction between the catalytic centre and a low-weight exogenous ligand like a water molecule.
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| 14. |
- Greco, Claudio, et al.
(författare)
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Mechanistic and Physiological Implications of the Interplay among Iron-Sulfur Clusters in [FeFe]-Hydrogenases. A QM/MM Perspective
- 2011
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 133:46, s. 18742-18749
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Tidskriftsartikel (refereegranskat)abstract
- Key stereoelectronic properties of Desulfovibrio desulfuricans [FeFe]-hydrogenase (DdH) were investigated by quantum mechanical description of its complete inorganic core, which includes a Fe6S6 active site (the H-cluster), as well as two ancillary Fe4S4 assemblies (the F and F' clusters). The partially oxidized, active-ready form of DdH is able to efficiently bind dihydrogen, thus starting H-2 oxidation catalysis. The calculations allow us to unambiguously assign a mixed Fe(H)Fe(I) state to the catalytic core of the active-ready enzyme and show that H-2 uptake exerts subtle, yet crucial influences on the redox properties of DdH. In fact, H-2 binding can promote electron transfer from the H-cluster to the solvent-exposed F'-cluster, thanks to a 50% decrease of the energy gap between the HOMO (that is localized on the H-cluster) and the LUMO (which is centered on the F'-cluster). Our results also indicate that the binding of the redox partners of DdH in proximity of its F'-cluster can trigger one-electron oxidation of the H-2-bound enzyme, a process that is expected to have an important role in H-2 activation. Our findings are analyzed not only from a mechanistic perspective, but also in consideration of the physiological role of DdH. In fact, this enzyme is known to be able to catalyze both the oxidation and the evolution of H-2, depending on the cellular metabolic requirements. Hints for the design of targeted mutations that could lead to the enhancement of the oxidizing properties of DdH are proposed and discussed.
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| 15. |
- Greco, Claudio, et al.
(författare)
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Probing the Effects of One-Electron Reduction and Protonation on the Electronic Properties of the Fe-S Clusters in the Active-Ready Form of [FeFe]-Hydrogenases. A QM/MM Investigation.
- 2011
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Ingår i: ChemPhysChem. - : Wiley. - 1439-7641 .- 1439-4235. ; 12:17, s. 3376-3382
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Tidskriftsartikel (refereegranskat)abstract
- A QM/MM investigation of the active-ready (Hox) form of [FeFe]-hydrogenase from D. desulfuricans, in which the electronic properties of all Fe-S clusters (H, F and F') have been simultaneously described using DFT, was carried out with the aim of disclosing a possible interplay between the H-cluster and the accessory iron-sulfur clusters in the initial steps of the catalytic process leading to H2 formation. It turned out that one-electron addition to the active-ready form leads to reduction of the F'-cluster and not of the H-cluster. Protonation of the H-cluster in Hox is unlikely, and in any case it would not trigger electron transfer from the accessory Fe4S4 clusters to the active site. Instead, one-electron reduction and protonation of the active-ready form trigger electron transfer within the protein, a key event in the catalytic cycle. In particular, protonation of the H-cluster after one-electron reduction of the enzyme lowers the energy of the lowest unoccupied molecular orbitals localized on the H-cluster to such an extent that a long-range electron transfer from the F'-cluster towards the H-cluster itself is allowed.
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| 16. |
- Greco, Claudio, et al.
(författare)
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Structural insights into the active-ready form of [FeFe]-Hydrogenase and mechanistic details of its inhibition by carbon monoxide
- 2007
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 46:18, s. 7256-7258
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Tidskriftsartikel (refereegranskat)abstract
- [FeFe]-Hydrogenases harbor a {2Fe3S} assembly bearing two CO and two CN- groups, a mu-CO ligand, and a vacant coordination site trans to the mu-CO group. Recent theoretical results obtained studying the isolated {2Fe3S} subsite indicated that one of the CN- ligands can easily move from the crystallographic position to the coordination site trans to the mu-CO group; such an isomerization would have a major impact on substrates and inhibitors binding regiochemistry and, consequently, on the catalytic mechanism. To shed light on this crucial issue, we have carried out hybrid QM/MM and free energy perturbation calculations on the whole enzyme, which demonstrate that the protein environment plays a crucial role and maintains the CN- group fixed in the position observed in the crystal structure; these results strongly support the hypothesis that the vacant coordination site trans to the mu-CO group has a crucial functional relevance both in the context of CO-mediated inhibition of the enzyme and in dihydrogen oxidation/evolution catalysis.
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| 17. |
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| 18. |
- Jawerth, Marcus, et al.
(författare)
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Renewable Thiol-Ene Thermosets Based on Refined and Selectively Allylated Industrial Lignin
- 2017
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 5:11, s. 10918-10925
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Tidskriftsartikel (refereegranskat)abstract
- Aromatic material constituents derived from renewable resources are attractive for new biobased polymer systems. Lignin, derived from lignocellulosic biomass, is the most abundant natural source of such structures. Technical lignins are, however, heterogeneous in both structure and polydispersity and require a refining to obtain a more reproducible material. In this paper the ethanol-soluble fraction of Lignoboost Kraft lignin is selectively allylated using allyl chloride by means of a mild and industrially scalable procedure. Analysis using 1H-, 31P-, and 2D HSQC NMR give a detailed structural description of lignin, providing evidence of its functionalization and that the suggested procedure is selective toward phenols with a conversion of at least 95%. The selectively modified lignin is subsequently cross-linked using thermally induced thiol-ene chemistry. FT-IR is utilized to confirm the cross-linking reaction, and DSC measurements determined the Tg of the thermosets to be 45-65 °C depending on reactive group stoichiometry. The potential of lignin as a constituent in a thermoset application is demonstrated and discussed.
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| 19. |
- Ryde, Ulf, et al.
(författare)
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Quantum refinement of [FeFe] hydrogenase indicates a dithiomethylamine ligand
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 132:13, s. 4512-4512
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Tidskriftsartikel (refereegranskat)abstract
- The active site of the [FeFe] hydrogenases contains two Fe ions bound to one Cys ligand, three CO molecules, two CN(-) ions, and a dithiolate ligand. The nature of the last of these has been much discussed, and it has been suggested that it contains C, N, or O as the bridgehead atom. Most experimental studies indicate a N atom, whereas a recent density functional theory (DFT) study of a crystal structure indicated an O atom. Here, we performed quantum refinement on the same crystal structure with five different models of the dithiolate ligand X(CH(2)S(-))(2), with X = CH(2), NH(2)(+), NH (two conformations), or O; we found that structures with a N bridgehead atom actually provide the best fit to the raw crystallographic data. Quantum refinement is standard crystallographic refinement in which the molecular mechanics force field normally used to supplement the experimental raw data to give a more chemical structure is replaced by more accurate DFT calculations for the active site. Thereby, we obtain structures that are an ideal compromise between DFT and crystallography.
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| 20. |
- Tagami, Ayumu, et al.
(författare)
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Solvent fractionation of softwood and hardwood kraft lignins for more efficient uses : Compositional, structural, thermal, antioxidant and adsorption properties
- 2019
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Ingår i: Industrial crops and products (Print). - : Elsevier. - 0926-6690 .- 1872-633X. ; 129, s. 123-134
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Tidskriftsartikel (refereegranskat)abstract
- This work summarizes the impact of solvent fractionation on the chemical structure, antioxidant activity, heating values, and thermal and adsorption properties of industrial hardwood and softwood kraft lignins. The aim of the research was to develop a simple approach for obtaining lignin fractions with tailored properties for applications in certain materials. Four common industrial solvents, namely, ethyl acetate, ethanol, methanol and acetone, in various combinations, were found to be efficient for separating spruce and eucalyptus kraft lignins into fractions with low polydispersities. The ethanol fraction of spruce and the ethyl acetate fraction of eucalyptus afforded the highest yields. Gel-permeation chromatography analysis was used to evaluate the efficiency of the chosen solvent combination for lignin fractionation. The composition and structure of the lignin material was characterized by elemental analysis, analytical pyrolysis (Py-GC/MS/FID) and 31P NMR spectroscopy. The thermal properties of the lignin samples were studied using thermogravimetric analysis. Proximate analysis data (ash, volatile components, organic matter and fixed carbon) was obtained through the direct measurement of weight changes in each experimental curve, and the high heating values (in MJ/kg) were calculated according to equations suggested in the literature. The adsorption properties of fractionated kraft lignins were studied using methylene blue dye. The correlations observed between molecular weight, composition and functionality and the thermal, radical scavenging and adsorption properties of the lignin fractions provides useful information for selecting the appropriate solvent combinations for specific applications of lignin raw materials (including their use as antioxidants, biofuels or sorbents in water treatment processes). © 2018
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| 21. |
- Tagami, Ayumu, et al.
(författare)
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Solvent fractionation of softwood and hardwood kraft lignins for more efficient uses: compositional, structural, thermal, antioxidant and sorption properties
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- This work summarizes the impact of solvent fractionation on the chemical structure, antioxidant activity, heating values, and thermal and sorption properties of industrial hardwood and softwood kraft lignins. The aim was to develop a simple approach for the obtaining of lignin fractions with a tailored properties for the certain material applications. Four common industrial solvents, namely, ethyl acetate, ethanol, methanol and acetone, in various combinations efficiently separated both spruce and eucalyptus kraft lignins into fractions with low polydispersities. The ethanol fraction of spruce and the ethyl acetate fraction of eucalyptus afforded the highest yields. Gel-permeation chromatography analysis was used to evaluate the efficiency of the chosen solvent combination for lignin fractionation. The composition and structure of the lignin material was characterized by elemental analysis, analytical pyrolysis (Py-GC/MS/FID) and 31P NMR spectroscopy. The thermal properties of the lignin samples were studied by thermogravimetric analysis. Proximate analysis data (ash, volatile components, organic matter and fixed carbon) were obtained through the direct measurement of weight changes in each experimental curve, and the high heating values (in MJ/kg) were calculated according to equations suggested in the literature. The sorption properties of fractionated kraft lignins were studied with respect to methylene blue dye. The clear correlation between certain structural features in the lignin fractions and the properties of the lignin provides useful information for selecting the appropriate solvent combinations for specific applications of lignin raw materials, including as antioxidants, biofuels or sorbents in water treatment processes.
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| 22. |
- Yu, Lian, et al.
(författare)
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Targeting Intermediates of [FeFe]-Hydrogenase by CO and CN Vibrational Signatures
- 2011
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 1520-510X .- 0020-1669. ; 50:9, s. 3888-3900
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we employ density functional theory to assign vibrational signatures of [FeFe]-hydrogenase intermediates to molecular structures. For this purpose, we perform an exhaustive analysis of structures and harmonic vibrations of a series of CN and CO containing model clusters of the [FeFe]-hydrogenase enzyme active site considering also different charges, counterions, and solvents. The pure density functional BP86 in combination with a triple-xi polarized basis set produce reliable molecular structures as well as harmonic vibrations. Calculated CN and CO stretching vibrations are analyzed separately. Scaled vibrational frequencies are then applied to assign intermediates,in [FeFe]-hydrogenase's reaction cycle. The. " results nicely complement the previous studies of Darensbourg and The infrared spectrum of the H-ox form is in very good agreement with the calculated Spectrum of the (FeFeII)-Fe-I-model complex featuring a free coordination site at the distal Fe atom, as well as, With the calculated spectra of the complexes in which H-2 or H2O are coordinated at this site The spectrum of H-red measured from Desulfovibrio desulfuricans is compatible with a mixture of a (FeFeI)-Fe-I species with all terminal COs, and a (FeFeI)-Fe-I species with protonated dtma ligand, while the spectrum of H-red recently measured from Chlamydomonas reinhardtii is compatible with a mixture of a (FeFeI)-Fe-I species with a bridged CO, and a (FeFeII)-Fe-II species with a terminal hydride bound to the Fe atom.
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