| 1. |
- Matxain, Jon M, et al.
(författare)
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New solids based on B12N12 fullerenes
- 2007
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Ingår i: The Journal of Physical Chemistry C. - Washington, DC : American Chemical Society. - 1932-7447 .- 1932-7455. ; 111:36, s. 13354-60
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, BN fullerenes have been synthesized experimentally. As their carbon counterparts, these BN fullerenes could be assembled in molecular solids, but this possibility has been studied little in the literature. In this work, we focus on the smallest synthesized BN fullerene, B12N12, which is built by squares and hexagons. First, the interaction between two of these fullerenes has been analyzed, using the hybrid B3LYP and MPW1PW91 density functional methods. Two different interactions have been studied in the dimer, a square facing a square (S−S) and a hexagon facing a hexagon (H−H). In both cases, a B is facing a N. The most stable dimer was found to be S−S facing, with covalent interactions between the monomers, but other dimers with weak interactions have been found as well, which opens possibilities of new systems, as in the case of fullerene dimers and solids. The solids resulting from the infinite repetition of the characterized dimers were optimized, finding two different solids, with covalent and weak interactions between monomers, respectively. The solid with covalent interactions is a nanoporous material that is more stable by around 12 eV. Because of the nanoporous character of this solid, it could be used for heterogeneous catalysis, molecular transport, and so forth. The SIESTA code with the GGA-PBE density functional method has been used for the solid-state calculations.
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| 2. |
- Matxain, Jon M., et al.
(författare)
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Endohedral (X@ZniSi)i=4-160,± Nanoclusters, X = Li, Na, K, Cl, Br
- 2007
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Ingår i: The Journal of Physical Chemistry C. - Washington, DC : American Chemical Society. - 1932-7447 .- 1932-7455. ; 111:9, s. 3560-3565
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Tidskriftsartikel (refereegranskat)abstract
- Endohedral (X@ZniSi)q structures have been characterized, with X being alkali metals such as Li, Na, and K or halogens such as Cl and Br, 4 > i > 16, and q = -1, 0, 1. In these structures, the atoms are trapped inside previously characterized spheroid hollow structures with positively charged Zn atoms and negatively charged S atoms. Moreover, although the radii of all atoms are similar, Zn atoms are located more inside the structure. The alkali metals are found to be trapped inside a larger number of spheroid structures than the halogens. The parameters determining the stability of the endohedral structures are the charge and size of the trapped atom, along with the sphericity of the cluster.
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| 3. |
- San Sebastian, Eider, et al.
(författare)
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Enantiospecific Response in Cross-Polarization Solid-State Nuclear Magnetic Resonance of Optically Active Metal Organic Frameworks
- 2020
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 142:42, s. 17989-17996
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Tidskriftsartikel (refereegranskat)abstract
- We report herein on a NMR-based enantiospecific response for a family of optically active metal-organic frameworks. Cross-polarization of the 1H-13C couple was performed, and the intensities of the 13C nuclei NMR signals were measured to be different for the two enantiomers. In a direct-pulse experiment, which prevents cross-polarization, the intensity difference of the 13C NMR signals of the two nanostructured enantiomers vanished. This result is due to changes of the nuclear spin relaxation times due to the electron spin spatial asymmetry induced by chemical bond polarization involving a chiral center. These experiments put forward on firm ground that the chiral-induced spin selectivity effect, which induces chemical bond polarization in the J-coupling, is the mechanism responsible for the enantiospecific response. The implications of this finding for the theory of this molecular electron spin polarization effect and the development of quantum biosensing and quantum storage devices are discussed.
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| 4. |
- Matxain, Jon M., et al.
(författare)
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Evidence of High dot OH Radical Quenching Efficiency by Vitamin B-6
- 2009
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Ingår i: Journal of Physical Chemistry B. - Washington, D. C. : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 113:29, s. 9629-9632
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Tidskriftsartikel (refereegranskat)abstract
- Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of the utmost importance in the living cell. The antioxidative properties of pyridoxine (vitamin B6) have recently been discovered. Previous theoretical calculations have shown a high reactivity of pyridoxine toward hydroxyl radicals, where the latter preferably abstract H from either carbon of the two methanol substituents (C8 or C9). In this study, we have explored the reactivity of pyridoxine toward further hydroxyl radicals, considering as the first step the H abstraction from either C8 or C9, also including addition reactions and cyclization. Many of the reactions display similar ΔG, and hence, the quenching of hydroxyl radicals by pyridoxine may undergo different pathways leading to a mix of products. In addition, we observe that pyridoxine, under high hydroxyl radical concentrations, may scavenge up to eight radicals, supporting its observed high antioxidant activity.
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| 5. |
- Matxain, Jon M., et al.
(författare)
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Theoretical study of the antioxidant properties of pyridoxine
- 2006
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Ingår i: Journal of Physical Chemistry A. - Washington, DC : American Chemical Society. - 1089-5639 .- 1520-5215. ; 110:48, s. 13068-13072
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Tidskriftsartikel (refereegranskat)abstract
- Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of utmost importance in the living cell. The antioxidative properties of pyridoxine (vitamin B6) have recently been discovered. In this study, we have analyzed the reactivity of pyridoxine toward the ROS .OH, .OOH, and .O2- at the density functional theory level (functionals B3LYP and MPW1B95). Two reaction types have been studied as follows: addition to the aromatic ring atoms and hydrogen/proton abstraction. Our results show that .OH is the most reactive species, while .OOH displays low reactivity and .O2- does not react at all with pyridoxine. The most exergonic reactions are those where .H is removed from the CH2OH groups or the ring-bound OH group and range from -33 to -39 kcal/mol. The most exergonic addition reactions occur by attacking the carbon atoms bonded to nitrogen but with an energy gain of only 6 kcal/mol.
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| 6. |
- Matxain, Jon M, et al.
(författare)
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Theoretical study of the reaction of vitamin B6 with 1O2
- 2007
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH Verlag. - 0947-6539 .- 1521-3765. ; 13:16, s. 4636-42
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Tidskriftsartikel (refereegranskat)abstract
- Singlet oxygen is known to cause oxidative stress in cells, leading to severe damage (e.g., lipid peroxidation, membrane degradation, mutagenic alterations to DNA, protein misfunctionality). Recently, pyridoxine has been discovered to be capable of quenching singlet oxygen, however, the mechanism of this reaction remains essentially unknown. In this work, we have investigated four sets of reactions: 1) 1,3-addition to a double bond connected to a hydrogen-carrying group,resulting in the formation of allylic hydroperoxides; 2) [p2+p2] 1,2-cycloaddition to an isolated double bond, resulting in the formation of 1,2-peroxides; 3) 1,4-cycloaddition to a system containing at least two conjugated double bonds, resulting in the formation of the so-called 1,4-peroxides;4) 1,4-addition to phenols and naphthols with the formation of hydroperoxide ketones. Thermodynamically, reaction 4 and the 6(9), 3(8), and 5(8) cases of reaction 1 are the most exergonic ones, with energies ranging from 16 to 18 kcalmol 1. Furthermore, reaction 4 shows the lowest barrier through the reaction path, and is predicted to be the preferred mechanismfor the pyridoxine + singlet-oxygen reaction, which is in agreement with previous experimental results.
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| 7. |
- Musa, Klefah A K, et al.
(författare)
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Mechanism of Photoinduced Decomposition of Ketoprofen
- 2007
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Ingår i: Journal of Medicinal Chemistry. - Washington, DC : American Chemical Society. - 0022-2623 .- 1520-4804. ; 50:8, s. 1735-1743
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Tidskriftsartikel (refereegranskat)abstract
- UV-induced decarboxylation of the NSAID ketoprofen, followed by activation of molecular oxygen or formation of a decarboxylated peroxide adduct, is explored using computational quantum chemistry. The excited energy surfaces reveal that the neutral species will not decarboxylate, whereas the deprotonated acid decarboxylates spontaneously in the triplet state, and with an associated 3-5 kcal/mol barrier from several low-lying excited singlet states. The observed long lifetimes of the decarboxylated anion is explained in terms of the high stability of the triplet benzoyl ethyl species with protonated carbonylic oxygen, from which there is no obvious decay channel. Mechanisms for the generation of singlet oxygen and superoxide are discussed in detail. Addition of molecular oxygen to give the corresponding peroxyl radical capable of initiating propagating lipid peroxidation reactions is also explored. The computed data explains all features of the observed experimental observations made to date on the photodegradation of ketoprofen.
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| 8. |
- Ristilä, Mikael, et al.
(författare)
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pH-dependent electronic and spectroscopic properties of pyridoxine (vitamin B6)
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 110:33, s. 16774-16780
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Tidskriftsartikel (refereegranskat)abstract
- The key electronic and spectroscopic properties of vitamin B6 (pyridoxine) and some of its main charged and protonated/deprotonated species are explored using hybrid density functional theory (DFT) methods including polarized solvation models. It is found that the dominant species at low pH is the N1-protonated form and, at high pH, the O3¢-deprotonated compound. Computed and experimental UV-spectra for these species (experimental spectra recorded at pH 1.7 and 11.1, respectively) show a very close resemblance. At pH 4.3, the protonated species dominates, but with onset of the zwitterionic oxo form which is also the dominant species at neutral pH. The computational studies furthermore show that neither a polarized continuum model of the polar aqueous solvent or explicit hydrogen bonding through additional water molecules are sufficient to describe accurately the spectrum at physiological pH. Instead, Na+ and Cl- counterions were required to give a blue-shift of approximately 0.15 eV.
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| 9. |
- Sebastian, Eider San, et al.
(författare)
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Metal ion dependent adhesion sites in integrins : A Combined DFT and QMC Study on Mn2
- 2007
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Ingår i: Journal of Physical Chemistry B. - Washington, DC : American Chemical Society. - 1520-6106 .- 1520-5207. ; 111:30, s. 9099-9103
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Tidskriftsartikel (refereegranskat)abstract
- The theoretical study of relative energies of different spin states of Mn2+ has been carried out for the isolated cation and for structures in which the cation is coordinated to ligands that represent the first coordination shell in a protein environment that contains a metal ion dependent adhesion site (MIDAS, found in the ligand binding domain of protein LFA-1). The calculations determine whether the ligand field generated by a prototype protein environment affects the relative energies between high, intermediate, and low spin states. Geometry optimizations and vibrational frequency calculations were carried out at the B3LYP/SKBJ+* level of theory. Single point calculations were performed at the B3LYP/6-311++G(2df,2p) and diffusion monte carlo (DMC) levels for the refinement of the electronic energies. These calculations reveal important differences in the relative energies between high/low spin complexes obtained by B3LYP and DMC and show that although both DFT and DMC show similar trends, a higher level method such as DMC is necessary for a quantitative description of the interactions between Mn2+ and its natural ligands. (G)s of acetate-type ligand binding reactions were calculated that show that the higher the spin of the manganese complex, the lower the affinity for the ligand.
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