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1.
Sci Adv ; 5(10): eaax2805, 2019 10.
Artigo em Inglês | MEDLINE | ID: mdl-31620556

RESUMO

Fabrication of biomimetic materials and scaffolds is usually a micro- or even nanoscale process; however, most testing and all manufacturing require larger-scale synthesis of nanoscale features. Here, we propose the utilization of naturally prefabricated three-dimensional (3D) spongin scaffolds that preserve molecular detail across centimeter-scale samples. The fine-scale structure of this collagenous resource is stable at temperatures of up to 1200°C and can produce up to 4 × 10-cm-large 3D microfibrous and nanoporous turbostratic graphite. Our findings highlight the fact that this turbostratic graphite is exceptional at preserving the nanostructural features typical for triple-helix collagen. The resulting carbon sponge resembles the shape and unique microarchitecture of the original spongin scaffold. Copper electroplating of the obtained composite leads to a hybrid material with excellent catalytic performance with respect to the reduction of p-nitrophenol in both freshwater and marine environments.

2.
Nat Commun ; 10(1): 2186, 2019 05 16.
Artigo em Inglês | MEDLINE | ID: mdl-31097703

RESUMO

The increasing availability of X-ray free-electron lasers (XFELs) has catalyzed the development of single-object structural determination and of structural dynamics tracking in real-time. Disentangling the molecular-level reactions triggered by the interaction with an XFEL pulse is a fundamental step towards developing such applications. Here we report real-time observations of XFEL-induced electronic decay via short-lived transient electronic states in the diiodomethane molecule, using a femtosecond near-infrared probe laser. We determine the lifetimes of the transient states populated during the XFEL-induced Auger cascades and find that multiply charged iodine ions are issued from short-lived (∼20 fs) transient states, whereas the singly charged ones originate from significantly longer-lived states (∼100 fs). We identify the mechanisms behind these different time scales: contrary to the short-lived transient states which relax by molecular Auger decay, the long-lived ones decay by an interatomic Coulombic decay between two iodine atoms, during the molecular fragmentation.

3.
Chemistry ; 25(23): 5865-5869, 2019 Apr 23.
Artigo em Inglês | MEDLINE | ID: mdl-30714648

RESUMO

X-ray absorption spectroscopy (XAS) was used to elucidate changes in the electronic structure caused by the pressure-induced structural collapse in EuCo2 P2 . The spectral changes observed at the L3 -edge of Eu and K-edges of Co and P suggest electron density redistribution, which contradicts the formal charges calculated from the commonly used Zintl-Klemm concept. Quantum-chemical calculations show that, despite the increase in the oxidation state of Eu and the formation of a weak P-P bond in the high-pressure phase, the electron transfer from the Eu 4f orbitals to the hybridized 5d and 6s states causes strengthening of the Eu-P and P-P bonds. These changes explain the increased electron density on P atoms, deduced from the P K-edge XAS spectra. This work shows that the formal electron counting schemes do not provide an adequate description of changes associated with phase transitions in metallic systems with substantial mixing of the electronic states.

4.
Int J Biol Macromol ; 78: 224-9, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-25889055

RESUMO

Chitinous scaffolds isolated from the skeleton of marine sponge Aplysina cauliformis were used as a template for the deposition of polyhedral oligomeric silsesquioxanes (POSS). These chitin-POSS based composites with hydrophobic properties were prepared for the first time using solvothermal synthesis (pH 3, temp 80 °C), and were thoroughly characterized. The resulting material was studied using scanning electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and thermogravimetry. A mechanism for the chitin-POSS interaction after exposure to these solvothermal conditions is proposed and discussed.


Assuntos
Quitina/química , Nanocompostos/química , Compostos de Organossilício/química , Microscopia Eletrônica de Varredura , Análise Espectral Raman , Termogravimetria
5.
Sci Rep ; 5: 8710, 2015 Mar 04.
Artigo em Inglês | MEDLINE | ID: mdl-25736576

RESUMO

The mechanisms of interaction between inorganic matter and biomolecules, as well as properties of resulting hybrids, are receiving growing interest due to the rapidly developing field of bionanotechnology. The majority of potential applications for metal-biohybrid structures require stability of these systems under vacuum conditions, where their chemistry is elusive, and may differ dramatically from the interaction between biomolecules and metal ions in vivo. Here we report for the first time a photoemission and X-ray absorption study of the formation of a hybrid metal-protein system, tracing step-by-step the chemical interactions between the protein and metals (Cu and Fe) in vacuo. Our experiments reveal stabilization of the enol form of peptide bonds as the result of protein-metal interactions for both metals. The resulting complex with copper appears to be rather stable. In contrast, the system with iron decomposes to form inorganic species like oxide, carbide, nitride, and cyanide.


Assuntos
Proteínas de Bactérias/química , Cobre/química , Ferro/química , Glicoproteínas de Membrana/química , Modelos Químicos , Oxirredução , Espectroscopia Fotoeletrônica , Ligação Proteica , Propriedades de Superfície , Vácuo , Espectroscopia por Absorção de Raios X
6.
Int J Biol Macromol ; 51(1-2): 129-37, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-22546360

RESUMO

Until now, there is a lack of knowledge about the presence of chitin in numerous representatives of corals (Cnidaria). However, investigations concerning the chitin-based skeletal organization in different coral taxa are significant from biochemical, structural, developmental, ecological and evolutionary points of view. In this paper, we present a thorough screening for the presence of chitin within the skeletal formations of a poorly investigated Mediterranean black coral, Parantipathes larix (Esper, 1792), as a typical representative of the Schizopathidae family. Using a wide array variety of techniques ((13)C solid state NMR, Fourier transform infrared (FTIR), Raman, NEXAFS, Morgan-Elson assay and Calcofluor White Staining), we unambiguously show for the first time that chitin is an important component within the skeletal stalks as well as pinnules of this coral.


Assuntos
Antozoários/química , Quitina/química , Animais , Antozoários/ultraestrutura , Quitina/isolamento & purificação , Quitinases/metabolismo
7.
J Phys Chem B ; 115(10): 2401-7, 2011 Mar 17.
Artigo em Inglês | MEDLINE | ID: mdl-21338139

RESUMO

Strong chemical interaction between bacterial surface protein layers and calcium atoms deposited in situ on top was revealed by means of photoemission spectroscopy. The interaction appears to mainly happen at the oxygen site of the peptide bonds and involves a large charge transfer from Ca 4s states into the peptide backbone. Chemical kinetics of this reaction was characterized using time-dependent valence band photoemission, and the reaction rate constant was determined.


Assuntos
Proteínas de Bactérias/química , Cálcio/química , Peptídeos/química , Bacillus , Proteínas de Bactérias/metabolismo , Cálcio/metabolismo , Cinética , Modelos Moleculares , Conformação Molecular , Espectroscopia Fotoeletrônica
8.
Nat Chem ; 2(12): 1084-8, 2010 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-21107374

RESUMO

The minerals involved in the formation of metazoan skeletons principally comprise glassy silica, calcium phosphate or carbonate. Because of their ancient heritage, glass sponges (Hexactinellida) may shed light on fundamental questions such as molecular evolution, the unique chemistry and formation of the first skeletal silica-based structures, and the origin of multicellular animals. We have studied anchoring spicules from the metre-long stalk of the glass rope sponge (Hyalonema sieboldi; Porifera, Class Hexactinellida), which are remarkable for their size, durability, flexibility and optical properties. Using slow-alkali etching of biosilica, we isolated the organic fraction, which was revealed to be dominated by a hydroxylated fibrillar collagen that contains an unusual [Gly-3Hyp-4Hyp] motif. We speculate that this motif is predisposed for silica precipitation, and provides a novel template for biosilicification in nature.


Assuntos
Colágeno/química , Poríferos/química , Dióxido de Silício/química , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Evolução Molecular , Hidroxilação , Nanopartículas/química , Nanopartículas/ultraestrutura
9.
J Phys Chem B ; 114(29): 9645-52, 2010 Jul 29.
Artigo em Inglês | MEDLINE | ID: mdl-20608694

RESUMO

The electronic structure of genomic DNA has been comprehensively characterized by synchrotron-based X-ray absorption and X-ray photoelectron spectroscopy. Both unoccupied and occupied states close to the Fermi level have been unveiled and attributed to particular sites within the DNA structure. A semiconductor-like electronic structure with a band gap of approximately 2.6 eV has been found at which the pi and pi* orbitals of the nucleobase stack make major contributions to the highest occupied and lowest unoccupied molecular orbitals, respectively, in agreement with previous theoretical predictions.


Assuntos
DNA/química , Genoma , Espectroscopia Fotoeletrônica , Teoria Quântica
10.
J Phys Chem B ; 114(24): 8284-9, 2010 Jun 24.
Artigo em Inglês | MEDLINE | ID: mdl-20518510

RESUMO

Bacterial surface layer protein sheets (S layer) coated with an ultrathin cobalt or silver film were studied by means of laterally resolved near-edge X-ray absorption fine structure spectroscopy performed by photoemission electron microscopy. Comparison with results obtained on pristine S layers allowed us to characterize both chemical interaction and X-ray damage in these protein-metal hybrid systems. In particular, we found that besides direct damage upon exposure to X-ray radiation the biomolecules experience additional contribution of the deposited metals, by low-energy electron generation in the metal particles.


Assuntos
Cobalto/química , Proteínas/química , Prata/química , Espectroscopia por Absorção de Raios X , Raios X
11.
J Phys Chem B ; 111(48): 13491-8, 2007 Dec 06.
Artigo em Inglês | MEDLINE | ID: mdl-17997540

RESUMO

The electronic structure of individual sheets of the bacterial surface protein layer (S layer) of Bacillus sphaericus NCTC 9602 was studied using a photoemission electron microscope (PEEM) operating in near-edge X-ray absorption fine structure spectroscopy mode. The laterally resolved measurements performed at the C 1s, N 1s, and O 1s thresholds on fresh samples revealed characteristic differences compared to the laterally integrated data, where substrate contributions were taken along with the protein signals. During the PEEM experiments an irradiation-induced increase of the C-C bond density at the cost of the densities of the C-O and C-N bonds related to a rearrangement of the contributing atoms of the S layer deposited onto a Si substrate was observed. The critical irradiation doses for the C-O and C-N bond breaking and formation of the new C-C bonds were derived.


Assuntos
Proteínas de Bactérias/análise , Microscopia Eletrônica/métodos , Proteínas de Bactérias/efeitos da radiação , Raios X
12.
J Phys Chem B ; 109(39): 18620-7, 2005 Oct 06.
Artigo em Inglês | MEDLINE | ID: mdl-16853396

RESUMO

The electronic structure of the regular, two-dimensional bacterial surface protein layer of Bacillus sphaericus NCTC 9602 has been examined by photoemission (PE) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Both the O 1s and the N 1s core-level PE spectra show a single structure, whereas the C 1s core-level spectrum appears manifold, suggesting similar chemical states for each oxygen atom and also for each nitrogen atom, while carbon atoms exhibit a range of chemical environments in the different functional groups of the amino acids. This result is supported by the element-specific NEXAFS spectra of the unoccupied valence electronic states, which exhibit a series of characteristic NEXAFS peaks that can be assigned to particular molecular orbitals of the amino acids by applying a phenomenological building-block model. The relative contributions of the C-O, C-N, and C-C bond originating signals into the C 1s PE spectrum are in good agreement with the number ratios of the corresponding bonds calculated from the known primary structure of the bacterial surface protein. First interpretation of the PE spectrum of the occupied valence states is achieved on the basis of electronic density-of-states calculations performed for small peptides. It was found that mainly the pi clouds of the aromatic rings contribute to both the lowest unoccupied and the highest occupied molecular orbitals.


Assuntos
Bacillus/química , Proteínas de Bactérias/química , Análise Espectral/métodos , Aminoácidos/química , Conformação Proteica
13.
Phys Rev Lett ; 93(23): 238103, 2004 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-15601208

RESUMO

We report photoemission and near-edge x-ray absorption fine structure measurements of the occupied and unoccupied valence electronic states of the regular surface layer of Bacillus sphaericus, which is widely used as the protein template for the fabrication of metallic nanostructures. The two-dimensional protein crystal shows a semiconductorlike behavior with a gap value of approximately 3.0 eV and the Fermi energy close to the bottom of the lowest unoccupied molecular orbital. We anticipate that these results will open up new possibilities for the electric addressability of biotemplated low-dimensional hybrid structures.


Assuntos
Fenômenos Fisiológicos Bacterianos , Biofísica/métodos , Bacillus/fisiologia , Cristalografia por Raios X , Elétrons , Cinética , Conformação Molecular , Nanotecnologia , Fótons , Proteínas/química
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