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1.
Nat Commun ; 11(1): 5075, 2020 10 08.
Artigo em Inglês | MEDLINE | ID: mdl-33033245

RESUMO

Nickel-iron composites are efficient in catalyzing oxygen evolution. Here, we develop a microorganism corrosion approach to construct nickel-iron hydroxides. The anaerobic sulfate-reducing bacteria, using sulfate as the electron acceptor, play a significant role in the formation of iron sulfide decorated nickel-iron hydroxides, which exhibit excellent electrocatalytic performance for oxygen evolution. Experimental and theoretical investigations suggest that the synergistic effect between oxyhydroxides and sulfide species accounts for the high activity. This microorganism corrosion strategy not only provides efficient candidate electrocatalysts but also bridges traditional corrosion engineering and emerging electrochemical energy technologies.


Assuntos
Desulfotomaculum/metabolismo , Hidróxidos/metabolismo , Níquel/metabolismo , Oxigênio/metabolismo , Corrosão , Teoria da Densidade Funcional , Eletroquímica , Eletrodos , Análise Espectral Raman , Espectroscopia por Absorção de Raios X
2.
PLoS One ; 15(8): e0229477, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32822343

RESUMO

The research was conducted in the "logical series" of seven ligands: chromone, flavone, 3-hydroxyflavone, 3,7-dihydroxyflavone, galangin, kaempferol and quercetin. Each subsequent ligand differs from the previous one, among others by an additional hydroxyl group. The studied chromone derivatives are plant secondary metabolites which play an important role in growth, reproduction, and resistance to pathogens. They are important food ingredients with valuable pro-health properties. The studies of the relationships between their molecular structure and biological activity facilitate searching for new chemical compounds with important biological properties not by trial and error, but concerning the impact of specific changes in their structure on the compound properties. Therefore several pectroscopic methods (FT-IR, FT-Raman, 1H and 13C NMR) were applied to study the molecular structure of the compounds in the series. Moreover the quantum-chemical calculations at B3LYP/6-311++G** were performed to obtained the theoretical NMR spectra, NBO atomic charge, global reactivity descriptors and thermodynamic parameters. The antioxidant activity of the compounds was tested in the DPPH and FRAP assays and the mechanism of antioxidant activity was discussed based on the results on theoretical calculations. The cytotoxicity of the ligands toward human epithelial colorectal adenocarcinoma Caco2 cells was estimated and correlated with the lipophilicity of the compounds. The principal component analyses (PCA) and hierarchical cluster analysis were used to study the dependency between the molecular structure of ligands and their biological activity. The experimental data were related to the theoretical ones. The found regular changes in physicochemical properties correlated well with the systematic changes in antioxidant and biological properties.


Assuntos
Antineoplásicos/química , Antineoplásicos/farmacologia , Antioxidantes/química , Antioxidantes/farmacologia , Cromonas/química , Cromonas/farmacologia , Dieta , Células CACO-2 , Teoria da Densidade Funcional , Humanos , Interações Hidrofóbicas e Hidrofílicas , Relação Estrutura-Atividade
3.
Phys Chem Chem Phys ; 22(33): 18272-18283, 2020 Sep 07.
Artigo em Inglês | MEDLINE | ID: mdl-32756685

RESUMO

The COVID-19 pandemic poses a severe threat to human health with unprecedented social and economic disruption. Spike (S) glycoprotein in the SARS-CoV-2 virus is pivotal in understanding the virus anatomy, since it initiates the early contact with the ACE2 receptor in the human cell. The subunit S1 in chain A of S-protein has four structural domains: the receptor binding domain (RBD), the n-terminal domain (NTD) and two subdomains (SD1, SD2). We report details of the intra- and inter-molecular binding mechanism of RBD using density functional theory, including electronic structure, interatomic bonding and partial charge distribution. We identify five strong hydrogen bonds and analyze their roles in binding. This provides a pathway to a quantum-chemical understanding of the interaction between the S-protein and the ACE2 receptor with insights into the function of conserved features in the ACE2 receptor binding domain that could inform vaccine and drug development.


Assuntos
Betacoronavirus/química , Peptidil Dipeptidase A/metabolismo , Glicoproteína da Espícula de Coronavírus/metabolismo , Sequência de Aminoácidos , Teoria da Densidade Funcional , Humanos , Ligação de Hidrogênio , Modelos Químicos , Peptidil Dipeptidase A/química , Ligação Proteica , Domínios Proteicos , Alinhamento de Sequência , Glicoproteína da Espícula de Coronavírus/química
4.
Free Radic Res ; 54(7): 535-539, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32838569

RESUMO

The relationship between radical-scavenging rate constants (k) in an aprotic medium and thermodynamic parameters calculated by density functional theory (DFT) was investigated for 7 flavonols, which are myricetin (Myr), quercetin (Que), morin (Mor), kaempferol (Kae), 2'-methylquercetin (2'-MeQue), 5'-methylquercetin (5'-MeQue), and 2',5'-dimethylquercetin (Me2Que). The k values were determined for the reaction between the flavonols and galvinoxyl radical used as a reactivity model of reactive oxygen species in deaerated acetonitrile at 298 K. The energy difference values (D HT, HT: hydrogen transfer) between the flavonols and the corresponding radicals, which equal to the relative O-H bond dissociation energies of the OH groups in the flavonols and ionisation potentials (IP) were calculated by DFT at the B3LYP/6-31++G(d) level with C-PCM solvation model parameterised for acetonitrile. Among the 7 flavonols used in this study, calculated IP values of 4 flavonols exhibited a linear correlation with log k, suggesting that the radical-scavenging reaction of these flavonols may proceed via an electron transfer as the rate determining step.


Assuntos
Flavonóis/química , Depuradores de Radicais Livres/química , Antioxidantes/química , Compostos Benzidrílicos/química , Teoria da Densidade Funcional , Cinética , Espécies Reativas de Oxigênio/química , Relação Estrutura-Atividade , Termodinâmica
5.
Phys Chem Chem Phys ; 22(34): 19069-19079, 2020 Sep 08.
Artigo em Inglês | MEDLINE | ID: mdl-32812956

RESUMO

A dynamical approach is proposed to discriminate between reactive (rES) and nonreactive (nES) enzyme-substrate complexes taking the SARS-CoV-2 main protease (Mpro) as an important example. Molecular dynamics simulations with the quantum mechanics/molecular mechanics potentials (QM(DFT)/MM-MD) followed by the electron density analysis are employed to evaluate geometry and electronic properties of the enzyme with different substrates along MD trajectories. We demonstrate that mapping the Laplacian of the electron density and the electron localization function provides easily visible images of the substrate activation that allow one to distinguish rES and nES. The computed fractions of reactive enzyme-substrate complexes along MD trajectories well correlate with the findings of recent experimental studies on the substrate specificity of Mpro. The results of our simulations demonstrate the role of the theory level used in QM subsystems for a proper description of the nucleophilic attack of the catalytic cysteine residue in Mpro. The activation of the carbonyl group of a substrate is correctly characterized with the hybrid DFT functional PBE0, whereas the use of a GGA-type PBE functional, that lacks the admixture of the Hartree-Fock exchange fails to describe activation.


Assuntos
Betacoronavirus/enzimologia , Cisteína Endopeptidases/metabolismo , Proteínas não Estruturais Virais/metabolismo , Betacoronavirus/isolamento & purificação , Domínio Catalítico , Infecções por Coronavirus/patologia , Infecções por Coronavirus/virologia , Cisteína/química , Cisteína/metabolismo , Teoria da Densidade Funcional , Elétrons , Humanos , Simulação de Dinâmica Molecular , Pandemias , Pneumonia Viral/patologia , Pneumonia Viral/virologia , Estrutura Terciária de Proteína , Especificidade por Substrato
6.
J Phys Chem Lett ; 11(15): 6262-6265, 2020 Aug 06.
Artigo em Inglês | MEDLINE | ID: mdl-32658489

RESUMO

The question of whether COVID protease (SARS-CoV-2 Mpro) can be blocked by inhibitors has been examined, with a particularly successful performance exhibited by α-ketoamide derivative substrates like 13b of Hilgenfeld and co-workers (Zhang, L., et al. Science 2020, 368, 409-412). After the biological characterization, here density functional theory calculations explain not only how inhibitor 13b produces a thermodynamically favorable interaction but also how to reach it kinetically. The controversial and unprovable concept of aromaticity here enjoys being the agent that rationalizes the seemingly innocent role of histidine (His41 of Mpro). It has a hydrogen bond with the hydroxyl group and is the proton carrier of the thiol of Cys145 at almost zero energy cost that favors the interaction with the inhibitor that acts as a Michael acceptor.


Assuntos
Antivirais/metabolismo , Betacoronavirus , Infecções por Coronavirus/tratamento farmacológico , Inibidores de Cisteína Proteinase/metabolismo , Histidina/química , Pneumonia Viral/tratamento farmacológico , Proteínas não Estruturais Virais/antagonistas & inibidores , Antivirais/química , Betacoronavirus/enzimologia , Sítios de Ligação , Cisteína Endopeptidases/química , Cisteína Endopeptidases/metabolismo , Inibidores de Cisteína Proteinase/química , Teoria da Densidade Funcional , Ligação de Hidrogênio , Cetonas/química , Cetonas/metabolismo , Modelos Químicos , Pandemias , Ligação Proteica , Proteínas não Estruturais Virais/química , Proteínas não Estruturais Virais/metabolismo
7.
Chemosphere ; 255: 127052, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32679636

RESUMO

In this study, polypyrrole/carboxymethyl cellulose nanocomposite particles (PPy/CMC NPs) were synthesized and applied for removal of reactive red 56 (RR56)and reactive blue 160 (RB160) as highly toxic dyes. The amount of CMC was found significantly effective on the surface adsorption efficiency. Different optimization methods including the genetic programming, response surface methodology, and artificial neural network (ANN) were used to optimize the effect of different parameters including pH, adsorption time, initial dye concentration and adsorbent dose. The maximum adsorption of RR56 and RB160 were found under the following optimum conditions: pH of 4 and 5, adsorption time of 55 min and 52 min for RR56 and RB160, respectively, initial dye concentration of 100 mg/L and adsorbent dose of 0.09 g for both dyes. were obtained for RR56 and RB160, respectively. Also, the results indicated that ANN method could predict the experimental adsorption data with higher accuracy than other methods. The analysis of ANN results indicated that the adsorbent dose is the main factor in RR56 removal, followed by time, pH and initial concentration, respectively. However, initial concentration mostly determines the RB160 removal process. The isotherm data for both dyes followed the Langmuir isotherm model with a maximum adsorption capacity of 104.9 mg/g and 120.7 mg/g for RR56 and RB160, respectively. In addition, thermodynamic studies indicated the endothermic adsorption process for both studied dyes. Moreover, DFT calculations were carried out to obtain more insight into the interactions between the dyes and adsorbent. The results showed that the hydrogen bondings and Van der Waals interactions are dominant forces between the two studied dyes and PPy/CMC composite. Furthermore, the interaction energies calculated by DFT confirmed the experimental adsorption data, where PPy/CMC resulted in higher removal of both dyes compared to PPy. The developed nanocomposite showed considerable reusability up to 3 cylces of the batch adsorption process.


Assuntos
Carboximetilcelulose Sódica/química , Corantes/química , Nanocompostos/química , Adsorção , Compostos Azo , Benzenossulfonatos , Teoria da Densidade Funcional , Cinética , Nanopartículas , Polímeros , Pirróis , Termodinâmica , Poluentes Químicos da Água
8.
Nature ; 583(7814): 66-71, 2020 07.
Artigo em Inglês | MEDLINE | ID: mdl-32612224

RESUMO

Dental enamel is a principal component of teeth1, and has evolved to bear large chewing forces, resist mechanical fatigue and withstand wear over decades2. Functional impairment and loss of dental enamel, caused by developmental defects or tooth decay (caries), affect health and quality of life, with associated costs to society3. Although the past decade has seen progress in our understanding of enamel formation (amelogenesis) and the functional properties of mature enamel, attempts to repair lesions in this material or to synthesize it in vitro have had limited success4-6. This is partly due to the highly hierarchical structure of enamel and additional complexities arising from chemical gradients7-9. Here we show, using atomic-scale quantitative imaging and correlative spectroscopies, that the nanoscale crystallites of hydroxylapatite (Ca5(PO4)3(OH)), which are the fundamental building blocks of enamel, comprise two nanometric layers enriched in magnesium flanking a core rich in sodium, fluoride and carbonate ions; this sandwich core is surrounded by a shell with lower concentration of substitutional defects. A mechanical model based on density functional theory calculations and X-ray diffraction data predicts that residual stresses arise because of the chemical gradients, in agreement with preferential dissolution of the crystallite core in acidic media. Furthermore, stresses may affect the mechanical resilience of enamel. The two additional layers of hierarchy suggest a possible new model for biological control over crystal growth during amelogenesis, and hint at implications for the preservation of biomarkers during tooth development.


Assuntos
Amelogênese , Esmalte Dentário/química , Ácidos/química , Cálcio/química , Carbonatos/química , Cristalização , Teoria da Densidade Funcional , Esmalte Dentário/ultraestrutura , Durapatita/química , Fluoretos/química , Humanos , Magnésio/química , Microscopia Eletrônica de Transmissão e Varredura , Sódio/química , Tomografia , Difração de Raios X
9.
Int J Mol Sci ; 21(15)2020 Jul 23.
Artigo em Inglês | MEDLINE | ID: mdl-32717853

RESUMO

As SARS-CoV-2 is spreading rapidly around the globe, adopting proper actions for confronting and protecting against this virus is an essential and unmet task. Reactive oxygen species (ROS) promoting molecules such as peroxides are detrimental to many viruses, including coronaviruses. In this paper, metal decorated single-wall carbon nanotubes (SWCNTs) were evaluated for hydrogen peroxide (H2O2) adsorption for potential use for designing viral inactivation surfaces. We employed first-principles methods based on the density functional theory (DFT) to investigate the capture of an individual H2O2 molecule on pristine and metal (Pt, Pd, Ni, Cu, Rh, or Ru) decorated SWCNTs. Although the single H2O2 molecule is weakly physisorbed on pristine SWCNT, a significant improvement on its adsorption energy was found by utilizing metal functionalized SWCNT as the adsorbent. It was revealed that Rh-SWCNT and Ru-SWCNT systems demonstrate outstanding performance for H2O2 adsorption. Furthermore, we discovered through calculations that Pt- and Cu-decorated SWNCT-H2O2 systems show high potential for filters for virus removal and inactivation with a very long shelf-life (2.2 × 1012 and 1.9 × 108 years, respectively). The strong adsorption of metal decorated SWCNTs and the long shelf-life of these nanomaterials suggest they are exceptional candidates for designing personal protection equipment against viruses.


Assuntos
Betacoronavirus/efeitos dos fármacos , Desinfetantes/farmacologia , Peróxido de Hidrogênio/análise , Nanotubos de Carbono/química , Adsorção , Infecções por Coronavirus/prevenção & controle , Teoria da Densidade Funcional , Desinfetantes/química , Estabilidade de Medicamentos , Humanos , Ferro/química , Ferro/farmacologia , Pandemias/prevenção & controle , Equipamento de Proteção Individual , Platina/química , Platina/farmacologia , Pneumonia Viral/prevenção & controle , Ródio/química , Ródio/farmacologia , Rutênio/química , Rutênio/farmacologia , Inativação de Vírus
10.
Food Chem ; 333: 127430, 2020 Dec 15.
Artigo em Inglês | MEDLINE | ID: mdl-32679413

RESUMO

Phytosterols (PS) are a group of sterols distributed in foods and plants, where it is prone to oxidation. In this work, we studied the reaction mechanism of phytosterols, using density functional theory (DFT) calculation and experimental methods to study the photooxidation of phytosterols. Under LED light illumination, experimental photooxidation of these phytosterols gives rise to the prior three kind oxides of phytosterol: 6α-OH, 7α-OH, and 7ß-OH. The mechanistic investigations by DFT suggest that singlet oxygen (1O2)-mediated photooxidation (Type II mechanism) generated radical adds to the C5 and C6 on the B Ring of steroid nucleus and reaction in C7 initiated from C5 products through rearrangement pathway. Furthermore, the stereoselectivity at C5, C6 and C7 provides a mechanistic guide for phytosterols photooxidation. These efforts are expected to serve as an essential exploratory study for the oxidation mechanism of phytosterols in the complex food matrix and antioxidation technology for phytosterols.


Assuntos
Processos Fotoquímicos , Fitosteróis/química , Alcenos/química , Teoria da Densidade Funcional , Hidrogênio/química , Luz , Oxidantes Fotoquímicos/química , Oxirredução , Óxidos/química , Esteroides/química
11.
PLoS One ; 15(6): e0234115, 2020.
Artigo em Inglês | MEDLINE | ID: mdl-32544157

RESUMO

The variation of the HOMO-LUMO band gap is explored for varying packing arrangements of the 4mod BT-4TIC donor-acceptor molecule pair, by means of a high-throughput ab-initio random structure search of packing possibilities. 350 arrangements of the dimer have been relaxed from initial random dispositions, using non-local density-functional theory. We find that the electronic band gap varies within 0.3 eV, and that this magnitude, the binding energy, and the geometry are not significantly correlated. A clearly favoured structure is found with a binding energy of 1.75±0.07 eV, with all but three other arrangements displaying values of less than one third of this highest binding one, which involves the aliphatic chain of 4TIC.


Assuntos
Compostos Orgânicos/química , Energia Solar , Teoria da Densidade Funcional , Tiadiazóis/química , Tiofenos/química
12.
Artigo em Inglês | MEDLINE | ID: mdl-32480237

RESUMO

Root growth is reduced in soils with low pH [H+] and abundant soluble aluminum [Al3+], which can be a consequence of the interaction between Al3+ and cell wall composition. The competition between Al3+ and Ca2+ toward binding to pectin molecules was evaluated in roots of Urochloa decumbens, an African grass highly adapted to acidic Al-rich soils. Variations in the composition and distribution of pectins can change the extensibility, rigidity, porosity, and adhesive properties of plant cell walls, which were tested in seedlings of U. decumbens exposed to pH 3.5, 4.5 and 5.8 and to 0, 80, 160 and 320 µM of Al3+ for 80h. Root growth corroborated that U. decumbens is very tolerant to soil acidity, with effective reduction of root growth only at pH 3.5. Immunocytochemical approaches demonstrated variations in pectin composition induced both by Al3+ and by H+ in root tissues and zones. Based on the usual linkage between Ca2+ and pectins, Density Functional Theory (DFT) analyses indicated that Al3+ bound easier to pectins than Ca2+ did, leading to the formation of more Al3+-pectate complexes than Ca2+-pectate complexes, which resulted in higher rigidity of cell walls, and hampered cell extension.


Assuntos
Alumínio/metabolismo , Cálcio/metabolismo , Pectinas/metabolismo , Raízes de Plantas/metabolismo , Poaceae/metabolismo , Parede Celular , Teoria da Densidade Funcional , Imuno-Histoquímica
13.
Chemosphere ; 258: 127289, 2020 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-32535447

RESUMO

Anammox-based processes and microbial consortia have drawn extensive attention for their use in high-efficiency wastewater treatment technologies. Metals substantially affect the activity of anammox consortia and the quality of wastewater treatment plant effluent. Here, we explored the role of anammox consortia in terms of metals complexation in both single and multi-metal systems. Adsorption edges of single metal cations indicate that the adsorption preference was in the order: Pb(II) > Cd(II) > Cr(VI). A competitive effect was observed in multi-metal cations systems, with Pb(II) being preferably adsorbed and the degree of adsorption somewhat reduced in the presence of either Cd(II) or Cr(VI), while Cd(II) and Cr(VI) were easily exchanged and substituted by other metals. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) further suggest that the adsorption of Pb(II) and Cd(II) are as inner-sphere ion-exchange mechanisms, while Cr(VI) adsorption is mainly by outer-sphere complexation. Density functional theory (DFT) calculations highlight that Cd(II) and Pb(II) have different binding sites compared to Cr(VI), and the order of binding energy (Ebd) of three metal cations were Pb(II) > Cd(II) > Cr(VI). These calculations support the adsorption data in that Pb forms more stable complexes with anammox bacterial surface ligands. Surface complexation modelling (SCM) further predicted both the sorption of single metal cations and competitive adsorption of the three metals to anammox consortia, the exception being Cd at higher loadings. The results of this study highlight the potential role of anammox consortia in removing metal cations from wastewater in treatment systems.


Assuntos
Amônia/metabolismo , Reatores Biológicos/microbiologia , Metais Pesados/química , Consórcios Microbianos/fisiologia , Adsorção , Anaerobiose , Cátions , Teoria da Densidade Funcional , Metais Pesados/metabolismo , Oxirredução , Espectroscopia Fotoeletrônica , Espectroscopia de Infravermelho com Transformada de Fourier , Eliminação de Resíduos Líquidos/métodos , Águas Residuárias/química , Poluentes Químicos da Água/química , Poluentes Químicos da Água/metabolismo
14.
Chemosphere ; 257: 127243, 2020 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-32505956

RESUMO

In order to protect selective catalytic reduction (SCR) catalysts for flue gas denitration in coal-fired power plants, the adsorption of As2O3 on γ-Al2O3(0 0 1) surface is investigated theoretically through density functional theory (DFT) in this study. The adsorption sites, adsorption structures, adsorption energies, electronic clouds, transition processes, and intermediate and transition structures are investigated. The theoretical results indicate that the adsorption of As2O3 molecule on the surface of γ-Al2O3(0 0 1) could be either physical or chemical, depending on the sites the molecule hangs over. Compared with the experimental results from other researchers, this study unveils that, although the apparent adsorption of As2O3 molecule on γ-Al2O3(0 0 1) surface is physical, some of the sites on γ-Al2O3(0 0 1) surface presents strong chemical affinity towards As2O3 adsorption. Further, this study depicts the adsorption process to clarify the reason of the net effect of As2O3 adsorption on γ-Al2O3 being physical. Meanwhile, the study also reveals that apparent physical adsorption of As2O3 on γ-Al2O3(0 0 1) surface is due to the high energy barrier that prohibits the transformation of physical adsorption to chemical adsorption. The research results provide useful information for exploiting γ-Al2O3 as a potential metal oxides sorbent.


Assuntos
Arseniatos/química , Adsorção , Catálise , Teoria da Densidade Funcional , Óxidos
15.
Food Chem ; 327: 127054, 2020 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-32460129

RESUMO

Interactions between saccharides and ions in aqueous solutions are of great importance in many fields (chemistry, physico-chemistry, biology, food industries). Thus, this work proposes to develop a methodology dealing with the characterization and the understanding of interactions between saccharides and cations in presence of water molecules, by a quantum mechanics approach. In the first part, the saccharide hydration properties (xylose, glucose, sucrose) in pure water are determined. Results show that the saccharide coordination numbers, as well as the saccharides hydration enthalpy, increase with the saccharide hydrophilic group number. In the second part, the influence of cations on saccharides hydration properties, and inversely, is evaluated. In saccharide/cation/water systems, the decrease in hydration enthalpy of cations and saccharides shows that both species are dehydrated and that saccharide dehydration depends on the nature of the cation. The dehydration sequence of saccharides was explained from the study of saccharide/cation interactions.


Assuntos
Carboidratos/química , Teoria da Densidade Funcional , Água/química , Cátions/química , Glucose/química , Interações Hidrofóbicas e Hidrofílicas , Metais/química , Sacarose/química , Termodinâmica , Xilose/química
16.
Environ Sci Technol ; 54(11): 6651-6660, 2020 06 02.
Artigo em Inglês | MEDLINE | ID: mdl-32396730

RESUMO

The Pb(II)-binding mechanism on an annealed hematite (1102) surface was studied using crystal truncation rod (CTR) X-ray diffraction coupled with density functional theory (DFT) calculations. The best fit CTR model suggested that Pb(II) sorbed selectively to one type of edge-sharing surface site (ES2) over two other potential surface sites. From the best fit model structure, it was found that the Pb surface complex species forms a trigonal pyramid geometry. The base consists of three oxygen groups, two of which are associated with the substrate surface (IO and IIIO) and one that is a distal O extending toward solution. The trigonal pyramid geometry is slightly distorted with Pb-O bond lengths ranging from 2.21 to 2.31 Å and O-Pb-O bond angles ranging from 72° to 75°. Under this structural distortion, the nearest distance between Pb and Fe is found to be 3.39(1) Å. Consistent with the CTR results, DFT calculations indicate the Pb binding energy at the ES2 site is at least 0.16 eV more favorable than that at the other two potential binding sites considered. Using bond-valence rules we propose a stoichiometry of Pb(II) binding on the hematite (1102) surface which indicates proton release through the deprotonation of all oxygen groups bonding to Pb.


Assuntos
Teoria da Densidade Funcional , Chumbo , Adsorção , Compostos Férricos , Difração de Raios X
17.
Phys Chem Chem Phys ; 22(19): 10924-10933, 2020 May 21.
Artigo em Inglês | MEDLINE | ID: mdl-32373808

RESUMO

Recent experimental investigations of the photochemical properties of a series of sulfur-substituted pyrimidine derivatives provide insights into the phototherapeutic potential of these nucleobase variants. Herein we elucidate the triplet formation mechanism of two prospective UVA-activated phototherapeutic molecules, 4-thiothymine and 2,4-dithiothymine, upon photo-excitation by applying the trajectory surface hopping dynamics at the LR-TDDFT level. Our simulations reasonably reproduce the experimental time constants and demonstrate the preferred triplet formation pathway which starts from the S1(nSπ*) state for both molecules. It is found that deactivation of the first bright state to the S1(nSπ*) state proceeds through a mechanism involving elongation of the C5-C6 and C4-S8 bond-lengths and C2-pyramidalization in 4-thiothymine and involving elongation of the C5-C6 and C2-S7 bond-lengths in 2,4-dithiothymine. The intersystem crossing of 2,4-dithiothymine occurs either at geometries characterized by elongated C5-C6 and C2-S7 bond-lengths or at geometries showing elongated C5-C6 and C4-S8 bond-lengths as seen in 4-thiothymine. The solvents are found to affect the S2 state decay of 4-thiothymine, leading to a competing pathway between S2→ S1 and S2→ T3. This study provides a molecular-level understanding of the underlying excited-state relaxation of the two UVA-activated thiopyrimidines, which may be linked to their potential applications in pharmacological science and also prove helpful for designing more effective phototherapeutic agents.


Assuntos
Timina/análogos & derivados , Teoria da Densidade Funcional , Modelos Químicos , Timina/química , Timina/efeitos da radiação , Raios Ultravioleta
18.
Chemosphere ; 255: 126910, 2020 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-32402874

RESUMO

In particulate matter, organic precursors generate environmentally persistent free radicals (EPFRs) on metal oxides and attract worldwide attentions in health risk assessment and environmental protection. For the first time, we determined characteristics and formation processes of EPFRs evolved from different organic precursors on PbO particulate. As a result, phenol resulted in phenoxyl radical at 230 °C by releasing one H atom. One Cl atom was eliminated from monochlorobenzene and 1,2-dichlorobenzene, producing phenyl and chlorobenzene radicals, respectively. The decays of these radicals had an order of chlorobenzene radical (4 d) > phenyl radical (3 d) > phenoxyl radical (2 d). Density functional theory calculations indicated that the long decay of chlorobenzene radical was contributed to the high adsorption energy of 1,2-dichlorobenzene on PbO particulate. Furthermore, chlorobenzene radical produced more reactive oxygen species than the other two radicals in oxidative-stress investigations. Therefore, 1,2-dichlorobenzene creates more persistent EPFR, which will cause more dangerous health impact. The main results of this article provide a new insight into the health risk assessment of organic and oxide-containing particulate matter.


Assuntos
Poluentes Atmosféricos/análise , Teoria da Densidade Funcional , Material Particulado/análise , Adsorção , Clorobenzenos , Carvão Mineral , Poeira , Monitoramento Ambiental , Radicais Livres/análise , Minerais , Óxidos , Fenol , Espécies Reativas de Oxigênio
19.
Biochim Biophys Acta Bioenerg ; 1861(8): 148203, 2020 08 01.
Artigo em Inglês | MEDLINE | ID: mdl-32305411

RESUMO

The quinol oxidation site QD in E. coli respiratory nitrate reductase A (EcNarGHI) reacts with the three isoprenoid quinones naturally synthesized by the bacterium, i.e. ubiquinones (UQ), menaquinones (MK) and demethylmenaquinones (DMK). The binding mode of the demethylmenasemiquinone (DMSK) intermediate to the EcNarGHI QD quinol oxidation site is analyzed in detail using 1,2H hyperfine (hf) spectroscopy in combination with H2O/D2O exchange experiments and DFT modeling, and compared to the menasemiquinone one bound to the QD site (MSKD) previously studied by us. DMSKD and MSKD are shown to bind in a similar and strongly asymmetric manner through a short (~1.7 Å) H-bond. The origin of the specific hf pattern resolved on the DMSKD field-swept EPR spectrum is unambiguously ascribed to slightly inequivalent contributions from two ß-methylene protons of the isoprenoid side chain. DFT calculations show that their large isotropic hf coupling constants (Aiso ~12 and 15 MHz) are consistent with both (i) a specific highly asymmetric binding mode of DMSKD and (ii) a near in-plane orientation of its isoprenyl chain at Cß relative to the aromatic ring, which differs by ~90° to that predicted for free or NarGHI-bound MSK. Our results provide new insights into how the conformation and the redox properties of different natural quinones are selectively fine-tuned by the protein environment at a single Q site. Such a fine-tuning most likely contributes to render NarGHI as an efficient and flexible respiratory enzyme to be used upon rapid variations of the Q-pool content.


Assuntos
Teoria da Densidade Funcional , Escherichia coli/enzimologia , Nitrato Redutase/metabolismo , Quinonas/metabolismo , Análise Espectral , Modelos Moleculares , Nitrato Redutase/química , Ligação Proteica , Conformação Proteica
20.
Bioresour Technol ; 307: 123204, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32224426

RESUMO

The performance of anaerobic digestion (AD) can be improved by the addition of accelerants. Three types of biomass-derived carbon-based composites (Co/C, CoO/C, and Co3O4/C) were used as accelerants to investigate the effect on AD systems in this work. These accelerants significantly improved the cumulative biogas yield (576-585 mL/g VS), and the total chemical oxygen demand degradation rate (68.48-71.11%) compared to the reference group (435.8 mL/g VS, 50.74%). The digestates with accelerants exhibited exceptional stability (59.24-63.67%) and superior fertilizer utilization (3.50-4.55%). In addition, first-principle density functional theory (DFT) calculations were conducted to provide the theoretical basis for the direct interspecies electron transfer (DIET), and a general strategy was proposed to help understand the enhanced methanogenesis pathway induced by the biomass-derived carbon-based composites. These important findings provide a novel avenue for the development of composite accelerants for AD systems.


Assuntos
Biocombustíveis , Fertilizantes , Anaerobiose , Biomassa , Reatores Biológicos , Carbono , Teoria da Densidade Funcional , Esterco , Metano
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