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1.
J Chem Phys ; 151(14): 144307, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31615216

RESUMO

Historically, structure determination of nanocrystals, proteins, and macromolecules required the growth of high-quality crystals sufficiently large to diffract X-rays efficiently while withstanding radiation damage. The development of the X-ray free-electron laser has opened the path toward high resolution single particle imaging, and the extreme intensity of the X-rays ensures that enough diffraction statistics are collected before the sample is destroyed by radiation damage. Still, recovery of the structure is a challenge, in part due to the partial fragmentation of the sample during the diffraction event. In this study, we use first-principles based methods to study the impact of radiation induced ionization of six amino acids on the reconstruction process. In particular, we study the fragmentation and charge rearrangement to elucidate the time scales involved and the characteristic fragments occurring.


Assuntos
Aminoácidos/química , Aminoácidos/efeitos da radiação , Teoria da Densidade Funcional , Modelos Químicos , Simulação de Dinâmica Molecular , Eletricidade Estática , Fatores de Tempo , Raios X
2.
J Chem Phys ; 151(14): 144504, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31615223

RESUMO

In this work, a R1SM approach was applied for the calculation of ideal-gas thermodynamic properties of five amino acids with aliphatic side chains: glycine, alanine, valine, leucine, and isoleucine. The first step of the calculation was an extensive conformational analysis that located several conformers not reported previously. A new systematic and user-friendly nomenclature of the conformers was introduced, and the stable conformers were clearly assigned with the previously used labeling where possible. Stability and calculated relative energies of the conformers were compared between various levels of theory and with several experimental studies, demonstrating a good performance of the selected B3LYP-D3/6-311+G(2df,p) level of theory. As a second step, the theoretically calculated vibrational frequencies were compared to the previously reported experimental spectra to verify the performance of the applied double-linear scaling factor. Finally, ideal-gas heat capacities, enthalpies, and absolute entropies were calculated, accounting for all stable conformers using the R1SM model. The resulting thermodynamic data are presented for the first time, since they cannot be determined experimentally and their rigorous calculation requires a complex thermodynamic model.


Assuntos
Aminoácidos/química , Termodinâmica , Teoria da Densidade Funcional , Gases/química , Modelos Químicos , Conformação Molecular , Estatística como Assunto
3.
J Chem Phys ; 151(13): 134114, 2019 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-31594320

RESUMO

We use real-time density functional theory on a real-space grid to calculate electronic excitations of bacteriochlorophyll chromophores of the light-harvesting complex 2 (LH2). Comparison with Gaussian basis set calculations allows us to assess the numerical trust range for computing electron dynamics in coupled chromophores with both types of techniques. Tuned range-separated hybrid calculations for one bacteriochlorophyll as well as two coupled ones are used as a reference against which we compare results from the adiabatic time-dependent local density approximation (TDLDA). The tuned range-separated hybrid calculations lead to a qualitatively correct description of the electronic excitations and couplings. They allow us to identify spurious charge-transfer excitations that are obtained with the TDLDA. When we take into account the environment that the LH2 protein complex forms for the bacteriochlorophylls, we find that it substantially shifts the energy of the spurious charge-transfer excitations, restoring a qualitatively correct electronic coupling of the dominant excitations also for TDLDA.


Assuntos
Bacterioclorofilas/química , Complexos de Proteínas Captadores de Luz/química , Beijerinckiaceae/química , Teoria da Densidade Funcional , Transferência de Energia , Modelos Químicos
4.
Phys Chem Chem Phys ; 21(38): 21305-21316, 2019 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-31549692

RESUMO

4-Thiopyrimidine (e.g., 4-thiouracil (4-TU) and 4-thiothymine (4-TT)) is a typical kind of thiobase. With the sulfur substitution at the C4 position of the canonical pyrimidine nucleobase, 4-thiopyrimidine displays unique photophysical and photochemical properties such as red-shifted maximum absorption peaks and efficient triplet state populations. One of the properties is the photocrosslinking reaction between 4-thiopyrimidine and pyrimidine base, which plays important roles in photochemotherapy and photolabeling applications. By using density functional theory (M06-2X), we have explored the potential energy profiles of the photocrosslinking reaction between 4-thiopyrimidine (4-TU and 4-TT) and thymine in the S0 and T1 states as well as the interaction between the two states. For both (6-4) and (5-4) photocrosslinking reactions, multiple nonadiabatic pathways via minimum energy crossing points (MECPs) between potential surfaces (PESs) of the T1 and S0 states greatly facilitate the proceeding of photocrosslinking reactions and lead to the relatively stable thietane intermediate in the S0 state. The subsequent H migration in the thietane intermediate takes place solely in the S0 state with surmountable energy barriers in bulk solution, resulting in the formation of the photocrosslinked product. This research provides not only a new mechanistic insight into the photocrosslinking reaction for 4-thiopyrimidines but also a rational explanation for the experiments of UVA irradiated Tp4ST dinucleotide and 4-thiothymidine-containing oligonucleotides, facilitating the deep understanding of the synergistic cytotoxicity of 4-thiopyrimidines and UVA as well as the development of alternative phototherapeutic agents and photolabeling probes.


Assuntos
Reagentes para Ligações Cruzadas/química , Pirimidinas/química , Timina/química , Simulação por Computador , Teoria da Densidade Funcional , Luz , Estrutura Molecular , Processos Fotoquímicos , Termodinâmica
5.
J Phys Chem A ; 123(40): 8644-8649, 2019 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-31536343

RESUMO

Most of the current efforts in drug discovery are devoted to the design of molecules able to mitigate side effects by concentrating the biological action in the targeted tissue. One promising strategy is photodynamic therapy, which is based on the in situ generation of reactive singlet oxygen upon radiation exposure. However, such an approach requires the use of an efficient photosensitizer. This contribution deals with the optical properties of an Ir(III) complex, [Ir(pbz)2(N^N)] (pbz = 2-phenylbenzimidazole; N^N = methyl 1-butyl-2-pyridyl-benzimidazole-5-carboxylate), which has recently been shown to exhort a strong photoactivity, but still needs further improvements to reach clinical applications. We performed density functional theory calculations at the M06, PBE0, ωB97xD, and CAM-B3LYP levels to predict the impact of introducing electron donor-acceptor groups into the nature of the lowest excited states. The simulations performed demonstrate that the presence of a NH2 at the pbz ligand and a NO2 group at the N^N ligand yield a bathochromic shift of absorption spectrum. We report the most sensitive positions to tune the optical signatures of this family of complexes.


Assuntos
Antineoplásicos/química , Complexos de Coordenação/química , Irídio/química , Antineoplásicos/efeitos da radiação , Complexos de Coordenação/efeitos da radiação , Teoria da Densidade Funcional , Ligantes , Luz , Modelos Químicos , Estrutura Molecular , Fármacos Fotossensibilizantes/química , Fármacos Fotossensibilizantes/efeitos da radiação
6.
Chem Commun (Camb) ; 55(77): 11511-11514, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31490471

RESUMO

A short metallofullere-peapod of Y2@C79N⊂[4]CHBC was constructed. The strong confinement effect from the large π-extended [4]CHBC nanoring induces molecular orientation of the wrapped Y2@C79N, which can be sensed by a Y2@C79N spin probe. The low susceptibility of the spin phase memory time (Tm) for the Y2@C79N spin was also found in a confined space.


Assuntos
Complexos de Coordenação/química , Fulerenos/química , Hidrocarbonetos Cíclicos/química , Marcadores de Spin , Ítrio/química , Compostos Aza/química , Teoria da Densidade Funcional , Conformação Molecular , Transição de Fase , Temperatura Ambiente , Termodinâmica
7.
Chem Commun (Camb) ; 55(77): 11567-11570, 2019 Sep 24.
Artigo em Inglês | MEDLINE | ID: mdl-31495830

RESUMO

A small series of fluorescent lysosome-targeting probes based on the BODIPY fluorophore and containing morpholine and nitro groups were rationally designed. These probes emitted light from green to NIR wavelengths, and provided specificity for imaging the lysosomes of hypoxic cells. The electron-withdrawing nitrophenyl group at the meso position was found to lead to highly efficient nonradiative decay of the S1 state, and hence a recovery of fluorescence when reduction of the nitro group occurred under hypoxic conditions.


Assuntos
Compostos de Boro/química , Hipóxia Celular , Corantes Fluorescentes/química , Lisossomos/metabolismo , Teoria da Densidade Funcional , Células Hep G2 , Humanos , Luz , Morfolinas/química , Espectrometria de Fluorescência/métodos
8.
Int J Nanomedicine ; 14: 5017-5032, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31371944

RESUMO

Background: Epigallocatechin gallate (EGCG), the major anti-inflammatory compound in green tea, has been shown to suppress osteoclast (OC) differentiation. However, the low aqueous solubility of EGCG always leads to poor bioavailability, adverse effects, and several drawbacks for clinical applications. Purpose: In this study, we synthesized EGCG-capped gold nanoparticles (EGCG-GNPs) to solve the drawbacks for clinical uses of EGCG in bone destruction disorders by direct reduction of HAuCl4 in EGCG aqueous solution. Methods and Results: The obtained EGCG-GNPs were negatively charged and spherical. Theoretical calculation results suggested that EGCG was released from GNPs in an acidic environment. Cellular uptake study showed an obviously large amount of intracellular EGCG-GNPs without cytotoxicity. EGCG-GNPs exhibited better effects in reducing intracellular reactive oxygen species levels than free EGCG. A more dramatic anti-osteoclastogenic effect induced by EGCG-GNPs than free EGCG was observed in lipopolysaccharide (LPS)-stimulated bone marrow macrophages, including decreased formation of TRAP-positive multinuclear cells and actin rings. Meanwhile, EGCG-GNPs not only suppressed the mRNA expression of genetic markers of OC differentiation but also inhibited MAPK signaling pathways. Furthermore, we confirmed that EGCG-GNPs greatly reversed bone resorption in the LPS-induced calvarial bone erosion model in vivo, which was more effective than applying free EGCG, specifically in inhibiting the number of OCs, improving bone density, and preventing bone loss. Conclusion: EGCG-GNPs showed better anti-osteoclastogenic effect than free EGCG in vitro and in vivo, indicating their potential in anti-bone resorption treatment strategy.


Assuntos
Catequina/análogos & derivados , Ouro/farmacologia , Nanopartículas Metálicas/química , Osteogênese/efeitos dos fármacos , Animais , Células da Medula Óssea/citologia , Células da Medula Óssea/efeitos dos fármacos , Reabsorção Óssea/patologia , Catequina/farmacologia , Morte Celular/efeitos dos fármacos , Teoria da Densidade Funcional , Regulação para Baixo/efeitos dos fármacos , Regulação para Baixo/genética , Liberação Controlada de Fármacos , Estabilidade de Medicamentos , Ligantes , Lipopolissacarídeos/farmacologia , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Masculino , Nanopartículas Metálicas/ultraestrutura , Camundongos Endogâmicos BALB C , Modelos Biológicos , Ligante RANK/farmacologia , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais/efeitos dos fármacos , Crânio/patologia , Transcrição Genética/efeitos dos fármacos
9.
Inorg Chem ; 58(17): 11649-11655, 2019 Sep 03.
Artigo em Inglês | MEDLINE | ID: mdl-31436093

RESUMO

A new mixed-valent dicopper complex [5] was generated from ligand exchange by dissolving a bis(CH3CN) precursor [3] in acetone. Introduction of a water molecule in place of an acetonitrile ligand was evidenced by base titration and the presence of a remaining coordinated CH3CN by IR, 19F NMR, and theoretical methods. The proposed structure (CH3CN-Cu-(SR)-Cu-OH2) was successfully DFT-optimized and the calculated parameters are in agreement with the experimental data. [5] has a unique temperature-dependence EPR behavior, with a localized valence from 10 to 120 K that undergoes delocalized at room temperature. The electrochemical signatures are in the line of the other aquo parent [2] and sensibly different from the rest of the series. Similar to the case of [2], [5] was finally capable of single turnover N2O reduction at room temperature. N2 was detected by GC-MS, and the redox character was confirmed by EPR and ESI-MS. Kinetic data indicate a reaction rate order close to 1 and a rate 10 times faster compared to [2]. [5] is thus the second example of that kind and highlights not only the main role of the Cu-OH2 motif, but also that the adjacent Cu-X partner (X = OTf- in [2] and CH3CN in [5]) is a new actor in the casting to establish structure/activity correlations.


Assuntos
Cobre/farmacologia , Inibidores Enzimáticos/farmacologia , Compostos Organometálicos/farmacologia , Oxirredutases/antagonistas & inibidores , Peptídeos/farmacologia , Cobre/química , Teoria da Densidade Funcional , Técnicas Eletroquímicas , Inibidores Enzimáticos/química , Estrutura Molecular , Compostos Organometálicos/química , Oxirredutases/metabolismo , Peptídeos/química
10.
J Chem Theory Comput ; 15(9): 5046-5057, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31390517

RESUMO

Halogenated BODIPY derivatives are emerging as important candidates for photodynamic therapy of cancer cells due to their high triplet quantum yield. We probed fundamental photophysical properties and interactions with biological environments of such photosensitizers. To this end, we employed static TD-DFT quantum chemical calculations as well as TD-DFT surface hopping molecular dynamics on potential energy surfaces resulting from the eigenstates of the total electronic Hamiltonian including the spin-orbit (SO) coupling. Matrix elements of an effective one-electron spin-orbit Hamiltonian between singlet and triplet configuration interaction singles (CIS) auxiliary wave functions are calculated using a new code capable of dealing with singlets and both restricted and unrestricted triplets built up from up to three different and independent sets of (singlet, alpha, and beta) molecular orbitals. The interaction with a biological environment was addressed by using classical molecular dynamics (MD) in a scheme that implicitly accounts for electronically excited states. For the surface hopping trajectories, an accelerated MD approach was used, in which the SO couplings are scaled up, to make the calculations computationally feasible, and the lifetimes are extrapolated back to unscaled SO couplings. The lifetime of the first excited singlet state estimated by semiclassical surface hopping simulations is 139 ± 75 ps. Classical MD demonstrates that halogenated BODIPY in the ground state, in contrast to the unsubstituted one, is stable in the headgroup region of minimalistic cell membrane models, and while in the triplet state, the molecule relocates to the membrane interior ready for further steps of photodynamic therapy.


Assuntos
Compostos de Boro/química , Simulação de Dinâmica Molecular , Fotoquimioterapia , Teoria da Densidade Funcional , Processos Fotoquímicos , Fármacos Fotossensibilizantes/química , Teoria Quântica , Propriedades de Superfície
11.
J Phys Chem Lett ; 10(19): 5861-5867, 2019 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-31464127

RESUMO

Circularly polarized luminescence (CPL) reflects the excited-state properties of the chiral system. However, compared to the singlet and triplet excited states, there are still many unknowns about CPL from the double excited state. Here, using the self-assembly strategy of a dipeptide substituted naphthalenediimide (NDI-GE) and the photogenerated radical anions, we have explored the ground-state (CD) and excited-state (CPL) chiral characteristics of neutral NDI and NDI•- radical anion assemblies. The neutral gelator assemblies showed CPL with the dissymmetry factor glum on the order of 10-3; the radical anion exhibited an inversed CPL signal with a significantly enhanced glum of 10-1. Time-dependent density functional theory calculation revealed that upon formation of the radical anions, the direction of the dipole moment changed, thus leading to the inversion of CD and CPL. The present work reveals a new platform for developing CPL materials based on the doublet excited state.


Assuntos
Dipeptídeos/química , Imidas/química , Naftalenos/química , Ânions/química , Teoria da Densidade Funcional , Dimerização , Cinética , Luminescência , Modelos Químicos , Modelos Moleculares , Processos Fotoquímicos , Solventes/química
12.
Phys Chem Chem Phys ; 21(35): 19226-19233, 2019 Sep 11.
Artigo em Inglês | MEDLINE | ID: mdl-31441492

RESUMO

As one of the main air pollutants, nitrogen oxides (NOx) have serious effects on human health and the environment. In our previous study, we found that Mn-MOF-74 shows excellent catalytic performance for the selective catalytic reduction (SCR) reaction with NH3 being the reductant (NH3-SCR) at low temperature. To obtain a further understanding of the NH3-SCR mechanism in Mn-MOF-74, in this paper, we investigated two important parts of the NH3-SCR process in Mn-MOF-74 using the density functional theory (DFT) method. On the one hand, the structural characteristics of two types of oxygen vacancies of Mn-MOF-74, namely carboxyl oxygen vacancies and hydroxyl oxygen vacancies, and their adsorption properties to reaction species were calculated. It was found that the oxygen vacancies not only activate the reaction species, but also promote the desorption of NO2 molecules from metal sites for the subsequent rapid SCR reactions. On the other hand, we studied the effect of H2O on the structural stability and catalytic performance of Mn-MOF-74. It was found that the interaction of Mn-O bonds was weakened by H2O. Therefore, the influence of H2O should be considered for the future design of MOF-based catalysts for the SCR process.


Assuntos
Teoria da Densidade Funcional , Estruturas Metalorgânicas/química , Oxigênio/química , Água/química , Poluentes Atmosféricos/química , Poluentes Atmosféricos/isolamento & purificação , Catálise , Óxidos de Nitrogênio/química , Óxidos de Nitrogênio/isolamento & purificação , Substâncias Redutoras/química
13.
Chem Commun (Camb) ; 55(73): 10920-10923, 2019 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-31441463

RESUMO

The development of new NIR-II fluorophores, particularly those with facile syntheses, high fluorescence quantum yields, and stable and tunable photophysical properties, is challenging. Herein, we report a new class of small molecular NIR-II fluorophores based on aza-dipyrromethene boron difluoride (aza-BODIPY) dyes. We demonstrate promising photophysical properties of these dyes, such as large Stokes shift, superior photostability, and good fluorescence brightness as nanoparticles in aqueous solution. Because of these properties and high resolution and deep penetration NIR-II imaging ability, the aza-BODIPY based dyes show great potential as NIR-II imaging agents.


Assuntos
Compostos de Boro/química , Corantes Fluorescentes/química , Imagem Óptica/métodos , Pirróis/química , Animais , Compostos de Boro/síntese química , Compostos de Boro/efeitos da radiação , Compostos de Boro/toxicidade , Linhagem Celular Tumoral , Teoria da Densidade Funcional , Desenho de Drogas , Fluorescência , Corantes Fluorescentes/síntese química , Corantes Fluorescentes/efeitos da radiação , Corantes Fluorescentes/toxicidade , Raios Infravermelhos , Camundongos , Modelos Químicos , Nanopartículas/química , Poloxâmero/química , Pirróis/síntese química , Pirróis/efeitos da radiação , Pirróis/toxicidade
14.
Phys Chem Chem Phys ; 21(31): 17142-17151, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31339149

RESUMO

In this work we compute high-coverage hydrogen adsorption energies and geometries on the stepped platinum surfaces Pt(211) and Pt(533) which contain a (100)-step type and the Pt(221) and Pt(553) surface with a (111) step edge. We discuss these results in relation to ultra-high-vacuum temperature programmed desorption (TPD) data to elucidate the origin of the desorption features. Our results indicated that on surfaces with a (100)-step type, two distinct ranges of adsorption energy for the step and terrace are observed, which mirrors the TPD spectra for which we find a clear separation of the desorption peaks. For the (111) step type, the TPD spectra show much less separation of the step and terrace features, which we assign to the low individual adsorption energies for H atoms on this step edge. From our results we obtain a much clearer understanding of the surface-hydrogen bonding at high coverages and the origin of the different TPD features present for the two step types studied.


Assuntos
Teoria da Densidade Funcional , Hidrogênio/química , Platina/química , Adsorção , Cristalização , Ligações de Hidrogênio , Temperatura Ambiente , Termodinâmica
15.
Phytochemistry ; 166: 112075, 2019 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-31351332

RESUMO

Isoflavonoids are one of the most important groups of naturally occurring antioxidants. Their structural features are important for evaluating their antioxidative activity. In this work, density functional theory (DFT) methods were applied to investigate the influence of the C2=C3 double bond on the antioxidative activity of isoflavonoids based on three currently accepted radical scavenging mechanisms from the viewpoint of thermodynamics. The C2=C3 double bond can make the compounds more flat, which would extend the conjugated system in the molecule and make the isoflavonoids higher antioxidant activity. The C2=C3 double bond would not alter the strongest antioxidative hydroxyl group of the isoflavonoids. In the gas, benzene and CHCl3 phases, the C2=C3 double bond will enhance the antioxidative activity of isoflavonoids by lowering the bond dissociation enthalpies of the hydroxyl groups in the B ring that are the strongest antioxidative sites for the hydrogen atom transfer (HAT) mechanism. In polar phases, a similar result is obtained by weakening the proton affinity of 7-OH that is the strongest antioxidative hydroxyl group in the sequential proton loss electron transfer (SPLET), mechanism. Thus, the C2=C3 double bond will enhance the antioxidative activity of isoflavonoids irrespective of the studied phases.


Assuntos
Antioxidantes/química , Carbono/química , Teoria da Densidade Funcional , Flavonoides/química , Solventes/química , Termodinâmica
16.
J Phys Chem A ; 123(29): 6241-6250, 2019 Jul 25.
Artigo em Inglês | MEDLINE | ID: mdl-31268328

RESUMO

The association of Ca2+ to serine and the subsequent gas-phase unimolecular reactivity of the [Ca(Ser)]2+ (Ser = Serine) adduct was investigated throughout the use of tandem mass spectrometry techniques and B3LYP/6-311+G(3df,2p)//B3LYP/6-311+G(d,p) density functional theory calculations. In a first step, the structure and relative stability of all possible conformers of serine were obtained and analyzed, as well as the most stable [serine-Ca]2+ adducts. For the analysis of the different potential energy surfaces associated with the gas-phase unimolecular reactivity of these adducts, only those that differ by less than 100 kJ·mol-1 from the global minimum were taken into account. In agreement with previous studies, the serine-Ca2+ global minimum corresponds to a charge-solvated structure in which Ca is tricoordinated to neutral serine. The major peaks observed in the nanoelectrospray-MS/MS spectrum of [Ca(Ser)]2+ adduct correspond to both Coulomb explosions, yielding either CaOH+ + [C3,H6,N,O2]+ or [C2,H4,O,N]+ + [Ca(C,H3,O2)]+, and to the loss of neutrals, namely, CH2O and H2O. Our theoretical survey of the energy profile allow us to conclude that, although all the aforementioned fragmentation processes can have their origin at the global minimum, similar fragmentations involving low-lying conformers, both zwitterionic and nonzwitterionic, compete and should be considered to account for the observed reactivity. We have also found that in some specific cases post-transition state dynamics similar to the ones described before in the literature for formamide-Ca2+ reactions, may also play a role.


Assuntos
Cálcio/química , Complexos de Coordenação/química , Gases/química , Serina/química , Teoria da Densidade Funcional , Espectrometria de Massas , Modelos Químicos , Conformação Molecular , Termodinâmica
17.
Phys Chem Chem Phys ; 21(30): 16515-16525, 2019 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-31298238

RESUMO

Isoniazid (INH) is converted into isonicotinyl radical through its interaction with the catalase-peroxidase (katG) enzyme present in the cells of Mycobacterium tuberculosis (M. tb.), the bacteria that causes the tuberculosis disease. This process is important because resistance of M. tb. cells to INH treatment has been associated with the failure of completion of this process. However, this process is poorly understood and there are a variety of conflicting theories about the details of the mechanism of this process. One theory suggests that INH binds to katG and transfers a single electron to the heme while the heme is in its two electron oxidized state, compound I [Fe(iv)Por˙+] (CpdI). In this study, DFT calculations at the UB3LYP/6-31g(d)-LANL2DZ level of theory are used to study the M. tb. katG CpdI molecule. Different models of the M. tb. CpdI molecule were prepared and the calculations revealed the impact of Trp321 on the electronic properties of the heme. Without Trp321 the heme assumed a triradical state with single electrons on the πxy and πyz orbitals of Fe and another on the a2u orbital of the porphyrin ring that can either be coupled with the first two, to assume a quartet state, or decoupled to form a doublet state. With Trp321, however, a transfer of an electron from the πTrp orbital to a2u porphyrin orbital leads to loss of radical character of the porphyrin and leaves the Trp321 group with a radical character. INH was observed to have strong interaction with CpdI and the absence of Trp321 significantly decreased the binding energy by 2 kcal mol-1 explaining the importance of Trp321 in the binding of INH. The results in this study show the importance of Trp321 in the binding of INH and its effect on its electronic properties, which is consistent with previous experimental findings that mutation of Trp321 results in an increase in drug resistance.


Assuntos
Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Catalase/química , Catalase/metabolismo , Teoria da Densidade Funcional , Isoniazida/metabolismo , Antituberculosos/metabolismo
18.
J Photochem Photobiol B ; 197: 111555, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31326844

RESUMO

A series of heterocyclic donor-acceptor systems were synthesized and well characterized by using 1H, 13C NMR, FT-IR, and elemental analysis. They were designed to investigate the effect of thiophene and cyanoacrylic acid number units on the thermal, optical, electrochemical and finally photovoltaic properties of dye-sensitized solar cells prepared with the selected compounds. The effect of chemical structure on their properties was demonstrated. They showed the beginning of thermal decomposition between 230 and 270 °C. The compounds absorbed the radiation in the range of 300-500 nm or 200-400 nm. They were electrochemically active and varied in energy band gap from 3.40 to 1.58 eV. Additionally, their optimized geometry, HOMO-LUMO levels, ionization potential, and electron affinity were evaluated using density functional theory. The photovoltaic devices based on TiO2 sensitized with the obtained molecules exhibited low power conversion efficiency, which was the highest for the device containing the symmetrical molecule with bithiophene structure. Under co-sensitization, the cell made of the same compound gave significant enhancement of efficiency of 6.3% being higher to that of the individual device prepared from dye N719 (5.75%). Moreover, the effects of immersion time of TiO2 electrode in the dye solution and co-sensitization methods were tested. The surface morphology of photoanode was investigated using atomic force microscopy.


Assuntos
Corantes/química , Cianoacrilatos/química , Energia Solar , Cianoacrilatos/síntese química , Teoria da Densidade Funcional , Fontes de Energia Elétrica , Microscopia de Força Atômica , Oxirredução , Titânio/química
19.
Analyst ; 144(16): 4908-4916, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31312834

RESUMO

A new benzothiazole azo dye [(E)-1-((6-methoxybenzo[d]thiazole-2-yl)diazenyl)naphthalene-2,6-diol] (also known as "BAN"), has been synthesised and used as a chemosensor for the rapid and selective detection of mercury(ii) ions in water. The pink coloured chemosensor turns blue when reacted with mercury(ii) ions due to the formation of a 2 : 1 coordination complex. The complex formation causes a bathochromic shift of the chemosensor's UV absorption peak from 540 to 585 nm and turns on a highly selective fluorescence emission at 425 nm. The change in the optical property of BAN upon complexation with mercury(ii) was confirmed by ab initio calculations. The new chemosensor was used to quantify mercury(ii) ions in water by fluorescence spectroscopy down to 5 × 10-8 M (10 ppb). The limit of detection (LOD) of Hg2+ was 9.45 nM (1.8 ppb) which satisfies the maximum allowable Hg2+ concentration in drinking water that is set by the WHO. The BAN-Hg(ii) complex was used for the determination of cysteine (Cys) in aqueous solution by UV-Vis spectroscopy down to 1 × 10-7 M. The thiol-containing amino acid preferentially coordinates the mercury ions of the BAN-Hg(ii) complex. This causes dissociation of the blue-coloured complex and the liberation of the pink-coloured BAN dye. The colour change of the BAN-Hg(ii) complex from blue to pink was selective to the Cys biothiol while other non-thiol containing amino acids did not cause a colour change. For the in-field application, filter paper strips were loaded with the BAN-Hg(ii) complex and used as a disposable sensor for the detection of cysteine (Cys) by the naked eye. Therefore, the BAN chemosensor offers a sensitive, and rapid tool for the detection of mercury(ii) in water. In addition, the BAN-Hg(ii) complex can be used as a simple and selective chemosensor of the screening of purified biothiols, such cysetine, homocysteine and glutathione in biology research and pharmaceutical/food industries.


Assuntos
Benzotiazóis/síntese química , Corantes Fluorescentes/síntese química , Mercúrio/análise , Compostos de Sulfidrila/análise , Poluentes Químicos da Água/análise , Cátions Bivalentes , Cor , Simulação por Computador , Complexos de Coordenação/química , Cisteína/análise , Teoria da Densidade Funcional , Glutationa/análise , Concentração de Íons de Hidrogênio , Ligantes , Limite de Detecção , Espectrometria de Fluorescência
20.
Photochem Photobiol Sci ; 18(8): 1972-1981, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31259994

RESUMO

Betalains are natural plant pigments found in certain plants belonging to the order Caryophyllales. This work presents theoretical calculations on the excited state properties of three betalains: betanin, an almost non-fluorescent natural betacyanin; indicaxanthin, a weakly fluorescent natural betaxanthin; and cBeet120, a synthetic betaxanthin fluorescence probe that is also weakly fluorescent. Calculations at the algebraic diagrammatic construction (ADC (2)) level of theory, combined with the conductor-like screening model (COSMO) to simulate solvent effects, predict absorption spectra in good agreement with experiment for all three of these betalains. Several distinct theoretical approaches identify torsions of the molecular geometry that can lead to conical intersections between the excited singlet (S1) and ground state (S0) potential surfaces and identify probable geometries at the minimum on the crossing seam (MXS). The present results thus emphasize the central role played by torsional modes in determining the fluorescence properties of natural betalains and of most synthetic betalain analogs as well. A direct implication of the results is that the fluorescence quantum yields of natural or synthetic betalains can potentially be enhanced by introducing structural modifications that permit the molecule to avoid these MXS geometries and/or by incorporation into a more rigid environment that hinders the specific bond rotations involved in the non-radiative relaxation of the excited state.


Assuntos
Betalaínas/química , Fluorescência , Corantes Fluorescentes/química , Betalaínas/síntese química , Caryophyllales/química , Teoria da Densidade Funcional , Corantes Fluorescentes/síntese química , Conformação Molecular
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