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1.
Inorg Chem ; 58(16): 10611-10615, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31380629

RESUMO

Luminescent lanthanides provide a promising alternative to organic chromophores for cellular bioimaging and bioassay applications; efficacy is closely governed by their respective quantum yields. Conventionally utilized quantum-yield measurements for lanthanides are laborious and not amenable to rapid relative comparison of compound performance. Here, we introduce a high-throughput optical imaging method to determine and directly compare relative quantum yield using Cherenkov-radiation-mediated excitation of luminescent lanthanide complexes.


Assuntos
Complexos de Coordenação/química , Ensaios de Triagem em Larga Escala , Elementos da Série dos Lantanídeos/química , Teoria Quântica , Luminescência , Conformação Molecular
2.
J Phys Chem Lett ; 10(16): 4720-4724, 2019 Aug 15.
Artigo em Inglês | MEDLINE | ID: mdl-31369281

RESUMO

Probing the atomic details of intrinsically disordered proteins is crucial to understanding their biological function and relation to pathogenesis. Although amide-detected NMR experiments are widely employed in protein studies, 3JHNHα couplings between amide (1HN) and alpha (1Hα) protons impose an intrinsic limit on the achievable 1HN linewidth. Here, we present a homonuclear decoupling method that narrows the α-synuclein 1HN linewidths to 3-5 Hz. Tightly distributed 1JCαHα coupling values were employed to generate homogeneous antiphase coherences of 2HαzHNy and 4Hα(2)zHα(3)zHNy for nonglycine and glycine residues, respectively, which were combined with their in-phase HNy counterparts to achieve homonuclear decoupling. By reducing the multiplet structure to a singlet, the width of the 1HN cross-peak was reduced by ∼3-fold in the 2D HSQC and 3D intra-HNCA spectra, and good spectral quality was achieved without the need for postprocessing.


Assuntos
Ressonância Magnética Nuclear Biomolecular , alfa-Sinucleína/química , Amidas/química , Glicina/química , Prótons , Teoria Quântica , Soluções/química
3.
J Chem Phys ; 151(4): 041101, 2019 Jul 28.
Artigo em Inglês | MEDLINE | ID: mdl-31370538

RESUMO

We chemically characterize the symmetries underlying the exact solutions of a stochastic negatively self-regulating gene. The breaking of symmetry at a low molecular number causes three effects. Two branches of the solution exist, having high and low switching rates, such that the low switching rate branch approaches deterministic behavior and the high switching rate branch exhibits sub-Fano behavior. The average protein number differs from the deterministically expected value. Bimodal probability distributions appear as the protein number becomes a readout of the ON/OFF state of the gene.


Assuntos
Proteínas/genética , Cinética , Teoria Quântica , Soluções , Processos Estocásticos
4.
J Chem Theory Comput ; 15(8): 4344-4350, 2019 Aug 13.
Artigo em Inglês | MEDLINE | ID: mdl-31318548

RESUMO

Uracil DNA glycosylase catalyzes the N-glycosidic bond cleavage of uracil, thereby initiating the base excision repair mechanism for this DNA lesion. Here we employ hybrid quantum mechanics/molecular mechanics calculations to investigate the exact mechanism of the nucleophile attack and the role of the conserved His148 residue. Our calculations suggest that the C1'-N1 bond dissociation proceeds by a migration of the electrophilic sugar in the direction of the water nucleophile, resulting in a planar, oxocarbenium-like transition state. The subsequent nucleophile addition and proton transfer to a nearby base occur without a barrier. We assign the role of a proton acceptor to His148 and elucidate why mutations of this residue curtail the enzymatic activity but do not fully suppress it.


Assuntos
Histidina/química , Uracila-DNA Glicosidase/química , Ácido Aspártico/química , Ácido Aspártico/metabolismo , Histidina/metabolismo , Humanos , Modelos Moleculares , Prótons , Teoria Quântica , Termodinâmica , Uracila-DNA Glicosidase/metabolismo , Água/química
5.
Molecules ; 24(13)2019 Jul 08.
Artigo em Inglês | MEDLINE | ID: mdl-31288375

RESUMO

Ureido-N-iso-propyl,N'-4-(3-pyridin-2-one)pyrimidine (1) and its 2-methoxy pyridine derivative (1Me) has been designed and prepared. The conformational equilibrium in urea moiety and tautomerism in the pyrimidine part have been investigated by variable temperature and 1H NMR titrations as well as DFT quantum chemical calculations. The studied compounds readily associate by triple hydrogen bonding with 2-aminonaphthyridine (A) and/or 2,6-bis(acetylamino)pyridine (B). In 1, the proton is forced to 1,3-tautomeric shift upon stimuli and keeps it position, even when one of the partners in the complex was replaced by another molecule. The observed tautomerism controlled by conformational state (kinetic trapping effect) opens new possibilities in molecular sensing that are based on the fact that reverse reaction is not preferred.


Assuntos
Pirimidinas/síntese química , Ureia/análogos & derivados , Ureia/síntese química , Catálise , Ligações de Hidrogênio , Isomerismo , Cinética , Conformação Molecular , Prótons , Teoria Quântica , Temperatura Ambiente , Termodinâmica
6.
Photochem Photobiol Sci ; 18(8): 2003-2011, 2019 Aug 01.
Artigo em Inglês | MEDLINE | ID: mdl-31268087

RESUMO

Here we report the activatable photosensitizer BromoAcroB, a brominated BODIPY dye incorporating a reactive acrolein warhead. The acrolein moiety serves as an intramolecular switch, deactivating the BODIPY dye in its singlet and triplet excited states via internal conversion. Thiolate addition to this moiety disables the intramolecular quenching mechanism restoring the photosensitizing properties of the parent dye, characterized by a quantum yield of singlet oxygen photosensitization of 0.69 ± 0.02. In cell cultures, and upon thiol adduct formation, BromoAcroB induced light-dependent cell death in MRC-5 and HeLa cell lines. Using fluorescence microscopy and upon measuring the low yet non-negligible emission of the activated compound, we show that the phototoxicity of the dormant photosensitizer correlated with the quantity of BromoAcroB adducts generated. BromoAcroB thus serves as a dormant photosensitizer sensitive to intracellular electrophile response. Our results highlight the effective control of a triplet state process by modulation of an unsaturated moiety on the BODIPY scaffold and underscore the mechanistic opportunities arising for controlled singlet oxygen production in cells specifically sensitive to electrophile stress.


Assuntos
Acroleína/farmacologia , Compostos de Boro/farmacologia , Corantes/farmacologia , Cisteína/farmacologia , Fármacos Fotossensibilizantes/farmacologia , Oxigênio Singlete/farmacologia , Acroleína/química , Compostos de Boro/química , Morte Celular/efeitos dos fármacos , Corantes/síntese química , Corantes/química , Cisteína/química , Células HeLa , Humanos , Luz , Microscopia de Fluorescência , Estrutura Molecular , Fármacos Fotossensibilizantes/síntese química , Fármacos Fotossensibilizantes/química , Teoria Quântica , Oxigênio Singlete/química
7.
Inorg Chem ; 58(16): 11091-11099, 2019 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-31353893

RESUMO

Several bacterial species have evolutionary developed protein systems specialized in the control of intracellular gold ion concentration. In order to prevent the detrimental consequences that may be induced even at very low concentrations, bacteria such as Salmonella enterica and Cupriavidus metallidurans utilize Au-specific merR-type transcriptional regulators that detect these toxic ions and control the expression of specific resistance factors. Among these highly specialized proteins, golB has been investigated in depth, and X-ray structures of both apo and Au(I)-bound golB have been recently reported. Here, the binding of Au(I) at golB was investigated by means of multilevel computational approaches. Molecular dynamics simulations evidenced how conformations amenable for the Au(I) chelation through the Cys-XX-Cys motif on helix 1 are extensively sampled in the phase space of apo-golB. Hybrid QM/MM calculations on metal-bound structures of golB also allowed to characterize the most probable protonation state for gold binding motif and to assess the structural features mostly influencing the Au(I) coordination in this protein. Consistently with experimental evidence, we found that golB may control its Au(I) affinity by conformational changes that affect the distance between Cys10 and Cys13, thus being able to switch between the Au(I) sequestration/release-prone states in response to external stimuli. The protein structure enveloping the metal binding motif favors the thiol-thiolate protonation state of Au(I)-golB, thus probably enhancing the binding selectivity for Au(I) compared to other cations.


Assuntos
Proteínas de Bactérias/química , Ouro/química , Metaloproteínas/química , Simulação de Dinâmica Molecular , Teoria Quântica , Cupriavidus/química , Salmonella enterica/química
8.
J Photochem Photobiol B ; 197: 111551, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31306954

RESUMO

Heavy metal pollution as one of the most serious pollution problems of marine environment, seriously threatens the safety of marine organism and human health, and will lead to potential risks for the marine ecological environment. In order to develop a rapid and sensitive toxicity detection method for marine heavy metals, in this study, marine diatom Nitzschia closterium was used as the test organism, and the effects of different concentrations of lead (Pb) on the five chlorophyll fluorescence parameters of N. closterium including the maximum photochemical quantum yield of PSII (Fv/Fm), the effective quantum yield of PSII photochemical energy conversion (ΦPSII), the effective absorption cross section of PSII photochemistry (σPSII'), the relative electron transfer rate of PSII (rP), and the PSII electron flux per unit volume (JVPII) at different exposure times were investigated based on chlorophyll fluorescence technology. By comparing with the photosynthetic activity fluorescence parameter Fv/Fm which is commonly used for toxicity analysis of pollutants using algae as test organisms, the optimal chlorophyll fluorescence parameter that could rapidly and sensitively determine Pb toxicity to N. closterium was selected. The results indicate that all the five chlorophyll fluorescence parameters of Fv/Fm, ΦPSII, σPSII', rP and JVPII showed good dose-response relationships with Pb within 8 h exposure time, and they all could be used as endpoints to rapidly determine Pb toxicity to N. closterium. Among the five chlorophyll fluorescence parameters, JVPII was the most sensitive fluorescence parameter for detecting the toxicity of Pb to N. closterium within 6 h exposure. And for JVPII, the median effective concentration (EC50) values of Pb at 2, 4 and 6 h were 0.329, 0.068 and 0.040 mmol L-1, respectively. However, when the exposure time was 8 h, ΦPSII was the most sensitive fluorescence parameter for the toxicity detection of Pb, and the EC50 value of Pb at 8 h was 0.038 mmol L-1. This study will provide an important basis for the development of a rapid and sensitive detection method for the biological toxicity of marine heavy metals, and those results will be helpful for ecological risk assessment in marine environment.


Assuntos
Clorofila/química , Chumbo/toxicidade , Microalgas/efeitos dos fármacos , Microalgas/química , Microalgas/metabolismo , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/metabolismo , Teoria Quântica , Espectrometria de Fluorescência , Poluentes Químicos da Água/química , Poluentes Químicos da Água/toxicidade
9.
J Photochem Photobiol B ; 197: 111535, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31319267

RESUMO

Measurement of Pulse-Amplitude-Modulated (PAM) chlorophyll a fluorescence is widely used method for obtaining information on the functional state of photosystem II (PSII). Recently, it has been shown that some of long-established fluorescence parameters must be interpreted with caution, when the light-induced chloroplast movements occur. In our work we have analyzed the effect of chloroplast movements on these parameters. We have derived new parameters that are independent of the change in PSII absorption occurring during measurement. To verify whether there is a need for new parameters or the difference between the parameters commonly used and the newly derived ones is insignificant, we conducted an experiment with Arabidopsis thaliana wild type plants and its phot1 phot2 mutant defective in chloroplast movement. Plants were exposed to light of different qualities (450, 470, 550 or 660 nm) and quantities (100, 400 or 1200 µmol m-2 s-1) for up to 40 min. Since the blue light-induced chloroplast avoidance reaction is a photoprotective mechanism, we expected that phot1 phot2 mutant will compensate the lack of this mechanism by increasing non-photochemical quenching. However, using the light at both 450 and 470 nm, the calculation of commonly used parameter, ΦNPQ (quantum yield of regulated light-induced thermal energy dissipation in PSII) based on Hendrickson et al. [L. Hendrickson, R.T. Furbank, W.S. Chow, Photosynth. Res. 82 (2004) 73-81] showed the opposite. On the other hand, the results obtained using our newly proposed formulae to determine quantum yield of PSII thermal energy dissipation were in line with our assumption. Thus, the experimental data showed that some formulae of fluorescence parameters are dependent on the change in PSII absorption and need to be interpreted carefully. On the contrary, the formulae introduced by us can remove the effect of changes in PSII absorption that occur during measurement, without additional measurements, and give the real estimate of light-induced non-photochemical quenching.


Assuntos
Proteínas de Arabidopsis/metabolismo , Clorofila A/química , Complexo de Proteína do Fotossistema II/metabolismo , Arabidopsis/metabolismo , Proteínas de Arabidopsis/química , Proteínas de Arabidopsis/genética , Cloroplastos/fisiologia , Luz , Modelos Teóricos , Mutagênese , Complexo de Proteína do Fotossistema II/química , Complexo de Proteína do Fotossistema II/genética , Folhas de Planta/química , Teoria Quântica , Termodinâmica
10.
Phys Chem Chem Phys ; 21(30): 16751-16761, 2019 Aug 14.
Artigo em Inglês | MEDLINE | ID: mdl-31322638

RESUMO

In the context of the decisive role that vibronic interactions play in the functioning of molecular quantum cellular automata, in this article we give a comparative analysis of the two alternative vibronic approaches to the evaluation of the key functional characteristics of molecular cells. Semiclassical Born-Oppenheimer approximation and quantum mechanical evaluations of the vibronic energy pattern, electronic density distributions and cell-cell response function are performed for two-electron square-planar mixed valence molecular cells subjected to the action of a molecular driver. Special emphasis is put on the description of the cell-cell response function, which describes strong non-linearity as a prerequisite for the effective action of quantum cellular automata. Comparison of results obtained within the semiclassical and quantum-mechanical approaches has revealed a drastic difference between the shapes of the cell-cell response functions evaluated within these two approaches in the case of moderate vibronic coupling when the energy levels of the square cell interacting with a weakly polarized driver undergo large tunneling splitting in shallow adiabatic potential minima. In contrast, in the limits of strong vibronic coupling (a double-well adiabatic potential with deep minima) and weak vibronic coupling (a single well adiabatic potential) the adiabatic approximation is shown to describe the cell-cell response function with rather good accuracy.


Assuntos
Nanotecnologia/métodos , Teoria Quântica , Nanotecnologia/instrumentação , Vibração
11.
J Photochem Photobiol B ; 197: 111553, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31326845

RESUMO

This paper describes a novel symmetric N,N'-diethylsalicylaldehyde boranyl hydrazone (1) and its in situ-generated assemblies displaying opto-analytical capabilities for the diagnosis of nucleic acids under physiological conditions. The sensing capabilities of these unprecedented supramolecular assemblies were characterized using UV-Vis spectroscopy, fluorescence spectroscopy, 1D and 2D NMR spectroscopy, dynamic light scattering, and zeta potential measurements. Model compounds lacking boranyl units (2, 3) were prepared to correlate and evaluate the sensing mechanism. The rationally designed probe 1 displays unusual aggregation-induced emissive (AIE) properties, with an average particle size of 1096 nm exhibiting green emission upon excitation at 377 nm in pH-7.2 TRIZMA buffer. A selective switch on response toward organic PO43- accompanied through specific nano-aggregations patterns and sizes, thereby causing a significant red-shift through AIE. Exploiting such switch on in green channel behavior has allowed the monitoring of DNase I activities and polymerase chain reactions.


Assuntos
Hidrazonas/química , Ácidos Nucleicos/análise , Espectrometria de Fluorescência , Boranos/química , Desoxirribonucleases/metabolismo , Cloreto de Magnésio/química , Espectroscopia de Ressonância Magnética , Ácidos Nucleicos/metabolismo , Tamanho da Partícula , Teoria Quântica
12.
J Chem Phys ; 151(1): 014104, 2019 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-31272170

RESUMO

Many important open quantum systems, such as light harvesting systems irradiated with natural incoherent light, present challenging computational problems. Specifically, such systems are characterized by multiple time scales over many orders of magnitude. We describe and apply an efficient approach to determine rates and dynamics in such systems. As an example, we present a theoretical and computational analysis of retinal isomerization under incoherent solar excitation using a minimal retinal model. Solar- and bath-induced Fano coherences are shown to have a small but non-negligible effect on the reaction dynamics, and the effect of Fano coherences on the reaction rate is shown to depend strongly upon the form and strength of the system-bath coupling. Using the isomerization probability to obtain the time-dependent cellular hyperpolarization, we show that the effect of coherence on hyperpolarization dynamics is small compared to the effect of natural variations in the solar intensity.


Assuntos
Luz , Teoria Quântica , Retina/fisiologia , Isomerismo , Cinética , Processos Fotoquímicos
13.
Inorg Chem ; 58(15): 9672-9690, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31282663

RESUMO

We have studied the geometry and electronic structure of the P-cluster in nitrogenase in four oxidation states: PN, P1+, P2+, and P3+. We have employed combined quantum mechanical and molecular mechanical (QM/MM) calculations, using two different density-functional theory methods, TPSS and B3LYP. The calculations confirm that the side chain of Ser-188 is most likely deprotonated in the partly oxidized P1+ state, thereby forming a bond to Fe6. Likewise, the backbone amide group of Cys-88 is deprotonated in the doubly oxidized P2+ state, forming a bond to Fe5. The calculations also confirm the two conformations of the P-cluster in the atomic-resolution crystal structure of the enzyme, representing the PN and P2+ states, but show that the finer differences between the two structures are not fully reflected in the crystal structure, because the coordinates of only two atoms differ between the two conformations. However, the recent crystal structure of the P1+ state seems to be of lower quality with many dubious Fe-Fe and Fe-S distances. Quantum refinement of this structure indicates that it is a mixture of the P1+ and P2+ states but confirms that the side chain of Ser-188 is most likely deprotonated in both states. TPSS gives structures that are appreciably closer to the crystal structures than does B3LYP. In addition, we have studied all 16-48 possible broken-symmetry states of the four oxidation states of the P-cluster with DFT in the one or two observed spin states. For the reduced PN state, we can settle the most likely state from the calculated energies and geometries. However, for the more oxidized states there are large differences in the predictions obtained with the two DFT methods.


Assuntos
Nitrogenase/química , Teoria Quântica , Elétrons , Modelos Moleculares , Nitrogenase/metabolismo , Oxirredução , Conformação Proteica
14.
Chem Commun (Camb) ; 55(59): 8556-8559, 2019 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-31271173

RESUMO

Non-hydrated organic solutions of a diphenylalanine amphiphile blocked at the C-terminus with a fluorenylmethyl ester and stabilized at the N-terminus with a trifluoroacetate have been used to prepare amyloid fibrils. The solvent used to prepare the stock solution together with the co-solvent added enables regulation of the characteristics of the fibrils, which is important for their use in technological applications.


Assuntos
Amiloide/síntese química , Proteínas Amiloidogênicas/química , Dipeptídeos/química , Tensoativos/química , Teoria da Densidade Funcional , Dimetilformamida/química , Metanol/química , Propanóis/química , Conformação Proteica em Folha beta , Multimerização Proteica , Teoria Quântica
15.
Nature ; 571(7763): 17-18, 2019 07.
Artigo em Inglês | MEDLINE | ID: mdl-31270491
16.
Phys Chem Chem Phys ; 21(28): 15487-15503, 2019 Jul 17.
Artigo em Inglês | MEDLINE | ID: mdl-31259332

RESUMO

In this paper we show a theoretical rational design approach on a series of intrinsically fluorescent analogues of cholesterol (FLACs), called polyene-sterols (P-sterols), followed by a step-by-step selection of potential candidates, employing, sequentially, state-of-the-art quantum mechanical (QM) computations of the optical properties (single- and multiphoton absorption electronic spectroscopies and emission), molecular dynamics (MD) simulations in model membranes, and multiscale approaches (polarizable embedding). This selection converged to a promising candidate that shows simultaneously interesting single- and multiphoton absorption properties as well as emitting properties and good abilities to mimic cholesterol order effects in model membranes.


Assuntos
Colesterol/análogos & derivados , Simulação de Dinâmica Molecular , Esteróis/química , Fluorescência , Membranas Artificiais , Teoria Quântica
17.
J Phys Chem A ; 123(28): 5995-6002, 2019 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-31268326

RESUMO

High-resolution X-ray crystallography and two-dimensional NMR studies demonstrate that water-mediated conventional hydrogen-bonding interactions (N-H···N, O-H···N, etc.) bridging two or more amino acid residues contribute to the stability of proteins and protein-ligand complexes. In this work, we have investigated single water-mediated selenium hydrogen-bonding interactions (unconventional hydrogen-bonding) between amino acid residues in proteins through extensive protein data bank (PDB) analysis coupled with gas-phase spectroscopy and quantum chemical calculation of a model complex consisting of indole, dimethyl selenide, and water. Here, indole and dimethyl selenide represent the amino acid residues tryptophan and selenomethionine, respectively. The current investigation demonstrates that the most stable structure of the model complex observed in the IR spectroscopy mimics single water-mediated selenium hydrogen-bonded structural motifs present in the crystal structures of proteins. The present work establishes that water-mediated Se hydrogen-bonding interactions are ubiquitous in proteins and the number of these interactions observed in the PDB is more than that of direct Se hydrogen-bonds present there.


Assuntos
Proteínas/química , Selênio/química , Água/química , Biologia Computacional , Cristalografia por Raios X , Bases de Dados de Proteínas , Ligações de Hidrogênio , Indóis/química , Ligantes , Modelos Moleculares , Compostos Organosselênicos/química , Teoria Quântica , Selenometionina/química , Espectrofotometria Infravermelho , Triptofano/química
18.
Chem Pharm Bull (Tokyo) ; 67(7): 717-720, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31257327

RESUMO

This study demonstrates the relation between the redox properties and cytotoxicity of anthraquinone derivatives with a hydroxyl and methoxy group. The redox behavior of the anthraquinone derivatives was initially observed via cyclic voltammetry and their characteristics were investigated using molecular orbital calculations. The cytotoxicity of the anthraquinone derivatives was then evaluated using human leukemia HL-60 and H2O2 resistant HP100 cells, and its correlation with the redox properties of these compounds was investigated. Therefore, it was suggested that the anthraquinone derivatives express cytotoxicity through H2O2 production, and that generation of the oxidized radical form influences their cytotoxicity.


Assuntos
Antraciclinas/química , Antraquinonas/química , Antineoplásicos/química , Antraciclinas/farmacologia , Antraquinonas/farmacologia , Antineoplásicos/farmacologia , Sobrevivência Celular/efeitos dos fármacos , Técnicas Eletroquímicas , Células HL-60 , Humanos , Peróxido de Hidrogênio/metabolismo , Oxirredução , Teoria Quântica
19.
J Photochem Photobiol B ; 197: 111543, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31279896

RESUMO

Taking into account the ultrastructure of the Pied Flycatcher foveal retina reported earlier and the earlier reported properties of Müller cell (MC) intermediate filaments (IFs) isolated from vertebrate retina, we proposed a quantum mechanism (QM) of light energy transfer from the inner limiting membrane level to visual pigments in the photoreceptor cells. This mechanism involves electronic excitation energy transfer in a donor-acceptor system, with the IFs excited by photons acting as energy donors, and visual pigments in the photoreceptor cells acting as energy acceptors. It was shown earlier that IFs with diameter 10 nm and length 117 µm isolated from vertebrate eye retina demonstrate properties of light energy guide, where exciton propagates along such IFs from MC endfeet area to photoreceptor cell area. The energy is mostly transferred via the contact exchange quantum mechanism. Our estimates demonstrate that energy transfer efficiencies in such systems may exceed 80-90%. Thus, the presently developed quantum mechanism of light energy transfer in the inverted retina complements the generally accepted classic optical mechanism and the mechanism whereby Müller cells transmit light like optical fibers. The proposed QM of light energy transfer in the inverted retina explains the high image contrast achieved in photopic conditions by an avian eye, being probably also active in other vertebrates.


Assuntos
Luz , Teoria Quântica , Retina/metabolismo , Animais , Aves , Transferência de Energia , Células Ependimogliais/metabolismo , Filamentos Intermediários/química , Células Fotorreceptoras/metabolismo , Retina/efeitos da radiação , Retinaldeído/química
20.
Phys Chem Chem Phys ; 21(31): 17118-17125, 2019 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-31339118

RESUMO

The electronic structural origin of the THz and IR spectral changes occurring upon halogen-bond formation is examined by employing the technique of electron density analysis. Theoretical calculations and analyses are conducted for the complexes of pentafluoroiodobenzene (C6F5I) and nitryl chloride (O2NCl) formed with other (halogen-bond accepting) molecules taken as typical examples. It is shown that, in the case of the C-I stretching mode of C6F5I appearing in the THz spectral region, the intensity enhancement occurring upon halogen-bond formation arises from the intermolecular charge flux and (together with the vibrational frequency) is correlated to the partial charge-transfer and covalent nature of the halogen bond. For the N-Cl stretching vibration of O2NCl, it is shown that the high-frequency shift occurring upon complex formation with NH3 arises mainly from the electrostatic effect, while the reduction of its IR intensity arises from the polarization effect and, to a larger extent, from the intermolecular charge flux. These results indicate, therefore, that there are some observable spectroscopic properties in the THz and IR region that are mainly controlled by (and, hence, shed light on) the partial charge-transfer and covalent nature of halogen bonding.


Assuntos
Halogênios/química , Modelos Moleculares , Derivados de Benzeno/química , Hidrocarbonetos Halogenados/química , Nitritos/química , Teoria Quântica , Espectrofotometria Infravermelho , Eletricidade Estática
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