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1.
Phys Chem Chem Phys ; 2020 Mar 26.
Artigo em Inglês | MEDLINE | ID: mdl-32215414

RESUMO

Photoelectron circular dichroism (PECD) is a highly sensitive enantiospecific spectroscopy for studying chiral molecules in the gas phase using either single-photon ionization or multiphoton ionization. In the short pulse limit investigated with femtosecond lasers, resonance-enhanced multiphoton ionization (REMPI) is rather instantaneous and typically occurs simultaneously via more than one vibrational or electronic intermediate state due to limited frequency resolution. In contrast, vibrational resolution in the REMPI spectrum can be achieved using nanosecond lasers. In this work, we follow the high-resolution approach using a tunable narrow-band nanosecond laser to measure REMPI-PECD through distinct vibrational levels in the intermediate 3s and 3p Rydberg states of fenchone. We observe the PECD to be essentially independent of the vibrational level. This behaviour of the chiral sensitivity may pave the way for enantiomer specific molecular identification in multi-component mixtures: one can specifically excite a sharp, vibrationally resolved transition of a distinct molecule to distinguish different chiral species in mixtures.

2.
J Chem Phys ; 152(4): 044101, 2020 Jan 31.
Artigo em Inglês | MEDLINE | ID: mdl-32007068

RESUMO

A generally applicable approach for the calculation of relativistic properties described by one-electron operators within a two-component wave function approach is presented. The formalism is explicitly evaluated for the example of quasirelativistic wave functions obtained within the zeroth order regular approximation (ZORA). The wide applicability of the scheme is demonstrated for the calculation of parity (P) and time-reversal (T ) symmetry violating properties, which are important for searches of physics beyond the standard model of particle physics. The quality of the ZORA results is shown exemplarily for the molecules RaF and TlF by comparison with data from four-component calculations as far as available. Finally, the applicability of RaF in experiments that search for P,T-violation not only in the electronic but also in the quark sector is demonstrated.

3.
Science ; 365(6454): 679-684, 2019 08 16.
Artigo em Inglês | MEDLINE | ID: mdl-31346140

RESUMO

The high-temperature, all-inorganic CsPbI3 perovskite black phase is metastable relative to its yellow, nonperovskite phase at room temperature. Because only the black phase is optically active, this represents an impediment for the use of CsPbI3 in optoelectronic devices. We report the use of substrate clamping and biaxial strain to render black-phase CsPbI3 thin films stable at room temperature. We used synchrotron-based, grazing incidence, wide-angle x-ray scattering to track the introduction of crystal distortions and strain-driven texture formation within black CsPbI3 thin films when they were cooled after annealing at 330°C. The thermal stability of black CsPbI3 thin films is vastly improved by the strained interface, a response verified by ab initio thermodynamic modeling.

4.
Chemistry ; 25(22): 5793-5802, 2019 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-30740806

RESUMO

[Br3 ][SbF6 ] and [Br3 ][IrF6 ] were synthesized by interaction of BrF3 with Sb2 O3 or iridium metal, respectively. The former compound crystallizes in the orthorhombic space group Pbcn (No. 60) with a=11.9269(7), b=11.5370(7), c=12.0640(6) Å, V=1660.01(16) Å3 , Z=8 at 100 K. The latter compound crystallizes in the triclinic space group P 1 ‾ (No. 2) with a=5.4686(5), b=7.6861(8), c=9.9830(9) Å, α=85.320(8), ß=82.060(7), γ=78.466(7)°, V=406.56(7) Å3 , Z=2 at 100 K. Both compounds contain the cation [Br3 ]+ , which has a bent structure and is coordinated by octahedron-like anions [MF6 ]- (M=Sb, Ir). Experimentally obtained cell parameters, bond lengths, and angles are confirmed by solid-state DFT calculations, which differ from the experimental values by less than 2 %. Relativistic effects on the structure of the tribromonium(1+) cation are studied computationally and found to be small. For the heaviest analogues containing At and Ts, however, pronounced relativistic effects are found, which lead to a linear structure of the polyhalogen cation.

6.
Sci Rep ; 8(1): 10530, 2018 Jul 12.
Artigo em Inglês | MEDLINE | ID: mdl-30002480

RESUMO

The extended Hückel (eH) tight-binding method has historically been prized for its computational ease and intuitive chemical clarity. However, its lack of quantitative predictiveness has prevented the eH method from being used as a tool for rapidly screening materials for desired electronic properties. In this work, we demonstrate that when eH input parameters are calibrated using density functional theory (DFT) calculations of carefully chosen sets of simple crystals, the eH parameters retain most of their quantitative accuracy when transferred to more complex, structurally related phases. Using solar-energy-relevant semiconductors and insulators in the Sr-Ti-O family as a case study, we show that calibrated eH parameters can match the features of DFT band structures within about two tenths of an eV, at a tiny fraction of the computational cost of DFT.

7.
Chimia (Aarau) ; 72(6): 375-378, 2018 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-29941071

RESUMO

Atoms can be cooled and trapped efficiently with the help of lasers. So-called Doppler cooling takes advantage of momentum transfer upon absorption and emission of photons and of Doppler shifts to facilitate effectively closed optical absorption-emission loops, by which atoms are slowed down and cooled. Due to the wealth of internal degrees of freedom accessible in molecules, it was assumed for a long time that similarly closed optical loops cannot be realised for molecules. After an early theoretical proposal by Di Rosa for diatomic molecules, such cooling has been achieved in this decade for SrF, YO, CaF and YbF. It has been outlined recently that also polyatomic molecules should be coolable with lasers and classes of molecules expected to be amenable to this have been proposed by the present authors. Experimental success in laser cooling of SrOH has been reported. The status of cooling polyatomic molecules with lasers and the prospects for obtaining ultracold chiral molecules is reviewed herein.

8.
Chimia (Aarau) ; 72(6): 384-388, 2018 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-29941073

RESUMO

It is a particularly challenging task in stereochemistry to determine the absolute configuration of chiral molecules, i.e. to assign to a given sample the microscopic enantiomeric structure. In recent years, Coulomb Explosion Imaging (CEI) has been shown to yield directly the absolute configuration of small molecules in the gas phase. This contribution describes the experimental basics of this approach, highlights the most significant results and discusses limitations. A short discussion on extending Coulomb Explosion Imaging beyond analytic aspects to fundamental questions of molecular chirality concludes this review.

9.
Chemistry ; 24(35): 8708-8716, 2018 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-29427387

RESUMO

In the current decade, perovskite solar cell research has emerged as a remarkably active, promising, and rapidly developing field. Alongside breakthroughs in synthesis and device engineering, halide perovskite photovoltaic materials have been the subject of predictive and explanatory computational work. In this Minireview, we focus on a subset of this computation: density functional theory (DFT)-based work highlighting the ways in which the electronic structure and band gap of this class of materials can be tuned via changes in atomic structure. We distill this body of computational literature into a set of underlying design principles for the band gap engineering of these materials, and rationalize these principles from the viewpoint of band-edge orbital character. We hope that this perspective provides guidance and insight toward the rational design and continued improvement of perovskite photovoltaics.

10.
Angew Chem Int Ed Engl ; 57(15): 3974-3980, 2018 04 03.
Artigo em Inglês | MEDLINE | ID: mdl-29431895

RESUMO

Ba(CO)+ and Ba(CO)- have been produced and isolated in a low-temperature neon matrix. The observed C-O stretching wavenumber for Ba(CO)+ of 1911.2 cm-1 is the most red-shifted value measured for any metal carbonyl cations, indicating strong π backdonation of electron density from Ba+ to CO. Quantum chemical calculations indicate that Ba(CO)+ has a 2 Π reference state, which correlates with the 2 D(5d1 ) excited state of Ba+ that comprises significant Ba+ (5dπ1 )→CO(π* LUMO) backbonding, letting the Ba(CO)+ complex behave like a conventional transition-metal carbonyl. A bonding analysis shows that the π backdonation in Ba(CO)+ is much stronger than the Ba+ (5dσ /6s)←CO(HOMO) σ donation. The Ba+ cation in the 2 D(5d1 ) excited state is a donor rather than an acceptor. Covalent bonding in the radical anion Ba(CO)- takes place mainly through Ba(5dπ )←CO- (π* SOMO) π donation and Ba(5dσ /6s)←CO- (HOMO) σ donation. The most important valence functions at barium in Ba(CO)+ cation and Ba(CO)- anion are the 5d orbitals.

11.
Parasit Vectors ; 11(1): 80, 2018 02 02.
Artigo em Inglês | MEDLINE | ID: mdl-29394910

RESUMO

BACKGROUND: The Asian tiger mosquito Aedes albopictus is an extremely invasive, globally distributed and medically important vector of various human and veterinary pathogens. In Germany, where this species was recently introduced, its establishment may become modulated by interspecific competition from autochthonous mosquito species, especially Culex pipiens (s.l.). While competitive superiority of Ae. albopictus to Cx. pipiens (s.l.) has been described elsewhere, it has not been assessed in the epidemiological conditions of Germany. The present study aimed to determine if such superiority exists under the physicochemical and microclimatic conditions typical for container habitats in Germany. METHODS: In a replacement series experiment, the larval and pupal responses of Ae. albopictus and Cx. pipiens (s.l.) (mortality, development time, growth) to interspecific interaction (five larval ratios) at (sub-)optimal temperatures (15, 20 and 25 °C) and differing food supply (3 and 6 mg animal-based food larva-1) were investigated using a randomized split-plot design. In addition to physicochemical measurements of the test media, natural physicochemical conditions were determined for comparative analyses in mosquito breeding sites across the Rhine-Main metropolitan region of Germany. RESULTS: Under the physicochemical and microclimatic conditions similar to the breeding sites of the Rhine-Main region, competitive superiority of Cx. pipiens (s.l.) to Ae. albopictus in terms of larval survival was more frequently observed than balanced coexistence. Food regime and multifactorial interactions, but not temperature alone, were controlling factors for interspecific competition. Larval food regime and the larval ratio of Ae. albopictus influenced the physicochemistry and algal growth at 15 °C, with increased Ae. albopictus mortality linked to a decreasing number of Scenedesmus, Oocystis and Anabaena algae. CONCLUSIONS: Under the present environmental conditions, the spread of Ae. albopictus from isolated foci in Germany may generally be slowed by biotic interactions with the ubiquitous Cx. pipiens (s.l.) (and potentially other container-breeding mosquito species) and by limnic microalgae in microhabitats with high resource levels. Detailed knowledge of the context dependency in temperate mosquito ecology, and interrelations of physicochemistry and phycology may help to achieve a better understanding of the upcoming Ae. albopictus colonization processes in central and northern Europe.


Assuntos
Aedes/fisiologia , Comportamento Competitivo , Culex/fisiologia , Larva/fisiologia , Animais , Cruzamento , Ecossistema , Microalgas , Microclima , Pupa/fisiologia , Temperatura , Água/química
12.
Sci Rep ; 7(1): 17561, 2017 12 14.
Artigo em Inglês | MEDLINE | ID: mdl-29242631

RESUMO

When existing, cumulants can provide valuable information about a given distribution and can in principle be used to either fully reconstruct or approximate the parent distribution function. A previously reported cumulant expansion approach for Franck-Condon profiles [Faraday Discuss., 150, 363 (2011)] is extended to describe also the profiles of vibronic transitions that are weakly allowed or forbidden in the Franck-Condon approximation (non-Condon profiles). In the harmonic approximation the cumulants of the vibronic profile can be evaluated analytically and numerically with a coherent state-based generating function that accounts for the Duschinsky effect. As illustration, the one-photon 1 1Ag → 1 1B2u UV absorption profile of benzene in the electric dipole and (linear) Herzberg-Teller approximation is presented herein for zero Kelvin and finite temperatures.

13.
J Chem Phys ; 147(1): 014109, 2017 Jul 07.
Artigo em Inglês | MEDLINE | ID: mdl-28688381

RESUMO

A quasi-relativistic two-component approach for an efficient calculation of P,T-odd interactions caused by a permanent electric dipole moment of the electron (eEDM) is presented. The approach uses a (two-component) complex generalized Hartree-Fock and a complex generalized Kohn-Sham scheme within the zeroth order regular approximation. In applications to select heavy-elemental polar diatomic molecular radicals, which are promising candidates for an eEDM experiment, the method is compared to relativistic four-component electron-correlation calculations and confirms values for the effective electric field acting on the unpaired electron for RaF, BaF, YbF, and HgF. The calculations show that purely relativistic effects, involving only the lower component of the Dirac bi-spinor, are well described by treating only the upper component explicitly.

14.
J Phys Chem Lett ; 8(13): 2780-2786, 2017 Jul 06.
Artigo em Inglês | MEDLINE | ID: mdl-28582620

RESUMO

Most large molecules are chiral in their structure: they exist as two enantiomers, which are mirror images of each other. Whereas the rovibronic sublevels of two enantiomers are almost identical (neglecting a minuscular effect of the weak interaction), it turns out that the photoelectric effect is sensitive to the absolute configuration of the ionized enantiomer. Indeed, photoionization of randomly oriented enantiomers by left or right circularly polarized light results in a slightly different electron flux parallel or antiparallel with respect to the photon propagation direction-an effect termed photoelectron circular dichroism (PECD). Our comprehensive study demonstrates that the origin of PECD can be found in the molecular frame electron emission pattern connecting PECD to other fundamental photophysical effects such as the circular dichroism in angular distributions (CDAD). Accordingly, distinct spatial orientations of a chiral molecule enhance the PECD by a factor of about 10.

15.
J Am Chem Soc ; 139(12): 4435-4442, 2017 03 29.
Artigo em Inglês | MEDLINE | ID: mdl-28319405

RESUMO

Acenes comprise an important class of organic semiconducting materials. As graphene nanoribbons of ultimate width, they are valuable atom-precise model systems for studying the properties of this form of nanoscale carbon materials. Heptacene is the smallest member of the acene series that could only be studied under matrix isolation conditions. Its existence in bulk had never been positively confirmed, despite efforts dating back more than 70 years. We report that the reduction of 7,16-heptacenequinone produces a mixture of two diheptacene molecules. The diheptacenes undergo thermal cleavage to heptacene at high temperatures in the solid state. Monitoring this cycloreversion by solid state 13C cross-polarized magic angle spinning NMR reveals that solid heptacene has a half-life time of several weeks at room temperature. The diheptacenes are valuable precursors for generating films of heptacene by vapor phase deposition that can be studied below or at room temperature.

16.
J Plant Physiol ; 208: 70-83, 2017 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-27889524

RESUMO

Drought is one of the most important environmental stressors resulting in increasing losses of crop plant productivity all over the world. Therefore, development of new approaches to increase the stress tolerance of crop plants is strongly desired. This requires precise and adequate modeling of drought stress. As this type of stress manifests itself as a steady decrease in the substrate water potential (ψw), agar plates infused with polyethylene glycol (PEG) are the perfect experimental tool: they are easy in preparation and provide a constantly reduced ψw, which is not possible in soil models. However, currently, this model is applicable only to seedlings and cannot be used for evaluation of stress responses in mature plants, which are obviously the most appropriate objects for drought tolerance research. To overcome this limitation, here we introduce a PEG-based agar infusion model suitable for 6-8-week-old A. thaliana plants, and characterize, to the best of our knowledge for the first time, the early drought stress responses of adult plants grown on PEG-infused agar. We describe essential alterations in the primary metabolome (sugars and related compounds, amino acids and polyamines) accompanied by qualitative and quantitative changes in protein patterns: up to 87 unique stress-related proteins were annotated under drought stress conditions, whereas further 84 proteins showed a change in abundance. The obtained proteome patterns differed slightly from those reported for seedlings and soil-based models.


Assuntos
Arabidopsis/fisiologia , Regulação da Expressão Gênica de Plantas , Metaboloma , Proteoma , Água/metabolismo , Ágar , Arabidopsis/crescimento & desenvolvimento , Metabolômica , Polietilenoglicóis , Proteômica , Plântula/crescimento & desenvolvimento , Plântula/fisiologia , Estresse Fisiológico
17.
J Exp Bot ; 67(22): 6283-6295, 2016 12.
Artigo em Inglês | MEDLINE | ID: mdl-27856706

RESUMO

Among the environmental alterations accompanying oncoming climate changes, drought is the most important factor influencing crop plant productivity. In plants, water deficit ultimately results in the development of oxidative stress and accumulation of osmolytes (e.g. amino acids and carbohydrates) in all tissues. Up-regulation of sugar biosynthesis in parallel to the increasing overproduction of reactive oxygen species (ROS) might enhance protein glycation, i.e. interaction of carbonyl compounds, reducing sugars and α-dicarbonyls with lysyl and arginyl side-chains yielding early (Amadori and Heyns compounds) and advanced glycation end-products (AGEs). Although the constitutive plant protein glycation patterns were characterized recently, the effects of environmental stress on AGE formation are unknown so far. To fill this gap, we present here a comprehensive in-depth study of the changes in Arabidopsis thaliana advanced glycated proteome related to osmotic stress. A 3 d application of osmotic stress revealed 31 stress-specifically and 12 differentially AGE-modified proteins, representing altogether 56 advanced glycation sites. Based on proteomic and metabolomic results, in combination with biochemical, enzymatic and gene expression analysis, we propose monosaccharide autoxidation as the main stress-related glycation mechanism, and glyoxal as the major glycation agent in plants subjected to drought.


Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/fisiologia , Pressão Osmótica , Arabidopsis/metabolismo , Proteínas de Arabidopsis/fisiologia , Desidratação , Produtos Finais de Glicação Avançada/metabolismo , Glicosilação , Monossacarídeos/metabolismo , Oxirredução , Proteoma/metabolismo , Transcriptoma
18.
Chemphyschem ; 17(16): 2465-72, 2016 Aug 18.
Artigo em Inglês | MEDLINE | ID: mdl-27298209

RESUMO

The absolute configuration of individual small molecules in the gas phase can be determined directly by light-induced Coulomb explosion imaging (CEI). Herein, this approach is demonstrated for ionization with a single X-ray photon from a synchrotron light source, leading to enhanced efficiency and faster fragmentation as compared to previous experiments with a femtosecond laser. In addition, it is shown that even incomplete fragmentation pathways of individual molecules from a racemic CHBrClF sample can give access to the absolute configuration in CEI. This leads to a significant increase of the applicability of the method as compared to the previously reported complete break-up into atomic ions and can pave the way for routine stereochemical analysis of larger chiral molecules by light-induced CEI.

19.
Birth Defects Res B Dev Reprod Toxicol ; 107(3): 157-68, 2016 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-27286044

RESUMO

Brominated flame retardants (BFRs) are stable environmental contaminants known to exert endocrine-disrupting effects. Developmental exposure to polybrominated diphenyl ethers (PBDEs) is correlated with impaired thyroid hormone signaling, as well as estrogenic and anti-androgenic effects. As previous studies have focused on a single congener or technical mixture, the purpose of the current study was to examine the effects of gestational and early postnatal exposure to an environmentally relevant mixture of BFRs designed to reflect house dust levels of PBDEs and hexabromocyclododecane on postnatal developmental outcomes. Pregnant Sprague-Dawley rats were exposed to the PBDE mixture from preconception to weaning (PND 21) through the diet containing 0, 0.75, 250, and 750 mg mixture/kg diet. BFR exposure induced transient reductions in body weight at PND 35 in male and from PND 30-45 in female offspring (250 and 750 mg/kg). Liver weights (PND 21) and xenobiotic metabolizing enzyme activities (PND 21 and 46) were increased in both male and female offspring exposed to 250 and 750 mg/kg diets. Furthermore, serum T4 levels were reduced at PND 21 in both,male and female offspring (250 and 750 mg/kg). At PND 21, Serum alkaline phosphatase (ALP) was decreased in males exposed to 750 mg/kg dietat, and females exposed to 250 and 750 mg/kg diets. At PND 46 ALP was significantly elevated in males (250 and 750 mg/kg). Variations in the cervical vertebrae and phalanges were observed in pups at PND 4 (250 and 750 mg/kg). Therefore, BFR exposure during gestation through to weaning alters developmental programming in the offspring. The persistence of BFRs in the environment remains a cause for concern with regards to developmental toxicity.


Assuntos
Desenvolvimento Ósseo/efeitos dos fármacos , Osso e Ossos/efeitos dos fármacos , Retardadores de Chama/toxicidade , Éteres Difenil Halogenados/toxicidade , Exposição Materna/efeitos adversos , Alanina Transaminase/sangue , Fosfatase Alcalina/sangue , Animais , Aspartato Aminotransferases/sangue , Biomarcadores/sangue , Peso Corporal , Osso e Ossos/patologia , Creatina Quinase/sangue , Creatinina/sangue , Modelos Animais de Doenças , Relação Dose-Resposta a Droga , Feminino , Hidrocarbonetos Bromados/toxicidade , Fígado/efeitos dos fármacos , Fígado/metabolismo , Tamanho do Órgão/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Reprodução/efeitos dos fármacos , Albumina Sérica/metabolismo
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