The ground and ionized states of azulene : a combined study of the vibrational energy levels by photoionization, configuration interaction, and density functional calculations

A synchrotron-based photoionization spectrum of azulene shows significant additional vibrational fine structure when compared to previous studies. This spectrum was successfully analysed by Franck-Condon (FC) methods. Previously reported zero-kinetic-energy electron spectra (ZEKE) for azulene, have been reinterpreted in FC terms, leading to some alternative assignments to the earlier work. The sequence of ionic states has been determined by ab initio configuration interaction (CI) methods, leading to reliable theoretical values for both the calculated adiabatic and vertical ionization energies (AIE and VIE respectively). VIE were calculated by both symmetry-adapted cluster (SAC-CI), together with Green’s function (GF) and Tamm Dancoff approximation (TDA), single excitation CI methods; AIE for highest states of each symmetry, were determined by open-shell self-consistent field (SCF) methods at the restricted Hartree-Fock level. Complete active space SCF(CASSCF) was used for the pairs of states 12A2 + 22A2 and 12B1 + 22B1 each of which occurs as antisymmetric and symmetric (higher energy) combinations. The combined ionic state sequences (AIE and VIE) from these methods are 12A2 < 12B1 < 22A2 < 22B1. The PES shows a series of broad bands above 11 eV, each of which are attributed to more than one ionisation. The calculated PES sequence of states up to 19 eV shows the SAC-CI and GF results are in almost exact agreement. The internal spacing of the bands is best reproduced by the simpler GF and TDA methods. States involving simultaneous ionization and electronic excitation are considered by both SAC-CI and TDA methods.PostprintPeer reviewe

On the electronic structure of methyl butyrate and methyl valerate

No. 2019-A0010806820 UIDB/00068/2020 PTDC/FIS-AQM/31281/2017Abstract: We present novel results of the analysis of the electronic structure of two aliphatic esters: methyl butyrate and methyl valerate. High-resolution photoabsorption spectra were collected and analyzed over the energy range 4.0–10.8 eV and showed for both the molecules not only a clear band of the HOMO to LUMO transition, but also vibronic structure associated with the first Rydberg-valence transition. Photoelectron spectra recorded from 9 to over 28 eV revealed many ionization states with the first adiabatic ionization energies found to be 9.977 eV and 9.959 eV for methyl butyrate and methyl valerate, respectively. Ab initio calculations have been performed in order to help assign the photoabsorption and photoelectron features. Photolysis life times in the atmosphere were calculated revealing that photolysis is not competitive over hydroxyl radical scavenging in the process of removal of these esters from the atmosphere. Graphical abstract: [Figure not available: see fulltext.]publishersversionpublishe

The ultraviolet and vacuum ultraviolet absorption spectrum of gamma-pyrone; the singlet states studied by configuration interaction and density functional calculations

A synchrotron based vacuum ultraviolet absorption spectrum for γ-pyrone has been interpreted in terms of singlet excited electronic states, using a variety of coupled cluster, configuration interaction, and density functional calculations. The extremely weak spectral onset at 3.557 eV shows 8 vibrational peaks and following previous analyses is attributed to a forbidden 1A2 state. A contrasting broad peak with maximum at 5.381 eV has a relatively high cross-section of 30 Mb; this arises from three overlapping states, where a 1A1 state dominates over progressively weaker 1B2 and 1B1 states. After fitting the second band to a polynomial Gaussian function, and plotting the regular residuals (RR), over 20 vibrational peaks were revealed. We have had limited success in analyzing this fine structure. However, the small separation between these three states clearly shows that their vibrational satellites must overlap. Singlet valence and Rydberg state vibrational profiles were determined by configuration interaction using the CAM-B3LYP density functional. Vibrational analysis, using both Franck-Condon and Herzberg-Teller procedures showed that both procedures contributed to the profiles. Theoretical Rydberg states were evaluated by a highly focused CI procedure. Super-position of the lowest photoelectron spectral band on the VUV spectrum near 6.4 eV, shows that the 3s and 3p Rydberg states based on the 2B2 ionic state are present; those based on the other low-lying ionic state (X2B1) are destroyed by broadening; this is a dramatic extension of the broadening previously witnessed in our studies of halogenobenzenes.Peer reviewe

Isobutyl acetate: electronic state spectroscopy by high-resolution vacuum ultraviolet photoabsorption, He(I) photoelectron spectroscopy and ab initio calculations

The high-resolution vacuum ultraviolet photoabsorption spectrum of isobutyl acetate, C6H12O2, is presented here and was measured over the energy range 4.3–10.8 eV (290–115 nm). Valence and Rydberg transitions with their associated vibronic series have been observed in the photoabsorption spectrum and are assigned in accordance with new ab initio calculations of the vertical excitation energies and oscillator strengths. The measured photoabsorption cross sections have been used to calculate the photolysis lifetime of this ester in the Earth’s upper atmosphere (20–50 km). Calculations have also been carried out to determine the ionization energies and fine structure of the lowest ionic state of isobutyl acetate and are compared with a photoelectron spectrum (from 9.5 to 16.7 eV), recorded for the first time. Vibrational structure is observed in the first photoelectron band of this molecule

Neuropathy-related mutations alter the membrane binding properties of the human myelin protein P0 cytoplasmic tail

Schwann cells myelinate selected axons in the peripheral nervous system (PNS) and contribute to fast saltatory conduction via the formation of compact myelin, in which water is excluded from between tightly adhered lipid bilayers. Peripheral neuropathies, such as Charcot-Marie-Tooth disease (CMT) and Dejerine-4 Sottas syndrome (DSS), are incurable demyelinating conditions that result in pain, decrease in muscle mass, and functional impairment. Many Schwann cell proteins, which are directly involved in the stability of compact myelin or its development, are subject to mutations linked to these neuropathies. The most abundant PNS myelin protein is protein zero (P0); point mutations in this transmembrane protein cause CMT subtype 8 1B and DSS. P0 tethers apposing lipid bilayers together through its extracellular immunoglobulin-like domain. Additionally, P0 contains a cytoplasmic tail (P0ct), which is membrane-associated and contributes to the physical properties of the lipid membrane. Six CMT- and DSS-associated missense mutations have been reported in P0ct. We generated recombinant disease mutant variants of P0ct and characterized them using biophysical methods. Compared to wild-type P0ct, some mutants have negligible differences in function and folding, while others highlight functionally important amino acids within P0ct. For example, the D224Y variant of P0ct induced tight membrane multilayer stacking. Our results show a putative molecular basis for the hypermyelinating phenotype observed in patients with this particular mutation and provide overall information on the effects of disease-linked mutations in a flexible, membrane-binding protein segment. Using neutron reflectometry, we additionally show that P0ct embeds deep into a lipid bilayer, explaining the observed effects of P0ct on the physical properties of the membrane

Radio- and photosensitization of DNA with compounds containing platinum and bromine atoms

Irradiations of plasmid DNA by both X-rays and UV light in the presence and absence of compounds containing platinum and bromine atoms were performed in order to asses the sensitization potential of these compounds. Plasmid DNA pBR322 was incubated with platinum (II) bromide, hydrogen hexabromoplatinate (IV), hydrogen hexahydroxyplatinate (IV) and sodium hexahydroxyplatinate (IV). Incubation was followed by X-ray or UV irradiations. It was found that amongst the sensitizers tested, during irradiations carried out in the presence of platinum (II) bromide, the highest levels of double strand breaks formation upon X-ray treatment were recorded. In contrast much less damage was induced by UV light. Data presented here suggests that this compound may be a promising radiosensitizer for cancer treatment