The Spin-Flip Variant of the Algebraic-Diagrammatic Construction Yields the Correct Topology of S/S Conical Intersections.

While the conventional variants of the algebraic-diagrammatic construction (ADC) scheme for the polarization propagator are generally incapable of correctly describing the topology of S/S conical intersections (CIs), its corresponding spin-flip (SF) variant of third-order ADC (ADC(3)) is herein demonstrated to successfully reproduce the S/S minimum-energy CI (MECI) of twisted formaldinium (HC═NH). Analytical nuclear excited-state gradients of ADC have been used in combination with the CIOpt program for the optimization of the MECI without the need for nonadiabatic-coupling vectors. For comparison, MS-CASPT2 calculations were performed via conventional CI optimization employing analytical nonadiabatic-coupling vectors.

The effects of radioactive iodine therapy on olfactory function.

Purpose: To determine the possible adverse effects of radioactive iodine (RAI) treatment on the olfactory functions of patients with differentiated thyroid carcinoma.

Materials And Methods: This prospective clinical study included 63 Turkish patients who had been diagnosed with papillary thyroid carcinoma only to ensure homogeneity. The Connecticut Chemosensory Clinical Research Center olfactory test was administered at 1 week before treatment and at the third week and the first year after treatment.

Conical-Intersection Topographies Suggest That Ribose Exhibits Enhanced UV Photostability.

Carbohydrates are essential building blocks of life that assume a multitude of biological functions in all living organisms found on Earth. It was recently reported that ribose was identified in UV-irradiated interstellar ice analogs, which suggests that it can be found on comets and that it may have been transported to Earth via the impact of comets. Herein, we present computational results obtained with multiconfigurational ab initio quantum-chemical methods showing that various photochemical processes for radiationless deactivation are available for photoexcited ribose.

Semiempirical Quantum-Chemical Orthogonalization-Corrected Methods: Benchmarks of Electronically Excited States.

The semiempirical orthogonalization-corrected OMx methods have recently been shown to perform well in extensive ground-state benchmarks. They can also be applied to the computation of electronically excited states when combined with a suitable multireference configuration interaction (MRCI) treatment. We report on a comprehensive evaluation of the performance of the OMx/MRCI methods for electronically excited states.

Onset of the Electronic Absorption Spectra of Isolated and π-Stacked Oligomers of 5,6-Dihydroxyindole: An Ab Initio Study of the Building Blocks of Eumelanin.

Eumelanin is a naturally occurring skin pigment which is responsible for developing a suntan. The complex structure of eumelanin consists of π-stacked oligomers of various indole derivatives, such as the monomeric building block 5,6-dihydroxyindole (DHI). In this work, we present an ab initio wave-function study of the absorption behavior of DHI oligomers and of doubly and triply π-stacked species of these oligomers.

Excited-state deactivation in 8-oxo-deoxyguanosine: comparison between anionic and neutral forms.

8-Oxoguanine is the most abundant oxidation product found in oxidatively damaged DNA. The study of the excited-state properties of the corresponding deoxyribonucleoside 8-oxo-deoxyguanosine is thus of important biological relevance. Herein, we present an ADC(2)-s ab initio study of the neutral and the anionic form of 8-oxo-deoxyguanosine, for each of which we have considered the intramolecularly 5'-O-H···N3 hydrogen-bonded syn conformer.

Assessment of Approximate Coupled-Cluster and Algebraic-Diagrammatic-Construction Methods for Ground- and Excited-State Reaction Paths and the Conical-Intersection Seam of a Retinal-Chromophore Model.

As a minimal model of the chromophore of rhodopsin proteins, the penta-2,4-dieniminium cation (PSB3) poses a challenging test system for the assessment of electronic-structure methods for the exploration of ground- and excited-state potential-energy surfaces, the topography of conical intersections, and the dimensionality (topology) of the branching space. Herein, we report on the performance of the approximate linear-response coupled-cluster method of second order (CC2) and the algebraic-diagrammatic-construction scheme of the polarization propagator of second and third orders (ADC(2) and ADC(3)). For the ADC(2) method, we considered both the strict and extended variants (ADC(2)-s and ADC(2)-x).

Photoinduced water splitting via benzoquinone and semiquinone sensitisation.

The splitting of water into H˙ and OH˙ radicals by sensitisation of a redox-active chromophore with sunlight may eventually become a viable way of producing unlimited, clean and sustainable energy. In this work, we explore the possibility of photo-oxidation of water via sensitisation of benzoquinone with ultraviolet (UV) light in the hydrogen-bonded complex of benzoquinone with a single water molecule. Using state-of-the-art quantum chemical calculations, the mechanisms of electron/proton transfer reactions between photoexcited benzoquinone and water are characterised.

Mechanisms of photostability in kynurenines: a joint electronic-structure and dynamics study.

Kynurenines are UV filters found in the human ocular lens which protect the retina from radiation damage. We report on ab initio investigations of the photochemistry of the cis and trans conformers of kynurenine and of an intramolecularly hydrogen-bonded conformer of 3-hydroxykynurenine O-β-D-glucoside. We have explored the excited-state reaction paths for several radiationless excited-state deactivation processes in kynurenines.

Photochemical mechanisms of radiationless deactivation processes in urocanic acid.

Urocanic acid is a UV filter found in human skin that protects the skin from UV damage but has also been linked to the onset of skin cancer and to photoimmunosuppression. We report on ab initio investigations of two rotameric forms of each of the two tautomers of neutral (E)- and (Z)-urocanic acid. We have computed the vertical singlet excitation energies of eight isomers and have explored the singlet excited-state reaction paths of several photochemical processes for radiationless excited-state deactivation: the E/Z photoisomerization, an electron-driven proton transfer for an intramolecularly hydrogen-bonded Z isomer, as well as the hydrogen-atom detachment process and the ring-puckering process involving the NH group inherent to the imidazole moiety.

Mechanisms of ultrafast excited-state deactivation in adenosine.

Recently, resonant two-photon ionization experiments on isolated adenine and adenosine suggested that adenosine exhibits a significantly shorter excited-state lifetime than adenine, which indicates the existence of an efficient excited-state deactivation mechanism in adenosine that is not existent in adenine. We report on ab initio investigations on a syn and an anti conformer of adenosine exhibiting an intramolecular O-H···N3 hydrogen bond. For both conformers, we have identified the existence of a barrierless excited-state deactivation mechanism that involves the forward-backward transfer of a proton along the intramolecular hydrogen bond and ultrafast radiationless deactivation through conical intersections.

Electronically excited states and photochemical reaction mechanisms of β-glucose.

Carbohydrates are important molecular components of living matter. While spectroscopic and computational studies have been performed on carbohydrates in the electronic ground state, the lack of a chromophore complicates the elucidation of the excited-state properties and the photochemistry of this class of compounds. Herein, we report on the first computational investigation of the singlet photochemistry of β-glucose.