The furan microsolvation blind challenge for quantum chemical methods: First steps

© 2018 Author(s). Herein we present the results of a blind challenge to quantum chemical methods in the calculation of dimerization preferences in the low temperature gas phase. The target of study was the first step of the microsolvation of furan, 2-methylfuran and 2,5-dimethylfuran with methanol. The dimers were investigated through IR spectroscopy of a supersonic jet expansion. From the measured bands, it was possible to identify a persistent hydrogen bonding OH-O motif in the predominant species. From the presence of another band, which can be attributed to an OH-π interaction, we were able to assert that the energy gap between the two types of dimers should be less than or close to 1 kJ/mol across the series. These values served as a first evaluation ruler for the 12 entries featured in the challenge. A tentative stricter evaluation of the challenge results is also carried out, combining theoretical and experimental results in order to define a smaller error bar. The process was carried out in a double-blind fashion, with both theory and experimental groups unaware of the results on the other side, with the exception of the 2,5-dimethylfuran system which was featured in an earlier publication

Trapping a silicon(I) radical with carbenes: a cationic cAAC-silicon(I) radical and an NHC-parent-silyliumylidene cation

The trapping of a silicon(I) radical with N-heterocyclic carbenes is described. The reaction of the cyclic (alkyl)(amino) carbene [cAACMe] (cAACMe=:C(CMe2)2(CH2)NAr, Ar=2,6-iPr2C6H3) with H2SiI2 in a 3:1 molar ratio in DME afforded a mixture of the separated ion pair [(cAACMe)2Si:.]+I− (1), which features a cationic cAAC–silicon(I) radical, and [cAACMe−H]+I−. In addition, the reaction of the NHC–iodosilicon(I) dimer [IAr(I)Si:]2 (IAr=:C{N(Ar)CH}2) with 4 equiv of IMe (:C{N(Me)CMe}2), which proceeded through the formation of a silicon(I) radical intermediate, afforded [(IMe)2SiH]+I− (2) comprising the first NHC–parent-silyliumylidene cation. Its further reaction with fluorobenzene afforded the CAr−H bond activation product [1-F-2-IMe-C6H4]+I− (3). The isolation of 2 and 3 confirmed the reaction mechanism for the formation of 1. Compounds 1–3 were analyzed by EPR and NMR spectroscopy, DFT calculations, and X-ray crystallography

Density functional theory

Density functional theory (DFT) finds increasing use in applications related to biological systems. Advancements in methodology and implementations have reached a point where predicted properties of reasonable to high quality can be obtained. Thus, DFT studies can complement experimental investigations, or even venture with some confidence into experimentally unexplored territory. In the present contribution, we provide an overview of the properties that can be calculated with DFT, such as geometries, energies, reaction mechanisms, and spectroscopic properties. A wide range of spectroscopic parameters is nowadays accessible with DFT, including quantities related to infrared and optical spectra, X-ray absorption and Mössbauer, as well as all of the magnetic properties connected with electron paramagnetic resonance spectroscopy except relaxation times. We highlight each of these fields of application with selected examples from the recent literature and comment on the capabilities and limitations of current methods

Reduction of CO\u3csub\u3e2\u3c/sub\u3e By a Masked Two-Coordinate Cobalt(I) Complex and Characterization of a Proposed Oxodicobalt(II) Intermediate

Fixation and chemical reduction of CO2 are important for utilization of this abundant resource, and understanding the detailed mechanism of C-O cleavage is needed for rational development of CO2 reduction methods. Here, we describe a detailed analysis of the mechanism of the reaction of a masked two-coordinate cobalt(i) complex, LtBuCo (where LtBu = 2,2,6,6-tetramethyl-3,5-bis[(2,6-diisopropylphenyl)imino]hept-4-yl), with CO2, which yields two products of C-O cleavage, the cobalt(i) monocarbonyl complex LtBuCo(CO) and the dicobalt(ii) carbonate complex (LtBuCo)2(μ-CO3). Kinetic studies and computations show that the κN,η6-arene isomer of LtBuCo rearranges to the κ2N,N′ binding mode prior to binding of CO2, which contrasts with the mechanism of binding of other substrates to LtBuCo. Density functional theory (DFT) studies show that the only low-energy pathways for cleavage of CO2 proceed through bimetallic mechanisms, and DFT and highly correlated domain-based local pair natural orbital coupled cluster (DLPNO-CCSD(T)) calculations reveal the cooperative effects of the two metal centers during facile C-O bond rupture. A plausible intermediate in the reaction of CO2 with LtBuCo is the oxodicobalt(II) complex LtBuCoOCoLtBu, which has been independently synthesized through the reaction of LtBuCo with N2O. The rapid reaction of LtBuCoOCoLtBu with CO2 to form the carbonate product indicates that the oxo species is kinetically competent to be an intermediate during CO2 cleavage by LtBuCo. LtBuCoOCoLtBu is a novel example of a thoroughly characterized molecular cobalt-oxo complex where the cobalt ions are clearly in the +2 oxidation state. Its nucleophilic reactivity is a consequence of high charge localization on the μ-oxo ligand between two antiferromagnetically coupled high-spin cobalt(ii) centers, as characterized by DFT and multireference complete active space self-consistent field (CASSCF) calculations

The first microsolvation step for furans : new experiments and benchmarking strategies

The site-specific first microsolvation step of furan and some of its derivatives with methanol is explored to benchmark the ability of quantum-chemical methods to describe the structure, energetics, and vibrational spectrum at low temperature. Infrared and microwave spectra in supersonic jet expansions are used to quantify the docking preference and some relevant quantum states of the model complexes. Microwave spectroscopy strictly rules out in-plane docking of methanol as opposed to the top coordination of the aromatic ring. Contrasting comparison strategies, which emphasize either the experimental or the theoretical input, are explored. Within the harmonic approximation, only a few composite computational approaches are able to achieve a satisfactory performance. Deuteration experiments suggest that the harmonic treatment itself is largely justified for the zero-point energy, likely and by design due to the systematic cancellation of important anharmonic contributions between the docking variants. Therefore, discrepancies between experiment and theory for the isomer abundance are tentatively assigned to electronic structure deficiencies, but uncertainties remain on the nuclear dynamics side. Attempts to include anharmonic contributions indicate that for systems of this size, a uniform treatment of anharmonicity with systematically improved performance is not yet in sight

Hyperfine coupling constants on inner‐sphere water molecules of GdIII‐based MRI contrast agents

[Abstract] Herein we present a theoretical investigation of the hyperfine coupling constants (HFCCs) on the inner‐sphere water molecules of [Gd(H2O)8]3+ and different GdIII‐based magnetic resonance imaging contrast agents such as [Gd(DOTA)(H2O)]−, [Gd(DTPA)(H2O)]2−, [Gd(DTPA‐BMA)(H2O)] and [Gd(HP‐DO3A)(H2O)]. DFT calculations performed on the [Gd(H2O)8]3+ model system show that both hybrid‐GGA functionals (BH&HLYP, B3PW91 and PBE1PBE) and the hybrid meta‐GGA functional TPSSh provide 17O HFCCs in close agreement with the experimental data. The use of all‐electron relativistic approaches based on the DKH2 approximation and the use of relativistic effective core potentials (RECP) provide results of essentially the same quality. The accurate calculation of HFCCs on the [Gd(DOTA)(H2O)]−, [Gd(DTPA)(H2O)]2−, [Gd(DTPA‐BMA)(H2O)] and [Gd(HP‐DO3A)(H2O)] complexes requires an adequate description of solvent effects. This was achieved by using a mixed cluster/continuum approach that includes explicitly two second‐sphere water molecules. The calculated isotropic 17O HFCCs (Aiso) fall within the range 0.40–0.56 MHz, and show deviations from the corresponding experimental values typically lower than 0.05 MHz. The Aiso values are significantly affected by the distance between the oxygen atom of the coordinated water molecule and the GdIII ion, as well as by the orientation of the water molecule plane with respect to the Gd‐O vector. 1H HFCCs of coordinated water molecules and 17O HFCCs of second‐sphere water molecules take values close to zero.Ministerio de Educación y Ciencia; CTQ2009‐10721Xunta de Galicia; IN845B‐2010/06

ProsCan for Couples: Randomised controlled trial of a couples-based sexuality intervention for men with localised prostate cancer who receive radical prostatectomy

Background: Prostate cancer is the most common male cancer in the Western world. The most substantial long term morbidity from this cancer is sexual dysfunction with consequent adverse changes in couple and intimate relationships. Research to date has not identified an effective way to improve sexual and psychosocial adjustment for both men with prostate cancer and their partners. As well, the efficacy and cost effectiveness of peer counselling as opposed to professional models of service delivery has not yet been empirically tested. This paper presents the design of a three arm randomised controlled trial (peer vs. nurse counselling vs. usual care) that will evaluate the efficacy of two couples-based sexuality interventions (ProsCan for Couples: Peer support vs. nurse counselling) on men's and women's sexual and psychosocial adjustment after surgical treatment for localised prostate cancer; in addition to cost-effectiveness. Methods/design: Seventy couples per condition (210 couples in total) will be recruited after diagnosis and before treatment through urology private practices and hospital outpatient clinics and randomised to (1) usual care; (2) eight sessions of peer-delivered telephone support with DVD education; and (3) eight sessions of oncology nurse-delivered telephone counselling with DVD education. Two intervention sessions will be delivered before surgery and six over the six months post-surgery. The intervention will utilise a cognitive behavioural approach along with couple relationship education focussed on relationship enhancement and helping the couple to conjointly manage the stresses of cancer diagnosis and treatment. Participants will be assessed at baseline (before surgery) and 3, 6 and 12 months post-surgery. Outcome measures include: Sexual adjustment; unmet sexuality supportive care needs; attitudes to sexual help seeking; psychological adjustment; benefit finding and quality of life. Discussion: The study will provide recommendations about the efficacy of peer support vs. nurse counselling to facilitate better sexual and couple adjustment after prostate cancer as well as recommendations on whether the interventions represent efficient health service delivery

Counseling patients about sexual health when considering post-prostatectomy radiation treatment

Prostate cancer is the second most frequently diagnosed cancer in men in the United States. Many men with clinically localized prostate cancer survive for 15 years or more. Although early detection and successful definitive treatments are increasingly common, a debate regarding how aggressively to treat prostate cancer is ongoing because of the effect of aggressive treatment on the quality of life, including sexual functioning. We examined current research on the effect of post-prostatectomy radiation treatment on sexual functioning, and suggest a way in which patient desired outcomes might be taken into consideration while making decisions with regard to the timing of radiation therapy after prostatectomy