Chiroptical studies on brevianamide B : vibrational and electronic circular dichroism confronted

Chiroptical spectroscopy, such as electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) are highly sensitive techniques to probe molecular conformation, configuration, solvation and aggregation. Here we report the application of these techniques to study the fungal metabolite brevianamide B. Comparison of the experimental ECD and VCD spectra with the density functional theory (DFT) simulated counterparts establishes that VCD is the more reliable technique to assign absolute configuration due to the larger functional and dispersion dependence of computed ECD spectra. Despite a low amount of available material, and a relatively unusual example of using VCD carbonyl multiplets, the absolute configuration could be reliably predicted, strengthening the case for application of VCD in the study of complex natural products. Spectral and crystallographic evidence for or against the formation of a dimeric aggregate is discussed; in solution the VCD spectra strongly suggest only monomeric species are present

Molecular Orbital Studies of Molecular Exciplexes. Part 1 : AM1 and PM3 Calculations of the Ammonia-Oxygen Complex and its Solvation by Water

Ground-and excited-state calculations of the triplet O,*NH,-nH,O complex as a model for solution photo-oxygenation of amines by triplet oxygen are reported at the AM1 and PM3 SCF-MO levels. For n < 3, the first excited AM1 triplet state corresponds t o local excitation on the ammonia (TN), whereas the polar excited state (T,) corresponding to N H 3 + * 0 2 --becomes the lowest excited triplet state when n 2 3. In contrast, the lowest excited PM3 triplet state is ionic even for n = 0, and the T, and ground-state (To) triplet surfaces intersect at an N -0 distance of 1.95 A for n = 5, with T, becoming a local minimum on ground triplet state surface at shorter N -0 distances. The reliability of these models are discussed in terms of known errors and properties of the AM1 and PM3 methods, and by a comparison of the solvation enthalpies and structures of systems such as NH,+*nH,O, NH,+-nNH,, and HO--nH,O ( n = 1-4) with known experimental values. Light-induced oxygenation of organic compounds has long been the subject of extensive investigation. Singlet oxygen ' is generally assumed to be the reactive species in the majority of photo-oxygenation reactions involving molecular oxygen, but there are a number of reactions where oxygenation proceeds under conditions where no singlet oxygen can be formed. One common example is the formation of hydroperoxides in rubber and similar materials exposed to the air and sun, and many so called 'auto-oxidation processes' may also belong to this category. We have investigated experimentally one such reaction,, for which the mechanism is thought to involve the formation of a loose complex between triplet oxygen and the s~b s t r a t e .~ The absorption of light causes the formation of a charge-transfer complex, which can then undergo chemical transformation to the products (Scheme). To TP Measurement of the rate constants involved in such reactions can be difficult experimentally., For this reason we wished to investigate various theoretical procedures for modelling photooxygenation and for predicting specific substituent and structural effects on the course of the reaction. The involvement of ionic excited state intermediates also renders the reaction sensitive to interactions with e.g. polar solven13 such as water. These properties, together with a requirement to handle relatively large substituents such as phenyl or similar stabilising groups, and the need for effective geometry optimisation of both the ground and excited triplet states, place severe demands on any quantitative theoretical procedure. Our initial studies focussed on the application of semiempirical SCF-MO procedures as pathfinders for charting the general characteristics of such reactions. The MNDO SCF-MO method7 has been extensively evaluated for a wide range of properties, including adiabatic singlet and triplet excitation energies. Although these are predicted to be generally too low by ca. 1 eV, the geometrical changes associated with excitation were found to be qualitatively reasonable.8a A recent MNDO (and AM1) study of the (S,-So) adiabatic energy gap in a series of primary amines revealed an average error (0.42 eV) to be significantly smaller for this specific series.8b MNDO has also proved to be useful in predicting substituent effects for reactions involving single-electron transfer and open-shell intermediate^.^ One noted defect of the MNDO method, however, is the very low hydrogen-bonding energies predicted for a range of systems, and the more recent AM 1 procedure was developed with this in mind. The interaction energies of simple hydrogen-bonded systems are indeed better reproduced, and the error in excitation energies is quite similar to those found for MND0.8 However, the AM1 method is now known to favour l 1 bifurcated molecular geometries for hydrogen-bonded complexes involving oxygen, which for water dimer, at least, is certainly incorrect.12 We have recently shown that AM 1 also contains a specific defect in the nitrogen parametrisation, which has the effect of overestimating core-core repulsions at distances to nitrogen of ca. 2.1 A and hence, in turn the geometries of transition states and complexes involving nitrogen bonds in this region. The most recent l 2 semiempirical method PM3 appears to predict geometries for neutral hydrogen-bonded complexes involving nitrogen or oxygen similar to those obtained at the ab initio MP2/6-3 1G** le~e1.I~ However, little is known about the PM3 method in respect of triplet or excited states. In the present study, we had several objectives. Firstly, we compare both methods with regard to the gas-phase (n = 0) geometries and energies of the ground and excited triplet states of the O2.NH,-nH,O system. Secondly, we compare AM1 and PM3 solvation enthalpies and structures of the charged species NH4+ and OH-with known experimental values. Finally, we discuss the validity of these AM1 and PM3 models of amine photooxygenation in the context of known errors of the methods. Computational Procedure.-The PM3 and AM 1 calculations were carried out using the MOPAC (V5.0) l 5 and AMPAC (V2.1) program systems,16 all geometrical variables being optimised. Calculations of the different electronic states of the NH, 0, complex were performed with the multi-electron configuration interaction facility (MECI) in either program, using the 'half-electron' open-shell approximation. An active space of four molecular orbitals was selected for the configuration interaction (CI), comprising the highest doubly occupied orbital (essentially a lone pair on nitrogen), the two singly occupied oxygen orbitals (degenerate at large N-0 distances) and the lowest unoccupied molecular orbital corresponding to the first antibonding orbital of A, symmetry o

Blunted neural response to anticipation, effort and consummation of reward and aversion in adolescents with depression symptomatology

Neural reward function has been proposed as a possible biomarker for depression. However how the neural response to reward and aversion might differ in young adolescents with current symptoms of depression is as yet unclear. 33 adolescents were recruited. 17 scoring low on the Mood and Feelings Questionnaire (MFQ) (Low Risk: LR) and 16 scoring high on the MFQ (High Risk: HR). Our fMRI task measured; anticipation (pleasant/unpleasant cue), effort (achieve a pleasant taste or avoid an unpleasant taste) and consummation (pleasant/unpleasant tastes) in Regions of Interest; ventral medial prefrontal cortex (vmPFC), pregenual cingulate cortex (pgACC), the insula and ventral striatum. We also examined whole brain group differences. In the ROI analysis we found reduced activity in the HR group in the pgACC during anticipation and reduced pgACC and vmPFC during effort and consummation. In the whole brain analysis we also found reduced activity in the HR group in the prefrontal cortex and the precuneus during anticipation. We found reduced activity in the hippocampus during the effort phase and in the anterior cingulate/frontal pole during consummation in the HR group. Increased anhedonia measures correlated with decreased pgACC activity during consummation in the HR group only. Our results are the first to show that adolescents with depression symptoms have blunted neural responses during the anticipation, effort and consummation of rewarding and aversive stimuli. This study suggests that interventions in young people at risk of depression, that can reverse blunted responses, might be beneficial as preventative strategies

Blue Obelisk - Interoperability in chemical informatics

The Blue Obelisk Movement (http://www.blueobelisk.org/) is the name used by a diverse Internet group promoting reusable chemistry via open source software development, consistent and complimentary chemoinformatics research, open data, and open standards. We outline recent examples of cooperation in the Blue Obelisk group:  a shared dictionary of algorithms and implementations in chemoinformatics algorithms drawing from our various software projects; a shared repository of chemoinformatics data including elemental properties, atomic radii, isotopes, atom typing rules, and so forth; and Web services for the platform-independent use of chemoinformatics programs

The past, present and future of Scientific discourse.

Published versio

Síntesis de control óptimo

El teorema de optimalidad de Pontryagin permite deducir condiciones necesarias de un control óptimo. Como no provee condiciones suficientes se debe analizar cada problema para terminar de caracterizar la solución. La bibliografía existente cubre algunos ejemplos con soluciones con el control recostado contra la frontera. Para problemas lineales se puede caracterizar por completo la solución. No así en otros. Este grupo ha comprobado que en algunos problemas las soluciones también asumen puntos interiores del espacio de control y ha desarrollado algoritmos que logran determinar los puntos de conmutación a valores extremos. Han demostrado que la unicidad de la solución está garantizada por propiedades de monotonía. El objeto de esta línea de investigación es estudiar la posibilidad de caracterizar los problemas que compartan estas propiedades, lo que permitiría aplicar a ellos el algoritmo diseñado.Eje: Procesamiento de señales y sistemas de tiempo realRed de Universidades con Carreras en Informática (RedUNCI

Spin states of zigzag-edged Mobius graphene nanoribbons from first principles

Mobius graphene nanoribbons have only one edge topologically. How the magnetic structures, previously associated with the two edges of zigzag-edged flat nanoribbons or cyclic nanorings, would change for their Mobius counterparts is an intriguing question. Using spin-polarized density functional theory, we shed light on this question. We examine spin states of zigzag-edged Mobius graphene nanoribbons (ZMGNRs) with different widths and lengths. We find a triplet ground state for a Mobius cyclacene, while the corresponding two-edged cyclacene has an open-shell singlet ground state. For wider ZMGNRs, the total magnetization of the ground state is found to increase with the ribbon length. For example, a quintet ground state is found for a ZMGNR. Local magnetic moments on the edge carbon atoms form domains of majority and minor spins along the edge. Spins at the domain boundaries are found to be frustrated. Our findings show that the Mobius topology (i.e., only one edge) causes ZMGNRs to favor one spin over the other, leading to a ground state with non-zero total magnetization.Comment: 17 pages, 4 figure

Síntesis de control óptimo

El teorema de optimalidad de Pontryagin permite deducir condiciones necesarias de un control óptimo. Como no provee condiciones suficientes se debe analizar cada problema para terminar de caracterizar la solución. La bibliografía existente cubre algunos ejemplos con soluciones con el control recostado contra la frontera. Para problemas lineales se puede caracterizar por completo la solución. No así en otros. Este grupo ha comprobado que en algunos problemas las soluciones también asumen puntos interiores del espacio de control y ha desarrollado algoritmos que logran determinar los puntos de conmutación a valores extremos. Han demostrado que la unicidad de la solución está garantizada por propiedades de monotonía. El objeto de esta línea de investigación es estudiar la posibilidad de caracterizar los problemas que compartan estas propiedades, lo que permitiría aplicar a ellos el algoritmo diseñado.Eje: Procesamiento de señales y sistemas de tiempo realRed de Universidades con Carreras en Informática (RedUNCI

Publishing ‘paper bullets’: Politics, propaganda, and Polish-English translation in wartime London

During World War 2, publishing was an important element of the war effort for both the Allies and the Axis powers. Wartime propaganda and cultural diplomacy relied primarily on books, magazines and the daily press. The exiled governments in London, including the Polish government, undertook a major effort to translate, publish and promote numerous books and pamphlets that would appeal to British readers and, thus, help sway public opinion. This paper focuses on translation as an important aspect of wartime publishing that has not yet received much scholarly attention. It offers a contribution to research into the role and place of translations in wartime publishing by discussing the Polish government-in-exile’s translation and publishing campaign. Drawing on various archival sources, it demonstrates that publishing translations was an important part of wartime cultural diplomacy and it led to the development of extensive state-private networks that brought together exiled governments and British publishers. By analysing this material in a broad cultural context, the paper highlights the historical, ideological and political relevance of translation studies research to wartime publishing and censorship