Two-Dimensional Impulsively Stimulated Resonant Raman Spectroscopy of Molecular Excited States

Monitoring the interactions between electronic and vibrational degrees of freedom in molecules is critical to our understanding of their structural dynamics. This is typically hampered by the lack of spectroscopic probes able to detect different energy scales with high temporal and frequency resolution. Coherent Raman spectroscopy can combine the capabilities of multidimensional spectroscopy with structural sensitivity at ultrafast timescales. Here, we develop a three-color-based 2D impulsive stimulated Raman technique that can selectively probe vibrational mode couplings between different active sites in molecules by taking advantage of resonance Raman enhancement. Three temporally delayed pulses generate nuclear wave packets whose evolution reports on the underlying potential energy surface, which we decipher using a diagrammatic approach enabling us to assign the origin of the spectroscopic signatures. We benchmark the method by revealing vibronic couplings in the ultrafast dynamics following photoexcitation of the green fluorescent protein

Two-Dimensional Impulsively Stimulated Resonant Raman Spectroscopy of Molecular Excited States

Monitoring the interactions between electronic and vibrational degrees of freedom in molecules is critical to our understanding of their structural dynamics. This is typically hampered by the lack of spectroscopic probes able to detect different energy scales with high temporal and frequency resolution. Coherent Raman spectroscopy can combine the capabilities of multidimensional spectroscopy with structural sensitivity at ultrafast timescales. Here, we develop a three-color-based 2D impulsive stimulated Raman technique that can selectively probe vibrational mode couplings between different active sites in molecules by taking advantage of resonance Raman enhancement. Three temporally delayed pulses generate nuclear wave packets whose evolution reports on the underlying potential energy surface, which we decipher using a diagrammatic approach enabling us to assign the origin of the spectroscopic signatures. We benchmark the method by revealing vibronic couplings in the ultrafast dynamics following photoexcitation of the green fluorescent protein.C. S. acknowledges financial support by the Royal Commission for the Exhibition of 1851. G. Bat. acknowledges the “Avvio Alla Ricerca 2018” grant by Sapienza Universitá di Roma. T. W. acknowledges the Marie Curie Intra-European Fellowship (PIEF-GA-2013-623651) within the 7th European Community Framework Programme. S. M. gratefully acknowledges the support of the National Science Foundation Grant No. CHE-1663822

probing ultrafast processes by fifth order stimulated raman scattering

We present the full diagrammatic description of non-resonant impulsive femtosecond stimulated Raman spectroscopy in a multimode model system. In this technique the pump-probe scheme is exploited to study the vibrational structure of the sample via stimulated Raman scattering. We apply closed-time-path-loop diagrams to calculate the complete response of the system at the relevant perturbation order. We show that, in presence of low-frequency modes, coherences created by the impulsive pump modify the resulting Raman signal, which oscillates from gain to loss features, depending on the time delay between the pump and probe pulses. This leads to a redistribution of photons among the fields involved in the process and, consequently, the energy flows between fields and matter. Moreover, through this formalism, we address the case of extremely short delays in which the pump and probe fields overlap in time. We find that, even in absence of photo-induced dynamics due to absorption of the pump pulse, the overlap condition can generate time dependent features, arising from additional diagrams, which offer no contribution for well separated pulses

Molecular Simplification in Bioactive Molecules: Formal Synthesis of (+)-Muconin

7 páginas, 1 figura, 7 esquemas, 1 tabla.-- El PDF es la versión post-print.The concept of molecular simplification as a drug design strategy to shorten synthetic routes, while keeping or enhancing the biological activity of the lead drug, has been applied to (+)-muconin, an acetogenin with remarkable cytotoxicity. A novel approach that enables the stereoselective synthesis of such a natural compound or its enantiomer from a common precursor is described. An additional advantage of the method is complete stereochemical control and the decrease in the number of chemical steps required, thus providing an enhancement of the overall yield. Antiproliferative studies against the human solid tumor cell lines showed that the aliphatic chain-THF/THP fragment of (+)-muconin has modest cytotoxic activity. The strategy opens the way to preparing novel bioactive acetogenin analogues by shorter synthetic routes.The authors thank the MYCT (PPQ2002- 04361-C04-02) of Spain and the Canary Islands Government for supporting this research. F.R.P.C. thanks CajaCanarias for a FPI fellowship. R.C. thanks the Spanish MEC for a FPU fellowship. J.M.P. thanks ICIC for a postdoctoral fellowship.Peer reviewe

Correlation between Fusarium graminearum and deoxynivalenol during the 2012/13 wheat Fusarium head blight outbreak in Argentina

Fusarium graminearum (Schwabe) is reported as the main causal agent of Fusarium head blight in Argentina. The disease causes great losses in humid and semi-humid regions of the world, reducing grain yield and quality. During 2012/13 harvest season, a severe epidemic occurred in Argentina. The aims of this work were to determine the F. graminearum incidence and deoxynivalenol accumulation in wheat grain and flour samples obtained from two of the main wheat growing regions from Argentina. Levels of the pathogen and deoxynivalenol content were correlated in heads, grains and flour. Out of 69 wheat grain samples, 55 (79.7%) showed deoxynivalenol levels between 0.4 and 8.5 μg/kg. Fusarium graminearum was the main species isolated, the isolation frequency ranged from 30 to 52% of the total grains analyzed. Correlations were observed between deoxynivalenol content, % of F. graminearum infection, presence of the pathogen in heads, grain and flour

Upper and lower spinal cord blood supply : the continuity of the anterior spinal artery and the relevance of the lumbar arteries

Objective: Thoracic and thoracoabdominal aortic repair are still complicated by spinal cord ischemia and paraplegia. The aim of the present article is to present the results of an anatomical study conducted by means of both postmortem injection of the vertebral artery and perfusion of the abdominal aorta. Methods: The spinal cord blood supply was investigated in 51 Caucasian cadavers: in 40 cases a methylene blue solution was hand-injected into the vertebral artery, whereas in the remaining 11 cases the abdominal aorta was perfused with a methylene blue solution by means of a roller pump. The level and side of the arteria radicularis magna and the continuity of the anterior spinal artery were recorded. Results: The anterior spinal artery was a continuous vessel without interruptions along the spinal cord in all 51 cases. The arteria radicularis magna level was variable, ranging from T9 to L5. The arteria radicularis magna arose from a lumbar artery in 36 cases (70.5%) and it was left-sided in 32 cases (62.7%). Conclusions: The anterior spinal artery constitutes an uninterrupted pathway between the vertebral arteries, the arteria radicularis magna, and the posterior intercostal and lumbar arteries. Moreover, the arteria radicularis magna arises from a lumbar artery in most of cases. Therefore, the sacrifice of the intercostal arteries during a thoracic aorta repair could be justified, at least from an anatomical standpoint. However, if an extended thoracoabdominal aortic repair is planned, it may be prudent to preserve the blood flow from the lumbar arteries

Pricing Python Parallelism: A Dynamic Language Cost Model for Heterogeneous Platforms

Execution times may be reduced by offloading parallel loop nests to a GPU. Auto-parallelizing compilers are common for static languages, often using a cost model to determine when the GPU execution speed will outweigh the offload overheads. Nowadays scientific software is increasingly written in dynamic languages and would benefit from compute accelerators. The ALPyNA framework analyses moderately complex Python loop nests and automatically JIT compiles code for heterogeneous CPU and GPU architectures. We present the first analytical cost model for auto-parallelizing loop nests in a dynamic language on heterogeneous architectures. Predicting execution time in a language like Python is extremely challenging, since aspects like the element types, size of the iteration space, and amenability to parallelization can only be determined at runtime. Hence the cost model must be both staged, to combine compile and run-time information, and lightweight to minimize runtime overhead. GPU execution time prediction must account for factors like data transfer, block-structured execution, and starvation. We show that a comparatively simple, staged analytical model can accurately determine during execution when it is profitable to offload a loop nest. We evaluate our model on three heterogeneous platforms across 360 experiments with 12 loop-intensive Python benchmark programs. The results show small misprediction intervals and a mean slowdown of just 13.6%, relative to the optimal (oracular) offload strategy