Giuseppe Mazzeo

Absolute configurations of fungal and plant metabolites by chiroptical methods. ORD, ECD, and VCD studies on phyllostin, scytolide, and oxysporone.

The absolute configuration (AC) of the bioactive metabolites phyllostin (1) and scytolide (2), two hexahydro-1,4-benzodioxines produced by Phyllosticta cirsii, and oxysporone (3), a dihydrofuropyranone recently isolated from a strain of Diplodia africana, has been assigned by computational analysis of their optical rotatory dispersion (ORD), electronic circular dichroism (ECD), and vibrational circular dichroism (VCD) spectra. Computational prediction of ORD, ECD, and VCD allowed us to assign (3S,4aR,8S,8aR) AC to naturally occurring (-)-1, while (4aR,8S,8aR) AC was assigned to (-)-2 employing only ECD and VCD, because in this case ORD analysis turned out to be unsuitable for AC assignment. Theoretical prediction of both ORD and ECD spectra of 3 led to assignment of (4S,5R,6R) AC to (+)-3. In this case a satisfactory agreement between experimental and calculated VCD spectra was obtained only after taking into account solvent effects. This study shows that in the case of flexible and complex natural products only a concerted application of more than a single chiroptical technique permits unambiguous assignment of absolute configuration.

Noncovalent Organocatalysis: A Powerful Tool for the Nucleophilic Epoxidation of α-Ylideneoxindoles

A novel asymmetric nucleophilic epoxidation for α-ylideneoxindole esters has been successfully devised, resulting in enantioenriched spiro compounds with two new contiguous stereocenters. The employed (S)-α,α-diphenylprolinol functions as a bifunctional catalyst, creating a complex H-bond network in conjunction with a substrate and an oxidant.

Circularly Polarized Luminescence: A Review of Experimental and Theoretical Aspects

We review the present status of experiments and calculations for circularly polarized luminescence (CPL) of simple organic molecules and of stimuli-responsive organic molecules. Together with the historical report of the main instrumental approaches, a few crucial points about experiments are tackled, with the aim of defining measurement protocols, in view of the wide availability of commercial apparatuses in the near future. The calculations aimed at interpreting the CPL spectra, mostly based on time-dependent Density Functional Theory (TD-DFT) calculations, which started around 2010, are reviewed, limiting the discussion to small to mid-sized molecules. Some applications of CPL spectra of organic molecules-based systems are presented, with a focus especially on two fields: material science and biology. Chirality 28:696-707, 2016.

Absolute configuration assignment of inherently chiral calix[4]arenes using DFT calculations of chiroptical properties.

The racemate of an inherently chiral meta-substituted calix[4]arene derivative 3 has been resolved via enantioselective HPLC. Measured optical rotation dispersion and electronic circular dichroism have been compared with DFT theoretical predictions. The comparison indicates that the absolute configuration of the dextrorotatory enantiomer (+)-3 is cS. The procedure has been successfully tested against a literature precedent confirming the validity of the method.

On the Exportability of Robust Satellite Techniques (RST) for Active Volcano Monitoring

Satellite remote sensing has increasingly become a crucial tool for volcanic activity monitoring thanks to continuous observations at global scale, provided with different spatial/spectral/temporal resolutions, on the base of specific satellite platforms, and at relatively low costs. Among the satellite techniques developed for volcanic activity monitoring, the RST (Robust Satellite Techniques) approach has shown high performances in detecting hot spots as well as in automatically identifying ash plumes, effectively discriminating them from weather clouds. This method, based on an extensive, multi-temporal analysis of long-term time series of homogeneous satellite records, has recently been implemented on EOS-MODIS and MSG-SEVIRI data for which further performance improvements are expected. These satellite systems, in fact, offer improved spectral and/or temporal resolutions. In this paper, some preliminarily results of these analyses are presented, both regarding hot spot identification and ash cloud detection and tracking. The potential of RST, to be used within early warning systems devoted to volcanic hazard monitoring and mitigation, will also be discussed.

A Multi-temporal Robust Satellite Technique (RST) for Forest Fire Detection

In this work, an innovative approach, based on a multi-temporal satellite data analysis, named RST (Robust Satellite Technique), which has already been successfully applied for the monitoring of major natural and environmental risks, has been proposed for the detection of forest fires in near real time. RST is applied in the case of some important forest fires occurred in Northern Italy in recent years using MIR sensors onboard polar (NOAA-AVHRR) and geostationary (MSG-SEVIRI) satellites, moreover, in order to assess the technique performances, also a comparison with well-established MODIS fire algorithm is carried out.

Absolute Configuration through the DFT Simulation of the Optical Rotation. Importance of the Correct Selection of the Input Geometry: A Caveat

In ab initio calculation of ORs of flexible molecules, the input geometries and conformer populations obtained at different levels of theory can yield opposite OR values. Therefore, when at the commonly used DFT/B3LYP/6-31G* level several conformers result, even showing the same sign of OR, additional geometry optimization at a higher level of theory will be absolutely required.

Vibrational circular dichroism and chiroptical properties of chiral Ir(III) luminescent complexes

The octahedral ionic Ir(iii) complex with a dual stereogenic centre of general formula Δ,Λ-(R,S)-[(ppy)2Ir(Me-Campy)]X, where ppy = 2-phenylpyridine and Me-Campy = 2-methyl-5,6,7,8-tetrahydroquinolin-8-amine, and the complex Λ-(R,S)-[(ppy)2Ir(H-Campy)]X, where ppy = 2-phenylpyridine, H-Campy = 8-amino-5,6,7,8-tetrahydroquinolines and X(-) = Cl(-) as a counterion in both cases, have been characterized by vibrational circular dichroism (VCD), which turns out to be efficacious in diastereomeric discrimination. Moreover, the single crystal X-ray structure of the complex Δ-(R)-[(ppy)2Ir(Me-Campy)]Cl is reported here. Density functional theory (DFT) calculations allow us to conclude that the most important doublet feature in the VCD spectra is associated with a clear vibrational exciton structure located on the two dissymmetrically disposed phenylpyridine ligands. The features in the VCD spectra associated with the (R) or (S)-central chirality configuration are identified and commented on. DFT calculations provide also the interpretation of electronic circular dichroism (ECD) spectra. Finally, circularly polarized luminescence (CPL) spectra are presented as an additional chiroptical characterization of these luminescent iridium complexes.

Mode Robustness in Raman Optical Activity.

By reformulating Raman and ROA invariants we provide ground for the definition of robust modes in ROA spectroscopy. Introduction of two parameters defining robustness helps characterization and assignment of ROA bands. Application and use of robustness parameters to [n]helicenes and oxirane/thiirane derivatives are presented.

Assessment of the Robust Satellite Technique (RST) for volcanic ash plume identification and tracking

Volcanic clouds pose a serious threat for both aircrafts and passengers because of ash, which may cause serious damages to the flight control systems and to jet engines. Starting from 2007, an automatic satellite monitoring system has been implemented at IMAA (Institute of Methodologies of Environmental Analysis) to identify and track volcanic ash plumes using NOAA-AVHRR data. This system is capable of providing reliable information about possible volcanic ash plumes over a region of interest (ROI) within a few minute after the sensing time, thanks to the implementation of a robust multi-temporal approach of satellite data analysis named RST (Robust Satellite Technique). This approach has already shown a high potential in successfully identifying and tracking volcanic ash clouds compared to traditional techniques, both in its standard (i.e. two-channel) and advanced (i.e. three-channel) configuration. In this paper, RST performances for ash plume detection and monitoring will be further assessed, showing some recent results obtained during December 2006 and analyzing a time series of satellite observations carried out over Mount Etna area for different months in different observational conditions. In order to validate and assess RST performances, a long-term time domain analysis is in progress, also investigating periods mainly characterised by quiescent phases (i.e. with no ash emission episodes). Preliminary results of such a statistical analysis will be presented and the possible contribution of this satellite monitoring system in supporting management of strong eruptive crisis will also be discussed.