Application of electronic circular dichroism in configurational and conformational analysis of organic compounds

This tutorial review is addressed to readers with a background in basic organic chemistry and spectroscopy, but without a specific knowledge of electronic circular dichroism. It describes the fundamental principles, instrumentation, data analysis, and different approaches for interpretation of ECD. The discussion focuses on the application of ECD, also in combination with other methods, in structural analysis of organic compounds, including host-guest complexes, and will emphasize the importance of the interplay between configurational and conformational factors. The tutorial also covers modern supramolecular aspects of ECD and recent developments in computational methods.     

A new, stereoselective, ring-forming reaction of 1,2-ethanedithiol with N-acylated indoles

While attempting to prepare 2,5-dithiacyclopentyl derivatives from N-acyl 5-fluoroindole by reaction with 1,2-ethanedithiol we discovered that, instead of the expected product, annelation occurred to give a tricyclic compound containing a 3,6-dithiaazepine ring. This reaction is stereoselective and was found to be general for N-acylindoles, not being affected by substituents on the indole ring.     

On the existence of a Gysin morphism for the Blow-up of an ordinary singularity

In this paper we characterize the Blowing-up maps of ordinary singularities for which there exists a natural Gysin morphism, i.e. a bivariant class \(\theta \in Hom_{D(Y)}(R\pi _*\mathbb {Q}_X, \mathbb {Q}_Y)\), compatible with pullback and with restriction to the complement of the singularity.     

Second order nonlocal boundary value problems at resonance

We present sufficient conditions for the existence of positive solutions for some second order boundary value problems at resonance. The boundary conditions that we study are quite general, involve a Stieltjes integral and include, as particular cases, multi‐point and integral boundary conditions. Our results are based on a Leggett‐Williams norm‐type theorem due to O'Regan and Zima. We employ a general abstract approach which allows us to improve and complement recent results in the literature. © 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim     

Efficient on-line algorithms for Euler diagram region computation

Euler diagrams are an accessible and effective visualisation of data involving simple set-theoretic relationships. Sets are represented by closed curves in the plane and often have wellformedness conditions placed on them in order to enhance comprehensibility. The theoretical underpinning for tool support has usually focussed on the problem of generating an Euler diagram from an abstract model. However, the problem of efficient computation of the abstract model from the concrete diagram has not been addressed before, despite this computation being a necessity for computer interpretations of user drawn diagrams. This may be used, together with automated manipulations of the abstract model, for purposes such as semantic information presentation or diagrammatic theorem proving. Furthermore, in interactive settings, the user may update diagrams “on-line” by adding and removing curves, for example, in which case a system requirement is the update of the abstract model (without the necessity of recomputation of the entire abstract model). We define the notion of marked Euler diagrams, together with a method for associating marked points on the diagram with regions in the plane. Utilising these, we provide on-line algorithms which quickly compute the abstract model of a weakly reducible wellformed Euler diagram (constructible as a sequence of additions or removals of curves, keeping a wellformed diagram at each step), and quickly updates both the set of curves in the plane as well as the abstract model according to the on-line operations. Efficiency is demonstrated by comparison with a common, naive algorithm. Furthermore, the methodology enables a straightforward implementation which has subsequently been realised as an application for the user classification domain.     

Structure, resolution and chiroptical analysis of stable lanthanide complexes of a pyridylphenylphosphinate triazacyclononane ligand

Lanthanide complexes of a pyridylphenylphosphinate ligand based on triazacyclononane form an isostructural series. The C(3)-symmetric Δ and Λ complexes of Eu and Tb are strongly emissive and can be resolved by chiral HPLC; the absolute configuration of each complex has been assigned using CD and CPL measurements.     

A melanin-inspired pro-oxidant system for dopa(mine) polymerization: mimicking the natural casing process

An oxygen-dependent biomimetic system for DOPA, dopamine and norepinephrine polymerization exploiting the redox properties of a 5-S-cysteinylDOPA (CD)-melanin polymer is disclosed. Kinetic, chemical and scanning electron microscopy (SEM) evidence indicates conversion of DOPA into a black insoluble polymer encapsulating the active CD-melanin core.     

Dansyl labeling and bidimensional mass spectrometry to investigate protein carbonylation

Carbonylation is a non-enzymatic irreversible post-translational modification. The adduction of carbonyl groups to proteins is due to the presence of excess of ROS in cells. Carbonylation of specific amino acid side chains is one of the most abundant consequences of oxidative stress; therefore, the determination of carbonyl groups content in proteins is regarded as a reliable way to estimate the cellular damage caused by oxidative stress. This paper reports a novel RIGhT (Reporter Ion Generating Tag) (A. Amoresano, G. Monti, C. Cirulli, G. Marino. Rapid Commun. Mass Spectrom. 2006, 20, 1400) approach for selective labeling of carbonyl groups in proteins using dansylhydrazide, coupled with selective analysis by bidimensional mass spectrometry. We first applied this approach to ribonuclease A and lysozyme as model proteins. According to the so-called 'gel-free procedures', the analysis is carried out at the level of peptides following tryptic digest of the whole protein mixture. Modified RNaseA was analyzed in combined MS(2) and MS(3) scan mode, to specifically select the dansylated species taking advantage of the dansyl-specific fragmentation pathways. This combination allowed us to obtain a significant increase in signal/noise ratio and a significant increase in sensitivity of analysis, due to the reduction of duty cycle of the mass spectrometer. The unique signal obtained was correlated to peptide 1-10 of RNaseA carbonylated and labeled by dansylhydrazide. This strategy represents the first method leading to the direct identification of the carbonylation sites in proteins, thus indicating the feasibility of this strategy to investigate protein carbonylation in a proteomic approach.     

Conformational aspects in the studies of organic compounds by electronic circular dichroism

The electronic circular dichroism (ECD) spectra of flexible molecules include the contributions of all conformers populated at the working temperature. ECD spectra of chiral substrates depend on their stereochemistry in terms of both absolute configuration, as reflected in the sign of the spectrum, and molecular conformation, which dictates the overall spectral shape (possibly including the sign) in a very sensitive manner. The unique high sensitivity of ECD towards conformation, as well as of other chiroptical spectroscopies, renders these techniques a useful alternative or complement to standard spectroscopic tools for conformational investigations, such as NMR. This tutorial review provides first a brief discussion of the main principles of ECD spectroscopy and related methods for interpretation of spectra, with special reference to conformational aspects. The review focuses on the common problems encountered in the application of ECD for assignments of absolute configuration of flexible molecules. These problems can be handled either by taking into account the whole conformational ensemble or by considering rigid derivatives prepared ad hoc. Finally, the review presents the relatively less common but very interesting application of ECD spectroscopy for conformational analyses of organic compounds.     

Identification of photodegradation products of Allura Red AC (E129) in a beverage by ultra high performance liquid chromatography–quadrupole-time-of-flight mass spectrometry

The study deals with the identification of the degradation products formed by simulated sunlight photoirradiation in a beverage that contains Allura Red AC (E129) dye. An UHPLC–MS/MS method that makes use of high resolution quadrupole-time-of-flight mass spectrometer, was developed. For the identification of the degradation products the software tool Information Dependent Acquisition (IDA) was used to automatically obtain information about the high resolution MS and MS/MS spectra of the species present.