Chiroptical Properties and Absolute Configuration of Chiral, Open Chain Di- and Tri-substituted Allenes: a Polarizability Approach

A second order treatment of the optical activity of chiral diand tri-substituted open chain allenes, by means of the polarizability model of DeVoe, makes it possible to establish a simple relationship between optical rotatory power and absolute configuration of these compounds

On the Chiroptical Behavior of Conjugated Multichromophoric Compounds of a New Pseudoaromatic Class: Bicolchicides and Biisocolchicides

It is well known that, stemming from the mutual interplay between chromophores, circular dichroism (CD) is a powerful technique to deal with structural problems for both the small organic molecule and the biopolymer. However, quantitative interpretations of the spectroscopic and structural terms that give rise to the exciton couplet are usually presented for ideal cases, or a few CD bands only are taken into account, overlooking the role of the solvent medium. Circular dichroism and UV absorption spectra were carried out for colchicide (3) and isocolchicide (6), as well as their coupling products, 10,10'-bicolchicide (2) and 9,9'-biisocolchicide (5), in both hydrogen bonding and non hydrogen bonding solvents, as well as MeCN/H(2)O mixtures. A dramatic control by the solvent emerged, as even tiny changes in the composition of solvent mixtures, at ca 1 water molar fraction, induced a dramatic modification of their CD bands. A mutarotation phenomenon--long known for isocolchicine (8)--was also observed for 5, and can be attributed to the interconversion between atropisomers (R(a),7S),(R(a),7'S)-5a and (R(a),7S),(S(a),7'S)-5b. Our data show that with molecules built on two structurally identical moieties which embody both hydrophilic and hydrophobic groups, even tiny changes in the composition of solvent mixtures cause a dramatic modification of the CD bands. Their analysis arrives at a qualitative rationalization of the observed CD couplets from the coupling of high energy transitions, while attempts at a quantitative interpretation of these phenomena through time-dependent density functional theory allowed to reproduce satisfactorily the CD spectrum in the 300-450 nm region only. Failure with higher energies probably reflects currently inadequate specific theoretical treatments of the solvent medium

Copper-Triggered Aggregation of Ubiquitin

Neurodegenerative disorders share common features comprising aggregation of misfolded proteins, failure of the ubiquitin-proteasome system, and increased levels of metal ions in the brain. Protein aggregates within affected cells often contain ubiquitin, however no report has focused on the aggregation propensity of this protein. Recently it was shown that copper, differently from zinc, nickel, aluminum, or cadmium, compromises ubiquitin stability and binds to the N-terminus with 0.1 micromolar affinity. This paper addresses the role of copper upon ubiquitin aggregation. In water, incubation with Cu(II) leads to formation of spherical particles that can progress from dimers to larger conglomerates. These spherical oligomers are SDS-resistant and are destroyed upon Cu(II) chelation or reduction to Cu(I). In water/trifluoroethanol (80∶20, v/v), a mimic of the local decrease in dielectric constant experienced in proximity to a membrane surface, ubiquitin incubation with Cu(II) causes time-dependent changes in circular dichroism and Fourier-transform infrared spectra, indicative of increasing β-sheet content. Analysis by atomic force and transmission electron microscopy reveals, in the given order, formation of spherical particles consistent with the size of early oligomers detected by gel electrophoresis, clustering of these particles in straight and curved chains, formation of ring structures, growth of trigonal branches from the rings, coalescence of the trigonal branched structures in a network. Notably, none of these ubiquitin aggregates was positive to tests for amyloid and Cu(II) chelation or reduction produced aggregate disassembly. The early formed Cu(II)-stabilized spherical oligomers, when reconstituted in 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) liposomes and in POPC planar bilayers, form annular and pore-like structures, respectively, which are common to several neurodegenerative disorders including Parkinson's, Alzheimer's, amyotrophic lateral sclerosis, and prion diseases, and have been proposed to be the primary toxic species. Susceptibility to aggregation of ubiquitin, as it emerges from the present study, may represent a potential risk factor for disease onset or progression while cells attempt to tag and process toxic substrates

Biochemical fluorometric method for the determination of riboflavin in milk

Methods of analysis of vitamin B2 in foods generally consist of the extraction of the sample, followed by enzymatic hydrolysis and quantitative measurement of the analyte, typically through RP-HPLC. The scope of our work here is to present a soft method to measure the free riboflavin content of a nontransparent and nonhomogeneous matrix such as milk, avoiding any extraction and separation of phases that are required in any published method for determination of the free RBF content in foods. We combine the front-face (FF) measurement of the light emission of milk with the ability of the apo-form of the riboflavin-binding protein (RBP) from chicken egg white to quench the riboflavin fluorescence. Thus, we titrate the RBF present in milk by gradually adding a solution of RBP to the milk sample and measuring, upon each addition, the FF residual emission due to uncomplexed RBF. The RBP binding capability has been measured in the same matrix of the analyte. Our results indicate a concentration of free RBF practically co-incident with the certified value for total B2 vitamin content in reference milk CRM 421

External constraints for inner-shell molecular ion calculations

Inner-shell ionization energies in some model molecular systems are reported. They were derived via direct calculation of the relevant upper states expanded over the same basis sets used for the ground state, neutral, configurations of the initial closed-shell Ψo(N) wavefunctions. External constraints included during the SCF process are shown to improve the agreement with ESCA experiments

Olio di Oliva Extravergine Toscano: uno studio sul contenuto dei pigmenti e prospettive per un nuovo indice di qualità

Nel 2014 il nostro gruppo di ricerca ha messo a punto un nuovo metodo di analisi degli spettri di assorbimento nella regione ultravioletto-visibile (UV-vis) dell’olio di oliva extravergine per ricavare, in modo rapido e semplice, la quantità di alcuni pigmenti, i principali, che conferiscono a questo tipo di olio di oliva alcune importanti caratteristiche. Il contenuto in -carotene, luteina, feofitina A e feofitina B dell’olio di oliva extra-vergine è legato infatti alla qualità, alla freschezza e allo stato di conservazione del prodotto. In questo articolo, descriveremo alcune recenti applicazioni di questo metodo ad un campione rappresentativo di oli di oliva extravergine prodotti in Toscana da olive toscane. Verranno discussi alcuni parametri derivati dall’analisi degli spettri UV-vis che possono essere correlati alle diverse annate (dal 2011 al 2015), alle condizioni di conservazione e al “tempo di vita” dell’olio di oliva extravergine. Queste ricerche sono importanti non solo per caratterizzare uno dei prodotti agroalimentari più legati alla cultura e alla cucina mediterranea, ma anche per evidenziare eventuali frodi e adulterazioni che rischiano di minare l’autenticità dell’olio di oliva extravergine prodotto nella nostra regione