Luigi Cassidei

Oxidations by methyl(trifluoromethyl)dioxirane. 3. Selective polyoxyfunctionalization of adamantane

Adamantane (1) can be converted directly into adamantan-1,3,5-triol (5) and into adamantan-1,3,5,7-tetraol (6) under remarkably mild conditions by employing an excess of isolated methyl(trifluoromethyl)dioxirane (3a) in solution. This new dioxirane species was found to be over 7,000-fold more reactive than dimethyldioxirane (3b) in performing adamantane hydroxylations.

Oxidations by methyl trifluoromethyl dioxirane. Epoxidation of enol ethers

Abstract Isolated methyl trifluoromethyl dioxirane 4b has been employed to achieve the rapid, low temperature epoxidation of enol ethers, such as alkoxy(aryl)methylidene adamantanes 1a–e and methoxy(2-naphthyl)methylidene 2-bornane 1f , affording the corresponding spirooxiranes in excellent (92–97%) yields.

Recent Theoretical Approaches to Minimal Artificial Cells

Minimal artificial cells (MACs) are self-assembled chemical systems able to mimic the behavior of living cells at a minimal level, i.e. to exhibit self-maintenance, self-reproduction and the capability of evolution. The bottom-up approach to the construction of MACs is mainly based on the encapsulation of chemical reacting systems inside lipid vesicles, i.e. chemical systems enclosed (compartmentalized) by a double-layered lipid membrane. Several researchers are currently interested in synthesizing such simple cellular models for biotechnological purposes or for investigating origin of life scenarios. Within this context, the properties of lipid vesicles (e.g., their stability, permeability, growth dynamics, potential to host reactions or undergo division processes…) play a central role, in combination with the dynamics of the encapsulated chemical or biochemical networks. Thus, from a theoretical standpoint, it is very important to develop kinetic equations in order to explore first—and specify later—the conditions that allow the robust implementation of these complex chemically reacting systems, as well as their controlled reproduction. Due to being compartmentalized in small volumes, the population of reacting molecules can be very low in terms of the number of molecules and therefore their behavior becomes highly affected by stochastic effects both in the time course of reactions and in occupancy distribution among the vesicle population. In this short review we report our mathematical approaches to model artificial cell systems in this complex scenario by giving a summary of three recent simulations studies on the topic of primitive cell (protocell) systems.

Atom scattering from disordered surfaces. Theoretical study on the validity of the cross section overlap hypothesis: the case of vacancies on Pt(111)

Abstract A theoretical analysis of the hypothesis of geometric overlap (GO) among cross sections has been performed by studying He scattering from two vacancies arranged on Pt(111) at mutual distances d vac ranging from 5.24 to 52.4 au and for collision wave-numbers k z = 1.0, 2.0, 3.0, and 4.0 bohr −1 . Comparison between quantum cross sections and the corresponding quantities obtained by the GO assumption shows that this hypothesis breaks down because in a wide d vac range the difference between the two kinds of cross sections is greater than experimental error and the overlap between cross sections is negative and therefore physically meaningless.

DISORDERED SURFACES : A SMOOTHED HE-TARGET SCATTERING POTENTIAL FOR METAL ATOMS ADSORBED ON METAL SURFACES

Abstract The theoretical interpretation of experimental results on He scattering from metal adatoms epitaxially grown on metal substrates makes use, in general, of an interaction potential that, as far as the He-adatom interaction is concerned, is a pairwise sum of Lennard-Jones ( V LJ ) terms. This approach results in more corrugated metal surfaces than expected on the basis of both experimental data and qualitative considerations on the contribution of the electron densities of the metal adatoms to the repulsive part of the interaction potential. The present work suggests a very simple way to significantly reduce or eliminate the surface corrugation by averaging the He-adsorbate potential over a unit cell of the substrate lattice. The so obtained potential ( V AV ) was compared with V LJ for the HeAg/Pt(111) colliding system on the basis of turning point surfaces, specular and diffractive intensities vs. surface coverage and angular intensity distribution of scattered atoms, calculated under the sudden approximation. These data show that V AV , although too simple to correctly reproduce all the features of the He-adatom interaction, could represent a useful tool in the study of the growth of metal adlayers.

Theoretical study of interactions among surface defects by He scattering technique: the reason for the failure of the cross section geometric overlap hypothesis

Abstract The study of interactions among surface defects by He scattering technique is mainly based on the hypothesis of geometric overlap (GO) of defect cross sections. Recently, quantum calculations have shown that this hypothesis is not valid. This result has been obtained by considering He scattering from targets consisting of a Pt(111) surface containing two defects, i.e. two CO admolecules or two vacancies arranged at different mutual distances, d def . Quantum cross sections Σ 2 , calculated by sudden approximation for both kinds of defects and in a wide d def range, were in large disagreement — up to 34%, namely more than the 3xperimental and sudden errors on cross section — with the corresponding quantities Σ 2 Δ obtained on a pure geometric ground by the GO hypothesis. Therefore, the main purpose of the present paper is to detect the reason for the GO hypothesis failure. To this end, because a more fruitful comparison can be made between homogeneous quantities, and Σ 2 and Σ 2 Δ are not, suitable target models have been built, containing two CO admolecules or two vacancies on Pt(111) arranged as in the case of the above-mentioned targets. The new targets are such that calculations on He scattering from them give the cross sections σ 2 and σ 2 Δ — both obtained by taking into account He-target interaction, and therefore homogeneous — whose trends versus d def are completely analogous to those of Σ 2 and Σ 2 Δ , respectively. In this way the comparison between σ 2 and σ 2 Δ , is useful to demonstrate that the GO hypothesis fails because it implies — translated in terms of atom-target interaction — that, in the region between the two defects, i.e. where their cross sections overlap, He scattering process could be described by taking into account the interaction of impinging atom with just one of the two defects and neglecting the contemporaneous effect of the other one.

1H-1H Inter-ring coupling constants in isoquinoline and quinazoline. Their relationship with corresponding 19F-19F couplings in perfluoro derivatives

Abstract Complete spectral analysis of 1 H NMR spectra of isoquinoline and quinazoline is performed. Signs of inter-ring coupling constants ( J HH ir ) are determined by INDOR experiments. The mechanisms of transmission of J HH ir are discussed. A linear correlation exists between the majority of J HH ir of quinoline, isoquinoline, and quinazoline and J HH ir of their perfluoroderivatives; exceptions are rationalized. The linear relationship with the near-zero value of intercept J HH ir = 0.02 4 + 0.04 0 J HH ir strongly suggests that J HH ir originate, almost quantitatively, from the Fermi contact term and are transmitted via the π-electron system, except for the peri J HH ir . A computation of the proportionality between J HH ir and J HH ir in quinoline using the Pople and Santry expression for the contribution of π electrons to interring coupling constants gives results which are in satisfactory agreement with those observed experimentally.

The correlation between the statistical properties of surface defect distribution and the specular intensity obtained from low energy He scattering technique

Abstract This paper shows that the He diffraction specular intensity does not depend in a simple, predictable way on single statistical parameters describing the surface defect lateral distribution. In particular it shows the lack of correlation between specular intensity and the geometrical overlap of single defect cross sections, a parameter widely used in the literature for a qualitative interpretation of He atom diffraction data. An approach to the problem of surface structure determination is attempted on the basis of a cluster expansion of the scattering matrix at reflection angle.

PCILO calculation on the ansa conformation of hexahydrorifamycin S

Abstract PCILO calculation on the conformation of the 16, 17, 18, 19, 28, 29 hexahydrorifamycin S points to an ansa chain conformation of the C(12)–C(28) fragment from the alternatives given by a previous 1H NMR spectroscopic study. The energetically favoured conformation of the C(19)–N fragment has also been determined.

Light particle scattering diffraction from surfaces in the sudden approximation

The sudden approximation can be the foundation of a code for performing inexpensive calculations on light particle scattering from huge surface systems. The paper describes the mathematical framework and a sample code which can be used to perform sudden calculations either in the semiclassical approximation or in an exact numerical approach. Also a straightforward extension to the treatment of inelastic collisions in a discrete set of excited states is derived and implemented.