NH‐Heterocyclic Aryliodonium Salts and their Selective Conversion into N1‐Aryl‐5‐iodoimidazoles

The synthesis of N‐arylimidazoles substituted at the sterically encumbered 5‐position is a challenge for modern synthetic approaches. A new family of imidazolyl aryliodonium salts is reported, which serve as a stepping stone on the way to selective formation of N1‐aryl‐5‐iodoimidazoles. Iodine acts as a “universal” placeholder poised for replacement by aryl substituents. These new λ³‐iodanes are produced by treating the NH‐imidazole with ArI(OAc)₂, and are converted to N1‐aryl‐5‐iodoimidazoles by a selective copper‐catalyzed aryl migration. The method tolerates a variety of aryl fragments and is also applicable to substituted imidazoles.     

Human capital estimation in higher education

The concept of human capital (HC) could be defined, from an economical viewpoint, as a stock variable representing the capacity of an individual to produce a sustained flow of income due to its investment in (higher) education and work experience. This paper focuses on the empirical estimation of the graduates’ latent variable HC, composed of two principal dimensions, Educational HC and Work Experience HC, within a realistic structural model, allowing causal relationship among endogenous and exogenous indicators, taking into account possible effects of external covariates. New administrative archives and a novel methodological approach are used. The methodology is applied to estimate HC of graduates in several universities of the Milan area in the early stages of their working career. The empirical results confirm the structure of the Italian job market, where investment in HC through higher education plays only a marginal role for explaining the economic performance.     

The Reaction Pathway of Cellulose Pyrolysis to a Multifunctional Chiral Building Block: The Role of Water Unveiled by a DFT Computational Investigation

LAC (hydroxylactone (1R,5S)‐1‐hydroxy‐3,6‐dioxabicyclo[3.2.1]octan‐2‐one) is one of the most interesting products of the pyrolysis of cellulose and represents a useful chiral building block in organic synthesis. A computational investigation at the DFT level on the mechanism of formation of LAC shows that this species can be obtained following two reaction paths, path A and path B , starting from a well‐known pyrolysis product (ascopyrone P). A series of internal rearrangements involving in all cases a proton transfer leads directly to LAC ( path B ). An alternative path ( path A ) can be also followed. From this path, via a “gate” connecting the two reaction channels, it is possible to reach path B and form LAC. In both cases, the rate‐determining step of the process is the initial keto‐enol isomerization. We found that water, which is present in the reaction mixture, “catalyzes” the reaction by assisting the proton transfers present in all the steps of the process. In particular, water lowers the barrier of the rate‐determining step that becomes 40.9 kcal mol^?1 (79.4 kcal mol^?1 in the absence of water). The corresponding computed rate constant is 4.3×10 s^?1 at 500 °C, a value which is consistent with the presence of LAC in the absence of metal catalysts. The results of this study on the non‐catalyzed process underpin the important role played by water in the formation of pyrolysis products of cellulose where proton transfer is a key mechanistic step.     

Periodic Solutions of the Burgers-Hopf Equation with Small Parameter and its Cellular Neural Network Model

This paper deals with the periodic solutions of the Cauchy problem to the Burgers-Hopf equation containing small viscosity term. We propose at first an explicit formula for the exact solution of the Cauchy problem and then we give an approximate formula. We use CNN approach for constructing the approximate solution and we find precise estimates of the remainder term. This work was supported by the NATO Grant ICS.NR.CLG 981757.     

Chemoenzymatic and yeast-catalysed synthesis of diastereomeric ethyl γ-phenyl and γ-(n-pyridyl)paraconates

The synthesis of γ-phenyl and γ-(n-pyridyl)paraconates was accomplished by chemical reduction of their respective ketodiester precursors followed by cyclisation of the resulting hydroxy diester intermediates. The cis- and trans-lactones thus obtained were separated and separately subjected to enzymatic hydrolysis with HLAP. The cis-lactonic esters had enantiomeric excesses ranging from 94% to 99%, while for the trans-isomers the ee’s ranged from 80% to 93%. The same ketodiester precursors were subjected to reduction with a series of yeasts. The absolute configuration of trans-(−)-2-pyridyl paraconic acid was assigned by means of X-ray analysis of its hydrobromide salt, while the absolute configurations of the other lactones were determined via analysis of their respective CD curves.     

Premicellar accelerated decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion and its 5-tetradecyloxy derivative

Didodecyldialkylammonium chloride and bromide (alkyl = Me, Et, n-Pr, n-Bu) accelerate the spontaneous decarboxylation of 6-nitrobenzisoxazole-3-carboxylate ion, 1,H, and its 5-tetradecyloxy derivative, 1,OTD. With most of these surfactants, first-order rate constants, kobs, go through maxima in very dilute surfactant and then decrease and go through minima as association colloids form. These phenomena are not explicable in terms of substrate-induced micellization. However, kobs increases in the N-alkyl sequence Me < Et < n-Pr < n-Bu, as is typical of decarboxylations in association colloids of single-chain surfactants. Reaction in premicelles is accelerated by an initial increase in 1,H. The factors that control relative rates of spontaneous reactions in premicelles and in the association colloids, in particular, depletion of water at the reaction center and association of substrate and quaternary ammonium centers, are discussed with respect to the roles of substrate and surfactant hydrophobicities.     

Characterization of protein folding by dominant reaction pathways

We assess the reliability of the recently developed approach denominated dominant reaction pathways (DRP) by studying the folding of a 16 residue beta-hairpin, within a coarse-grained Go-type model. We show that the DRP predictions are in quantitative agreement with the results of molecular dynamics simulations performed in the same model. On the other hand, in the DRP approach, the computational difficulties associated with the decoupling of time scales are rigorously bypassed. The analysis of the important transition pathways supports a picture of the beta-hairpin folding, in which the reaction is initiated by the collapse of the hydrophobic cluster.     

An SFG and DFG investigation of Au(111), Au(100), Au(110) and Au(210) electrodes in contact with aqueous solutions containing KCN

In this paper, the behaviour of Au(111), (100), (110) and (210) electrodes in contact with pH-neutral aqueous solutions of KCN has been studied as a function of potential by means of in situ sum frequency generation (SFG) and difference frequency generation (DFG) spectroscopies. The contribution of both free and bound electrons has been included. Spectroelectrochemical results were complemented with cyclic voltammetric measurements. The main emphasis in this work has been placed on systematising and quantifying the interaction between the vibrational and electronic structures of the electrodic interfaces studied by the systematic comparison of SFG and DFG spectra measured under the same electrochemical conditions for different crystal orientations.     

Transport and separation of biomolecular cargo on paramagnetic colloidal particles in a magnetic ratchet

Paramagnetic particles in a magnetic ratchet potential were transported in discrete steps in an aqueous solution on the surface of a magnetic garnet film. The proposed technique allows the simultaneously controlled, dispersion-free movement of an ensemble of paramagnetic particles across the surface. External magnetic modulations were used to transport the particles in a defined direction, and a current reversal upon changing the size of the particles was used to separate particles having different diameters. Doublets consisting of a larger and a smaller particle functionalized with complimentary oligonucleotides and bound via Watson-Crick base pairing were separated after melting the double stranded DNA.     

Magnetically driven colloidal microstirrer

Paramagnetic colloidal particles dispersed in water and deposited above magnetic bubble domains of a uniaxial ferrimagnetic garnet film are used as microscopic stirrer when subjected to external rotating magnetic fields. The hydrodynamic flow field above the stirrer is detected by tracking of nonmagnetic microspheres. The vorticity of the flow falls off inversely proportionally to the distance from the bubble center and is proportional to the field frequency. The device provides complete control over the mixing capability. This alternative method of active mixing might be used for microfluidics applications where mechanical stirring cannot be achieved easily with other machinery parts.