On a possible catalytic effect of water on some nucleophilic substitution reactions in “Inert” solvents

Ab initio SCF MO LCAO calculations with the 4-31G basis set on the ten most stable complexes involving H₂O, HF, HC1, F^– and Cl^– have been examined in order to verify whether there is some evidence supporting the hypothesis that water can act as a catalyst for some nucleophilic substitution reactions performed in inert solvents with hydrogen halides as nucleophile agents (e.g. the formation of halohydrins from epoxides). Energetic considerations and an analysis of the electrostatic contribution to the reactivity of the H₂O-HX adduct seem to support this hypothesis.     

The cis—trans thermal and photochemical interconversion mechanism in the dimide N-oxide. A comparison of the results obtainable with different ab initio calculation techniques

Two possible pathways have been investigated for the cis—trans conversion in diimide N-oxide, viz. a rotation around the NN bond and an in-plane inversion. Calculations have been performed for the ground and lowest excited states by means of a Cl treatment including the configurations found to be the most important in large Cl calculations performed in a few points. It is shown that the rotational mechanism is favoured in the excited states and is probable also in the thermal reaction. Such investigation has been repeated in parallel by using other techniques of lower accuracy: (1) Cl limited to single excitations (EHP method); (2) rigid excitation to virtual orbitals; (3) the half electron methods. Deficiencies of such methods have been brought out and analyzed. In particular methods (2) and (3) lead to an erroneus interpretation of the actual mechanism of the photochemical conversion by rotation.     

Mechanochemical Synthesis of Catalytic Materials

The mechanochemical synthesis of nanomaterials for catalytic applications is a growing research field due to its simplicity, scalability, and eco-friendliness. Besides, it provides materials with distinct features, such as nanocrystallinity, high defect concentration, and close interaction of the components in a system, which are, in most cases, unattainable by conventional routes. Consequently, this research field has recently become highly popular, particularly for the preparation of catalytic materials for various applications, ranging from chemical production over energy conversion catalysis to environmental protection. In this Review, recent studies on mechanochemistry for the synthesis of catalytic materials are discussed. Emphasis is placed on the straightforwardness of the mechanochemical route—in contrast to more conventional synthesis—in fabricating the materials, which otherwise often require harsh conditions. Distinct material properties achieved by mechanochemistry are related to their improved catalytic performance.     

Hyaluronic Acid Derivative Effect on Niosomal Coating and Interaction with Cellular Mimetic Membranes

Hyaluronic acid (HA) is one of the most used biopolymers in the development of drug delivery systems, due to its biocompatibility, biodegradability, non-immunogenicity and intrinsic-targeting properties. HA specifically binds to CD44; this property combined to the EPR effect could provide an option for reinforced active tumor targeting by nanocarriers, improving drug uptake by the cancer cells via the HA-CD44 receptor-mediated endocytosis pathway. Moreover, HA can be easily chemically modified to tailor its physico-chemical properties in view of specific applications. The derivatization with cholesterol confers to HA an amphiphilic character, and then the ability of anchoring to niosomes. HA-Chol was then used to coat Span^® or Tween^® niosomes providing them with an intrinsic targeting shell. The nanocarrier physico-chemical properties were analyzed in terms of hydrodynamic diameter, ζ-potential, and bilayer structural features to evaluate the difference between naked and HA-coated niosomes. Niosomes stability was evaluated over time and in bovine serum. Moreover, interaction properties of HA-coated nanovesicles with model membranes, namely liposomes, were studied, to obtain insights on their interaction behavior with biological membranes in future experiments. The obtained coated systems showed good chemical physical features and represent a good opportunity to carry out active targeting strategies.     

How solvent controls electronic energy transfer and light harvesting

The way that solvent (or host medium) modifies the rate of electronic energy transfer (EET) has eluded researchers for decades. By applying quantum chemical methods that account for the way solvent (in general any host medium including liquid, solid, or protein, etc.) responds to the interaction between transition densities, we quantify the solvent screening. We find that it attains a striking exponential attenuation at separations less than about 20 A, thus interpolating between the limits of no apparent screening and a significant attenuation of the EET rate. That observation reveals a previously unidentified contribution to the distance dependence of the EET rate.     

Effective generation of molecular cavities in polarizable continuum model by DefPol procedure

A new computational strategy for the building of molecular cavities (named DefPol) has been linked to the most recent implementation of the polarizable continuum model (PCM) for the representation of solvent effects on physicochemical properties of large molecules. Free energies, analytical gradients, and Hessians can be computed in this framework in the rigid cavity approximation. Coupling DefPol cavities with a number of other recent improvements of the standard algorithm (e.g., effective use of symmetry, iterative procedures with linear scaling) significantly enlarges the dimensions of systems amenable to refined computations and strongly reduces the gap between computations for isolated molecules and in solution. © 1999 John Wiley & Sons, Inc. J Comput Chem 20: 1693–1701, 1999     

Robust mean–variance hedging via G-expectation

In this paper we study mean–variance hedging under the $G$-expectation framework. Our analysis is carried out by exploiting the $G$-martingale representation theorem and the related probabilistic tools, in a continuous financial market with two assets, where the discounted risky one is modeled as a symmetric $G$-martingale. By tackling progressively larger classes of contingent claims, we are able to explicitly compute the optimal strategy under general assumptions on the form of the contingent claim.     

Adaptive Organic Nanoparticles of a Teflon‐Coated Iron (III) Porphyrin Catalytically Activate Dioxygen for Cyclohexene Oxidation

Self‐organized organic nanoparticles (ONP) are adaptive to the environmental reaction conditions. ONP of fluorous alkyl iron(III) porphyrin catalytically oxidize cyclohexene to the allylic oxidation products. In contrast, the solvated metalloporphyrin yields both allylic oxidation and epoxidation products. The ONP system facilitates a greener reaction because about 89% reaction medium is water, molecular oxygen is used in place of synthetic oxidants, and the ambient reaction conditions used require less energy. The enhanced catalytic activity of these ONP is unexpected because the metalloporphyrins in the nanoaggregates are in the close proximity and the TON should diminish by self‐oxidative degradation. The fluorous alkyl chain stabilizes the ONP toward self‐oxidative degradation.