Paolo Roberto Livotto

The Formation of Imidazolium Salt Intimate (Contact) Ion Pairs in Solution

1-n-Butyl-2,3-dimethylimidazolium (BMMI) ionic liquids (ILs) associated with different anions undergo H/D exchange preferentially at 2-Me group of the imidazolium in deuterated solvents. This process is mainly related to the existence of ion pairs rather than the anion basicity. The H/D exchange occurs in solvents (CDCl3 and MeCN for instance) in which intimate contact ion pairs are present and the anion possesses a labile H in its structure, such as hydrogen carbonate and prolinate. In D2 O, separated ion pairs are formed and the H/D exchange does not occur. A plausible catalytic cycle is that the IL behaves as a neutral base in the course of all H/D exchange processes. NMR experiments, density functional calculations, and molecular dynamics simulations corroborate these hypotheses.

An automated approach for the parameterization of accurate intermolecular force-fields. Pyridine as a case study

An automated protocol is proposed and validated, which integrates accurate quantum mechanical calculations with classical numerical simulations. Intermolecular force fields, (FF) suitable for molecular dynamics (MD) and Monte Carlo simulations, are parameterized through a novel iterative approach, fully based on quantum mechanical data, which has been automated and coded into the PICKY software, here presented. The whole procedure is tested and validated for pyridine, whose bulk phase, described through MD simulations performed with the specifically parameterized FF, is characterized by computing several of its thermodynamic, structural, and transport properties, comparing them with their experimental counterparts.

Accuracy of Quantum Mechanically Derived Force-Fields Parameterized from Dispersion-Corrected DFT Data: The Benzene Dimer as a Prototype for Aromatic Interactions

A multilevel approach is presented to assess the ability of several popular dispersion corrected density functionals (M06-2X, CAM-B3LYP-D3, BLYP-D3, and B3LYP-D3) to reliably describe two-body interaction potential energy surfaces (IPESs). To this end, the automated Picky procedure ( Cacelli et al. J. Comput. Chem. 2012 , 33 , 1055 ) was exploited, which consists in parametrizing specific intermolecular force fields through an iterative approach, based on the comparison with quantum mechanical data. For each of the tested functionals, the resulting force field was employed in classical Monte Carlo and Molecular Dynamics simulations, performed on systems of up to 1000 molecules in ambient conditions, to calculate a number of condensed phase properties. The comparison of the resulting structural and dynamic properties with experimental data allows us to assess the quality of each IPES and, consequently, even the quality of the DFT functionals. The methodology is tested on the benzene dimer, commonly used as a benchmark molecule, a prototype of aromatic interactions. The best results were obtained with the CAM-B3LYP-D3 functional. Besides assessing the reliability of DFT functionals in describing aromatic IPESs, this work provides a further step toward a robust protocol for the derivation of sound force field parameters from quantum mechanical data. This method can be relevant in all those cases where standard force fields fail in giving accurate predictions.

Semi-empirical study of a set of 2- 2 -hydroxyphenyl benzazoles using the polarizable continuum model

Abstract A set of molecules (2-(2′-hydroxyphenyl)benzoxazol (HBO), 2-(2′-hydroxyphenyl benzothiazole (HBT) and 2-(2′-hydroxyphenyl)benzimidazole (HBI)) exhibiting excited-state intramolecular proton transfer was studied using the polarizable continuum model in low-polar, non-protic solvents (chloroform and carbon tetrachloride), combined with the AM1 semi-empirical molecular orbital method in both gaseous and condensed phase. The heats of formations (Δ H f ) are lowered by the solvent effect, especially in chloroform. The increase in the solvent polarity causes an enlargement of the Stokes shift between absorption and emission.

Silica imprinted materials containing pharmaceuticals as a template: textural aspects

Silica-based materials were prepared by the acid catalyzed sol–gel method using different pharmaceuticals as a template. The template molecules investigated were fluoxetine, gentamicin, lidocaine, morphine, nifedipine, paracetamol and tetracycline. The resulting hybrid silicas underwent ultrasound extraction in the presence of several solvents and were characterized by elemental analysis, porosimetry by adsorption/desorption of nitrogen (BET method), small-angle X-ray scattering and X-ray diffraction. Drug extraction was carried out by the combination of solvent and ultra-sound. The textural characteristics of the hybrid xerogels and resulting imprinted materials were shown to be highly dependent on the molecular weight and molecular volume of the drug template. Increasing the molecular weight of the template results in a decrease in the encapsulation content of the resulting material. In the case of paracetamol and fluoxetine, the dimensions of the surface area are not sufficient to guarantee the adsorption of the smaller molecule. Instead, the shape generated through encapsulation and extraction during the production of the imprinted silica dictates the adsorption behavior.

Experimental and theoretical study on the reactivity of the R-CN/H2O2 system in the epoxidation of unfunctionalized olefins

A reatividade da acetonitrila, tricloroacetonitrila, benzonitrila, m-clorobenzonitrila, 3-cianopiridina, 1-naftonitrila e 9-antracenonitrila na geracao in situ do respectivo acido peroxicarboximidico foi estudada por calculos de OM, utilizando o metodo AM1, e experimentalmente na epoxidacao do cicloexeno e R-(+)-limoneno. Os resultados experimentais mostraram que a reatividade do sistema Cl3CCN/H2O2 foi semelhante ao MCPBA na epoxidacao de olefinas nao-funcionalizadas, quando o solvente utilizado foi uma mistura bifasica CH2Cl2/H2O.

Computational study of the geometry and electronic structure of triazolephthalocyanines

Semiempirical molecular orbital methods were used to simulate the molecular structure and electronic spectra of a series of triazolephthalocyanines (Tpcs). All molecular studies are in agreement with an aromatic macrocycle where a hypothetical substitution on both triazole and meso nitrogens of the core causes a partial breakdown in the Goutermans four level model. Minor effects are predicted for the substitution in the isoindole subunit. Comparison between the experimental and theoretical UV–VIS spectra of different metal substituted triazolephthalocyanines is also made.

Optimization of molecular cavities in the PCM of neutral molecules using charge dependent atomic radii: applications to the semi-empirical AM1 and MNDO/PM3 methods

Abstract An improvement in the results from the polarizable continuum model (PCM), when coupled to the AM1 and MNDO/PM3 semi-empirical methods, has been obtained by an optimization of the molecular cavities using charge-dependent atomic radii. A set of neutral molecules, containing different functional groups, was used to parametrize functions relating Mulliken atomic net charges to atomic radii. Another set of neutral molecules was utilized to test these functions. The RMS errors in free energy of hydration were 0.47 kcal mol−1 for AM1 and 0.74 kcal mol−1 for MNDO/PM3.

Synthesis of new family of thiazoline and thiazole esters and investigation of their thermal properties

A new family of thiazoline and thiazole esters has been synthesized and their thermal properties are presented and discussed. Thiazoline esters were obtained by cyclization reaction from 4-substituted benzenenitrile and amino acid L-cysteine followed by esterification reaction with selected alcohols and phenol. Subsequent oxidation step to transform thiazoline esters into thiazole esters was applied mediated by BrCCl3/DBU. The final thiazoline and thiazole esters are composed by terminal flexible hydrogenated alkyl chain from one side and to the other side by terminal segments of flexible alkyl chains (hydrogenated chain), (perfluoralkyl)alkyl chains (semifluorinated alkane) p-alkoxyphenyl chains. Some liquid crystals compounds for thiazoline and thiazole esters showed to be relevant. One of the thiazoline esters display a monotropic smectic A (SmA) mesophase while some thiazole esters show stable SmA mesophase. As expected semifluorinated alkane chain induce the formation of orthogonal mesophase by means of segregation effect.

The retro-chloropalladation reaction of heterosubstituted alkynes

Abstract The bridge-splitting reaction of dimeric palladacycles of the type {Pd[κ1-C, κ1-N-C(R)C(Cl)CH2NMe2](μ-Cl)}2 (R=Ph, Me, CH2CH2OH), derived from the chloropalladation of propargyl amines (RCCCH2NMe2), with pyridine (Py), triphenylphosphine (PPh3) and tert-butylisonitrile (tBuNC) affords the monomeric compounds [PdC(R)CCH2NMe2(Cl)L] (L=Py, PPh3, tBuNC). These monomeric compounds are not stable in solution and undergo retro-chloropalladation reactions yielding the propargyl amines and [PdCl(L)-μ-Cl]2. This process is strongly dependent upon the nature of the incoming nucleophile (L), the R group on the metallated ligand and the temperature. The retro-halopalladation reaction is almost instantaneous in the case of the reaction of the bromo derivative [PdC(Ph)C(Br)CH2NMe2-μ-Br]2 and pyridine at room temperature. These results can be rationalized in terms of the stability of the PdC bond of the intermediate monomeric compound [PdC(R)C(X)CH2NMe2(X)L], that is directly related to the nature of its substituents R (Ph, Me and CH2CH2OH), of ligands which are both cis and trans to it (Py, CNtBu, PPh3, Cl and Br) and the temperature.