Towards the elaboration of a QM method to describe molecular solutes under the effect of a very high pressure

In this paper, we present a new computational QM method for the study of structural properties (i.e. equilibrium geometry) of molec- ular systems at very high pressure. The procedure is based on the polarizable continuum model (PCM) method, usually used to study molecular solutes under standard pressure conditions. The paper considers two critical items: the definition of the pressure and the elab- oration of an analytical code for the calculation of molecular gradients. The method has been developed at HF and DFT levels, with computational costs comparable with those of similar calculations in vacuo. The numerical examples regarding the equilibrium geome- tries and conformational energies of 1,3-butadiene under high pressure give an indication of the potentialities of the approach and of the problems to which it may be applied

Combined Computational and Experimental NMR Study of Calix[4]arene Derivatives

A combined computational and experimental study of a complex supramolecular system constituted by calix[4]arene derivatives that dimerize upon CO2 binding is presented. The theoretical investigation includes ab initio density functional theory, molecular dynamics, and metadynamics analysis of both monomers and dimers. The ab initio calculation of the dimerization energy demonstrates the exergonic character of the process, due to the formation of a strong hydrogen bond network between ammonium and carbamate groups. The dimerization is driven by −31.1 kcal/ mol in the case of the fully outward orientation of the carbamic hydrogens, while it results in a weaker process when different carbamic orientations are considered. The molecular dynamics simulations show the critical conformational degrees of freedom driving monomers and dimers toward common structures. These conformations show tilted orientations of the carbamic groups highlighting the fundamental role of dynamics in evaluating the most stable configurations. Metadynamics simulations describe, in agreement with the other computational tools, the conformational free energy surface of these calix[4]arenes defining three stable conformational families. ROESY and variable temperature 1H NMR experiments are in agreement with our simulations. The presented approach aims to be the reference for investigating complex supramolecular systems

Calculation of pKa Values of Nucleobases and the Guanine Oxidation Products Guanidinohydantoin and Spiroiminodihydantoin using Density Functional Theory and a Polarizable Continuum Model

An efficient computational method has been identified that uses B3LYP density functional theory, IEF-PCM solvation modeling with a modified UFF cavity, and Boltzmann weighting of tautomers to predict the site-specific and global pK(a) of DNA nucleobases and their oxidation products. The method has been used to evaluate the acidity of guanidinohydantoin (Gh) and spiroiminodihydantoin (Sp), two highly mutagenic guanine oxidation products. The trend observed for the pK(a) values of Gh (9.64 and 8.15) is consistent with the experimentally observed values for guanidine cation (13.7) and hydantoin (9.16). The pK(a1)(calc) value for deprotonation of Sp cation (Sp(+) --> Sp) is very close to the experimentally observed pK(a1) for 8-oxoG and is consistent with the similarity in their structures. The data suggest that the imide (N7) proton in Sp is considerably more acidic than that in Gh, possibly due to the presence of the through-space electronic effects of the carbonyl group located at C6. This difference in the acidity of Gh and Sp may be an indication of their potential toxicity and mutagenicity in vivo and remains a fertile area for experimental study

Synthesis, characterization, crystal structure and luminescence properties of phosphinic silver(I) complexes with thiourea derivatives

Reaction of phenylisothiocyanate with different aromatic amines allowed the synthesis of compounds containing the thiourea moiety. By reacting silver bis(triphenylphosphine)nitrate with suitable ligands belonging to this family of sulphurated compounds, three new complexes have been afforded. Ligands and complexes were characterized also by X-ray diffraction. The structures reveal remarkable differences in the silver coordination geometry in function of the nature and size of the ligand. The emission properties of all compounds were characterized at 10 and at 298 K

Oxidative Addition of Iodomethane to Charge-Tuned Rhodium(I) Complexes

The zwitterionic Rh(I) monocarbonyl complex [Rh(EtSNS)(CO)] (1, EtSNS =EtNC(S)Ph(2)P=NPPh(2)C(S)NEt(-)) was reacted with iodomethane in dichloromethane, yielding the stable acetyl-Rh(III) complex [Rh(EtSNS)(COCH(3))I] (4). Complex 4 was characterized in solution and in the solid state by X-ray diffraction analysis.. The rate constant of the reaction [5.48 (7) x 10(-2) M(-1) s(-1) at 25 degrees C CH(2)Cl(2)] and the activation parameters Delta H(double dagger) [28(3) kJ mol(-1)] and Delta S(double dagger)[-173(10) J mol(-1) K(-1)] were determined, confirming a nucleophilic addition mechanism. The rate constant was obtained by monitoring the acetylic product by (1)H NMR, under second-order conditions ([Rh]/[CH(3)I]=1). Complex 1 can be mono- and biprotonated with HX (X=PF(6), OTf, NO(3)), forming [Rh(HEtSNS)(CO)]X (2 center dot X) and [Rh(H(2)EtSNS)(CO)]X(2) (3 center dot X(2)), respectively. A decrease of the calculated DFT Mulliken atomic population on the Rh atom is observed along the series 1 > 2 > 3 in accordance with the variation of the coordinated CO stretching frequency. Compounds 2 center dot X were also reacted with iodomethane, forming complexes [Rh(HEtSNS)(COCH(3))I]X (5 center dot X), stable in solution for a short time, that transform by deprotonation into 4 and into unidentified decomposition products. The rate constants were determined under pseudo-first-order conditions due to the lower reactivity [2 center dot NO(3)=24.6 (6) x 10(-5) M(-1) s(-1); 2 center dot OTf=12.7 (3) x 10(-5) M(-1) s(-1); 2 center dot PF(6)=2.50 (6) x 10(-5) M(-1) s(-1)]. The activation parameters for 2 center dot PF(6) were also determined. The influence of the counterion could be explained assuming that the different non-metal-coordinated anions form hydrogen bonding with the NH group of 2 center dot X, which in turn causes a variation of the electron density on the Rh center. A good correlation between the CO stretching frequencies and the rate constants was observed. The experimental rate constant for complex 1 is 1 order of magnitude higher than the one calculated using the linear regression function obtained for the 2 center dot X series (experimental=5.48 x 10(-2) M(-1) s(-1); calculated=1.29 x 10(-3) M(-1) s-(1)), pointing out that the monoprotonated complexes react more slowly than expected. Both steric and electronic effects were examined and held responsible for this reduced reactivity. Complexes 3 center dot X(2) reacted too slowly, yielding complex 4 and unidentified decomposition products, hindering the determination of the rate constants

Mechanistic insights into acetophenone transfer hydrogenation catalyzed by half-sandwich ruthenium(II) complexes containing 2-(diphenylphosphanyl)aniline - a combined experimental and theoretical study

Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphanyl)aniline (PNH2) of formula {Ru[(kappa P-2,N)PNH2](p-cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4 (1d), TfO (1e)] were synthesized and fully characterized both in solution (H-1 NMR and P-31{H-1) NMR spectroscopy) and in the solid state (FTIR, X-ray analysis on single crystal). Complexes 1a and 1b are active precatalysts in the hydrogen transfer reaction of acetophenone, leading to tof values up to 4440h(-1). In comparison, the {Ru[(kappa P-2,N)-PNMe2](p-cymene)Cl}Cl complex leads to a tof value of 100 h(-1) under the same catalytic conditions. The mechanism through which the precatalysts operate was deeply explored by high-resolution MS (ESI) and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through a bifunctional mechanism analogous to that proposed for diamines and amino alcohol ligands

Mechanistic Insights Into Acetophenone Transfer Hydrogenation Catalyzed by Half-Sandwich Ruthenium(II) Complexes Containing 2-(Diphenylphosphanyl)aniline - A Combined Experimental and Theoretical Study

Several new half-sandwich ruthenium(II) complexes containing 2-(diphenyphosphino)aniline (PNH2) of formula {Ru[(κ2PN)-PNH2](p-cymene)Cl}Y [Y = Cl (1a), PF6 (1b), BF4 (1c), BPh4(1d), TfO (1d)] have been synthesized and fully characterized bothin solution (H NMR and P{H} NMR) and in the solid state (FT-IR, X-ray analysis on single crystal). The complexes 1a an1311d 1b are active pre-catalysts in the hydrogen transfer reaction (HTR) of acetophenone, leading to tof values up to 4440 h. In comparison the complex {Ru[(κ2PN)-PNMe2](p-cymene)Cl}Clleads to a tof value of 100 h-1 under the same catalytic conditions. The mechanism through which the pre-catalysts operate has been deeply explored by high resolution ESI-MS and DFT/PCM studies. The results reveal that the complexes containing PNH2 operate through the bifunctional mechanism analogous to that proposed for diamines and aminoalcohol ligands