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The synthesis and catalytic behavior of the osmium(II) complexes [OsCl2 (η6 -p-cymene)(PR2 OH)] [R=Me (2 a), Ph (2 b), OMe (2 c), OPh (2 d)] in nitrile hydration reactions is presented. Among them, the best catalytic results were obtained with the phosphinous acid derivative [OsCl2 (η6 -p-cymene)(PMe2 OH)] (2 a), which selectively provided the desired primary amides in excellent yields and short times at 80 °C, employing directly water as solvent, and without the assistance of any basic additive (TOF values up to 200 h-1 ). The process was successful with aromatic, heteroaromatic, aliphatic, and α,β-unsaturated organonitriles, and showed a high functional group tolerance. Indeed, complex 2 a represents the most active and versatile osmium-based catalyst for the hydration of nitriles reported so far in the literature. In addition, it exhibits a catalytic performance similar to that of its ruthenium analogue [RuCl2 (η6 -p-cymene)(PMe2 OH)] (4). However, when compared to 4, the osmium complex 2 a turned out to be faster in the hydration of less-reactive aliphatic nitriles, whereas the opposite trend was generally observed with aromatic substrates. DFT calculations suggest that these differences in reactivity are mainly related to the ring strain associated with the key intermediate in the catalytic cycle, that is, a five-membered metallacyclic species generated by intramolecular addition of the hydroxyl group of the phosphinous acid ligand to the metal-coordinated nitrile.

The synthesis of a large variety of ureas R1R2NC(O)NH2 (R1 and R2 = alkyl, aryl or H; 26 examples) was successfully accomplished by hydration of the corresponding cyanamides R1R2NCN using the phosphinous acid-based complexes [MCl2(η6-p-cymene)(PMe2OH)] (M = Ru (1), Os (2)) as catalysts. The reactions proceeded cleanly under mild conditions (40-70 °C), in the absence of any additive, employing low metal loadings (1 mol%) and water as the sole solvent. In almost all the cases, the osmium complex 2 featured a superior reactivity in comparison to that of its ruthenium counterpart 1. In addition, for both catalysts, the reaction rates observed for the hydration of the cyanamide substrates were remarkably faster than those involving classical aliphatic and aromatic nitriles. Computational studies allowed us to rationalize all these trends. Thus, the calculations indicated that the presence of a nitrogen atom directly linked to the CN bond depopulates electronically the nitrile carbon by inductive effect when coordinated to the metal center, thus favouring the intramolecular nucleophilic attack of the OH group of the phosphinous acid ligand to this carbon. On the other hand, the higher reactivity of Os vs. Ru seems to be related with the lower ring strain on the incipient metallacycle that starts to form in the transition state associated with this key step in the catalytic cycle. Indirect experimental evidence of the generation of the metallacyclic intermediates was obtained by studying the reactivity of [RuCl2(η6-p-cymene)(PMe2OH)] (1) towards dimethylcyanamide in methanol and ethanol. The reactions afforded compounds [RuCl(η6-p-cymene)(PMe2OR)(NCNMe2)][SbF6] (R = Me (5a), Et (5b)), resulting from the alcoholysis of the metallacycle, which could be characterized by single-crystal X-ray diffraction. This journal is

This article belongs to the Special Issue Theoretical Inorganic Chemistry., A comparative theoretical study on the reactivity of the complexes [ReY(CO)3(bipy)] (Y = NH2, NHMe, NHpTol, OH, OMe, OPh, PH2, PHMe, PMe2, PHPh, PPh2, PMePh, SH, SMe, SPh; bipy = 2,2′-bipyridine) towards methyl propiolate was carried out to analyze the influence of both the heteroatom (N, O, P, S) and the alkyl and/or aryl substituents of the Y ligand on the nature of the product obtained. The methyl substituent tends to accelerate the reactions. However, an aromatic ring bonded to N and O makes the reaction more difficult, whereas its linkage to P and S favour it. On the whole, ligands with O and S heteroatoms seem to disfavour these processes more than ligands with N and P heteroatoms, respectively. Phosphido and thiolato ligands tend to yield a coupling product with the bipy ligand, which is not the general case for hydroxo, alcoxo or amido ligands. When the Y ligand has an O/N and an H atom the most likely product is the one containing a coupling with the carbonyl ligand, which is not always obtained when Y contains P/S. Only for OMe and OPh, the product resulting from formal insertion into the Re-Y bond is the preferred., This research was funded by the Ministerio de Ciencia, Innovación y Universidades (MCIU) of Spain, grant number PGC2018-100013-B-I00.

A computational study is performed for the elucidation of the role played by CuCl in the condensation of two polychlorophenol molecules to yield PCDDs. The mechanism found consists of six sequential steps, which allow the final recuperation of the CuCl molecule, and applies for phenol molecules with an ortho chlorine. In the temperature range of 453-473 K (previously reported as adequate to diminish PCDDs formation in the post-combustion area), CuCl is able to softly retain chlorophenol molecules, mainly those less chlorinated. After a first HCl release, Cu(I) remains bonded to phenol oxygen atom, thus avoiding the formation of phenoxy radicals and the subsequent radical processes. A temperature raise up to 1200 K destabilizes the initial CuCl-chlorophenol complexes and causes that the rate limiting step change from the formation of the first oxygen bridge to HCl elimination. It has been checked that tetra and penta-chlorophenols undergo essentially the same reaction process of 2-chlorophenol. In view of our results and trying to arrive at a practical way to diminish the rate of formation of PCDDs, we propose that an extra addition of powdered CuCl to the post-combustion zone, cooled down to temperatures lower than 473 K, could act as an inhibitor in the formation of these pollutants.

Density functional theory (DFT) calculations have been performed on a homogeneous gold-catalyzed reaction between acetylene/propyne and the cyclic ketal 2,2-dimethyl-1,3-dioxolane, DMDO, in the presence of water, with the aim of understanding the actual role played by water. After the addition of DMDO to the alkyne, hydrolysis may happen through two possible reaction routes. In the so-called H-route (previously proposed for similar intramolecular reactions), a water proton is initially added to the alkyne C atom still linked to gold and, afterwards, an OH group adds to a DMDO C atom to allow the release of acetone, whereas in the newly proposed OH-route, a water OH group firstly adds to the most substituted DMDO C atom with simultaneous addition of H to the alkyne C atom linked to gold. A 1,3-H transposition from the just added OH group allows the release of acetone. An intramolecular nucleophilic OH addition to the gold-activated alkene intermediate formed from both hydrolysis paths drives the system to the corresponding 1,3-dioxolane product. The H-route is unable to explain the formation of the dioxolane addition products (observed in similar intramolecular reactions) instead of those coming from the direct addition of water to the alkyne, since it is energetically more demanding than the direct hydration. However, OH-route goes through structures that are more stable than those in the water addition, so, it is the one actually happening for the reaction under study. The regioselective addition of DMDO to the internal C atom of propyne is predicted on the basis of the large polarity of the structures formed in this approach, which makes them capable of strong interactions with water.

We are thankful for the financial support from CONICYT/CHILE under FONDECYT Project 1171719 (G.C.J.) and USACH/CHILE under DICYT 021841CJ Postdoctoral Project (N.M.-P., G.C.-J), Proyecto Fortalecimiento USACH USA1799_CG241216 (G.C.-J.), and DICYT-Universidad de Santiago de Chile. We also acknowledge CONICYT-PCHA/Doctorado Nacional/2015-21150093 for a Doctoral Fellowship for M.B.-M. and for financial support to perform a research stay at the Universidad de Oviedo (Spain) under the supervision of Professor Ramon Lopez, where part of this work was carried out. Powered@NLHPC: This research was partially supported by the supercomputing infrastructure of the NLHPC (ECM-02) of the Universidad de Chile. RI., M.I.M., and D.A. also thank the Ministerio de Economia y Competitividad (Grant No. CTQ2015-70231-P) and Universidad de Oviedo (Grant No. PAPI-18-PF-05) of Spain for their financial support.

Three chiral Schiff base ligands H2L1, H2L2, H2L3 have been synthesized by treating (R)-1,2-diaminopropane separately with 3,5-dichlorosalicylaldehyde, 3,5-dibromosalicylaldehyde and 3,5-diiodosalicylaldehyde, respectively. Three new asymmetric FeIII complexes, namely, FeL1Cl (1), FeL2Cl (2), FeL3Cl (3) have been prepared from their corresponding ligands. The crystal structure of 2 reveals that the complexes are mononuclear in nature. Circular dichroism (CD) studies suggest that the ligands and their corresponding complexes contain an asymmetric center. The catalytic activity of these complexes toward the epoxidation of alkenes has been investigated in the presence of iodosylbenzene (PhIO), in two solvents CH3CN and CH2Cl2. The epoxide yield suggests that the order of their catalytic efficiency is 3 > 2 > 1. This trend as well as the role of substitution on the ligand backbone on alkene epoxidation has also been confirmed by density functional theory (DFT) calculations. For further adaptation, we attached our most efficient homogeneous catalyst, 3, with surface modified magnetic nanoparticles (Fe3O4@dopa) and thereby obtained the new magnetically separable nanocatalyst Fe3O4@dopa@FeL3Cl. This catalyst has been characterized and its olefin epoxidation ability investigated in similar conditions to those used for homogeneous catalysts. The enantiomeric excess of the epoxide yield reveals the retention of chirality of the active site of Fe3O4@dopa@FeL3Cl. The catalyst can be easily recovered by magnetic separation and recycled several times without significant loss of its catalytic activity.

The heterogeneous equilibrium of the solubility of calcium hydroxide in water is used to predict both its solubility product from solubility and solubility values from solubility product when inert salts, in any concentration, are present. Accepting the necessity of including activity coefficients to treat the saturated solution of calcium hydroxide (and by extension, all electrolyte solutions) and the inadequacy of any general or nonspecific equation (such as the Debye–Huckel limiting law or Davies equations) to calculate activity coefficients of 1:2 electrolytes, our results uncover (i) how the inclusion of ion pairs in the last mentioned equations makes them adequate for low ionic strength solutions and (ii) the need of sophisticated models, such as the ion-interaction Pitzer equations, for calculating the activity coefficients when ionic strength is high. In addition, we have developed a set of MATLAB scripts and propose the use of the free code PHREEQC version 3 to perform all the calculations descri...

Herein we present a theoretical study on the reaction of [Re(PPh) (CO)(phen)] (phen = 1,10-phenanthroline) and [Re(PPh) (CO)(bipy)] (bipy = 2,2′-bipyridine) toward methyl propiolate. In agreement with experimental results for the phen ligand, the coupling of the substituted acetylenic carbon with the nonsubstituted ortho carbon of the phen ligand is the preferred route from both kinetic and thermodynamic viewpoints with a Gibbs energy barrier of 18.8 kcal/mol and an exoergicity of 11.1 kcal/mol. There are other two routes, the insertion of the acetylenic fragment into the P-Re bond and the coupling between the substituted acetylenic carbon and a carbonyl ligand in cis disposition, which are kinetically less favorable than the preferred route (by 2.8 and 1.9 kcal/mol, respectively). Compared with phen, the bipy ligand shows less electrophilic character and also less π electron delocalization due to the absence of the fused ring between the two pyridine rings. As a consequence, the route involving the coupling with a carbonyl ligand starts to be kinetically competitive, whereas the product of the attack to bipy is still the most stable and would be the one mainly obtained after spending enough time to reach thermal equilibrium., The authors thank Ministerio de Economia y Competitividad (Grant No. CTQ2015-70231-P) and Principado de Asturias (Grant No. FC-15-GRUPIN14-103) for financial support. We also acknowledge financial support from CONICYT/CHILE under the Project PAI No. 79150043 (G.I.C.-J. and R.M.-A.) and computing resources from the Fundacion Computacion y Tecnologias Avanzadas de Extremadura (J.D.).

4,4’-Disubstituted-2,2′-bipyridine ligands coordinated to Mo and Re cationic fragments become dearomatized by an intramolecular nucleophilic attack from a deprotonated N-alkylimidazole ligand in cis disposition. The subsequent protonation of these neutral complexes takes place on a pyridine carbon atom rather than at nitrogen, weakening an aromatic C−C bond and affording a dihydropyridyl moiety. Computational calculations allowed for the rationalization of the formation of the experimentally obtained products over other plausible alternatives., Financialsupport from Ministerio de Economía y Competitividad/FEDER (grant CTQ2015-70231-P) and Principado de Asturias (grant GRUPIN14-103) is gratefully acknowledged. J.D.thanks COMPUTAEX for granting access to LUSITANIA supercomputing facilities.

We performed a theoretical study, using density functional theory, about the physical–chemical properties of porphyrin–glucose complexes bonded by a triazine ring (TA) as models of the type photosensitizer-cellulose with potential antibacterial applications. Firstly, we explore the tautomerization mechanism (B3LYP/6-31G(d,p)) in the fragment TA considering three porphyrin–glucose complexes that varies in the porphyrin nature (anionic, cationic, neutral). We characterized the tautomers and the transition states connecting them, and found the keto form [–CONH–] as the most stable tautomer (TA-1). In a second stage, we analyze the ability of the porphyrins as photosensitizers in each porphyrin–glucose complexes in its form TA-1. For the calculation of the UV–Vis spectra, we assessed seven functionals (B3LYP, M05, MPWB1K, PBE, CAM-B3LYP, M06-2X, and LC-BLYP) on a porphyrin, some of which we previously have used. The best agreement with experimental data was obtained at the CPCM(UAKS)-M05/6-31G(d,p) level that then we used to calculate the spectra of the complexes. This functional predicts maximum errors of 0.09 eV for the Q bands. It is showed that the glucose unit does not significantly affect the ability of porphyrin as photosensitizer, and the absorption of Q band of the cationic complex (624 nm) is red shifted with respect to other complexes, which favors its action as photosensitizer. Finally, we focus on the energy released from the fully optimized triplet excited states, which straight relates to the formation of active singlet oxygen. We found that all the porphyrins and their complexes fulfill the requirements to be a good photosensitizer, absorb in the visible light region and release the enough energy to yield the more stable excite state 1Δg for singlet oxygen, which demonstrate that all the systems studied here could be used as antibacterial materials.

A method for the rational design of molecularly imprinted polymers with catalytic activity (MICs) that mimic hemeproteins is described. Density Functional Theory calculations applied to the pre-polymerization adduct and to a possible reaction intermediate allow to choose the best functional monomer that builds up the active sites. This functional monomer should stabilize both relevant stages, the first one in an adequate porogenic solvent and the second one in the aqueous reaction medium. In this work, a MIC was synthesized to catalyze the oxidation of 2,4,6-trichlorophenol (TCP), the substrate and template molecule. A hemin molecule was used as the catalytic centre and four functional monomers and six solvents were tested. According to the theoretical predictions, methacrylamide and 4-vinylpyridine MIPs successfully mimic the recently discovered ability of Chloroperoxidase (CPO) to catalyze the oxidative dechlorination of TCP in batch analysis. They exhibit good catalytic properties and substrate selectivity.

A theoretical study of the geometry, the electronic structure, the electronic absorption spectra, and (1)H and (13)C NMR spectra of the [14]subporphine(1.1.1)-hydroxyboron(III) complex, free-base subporphyrin, and its dioxygen and dithio pyrrole substituted derivatives using CH, N, and P as bridging meso linkages was performed at the B3LYP/6-311+G(2d,p)//B3LYP/6-31G(d) theory level. The geometrical structure of these systems is mainly determined by the internal area delimited by the meso atoms and the alpha-carbon atoms of the pyrrolic rings, and by the number and nature of the atoms located on this area. All the hydroxyboron subporphyrins and dioxo and dithio subporphyrins with CH meso connectors display a conical shaped geometry. The presence of strong repulsions between the atoms on the central zone of the remaining systems provokes a correlative tilting of one of the three rings with loss of the conical shape with important consequences on spectroscopic properties. A particularly interesting case is the dioxosubporphyrin with P connectors in which the large area of the central zone determined by these connectors allows for an almost planar geometry that endows it with special features. The molecules presenting a tilted ring display weak absorption bands. Generally, the intensity of the bands moderately increases when the geometry is cone shaped. The dioxo heterosubporphyrins with CH (conical shape) and P (almost planar) connectors present strong absorption bands. (1)H and (13)C chemical shifts clearly reflect the effect of geometry distortion provoked by the repulsion among the atoms of the central area of the system indicating a deep perturbation of the pi system of the molecules.

KN(SiMe3)2 reacts with [Re(CO)3(phen)(PMe3)]OTf via reversible addition to the phen ligand and irreversible deprotonation of the PMe3 ligand followed by intramolecular attack to phen by the deprotonated phosphane, whereas MeLi irreversibly adds to phen. The addition of MeLi has been shown to be intermolecular, unlike previously known nucleophilic additions to pyridines., The authors thank MINECO and FEDER (grant CTQ2015-70231-P) and Principado de Asturias (grantFC-15-GRUPIN14-103) forfunding, and Ministerio de Educación for an FPU predoctoral fellowship (to R.A.).

The aqueous intramolecular cyclization of 3a-hydroperoxitryptophan, Trp-OOH, (an intermediate in the photodynamic treatment of cancer) is studied at the PCM-MP2/aug-cc-pVDZ//PCM-B3LYP/aug-cc-pVDZ computational level with and without explicit water molecules. The three-cycle product may evolve to the metabolite N-formyl kynurenine in living beings or can be a building block in the formation of indole alkaloids in organic synthesis. When the pH is close to the isoelectric point of tryptophan, we have found two cyclization mechanisms, one passing along zwitterion intermediates, I-route (beginning with a proton transfer from the ammonium to the N-indole atom) and the other involving neutral isomers, C-route (starting with the attack of N-amino to C2-indole). At this pH, the discrete-continuum model with six explicit water molecules predicts a Gibbs energy barrier of 14.6 kcal mol(-1) for the I-route and of 11.6 kcal mol(-1) for the C-route. It is possible to experimentally tune the operating mechanism since in acidic environments only the I-route is available (Gibbs energy barrier of 8.4 kcal mol(-1)) whereas in basic media only the C-route can operate (Gibbs energy barrier of 6.7 kcal mol(-1)). These data explain the trend of Trp-OOH to easily decompose under basification.

A theoretical study of the cycloaddition reactions of ketene and N-silyl-, N-germyl-, and N-stannylimines were performed at the B3LYP/6-311+G(d,p) theory level using the LANL2DZ effective core potential for Ge and Sn and taking into account the effect of diethyl ether solvent by means of the polarizable continuum model method. According to the obtained results the reaction between ketene and N-germylimine is a two-step process due to the effect of solvent, whereas the cycloaddition of ketene and N-silylimine follows a three-step mechanism because in this case the evolution of the electronic energy along the reaction coordinate predominates over the effect of solvent. For N-stannylimine the two- and three-step mechanisms are competitive. In all the cases the rate-determining barrier corresponds to the evolution of the azadiene intermediate. The cycloaddition of ketene and N-germylimine is kinetically the most favorable reaction of the three studied by us and can take place as a domino process. In the three cases the isomerization of the imine through the inversion at the nitrogen atom is easier than the formation of the azadiene intermediate so that the three processes would afford the trans-beta-lactam.

The interaction of CuII with 6-formylamino-3alpha-carboxypenam and 6-acetylamino-3alpha-carboxypenam was investigated by means of DFT calculations with the UB3LYP functional. Nine different modes of complexation between CuII and 6-formylamino-3alpha-carboxypenam were located. When two water molecules directly bonded to CuII are included in the calculations on 6-acetylamino-3alpha-carboxypenam as penicillin model, only six CuII(H2O)2-6-acetylamino-3alpha-carboxypenam complexes (1S-6S) are found. In solution the four most stable complexes obtained from our calculations, 6S, 1S, 2S, and 3S, exhibit CuII in square-planar coordination with at least one bond to the carboxylate group, in agreement with experimental evidence. Complexes 6S, 1S, and 3S were previously suggested by available experimental evidence. In three of the most stable complexes (6S, 2S, and 3S) the beta-lactam C-N bond is remarkably activated and displays C-N bond lengths similar to those found in some tetrahedral intermediates located for the hydrolysis of 2-azetidinones. This suggests that these kinds of complexes belong to the reaction coordinate for the degradation of beta-lactam antibiotics in the presence of CuII.

We report a theoretical analysis of the electronic structure of the enolic form of acetylacetone with the B3PW91, MP2 and CCSD methods using the aug-cc-pVDZ basis set. Although both the GIAO-NICS values and the current density maps display a clear non-aromatic character for cis-2-enol of acetylacetone, C2A, and for the TS for the interconversion of two equivalent cis-2-enols of acetylacetone, TSA, an NBO analysis reveals an important stabilising conjugation stretching all over the skeleton of heavy atoms. The stabilization of TSA by resonance makes possible the dynamic process producing the crystal disorder observed in X-ray diffraction.

A theoretical study of the intramolecular cyclization of a series of propanamides to yield β-lactams was performed at the B3LYP/6-31+G(d,p) and MP2/6-31+G(d,p)//B3LYP/6-31+G(d,p) levels. The effect of the Cl- and OH- leaving groups and of several substituents on N1 and on C4 was investigated. As expected, OH- is a much worse leaving group than Cl-, rendering an energy barrier about 2 times larger. An SO3- substituent on N1 diminishes the energy barrier by destabilizing the intermediate prior to the rate-determining TS, whereas OH and OCH3 substituents do not produce an appreciable effect. According to the MP2 method, one and two methyl substituents on C4 increase the energy barrier of the process. The simultaneous presence of a sulfonate group on N1 and a methyl group on C4 render the corresponding combined effect, while combination of an OH on N1 and two methyl groups on C4 is not simply additive.

The reaction of propargyl cation with NH3 was investigated at the CCSD(T)/6-311+G(2df,2p)//MP2-FULL/6-31+G(d,p) theory level by performing a statistical thermodynamics analysis of the theoretical results. Three different reactive channels starting at an association complex were found. The first one is the C2H4 + HCNH+ channel, which proceeds under the energy level corresponding to reactants and is the most exothermic one, −34.1 kcal/mol in Gibbs energy, but which implies complex molecular rearrangements giving rise to several adducts much more stable than reactants. The other two channels are the c-C3H2 + NH4+ channel, which is exothermic by only 3.3 kcal/mol, and the H2CCC + NH4+ channel, which presents an energy barrier of 8.8 kcal/mol owing to its endothermicity. The c-C3H2 + NH4+ channel proceeds through a TS for the cyclization of HCCCH2+ efficiently catalyzed by NH3 and presents the largest Gibbs energy barrier, 24.2 kcal/mol. For the cyclization of H2CCC, we have found two different pathways with e...

Replacement of a hydrogen atom by fluorine in CH + 3 makes a cyclic transition structure (TS) appearing on the C 3 H + 5 potential energy surface (PES) become a minimum on the C 3 H 4 F + PES owing to the formation of a strong polar FC bond in the CH 2 F + fragment that avoids a destabilizing four-electron interaction.

We have prepared two chiral Schiff base ligands, H2L1 and H2L2, and one achiral Schiff base ligand, H2L3, by treating 2,6-diformyl-4-methylphenol separately with (R)-1,2-diaminopropane, (R)-1,2-diaminocyclohexane and 1,1′-dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL1ClO4 (1), MnL2ClO4 (2), MnL3ClO4 (3), FeL1ClO4 (4), FeL2ClO4 (5) and FeL3ClO4 (6) have been obtained by reacting the ligands H2L1, H2L2 and H2L3 with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H2L1 and H2L2 and their corresponding complexes have asymmetric character. Complexes 1–6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4, so they were attached to surface-modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe3O4@dopa@MnL1 and Fe3O4@dopa@FeL4. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.

A density functional theory (DFT) study of the V/UV spectrum and the adiabatic energy released from the triplet excited state of sapphyrin and three disubstituted derivatives (with O, S or Se atoms) is performed in order to obtain an accurate theoretical description of their capability as photosensitizers in photodynamic therapy (PDT). For the calculation of the V/UV spectra, we used two functionals already tested for porphyrin derivatives, B3LYP and PBE0, and two new ones recently proposed, MPWB1 K and M05, all of them with two different basis sets and two continuum solvent models. The best agreement with experimental data was obtained at the CPCM-M05/6-31 + G(d)//B3LYP/6-31 + G(d) level, at which errors lie in the range of 0.13–0.20 eV for the Q band in CH2Cl2 solution. A careful comparison between triplet and singlet geometries shows that the inner macrocycle enlarges, but planarity distortions lead to a volume contraction upon excitation to the triplet state for sapphyrin, and O and S heterosapphyrins, and to negligible volume changes for Se heterosapphyrin. Actually, the heterosapphyrins with S and Se atoms acquire a saddle shape in the triplet state. According to our results, the energy released from the triplet state for S- and Se- disubstituted sapphyrins could be adequate to generate activated oxygen both in the gas phase and in CH2Cl2 solution.

The mechanisms for the evolution of pentacarbonyl-5-hexenylchromate complexes, unsubstituted and methyl substituted at C2, formed from a pentacarbonyl(alkoxy)carbene complex of chromium, the corresponding ketone lithium enolate, and allylmagnesium bromide, were theoretically investigated by using DFT (Density Functional Theory) at the B3PW91/6-31G* level (LANL2DZ for Cr and Br) taking into account the effect of THF solvent through the PCM model (Polarizable Continuum Model). Methyl substitution at C2 provokes a shortening of about 5 degrees in the C1-C2-C3 angle that favors the formation of the pentacyclic product. Also, the presence of this methyl substituent at C2 sterically disfavors the formation of the hexacyclic product. Thus, our results yield the hexacyclic system as the most favored product for the evolution of the unsubstituted alkylpentacarbonylchromate complex, and the pentacyclic product in the case of the substituted system, in good agreement with the experimental findings. The stereochemistry of the products experimentally observed is determined at the transition state for the migration of the Cr(CO)(5) fragment from C1 to C6 and the conformational rearrangement of the C1-C6 skeleton. Amine molecules, present in the reaction medium, can play a catalytic role by assisting the 1,2-H migration in the last step for the formation of hexacyclic products.

Density functional calculations at the B3LYP/6-31+G(d) (LACVP(D) for Se) theory level have been carried out on 5,10,15,20-tetraphenylsapphyrin ( TPS), 5,10,15,20-tetraphenyl-26,28-dioxasapphyrin ( TP2OS), 5,10,15,20-tetraphenyl-26,28-dithiasapphyrin ( TP2SS), and 5,10,15,20-tetraphenyl-26,28-diselenasapphyrin ( TP2SeS). In agreement with experimental findings, our theoretical results show that TPS and TP2OS present an inverted conformation, whereas TP2SS and TP2SeS are more stable in the normal one. It was found that the relative stability of the normal and inverted conformers of the just mentioned sapphyrins correlates positevily with their degree of planarity and aromaticity, which depends on the size of the heteroatom, the steric repulsions produced by phenyl rings at the meso C atoms, and the network and nature of the bond critical points (BCPs) inside the macrocycle. These BCPs have been characterized by means of the AIM analysis and, some selected ones, by the changes in the total energy of significant fragments when distorted to avoid them.

In this work eight porphyrins (p) and eight chlorins (c) are theoretically characterized [BLYP/6-31G(d)] in their singlet and triplet states. Nine of them (1p, 1c, 2p, 3p, 4p, 5p, 6c, 7c, and 8c) have already been synthesized and are in trial use in photodynamic therapy (PDT). The seven remaining were built up as chlorins analogous to porphyrins 2p-5p and porphyrins analogous to chlorins 6c-8c. The aim is to investigate the effect of the chlorin structure on the Q-band of electronic spectra at BLYP/6-31G(d) (gas phase, methanol solution) and at BHANDHLYP/6-31+G(d) (methanol solution), and on the triplet --singlet energy emission, as these two factors determine the quality of a good photosensitizer. It is found that meso substituents lead to greater geometry distortions than beta-substituents in both porphyrins and chlorins and in both singlet and triplet states. In methanol solution, chlorin-like structures with beta substitution present significantly red-shifted Q-bands in comparison with their porphyrin analogues, so they would be better photosensitizers than porphyrins. Concerning to the triplet --singlet energy emission calculated in methanol solution, three porphyrins (4p, 6p, and 8p) and all the studied substituted chlorins could be useful to generate active (1)O2. 4c would be the best photosensitizer, as it absorbs the largest wavelength in the therapeutic window (approximately 690 nm) and releases the amount of energy closest to the required one (1.22 eV).

The synthesis of carbapenems from 4-(2-propynyl)azetidinones assisted by both Ag+ and [W(CO)5] was theoretically investigated by using the B3LYP/6-31+G(d)-LANL2DZ level, taking into account the effect of solvent by the PB-SCRF model implemented in Jaguar. According to our results, the silver-assisted cyclization is a concerted process for which the low yield experimentally observed could mainly stem from the alkaline hydrolysis of the beta-lactam ring. This process is very efficiently catalyzed by Ag+, making it competitive with the formation of the carbapenem. The cycloisomerization of 4-(2-propynyl)azetidinone promoted by [W(CO)5] is proposed as an alternative synthetic strategy to obtain the carbapenem. The endo cycloisomerization is by far the most favorable one. When the process is assisted by [(thf)W(CO)5], although the main product is the carbapenem, the formation of a carbene complex represents a certain competition. The presence of a Me3N molecule from the very start of the reaction causes an important catalytic effect considerably reducing the energy barriers corresponding to the H atom transfers and rendering a very efficient process. Moreover, this catalytic action determines the evolution of the system through only one mechanistic route which produces the carbapenem, hindering the formation of the carbene. Therefore, the cycloisomerization of 4-(2-propynyl)azetidinone promoted by [(Me3N)W(CO)5] constitutes an interesting alternative to the silver-assisted cyclization.

A methodology based on density functional theory calculations for the design of molecularly imprinted polymers (MIPs) is described. The method allows the rational choice of the most suitable monomer and polymerization solvent among a set of chemicals traditionally used in MIP formulations for the molecular imprinting of a given template. It is based on the comparison of the stabilization energies of the prepolymerization adducts between the template and different functional monomers. The effect of the polymerization solvent is included using the polarizable continuum model. A voltammetric sensor for homovanillic acid was constructed using different MIPs as recognition element, confirming that the solvent (toluene) and functional monomer (methacrylic acid) selected according to the theoretical predictions lead to the most efficient molecular recognition sensing phase. With the voltammetric sensor prepared using the MIP designed according to the theoretical predictions, a linear response for concentrations of homovanillic acid between 5 x 10(-8) and 1 x 10(-5) M can be obtained. The limit of detection is 7 x 10(-9) M. The selectivity obtained for homovanillic acid over other structurally related compounds buttresses the validity of this strategy of design.

Density Functional Theory calculations have been used to select, among a set of chemicals traditionally used in the formulation of non-covalent molecularly imprinted polymers (MIPs), the best functional monomer and porogenic solvent for the construction of a recognition element for the dopamine metabolite homovanillic acid (HVA). Theoretical predictions were confirmed through batch binding assays and voltammetric detection. The computational method predicts that trifluoromethacrylic acid and toluene are the monomer and solvent rendering the highest stabilization energy for the pre-polymerization adducts. HVA-MIP prepared using this formulation gives rise to a binding isotherm that is accurately modelled by the Freundlich isotherm. The binding properties of this polymer were estimated using affinity distribution analysis. An apparent number of sites of 13 micromol g(-1) with an average affinity constant of 2 x 10(4) M(-1) was obtained in the concentration window studied.

The mechanism of reaction between NO and two models of carbonaceous materials with active sites was investigated at the UB3LYP/6-31 + G(d) and UM06-2X theory levels. The small model is the anthracene radical and the large one is also a monoradical built with ten benzene rings. The mechanistic routes found with both models lead to a satisfactory justification of the experimental data and showed the important role of the temperature and the oxygen and nitrogen surface complexes, generated in the carbonaceous material at intermediate steps of the mechanism, in the global process. The computational results presented in this work revealed that, at low temperatures, the high Gibbs energy barrier that appears after N-2 release from the (NO)(2) dimer, initially chemisorbed on the char surface, prevents the subsequent evolution of the system with the result that CO2 emission does not take place. On the other hand, at high temperatures, the mean energy available to the reactants may be sufficient to overcome this energy barrier giving rise to the formation of N-2 and CO2 as reduction products. The N-2 may come from two sources depending on the approach of the NO molecule at different points of the reaction coordinate. The best description of the carbonaceous surface through a larger model confirms the absence of N2O release in the reduction of nitric oxide on carbon surfaces.