The mechanism of the cascade reaction between N-methylbenzamide (1) and diphenylcyclopropenone (2), catalyzed by Cp*Rh(III) (110 °C, dichloroethane), was studied using density functional theory ...(DFT) calculations. To assemble cyclopentene spiroisoindolenones (3) and water, 1 and 2 coordinate to Rh(III). Metal-catalyzed C–H activation is preferred to cyclopropenone opening by 3.7 kcal mol–1. 1 acts as a proton carrier with both 1 and 1H + assisting hydrogen transfer steps during the reaction. The κ-O cyclopropenone isomerizes to a η2-CC bonding mode, the ring opens, and the first C–C bond is formed. Proton transfer from N–H to the vinyl group opens the way for obtaining the C–N bond. Two protonation steps, requiring protons from Cvinyl–H and 1H + , lead to cleavage of the C–O group and formation of water (byproduct). The second C–C bond results from an intramolecular Friedel–Crafts alkylation, in which the closest ortho-phenyl carbon binds the formal carbocation in the C5 indolenone ring. The release of 3 and the regeneration of the catalyst occur after two proton transfers assisted by 1 and 1H + in an exergonic final step (9.3 kcal mol–1). The highest barrier corresponds to the protonation of the vinylic group during the formation of the first C–C bond (29.1 kcal mol–1).
The interaction of two isomers, equatorial (Eq) and axial (Ax), of the Mo(η3-C3H5)Br(CO)2(phen) metal complex with DNA was studied by using large-scaling density functional theory methods ...including dispersion for the whole system, represented as a d(AGACGTCT)2 DNA octamer, to gain insight into its experimentally found cytotoxicity. Three different modes of interaction were considered: (1) minor groove (mg) binding, (2) intercalation through the major groove (MG), and (3) the apparently unexpected intercalation via the mg. Computed formation energies, energy decomposition analysis, solvation energies, and noncovalent interaction analysis explain the preference for Eq and Ax isomers of the complex for intercalation via the mg. π–π interactions of the phenanthroline (phen) flat ligand that appear in the intercalation mode and do not exist for the mg binding mode suggest the preference of Mo(η3-C3H5)Br(CO)2(phen) for intercalation. On the other hand, the role of the ancillary ligands is crucial for better interaction of the metal complex including phen than when the phen ligand alone is considered because of their additional interactions with base pairs (bps). The role of the ancillary ligands is enhanced when intercalation takes place through the mg because such ligands are able to interact not only with bps but also with the sugar and phosphate backbone, whereas for intercalation through the MG, the interaction of these ligands is only with bps. This feature explains the preference of Mo(η3-C3H5)Br(CO)2(phen) for intercalation via the mg in crystal structures. Finally, the solvation penalty is more important for intercalation through the mg than via the MG, which suggests a subtle mechanism involving weak interactions with solvent molecules to explain the selectivity for intercalation in solution to answer the MG versus mg question.
Three new complexes Mo(η³-C₃H₅)Br(CO)₂{
PrN=C(R)C₅H₄N}, where R = H (IMP =
-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most ...interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls
), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)₃, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR,
C- and
Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the
-cyclooctene and
-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.
This work provides new insights from our team regarding advances in targeting canonical and non-canonical nucleic acid structures. This modality of medical treatment is used as a form of molecular ...medicine specifically against the growth of cancer cells. Nevertheless, because of increasing concerns about bacterial antibiotic resistance, this medical strategy is also being explored in this field. Up to three strategies for the use of DNA as target have been studied in our research lines during the last few years: (1) the intercalation of phenanthroline derivatives with duplex DNA; (2) the interaction of metal complexes containing phenanthroline with G-quadruplexes; and (3) the activity of Mo polyoxometalates and other Mo-oxo species as artificial phosphoesterases to catalyze the hydrolysis of phosphoester bonds in DNA. We demonstrate some promising computational results concerning the favorable interaction of these small molecules with DNA that could correspond to cytotoxic effects against tumoral cells and microorganisms. Therefore, our results open the door for the pharmaceutical and medical applications of the compounds we propose.
Searching for receptors selective for the binding of dicarboxylate anions, the copper(II) complexes of the known ditopic octaazacryptand (t2pN8), derived from bistren tren = ...tris(2-aminoethyl)amine linked by p-xylyl spacers, were re-examined, with the expectation of observing a selective binding of oxalate or malonate by bridging the two copper centers of the Cu2(t2pN8)(H2O)24+ receptor. Solution studies involving the supramolecular species formed by the receptor and oxalate (oxa2–), malonate (mal2–), and succinate (suc2–) anions are reported. The determined association constants revealed the unexpected formation of a 3:1:1 Cu/t2pN8/anion stoichiometry for the cascade species with oxa2– and mal2–, and the single crystal X-ray structural characterization confirmed the presence of tricopper(II) complexes, with an unusual binding mode for the dicarboxylate anions. Each of the two copper atoms binds four nitrogen donor atoms of the t2pN8 cryptand and one additional hydroxide group, which bridges to the third copper. The square planar environment of this one is complete with two oxygen atoms from the oxalate (or the malonate). The two copper centers bound to the tren heads are ∼6.5 Å apart, each one at about 3.5 Å from the third Cu center. These studies were complemented by SQUID magnetization measurements and DFT calculations. The magnetic susceptibility measurements of the oxalate cascade complex showed a strong magnetic coupling (J = – 210 cm–1) between the Cu centers at a short distance (3.5 Å), while the coupling between the two equivalent Cu atoms (∼6.5 Å) was only −70 cm–1. This result was well reproduced by DFT calculations.
The increased use of pharmaceutical and personal care products (PPCPs) has contributed to the contamination of water systems and put pressure on the development of new techniques to deal with this ...problem. Acetaminophen (paracetamol), a common analgesic and antipyretic drug, and caffeine, a known central nervous system stimulant, are being used frequently by many people and found in large amounts in wastewater systems. In this work, their removal, by photocatalytic degradation, was promoted using magnetic nanoparticles (NPs) based on iron oxides. Besides being obtained from cheap and plentiful source, the magnetic properties of these NPs provide an easy way to separate them from the solution when the reaction is complete. Three types of hematite-based NPs, one pure (
1
) and two of them composed by a magnetite core partially (
2
) or completely (
3
) covered by a hematite shell, were synthesized and characterized. Sample
2
was the best photocatalyst for both pollutants’ photo-assisted degradation. Under UV-vis irradiation and using a 0.13 g catalyst/L solution, the total acetaminophen and caffeine degradation (20 ppm/150 mL) was achieved in 45 min and 60 min, respectively. The identification of some of the intermediate products was carried out by liquid chromatography in combination with electrospray ionization mass spectrometry. A complementary Density Functional Theory (DFT) study revealed the relative stability of several species formed during the acetaminophen and caffeine degradation processes and gave some insight about the most favorable degradation pathways.
Fragmentation of transient negative ions of tryptophan molecules formed through electron transfer in collisions with potassium atoms is presented for the first time in the laboratory collision energy ...range of 20 up to 100 eV. In the unimolecular decomposition process, the dominating side-chain fragmentation channel is assigned to the dehydrogenated indoline anion, in contrast to dissociative electron attachment of free low-energy electrons to tryptophan. The role of the collision complex formed by the potassium cation and tryptophan negative ion in the electron transfer process is significant for the mechanisms that operate at lower collision energies. At those collision times, on the order of a few tens of fs, the collision complex may not only influence the lifetime of the anion but also stabilize specific transition states and thus alter the fragmentation patterns considerably. DFT calculations, at the BHandHLYP/6-311++G(3df,2pd) level of theory, are used to explore potential reaction pathways and the evolvement of the charge distribution along those.
The accumulation of marine biofouling on ship hulls causes material damage, the spread of invasive species, and, indirectly, an increase in full consumption and subsequent pollutant gas emissions. ...Most efficient antifouling (AF) strategies rely on the conventional release of persistent, bioaccumulative, and toxic biocides incorporated in marine coatings. A simple oxygenated xanthone, 3,4-dihydroxyxanthone (1), was previously reported as a promising AF agent toward the settlement of Mytilus galloprovincialis larvae, with a therapeutic ratio higher than the commercial biocide Econea®. In this work, a structure-AF activity relationship study, an evaluation of environmental fate, and an AF efficiency in marine coatings were performed with compound 1. Hydroxy or methoxy groups at 3 and 4 positions in compound 1 favored AF activity, and groups with higher steric hindrances were detrimental. Compound 1 demonstrated low water-solubility and a short half-life in natural seawater, contrary to Econea®. In silico environmental fate predictions showed that compound 1 does not bioaccumulate in organism tissues, in contrast to other current emerging biocides, has a moderate affinity for sediments and slow migrates to ground water. No toxicity was observed against Vibrio fischeri and Phaeodactylum tricornutum. Polyurethane-based marine coatings containing compound 1 prepared through an innovative non-release-strategy were as efficient as those containing Econea® with low releases to water after 45 days. This proof-of-concept helped to establish compound 1 as a promising eco-friendly AF agent.
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•From several synthetic derivatives, 1 was the most promising anti-macrofouling agent.•1 was predicted to have low Log Kow, BCF, and Log Koc.•1 was non-persistent in seawater (DT50 < 60 days).•No ecotoxicity was observed on a marine bacteria (750 mg/L) and a diatom (100 mg/L).•A non-release polyurethane marine coating containing 1 was successfully prepared.
Three new mononuclear oxovanadium(IV) complexes VO(acac)(R-BIAN)Cl (BIAN = 1,2-bis{(R-phenyl)imino}acenaphthene, R = H, 1; CH3, 2; Cl, 3) were prepared and characterized. They promoted the catalytic ...oxidation of olefins such as cyclohexene, cis-cyclooctene, and styrene with both tbhp (tert-butylhydroperoxide) and H2O2, and of enantiopure olefins (S(-)- and R(+)-pinene, and S(-)- and R(+)-limonene) selectively to their epoxides, with tbhp as the oxidant. The TOFs for styrene epoxidation promoted by complex 3 with H2O2 (290 mol mol(-1)V h(-1)) and for cis-cyclooctene epoxidation by 2 with tbhp (248 mol mol(-1)V h(-1)) are particularly good. Conversions reached 90% for several systems with tbhp, and were lower with H2O2. A preference for the internal C=C bond, rather than the terminal one, was found for limonene. Kinetic data indicate an associative process as the first step of the reaction and complex VO(acac)(H-BIAN)(+) (1(+)) was isolated in an FTICR cell after adding tbhp to 1. EPR studies provide evidence for the presence of a V(IV) species in solution, until at least 48 hours after the addition of tbhp and cis-cyclooctene, and cyclic voltammetry studies revealed an oxidation potential above 1 V for complex 1. DFT calculations suggest that a VO(H-BIAN)(MeOO)(+) complex is the likely active V(IV) species in the catalytic cycle from which two competitive mechanisms for the reaction proceed, an outer sphere path with an external attack of the olefin at the coordinated peroxide, and an inner sphere mechanism starting with a complex with the olefin coordinated to vanadium.
η5-Cyclopentadienyl(tricarbonyl)methylmolybdenum(II) (1) is oxidized by tert-butylhydroperoxide (TBHP) to yield η5-cyclopentadienyl(dioxo)methylmolybdenum(VI) (2) and ...η5-cyclopentadienyl(oxo)-(peroxo)methylmolybdenum(VI) (3). These two complexes are active catalysts for olefin epoxidation in the presence of TBHP, but inactive in its absence. DFT calculations of the possible pathways, with MP2 single-point energies, indicate that TBHP can react with 2 to form the active intermediate CpMo(O)(OH)(OOCH3)CH3 (B) or the peroxo complex 3. Formation of B and epoxidation from B have relatively low activation barriers (gas-phase MP2 ΔE 21 kcal mol−1), while formation of complex 3 from 2 exhibits a higher barrier (38 kcal mol−1). The peroxo complex 3 can be further activated by excess TBHP to yield a second active intermediate, CpMo(O2)(OH)(OOCH3)CH3 (C) (24 kcal mol−1), that undergoes reaction with olefin, forming epoxide and the intermediate B. Both intermediates B and C display end-on-bound alkyl peroxo ligands. Barriers are comparable for several pathways, suggesting that more than one may take place. The role of solvent (PCM, dichloromethane) is negligible, since the deviations between gas-phase and solvent free energies are ∼1−3 kcal mol−1.
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