Interplay between cation-pi, anion-pi and pi-pi interactions.
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Anions↗
Biomedical subjects
David Quiñonero
Publications and source records attributed to David Quiñonero.
Rational design, synthesis, and application of a new receptor for the molecular recognition of tricarboxylate salts in aqueous media.
A rational design of a tripodal receptor for the molecular recognition of tricarboxylate salts in aqueous media, based on squaramide, has been performed using high-level DFT calculations (RI-BP86/SVP level of theory) in solution using the COSMO treatment, including some preliminary ab initio calculations at the higher RI-MP2/TZVP level of theory, comparing the ability of squaramide to bind carboxylate salts with two widely used guanidinium salts. The tripodal receptor has been synthesized using a new methodology that has been recently reported by some of us, and its capability of recognizing several mono-, di-, and tricarboxylate salts has been studied experimentally by means of microcalorimetry experiments in a very high competitive media, H(2)O:EtOH 1:3. These experiments give enthalpic and entropic data, which are unfortunately scarce in the literature of molecular recognition of anions. Finally, a fluorimetric ensemble of the receptor with fluorescein has been found to be useful for the fluorimetric determination of zinc citrate in a commercial toothpaste using competition assays.
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MP2 study of cation-(pi)n-pi interactions (n = 1-4).
Ab initio calculations at the MP2(full)/6-31++G**, RI-MP2(full)/6-31++G**, and RI-MP2(full)/6-311++G(2d,2p) levels of theory demonstrate important synergic effects between two noncovalent interactions that involve aromatic rings, that is, cation-pi and pi-pi interactions. The presence of a cation interacting with the pi cloud of an aromatic ring favors the face-to-face stacking interaction with additional aromatic rings. This effect is extended in the space up to five stacked aromatic rings.
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Ab initio study of [n.n]paracyclophane (n = 2, 3) complexes with cations: unprecedented through-space substituent effects.
Several cation-pi complexes between substituted [n.n]paracyclophanes (n = 2, 3) and cations have been studied using high level ab initio calculations. The chemical substitution at the aromatic ring that is not interacting with the cation has a strong influence upon the binding energy. This strong through-space substituent effect has been studied using the "atoms-in-molecules" theory, which has been found useful to explain the energetic results.
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The role of the central atom in structure and reactivity of polyoxometalates with adjacent d-electron metal sites. computational and experimental studies of gamma-[(Xn+O4)RuIII2(OH)2(MFM)10O32](8-n)-) for MFM = Mo and W, and X = AlIII, SiIV, PV, and SVI.
The role of the central atom X in the structure and reactivity of di-Ru-substituted gamma-Keggin polyoxometalates (POMs), gamma-[(Xn+O4)RuIII2(OH)2(MFM)10O32](8-n)-), where MFM = Mo and W, and X = AlIII, SiIV, PV, and SVI., was computationally investigated. It was shown that for both MFM = Mo and W the nature of X is crucial in determining the lower lying electronic states of the polyoxoanions, which in turn likely significantly impacts their reactivity. For the electropositive X = AlIII, the ground state is a low-spin state, while for the more electronegative X = SVI the ground state is a high-spin state. In other words, the heteroatom X can be an "internal switch" for defining the ground electronic states of the gamma-M2-Keggin POMs. The obtained trends, in general, are less pronounced for MFM = Mo than for W. On the basis of the comparison of the calculated energy gaps between low-spin and high-spin states of polytungstates and polymolybdates, we predict that the gamma-M2-Keggin polytungstates could be more reactive than their polymolybdate analogues. For purposes of experimental verification the computationally predicted and evaluated polytungstate gamma-[(SiO4)RuIII2(OH)2(OH2)2W10O32]4- was prepared and characterized.
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Anion-pi interactions in cyanuric acids: a combined crystallographic and computational study.
Several structures of pi complexes of isocyanuric acid and of several thio derivatives with anions have been computed by using high level ab initio calculations. The nature of the complexes has been studied by means of the method of molecular interaction potential with polarization (MIPp) and Bader's theory of atoms-in-molecules. These molecules form favorable complexes with anions and can be used as binding units for building receptors for the molecular recognition of anions. In several cases, the anion-pi interaction has been demonstrated experimentally by means of X-ray crystallography.
Anions↗
Approximate additivity of anion-pi interactions: an ab initio study on anion-pi, anion-pi(2) and anion-pi(3) complexes.
We have studied the additivity of the anion-pi interaction using high level ab initio calculations. We have optimized chloride and bromide complexes with one, two and three aromatic units (such as trifluoro-s-triazine and s-triazine). We have analyzed the interaction using the atoms in molecules theory and studied the charge transfer using several methods for deriving atomic charges. The results revealed additivities of both the geometries and the binding energies. We have also proposed a neutral receptor for chloride based on multiple anion-pi interactions. Finally, we have simulated solvent effects within the self-consistent reaction field model.
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Structure and binding energy of anion-pi and cation-pi complexes: a comparison of MP2, RI-MP2, DFT, and DF-DFT methods.
Several complexes of benzene with cations, hexafluorobenzene with anions, 1,3,5-trifluorobenzene with cations and anions, and s-triazine with cations and anions have been evaluated and compared at the MP2 and resolution of the identity MP2 (RI-MP2) levels. The RI-MP2 method is considerably faster than the MP2 and the interaction energies and equilibrium distances are almost identical for both methods. A similar result is found when comparing DFT and density fitting DFT (DF-DFT) levels. Therefore RI-MP2 and DF-DFT methods are well suited for the study of ion-pi interactions.
Anions↗
Metal-peroxo versus metal-oxo oxidants in non-heme iron-catalyzed olefin oxidations: computational and experimental studies on the effect of water.
Computational and experimental studies show that Fe(BPMEN)-catalyzed olefin oxidation has two (FeIII-OOH and FeV=O) oxidant species, which act with comparable activation barriers. The presence of water favors formation of an HO-FeV=O oxidant via water-assisted O-OH bond cleavage and leads to both epoxide and cis-diol products. In the absence of water, the oxidant is the FeIII-OOH [or (MeCN)FeIII-OOH], and oxidation mainly leads to epoxide. This conclusion differs from that derived from DFT investigations of iron-porphyrin-catalyzed olefin epoxidation, where the FeIII-OOH pathway is deemed too high in energy to be plausible. The difference between these two systems may lie in the more flexible coordination environment of the non-heme iron complex, which has an available adjacent coordination site that contributes to the activation of the peroxide in both wa and nwa pathways.
Alkenes↗
Preparation, solid-state characterization, and computational study of a crown ether attached to a squaramide.
[structure: see text] Crystals of a disecondary squaramide covalently linked to a crown ether presents a great variety of inter- and intramolecular nonbonded interactions including C-H/pi contacts, C-H...O and N-H...O hydrogen bonds, and pi-pi stacking between squaramide rings. Latter interaction, the stacking between squaramide rings, can be considered as an experimental evidence for the proposed aromaticity of squaramide when it is forming hydrogen bonds, either as acceptor or donor.
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A topological analysis of the electron density in anion-pi interactions.
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Theoretical studies of the complex [(BPMEN)Fe(II)(NCCH3)2](2+), precursor of non-heme iron catalysts for olefin epoxidation and cis-dihydroxylation.
The density functional theory (DFT) was applied to elucidate the electronic structure of the BPMEN [N,N'-bis(6-R-2-pyridylmethyl)-1,2-diaminoethane] iron complex, [(BPMEN)Fe(NCCH3)2](2+), a precursor of catalysts that catalyze the stereospecific olefin oxidation. The low-lying high and low spin states of complex 1 (R=H) are nearly degenerate with a slight preference for the high spin state. For complexes with substituents (R) at the 6-positions of two pyridine rings of BPMEN, the ground state is the high spin (HS) state, with the low spin (LS) state higher in energy by 9.5, 5.3, 8.5, 6.3, and 5.1 kcal/mol for complexes 2 (R=CH3), 3 (R=SiH3), 4 (R=OH), 5 (R=F), and 6 (R=CN), respectively, with the B3LYP method. Our findings for complexes 1 and 2 are in good agreement with the experimental observations. The calculated LS-HS difference of 17.9 kcal/mol for complex 7 (R=t-Bu) clearly demonstrates that the steric effect causes the Fe-N bonds to stretch and favors the high spin state. Comparison of the B3LYP and B3PW91 results with experiments and ab initio MP2 and CCSD(T) as well as pure DFT results shows that hybrid DFT methods provide a qualitatively correct description of the relative energies of low-lying electronic states of a model of the [(BPMEN)Fe(NCCH3)2](2+) complex, while pure DFT methods underestimate the stability of the HS state.
Alkenes↗
Dual binding mode of s-triazine to anions and cations.
Ab initio calculations were performed on complexes between cations and s-triazine, which has a small and positive quadrupole moment. Minimum energy pi-complexes were found between s-triazine and cations. Minimum pi-complexes with anions were previously reported. This ability of s-triazine to form stable complexes with either anions or cations is studied using several theoretical methods. A likely explanation of this duality is the stabilization obtained from the ion-induced polarization. [structure: see text]
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Weak C-H/pi interaction participates in the diastereoselectivity of a host-guest complex in the presence of six strong hydrogen bonds.
[structure: see text] We report a study of the interaction between methylmethanetriacetic acid (MMTA) and a tripodal amidopyridine receptor 1, where the geometry of the binding is in part governed by a weak C-H/pi interaction in the presence of six strong N(O)-H.O(N) hydrogen bonds. There are two possible binding geometries for the 1:1 complex 1.MMTA; combining computational and experimental evidence we demonstrate that the endo binding mode is more favorable as the result of a C-H/pi interaction.
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Anion-pi Interactions: do they exist?
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Predicting experimental complexation-induced changes in (1)H NMR chemical shift for complexes between zinc-porphyrins and amines using the ab initio/GIAO-HF methodology.
Ab initio calculations were carried out on zinc-porphyrins complexed to several amines: N-(3,5-dimethyl-pyridin-4-yl)-formamide, 1,4-diazabiciclo[2.2.2]octane (DABCO), and 1-azabiciclo[2.2.2]octane (quinuclidine). The proton chemical shifts of these complexes were calculated ab initio at the GIAO-HF/6-311G//HF/3-21G level of theory, and the obtained values agree satisfactorily with experimental results. The complexation-induced changes in (1)H NMR chemical shifts correlate well with differences in association constants of several host-guest complexes.
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Quantification of aromaticity in oxocarbons: the problem of the fictitious "nonaromatic" reference system.
Despite the extensive research reported in the literature, the concept of aromaticity has eluded rigorous quantification. The main reason for this undesirable reality is the fact that aromaticity is a differential property. While bond orders, atomic charges and electronegativity differences are properties of the molecule under analysis, the aromaticity concept often refers to the difference between some property of the molecule and that of an artificial "nonaromatic" reference system. A rigorous definition of such a reference system is non-existing and therefore constituting the main barrier to obtain a satisfactory quantification of the aromatic concept. Oxocarbon acids and their anions are examples where the criteria of aromaticity that use reference systems are unsuccessful, only NICS criterion gives satisfactory results. Wiberg bond indexes and 17O NMR chemical shifts are also useful to study such compounds.
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