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11.
We present here an ab-initio STO-3G and advanced semiempirical AM1 calculation for the structure and the conformational behavior of phenyltetrazine and bitetrazine molecules. Results for phenyltetrazine isomers show that in the absence of H-H interactions, the preferred conformation is the planar one. Instead, in the case of bitetrazines, the systems dominated by the lone pair-lone pair interactions are not planar. In the presence of direct H-H interaction as for 5-5-1,2,3,4 bitetrazine, the antiplanar conformation is the preferred one. Comparison with other systems (including one or more nitrogen lone pairs) shows that the compounds with the same ortho substituents have very similar conformational behavior irrespective of their composition. The AM1 results indicate that this method is able to give reliable conformational information for compounds in which H-H interactions are involved. A Fourier expansion of the torsional potential suggests that the first two terms fit the calculated torsional potentials well except in the case of two H-H interactions in the same molecule. 相似文献
12.
Capodaglio G Toscano G Barbante C Gambaro A Scarponi G Cescon P 《Annali di chimica》2002,92(3):163-176
The methodology for using DPASV to study cadmium complexation in seawater is evaluated using EDTA as a model ligand and by analysing natural samples. The results show that the methodology gives an accurate evaluation of metal complexation when inert complexes are studied, both as regards the ligand concentration and the conditional stability constant; the error for both the parameters is lower than 10% at a ligand concentration of about 10(-8) M and a conditional stability constant of 10(9) M-1. Cadmium complexes with ligands present in natural seawater show an evident kinetic lability that may lead to underestimation of the conditional stability constant when a working electrode characterised by a very thick diffusion layer is used. The conditional stability constant in one water sample of the Adriatic coast ranged between 0.14 and 1.4 l/nmol using a rotating disk electrode at rotation rates of 300 and 6000 rpm. The results of cadmium complexation obtained for samples collected in coastal seawater show that the ligands present low specificity for the metal. 相似文献
13.
Armando Navarro-Huerta Marcus J. Jellen Jessica Arcudia Simon J. Teat Rubn A. Toscano Gabriel Merino Braulio Rodríguez-Molina 《Chemical science》2021,12(6):2181
This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. The crystal structures of these rotors, determined by synchrotron radiation experiments at different temperatures, show the presence of such C–H⋯F–C contacts between extended carbazole stators featuring fluorinated phenyl rings and the 1,4-diazabicyclo[2.2.2]octane (DABCO) rotator. According to the 2H NMR results, using deuterated samples, and periodic density functional theory computations, the rotators experience fast angular displacements (preferentially 120° jumps) due to their low rotational activation energies (Ea = 0.8–2.0 kcal mol−1). The higher rotational barrier for 1 (2.0 kcal mol−1) is associated with a larger number of weak C–H⋯F–C contacts generated by the stators. This strategy offers the possibility to explore the correlation among weak intermolecular forces, cavity shape, and internal dynamics, which has strong implications in the design of future fine-tuned amphidynamic crystals.This work describes the use of C–H⋯F–C contacts in the solid-state from the stator towards the rotator to fine-tune their internal motion, by constructing a set of interactions that generate close-fitting cavities in three supramolecular rotors 1–3I. 相似文献
14.
15.
Geise CM Wang Y Mykhaylova O Frink BT Toscano JP Hadad CM 《The Journal of organic chemistry》2002,67(9):3079-3088
The effect of aromatic substitution on the singlet-triplet energy gap in substituted phenyl(carbomethoxy)carbene (X-Ph-C-CO(2)CH(3), PCC) has been explored by time-resolved infrared (TRIR) spectroscopy and gas-phase computational methods. The ground state of para-substituted PCC is calculated to change from the triplet state in p-NO(2)-PCC (Delta G(ST) = 6.1 kcal/mol) to the singlet state in p-NH(2)-PCC (Delta G(ST) = -2.8 kcal/mol). The absence of solvent perturbation in the TRIR spectra of p-N(CH(3))(2)-PCC (which should have electronic properties similar to p-NH(2)-PCC) and parent PCC is consistent with their ground states lying > +/-2 kcal/mol from the next available electronic state, in line with the computational results. The observation of solvent perturbation in the TRIR spectra of p-OCH(3)-PCC and p-CH(3)-PCC implies that their ground states lie < +/-1 kcal/mol from their next available electronic state. This is in agreement with our computational results, which predict a gas-phase Delta G(ST) of -0.8 and 1.6 kcal/mol for p-OCH(3)-PCC and p-CH(3)-PCC as compared to Delta G(ST) values of -3.9 and -1.3 kcal/mol from polarizable continuum model (PCM) calculations with acetonitrile as a solvent. Gas-phase computational results for the meta- and ortho-substituted PCC species are also presented, along with selected linear free energy (LFE) relationships for the para and meta species. 相似文献
16.
Carlos Camacho‐Camacho Irma Rojas‐Oviedo Ariadna Garza‐Ortiz Rubén Alfredo Toscano Luis Sánchez‐Sánchez Jorge Cardenas Hugo López‐Muñoz 《应用有机金属化学》2016,30(4):199-207
The synthesis in one‐pot reactions and structural characterization of six new tri‐n‐butyltin(IV) derivatives of Schiff bases are reported. The compounds are derived from a condensation reaction between l ‐alanine, l ‐valine, l ‐isoleucine, l ‐methionine, l ‐phenylalanine or l ‐tryptophan and 3,5‐di‐tert‐butyl‐2‐hydroxybenzaldehyde. Characterization was completed using elemental analysis, infrared spectroscopy, mass spectrometry, one‐ and two‐dimensional solution NMR (1H, 13C and 119Sn) as well as solid‐state 119Sn NMR. In addition, the crystal structures of three of the compounds were confirmed using single‐crystal X‐ray diffraction. Although five‐coordinated and polymeric in the solid state, the tin compounds are four‐coordinated and monomeric in solution. The coordination environment around the triorganotin units comprises three carbon atoms and two oxygen atoms from two ligands in a trigonal bipyramidal geometry. The anti‐proliferative effect of these compounds on the cervical carcinoma cell lines HeLa, CaSki and ViBo was screened in vitro, the compounds showing cytotoxic activity against all three strains and null or low cytotoxic activity (necrotic) as well. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
17.
Labile metal species in aquatic humic substances (HSs) were characterized by ion exchange on cellulose phosphate (CellPhos) by applying an optimized batch procedure. The HSs investigated were pre-extracted from humic-rich waters by ultrafiltration and a resin XAD 8 procedure. The HS-metal species studied were formed by complexation with Cd(II), Ni(II), Cu(II), Mn(II) and Pb(II) as a function of time and the ratio ions to HSs. The kinetics and reaction order of this exchange process were studied. At the beginning (<3 min), the labile metal fractions are separated relatively quickly. After 3 min, the separation of the metal ions proceeds with uniform half-lives of about 12-14 min, revealing rather slow first-order kinetics. The metal exchange between HSs and CellPhos exhibited the following order of metal lability with the studied HSs: Cu > Pb > Mn > Ni > Cd. The required metal determinations were carried out by atomic absorption spectrometry. 相似文献
18.
Michelle Hernández-Arganis Rubén A. Toscano Mónica Moya-Cabrera Verónica García-Montalvo Raymundo Cea-Olivares Dr. 《无机化学与普通化学杂志》2004,630(11):1627-1631
The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C6H5N4CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB+) and NMR (1H; 13C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs+ and Rb+ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group. 相似文献
19.
Bond energies and attachments sites of sodium and potassium cations to DNA and RNA nucleic acid bases in the gas phase 总被引:2,自引:0,他引:2
Gas-phase metal affinities of DNA and RNA bases for the Na(+) and K(+) ions were determined at density functional level employing the hybrid B3LYP exchange correlation potential in connection with the 6-311+G(2df,2p) basis set. All the molecular complexes, obtained by the interaction between several low-lying tautomers of nucleic acid bases and the alkali ions on the different binding sites, were considered. Structural features of the sodium and potassium complexes were found to be similar except in some uracil and thymine compounds in which the tendency of potassium ion toward monocoordination appeared evident. B3LYP bond energies for both metal ions were in agreement with the available experimental results in the cases of uracil and thymine for which the most stable complex was obtained starting from the most stable tautomer of the free nucleic acid base. For adenine, although the interaction of the ions with the most stable free tautomer generated the least stable molecular complex, the best agreement with experiment was found in just this case. For the remaining cytosine and guanine bases, our calculations indicated that the metal ion affinity value closest to experiment should be determined taking into account the role played by the different tautomers of the free bases with similar energy and all the possible complexes obtained by them. 相似文献
20.
Rubn A. Toscano Emma Maldonado Alfredo Ortega Jorge Crdenas 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(7):846-847
The absolute configuration of the neoclerodane glycoside amarisolide, presented here as the monohydrate, C26H36O9·H2O, has been determined by association with the known configuration of the glucose moiety. Its structure was established as 2β‐(O‐β‐d ‐glucopyranosyl)neocleroda‐3,13(16),14‐trien‐15,16‐epoxy‐18,19‐olide. Extensive hydrogen bonding among the hydroxyl groups of the sugar moiety forms layers which are interconnected by water molecules. 相似文献