Complexation of common metal cations by cyanins: binding affinity and molecular structure

The ability of diverse metal cations to form complexes with cyanin has been investigated by means of Density Functional Theory (DFT) and the Quantum Theory of Atoms in Molecules (QTAIM). The strongest preference is shown by trivalent metals which exceed that of Mg(II), indicating that ion replacement processes are suitable detoxification mechanisms for plants. Molecular structure analysis indicates that the larger the metal affinity of Cy- the longer the C2‐C1’ bond length and smaller ρb value. This is understood as upon metal complexation the Cy− ligand molecular structure is more compatible with a dienolate‐like structure rather than the 4′‐keto‐quinoidal‐like structure. The weight of the former increases as stronger the binding. QTAIM charges indicate that the stronger the binding energy the larger the charge transfer from Cy− to the metal, reducing its positive charge below the values indicated by the corresponding Lewis structure.Ministerio de Ciencia e Innovación | Ref. CTQ2010‐2150

Do one‐step mechanisms always involve simultaneous evolution of electron density? QTAIM/IQA analysis of the Curtius rearrangement

The Curtius rearrangement reaction is studied by using quantum theory of atoms in molecules (QTAIM) analysis of the electron density and the interacting quantum atoms (IQA) formalism. Although the rearrangements take place in one stage, two phases are distinguished when the rearranged atom is H: the first one corresponds to the separation of N2, and the second one to the N‐H/C‐H bond rearrangement. The transition state (TS) for the reaction does not represent an intermediate between reagent and product for the migration but for the isolation of the N2 molecule. When the migration is undergone by a fluorine atom, no electronic phases can be distinguished and the process is really concerted. As the migration happens closer to the TS, the TS is more similar to the product. The IQA analysis reveals different electron density evolutions for H and F migrations, and the scarce relevance (in terms of energy) of the point where BCPs appear or disappear.Xunta de Galicia | Ref. ED431C 2019/2

Electron density analysis on the alpha acidity of nitriles

24 substituted cyanocompounds and the corresponding anions obtained upon H + -abstraction from diverse positions were subjected to an electron density analysis with the quantum theory of atoms in molecules (QTAIM). All the electron densities were obtained at the B3LYP/6–31 +  + G(2d,2p) level on completely optimized geometries. In accordance to experimental evidence, α-H + abstraction is found as the most favored one (by at least 100 kJ mol −1 in all the tested compounds). The presence of additional resonance electron attractors reduces significantly the α-deprotonation energy, whereas this magnitude is quite insensitive to the inclusion of resonance electron donors. The electron density rearrangement accompanying the deprotonation is apparently in line with the predictions of the resonance model (RM). In fact, a significant part of the electron density gained by expelling the proton is transferred to cyano N and to other groups where significant resonance structures delocalize the negative charge. Nevertheless, some significant modifications have to be introduced on the RM picture when the QTAIM results are studied in detail.Xunta de Galicia | Ref. GRC 2019/24Universidade de Vigo/CISU

Chiroptical symmetry analysis: exciton chirality-based formulae to understand the chiroptical responses of Cn and Dn symmetric systems

The high sensitivity of chiroptical responses to conformational changes and supramolecular interactions has prompted an increasing interest in the development of chiroptical applications. However, prediction of and understanding the chiroptical responses of the necessary large systems may not be affordable for calculations at high levels of theory. In order to facilitate the development of chiroptical applications, methodologies capable of evaluating the chiroptical responses of large systems are necessary. The exciton chirality method has been extensively used for the interaction between two independent chromophores through the Davydov model. For systems presenting C2 or D2 symmetry, one can get the same results by applying the selection rules. In the present article, the analysis of the selection rules for systems with symmetries Cn and Dn with n = 3 and 4 is used to uncover the origin of their chiroptical responses. We foresee that the use of the Chiroptical Symmetry Analysis (CSA) for systems presenting the symmetries explored herein, as well as for systems presenting higher symmetries will serve as a useful tool for the development of chiroptical applications.Ministerio de Economía y Competitividad | Ref. CTQ2014-58629-RMinisterio de Economía y Competitividad | Ref. CTQ2013-50575-EXPMinisterio de Economía y Competitividad | Ref. RYC-2012-10364Xunta de Galicia | Ref. EM2013/017Xunta de Galicia | Ref. GRC2015/17Xunta de Galicia | Ref. ED431F 2016/00

Estudio conformacional y mecanica molecular de compuestos con pares solitarios. Aminas, poliaminas, hidracinas y peroxidos

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Estudio conformacional y mecanica molecular de compuestos con pares solitarios. Aminas, poliaminas, hidracinas y peroxidos

Centro de Informacion y Documentacion Cientifica (CINDOC). C/Joaquin Costa, 22. 28002 Madrid. SPAIN / CINDOC - Centro de Informaciòn y Documentaciòn CientìficaSIGLEESSpai

Computational study on the conformational preferences of neutral, protonated and deprotonated glycine dimers

A conformational analysis has been carried out for monoprotonated, unprotonated and deprotonated glycine dimers in the gas phase and an aqueous solution. MP2/6-311++(d,p), B3LYP/6-311++(d,p) and M06/6-311++(d,p) optimizations were performed for more than 200 initial conformations comprising nonionic (COOH–CH2–NH2) (N) and zwitterionic (COO−–CH2–NH3+) (Z) structures for neutral monomers. All the methods indicate that Z monomers are preferred over N ones for the neutral and deprotonated dimers in aqueous solutions, whereas the reverse trend is observed in the gas phase (including also protonated dimers). NC and ZC structures coexist in aqueous solutions for the protonated glycine dimer. The preferred geometries are significantly different depending on the media and total dimer charge. Moreover, several minima display close energies in each series (media and total dimer charge). New conformers, not previously reported, are found to be significantly populated in those conformational mixtures. Dimers containing Z monomers are associated with larger absolute solvation energies and are more prone than N-containing ones to experience protonation and deprotonation in the gas phase, whereas the reverse trend is observed in the aqueous solution. The Quantum Theory of Atoms in Molecules (QTAIM) analysis reveals that uncharged dimers display trifling electron density transfer between monomers, whereas it is significant in anionic and cationic dimers

First characterization of the formation of anthocyanin–ge and anthocyanin–B complexes through UV–Vis spectroscopy and density functional theory quantum chemical calculations

The occurrence of anthocyanin (ACN) and metal (Me) complexes has been widely supported by many research works while the possibility that ACNs bind to metalloids (Mds) is yet to be proven. Here, metalloids (H3BO3 for B; GeO2 for Ge) were added to cyanidin-based solutions at pH 5, 6, and 7 and ACN–Md stoichiometric ratios of 1:1, 1:10, 1:100, and 1:500, and UV–vis transmittance spectroscopy as well as density functional theory (DFT) calculations were performed to test this hypothesis. Ge and B addition caused bathochromic and hyperchromic shifts on ACN UV–vis spectra, particularly pronounced at pH 5 and a 1:500 (ACN:Md) ratio. ACN–Me complexation reactions have been evaluated where Ge showed a higher capability to bind to ACNs than B. Among the complexes envisioned, those labeled as b1, b2, and b3 feature UV–vis spectra compatible with experiments. The combination of experimental and computational data offers for the first time evidence of the formation of ACN–Md complexesXunta de Galicia | Ref. GRC2019/24Universidade de Vig

Chiroptical symmetry analysis of Trianglimines: a case study

It is well established that chiroptical responses, based on the unique reaction to circularly polarized light by chiral non-racemic systems, are sensitive to the stereochemistry of the featuring systems. This behavior has promoted the use of chiroptical spectroscopies as a mandatory tool in the structure determination of molecules for decades. Recently, the higher sensitivity of chiroptical techniques compared to the conventional UV/Vis absorption and fluorescence spectroscopies or electrochemistry has awakened much interest in the development of chiroptical everyday applications. While chiroptical responses could be predicted by ab initio calculations, large systems calculated at a high level of theory may have an important computational cost; therefore, more intuitive methods are desired to design systems with tailored chiroptical responses. In this regard, the exciton chirality method has been often used in conformationally stable systems incorporating at least two independent chromophores. Taking this method into consideration, in our previous work, we described the chiroptical symmetry analysis (CSA) based on symmetry selection rules. To explore the scope of the CSA, herein we perform the chiroptical symmetry analysis of diverse trianglimines and draw general conclusions to assist on the design of chiroptical systems with high symmetry.Xunta de Galicia | Ref. ED431F 2016/005Xunta de Galicia | Ref. GRC2019/24European Commission | Ref. 0245_IBEROS_1_

Red de docentes y repositorio digital de recursos educativos: Una historia del capitalismo contemporáneo III. El neoliberalismo y la crisis multifactorial contemporánea a través fuentes fílmicas, literarias y estéticas

Depto. de Filosofía y SociedadFac. de FilosofíaFALSEsubmitte