Al Mokhtar Lamsabhi
Autonomous University of Madrid
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Featured researches published by Al Mokhtar Lamsabhi.
Chemical Communications | 2008
Anaı̈s Medina; Christian G. Claessens; G. M. Aminur Rahman; Al Mokhtar Lamsabhi; Otilia Mó; Manuel Yáñez; Dirk M. Guldi; Tomás Torres
We have designed, synthesized and probed a dodecafluoro-subphthalocyaninato boron(III) unit, which bears a triphenylamine moiety in its axial position, as a novel electron donor-acceptor system.
Organic and Biomolecular Chemistry | 2008
Cristina Trujillo; Al Mokhtar Lamsabhi; Otilia Mó; Manuel Yáñez; Jean-Yves Salpin
The structures and relative stabilities of the complexes formed by uracil and its sulfur derivatives, namely, 2-thio-, 4-thio, and 2,4-dithio-uracil when interacting with Ca(2+) in the gas phase have been analyzed by means of density functional theory (DFT) calculations carried out at the B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) level. For uracil and 2,4-dithiouracil, where the two basic sites are the same, Ca(2+) attachment to the heteroatom at position 4 is preferred. However, for the systems where both types of basic centers, a carbonyl or a thiocarbonyl group, are present, Ca(2+)-oxygen association is favored. The most stable complexes correspond to structures with Ca(2+) bridging between the heteroatom at position 2 of the 4-enol (or the 4-enethiol) tautomer and the dehydrogenated ring nitrogen, N3. The enhanced stability of these enolic forms is two-fold, on the one hand Ca(2+) interacts with two basic sites and on the other triggers a significant aromatization of the ring. Besides, Ca(2+) association has a clear catalytic effect on the tautomerization processes which connect the oxo-thione forms with the enol-enethiol tautomers. Hence, although the enol-enethiol tautomers of uracil and its thio derivatives should not be observed in the gas phase, the corresponding Ca(2+) complexes are the most stable species and should be accessible, because the tautomerization barriers are smaller than the Ca(2+) binding energies.
Journal of Computational Chemistry | 2009
Al Mokhtar Lamsabhi; Otilia Mó; Soledad Gutiérrez-Oliva; Patricia Pérez; Alejandro Toro-Labbé; Manuel Yáñez
The intermolecular double proton transfer in dimers of uracil and 2‐thiouracil is studied through density functional theory calculations. The reaction force framework provides the basis for characterizing the mechanism that in all cases has been associated to a dynamic balance between polarization and charge transfer effects. It has been found that the barriers for proton transfer depend upon the nature of the acceptor atoms and its position within the seminal monomer. Actually, the change in the nature of the hydrogen bonds connecting the two monomers along the reaction coordinate may favor or disfavor the double‐proton transfer.
Chemistry: A European Journal | 2014
M. Merced Montero-Campillo; Manuel Yáñez; Al Mokhtar Lamsabhi; Otilia Mó
The most stable complexes between squaric acid and its sulfur- and selenium-containing analogues (C4X4H2 ; X = O, S, Se) with BeY2 (Y = H, F) were studied by means of the Gaussian 04 (G4) composite ab initio theory. Squaric acid derivatives are predicted to be very strong acids in the gas phase; their acidity increases with the size of the chalcogen, with C4Se4H2 being the strongest acid of the series and stronger than sulfuric acid. The relative stability of the C4X4H2⋅BeY2 (X = O, S, Se; Y = H, F) complexes changes with the nature of the chalcogen atom; but more importantly, the formation of the C4X4H2⋅BeF2 complexes results in a substantial acidity enhancement of the squaric moiety owing to the dramatic electron-density redistribution undergone by the system when the beryllium bond is formed. The most significant consequence of this acidity enhancement is that when BeF2 is replaced by BeH2, a spontaneous exergonic loss of H2 is observed regardless of the nature of the chalcogen atom. This is another clear piece of evidence of the important role that closed-shell interactions play in the modulation of physicochemical properties of the Lewis acid and/or the Lewis base.
Chemistry: A European Journal | 2012
Ana Martín-Sómer; Al Mokhtar Lamsabhi; Manuel Yáñez; Juan Z. Dávalos; Javier González; Rocío Ramos; Jean-Claude Guillemin
The gas-phase acidity of a series of amine-borane complexes has been investigated through the use of electrospray mass spectrometry (ESI-MS), with the application of the extended Cooks kinetic method, and high-level G4 ab initio calculations. The most significant finding is that typical nitrogen bases, such as aniline, react with BH(3) to give amine-borane complexes, which, in the gas phase, have acidities as high as those of either phosphoric, oxalic, or salicylic acid; their acidity is higher than many carboxylic acids, such as formic, acetic, and propanoic acid. Indeed the complexation of different amines with BH(3) leads to a substantial increase (from 167 to 195 kJ mol(-1)) in the intrinsic acidity of the system; in terms of ionization constants, this increase implies an increase as large as fifteen orders of magnitude. Interestingly, this increase in acidity is almost twice as large as that observed for the corresponding phosphine-borane analogues. The agreement between the experimental and the G4-based calculated values is excellent. The analysis of the electron-density rearrangements of the amine and the borane moieties indicates that the dative bond is significantly stronger in the N-deprotonated anion than in the corresponding neutral amine-borane complex, because the deprotonated amine is a much better electron donor than the neutral amine. On the top of that, the newly created lone pair on the nitrogen atom in the deprotonated species, conjugates with the BN bonding pair. The dispersion of the extra electron density into the BH(3) group also contributes to the increased stability of the deprotonated species.
New Journal of Chemistry | 2001
Al Mokhtar Lamsabhi; W. Bouab; M. Esseffar; Manuel Alcamí; Manuel Yáñez; José-Luis M. Abboud
Intermolecular charge-transfer (CT) complexes between a wide range of carbonyl compounds and iodine monochloride were spectroscopically studied in the UV–visible region. Equilibrium constants and Gibbs energy changes of 1:1 charge transfer complexes were determined in CCl4 solution. The ICl basicity scale in CCl4 of the set of carbonyl derivatives included in this study is well correlated with the I2 basicity scale in the same solvent. Ab initio calculations at HF/LANL2DZ* and MP2(full)/LANL2DZ* were carried out in order to clarify the structures of these CT complexes. Two different conformations, depending on the characteristics of the substituents, may be found. In one of them the ICl moiety lies in the plane of the carbonyl group, in the other the ICl subunit is perpendicular to the CO group. The perpendicular complexes are favored by bulky substituents for which the HOMO has a clear π-character. Both kinds of complexes can be spectroscopically distinguished since they present the CT absorption at different wavelengths. In both kinds of complexes the carbonyl–ICl interaction is essentially electrostatic. The substituent effects were analyzed through the use of the Taft–Topsom model. Experimental data in solution and theoretical estimates were found to follow a good linear relationship.
Journal of Porphyrins and Phthalocyanines | 2011
Al Mokhtar Lamsabhi; Manuel Yáñez; Otilia Mó; Cristina Trujillo; Fernando Blanco; Ibon Alkorta; José Elguero; Esmeralda Caballero; M. Salomé Rodríguez-Morgade; Christian G. Claessens; Tomás Torres
The UV-vis spectra of a series of subporphyrazines, SubPz(A,R), and subphthalocyanines, SubPc(A,R) (A = F, Cl; R = H, F, CH3, C3H7, SCH3, SC2H5 and SPh), where A is the substituent attached to the central boron atom and R is the substituent attached to the periphery of the molecule have been analyzed through the use of TD–DFT calculations in vacuum and using chloroform as a solvent. The absorption spectra depend on both, the characteristics of the substituent attached to the periphery of the molecule and the extension of the π-system on going from SubPz to the SubPc analog. These latter effects lead to a red-shift of both the Q-band and the B-band, although the effect is larger for the former, mainly due to the increase of HOMO–LUMO energy gap on going from the SubPz to the SubPc analog. The effect of the substituents R is more intricate, because the profile of the absorption spectra changes depending on whether both substituents are on the same side (uu or dd) or on opposite sides (ud) of the molecular cone. Since the three conformers are rather close in energy, the observed spectra correspond, very likely, to the sum of the spectra of all of them.
Journal of Chemical Theory and Computation | 2008
Al Mokhtar Lamsabhi; Otilia Mó; Manuel Yáñez; Russell J. Boyd
The structures and relative stabilities of the complexes between Ca(2+) and 2-selenouracil, 4-selenouracil, and 2,4-diselenouracil have been investigated through the use of B3LYP/6-311++G(3df,2p)//B3LYP/6-31+G(d,p) density functional theory (DFT) calculations. In those systems where both types of basic centers, a carbonyl or a selenocarbonyl group, are present, Ca(2+) association with the oxygen is favored. For 2,4-diselenouracil the nitrogen atom at position 3 is the most basic site toward Ca(2+) attachment followed by heteroatoms attached to positions 4 and 2. Although the enolic and selenol forms of selenouracils should not be observed in the gas phase, the corresponding Ca(2+) complexes are the most stable ones. More importantly, all the activation barriers associated with the corresponding tautomeric processes are lower than the entrance channel, and therefore not only these complexes should be observed but also they should be the dominant species in the gas phase. Also, Ca(2+) association has a clear catalytic effect on these tautomerization processes, whose activation barriers decrease between 10 and 15 kcal mol(-1).
ChemPhysChem | 2014
Jean-Yves Salpin; Violette Haldys; Sébastien Guillaumont; Jeanine Tortajada; Marcela Hurtado; Al Mokhtar Lamsabhi
Gas-phase interactions between Pb(2+) ions and cytosine (C) were studied by combining tandem mass spectrometry, infrared multiple photon dissociation spectroscopy, and density functional theory (DFT) calculations. Both singly and doubly charged complexes were generated by electrospray. The [Pb(C)-H](+) complex was extensively studied, and this study shows that two structures, involving the interaction of the metal with the deprotonated canonical keto-amino tautomer of cytosine, are generated in the gas phase; the prominent structure is the bidentate form involving both the N1 and O2 electronegative centers. The DFT study also points out a significant charge transfer from the nucleobase to the low-lying p orbitals of the metal and a strong polarization of the base upon complexation. The various potential energy surfaces explored to account for the fragmentation observed are consistent with the high abundance of the [PbNH2](+) fragment ion.
Journal of Physical Chemistry A | 2010
M. Merced Montero-Campillo; Nelaine Mora-Diez; Al Mokhtar Lamsabhi
The thermodynamic stability of the 89 isomers of the eight-carbon-atom compound perfluorooctane sulfonate (PFOS) in their neutral and anionic forms has been studied in the gas phase, n-octanol, and water using density functional theory (B3LYP/6-311+G(d,p)). The gas-phase calculations are compared with previous semiempirical and partial ab initio studies; the calculations in water and n-octanol are reported for the first time. The results obtained indicate that the thermodynamic stability assessment of this family of persistent organic pollutants is independent of the environment and type of species (neutral or anionic) considered and that it is important to consider other PFOSs outside of the 83-89 set, which is the most frequently studied.