RESUMEN
The chiroptical properties of multi-chromophoric systems are governed by the intermolecular arrangement of the monomeric units. We report on a computational and experimental study of the linear optical properties and supramolecular structure of a rhodamine heterodimer assembled on a DNA scaffold. The experimental absorption and circular dichroism (CD) profiles confirm the dimer formation. Computationally, starting from low-cost DFT/TDDFT simulations of the bare dimer we attribute the measured -/+ CD sign sequence of the S1/S2 bands to a specific chiral conformation of the heterodimer. In the monomers, as typical for rhodamine dyes, the electric transition dipole of the lowest π-π* transition is parallel to the long axis of the xanthene planes. We show that in the heterodimer the sign sequence of the two CD bands is related to the orientation of these long axes. To account explicitly for environment effects, we use molecular dynamics (MD) simulations for characterizing the supramolecular structure of the two optical isomers tethered on DNA. Average absorption and CD-profiles were modeled using ab initio TDDFT calculations at the geometries sampled along a few nanosecond MD run. The absorption profiles computed for both optical isomers are in good agreement with the experimental absorption spectrum and do not allow one to discriminate between them. The computed averaged CD profiles provide the orientation of monomers in the enantiomer that is dominant under the experimental conditions.
Asunto(s)
ADN/química , Modelos Moleculares , Rodaminas/química , Dicroismo Circular , Química Computacional , Simulación de Dinámica Molecular , Estructura MolecularRESUMEN
Elucidating the role of quantum coherences in energy migration within biological and artificial multichromophoric antenna systems is the subject of an intense debate. It is also a practical matter because of the decisive implications for understanding the biological processes and engineering artificial materials for solar energy harvesting. A supramolecular rhodamine heterodimer on a DNA scaffold was suitably engineered to mimic the basic donor-acceptor unit of light-harvesting antennas. Ultrafast 2D electronic spectroscopic measurements allowed identifying clear features attributable to a coherent superposition of dimer electronic and vibrational states contributing to the coherent electronic charge beating between the donor and the acceptor. The frequency of electronic charge beating is found to be 970 cm-1 (34 fs) and can be observed for 150 fs. Through the support of high level ab initio TD-DFT computations of the entire dimer, we established that the vibrational modes preferentially optically accessed do not drive subsequent coupling between the electronic states on the 600 fs of the experiment. It was thereby possible to characterize the time scales of the early time femtosecond dynamics of the electronic coherence built by the optical excitation in a large rigid supramolecular system at a room temperature in solution.
Asunto(s)
ADN/química , Rodaminas/química , Materiales Biocompatibles/química , Dimerización , Electrones , Modelos Moleculares , Conformación de Ácido NucleicoRESUMEN
A new Cu-based anticancer metallodrug which targets the translocator protein is reported. [CuBr2(TZ6)] elicits a remarkable in vitro cytotoxicity in sensitive and multidrug resistant cell lines and induces a 98% reduction of tumor mass in a murine tumor model. Target binding was studied by experimental and computational methods.
Asunto(s)
Antineoplásicos/química , Antineoplásicos/farmacología , Cobre/química , Terapia Molecular Dirigida , Compuestos Organometálicos/química , Compuestos Organometálicos/farmacología , Receptores de GABA/metabolismo , Animales , Antineoplásicos/metabolismo , Línea Celular Tumoral , Regulación Neoplásica de la Expresión Génica/efectos de los fármacos , Humanos , Ratones , Modelos Moleculares , Compuestos Organometálicos/metabolismo , Conformación Proteica , Receptores de GABA/química , Ensayos Antitumor por Modelo de XenoinjertoRESUMEN
We show computationally that ligation allows tuning of the magnetostructural properties of the Pd(13) cluster. The bare, phosphine and thiol capped clusters were investigated at the density functional level. The most stable conformers of the bare cluster are of high spin, septet and nonet and of distorted C(3v), C(s) and I(h) geometries. Ligation stabilizes the I(h) geometry and quenches the high spin states, down to a triplet for Pd(13)(PH(3))(12) and to a quintet for Pd(13)(SCH(3))(12).The influence of the two capping systems on the magnetostructural properties of the ligated clusters is analyzed in connection with their different bonding properties. The mixed ligand species Pd(13)(SCH(3))(6)(PH(3))(6) is also characterized. Due to the multiple energetically accessible spin states, unusual thermal behaviour of the average magnetic moment is predicted for these clusters.