Conformational and electronic study of dopamine interacting with the D2 dopamine receptor

We report an exhaustive conformational and electronic study on dopamine (DA) interacting with the D₂ dopamine receptor (D₂DR). For the first time, the complete surface of the conformational potential energy of the complex DA/D₂DR is reported. Such a surface was obtained through the use of QM/MM calculations. A detailed study of the molecular interactions that stabilize and destabilize the different molecular complexes was carried out using two techniques: Quantum Theory of Atoms in Molecules computations and nuclear magnetic shielding constants calculations. A comparative study of the behavior of DA in the gas phase, aqueous solution, and in the active site of D₂DR has allowed us to evaluate the degree of deformation suffered by the ligand and, therefore, analyze how rustic are the lock-key model and the induced fit theory in this case. Our results allow us to propose one of the conformations obtained as the “biologically relevant” conformation of DA when it is interacting with the D₂DR.     

Dissolving Hydroxyolite: A DNA Molecule into Its Hydroxyapatite Mold

In spite of the clinical importance of hydroxyapatite (HAp), the mechanism that controls its dissolution in acidic environments remains unclear. Knowledge of such a process is highly desirable to provide better understanding of different pathologies, as for example osteoporosis, and of the HAp potential as vehicle for gene delivery to replace damaged DNA. In this work, the mechanism of dissolution in acid conditions of HAp nanoparticles encapsulating double‐stranded DNA has been investigated at the atomistic level using computer simulations. For this purpose, four consecutive (multi‐step) molecular dynamics simulations, involving different temperatures and proton transfer processes, have been carried out. Results are consistent with a polynuclear decalcification mechanism in which proton transfer processes, from the surface to the internal regions of the particle, play a crucial role. In addition, the DNA remains protected by the mineral mold and transferred proton from both temperature and chemicals. These results, which indicate that biomineralization imparts very effective protection to DNA, also have important implications in other biomedical fields, as for example in the design of artificial bones or in the fight against osteoporosis by promoting the fixation of Ca²⁺ ions.     

SU(1,1) Coherent States for Position-Dependent Mass Singular Oscillators

The Schr?dinger equation for position-dependent mass singular oscillators is solved by means of the factorization method and point transformations. These systems share their spectrum with the conventional singular oscillator. Ladder operators are constructed to close the su(1,1) Lie algebra and the involved point transformations are shown to preserve the structure of the Barut-Girardello and Perelomov coherent states.     

First stability eigenvalue characterization of Clifford hypersurfaces

The stability operator of a compact oriented minimal hypersurface is given by , where is the norm of the second fundamental form. Let be the first eigenvalue of and define . In 1968 Simons proved that for any non-equatorial minimal hypersurface . In this paper we will show that only for Clifford hypersurfaces. For minimal surfaces in , let denote the area of and let denote the genus of . We will prove that . Moreover, if is embedded, then we will prove that . If in addition to the embeddeness condition we have that , then we will prove that .

     

Transient reduction in the tRNA 4-thiouridine content induced by ultraviolet A during post-irradiation growth in Enterobacter cloacae

The influence of previous exposure to ultraviolet-A radiation (UVA) was studied on the susceptibility of Enterobacter cloacae to undergo the growth delay effect. Comparison of growth curves corresponding to irradiated and control cells showed that a previous treatment with UVA almost abolished the growth delay effect. UV absorption spectra of tRNA, and reverse phase HPLC analysis of hydrolysed tRNA, demonstrated a low content of 4-thiouridine in E. cloacae cells grown after UVA exposure at low doses. Since 4-thiouridine is the UVA target responsible for initiation of growth delay, this observation explained the influence of previous exposure to UVA on the susceptibility of this organism to undergo growth delay. A similar but weaker alteration was found when Escherichia coli was assayed. The results suggest that, in addition to cross-linking with cytidine residues, the content of 4-thiouridine in tRNA may be modified by UVA by an unknown mechanism.     

Complete rotation hypersurfaces with Hk constant in space forms

In this paper we classify all complete rotation hypersurfaces withH _k constant in ⁿ⁺¹ andH ⁿ⁺¹, is the normalizedk-th symmetric function of the principal curvatures. Partial results are also given forH ⁿ⁺¹.Partially supported by DGAPA-UNAM, México, CONACYT, México, under Project 1068P, and CNPp, Brazil.