Biomedical subjects

José A Dobado

Publications and source records attributed to José A Dobado.

3 recordsLinked to original sources

PubMed2005

On the nature of metal-carbon bonding: AIM and ELF analyses of MCH(n) (n = 1-3) compounds containing early transition metals.

Ab initio and DFT calculations have been performed on a series of organometallic compounds, according to the formula MCH(n), where M = K, Ca, Sc, Ti, V, Cr, or Mn and n = 1-3. Various theoretical methods are compared, the B3LYP level yielding the same agreement with the experimental geometries available as the correlated MP2 and CISD methods, with the 6-311++G(3df,2p) basis set for C and H and Wachter's (15s11p6d3f1g)/[10s7p4d3f1g] basis set for transition metals. The main geometric and electronic features of the molecules studied are described, analyzing the M-C bonding characteristics in terms of the atoms in molecules theory (AIM) and the electron localization function (ELF). Although multiple bonding is expected from the Lewis bonding scheme, the results indicate an almost pure ionic bond for all of the systems studied. The net charge transfer from the metal to the carbon atom ranges from 0.5 to 1 e(-), and the electronic structure of the CH(n)(-) moiety is unaltered after the interaction with the metal cation, showing little or no effect on the shape of the electron pairing. The bond paths corresponding to a possible alpha-agostic bond for these systems are not present.

Algorithms↗

PubMed2003

Epoxides, cyclic sulfites, and sulfate from natural pentacyclic triterpenoids: theoretical calculations and chemical transformations.

Several triterpenic derivatives, with the A-ring functionalized, were semisynthesized from oleanolic and maslinic acids. The reactivities of sulfites, sulfate, and epoxides in these triterpene compounds were investigated under different reaction conditions. Moreover, contracted A-ring triterpenes (five-membered rings) were obtained, by different treatments of the sulfate 7. From the epoxide 8, deoxygenated and halohydrin derivatives were semisynthesized with several nucleophiles. Ozonolysis and Beckmann reactions were used to yield 4-aza compounds, from five-membered ring olanediene triterpenes. The X-ray structure of sulfate 7 is given and compared with density functional theory geometries. Theoretical (13)C and (1)H chemical shifts (gauge-invariant atomic orbital method at the B3LYP/6-31G*//B3LYP/6-31G* level) and (3)J(H,H) coupling constants were calculated for compounds 5-9 and 34-36, identifying the (R)- or (S)-sulfur and alpha- or beta-epoxide configurations together with 4-aza or 3-aza structures.

Aza Compounds↗

PubMedDate not supplied

CoNTub: an algorithm for connecting two arbitrary carbon nanotubes.

We have developed the first computer program for determining the coordinates of heterojunctions between two arbitrary carbon nanotubes. This software implements the topological algebra based on the concept of strip, a continuous subset of carbon rings containing all the topological defects (nonhexagonal carbon rings). The user easily generates any heterojunction by merely introducing the indices (i,j) and length of the two nanotubes to be connected. The resulting structure is immediately visualized and can be exported in the protein-data-bank (PDB) format. Two classes of heterojunctions are distinguished depending on whether a cone between the connected nanotubes is required. This method is applicable to all kinds of two nanotube heterojunctions, including Dunlap's knees and others related. In addition, this program also generates single- and multiwalled carbon nanotubes (SWNT and MWNT). This application has been implemented as a Java applet, and it is freely available at the following web address: http://www.ugr.es/local/gmdm/java/contub/contub.html

Journal Article↗