Juan Carlos Ramírez

Theoretical assessment of the mechanisms involved in the cholesterol biosynthesis from lanosterol

A theoretical approach to describe the mechanisms of the isomerization and reduction of a double bond, involved in the lanosterol conversion to cholesterol was undertaken. Also, the 14α-demethylation and 4α-demethylation in this biosynthesis were studied, and some similarities were found between the two; however they are different and their mechanisms have not been explained yet. Ab initio calculations were performed in order to prove these mechanisms. Two different characteristics involved in this biosynthesis were explained, namely (i) the stability of each molecule during this reaction using total energy, hardness and dipole moment, and (ii) the explanation of proposed mechanisms [Steroid Biochemistry and Pharmacology, 1970, p. 57] of the two different reactions, using frontier orbitals and atomic charges. For this sequence of reactions, the hardness and dipole moment indicate the hydro-solubility of the molecules, which means that carrying properties change through cell membrane. It is possible to explain the reaction mechanisms using frontier molecular orbitals theory and the atomic charge. The localization of highest occupied molecular orbital, lowest unoccupied molecular orbital and the flow of atomic charge are in agreement with reported mechanisms [Steroids 8 (1966) 353; Medicinal Natural Products, 1997, p. 218; Biochemistry of Steroid Hormones, 1975, p. 1].

Characterizing off-diagonal regions of one-electron density matrix

The off-diagonal regions of the one-electron density matrix (ODM) are characterized according to their contributions to the chemical bond. In particular, these regions of the ODM difference maps were used to characterize the chemical bond in various diatomic molecules. The nature of a critical point, core interaction critical point, in the off-diagonal part of ODM reveals the chemical bond type: maximum for covalent bond, minimum for closed-shell interaction, and saddle point for a charge-shift bond.

(E)-1-(2,4-Di-nitro-benzyl-idene)-2,2-di-phenyl-hydrazine.

In the crystal of the title compound, C19H14N4O4, the asymmetric unit consists of two discrete molecules. The C=N bonds in both molecules show an E conformation. The dihedral angles between the C atoms of the 2,4-dinitrobenzene rings and the C=N—N planes are 13.52 (9) and 13.82 (9)° for the two molecules. In the crystal, C—H⋯O hydrogen bonds, mainly between the phenyl ring and the nitro group along the b axis.

(1E,2E)-1,2-Bis(2,2-diphenyl­hydrazin-1-yl­idene)ethane

In the crystal structure of the title compound, C26H22N4, the molecule is located on an inversion centre and shows an E configuration with respect to each C=N bond. The dihedral angle between the phenyl rings in the diphenylhydrazone group is 83.69 (11)°. These two rings make dihedral angles of 30.53 (15) and 84.53 (16)° with the central N—N=C—C=N—N dihydrazonoethane plane. Intermolecular C—H⋯π interactions are observed.

Theoretical study of the 4α-demethylation mechanism involved in the biosynthesis of cholesterol

Abstract This report deals with the biosynthetic route from lanosterol to cholesterol, particularly exploring the demethylations of which there are three, the 14α- and two 4α-demethylations. Ab-initio calculations were used to analyse the 14α- and 4α-demethylations, and the possibility of carrying out the 4α- or 4β-demethylations. The energy profile was analysed for the complete biosynthetic route, an explanation is also given as to why the 4α is preferred over the 4β-demethylation inside the body; using hardness and electrostatic potential maps. Also for the intermediates involved when the C–C bond is enlarged for the 4α- and 4β-demethylation, the hardness, the electrostatic potential maps and dipole moment were used. When C–C is enlarged of 4α, there exists an equatorial carboxyl group which shows big electrostatic potential maps on this side, which enables the receptor could be attacked by the enzyme. Therefore the reaction on this side is easier and faster than the 4β-demethylation. The dipole moment for 4α-demethylation has noticeable variation while for 4β-demethylation does not.

An Architecture for Cognitive Modeling to Support Real-Time Adaptation and Motivational Responses in Video Games

Currently, there are tremendous advances in gaming technologies to improve physical realism of environments and characters. However, game characters are still lacking in the cognitive realism, thus video games and game development tools need to provide functionality to support real-time adaptation and appropriate response to internal motivations. In this paper we propose an architecture for cognitive modeling based on well-known cognitive architectures like ACT-R and Soar. It describes a methodology for developing a behavioral system and it emphasizes an ethological sensing modeling to simulate more realistic behaviors. This methodology serves to develop a component-based system that could improve the ability to create intelligent virtual agents. In this phase of implementation, we present preliminary results of modeling behavior of a fish character in an undersea world using a game engine.

(E)-1,1-Diphenyl-2-(thio-phen-2-yl-methyl-idene)hydrazine.

The asymmetric unit of the title compound, C17H14N2S, consists of two crystallographically independent molecules with similar conformations. The dihedral angles between the phenyl rings are 89.32 (5) and 82.80 (5)° in the two molecules. In the crystal, molecules are linked by C—H⋯π interactions, forming a three-dimensional network.