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9. Planar pentacoordinate s-block metals.

Author

Wang, Meng-hui, Kalita, Amlan J., Orozco-Ic, Mesías, Yan, Gai-ru, Chen, Chen, Yan, Bing, Castillo-Toraya, Gabriela, Tiznado, William, Guha, Ankur K., Pan, Sudip, Merino, Gabriel, and Cui, Zhong-hua

Published
2023
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11. Searching for Systems with Planar Hexacoordinate Carbons.

Author

Inostroza, Diego, Leyva-Parra, Luis, Yañez, Osvaldo, Solar-Encinas, José, Vásquez-Espinal, Alejandro, Valenzuela, Maria Luisa, and Tiznado, William

Subjects
POTENTIAL energy surfaces, ELECTROSTATIC interaction, CARBON, BERYLLIUM
Abstract

Here, we present evidence that the D2h M2C50/2+ (M = Li-K, Be-Ca, Al-In, and Zn) species comprises planar hexacoordinate carbon (phC) structures that exhibit four covalent and two electrostatic interactions. These findings have been made possible using evolutionary methods for exploring the potential energy surface (AUTOMATON program) and the Interacting Quantum Atoms (IQA) methodology, which support the observed bonding interactions. It is worth noting, however, that these structures are not the global minimum. Nonetheless, incorporating two cyclopentadienyl anion ligands (Cp) into the CaC52+ system has enhanced the relative stability of the phC isomer. Moreover, cycloparaphenylene ([8]CPP) provides system protection and kinetic stability. These results indicate that using appropriate ligands presents a promising approach for expanding the chemistry of phC species. [ABSTRACT FROM AUTHOR]

Published
2023
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14. Planar Elongated B 12 Structure in M 3 B 12 Clusters (M = Cu-Au).

Author

Solar-Encinas, José, Vásquez-Espinal, Alejandro, Leyva-Parra, Luis, Yañez, Osvaldo, Inostroza, Diego, Valenzuela, Maria Luisa, Orellana, Walter, and Tiznado, William

Subjects
POTENTIAL energy surfaces, CHEMICAL bonds, DENSITY functional theory, ANALYTICAL chemistry, GENETIC algorithms
Abstract

Here, it is shown that the M3B12 (M = Cu-Au) clusters' global minima consist of an elongated planar B12 fragment connected by an in-plane linear M3 fragment. This result is striking since this B12 planar structure is not favored in the bare cluster, nor when one or two metals are added. The minimum energy structures were revealed by screening the potential energy surface using genetic algorithms and density functional theory calculations. Chemical bonding analysis shows that the strong electrostatic interactions with the metal compensate for the high energy spent in the M3 and B12 fragment distortion. Furthermore, metals participate in the delocalized π-bonds, which infers an aromatic character to these species. [ABSTRACT FROM AUTHOR]

Published
2023
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18. In Silico Study of Coumarins and Quinolines Derivatives as Potent Inhibitors of SARS-CoV-2 Main Protease

Author

Universidade de Santiago de Compostela. Departamento de Química Orgánica, Yañez, Osvaldo, Osorio, Manuel Isaías, Uriarte Villares, Eugenio, Areche, Carlos, Tiznado, William, Pérez Donoso, José M., García Beltrán, Olimpio, González Nilo, Fernando, Universidade de Santiago de Compostela. Departamento de Química Orgánica, Yañez, Osvaldo, Osorio, Manuel Isaías, Uriarte Villares, Eugenio, Areche, Carlos, Tiznado, William, Pérez Donoso, José M., García Beltrán, Olimpio, and González Nilo, Fernando

Abstract

The pandemic that started in Wuhan (China) in 2019 has caused a large number of deaths, and infected people around the world due to the absence of effective therapy against coronavirus 2 of the severe acute respiratory syndrome (SARS-CoV-2). Viral maturation requires the activity of the main viral protease (Mpro), so its inhibition stops the progress of the disease. To evaluate possible inhibitors, a computational model of the SARS-CoV-2 enzyme Mpro was constructed in complex with 26 synthetic ligands derived from coumarins and quinolines. Analysis of simulations of molecular dynamics and molecular docking of the models show a high affinity for the enzyme (∆Ebinding between −5.1 and 7.1 kcal mol−1). The six compounds with the highest affinity show Kd between 6.26 × 10–6 and 17.2 × 10–6, with binding affinity between −20 and −25 kcal mol−1, with ligand efficiency less than 0.3 associated with possible inhibitory candidates. In addition to the high affinity of these compounds for SARS-CoV-2 Mpro, low toxicity is expected considering the Lipinski, Veber and Pfizer rules. Therefore, this novel study provides candidate inhibitors that would allow experimental studies which can lead to the development of new treatments for SARS-CoV-2

Published
2021

21. Theoretical study of the interaction of molecular oxygen with copper clusters

Author

Florez, Elizabeth, Tiznado, William, Mondragon, Fanor, and Fuentealba, Patricio

Subjects
Copper compounds -- Chemical properties, Copper compounds -- Atomic properties, Molecular dynamics -- Research, Electron donor-acceptor complexes -- Research, Chemicals, plastics and rubber industries
Abstract

A new method based on frontier orbital theory is used to investigate the binding site of molecular oxygen to neutral and anion copper clusters. Useful predictions of the binding sites can be made based on the knowledge of the donor local reactivity of the cluster using the condensed Fukui function f(super -)(sub Ff) and it is found that Cu3, Cu5 and Cu5- have the highest reactivity toward molecular oxygen.

Published
2005

26. Analysis of Local and Global Aromaticity in Si3C5 and Si4C8 Clusters. Aromatic Species Containing Planar Tetracoordinate Carbon.

Author

Torres-Vega, Juan J., Alcoba, Diego R., Oña, Ofelia B., Vásquez-Espinal, Alejandro, Báez-Grez, Rodrigo, Lain, Luis, Torre, Alicia, García, Víctor, and Tiznado, William

Subjects
MICROCLUSTERS, AROMATICITY, CHEMICAL bonds, ELECTRIC circuits, ELECTRONS
Abstract

The minimum energy structures of the Si3C5 and Si4C8 clusters are planar and contain planar tetracoordinate carbons (ptCs). These species have been classified, qualitatively, as global (π) and local (σ) aromatics according to the adaptive natural density partitioning (AdNDP) method, which is an orbital localization method. This work evaluates these species’ aromaticity, focusing on confirming and quantifying their global and local aromatic character. For this purpose, we use an orbital localization method based on the partitioning of the molecular space according to the topology of the electronic localization function (LOC-ELF). In addition, the magnetically induced current density is analyzed. The LOC-ELF-based analysis coincides with the AdNDP study (double aromaticity, global, and local). Moreover, the current density analysis detects global and local ring currents. The strength of the global and local current circuit is significant, involving 4n + 2 π- and σ-electrons, respectively. The latter implicates the Si-ptC-Si fragment, which would be related to the 3c-2e σ-bond detected by the orbital localization methods in this fragment. [ABSTRACT FROM AUTHOR]

Published
2021
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30. Theoretical study on CDK2 inhibitors using a global softness obtained from the density of the states

Author

Alzate-Morales, Jans H., Tiznado, William, Santos, Juan C., Cardenas, Carlos, and Contreras, Renato

Subjects
Protein kinases -- Structure, Protein kinases -- Electric properties, Polarization (Electricity) -- Analysis, Density functionals -- Analysis, Cellular control mechanisms -- Research, Chemicals, plastics and rubber industries
Abstract

A range of cyclin-dependent kinases (CDK2) inhibitors are analyzed by a model of active site called the hinge region (HR) by utilizing a group of global reactivity indices decided with respect to density of states. It is proposed that in the HR-ligand interaction, the polarization effect is more than the charge transfer contribution by comparing the biological activity and global softness.

Published
2007

31. Definition of a nucleophilicity scale

Author

Jaramillo, Paula, Perez, Patricia, Contreras, Renato, Tiznado, William, and Fuentealba, Patricio

Subjects
Nucleophilic reactions -- Research, Vibrational spectra -- Research, Chemicals, plastics and rubber industries
Abstract

A simple model is presented to develop an empirical nucleophilicity scale based on the stretching force constants of the vibrational spectrum, where the B-HX hydrogen bonding system (where B is a base Lewis and HX is a dipole) is the benchmark to test the model. The results have shown that Legon and Millen nucleophilicity scale and the electrostatic potential derived scales can elucidate in good approximation the reactivity order of the nucleophiles only when the interactions with a probe electrophile is of the hard-hard type.

Published
2006

42. Análisis directo de elementos traza en agua natural por fluorescencia de rayos X en reflexión total

Author

Tiznado, William and Olivera, Paula

Subjects
Materiales de referencia, Análisis químico, Agua, Fluorescencia de rayos X
Abstract

Se ha desarrollado un método de análisis directo para la determinación simultánea de Cr, Mn, Fe, Co, Ni, Cu, Zn y As a niveles de traza (ng/g) en muestras de agua de río, mediante la técnica de Fluorescencia de rayos en Reflexión Total y el uso de Ga como estándar interno. El método se ha puesto a punto con el material de referencia NIST 1643 d y los límites de detección para dichos elementos oscilan entre 11 y 41 ng/g. Se ha observado una alta precisión, exactitud y sensibilidad del método. Instituto Peruano de Energía Nuclear

Published
2002

43. Determinación de Cr, Mn, Fe, Co, Ni, Cu, Zn y As en aguas del río Rímac por fluorescencia de rayos-X en reflexión total

Author

Olivera, Paula and Tiznado, William

Subjects
Contaminación de las aguas, Agua, Río Rimac, Fluorescencia de rayos X
Abstract

Se han analizado muestras tomadas en trece estaciones a lo largo de la cuenca del río Rímac. Los muestreos se realizaron durante un período de un año (septiembre 1998 – agosto 1999), con una frecuencia de un muestreo por mes. Se ha utilizado la técnica de Análisis por Fluorescencia de Rayos-X en Reflexión Total para determinar los elementos Cr, Mn, Fe, Co, Ni, Cu, Zn y As en su fase disuelta. De los resultados obtenidos se observa: que la relación de la presencia de estaciones mineras con el nivel de concentración de metales, especialmente de Zn, Fe y As, está presente en concentraciones por encima de los niveles máximos permisibles en algunas de las estaciones muestreadas; además, el Ni y el Cr -que son elementos de importancia tóxica- se encuentran en concentraciones muy bajas. Por otro lado, ha quedado demostrado que el método de análisis empleado es útil como herramienta de monitoreo de la calidad de aguas superficiales debido a sus bajos límites de detección y a la rapidez con que se ejecutan los análisis. Instituto Peruano de Energía Nuclear

Published
2002

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