Computed NMR shielding values of unsaturated five-membered-heterocyclic ring compounds and their benzo-analogs as a measure of aromaticity

The gauge independent atomic orbital (GIAO) Hartree-Fock (HF) technique with a 6-31 G(d, p) basis set was used to calculate the isotropic NMR shielding values of a diatomic hydrogen probe above a set of unsaturated 5-membered heterocyclic aromatic compounds and their benzo- analogs. It has been shown that this technique produced results indicating substantial shielding of the probe over the center of aromatic rings. The current study was conducted to determine if the computed shielding of a diatomic H2 probe is related quantitatively to the extent of aromaticity. Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs of electrons or empty orbitals exhibits a stabilization due to conjugation alone. Aromaticity is both a qualitative and quantitative concept. The qualitative aspect, which is the method for identifying a molecule or species as either aromatic, non-aromatic or anti-aromatic, is soundly understood, but the quantitative aspect of aromaticity is less well defined. There are several established methods for measuring aromaticity quantitatively but they are only loosely correlated. This study’s method (?s) for calculations done over the fivemembered rings correlated well with Cyransky’s published data of ASE, ?, NICS(0), NICS(1) and HOMA calculations to yield correlation coefficients of 0.64, 0.49, 0.66, 0.88 and 0.69, respectively. This study’s method (?s) with calculations done over the heterocyclic ring portion of the benzo-analogs yielded a correlation coefficient of 0.67 when matched with Bird’s published ASE data

Bioactive Marine Heterocyclic Compounds

This Special Issue of Marine Drugs, entitled “Bioactive Marine Heterocyclic Compounds”, aimed to collect excellent original research articles and reviews focused on the isolation of new heterocyclic marine natural products, total synthesis, synthetic modification, or on finding important bioactivities of known heterocyclic marine natural products. As a result, five original papers on isolation and one synthetic study of metabolites from marine-derived bioorganisms or a marine sponge, along with one review paper on thiazole-based peptides, were published. I am proud to show these most recent works of outstanding scientists in this field and hope this Special issue will affect new drug developments or innovation in the future

DFT and PM3 Computational Studies of the Reaction Mechanism of the Oxidation of L-Tyrosine by Iodine in the Gas Phase

- The oxidation of L-Tyrosine by molecular iodine was studied using semi-empirical and density functional theory methods. Molecular information such as net charges, values of frontier orbital energies, composition, proportions and bonding contribution were obtained and analyzed. Thus, possible reactive sites were proposed and the reaction mechanism was postulated. The postulated transition states, intermediates and products were also computed using the PM3 and DFT methods. Computed enthalpies of the oxidation reaction at standard conditions for the PM3 and DFT calculation were 216.97 kJ/mol and -36327404.72 kJ/mol respectively. The calculated ΔGo andΔSo, for the transition states according to the DFT model were both large and negative indicating that the processes were exergonic associative substitution reactions

Evaluating Self-Supervised Learning for Molecular Graph Embeddings

Graph Self-Supervised Learning (GSSL) provides a robust pathway for acquiring embeddings without expert labelling, a capability that carries profound implications for molecular graphs due to the staggering number of potential molecules and the high cost of obtaining labels. However, GSSL methods are designed not for optimisation within a specific domain but rather for transferability across a variety of downstream tasks. This broad applicability complicates their evaluation. Addressing this challenge, we present "Molecular Graph Representation Evaluation" (MOLGRAPHEVAL), generating detailed profiles of molecular graph embeddings with interpretable and diversified attributes. MOLGRAPHEVAL offers a suite of probing tasks grouped into three categories: (i) generic graph, (ii) molecular substructure, and (iii) embedding space properties. By leveraging MOLGRAPHEVAL to benchmark existing GSSL methods against both current downstream datasets and our suite of tasks, we uncover significant inconsistencies between inferences drawn solely from existing datasets and those derived from more nuanced probing. These findings suggest that current evaluation methodologies fail to capture the entirety of the landscape.Comment: update result

Rational redox tuning of transition metal sites : Learning from superoxide reductase

Using superoxide reductase as a model system, a computational approach reveals how histidine tautomerism tunes the redox properties of metalloenzymes to enable their catalytic function. Inspired by these experimentally inaccessible insights, non-canonical histidine congeners are introduced as new versatile tools for the rational engineering of biological transition metal sites

Synthesis, Characterization and Antimicrobial Evaluation of Cr (III) Complexes of 2-Amino -3-(2-hydroxy phenyl) -1-oxazolidin-4-one and 2-Amino -3-(2-hydroxy phenyl) -1-thiozolidin-4-one

The ligands 2-Imino-3-(2-hydroxyphenyl)-1-oxazolidine-4-one and 2-Imino-3-(2-hydroxy phenyl)-

Scope of Selective Heterocycles from Organic and Pharmaceutical Perspective

Scope of Selective Heterocycles from Organic and Pharmaceutical Perspective is a compilation of bioactive-chosen heterocyclic scaffolds intended for postgraduates, research scholars, pharmaceutical scientists, and others interested in an appreciation of the title subject. It is an edited book and is not comprehensive as well in the mentioned field. Few synthetic strategies along with bioactivity are presented, and some limitations were raised in order to arouse curiosity of the reader