Effects of halogen substitution on Watson–Crick base pairing: A possible mechanism for radiosensitivity

A Bayesian Regularized Artificial Neural Network for Simultaneous Determination of Loratadine, Naproxen and Diclofenac in Wastewaters

Background::

Simultaneous determination of medication components in pharmaceutical samples using ordinary methods have some difficulties and therefore these determinations usually were made by expensive methods and instruments. Chemometric methods are an effective way to analyze several components simultaneously.

Objective::

In this paper, a novel approach based on Bayesian regularized artificial neural network is developed for the determination of Loratadine, Naproxen, and Diclofenac in water using UV-Vis spectroscopy.

Methods:

A dataset is collected by performing several chemical experiments and recording the UV-Vis spectra and actual constituent values. The effect of a different number of neurons in the hidden layer was analyzed based on final mean square error, and the optimum number was selected. Principle Component Analysis (PCA) was also applied to the data. Other back-propagation methods, such as Levenberg-Marquardt, scaled conjugate gradient, and resilient backpropagation, were tested.

Results::

In order to see the proposed network performance, it was performed on two crossvalidation methods, namely partitioning data into train and test parts, and leave-one-out technique. Mean square errors between expected results and predicted ones implied that the proposed method has a strong ability in predicting the expected values.

Conclusion::

he results showed that the Bayesian regularization algorithm has the best performance among other methods for simultaneous determination of Loratadine, Naproxen, and Diclofenac in water samples.

Halogen Bonding in Nucleic Acid Complexes

Halogen bonding (X-bonding) has attracted notable attention among noncovalent interactions. This highly directional attraction between a halogen atom and an electron donor has been exploited in knowledge-based drug design. A great deal of information has been gathered about X-bonds in protein-ligand complexes, as opposed to nucleic acid complexes. Here we provide a thorough analysis of nucleic acid complexes containing either halogenated building blocks or halogenated ligands. We analyzed close contacts between halogens and electron-rich moieties. The phosphate backbone oxygen is clearly the most common halogen acceptor. We identified 21 X-bonds within known structures of nucleic acid complexes. A vast majority of the X-bonds is formed by halogenated nucleobases, such as bromouridine, and feature excellent geometries. Noncovalent ligands have been found to form only interactions with suboptimal interaction geometries. Hence, the first X-bonded nucleic acid binder remains to be discovered.

Cocrystals of 6-chlorouracil and 6-chloro-3-methyluracil: exploring their hydrogen-bond-based synthon motifs with several triazine and pyrimidine derivatives

In order to obtain complexes held together by hydrogen as well as halogen bonds, 6-chlorouracil [6-chloropyrimidin-2,4(1H,3H)-dione; 6CU] and its 3-methyl derivative [6-chloro-3-methylpyrimidin-2,4(1H,3H)-dione; M6CU] were cocrystallized with 2,4,6-triaminopyrimidine and the three triazine derivatives 2,4,6-triamino-1,3,5-triazine (melamine), 2,4-diamino-6-methyl-1,3,5-triazine and 2-chloro-4,6-diamino-1,3,5-triazine, which all offer complementary hydrogen-bonding sites. Three of these compounds form cocrystals with 6CU; however, melamine yielded only a new pseudopolymorph with 6CU, but formed a cocrystal with M6CU. All six cocrystals contain solvent molecules (N,N-dimethylformamide,N,N-dimethylacetamide orN-methylpyrrolidin-2-one), whose intermolecular interactions contribute significantly to the stabilization of the crystal packing. Each of these structures comprises chains, which are primarily formed by strong hydrogen bonds with a basic framework built byR22(8) hydrogen bonds of either pure N—H...N or mixed patterns. Solvent molecules are aligned to the border of these chainsviaN—H...O hydrogen bonds. Two of the reported crystal structures containing 6CU show additional Cl...O halogen bonds, which connect the chains to two-dimensional layers, while one weak and one strong Cl...Cl interaction are observed in the two structures in which molecules of M6CU are present.

A Protein Data Bank survey reveals shortening of intermolecular hydrogen bonds in ligand-protein complexes when a halogenated ligand is an H-bond donor

Halogen bonding in ligand-protein complexes is currently widely exploited, e.g. in drug design or supramolecular chemistry. But little attention has been directed to other effects that may result from replacement of a hydrogen by a strongly electronegative halogen. Analysis of almost 30000 hydrogen bonds between protein and ligand demonstrates that the length of a hydrogen bond depends on the type of donor-acceptor pair. Interestingly, lengths of hydrogen bonds between a protein and a halogenated ligand are visibly shorter than those estimated for the same family of proteins in complexes with non-halogenated ligands. Taking into account the effect of halogenation on hydrogen bonding is thus important when evaluating structural and/or energetic parameters of ligand-protein complexes. All these observations are consistent with the concept that halogenation increases the acidity of the proximal amino/imino/hydroxyl groups and thus makes them better, i.e. stronger, H-bond donors.