Sulfonamides are an important class of therapeutic agents. The increase in the number of new sulfonamide derivatives makes it necessary to study more rationally the chemical structure, because the solid forms often display different mechanical, thermal and physicochemical properties that can influence the bioavailability and stability of the drugs; consequently, the polymorphic structures are of great interest to the pharmaceutical industry because of their ability to modify the physical properties of the active pharmaceutical ingredient. The molecular interactions of these drugs in their crystal lattice are important for the stability of the crystals and polymorphism and for preparing composite complexes for optimizing the use of these drugs. In this work, the crystal structure of these drugs and crystal polymorphism is investigated. So, the crystal forms of antibiotics derivatives of the sulfonamides, sulfamethoxazole, sulfamethazine, sulfachloropyridazine, and sulfacetamide are studied at the molecular and supramolecular level by using computational modeling approach at quantum mechanical level. The spectroscopic properties of these systems are also studied explaining assignments of previous experimental data. The results of DFT calculations reproduce the crystal structures of sulfonamides determined experimentally and the polymorphism in these molecules have been clarified. Likewise, the main intermolecular interactions in all crystal forms of these sulfonamides are H-bonds among the sulfonic and amino groups and SNH groups, and also some π-π interactions. Also, these 3-D periodical models allow the exploration of the intermolecular interactions included in the crystal structures and some of these interactions can alter the vibration modes of the molecules. Therefore, the use of these models can be useful for experimental spectroscopy studies where use actual crystal solids.

Flexoelectric actuation employs an applied electric field to induce membrane curvature, which is the mechanism utilized by the outer hair cells (OHC) present in the inner ear. The model developed for this study, representing the OHC, integrates two key components: (i) an approximation of the flexoelectric membrane shape equation for circular membranes attached to the inner surface of a circular capillary, and (ii) the coupled capillary flow of contacting liquid viscoelastic phases characterized by the Tanner-Power law rheological equation of state. A second-order non-linear differential equation for average curvature has been derived, and a robust numerical method has been programmed. This model simplifies to a linear model used previously. The main challenge involves identifying and describing the enhancement in curvature change rate. It was observed that low symmetry, low viscosity, and soft membrane and shear-thickening behavior of the phases enhance the curvature change rate. Additionally, there exists a critical electric field frequency value that maximizes the curvature change rate (resonance effect). The current theory, model, and computational simulations add to the ongoing development comprehension of how biological membrane shape actuation through electromechanical couplings.

Neglected tropical diseases caused by parasitic pathogens have caused an increase in research interest in drug discovery. Chagas disease is caused by protozoan Trypanosoma cruzi. Benznidazole and nifurtimox are effective drugs in the acute phase; nevertheless, for long-time treatment, they are toxic and have side effects, because these molecules produce free radicals and suffer oxidation–reduction processes. Studies of the structure and mode of action of these drugs have been performed and, until today, no effective treatment for this disease has been established yet. DFT-M06-2X studies in solution allowed us to explore the substituent effects on stability energy, physicochemical properties and chemical reactivity of nitroimidazoles with potential antiparasitic effects, using quantum-chemical descriptors: proton affinities, substituent effect stabilization energy, ionization potential, electrophilicity, hardness, atomic charges, dipole moment and Fukui functions. The basicity of the N3 atom and dipole moment decrease while the ionization potential, electrophilicity, and hardness increase with the electron-withdrawing substituents. Atomic charges, Fukui functions, and electrostatic potential showed that the main reactivity was on the nitro group and N3 atom. The methyl group linked to C2, and the position and inductive effect caused by the nitro group provoked major changes in the physicochemical features, chemical reactivity, and geometrical and energetic stabilities. Quantum-chemical descriptors allowed us to analyze and design novel nitroimidazole derivatives.

Chagas disease is caused by Trypanosoma cruzi. Benznidazole and nifurtimox are drugs used for its therapy; nevertheless, they have collateral effects. NADH‐fumarate (FUM) reductase is a potential pharmacological target since it is essential for survival of parasite and is not found in humans. The objectives are to design and characterize the electronic structure of imidazole and nitroimidazole derivatives at DFT‐M06‐2X level in aqueous solution; also, to model the NADH‐FUM reductase and analyze its intermolecular interactions by molecular docking. Quantum‐chemical descriptors allowed to select the molecules with the best physicochemical properties and lowest toxicity. A high‐quality three‐dimensional structure of NADH‐FUM reductase was obtained by homology modeling. Water molecules do not have influence in the interaction between FUM and NADH‐FUM reductase. The main hydrogen‐binding interactions for FUM were identified in NADH, Lys172, and Arg89; while hydrophobic interactions in Phe479, Thr174, Met63. The molecules S3‐8, S2‐8, and S1‐8 could be inhibitors of NADH‐FUM reductase.

In this work, the viscoelastic behavior of a complex structured liquid in a continuous squeeze flow is analyzed. This flow is simulated allowing a continuous flow of liquid into the narrow gap between two circular plates though the lower plate. The complex liquid is characterized by the exponential structure rheological (ESR) constitutive equation, which is a generalized exponential thixotropic-elasto-viscoplastic-banded model, chosen for this study due to its capacity to predict non-Newtonian and complex behavior such as (i) shear-thinning, (ii) shear-thickening, (iii) yield stress, (iv) thixotropy, (iv) rheopexy, and (v) shear banding flow behavior. The exponential rheological equation of state is defined by a class of exponential Phan-Thien–Tanner-type models, which includes specific cases documented in the literature. The viscoelastic, kinetic, and structural mechanisms in the ESR model are characterized by the association of non-dimensional numbers to each mechanism. To solve the set of non-linear partial differential equations, a perturbation scheme is suggested, based on a small parameter that represents the ratio between two characteristic lengths. At zeroth order (neglecting the inertial mechanisms of the momentum equation), it is found that the normal force on the upper disk is directly related to shear dependent viscosity (thixotropy, shear-thinning, shear-thickening, yield stress behavior, and concentration effects). At first order, the normal force is related to the effects of the elasticity, and it is parallel to the first normal stress difference associated with the elasticity of the ESR structured fluid.