Mauricio Maldonado-Domínguez

The amide bridge in donor–acceptor systems: delocalization depends on push–pull stress

Transmission of electronic information through amide bonds may be, under appropriate conditions, effectively achieved. In this work, a family of explicitly designed donor–(amide bridge)–acceptor architectures was synthesized. NMR studies and UV-vis absorption solvatochromism support that cross-conjugation leads to measurable polarization across push–pull, amide-bridged molecules. Computational analysis of structural parameters and frontier molecular orbitals shows the contribution of an additional, dienoid amide canonical structure to intramolecular electron delocalization, as the electron donor–acceptor strength of the substituents increases. Within the context of nonlinear optics and molecular materials, computational comparison between amide-bridged molecules and those containing typical linkers shows that there is a compromise between nonlinear optical response, ease of synthesis and chemical inertness, making the systems studied herein interesting alternatives for such applications.

Experimental–Theoretical Approach to the Adsorption Mechanisms for Anionic, Cationic, and Zwitterionic Surfactants at the Calcite–Water Interface

The adsorption of surfactants (DTAB, SDS, and CAPB) at the calcite-water interface was studied through surface zeta potential measurements and multiscale molecular dynamics. The ground-state polarization of surfactants proved to be a key factor for the observed behavior; correlation was found between adsorption and the hard or soft charge distribution of the amphiphile. SDS exhibits a steep aggregation profile, reaching saturation and showing classic ionic-surfactant behavior. In contrast, DTAB and CAPB featured diversified adsorption profiles, suggesting interplay between supramolecular aggregation and desorption from the solid surface and alleviating charge buildup at the carbonate surface when bulk concentration approaches CMC. This manifests as an adsorption profile with a fast initial step, followed by a metastable plateau and finalizing with a sharp decrease and stabilization of surface charge. Suggesting this competition of equilibria, elicited at the CaCO3 surface, this study provides atomistic insight into the adsorption mechanism for ionic surfactants on calcite, which is in accordance with experimental evidence and which is a relevant criterion for developing enhanced oil recovery processes.

Engineering organic semiconducting solids. Multicomponent access to crystalline 3-(4-aryl-1,2,3-triazolyl)coumarins

Crystalline 3-(4-aryl-1,2,3-triazol-1-yl)coumarins (ATCs) were prepared from commercial materials using a four-component methodology as a key step. In the present work, a feasible and environmentally friendly route to the title compounds was developed through the reaction between salicylaldehydes, ethyl bromoacetate, phenylacetylenes and sodium azide under mild conditions, with short reaction times and a simple workup. Crystalline solids are readily accessed from the featured products via solution processing and their arrays in the solid state were elucidated through SXRD; these molecules display a periodic overlap of π-systems, which facilitates carrier transport in organic electronic devices. Semiconductor band gaps for the obtained solids were derived through plane-wave DFT and compared with reference systems known to display superior performance in organic electronics. Thus ATCs represent attractive systems for research and implementation in molecular materials, a task which will be facilitated by the concise route herein described.

On the Brassard's rule of regioselectivity in Diels–Alder reactions between haloquinones and polar dienes

The [4 + 2] polar Diels–Alder reaction between nucleophilic dienes and haloquinones proceeds with remarkably high regioselectivity. In the present work, we simulated diene–dienophile bimolecular encounters in a model stoichiometric reaction between haloquinones and Brassards diene, using Monte Carlo sampling; the energetics of the stacking modes was then studied through DFT calculations. QTAIM analysis for the theoretical electron density was applied to describe contacts between π-systems, foreseeing chemically-productive paths for pre-cycloaddition assemblies associated with the experimental regioisomer. Upon thermally-triggered cycloaddition, Brassards rule of selectivity manifests: only certain stacked microstates consolidate asynchronously into cycloadducts. The halogen atom tunes electron density at the reactive centers, as confirmed by NMR and calculations. Unidimensional energy landscapes were derived to capture energetic profiles of the studied reaction. The model systems were synthesized with high regioselectivity, delving further into the role of halogen substituents.

Synthesis of steroidal molecular compasses: exploration of the controlled assembly of solid organic materials

In this work, five steroid-flanked derivatives of p-nitroaniline were studied to assess the influence of these rigid, chiral frameworks on the solid-state patterning of a dipolar dye, striving to drive the self-assembly of noncentrosymmetric crystals, which is of interest in the development of organic materials for nonlinear optics and piezoelectricity. The featured compounds were prepared using Sonogashira cross-coupling reaction with 17α-ethynyl steroids as a single key step. The structures of these new steroidal derivatives were established using one and two dimensional NMR 1H and 13C experiments. Single X-ray diffraction analysis unequivocally confirmed the presence of the steroidal molecular compasses 8 and 11, whose potential applicability for organic materials is preliminarily assessed via computational modeling, finding candidates for nonlinear optics, organic electronic materials and molecular recognition.

Synthesis of 1,3- and 1,2,3-functionalized pyrroles via Ir(I)-catalyzed vinylation of allyl alcohols

n An efficient method for the preparation of 1,3-disubstituted and 1,2,3-trisubstituted pyrroles was developed through a sequence involving O-vinylation of allyl alcohols followed by Claisen rearrangement and further ozonolysis, concurring in a Paal–Knorr reaction with primary amines. Hg(II) and Ir(I) catalysts and different vinylating reagents were tested. The best results were consistently obtained with the [Ir(cod)Cl]2–vinyl acetate system. The featured methodology gives access to functionalized pyrroles in overall good yields, whose chemical architecture may awake interest for assorted applications.

Structural and morphological studies of meso-ethylcarbazole F-BODIPY thin films

In this work, we describe the synthesis of meso-(9-ethyl-9H-carbazol-3-yl)-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene and its incorporation as thin film by vapor deposition on indium tin oxide. The morphology of the film was analyzed by scanning electron microscopy and atomic force microscopy showing a granular and homogeneous structure, contact angle measurements revealed that this film exhibits a hydrophobic surface. Packing of the compound was simulated through molecular dynamics and Monte Carlo sampling, and the electronic features of aggregates were modeled with plane-wave DFT. A semiconductor behavior for the featured compound in aggregated state, which compares well with systems applied on electronic devices, is predicted for the featured F-BODIPY.Graphical Abstract

Design, synthesis, in vitro evaluation and preliminary SAR studies of N-(2-(heteroaryloxy)propyl)phenothiazines against Rhipicephalus microplus cattle tick.

A family of 15 N-substituted phenothiazines was designed, synthesized and their acaricidal activity against Rhipicephalus microplus was determined in vitro. The synthetic methodology is simple and can be employed in multigram scale. The rationale for the structure-based design of these compounds is the potential for azines and phenothiazine to engage in π-π interactions; these fragments, joined together by a short, flexible alkoxide linker, structurally resemble phenothiazine-based cholinesterase inhibitors, while their weak basicity implies a neutral active form, rather than a cationic one, thus facilitating penetration of the cuticle of ticks. One compound displayed excellent acaricidal activity (LD50=0.58 μg/mL). Preliminary SAR analysis suggests that the activity is influenced by the presence of a weakly basic nitrogen atom, as well as the substitution pattern within the heterocycles.