Synthesis of 1-aryl-3H-[1,2,5]triazepino[5,4-a]benzimidazol-4(5H)-ones and quantum chemical investigation of the rotamers of the Boc-protected hydrazide key intermediate

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Design and Sensing Properties of a Self‐Assembled Supramolecular Oligomer

Supramolecular polymers are a class of macromolecules stabilized by weak non‐covalent interactions. These self‐assembled aggregates typically undergo stimuli‐induced reversible assembly and disassembly. They thus hold great promise as so‐called functional materials. In this work, we present the design, synthesis, and responsive behavior of a short supramolecular oligomeric system based on two hetero‐complementary subunits. These “monomers” consist of a tetrathiafulvalene‐functionalized calix[4]pyrrole (TTF‐C[4]P) and a glycol diester‐linked bis‐2,5,7‐trinitrodicyanomethylenefluorene‐4‐carboxylate (TNDCF), respectively. We show that when mixed in organic solvents, such as CHCl₃, CH₂ClCH₂Cl, and methylcyclohexane, supramolecular aggregation takes place to produce short oligomers stabilized by hydrogen bonding and donor–acceptor charge‐transfer (CT) interactions. The self‐associated materials were characterized by ¹H NMR and UV/Vis/NIR absorption spectroscopy, as well as by concentration‐ and temperature‐dependent absorption spectroscopy and dynamic light scattering (DLS) analyses of both the monomeric and oligomerized species. The self‐associated system produced from TTF‐C[4]P and TNDCF exhibits a concentration‐dependent aggregation behavior typical of supramolecular polymers. Further support for the proposed self‐assembly came from theoretical calculations. The fluorescence emitting properties of TNDCF are quenched under conditions that promote the formation of supramolecular aggregates containing TTF‐C[4]P and TNDCF. This quenching effect has been utilized as a probe for the detection of substrates in the form of anions (i.e., chloride) and nitroaromatic explosives (i.e., 1,3,5‐trinitrobenzene). Specifically, the addition of these substrates to mixtures of TTF‐C[4]P and TNDCF produced a fluorescence “turn‐on” response.     

Enzymatic resolution of five membered heterocyclic bromohydrins

The lipase catalyzed resolution of trans-3,4-tetrahydrofuran and pyrrolidine bromohydrins by acylation or hydrolysis of their acylated derivatives has been studied. For both heterocycles, the best enantioselectivity was obtained using Candida antarctica lipase B as the catalyst in the hydrolytic processes. The enantiomerically pure bromohydrins are useful intermediates for the preparation of 3,4-fuctionalized cis-heterocycles.     

Conformational landscape of l-threonine in neutral,acid and basic solutions from vibrational circular dichroism spectroscopy and quantum chemical calculations

The biological relevance of amino acids is well known. They can be used as zwitterionic, cationic or anionic forms according to the pH of the medium where they are. Thus, our aim herein was to study the conformational preference of the polar amino acid l-threonine [C₄H₉NO₃, (2S,3R)-2-amino-3-hydroxybutyric acid] under different pH conditions. A conformational study in an aqueous solution of the dissociation equilibrium of the amino acid l-threonine was carried out for this purpose. We recorded, at room temperature, the Mid-IR, Far-IR, Raman and VCD spectra of l-threonine from the aqueous solutions at pH values 5.70 (zwitterionic species), 1.00 (protonated species) and 13.00 (deprotonated species). The number of conformers found with the conformational search was 9 zwitterions, 27 anions and 52 cations. Both the study of the conformational landscape and the theoretical analysis of the vibrational features were accomplished by using DFT and ab initio calculations, that is, B3LYP/6-311++G(d,p) level of theory for all the conformers obtained from the conformational search, M062X/6-311++G(d,p) and MP2/6-311++G(d,p) levels of theory for the most stable conformers. The presence of water was included with the IEF-PCM implicit hydration model. With regard to the zwitterion, the importance of the analysis of the low frequency region (700–30 cm^–1) in the Far-IR spectra should be noted, because it provides relevant information that can be used to determine the presence of the most stable structures.     

Highly Selective Zeolite Topologies for Flue Gas Separation

The separation of carbon dioxide from flue gas is essential for the reduction of greenhouse gas emissions. In adsorptive methods, the challenge lies in the choice of suitable porous materials. Among all zeolite topologies, a number of adsorbents with pore dimensions in the range of the guest molecules were identified to allow an excellent separation by diffusion, and MRE and AFO zeolite topologies appear to be the best candidates based on equilibrium adsorption. Also, it was found that the behavior of this gas mixture in DFT and APD zeolites differed from the normal behavior.     

Photochemistry in Real Space: Batho- and Hypsochromism in the Water Dimer

The development of chemical intuition in photochemistry faces several difficulties that result from the inadequacy of the one-particle picture, the Born–Oppenheimer approximation, and other basic ideas used to build models. It is shown herein how real-space approaches can be efficiently used to gain valuable insights in photochemistry through a simple example of red and blue shift effects: the double hypso- and bathochromic shifts in the low-lying valence excited states of (H₂O)₂. It is demonstrated that 1) the use of these techniques allows the perturbative language used in the theory of intermolecular interactions, even in the strongly interacting short-range regime, to be maintained; 2) one and only one molecule is photoexcited in each of the addressed excited states and 3) the electrostatic interaction between the in-the-cluster molecular dipoles provides a fairly intuitive rationalisation of the observed batho- and hypsochromism. The methods exploited and illustrated herein are able to maintain the individuality and properties of the interacting entities in a molecular aggregate, and thereby they allow chemical intuition in general states, at any geometry and using a broad variety of electronic structure methods to be kept and built.