Molecular structure and selective theophylline complexation by conformational change of diethyl N,N'-(1,3-phenylene)dicarbamate.

The receptor ability of diethyl N,N'-(1,3-phenylene)dicarbamate (1) to form host-guest complexes with theophylline (TEO) and caffeine (CAF) by mechanochemistry was evaluated. The formation of the 1-TEO complex (C12H16N2O4·C7H8N4O2) was preferred and involves the conformational change of one of the ethyl carbamate groups of 1 from the endo conformation to the exo conformation to allow the formation of intermolecular interactions. The formation of an N-H...O=C hydrogen bond between 1 and TEO triggers the conformational change of 1. CAF molecules are unable to form an N-H...O=C hydrogen bond with 1, making the conformational change and, therefore, the formation of the complex impossible. Conformational change and selective binding were monitored by IR spectroscopy, solid-state 13C nuclear magnetic resonance and single-crystal X-ray diffraction. The 1-TEO complex was characterized by IR spectroscopy, solid-state 13C nuclear magnetic resonance, powder X-ray diffraction and single-crystal X-ray diffraction.

Synthetic Polyisoprene Rubber as a Mimic of Natural Rubber: Recent Advances on Synthesis, Nanocomposites, and Applications.

Up to now, rubber materials have been used in a wide range of applications, from automotive parts to special-design engineering pieces, as well as in the pharmaceutical, food, electronics, and military industries, among others. Since the discovery of the vulcanization of natural rubber (NR) in 1838, the continuous demand for this material has intensified the quest for a synthetic substitute with similar properties. In this regard, synthetic polyisoprene rubber (IR) emerged as an attractive alternative. However, despite the efforts made, some properties of natural rubber have been difficult to match (i.e., superior mechanical properties) due not only to its high content of cis-1,4-polyisoprene but also because its structure is considered a naturally occurring nanocomposite. In this sense, cutting-edge research has proposed the synthesis of nanocomposites with synthetic rubber, obtaining the same properties as natural rubber. This review focuses on the synthesis, structure, and properties of natural and synthetic rubber, with a special interest in the synthesis of IR nanocomposites, giving the reader a comprehensive reference on how to achieve a mimic of NR.

Indolealkylamines in the venom of the scorpion Thorellius intrepidus.

Scorpions are a group of arthropods that strike fear in many people due to their severe medical symptoms, even death, caused by their venomous stings. Even so, not all scorpion species contain harmful venoms against humans but still have valuable bioactive molecules, which could be used in developing new pharmaceutical leads for treating important diseases. This work conducted a comprehensive analysis of the venom from the scorpion Thorellius intrepidus. The venom of T. intrepidus was separated by size exclusion chromatography, and four main fractions were obtained. Fraction IV (FIV) contained small molecules representing over 90% of the total absorbance at 280 nm. Analysis of fraction FIV by RP-HPLC indicated the presence of three main molecules (FIV.1, FIV.2, and FIV.3) with similar UV absorbance spectra profiles. The molecular masses of FIV.1, FIV.2, and FIV.3 were determined, resulting in 175.99, 190.07, and 218.16 Da, respectively. Further confirmation through 1H-NMR and 13C-NMR analyses revealed that these molecules were serotonin, N-methylserotonin, and bufotenidine. These intriguing compounds are speculated to play a pivotal role in self-defense and increasing venom toxicity and could also offer promising biotechnological applications as small bioactive molecules.

Two-photon isomerization properties of donor-acceptor Stenhouse adducts.

Donor-acceptor Stenhouse adducts (DASAs) are important photo-responsive molecules that undergo electrocyclic reactions after light absorption. From these properties, DASAs have received extensive attention as photo-switches with negative photochromism. Meanwhile, several photochemical applications require isomerization events to take place in highly localized volumes at variable depths. Such focused photoreactions can be achieved if the electronic excitation is induced through a non-linear optical process. In this contribution we describe DASAs substituted with extended donor groups which provide them with significant two-photon absorption properties. We characterized the photo-induced transformation of these DASAs from the open polymethinic form to their cyclopentenic isomer with the use of 800 nm femtosecond pulses. These studies verified that the biphotonic excitation produces equivalent photoreactions as linear absorbance. We also determined these DASAs' two-photon absorption cross sections from measurements of their photoconverted yield after biphotonic excitation. As we show, specific donor sections provide these systems with important biphotonic cross-sections as high as 615 GM units. Such properties make these DASAs among the most non-linearly active photo-switchable molecules. Calculations at the TDDFT level with the optimally tuned range-separated functional OT-CAM-B3LYP, together with quadratic response methods indicate that the non-linear photochemical properties in these molecules involve higher lying electronic states above the first excited singlet. This result is consistent with the observed relation between their two-photon chemistry and the onset of their short wavelength absorption features around 400 nm. This is the first report of the non-linear photochemistry of DASAs. The two-photon isomerization properties of DASAs extend their applications to 3D-photocontrol, non-linear lithography, variable depth birefringence, and localized drug delivery schemes.

Crystal structure and characterization of the sulfamethazine-piperidine salt.

Sulfamethazine [N1-(4,6-dimethylpyrimidin-2-yl)sulfanilamide] is an antimicrobial drug that possesses functional groups capable of acting as hydrogen-bond donors and acceptors, which make it a suitable supramolecular building block for the formation of cocrystals and salts. We report here the crystal structure and solid-state characterization of the 1:1 salt piperidinium sulfamethazinate (PPD+·SUL-, C5H12N+·C12H13N4O2S-) (I). The salt was obtained by the solvent-assisted grinding method and was characterized by IR spectroscopy, powder X-ray diffraction, solid-state 13C NMR spectroscopy and thermal analysis [differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA)]. Salt I crystallized in the monoclinic space group P21/n and showed a 1:1 stoichiometry revealing proton transfer from SUL to PPD to form salt I. The PPD+ and SUL- ions are connected by N-H+...O and N-H+...N interactions. The self-assembly of SUL- anions displays the amine-sulfa C(8) motif. The supramolecular architecture of salt I revealed the formation of interconnected supramolecular sheets.

Synthesis of a New Co Metal-Organic Framework Assembled from 5,10,15,20-Tetrakis((pyridin-4-yl) phenyl)porphyrin "Co-MTPhPyP" and Its Application to the Removal of Heavy Metal Ions.

The synthesis of a Co metal-organic framework assembled from 5,10,15,20-tetrakis((pyridin-4-yl)phenyl)porphyrin; TPhPyP) "Co-MTPhPyP" is reported. The TPhPyP ligand was synthesized via aldehyde condensation in 28% yield and characterized by 1H nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FTIR), high-resolution mass spectrometry (HRMS), and UV-visible spectroscopy (UV-vis). Co-MTPhPyP was prepared by the solvothermal method from TPhPyP and CoCl2·H2O in 55% yield and characterized by X-ray powder diffraction (XRD), FTIR, thermogravimetric analysis (TGA), field-emission scanning electron microscopy with energy-dispersive X-ray (FESEM-EDS), X-ray photoelectron spectroscopy (XPS), and dynamic light scattering (DLS), showing a particle size distribution of 418 ± 58 nm. The sorption properties of the Co-MTPhPyP for the effective removal of Pb(II) and Cu(II) were evaluated in an aqueous medium and Cthe results showed uptake capacities of 383.4 and 168 mg of the metal g-1 after 2 h, respectively. Kinetic studies of Pb(II) adsorption by Co-MTPhPyP were adjusted to the pseudo-second-order model with a maximum adsorption capacity of 458.8 mg g-1 at 30 min of exposition.

Crystal structures of cocrystals of 2,7-dihydroxynaphthalene with isoniazid and piracetam.

Cocrystals of 2,7-dihydroxynaphthalene (DHN, or naphthalene-2,7-diol) with isoniazid (pyridine-4-carbohydrazide) (INH), denoted DHN-INH [C10H8O2·C6H7N3O, (I)], and piracetam [2-(2-oxopyrrolidin-1-yl)acetamide] (PIR), denoted DHN-PIR [C10H8O2·C6H10N2O2, (II)], were obtained by the solvent-assisted grinding method and characterized by IR spectroscopy, powder X-ray diffraction and single-crystal X-ray diffraction. Cocrystal (I) crystallized in the triclinic space group P-1 and showed a 2:2 stoichiometry. DHN and INH molecules are connected by O-H...N(pyridine) and O-H...N(hydrazide) hydrogen bonds. Cocrystal (II) crystallized in the space group Pca21 with a 1:1 stoichiometry. DHN and PIR molecules are connected by O-H...O=C hydrogen bonds. The supramolecular architecture of cocrystal (I) showed interlinked supramolecular tapes; meanwhile, in cocrystal (II), interlinked supramolecular sheets were observed.

Coumarin Derivative Directly Coordinated to Lanthanides Acts as an Excellent Antenna for UV-Vis and Near-IR Emission.

A chelating coumarin-derived ligand sensitizes all emitting lanthanide ions in the solid state and gives high absolute quantum yields for ethanol solutions of complexes of Sm, Eu, Tb, and Dy, above 20% for the last two. Crystal structures of these four complexes are [Ln(Cum)3(H2O)(X)]·X where X = MeOH or EtOH.

Crystal structure of the chalcone (E)-3-(furan-2-yl)-1-phenylprop-2-en-1-one.

The title chalcone derivative, C13H10O2, adopts an E conformation about the C=C double bond. The mol-ecule is composed of a furanyl and a phenyl ring, bridged by an α,ß-unsaturated carbonyl system, which are inclined to one another by 24.07 (7)°. In the crystal, mol-ecules are connected by weak C-H⋯O hydrogen bonds involving the carbonyl O atom acting as a trifurcated acceptor and C-H⋯π inter-actions, forming ribbons extending along the c-axis direction.

High-boron-content porphyrin-cored aryl ether dendrimers: controlled synthesis, characterization, and photophysical properties.

The synthesis and characterization of a set of poly(aryl ether) dendrimers with tetraphenylporphyrin as the core and 4, 8, 16, or 32 closo-carborane clusters are described. A regioselective hydrosilylation reaction on the allyl-terminated functions with carboranylsilanes in the presence of Karstedt's catalyst leads to different generations of boron-enriched dendrimers. This versatile approach allows the incorporation of a large number of boron atoms in the dendrimers' periphery. Translational diffusion coefficients (D) determined by DOSY NMR experiments permit estimation of the hydrodynamic radius (RH) and molecular size for each dendrimer. Furthermore, a notable correlation between D and the molecular weight (MW) is found and can be used to predict their overall size and folding properties. The UV-vis and emission behavior are not largely affected by the functionalization, therefore implying that the presence of carboranes does not alter their photoluminescence properties.

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.

exo-1,7-Dimethyl-4-phenyl-10-oxa-4-aza-tri-cyclo-[5.2.1.0(2,6)]dec-8-ene-3,5-dione.

The title compound, C16H15NO3, consists of an oxabicycle fused to an N-phenyl-substituted pyrrolidine ring anti to the double bond, affording the exo isomer. In the oxabicycle system, the six-membered ring presents a boat conformation, while the heterocyclic rings show envelope conformations with the O atom projected out of the plane. In the crystal, adjacent mol-ecules are linked via weak C-H⋯O hydrogen bonds, forming chains propagating along the a-axis direction. The chains are linked by C-H⋯π inter-actions, forming two-dimensional networks lying parallel to the ac plane.

Modulation of the porphyrin inner proton exchange rates by the steric effects of bridge substitution.

The tautomeric equilibria and H-N proton transfer taking place in the nonsymmetrically substituted water-soluble 2-sulfonato-5,15-bis(4-sulfonatophenyl)porphyrin (1) and in its 10-bromo-substituted derivative (2) were analyzed by NMR methods: 1H and 13C spectroscopies and heteronuclear multiple bond correlation (HMBC) and heteronuclear single quantum coherence (HSQC) 1H-13C and 1H-15N techniques. The existence of preferred pathways of H-N transfer was detected. The conclusions are rationalized by taking into account the effect partial meso-substitution exerts on the relative energies of the different cis-tautomer intermediates involved in the tautomerism. These results underline the experimental consequences stemming from the nonequivalence in porphyrins between the 'tautomeric interconversion' and 'proton transfer' terms, when observed by NMR techniques, as a consequence of the existence of two pairs of degenerate tautomers and transformation pathways.