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.

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\overline{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.

Bis(4-nitroanilines) in interactions through a π-conjugated bridge: conformational effects and potential molecular switches

DFT computation suggests that two dipolar chromophores in rotation around an organic bridge could be aligned by an electric field.

Optical properties of two fluorene derived BODIPY molecular rotors as fluorescent ratiometric viscosity probes

Two fluorescent ratiometric fluorene derived BODIPY probes present a sensitive response to microviscosity changes.

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,β-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.

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-azatricyclo[5.2.1.02,6]dec-8-ene-3,5-dione

The title compound, C16H15NO3, consists of an oxabicycle fused to anN-phenyl-substituted pyrrolidine ringantito the double bond, affording theexoisomer. 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 molecules are linkedviaweak C—H...O hydrogen bonds, forming chains propagating along thea-axis direction. The chains are linked by C—H...π interactions, forming two-dimensional networks lying parallel to theacplane.

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.