Alkyl Thiocyanurates as Thioester Mimetics. Transthioesterification and Ligation Reactions with High Potential in Dynamic Covalent Chemistry.

Alkyl thiocyanurates, the compounds formed in the SN reaction of thiocyanuric acid and alkyl halides, are susceptible to transthioesterification and ligation with molecules containing cysteamine, analogous to native chemical ligation of thioesters with peptides with an N-terminal cysteine moiety. The ligation is irreversible and results in the formation of mono- and disubstituted products dominantly. Transthioesterification, in contrast, is fully reversible and may be used in constructing dynamic systems. The application of this reactivity in dynamic covalent chemistry has been exemplified by the preparation of a library of mixed thiocyanurates of glutathione and thioglycolic acid with self-assembly abilities and metathesis between thiocyanurates of tris(carboxymethyl) and tris(carboxamidomethyl) catalyzed by MESNa (sodium 2-mercaptoethylsulphonate) or MPAA (4-mercaptophenylacetic acid). Differences in reactivity of thiocyanurates toward cysteamines and thiols has been explained based on conceptual DFT.

(C3N2H5)3Sb2I9 and (C3N2H5)3Bi2I9: ferroelastic lead-free hybrid perovskite-like materials as potential semiconducting absorbers.

We have synthesised and characterised novel organic-inorganic hybrid crystals: (C3N2H5)3Sb2I9 and (C3N2H5)3Bi2I9 (PSI and PBI). The thermal DSC and TG analyses indicate four structural phase transitions (PTs) at 366.2/366.8, 274.6/275.4, 233.3/233.3 and 142.8/143.1 K (on cooling/heating) for PSI and two reversible PTs at 365.2/370.8 and 252.6/257.9 K for PBI. Both analogues crystallize at room temperature in the orthorhombic Cmcm structure, which transforms, in the case of PBI, to monoclinic P21/n at low temperature. According to the X-ray diffraction results, the anionic component is discrete and built of face-sharing bioctahedra, [M2I9]3-, in both compounds, whereas cations exhibit distinct dynamical disorder over high temperature phases. Dielectric spectroscopy and 1H NMR spectroscopy have been used to characterise the dynamical state of the C3N2H5+ cations. The ferroelastic domain structure has been characterised by observations under a polarized optical microscope. Both compounds are semiconductors with narrow bandgaps of 1.97 eV (PBI) and 2.10 eV (PSI).

Towards biocompatible NIR-II nanoprobes - transfer of hydrophobic Ag2S quantum dots to aqueous solutions using phase transfer catalysed hydrolysis of poly(maleic anhydride-alt-1-octadecene).

Development of protocols for transferring of hydrophobic quantum dots (QDs) into aqueous solution is of special importance for their biomedical applications. Particularly, hydrophilization of Ag2S without quenching of photoluminescence is a great challenge. Application of standard protocol for amphiphilic polymer coating of hydrophobic Ag2S nanocrystals failed, whereas ligand exchange and direct synthesis of Ag2S in aqueous solution leads to poorly emitting materials. In this paper we present the facile method for transferring of hydrophobic Ag2S QDs into aqueous solution employing the phase transfer catalysed hydrolysis of a commercially available polymer - poly(maleic anhydride-alt-1-octadecene), (PMAO) in the presence of tetramethylammonium hydroxide. Because the original surface ligands are retained and we do not use solvents (like THF) detrimental for Ag2S emission, the modification does not deteriorate photoluminescence properties and quantum yield of modified QDs in aqueous solution reaches 60% of that for hydrophobic QDs in chloroform. The hydrodynamic diameter of modified, water soluble Ag2S QDs is about 10 nm and is only slightly larger than their original size. Moreover, the polymer coated nanocrystals are not aggregated and are stable for months. Surface characterization of QDs by NMR and IR spectroscopy indicates that polymer chains intercalate alkyl chains of dodecanethiol (DDT) bound to the surface of Ag2S. The cytotoxicity studies indicate that the presented method should be regarded as a notable progress towards the biocompatible Ag2S NIR-II emitting nanoprobes.

Dithiocarbamates: Reliable Surface Ligands for NIR-Emitting Quantum Dots.

In this paper, we report a reliable method for transferring hydrophobic, NIR-emitting PbS/CdS core-shell quantum dots (QDs) to water solutions using synthesized in situ dithiocarbamate derivatives of amino acids as stabilizing ligands. Such ligands offer apparent advantages over dihydrolipoic acid (DHLA) derivatives commonly used as ligands stabilizing quantum dots. The most effective phase transfer and the best long-term stability of water dispersions of amino acid-DTC-capped QDs were achieved using lysine dithiocarbamate. In this case, the phase transfer of PbS/CdS nanoparticles from organic to aqueous phase can be completed in 6-8 h. Prepared amino acid-DTC-capped QDs nanoparticles have narrow size distributions, and their hydrodynamic diameter remains below 9 nm. After transferring to water, lysine-DTC-capped PbS/CdS nanoparticles retain their spectroscopic properties for at least 48 h. Moreover, they are not toxic up to concentration corresponding to about 7 µg/cm3 of PbS/CdS, which is sufficient for their application in biological systems. In addition, lysine-DTC-capped PbS/CdS QDs can be straightforwardly modified by layer-by-layer polyelectrolyte coating.

Toxicity Mechanism of Low Doses of NaGdF4:Yb3+,Er3+ Upconverting Nanoparticles in Activated Macrophage Cell Lines.

Gadolinium-doped nanoparticles (NPs) are regarded as promising luminescent probes. In this report, we studied details of toxicity mechanism of low doses of NaGdF4-based fluorescent nanoparticles in activated RAW264.7, J774A.1 macrophages. These cell lines were specifically sensitive to the treatment with nanoparticles. Using nanoparticles of three different sizes, but with a uniform zeta potential (about -11 mV), we observed rapid uptake of NPs by the cells, resulting in the increased lysosomal compartment and subsequent superoxide induction along with a decrease in mitochondrial potential, indicating the impairment of mitochondrial homeostasis. At the molecular level, this led to upregulation of proapoptotic Bax and downregulation of anti-apoptotic Bcl-2, which triggered the apoptosis with phosphatidylserine externalization, caspase-3 activation and DNA fragmentation. We provide a time frame of the toxicity process by presenting data from different time points. These effects were present regardless of the size of nanoparticles. Moreover, despite the stability of NaGdF4 nanoparticles at low pH, we identified cell acidification as an essential prerequisite of cytotoxic reaction using acidification inhibitors (NH4Cl or Bafilomycin A1). Therefore, approaching the evaluation of the biocompatibility of such materials, one should keep in mind that toxicity could be revealed only in specific cells. On the other hand, designing gadolinium-doped NPs with increased resistance to harsh conditions of activated macrophage phagolysosomes should prevent NP decomposition, concurrent gadolinium release, and thus the elimination of its toxicity.

Helicenophyrins: Expanded Carbaporphyrins Incorporating Aza[5]helicene and Heptacyclic S-Shaped Aza[5]helicene Motifs.

Incorporation of phenanthrene into a hexaphyrin(1.1.1.1.1.0) frame resulted in intramolecular ring fusion, thus giving rise to chiral helicenophyrins. These molecules contain helicene and porphyrin features by incorporating either an aza[5]helicene or heptacyclic S-shaped aza[5]helicene.

The High-Resolution 4f-5d Absorption Spectrum of Divalent Dysprosium (Dy2+) in Strontium Chloride Host SrCl2: Fine Structure and Zero-Phonon Transitions Revealed.

The virtual lack of information on electronic spectra of divalent lanthanide elements (Ln2+) other than Sm2+, Eu2+, Tm2+, and Yb2+ has prompted us to set for synthesis and characterization of novel Ln2+ systems. First successful attempt concerned SrCl2/Nd2+ single crystals. Here, we report stabilization of divalent dysprosium in a chloride host. Importantly this has been accomplished with Dy ions introduced in a divalent state during synthesis, unlike by γ-irradiation of Dy3+ systems employed previously. This synthesis method yields good quality SrCl2/Dy2+ single crystals. The electronic absorption spectra of Dy2+ doped in SrCl2 have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000-45000 cm-1 is achieved. On the basis of theoretical calculations using semiempirical Hamiltonian model, assignment of bands and determination of the Hamiltonian parameters for Dy2+(4f95d1) configuration is carried out. The experimental and theoretical studies reveal fine structure and zero-phonon transitions and thus enable high-resolution assignment of spectral lines. It is shown that spin-forbidden transitions gain relatively high intensity due to significant admixing of low-spin character to nominally high-spin states.

Extension of High-Resolution Optical Absorption Spectroscopy to Divalent Neodymium: Absorption Spectra of Nd2+ Ions in a SrCl2 Host.

There is a lack of information on electronic spectra of divalent neodymium, and thus the synthesis and characterization of Nd2+ systems is now reported. Stabilization of neodymium is observed in a chloride host, which importantly has been accomplished with Nd ions introduced in a divalent state during synthesis, unlike by γ-irradiation of Nd3+ system employed previously. This method yields good-quality SrCl2 :Nd2+ single crystals. For the first time the electronic absorption spectra of Nd2+ doped in SrCl2 have been recorded with high resolution at liquid helium temperature (4.2 K). Identification of the absorption bands occurring in the spectral range of 5000-40 000 cm-1 (2000-250 nm) has been achieved and their tentative assignment proposed. This uniquely detailed Nd2+ absorption spectrum provides basis for fingerprinting method enabling identification of the presence of Nd2+ ions in future spectra as well as in existing but as-yet not fully resolved spectra.

Triazolyl, Imidazolyl, and Carboxylic Acid Moieties in the Design of Molybdenum Trioxide Hybrids: Photophysical and Catalytic Behavior.

Three organic ligands bearing 1,2,4-triazolyl donor moieties, (S)-4-(1-phenylpropyl)-1,2,4-triazole (trethbz), 4-(1,2,4-triazol-4-yl)benzoic acid (trPhCO2H), and 3-(1H-imidazol-4-yl)-2-(1,2,4-triazol-4-yl)propionic acid (trhis), were prepared to evaluate their coordination behavior in the development of molybdenum(VI) oxide organic hybrids. Four compounds, [Mo2O6(trethbz)2]·H2O (1), [Mo4O12(trPhCO2H)2]·0.5H2O (2a), [Mo4O12(trPhCO2H)2]·H2O (2b), and [Mo8O25(trhis)2(trhisH)2]·2H2O (3), were synthesized and characterized. The monofunctional tr-ligand resulted in the formation of a zigzag chain [Mo2O6(trethbz)2] built up from cis-{MoO4N2} octahedra united through common µ2-O vertices. Employing the heterodonor ligand with tr/-CO2H functions afforded either layer or ribbon structures of corner- or edge-sharing {MoO5N} polyhedra (2a or 2b) stapled by tr-links in axial positions, whereas -CO2H groups remained uncoordinated. The presence of the im-heterocycle as an extra function in trhis facilitated formation of zwitterionic molecules with a protonated imidazolium group (imH+) and a negatively charged -CO2- group, whereas the tr-fragment was left neutral. Under the acidic hydrothermal conditions used, the organic ligand binds to molybdenum atoms either through [N-N]-tr or through both [N-N]-tr and µ2-CO2- units, which occur in protonated bidentate or zwitterionic tetradentate forms (trhisH+ and trhis, respectively). This leads to a new zigzag subtopological motif (3) of negatively charged polyoxomolybdate {Mo8O25}n2n- consisting of corner- and edge-sharing cis-{MoO4N2} and {MoO6} octahedra, while the tetradentate zwitterrionic trhis species connect these chains into a 2D net. Electronic spectra of the compounds showed optical gaps consistent with semiconducting behavior. The compounds were investigated as epoxidation catalysts via the model reactions of achiral and prochiral olefins (cis-cyclooctene and trans-ß-methylstyrene) with tert-butylhydroperoxide. The best-performing catalyst (1) was explored for the epoxidation of other olefins, including biomass-derived methyl oleate, methyl linoleate, and prochiral dl-limonene.

Use of Stable Amine-Capped Polyynes in the Regioselective Synthesis of Push-Pull Thiophenes.

The reactions of a series of 1-halopolyynes with secondary amines led to novel amine end-capped polyynes exhibiting surprisingly high stability toward moisture. The new compounds were characterized by NMR spectroscopy, ESI-MS spectrometry, and X-ray single-crystal diffractometry. The use of amine end-capped polyynes as precursors to substituted push-pull thiophenes was next presented. The results show the first-to the best of our knowledge-transformation of ynamine to thiophene and the first regioselective transformation of a longer polyynes to butadiyne-substituted thiophene. Photophysical studies of the resulting compounds show that some of the substituted thiophenes have high quantum yield photoluminescence upon UV light irradiation.