Mechanical Properties of Poly(dimethylsiloxane)-block-poly(2-methyloxazoline) Polymersomes Probed by Atomic Force Microscopy

Poly(dimethylsiloxane)-block-poly(2-methyloxazoline) (PDMS-b-PMOXA) vesicles were characterized by a combination of dynamic light scattering (DLS), cryogenic transmission electron microscopy (cryo-TEM), and atomic force microscopy imaging and force spectroscopy (AFM). From DLS data, a hydrodynamic radius of ～150 nm was determined, and cryo-TEM micrographs revealed a bilayer thickness of ～16 nm. In AFM experiments on a silicon wafer substrate, adsorption led to a stable spherical caplike conformation of the polymersomes, whereas on mica, adsorption resulted also in vesicle fusion and formation of bilayer patches or multilayer stacks. This indicates a delicate balance between the mechanical stability of PDMS-b-PMOXA polymersomes on one hand and the driving forces for spreading on the other. A Young's modulus of 17 ± 11 MPa and a bending modulus of 7 ± 5 × 10(-18) J were derived from AFM force spectroscopy measurements. Therefore, the elastic response of the PDMS-b-PMOXA polymersomes to external stimuli is much closer to that of lipid vesicles compared to other types of polymersomes, such as polystyrene-block-poly(acrylic acid) (PS-b-PAA).     

Dual anticancer activity in a single compound: visible-light-induced apoptosis by an antiangiogenic iridium complex

A metal complex is identified in which the metal fulfills two independent functions: as a structural scaffold for the specific molecular recognition of protein kinases resulting in antiangiogenic properties, together with a visible-light-induced photoreactivity triggering apopotosis in cancer cells.     

Cellular uptake studies of two hexanuclear, carboxylate bridged, zinc ring structures using fluorescence microscopy

Two hexanuclear zinc complexes have been structurally characterized, and evaluation against several cells showed selective toxicity. Cellular uptake revealed a non-specific process, resulting in accumulation within the cell cytoplasm.     

Synthesis of functionalized furopyrazines as restricted dipeptidomimetics

Herein, an efficient synthetic approach to a furopyrazine scaffold with four points of diversity, starting from 2(1H)-pyrazinones, with dipeptomimetic properties, is presented. R-groups corresponding to amino acid side chains were introduced during the 2(1H)-pyrazinone and subsequent furopyrazine formation. The furopyrazine scaffold was further functionalized with an amino- and a carboxy-terminus resulting in a conformationally restricted dipeptidomimetic scaffold. The carboxy-terminus was introduced via a chemoselective vinylation of the 7-position followed by oxidative cleavage, while the amino-terminus was obtained via Buchwald–Hartwig amidation of the 2-position of the scaffold. The versatility of the synthetic method was demonstrated by the synthesis of a small library of diversely substituted furopyrazines having various amino acid side chains on the four points of diversity. Evaluation with an X-ray structure of the scaffold and computational analysis supports the exploitation of the furopyrazine scaffold as a restricted dipeptide mimic, which can mimic the two central residues of a β-turn.     

pH-induced release from P2VP-PEO block copolymer vesicles

The pH-induced release of hydrophilic dyes from poly(2-vinylpyridine-b-ethylene oxide) (P2VP-PEO) block copolymer vesicles is investigated. The structure of the vesicles is characterized using small-angle neutron scattering (SANS) and cryo-electron microscopy (cryo-TEM). A decrease of the pH below 5 leads to protonation and dissolution of the poly-2-vinylpyridine blocks which induces rupture and dissolution of the vesicle membrane. Details of the rupture, dissolution, and release process are studied by fluorescence video microscopy, gel electrophoresis, and high-performance ultrafiltration.     

An experimental and theoretical study of spin-spin coupling in chlorosilanes

An experimental and theoretical study of the absolute value of the one-bond spin-spin coupling constant |(1)J(Si,H)| in SiH(n)Cl(4-n) (n = 0-4) dissolved in THF-d(8) is presented. We found |(1)J(Si,H)| to increase with an increasing number of chlorine substituents, and the quantitative changes were found to differ from the values previously reported for the same compounds dissolved in cyclohexane-d(12). We also report on the variations in |(1)J(Si,H)| as a function of temperature, which we found to be linearly temperature dependent for the chlorine-substituted silanes and temperature independent for SiH(4). Furthermore, the temperature dependence of |(1)J(Si,H)| varied between the different chlorosilanes. Solvent-solute interactions were studied by quantum chemical DFT calculations. The variations in chloro-silane bond lengths upon adduct formation and the different adduct interaction energies may explain the temperature dependences of the coupling constants.     

Highly enantioselective michael additions of indole to benzylidene malonate using simple bis(oxazoline) ligands: importance of metal/ligand ratio

[Structure: see text] Simple bis(oxazoline) ligands, especially azabis(oxazolines), can catalyze the copper-catalyzed addition of indoles to benzylidene malonates in up to >99% ee, provided that excess of chiral ligand is avoided. The paradigm followed in many asymmetric catalyses that an excess of chiral ligand with respect to the metal should improve enantioselectivity because a background reaction by free metal is suppressed, is not applicable here, which might call for revisiting some of the many copper(II)-bis(oxazoline)-catalyzed processes known.     

Heteroleptic Cu(II) dipyrromethene complexes linked via hydrogen bonds, coordinative bonds, and covalent bonds: probing the coordination environment by electron paramagnetic resonance spectroscopy

meso-Phenyldipyrromethene acetylacetonato copper(II) complexes [Cu(dpm-C6H4R)(acac)] (dpm-C6H4R = phenyl-substituted dipyrromethene, acac = acetylacetonato) with different substituents R at the phenyl moiety were synthesized. These substituents determine the mode of assembly into polymeric chains, namely, via hydrogen bonds, coordinative bonds, or covalent bonds (by immobilization on a polymer). Although the primary coordination sphere around the copper center is essentially identical for all complexes reported in this study (square-planar geometry with N2O2 coordination), subtle differences due to the different microenvironments have been observed in their structures, properties, and reactivity as probed by IR spectroscopy, electron paramagnetic resonance spectroscopy, magnetic measurements, thermal analyses, density functional theory calculations, and reaction with pyridine.     

A synthetic breakthrough into an unanticipated stability regime: a series of isolable complexes in which C6, C8, C10, C12, C16, C20, C24, and C28 polyynediyl chains span two platinum atoms

The reaction of trans-[PtCl(p-tol){P(p-tol)3}2] (PtCl) and H(C[triple chemical bond]C)2H (cat. CuI, HNEt2) gives PtC4H (82 %), which can be cross-coupled with excess HC[triple chemical bond]CSiEt3 (acetone, O2, CuCl/TMEDA; Hay conditions) to yield PtC6Si (77 %). The addition of nBu4N+F- in wet acetone gives PtC6H (84 %), and further addition of ClSiMe3 (F- scavenger) and excess HC[triple chemical bond]CSiEt3 (Hay conditions) yields PtC(8)Si (23 %). Similar cross-coupling reactions of PtCxH (generated in situ for x>6) and excess H(C[triple chemical bond]C)2SiEt3 give a) x=4, PtC8Si (29 %), PtC12Si (30 %), and PtC16Si (1 %); b) x=6, PtC10Si (59 %) and PtC14Si (7 %); c) x=8, PtC12Si (42 %); and d) x=10, PtC14Si (20 %). Hay homocoupling reactions of PtC4H, PtC6H, PtC8H, and PtC10H give PtC8Pt, PtC12Pt, PtC16Pt, and PtC20Pt (88-70 %), but PtC12H decomposes too rapidly. However, when PtC12Si and PtC14Si are subjected to Hay conditions, protodesilylation occurs in the presence of the oxidizing agent and PtC24Pt (36 %) and PtC28Pt (51 %) are isolated. Reactions of PtC6H and PtC10H with PtCl (CuI, HNEt2) give PtC6Pt (56 %) and PtC10Pt (84 %). The effect of the chain lengths in PtCxPt upon thermal stabilities (>200 degrees C for x< or =20), IR nu(C[triple chemical bond]C) patterns (progressively more bands), colors (yellow to orange to deep red), UV/Vis spectra (progressively red-shifted and more intense bands with epsilon>400,000 M(-1) cm(-1)), redox properties (progressively more difficult oxidations), and NMR spectra (many monotonic trends) are analyzed, including implications for the sp carbon allotrope carbyne. Whereas all other dodecaynes and tetradecaynes rapidly decompose at room temperature, PtC24Pt and PtC28Pt remain stable at >140 degrees C. Crystal structures of PtCxSi (x=6, 8, 10) and PtCxPt (x=6, 8, 10, 12) have been determined.