A metal-ligand crosslinked internal self-healing polyurethane is developed using low-cost and commercially available compounds. The mechanical, photoluminescent, and self-healing properties can be governed by incorporating multiple metal-ligand crosslinks with weak and strong coordination bonds and varying the metal ion. In-situ attenuated total reflectance Fourier transform infrared spectroscopy reveals that the metal-ligand bond is cleaved during the damage process while metal ion is still coordinated with the ligand by stronger metal-pyridyl interaction. The multiple metal-ligand coordination facilitates the crosslinks to be fully reformed during the repairing process, leading to the superior self-healing property.

A pH- and ultrasound dual-responsive drug release pattern was successfully achieved using mesoporous silica nanoparticles (MSNs) coated with polydopamine (PDA). In this paper, the PDA shell on the MSN surface was obtained through oxidative self-polymerization under the alkaline condition. The morphology and structure of this composite nanoparticle were fully characterized by a series of analyses, such as infrared (IR), transmission electron microscopy, and thermogravimetric analysis. Doxorubicin hydrochloride (DOX)-loaded composite nanoparticles were used to study the performances of responsive drug storage/release behavior, and this kind of hybrid material displayed an apparent pH response in DOX releasing under the acidic condition. Beyond that, upon high-intensity focused ultrasound exposure, loaded DOX in composite nanoparticles was successfully triggered to release from pores because of the ultrasonic cavitation effect, and the DOX-releasing pattern could be optimized into a unique pulsatile fashion by switching the on/off status. From the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, it was observed that our blank nanoparticles showed no toxicity to HeLa cells, but DOX-loaded nanoparticles could inhibit the growth of tumor cells. Furthermore, these composite nanoparticles displayed an effective near-IR photothermal conversion capability with a relatively high conversion efficiency (∼37%). These as-desired drug delivery carriers might have a great potential for future cancer treatment that combine the chemotherapy and photothermal therapy.

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The preparation and characterization of iron(II) complexes of three new sexidentate N6 ligands are reported. The three new ligands are constructed from 2,5,8-triazanonane, 1,4,7-triazacyclononane, or 1,5,9-triazacyclododecane by adding three pendant pyridylmethyl arms to each triamine. The X-ray structure of [Fe(tptcn)](C104)2, where tptcn is tris(2-pyridylmethyl)-1,4,7-triazacyclononane, has been determined by using Patterson methods, in conjunction with data measured on a four-circle diffractometer, to give discrepancy factors of R¡¡ = 0.041 and RvF = 0.052 for 1841 observed (/ > 2.58 (/)) reflections. The compound crystallizes in the trigonal space group P3 with three formula weights in a cell having the dimensions a = 16.978 (3) A and c = 7.909 (3) A. There are three crystallographically independent Fe(tptcn)2"1" cations; each cation has a C3 axis perpendicular to the plane of the three pyridine nitrogen atoms as well as the plane of the three aliphatic nitrogen atoms of a tptcn ligand. All three cations have similar dimensions; the bond distances are appropriate for a low-spin Fe(II) complex, a description that is in agreement with the variable-temperature Móssbauer and magnetic susceptibility data that are obtained. The C104~a nd SbF6" salts of [Fe(tptan)]2+ and [Fe(tptcd)]2+ are high-spin Fe(II) compounds, where tptan is tris(2-pyridylmethyl)-2,5,8-triazanonane and tptcd is tris(2pyridylmethyl)-l,4,7-triazacyclododecane. Electronic absorption spectral data are presented for the three iron(II) complexes in solution, as well as for the analogous cobalt(III) and nickel(II) complexes, to show that the [Fe(tptcn)]2"1" complex is close to the spin-crossover point. The interrelationships between the kinetics of reactions such as racemization and the possibility of converting from low spin to high spin, i.e. the existence of the spin-crossover phenomenon, are examined for the tptcn complex. 13C NMR results are presented to show that [Fe(tptcn)]2"1" undergoes a relatively rapid racemization with a rate constant in excess of 150 s"1 at 90 °C. P3 is a polar space group, so the iron(II) cations in [Fe(tptcn)](C104)2 are one of an enantiomeric pair; i.e., the cations are optically active and resolved. The kinetics of racemization that develop after a crushed large single crystal is dissolved, monitored with a CD spectrometer, give a rate constant of k = 2.7 X 10~3 s'1 at 5 eC. It is suggested that the racemization takes place via an intramolecular twist mechanism and that such a mechanism is strongly favored by having a situation where the triplet excited state is close in energy to the singlet ground state of an iron(II) complex.

BackgroundDiabetes can lead to serious microvascular complications such as proliferative diabetic retinopathy (PDR), which results in severe vision loss. The diabetes-induced alterations in the vitreous protein composition in diabetic patients with PDR may be responsible for the presence of PDR. The vitreous humour can be utilised in a variety of studies aimed toward the discovery of new targets for the treatment or prevention of PDR and the identification of novel disease mechanisms. The aim of this study was to compare the protein profile of vitreous humour from diabetic patients with PDR with that of vitreous humour from normal human eyes donated for corneal transplant.ResultsVitreous humour from type 2 diabetic patients with PDR (n = 10) and from normal human eyes donated for corneal transplant (n = 10) were studied. The comparative proteomic analysis was performed using two-dimensional fluorescence difference gel electrophoresis (2-D DIGE). Differentially produced proteins (abundance ratio > 2 or < -2, p < 0.01) were identified by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS) and MALDI-TOF tandem mass spectrometry. A total of 1242 protein spots were detected on the 2-D master gel of the samples, and 57 spots that exhibited statistically significant variations were successfully identified. The spots corresponded to peptide fragments of 29 proteins, including 8 proteins that increased and 21 proteins that decreased in PDR. Excluding the serum proteins from minor vitreous haemorrhage, 19 proteins were found to be differentially produced in PDR patients compared with normal subjects; 6 of these proteins have never been reported to be differentially expressed in PDR vitreous: N(G),N(G)-dimethylarginine dimethylaminohydrolase 1 (DDAH 1), tubulin alpha-1B chain, gamma-enolase, cytosolic acyl coenzyme A thioester hydrolase, malate dehydrogenase and phosphatidylethanolamine-binding protein 1 (PEBP 1). The differential production of pigment epithelium-derived factor (PEDF) and clusterin was confirmed by Western blot analysis.ConclusionsThese data provide an in-depth analysis of the human vitreous proteome and reveal protein alterations that are possibly involved in the pathogenesis of PDR. Further investigation of these special proteins may provide potential new targets for the treatment or the prevention of PDR.

Homogeneous nucleation process of polyethylene (PE) is studied with full-atom molecular dynamic simulation. To account the complex shape with low symmetry and the peculiar intra-chain conformational order of polymer, we introduce a shape descriptor OCB coupling conformational order and inter-chain rotational symmetry, which is able to differentiate hexagonal and orthorhombic clusters from melt. With the shape descriptor OCB, we find that coupling between conformational and inter-chain rotational orderings results in the formation of hexagonal clusters first, which is dynamic in nature. Whilst nucleation of orthorhombic structure occurs inside of hexagonal clusters later, which proceeds via the coalescence of neighboring hexagonal clusters rather than standard stepwise growth process. This demonstrates that nucleation of PE crystal is a two-step process with the assistance of OCB order, which is different from early models for polymer crystallization but similar with that proposed for spherical 'atoms' like colloid and metal. 3 Significance StatementBy introducing a shape descriptor OCB that couples intra-chain conformational order and inter-chain rotational order, we successfully differentiate local structures with hexagonal and orthorhombic symmetries and observe OCB order assisted two-step nucleation process in polyethylene crystallization. OCB order is demonstrated to promote the transformation from flexible chains to conformational ordered segments, which is the most peculiar and critical step in polymer crystallization. The shape descriptor OCB may be universal on differentiating local orders in polymer or systems with connectivity.

The supreme mechanical performance of natural rubber (NR) is commonly attributed to strain-induced crystallization (SIC). The SIC of NR during uniaxial stretch has been extensively investigated, whereas that under multiaxial deformation has been rarely reported, which is close to real service conditions (i.e., tire). In this work, the crystallization behavior of NR under biaxial stretch was studied with in situ synchrotron radiation wide-angle X-ray diffraction in combination with a custom-built biaxial stretch machine. It is observed that biaxial stretch frustrates the SIC of NR: within λ x /λ y < 1.6, where λ x and λ y are stretch ratios of two mutually perpendicular axes, no crystallization emerges even under large drawing ratio until sample fracture at ambient temperature. This finding challenges the common wisdom of the self-reinforcement mechanism of SIC in NR under multiaxial deformation in real service conditions. A theoretical SIC model is proposed, which can decouple the contributions of conformational entropy reduction ΔS f and amorphous chain orientation f to final Gibbs free energy change (ΔG) during multiaxial deformation. This model quantitatively renders a reproduction of the crystallinity during the biaxial stretch, which is well consistent with experimental results and can be further generalized for flow-induced crystallization of semicrystalline polymers.

The nucleation process of polyethylene under quiescent and shear flow conditions are comparatively studied with all-atom molecular dynamical simulations. At both conditions, nucleation are demonstrated to be two-step processes, which, however, proceed via different intermediate orders. Quiescent nucleation is assisted by local structure order coupling conformational and local rotational symmetric orderings, while flow-induced nucleation is promoted by density fluctuation, which is a coupling effect of conformational and orientation orderings. Flow drives the transformation from flexible chains to rigid conformational ordered segments and circumvents the entropic penalty, which is the most peculiar and rate-limited step in polymer crystallization. Current work suggests that flow accelerates nucleation in orders of magnitude is not simply due to flow-induced entropic reduction of melt as early models proposed, which is mainly attributed to the different kinetic pathway via conformational/orientational orderingdensity fluctuationnucleation.