Long Jiang

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) in D2O studied by two-dimensional infrared correlation spectroscopy.

Microdynamics mechanism of thermal-induced hydrogel network destruction of poly(vinyl alcohol) (PVA) in D2O at heating (25-62 °C) was studied by in situ Fourier transform infrared (FTIR) spectroscopy combining with moving-window two-dimensional (MW2D) technique and two-dimensional (2D) correlation analysis. The temperature range of hydrogel destruction was determined within 34-52 °C by dynamic rheological test at first, and then also monitored by MW2D FTIR spectra. The motion of vs(-C-O-, microcrystals) was important in the entire hydrogel destruction process. The microdynamics mechanism of PVA molecular chains can be elaborated as follows: At 32 °C, the number of D2O molecules in the swollen amorphous remains unchanged. At 32-37 °C, more D2O molecules enter into the swollen amorphous region, and the groups of -C-O-, together with -CH2-, are partially hydrated. At 37 °C, the intramolecular or intermolecular hydrogen bonds of PVA are dissociated. The physical cross-linking points of hydrogel are broken due to the melting of PVA microcrystals. At 42 °C, the dissociated hydroxyls from PVA microcrystals rapidly integrate solid hydrogen bonds with D2O molecules. The groups of -C-O- and -CH- are completely hydrated by D2O simultaneously. At 45-55 °C, PVA molecules are surrounded by more D2O molecules. The partially hydrated -CH2- is completely hydrated, and all of the PVA molecules are fully dissolved in D2O.

Time‐Dependent Aggregation‐Induced Enhanced Emission, Absorption Spectral Broadening, and Aggregation Morphology of a Novel Perylene Derivative with a Large D–π–A Structure

Strong aggregation-caused quenching of perylene diimides (PDI) is changed successfully by simple chemical modification with two quinoline moieties through C=C at the bay positions to obtain aggregation-induced enhanced emission (AIEE) of a perylene derivative (Cya-PDI) with a large π-conjugation system. Cya-PDI is weakly luminescent in the well-dispersed CH(3)CN or THF solutions and exhibits an evident time-dependent AIEE and absorption spectra broadening in the aggregated state. In addition, morphological inspection demonstrates that the morphology of the aggregated form of Cya-PDI molecules changed from plate-shaped to rod-like aggregates under the co-effects of time and water. An edge-to-face arrangement of aggregation was proposed and discussed. The fact that the Cya-PDI aggregates show a broad absorption covering the whole visible-light range and strong intermolecular interaction through π-π stacking in the solid state makes them promising materials for optoelectric applications.

ORAOV1-A Correlates with Poor Differentiation in Oral Cancer

Oral cancer overexpressed 1 (ORAOV1) is a crucial oncogene in oral squamous cell carcinoma (OSCC). In this study, we have identified a novel splice variant of ORAOV1, designated as ORAOV1-A. To study the potential role of ORAOV1-A in OSCC, we tested its expression in 7 OSCC cell lines, as well as in 19 normal oral tissue samples and 47 OSCC tissue samples. The expression of ORAOV1-A was detectable in 6 out of 7 OSCC cell lines tested. In OSCC tissue samples, the expression frequency of ORAOV1-A (51.1%) was much higher than that in normal samples (10.5%). Notably, an inverse correlation was found between the expression frequency of ORAOV1-A and the degree of differentiation in OSCC (P = 0.0017). In conclusion, our results suggested that ORAOV1-A may play a functional role in the tumorigenesis of OSCC, and ORAOV1-A expression may serve as an adjunctive prognostic indicator for persons with OSCC.

Vanadium(V) phenolate complexes for ring opening homo- and co-polymerisation of ε-caprolactone, L-lactide and rac-lactide

The vanadyl complexes [VO(OtBu)L1] (1) and {[VO(OiPr)]2(μ-p-L2p)} (2) {[VO(OR)]2(μ-p-L2m)} (R = iPr 3, tBu 4) have been prepared from [VO(OR)3] (R = nPr, iPr or tBu) and the respective phenol, namely 2,2′-ethylidenebis(4,6-di-tert-butylphenol) (L1H2) or α,α,α′,α′-tetra(3,5-di-tert-butyl-2-hydroxyphenyl–p/m-)xylene-para-tetraphenol (L2p/mH4). For comparative studies, the known complexes [VO(μ-OnPr)L1]2 (I), [VOL3]2 (II) (L3H3 = 2,6-bis(3,5-di-tert-butyl-2-hydroxybenzyl)-4-tert-butylphenol) were prepared. An imido complex {[VCl(Np-tolyl)(NCMe)]2(μ-p-L2p)} (5) has been prepared following work-up from [V(Np-tolyl)Cl3], L2pH4 and Et3N. The molecular structures of complexes 1–5 are reported. Complexes 1–5 and I and II have been screened for their ability to ring open polymerise e-caprolactone, L-lactide or rac-lactide with and without solvent present. The co-polymerization of e-caprolactone with L-lactide or rac-lactide afforded co-polymers with low lactide content; the reverse addition was ineffective.

Effect of the content and distribution of ultraviolet absorbing groups on the UV protection and degradation of polylactide films

Introduction of a UV absorbing group onto a polymer chain through covalent bonding greatly reduced the UV light transmittance of the resulting polylactide (PLA) film and preserved the high transparency to visible light. Compared to simply blending a UV absorber with a PLA matrix, covalent bonding of the UV absorbing group with polylactide enabled the prepared films to have better dispersion of the UV absorbing group, stable solvent resistance, better protection effect against UV damage and a slower rate of UV irradiated degradation, while the distribution of the UV absorbing group made no difference to the aforementioned properties. The degradation of both the PLA film covalently bonded with a UV absorbing group and the PLA/UV-absorber blended film followed the same mechanism as pure PLA films, in that the alkyl-oxygen bond broke first to produce acyl-oxygen and secondary carbon radicals, which then captured hydrogen to form carboxyl groups and alkyl groups at the end of the fractured polymer chain. More UV absorbing groups at the chain end were favorable for reducing UV transmittance, providing a better protection effect on the packaged probe, and slowing the UV irradiated degradation of PLA film. The thermal stability was dependent on the molecular weight of polylactide and was hardly affected by the introduction of the UV absorber or UV absorbing group.

Systematic investigation of the synthesis and light-absorption broadening of a novel diketopyrrolopyrrole conjugated polymer of low and high molecular weight with thermo-labile groups

To strengthen the π–π stacking interaction of conjugated polymer chains and study the absorption broadening effect, a narrow band-gap copolymer with high (DPP-Car-Boc-H) and low (DPP-Car-Boc-L) molecular weight, comprising alkyl substituted diketopyrrolopyrrole (DPP) and t-butoxycarbonyl (t-Boc)-protected carbazole (Car-Boc) units, is designed and synthesized. The absorption broadening is investigated on the basis of molecular weight, solution and solid state, solution temperature and nonsolvent effect. FTIR analysis confirmed the decomposition of t-butoxycarbonyl protecting groups after thermal annealing treatment. It is found that the removal of thermo-labile groups (t-Boc) at 180 °C and the liberation of active NH groups further broaden the light-absorption spectra in thin films due to the intensified π–π stacking interaction between polymer chains which is verified through TGA, SEM and XRD. After thermal annealing, SEM images exhibited cubic crystals spread uniformly and the increased order degree of aggregation was verified further. Additionally, the impact of electronic structure change on the photo-response broadening effect is excluded by Gaussian molecular simulation. This work provides a viable approach and convincing evidence that thermal fabrication strengthens conjugated polymer chain stacking through the large π-delocalized plane and provides broad absorption properties for use in photoelectric devices.

Macromolecular chain structure design, synthesis and analysis of poly(L-lactide) linking ultraviolet absorbing groups

Poly(L-lactide) (PLA) with different chain structures was designed, and successfully synthesized by ring opening polymerization using 2-hydroxy-4-(3-methacryloxy-2-hydroxylpropoxy) benzophenone (BPMA), 2,2′-dihydroxy-4,4′-(2-hydroxylpropoxy) dibenzophenone (DHDBP) and 2-hydroxy-4-(2,3-dihydroxylpropoxy) benzophenone (HPBP) as initiators, respectively, to produce corresponding PLA-B (end-capped with BPMA), PLA-DB (end-capped with DHDBP) and PLA-HB-PLA (blocked with HPBP in the middle). High-molecular-weight PLA-DB400 with good visible light transparency and UV opacity was prepared. The chemical structures of the samples were characterized, the crystallization behavior, thermal stability, UV absorption properties and transmittance of PLA were investigated and analyzed. Results of GPC and DSC reveal that when the number average molecular weights (Mn) of PLA are around 4000, termination of a UV absorbing group like DHDBP greatly restricts the crystallization of PLA due to the larger volume and rigidity of the end-capping group, but increasing Mn to about 12000 or higher weakens the hindering effect, resulting in a similar degree of crystallization (Xc). TG results show that PLA-DB400 has the best thermal stability due to the highest molar mass. When the UV absorber is blocked in the PLA chain, the restriction and steric hindrance of the absorber are much stronger than that in the end-capped material, making Xc significantly reduced. UV absorbance of the PLA solutions reveals that the introduction of UV absorbing groups gives an absorption to UV light below 350 nm and the position of the introduced groups has no influence on the UV absorption properties although the content of the UV group does enhance the UV absorbance, of which PLA-DB has the highest since DHDBP bears two 2-dihydroxybenzophenone groups. The transparency of PLA films is neither affected by position nor content of the introduced UV absorbing groups, which is very beneficial for the application of PLA in packaging materials that require high transparency.

Acrylamide modified poly(vinyl alcohol): crystalline and enhanced water solubility

Acrylamide (AAm) modified polyvinyl alcohol (PVA) with enhanced water solubility and tunable tacticity and crystallinity was prepared by alcoholysis of vinyl acetate (VAc) and acrylamide copolymers. The chemical structures and performance of VAc–AAm copolymers and AAm-modified PVA were measured by FTIR, UV-vis, XRD, elemental analysis as well as rheometry. FTIR and XRD analysis reveals that AAm units in PVA chain can reduce the stereoregularity effectively, and suppress the crystallinity. And a decreasing linear relationship between crystallinity and AAm mole fractions is observed. Furthermore, the influence of AAm modification on the water solubility of PVA was studied, and a significant enhancement either at low temperature (30 °C) or at high temperature (70 °C) was achieved through AAm modification. Moreover, the rheological investigation suggested that the relative strength of the hydrogen bonding interactions existing between PVA chains was weakened, while those between PVA chains and water molecules, to some extent, were enhanced after AAm modification. The method presented is an easy but promising way to prepare PVA that can have good water solubility even at low temperature while exhibiting high degrees of alcoholysis.

Study on the photophysical and electrochemical property and molecular simulation of broadly absorbing and emitting perylene diimide derivatives with large D–π–A structure

To obtain broadly absorbing perylene derivatives with the synchronous impact of the intrinsic π–π* transition of a large conjugated system and intramolecular charge transfer (ICT), we report here the facile synthesis and physical characterization of new N,N′-(di-n-octyl)-3,4,9,10-perylenetetracarboxylic acid diimides (PDI) bearing benzyl-substituted quinoline-4(1H)-ylidene-methyl units as effective donors on the 1,7-positions (C1) and 1-position (C2). Compared to unsubstituted PDI, C1 and C2 both show a pronounced bathochromic shift to the near-infrared region, a high molar extinction coefficient, concentration-dependent π–π-stacking-induced fluorescence and a low LUMO energy level. The investigation of spectroscopic properties and molecular simulation reveal an effective ICT character in compounds C1 and C2. All the properties and analysis indicate that the derivatives are efficient at solar harvesting and are potential candidate materials for use in photovoltaic devices and photocatalysts.

Study of the Thermal Decomposition Behavior of Poly(vinyl alcohol) with NaHSO4

The thermal decomposition behavior of poly(vinyl alcohol) (PVA) with NaHSO4 at 280∼290°C as well as the optical characteristics and the thermal stability of the resulting thermally decomposed PVA were investigated by means of UV-Vis spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results suggest that (1) the elimination reactions of side groups in PVA with NaHSO4 can occur under our conditions resulting in formation of carbon–carbon double and triple bonds; (2) most of the carbon–carbon double bonds were conjugated; (3) the PVA thermally treated with NaHSO4 could absorb light in the region of 190∼600 nm; (4) the thermal stability of the resulting PVA was better than that of PVA without thermal treatment; and (5) compared with the thermal reaction of PVA without NaHSO4, the addition of NaHSO4 can promote the thermal elimination of side groups of PVA.