Birong Zeng

Study on the binding of chloroamphenicol with bovine serum albumin by fluorescence and UV-vis spectroscopy

The binding of chloroamphenicol (CPC) to bovine serum albumin (BSA) at 296 K, 303 K, and 310 K by fluorescence and UV-visible absorption spectroscopy were investigated under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between CPC and BSA was combined quenching (dynamic and static quenching) procedure at low CPC concentration, or a dynamic quenching procedure at high concentrations. The binding constants, binding sites and the corresponding thermodynamic parameters of the interaction system were calculated. According to Förster non-radiation energy transfer theory, the binding distance between CPC and BSA was calculated to be 3.02 nm. Both synchronous fluorescence and FT-IR spectra confirmed the interaction, and indicated the conformational changes of BSA. The effects of some common metal ions Ca(2+), Ni(2+), Mg(2+), Fe(2+), and Cu(2+) on the binding constant between CPC and BSA were examined. Furthermore, we investigated the possible sub-domains on BSA that bind CPC by displacement experiments.

A Simple Dual-pH Responsive Prodrug-Based Polymeric Micelles for Drug Delivery

To precisely deliver drug molecules at a targeted site and in a controllable manner, there has been great interest in designing a synergistical drug delivery system that can achieve both surface charge-conversion and controlled release of a drug in response to different stimuli. Here we outline a simple method to construct an intelligent drug carrier, which can respond to two different pH values, therefore achieving charge conversion and chemical-bond-cleavage-induced drug release in a stepwise fashion. This drug carrier comes from the self-assembly of a block copolymer-DOX conjugate synthesized through a Schiff base reaction between poly(2-(diisopropylamino)ethyl methacrylate-b-poly(4-formylphenyl methacrylate-co-polyethylene glycol monomethyl ether methacrylate) (PDPA-b-P(FPMA-co-OEGMA)) and DOX. The surface charge of the BCP-DOX micelles reversed from negative to positive when encountering a weakly acidic environment due to the protonation of PDPA segments. In vitro cellular uptake measurement shows that the cellular uptake and internalization of the BCP-DOX micelles can be significantly enhanced at pH ∼ 6.5. Moreover, this drug carrier exhibits a pH-dependent drug release owing to the cleavage of the imine bond at pH < 5.5. With this dual-pH responsive feature, these micelles may have the ability to precisely deliver DOX to the cancer cells.

Reactivity study of a hydroxyl coordinated osmium vinyl complex OsCl2(PPh3)2[CH=C(PPh3)CHPh(OH)]

We studied the reactivity of an osmium vinyl complex containing a coordinated hydroxyl group OsCl2(PPh3)2[CH=C(PPh3)-CHPh(OH)] (1) toward bidentate ligand 1,4-bis(diphenylphosphino)butane (DPPB), π acid ligand (CO), base (Cs2CO3) and heat. Two osmium vinyl complexes OsCl2(dppb)[CH=C(PPh3)CHPh(OH)] (2) and OsCl2(CO)2(PPh3)[CH=C(PPh3)CHPh(OH)] (3), as well as two relatively rare phosphonium-containing osmafuran complexes Os(η2-OCOO)(PPh3)2[CHC(PPh3)CPhO] (4) and OsCl2(PPh3)2[CHC(PPh3)CPhO] (5), were obtained in high yields from these reactions. All products were characterized by NMR spectroscopy, elemental analysis, and their structures were further confirmed by single crystal X-ray diffraction.

Controllable fabrication of a N and B co-doped carbon shell on the surface of TiO2 as a support for boosting the electrochemical performances

A valid pathway has been exploited to create a B,N co-doped carbon shell on the surface of TiO2 nanoparticles (TiO2@CNB) as a support of Pt nanoparticles. The shell thickness of TiO2@CNB can be easily controlled by pyrolysis of TiO2@polymer networks. The as-prepared Pt/TiO2@CNB catalyst with a thicker CNB layer of 5.0 ± 0.5 nm shows improved performance for the oxygen reduction reaction (ORR) with high onset (0.65 V) and half-wave potentials (0.56 V), which are significantly higher than those of commercial Pt/C (20 wt%) catalysts. For the methanol oxidation reaction (MOR), the Pt/TiO2@CNB catalyst with a moderate CNB layer of 3.3 ± 0.3 nm thickness demonstrates the highest activity and stability compared with that with a CNB thickness of 2.1 ± 0.3, or 5.0 ± 0.5 nm, even Pt/C. Our findings indicate that the synergy between Pt nanoparticles and the B,N co-doped carbon shell, as well as the shell thickness plays a key role in improving the electrochemical performances of the Pt/TiO2@CNB composite materials.

A novel hybrid random copolymer poly(MAPOSS-co-NIPAM-co-OEGMA-co-2VP): Synthesis, characterization, self-assembly behaviors and multiple responsive properties

AbstractA novel organic/inorganic hybrid amphiphilic random copolymer poly(methacrylate isobutyl POSS-co-N-isopropylacrylamide-co-oligo(ethylene glycol) methyl ether methacrylate-co-2-vinylpyridine), poly(MAPOSS-co-NIPAM-co-OEGMA-co-2VP), was synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The self-assembly behavior of random copolymers in aqueous solution was investigated by dynamic light scattering (DLS) as well as transmission electron microscopy (TEM). The results indicate the novel random copolymer in water could self-assemble into spherical aggregates and the self-aggregate size displays a remarkable dependence on pH. The stimuli-responsive characteristics of these assembles were tested by means of UV-vis spectra, DLS and TEM. There is a critic Zn2+ concentration over which the aggregates can be coordinated into well-define spherical aggregate clusters. The critic Zn2+ concentration can be tuned finely through adjusting solution concentration or 2VP amount. Results from UV-vis and DLS reveal that the copolymer solutions exhibit a sharp and intensive lower critical solution temperature (LCST). Some factors such as the solution concentration, molecular weight, pH and copolymer generation, which could affect the cloud point, were studied systematically. The essentially predetermined LCST can be achieved by altering the content of 2VP or pH. In addition, these novel hybrid aggregates can undergo an association/disassociation cycle with the heating and cooling of solution and the degree of reversibility shows a strong concentration dependence. As a novel organic-inorganic hybrid material which can respond to multiple external stimuli including temperature, pH, metal ions with sharp stimuli-responsive behaviors, it is potentially used for biomedicine, catalysis, diagnostics, bioseparations, biosensors and for fundamental investigation.

A novel hybrid polyhedral oligomeric silsesquioxane-based copolymer with zwitterion: Synthesis, characterization, self-assembly behavior and pH responsive property

A novel zwitterionic hybrid amphiphilic copolymer containing polyhedral oligomericsilsesquioxane (POSS), and poly(methacrylate isobutyl POSS)-b-poly (3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonaten-co-2-(diethylamino) ethyl methacrylate-co-styrene) (PMAiBuPOSS-b-P(DMAPS-co-DMAEMA-co-St)), was prepared by the ring open reaction of 1, 3-propane sultone with tertiary amine on the precursor polymer. This hybrid copolymer could self-assemble into spherical micelle with a relatively narrow size distribution. The micelle size exhibited a great dependence on pH, as the size of the micelles was of evidently decreases with the increase of the pH value. Controllable release of pyrene from the micelles was investigated by fluorescent emission spectra. Micelles with more zwitterionic units would lead to less pyrene release and longer equilibrium time. The protein adsorption resistance of the micelles was tested by mixing them with fetal bovine serum. The antifouling ability was improved by increasing the number of zwitterionic units as well as decreasing the number of DMAEMA units. This novel hybrid amphiphilic random copolymer with the pH-responsive and anti-protein-fouling ability, can be potentially used for drug carriers for controlled release.

Interpenetration enhancing of Chitosan-PEGLM double network (DN) hydrogel and its properties

AbstractA series of polylactic acid-polyethylene glycol-polylactic acid diacrylate macromers (PEGLM) were synthesized, and a novel chitosan-PEGLM double network (DN) hydrogel was further successfully fabricated by the sequential interpenetrating technology with highly cross-linked chitosan as the rigid component and PEGLM as the flexible component. Their structures and components were characterized by 1H NMR, FTIR, and XRD. Their fracture morphology was investigated by SEM. It was interesting to found that the compressive strength of hydrogel wound reach its maximum value when the chitosan content was 10%, no matter what the molecular weight of PEGLM component was. What’s more, we found that the compressive strength of 6KL7 could reach 1.07 MPa at gel state, whose PEG segment molecular weight was 6,000, and polymerization degree of PLA was 7. The effects of glutaraldehyde ratio, polymerization degree of PLA, and molecular weight of PEG segment on the mechanical strength of DN hydrogels were also discussed in this article. To further strengthen DN hydrogels, the double network-linear (DNL) hydrogels were fabricated by introducing linear poly(vinyl alcohol) (PVA) into the DN hydrogels. The DN-L hydrogels exhibited better mechanical properties, with the compressive strength up to 1.45 MPa. These hydrogels may have prospective applications in the fields of wound dressing, artificial cartilage and tissue engineering scaffold materials which require high mechanical properties.

Predictable particle engineering: programming the energy level, carrier generation and conductivity of core-shell particles

Core-shell structures are of particular interest in the development of advanced composite materials as they can efficiently bring different components together at nanoscale. The advantage of this structure greatly relies on the crucial design of both core and shell, thus achieving an intercomponent synergistic effect. In this report, we show that decorating semiconductor nanocrystals with a boronate polymer shell can easily achieve programmable core-shell interactions. Taking ZnO and anatase TiO2 nanocrystals as inner core examples, the effective core-shell interactions can narrow the band gap of semiconductor nanocrystals, change the HOMO and LUMO levels of boronate polymer shell, and significantly improve the carrier density of core-shell particles. The hole mobility of core-shell particles can be improved by almost 9 orders of magnitude in comparison with net boronate polymer, while the conductivity of core-shell particles is at most 30-fold of nanocrystals. The particle engineering strategy is based on two driving forces: catechol-surface binding and B-N dative bonding and having a high ability to control and predict the shell thickness. Also, this approach is applicable to various inorganic nanoparticles with different components, sizes, and shapes.

Flame retardant epoxy resin based on organic titanate and polyhedral oligomeric silsesquioxane-containing additives with synergistic effects

In order to develop a new epoxy resin (EP) possessing good thermal and mechanical properties as well as flame retardancy performance, the compound POSS-bisDOPO consisting of one polyhedral oligomeric silsesquioxane (POSS) and two unit of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was synthesized and used as co-additive with tetrabutyl titanate to construct a phosphorous–silicon–titanium synergy system. Compared to pure EP, the char yields of the EP composites were increased. The LOI value and UL-94 ratings of the EP composite with a loading of 5% POSS-bisDOPO reached 31.0% and V-0 grade, respectively. The PHRR and THR reduced to 28.4 W g−1 and 1.7 kJ g−1. SEM results indicated that the char of the EP composites had an alveolate inner layer and continual compact outer layer, which was conducive to form effectively physical barrier to hinder the penetrating of oxygen and heat. DMA and three-point bending test results showed the mechanical property of the EP composites had no decline.

Cross-Linking Induced Self-Organization of Polymers into Degradable Assemblies

Covalently stabilized polymer assemblies are normally fabricated from the self-assembly of polymer chains followed by a cross-linking reaction. In this report, we show that a cross-linking-induced self-assembly approach, in which boronate cross-linking sites are formed by the condensation reaction between boronic and catechol groups, can organize polymer networks into uniform assemblies. Self-assembly of these boronate cross-linked polymer networks adopts two different driving forces in water and methanol solutions. Hydrophobic aggregation of polymer networks in water solution affords spherical assemblies, while B-N dative bond formed between boronate and imine functionalities in methanol solution organizes the polymer networks into bundle-like assemblies. We not only demonstrate the intrinsic stimuli-responsive degradability of these cross-linked assemblies but also show that their degradation can cause a controllable release of guest molecules. Moreover, bundle-like assemblies with rough surface and exposed boronate functionalities exhibit dramatically higher cell penetration capability than the spherical assemblies with smooth surface and embedded boronate functionalities.