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Junbai Li

Publications and source records attributed to Junbai Li.

At least 19 recordsLinked to original sources
PubMed2007

Hydrolysis characterization of phospholipid monolayers catalyzed by different phospholipases at the air-water interface.

Combination of some newly developed microscopic and spectroscopic techniques with conventional Langmuir monolayer method can provide more quantitative information with the molecular orientation and reorganization process of spread amphiphilic molecules at the air/water interface. These techniques are extended to investigate the hydrolysis process of spreading lipid monolayer catalyzed by different enzymes, phospholipases A2, C and D, respectively. Synchrotron X-ray diffraction and infrared reflection absorption spectroscopy are able directly to give the structural information of the assembled monolayer, interfacial activity of amphiphiles and their components at the interface. Microscopic technique such as Brewster angle microscopy (BAM), fluorescence microscopy (FM) can be used to trace the morphological changes dynamically as the spreading lipid monolayer is hydrolyzed at the air/water interface. We summary here some latest progress in this filed and give a brief review over the hydrolysis features of phospholipid monolayer catalyzed by different enzymes. It is attempted to establish a model of membrane hydrolysis process in order to better understand the mechanism of membrane metabolism and signal transduction in a living system.

Air↗
PubMed2007

Thermosensitive copolymer networks modify gold nanoparticles for nanocomposite entrapment.

The core-shell gold nanoparticles and copolymer of N-isopropylacrylamide (NIPAM) and N,N'-methylenebisacrylamide (MBAA) hybrids (Au@copolymer) were fabricated through surface-initiated atom-transfer radical polymerization (ATRP) on the surface of gold nanoparticles in 2-propanol/water mixed solvents. The surface of citrate-stabilized gold nanoparticles was first modified by a disulfide initiator for ATRP. The slight cross-linking polymerization between NIPAM and MBAA occurred on the gold surface and resulted in the formation of core-shell Au@copolymer nanostructures that were characterized by TEM, and FTIR and UV-visible spectroscopy. Such synthesized Au@copolymer hybrids possess clearly thermosensitive properties and exhibit "inspire" and "expire" water behavior in response to temperature changes in aqueous solution. Because of this property, we enable to trap and encapsulate smaller nanoparticles by using the free space of the copolymer-network scaffold anchored at the gold surface.

Gold↗
PubMed2006

Synthesis of PNIPAM-co-MBAA copolymer nanotubes with composite control.

We report the preparation of copolymer, poly(N-isopropylacrylamide)-co-(N,N'-methylenebisacrylamide) (PNIPAM-co-MBAA) nanotubes with different composite ratios through surface-initiated atom transfer radical polymerization using a porous anodic aluminum oxide membrane as a template. It is found that the tubular wall strongly depends on the monomer concentration. The composite-induced changes in dimension and shape of nanotubes, especially the wall thickness, were studied by scanning electron microscopy, transmission electron microscopy, atom force microscopy, FT-IR, and gel permeation chromatography. The PNIPAM-co-MBAA nanotubes exhibit a high flexibility and stability.

Journal Article↗
PubMed2006

Human serum albumin supported lipid patterns for the targeted recognition of microspheres coated by membrane based on ss-DNA hybridization.

Human serum albumin (HSA) patterns have been successfully fabricated for the deposition of lipid bilayer, 1,2-dimyristoyl-sglycerophosphate (DMPA), by making use of the micro-contact printing (microCP) technique and liposome fusion. Confocal laser scanning microscopy (CLSM) results indicate that lipid bilayer has been assembled in HSA patterns with a good stability. Such well-defined lipid patterns formed on HSA surface create possibility to incorporate specific components like channels or receptors for specific recognition. In view of this, microspheres coated with lipid membranes were immobilized in HSA-supported lipid patterns via the hybridization of complementary ss-DNAs. This procedure enables to transfer solid materials to a soft surface through a specific recognition.

DNA, Single-Stranded↗
PubMed2006

Assembly of nanotubes of poly(4-vinylpyridine) and poly(acrylic acid) through hydrogen bonding.

Nanotubes of poly(4-vinylpyridine) (PVP) and poly(acrylic acid) (PAA) were fabricated by hydrogen bonding based on layer-by-layer (LbL) assembly. The uniform and flexible tubular structures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR and X-ray photoelectron spectroscopy (XPS) measurements confirm the formation of hydrogen bonds in the assembled nanotubes. PAA can be released from the assembled PAA/PVP nanotubes in a basic aqueous solution to give the walls of the tubes a porous structure. Such assembled nanotubes can be considered as carriers for catalysts or drugs, especially in aqueous solution against capillary force.

Acrylic Resins↗
PubMed2006

Fabrication of fluorescent nanotubes based on layer-by-layer assembly via covalent bond.

A pressure-filter-template approach was employed to prepare fluorescent nanotubes of polyethyleneimine (PEI) and 3,4,9,10-perylenetetracarboxylicdianhydride (PTCDA) through covalent combination in the porous of alumina template based on the layer-by-layer (LbL) assembly technique. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images exhibited a tubular structure of the obtained samples. The wall thickness of the nanotubes is well controlled by varying the assembled cycle number, which is detected by UV-visible spectroscopy. Fourier transform infrared (FT-IR) spectroscopy confirmed the formation of covalent bonds between PEI and PTCDA in nanotubes.

Journal Article↗
PubMed2006

pH controlled permeability of lipid/protein biomimetic microcapsules.

The permeability of lipid and protein microcapsules fabricated by alternating adsorption of human serum albumin (HSA) and L-alpha-dimyristoylphosphatidic acid (DMPA) on a template and subsequent removal of the core is studied as a function of pH value and supplementary layers. The capsules were permeable for macromolecules (FITC-labeled dextran, M(w) 40 kDa) at pH < 4.8 and impermeable at pH > 7.4. The assembly of supplementary DMPA bilayers rendered the capsules impermeable for small hydrophilic molecules such as 6-carboxyfluorescein (6-CF). Hence DMPA/HSA capsules can be resealed after fabrication by supplementary layers. This provides the opportunity of applying such biomimetic membrane capsules as drug carriers or model systems to study biological processes at membranes.

Adsorption↗
PubMed2006

Fabrication of protein nanotubes based on layer-by-layer assembly.

Nanotubes of cytochrome C (cyto-c) with glutaraldehyde (GA) or PSS based on the layer-by-layer (LbL) assembly through covalent binding and electrostatic adsorption have been fabricated. The combination of the template method and the LbL method for fabrication of nanotubes exhibits low cost, simplicity, and versatility. The tubular morphology of the assembled glutaraldehyde and cytochrome C film was demonstrated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. The components of the tubes were determined by energy-dispersive X- ray spectra (EDAX). It is found that the assembled tubes keep the proteins' biochemical activity and electronic activity by cyclic voltammograms. The measurements of ultraviolet spectra and circular dichroism (CD) on the assembled nanotubes confirmed the cyto-c existence in the tubes.

Absorption↗
PubMed2006

Template-synthesized nanotubes through layer-by-layer assembly under charge interaction.

Aqueous polymer nanotubes can be assembled by combining the layer-by-layer (LbL) assembly and template technique under charge interaction. This method allows lots of species, especially in an aqueous system to form a tubular structure in the pores of the template. The tubes functions can be readily modified by introducing various functional components. Such assembled nanotubes are often mechanically stable and highly flexible. They have also numerous potential applications in delivering materials.

Aniline Compounds↗
PubMed2006

Fabrication of polyethyleneimine and poly(styrene-alt-maleic anhydride) nanotubes through covalent bond.

Nanotubes of Polyethyleneimine (PEI) and Poly(styrene-alt-maleic anhydride) (PSMA) based on the layer-by-layer (LbL) technique and template method through covalent bond have been fabricated. The combination of LbL assembly and the template method can well control the length, wall thickness, outside, and inner diameters of the resulting nanotubes. The formation of covalent between PEI and PSMA enables the nanotubes with a good mechanical stability. The uniform tubular structure has been characterized by scanning electron microscopy (SEM) and transmission Electron Microscopy (TEM). Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) measurements confirms the formation of covalent bond in the assembled nanotubes.

Binding Sites↗
PubMed2006

Mechanical property of lipid-coated polyelectrolyte microcapsules.

The deformations of lipid coated polyelectrolyte capsules induced by osmotic pressure were determined in poly(styrene sulfonate, sodium salt) (PSS) solution by making use of the fact that PSS molecules with a molecular weight 70000 will not penetrate into the capsules. At a critical osmotic pressure the initial spherical capsules changed their shape and became an invagination. The measurements of single particle light scattering provided the wall thickness of the lipid-coated capsules with 25.6 nm while the thickness for pure polyelectrolyte capsules in solution is about 21.6 nm, indicating that the coating lipid layer has about 4 nm thickness. It demonstrates that DMPA forms a bilayer on the surface of polyelectrolyte capsules. With these data, that the elasticity coefficient of the lipid-coated capsules is about 426 Mpa can be obtained.

Adsorption↗
PubMed2005

Layer-by-layer assembly of human serum albumin and phospholipid nanotubes based on a template.

The preparation of nanotubes from human serum albumin (HSA) and mixtures of L-alpha-dimyristoylphosphatidic acid (DMPA)/HSA is described. The nanotubes were prepared via alternate adsorption of HSA of different/opposite charges (by variation of the pH) or by sequential adsorption of DMPA and HSA, respectively, onto the inner surfaces of porous anodic alumina templates. This simple layer-by-layer assembly results in a monodisperse size distribution and a uniform orientation. The nanotubes allow the specific incorporation of lipophilic components such as channels or receptors and may thus serve as probes or sensors for biological systems.

Circular Dichroism↗
PubMed2005

Hydrolysis reaction analysis of L-alpha-distearoylphosphatidylcholine monolayer catalyzed by phospholipase A2 with polarization-modulated infrared reflection absorption spectroscopy.

The hydrolysis reaction of L-alpha-distearoylphosphatidylcholine (DSPC) monolayers catalyzed by phospholipase A2 (PLA(2)) has been studied using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) with film balance measurements. The PM-IRRAS analysis provides quantitative information about the reaction efficiency at different surface pressures. It was found that the reaction efficiency of L-DSPC monolayer hydrolysis catalyzed by PLA(2) decreased with increasing surface pressure. At zero pressure (lift-off point), the hydrolysis reaction efficiency has the highest value of 45%. Increasing surface pressure leads to the decrease of the hydrolysis efficiency. Since the surface pressure is above 20 mN/m, the hydrolysis reaction nearly stopped. PM-IRRAS technique provides a powerful means to study the hydrolysis process catalyzed by phospholipase A2 at the air/water interface.

Hydrolysis↗
PubMed2005

Small angle X-ray scattering (SAXS) and differential scanning calorimetry (DSC) studies of amide phospholipids.

Varying chemically the structure of phospholipids in the region between hydrophobic and hydrophilic segments is expected to have a strong influence on the interaction with water and the phase behavior. This is studied in this work with the motivation to investigate these lipids as potential inhibitors of phospholipase A2. Thus the amide phospholipids L-ether-amide-PC (1-O-hexadecyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine), L-ester-amide-PC (1-palmitoyl-2-N-palmitoyl-2-amino-2-deoxy-sn-glycero-3-phosphocholine) and L-ether-amide-PE (1-O-hexadecyl-2-N-palmitoyl-2-deoxy-sn-glycero-3-phosphoethanolamine) have been synthesized and characterized. The phase behavior and thermal transitions in buffer dispersions are examined by a combination of high-sensitivity differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) experiments between 10 and 80 degrees C at pH 8.9. The onset temperatures determined from DSC measurements agree well with the starting temperatures of changes in the repeat distance obtained by SAXS measurements. The phases observed are lamellar both below and above the main phase transition. The phase transition temperatures and enthalpies depend strongly on the substitutions in sn-1 position and head group structure. The lamellar repeat distance in gel and liquid-crystalline phases increases with increasing temperature for L-ester-amide-PC and L-ether-amide-PC, whereas the temperature dependence is opposite for the L-ether-amide-PE. The observed behavior is discussed and compared with that of DPPC and DPPE, indicating the strong dependence of hydration and phase behavior on head group structure.

Amides↗
PubMed2004

Self-assembly of human serum albumin (HSA) and L-alpha-dimyristoylphosphatidic acid (DMPA) microcapsules for controlled drug release.

Human serum albumin (HSA) and L-alpha-dimyristoylphosphatidic acid (DMPA) were applied as a pair to encapsulate ibuprofen microcrystals by means of a technique based on the layer-by-layer (LbL) assembly of oppositely charged species, for the purpose of controlling drug release. The successful adsorption of HSA and DMPA multilayers onto ibuprofen crystals was confirmed by optical microscopy. The drug release process, in a solution of pH 7.4, was monitored by optical microscopy and UV spectroscopy. The results revealed that the rate of release of ibuprofen from HSA/DMPA microcapsules decreased as the capsule wall thickness and drug crystal size increased, indicating that the permeability of the microcapsules can be controlled by simply varying the number of HSA/DMPA deposition cycles.

Capsules↗
PubMed2004

Self-assembly, optical behavior, and permeability of a novel capsule based on an azo dye and polyelectrolytes.

A novel capsule composed of an azo dye, Congo red (CR), and different polymers, including poly(styrenesulfonate, sodium salt) (PSS), poly(allylamine hydrochloride) (PAH), and poly(diallyldimethylammonium chloride) (PDDA), have been successfully fabricated by the layer-by-layer self-assembly technique. The stepwise linear deposition process was monitored by means of UV-visible absorption measurements. The formation of hollow capsules was verified by confocal laser scanning microscopy (CLSM) and scanning force microscopy (SFM). The resulting hollow PSS/PAH/CR/PDDA capsules displayed a sensitive response to visible light. Optical changes of the hollow capsules prior to and after the photoreaction were investigated in detail by means of UV-visible spectroscopy, CLSM, and SFM. It was found that the photochemical reaction of the assembled hollow capsules depends strongly on the matrix. Qualitative results on the permeability of the hollow capsule walls with CR as one component indicate that the permeability of the walls can be easily photo-controlled at varying irradiation time intervals without addition of external chemicals.

Azo Compounds↗
PubMed2004

Biogenic capsules made of proteins and lipids.

Multilayer biogenic capsules with a micrometer scale were fabricated by self-assembly of proteins and lipids at the interface of emulsion droplets. The optical microscopy images demonstrate that spherical capsules at a fluid interface have uniform walls and the dried capsules possess a high mechanical strength. The hollow shells obtained provide a novel class of assembly with encapsulating drug molecules based on the layer-by-layer technique.

Adsorption↗