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Shuiqin Zhou

Publications and source records attributed to Shuiqin Zhou.

7 recordsLinked to original sources
PubMed2007

Homocysteine-mediated reactivity and assembly of gold nanoparticles.

This paper reports the findings of an investigation of the reactivity and assembly of gold nanoparticles mediated by homocysteine (Hcys), a thiol-containing amino acid found in plasma. The aim is to gain insight into the interparticle interaction and reactivity, which has potential application for the detection of thiol-containing amino acids. By monitoring the evolution of the surface plasmon resonance absorption and the dynamic light scattering of gold nanoparticles in the presence of Hcys, the assembly was shown to be dependent on the nature and concentration of the electrolytes, reflecting an effective screening of the diffuse layer around the initial citrate-capped nanoparticles that decreases the barrier to the Hcys adsorption onto the surface, and around the subsequent Hcys-capped nanoparticles that facilitate the zwitterion-type electrostatic interactions between amino acid groups of Hcys bound to different nanoparticles. A key element of the finding is that the interparticle zwitterion interaction of the Hcys-Au system is much stronger than the expectation for a simple Hcys or Au solution, a new phenomenon originating from the unique nanoscale interparticle interaction. The strength and reversibility of the interparticle zwitterion-type electrostatic interactions between amino acid groups are evidenced by the slow disassembly upon increasing pH at ambient temperatures and its acceleration at elevated temperature. These findings provide new insight into the precise control of interfacial interactions and reactivities between amino acids anchored to nanoparticles and have broad implications in the development of colorimetric nanoprobes for amino acids.

Chemistry, Physical↗
PubMed2006

Synthesis and volume phase transitions of glucose-sensitive microgels.

By the functionalization of poly(N-isopropylacrylamide-co-acrylic acid) microgels with 3-aminophenylboronic acid (APBA) via carbodiimide coupling, nearly monodisperse glucose-sensitive P(NIPAM-PBA) microgels with a diameter of several hundred nanometers were synthesized in aqueous media. Dynamic laser light scattering was used to study the glucose-sensitive and thermosensitive behaviors of the resultant microgels under various conditions. The introduction of the hydrophobic phenylboronic acid (PBA) group significantly decreases the volume phase transition temperature of the resultant microgels. As a result, the P(NIPAM-PBA) microgels with a 10.0 mol % PBA content are in a collapsed state at room temperature. However, the addition of glucose makes the microgels swell dramatically. The glucose-sensitivity of the PBA-containing microgels relies on the stabilization of the charged phenylborate ions by binding with glucose, which can convert more hydrophobic PBA groups to the hydrophilic phenylborate ions. The presence of glucose also induces a two-stage volume phase transition of the P(NIPAM-PBA) microgels, which is explained by the core-shell-like heterogeneous structure of the microgels induced by the formation of the unique glucose-bis(boronate) complex in the "core" area of the microgels. The effects of pH, ionic strength, and PBA content on the glucose sensitivity of the P(NIPAM-PBA) microgels were investigated.

Gels↗
PubMed2005

Structural study of the self-assembled fullerene carboxylates: monoadducts versus bisadducts.

Laser light scattering and transmission electronic microscopy have been used to study the self-assembled structures of mono- and bisadducts of fullerene carboxylic acids in tetrahydrofuran (THF) and their sodium salts in aqueous solutions, respectively. In THF, the self-association of monoadducts of fullerene carboxylic acid (MFCA) produces large but narrowly distributed particles with R(h) approximately 145 nm. The self-aggregates from the bisadducts of fullerene carboxylic acid (BFCA) in THF are relatively small in size (R(h) approximately 80 nm) due to the better solubility. After the ionization of carboxylic acid groups on the C(60) cage in dilute NaOH solutions, these aggregates dissolved and reorganized. The self-assembly of the monoadducts of sodium carboxylate fullerenes (MSCF) produces small solid spherical particles with R(h) approximately 32 nm. The ratio of R(g)/R(h) approximately 0.83 indicates that the particles have a nearly uniform density. The increase in concentrations leads to strong interparticle associations to form rodlike and irregularly shaped large aggregates. In contrast, the self-assembly of bisadducts of sodium carboxylate fullerenes (BSCF) results in hollow shells with mainly two different size scales of R(h) approximately 23 nm and R(h) approximately 104 nm. At high concentrations, the hollow shells associate and melt together to generate three-dimensional networks.

Acids↗
PubMed2004

Phase behavior of cationic hydroxyethyl cellulose-sodium dodecyl sulfate mixtures: effects of molecular weight and ethylene oxide side chain length of polymers.

Novel cationic hydroxyethyl cellulose (HEC) polymers with different molecular weights (1.1 x 10(5) to 1.7 x 10(6) g/mol) and ethylene oxide (EO) side chain lengths (1.5-2.9 EO units) were mixed with sodium dodecyl sulfate (SDS) in aqueous solutions. The phase diagrams of cationic HEC-SDS complexes were determined in the dilute polymer concentration regime (< 0.5 wt %) with gradual addition of SDS molecules. The viscosity and structures of the complexes during the phase evolution were studied using rheometry and dynamic light scattering. The gradual addition of SDS first induced interchain associations with the bound SDS aggregates serving as cross-linkers to form an open network structure, producing a very broad size distribution and high viscosities of the complex solutions, and then condensed the network and induced a structure reorganization, resulting in globular aggregates with narrow size distributions. The growth of these globular aggregates in size eventually led to macroscopic sedimentation near charge neutralization. Further addition of SDS randomly broke the sedimentary aggregates into small particles and SDS micelles with low solution viscosities. The effects of molecular weight and EO side chain length of polymers on the phase boundary, viscosity, and structure of cationic HEC-SDS complexes were discussed.

Cations↗
PubMed2004

Supramolecular assemblies of a naturally derived sophorolipid.

Acidic sophorolipid (SL) molecules derived from yeasts represent a novel type of asymmetrical bolaamphiphiles due to their unique structural features that include an asymmetrical polar head size (disaccharide vs COOH), a kinked hydrophobic core (cis-9-octadecenoic chain), and a non-amide polar-nonpolar linkage. Light microscopy, small- and wide-angle X-ray scattering, FT-IR spectroscopy, and dynamic laser light scattering were used to investigate the supramolecular structures of the self-assembled aggregates of SL molecules at different pH values. In acidic conditions (pH < 5.5), giant twisted and helical ribbons of 5-11 microm width and several hundreds of micrometers length were observed for the first time. Increase in solution pH values slowed ribbon formation, decreased ribbon yield, and increased the helicity and entanglements of the giant ribbons. An interdigitated lamellar packing model of acidic SL-COOH molecules with a long period of 2.78 nm, stabilized by both the strong hydrophobic association between the cis-9-octadecenoic chains and strong disaccharide-disaccharide hydrogen bonding, is proposed. The neutralization of SL-COOH in water to SL-COONa produced clear solutions with the formation of short-range ordered aggregates. At concentrations below 1.0 mg/mL, the size of self-assembled aggregates increased as the concentration increased. At concentrations above 1.0 mg/mL, narrowly distributed micellar aggregates with a constant hydrodynamic radius (R(h)) of about 100 nm are formed. The large micelles show strong angular dependence with the fast mode appearing at scattering angle theta >/= 60 degrees.

Glycolipids↗
PubMedDate not supplied

Nanostructures of complexes formed by calf thymus DNA interacting with cationic surfactants.

Synchrotron small-angle X-ray scattering was used to study the nanostructures of the complexes formed by calf thymus DNA interacting with cationic lipids (or surfactants) of didodecyldimethylammonium bromide (DDAB), cetyltrimethylammonium bromide (CTAB), and their mixture with a zwitterionic lipid of 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphocholine (PHGPC). The effects of lipid/DNA ratios, DNA chain flexibility, lipid topology, and neutral lipid mixing on the nanostructures of DNA-lipid complexes were investigated. The complexes between double-stranded DNA (dsDNA) and double-tailed DDAB formed a bilayered lamellar structure, whereas the complexes between dsDNA and single-tailed CTAB preferred a structure of 2D hexagonal close packing of cylinders. With single stranded DNA (ssDNA) interacting with CTAB, the complexes showed a Pm3n cubic structure due to the different chain flexibility between dsDNA and ssDNA. The lipid molecules bound by rigid dsDNA like to form cylindrical micelles, whereas lipids bound to flexible ssDNA could form spherical or short cylindrical micelles. The addition of the neutral single-chained PHGPC lipids to the CTAB lipids could induce a structural transition of dsDNA-lipid complexes from a 2D hexagonal to a multi-bilayered lamellar structure. The parallel DNA strands were intercalated in the water layers of lamellar stacks of the mixed lipid bilayers. The DNA-DNA spacing depended on the ratios of charged lipid to neutral lipid, and charged lipid to DNA, respectively.

Animals↗