Capillary electrophoresis of urinary normal and modified nucleosides of cancer patients

This paper gives a capillary electrophoretic method for the separation of 15 urinary normal and modified nucleosides from cancer patients in less than 40 min. A 500 mmx50 mu m uncoated capillary column (437.5 mm to window) was used. The effects of the voltage and the sodium dodecyl sulfate (SDS) concentration in the buffer on the separation were studied. With reproducibilities of migration times better than 1.2% (R.S.D.) and determined concentrations better than 5-25%, depending on the concentrations of nucleosides in the urine, the analytical characteristics of the method were food. Using this developed method, the concentrations of 13 normal and modified nucleosides, extracted on a phenyl boronic acid affinity chromatography column, in 25 urines from patients of 14 kinds of cancer were determined. The levels (nmol/mol creatinine) of modified nucleosides in urines from cancer patients were increased as compared with those in normal urines. (C) 1998 Elsevier Science B.V.

Effects of pH on the Interactions and Conformation of Bovine Serum Albumin: Comparison between Chemical Force Microscopy and Small-Angle Neutron Scattering

The conformation of bovine serum albumin (BSA), as well as its interactions with negatively charged mica surfaces in saline solutions of different pH values, have been studied by small-angle neutron scattering (SANS) and chemical force microscopy (CFM), respectively. A new approach to extract the contribution of elementary interactions from the statistically averaged force-extension curves through self-consistent fitting was proposed and used to understand the effects of pH on the interactions and conformation of BSA in saline solutions. When pH increases, the SANS results reveal that the sizes of BSA molecules increase slightly, while the statistical analysis of the CFM results shows that the averaged pull-off force for the elongation monotonously decreases. The decrease of pull-off force with the increase of pH results from the decrease in the strength of hydrogen bonding and the number of interaction pairs, as well as the slight increase of the strength of van der Waals interaction. When pH approaches the isoelectric point (pI) of BSA, results from both SANS and CFM suggest a loss of long-range interactions in BSA molecules. Our results also suggest that the force-extension curve is mainly contributed by the van der Waals interaction. The combination of SANS and CFM provides new insight to understand the interactions and conformation of BSA molecules

Length dependence of electron conduction for oligo(1,4-phenylene ethynylene)s: A conductive probe-atomic force microscopy investigation

The dependence of electron conduction of oligo(1,4-phenylene ethynylene)s (OPEs) on length, terminal group, and main chain structure was examined by conductive probe-atomic force microscopy (CP-AFM) via a metal substrate-molecular wire monolayer-conductive probe junction. The electron transport in the molecular junction was a highest occupied molecule orbital (HOMO)-mediated process following a coherent, non-resonant tunneling mechanism represented by the Simmons equation.

Atomic force microscopic study of low temperature induced disassembly of RecA-dsDNA filaments

The assembly and disassembly of RecA-DNA nucleoprotein filaments on double-stranded DNA (dsDNA) or single-stranded DNA (ssDNA) are important steps for homologous recombination and DNA repair. The assembly and disassembly of the nucleoprotein filaments are sensitive to the reaction conditions. In this work, we investigated different morphologies of the formed nucleoprotein filaments at low temperature under different solution conditions by atomic force microscopy (AFM). We found that low temperature and long keeping time could induce the incomplete disassembly of the formed nucleoprotein filaments.

Surface potential images of polycrystalline organic semiconductors obtained by Kelvin probe force microscopy

P-type copper phthalocyanine (CuPc) and n-type hexadecafluorophthalocyanina-tocopper (F16CuPc) polycrystalline films were investigated by Kelvin probe force microscopy (KPFM). Topographic and corresponding surface potential images are obtained simultaneously. Surface potential images are related with the local work function of crystalline facets and potential barriers at the grain boundaries (GBs) in organic semiconductors. Based on the spatial distribution of surface potential at GBs, donor- and acceptor-like trapping states in the grain boundaries (GBs) of p-CuPc and n-F16CuPc films are confirmed respectively.

Atomic force microscopy and surface-enhanced Raman scattering detection of DNA based on DNA-nanoparticle complexes

We report a simple method for the label-free detection of double-stranded DNA using surface-enhanced Raman scattering (SERS). We prepared cetyltrimethylammonium bromide (CTAB)-capped silver nanoparticles and a DNA-nanoparticle complex by adding silver nanoparticles to lambda-DNA solutions. In the present study, the utilization of CTAB-capped silver nanoparticles facilitates the electrostatic interaction between DNA molecules and silver nanoparticles; at the same time, the introduction of DNA avoids adding aggregating agent for the formation of nanoparticle aggregates to obtain large enhancement of DNA, because the DNA acts as both the probe molecules and aggregating agent of Ag nanoparticles.

DEFORMATION OF SOFT COLLOIDAL CRYSTALLINE STRUCTURE - THEORETICAL CONSIDERATIONS AND EXPERIMENTAL EVIDENCES BY SYNCHROTRON SMALL-ANGLE X-RAY SCATTERING ON TENSILE STRETCHED POLYMERIC LATEX FILM

Films obtained via drying a polymeric latex dispersion are normally colloidal crystalline where latex particles are packed into a face centered cubic (fcc) structure. Different from conventional atomic crystallites or hard sphere colloidal crystallites, the crystalline structure of these films is normally deformable due to the low glass transition temperature of the latex particles. Upon tensile deformation, depending on the drawing direction with respect to the normal of specific crystallographic plane, one observes different crystalline structural changes. Three typical situations where crystallographic c-axis, body diagonal or face diagonal of the fcc structure of the colloidal crystallites being parallel to the stretching direction were investigated.

Rapid fabrication of Au nanoparticle films with the aid of centrifugal force

In this work, rapid fabrication of Au nanoparticle (Au NP) films has been simply achieved by alternate adsorption of citrate-stabilized Au NPs and poly(diallyldimethylammonium chloride) with the aid of centrifugal force. In contrast to conventional electrostatic assembly, we carried out the assembly process in a centrifuge with a rotating speed of 4000 rpm, where centrifugal force can be imposed on Au NPs. Scanning electron microscopy and cyclic voltammetry were employed to characterize the assembly procedure and the thus-prepared thin solid films. Our results demonstrate that centrifugal force can promote the assembly of Au NPs and therefore enable the rapid fabrication of functional Au NP films.

Effect of block sequence and block length on the stimuli-responsive behavior of polyampholyte brushes: hydrogen bonding and electrostatic interaction as the driving force for surface rearrangement

Diblock polyampholyte brushes with different block sequences (Si/SiO2/poly(acrylic acid)-b-poly (2-vinylpyridine) (PAA-b-P2VP) brushes and Si/SiO2/P2VP-b-PAA brushes) and different block lengths were synthesized by sequent surface-initiated atom transfer radical polymerization (ATRP). The PAA block was obtained through hydrolysis from the corresponding poly(tert-butyl acrylate). The polyampholyte brushes demonstrated unique pH-responsive behavior. In the intermediate pH region, the brushes exhibited a less hydrophilic wetting behavior and a rougher surface morphology due to the formation of polyelectrolyte complex through electrostatic interaction between oppositely charged blocks. In the low pH and high pH regions, the rearrangement of polyampholyte brushes showed great dependence on the block sequence and block length. The polyampholyte brushes with P2VP-b-PAA sequence underwent rearrangement during alternative treatment by acidic aqueous solution (low pH value) and basic aqueous solution (high pH value).

Full View of Single-Molecule Force Spectroscopy of Polyaniline in Oxidized, Reduced, and Doped States

The macroscopic mechanical properties of polyaniline (PANI) lie mainly on two factors, the structure of molecular aggregations of polymers and the mechanical properties of a single polymer chain. The former factor is swell revealed; however, the latter is rarely studied. In this article, we have employed atomic force microscopy-based single-molecule force spectroscopy to investigate the mechanical properties of a kind of water-soluble PANI at a single-molecular level. We have carried out the study comparatively on single-chain-stretching experiments of oxidized, reduced, and doped PANI and obtained a full view of the single-chain elasticity of PANI in all these states. It is found that oxidized and reduced PANI chains are rigid, and the oxidized PANI is more rigid than the reduced PANI. Such a difference in single-chain elasticity can be rationalized by the molecular structures that are composed of benzenoid diamine and quinoid diimine its different proportions. The doped PANI has been found to be more flexible than the oxidized and reduced PANI, and the modified freely jointed chain parameters of doped PANI are similar with those of a common flexible-chain polymer.

A general route to transform normal hydrophilic cloths into superhydrophobic surfaces

Herein, we describe a simple and inexpensive method for forming superhydrophobic cloths with the highest water contact angle of close to 180 degrees, in which normal commercial cloths serving as pristine materials are modified with suitable gold micro/nanostructures.

Extended-chain lamellar packing of poly(3-butylthiophene) in single crystals

We developed an approach, i.e. solvent-assist crystallization (SAC), for growing high quality single crystals of head-to-tail regio-regular poly(3-butylthiophene) (P3BT). By means of atomic force microscopy, electron diffraction and X-ray diffraction, we found that P3BT macromolecules formed lamella single crystals through gradient crystallization, and in the single crystals, molecules packed normal to the lamella with extended-chain conformation with alkyl side chains in the growth front during crystallization.

Large-scale, uniform DNA network on 11-mercaptoundecanoic acid modified gold (111) surface: Atomic force microscopy study

Large-scale, uniform plasmid deoxyribonucleic acid (DNA) network has been successfully constructed on 11-mercaptoundecanoic acid modified gold (111) surface using a self-assembly technique. The effect of DNA concentration on the characteristics of the DNA network was investigated by atomic force microscopy. It was found that the size of meshes and the height of fibers in the DNA network could be controlled by varying the concentration of DNA with a constant time of assembly of 24 h.

Electrostatic assembly of protein lysozyme on DNA visualized by atomic force microscopy

In the present work, atomic force microscopy (AFM) has been used to study the assembly of protein lysozyme on DNA molecule. Based on the electrostatic interaction, the positively charged lysozyme can easily bind onto the negatively charged DNA molecule surface. The protein molecules appear as globular objects on the DNA scaffold, which are distinguishable in the AFM images. At the same time, lysozyme molecules can be assembled onto DNA as dense or sporadic pattern by varying the protein concentration. This work may provide fundamental aspects for building protein nanostructures and studying of DNA-protein interaction.