Experimental measurement of polyethylene chain modulus by scanning force microscopy

Nanoindentation technique and scanning force microscopy have been used to measure directly the polyethylene modulus along the chain axis. Single crystals of polyethylene were employed in order to obtain well-aligned chain segments. To minimize effects of scanner creep, a Z scan rate of 3 Hz was employed. The "X Rotate" value of 25 degrees was selected to eliminate effects of lateral tip motion. The results were analyzed by the Oliver -Pharr method for which direct observation and measurement of the contact area are not required. Considering the influence of tip roundness on the projected contact area, the nanoindentation results were analyzed by the Sawa method. The chain modulus obtained from the thinner polyethylene single crystal sample was 204 +/- 21 GPa by the Oliver-Pharr method and 168 +/- 17 GPa by the Sawa method. The lower values than expected were due to substrate effects and anisotropy of chain deformation during nanoindentation. An extrapolation of the chain modulus obtained by various strains to zero nanoindentation eliminated the effect of substrate and anisotropy of chain deformation. The corresponding chain modulus obtained from the thicker sample was 278 GPa by the Oliver-Pharr method and 267 GPa by the Sawa method, respectively, in better agreement with the value of 340 Cpa determined theoretically. (C) 2001 Elsevier Science Ltd. All rights reserved.

Synchronous fluorescence spectra of myoglobin

The synchronous fluorescence spectra of myoglobin were studies for the first time. The fluorescence peals observed in the spectra were assigned, When the wavelength interval (Delta lambda) is 80 nm, the main peak at 335 nm is originated from the tryptophan residues in the myoglobin molecule. When Delta lambda is 20 nn, the peak at 308 nm is mainly due to the tyrosine residues in the myoglobin molecule and in a small part due to the tryptophan residues. Two peaks at 322 and 596 nm were observed in the spectrum of myoglobin for Delta lambda = 40 nm. The peak at 322 nm is due to both tyrosine and tryptophan residues. The peak at 596 nm is attributed to the heme group in the myoglobin molecule.

Scanning electrochemical microscopy study of electron transfer across the water/1,2-dichloroethane interface induced by common ions

In this work, we report the reverse electron transfer reaction between TCNQ in 1, 2-dichloroethane (DCE) and ferrocyanide in water. This process is a thermodynamic unfavorable reaction and the reverse electron transfer reaction can only be obtained by scanning electrochemical microscopy(SECM) in the presence of suitable potential-determining ions, which govern the interfacial potential difference. In our case, the potential determining ions are tetrabutylammonium ion(TBA(+)) and tetraphenylarsonium ion (TPAs+). The effects of the concentrations of TBA(+) and TPAs+ in two phases and other parameters have been studied in detail. The apparent heterogeneous rate constants(k(i)) were obtained under different values of K-p(K-p=c(i)(w)/c(i)(o)) for both cases by fitting the SECM approach curves with theoretical ones and the results showed that they were controlled by the interfacial potential differences. The relationship between apparent heterogeneous rate constants and the interfacial potential differences obeys Butler-Volmer theory.

Recent advances in scanning electrochemical microscopy

The basic principle, instrumentation and recent advances of scanning electrochemical microscopy are briefly reviewed with 55 references.

Synthesis, electrochemistry, and fluorescence of two Ru(phen)(3)(2+)-based surfactants

Two new Ru(phen)(3)(2+)-based surfactants, Ru(phen)(2)(phenNHCO-C-11)(PF6)(2) and Ru(phen)(2)(phenNHCO-C-17)(PF6)(2), have been designed and synthesized, whose chemical structures were characterized by means of IR, H-1 NMR and MS. Also, electrochemistry and fluorescence of them are reported.

Fluorescence spectra of hemorrhagin III from the snake venom of Agkistrodon acutus

Hemorrhagin III (AaH III) was separated and purified from the crude snake venom of Agkistrodon acutus, and its molecule weight was determined accurately to be 23; 284.4 +/- 0.1 by LDI1700-MALDI-TOF-MS. Emission spectra of AaH III showed that Trp residues were located by a great degree in the hydrophobic area. Addition of SDS and guanidine-HCl led to change of the molecular conformation of AaH III, and caused the fluorescence quenching of Trp residues. The red-shifted emission band of AaH III after adding guanidine-HCl showed that Trp residues exposed in polar solvents. The effects of pH, EDTA and metal ions on the fluorescence spectra of AaH III were also investigated.

Synthesis, electrochemistry and fluorescence of four new Ru(phen)(3)(2+) derivatives

Four typical LB monolayer film materials, Ru(phen)(3)(2+) complexes with one ligand attached to different long chain alkyl amides, were designed and synthesized. Their chemical structures were identified by the techniques of FT-IR, H-1 NMR and ESI-MS. Also, UV-Vis, electrochemistry and fluorescence of these complexes are reported.

Atomic force microscopy imaging of molybdenum oxide film electrodeposited on a carbon electrode

Non-stoichiometric mixed-valent molybdenum(VI, V) oxide film was grown on carbon substrates by the electrodeposition method. Responses of the prepared molybdenum oxide thin films to potential and to different solution acidities were studied by cyclic voltammetry, and the corresponding morphological changes of the film were monitored by atomic force microscopy (AFM). AFM images of the molybdenum oxide film show that the characteristic domed structure on the film surface increased during the transition from the oxidized state to the reduced state without signification change in the KMS surface roughness value. Furthermore, AFM studies show that the solution acidity has great effect on the morphology of the films, and the films undergo a homogenizing process with increasing pH of the solutions. (C) 1999 Elsevier Science S.A. All rights reserved.

A new series of Ru(II)polypyridine surfactants: Synthesis, 2D NMR, fluorescence, electrochemistry and electrochemiluminescence

A new series of Ru(II) polypyridine surfactants, Ru(bpy)(2)[phenNH CO(CH2)(n)CH3](PF6)(2), where n is 10, 12, 14 or 16, has been prepared and characterized. The H-1-NMR spectra of these new Ru(II) complexes were attributed and discussed by the H-1-H-1 COSY method. The comparative analysis of IR spectra of these complexes and their responding free ligands has shown that there are intensive d --> pi* feedback interactions between central Ru(II) and their ligands. Their fluorescent, electrochemical and electrochemiluminescent behaviours are also reported.

Structural changes of TiO2 gel using Eu3+ ion as the fluorescence probe

Because of the extremely sensitivity to the local environment of the D-5(0) --> F-7(2) transition of Eu3+ ion, the fluorescence of Eu3+ ions was Studied by introducing Eu3+ ions to TiO2 gel by the sol-gel method, from which the structural changes of TiO2 gel were characterized. The results showed that the intensity of D-5(0) --> F-7(2) transition increased with the increasement of heat treatment temperature, which indicated the evaporation of molecular water and the completeness of the condensation reaction. Because of the quenching of the fluorescence induced by the cluster of Eu3+ ions, the addition of Al3+ ions greatly enhanced the emission intensity of Eu3+ ion.

Synthesis, electrochemistry, fluorescence and ECL of Ru (phen)(2) (dcbpy) (PF6)(2)

A new ECL-active species, Ru (phen)(2) (dcbpy) (PF6)(2), has been designed and synthesized. Its structure was confirmed by means of IR, ESI-MS and 2D NMR. Also, its properties of electrochemistry, fluorescence and ECL are reported, which have suggested a good hope of being used in electrochemiluminescent immunoassay and nucleic acid hybridization.

Preparation and characterization of ternary europium complex-doped thin sol-gel hybrid film by fluorescence spectroscopy

Ternary europium complex with dibenzoylmethane (DBM) and 1,10-phenanthroline (phen) was in-situ synthesized in thin SiO2/polyvinyl butyral (PVB) hybrid films by a two-step sol-gel process and characterized by;means of fluorescence spectroscopy. The luminescence spectra, fluorescence lifetimes and photostability were all investigated. The results showed that the hybrid films exhibited the characteristic emission bands of the Central rare earth Eu3+. In addition, Eu3+ presented longer fluorescence lifetime than in an ethanol solution and the complex had a higher photostability in the hybrid film than in the PVB film containing the corresponding pure complex.

Observations on photochemical fluorescence enhancement of the terbium(III) sparfloxacin system

Fluorescence of terbium(III) was sensitized when excited in the presence of sparfloxacin (SPFX) in the aqueous solution because a Tb(III)-SPFX complex was formed. The sensitized fluorescence was further enhanced when this system was exposed to 365 nm ultraviolet light. By the spectral properties and contrast experiments, it is proved that irradiation makes this system undergo photochemical reactions and a new terbium complex which is more favorable to the intramolecular energy transfer is formed. The mechanism of photochemical fluorescence enhancement of the Tb(III)-SPFX system is discussed and a new sensitive and selective photochemical fluorimetry for the determination of SPFX is established. Under the optimum conditions, the linear range is 1.0-50 x 10(-7) M for SPFX, the detection limit is 3.0 x 10(-9) M and the R.S.D. for 5.0 x 10(-7) M SPFX is 1.3% (n = 9). Without any pretreatment the recovery of SPFX in human urine was determined with satisfaction. (C) 1999 Elsevier Science B.V. All rights reserved.