Stephen J. Parus

Exciton reactions in ultrathin molecular wires, filaments and pores: A case study of kinetics and self-ordering in low dimensions

Abstract When are molecular wires thin enough to show one-dimensional exciton kinetics? Cylindrical naphthalene wires ( 5–5000 nm radius) show a definite one- to three-dimensional transition (about 25 nm for triplet excitons at 4 K; 40 nm at 77 K). Nuclear channel pore membranes (polycarbonate) serve as templates and calibrators. The triplet exciton migration (multiple hopping) length is 50–100 molecules. The closest neighbor distribution is used as an order criterion. Steady-state simulations of the reactions:A+A→0 and A+A→A in low-dimensional media give non-random reactant distributions, e.g. Wigner-like rather than Poissonian spacings in one dimension. Effectively, a dynamic, quasi-ordered superlattice of excitations is created (excitation grating with a 5 nm spacing). Experimental verification involves a new technique: excitation time modulation. Porous glass (Vycor) is shown to have an effective one-dimensional channel topology. Naphthalene powder and isotopic alloys also show nonrandom steady-state exciton distributions.

On-line capillary liquid chromatography tandem mass spectrometry on an ion trap/ reflectron time-of-flight mass spectrometer using the sequence tag database search approach for peptide sequencing and protein identification

Capillary high-performance liquid chromatography has been coupled on-line with an ion trap storage/reflectron time-of-flight mass spectrometer to perform tandem mass spectrometry for tryptic peptides. Selection and fragmentation of the precursor ions were performed in a three-dimensional ion trap, and the resulting fragment ions were pulsed out of the trap into a reflectron time-of-flight mass spectrometer for mass analysis. The stored waveform inverse Fourier transform waveform was applied to perform ion selection and an improved tickle voltage optimization scheme was used to generate collision-induced dissociation. Tandem mass spectra of various doubly charged tryptic peptides were investigated where a conspicuous y ion series over a certain mass range defined a partial amino acid sequence. The partial sequence was used to determine the identity of the peptide or even the protein by database search using the sequence tag approach. Several peptides from tryptic digests of horse heart myoglobin and bovine cytochrome c were selected for tandem mass spectrometry (MS/MS) where it was demonstrated that the proteins could be identified based on sequence tags derived from MS/MS spectra. This approach was also utilized to identify protein spots from a two-dimensional gel separation of a human esophageal adenocarcinoma cell line.

Comparison of the capabilities of liquid isoelectric focusing-one-dimensional nonporous silica reversed-phase liquid chromatography-electrospray ionization time-of-flight mass spectrometry and liquid isoelectric focusing-one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis mass mapping for the analysis of intact protein molecular masses

Nonporous silica reversed-phase HPLC coupled to electrospray ionization with on-line time-of-flight mass spectrometric detection (NPS-RP-HPLC-ESI-TOF-MS) is shown to be an effective liquid phase method for obtaining the molecular masses of proteins from pH fractionated cellular lysates where the method is capable of generating the same banding patterns typically observed using gel phase one-dimensional sodium dodecyl sulfatepolyacrylamide gel electrophoresis. The liquid-phase mass spectrometry-based method provides a mass accuracy of at least 150 ppm, with 4000 mass resolution and provides improved sensitivity as the protein molecular mass (MW) decreases. The liquid and gel phase methods are shown to be complementary in terms of their mass range but the liquid phase method has the advantage over the gel method in that the analysis times are 50 times shorter, the mass accuracy is 70 times better and the resolution is 130 times higher. The liquid phase method is shown to be more effective for detection of proteins below 40 kDa, while the gel phase separation can access many more proteins, including more hydrophobic proteins, at increasing MW.

Detection of Chlorinated Hydrocarbons in Aqueous Surfactant Solutions by Near-IR Raman Spectroscopy

Near-IR Raman spectroscopy is used to detect chlorinated hydrocarbons under surfactant-enhanced solubilization conditions. The Raman bands of tetrachloroethylene (PCE) and 1,2-dichlorobenzene (DCB) in micelle solutions could be observed in the presence of humic acid when a 784-nm diode laser was used. With 532- or 632.8-nm excitation, humic acid fluorescence obscured the Raman signals. For quantification, the integrated area of the carbon-chlorine stretch mode (PCE) or the phenyl ring-breathing mode (DCB) was used. Test results for samples with unknown concentrations based on linear calibration curves were in agreement with results from an accepted gas chromatography method. Detection limits were calculated to be 240 ppm for tetrachloroethylene and 500 ppm for 1,2-dichlorobenzene. Our study has shown the feasibility of this technique for field applications.