Department of Chemistry

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Physical interaction of nitrogen with Pyrex, stainless-steel, and nickel at very low-pressure
Outlaw, R. A.; Brock, F. J.; Wightman, James P. (American Institute of Physics, 1974)
The physical adsorption of nitrogen on the surfaces of Pyrex, 347 stainless steel, and polycrystallinenickel was investigated over the pressure range 1×10−12–3×10−7 Torr and for the temperatures 77.4 and 87.4 °K. The metal surfaces were prepared by vacuum firing, by chemical cleaning, and, following bakeout, by electron impact desorption (EID). Work function measurements were used to indicate changes in the surface condition following electron bombardment, and a mass spectrometer was used to monitor gas composition. The isotherms revealed that the stainless surface was very heterogeneous and that the Pyrex surface area had a roughness factor of 1.7. Nitrogen isotherms were also taken on the metal surfaces after they had been exposed to oxygen. Very little change in physical adsorption on the nickel was detected, presumably because the chemisorbed oxygen was incorporated into the bulk. The chemical adsorption of N2 on nickel at room temperature and below was not observed.
An improved laser-schlieren system for measurement of shock-wave velocity
Bander, J. A.; Sanzone, G. (AIP Publishing, 1974-07)
An improved laser_schlieren system for the measurement of shock_wave velocities has been developed which employs a single detector.Calibration of multiple detectors has been obviated. The system has been shown to yield, in addition to the shock_wave velocity, additional information on the arrival time of the contact surface. Shock_tube performance is compared to the predictions of Mirels' theories.
High-resolution time-of-flight mass spectrometry impulse-field focusing pulse generators
Miller, R. L.; Browder, J. A.; Sanzone, G. (AIP Publishing, 1986-08)
Experiments have shown that the unit mass resolution of conventional Wiley-McLaren time_of_flight (TOF)mass spectrometers can be significantly improved using the technique of impulse_field focusing (IFF). Details of the circuitry used to test the IFF theory are presented. Generators of electrical pulses with nanosecond rise times and 100_V amplitudes are described.
Surface-analysis of gold containing polyimide films
Madeleine, Dennis Gerard; Spillane, S. A.; Taylor, Larry T. (American Institute of Physics, 1987-05)
Polyimide films with metallic surfaces were produced by thermal treatment of solutions containing HAuCl4⋅3H2O, hydrogen tetrachloroaurate trihydrate, and either Ciba–Geigy XU 218, poly[5(6)‐amino‐1‐(4’ phenyl)‐1,3,3 trimethylindane‐3,3’,4,4’‐benzophenonetetracarboxylimide] or BTDA‐ODA, poly [ p, p’‐oxybis (phenylene)‐3,3’,4,4’‐benzophenonetetracarboxylimide]. Scanning electron microscopy indicated that 0.1‐μ particles covered a large portion of the air side surface; whereas, 10‐μ particles covered the glass side surface of these films.Auger electron spectroscopy and x‐ray photoelectron spectroscopy(XPS) indicated that the particles were gold in the metallic state. Model imide compounds were synthesized and used to evaluate the XPS spectra of both unmodified and gold containing films.Surfaceanalysis data suggested that only a small amount of gold was located within the XPS sampling depth and that the observed gold particles resided underneath a polyimide overlayer. The discrete metal particles had an unexpected influence on the photoelectron spectra of the polyimide and the influence was dependent on particle size. A schematic model of the multilayered modified filmsurface was developed and the model further probed by electron flood gun and metal vapor deposition studies.
Raman-scattering and optical studies of argon-etched GaAs surfaces
Feng, G. F.; Zallen, Richard H.; Epp, June Miriam; Dillard, John G. (American Physical Society, 1991-04)
We have studied the structual damage in low-energy argon-ion-bombarded (ion-etched) GaAs using Raman scattering and ultraviolet reflectivity. When combined with post-bombardment sequential chemical etching, the Raman results reveal a graded depth profile of the damage layer, with a nearly linear damage dropoff with depth. The total damage-layer thickness is about 600 angstrom for high-fluence bombardment with 3.89-keV Ar+ ions. The spectral effects produced by argon etching are very different from those produced by high-energy ion implantation. The longitudinal-optic Raman line seen for argon-etched GaAs is not shifted and broadened as in ion-implanted GaAs. More striking are the results of the reflectivity measurements. For argon-etched GaAs, the electronic interband peaks are both broadened and strongly red shifted relative to the crystal peaks; for ion-implanted GaAs, only the broadening occurs. Distinct nanocrystals, which account for the effects seen in ion-implanted GaAs, are evidently absent in argon-etched GaAs. Instead, the damage layer caused by argon etching appears to be characterized by a very high density of point defects, which previous work suggests may be arsenic vacancies.
Method for the conversion of cephalomannine to taxol and for the preparation of n-acyl analogs of taxol
(United States Patent and Trademark Office, 1995-11-28)
The natural product cephalomannine can be converted to the important anticancer natural product taxol by a simple process involving the steps of dihydroxylation to give cephalomannine-diols, diol cleavage, benzoylation at the 2'-position and reaction with a 1,2-diamine. The same process when applied to mixtures of taxol and cephalomannine makes it possible to separate taxol from cephalomannine-diols by simple flash-chromatography after the dihydroxylation step. If the benzoylation step is avoided in the above sequence of conversions, the process leads to the free amine (N-debenzoyltaxol). In addition, the selection of an acylating reagent other than that with the benzoyl group for acylation of the free amine (N-debenzoyltaxol), allows the preparation of taxol analogs with other N-acyl substituents.
Synthesis of sphingosines
(United States Patent and Trademark Office, 1996-01-30)
Provided by the present invention is a process for the biocatalytic synthesis of optically pure sphingosines from achiral starting material. The stereoisomers of sphingosine are prepared from chiral arene diols using stereospecific reaction techniques to obtain the desired sphingosine or derivative thereof.
Synthesis of sphingosines
(United States Patent and Trademark Office, 1996-01-30)
Provided by the present invention is a process for the biocatalytic synthesis of optically pure sphingosines from achiral starting material. The stereoisomers of sphingosine are prepared from chiral arene diols using stereospecific reaction techniques to obtain the desired sphingosine or derivative thereof.
Aryl ethynyl phthalic anhydrides and polymers with terminal or pendant amines prepared with aryl ethynyl phthalic anhydrides
(United States Patent and Trademark Office, 1996-02-20)
Arylethynyl phthalic anhydrides have been synthesized and shown to have particular application as endcappers or pendant groups in high performance/high temperature thermosets which include amine terminal or amine pendant groups.
Metallic material with low melting temperature
(United States Patent and Trademark Office, 1996-04-16)
A gallium-indium-zinc-copper metallic material has been found to exhibit many of the advantageous properties of mercury, such as electrical conductivity, fluidity, and high vaporization temperature. The metallic material is formulated by combining individual components in the presence of aqueous base, isolating the metallic phase, and heating the metallic combination. The metallic material is formulated to have sufficient quantities of each of the individual components such that the metallic material has a solidification temperature below 0.degree. C.
Elements, 1998
(Virginia Tech, 1998)
This is the alumni magazine of the Department of Chemistry at Virginia Tech. Inside: An up-close look at alumnus Gene Weedon and his role with chemistry’s new AlliedSignal Polymer Characterization Lab. Plus: Learn about the department’s plans to expand and meet the plastic man with a heart of gold.
Enhanced nonlinear optical response of an endohedral metallofullerene through metal-to-cage charge transfer
Heflin, James R.; Marciu, D.; Figura, C.; Wang, S.; Burbank, P.; Stevenson, Steven A.; Dom, H. C. (AIP Publishing, 1998-06)
A new mechanism for increasing the third-order nonlinear optical susceptibility, X-(3), is described for endohedral metallofullerenes. A two to three orders of magnitude increase in the nonlinear response is reported for degenerate four-wave mixing experiments conducted with solutions of Er-2@C-82 (isomer III) relative to empty-cage fullerenes. A value of - 8.7x 10(-32) esu is found for the molecular susceptibility, gamma(xyyx), of Er-2@C-82 compared to previously reported values of gamma(xxxx) = 3 x 10(-34) esu and gamma(xyyx) = 4 x 10(-35) esu for C-60. The results confirm the importance of the metal-to-cage charge-transfer mechanism for enhancing the nonlinear optical response in endohedral metallofullerenes. (C) 1998 American Institute of Physics.
Elements, 1999
(Virginia Tech, 1999)
This is the alumni magazine of the Department of Chemistry at Virginia Tech. Inside: Sticking with Louis Sharpe as he starts to slow down. Plus: The new learning center expands and a brain researcher probes neurological disorders.
Dependence of fluorescence lifetimes of Y2O3 : Eu3+ nanoparticles on the surrounding medium
Meltzer, R. S.; Feofilov, S. P.; Tissue, B.; Yuan, H. B. (American Physical Society, 1999-11)
The radiative lifetime, tau(R), of the D-5(0) metastable excited state of Eu3+ ions in nanocrystalline monoclinic Y2O3 samples is about four times longer than that in the micron size powder of the same material. The Eu3+ radiative lifetime was measured in nanocrystals surrounded with air as well as those immersed in different liquids. It is shown that the radiative lifetime changes with the index of refraction of the immersion medium and provides a unique test of the standard formula relating tau(R) and the oscillator strength. The magnitude of the effect is determined by the "filling factor" (the fraction of the sample volume occupied by nanocrystals) which can therefore be determined. [S0163-1829(99)51144-2].
Elements, 2000
(Virginia Tech, 2000)
This is the alumni magazine of the Department of Chemistry at Virginia Tech. Inside: Gary Cook reveals the places a chemist can go. Plus: Harry Dorn helps create a new molecule family: a wheel within a ball.
Elements, 2001
(Virginia Tech, 2001)
This is the alumni magazine of the Department of Chemistry at Virginia Tech. Inside: Joseph M. DeSimone proves that green chemistry can provide a clean environment.
Evidence for long-range interactions between rare-earth impurity ions in nanocrystals embedded in amorphous matrices with the two-level systems of the matrix
Meltzer, R. S.; Yen, W. M.; Zheng, H. R.; Feofilov, S. P.; Dejneka, M. J.; Tissue, B. M.; Yuan, H. B. (American Physical Society, 2001-09)
The low-temperature homogeneous broadening of the electronic transitions of Eu3+ and Pr3+ rare-earth impurity ions in Y2O3 and LaF3 nanocrystals embedded into amorphous materials (polymer and oxyfluoride glass ceramics) was studied with hole-burning and fluorescence line narrowing techniques. It is-shown that the homogeneous linewidth is determined by the interaction of the impurity ions contained in the nanocrystals with the two-level systems (TLS's) of the surrounding glass matrix. A comparison of the experiments with a calculation provides direct evidence for the long-range nature of the interaction with the TLS's.
Low-resistance films of polyimides with impregnated copper sulfide
Rowe, R. V. A.; Kunita, M. H.; Porto, M. F.; Muniz, E. C.; Rubira, A. F.; Nery, R. C.; Radovanovic, E.; Taylor, Larry T.; Nazem, N. (Cambridge University Press, 2001-11)
Surface modification of polyimides has been used to obtain better interaction with an inorganic material. Copper sulfide incorporation onto the surface of commercial Kapton (R) polyimide showed that treatment with base was necessary for adherence of the copper sulfide to the polymeric matrix. The optimized conditions for composite preparation, obtained by response surface methodology, was pH 1.4 at 80 degreesC for 3.67 h. Using these conditions, we obtained electrical resistance as low as 1.0 ohm for CuS\Kapton (R) composites. These optimized conditions were used to prepare other low-resistance polyimide composites. The resulting composites were analyzed by photoelectron spectroscopy. The presence of S(2p) and Cu(2p) peaks demonstrated the incorporation of copper sulfide onto the polyimide surface. Scanning electron microphotographs and the images from atomic force microscopy showed a homogeneous CuS distribution in all composites.
Measurement of 3-alkyl-2-methoxypyrazine by headspace solid-phase microextraction in spiked model wines
Hartmann, Peter J.; McNair, Harold M.; Zoecklein, Bruce W. (American Society for Enology and Viticulture, 2002)
The effect of wine matrix ingredients and conditions on the headspace sampling of 3-alkyl-2-methoxypyrazines was investigated with solid-phase microextraction (SPME) and capillary gas chromatography, using a nitrogen phosphorus detector. Changes in the recovery of 3-ethyl-, isopropyl-, sec-butyl-, and isobutyl-2-methoxypyrazines from the static headspace of synthetic wine matrices spiked with 5 mug/L of each analyte were investigated and reported as a function of SPME fiber type, extraction time, and temperature. The influence of pH, ethanol, phenolics, and oak was studied. Divinylbenzene/carboxen/polyclimethylsiloxane (PDMS) SPME fibers at an extraction temperature of 50degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in the highest analyte recoveries. Although PDMS (100 mum) SPME fibers at an extraction temperature of 35degreesC for 30 minutes with 30% (w/v) added sodium chloride resulted in lower analyte recoveries, the fiber remained functional for 50 to 75 analyses after other coatings deteriorated. Changing the sample ethanol concentration from 0 to 20% (v/v) resulted in an exponential decrease in the recovered analytes. Below pH 2, there was extensive loss of the analytes in the headspace. No measurable impact on alkyl-methoxypyrazine headspace concentrations was observed with exposures to selected phenolics and to oak.
Elements, Spring 2002
(Virginia Tech, 2002)
This is the alumni magazine of the Department of Chemistry at Virginia Tech. Inside: Mary Gum: Life and work, it’s all about fun.

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