Tien-Sung Lin

Buckminsterfullerenol Free Radical Scavengers Reduce Excitotoxic and Apoptotic Death of Cultured Cortical Neurons

Novel anti-oxidants based on the buckminsterfullerene molecule were explored as neuroprotective agents in cortical cell cultures exposed to excitotoxic and apoptotic injuries. Two polyhydroxylated C60 derivatives, C60(OH)n, n = 12, and C60(OH)nOm, n = 18-20, m = 3-7 hemiketal groups, demonstrated excellent anti-oxidant capabilities when tested by electron paramagnetic spectroscopy with a spin-trapping agent and a hydroxyl radical-generating system. These water-soluble agents decreased excitotoxic neuronal death following brief exposure to NMDA (by 80%), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA; by 65%), or kainate (by 50%). Electrophysiology and tracer 45Ca(2+)-uptake studies verified that buckminsterfullerenois are not NMDA or AMPA/kainate receptor antagonists. Buckminsterfullerenols also reduced neuronal apoptosis induced by serum deprivation. These results support the idea that oxidative stress contributes to both excitotoxic and apoptotic neuronal death, and furthermore suggest that fullerenols represent a novel type of biological anti-oxidant compound.

Strong metal-support interactions between gold nanoparticles and ZnO nanorods in CO oxidation.

The catalytic performances of supported gold nanoparticles depend critically on the nature of support. Here, we report the first evidence of strong metal-support interactions (SMSI) between gold nanoparticles and ZnO nanorods based on results of structural and spectroscopic characterization. The catalyst shows encapsulation of gold nanoparticles by ZnO and the electron transfer between gold and the support. Detailed characterizations of the interaction between Au nanoparticles and ZnO were done with transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), electron paramagnetic resonance (EPR), and FTIR study of adsorbed CO. The significance of the SMSI effect is further investigated by probing the efficiency of CO oxidation over the Au/ZnO-nanorod. In contrast to the classical reductive SMSI in the TiO(2) supported group VIII metals which appears after high temperature reduction in H(2) with electron transfer from the support to metals, the oxidative SMSI in Au/ZnO-nanorod system gives oxygen-induced burial and electron transfer from gold to support. In CO oxidation, we found that the oxidative SMSI state is associated with positively charged gold nanoparticles with strong effect on its catalytic activity before and after encapsulation. The oxidative SMSI can be reversed by hydrogen treatment to induce AuZn alloy formation, de-encapsulation, and electron transfer from support to Au. Our discovery of the SMSI effects in Au/ZnO nanorods gives new understandings of the interaction between gold and support and provides new way to control the interaction between gold and the support as well as catalytic activity.

Magnetic and Electric Field Spectra of Organic Crystals: Optical Measurements of Zero‐Field Splittings

The theory of the Zeeman and Stark effects in molecular crystal exciton bands is presented. The development emphasizes the role of the intermolecular potential in determining the spin alignments in the crystal, and it is shown that the interactions V, and the projections of spins from one molecule onto those of another 〈Tα | Tβ〉, determine the crystal spin quantization in the absence of external fields through matrix elements of the type V 〈Tα | Tβ〉. A complete anisotropic Zeeman study in weak and strong fields is presented for the benzophenone crystal. It is shown that relatively low‐resolution optical studies can be used to determine zero‐field splitting parameters to about 5% accuracy. The higher resolution studies have led to the assignments, and relative ordering of the twelve k = 0 exciton components of the 3nπ* state of benzophenone crystals. These results are confirmed by Stark and Stark–Zeeman experiments which demonstrate the applicability of the theory outlined. The final best set of molecular ...

Electron spin echoes of a photoexcited triplet: Pentacene in p‐terphenyl crystals

Electron spin echo observations of the photoexcited triplet state of 0.1 mol % pentacene‐h14 and ‐d14 in p‐terphenyl crystals at room temperature are presented. Theory is presented for calculation of the echo envelope modulations for an S = 1, I = 1/2 spin system including zero field splittings in the high field limit. Echo envelope modulations due to proton and deuteron hyperfine interactions in the pentacene molecule have been observed. The echo decay data are used to calculate triplet state decay parameters.

High dynamic nuclear polarization at room temperature

Abstract The highly polarized photo-excited triplet state of pentacene in a naphthalene crystal is used for pulsed dynamic nuclear polarization at room temperature. Thus far an enhancement of 5500 of the naphthalene proton polarization has been reached. For this purpose, a newly developed technique, the integrated solid effect, performed while obeying the Hartmann-Hahn condition, is used to transfer the triplet polarization efficiently to the nuclear spin system.

Detection of Free Radicals by Microdialysis/Spin Trapping Epr Following Focal Cerebral Ischemia-Reperfusion and a Cautionary Note on the Stability of 5,5-Dimethyl-1-Pyrroline N-Oxide (DMPO)

We have examined free radical production in a rat model of focal cerebral ischemia using microdialysis coupled with EPR analysis. A microdialysis probe was inserted 2 mm into the cerebral cortex, supplied by the right middle cerebral artery (MCA), and after a 2-hour washout period with artificial cerebral spinal fluid (ACSF), the perfusate solution was changed to ACSF containing the spin trapping agent, 5,5-dimethyl-1-pyrroline N-oxide (DMPO). No free radicals were detected by DMPO during the pre-ischemia period. Both common carotid arteries and the right MCA were then ligated for 90 minutes. Microdialysate collected every 15 min during the ischemic period demonstrated predominantly superoxide or peroxyl radical production. After release of the occlusive sutures, hydroxyl radical became apparent initially, then thiyl and carbon centered radicals appeared later in samples collected every 15 min for two hours following cortical reperfusion. Careful studies on the purification and stability of DMPO solution were performed to circumvent artifacts and spurious signals.

Cytochrome c covalently immobilized on mesoporous silicas as a peroxidase: Orientation effect

Cytochrome c (cyt c), a heme protein with positive electric charge and global dimensions of 2.5 × 2.5 × 3.7 nm, is immobilized by covalent bonding in the nanochannels and on the surface of IBN4 (pore size = 5.3–7.1 nm) mesoporous silicas. The composite material behaves as a peroxidase in the oxidation of organic molecules in the presence of hydrogen peroxide. The surface of IBN4 was first modified with three different linkers, glutaric anhydride (GAC), glutaraldehyde (GAH) and succinimido-3-maleimidopropanoate (SMP), to facilitate the binding (bioconjugation) with cyt c. Different linkers expose the catalytic active site (Fe-heme) to different environments, which allows us to examine the orientation effect imposed by the binding linker. Molecular modeling further allows us to assess the orientation effect on the catalytic activity arising from the distribution of electric charges of cyt c immobilized in different surface-modified nanochannels. The accessibility of the Fe active center in immobilized cyt c is found to be in the following order: IBN4-N-SMP-cyt c > IBN4-N-GAH-cyt c > IBN4-N-GAC-cyt c, which is correlated to the measured trend of the initial specific peroxidase-like activities of immobilized cyt c in three different modified surfaces towards the oxidation of 4-aminoantipyrine. The surface-modified nanochannels of mesoporous silica provide the confining spaces that could prevent cyt c from protein unfolding and orient the active site in a favorable location in the pores to facilitate its activity. However, there is much more structural decay after hydrothermal treatment and the activities diminish accordingly: the IBN4-N-GAH-cyt c sample lost most of its activity, the IBN4-N-SMP-cyt c lost its activity due to less protection of the active center of Fe-heme, and the IBN4-N-GAC-cyt c retained good activity. These temperature effects are further confirmed in the UV-Vis spectra and EPR studies. Cyt c immobilized on functionalized IBN4 surfaces exists in high spin state, as inferred from EPR and UV-Vis studies, which differs from the primarily low spin state of native cyt c. The high spin state arises from the replacement of Met-80 ligands of heme Fe(III) by water or silanol groups on the silica surface, which could open up the heme groove for easy access of oxidants to the iron center and facilitate the catalytic activity. Finally, we apply the covalently immobilized cyt c in the oxidation of a representative polycyclic aromatic hydrocarbon (PAH)—pyrene. The trend in activity can be understood from the design principle we learned in this work.

Optical and Magnetic Field Studies of the Lowest Triplet State of the Pyrazine Crystal

The electronic absorption spectrum of pyrazine crystals has been studied using single crystals at 4.2°K and polarized light. The origin shows three lines that are interpreted as (i) a B3u+, k = 0, factor group state at 26247.6 cm−1, (ii) two lines at 26254.7 and 26253.4 cm−1 corresponding to a split B2u−, k = 0, factor group state. These interpretations are made on the basis of high‐field Zeeman effect studies. A low‐field Zeeman study has revealed the ordering of magnetic substates in each factor group level at Tc < Tb < Ta. This yields the order Ty < Tz < Tx for the free molecule. The zero‐field splitting is approximately + 0.3 cm−1 (D = − 32Y). A discussion of the relationship between such spin‐state ordering and the electronic structure of pyrazine in a 3n+π4*(nπbb) state is also presented.

Zero-field magnetic resonance of the photo-excited triplet state of pentacene at room temperature

The pulsed EPR free induction decay (FID) signals of the photo-excited pentacene triplet state are reported for three mixed crystals at room temperature: pentacene-h14 in p-terphenyl, pentacene-h14 in benzoic acid, and pentacene-d14 in p-terphenyl. The recorded FID signals have relatively long decay times of about four microseconds, presumably due to the reduced hyperfine interactions in the zero magnetic field. The time domain FID signals transform to spectral components typically narrower than 500 kHz, allowing us to determine the pentacene triplet zero field splitting parameters to better accuracy than previously reported. Further, a new experimental technique using the high speed magnetic field jumping capability enables us to examine the anisotropic hyperfine and quadrupole interactions.

Transient oscillations in pulsed dynamic nuclear polarization

Abstract We have measured the time evolution of the cross-polarization processes between the proton spins of a naphthalene host crystal and the photo-excited triplet electron spins of pentacene guest molecules in a pulsed DNP experiment. The observed oscillatory behaviour is explained as arising from dominant dipolar interactions between the nuclear and electron spins.