We have studied fragmentation processes of the gas-phase tetrahydrofuran (THF) molecules in collisions with the H(+), C(+), and O(+) cations. The collision energies have been varied between 25 and 1000 eV and thus covered a velocity range from 10 to 440 km/s. The following excited neutral fragments of THF have been observed: the atomic hydrogen H(n), n = 4-9, carbon atoms in the 2p3s (1)P1, 2p4p (1)D2, and 2p4p (3)P states and vibrationally and rotationally excited diatomic CH fragments in the A(2)Δ and B(2)Σ(-) states. Fragmentation yields of these excited fragments have been measured as functions of the projectile energy (velocity). Our results show that the fragmentation mechanism depends on the projectile cations and is dominated by electron transfer from tetrahydrofuran molecules to cations. It has been additionally hypothesized that in the C(+)+THF collisions a [C-C4H8O](+) complex is formed prior to dissociation. The possible reaction channels involved in fragmentation of THF under the H(+), C(+), and O(+) cations impact are also discussed.

The local environment of the chromium ion in calcined CrAPSO-11, which may involve framework sites, is compared with the Cr ion environment in solid-state ion-exchanged (S)Cr−SAPO-11 which involves ion exchange into nonframework sites at high temperature. Powder X-ray diffraction confirms that CrAPSO-11 has the SAPO-11 framework and is highly crystalline. The 27Al and 29Si magic-angle-spinning nuclear magnetic resonance spectra are similar to those of corresponding SAPO-11 showing only one type of tetrahedral atom. As-synthesized CrAPSO-11 shows an ESR spectrum assignable to Cr(III), but on calcination this converts to Cr(V). (S)Cr−SAPO-11 forms Cr(V) directly since solid-state ion exchange occurs at high temperature. The UV−vis spectrum of calcined, hydrated CrAPSO-11 is assigned to Cr(V), and after dehydration the coordination for Cr(V) seems consistent with tetrahedral as expected for a framework site. Electron spin resonance (ESR) of calcined, hydrated CrAPSO-11 shows Cr(V) which is consistent with square-pyramidal coordination which gradually converts to Cr(V) in distorted tetrahedral coordination upon dehydration by heating in vacuum. The ESR spectrum of ion-exchanged (S)Cr−SAPO-11 shows Cr(V), but it does not convert to tetrahedral coordination upon heating in vacuum. Hydrogen reduction shows that Cr(V) in (S)Cr−SAPO-11 can be reduced to a several hundred gauss broad ESR signal assignable to Cr(III). Reduction by H2 of calcined CrAPSO-11 does not produce Cr(III) observable by ESR. The interactions between Cr(V) in calcined CrAPSO-11 and (S)Cr−SAPO-11 with D2O, CH3OD, CD3OH, ND3, and pyridine adsorbates are also compared. Differences in the kinetics of absorbate coordination between calcined CrAPSO-11 and (S)Cr−APSO-11 are observed. All these differences support different Cr(V) sites in these two materials. 31P electron spin echo modulation of CrAPSO-11 shows that Cr(V) is surrounded by about 11−12 phosphorus nuclei at 0.58 nm, which is consistent with Cr(V) in CrAPSO-11 being in a framework phosphorus position.

Electron paramagnetic resonance imaging (EPRI) is a powerful technique that enables spatial mapping of free radicals or other paramagnetic compounds; however, it does not in itself provide anatomic visualization of the body. Proton magnetic resonance imaging (MRI) is well suited to provide anatomical visualization. A hybrid EPR/NMR coimaging instrument was constructed that utilizes the complementary capabilities of both techniques, superimposing EPR and proton-MR images to provide the distribution of paramagnetic species in the body. A common magnet and field gradient system is utilized along with a dual EPR and proton-NMR resonator assembly, enabling coimaging without the need to move the sample. EPRI is performed at ϳ1.2 GHz/ ϳ40 mT and proton MRI is performed at 16.18 MHz/ϳ380 mT; hence the method is suitable for whole-body coimaging of living mice. The gradient system used is calibrated and controlled in such a manner that the spatial geometry of the two acquired images is matched, enabling their superposition without additional postprocessing or marker registration. The performance of the system was tested in a series of phantoms and in vivo applications by mapping the location of a paramagnetic probe in the gastrointestinal ( Key words: proton MRI; EPR imaging; free radicals, oxygen; image coregistration; in vivo NMR; in vivo EPRThe techniques of electron paramagnetic resonance (EPR) spectroscopy and imaging (EPRI) have been widely used to measure and map the distribution of paramagnetic materials and free radicals in biological systems, including ex vivo tissues and in vivo living animals (1-8). These techniques provide unique information that enables measurement and imaging of the processes of free radical metabolism, tissue oxygenation, and nitric oxide generation in normal physiology and disease (9 -17). While EPRI provides specific mapping of the location of a given paramagnetic species, this is often not sufficient in itself to enable anatomic mapping of the precise organ-specific location of the paramagnetic probe in the body of a living animal. On the other hand, proton magnetic resonance imaging (MRI) has been established as a powerful diagnostic imaging technique capable of obtaining high-resolution images of the anatomical structure of humans and animals (18 -22). While proton MRI is a powerful technique for imaging biological systems based on their high content of water, it can not directly localize low, submillimolar levels of free radicals.Several noninvasive MRI-based methods for detection and mapping of paramagnetic substances in vivo are under development. Both contrast-enhanced MRI (15,16) and proton electron double resonance imaging (PEDRI) (23,24) utilize proton MRI-based detection and therefore automatically provide coregistration of free radical distribution with anatomical structure. The availability of anatomic information, as well as superior spatial and temporal resolution, make MRI-based techniques more efficient in these aspects compared to direct EPRI methods. However, since t...

Background: Ovarian carcinoma is the leading cause of mortality among gynecological cancers in the world. The high mortality rate is associated with lack of early diagnosis and development of drug resistance. The antitumor efficacy and mechanism of NCX-4040, a nitric oxide-releasing aspirin derivative, against ovarian cancer is studied.