The microwave spectrum and structure of chloryl fluoride

The microwave spectra of three isotopic species of chloryl fluoride, FClO₂, in its ground vibrational state, have been measured in the frequency region 8–37 GHz. The spectra have yielded values for the rotational constants, centrifugal distortion constants, and chlorine nuclear quadrupole coupling constants, as well as the molecular dipole moment, 1.722 ± 0.03 D. The molecule has been shown to have C_s symmetry, and a pyramidal configuration, with the chlorine atom at the apex of the pyramid. The following internuclear parameters were obtained:r(Cl?F)1.697±0.003 A r(Cl?F)=1.418±0.002AThe structural parameters, quadrupole coupling constants, dipole moment and force field are explained in terms of a bonding scheme in which a fluorine 2p atomic orbital overlaps with the highest occupied orbital of ClO₂; there is considerable evidence for withdrawal of electron density from this singly occupied antibonding orbital of ClO₂ toward the fluorine atom.     

Gas chromatographic analysis of triethylenethiophosphoramide and triethylenephosphoramide in biological specimens

Comprehensive pharmacokinetic studies could realise a greater potential for the antitumour agent triethylenethiophosphoramide (ThioTEPA), and these would be aided by the development of a selective and sensitive assay. After extraction of ThioTEPA and its metabolite, triethylenephosphoramide (TEPA), from plasma using Sep-Pak C18 cartridges, the compounds were separated by capillary chromatography, detected using a nitrogen detector and quantified by reference to an internal standard, hexaethylphosphoramide. The limits of sensitivity were 1-5 ng/ml. Analytical recoveries were 74 and 95%, for TEPA and ThioTEPA, respectively, in the therapeutic range. At similar concentrations, extents of protein binding, determined by ultrafiltration, were not significant. Preliminary investigations of the elimination of ThioTEPA show that drug loss occurs more quickly in mice than in humans and in both species the metabolite is extensively recycled.     

State tomography of capacitively shunted phase qubits with high fidelity

We introduce a new design concept for superconducting phase quantum bits (qubits) in which we explicitly separate the capacitive element from the Josephson tunnel junction for improved qubit performance. The number of two-level systems that couple to the qubit is thereby reduced by an order of magnitude and the measurement fidelity improves to 90%. This improved design enables the first demonstration of quantum state tomography with superconducting qubits using single-shot measurements.     

A virtually nondestructive EPR technique accounting for diagnostic X-rays

We have implemented the method proposed by Aldrich and Pass (Aldrich, J.E., Pass, B., 1988. Determining radiation exposure from nuclear accidents and atomic tests using dental enamel. Health Phys. 54, 469–471.) to measure both the interior and exterior portions of a tooth in order to determine the diagnostic X-ray component of the total dose in the teeth. This was done using a modified nondestructive approach of Haskell et al. (Haskell, E.H., Hayes, R.B., Romanyukha, A.A., Kenner, G.H., 2000. Preliminary report on the development of a virtually non-destructive additive dose technique for EPR dosimetry Appl. Radiat Isot. 52, 1065–1070.) given in Hayes et al. ( Hayes, R.B., Haskell, E.H., Barrus, J.K., Kenner, G.H., Romanyukha, A.A., 2000. Accurate EPR radiosensitivity calibration using small sample masses. Nucl. Instr. Meth. A. 441, 535–550). Here only 5% of the total tooth enamel sample from an enamel crown was used for individual sample sensitivity calibration. A cavity response correction for the low mass samples was also used ( Hayes et al., 2000). The teeth were American wisdom teeth having unknown doses applied by the IAEA in the range of 0 to 1 Gy as part of the second international intercomparison ( Wieser, A., Mehta, K., Amira, S., Aragno, S., Bercea, S., Brik, A., Bugai, A., Callens, F., Chumak, V., Ciesielski, B., Debuyst, R., Dubovsky, S., Duliu, O., Fattibene, P., Haskell, E., Hayes, R., Ignatiev, E., Ivannikov, A., Kirillov, V., Kleschenko, E., Nakamura, N., Nathe, M., Nowak, J., Onori, S., Pass, B., Pivovarov, S., Romanyukha, A., Scherbina, O., Shames, A., Sholom, S., Skvortsov, V., Stepanenko, V., Tikounov, D., Toyoda, S., 2000. The 2nd international intercomparison on EPR tooth dosimetry. Radiat. Meas. in press). Final dose reconstruction estimates of the IAEA applied values showed a very high correlation (R=0.996). The approximate excess dose measured on the outside of the teeth relative to the inside was 49±35 mGy which is attributed to the diagnostic X-ray exposure given to the America wisdom teeth prior to extraction. The method used showed only a small dependence on the accelerating voltage of the X-ray source.     

Magnetism in SQUIDs at millikelvin temperatures

We have characterized the temperature dependence of the flux threading dc SQUIDs cooled to millikelvin temperatures. The flux increases as 1/T as temperature is lowered; moreover, the flux change is proportional to the density of trapped vortices. The data are compatible with the thermal polarization of surface spins in the trapped fields of the vortices. In the absence of trapped flux, we observe evidence of spin-glass freezing at low temperature. These results suggest an explanation for the universal 1/f flux noise in SQUIDs and superconducting qubits.     

(2E)‐N‐(2‐Iodo‐4,6‐dimethylphenyl)‐2‐methylbut‐2‐enamide

The title compound, C₁₄H₁₈INO, crystallizes as +sc/+sp/+sc 2‐iodoanilide molecules (and racemic opposites) and shows significant intermolecular I...O interactions in the solid state, forming dimeric pairs about centres of symmetry. Under asymmetric Heck conditions, the S enantiomer of the dihydroindol‐2‐one was obtained using (R)‐(+)‐2,2′‐bis(diphenylphosphino)‐1,1′‐binaphthyl [(R)‐BINAP], suggesting a mechanism that proceeds by oxidative addition to give the title (P) enantiomer of the compound and pro‐S coordination of the Re face of the alkene in a conformation similar to that defined crystallographically, except that rotation about the C—C bond of the butenyl group is required.     

Conformational equilibrium of cytochrome P450 BM-3 complexed with N-palmitoylglycine: a replica exchange molecular dynamics study

UV-vis absorbance measurements and associated studies of cytochrome P450 BM-3 in complex with N-palmitoylglycine (NPG) indicate that a conformational change occurs in the active site of the complex where the terminal atoms of the ligand move from a site distant from the heme iron, as seen in the low temperature crystal structure to a site proximal to the heme iron at biological temperatures. We employ replica exchange molecular dynamics simulations to study this conformational change. The population of the proximal state is found to increase with temperature in agreement with UV-vis absorbance and NMR measurements. In addition to the conformations characterized by X-ray crystallography and computer modeling, this study shows that a new conformational state is significantly populated at room temperature. The observed increase in the population of conformations where the terminal atoms of NPG are proximal to the heme iron with increasing temperature indicates that the proximal state is stabilized by conformational entropy. A proposal for the origin of this entropic stabilization is provided on the basis of the structure of the newly identified state. We use the temperature weighted histogram (T-WHAM) method to characterize the transition state regions of the conformational ensemble and propose a mechanism of interconversion between these low free energy conformational states.     

Three-dimensional magnetic resonance spectroscopic imaging of histologically confirmed brain tumors

The goal of this study was to determine whether presurgical metabolite levels measured by 3D MR Spectroscopic Imaging (MRSI) can accurately detect viable cancer within human brain tumor masses. A total of 31 patients (33 exams, 39 pathology correlations) with brain tumors were studied prior to surgical biopsy and/or resection. The 3D MRSI was obtained with a spatial resolution of 0.2 to 1 cc throughout the majority of the mass and adjacent brain tissue using PRESS-CSI localization. Levels of choline, creatine and NAA were estimated from the locations of the resected tissue and normalized to normal appearing brain tissue. The data were correlated with subsequent histologic analysis of the biopsy tissue samples. Although there were large variations in the metabolite ratios, all regions of confirmed cancer demonstrated significant choline levels and a mean choline/NAA ratio of 5.84 + 2.58 with the lowest value being 1.3. This lowest value is greater than 4 standard deviations above the mean (0.52 +/- 0.13) found in 8 normal volunteers. The choline signal intensities in confirmed cancers were significantly elevated compared to normal appearing brain tissue with a mean ratio of 1.71 +/- 0.69. Spectra with no significant metabolite levels were observed in the non-enhancing necrotic core of the tumor masses. The results of this study indicate that 3D MRSI of brain tumors can detect abnormal metabolite levels in regions of viable cancer and grades and can differentiate cancer from necrosis and/or normal brain tissue.