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Notes: Phosphorus is one of several dopants that electronically compensate the native deep donor responsible for the yellow coloration observed in bismuth silicon oxide (BSO). Low-temperature optical absorption measurements of a series of Czochralski-grown P-doped BSO crystals show that ∼0.1–0.15 at. % P is needed in the sample to fully remove the yellow coloration. The absorption cutoff in the fully compensated P-doped sample was at 3.2 eV while compensated Al- and Ga-doped samples cutoff at 3.35 eV. Excitation at 10–15 K with near band-edge light produces photochromic absorption bands. In the lightly-doped (partially bleached) samples these bands were identical to those observed in undoped BSO. In the fully bleached sample a new spectrum was observed. Its major contribution was a band centered near 1.8 eV with a weaker absorption in the blue-green. By comparison with the spectra observed in undoped and in Al-doped material before and after photoexcitation it is believed that the 1.8 eV band is due to the [PO4]− center and that the broad 2.45 eV band observed in Al- and Ga-doped BSO is due to the [BiO4]0 center. © 1995 American Institute of Physics.

Notes: Objective To investigate the status of the fetal renin-angiotensin system (RAS) in pregnancies complicated by severe intrauterine growth retardation (IUGR), and its possible relationship to elevated fetoplacental vascular resistance as indicated by abnormal umbilical artery Doppler flow velocity waveforms (FVW).Design Prospective survey of pregnancies falling into predefined categories and presenting at the Queen Mothers Hospital, Glasgow, over the study period.Subjects Effects of mode of delivery and gestational age were investigated using uncomplicated term pregnancies delivered vaginally (SVD group, n= 15) or by elective caesarean section (ECS group, n= 9), and normal pregnancies with spontaneous preterm onset of labour (PREM group, n= 6; normal birthweight for gestational age (31 weeks)). These groups were used as controls for the 13 IUGR cases delivered preterm (31 weeks) by caesarean section in the fetal interest.Main outcomes measures Umbilical artery FVW, birthweight, cord venous angiotensin II concentration ([cv ANG II]), fetoplacental vascular ANG II receptor concentration.Results Cord venous angiotensin II concentration was similar to maternal values in the ECS group (31–101 pmol/1, 95% CI), but was elevated (81–288 pmol/l, P= 0.03) after vaginal delivery. The concentration of ANG II receptors (type AT1, dissociation equilibrium constant, 1.27 nmol/l) in placental primary/secondary stem vascular tissue was lower in the SVD group (18–44 fmol/mg membrane protein, 95% CI), compared with the ECS group (29–122 fmol/mg, P= 0.03) consistent with acute receptor down-regulation by the elevated ANG II levels. No effect of gestational age on receptor number was demonstrable (P= 0.13, PREM (premature delivery) vs ECS group). In the IUGR group, [cv ANG II] (94–378 pmol/l) was markedly elevated compared with the ECS controls (P= 0.001) but receptor concentration (28–84 fmol/mg) was not significantly altered (P= 0.13). No relationships between [cv ANG II] or receptor number and umbilical artery FVW could be identified. No changes in receptor affinity were observed.Conclusion These results indicate activation of the fetal RAS in IUGR and suggest that responsiveness of the fetoplacental vasculature to the peptide is not diminished as would be expected from the elevated plasma ANG II levels. ANG II may contribute to the increased fetoplacental vascular resistance observed in this disorder, but does not apparently account for the abnormal umbilical artery FVW that is observed in a proportion of IUGR cases.

Notes: Photolysis of dimethyl sulfoxide in a molecular beam with 210 and 222 nm photons reveals the decomposition mechanism and energy disposal in the products. Using vacuum ultraviolet light and a time-of-flight spectrometer, we identify CH3 and CH3SO as primary fragments and CH3 and SO as secondary fragments. From CH3 quantum yield measurements, we find that secondary decomposition is minor for 222 nm photolysis, occurring in only about 10% of the fragments, but it increases to about 30% in the 210 nm photolysis. Laser-induced fluorescence measurements on the B3Σ−←X3Σ− transition of SO in the 235 to 280 nm region determine the internal energy of that photoproduct. We compare our results to a simple statistical model that captures the essential features of the decomposition, predicting both the extent of secondary decomposition and the recoil energy of the primary and secondary methyl fragments. © 1999 American Institute of Physics.

Notes: A recently developed form of threshold ionization spectroscopy has been used to determine the bond energy for HCl to spectroscopic accuracy (±0.8 cm−1). This method is based on excitation to highly vibrationally excited ion-pair states using single-photon transitions from the ground state of HCl. These metastable Rydberg-like states were selectively detected using electricfield induced dissociation. By systematically varying the electric fields involved, and scanning the exciting photon energy, it was possible to determine the field-free energetic threshold for H35Cl+hν→H++35Cl−. Using this energy, together with the known values of the ionization potential of H and electron affinity of Cl, a new estimate for the dissociation energy of HCl was obtained: D0(H35Cl)=35 748.2±0.8 cm−1. © 1998 American Institute of Physics.

Notes: The near ultraviolet (UV) and visible photodissociation dynamics of BrCl have been explored using the technique of photofragment ion imaging at 26 wavelengths in the range 235 to 540 nm. Ion images of the Cl(2P3/2), Cl(2P1/2), Br(2P3/2) and Br(2P1/2) photofragments reveal both the angular distributions of photofragment velocities (characterized by anisotropy parameters, β) and which of the four possible photofragment pathways are active at different wavelengths. The anisotropy parameters show extensive variation both with wavelength and for the different fragmentation channels, and these variations are interpreted largely in terms of excitations to the A 3Π(1), B 3Π(0+), C 1Π(1) and D(0+) states as the wavelength is reduced. At wavelengths between 235 and 262 nm, the Br(2P1/2)+Cl(2P3/2) channel is dominant and β=2.0±0.1 at 235 nm, characteristic of a parallel parent transition (ΔΩ=0) and supporting previous assignments of the absorption in this wavelength range being due to the D(0+)–X 1Σ+(0+) transition. A minor channel forms Cl(2P1/2)+Br(2P3/2) with an anisotropy indicative of the involvement of an underlying perpendicular absorption (ΔΩ=±1) to a state with Ω=1. Br(2P3/2)+Cl(2P3/2) and Br(2P1/2)+Cl(2P1/2) fragmentation channels are not observed. Excitation in the wavelength range 320 nm to 410 nm results in Cl(2P3/2)+Br(2P3/2) products with an anisotropy parameter of β=−1.0±0.1, consistent with assignment of the strong parent absorption to the C 1Π(1)–X 1Σ+(0+) transition. For photolysis wavelengths longer than 400 nm, the Cl(2P1/2)/Cl(2P3/2) branching ratio increases [with β∼1.0 to 1.4 for the Cl(2P1/2)], β for Cl(2P3/2) becomes less negative (and for λ≥450 nm, values lie in the range 0 to −0.2) and Br(2P3/2) β-parameters also increase. No formation of Br(2P1/2) is observed. These observations are, in part, consistent with absorption via the B 3Π(0+)–X 1Σ+(0+) transition, although the nonlimiting β-parameter values imply a significant perpendicular contribution to the absorption spectrum. The measured anisotropy parameters for λ≥410 nm are interpreted in terms of excitation both to an Ω=0 state [B 3Π(0+)] and an Ω=1 state [A 3Π(1) or C 1Π(1)], together with transfer of dissociating flux between states during the dissociation. © 1998 American Institute of Physics.

Notes: The tautomeric equilibrium involving the amine and imine forms of creatinine are studied theoretically in both the gas phase, the aqueous environment, and the solid state. High level ab initio calculations predict the imine form to be preferred in the gas phase by 2.0 kcal mol−1. In the aqueous environment, both continuum and explicit solvent models predict the amine form to be the most stable, with solute polarization being an important contributing factor. An embedding procedure is used to model solid state effects when again the amine is preferred, in agreement with experimental crystallographic studies. The predicted solid state molecular geometry is compared to the experimental structure. © 1997 American Institute of Physics.

Notes: Abstract: An ˜950-kDa heteromeric particle was purified from guinea-pig and rat brain by sucrose gradient fractionation of post-mitochondrial supernatants. Further purification, by affinity chro-matography on ATP-Sepharose and anion exchange FPLC on MonoQ, yielded a particle with typical chaperonin ultrastructure. One of the component polypeptides was recognized by a monoclonal antibody to murine T-complex polypeptide 1. Brain cytosolic chaperonin particles formed a binary complex with unfolded tubulin subunits. The polypeptide compositions of the cytosolic chaperonin particles appeared very similar between brain and testicular tissues of the same animal, but differed subtly between the guineapig and rat.

Notes: A1 adenosine receptors were labeled in rat brain sections with the antagonist [3H]8-cyclopentyl-1,3-dipropylxanthine ([3H]DPCPX) and visualized at the light microscopic level using autoradiography. The specific binding of [3H]DPCPX to the sections showed the pharmacological characteristics of A1 adenosine receptors and was accompanied by very low levels of nonspecific binding. Whereas GTP had no significant effect on [3H]DPCPX binding to rat brain membranes, the addition of 100 μM GTP increased the apparent affinity of [3H]DPCPX to tissue sections fivefold (from 1.83 to 0.35 nM), enhancing it to the affinity measured in membranes. However, GTP altered neither the binding capacity nor the distribution of binding sites in tissue sections. It is suggested that a competitive antagonism with endogenous adenosine explains the lower affinity of [3H]DPCPX in the absence of GTP. The autoradiographic pattern of [3H]DPCPX binding was characteristic for A1 adenosine receptors. Distinct labeling of the different layers of the cerebellar cortex was shown by photomicrographs generated with the coverslip technique. In addition, several fiber tracts were found to be labeled. The high selectivity for A1 adenosine receptors and low nonspecific binding of [3H]DPCPX, the ability to produce high-resolution autoradiograms, together with the fact that the effects of endogenous adenosine can be eliminated by the addition of GTP make [3H]DPCPX a very useful tool in the autoradiographic study of A1 adenosine receptors.

Notes: Abstract: A1 adenosine receptors from rat brain membranes were solubilized with the zwitterionic detergent 3-[3-(cholamidopropyl)dimethylammonio]-1-propanesulfonate. The solubilized receptors retained all the characteristics of membrane-bound A1 adenosine receptors. A high and a low agonist affinity state for the radiolabelled agonist (R)-N6-[3H]phenylisopropyladenosine(3H]PIA) with KD values of 0.3 and 12 nM, respectively, were detected. High-affinity agonist binding was regulated by guanine nucleotides. In addition agonist binding was still modulated by divalent cations. The solubilized A1 adenosine receptors could be labelled not only with the agonist [3H]PIA but also with the antagonist 1,3-diethyl-8-[3H]phenylxanthine. Guanine nucleotides did not affect antagonist binding as reported for membrane-bound receptors. These results suggest that the solubilized receptors are still coupled to the guanine nucleotide binding protein Ni and that all regulatory functions are retained on solubilization.