ALBERT

Notes: The IBr fragment rotational state distributions that result when the NeIBr van der Waals molecule undergoes vibrational predissociation have been measured in a pump–probe laser-induced fluorescence experiment. Independent of initial vibrational state and the number of quanta of vibrational energy lost from the I–Br coordinate, the rotational distributions extend over the full range of energetically accessible states. From the observation of energetic constraints on the rotational distribution, the dissociation energy (D0) is calculated to be 65.5±1.2 cm−1 for the A electronic state, v=16. For the X electronic state, v=0, D0=71.8±1.2 cm−1. Quantum mechanical bound state calculations carried out on a model A electronic state potential energy surface are in quantitative agreement with this result. The rotational distributions are broader than that predicted by either a Franck–Condon or classical impulsive model for the dissociation. The distributions are qualitatively in accord with classical trajectory calculations. Analysis of specific rotational distributions in the context of the energy gap law shows poor quantitative agreement. The average fragment rotational energy relative to analogous Ne-containing complexes is, however, qualitatively predicted by the energy gap relations.

Notes: The degree of vibrational excitation in the IBr fragment from the vibrational predissociation of NeIBr (A 3Π1) has been measured using two-color pump–probe laser-induced fluorescence spectroscopy. We find that for the lowest initial vibrational states examined, Δv=−1 dissociation pathways dominate the dynamics, while this channel is closed for v≥17. From this result, the A state binding energy (D0) of the complex is determined to be 67±4 cm−1, while that in the X electronic state is found to be 73±4 cm−1. The X state binding energy is identical to that for NeI2 and NeBr2, suggesting that the potential energy surface for NeIBr can be constructed from a summation of atom–atom pair potentials; we present such a model potential energy surface. The variations in the vibrational branching ratios, when combined with the trends in the predissociation rates, point to the importance of fragment rotational excitation in the dynamics of the dissociation.

Notes: The rotational, vibrational and fine-structure state distributions for the reaction 16O(1D)+ H218O →16OH +18OH, triggered by 266 nm photolysis of O3, have been measured under conditions where less than 1% of the nascent fragments experienced collisions prior to detection. The distributions are qualitatively different than those reported earlier for 266 nm photolysis, which were evidently affected by collisions. The rotational and vibrational state distributions are similar to recent 248 nm photolysis experiments, but with differences attributed to collisional and/or energetic effects in those experiments. The "new'' 16OH is formed with vibrational populations in the ratio 0.39(v=0):0.29(v=1):0.3(v≥2). Gaussian rotational energy distributions peaked near N=12 give average rotational energies of 〈Erot〉 = 3440 and 2780 cm−1 for 16OH v=0 and v=1, respectively. The "old'' 18OH is much colder with vibrational populations 0.94(v=0):0.06(v=1) and a 18OH v=0 Gaussian rotational energy distribution characterized by 〈Erot〉 = 1920 cm−1.There is negligible rotational alignment of the 16OH fragments [βμJ' = β20(02) = 5A(0)2/4 = 0.06± 0.09], which is significantly less than expected for fragment rotations aligned with respect to the O+H2O relative velocity vector. The spin-orbit propensities deviate slightly from the statistical expectation and are characterized by [F2,N]/[F1,N]=(0.89±0.06) ×N/(N + 1). The Λ-doublet distributions for 18OH (all N) and 16OH (low-to-moderate N) fragments conform to an unconstrained-dynamics prior distribution. A slight propensity for Π(A') in excess of this expectation is seen for the 16OH (high N) fragments. These new results are discussed in terms of possible insertion and abstraction mechanisms for the reaction.

Notes: The assessment of signal to noise (S/N) values in x-ray absorption spectroscopy is important for a number of reasons. Two methods will be described that remove the signal to give the noise. The first uses polynomials and the second Fourier filtering. Having extracted the noise the signal can then be used to calculate the S/N ratio. The method described operates on a background subtracted spectrum and is quick so it can be done on line in an experimental situation.

Notes: In situ surface x-ray scattering studies of the GaAs(001) surface were used to determine whether specific surface reconstructions occur during organometallic vapor-phase epitaxy. Prior to growth, we find that surfaces heated in the presence of As form a c(4×4) structure, while those heated in the absence of organometallics or in Ga form two similar fourfold reconstructions. We find no evidence for the presence of any surface reconstruction during the actual layer-by-layer growth process.

Notes: Abstract Quantitative tectonic modelling demonstrates an interaction of flexure of the lithosphere underlying the western Betics with crustal thinning in the Alboran Basin and flank uplift in the Internal Zone. In the eastern Betics the flexural response is overprinted by post-thrusting extensional events. Lateral variations in thermal structure and rheology of the lithosphere along strike of the Betics shed light on changes in tectonic configuration and are consistent with evidence for lateral variations in the mode of extension in the Alboran Basin. Flexural modelling and subsidence analysis of Neogene basins in the Internal Zone of the Betics, with spatial development controlled by contrasts in lithosphere rheology, demonstrate that at least two extensional events have affected the orogenic evolution of the Betics. The first event appears to reflect Oligocene-Early Miocene rifting observed throughout the Western Mediterranean. The second phase, which caused the present configuration of the Betics, corresponds to Tortonian-Recent extension centered in the Alboran Basin.

Notes: Abstract The first intron of the human Proα1(I) collagen gene contains an orientation-dependent enhancer composed of both positive and negative cis-acting elements involved in the transcriptional regulation of this gene. Deletion of a 360 bp Sau 3A intronic fragment spanning nucleotide + 494 to + 854 (S360) resulted in dramatic down-regulation of pCOL-KT (Thompson et al., J Biol Chem 266: 2549–2556, 1991). Using a DNaseI protection assay, we demonstrate a single footprint located at + 590 to + 615 in the S360 fragment; nuclear extracts prepared from mesenchymal and nonmesenchymal cells exhibited similar binding characteristics. A double stranded oligonucleotide representing a consensus Ap-1 binding sequence competed with S360 for binding. In contrast to what occurred in response to S360 deletion which was always accompanied by reduced expression, the deletion of the Ap-1 binding site (+ 598 to + 604) caused either increased or decreased expression of the reporter gene depending on the target cell. Site-directed mutations in the Ap-1-like cis-element of Proα1(I) were also tested in transient expression assays. Consistent with the paradoxical results of Ap-1 deletion, we observed that the functional consequences of mutations in the Ap-1 site also varied in different cells. In A204 cells, one point mutation, which resulted in the loss of protein binding to S360, led to increased CAT activity while another point mutant, which retained binding of the Ap-1 like trans-acting factor(s), showed decreased CAT expression. The effects of these two mutations in the HFL-1 cells were exactly opposite of what was seen for A204 cells. Based on these observations, we postulate that the Ap-1 site plays a critical role in the transcriptional activity of the human Proα1(I) gene. The implications of an apparently dual mode of regulation through a single cis-regulatory element are discussed. (Mol Cell Biochem 118: 119–129, 1992)

Notes: Abstract A bioassay was used to evaluate the effects of cuticular leaf components, isolated fromN. tabacum, N. glutinosa (accessions 24 and 24a), and 23other Nicotiana species, on germinationof P. tabacina (blue mold). The leaf surface compounds includedα- andβ-4,8,13,-duvatriene-l,3-diols (DVT-diols), (13-E)-labda-13-ene-8α-,15-diol (labdenediol), (12-Z)-labda-12,14-diene-8α-ol (cis-abienol), (13-R)-labda-8,14-diene-13-ol (manool), 2-hydroxymanool, a mixture of (13-R)-labda-14-ene-8α,13-diol (sclareol), and (13-S)-labda-14-ene-8α,13-diol (episclareol), and various glucose and/or sucrose ester isolates. The above in acetone were applied onto leaf disks of the blue moldsusceptibleN. tabacum cv. TI 1406, which was then inoculated with blue mold sporangia. Estimated IC50 values (inhibitory concentration) were 3.0μg/cm2 forα-DVT-diol, 2.9μ/cm2 forβ-DVT-diol, 0.4μg/cm2 for labdenediol and 4.7μg/cm2 for the sclareol mixture. Manool, 2-hydroxymanool, andcis-abienol at application rates up to 30μg/cm2 had little or no effect on sporangium germination. Glucose and/or sucrose ester isolates from the cuticular leaf extracts of 23Nicotiana species and three different fractions fromN. bigelovii were also evaluated for antimicrobial activity at a concentration of 30μg/cm2. Germination was inhibited by 〉20% when exposed to sugar esters isolated fromN. acuminata, N. benthamiana, N. attenuata, N. clevelandii, andN. miersii, and accessions 10 and 12 ofN. bigelovii. These results imply that a number of compounds may influence resistance to blue mold in tobacco.

Notes: Summary Single fibres of different sarcomere length at rest have been isolated from the claw muscle of the yabby (Cherax destructor), a decapod crustacean. Fibres of either long (SL 〉 6 μm) or short (SL 〈 4 μm) sarcomere length have been mechanically skinned and were maximally activated by Ca2+ and Sr2+ under various experimental conditions (ionic strength, in the presence of 2,3 butanedione monoxime (BDM)) to determine differences in their contractile properties. Isometric force was measured simultaneously with either myofibrillar MgATPase or fibre stiffness in both fibre types. The ultrastructure of individual long- and short-sarcomere fibres was also determined by electron microscopy. The long-sarcomere fibres developed greater tension (30.48±1.72 N cm−2) when maximally activated by Ca2+ compared with the short-sarcomere fibres (18.60±0.80 N cm−2). The difference in the maximum Ca2+-activated force can be explained by the difference in the amount of filament overlap between the two fibre types. The maximum Ca2+-activated myofibrillar MgATPase rate in the short-sarcomere fibres (1.60±0.27 mmol ATP l−1 s−1) was higher, but not significantly different from the ATPase rate in fibres with long-sarcomeres (1.09±0.14 mmol ATP l−1 s−1). As the concentration of myosin is estimated to be higher only by a factor of 1.22 in the short-sarcomere preparations there is no evidence to suggest that the myofibrillar MgATPase activity is different in the long- and short-sarcomere preparations. The maximum Ca2+-activated force (P 0) of both short- and long-sarcomere fibres was quite insensitive to BDM compared with vertebrate muscle. Force decreased to 60.2±5.3% and 76.1±2.7% in the short- and long-sarcomere fibres respectively in the presence of 100 mmol l−1 BDM. The difference in the force depression between the. long- and short-sarcomere fibres is statistically significant (p〈0.05). Fibre stiffness during maximum Ca2+-activation expressed as percentage maximum force per nm per half sarcomere was higher by a factor of 3.5 in short-sarcomere fibres than in long-sarcomere fibres suggesting that the compliance of the filaments in the long-sarcomere fibres is considerably higher than in the short-sarcomere fibres. Sr2+ could not activate the contractile apparatus to the same level as that seen by Ca2+ in either fibre type: the maximum Sr2+-activated force was (20±3%) and (63±3%) of the maximum Ca2+-activated force response in short- and long-sarcomere fibres, respectively. The ratio between fibre stiffness in the maximum Sr2+-activating solution and the Ca2+-activating solution was very similar to the ratio between the maximum Sr2+-activated force and Ca2+-activated force in either type of fibres, suggesting that the number of attached crossbridges is lower in the fibres when maximally activated by Sr2+ than when maximally activated by Ca2+. The short-sarcomere fibres were also more sensitive to changes in ionic strength than long-sarcomere fibres. In conclusion these results indicate that while several important specific characteristics of the short- and long-sarcomere length fibres (ATPase, maximum Ca2+-activated force and fibre stiffness) can be explained solely on differences in the ultrastructure (length and density per cross-sectional area of myosin filaments) there are also differences in the properties of the proteins involved in the force production and regulation evidenced by the differential effect of Sr2+, BDM and ionic strength on contractile activation in the two fibre types.