What can a "quantum black-box" do for the inorganic thermochemist?

Enthalpies of formation of ABO3 (A = Ca, Sr, Ba; B = Ti, Zr, Hf) from the binary constituent oxides have been calculated by ab initio density functional theory. The resulting values compare well with the large number of experimental determinations reported in literature. The trends in the calculated enthalpies of formation correlate with the difference in acidity between the binary constituent oxides. Density functional theory is shown to be a valuable tool that should be used routinely in thermochemical studies of inorganic compounds.     

The interaction of the antitoxin DM43 with a snake venom metalloproteinase analyzed by mass spectrometry and surface plasmon resonance

DM43 is a circulating dimeric antitoxin isolated from Didelphis aurita, a South American marsupial naturally immune to snake envenomation. This endogenous inhibitor binds non-covalently to jararhagin, the main hemorrhagic metalloproteinase from Bothrops jararaca snake venom, and efficiently neutralizes its toxicity. The aim of this study was to apply mass spectrometry (MS) and surface plasmon resonance (SPR) to improve the molecular characterization of this heterocomplex. The stoichiometry of the interaction was confirmed by nanoelectrospray ionization-quadrupole-time-of-flight MS; from native solution conditions, the complex showed a molecular mass of ~94 kDa, indicating that one molecule of jararhagin (50 kDa) interacts with one monomer of DM43 (43 kDa). Although readily observed in solution, the dimeric structure of the inhibitor was barely preserved in the gas phase. This result suggests that, in contrast to the toxin-antitoxin complex, hydrophobic interactions are the primary driving force for the inhibitor dimerization. For the real-time interaction analysis, the toxin was captured on a sensor chip derivatized with the anti-jararhagin monoclonal antibody MAJar 2. The sensorgrams obtained after successive injections of DM43 in a concentration series were globally fitted to a simple bimolecular interaction, yielding the following kinetic rates for the DM43/jararhagin interaction: k(a) = 3.54 ± 0.03 × 10(4) M(-1) s(-1) and k(d) = 1.16 ± 0.07 × 10(-5) s(-1), resulting in an equilibrium dissociation constant (K(D) ) of 0.33 ± 0.06 nM. Taken together, MS and SPR results show that DM43 binds to its target toxin with high affinity and constitute the first accurate quantitative study on the extent of the interaction between a natural inhibitor and a metalloproteinase toxin, with unequivocal implications for the use of this kind of molecule as template for the rational development of novel antivenom therapies.     

Direct measurement of the formation length of photons

We report the first observation of a shoulder in the radiation spectrum from GeV electrons in a structured target consisting of two thin and closely spaced foils. The position of the shoulder depends on the target spacing and is directly connected to the finite formation length of a low-energy photon emitted by an ultrarelativistic electron. With the present setup it is possible to control the separation of the foils on a μm scale and hence measure interference effects caused by the macroscopic dimensions of the formation length. Several theoretical groups have predicted this effect using different methods. Our observations have a preference for the modified theory by Blankenbecler but disagree with the results of Baier and Katkov.     

Assigning environmental variables to observed biological changes

A method for assigning environmental variables to observed biological changes in benthic communities is proposed. The approach requires biological and environmental sampling at the same sites. Additionally, a biological gradient or trend such as a change in observed species or a significant change in their relative abundances is necessary in order to connect the biological observations to the environmental measurements. Whether there is a statistical significant correspondence between the environmental measurements and the biological changes is tested after quantifying the biological changes by using the community disturbance index (CDI). Finally, the environmental variables that are most strongly associated with the biological changes are identified, and it is proposed that these are strong candidates as the pollutants responsible for the biological changes observed. However, this cannot be confirmed using the monitored data only. The approach is tested on data collected in monitoring surveys at the Ekofisk oil field in the North Sea. The results indicate the method is feasible for assigning environmental variables to observed biological changes.     

Mutation at minisatellite locus DYF155S1: allele length mutation rate is affected by age of progenitor

A father/son material consisting of 1071 pairs was screened for de novo allele length mutation in locus DYF155S1. Six hundred of these pairs were also analyzed in locus DYF155S1 to detect de novo mutations in the minisatellite variant repeat (MVR)-code not resulting in a length change ("boundary switch" mutations). A modified MVR-polymerase chain reaction (PCR) method was used for this purpose. Twenty-seven de novo allele length mutations and eight "boundary switch" mutations were detected indicating mutation frequencies of approximately 2.5% and 1.3%, respectively. The combined mutation rate for MVR-code mutation is approximately 3.8%. There is a significant increase in mutation rate with paternal age (p = 0.049) in allele length mutations. In the present material, the mutation rate in the oldest age group is three times that of the youngest age group. A similar age relationship is not observed in "boundary switch" mutations. A comparison between progenitors and the other fathers in the material revealed no obvious association between mutation rate and allele length or modular structure (variation in repeat sequence). More than 75% of the length mutations involved the gain or loss of one repeat only. This finding as well as the observed paternal age influence on mutation rate, suggests replication slippage to be the major mutation mechanism in length mutations. However, in one particular case, an allele length mutant revealed rearrangements with direct duplication of repeats at distant sites within the repeat array, and with both loss and gain of repeats. Such complex structural changes could indicate that some of the mutants might arise from sister chromatide exchange. The mutation rate of "boundary switch" mutations is by far higher than would be expected if these mutations are two independent one-step allele length mutations. A different age distribution of "boundary switch" mutations than of allele length mutations also argue against such a hypothesis. Together this could indicate that "boundary switches" are products of another mutation mechanism than the one-step allele length mutations.     

Hydrogen bond studies: 67. The crystal structure of rubidium trihydrogen selenite,RbH3(SeO3)2

The crystal structure of RbH₃(SeO₃)₂ has been determined from three-dimensional single crystal X-ray diffractometer data obtained at room temperature. Four formula units crystallize in an orthorhombic unit cell of dimensions: a = 5.9192(2), b = 17.9506(5), and c = 6.2519(3) Å. The space group is P2₁2₁2₁. The structure consists of two types of chains at a right angle. One chain is built up of H₂SeO₃ molecules linked by 2.594(8)-Å hydrogen bonds and the other of HSeO₃^? ions linked by 2.571(12)-Å hydrogen bonds. These two types of chains are cross-linked by a third hydrogen bond of length 2.521(7) Å. The rubidium ion is surrounded by eight oxygen atoms forming a distorted cube. The Rb⁺O distances are in the range 2.94–3.19 Å.