Minimax least squares and quasiminimax estimation in linear models with missing values

We consider the problem of estimating the parameter vector in the linear model when observations on the independent variables are partially missing or incorrect. New estimators are developed, which systematically combine prior information with the incomplete data. We compare these methods with the alternative strategy of deleting incomplete observations.Support by Deutsche Forschungsgemeinschaft, Grant No. 284/1-2 is gratefully acknowledged.     

Thermolysis of 3-azidophenalen-1-ones to naphtho[8,1-ab]carbazolones and naphtho[8,1-ab]-8a-azonia-9-λ2-azafluoren-7-ones

3-Azido-1-phenalenones 4 with aryl- or hetarylsubstituents in position 2 cyclized by thermolysis to give naphtho[8,1-ab]carbazolones 5 or naphtho[8,1-ab]-8a-azonia-9-λ²-azafluorenones 7. Reduction of the azides 4 gave the corresponding amino derivatives 9. The thermolysis conditions were studied by differential scanning calorimetry.     

Fragmentation of doubly-protonated Pro-His-Xaa tripeptides: Formation of b 2 2+ ions

When ionized by electrospray from acidic solutions, the tripeptides Pro-His-Xaa (Xaa=Gly, Ala, Leu) form abundant doubly-protonated ions, [M+2H]²⁺. Collision-induced dissociation (CID) of these doubly-protonated species results, in part, in formation of b ₂ ²⁺ ions, which fragment further by loss of CO to form a ₂ ²⁺ ions; the latter fragment by loss of CO to form the Pro and His iminium [immonium is commonly used in peptide MS work] ions. Although larger doubly-charged b ions are known, this represents the first detailed study of b ₂ ²⁺ ions in CID of small doubly protonated peptides. The most abundant CID products of the studied doubly-protonated peptides arise mainly in charge separation involving two primary fragmentation channels, formation of the b ₂ /y ₁ pair and formation of the a ₁ /y ₂ pair. Combined molecular dynamics and density functional theory calculations are used to gain insight into the structures and fragmentation pathways of doubly-protonated Pro-His-Gly including the energetics of potential protonation sites, backbone cleavages, post-cleavage charge-separation reactions and the isomeric structures of b ₂ ²⁺ ions. Three possible structures are considered for the b ₂ ²⁺ ions: the oxazolone, diketopiperazine, and fused ring isomers. The last is formed by cleavage of the His-Gly amide bond on a pathway that is initiated by nucleophilic attack of one of the His side-chain imidazole nitrogens. Our calculations indicate the b ₂ ²⁺ ion population is dominated by the oxazolone and/or fused ring isomers.     

Nuclear localization of Annexin A7 during murine brain development

Background  

Annexin A7 is a member of the annexin protein family, which is characterized by its ability to interact with phospholipids in the presence of Ca²⁺-ions and which is thought to function in Ca²⁺-homeostasis. Results from mutant mice showed altered Ca²⁺-wave propagation in astrocytes. As the appearance and distribution of Annexin A7 during brain development has not been investigated so far, we focused on the distribution of Annexin A7 protein during mouse embryogenesis in the developing central nervous system and in the adult mouse brain.     

Combined 17O NMR and 11B-31P double resonance NMR studies of sodium borophosphate glasses

17O enriched sodium borophosphate glasses were prepared from isotopically enriched NaPO3 and H3BO3. These glasses have been studied by 17O, 11B and 31P NMR including 17O and 11B multiple quantum magic angle sample spinning (MQMAS), 11B-31P heteronuclear correlation (HETCOR) NMR and 11B{31P} rotational echo double resonance (REDOR). For comparison, the crystalline borophosphates BPO4 and Na5B2P3O13 were included in the investigations. The latter compound shows three sharp 31P resonances at -0.2, -2 and -8 ppm and two BO4 sites that can only be resolved by MQMAS. The 17O NMR spectra were recorded using both the static echo method at medium magnetic field (9.4 T) as well as MAS and MQMAS methods at high field (17.6 T). In total, five oxygen sites were identified in these borophosphate glasses: P-O-P, Na...O-P, P-O-B, B-O-B, Na...O-B. However, these five sites are not present simultaneously in any of the glasses. The 17O MQMAS spectra prove that P-O-B links play a major role in borophosphate glasses. These results are confirmed by the complementary 11B MAS spectra that show the presence of asymmetric and symmetric trigonal groups BO3a and BO3s and two tetrahedral BO4 units. 11B{31P} REDOR NMR is used to give independent information to assign the 11B lines to structural units present in the glasses. These REDOR measurements reveal that B-O-P bonds are present for each borate unit, including the BO3 groups. Particularly, a structural proposal for the two different BO4 resonances is given in terms of a different number of bonded phosphate tetrahedra. The 31P MAS spectra are usually broad and not well resolved. It is shown by 11B-31P HETCOR NMR that a possible structural assignment of a 31P signal at about -20 ppm to Q2 units as in binary sodium phosphate glasses is wrong and that the phosphate tetrahedron belonging to this resonance must be connected to borate groups.     

A New Fluorescence Resonance Energy Transfer Pair and Its Application to Oligonucleotide Labeling and Fluorescence Resonance Energy Transfer Hybridization Studies

We describe two new fluorescence resonance energy transfer (FRET) compatible labels, their covalent linkage to oligonucleotides, and their use as donor and acceptor, respectively, in FRET hybridization studies. The dyes belong to the cyanine dyes, and water solubility is imparted by a phosphonate which represents a new solubilizing group in DNA labels. They were linked to amino-modified synthetic oligonucleotides via oxysuccinimide (OSI) esters. The studies performed include binding assays, determinations of molecular distances, homogeneous competitive assays, and limits of detection, which are in the order of 5 pmol/L for a 15-mer.     

Comparison of extraction techniques for the isolation of explosives and their degradation products from soil

A comparison of four extraction techniques used for the isolation of 14 explosive compounds (Method 8330-Explosives) from spiked soil samples is described. Soxhlet warm extraction (SWE), pressurized solvent extraction (PSE), microwave assisted extraction (MAE) and supercritical fluid extraction (SFE) were included. The effects of basic extraction conditions – i.e. type of extraction solvent, temperature, pressure, and extraction time – were investigated. The best extraction recovery of the monitored compounds from spiked soil was obtained using pressurized solvent extraction. Recoveries of explosives using the PSE technique were in the range from 65 to 112%. Extraction recoveries by Soxhlet warm extraction and supercritical fluid extraction reached 65–99% and 52–75%, respectively. The lowest extraction recoveries (28–65%) were obtained using microwave assisted extraction. A very low extraction recovery for tetryl was observed in all cases but the best results were achieved by pressurized solvent extraction (58%).     

Synthesis and Solid-State Molecular Structure of Bi(silacyclohexyls) C5H10SiX-XSiC5H10 with X = H,PH, F,CL, BR,and I

The synthesis and purification of novel bi(silacyclohexyls) C₅H₁₀SiX-XSiC₅H₁₀ with X = H (1), Ph (2), F (3), Cl (4), Br (5), and I (6), which are composed of two silacyclohexyl rings connected by a silicon–silicon single bond, is described. Molecular structures for 2, 4, 5, and 6 were determined employing X-ray crystallography. Surprisingly, the SiSi bond lengths increase in the order I < Br < Cl, contrary to what is observed for methylated disilanes Me₂XSiSiXMe₂. The bond lengthening can be traced back to 1, 3 nonbonded interactions between the halogen atoms and the axial hydrogen atoms in the SiC₅ ring, which also cause a decrease of the SiSiX bond angles with increasing size of the halogen atom. Both rings substitute each other in the equatorial position for 4, 5, and 6, but in the axial position for 2.