New spectroscopic analyses and potential energy curves for the X1Σ+ and A1Σ+ states of NaH

The emission spectrum of NaH has been photographed in the ～6000–7300-Å region. Additional bands of the A¹Σ⁺ electronic transition have been analyzed and in particular the observed vibrational structure of the excited A state has been extended down to v′ = 0. New spectroscopic constants have been obtained, the v′ = 0 data leading to especially large changes in the constants of the anomalous A¹Σ⁺ state. New Rydberg-Klein-Rees (RKR) potential energy curves have been calculated up to v″ = 8 of the X¹Σ⁺ state and up to v′ = 20 in the A¹Σ⁺ state.     

Zur Struktur verstreckter Folien und Fäden sowie aus verdünnten Lösungen hergestellter Einkristalle aus Polyacrylnitril

Zusammenfassung Kolloid- und Kristallstruktur von verstreckten Folien und Fäden und aus verdünnten Lösungen hergestellten Einkristallen von Polyacrylnitril wurden mit Hilfe von Röntgenklein- und -weitwinkeluntersuchungen, Elektronenbeugung und Elektronenmikroskopie untersucht. Es kann gezeigt werden, da entgegen den bisher publizierten Ergebnissen bei dem verstreckten Polyacrylnitril eine periodische Abfolge von besser und schlechter geordneten Bereichen erzielt werden kann, die sich in dem Auftreten einer röntgenografisch erfaßbaren Langperiode äußert und, wie die vergleichenden Untersuchungen an Einkristallen zeigen, durch eine Zwei-Phasen-Struktur beschrieben werden kann. Innerhalb der besser geordneten Bereiche ordnen sich die Ketten, indem ein zwar stark gestörtes, aber dreidimensionales Gitter mit der orthorhombischen Elementarzellea=10,6 Å,b=11,6 Å,c=5,04 Å aufgebaut wird. Kristallisationsfähig sind nur die syndiotaktischen Kettensequenzen des Polyacrylnitrils.

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Summary Colloidal and crystallographic structure of drawn films and solution grown single crystals of polyacrylonitrile were investigated by small and wide angle X-ray scattering, electron scattering and electron microscopical observations. In contrast to the published results it is shown that in the case of drawn polyacrylonitrile there exists a periodical arrangement of more and less ordered regions which manifests in the appearance of a so called long period and which — as shown by comparative investigations on single crystals — can be described by a two-phase-model. Within the ordered regions chains are arranged building up a strongly disturbed but three-dimensional crystal lattice. The orthorhombic unit cell has the dimensiona=10,6 Å,b=11,6 Å,c=5,04 Å. Only the syndiotactic chain sequences are able to crystallize.

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Vorgetragen auf der Arbeitssitzung des Fachausschusses Physik der Hochpolymeren in der Frühjahrstagung Berlin 1971 vom 9. bis 13. März des Regionalverbandes Physikalische Gesellschaft zu Berlin.

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Für die Hilfe bei den experimentellen Arbeiten danken die Verfasser FräuleinM. Collatz und den HerrenE. Vey undH. Gladbach.     

Low-energy positrons from metallic moderators in a back scattering mode

The energy spectra of thermalized positrons emitted in the “back scattering mode” from Cu, Au, and Al moderators are reported.     

Vitrification of human spermatozoa without cryoprotectants

The aim of our study was to investigate the effects of vitrification (cooling rate approximately 10000(C/min) without cryoprotectants on swim-up prepared human spermatozoa in comparison to standard conventional freezing with cryoprotectants. Motility, morphology, rate of viability and acrosome reaction of spermatozoa were evaluated. The described method of cryopreservation of human spermatozoa by direct plunging into liquid nitrogen slush without cryoprotectants was effective and could be recommended for routine IVF.     

A chemical reporter for protein AMPylation

Protein AMPylation is an emerging post-translational modification, which plays key roles in bacterial pathogenesis and cell biology. Enzymes with AMPylation activity, referred to as AMPylators, have been identified in several bacterial pathogens and eukaryotes. To facilitate the study of this unique modification, we developed an alkynyl chemical reporter for detection and identification of protein AMPylation substrates. Covalent functionalization of AMPylation substrates with the alkynyl reporter in lieu of adenylyl 5'-monophosphate (AMP) allows their subsequent bioorthogonal ligation with azide-fluorescent dyes or affinity enrichment tags. We show that this chemical reporter is transferred by a range of AMPylators onto their cognate protein substrates and allows rapid detection and identification of AMPylated substrates.     

Spray coating of cellulose aerogel particles in a miniaturized spouted bed

Cellulose - Aim of this work is to apply protective and homogeneous shellac coating layers on the surface of hydrophilic open-pore cellulose aerogel particles with low...     

The Tetracycline Repressor-A Paradigm for a Biological Switch

The excessive use of antibiotics has enabled bacteria to develop resistance through a variety of mechanisms. The most common bacteriostatic action of the broad-spectrum antibiotic tetracycline (Tc) is by the inactivation of the bacterial ribosome so that the protein biosynthesis is interrupted and the bacteria die. The most common mechanism of resistance in gram-negative bacteria against Tc is associated with the membrane-intrinsic protein TetA, which exports invaded Tc out of the bacterial cell before it can attack its target, the ribosome. The expression of TetA is tightly regulated by the homodimeric Tet repressor (TetR)(2), which binds specifically with two helix-turn-helix motifs of operator DNA (tetO; K(ass) approximately 10(11) M(-1)) located upstream from the tetA gene on a plasmid or transposon. When Tc diffuses into the cell it chelates Mg(2+) and the complex [MgTc](+) binds to (TetR)(2) to form the induced complex (TetR small middle dot[MgTc](+))(2). This process is associated with conformational changes, which sharply reduce the affinity of (TetR)(2) to tetO, so that expression of TetA can take place, thus conferring resistance to the bacteria cells against Tc. Crystallographic studies show sequence-specific protein-nucleic acid interactions in the (TetR)(2) small middle dottetO complex and how the binding of two [MgTc](+) to (TetR)(2) enforces conformational changes that are stabilized by cooperative binding of two chains of eight water molecules each so that the formed (TetR small middle dot[MgTc](+))(2) is no longer able to recognize and bind to tetO. Since the switching mechanisms of the TetR/[MgTc](+) system is so tight, it has proven very useful in the regulation of eukaryotic gene expression and may also be applicable in gene therapy.     

A spectrum of rhenium oxide

The arc emission spectrum of the ReO molecule has been photographed in the region 590–860 nm and three bands of a single electronic transition have been rotationally analyzed. The separation of lines of the isotopic molecules ¹⁸⁵ReO and ¹⁸⁷ReO leads to the conclusion that the vibrational assignments for these bands are 1-0, 0-0, and 0–1. It is conceivable that an electronic isotope shift of ～0.08 cm^?1 exists. The following vibrational and rotational data (cm^?1) have been determined: ν₀(0-0) = 14 038.42, $\text{Δ}\text{G′(}\text{1}\text{2}\text{) = 867.85}$, $\text{Δ}\text{G″(}\text{1}\text{2}\text{) = 979.14}$; B′_e = 0.3889, α′_e = 0.0019, B″_e = 0.4257, α″_e = 0.0043. It is concluded that Λ′ ? Λ″ = +1 with Λ″ ≥ 2.     

Analytische Näherung für elastische Wellen in anisotropen kubischen Kristallen

It is shown that the frequencies ω_α(k) and the polarisation vectorse _α(k) (α=1, 2, 3) of the elastic waves in anisotropic cubic crystals can be described exactly as Taylor series in the parameter \(\delta = \frac{{c_{11} - c_{12} - 2c_{44} }}{{c_{12} + c_{44} }}\) for all wave number vectorsk. As the expansion functions of these series include no elastic constants, δ is taken as the proper anisotropy parameter. The series are converging very fast for almost all substances and may be broken off after the third expansion term.