Irregularity strength of trees

The main result of this paper establishes that the irregularity strength of any tree with no vertices of degree two is its number of pendant vertices.     

Reversible Mechanical Switching of Magnetic Interactions in a Molecular Shuttle

An acid–base switchable molecular shuttle based on a [2]rotaxane, incorporating stable radical units in both the ring and dumbbell components, is reported. The [2]rotaxane comprises a dibenzo[24]crown-8 ring (DB24C8) interlocked with a dumbbell component that possesses a dialkylammonium (NH₂⁺) and a 4,4′-bipyridinium (BPY²⁺) recognition site. Deprotonation of the rotaxane NH₂⁺ centers effects a quantitative displacement of the DB24C8 macroring to the BPY²⁺ recognition site, a process that can be reversed by acid treatment. Interaction between stable 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals connected to the ring and dumbbell components could be switched between noncoupled (three-line electron paramagnetic resonance (EPR) spectrum) and coupled (five-line EPR spectrum) upon displacement of the spin-labelled DB24C8 macroring. The complete base- and acid-induced switching cycle of the EPR pattern was repeated six times without an appreciable loss of signal, highlighting the reversibility of the process. Hence, this molecular machine is capable of switching on/off magnetic interactions by chemically driven reversible mechanical effects. A system of this kind represents an initial step towards a new generation of nanoscale magnetic switches that may be of interest for a variety of applications.     

Vibrational Spectra of 2,2′-Pyridil and 2,2′-Pyridil-18O and Assignment of Infrared and Raman Bands

Abstract

Vibrational spectra of 2,2′-pyridil and 2,2′-pyridil-¹⁸O in the solid state and in solutions have been measured in the Raman (4000–50 cm^?1) and infrared (4000–100 cm^?1). The assignment of the bands observed is performed using the group vibrational concept and isotopic shifts data of the normal modes. The presence of synand anti-phase vibrations of both pyridyl rings is discussed. The results are compared to the corresponding data for some similar molecules.     

Visualisation of biopolymer mixtures using confocal scanning laser microscopy (CSLM) and covalent labelling techniques

Confocal scanning laser microscopy (CSLM) has been used to study the behaviour of mixtures of proteins, gelatine, whey proteins and β-lactoglobulin, and polysaccharides, dextran, gellan gum, carrageenan, gum Arabic, and starch. CSLM proved to be a suitable technique to visualise the microstructure of these (phase separated) mixtures in two and three-dimensional images. Contrast through fluorescence is obtained either by covalent labelling (polysaccharides and proteins) or non-covalent labelling (proteins and starch). Double and triple labelling allows the visualisation of individual components in a complex mixture of biopolymers.     

Radiophotosynthesis of some 14C-labelled Amino Acids using the Unicellular Green Alga Scenedesmus acutus

Radiophotosynthesis has been carried out using the unicellular green algea Scenedesmus acutus grown, as a substrate for preparing some carbon-14 labelled amino acids. Gaseous ¹⁴CO₂, in an air tight photosynthesis chamber or NaH¹⁴CO₃ solution, in an ordinary photosynthesis chamber, were used as radioactive carbon sources. The yields, radiochemical yields and specific activities of the formed radioactive products are reported in both cases. The results obtained clearly showed the advantages of using the NaH¹⁴CO₃ method. In that case the process was by far less tedious. Moreover, the chemical and radiochemical yields of the formed amino acids were relatively much more higher than the values obtained on using ¹⁴CO₂ in the tight photosynthesis chamber.     

Originalarbeiten 133m Xe zur Markierung von Gasphasen bei technischen Tracerexperimenten

Bei technischen Tracerexperimenten bereitet die Markierung von Gasphasen Schwierigkeiten, wenn man auf Außenwandmessungen angewiesen ist, da die Auswahl an geeigneten Radionukliden bzw. radioaktiv markierten Verbindungen dann sehr beschrānkt ist. Eine gute Ergänzung des Radionuklidangebotes für den genannten Zweck bietet ^133mXe, Halbwertszeit 2,3 d, E_γ = 0,23 MeV (16%). ^133mXe erhält man mit guten Ausbeuten bei einer Reaktoraktivierung von natürlichem Xenon. Die Sälligungsaktivität fär ^133mXe beträgt bei einem Fluß von 5,0 μ 10¹³ n/cm²s 48,5 mCi/cm³ Xenon (unter Normalbedingungen). An Veweilzeitmessungen von Gasphasen in technischen Anlagen werden die Einsatzmöglichkeiten des ^133mXe dargestellt.     

图P^3n的奇优美标号算法

本文讨论了图P^3n的奇优美性,给出了图只奇优美标号算法．     

Vibrational Assignment of N-Phenylphthalimide and 15N-Phenylphthalimide

Abstract

The i.r. spectra of N-phenylphthalimide and ¹⁵N-phenylphthalimide have been measured in 4000–100 cm^?1 frequency range as KBr and polyethylene pellets and as chloroform solutions. The Raman spectra (4000–50) cm^?1 of microcrystalline powder of the of the same compounds have also been investigated.

A detailed assignment of most of the observed frequencies has been proposed on the basis of the group vibrational concept, isotopic shift data and analogies with the spectra of related molecules. Some literature data have been discussed and some frequencies are reassigned.     

功能材料在蛋白质组研究中的应用进展

随着对蛋白质组鉴定深度、定量准确性及分析速度越来越高的要求,对蛋白质组学方法的研发提出了新的挑战。为了应对这些挑战,传统的蛋白质组学方法因其灵敏度低、准确性差以及耗时长等不足已经难以满足蛋白质组学研究领域不断提出的新需求。而将通过光、电、磁、热、化学、生化等作用合成具有特定功能的材料用于蛋白质组的研究,可以克服传统蛋白质组学分析技术的局限性,为蛋白质组学研究起到促进作用。该文对功能材料在蛋白质组研究中应用的新进展进行综述。     

Synthesis and Cellular Labeling of Caged Phosphatidylinositol Derivatives

Phosphatidylinositol (PI) is the biosynthetic precursor for seven phosphoinositides, important signaling lipids in cells. A membrane-permeant caged PI derivative featuring a photo-removable coumarinyl group masking the negative charge of the phosphate, as well as two enzymatically removable butyrate esters for increased lipophilicity and for preventing phosphate migration, were synthesized. Rapid cell entry and cellular labeling in fixed cells was demonstrated by a photo-cross-linkable diazirine followed by attachment of a fluorophore through click chemistry. Using this technique, we found that the multifunctional caged PI derivative resided predominantly at internal membranes but rapidly changed to the plasma membrane after uncaging. Accordingly, a preliminary proteomic analysis of the lipid–protein conjugates revealed that the two major PI transport proteins PITPα and β were prime targets of the photo-cross-linked PI derivative.