Molecular flow and wall collision age distributions

The use of storage cells has become a standard technique for internal gas targets in conjunction with high energy storage rings. In case of spin-polarized hydrogen and deuterium gas targets the interaction of the injected atoms with the walls of the storage cell can lead to depolarization and recombination. Thus the number of wall collisions of the atoms in the target gas is important for modeling the processes of spin relaxation and recombination. It is shown in this article that the diffusion process of rarefied gases in long tubes or storage cells can be described with the help of the one-dimensional diffusion equation. Mathematical methods are presented that allow one to calculate collision age distributions (CAD) and their moments analytically. These methods provide a better understanding of the different aspects of diffusion than Monte Carlo calculations. Additionally it is shown that measurements of the atomic density or polarization of a gas sample taken from the center of the tube allow one to determine the possible range of the corresponding density weighted average values along the tube. The calculations are applied to the storage cell geometry of the HERMES internal polarized hydrogen and deuterium gas target. Received 9 July 2001 and Received in final form 18 September 2001     

Theoretical study of cyclization of 2′-hydroxychalcone

The isomerization mechanism of 2′(OH)chalcone (1) in flavanone (2) was studied. The calculations were performed with the semiempirical method AM1, using totally optimized molecular geometries. A 6-step mechanism including several equilibrium states was proposed. It was concluded that: (a) At the conformational equilibrium of 1 there could be 43.9% of s-cis conformer; (b) The acid dissociation of 1 trans-s-trans is considerable; (c) The E_E, ΔH_f and net charges show that the rotation of ring A of 1 and the formation of ring C of 2 occurs without greater impairments; (d) Although the keto structure is the most stable one, the enolate of 2 is present in the reaction medium; (e) The conversion of enol of 2 in the keto form would be the limiting step of the analyzed isomerization rate.     

First measurement of the ϱ spectral function in nuclear collisions

The NA60 experiment at the CERN SPS has studied low-mass muon pairs in 158 A GeV In–In collisions. A strong excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size close to 400000 events and the good mass resolution of about 2% made it possible to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum shows some non-trivial centrality dependence, but is largely consistent with a dominant contribution from π⁺π^-→ϱ→μ⁺μ^- annihilation. The associated ϱ spectral function exhibits considerable broadening, but essentially no shift in mass. The p_T-differential mass spectra show the excess to be much stronger at low p_T than at high p_T. The results are compared to theoretical model predictions; they tend to rule out models linking hadron masses directly to the chiral condensate. PACS 25.75.-q; 12.38.Mh; 13.85.Qk     

Phase separation of p53 precedes aggregation and is affected by oncogenic mutations and ligands

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF). The mechanism of the formation of the aggregates in the nucleus remains uncertain. The present study demonstrated that the DNA-binding domain of p53 (p53C) underwent phase separation (PS) on the pathway to aggregation under various conditions. p53C phase separated in the presence of the crowding agent polyethylene glycol (PEG). Similarly, mutant p53C (M237I and R249S) underwent PS; however, the process evolved to a solid-like phase transition faster than that in the case of wild-type p53C. The data obtained by microscopy of live cells indicated that transfection of mutant full-length p53 into the cells tended to result in PS and phase transition (PT) in the nuclear compartments, which are likely the cause of the GoF effects. Fluorescence recovery after photobleaching (FRAP) experiments revealed liquid characteristics of the condensates in the nucleus. Mutant p53 tended to undergo gel- and solid-like phase transitions in the nucleus and in nuclear bodies demonstrated by slow and incomplete recovery of fluorescence after photobleaching. Polyanions, such as heparin and RNA, were able to modulate PS and PT in vitro. Heparin apparently stabilized the condensates in a gel-like state, and RNA apparently induced a solid-like state of the protein even in the absence of PEG. Conditions that destabilize p53C into a molten globule conformation also produced liquid droplets in the absence of crowding. The disordered transactivation domain (TAD) modulated both phase separation and amyloid aggregation. In summary, our data provide mechanistic insight into the formation of p53 condensates and conditions that may result in the formation of aggregated structures, such as mutant amyloid oligomers, in cancer. The pathway of mutant p53 from liquid droplets to gel-like and solid-like (amyloid) species may be a suitable target for anticancer therapy.

Mutant p53 tends to form aggregates with amyloid properties, especially amyloid oligomers inside the nucleus, which are believed to cause oncogenic gain-of-function (GoF).     

Confirmatory analysis of residues of stanozolol and its major metabolite in bovine urine by liquid chromatography-tandem mass spectrometry

A reliable method for the confirmation of the synthetic hormone stanozolol and its major metabolite, 16beta-hydroxystanozolol, in bovine urine by liquid chromatography coupled with tandem mass spectrometry has been developed. [2H3]Stanozolol was used as internal standard. Sample preparation involved enzymatic hydrolysis, liquid-liquid extraction and purification on an amino solid-phase extraction column. The analytes were ionized using atmospheric pressure chemical ionization with a heated nebulizer interface operating in the positive ion mode, where only the protonated molecules, [M+H]+, at m/z 329 and m/z 345, for stanozolol and 16beta-hydroxystanozolol, respectively, were generated. These served as precursor ions for collision-induced dissociation and three diagnostic product ions for each analyte were identified for the unambiguous hormone confirmation by selected reaction monitoring liquid chromatography-tandem mass spectrometry. The accuracy ranged from 19.7 to 14.9% and from 18.9 to 13.2% for stanozolol and 16beta-hydroxystanozolol, respectively. The precision ranged from 12.4 to 2.4% and from 13.1 to 1.8% for stanozolol and 16beta-hydroxystanozolol, respectively. The limit of quantification of the method was 1 ng/ml in the bovine urine for both stanozolol and 16beta-hydroxystanozolol. The developed method fulfils the European Union requirements for confirmatory methods.     

Trinuclear pyrazine-bridged ruthenium complexes: syntheses, electrochemistry, NIR-Vis spectra, and their interpretation in terms of a 5-orbital-3-parameter model

A study of absorption spectra in the near-infrared (NIR) and visible (vis) regions of trinuclear Ru complexes containing pyrazine (pyz) as bridging ligand, trans-[(Ru(NH(3))(5)pyz)(2)Ru(NH(3))(4)](m+)(m = 6-9), is reported. The spectra were recorded on aqueous solutions containing the described species formed in situ by stoichiometric additions of a standard solution of Ce(SO(4))(2). They were interpreted in terms of a simple 5-orbital-3-parameter model which includes the effects of d-pi interaction and electronic correlation. The model is shown to account for the observed NIR-vis spectra of the complex ions. The 6+ parent species was synthesized by an improved literature method and fully characterized. The novel 8+ complex was also prepared and characterized. The 9+ ion was established to be slowly reduced by water, with dioxygen formation. Electrochemical (CV and DPV) studies were performed on the trinuclear 6+ complex, as well as on its constituent fragments [Ru(NH(3))(5)(pyz)](2+) and trans-[Ru(NH(3))(4)(pyz)(2)](2+).     

Quantitation of anabolic hormones and their metabolites in bovine serum and urine by liquid chromatography-tandem mass spectrometry

A specific and sensitive method based on tandem mass spectrometry with on-line high-performance liquid chromatography using atmospheric pressure chemical ionisation (LC–APCI-MS–MS) for the quantitation of anabolic hormone residues (17β-19-nortestosterone, 17β-testosterone and progesterone) and their major metabolites (17-19-nortestosterone and 17-testosterone) in bovine serum and urine is reported. [²H₂]17β-Testosterone was used as internal standard. The analytes were extracted from urine (following enzymatic hydrolysis) and serum samples by liquid–liquid extraction and purified by C₁₈ solid-phase extraction. Ionisation was performed in a heated nebulizer interface operating in the positive ion mode, where only the protonated molecule, [M+H]⁺, was generated for each analyte. This served as precursor ion for collision-induced dissociation and two diagnostic product ions for each analyte were identified for the unambiguous hormone confirmation by selected reaction monitoring LC–MS–MS. The overall inter-day precision (relative standard deviation) ranged from 6.37 to 2.10% and from 6.25 to 2.01%, for the bovine serum and urine samples, respectively, while the inter-day accuracy (relative error) ranged from −5.90 to −3.18% and from −6.40 to −2.97%, for the bovine serum and urine samples, respectively. The limit of quantitation of the method was 0.1 ng/ml for all the hormones in bovine serum and urine. On account of its high sensitivity and specificity the method has been successfully used to confirm illegal hormone administration for regulatory purposes.     

Cyclic guanidines: Synthesis of 4,6,7,8-tetrahydro-1H-imidazo[1,2-a]pyrazolo[3,4-d]pyrimidin-7-ones and 1,4,6,7,8,9-hexahydropyrazolo[3′,4′:4,5]pyrimido[2,1-c] [1,2,4]triazin-7-ones

The synthesis of potential platelet aggregation inhibitors 4,6,7,8-tetrahydroimidazo[1,2-a]pyrazolo[3,4-d]-pyrimidin-7-ones and 1,4,6,7,8,9-hexahydropyrazolo[3′,4′:4,5]pyrimido[2,1-c] [1,2,4]triazin-7-ones derivatives is described starting from 4,6-dichloropyrazolo[3,4-d]pyrimidines.