New type of drift tubes for gas-discharge detectors operating in vacuum: Production technology and quality control

A device for fabricating thin-wall (straw) drift tubes using polyethylene terephthalate film 36 μm thick by ultrasonic welding is described together with the technique for controlling their quality. The joint width amounts to 0.4–1.0 mm. The joint breaking strength is 31.9 kg/mm². The argon leakage from a tube of volume 188.6 cm³ under a pressure gradient of 1.0 atm does not exceed 0.3 × 10^–3 cm³/min, which is mainly related to the absence of metallization in the joint vicinity. The high strength, the low tensile creep due to the absence of glued layers, the small value of gas leakage makes the new tubes capable of reliable and long-term operation in vacuum, which is confirmed by the operation of 7168 straw tubes for two years in the NA62 experiment.     

Platinum(IV)-mediated nitrile-sulfimide coupling: a route to heterodiazadienes

Pt(IV)-mediated addition of the sulfimide Ph2S = NH and the mixed sulfide/sulfimides o- and p-[PhS(=NH)](PhS)-C6H4 by the S=NH group to the metal-bound nitriles in the platinum(IV) complexes [PtCl4(RCN)2] proceeds smoothly at room temperature in CH2Cl2 and results in the formation of the heterodiazadiene compounds [PtCl4[NH=C(R)N=SR'Ph]2] (R' = Ph, R = Me, Et, CH2Ph, Ph; R' = o- and p-(PhS)C6H4; R = Et). While trans-[PtCl4(RCN)2] (R = Et, CH2Ph, Ph) reacting with Ph2S=NH leads exclusively to trans-[PtCl4[NH=C(R)N=SPh2]2], cis/trans-[PtCl4(MeCN)2] leads to cis/trans mixtures of [PtCl4[NH=C(Me)N=SPh2]2] and the latter have been separated by column chromatography. Theoretical calculations at both HF/HF and MP2//HF levels for the cis and trans isomers of [PtCl4[NH=C(Me)N=SMe2]2] indicate a higher stability for the latter. Compounds trans-[PtCl4[E-NH=C(R)N=SPh2]2] (R = Me, Et) and cis-[PtCl4[E-NH=C(Me)N=SPh2][Z-NH=C(Me)N=SPh2]] have been characterized by X-ray crystallography. The complexes [PtCl4[NH=C(R)N=SPh2]2] undergo hydrolysis when treated with HCl in nondried CH2Cl2 to achieve the amidines [PtCl4[NH=C(NH2)R]2] the compound with R = Et has been structurally characterized) and Ph2SO. The heterodiazadiene ligands, formed upon Pt(IV)-mediated RCN/sulfimide coupling, can be liberated from their platinum(IV) complexes [PtCl4[NH=C(R)N=SR'Ph]2] by reaction with Ph2PCH2CH2PPh2 (dppe) giving free NH=C(R)=SR'Ph and the dppe oxides, which constitutes a novel route for such rare types of heterodiazadienes whose number has also been extended. The hybrid sulfide/sulfimide species o- and p-[PhS(=NH)](PhS)C6H4 also react with the Pt(II) nitrile complex [PtCl2(MeCN)2] but the coupling--in contrast to the Pt(IV) species--gives the chelates [PtCl2[M-I=C(Me)N=S(Ph)C6H4SPh]]. The X-ray crystal structure of [PtCl2[M-I=C(Me)N=S(Ph)C6H4SPh-o]] reveals the bond parameters within the metallacycle and shows an unusual close interaction of the sulfide sulfur atom with the platinum.     

Relationship between Reactivity Ratios and Configuration for Donor—Acceptor Type Copolymers

For binary copolymers from an acrylic monomer (acceptor type, M¹) and an aromatic-substituted monomer (donor type, M₂) a linear relation between log (r₂/r¹) and the probability of “coisotactic” alternating addition is observed. This can be a proof for the influence of monomer polarity on the copolymer configuration.     

The Role of Torsional Dynamics on Hole and Exciton Stabilization in π‐Stacked Assemblies: Design of Rigid Torsionomers of a Cofacial Bifluorene

Exciton and charge delocalization across π‐stacked assemblies is of importance in biological systems and functional polymeric materials. To examine the requirements for exciton and hole stabilization, cofacial bifluorene ( F 2) torsionomers were designed, synthesized, and characterized: unhindered (model) ^Me F 2, sterically hindered ^tBu F 2, and cyclophane‐like ^C F 2, where fluorenes are locked in a perfect sandwich orientation via two methylene linkers. This set of bichromophores with varied torsional rigidity and orbital overlap shows that exciton stabilization requires a perfect sandwich‐like arrangement, as seen by strong excimeric‐like emission only in ^C F 2 and ^Me F 2. In contrast, hole delocalization is less geometrically restrictive and occurs even in sterically hindered ^tBu F 2, as judged by 160 mV hole stabilization and a near‐IR band in the spectrum of its cation radical. These findings underscore the diverse requirements for charge and energy delocalization across π‐stacked assemblies.     

Synthesis, structure, and X-band (9.5 GHz) EPR characterization of the new series of pH-sensitive spin probes: N,N-disubstituted 4-amino-2,2,5,5-tetramethyl-3-imidazoline 1-oxyls

[reaction: see text] An approach to the synthesis of new imidazoline nitroxides bearing an N',N'-disubstituted amidine group is reported. The approach is based on the alkylation of diamagnetic 4-R-amino-1,2,2,5,5-pentamethyl-3-imidazolines with bromoacetic acid ethyl ester; the products of alkylation are further oxidized to the corresponding nitroxides. The approach allows a variety of functional groups to be introduced into the nitroxide molecule structure. Alkylation with bromoacetic acid ethyl ester was found to proceed with high regioselectivity and afford the products of exo-alkylation. The regiochemical assignment is made on the basis of 13C NMR spectra and confirmed by X-ray diffraction study. All of the nitroxides synthesized here were shown to have pH-dependent EPR spectra with pKa ranging from 3.5 to 6.2. For nitroxides 13 bearing the carboxylic group remote to the nitroxide moiety, the changes in isotropic magnetic parameters of EPR spectra due to reversible deprotonation of the carboxylic group were found to be small. For these nitroxides, we demonstrate an alternative approach for pKa determination that is based on measuring the peak-to-peak line width of the EPR spectrum in the presence of the paramagnetic broadening agent potassium ferricyanide. The partition coefficients of nitroxides in octanol/H2O and octanol/phosphate buffer solution mixtures were measured to reveal a range of their lipophilicities.     

New phosphonium salts based on 3-(diphenylphosphino)propanoic and ω-haloalkanoic acids

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