Xenon porometry at room temperature

Xenon porometry is a method in which porous material is immersed in a medium and the properties of the material are studied by means of 129Xe nuclear magnetic resonance (NMR) of xenon gas dissolved in the medium. For instance, the chemical shift of a particular signal (referred to as signal D) arising from xenon inside small pockets formed in the pores during the freezing of the confined medium is highly sensitive to the pore size. In the present study, we show that when naphthalene is used as the medium the pore size distribution of the material can be determined by measuring a single one-dimensional spectrum near room temperature and converting the chemical shift scale of signal D to the pore radius scale by using an experimentally determined correlation. A model has been developed that explains the curious behavior of the chemical shift of signal D as a function of pore radius. The other signals of the spectra measured at different temperatures have also been identified, and the influence of xenon pressure on the spectra has been studied. For comparison, 129Xe NMR spectra of pure xenon gas adsorbed to porous materials have been measured and analyzed.     

Hydroboration with pyridine borane at room temperature

Treatment of pyridine borane (Py.BH3) with iodine, bromine, or strong acids affords activated Py.BH2X complexes that are capable of hydroborating alkenes at room temperature. Evidence is presented for an unusual hydroboration mechanism involving leaving group displacement. In contrast to THF.BH3, hydroboration with Py.BH2I selectively affords the monoadducts. The crude hydroboration products are converted into synthetically useful potassium alkyltrifluoroborate salts upon treatment with methanolic KHF2.     

Cationic polymerization of isobutylene at room temperature

This review highlights recent approaches toward polyisobutylene (PIB) by an energy efficient room temperature cationic polymerization. Special focus is laid on our own work using modified Lewis acids and nitrile‐ligated metal complexes associated with weakly coordinating anions. In both cases, suitable conditions have been found for efficient production of PIB characterized by medium to low molar masses and a high content of exo double bonds as end groups—the typical features of highly reactive PIB, an important commercial intermediate toward oil and gasoline additives. These and other approaches demonstrate that the cationic polymerization of isobutylene is still not fully explored, and new innovative catalyst systems can lead to surprising results of high commercial interest. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Thermal properties at room temperature of polytetrafluoroethylene

Through Differential Scanning Calorimetry (DSC), at least three room temperature transitions are clearly observable for native polytetrafluoroethylene (PTFE). The influence of the thermal history on the room temperature transitions has been investigated. Possible interpretations for the lowest room temperature transition are suggested.

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Zusammenfassung Bei der Untersuchung von nativen Polytetrafluoroethylen (PTFE) lassen sich im Raumtemperaturbereich zumindest drei Umwandlungen eindeutig beobachten. Der Einfluss der termischen Vorgeschichte von PTFE Proben auf die Umwandlungen im Raumtemperaturbereich wurde untersucht.Mögliche ErklÄrungen für den tiefstliegenden übergang im genannten Temperaturbereich werden vorgeschlagen.

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Dr. G. Ajroldi and Prof. G. Guerra are gratefully acknowledged for useful advice and stimulating discussions.     

Synthesis of zeolite nanocrystals at room temperature

Zeolite A nanoparticles were synthesized under room-temperature conditions from a very reactive organic-template-free gel system. The optimization of the syntheses parameters, namely, the composition of the initial system and the careful choice of the reactants, allowed the crystallization to be accomplished within 3 days. At this stage the individual zeolite crystals were in the range of 100-300 nm without well-developed crystal faces. The prolongation of the synthesis time up to 10 days led to formation of larger well-faceted cubic crystals averaging about 400-500 nm in size. The high-resolution transmission electron microscopy (HRTEM) study revealed that a thin layer of amorphous material covers the zeolite particles acting as a binder between individual zeolite crystals. The postsynthesis treatment of the product in NH(3) media under ultrasonic radiation disintegrated the loosely attached zeolite particles and decreased the fraction of zeolite A particles with low colloidal stability. The employed approach, however, did not result in complete disintegration of aggregated crystals. The zeolite crystals obtained under ambient conditions were characterized by XRD, SEM, dynamic light scattering, and N(2) adsorption measurements.     

Crystallization-induced phosphorescence of benzils at room temperature

Efficient room temperature phosphorescence (RTP) is rarely observed in pure organic luminogens. However, we have newly observed that benzil and its derivatives are nonluminescent in solvents and thin layer chromatography (TLC) plates, but become highly phosphorescent in crystal state at room temperature, exhibiting typical crystallization-induced phosphorescence (CIP) characteristics. The CIP phenomenon is ascribed to the restriction of intramolecular rotations in crystals owing to effective intermolecular interactions. Such intermolecular interactions greatly rigidify the molecular conformation and significantly decrease the nonradiative deactivation channels of the triplet excitons, thus giving boosted phosphorescent emission at room temperature.     

Polyurethane adhesive composition cured at room temperature

The influence of polyfunctional hydroxyl-containing oligomer on the rheological, physicomechanical, and adhesive properties of polyurethane composite based on multicomponent oligomer blend and polyisocyanate is investigated. The kinetics of curing is investigated by the viscometric method, and the composition lifetime is determined. It is shown that the polyurethanes under investigation can be used as fast-curing adhesive composites of cold curing operating in a temperature interval of up to +90°C.     

Transition-metal-free C-arylation at room temperature by arynes

A facile, fluoride-induced transition-metal-free chemoselective α-arylation of β-dicarbonyl compounds (malonamide esters) at room temperature using aryne intermediates has been demonstrated. Selective mono- or diarylation and generation of a quaternary benzylic stereocenter have also been achieved. The methodology will be highly useful for the synthesis of a library of CNS depressant barbiturate drugs like Phenobarbital.     

The triplet-state lifetime of indole in aqueous and viscous environments: significance to the interpretation of room temperature phosphorescence in proteins

The interpretation of room temperature phosphorescence studies of proteins requires an understanding of the mechanisms governing the tryptophan triplet-state lifetimes of residues fully exposed to solvent and those deeply buried in the hydrophobic core of proteins. Since solvents exposed tryptophans are expected to behave similarly to indole free in solution, it is important to have an accurate measure of the triplet state lifetime of indole in aqueous solution. Using photon counting techniques and low optical fluence (J/cm(2)), we observed the triplet-state lifetime of aqueous, deoxygenated indole and several indole derivatives to be approximately 40 micros, closely matching the previous reports by Bent and Hayon based on flash photolysis (12 micros; Bent, D. V.; Hayon, E. J. Am. Chem. Soc. 1975, 97, 2612-2619) but much shorter than the 1.2 ms lifetime observed more recently (Strambini, G. B.; Gonnelli, M. J. Am. Chem. Soc. 1995, 117, 7646-7651). However, we have now been able to reproduce the long lifetime reported by the latter workers for aqueous indole solutions and show that it likely arises from geminate recombination of the indole radical cation and solvated electron, a conclusion based on studies of the indole radical cation in water (Bent and Hayon, 1975). The evidence for this comes from a fast rise in the phosphorescence emission and measurements of a corresponding enhanced quantum yield in unbuffered solutions. This species can be readily quenched, and the corresponding fast rise disappears, leaving a monoexponential 40 micros decay, which we argue is the true indole triplet lifetime. The work is put in the context of room temperature phosphorescence studies of proteins.     

Bis(ammonium) fluorophosphate at room temperature

The title room‐temperature phase of (NH₄)₂(PO₃F) is orthorhombic (Pna2₁) and is related to the β‐K₂SO₄ structure family. The title structure consists of ammonium cations, NH₄⁺, and fluoro­phosphate anions, (PO₃F)^2?. These ions are connected by N—H?O hydrogen bonds. Two‐centre N—­H?F hydrogen bonds are not present in the structure. Phase transitions were detected at 251±2 and 274±2 K during cooling and heating, respectively.     

Compounds in the system Cs-Te at room temperature

In the system CsTe the compounds Cs₂Te, Cs₃Te₂, Cs₂Te₃, Cs₂Te₅ and CsTe₄ are stable at room temperature. The powder pattern of Cs₂Te was indexed.     

Rapid elongation of CdS nanowire at room temperature

The CdS nanowires synthesized by solvothermal route are rapidly elongated in the presence of the ethylenediamine by ultrosonication method at room temperature. Transmission electron microscopy (TEM) analysis reveals that the influential factors on the rapid elongate process are the concentration of ethylenediamine and duration of the ultrosonication reaction. The elongated CdS nanowires are further characterized by UV–vis absorption spectra, which has no apparent difference in the position of the maximum absorption peak comparing with the starting CdS nanowires synthesized by solvothermal method. A mechanism of oriented attachment is proposed to explain the phenomena based on a series of experimental results.