Covering Dimension and Universality Property on Frames

Order - Studies such as Dube et al. (Topology Appl. 160(18):2454–2464 2013), Georgiou et al. (Algebra Universalis 80(2):16, 2019), Iliadis (2005; Topology Appl. 179, 99–110, 2015;...     

Bis(cyclopropenium)phosphines: Synthesis,Reactivity, and Applications

A straightforward route for the preparation of a set of bis(cyclopropenium)‐substituted phosphines is reported. Due to their dicationic nature, these ligands depict an excellent π‐acceptor character. The effect of the ligand substituent pattern on the catalytic activity of the metal complexes thereof derived is also studied. Whereas sterically demanding biaryl groups directly attached to the phosphorus atom seem to facilitate elementary steps such as the product release from the catalyst, long chain dialkylamino groups on the cyclopropenium units maximize the catalysts solubility and, thus, allow the use of typical apolar solvents such as toluene. Importantly, all new ligands prepared can be easily handled in air. Finally, the impact of the newly prepared dicationic phosphines in hydroarylation reactions is demonstrated. In particular, their use in the synthesis of several naphtho[1,2‐b]furanes and naturally occurring naphthalene derivatives such as Calanquinone C is reported.     

Notes on Pointfree Disconnectivity with a Ring-theoretic Slant

We give characterizations of extremally disconnected frames, basically disconnected frames and F-frames L in terms of ring-theoretic properties of the ring RL\mathcal{R}L of continuous real-valued functions on L. Emanating from these are new (and purely ring-theoretic) proofs that a frame is extremally disconnected, basically disconnected or an F-frame iff the same holds for its Čech-Stone compactification.     

Metal complexes of bridging neutral radical ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.     

Some algebraic characterizations of F-frames

In pointfree topology, F-frames have been defined by Ball and Walters-Wayland by means of a frame-theoretic translation of the topological characterization of F-spaces as those whose cozero-sets are C*-embedded. This is a departure from the way in which F-spaces were defined by Gillman and Henriksen as those spaces X for which the ring C(X) is Bézout, meaning that every finitely generated ideal is principal. In this note, we show that, as in the case of spaces, a frame L is an F-frame precisely when the ring ${\mathcal{R}L}$ of continuous real-valued functions on L is Bézout. A commutative ring with identity is called almost weak Baer if the annihilator of each element is generated by idempotents. We establish that ${\mathcal{R}L}$ is almost weak Baer iff L is a strongly zero-dimensional F-frame.     

Hysteretic spin crossover between a bisdithiazolyl radical and its hypervalent σ-dimer

The bisdithiazolyl radical 1a is dimorphic, existing in two distinct molecular and crystal modifications. The α-phase crystallizes in the tetragonal space group P4?2(1)m and consists of π-stacked radicals, tightly clustered about 4? points and running parallel to c. The β-phase belongs to the monoclinic space group P2(1)/c and, at ambient temperature and pressure, is composed of π-stacked dimers in which the radicals are linked laterally by hypervalent four-center six-electron S···S-S···S σ-bonds. Variable-temperature magnetic susceptibility χ measurements confirm that α-1a behaves as a Curie-Weiss paramagnet; the low-temperature variations in χ can be modeled in terms of a 1D Heisenberg chain of weakly coupled AFM S = (1)/(2) centers. The dimeric phase β-1a is essentially diamagnetic up to 380 K. Above this temperature there is a sharp hysteretic (T↑= 380 K, T↓ = 375 K) increase in χ and χT. Powder X-ray diffraction analysis of β-1a at 393 K has established that the phase transition corresponds to a dimer-to-radical conversion in which the hypervalent S···S-S···S σ-bond is cleaved. Variable-temperature and -pressure conductivity measurements indicate that α-1a behaves as a Mott insulator, but the ambient-temperature conductivity σ(RT) increases from near 10(-7) S cm(-1) at 0.5 GPa to near 10(-4) S cm(-1) at 5 GPa. The value of σ(RT) for β-1a (near 10(-4) S cm(-1) at 0.5 GPa) initially decreases with pressure as the phase change takes place, but beyond 1.5 GPa this trend reverses, and σ(RT) increases in a manner which parallels the behavior of α-1a. These changes in conductivity of β-1a are interpreted in terms of a pressure-induced dimer-to-radical phase change. High-pressure, ambient-temperature powder diffraction analysis of β-1a confirms such a transition between 0.65 and 0.98 GPa and establishes that the structural change involves rupture of the dimer in a manner akin to that observed at high temperature and ambient pressure. The response of the S···S-S···S σ-bond in β-1a to heat and pressure is compared to that of related dimers possessing S···Se-Se···S σ-bonds.     

Total synthesis of myxothiazols, novel bis-thiazole beta-methoxyacrylate-based anti-fungal compounds from myxobacteria

Convergent total syntheses of myxothiazols A and Z are described. The syntheses are based on elaboration of the (S)-E,E-diene thioamide 22, conversion of 22 into the bis-thiazole 27 and Wittig reactions between 27c and the aldehyde 30. The substituted beta-methoxyacrylate aldehyde 30 was produced via an Evans asymmetric aldol protocol or via the 2H-pyran-2-one 31. An E-selective Wittig reaction between the ylide derived from the phosphonium salt 27c and the (+)-aldehyde 30 led to (+)-myxothiazol Z (1b), and a corresponding reaction with the (+/-)-acrylamide aldehyde 44 gave (+/-)-myxothiazol A (1a). Complementary studies led to synthesis of the ester 47b, corresponding to myxothiazol R and myxothiazol S.     

Characterization of amino acids in silk sericin protein from Gonometa rufobrunnae by MEKC with phenyl isothiocyanate derivatization

An MEKC method was developed for the separation and characterization of phenyl-isothiocyanate (PITC)-labeled amino acids derived from Gonometa rufobrunnae silkworm after microdialysis sample cleanup. The influence of the buffer and SDS concentration on the resolution of the amino acids was investigated. A buffer system consisting of 25 mM phosphate, 10 mM borate buffer at pH 9.00, and 70 mM SDS showed the best results, with 13 PITC-amino acid derivatives being resolved out of 15 possible amino acids that were under study. Microdialysis sampling demonstrated its efficiency as a sample cleanup technique. Sericin protein from G. rufobrunnae was found to be characterized by at least 11 positively identified amino acids. These included His, Tyr, Ser, Ala, Phe, Lys, Gly, Arg, Cys, Glu, and Asp. Leu/Met and Val/Thr were coeluting pairs and hence could not be positively confirmed.     

An algebraic view of weaker forms of realcompactness

We study a property of frames which is akin to realcompactness and obtained by replacing the cozero part of a frame in the definition of realcompactness with its Booleanization. Unlike the case of realcompactness, which is defined only for completely regular frames, this new concept is defined for all frames. We also investigate a weaker variant of this notion, and note that in both cases the frame results extend their topological precursors. This paper is dedicated to Walter Taylor. Received September 29, 2004; accepted in final form May 14, 2005.