Synthesis,Structure, and Two Polymorphs of 4-((1,3-Dioxoisoindolin-2-yl)methyl)-1-methoxypyridinium tetrafluoroborate

Abstract  

4-((1,3-Dioxoisoindolin-2-yl)methyl)-1-methoxypyridinium tetrafluoroborate, C₁₅H₁₃BF₄N₂O₃, 1, was obtained by alkylation of the corresponding N-oxide and has been characterized by ¹H and ¹³C NMR, IR, UV spectroscopy and by X-ray crystallography. The crystal undergoes a reversible phase transition between 173 and 293 K. At room temperature, crystals are orthorhombic, space group Pna2₁ with a = 7.2487(3) ?, b = 17.8359 (8) ?, c = 12.4077(6) ?, V = 1604.16(12) ?³, and Z = 4. At 173 K, cations adopt four conformations in monoclinic space group Cc with a = 24.7076(29) ?, b = 14.4145(9) ?, c = 21.8765(25) ?, β = 126.249(17)°, V = 6283.3(7) ?³, and Z = 16. The compound is photostable in the crystal and does not undergo homolytic N–O bond cleavage as observed in solution.     

Temporal processing deficits in the pre-senescent auditory system

This study tested the hypothesis that temporal processing deficits are evident in the pre-senescent (middle-aged) auditory system for listening tasks that involve brief stimuli, across-frequency-channel processing, and/or significant processing loads. A gap duration discrimination (GDD) task was employed that used either fixed-duration gap markers (experiment 1) or random-duration markers (experiment 2). Independent variables included standard gap duration (0, 35, and 250 ms), marker frequency (within- and across-frequency), and task complexity. A total of 18 young and 23 middle-aged listeners with normal hearing participated in the GDD experiments. Middle age was defined operationally as 40-55 years of age. The results indicated that middle-aged listeners performed more poorly than the young listeners in general, and that this deficit was sometimes, but not always, exacerbated by increases in task complexity. A third experiment employed a categorical perception task that measured the gap duration associated with a perceptual boundary. The results from 12 young and 12 middle-aged listeners with normal hearing indicated that the categorical boundary was associated with shorter gaps in the young listeners. The results of these experiments indicate that temporal processing deficits can be observed relatively early in the aging process, and are evident in middle age.     

Efficient reflection grisms for pulse compression and dispersion compensation of femtosecond pulses

Efficient reflection grisms for pulse-compression and material-dispersion compensation have been designed and demonstrated in a 40 fs, 300 microJ, 5 kHz downchirped pulse amplification system for the first time to our knowledge. A grism design for 800 nm femtosecond laser pulse dispersion compensation applications is realized by using standard, commercial diffraction gratings.     

Spectroscopic and kinetic studies of the reaction of [CuI(6-PhTPA)]+ with O2

Oxygenation of [Cu(I)(6-PhTPA)](SbF(6)) in acetone at -90 degrees C produces a short-lived Cu(III)(2)(mu-O)(2) intermediate that exhibits an oxygen-isotope-sensitive nu(Cu-O) mode at 599 cm(-1) and an overtone at 1192 cm(-1). The formation of this intermediate is very fast and is second-order in copper(I) complex, implying that two copper-containing species interact in the rate-limiting step or in pre-equilibrium steps prior to the rate determining step. The decay of this intermediate was facile even at -90 degrees C but did not afford any arene hydroxylation product. Interestingly, the effect of introducing a 6-phenyl substituent on the TPA ligand framework differs from that of a 6-methyl substituent, providing access to a bis(mu-oxo)dicopper(III) intermediate in the former and a (mu-1,2-peroxo)dicopper(II) species in the latter.     

The detection of red pigment-concentrating hormone (RPCH) in crustacean eyestalk tissues using matrix-assisted laser desorption/ionization-Fourier transform mass spectrometry: [M + Na]+ ion formation in dried droplet tissue preparations

Red pigment-concentrating hormone (RPCH), an octapeptide found in crustaceans and insects with the sequence pGlu-Leu-Asn-Phe-Ser-Pro-Gly-Trp-NH2, is an N- and C-terminally blocked uncharged peptide. These structural features are shared with many members of the larger adipokinetic hormone (AKH)/RPCH peptide family in insects. We have applied vacuum UV matrix-assisted laser desorption/ionization (MALDI)-Fourier transform ion cyclotron mass spectrometry (FTMS) to the direct analysis of crustacean sinus gland tissues, using 2,5-dihydroxybenzoic acid (DHB) as the MALDI matrix, and have found that RPCH is detected in the cationized, [M + Na]+, form under conditions where other peptides in the direct tissue spectra are protonated without accompanying [M + Na]+ or [M + K]+ satellite peaks. The [M + H]+ ion for RPCH is not detected in tissue samples or for an RPCH standard, even when care is taken to eliminate metal ions. This behavior is not unprecedented; however, both direct tissue spectra and SORI-CID spectra provide no clues to suggest that the ionizing agent is a metal cation. In this communication, we characterize the MALDI-FTMS ionization and SORI-CID mass spectra of the [M + Na]+ and [M + K]+ ions from RPCH, and report on the detection of this neuropeptide in sinus gland tissues from the lobster Homarus americanus and the kelp crab Pugettia producta. We describe two strategies, an on-probe extraction procedure and a salt-doping approach, that can be applied to previously analyzed MALDI tissue samples to enhance and unmask sodiated peptides that may otherwise be mistaken for novel neuropeptides.     

Metal-organic frameworks from zinc sulfite clusters, chains, and sheets: 4-connected, (3,4)-connected 3-D frameworks and 2-D arrays of catenane-like interlocking rings

Even though open-framework solids have been made in a variety of compositions such as silicates, phosphates, germanates, borates, and phosphites, few are known that are based on trigonal-pyramidal sulfite anions. We report here the first synthetic and structural studies of metal-organic framework materials in the zinc sulfite composition. It is demonstrated here that Zn2+ and SO32- can form various neutral inorganic subunits that can be 0-D clusters, 1-D chains, or 2-D sheets. These inorganic subunits of different dimensionality can subsequently be connected into extended frameworks of higher dimensionality through bifunctional ligands. In (ZnSO3)2en, infinite corrugated ZnSO3 layers are pillared by ethylenediamine (en) molecules into a 3-D network that can be classified as a (3,4)-connected net based on tetrahedral Zn nodes and trigonal-pyramidal S nodes. In (ZnSO3)pip, infinite ZnSO3 chains are cross-linked with piperazine molecules into a 3-D framework that can be classified as 4-connected net based on tetrahedral Zn nodes only. In (ZnSO3)2(TMDPy)2, (ZnSO3)2 dimers are doubly bridged by trimethylenedipyridine molecules into an infinite chain with a string of circles. Each circle along the chain is interlocked with another circle from a chain in the perpendicular direction, creating a 2-D pattern with an infinite-square array of catenane-like units.     

Tren-based analogues of bacillibactin: structure and stability

Synthetic analogues were designed to highlight the effect of the glycine moiety of bacillibactin on the overall stability of the ferric complex as compared to synthetic analogues of enterobactin. Insertion of a variety of amino acids to catecholamide analogues based on a Tren (tris(2-aminoethyl)amine) backbone increased the overall acidity of the ligands, causing an enhancement of the stability of the resulting ferric complex as compared to TRENCAM. Solution thermodynamic behavior of these siderophores and their synthetic analogues was investigated through potentiometric and spectrophotometric titrations. X-ray crystallography, circular dichroism, and molecular modeling were used to determine the chirality and geometry of the ferric complexes of bacillibactin and its analogues. In contrast to the Tren scaffold, addition of a glycine to the catechol chelating arms causes an inversion of the trilactone backbone, resulting in opposite chiralities of the two siderophores and a destabilization of the ferric complex of bacillibactin compared to ferric enterobactin.     

Dioxygen-initiated oxidation of heteroatomic substrates incorporated into ancillary pyridine ligands of carboxylate-rich diiron(II) complexes

Progress toward the development of functional models of the carboxylate-bridged diiron active site in soluble methane monooxygenase is described in which potential substrates are introduced as substituents on bound pyridine ligands. Pyridine ligands incorporating a thiol, sulfide, sulfoxide, or phosphine moiety were allowed to react with the preassembled diiron(II) complex [Fe(2)(mu-O(2)CAr(R))(2)(O(2)CAr(R))(2)(THF)(2)], where (-)O(2)CAr(R) is a sterically hindered 2,6-di(p-tolyl)- or 2,6-di(p-fluorophenyl)benzoate (R = Tol or 4-FPh). The resulting diiron(II) complexes were characterized crystallographically. Triply and doubly bridged compounds [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-MeSpy)] (4) and [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(2-MeS(O)py)(2)] (5) resulted when 2-methylthiopyridine (2-MeSpy) and 2-pyridylmethylsulfoxide (2-MeS(O)py), respectively, were employed. Another triply bridged diiron(II) complex, [Fe(2)(mu-O(2)CAr(4)(-)(FPh))(3)-(O(2)CAr(4)(-)(FPh))(2-Ph(2)Ppy)] (3), was obtained containing 2-diphenylphosphinopyridine (2-Ph(2)Ppy). The use of 2-mercaptopyridine (2-HSpy) produced the mononuclear complex [Fe(O(2)CAr(Tol))(2)(2-HSpy)(2)] (6a). Together with that of previously reported [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-PhSpy)] (2) and [Fe(2)(mu-O(2)CAr(Tol))(3)(O(2)CAr(Tol))(2-Ph(2)Ppy)] (1), the dioxygen reactivity of these iron(II) complexes was investigated. A dioxygen-dependent intermediate (6b) formed upon exposure of 6a to O(2), the electronic structure of which was probed by various spectroscopic methods. Exposure of 4 and 5 to dioxygen revealed both sulfide and sulfoxide oxidation. Oxidation of 3 in CH(2)Cl(2) yields [Fe(2)(mu-OH)(2)(mu-O(2)CAr(4)(-)(FPh))(O(2)CAr(4)(-FPh))(3)(OH(2))(2-Ph(2)P(O)py)] (8), which contains the biologically relevant {Fe(2)(mu-OH)(2)(mu-O(2)CR)}(3+) core. This reaction is sensitive to the choice of carboxylate ligands, however, since the p-tolyl analogue 1 yielded a hexanuclear species, 7, upon oxidation.     

Stable Aziridinium Salts as Versatile Intermediates: Isolation and Regio‐ and Stereoselective Ring‐Opening and Rearrangement

Rock trapping and exploration : Aziridinium bromide salts were discovered serendipitously during bromination of N,N‐dicarboxymethylated β‐amino alcohols. Regiospecific ring‐opening and rearrangement of the isolated, surprisingly stable aziridinium salts produces useful molecules including C‐functionalized oxomorpholines and α,β‐unsaturated amines.

     

An application of the Krasnoselskii theorem to systems of algebraic equations

Based on the Krasnoselskii theorem, we study the existence, multiplicity and nonexistence of positive solutions of general systems of nonlinear algebraic equations under superlinearity and sublinearity conditions. Systems of nonlinear algebraic equations often arise from studies of differential and difference equations. Our results significantly extend and improve those in the literature. A?number of examples and open questions are given to illustrate these results.