Infrared multiphoton and collision-induced dissociation studies of some gaseous alkylamine ions

Collision-induced dissociation and infrared multiphoton dissociation of ions formed in di- and tri-ethylamine, di- and tri-n-propylamine, and di-isopropylamine were investigated by Fourier-transform ion-cyclotron resonance mass spectrometry. Molecular ions of all amines except di-n-propylamine produced similar fragment ions when subjected to either dissociation technique. The initial fragmentation involved C_αC_β bond cleavage, loss of an alkyl radical, and formation of an immonium ions. Subsequent fragmentations of the immonium ions produced by both dissociation mechanisms involved McLafferty-type rearrangements and loss of alkenes. The molecular ion of di-n-propylamine fragmented by a different mechanism when subjected to infrared irradiation. Protonated molecules of di- and tri-n-propylamine yielded C₃H₆ and an ammonium ion upon infrared multiphoton dissociation, while protonated molecules of the other amines did not dissociate when this technique was applied. In contrast, collision-induced dissociation produced fragmentation for all protonated molecules. Explanation of the different fragmentations observed for the two dissociation techniques is given in terms of a mechanism involving a tight transition state for protonated di- and tri-n-propylamine dissociation.     

Characterization of inorganic coordination complexes by matrix-assisted laser desorption/ionization mass spectrometry

We report the direct laser desorption/ionization (LDI) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOFMS) analysis of four inorganic coordination complexes: monometallic [Ir(dpp)(2)Cl(2)](PF(6)), homonuclear trimetallic ([(bpy)(2)Ru(dpp)](2)RuCl(2))- (PF(6))(4), and heteronuclear [(tpy)Ru(tpp)Ru(tpp)RhCl(3)](PF(6))(4) and ([(bpy)(2)Ru(dpp)](2)IrCl(2))(PF(6))(5) (dpp = 2,3-bis-(2'-pyridyl)pyrazine, bpy = 2,2'-bipyridine, tpy = 2,2',6',2"-terpyradine, tpp = 2,3,5,6,-tetrakis-(2'-pyridyl)pyrazine). Spectral intensities and fragmentation patterns are compared and evaluated for instrument parameters, matrix selection, and matrix-to-analyte ratio. Direct LDI and MALDI mass spectra of the monometallic complex showed the same ion peaks and differed only in the relative peak intensities. Direct LDI of the trimetallic complexes produced only low-mass fragments containing one metal at most. MALDI spectra of the trimetallic complexes exhibited little fragmentation in the high-mass region (>1500 Da) and less fragmentation in the low-mass region compared to direct LDI. Significant fragments of the molecules were detected and identified, including ligand fragments, intermediate-mass fragments such as [Ru(tpy)](+), and molecular ions with varying degrees of PF(6)(-) loss ([M - n(PF(6))](+), where n = 1-3). A correlation exists between the solution-phase electrochemistry and the observed [M - n(PF(6))](+) series of peaks for the trimetallic complexes. Proper matrix selection for MALDI analysis was vital, as was an appropriate matrix-to-analyte ratio. The results demonstrate the applicability of MALDI-TOFMS for the structural characterization of labile inorganic coordination complexes.     

Rasta silanes: new silyl resins with novel macromolecular architecture via living free radical polymerization

Heating TEMPO-methyl resin with dialkylsilane styrenes affords larger resin beads via living free radical polymerization. The new silyl resins prepared by this solvent-free suspension polymerization protocol have been coined "Rasta silanes". Rasta silanes have a novel macromolecular architecture typified by long straight chain polymers bearing the silanes which emanate from the phenyl rings of a cross-linked polystyrene core. By careful selection of comonomers during the polymerization step, loading capacity, silane spacing, and the relative distance of the silane moieties from the resin core can be controlled. The consistently high-loading Rasta silane resins produced can be easily converted into either a reactive silyl chloride or triflate to subsequently anchor alcohols and phenols to the solid phase. Cleavage from the resin can be mediated by treatment with HF.pyridine, TFA solutions, or TBAF.     

Aromatic vs aliphatic C-H cleavage of alkyl-substituted pyridines by (PNPiPr)Re compounds

Both (PNP)Re(H)(4) and (PNP)ReH(cyclooctyne) (PNP(i)(Pr) = ((i)Pr(2)PCH(2)SiMe(2))(2)N) react with alkylpyridines NC(5)H(4)R to give first (PNP)ReH(2)(eta(2)-pyridyl) and cyclooctene and then, when not sterically blocked, (PNP)Re(eta(2)-pyridyl)(2) and cyclooctane. The latter are shown by NMR, X-ray diffraction, and DFT calculations to have several energetically competitive isomeric structures and pyridyl N donation in preference to PNP amide pi-donation. DFT studies support NMR solution evidence that the most stable bis pyridyl structure is one that is doubly eta(2)- with the pyridyl N donating to the metal center. When both ortho positions carry methyl substituents, cyclooctane and the carbyne complex (PNP)ReH(tbd1;C-pyridyl) are produced. Excess 2-vinyl pyridine reacts with (PNP)Re(H)(4) preferentially at the vinyl group, to give 2-ethyl pyridine and the sigma-vinyl complex (PNP)ReH[eta(2)-CH=CH(2-py)]. The DFT and X-ray structures show, by various comparisons, the ability of the PNP amide nitrogen to pi-donate to an otherwise unsaturated d(4) Re(III) center, showing short Re-N distances consistent with the presence of pi-donation.     

Amplified detection of nucleic acids and proteins using an isothermal proximity CRISPR Cas12a assay

Herein, we describe an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced indiscrimitive single-stranded DNase activity of Cas12a for the quantitative profiling of gene expression at the mRNA level and detection of proteins with high sensitivity and specificity. The target recognition is achieved through proximity binding rather than recognition by CRISPR RNA (crRNA), which allows for flexible assay design. A binding-induced primer extension reaction is used to generate a predesigned CRISPR-targetable sequence as a barcode for further signal amplification. Through this dual amplification protocol, we were able to detect as low as 1 fM target nucleic acid and 100 fM target protein isothermally. The practical applicability of this assay was successfully demonstrated for the temporal profiling of interleukin-6 gene expression during allergen-mediated mast cell activation.

Herein, we develop an isothermal proximity CRISPR Cas12a assay that harnesses the target-induced collateral cleavage activity of Cas12a for the quantitative profiling of gene expression and detection of proteins with high sensitivity and specificity.     

Development of chiral heteroleptic magnesium amides; asymmetric deprotonations mediated by six-membered metallocyclic amidomagnesium naphtholates

A series of enantioenriched six-membered metallocyclic amidomagnesium naphtholates were prepared and used to probe the structure–reactivity/selectivity relationships of heteroleptic magnesium base complexes within asymmetric deprotonation reactions. An effective complex was identified and applied within enantioselective enolisation processes, delivering good levels of enantioselectivity and also revealing key structural requirements for achieving such selectivity.     

Copper‐Catalyzed Amidation of Primary and Secondary Alkyl Boronic Esters

The oxidative copper‐catalyzed cross‐coupling of functionalized alkyl boronic esters with primary amides is reported. Through the identification of appropriate diketimine ligands, conditions for efficient coupling of both primary and secondary alkyl boronic esters with diverse primary amides, including acetamide, have been developed.     

Markov processes on Riesz spaces

Measure-free discrete time stochastic processes in Riesz spaces were formulated and studied by Kuo, Labuschagne and Watson. Aspects relating martingales, stopping times, convergence of these processes as well as various decomposition were considered. Here we formulate and study Markov processes in a measure-free Riesz space setting.     

Comparisons of the vector method and tensor method for simulating liquid crystal devices

In calculating the director configuration in a liquid crystal device, two methods are commonly employed: a vector model and a tensor model. In this paper, we compare and contrast these methods for liquid crystal devices consisting of a layer of liquid crystal sandwiched between two plates. We compare the reliability and accuracy of the results, the speed of computation and the complexity of implementations of each method.