Sub-nanosecond, 1–10?kHz, low-threshold, non-critical OPOs based on periodically poled KTP crystal pumped at 1,064?nm

We employed a 9-mm long periodically poled KTiOPO₄ (PPKTP) crystal in an optical parametric oscillator (OPO) to generate sub-nanosecond idler pulses around 2.8???m. With a 1-cm long OPO cavity in a singly resonant configuration and double pass pumping by 1-ns pulses at 1,064?nm, the maximum idler energy reached 110???J at 1?kHz. Pumping with 500?ps pulses at 1?C10?kHz, resulted in an idler energy of ~50???J and the shortest pulse duration of ~250?ps, ever reported for an OPO. The corresponding quantum conversion efficiencies were 32.5 and 34.9?%, respectively.     

An unusual cationic [2 + 2] cycloaddition in a divergent total synthesis of hongoquercin A and rhododaurichromanic acid A

An unusual polyene cyclization pathway that led to a divergent total synthesis of hongoquercin A and rhododaurichromanic acid A is described here. This work uncovered a unique cationic cyclobutane formation that could be relevant to the biosynthetic pathway for the formation of cyclobutane containing terpenoids in addition to rhododaurichromanic acids.     

Improving mass spectrometer sensitivity using a high-pressure electrodynamic ion funnel interface

We report on a new electrodynamic ion funnel that operates at a pressure of 30 torr with no loss of ion transmission. The enhanced performance compared with previous ion funnel designs optimized for pressures of <5 torr was achieved by reducing the ion funnel capacitance and increasing the RF drive frequency (1.7 MHz) and amplitude (100-170 V peak-to-peak). No degradation of ion transmission was observed for pressures from 2 to 30 torr. The ability to operate at higher pressure enabled a new tandem ion funnel mass spectrometer interface design that can accommodate a greater gas load (e.g., from an ESI source). When combined with a multicapillary inlet, the interface provided more efficient introduction of ions, resulting in a significant enhancement in mass spectrometer sensitivity and detection limits.     

Stereodivergent total syntheses of precoccinelline, hippodamine, coccinelline, and convergine

[structure: see text] A stereodivergent approach toward total syntheses of Coccinellidae defensive alkaloids is described. These syntheses feature a highly diastereoselective intramolecular aza-[3 + 3] annulation strategy, which represents a de novo approach to this family of natural products.     

Intramolecular cyclization of 1-(2-arylethyl)tetrahydro-6-hydroxy-1H-pyrimidin-2-thiones: effect of substituents on reactivity

Convenient synthetic procedures for 1,2,3,6,7, 11b-hexahydro-4H-pyrimido[6, 1 -a] isoquinolin-4-thiones and 2,3,6,7,12,12b-hexahydro-1H-pyrimido[1′,6′:1,2]pyrido[3,4-b]indole-4-thiones have been developed. Structural factors which influence on a cascade cyclization process have been elucidated.     

On the structure of certain natural cones over moduli spaces of genus-one holomorphic maps

We show that certain naturally arising cones over the main component of a moduli space of J₀-holomorphic maps into Pn have a well-defined Euler class. We also prove that this is the case if the standard complex structure J₀ on Pn is replaced by a nearby almost complex structure J. The genus-zero analogue of the cone considered in this paper is a vector bundle. The genus-zero Gromov-Witten invariant of a projective complete intersection can be viewed as the Euler class of such a vector bundle. As shown in a separate paper, this is also the case for the “genus-one part” of the genus-one GW-invariant. The remaining part is a multiple of the genus-zero GW-invariant.     

Simulation of Electric Potentials and Ion Motion in Planar Electrode Structures for Lossless Ion Manipulations (SLIM)

We report a conceptual study and computational evaluation of novel planar electrode structures for lossless ion manipulations (SLIM). Planar electrode SLIM components were designed that allow for flexible ion confinement, transport, and storage using a combination of radio frequency (rf) and DC fields. Effective potentials can be generated that provide near ideal regions for confining and manipulating ions in the presence of a gas. Ion trajectory simulations using SIMION 8.1 demonstrated the capability for lossless ion motion in these devices over a wide m/z range and a range of electric fields at low pressures (e.g., a few Torr). More complex ion manipulations (e.g., turning ions by 90^o and dynamically switching selected ion species into orthogonal channels) are also shown feasible. The performance of SLIM devices at ~4 Torr pressure for performing ion mobility-based separations (IMS) is computationally evaluated and compared with initial experimental results, and both are also shown to agree closely with experimental and theoretical IMS performance for a conventional drift tube design. Graphical Abstract

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Interaction of Tris(3-Hydroxymethyl)Phosphine with Cinnamic Acids

Abstract

Phosphonium zwitterions of the known type R₃P⁺CH(Ar)CH₂CO₂ ^? (II) are obtained as a racemic mixture in moderate yield via a 1:1 reaction of cinnamic acids (Ar = phenyl, or substituted phenyl) with [HO(CH₂)₃]₃P in acetone at room temperature under Ar. The products are characterized by elemental analysis, ³¹P{¹H}-, ¹H-, and ¹³C{¹H}-NMR spectroscopies, and mass spectrometry, although they contain a minor coproduct formed via neutralization of the positive and negative charges of II with the respective acid and phosphine reactants (see Experimental Section). In CD₃OD, the monodeuterated salts R₃P⁺CH(Ar)CH(D)CO₂ ^? are formed as a mixture of diastereomers with d.r. values of ～2 to 8, depending on substituent groups present in the organic acid; in these studies, 2-HO-cinnamic acid is the most reactive, and β-methylcinnamic acid is the least reactive.     

A Highly K+‐Selective Phenylaza‐[18]crown‐6‐Lariat‐Ether‐Based Fluoroionophore and Its Application in the Sensing of K+ Ions with an Optical Sensor Film and in Cells

Herein, we report the synthesis of two phenylaza‐[18]crown‐6 lariat ethers with a coumarin fluorophore ( 1 and 2 ) and we reveal that compound 1 is an excellent probe for K⁺ ions under simulated physiological conditions. The presence of a 2‐methoxyethoxy lariat group at the ortho position of the anilino moiety is crucial to the substantially increased stability of compounds 1 and 2 over their lariat‐free phenylaza‐[18]crown‐6 ether analogues. Probe 1 shows a high K⁺/Na⁺ selectivity and a 2.5‐fold fluorescence enhancement was observed in the presence of 100 mM K⁺ ions. A fluorescent membrane sensor, which was prepared by incorporating probe 1 into a hydrogel, showed a fully reversible response, a response time of 150 s, and a signal change of 7.8 % per 1 mM K⁺ within the range 1–10 mM K⁺. The membrane was easily fabricated (only a single sensing layer on a solid polyester support), yet no leaching was observed. Moreover, compound 1 rapidly permeated into cells, was cytocompatible, and was suitable for the fluorescent imaging of K⁺ ions on both the extracellular and intracellular levels.