Pulsed fluorescence measurements of trapped molecular ions with zero background detection

Sensitive methods have been developed to measure laser-induced fluorescence from trapped ions by reducing the detection of background scattering to zero levels during the laser excitation pulse. The laser beam diameter has been reduced to approximately 150 microm to eliminate scattering on trap apertures and the resulting laser-ion interaction is limited to a volume of approximately 10(-5) cm which is approximately 0.03-0.15 of the total ion cloud volume depending on experimental conditions. The detection optics collected fluorescence only from within the solid angle defined by laser-ion interaction volume. Rhodamine 640 and Alexa Fluor 350 ions, commonly used as fluorescence resonance energy transfer (FRET) fluorophores, were generated in the gas phase by using electrospray ionization and injected into a radiofrequency Paul trap where they were stored and exposed to Nd:YAG laser pulses at 532 and 355 nm for times up to 10 m. Fluorescence emitted by these ions was investigated for several trap q(z) values and ion cloud temperatures. Analysis of photon statistics indicated an average of approximately 10 photons were incident on the PMT detector per 15 ns pulse for approximately 10(3) trapped ions in the interaction volume. Fluorescence measurements displayed a dependence on trapped ion number which were consistent with calculations of the space charge limited ion density. To investigate the quantitative capability of these fluorescence techniques, the laser-induced fragmentation of trapped Alexa Fluor 350 ions was measured and compared with a rate equation model of the dynamics. Decay of the fluorescence signal as well as the parent ion number compared closely with quantitative predictions of the photofragmentation model.     

A new tri-orthogonal strategy for peptide cyclization

A solid phase tri-orthogonal protection/cleavage strategy that uses acidic, basic, and neutral conditions is described. Strategically protected alpha-azido-gamma-9-fluorenylmethyl-L-glutamate (1) and alpha-azido-epsilon-N-Fmoc-L-lysine (2) were incorporated into growing peptides on Wang resin using a novel azide protection strategy. These residues, separated by 1-3 monomers, were deprotected at the side chains and cyclized via lactam formation. The N-terminus was further functionalized to extend the chain. This method represents a straightforward protocol for peptide cyclization on solid support.     

“Statistical” symmetry with applications to phase transitions

Hermann proposed that mesomorphic media should be classified by assigning certain statistical symmetry groups to each possible partially ordered array. Two translational groups introduced were called superordinate and subordinate. We find that the average density in such a partially ordered medium has the superordinate symmetry ₁, while the pair correlation function has the subordinate symmetry ₂. A complete listing is made of all compatible combinations of ₁ and ₂ in two and three dimensions. This leads to more possible symmetries than Hermann obtained, e.g., also to nonstoichiometric crystals. The order parameter space for the systems is found to be the quotient space ₁/₂. In most cases it is identical to the order parameter space of low-dimensionalXY spin systems. The Landau free energy is expanded as functional of the two-particle correlation functionK; the translation group is found to be ₁×₂. A Landau mean-field theory can then be carried out by expanding the system free energy into a series of invariants of the active irreducible representations ofK and mapping the free energy onto that for anXY planar spin system. We predict novel critical behavior for transitions between mesomorphic phases and go nogo selection rules for continuous transitions. We give the structure factors for X-ray scattering so changes in all such phase transitions are observable. The statistical symmetry groups, which describe point and translational symmetries of the mesophases, are classified. Proposals are made to include quasi-long-range or topological order in the classification scheme.This work supported in part by National Science Foundation (Division of International Programs), the PSC-BHE—Faculty Research Award CUNY and Deutsche Forschungsgemeinschaft.     

Matchings and radon transforms in lattices. I. Consistent lattices

An element in a lattice is join-irreducible if x=ab implies x=a or x=b. A meet-irreducible is a join-irreducible in the order dual. A lattice is consistent if for every element x and every join-irreducible j, the element xj is a join-irreducible in the upper interval [x, î]. We prove that in a finite consistent lattice, the incidence matrix of meet-irreducibles versus join-irreducibles has rank the number of join-irreducibles. Since modular lattices and their order duals are consistent, this settles a conjecture of Rival on matchings in modular lattices.     

Synthesis of the methanesulfonates of α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)emenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol,alpha styryl carbinol antifungal agents

The methanesulfonates of (α-(4-chlorophenyl)-α-[1-(2-chlorophenyl)ethenyl]-1H-1,2,4-triazole-1-ethanol and α-[1-(2-chlorophenyl)ethenyl]-α-(2,4-difluorophenyl)-1H-1,2,4-triazole-1-ethanol ( 1a, b ) are orally effective α-styryl carbinol derivatives developed for the treatment and prevention of systemic fungal infections. Practical new processes amenable for the large-scale production of these compounds are described. Of note is the selection of dichlorostyrene as a convenient precursor of the styryl portion, modification of a sensitive Grignard addition into a realistic preparative reaction and the use of 1,2,4-triazole simultaneously as a base transfer agent and nucleophile.     

Second-order Green's function calculations of the ionization potential of a (H2)7 chain embedded in a homogeneous electric field

Summary The vertical ionization potential and the related pole strength of a model alternant chain of 14 hydrogen atoms subject to a homogeneous electric field, parallel to the chain and of increasing intensity are calculated, in the framework of a 6–31G** basis set, at the second-order level of the many-body Green's function theory. Trends observed with orbital relaxation, pair removal and pair relaxation effects are interpreted in terms of deformations of the electron density.     

Efficient unimolecular deprotonation of aniline radical cations

[reaction: see text] Deprotonation of the radical cations of aromatic amines, such as anilines, generally occurs much more slowly than other fragmentation reactions. Here we report a stereoelectronic effect involving twisting of the anilino group out of the plane of the benzene ring that results in a significantly increased rate of reactivity toward deprotonation. Quantitative studies of the rate constants for deprotonation as a function of aniline radical cation pKa (Br?nsted plots) demonstrate that the effect is not simply due to a change in the reaction thermodynamics. By combining this stereoelectronic effect with covalent attachment of carboxylate as a base, aniline radical cations that undergo unimolecular deprotonation with rate constants as high as 10(8) s(-1), even in unfavorable protic media, are described.     

Dinitrogen reduction by TmII,DyII, and NdII with simple amide and aryloxide ligands

Dinitrogen can be reduced to the planar M2(mu-eta2:eta2-N2) structure without employing cyclopentadienyl or complicated polydentate ligands using the recently discovered divalent oxidation states of Tm(II), Dy(II), and Nd(II). Complexes of these ions with common monodentate amide and aryloxide ligands can effect N2 reduction. THF solutions of LnI2 (Ln = Tm, Dy) in the presence of 2 equiv of NaN(SiMe3)2 reduce dinitrogen to form {[(Me3Si)2N]2(THF)Ln}2(mu-eta2:eta2-N2) complexes that have planar Ln2N2 units and 1.264(7) and 1.305(6) A NN bonds consistent with (N2)2- moieties. With the stronger reductant Nd(II), aryloxides are sufficient ancillary ligands: the NdI2/2KOC6H3tBu2-2,6 (KOAr) system forms [(ArO)2(THF)2Nd]2(mu-eta2:eta2-N2), which has a 1.242(7) A NN bond.     

Synthesis of fluorinated 1,8-naphthyridinone derivatives

Processes for the synthesis of fluorinated 1,8-naphthyridinone derivatives including 6,7-difluoro-1,8-naphthyridin-2-one are described.