A post aza Baylis-Hillman/Heck coupling approach towards the synthesis of constrained scaffolds

An intramolecular Heck coupling of the product of an aza Baylis-Hillman reaction to afford conformationally constrained scaffolds is reported.     

Energetics of retro-Diels–Alder fragmentation in limonene as characterized by surface-induced dissociation,and energy- and angle-resolved mass spectrometry

Ionized limonene and related isomeric compounds have been examined by collisional activation at both gaseous and solid targets. The gas-phase collision-induced dissociation (CID) experiments were performed as a function of collision energy and scattering angle and the surface-induced dissociation (SID) experiments as a function of collision energy, in order to vary systematically the internal energy deposited in the molecular ion. The virtual absence of retro-Diels–Alder (RDA) fragmentation upon conventional CID, as compared to its importance in the electron impact (EI) mass spectrum, the subject of a study by Boyd and coworkers, was confirmed. However, as the ion internal energy was increased by raising the collision energy or the scattering angle, RDA fragmentation was observed and it became a dominant mode of fragmentation for SID at collision energies in the range of 25–50 eV. The energy deposited into the colliding ion in the SID technique is compared with that deposited upon CID in the eV and keV energy ranges and upon EI. The order obtained is: SID > EI > low-energy, multiple-collision CID > high-energy, single-collision CID > low-energy, single-collision CID. The distribution of energies in SID is narrower than in the other techniques. High internal energies are accessible by increasing the scattering angle in CID; however, this is accompanied by an increase in the width of the internal energy distribution, and it is therefore not possible to channel fragmentation predominantly into RDA by this method. It is concluded that RDA fragmentation of limonene is a high-energy process and that this is the explanation for its behavior. Isomerization, occurring through 1,3-hydrogen migrations of the molecular ions of limonene, isolimonene, terpinolene and α-terpinene, was investigated and long-lived molecular ions of the first three compounds were found to maintain distinct structures.     

Hyperbolic conservation laws with vanishing nonlinear diffusion and linear dispersion in heterogeneous media

We analyze family of solutions to multidimensional scalar conservation law, with flux depending on the time and space explicitly, regularized with vanishing diffusion and dispersion terms. Under a condition on the balance between diffusion and dispersion parameters, we prove that the family of solutions is precompact in L¹_loc{L^1_{\rm loc}}. Our proof is based on the methodology developed in Sazhenkov (Sibirsk Math Zh 47(2):431–454, 2006), which is in turn based on Panov’s extension (Panov and Yu in Mat Sb 185(2):87–106, 1994) of Tartar’s H-measures (Tartar in Proc R Soc Edinb Sect A 115(3–4):193–230, 1990), or Gerard’s micro-local defect measures (Gerard Commun Partial Differ Equ 16(11):1761–1794, 1991). This is new approach for the diffusion–dispersion limit problems. Previous results were restricted to scalar conservation laws with flux depending only on the state variable.     

Synthesis of substituted 3,4-dihydroquinolin-2(1H)-one derivatives by sequential Ugi/acrylanilide [6π]-photocyclizations

We report the synthesis of highly functionalized 3,4-dihydroquinolin-2(1H)-ones via sequential Ugi/acrylanilide photocyclization reactions. The [6π]-photocyclization proceeds in excellent yields and with preferential trans-selectivity for the newly formed ring system.     

On the Characterizations of Wave Front Sets in Terms of the Short-Time Fourier Transform

Mathematical Notes - It is well known that the classical and Sobolev wave fronts were extended to nonequivalent global versions by the use of the short-time Fourier transform. In this very short...     

MALDI produced ions inspected with a linear ion trap-orbitrap hybrid mass analyzer

A MALDI source is interfaced to a modified LTQ Orbitrap XL instrument. This work gives insight into the MALDI source design and shows results obtained with the MALDI source coupled to an accurate mass, high-resolution hybrid mass spectrometer. MALDI-produced ions and fragment ions thereof produced in the mass spectrometer may be analyzed and detected by the Orbitrap analyzer at a maximum mass resolution of 100,000 (FWHM) at m/z 400 with high mass accuracy. An accuracy of ≤2 ppm is achieved by internal mass calibration using lock mass functionality; using external mass calibration, an accuracy of ≤3 ppm is routinely obtained. External mass calibration of the hybrid mass spectrometer is performed using a standard calibration mixture of different peptides and matrix components. The instrumental capabilities are demonstrated for analytical methodologies such as Protein ID using Peptide Mass Fingerprint (PMF) and MS/MS analyses of small molecule samples. Stability of mass accuracy and signal-to-noise ratio for low samples loads (on plates) are demonstrated as well as the experimental dynamic range using α-cyano-4-hydroxy cinnamic acid (CHCA) matrix.     

Dynamic range of mass accuracy in LTQ orbitrap hybrid mass spectrometer

Using a novel orbitrap mass spectrometer, the authors investigate the dynamic range over which accurate masses can be determined (extent of mass accuracy) for short duration experiments typical for LC/MS. A linear ion trap is used to selectively fill an intermediate ion storage device (C-trap) with ions of interest, following which the ensemble of ions is injected into an orbitrap mass analyzer and analyzed using image current detection and fast Fourier transformation. Using this technique, it is possible to generate ion populations with intraspectrum intensity ranges up to 10(4). All measurements (including ion accumulation and image current detection) were performed in less than 1 s at a resolving power of 30,000. It was shown that 5-ppm mass accuracy of the orbitrap mass analyzer is reached with >95% probability at a dynamic range of more than 5000, which is at least an order of magnitude higher than typical values for time-of-flight instruments. Due to the high resolving power of the orbitrap, accurate mass of an ion could be determined when the signal was reliably distinguished from noise (S/Np-p)>2...3).     

Microlocal hypoellipticity of linear partial differential operators with generalized functions as coefficients

We investigate microlocal properties of partial differential operators with generalized functions as coefficients. The main result is an extension of a corresponding (microlocalized) distribution theoretic result on operators with smooth hypoelliptic symbols. Methodological novelties and technical refinements appear embedded into classical strategies of proof in order to cope with most delicate interferences by non-smooth lower order terms. We include simplified conditions which are applicable in special cases of interest.