Improved procedures for N-terminal sulfonation of peptides for matrix-assisted laser desorption/ionization post-source decay peptide sequencing

Post source decay (PSD) analysis of precursor ions generated from matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry is a powerful tool for amino acid sequencing and primary structure analysis of proteins. N-Terminal sulfonation has become an effective derivatization strategy in facilitating de novo peptide sequencing by the formation of predominate y-type ion series in MALDI PSD spectra. Recently, an effective and inexpensive N-terminal derivatization method has been reported using 4-sulfophenyl isothiocyanate (SPITC) as the derivatization reagent (J. Mass. Spectrom. 2003; 38: 373-377). In this paper, we report an improvement in the derivatization procedure with this reagent that involves replacing an organic co-reagent with other chemicals and eliminating the use of organic solvent. The method is demonstrated on a model peptide and on tryptic digests of two proteins. The results indicate that the improved sulfonation reaction can be implemented with high efficiency under aqueous conditions and that the sensitivity of mass detection can be increased considerably.     

Synthesis and Cytotoxicity Studies of New (Dimethylamino)‐Functionalised and 7‐Azaindole‐Substituted ‘Titanocene’ Anticancer Agents (7‐Azaindole=1H‐Pyrrolo[2,3‐b]pyridine)

From the carbolithiation of 1‐(cyclopenta‐2,4‐dien‐1‐ylidene)‐N,N‐dimethylmethanamine (=6‐(dimethylamino)fulvene; 3 ) and different lithiated azaindoles 2 (1‐methyl‐7‐azaindol‐2‐yl, 1‐[(diethylamino)methyl]‐7‐azaindol‐2‐yl, and 1‐(methoxymethyl)‐7‐azaindol‐2‐yl), the corresponding lithium cyclopentadienide intermediates 4a – 4c were formed (7‐azaindole=1H‐pyrrolo[2,3‐b]pyridine). The latter underwent a transmetallation reaction with TiCl₄ resulting in the (dimethylamino)‐functionalised ‘titanocenes’ 5a – 5c . When the ‘titanocenes’ 5a – 5c were tested against LLC‐PK cells, the IC₅₀ values obtained were of 8.8, 12, and 87 μM , respectively. The most cytotoxic ‘titanocene’, 5a , with an IC₅₀ value of 8.8 μM is nearly as cytotoxic as cis‐platin, which showed an IC₅₀ value of 3.3 μM when tested on the epithelial pig kidney LLC‐PK cell line, and ca. 200 times better than ‘titanocene dichloride’ itself.     

Large nonlinear pulse broadening in long lengths of monomode fibre

Very large nonlinear pulse broadening in 10–20 km lengths of monomode fibre is reported. Broadening of 150 ps pulses to as much as 2.5 ns has been observed. There is good qualitative agreement with a numerical analysis of the nonlinear Schrödinger equation.     

Peptide sequence information derived by pronase digestion and ammonium sulfate in-source decay matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We present the use of Pronase digestion and in-source decay in the presence of ammonium sulfate as complementary techniques to confirm the amino acid sequence of a peptide. Pronase, a commercial preparation from Streptomyces griseus, is a combination of proteolytic enzymes. It produces carboxypeptidase and aminopeptidase ladders using a single Pronase digestion and represents an inexpensive, nonspecific, and fast supplement to traditional sequencing enzymes. However, N-terminal peptidase activity appears dependent on the terminal amino acid residue. We also introduce the use of saturated ammonium sulfate as an "on-slide" sample additive to promote in-source fragmentation of peptides. Use of saturated ammonium sulfate resulted in a simple way to increase peptide backbone fragmentation and essentially produced either a cn or yn ion series. Together these techniques provide useful supplements to existing methods for peptide sequence information.     

Picosecond pulse generation in the infrared by stimulated Raman scattering in atomic vapours

We report the generation of high-power picosecond infrared pulses by stimulated electronic Raman scattering in an atomic vapour. Single 30 ps pulses at 532 nm were Raman-shifted in caesium vapour to produce 0.4 mJ pulses at 2.38 μm, with 20% quantum efficiency. This technique can be extended to cover a wide range of infrared wavelenghts by using various Raman transitions.     

Adiabatic Invariance and Applications: From Molecular Dynamics to Numerical Weather Prediction

A wide class of Hamiltonian systems exhibit a mixture of slow motion with superimposed fast oscillations. Under the assumption of scale separation, these systems can be investigated using the principle of adiabatic invariance. In this paper, we start with a review of some of the main theoretical and numerical findings. We then briefly summarize a few important implications for molecular dynamics (MD) before we provide a more extensive discussion of numerical weather prediction (NWP). In particular, the conservative Hamiltonian particle-mesh (HPM) method is extended to Euler's equation and the fundamental concepts of geostrophic and hydrostatic balance are illustrated on the level of fluid blobs. We also demonstrate numerically that symplectic time-stepping methods are able to maintain hydrostatic balance to high accuracy.