Getting a look‐in: An optimized MALDI‐MS procedure has been developed to detect endogenous primary metabolites directly in the cell extract. A detection limit corresponding to metabolites from less than a single cell has been attained, opening the door to single‐cell metabolomics by mass spectrometry.

The formation of inorganic nanoparticles has been understood based on the classical crystallization theory described by a burst of nucleation, where surface energy is known to play a critical role, and a diffusion-controlled growth process. However, this nucleation and growth model may not be universally applicable to the entire nanoparticle systems because different precursors and surface ligands are used during their synthesis. Their intrinsic chemical reactivity can lead to a formation pathway that deviates from a classical nucleation and growth model. The formation of metal oxide nanoparticles is one such case because of several distinct chemical aspects during their synthesis. Typical carboxylate surface ligands, which are often employed in the synthesis of oxide nanoparticles, tend to continuously remain on the surface of the nanoparticles throughout the growth process. They can also act as an oxygen source during the growth of metal oxide nanoparticles. Carboxylates are prone to chemical reactions with different chemical species in the synthesis such as alcohol or amine. Such reactions can frequently leave reactive hydroxyl groups on the surface. Herein, we track the entire growth process of iron oxide nanoparticles synthesized from conventional iron precursors, iron-oleate complexes, with strongly chelating carboxylate moieties. Mass spectrometry studies reveal that the iron-oleate precursor is a cluster comprising a tri-iron-oxo core and carboxylate ligands rather than a mononuclear complex. A combinatorial analysis shows that the entire growth, regulated by organic reactions of chelating ligands, is continuous without a discrete nucleation step.

Photodissociation at 266 nm of protonated synthetic polypeptides containing a tryptophanyl residue was investigated using a homebuilt tandem time-of-flight mass spectrometer equipped with a matrix-assisted laser desorption/ionization source. Efficient photodissociation of the protonated peptides was demonstrated. Most of the intense peaks in the laser-induced tandem mass spectra were sequence ions. Furthermore, sequence ions due to cleavages at all the peptide bonds were observed; this is a feature of the technique that is particularly useful for peptide sequencing. Fragmentations at both ends of the tryptophanyl residue were especially prevalent, which can be useful for location of the tryptophanyl chromophore in a peptide.

A tandem time-of-flight mass spectrometer for the study of photodissociation of biopolymer ions generated by matrix-assisted laser desorption ionization was designed and constructed. A reflectron with linear and quadratic (LPQ) potential components was used. Characteristics of the LPQ reflectron and its utility as the second stage analyzer of the tandem mass spectrometer were investigated. Performance of the instrument was tested by observing photodissociation of [M ϩ H] ϩ from angiotensin II, a prototype polypeptide. Quality of the photodissociation tandem mass spectrum was almost comparable to that of the post-source decay spectrum. Monoisotopic selection of the parent ion was possible, which was achieved through the ion beam-laser beam synchronization. General theoretical considerations needed for a successful photodissociation of large biopolymer ions are also presented. [3] has revolutionized the application of mass spectrometry for the determination of molecular weights of biopolymers. The natural next step in this field is the tandem mass spectrometry, which detects fragmentation of a mass-selected parent ion. When the internal energy of a polyatomic ion acquired at the time of its formation is sufficient for its dissociation after exiting the source, it may dissociate unimolecularly during its flight to the detector, which is called the metastable ion decomposition (MID) [4]. A more popular way to supply additional energy is to introduce collision gas on the ion flight path such that some of parent ion translational energy is converted to its internal energy. This is called the collision-induced dissociation (CID) or collisionally activated dissociation (CAD) [2]. In the case of the tandem time-of-flight (TOF) mass spectrometry of ions generated by MALDI without the collision gas, the term post source decay (PSD) [5,6] rather than MID has been popular because CID may also contribute to the observed fragment ion signals. When tandem mass spectra generated by PSD are either very weak or do not contain sufficient structural information, CID [7][8][9] may be attempted by introducing collision gas intentionally. Excitation via multiple collisions is thought to be important in the CID tandem mass spectrometry of high mass biopolymers with many degrees of freedom. Recently, dissociation of multiply protonated molecules induced by electron capture, or electron capture dissociation (ECD) [10,11], is attracting a lot of attention as a method to obtain site-specific information.Photodissociation (PD) has been utilized in the field of tandem mass spectrometry mostly as a method to study the structure and dissociation dynamics of small polyatomic ions [12]. Infrared multiphoton dissociation (IRMPD) [13,14] has been used to induce dissociation of biopolymer ions also, even though a large amount of internal energy needed for such a dissociation necessitates absorption of a large number of infrared photons. When electronic transitions of chromophores by ultraviolet radiation are utilized, the number of photons that m...

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