Hydrazide and hydrazine reagents as reactive matrices for MALDI‐MS to detect gaseous aldehydes

The reagents 19 hydrazide and 14 hydrazine were examined to function as reactive matrices for matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) to detect gaseous aldehydes. Among them, two hydrazide (2‐hydroxybenzohydrazide and 3‐hydroxy‐2‐naphthoic acid hydrazide) and two hydrazine reagents [2‐hydrazinoquinoline and 2,4‐dinitrophenylhydrazine (DNPH)] were found to react efficiently with carbonyl groups of gaseous aldehydes (formaldehyde, acetaldehyde and propionaldehyde); these are the main factors for sick building syndrome and operate as reactive matrices for MALDI‐MS. Results from accurate mass measurements by JMS‐S3000 Spiral‐TOF suggested that protonated ion peaks corresponding to [M + H]⁺ from the resulting derivatives were observed in all cases with the gaseous aldehydes in an incubation, time‐dependent manner. The two hydrazide and two hydrazine reagents all possessed absorbances at 337 nm (wavelength of MALDI nitrogen laser), with, significant electrical conductivity of the matrix crystal and functional groups, such as hydroxy group and amino group, being important for desorption/ionization efficiency in MALDI‐MS. To our knowledge, this is the first report that gaseous molecules could be derivatized and detected directly in a single step by MALDI‐MS using novel reactive matrices that were derivatizing agents with the ability to enhance desorption/ionization efficiency. Copyright © 2014 John Wiley & Sons, Ltd.     

Evaluation of “method uncertainty” in the calibration of piston pipettes (micropipettes) using the gravimetric method in accordance with the procedure of ISO 8655-6

The gravimetric method specified by ISO 8655-6 is a standard method for calibrating piston pipettes (micropipettes). The quality of the calibration can be assessed by uncertainty evaluation, the procedure for which is described in ISO/Technical Report (TR) 20461. However, the existence of “method uncertainty” due to ambiguity in the calibration operation, which is not described in the TR, has been found in various experiments, such as the interlaboratory comparison of CCM.FF-K4.2.2011. In this report, the “method standard uncertainty” is quantified as exp(?4.51 + 0.36 ln(V ^nom/μL) + 0.05{ln(V ^nom/μL)}²) μL for a nominal volume, V ^nom, in the range from 2 μL to 10000 μL. Furthermore, the reported values in an interlaboratory comparison are confirmed to be consistent using the quantified method standard uncertainty.     

Asymmetric Aldol Reactions between Acetone and Benzaldehydes Catalyzed by Chiral Zn2+ Complexes of Aminoacyl 1,4,7,10‐Tetraazacyclododecane: Fine‐Tuning of the Amino‐Acid Side Chains and a Revised Reaction Mechanism

We previously reported that chiral Zn²⁺ complexes that were designed to mimic the actions of class‐I and class‐II aldolases catalyzed the enantioselective aldol reactions of acetone and its analogues thereof with benzaldehyde derivatives. Herein, we report the synthesis of new chiral Zn²⁺ complexes that contain Zn²⁺? tetraazacyclododecane (Zn²⁺? [12]aneN₄) moieties and amino acids that contain aliphatic, aromatic, anionic, cationic, and dipeptide side chains. The chemical and optical yields of the aldol reaction were improved (up to 96 % ee) by using ZnL complexes of L ‐decanylglycyl‐pendant [12]aneN₄ (L ‐ZnL⁷), L ‐naphthylalanyl‐pendant [12]aneN₄ (L ‐ZnL¹⁰), L ‐biphenylalanyl‐pendant [12]aneN₄ (L ‐ZnL¹¹), and L ‐phenylethylglycyl‐pendant [12]aneN₄ ligands (L ‐ZnL¹²). UV/Vis and circular dichroism (CD) titrations of acetylacetone (acac) with ZnL complexes confirmed that a ZnL? (acac)^? complex was exclusively formed and not the enaminone of ZnL and acac, as we had previously proposed. Moreover, the results of stopped‐flow experiments indicated that the complexation of (acac)^? with ZnL was complete within milliseconds, whereas the formation of an enaminone required several hours. X‐ray crystal‐structure analysis of L ‐ZnL¹⁰ and the ZnL complex of L ‐diphenylalanyl‐pendant [12]aneN₄ (L ‐ZnL¹³) shows that the NH₂ groups of the amino‐acid side chains of these ligands are coordinated to the Zn²⁺ center as the fourth coordination site, in addition to three nitrogen atoms of the [12]aneN₄ rings. The reaction mechanism of these aldol reactions is discussed and some corrections are made to our previous mechanistic hypothesis.     

Surface‐plasmon wavefront and spectral shaping by near‐field holography

Surface‐plasmon‐polariton waves are two‐dimensional electromagnetic surface waves that propagate at the interface between a metal and a dielectric. These waves exhibit unusual and attractive properties, such as high spatial confinement and enhancement of the optical field, and are widely used in a variety of applications, such as sensing and subwavelength optics. The ability to precisely control the spatial and spectral properties of the surface‐plasmon wave is required in order to support the growing interest in both research and applications of plasmonic waves, and to bring it to the next level. Here, we review the challenges and methods for shaping the wavefront and spectrum of plasmonic waves. In particular, we present the recent advances in plasmonic spatial and spectral shaping, which are based on the realization of plasmonic holograms for the optical nearfield.

     

Decarbonylative Radical Coupling of α‐Aminoacyl Tellurides: Single‐Step Preparation of γ‐Amino and α,β‐Diamino Acids and Rapid Synthesis of Gabapentin and Manzacidin A

A new radical‐based coupling method has been developed for the single‐step generation of various γ‐amino acids and α,β‐diamino acids from α‐aminoacyl tellurides. Upon activation by Et₃B and O₂ at ambient temperature, α‐aminoacyl tellurides were readily converted into α‐amino carbon radicals through facile decarbonylation, which then reacted intermolecularly with acrylates or glyoxylic oxime ethers. This mild and powerful method was effectively incorporated into expeditious synthetic routes to the pharmaceutical agent gabapentin and the natural product (?)‐manzacidin A.     

Concentration Threshold and Amplification Exhibited by a Helicene Oligomer during Helix‐Dimer Formation: A Proposal on How a Cell Senses Concentration Changes of a Chemical

Sulfonamidohelicene tetramer (M)‐ 1 exhibits a concentration threshold and amplification phenomena in solution during helix‐dimer formation from a random‐coil. The (M)‐tetramer is a random‐coil below a threshold concentration, and the concentration of the helix‐dimer is irreversibly amplified once the threshold concentration is exceeded. For example, a 15 % increase in (M)‐tetramer total concentration from 0.6 to 0.7 mM induces an 8‐fold increase in the concentration of the helix‐dimer, being 8:0.15=53‐fold amplification, under temperature oscillation conditions between 47 and 49 °C. Experiments without oscillation also exhibit concentration amplification. The threshold and amplification phenomenon involves concentration hysteresis, being away from equilibrium, and self‐catalysis. On the basis of this study, a proposal on how a biological cell senses concentration changes of a chemical substance is provided.