Electrospray ionization mass spectrometry (ESI-MS) is found to gently and efficiently transfer small to large as well as singly to multiply charged [X+]n[A-]m supramolecules of imidazolium ion (X+) ionic liquids to the gas phase, and to reveal "magic numbers" for their most favored assemblies. Tandem mass spectrometric experiments (ESI-MS/MS) were then used to dissociate, via low-energy collision activation, mixed and loosely bonded [A- - - -X- - - -A']- and [X- - - -A- - - -X']+ gaseous supramolecules, as well as their higher homologues, and to estimate and order via Cooks' kinetic method (CKM) and B3LYP/6-311G(d,p) calculations the intrinsic solvent-free magnitude of hydrogen bonds. For the five anions studied, the relative order of intrinsic hydrogen-bond strengths to the 1-n-butyl-3-methylimidazolium ion [X1]+ is: CF3CO2- (zero) > BF4- (-3.1) > PF6- (-10.0) > InCl4- (-16.4) and BPh4- (-17.6 kcal mol(-1)). The relative hydrogen-bond strength for InCl4- was measured via CKM whereas those for the other anions were calculated and used as CKM references. A good correlation coefficient (R=0.998) between fragment ion ratios and calculated hydrogen-bond strengths and an effective temperature (Teff) of 430 K demonstrate the CKM reliability for measuring hydrogen-bond strengths in gaseous ionic liquid supramolecules. Using CKM and Teff of 430 K, the intrinsic hydrogen-bond strengths of BF4- for the three cations investigated is: 1-n-butyl-3-methyl-imidazolium ion (0) > 1,3-di-[(R)-3-methyl-2-butyl]-imidazolium ion (-2.4) > 1,3-di-[(R)-alpha-methylbenzyl]-imidazolium ion (-3.0 kcal mol(-1)). As evidenced by "magic" numbers, greater stabilities are found for the [(X1)2(BF4)3]- and [(X1)5A4]+ supramolecules (A not equal InCl4-).

Rapid quantitative enantiomeric analysis of mannose, glucose, galactose, and ribose is achieved using electrospray ionization and cluster ion dissociation with data analysis by the kinetic method. Several modified amino acids (N-Ac-L-Phe, N-benzoyl-L-Phe, N-t-Boc-L-Phe, N-Ac-L-Pro, N-t-Boc-L-Pro, N-Fmoc-L-Pro, N-Ac-L-Tyr, O-Me-L-Tyr) and four transition divalent metal cations (Co2+, Cu2+, Ni2+, and Zn2+) were tested to select the best system for chiral recognition and quantitation of each sugar. Quantitative determinations of the enantiomeric compositions of sugar solutions were achieved using either multiple- or two-point calibration curves; differences between the actual and experimental values were <2% enantiomeric excess (ee).

High performance liquid chromatography (HPLC), ultraviolet spectroscopy (UV), and total organic carbon (TOC) analyses show that caffeine is quickly and completely degraded underthe oxidative conditions of the UV/H2O2,TiO2/ UV, and Fenton systems but that the organic carbon content of the solution decreases much more slowly. Continuous on-line and real-time monitoring by electrospray ionization mass (ESI-MS) and tandem mass spectrometric experiments (ESI-MS/MS) as well as high accuracy MS measurements and gas chromatography-mass spectrometry analysis show that caffeine is first oxidized to N-dimethylparabanic acid likely via initial OH insertion to the C4=C8 caffeine double bond. A second degradation intermediate, di(N-hidroxymethyl)parabanic acid, has been identified by ESI-MS and characterized by ESI-MS/MS and high accuracy mass measurements. This polar and likely relatively unstable compound, which is not detected by off-line GC-MS analysis, is likely formed via further oxidation of N-dimethylparabanic acid at both of its N-methyl groups and constitutes an unprecedented intermediate in the degradation of caffeine.

No abstract

Paper spray ionization can be used to study organic reactions in solution under ambient conditions by utilizing the rate acceleration that occurs in reactions in small volumes of solution. In this novel approach to performing reactions, reagents are transferred onto a triangular paper surface by drop‐casting and charged droplets of the reaction product mixture are released by field evaporation and examined online by mass spectrometry. The increase in the rate of product formation is attributed to solvent evaporation, which increases reagent concentrations, changes the pH, and enhances intermolecular interactions. As a proof of principle, the Katritzky reaction between a pyrylium salt and mono‐ or diamines, including substituted anilines, was investigated. The influence of electronic and steric effects was evaluated straightforwardly. The carbon chain length of α,ω‐diamines was found to control the formation of mono‐ versus disubstituted products, thus reflecting the strong destabilizing coulombic effects in the shorter carbon‐chain systems. Information on the mechanism was provided by the observation of 2H‐pyran intermediates and mixed pyridinium–2H‐pyran ions. The rates of product formation in the base‐assisted Katritzky reaction increase linearly from 0.1 to 10 equivalents of triethylamine. The reactive paper spray technique, owing to its speed and information content, has potential pedagogical value and provides a tool to explore organic reactions and correlate experimental results with current mechanistic understanding.

Membrane introduction mass spectrometry (MIMS) was used to investigate kinetic and mechanistic aspects of the reaction of benzene derivatives with Fenton's reagent (Fe 2+ /H 2 O 2 ) in water. Under the conditions employed, the reaction rate showed a first-order dependence on the aromatic compound concentration. The order of reactivity observed was C 6 H 5 Cl > C 6 H 5 Br > C 6 H 6 > C 6 H 5 CH 3 > C 6 H 5 OCH 3 > C 6 H 5 NO 2 > C 6 H 5 -OH, and, with the exception of C 6 H 5 NO 2 , a linear Hammett relationship (log k X /k H versus σ p ) was observed. This fact suggests that electronic factors significantly influence reactivity with the Fenton's reagent. Experiments with C 6 H 6 and C 6 D 6 showed the presence of an isotopic effect of k H /k D ) 1.7, suggesting that cleavage of the benzene C-H bond occurs in the reaction rate controlling step. Mechanistic studies with chlorobenzene showed that mineralization to CO 2 and chloride proceeds via hydroxylation steps producing phenolic, hydroquinonic, and quinonic intermediates.

The degradation of tetracycline (1) by ozone in aqueous solution was investigated. High performance liquid chromatography (HPLC), UV-visible spectroscopy (UV-Vis), and total organic carbon (TOC) analyses revealed that although tetracycline was quickly consumed under this oxidative condition, it did not mineralize at all. Continuous monitoring by electrospray ionization mass spectrometry in the positive ion mode, ESI(ϩ)-MS, revealed that tetracycline (1), detected in its protonated form ([1 ϩ H] ϩ ) of m/z 445, reacted to yield almost exclusively two unprecedented oxidation products (2 and 3) via a net insertion of one and two oxygen atoms, respectively. Compound 2, suggested to be formed via an initial 1,3-dipolar cycloaddition of ozone at the C11a-C12 double-bond of 1, and Compound 3, proposed to be produced via a subsequent ozone attack at the C2-C3 double-bond of 2, were detected in their protonated forms in the ESI(ϩ)-MS, i.e.,

Herein we describe a new protocol that allows direct mass spectrometry imaging (IMS) of agar cultures. A simple sample dehydration leads to a thin solid agar, which enables the direct use of spray-based ambient mass spectrometry techniques. To demonstrate its applicability, metal scavengers siderophores were imaged directly from agar culture of S. wadayamensis, and well resolved and intense images were obtained using both desorption electrospray ionization (DESI) and easy ambient sonic-spray ionization (EASI) with well-defined selective spatial distributions for the free and the metal-bound molecules, providing clues for their roles in cellular metabolism.