Isolation and Identification of Novel Taste-Modulating N2-Guanosine 5'-Monophosphate Derivatives Generated by Maillard-Type Reactions

Several compounds with taste-modulating properties have been investigated, improving the taste impression without having a pronounced intrinsic taste. The best-known representatives of umami taste-modulating compounds are ribonucleotides and their derivatives. Especially the thio derivatives showed high taste-modulating potential in structure-activity relationship investigations. Therefore, this study focuses on the formation of guanosine 5'-monophosphate derivatives consisting of Maillard-type generated compounds like the aroma-active thiols (2-methyl-3-furanthiol, 3-mercapto-2-pentanone, 2-furfurylthiol) and formaldehyde to gain insights into the potential of combinations of taste and aroma-active compounds. One literature-known (N2-(furfurylthiomethyl)-guanosine 5'-monophosphate) and three new derivatives (N2-(2-methyl-1-furylthiomethyl)-guanosine 5'-monophosphate, N2-((5-hydroxymethyl)-2-methyl-1-furylthiomethyl)-guanosine 5'-monophosphate, N2-((2-pentanon-1-yl)thiomethyl)-guanosine 5'-monophosphate) were successfully produced using green natural deep eutectic solvents and isolated, and their structures were completely elucidated. Besides the intrinsic taste properties, the kokumi and umami taste-modulating effects of the four derivatives were evaluated via psychophysical investigations, ranging from 19 to 22 μmol/L.

Evaluation of identification accuracy using AIQS for GC-MS for measuring heavily contaminated samples

Automated identification and quantification systems with gas chromatography-mass spectrometry (GC-MS) (i.e., AIQS-GC) are used as a simple and comprehensive method for screening chemicals existing in the environment and are expected to be useful for emergency surveys in the event of a disaster. However, reports on the potential of AIQS-GC in heavily contaminated samples (HCSs) are limited. In this study, the identification performance of AIQS-GC was confirmed by comparing the exact mass of the targets identified by AIQS-GC with the measured accurate mass using GC-quadrupole-time-of-flight MS (GC-QTofMS) and by employing firefighting wastewater as HCS. In HCS, the mass spectrum interference was determined to cause false positives. The GC-QTofMS method revealed the presence of false positives and the false rate of AIQS-GC in HCS. Herein, AIQS-GC showed high identification accuracy in a normal sample such as river water. Conversely, in HCS, AIQS-GC may lead to incorrect evaluations. The combination of AIQS-GC and support method using GC-QTofMS, which can avoid the false positive is extremely useful for the rapid and easy analysis of HCS.

Molecular ions of ionic liquids in the gas phase

Ionic liquids form neutral ion pairs (CA) upon evaporation. The softness of the gas-phase ionization of field ionization has been used to generate "molecular ions," CA(+*), of ionic liquids, most probably by neutralization of the anion. In detail, 1-ethyl-3-methylimidazolium-thiocyanate, [C(6)H(11)N(2)](+) [SCN](-), 1-butyl-3-methylimidazolium-tricyanomethide, [C(8)H(15)N(2)](+) [C(4)N(3)](-), N-butyl-3-methylpyridinium-dicyanamide, [C(10)H(16)N](+) [C(2)N(3)](-), and 1-butyl-1-methylpyrrolidinium-bis[(trifluormethyl)sulfonyl]amide, [C(9)H(20)N](+) [C(2)F(6)NO(4)S(2)](-) were used. The assignment as CA(+*) ions, which has been confirmed by accurate mass measurements and misassignments due to thermal decomposition of the ionic liquids, has been ruled out by field desorption and electrospray ionization mass spectrometry of the residues.

Four decades of joy in mass spectrometry

Tremendous developments in mass spectrometry have taken place in the last 40 years. This holds for both the science and the instrumental revolutions in this field. In chemistry the research was heavily focused on organic molecules that upon electron ionization fragmented via complex mechanistic pathways as shown by isotopic labeling experiments. These studies, including ion structure determinations, were performed with use of double focusing mass spectrometers of both conventional and reversed geometry, and equipped with various types of metastable ion scanning and collision-induced dissociation techniques developed by physical and analytical chemists. Time-resolved mass spectrometry by use of the field ionization kinetics method, developed by physical chemists, was another powerful way to unravel details of unimolecular gas phase ion dissociations. Then the development of new ionization methods, such as desorption chemical ionization, field desorption, and fast atom bombardment permitted not only to analyze unvolatile, thermally labile and higher molecular weight compounds, but also to study their chemical behavior in the gas phase, initially with use of double focusing instruments and later on with multisector and hybrid mass spectrometers. These ionization methods also enabled to study organometallic compounds and increasingly the field of medium-sized to large biomolecules, the latter being exploded in the last decade by the development of electrospray- and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry. Another area of research concerned the bimolecular chemistry of organic ions with organic molecules in the gas phase. Initially this was performed with use of among others drift-cell ion cyclotron resonance spectroscopy, that later on was replaced by the developed method of ion trapping and Fourier transform ion cyclotron resonance. Combination of the latter with the afore-mentioned ionization methods has shifted also in this case the research on organic molecules to organometallic/inorganic systems, and predominantly to biomolecules in the last decade. This invited review will describe the research efforts made by the author's group over the last 40 years together with some personal experiences during his career.

A photoionization study of the ion-neutral complexes CH3CH (+)CH 3 (·) CH 2CH 3] and CH 3CH 2CH (+)CH 3 (·) CH 3 in the gas phase: Formation, H-transfer and C-C bond formation between partners, and channeling of energy into dissociation

Photoionization mass spectrometry was used to investigate the dynamics of ion-neutral complex-mediated dissociations of the n-pentane ion (1). Reinterpretation of previous data demonstrates that a fraction of ions 1 isomerizes to the 2-methylbutane ion (2) through the complex CH3CH(+)CH 3 (·) CH2CH3 (3), but not through CH3CH(+)CH2CH 3 (·) CH3 (4). The appearance energy for C3Hin 7 (+) formation from 1 is 66 kJ mol(-1) below that expected for the formation of n-C3H 7 (+) and just above that expected for formation of i-C3H 7 (+) . This demonstrates that the H shift that isomerizes C3H 7 (+) is synchronized with bond cleavage at the threshold for dissociation to that product. It is suggested that ions that contain n-alkyl chains generally dissociate directly to more stable rearranged carbenium ions. Ethane elimination from 3 is estimated to be about seven times more frequent than is C-C bond formation between the partners in that complex to form 2, which demonstrates a substantial preference in 3 for H abstraction over C-C bond formation. In 1 → CH3CH(+)CH2CH3 + CH3 by direct cleavage of the C1-C2 bond, the fragments part rapidly enough to prevent any reaction between them. However, 1 → 2 → 4 → C4H 8 (+) + CH4 occurs in this same energy range. Thus some of the potential energy made available by the isomerization of n-C4H9 in 1 is specifically channeled into the coordinate for dissociation. In contrast, analogous formation of 3 by 1 → 3 is predominantly followed by reaction between the electrostatically bound partners.