High Proton Affinity Research Articles

Ion mobility analyzer – quadrupole mass spectrometer system design

Because of their extremely high sensitivity for chemicals with elevated electronegativity or high proton affinity the ion mobility analysers are ideal for the ultra-trace detection of toxic or explosive chemicals, most of these situated often at concentration levels of sub-ppb (parts-per-billion). Ion mobility spectrometers (IMS) can be used to identify illicit drugs or environmental pollutants. Since resolution of an IMS is relatively low, to achieve an accurate identification of target analyte it is recommended to couple the IMS with a quadrupole mass spectrometer (QMS) or a time of flight mass spectrometer, acquiring in this way confirmatory information. This coupling is made through a specific interface. In this paper, an experimental model of such a tandem instrument, IMS-QMS is described. Accomplishment of this general purpose will be done, overcoming a series of specific issues. This implies the solving, using innovative solutions, of a series of complex issues: ensuring the stability of the ions beam generated by ion source; transfer with a good efficiency of the ionic current from IMS analyser to QMS; and realization of a special electronic circuitry which will be able to detect both positive and negative ions.

Ionization Mechanism of the Ambient Pressure Pyroelectric Ion Source (APPIS) and Its Applications to Chemical Nerve Agent Detection

We present studies of the ionization mechanism operative in the ambient pressure pyroelectric ionization source (APPIS), along with applications that include detection of simulants for chemical nerve agents. It is found that ionization by APPIS occurs in the gas-phase. As the crystal is thermally cycled over a narrow temperature range, electrical discharges near the surface of the crystal produce energetic species which, through reactions with atmospheric molecules, result in reactant ions such as protonated water clusters or clusters of hydroxide and water. Reactant ions can be observed directly in the mass spectrometer. These go on to react with trace neutrals via proton transfer reactions to produce the ions observed in mass spectra, which are usually singly protonated or deprotonated species. Further implicating gas-phase ionization, observed product distributions are highly dependent on the composition of ambient gases, especially the concentration of water vapor and oxygen surrounding the source. For example, basic species such as triethylamine are observed as singly protonated cations at a water partial pressure of 10 torr. At a water pressure of 4 torr, reactive oxygen species are formed and lead to observation of protonated amine oxides. The ability of the APPIS source to detect basic molecules with high proton affinities makes it highly suited for the detection of chemical nerve agents. We demonstrate this application using simulants corresponding to VX and GA (Tabun). With the present source configuration pyridine is detected readily at a concentration of 4 ppm, indicating ultimate sensitivity in the high ppb range.

Probing the mechanism of electron capture and electron transfer dissociation using tags with variable electron affinity.

Electron capture dissociation (ECD) and electron transfer dissociation (ETD) of doubly protonated electron affinity (EA)-tuned peptides were studied to further illuminate the mechanism of these processes. The model peptide FQpSEEQQQTEDELQDK, containing a phosphoserine residue, was converted to EA-tuned peptides via beta-elimination and Michael addition of various thiol compounds. These include propanyl, benzyl, 4-cyanobenzyl, perfluorobenzyl, 3,5-dicyanobenzyl, 3-nitrobenzyl, and 3,5-dinitrobenzyl structural moieties, having a range of EA from -1.15 to +1.65 eV, excluding the propanyl group. Typical ECD or ETD backbone fragmentations are completely inhibited in peptides with substituent tags having EA over 1.00 eV, which are referred to as electron predators in this work. Nearly identical rates of electron capture by the dications substituted by the benzyl (EA = -1.15 eV) and 3-nitrobenzyl (EA = 1.00 eV) moieties are observed, which indicates the similarity of electron capture cross sections for the two derivatized peptides. This observation leads to the inference that electron capture kinetics are governed by the long-range electron-dication interaction and are not affected by side chain derivatives with positive EA. Once an electron is captured to high-n Rydberg states, however, through-space or through-bond electron transfer to the EA-tuning tags or low-n Rydberg states via potential curve crossing occurs in competition with transfer to the amide pi* orbital. The energetics of these processes are evaluated using time-dependent density functional theory with a series of reduced model systems. The intramolecular electron transfer process is modulated by structure-dependent hydrogen bonds and is heavily affected by the presence and type of electron-withdrawing groups in the EA-tuning tag. The anion radicals formed by electron predators have high proton affinities (approximately 1400 kJ/mol for the 3-nitrobenzyl anion radical) in comparison to other basic sites in the model peptide dication, facilitating exothermic proton transfer from one of the two sites of protonation. This interrupts the normal sequence of events in ECD or ETD, leading to backbone fragmentation by forming a stable radical intermediate. The implications which these results have for previously proposed ECD and ETD mechanisms are discussed.

ESI-MS spectra of 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridinones

Twelve 3-cyano-4-(substituted phenyl)-6-phenyl-2(1H)-pyridinones were investigated by tandem mass spectrometry using positive as well as negative electrospray ionization. The influence of the electron affinity of the substituent and the steric effect on the fragmentation is discussed. Pyridinones with a substituent of low proton affinity show loss of water, HCN or benzene from the pyridinone ring in the first step of MS2 fragmentations. Oppositely, if a substituent with high proton affinity is present on the phenyl ring in the 4-position of pyridinone, the fragmentation paths are complex, depending mainly on the substituent proton acceptor ability. Elimination of neutral molecules CO, HCN, H2O, PhH (benzene) or Ph and CN radicals are fragmentation processes common for all compounds in the subsequent steps of the fragmentations.

Sodium Controlled Selective Reactivity of Protonated Deoxy-Oligonucleotides in the Gas Phase

Metastable fragmentation of the positively charged, hexameric oligonucleotides 5'-d(TTXYTT) (X and Y are dC, dG, or dA) and 5'-d(CTCGTT), 5'-d(TTCGTC) and 5'-d(CTCGTC) is studied after matrix assisted laser desorption/ionization (MALDI). The influence of the degree of sodiation, i.e., when the acidic protons are one by one exchanged against sodium ions, is systematically studied for the exchange of up to seven protons against sodium ions. Exchanging the acidic protons against sodium gradually quenches the backbone cleavage through the w and a-B channels, and quantitative quenching of these channels is generally achieved with the exchange of four protons against sodium ions. At the same time, the exchange of protons against sodium ions promotes the loss of a neutral, high proton affinity base. The formation of the w and a-B fragments is found to be highly dependent on the sequence of the central bases. A single mechanism consistent with these observations is proposed. In addition to the quenching of the classical w and a-B reaction channels, a drastic and abrupt on/off-switching of new reaction channels is observed as the degree of sodiation successively increases. These channels involve selective loss of the two central bases and the excision of a phosphodiester group and a sugar unit from the center of the oligonucleotides. Synchronously, the two terminal fragments recombine to form a tetramer containing the two terminal nucleosides from each end of the hexamer. Possible mechanism explaining these remarkable channels are discussed.

Rapid UPLC-MS/MS method for routine analysis of plasma pristanic, phytanic, and very long chain fatty acid markers of peroxisomal disorders

Quantification of pristanic acid, phytanic acid, and very long chain fatty acids (i.e., hexacosanoic, tetracosanoic, and docosanoic acids) in plasma is the primary method for investigateing a multitude of peroxisomal disorders (PDs). Typically based on GC-MS, existing methods are time-consuming and laborious. In this paper, we present a rapid and specific liquid chromatography tandem mass spectrometric method based on derivatization with 4-[2-(N,N-dimethylamino)ethylaminosulfonyl]-7-(2-aminoethylamino)-2,1,3-benzoxadiazole (DAABD-AE). Derivatization was undertaken to improve the poor mass spectrometric properties of these fatty acids. Analytes in plasma (20 mul) were hydrolyzed, extracted, and derivatized with DAABD-AE in approximately 2 h. Derivatives were separated on a reverse-phase column and detected by positive-ion electrospray ionization tandem mass spectrometry with a 5 min injection-to-injection time. Calibration plots were linear over ranges that cover physiological and pathological concentrations. Intraday (n = 12) and interday (n = 10) variations at low and high concentrations were less than 9.2%. Reference intervals in normal plasma (n = 250) were established for each compound and were in agreement with the literature. Using specimens from patients with established diagnosis (n = 20), various PDs were reliably detected. In conclusion, this method allows for the detection of at least nine PDs in a 5 min analytical run. Furthermore, this derivatization approach is potentially applicable to other disease markers carrying the carboxylic group.

First and Second Proton Affinities of Carbon Bases

Quantum chemical calculations at the MP2/TZVPP//BP86/SVP level are reported for the first and second proton affinities (PAs) of divalent carbon-donor molecules. The molecules investigated are imidazol-2-ylidenes ("normal" NHCs) and the tautomeric imidazol-4/5-ylidenes ("abnormal" NHCs). PAs are also calculated for acyclic and cyclic carbodiphosphoranes, carbophosphoranesulfide, unsaturated and saturated carbodicarbenes, tetraaminoallenes and carbon suboxide. The results are discussed in terms of divalent carbon(II) compounds (carbenes) CR(2), which have one lone electron pair at carbon, and carbon(0) compounds CL(2), which have two lone pairs at carbon and two C<--L donor-acceptor bonds. Divalent C(0) compounds (carbones) not only have very high first PAs, but the second PA is also large and strong enough to isolate doubly protonated C(0) species as salts in a condensed phase. The first PA of divalent carbon(II) compounds (carbenes) are also large. However, they have much smaller second PAs than the divalent carbon(0) compounds. The divalent C(0) character of a compound is not always obvious when the bonding situation in the equilibrium geometry is considered. This is the case, for example, for tetraaminoallenes (TAAs). Protonation of TAAs changes the bonding situation of the central moiety from doubly bonded (R(2)N)(2)C=C=C(NR(2))(2) to a donor-acceptor description (R(2)N)(2)C-->C(H(+))(n)<--C(NR(2)) [n = 1, 2]. The atomic partial charge at the carbon donor atom does not correlate with the PA and the trend of the second PA may be quite different from the trend of the first. The trends of the first and second PA correlates quite well with the eigenvalues of the highest-lying carbon lone-pair orbitals.

Screening of In Vitro Synthesised Metabolites of 4,9,11-Trien-3-One Steroids by Liquid Chromatography-Mass Spectrometry

The aim of the work was to develop a flexible in vitro synthesis procedure, which can be applied in order to study and predict the metabolic patterns of new derivatives of anabolic androgenic steroids (AAS) with respect to most prominent target compounds for doping control purposes. Microsomal and S9 fraction of human liver preparations were used as a source of metabolising enzymes and the co-substrates of the synthesis mixture were selected to favour phase-I metabolic reactions and glucuronidation as phase-II conjugation reactions. Model compounds within the study were 4,9,11-trien-3-one steroids, structural derivatives of gestrinone and trenbolone, which both are included in the list of prohibited compounds in sports by the World Anti-Doping Agency (WADA). The correlation between in vitro metabolism of human microsomes and in vivo excretion studies in human was compared with gestrinone and subsequently, the applicability of the in vitro model for prediction of AAS metabolic pathways for new doping agents was evaluated. All the AAS examined within this study were successfully metabolised using the developed in vitro model, hydroxylation, reduction and glucuronide conjugation being the most prominent reaction pathways. Hydroxylated and glucuronide-conjugated metabolites of in vivo experiment with gestrinone were the same metabolites formed in the enzyme-driven process, thus showing good in vitro-in vivo correlation. Liquid chromatographic-mass spectrometric and tandem mass spectrometric methods were developed, relying on the positive polarity of electrospray ionisation, which also allowed the direct detection of intact glucuronide-conjugated AAS metabolites. Due to charge delocalisation and high proton affinity, the developed method was proven effective in the analysis of AAS metabolites bearing extensive conjugated double bond systems in their structures.

Anomalous phenomenon in hydrogen gas sensors based upon pyridylimidazoperylene or pyridylimidazonaphthalene

We have been involved in the research and development on H2 gas sensors utilizing a high proton affinity of the pyridyl rings integrated in organic pigments such as diketopyrrolopyrroles, peryleneimides, and copperphthalocyanes. Our sensors exhibit a remarkable increase in electrical conductivity by three orders of magnitude even under 0.01% H2. However, an anomalous phenomenon has been observed in the title compounds (pyridylimidazoperylene and pyridylimidazonaphthalene) that shows an additional increase in conductivity (i.e., reverse of the sensor current) as soon as H2 shuts off. The unusual effect has been investigated in the present investigation on the basis of the crystal structure, molecular orbital calculations, and UV-visible/IR spectra with special attention to the sign of the charge carriers before and after exposure to H2. As a result, the pyridylimidazole ring is found to be responsible for the unusual effect that involves two protonation sites. In addition, the charge carriers have been determined to be solely electrons in the build up of the sensor current; whereas both electrons and protons are involved in the decay process. The contribution of the proton conduction in the decay process prevails over the electron current, ending up with the reverse in sensor current.

Differentiation of diastereomeric cyclic β‐amino acids by varying the neutral reagent in ion/molecule reactions studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Stereochemical differentiation of diasteromeric pairs of cis- and trans-2-aminocyclohexane-, -2-amino-4-cyclohexene-, and -2-aminocyclopentanecarboxylic acids was investigated with host-guest complexes where tetraethyl resorcarene was the host molecule. Diastereoselectivity was evaluated by ion/molecule reactions and collision-induced dissociation with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICRMS). The effect of varying the neutral reagent (n-propylamine, i-propylamine, diethylamine, and triethylamine) in ion/molecule reactions was evaluated. Both steric interactions and proton affinity of the neutral reagents influenced the reaction rates. High proton affinity of the neutral reagent apparently had a twofold effect. If the proton affinity of the neutral reagent was too high, the reaction tended to become too exothermic and part of the host-guest complex decomposed instead of transforming to a new host-guest complex, effecting a decrease in the reaction rate. The remaining portion of the host-guest complexes meanwhile reacted very fast with the neutral reagent due to high proton affinity causing an increase in the reaction rate. n-Propylamine and i-propylamine proved to be the best neutral reagents, providing clear diastereoselectivity for beta-amino acids in ion/molecule reactions. Interestingly, diastereoselectivity was better for flexible cyclohexane beta-amino acids (2 and 3) than for more rigid cyclopentane beta-amino acids (6 and 7). The results of ab initio and hybrid density functional theory calculations on the structures of the host-guest complexes of saturated beta-amino acids were in good agreement with the experimental results.

Analysis of steroidal estrogens as pyridine-3-sulfonyl derivatives by liquid chromatography electrospray tandem mass spectrometry

Sulfonyl chlorides substituted with functional groups having high proton affinity can serve as derivatization reagents to enhance the sensitivity for steroidal estrogens in liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). The most commonly used reagent for derivatization of estrogens for LC-ESI-MS/MS is dansyl chloride. In this study, we compared dansyl chloride, 1,2-dimethylimidazole-4-sulfonyl (DMIS) chloride, pyridine-3-sulfonyl (PS) chloride, and 4-(1H-pyrazol-1-yl)benzenesulfonyl (PBS) chloride for derivatization of 17β-estradiol (E2) prior to LC-ESI-MS/MS. The product ion spectra of the dansyl and DMIS derivatives were dominated by ions representing derivatization reagent moieties. In contrast, the product ion spectrum of the PS derivative of E2 and, to a lesser extent, the PBS derivative, showed analyte-specific fragment ions. Derivatization with PS chloride was therefore chosen for further investigation. The product ion spectrum of the PS derivative of E2 showed intense ions at m/z 272, assigned to the radical E2 cation, and at m/z 350, attributed to the loss of SO2 from the [M+H]+ ion. Third-stage mass spectrometry of the PS derivative of E2 with isolation and collisional activation of the m/z 272 ion resulted in steroid C and D ring cleavages analogous to those observed in electron ionization mass spectrometry. The product ion spectra of the PS derivatives of estrone, 17α-ethinylestradiol, equilin, and equilenin showed similar estrogen-specific ions. Using derivatization with PS chloride, we developed an LC-ESI-MS/MS method with multiple reaction monitoring of primary and confirmatory precursor-to-product ion transitions for the determination of E2 in serum.

Heterogeneous Proton-Bound Dimers with a High Dipole Moment Monomer: How Could We Experimentally Observe These Anomalous Ionic Hydrogen Bonds?

Electronic structure calculations (CBS-QB3 and G3MP2) have been used to predict a suitable method to experimentally observe the anomalous structure which is predicted to exist in a proton-bound dimer with a high dipole moment monomer. The enthalpy associated with forming the proton-bound dimer from its protonated and neutral monomers is shown to be linearly related to the difference in proton affinities which has been observed experimentally. However, unlike previous experimental studies, the linear correlation is not predicted to depend strongly, if at all, on whether the basic sites are C=O, C=N, or O(H) n-donor bases. Thermochemical measurements, then, are probably not the best method to distinguish between the structures of heterogeneous proton-bound dimers. It has been shown that a suitable method to experimentally observe the anomalous structure of proton-bound dimers containing a high dipole moment monomer (or very polar monomer) is by spectroscopic measurement. The O-H+-O asymmetric stretch is probably not the best infrared band to try to correlate with structure. The best band to observe is one which is in a region of the spectrum not masked by other absorptions and is also sensitive to the proximity of the binding proton. For example, it is shown that the methanol-free O-H stretch is very sensitive to the O-H+ bond distance for a series of heterogeneous proton-bound dimers containing methanol. It is predicted that the free O-H stretch of the methanol/acetonitrile proton-bound dimer is more closely related to the O-H stretch in protonated methanol than the O-H stretch in neutral methanol. Observations of these bands should confirm that the proton is closer to methanol in the methanol/acetonitrile proton-bound dimer despite acetonitrile having a higher proton affinity.

Reductive Halogen Elimination from Phenols by Organic Radicals in Aqueous Solutions; Chain Reaction Induced by Proton-Coupled Electron Transfer

Gamma-radiolysis and measurements of halide ions by means of ion chromatography have been employed to investigate reductive dehalogenation of chloro-, bromo-, and iodophenols by carbon-centered radicals, *CH(CH(3))OH, *CH(2)OH, and *CO(2)-, in oxygen-free aqueous solutions in the presence of ethanol, methanol, or sodium formate. While the reactions of 4-IC(6)H(4)OH with *CH(CH(3))OH and *CH(2)OH radicals are endothermic in water/alcohol solutions, the addition of bicarbonate leads to iodide production in high yields, indicative of a chain reaction. The maximum effect has been observed with about 10 mM sodium bicarbonate present. The complex formed from an alpha-hydroxyalkyl radical and a bicarbonate anion is considered to cause the enhancement of the reduction power of the former to the extent at which the reduction of the iodophenol molecule becomes exothermic. No such effect has been observed with phosphate, which is a buffer with higher proton affinity, when added in the concentration of up to 20 mM at pH 7. This indicates that one-electron reduction reactions by alpha-hydroxyalkyl radicals occur by the concerted proton-coupled electron transfer, PCET, and not by a two-step ET/PT or PT/ET mechanisms. The reason for the negative results with phosphate buffer could be thus ascribed to a less stable complex or to the formation of a complex with a less suitable structure for an adequate support to reduce iodophenol. The reduction power of the carbonate radical anion is shown to be high enough to reduce iodophenols by a one-electron-transfer mechanism. In the presence of formate ions as H-atom donors, the dehalogenation also occurs by a chain reaction. In all systems, the chain lengths depend on the rate of reducing radical reproduction in the propagation step, that is, on the rate of H-atom abstraction from methanol, ethanol, or formate by 4-*C(6)H(4)OH radicals liberated after iodophenol dehalogenation. The rate constants of those reactions were determined from the iodide yield measurements at a constant irradiation dose rate. They were estimated to be 6 M(-1)(s-1) for methanol, 140 M(-1)(s-1) for ethanol, and 2100 M(-1)(s-1) for formate. Neither of the tested reducing C-centered radicals was able to dehalogenate the bromo or chloro derivative of phenol.

Consistency between chemotyping of single filaments of Planktothrix rubescens (cyanobacteria) by MALDI‐TOF and the peptide patterns of strains determined by HPLC‐MS

The high metabolic diversity of potentially toxigenic cyanobacteria has been recently demonstrated for several bloom-forming genera. To understand the dynamics of cyanobacterial blooms and fluctuations in toxin content, techniques are required that allow the distinction of clones in field samples on a subspecific taxonomic level. We evaluated the possibility to analyze single filaments of a common toxigenic taxon, Planktothrix rubescens, by comparing peptide profiles obtained from HPLC/MS analyses of bulk biomass to mass spectra of single filaments for 11 clonal strains. For all strains a significant relationship of chromatogram peak area to mass spectrum peak height was found for individual peptides. Individual peptide's response in mass spectrometry compared to HPLC, however, differed, likely attributable to the presence of particular moieties with high proton affinities in the molecules. Thirty-four individual peptides detected in HPLC fractions of all strains could also be detected in the corresponding single filaments. In conclusion, MALDI-TOF MS analysis of single filaments is shown to be an efficient tool for the study of chemotype diversity and dynamics in field studies and laboratory experiments. The good correspondence between peak area and peak height in chromatograms and mass spectra, respectively, is promising with respect to the use of MALDI-TOF MS as a quantitative analytical tool for natural products studies and cyanotoxin research.

Hydrogen Gas Sensor Based Upon Proton Acceptors Integrated in Copper-Tetra-2,3-Pyridinoporphyradine

We have previously developed a novel H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensor based upon a high proton affinity of diketodipyridylpyrrolopyrrole. Protonation is found to bring about a remarkable reduction of the electrical resistivity and this effect has been applied to H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> gas sensors. In the present investigation, an attempt was made to integrate proton acceptors (i.e., pyridyl rings) into copperphthalocyanine in order to improve the sensor characteristics. The present sensor exhibits a remarkable change in electrical resistivity by three orders of magnitude even under 0.01% H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> . Furthermore, the sensor is found to operate reversibly at room temperature and is scarcely influenced by ambient gases such as CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> , CO, CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , NO, SO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , CH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> OH, C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sub> OH, and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O moisture

The Stereostructure of Porphyra‐334: An Experimental and Calculational NMR Investigation. Evidence for an Efficient ‘Proton Sponge’

AbstractThe mycosporine‐like amino acid (MAA) porphyra‐334 (1) is subjected to extensive 1H‐ and 13C‐NMR analysis as well as to density‐functional‐theory (DFT) calculations. All 1H‐ and 13C‐NMR signals of 1 are assigned, as well as the resonances of prochiral proton pairs. This is achieved by 500‐MHz standard COSY, HMQC, and HMBC experiments, as well as by one‐dimensional (DPFGSE‐NOE) and two‐dimensional (NOESY) NOE experiments. Diffusion measurements (DOSY) confirm that 1 is monomeric in D2O solution. DFT Calculations yield 13C‐NMR chemical shifts which are in good agreement for species 6 which is the imino N‐protonated form of 1. An exceptionally high proton affinity of 265.7 kcal/mol is calculated for 1, indicating that 1 may behave as a very powerful ‘proton sponge’ of comparable strength as synthetic systems studied so far. Predictions of 13C‐NMR chemical shifts by the ‘NMRPredict’ software are in agreement with the DFT data. The absolute configuration at the ring stereogenic center of 1 is concluded to be (S) from NOE data as well as from similarities with the absolute configuration (S) found in mycosporine‐glycine 16. This supports the assumption that 1 is biochemically derived from 3,3‐O‐didehydroquinic acid (17). The data obtained question the results recently published by a different research group claiming that the configuration at the imino moiety of 1 is (Z), rather than (E) as established by the here presented study.

Gem-diamines as highly active organocatalysts for carbon–carbon bond formation

Diamines with neighbour nitrogen atoms have been used as base catalysts in the Knoevenagel condensation reaction between benzaldehyde and ethyl cyanoacetoacetate. The catalytic results show that a good basic catalyst requires a combination of two factors: high proton affinity and the ability to return the proton to the oxoanion intermediate. Computational chemistry calculations show this by characterizing the reactants, products, and transition states and by calculating the activation energies of the different reaction steps. A diamine, di(3-methylpiperidine)methane ( B), has been found with a higher catalytic activity than DMAN despite its lower proton affinity, demonstrating that not only the proton affinity, but also the steric ability to abstract the protons, are important in explaining the catalytic results.

Protonated Heme

The ions formally corresponding to protonated heme [Fe(II)-hemeH](+) have been obtained by collision-induced dissociation from the electrospray ionization of microperoxidase (MP11) and their gas-phase chemistry has been studied by FTICR mass spectrometry. H/D-exchange reactions, used as a tool to gain information on the protonation sites in polyfunctional molecules, show that labile hydrogens pertain to the propionyl substituents at the periphery of the protoporphyrin IX. Several conceivable isomers for protonated heme have been evaluated by density functional theory. The most stable among the species investigated is the one corresponding to protonation at the beta carbon atom of a vinyl group, yielding a proton affinity (PA) value for [Fe(II)-heme] of 1220 kJ mol(-1). This high PA is consistent with the inertness of the hydrogen atoms at the protonation site towards H/D exchange with ND(3) and CD(3)CO(2)D. Peculiar features of this [Fe(II)-hemeH](+) isomer emerge by analysis of its electronic structure, showing that the vinyl group undergoing formal protonation has gained significant radical character due to electron transfer from the metal center. As a consequence, the iron atom acquires partial iron(III) character and none of the two formal descriptions [Fe(II)-hemeH(+)] and [Fe(III)-hemeH(.)](+) alone may adequately illustrate the protonated heme ion. In agreement with this description, the reactivity of protonated heme presents dual facets, resembling iron(III) in some aspects and iron(II) in others. On the one hand, protonated heme behaves like [Fe(III)-heme](+) ions in H/D-exchange reactions. On the other, it shows markedly decreased reactivity towards the addition of ligands with the notable exception of NO, in line with the high affinity shown by iron(II) complexes towards this molecule, NO, of key biological role.

Anomalous phenomenon in pyridyl-imidazoperylene H&lt;sub&gt;2&lt;/sub&gt; gas sensor

Organic pigments were once extensively investigated as a photoconductor for the electrophotographic photoreceptor. Nowadays, they play an important role as colorants for color copies as well as materials for optical discs, electroluminescence, FET etc. Here, we report another novel application of organic pigments for H2 gas sensors. We are involved in the research and development on H2 gas sensors utilizing high proton affinity of the pyridyl rings integrated in the title compound (PIP). An anomalous phenomenon in PIP-based H2 sensors has been observed that the sensor current increases even after H2 interruption. Two N-sites in PIP are found to be involved in the protonation: N1 at the pyridyl ring and N2 at the five-membered ring. Among these, N1 is especially sensitive to water moisture as well as H2; whereas N2 behaves as an ordinary proton acceptor as found in other pyridylring-integrted pigments. The anomalous effect is found to be due to the former N1 behavior.

Abnormal effect in hydrogen gas sensors based upon pyridylimidazonaphthalene

Organic pigments were once extensively investigated as photoconductors for the electrophotographic photoreceptor. Nowadays, they play an important role as colorants for color copies as well as materials for optical discs, electroluminescence, FET etc. Here, we report another novel application of organic pigments for H2 gas sensors. We have previously developed a H2 gas sensor that utilizes a high proton affinity of diketodipyridylpyrrolopyrrole. We extended our system to other pigments such as perylene-imides with pyridyl rings. Then, we encountered an anomalous effect in pyridyl-imidazoperylene(PIP) that the sensor current increases even after shut-off of H2. In the present investigation, a similar compound called pyridylimidazonaphthalene (PIN) has been tackled in order to systematically interpret the anomalous effect in PIP and PIN. As a result, the two N atoms in the pyridylimidazo group are responsible for the effect. Furthermore, PIP is found to be quite inert to H2O and H2. This makes a string difference between PIN and PIP which is closely linked to the sensitivity of the H2 sensor.