Nitrogen-containing Cations Research Articles

Formamidinium Nitroformate: An Insensitive RDX Alternative.

Five nitroformate (trinitromethanide) salts featuring nitrogen-containing cations were prepared. The salts were characterized by multinuclear NMR, IR, and Raman spectroscopy, single-crystal X-ray analysis, differential thermal analysis, and friction and impact sensitivity testing. These experimental data are supplemented with thermochemical calculations using the Gaussian-4 composite method, and the performance of these energetic materials was calculated based on the Chapman-Jouguet thermodynamic detonation theory. Out of the five compounds studied by us, the formamidinium salt, [CH(NH2)2]+[C(NO2)3]-, is most interesting. Its performance matches that of RDX (research department explosive, cyclotrimethylenetrinitramine), while it is much less sensitive to impact and friction and, therefore, might be an excellent, less sensitive replacement for RDX.

Ionic liquid matrices for MALDI mass spectrometry of lignin.

The use of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for the study of lignin is still extremely limited due to its low ionization efficiency. We have developed an approach for obtaining high-intensity MALDI mass spectra of lignin, based on the use of ionic liquids as matrices. Thirty-two ionic liquids consisting of large nitrogen-containing cations and anions of aromatic acids, traditionally used as crystalline matrices, were tested. It was established that ionic liquids based on N,N-diisopropyl-N-ethylammonium, N-isopropyl-N-methyl-N-tert-butylammonium, 3-aminoquinolinium, pyridinium, and 1-methylimidazolium cations and anions of ferulic, α-cyanohydroxycinnamic, and 2,5-dihydroxybenzoic acids as MALDI matrices provided high efficiency of lignin desorption/ionization with generation of singly charged protonated molecules of its oligomers. The use of such matrices in combination with the MALDI quadrupole ion trap-time-of-flight technique allows high-intensity mass spectra of lignin to be obtained without interferences from the matrix in the molecular weight range up to 3kDa, adequately reflecting the molecular mass characteristics of lignin preparations. Using ionic liquid matrices, MS2 and MS3 MALDI mass spectra of lignins for various precursor ions were first obtained, including in the region of large (> 2kDa) molecular weights. Differences in tandem mass spectra of coniferous and deciduous lignins, reflecting the structural features of corresponding oligomers were demonstrated. Graphical abstract ᅟ.

(Invited) Ionic Liquids in Separations and Mass Spectrometry

Room-temperature ionic liquids (RTILs), are a class of nonmolecular ionic solvents with low melting points. Most common RTILs are composed of unsymmetrically substituted nitrogen-containing cations (e.g., imidazolium, pyrrolidinium, pyridinium) or phosphonium cations with inorganic anions (e.g., Clˉ, PF6ˉ, BF4ˉ). Most of these more common ILs are of limited use analytically. Consequently many ILs containing a variety of cations and anions of different sizes have been synthesized to provide specific characteristics. In this presentation an overview of the structure and properties of ILs and a description of their expanding use in various applications in separations, chromatography and mass spectrometry will be given. A number of studies have appeared indicating that ILs have exceptional promise as stationary phases. They have a dual nature selectivity in that they separate nonpolar molecules as would a nonpolar stationary phase and they separate polar molecules as would a polar stationary phase. Many ILs have exceptional thermal stability. They are being used increasingly in a variety of applications including 2-D GC, enantiomeric separations, the measurement of water in samples/solvents/materials and compact field GC units. ILs have proven to be the best liquid MALDI-MS matrix since we introduced them as such a few years ago. The properties of ILs that make them effective will be discussed. Further, the dications developed for high stability ILs have found another novel use in electrospray ionization (ESI) MS as a reagent for ultra sensitive anion analysis. These will be discussed as well.

Ion conduction and selectivity in acid-sensing ion channel 1.

The ability of acid-sensing ion channels (ASICs) to discriminate among cations was assessed based on changes in conductance and reversal potential with ion substitution. Human ASIC1a was expressed in Xenopus laevis oocytes, and acid-induced currents were measured using two-electrode voltage clamp. Replacement of extracellular Na(+) with Li(+), K(+), Rb(+), or Cs(+) altered inward conductance and shifted the reversal potentials consistent with a selectivity sequence of Li ∼ Na > K > Rb > Cs. Permeability decreased more rapidly than conductance as a function of atomic size, with P(K)/P(Na) = 0.1 and G(K)/G(Na) = 0.7 and P(Rb)/P(Na) = 0.03 and G(Rb)/G(Na) = 0.3. Stimulation of Cl(-) currents when Na(+) was replaced with Ca(2+), Sr(2+), or Ba(2+) indicated a finite permeability to divalent cations. Inward conductance increased with extracellular Na(+) in a hyperbolic manner, consistent with an apparent affinity (K(m)) for Na(+) conduction of 25 mM. Nitrogen-containing cations, including NH4(+), NH3OH(+), and guanidinium, were also permeant. In addition to passing through the channels, guanidinium blocked Na(+) currents, implying competition for a site within the pore. The role of negative charges in an external vestibule of the pore was evaluated using the point mutation D434N. The mutant channel had a decreased single-channel conductance, measured in excised outside-out patches, and a macroscopic slope conductance that increased with hyperpolarization. It had a weakened interaction with Na(+) (K(m) = 72 mM) and a selectivity that was shifted toward larger atomic sizes. We conclude that the selectivity of ASIC1 is based at least in part on interactions with binding sites both within and internal to the outer vestibule.

The death and life of the resurrection drug.

In his own words, it was the most dramatic moment of his scientific career. At the back of an auditorium in Nairobi, Kenya, Cyrus Bacchi met Simon Van Nieuwenhove. Bacchi, at the time, was essentially a biochemist whose interest was the African trypanosome. Van Nieuwenhove was a clinician who had worked for many years in the field in Africa. The topic of their conversation was eflornithine—a small and simple compound that would eventually make a big impact. Bacchi had shown that the compound had an effect on the parasite that causes Human African Trypanosomiasis. Van Nieuwenhove was dosing patients with it. The story of eflornithine did not start with eflornithine.It started because no one knew how to purify an enzyme. Bacchi was working on his thesis, which centred on the α-glycerophosphate shuttle in hemoflagellates. The shuttle acts as a way to transport reducing equivalents from the cytosol to the mitochondrion. α-glycerophosphate dehydrogenase was the enzyme he spent much of his time trying to purify. The reason he could not purify it was it was hidden within another compartment of the trypanosome. It would not be until several years later, and published in 1977, that Fred Opperdoes discovered the glycosome [1]: the organelle that encapsulates glycolysis in trypanosomes, and the organelle that was hiding the enzyme. At every step of the purification process Bacchi lost activity in his enzyme extracts. Magnesium chloride, surprisingly, managed to boost activity. Bacchi looked into other nonmetallic compounds that would act as cations and eventually chose the polyamines: naturally occurring, nitrogen-containing cations whose concentration is closely controlled by the cell. Spermidine and spermine were found to be the best replacements for magnesium, yielding higher activities. With evidence that the enzyme he was trying to purify was most likely locked within the glycosome, Bacchi moved his attention to how the polyamines were made within the trypanosome. This was an area that had amassed a lot of knowledge everywhere apart from in trypanosomes. It was in 1677 that Anton van Leeuwenhoek first observed spermatozoa in humans, dogs, and a host of other organisms, and he later discovered crystals of spermine phosphate in human semen. Modern research had identified the biologically active polyamines—spermidine and spermine—in plants and many types of mammalian cells. The biochemical pathways that make and degrade the polyamines, along with some of their enzymes, had also been identified. At the time, nothing was known about polyamines in protozoa, and in trypanosomes in particular. Did these parasites contain polyamines? Could polyamine metabolism be a useful chemotherapeutic target?

Supramolecular compounds of indium sulfates with nitrogen-containing cations

Compounds with a general formula [Cat][In(H2O) n (SO4)2] x · mH2O (where Cat = C(NH2)3, H(2,2′-Bipy), H2(4,4′-Bipy), H2[Py(CH2)3Py], and H3N(CH2)6NH3) were synthesized and identified from the elemental analysis, IR, and thermogravimetric analysis data. X-ray diffraction analysis of crystalline [C(NH2)3][In(H2O)2(SO4)2] complex showed that the polymer chains of In aquasulfate form ensembles with guanidinium ions. The structure of [H2(4,4′-Bipy)][In2(H2O)6(SO4)4] · 2H2O consists of the dimeric anions of indium sulfate. The coordination sphere of In includes three O atoms of three SO4 groups and three O atoms of water molecules. The dimers are united into framework by diprotonated Bipy cations.

The Association of Picrate Ions with Amphiphilic Cations in Water and Aqueous Solutions of Nonionic Surfactant and β-Cyclodextrin

The interaction of cetyltrimethylammonium and cetylpyridinium bromides with picrate ions in water and aqueous solutions of the nonionic surfactant Brij 35 is studied by spectrophotometry. Spectral characteristics of the associates of picrate ions with long-chain nitrogen-containing cations depend on the concentration of a cationic surfactant. When β-cyclodextrin is added, these associates decompose owing to the formation of the strong inclusion complexes of the guest-host type with amphiphilic ions of a cationic surfactant or Brij 35 molecules. The conclusion is made that the driving force for the formation of premicellar aggregates involving picrate ions is the interactions between alkyl chains of surfactant cations. It is shown that, in the presence of various surfactants, as β-cyclodextrin concentration increases, first the molecules of nonionic surfactant and then amphiphilic cations bind with the receptor cavity. It is confirmed that there is no interaction between polyethylene glycol and β-cyclodextrin in aqueous solution.

Spectrophotometric Determination of the Polyiodohalides of Organic Nitrogen-Containing Cations

The following biologically active diiodohalides of organic cations were studied: N-cetylpyridinium, trimethylbenzylammonium, triethylbenzylammonium, and N,N-dimethylmorpholinium diiodochlorides; N-cetylpyridinium, tetramethylammonium, tetrabutylammonium, and N,N-dimethylmorpholinium diiodobromides; and N,N-dimethylmorpholinium and butyroylcholinium triiodides. A simple and rapid procedure was proposed for the determination of the above compounds; it is based on the conversion of organic diiodohalides into the corresponding triiodides (e300 nm ≈ 4 × 104; e370 nm ≈ 2 × 104) in the presence of excess potassium iodide (RSD ≤ 2%). An extraction–spectrophotometric method was developed for the quantitative determination of the biologically active compounds in pharmaceutical dosage forms based on their ion associates with anionic dyes, erythrosine (mmin = 1.25–3.30 μg; RSD ≤ 3%) and Bromothymol Blue (mmin = 3.85 μg; RSD = 3%), or a cationic dye—1,3-dimethyl-2-(4-morpholinophenyl)azobenzimidazolium phenylsulfate (mmin = 2.32–8.26 μg; RSD ≤ 4%). The developed procedures were used for monitoring drug substances in model pharmaceutical preparations (RSD ≤ 4%).

The Tightness Contribution to the Brønsted α for Hydride Transfer between NAD+ Analogues

It has been shown that the rate of symmetrical hydride transfer reaction varies with the hydride affinity of the (identical) donor and acceptor. In that case, Marcus theory of atom and group transfer predicts that the Brønsted alpha depends on the location of the substituent, whether it is in the donor or the acceptor, and the tightness of the critical configuration, as well as the resemblance of the critical configuration to reactants or products. This prediction has now been confirmed for hydride transfer reactions between heterocyclic, nitrogen-containing cations, which can be regarded as analogues of the enzyme cofactor, nicotinamide adenine dinucleotide (NAD+). A series of reactions with substituents in the donor gives Brønsted alpha of 0.67 +/- 0.03 and a tightness parameter, tau, of 0.64 +/- 0.06. With substituents in the acceptor alpha = 0.32 +/- 0.03 and tau = 0.68 +/- 0.08. The reactions are all spontaneous, with equilibrium constants between 0.4 and 3 x 10(4), and the two sets span about the same range of equilibrium constants. The two tau values are essentially identical with an average value of 0.66 +/- 0.05. These results can be semiquantitatively mimicked by rate constants calculated for a linear, triatomic model of the reaction. Variational transition state theory and a physically motivated but empirically calibrated potential function were used. The computed rate constants generate an alpha value of 0.56 if the hydride affinity of the acceptor is varied and an alpha of 0.44 if the hydride affinity of the donor is varied. The calculated kinetic isotope effects are similar to the measured values. A previous error in the Born charging term of the potential function has been corrected. Marcus theory can be successfully fitted to both the experimental and computed rate constants, and appears to be the most compact way to express and compare them. The success of the linear triatomic model in qualitatively reproducing these results encourages the continued use of this easily conceptualized model to think about group, ion, and atom transfer reactions.

Complexation of planar, organic, five-membered cations with crown ethers

Complexation of six aromatic, nitrogen-containing cations with various crown ethers has been studied using 1H NMR, mass spectrometric and crystallographic methods. Hydrogen bonding appears to be the most important interaction in complexation, but minor effects such as π-stacking or cation–π interactions have also been observed. The stability constants of five different imidazolium perchlorate ·crown ether complexes and five other similar cation·DB18C6 complexes were determined by 1H NMR titration in acetonitrile solution. The stability of these complexes in solution and in the gas phase is discussed. The crystal structures of seven complexes were determined in order to study complexation in the solid state. Four of these are imidazolium complexes with different crown ethers and three are complexes of dibenzo-18-crown-6 with similar planar cations.

Adiabatic structural relaxation in heterocyclic nitrogen-containing cations: The structure, absorption and fluorescence of the 2,4,6-triarylsubstituted pyridinium cations

The detailed studies of the 2,4,6-(N-alkyl)triarylsubstituted pyridinium cations I as well as the large series of the model structures have been carried out by absorption, fluorescent and polarization methods in the solvents of various polarity and viscosity at different temperatures. The localizations of the lowest electron transitions are determined. It is shown that the fluorescence with anomalous Stokes shift (ASS-fluorescence) arises owing to the adiabatic structural relaxation (ASR) with the formation of the flattened (but not twisted) structure. The advantages of I as the objects for ASR study are discussed. The crude determination of the ASR kinetic parameters has been conducted. A data assume that the ASS fluorescence quantum yields of the cations I are conditioned mainly by deactivation processes in the final flattened structure.