Distinguishing isomeric representatives of "bath salts", "plant food", "spice", or "legal high" remains a challenge for analytical chemistry. In this work, we used vacuum ultraviolet spectroscopy combined with gas chromatography to address this issue on a set of forty-three designer drugs. All compounds, including many isomers, returned differentiable vacuum ultraviolet/ultraviolet spectra. The pair of 3- and 4-fluoromethcathinones (m/z 181.0903), as well as the methoxetamine/meperidine/ethylphenidate (m/z 247.1572) triad, provided very distinctive vacuum ultraviolet spectral features. On the contrary, spectra of 4-methylethcathinone, 4-ethylmethcathinone, 3,4-dimethylmethcathinone triad (m/z 191.1310) displayed much higher similarities. Their resolution was possible only if pure standards were probed. A similar situation occurred with the ethylone and butylone pair (m/z 221.1052). On the other hand, majority of forty-three drugs was successfully separated by gas chromatography. The detection limits for all the drug standards were in the 2-4 ng range (on-column amount), which is sufficient for determinations of seized drugs during forensics analysis. Further, state-of-the-art time-dependent density functional theory was evaluated for computation of theoretical absorption spectra in the 125-240 nm range as a complementary tool.

• Klíčová slova
• Bath salts, Fourier transform ion cyclotron resonance, Gas phase absorption, Isomeric drugs, Time-dependent density functional theory, VUV absorption spectroscopy,
• MeSH
• chromatografie plynová * MeSH
• isomerie MeSH
• nové syntetické drogy analýza   MeSH
• spektrální analýza * MeSH
• stimulanty centrálního nervového systému analýza   MeSH
• vakuum MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• nové syntetické drogy MeSH
• stimulanty centrálního nervového systému MeSH

The transformation of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers from the gel (Lβ') to the fluid (Lα) phase involves an intermediate ripple (Pβ') phase forming a few degrees below the main transition temperature (Tm). While the exact cause of bilayer rippling is still debated, the presence of amphiphilic molecules, pH, and lipid bilayer architecture are all known to influence (pre)transition behavior. In particular, fatty acid chains interact with hydrophobic lipid tails, while the carboxylic groups simultaneously participate in proton transfer with interfacial water in the polar lipid region which is controlled by the pH of the surrounding aqueous medium. The molecular-level variations in the DPPC ripple phase in the presence of 2% palmitic acid (PA) were studied at pH levels 4.0, 7.3, and 9.1, where PA is fully protonated, partially protonated, or fully deprotonated. Bilayer thermotropic behavior was investigated by differential scanning calorimetry (DSC) and Fourier-transform infrared (FTIR) spectroscopy which agreed in their characterization of (pre)transition at pH of 9.1, but not at pH 4.0 and especially not at 7.3. Owing to the different insertion depths of protonated and deprotonated PA, along with the ability of protonated PA to undergo flip-flop in the bilayer, these two forms of PA show a different hydration pattern in the interfacial water layer. Finally, these results demonstrated the hitherto undiscovered potential of FTIR spectroscopy in the detection of the events occurring at the surface of lipid bilayers that obscure the low-cooperativity phase transition explored in this work.

• Klíčová slova
• 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) lipid bilayers, DSC and FTIR spectroscopy, Palmitic acid (PA), Ripple phase, pH-dependent (de)protonation,
• MeSH
• 1,2-dipalmitoylfosfatidylcholin * analogy a deriváty   MeSH
• diferenciální skenovací kalorimetrie MeSH
• koncentrace vodíkových iontů MeSH
• kyselina palmitová * chemie   MeSH
• lipidové dvojvrstvy * chemie   MeSH
• molekulární struktura MeSH
• protony MeSH
• spektroskopie infračervená s Fourierovou transformací MeSH
• teplota MeSH
• změna skupenství MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• 1,2-dipalmitoylfosfatidylcholin * MeSH
• colfosceril palmitate MeSH Prohlížeč
• kyselina palmitová * MeSH
• lipidové dvojvrstvy * MeSH
• protony MeSH

The radical cation of cytosine (Cyt.+ ) is generated by dissociative oxidation from a ternary CuII complex in the gas phase. The radical cation is characterized by infrared multiple photon dissociation (IRMPD) spectroscopy in the fingerprint region, UV/Vis photodissociation (UVPD) spectroscopy, ion-molecule reactions, and theoretical calculations (density functional theory and ab initio). The experimental IRMPD spectrum features diagnostic bands for two enol-amino and two keto-amino tautomers of Cyt.+ that are calculated to be among the lowest energy isomers, in agreement with a previous study. Although the UVPD action spectrum can also be matched to a combination of the four lowest energy tautomers, the presence of a nonclassical distonic radical cation cannot be ruled out. Its formation is, however, unlikely due to the high energy of this isomer and the respective ternary CuII complex. Gas-phase ion-molecule reactions showed that Cyt.+ undergoes hydrogen-atom abstraction from 1-propanethiol, radical recombination reactions with nitric oxide, and electron transfer from dimethyl disulfide.

• Klíčová slova
• IRMPD spectroscopy, UVPD spectroscopy, ion-molecule reactions, nucleobases, radical ions,
• Publikační typ
• časopisecké články MeSH

The reaction mechanism of copper(II)-mediated naphthol coupling in the presence of TMEDA (N,N,N',N'-tetramethylethylenediamine) is studied using infrared multiphoton dissociation (IRMPD) spectroscopy and DFT calculations. It is shown that the coupling reaction proceeds in ad hoc formed binuclear clusters [(1-H)(2)Cu(2)Cl(TMEDA)(2)](+), where (1-H) is a deprotonated naphthol molecule (methyl ester of 3-hydroxy-2-naphthoic acid). The IRMPD spectra of the isolated cluster in the gas phase reveal that it contains two uncoupled naphtholate subunits and only the irradiation promotes the coupling reaction, which is thus observed as a genuine gas-phase reaction. The driving force for the C-C coupling is a keto-enol tautomerization of the initial coupling product, and the formation of the corresponding binol in the cluster is exothermic by 0.61 eV. In contrast, analogous C-O and O-O couplings are endothermic reactions.

• Publikační typ
• časopisecké články MeSH

Due to the nature of the carboxylic group, acetic acid can serve as both a donor and acceptor of a hydrogen bond. Gaseous acetic acid is known to form cyclic dimers with two strong hydrogen bonds. However, trimeric and various oligomeric structures have also been hypothesized to exist in both the gas and liquid phases of acetic acid. In this work, a combination of gas-phase NMR experiments and advanced computational approaches were employed in order to validate the basic dimerization model of gaseous acetic acid. The gas-phase experiments performed in a glass tube revealed interactions of acetic acid with the glass surface. On the other hand, variable-temperature and variable-pressure NMR parameters obtained for acetic acid in a polymer insert provided thermodynamic parameters that were in excellent agreement with the MP2 (the second order Møller-Plesset perturbation theory) and CCSD(T) (coupled cluster with single, double and perturbative triple excitation) calculations based on the basic dimerization model. A slight disparity between the theoretical dimerization model and the experimental data was revealed only at low temperatures. This observation might indicate the presence of other, entropically disfavored, supramolecular structures at low temperatures.

• Klíčová slova
• NMR spectroscopy, carboxylic acids, hydrogen bonding, phase transitions, quantum-chemical calculations,
• MeSH
• algoritmy MeSH
• chemické modely * MeSH
• kvantová teorie * MeSH
• kyselina octová chemie   MeSH
• magnetická rezonanční spektroskopie * metody   MeSH
• plyny chemie   MeSH
• tlak MeSH
• vodíková vazba MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• kyselina octová MeSH
• plyny MeSH

In crystalline molecular solids, in the absence of strong intermolecular interactions, entropy-driven processes play a key role in the formation of dynamically modulated transient phases. Specifically, in crystalline simvastatin, the observed fully reversible enantiotropic behavior is associated with multiple order-disorder transitions: upon cooling, the dynamically disordered high-temperature polymorphic Form I is transformed to the completely ordered low-temperature polymorphic Form III via the intermediate (transient) modulated phase II. This behavior is associated with a significant reduction in the kinetic energy of the rotating and flipping ester substituents, as well as a decrease in structural ordering into two distinct positions. In transient phase II, the conventional three-dimensional structure is modulated by periodic distortions caused by cooperative conformation exchange of the ester substituent between the two states, which is enabled by weakened hydrogen bonding. Based on solid-state NMR data analysis, the mechanism of the enantiotropic phase transition and the presence of the transient modulated phase are documented.

• Klíčová slova
• dynamics, enantiotropy, entropy, polymorphism, solid-state nuclear magnetic resonance (NMR), transient modulated phase,
• MeSH
• entropie * MeSH
• magnetická rezonanční spektroskopie metody   MeSH
• molekulární konformace * MeSH
• molekulární modely MeSH
• nízká teplota MeSH
• simvastatin chemie   MeSH
• vodíková vazba MeSH
• změna skupenství * MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• simvastatin MeSH

This work focused on the development and validation of the analytical procedure using gas chromatography equipped with vacuum-ultraviolet detection for the specific and sensitive determination of nine photoinitiators in food packages. Subsequently, a comparison of the combination of vacuum ultraviolet spectroscopy with gas chromatography and a developed gas chromatography with mass spectrometry method was performed. The vacuum-ultraviolet spectra of all tested photoinitiators were collected and found to be highly distinct, even for isomers. Under the optimal conditions, the limits of detection for nine photoinitiators ranged from 1 to 5 mg/L using vacuum ultraviolet detection and from 0.15 to 0.5 mg/L using mass spectrometric detection. Both techniques were successfully applied for screening of photoinitiators in seven kinds of food packages and the obtained data showed good agreement (the relative difference was between 3 and 18%). The variability in concentrations found in triplicate samples was assessed to be below 18%. Predominantly benzophenone was found in all analysed samples in the range of 0.31-4.23 mg/kg. It appears to be preferably selected by food packaging manufacturers. This study proposes a new simple and sensitive technique used for analysis of photoinitiators that could be a good alternative to gas chromatography with mass spectrometry.

• Klíčová slova
• food packaging, food safety, gas phase absorption spectroscopy, leaching, photoinitiators,
• MeSH
• benzofenony analýza   MeSH
• fotosenzibilizující látky analýza   MeSH
• inkoust * MeSH
• kontaminace potravin analýza   MeSH
• obaly potravin * MeSH
• plynová chromatografie s hmotnostně spektrometrickou detekcí MeSH
• spektrofotometrie ultrafialová MeSH
• vakuum MeSH
• Publikační typ
• časopisecké články MeSH
• srovnávací studie MeSH
• Názvy látek
• benzofenony MeSH
• benzophenone MeSH Prohlížeč
• fotosenzibilizující látky MeSH

An efficient way to generate [(L)CuO]+ complexes with a number of monodentate and bidentate ligands (L) from their [(L)Cu(ClO3 )]+ precursors by electrospray ionization was herein explored. Further, we studied [(L)CuO]+ with L=9,10-phenanthraquinone, 1,10-phenanthroline, and acetonitrile in detail. The signature of these terminal copper-oxo complexes was found to be elimination of the oxygen atom upon collisional activation. We investigated and compared their reactions with water, ethane, ethylene, and 1,4-cyclohexadiene. The [(MeCN)CuO]+ complex oxidized water and performed C-H activation and hydroxylation of ethane. The complexes with bidentate ligands did not react with water and oxidized only larger hydrocarbons. All the investigated complexes showed comparable reactivities in the oxygen-transfer reaction with ethylene.

• Klíčová slova
• C−H activation, IR spectroscopy, copper, gas-phase reactivity, oxygen transfer,
• Publikační typ
• časopisecké články MeSH

The structures of C(7)H(9)(+) ions generated by protonation of toluene are investigated by means of gas-phase infrared spectroscopy in conjunction with labeling experiments and complementary mass spectrometric studies. In full consistency with previous studies, the unimolecular as well as the multiphoton-induced dissociation of mass-selected C(7)H(9)(+) ions lead to losses of molecular hydrogen and methane. Labeling data clearly imply the occurrence of skeletal rearrangements of protonated toluene to isomeric structures in the course of fragmentation. Complementary reactivity studies indicate, however, that the C(7)H(7)(+) ions generated upon dehydrogenation of C(7)H(9)(+) bear the benzylium structure, rather than that of the more stable tropylium ion. Combination of labeling data and extensive theoretical studies lead to a scheme for the fragmentation of protonated toluene, which can account for all experimental findings reasonably well. As far as infrared spectroscopy of gaseous ions is concerned, the present results confirm the structural predictions derived from theory and provide evidence for the existence of protonated cycloheptatriene but also pose some questions about the comparability of intensities in multiphoton dissociation and linear absorption spectra.

• Publikační typ
• časopisecké články MeSH

We report valence band photoelectron spectroscopy measurements of gas-phase and liquid-phase benzene as well as those of benzene dissolved in liquid ammonia, complemented by electronic structure calculations. The origins of the sizable gas-to-liquid-phase shifts in electron binding energies deduced from the benzene valence band spectral features are quantitatively characterized in terms of the Born-Haber solvation model. This model also allows to rationalize the observation of almost identical shifts in liquid ammonia and benzene despite the fact that the former solvent is polar while the latter is not. For neutral solutes like benzene, it is the electronic polarization response determined by the high frequency dielectric constant of the solvent, which is practically the same in the two liquids, that primarily determines the observed gas-to-liquid shifts.

• MeSH
• amoniak * MeSH
• benzen * MeSH
• elektrony MeSH
• fotoelektronová spektroskopie MeSH
• rozpouštědla MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• amoniak * MeSH
• benzen * MeSH
• rozpouštědla MeSH