High-performance liquid chromatographic determination of morphine and its 3- and 6-glucuronide metabolites: improvements to the method and application to stability studies

Improvements to previously reported methods for the determination of morphine, morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) in human plasma are described. The improved methods involve the use of a solid-phase extraction cartridge and a chromatographic system which uses paired-ion reversed-phase high-performance liquid chromatography with a radially compressed column. Only one cartridge is used to prepare each sample for chromatography and each cartridge may be used for at least fourteen 1-ml plasma samples. The recovery is greater than 85%. The improvements to the method of sample pretreatment and in the chromatographic conditions have allowed determination of morphine, M3G and M6G in human plasma down to 13.3 nmol/l (coefficient of variation = 9.3%), 108 nmol/l (6.6%) and 41 nmol/l (6.7%), respectively, using ultraviolet detection alone. It was shown that all three compounds were stable in plasma for up to 101 weeks when stored at -20 degrees C.     

Study of transport processes in plants by radioabsorption and microradiographic methods

The passive transport processes in plants of²²Na⁺,¹³⁷Cs⁺,⁴⁵Ca²⁺,⁶⁵Zn²⁺,⁵⁹Fe³⁺ and³²PO ₄ ³⁻ ions and the plant-protecting agent “Saphidon (¹⁴C)” were studied by a radioabsorption method. The parameters of the passive transport processes of²¹²Pb²⁺, borate and tetraborate ions in plants were measured by quantitative microradiographic methods, using photoemulsion and solid state nuclear track detectors. Ion diffusion concentration profiles within the plants were determined at various diffusion times and temperatures. The equation of linear diffusion combined with convection was used to determine the diffusion coefficients characteristic of the transport processes.     

Studies on structure characterization of tryptophan melanin: Comparison between filament and curie-point pyrolysis gas chromatography/mass spectrometry

Structural studies of a synthetic melanin, obtained by means of performic acid oxidation of tryptophan, were carried out by pyrolysis gas chromatography/mass Spectrometry (Py-GC/MS). To identify the best pyrolysis conditions, both Curie-point pyrolysis and filament pyrolysis were employed and the effects of pyrolysis temperatures and times were studied. Using the first approach, various compounds were identified: toluene, ethylbenzene, styrene, indole, methylindole, ethylindole, phenol, cresol and ethylphenol. Using filament pyrolysis some interesting differences could be observed. Whereas toluene, ethylbenzene, phenol, cresol and methylindole were found, neither indole nor ethylindole was detected. Instead, new pyrolysis products were evident, such as methylpyrrole and indolin-2-one. Hence filament pyrolysis seems to activate different thermal decomposition pathways of the melanin under study. It is suggested that tryptophan melanin is a polymer containing indole and hydroxyindole derivatives as subunits.     

Using Gas-Phase Guest–Host Chemistry to Probe the Structures of b Ions of Peptides

Middle-sized b _n (n????5) fragments of protonated peptides undergo selective complex formation with ammonia under experimental conditions typically used to probe hydrogen?Cdeuterium exchange in Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Other usual peptide fragments like y, a, a*, etc., and small b _n (n????4) fragments do not form stable ammonia adducts. We propose that complex formation of b _n ions with ammonia is characteristic to macrocyclic isomers of these fragments. Experiments on a protonated cyclic peptide and N-terminal acetylated peptides fully support this hypothesis; the protonated cyclic peptide does form ammonia adducts while linear b _n ions of acetylated peptides do not undergo complexation. Density functional theory (DFT) calculations on the proton-bound dimers of all-Ala b ₄ , b ₅ , and b ₇ ions and ammonia indicate that the ionizing proton initially located on the peptide fragment transfers to ammonia upon adduct formation. The ammonium ion is then solvated by N⁺-H??O H-bonds; this stabilization is much stronger for macrocyclic b _n isomers due to the stable cage-like structure formed and entropy effects. The present study demonstrates that gas-phase guest?Chost chemistry can be used to selectively probe structural features (i.e., macrocyclic or linear) of fragments of protonated peptides. Stable ammonia adducts of b ₉ , b ₉ -A, and b ₉ -2A of A₈YA, and b ₁₃ of A₂₀YVFL are observed indicating that even these large b-type ions form macrocyclic structures.     

Interface Amorphization of Two-Dimensional Black Phosphorus upon Treatment with Diazonium Salts

Two-dimensional (2D) black phosphorus (BP) represents one of the most appealing 2D materials due to its electronic, optical, and chemical properties. Many strategies have been pursued to face its environmental instability, covalent functionalization being one of the most promising. However, the extremely low functionalization degrees and the limitations in proving the nature of the covalent functionalization still represent challenges in many of these sheet architectures reported to date. Here we shine light on the structural evolution of 2D-BP upon the addition of electrophilic diazonium salts. We demonstrated the absence of covalent functionalization in both the neutral and the reductive routes, observing in the latter case an unexpected interface conversion of BP to red phosphorus (RP), as characterized by Raman, ³¹P-MAS NMR, and X-ray photoelectron spectroscopies (XPS). Furthermore, thermogravimetric analysis coupled to gas chromatography and mass spectrometry (TG-GC-MS), as well as electron paramagnetic resonance (EPR) gave insights into the potential underlying radical mechanism, suggesting a Sandmeyer-like reaction.     

Enhancement of Ion Pairing of Sr(II) and Ba(II) Salts by a Tritopic Ion-Pair Receptor in Solution

Tritopic ion-pair receptors can bind bivalent salts in solution; yet, these salts have a tendency to form ion-pairs even in the absence of receptors. The extent to which such receptors can enhance ion pairing has however remained elusive. Here, we study ion pairing of M²⁺ (Ba²⁺, Sr²⁺) and X⁻ (I⁻, ClO₄⁻) in acetonitrile with and without a dichlorooxacalix[2]arene[2]triazine-related receptor containing a pentaethylene-glycol moiety. We find marked ion association already in receptor-free solutions. When present, most of the MX⁺ ion-pairs are bound to the receptor and the overall degree of ion association is enhanced due to coordinative, hydrogen-bonding, and anion-π interactions. The receptor shows higher selectivity for iodides but also stabilizes perchlorates, despite the latter are often considered as weakly coordinating anions. Our results show that ion-pair binding is strongly correlated to ion pairing in these solutions, thereby highlighting the importance of taking ion association in organic solvents into account.     

Notes on Semiarcs

The semiarcs are generalizations of semiovals. Estimates on the sizes of semiarcs, some characterization theorems of semiarcs with large collinear subsets, of semiarcs contained in the union of three concurrent lines and the complete classification of strong semiovals in PG(2, q), q odd, are given.     

Surface corrosion as an apparent cause of degradation of GaP : N LED’s

The effect of heat treatment and subsequent current stressing was studied and compared on passivated and non-passivated VPE GaP∶N LED’s. It was found that the drastically increased degradation rate of the non-protected diodes is due completely to increased surface leakage current, no structural change or contamination of the semiconductor-bulk was observed.

     

Konstitution und Indikatoreigenschaften einiger Azofarbstoffe

Ohne ZusammenfassungDr. Zoltán Somogyi starb infolge einer schweren Verletzung am 14. Februar 1945 in Budapest.Gewidmet aus Anlaß des 100jährigen Bestehens des Laboratoriums Fresenius.     

What is the Structure of b2 Ions Generated from Doubly Protonated Tryptic Peptides?

A recent statistical study (Savitski, M. M.; Falth, M.; Eva Fung, Y. M.; Adams, C. M.; Zubarev, R. A. J. Am. Soc. for Mass Spectrom. doi: 10.1016/j.jasms.2008.08.003) of a large spectral database indicated that the product ion spectra of doubly protonated tryptic peptides fall into two distinct classes. The main factor distinguishing the two classes is the relative abundance of the y _N-2 fragment: for Class I spectra y _N-2 is the most abundant y fragment while for Class II other y ions dominate the corresponding spectra. To explain the dominance of y _N-2 for Class I spectra formation of a nontraditional b ₂ ion with a diketopiperazine (6-membered cyclic peptide) rather than an oxazolone structure was proposed. Here we present evidence from tandem mass spectrometry, hydrogen/deuterium exchange, and density functional calculations that do not support this proposal. Namely, that CID of doubly protonated YIGSR, YGGFLR, and YIYGSFK produce Class I product ion spectra, yet the b ₂ fragment is shown to have the traditional oxazolone structure.