N-terminal derivatization and fragmentation of neutral peptides via ion--molecule reactions with acylium ions: toward gas-phase Edman degradation?

The gas-phase ion-molecule reactions of neutral alanylglycine have been examined with various mass-selected acylium ions RCO(+) (R= CH(3), CD(3), C(6)H(5), C(6)F(5) and (CH(3))( 2)N), as well as the transacylation reagent O-benzoylbenzophenone in a Fourier transform ion cyclotron resonance mass spectrometer. Reactions of the gaseous dipeptide with acylium ions trapped in the ICR cell result in the formation of energized [M + RCO](+) adduct ions that fragment to yield N-terminal b-type and C-terminal y-type product ions, including a modified b(1) ion which is typically not observed in the fragmentation of protonated peptides. Judicious choice of the acylium ion employed allows some control over the product ion types that are observed (i.e., b versus y ions). The product ion distributions from these ion--molecule reactions are similar to those obtained by collision-activated dissociation in a triple quadrupole mass spectrometer of the authentic N-acylated alanylglycine derivatives. These data indicate that derivatization of the peptide in the gas-phase occurs at the N-terminal amine. Ab initio molecular orbital calculations, performed to estimate the thermochemistry of the steps associated with adduct formation as well as product ion formation, indicate that (i) the initially formed adduct is energized and hence likely to rapidly undergo fragmentation, and (ii) the likelihood for the formation of modified b(1) ions in preference to y(1) ions is dependent on the R substituent of the acylium ion. The reaction of the tetrapeptide valine--alanine--alanine--phenylalanine with the benzoyl cation was also found to yield a number of product ions, including a modified b(1) ion. This result suggests that the new experimental approach described here may provide a tool to address one of the major limitations associated with traditional mass spectrometric peptide sequencing approaches, that is, determination of the identity and order of the two N-terminal amino acids. Analogies are made between the reactions observed here and the derivatization and N-terminal cleavage reactions employed in the condensed-phase Edman degradation method.

Polarity of the transition state controls the reactivity of related charged phenyl radicals toward atom and group donors.

Polar effects are demonstrated to be a key factor in controlling the reactivities of related charged phenyl radicals in different exothermic atom and group abstraction reactions in the gas phase. The effects of various meta substituents on the phenyl radicals' reactivity were probed via the measurement of bimolecular reaction rate constants by using Fourier transform ion cyclotron resonance mass spectrometry. This approach requires an additional, charged substituent to be present in the phenyl radical to allow mass spectrometric manipulation. The m-pyridinium group was chosen for this purpose. The substrates studied were allyl iodide, dimethyl disulfide, and tert-butyl isocyanide. Two of the reactions of interest, *I and *SCH(3) transfer, are thought to occur by concerted bimolecular homolytic substitution (S(H)2), and the third one, *CN transfer, by an addition/elimination mechanism. For all three substrates, the reaction rate was found to increase in the following order for the differently substituted phenyl radicals: CH(3) approximately H < Br approximately Cl approximately COOH < NO(2) approximately CN. This trend does not arise from differences in reaction exothermicities or bond dissociation energies but via lowering the reaction barrier by electronic effects. The stabilization of the transition state is attributed to its increased polar character. A semiquantitative measure of the barrier lowering effect for each substituent is obtained from its influence on the electron affinity of the charged radical, as the calculated (B3LYP/6-31+G(d)) adiabatic electron affinities of the radical model systems (ammonium instead of pyridinium charge site) follow the same trend as the reactivities.

Gas-phase reactions of glycine, alanine, valine and their N-methyl derivatives with the nitrosonium ion, NO+.

The gas-phase reactions of the nitrosonium ion, NO+ with the amino acids glycine, alanine and valine and their N-methyl derivatives were investigated under chemical ionization mass spectrometric (CIMS) conditions. Two products were observed in all cases: the formation of the iminium ion and the formation of an [M-H]+ ion. The latter product is consistent with a reaction channel involving hydride abstraction by NO+, and was confirmed by (i) examining the Ar+CI mass spectra of the same amino acids under similar source conditions and (ii) examining the unimolecular fragmentation reactions of the [M + H]+ ions of the N-nitroso-N-methyl derivatives of each of the amino acids in a tandem mass spectrometer. Further insights into the reaction of glycine with NO+ were obtained by performing ab initio calculations (at the MP2/6-31G* parallel HF/6-31G* level). These results indicate that four reactions are thermodynamically viable for glycine: (i) hydride abstraction; (ii) iminium ion formation (with concomitant loss of HONO and CO); (iii) diazonium ion formation; and (iv) diazonium ion formation followed by loss of N2. Possible reasons why reactions (iii) and (iv) are not observed are discussed, and comparisons with solution reactivity and the gas-phase reactivity of NO+ are also made.

[Comparative study of the efficiency of bacterial filters in long-term mechanical ventilation]. / Vergleichende Untersuchung über die Abscheidungsleistung von Bakterienfiltern unter Beatmungsbedingungen.

UNLABELLED: Two commercially available bacterial filters to be used as part of the mechanical ventilation unit during anaesthesia were tested for hygienic criteria. Manufacturers claim that bacterial breathing filters have a filtration capacity of about 99.995%, so that there would be no need for thermal disinfection of tubing and ventilation circuits after each use. One filter is designed for a single use only, the other can be used up to 24 times after sterilisation. Both filters consist of hydrophobic glass fibres. METHODS: During simulated mechanical ventilation for 24 h, an alcoholic suspension of Bacillus subtilis was atomized in front of the filters tested. A gelatin membrane filter was integrated in the ventilation circuit and captured the filtered gas behind the test filter. RESULTS: During simulated mechanical ventilation for 24 h, the filtration capacity of both the disposable and reusable filters (Table 2) did not confirm the manufacturers' short-term technical findings over 8 s (DIN-EN 143). CONCLUSIONS: The use of bacterial filters during mechanical ventilation reduces the probability of bacterial contamination, but does not make sterilisation of the tubes and ventilation circuit unnecessary.

[Early paralysis of the recurrent nerve in bronchogenic carcinoma]. / Casná obrna zvratného nervu u bronchogenního karcinomu.

In 1983-1987 34 patients with paresis of the recurrent nerve were examined. In 4 patients with left-sided paresis bronchogenic carcinoma was revealed, i. e. in 12% of all examined subjects. In relation to the group of patients with left-sided paresis bronchogenic carcinoma was detected in every fifth patient. As no other symptoms than hoarseness are present in paresis of the recurrent nerve and the results of examinations are frequently negative, the diagnosis is difficult. The authors summarize their experience and draw attention to systematic examination and possible new examination methods which must be indicated. Early diagnosis in two patients made radical therapy possible.

[Post-traumatic stenoses of the larynx and subglottic space]. / Poúrazové stenózy hrtanu a subglotického prostoru.

The authors give the basic principles of the etiopathogenesis of post-traumatic stenoses of the larynx and subglottic space. Therapeutic tactics are briefly described. Three basic types of treatment are illustrated on their own observations.

[Carcinoma of the tonsils and tonsillar fossa. Tactics of our surgical approach]. / Karcinom tonzil a fossa tonsillaris. Taktika naseho operacního prístupu.

The authors discuss the most frequent symptoms associated with the disease. In a group of 34 patients they revealed the advanced stage of the disease in 75%. In all instances they confirmed on histological examination a squamous-cell carcinoma in different stages of differentiation. The authors describe the tactics of surgical treatment and its results.

[Treatment of benign laryngeal diseases using a CO2 laser]. / Lécba benigních onemocnení hrtanu CO2 laserem.

CO2 laser surgery is becoming a part of larynx surgery. The authors inform about their experience in benign larynx tumours treatment. They present analysis of concrete therapeutic procedures in individual larynx affections. They conclude that laser surgery is an advantegous method for benign larynx tumours treatment.

Inappropriate antidiuretic hormone secretion after cataract extraction under local anesthesia.

We report a case of a patient who underwent bilateral cataract extractions under local anesthesia. In both operations, the patient developed signs, symptoms, and laboratory data consistent with the syndrome of inappropriate secretion of antidiuretic hormone. In this era of outpatient cataract surgery, we believe this diagnosis should be entertained postoperatively in the proper clinical setting.

Iris injury from enzyme cannula.

The manuever of inserting an olive-tipped irrigator behind the iris in cataract patients and in rabbits causes iris injury as manifested by transillumination of the iris. In some brown eyes a depigmentation of the stroma of the iris developed over the transilluminated area.