A surprisingly complex aqueous chemistry of the simplest amino acid. A pulse radiolysis and theoretical study on H/D kinetic isotope effects in the reaction of glycine anions with hydroxyl radicals.

A pulse radiolysis study was carried out of the reaction rate constants and kinetic isotope effects of hydroxyl-radical-induced H/D abstraction from the most-simple alpha-amino acid glycine in its anionic form in water. The rate constants and yields of three predominantly formed radical products, glycyl (NH2-*CH-CO2-), aminomethyl (NH2-*CH2), and aminyl (*NH-CH2-CO2-) radicals, as well as of their partially or fully deuterated analogs, were found to be of comparable magnitude. The primary, secondary, and primary/secondary H/D kinetic isotope effects on the rate constants were determined with respect to each of the three radicals. The unusual variety of products for such an elementary reaction between two small and simple species indicates a complex mechanism with several reactions taking place simultaneously. Thus, a theoretical modeling of the reaction mechanism and kinetics in the gas- and aqueous phase was performed by using the unrestricted density functional theory with the BB1K functional (employing the polarizable continuum model for the aqueous phase), unrestricted coupled cluster UCCSD(T) method, and improved canonical variational theory. Several hydrogen-bonded prereaction complexes and transition states were detected. In particular, the calculations pointed to a significant mechanistic role of the three-electron two-orbital (sigma/sigma* N therefore O) hemibonded prereaction complexes in the aqueous phase. A good agreement with the experimental rate constants and kinetic isotope effects was achieved by downshifting the calculated reaction barriers by 3 kcal mol(-1) and damping the NH(D) stretching frequency by a factor of 0.86.

Cartilage palisade tympanoplasty and diving.

OBJECTIVE: To determine whether a patient with a serious defect of the tympanic membrane (TM) will be able to dive after surgery. PATIENTS AND METHODS: The authors describe three patients who were divers with serious defects of the TM (more than 75% of TM). In all three cases, cartilage palisade tympanoplasty was used to reconstruct the TM. RESULTS: Six months after surgery, the patients passed clinical examinations, audiograms (hearing restored to normal), tympanometry (increased stiffness of the TM), and pressure tolerance tests in hyperbaric chamber (30-m immersion was simulated for 4 minutes), and they began to dive again. Approximately 2 years after the surgery, all three patients are able to dive without any difficulties. CONCLUSION: The authors conclude that patients can dive after cartilage palisade tympanoplasty.

Polymethyl-methacrylate implants in forehead and supraorbital arches reconstruction: retrospective study.

Frontobasal injuries and some other diseases of frontal sinuses sometimes require radical surgery with the obliteration of the sinus. A cosmetic correction of the forehead and supraorbital arches has to be performed after such a procedure. Nowadays, there is a wide choice of alloplastic materials on the market. We tried polymethyl methacrylate implants in correction of the exterior appearance of the forehead and supraorbital arches and followed the behaviour of the implants up to 25 years after surgery. The result was 18 (94.7%) successful implantations and one failure (5.3%) with a mild sagging of the borders of the implant. Polymethyl-methacrylate proved pliable for work and modelling, not invasive for the organism and stable. In conclusion, the cure of some frontobasal injuries and diseases with the first surgical step followed by cosmetic correction of the forehead and supraorbital arches (2nd surgical step) using this alloplastic material provides a safe, durable and aesthetically satisfactory solution for the patient.

Gastroesophageal reflux, allergy and chronic tubotympanal disorders in children.

The purpose of this study is to examine the relation between gastroesophageal reflux and allergy as possible causes of chronic tubotympanal pathology. The 30 examined children (ages 2-13) were divided into two groups based on the otological criteria. The 16 examined children suffered from a secretory otitis, which lasted more than four months. Upon further examination with a microscope, seven of these children exhibited symptoms of the adhesive process of the middle ear. Furthermore, 14 patients suffered from a recurrent otitis, i.e. more than five cases of otitis per year, while five patients from this group suffered from a chronic otitis with a central defect of the tympanum. The method used for the examination of the gastroesophageal reflux consisted of a continual 24 h esophageal pH monitoring. The particular apparatus used for this included antimony electrode (Synetics Medical, Sweden), while the analysis we performed was processed through the PC software program Gastrosoft Inc. The reflux index higher than five was considered pathological. At the time of the gastroesophageal reflux examination, we also performed the allergological analysis. The presence of allergy was confirmed by three methods: the positive allergological anamnesis, the positive skin pick test and by the elevated quantities of specific IgEs (Pharmacia CAP system). The examination resulted in the following: 18 of the examined children suffered from the pathological gastroesophageal reflux (60%); further seven of our patients tested positive on the allergological test (23%); and the four who tested positive for allergy also suffered from the pathological gastroesophageal reflux (13%). In comparison with allergies, the pathological GER was substantially more frequent in the patients who suffered from chronic tubotympanal disorders.

One-electron reduction of selenomethionine oxide.

Experimental evidence is provided that selenomethionine oxide (MetSeO) is more readily reducible than its sulfur analogue, methionine sulfoxide (MetSO). Pulse radiolysis experiments reveal an efficient reaction of MetSeO with one-electron reductants, such as e(aq)-, (k = 1.2x10(10) M(-1) s(-1)), CO2*- (k = 5.9x10(8) M(-1) s(-1)) and (CH3)2 C*OH (k = 3.5x10(7) M(-1) s(-1)), forming an intermediate selenium-nitrogen coupled zwitterionic radical with the positive charge at an intramolecularly formed Se(three-electron bond)N 2sigma/1sigma* three-electron bond, which is characterized by an optical absorption with lambda(max) at 375 nm, and a half-life of about 70 micros. The same transient is generated upon HO* radical-induced one-electron oxidation of selenomethionine (MetSe). This radical thus constitutes the redox intermediate between the two oxidation states, MetSeO and MetSe. Time-resolved optical data further indicate sulfur-selenium interactions between the Se(three-electron bond)N transient and GSH. The Se(three-electron bond)N transient appears to play a key role in the reduction of selenomethionine oxide by glutathione.

The role of electromyography in the diagnosis of velopharyngeal insufficiency: our experiences.

The subject of this study is the electromyographic investigation of the velopharyngeal sphincter structures. Seventy-five patients underwent examination, both patients with symptoms of velopharyngeal insufficiency and patients who were thought to have latent pathological sphincter changes based on local findings. A control group of 10 healthy examinees was also investigated. On the basis of electromyographic findings we divided patients into 2 groups: 57 patients without neuromuscular disorders and 18 patients with neuromuscular disorders of the velopharyngeal sphincter. Twelve patients from the latter group had acute, and 6 had chronic lesions of the velopharyngeal sphincter. Particular cases of illness within these 2 groups were investigated further. This study shows the usefulness of electromyography for diagnosing the exact causes of velopharyngeal insufficiency and for choosing the best approach to treatment.

One-electron oxidation and reduction reactions of vitamin C derivatives: 6-bromo- and 6-chloro-6-deoxy-ascorbic acid.

6-Bromo- and 6-chloro-6-deoxy derivatives of ascorbate anion are able to transfer an electron to the oxidizing radicals .OH, Br2.- and RS. with the same rate constants as the ascorbate anion itself. The resulting radicals also show the same kinetic stabilities and optical absorption spectra as the well-characterized ascorbate radical anion (lambda max = 360 nm; epsilon 360 = 330 m2 mol-1). This proves that there is no influence of the structural changes in the side chain on the antioxidant capacity of the ascorbate moiety. In contrast, measured reduction of the 6-halo-6-deoxy derivatives occurs significantly faster (up to one order of magnitude) than the reduction of unsubstituted ascorbate. For example, absolute rate constants of 4.6 x 10(9) and 2.2 x 10(7) dm3 mol-1 s-1 have been measured for the reactions of bromo-derivative with eaq- and (CH3)2COH respectively. These radical-induced reductions proceed via dissociative electron capture and, under cleavage of the C-halogen bond, yield C-6 carbon-centered radicals. In the presence of oxygen the corresponding peroxyl radical is readily formed. This radical is again able to oxidize the ascorbate moiety (rate constant 2 x 10(7) dm3 mol-1 s-1). Results are discussed in terms of biological relevance of the investigated compounds regarding their ability to act as efficient antioxidants and bioreductive antitumour agents simultaneously.

Reversible H-atom abstraction from alcohols by thiyl radicals: determination of absolute rate constants by pulse radiolysis.

Penicillamine thiyl radicals, PenS., are shown to abstract hydrogen atoms from 2-propanol and to establish an equilibrium PenS. + (CH3)2 CHOH in equilibrium PenSH + (CH3)2 COH. The rate constants for the forward and back reaction have been determined to (1.4 +/- 0.3) x 10(4) and (1.2 +/- 0.3) x 10(8) M-1 s-1, respectively, by means of pulse radiolysis. The data have been obtained from various independent methods which include direct measurements and competitive schemes involving irreversible interception of the alcohol radical by electron acceptors (e.g. CCl4, PNAP) and/or the thiyl radical by antioxidants (e.g. alpha-tocopherol). The results demonstrate that the reaction of carbon-centered radicals with thiols, in radiation biology commonly known as "repair" reaction, may be reversed and thus imply the possibility of thiyl radical induced biological damage.

Radical reactions in aqueous disulphide-thiol systems.

Absolute rate constants have been measured for the reaction of (CH3SSCH3)+. and sulphur centred radical cations of lipoic acid, lip (SS)+., with various thiols including penicillamine, cysteamine and cysteine. Under pulse radiolysis conditions no reactions was observed between the disulphide radical cations and the neutral thiols, RSH, i.e. kappa less than or equal to 10(7) M-1 s-1. Rate constants in the order of 10(9) M-1 s-1, i.e. close to the diffusion controlled limit, were, however, found for the corresponding reactions with the thiolates, RS-. In systems containing lipoate and cysteamine the lip (S therefore S)+. induced oxidation of CyaS- proceeds via CyaS., (CyaS therefore SCya)- and lip (S S)- as intermediates, i.e. results in a cysteamine mediated conversion of an oxidizing lip (S therefore S)+. radical cation to a reducing lip (S S)- radical anion along the reaction route. In other cases the reaction of disulphide radical cations with thiolate anions was found to proceed via an optically absorbing transient (lambda max approximately 380 nm) which is suggested to be an adduct radical. The mechanism of the (RSSR)+. induced oxidation of thiolate appears to depend on the stability of the 3-electron bonded disulphide radical anion.