Contrasting Dynamics in Isoelectronic Anions Formed by Electron Attachment.

Cyanogen NCCN and cyanoacetylene HCCCN are isoelectronic molecules, and as such, they have many similar properties. We focus on the bond cleavage in these induced by the dissociative electron attachment. In both molecules, resonant electron attachment produces CN- with very similar energy dependence. We investigate the very different dissociation dynamics, in each of the two molecules, revealed by velocity map imaging of this common fragment. Different dynamics are manifested both in the excess energy partitioning and in the angular distributions of fragments. Based on the comparison with electron energy loss spectra, which provide information about possible parent states of the resonances (both optically allowed and forbidden excited states of the neutral target), we ascribe the observed effect to the distortion of the nuclear frame during the formation of core-excited resonance in cyanoacetylene. The proposed mechanism also explains a puzzling difference in the magnitude of the CN- cross section in the two molecules which has been so far unexplained.

Distant Symmetry Control in Electron-Induced Bond Cleavage.

We experimentally show that N-H bond cleavage in the pyrrole molecule following resonant electron attachment is allowed and controlled by the motion of the atoms which are not dissociating, namely, of the carbon-attached hydrogen atoms. We use this fact to steer the efficiency of this bond cleavage. In order to interpret the experimental findings, we have developed a method for locating all resonant and virtual states of an electron-molecule system in the complex plane, based on all-electron R-matrix scattering calculations. Mapping these as a function of molecular geometry allows us to separate two contributing dissociation mechanisms: a π* resonance formation inducing strong bending deformations and a nonresonant σ* mechanism originating in a virtual state. The coupling between the two mechanisms is enabled by the out-of-plane motion of the C-H bonds, and we show that it must happen on an ultrafast (few fs) time scale.

Temporary anions of the dielectric gas C3F7CN and their decay channels.

We probe the transient anion states (resonances) in the dielectric gas C4F7N by the electron energy loss spectroscopy and the dissociative electron attachment spectroscopy. The vibrationally inelastic electron scattering leads to two excitation types. The first is the excitation of specific vibrational modes that are assigned with the help of an infrared spectrum of this molecule and quantum chemistry calculations. In the second type of vibrational excitation, the excess energy is randomized via internal vibrational redistribution in the temporary anion, and the electrons are emitted statistically. The electron attachment proceeds in three different regimes. The first is the formation of the parent C4F7N- anion at energies close to 0 eV. The second is a statistical evaporation of the F-atom, leading to the defluorinated anion C4F6N-. Finally, the third is dissociative electron attachment proceeding via the formation of several resonances and leading to a number of fragments. The present data explain the puzzling recent results of the pulsed-Townsend experiments with this gas.

Dissociative ionization dynamics of dielectric gas C3F7CN.

Fluoronitrile C3F7CN is a promising candidate for the replacement of SF6 dielectric gas in high-voltage insulation. We present a combined experimental and theoretical study on its ionization dynamics probed in the 0-100 eV energy range. We exploited the total ion collection technique to determine the absolute ionization cross section, mass spectrometry to determine the fragment branching ratios and ab initio nonadiabatic molecular dynamics to simulate the ionization process. The latter two approaches showed the dominating presence of the CF3+ cation over the whole electron energy range. The Binary-Encounter-Bethe (BEB) approximation reproduces experimental cross sections very well and reveals that the ionization from a surprisingly large number of orbitals contributes almost equally to the processes. We show that the initially populated cation excited states undergo an ultrafast internal conversion to the ground state where the dissociation into a single decay channel takes place. Implications for the use of C3F7CN as an insulating material are discussed.

Dissociative electron attachment and anion-induced dimerization in pyruvic acid.

We report partial cross sections for the dissociative electron attachment to pyruvic acid. A rich fragmentation dynamics is observed. Electronic structure calculations facilitate the identification of complex rearrangement reactions that occur during the dissociation. Furthermore, a number of fragment anions produced at electron energies close to 0 eV are observed, that cannot originate from single electron-molecule collisions. We ascribe their production to secondary reactions of the transient anions with neutral molecules. Such reactions turn out to be unusually efficient; the most probable reason for this is that they proceed via the formation of a double-hydrogen-bonded complex followed by an ultrafast proton transfer between the reaction partners.

VUV action spectroscopy of protonated leucine-enkephalin peptide in the 6-14 eV range.

We have studied the Vacuum Ultraviolet (VUV) photodissociation of gas-phase protonated leucine-enkephalin peptide ion in the 5.7 to 14 eV photon energy range by coupling a linear quadrupole ion trap with a synchrotron radiation source. We report VUV activation tandem mass spectra at 6.7, 8.4, and 12.8 eV photon energies and photodissociation yields for a number of selected fragments. The obtained results provide insight into both near VUV radiation damage and electronic properties of a model peptide. We could distinguish several absorption bands and assign them to particular electronic transitions, according to previous theoretical studies. The photodissociation yields appear to be very different for the various observed fragmentation channels, depending on both the types of fragments and their position along the peptide backbone. The present results are discussed in light of recent gas-phase spectroscopic data on peptides.

Allosteric modulation of metabotropic glutamate receptor 5 affects phosphorylation, internalization, and desensitization of the micro-opioid receptor.

Recent evidence suggests that opioid analgesia and tolerance can be modulated by metabotropic glutamate receptors. Therefore, we studied the functional coupling and desensitization of the micro-opioid receptor (MOR) in human embryonic kidney (HEK) 293 cells which co-express metabotropic glutamate receptor 5 (mGluR5). As demonstrated by the D-Ala2,N-MePhe4,Gl-ol5-enkephalin (DAMGO)-induced inhibition of intracellular cAMP level and by binding studies, the co-expression of mGluR5 had no substantial effect on the agonist binding sites and functional coupling of the MOR. However, in MOR/ mGluR5 co-expressing cells, the non-competitive mGluR5 antagonist MPEP (2-methyl-6-(phenyl-ethynyl)-pyridine) decreases the DAMGO-induced MOR phosphorylation, internalization, and desensitization, whereas non-selective competitive mGluR antagonists or agonists had no effects. These findings indicate that an allosteric modulation of mGluR5 can affect the agonist-induced MOR signalling and regulation. As a mechanistic basis for the observed effects we suggested an interaction/heterodimerization of MOR and mGluR5, which is supported by the DAMGO-induced co-internalization of MOR and mGluR5 and by the increase of MPEP binding sites (Bmax) and a change of the binding affinity (K(D)) of mGluR5 receptors after the co-expression of MOR. In addition, co-immunoprecipitation experiments revealed evidence for an interaction between MOR and mGluR5 which is facilitated by MPEP treatment.

[Total intravenous anesthesia using remifentanil and propofol with midazolam co-induction in laparoscopic surgery of the gallbladder]. / TIVA remifentanilom i propofolom uz koindukciju midazolamom za laparoskopske operacije zucne kese.

We investigated effects of total intravenous anesthesia (TIVA) with propofol and remifentanil (in two parallel continuous infusions), on 28 ASA I-II patients undergoing laparoscopic cholecystectomy. All patients received midazolame (0.05 mg/kg b.w.), and 90 sec thereafter, remifentanil (0.5 g/kg b.w.). Computer controlled intravenous infusion of propofol started at dose of 6 mg/kg/h (by Graseby 3400 Syringe Pump). Muscle relaxation was achieved by rocuronium (0.6 mg/kg b.w.). After endotracheal intubation, rate of propofol was decreased on 3 mg/kg/h and started with another infusion of remifentanil (0.5 ug/kg/min). Before (T0) and after induction (T1), after start of surgery (T2), and at the end of surgery (T3), we evaluated: systolic, diastolic, and medial arterial blood pressure (SAP, DAP, MAP), heart rate (HR), peripheral saturation of O2 (O2Sat), and capnometry (ETCO2), by Datex-Engstrome AS/3 Monitore. It was followed side effects of anaesthesia, early and complete recovery rate, and frequency of nausea and vomiting in postoperative period. Results showed haemodynamic stability of patients after induction in anaesthesia (defined as decreasing of MAP 20%, compared with preinduction values). During investigation (T0-T3), results of 0.2Sat and ETCO2 were excellent (0.60 +/- 2 and 5.1 +/- 2.4 min). There wasonly one case of postoperative nausea and vomiting, and no significant side effects of anaesthesia. TIVA remifentanil-propofol and co-induction with midazolame makes possible haemodynamic stability of patients after induction in anaesthesia, good oxygenation during surgery, fast early and complete recovery, and avoiding of side effects of anaesthesia and postoperative nausea and vomiting. We concluded that it is a good choice of anaesthesia for laparoscopic cholecystectomy.

[Sodium balance in premature infants]. / Bilanc natrijuma kod prevremeno rodjene dece.

INTRODUCTION: The understanding of water and electrolytes metabolism is essential in providing an adequate therapy in the treatment of low birth weight infants. In the first days of life sodium balance is negative [10, 11], since sodium renal loss is rather big and sodium peroral intake is inadequate [12]. It is not recommended to add sodium in the first 24-48 hours of life to extremely immature babies (Usher) [13]. The daily requirements of sodium in preterm infants range from 2 to 3 mmol/kg. Sodium intake should be adjusted to each patient, considering the gestational age, the severity of illness, plasma sodium concentration, sodium excretion by urine, which depends on morphological maturity and reabsorbitional capacity of the proximal tubule. AIM OF THE STUDY: Aim of the study was to investigate the relation between sodium balance and body weight gain in the first 10 days of life in preterm infants on different feeding regimens. METHODS: Twenty-one preterm infants, gestational age from 28 to 36 weeks, eutrophic, postnatal age from 1 to 10 days, treated at the Institute for Preterm Infants in Belgrade, were included in the study. All infants were divided into three groups: the first group, eight babies, fed by mothers' milk, were additionally given 10% glucose with physiological solution of sodium chloride; the second group, six infants, also fed by mothers' milk, were additionally fed by amino acids, and 10% glucose solution and physiological sodium chloride solution; the third group, seven infants, were on total parenteral nutrition (10% glucose solution, 0.9% sodium chloride solution, amino acis and fatty emulsions). We organised a prospective balance study over the period from 20.01, to 01.11.1986 during which we calculated sodium retention by measuring sodium intake and urine sodium excretion. All infants had the same fluid intake from 70 to 150 ml/kg/day, both enteral and parenteral. Sodium intake varied from 1 to 3 mmol/kg/day. Sodium excretion was measured on the fifth and tenth day of life in a 24-hour-urine collection and was calculated by the following formulas: Osmolal index was calculated as urine osmolality-serum osmolality ratio. Osmolal clearance was calculated: Water balance was calculated on the basis of total fluid intake in ml/kg/day and diuresis in ml/kg/day. RESULTS: The initial body weight loss was within physiological limits, 7-8% of the birth weight. In the study period none of the infants achieved his/her birth weight. In the third group the weight gain was 3% comparing to the birth weight, which was statistically significant (p < 0.05) (Table 2). The sodium intake was within expected levels-from 1.32 to 2.03 mmol/kg/day. Sodium intake was statistically higher in the third group (2.03 mmol/kg/day) than in the first and second groups (p < 0.05). We found negative sodium balance in three infants in the first group and two in the second group, and in all infants of the third group sodium balance was positive on the fifth day of life. We found no statistically significant differences among the groups when testing their sodium balances by hi-square test (Graph 2). When studying serum and urine osmolality and calculating osmolality index and osmolar clearance, we found that these levels were between normal values, without statistically significant differences among the groups (Graph 3). Sodium, protein, urea and creatinine levels were also normal, without statistically significant differences among the groups (Table 3). DISCUSSION: On the basis of our study we can emphasize the following findings regarding the relation between weight gain and sodium balance. In the first group three babies started with weight gain from 6th to 10th day of life. In the second group six babies started with weight gain in the same period-from 6th to 10th day. Gain weight of babies in the third group was by 3% greater in the same period compared to the birth weight, what makes a significant difference (p < 0. (ABSTRACT TRUNCAT