Showing papers on "Iodide published in 1972"

Excited fragments from excited molecules: energy partitioning in the photodissociation of alkyl iodides

Abstract: Photofragment spectroscopy has been applied to the photodissociation of methyl, ethyl, n-propyl and isopropyl iodide at 266.2 nm, both to study the process of unimolecular break-up of electronically excited molecules and to determine the energy distributions of the resulting excited fragments. By crossing a molecular beam with a powerful pulsed laser beam in high vacuum and monitoring the arrival times of the recoiling photofragments with a mass spectrometer detector, the translational energy distribution of the photodissociation products is measured. From energy balance, the distribution of fragment internal energy is then calculated. Two peaks are seen in these distributions for both methyl and ethyl iodide, corresponding to formation of ground- and excited-state iodine atoms. The fraction of the energy available after exciting the I atom which goes into internal excitation of the alkyl fragments increases from ∼12% for methyl iodide to ∼50% for the propyl iodides. Thus, the “hot” methyl radicals formed in methyl iodide photolysis are predominantly translationally, rather than internally, excited. The experimental results are disscused in relation to the processes involved in alkyl iodide photodissociation lasers. Dynamic models for energy partitioning in molecular photodissociation are compared with the observed data. The simplest statistical models predict much too high excitation in the alkyl radical. The measured results fall in between the predictions of direct impulsive models based on “rigid” and “soft” radicals, and thus a possible picture for the photodissociation of the alkyl iodides is quasi-diatomic excitation of the C—I bond, followed by recoil of the I atom and a partially deformable alkyl radical. An illustrative example is given of how one might use these unimolecular results in modelling the bimolecular reactions of alkali metal atoms with alkyl iodides, following the analogy drawn by Herschbach and co-workers between photodissociation and “harpooning”, i.e., electron transfer, reactions.

Temperature dependence of chloride, bromide, iodide, thiocyanate and salicylate transport in human red cells

Abstract: 1. The temperature dependence of the steady-state self-exchange of chloride between human red cells and a plasma-like electrolyte medium has been studied by measuring the rate of (36)Cl(-) efflux from radioactively labelled cells. Between 0 and 10 degrees C the rate increased by a factor of eight corresponding to an Arrhenius activation energy of 33 kcal/mole.2. The rate of chloride exchange decreased significantly in experiments where 95% of the chloride ions in cells and medium were replaced by other monovalent anions of a lyotropic series. The rate of chloride self-exchange was increasingly reduced by bromide, bicarbonate, nitrate, iodide, thiocyanate, and salicylate. The latter aromatic anion was by far the most potent inhibitor, reducing the rate of chloride self-exchange to 0.2% of the value found in a chloride medium.3. The temperature sensitivity of the chloride self-exchange was not affected significantly by the anionic inhibitors. The Arrhenius activation energies of chloride exchange were between 30 and 40 kcal/mole in the presence of the six inhibitory anions mentioned above.4. The rate of self-exchange of bromide, thiocyanate, and iodide between human red cells and media was determined after washing and labelling cells in media containing 120 mM bromide, thiocyanate, or iodide respectively. The rate of self-exchange of the three anions were 12, 3, and 0.4% of the rate of chloride self-exchange found in the chloride medium.5. The Arrhenius activation energies of the self-exchange of bromide, iodide, and thiocyanate were all between 29 and 37 kcal/mole, the same magnitude as found for the self-exchange of chloride.6. Although approximately 40% of the intracellular iodide and salicylate ions appeared to be adsorbed to intracellular proteins, the rate of tracer anion efflux followed first order kinetics until at least 98% of the intracellular anions had been exchanged.7. The self-exchange of salicylate across the human red cell membrane occurred by a different mechanism than the one utilized by the inorganic monovalent anions. The activation energy of salicylate exchange (13.2 kcal/mole) was significantly lower than that of inorganic anion exchange. Salicylate exchange increased with decreasing pH in contrast to the exchange of chloride, which decreases when pH is lowered.

Photochemical characteristics of cyanine dyes. Part 1.—3,3′-diethyloxadicarbocyanine iodide and 3,3′-diethylthiadicarbocyanine iodide

Abstract: The dyes 3,3′-diethyloxadicarbocyanine iodide (DODI) and 3,3′-diethylthiadicarbocyanine iodide (DTDI) were investigated using laser and conventional flash photolysis techniques. In both cases direct excitation results in the formation of a photo-isomer having an absorption similar to and slightly to the red of the normal ground state absorption. The quantum efficiency for photo-isomer formation in both cases is less than 0.1. The quantum efficiency for intersystem crossing to the triplet state was observed to be < 0.01 in both cases and the triplet state extinction coefficients and spectra were therefore obtained by energy transfer techniques. The quantum efficiencies for fluorescence and radiative lifetimes obtained indicated that the fluorescence lifetimes were 1.24 and 1.20 ns for DODI and DTDI respectively.

Gaseous and particulate iodine in the marine atmosphere

Abstract: Sixty gaseous iodine samples collected from a 20-meter tower on the windward shore of Oahu, Hawaii, during the summer of 1969 showed that the concentration of gaseous iodine ranged from 5 to 20 ng/m3. Particulate samples collected simultaneously with the gaseous samples showed that the atmospheric concentrations of gaseous iodine in marine air are 2–4 times the concentration of particulate iodine. Statistical calculations indicate that the particulate iodine concentration and gaseous iodine concentrations are directly related. Thermodynamic calculations indicate that, if only inorganic ionic equilibriums including the species I−, IO3−, I2(g), and I2(aq) are considered, sea salt particles in the marine atmosphere should act as an almost perfect sink for gaseous iodine. Similar thermodynamic calculations indicate that the sea surface should also be a sink for gaseous iodine if the iodide concentration at the sea surface is that which has been reported for bulk sea water. Although the mechanism of gaseous iodine injection into the atmosphere is still uncertain, it is possible that gaseous iodine is released to the atmosphere as iodine-rich organic material decomposes at the surface of the ocean and on sea salt particles. The fact that particulate iodine concentration is inversely proportional to particle size may be explained by the atmospheric residence time of particulate matter if the ionic equilibrium reactions involving gaseous iodine and particulate iodine proceed slowly in relation to these residence times.

Crystal structures of complexes between alkali-metal salts and cyclic polyethers. Part V. The 1 : 2 complex formed between potassium iodide and 2,3,5,6,8,9,11,12-octahydro-1,4,7,10,13-benzopentaoxacyclopentadecin (benzo-15-crown-5)

Abstract: Potassium iodide forms a 1 : 2 complex with the cyclic polyether ‘benzo-15-crown-5’. The crystals are tetragonal with a=b= 17·84(1), c= 9·750(6)A, Z= 4, space group P4/n. The crystal structure has been determined by the heavy-atom method and refined by full-matrix least-squares to a final R of 0·09 on 1603 diffractometer data. The complex cation has crystallographic symmetry , the potassium being ‘sandwiched’ between two centro-symmetrically related ligand molecules. In each of these the five ether-oxygen atoms are approximately coplanar, the cation lying 1·67 A away from this plane, so that the ten-co-ordination is an irregular pentagonal antiprism. The K–O distances range from 2·777(7) to 2·955(8)A. Iodide ions occupy two sets of positions with 4 or symmetry and the arrangement of complex cations and anions resembles the caesium chloride structure; there is no interaction between the anions and the metal.

Crystal structures of complexes between alkali-metal salts and cyclic polyethers. Part IV. The crystal structures of dibenzo-30-crown-10 (2,3:17,18-dibenzo-1,4,7,10,13,16,19,22,25,28-decaoxacyclotriaconta-2,17-diene) and of its complex with potassium iodide

Abstract: The crystal structures of the title compounds have been determined from X-ray diffractometer observations. The molecules of the cyclic ether are centrosymmetric with Z= 2 in a monoclinic unit cell having a= 16·960, b= 8·920, c= 9·096 A, β= 90·03°, and space group P21/c. They form loops approximately parallel to the a axis. The structure was solved by the iterative application of Sayres' equation, and refined by least-squares methods to R 0·056 for 1414 independent observations.In the complex Z= 4 in an orthorhombic unit cell having a= 19·576, b= 12·405, and c= 12·965 A with space group Pnna. The structure was solved by conventional Patterson and Fourier methods and refined by least-squares techniques to R 0·046 for 1102 independent observations. Each potassium ion lies on a two-fold axis, and is enclosed by a ligand molecule wrapped round to give ten K–O distances in the range 2·850(6)–2·931(6)A. The iodide ions also lie on two-fold axes and are not in contact with potassium. The packing of the complex cations and the iodide ions is a distorted sodium chloride structure.Bond lengths and angles in the complexed and free molecules are the same; the conformations and different. Four of the C–C–O–C angles change from trans in the free molecule to gauche in the complex; the remaining torsion angles are of the same type in both forms but corresponding ones differ by as much as 30° and the sign may be reversed.

Iodine metabolism in chronic renal insufficiency.

Abstract: Iodine metabolism has been studied in 20 patients with advanced chronic renal insufficiency due to primary renal disease, and thyroxine turnover in another 5 similar patients. Comparatively to 18 controls, the uremic patients had a lower urinary iodine excretion, and a much lower renal iodide clearance, which, however, was not as much decreased as the creatinine clearance. The normal relation between the renal iodide and creatinine clearances was disturbed when the latter was 6.3 ml/min or lower, and in these cases the renal iodide clearance exceeded the corresponding creatinine value. The plasma inorganic iodine (PII) was increased because of the iodide retention to (mean ± SE) 0.84 ± 0.17 µg/100 ml, compared to 0.12 ± 0.01 in the controls. The thyroidal iodide clearance (Th. Cl.) rate was decreased (22.8 ± 4.44 ml/min vs. 36.7 ± 6.48), but in spite of this decrease, the absolute iodine uptake (AIU) by the thyroid, which is calculated as AIU = Th. Cl. X PII, was increased (7.1 ± 1.37 vs. 1.9 ± 0.30 µg/h). The serum protein-bound iodine was normal. The PII, Th. Cl. and AIU values and the relation among them in renal insufficiency were comparable to those observed after chronic administration of small amounts of iodine. The radiothyroxine studies suggested an increased space of distribution and so, despite a decreased fractional turnover rate, an increased metabolic clearance and degradation rate.

Methylene and oxymethylene bis-ester production

Abstract: Methylene and oxymethylene bis-esters are produced by the reaction of an aliphatic ester of a carboxylic acid, formaldehyde and carbon monoxide in the presence of a catalytic amount of a Group VIII noble transition metal compound, an iodide or bromide promoter, and a proton donor.

Light scattering studies on n-dodecyltrimethylammonium bromide and n-dodecylpyridinium iodide

Abstract: The aggregation numbers and effective charges of the micelles of n-dodecyltrimethylammonium bromide and n-dodecylpyridinium iodide have been measured over a range of temperature and ionic strength in aqueous solutions by light scattering. From the micellar parameters the hydrophobic and electrostatic contributions to the free energy and enthalpy of micellization have been calculated and a comparison between the calculated enthalpy of micellization and the calorimetric values is made.

N-methylation and electrophilic substitution reactions of octa-alkyl-porphins, octaethylchlorin, and metalloporphins

Abstract: Methylation of octaethylporphin with methyl iodide yields the 21,22-dimethylporphin iodide as well as the 21-monomethyl derivative. The structure of the salt (trans arrangement of methyl groups) is assigned from n.m.r. data as well as evidence for chirality provided by partial resolution of the corresponding D-camphorsulphonate. Methylation of octaethylporphin with methyl fluorosulphonate gives the 21,23-dimethylporphin fluorosulphonate, probably through the intermediacy of the 21,22,23-trimethylporphin salt, suggesting that the 21- and 23-methyl substituents are cis-oriented. Methylation of Octaethylchlorin gives the 23-monomethyl derivative (methyl fluorosulphonate) or the 22,23,24-trimethylchlorin iodide (methyl iodide). Electrophilic meso-substitution, exemplified by deuteriation, formylation, and nitration, takes place more readily with the metal complexes of porphins than with the free porphins; the first direct meso-methylation of a metalloporphin (PdII complex) is reported.

Molecular Structures of Perfluoromethyl Iodide, Perfluoroethyl Iodide, and Perfluoroisopropyl Iodide

Abstract: The molecular structures of three fully halogenated alkanes have been investigated by electron diffraction. The following rg parameters were determined for CF3I: C–I=2.101±0.009 A; C–F=1.344±0.004 A; and ∠FCI=111.3°±0.4°. For CF3CF2I: C–I=2.142±0.023 A; C–F=1.338±0.004 A; C–C=1.523±0.027 A; with ∠CCI=113.4°±0.8°; ∠CCF=109.9°±0.8°; and ∠ICF=109.4°±1.0°. The rg parameters determined for (CF3)2CFI are: C–I=2.139±0.017 A; C–F=1.338±0.003 A; C–C=1.554±0.012 A; ∠CCF=111.0°±0.4°; ∠ICF=111.8°±1.4°; ∠CCI=109.4°±0.6°; and ∠CCC=113.2°±1.2°. These are thermally averaged (nearly harmonic approximation) values.