Interpretation of inorganic arsenic metabolism in humans in the light of observations made in vitro and in vivo in the rat

The toxicity of inorganic trivalent arsenic for living organisms is reduced by in vivo methylation of the element. In man, this biotransformation leads to the synthesis of monomethylarsonic (MMA) and dimethylarsinic (DMA) acids, which are efficiently eliminated in urine along with the unchanged form (As_i). In order to document the methylation process in humans, the kinetics of As_i, MMA and DMA elimination were studied in volunteers given a single dose of one of these three arsenicals or repeated doses of As_i. The arsenic methylation efficiency was also assessed in subjects acutely intoxicated with arsenic trioxide (As₂O₃) and in patients with liver diseases. Several observations in humans can be explained by the properties of the enzymic systems involved in the methylation process which we have characterized in vitro and in vivo in rats as follows: (1) production of As_i metabolites is catalyzed by an enzymic system whose activity is highest in liver cytosol; (2) different enzymic activities, using the same methyl group donor (S-adenosylmethionine), lead to the production of mono- and di-methylated derivatives which are excreted in urine as MMA and DMA; (3) dimethylating activity is highly sensitive to inhibition by excess of inorganic arsenic; (4) reduced glutathione concentration in liver moderates the arsenic methylation process through several mechanisms, e.g. stimulation of the first methylation reaction leading to MMA, facilitation of As_i uptake by hepatocytes, stimulation of the biliary excretion of the element, reduction of pentavalent forms before methylation, and protection of a reducing environment in the cells necessary to maintain the activity of the enzymic systems.     

Production of radicals in the ozonolysis of propene in air

Radical production in the ozonolysis of propene in air was monitored directly by a peroxy radical chemical amplification (PERCA) instrument at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The ozonolysis reactions were conducted in a flow tube under pseudo-first-order conditions for ozone. The decay in ozone was calculated based on reaction time tr and effective rate constant keff (keff = k1[C3H6]0)) for the ozone-propene reaction. The total radical yields relative to consumed ozone were d...     

Uses of ion-exchangers in the determination of trace elements in waters

Summary The use of ion-exchangers has not only increased in importance in water technology but also in the analysis of waters of different origin. By means of cation- or anion-exchangers, cations or anions may be concentrated and separated, or interfering ions removed. This methodology is applicable not only to inorganic substances but also to organic compounds, particularly acids and bases. Examples are given of the applicability of the procedures.

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Spezielle Anwendungen von Ionenaustauschern in der Spurenanalytik von Wässern

Zusammenfassung Die Anwendung von Ionenaustauschern hat nicht nur in der Wassertechnologie, sondern auch bei der Analytik von Wässern verschiedener Provenienz an Bedeutung gewonnen. Mittels Kationen- oder Anionenaustauschern können Metalle oder verschiedene Anionen angereichert und voneinander getrennt oder auch Störionen entfernt werden. Die Methodik ist aber nicht nur für anorganische Substanzen, sondern auch für organische Verbindungen, insbesondere Säuren und Basen anwendbar. Die Brauchbarkeit der Verfahren wird an Beispielen erläutert.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Photoisomerisation in single molecules of nitroprusside embedded in mesopores of xerogels

Photoswitchable hybrid materials are successfully prepared by embedding guanidinium nitroprussides (GuNP, (CN₃H₆)₂[Fe(CN)₅NO]) into mesopores of transparent xerogel monoliths. The such prepared hybrid materials exhibit a higher photostability than the corresponding GuNP solutions, whereby the chemical stability of the [Fe(CN)₅NO]²⁻-anion in titania gel is nearly infinite. By irradiation with light in the blue-green spectral range one nitrosyl isomer is formed by a 180° rotation of the NO ligand changing the Fe–NO into a Fe–ON coordination (SI), which is detected by the shift of the ν(NO) stretching vibration from 1945 cm⁻¹ (Fe–NO) to 1820  cm⁻¹ (Fe–ON). Consequently there is enough space around the NO-ligand for such movement in xerogel mesopores. The embedding in silica xerogels increases the achievable population of the isomeric nitrosyl configuration to about 15% with respect to a single crystalline powder where only 9% are reached.     

Increase in the para selectivity in the nitration of alkylbenzenes in the presence of aryl iodides

Conclusions Additives of iodobenzene, para-iodotoluene, and ortho-iodotoluene increase the relative yield of the para isomer in the nitration of toluene, ethylbenzene, and cumene as well as the yield of 4-nitro-o-xylene in the KNO₃/CF₃CO₂H system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 714–716, March, 1988.     

Determination of fluoroquinolone residues in poultry muscle in Portugal

A total of 98 poultry samples, including chicken and turkey muscle, were analysed, using a sensitive and reliable analytical method based on liquid chromatography (LC) with spectrofluorimetric detection, for simultaneous determination of four fluoroquinolone (FQ) antibiotics, namely enrofloxacin (ENRO), ciprofloxacin (CIPRO), norfloxacin (NOR), and sarafloxacin (SARA). The method involved extraction with 0.15 mol L⁻¹ HCl and clean-up by solid-phase extraction using Oasis HLB cartridges. Chromatographic separation was carried out on a C₁₈ TSK gel column, in isocratic mode, with 0.025 mol L⁻¹ H₃PO₄ solution, adjusted to pH 3.0 with tetrabutylammonium hydroxide-methanol (78:22) as mobile phase. Good linearity over the investigated concentration range was observed, with mean values of correlation coefficients higher than 0.9989 for all the analytes studied. The limits of quantification (LOQ), expressed as the lowest fortification level with acceptable precision were 15 μg kg⁻¹ for ENRO, CIPRO, and NOR, and 30 μg kg⁻¹ for SARA; these values are in compliance with requirements for monitoring of maximum residues levels (MRLs). Overall recoveries from spiked samples ranged from 80% to 92% with relative standard deviations (RSD) lower than 6.1%. Of the chicken and turkey samples analysed, 44.2% and 37.8%, respectively, were contaminated. The levels found in the analysed poultry samples, collected from markets of Oporto and Coimbra, located in the north and central zones of Portugal, respectively, were lower than 114.2 and 87.6 μg kg⁻¹ in chicken and turkey muscle samples, respectively. One positive chicken sample was contaminated with ENRO at levels higher than the MRL.     

Determination of micro-amounts of indium in zinc and in gallium by radioactivation

Summary A method was developed to determine micro-amounts of indium in zinc and in gallium by radioactivation analysis, using 1 g Ra-Be as thermalneutron source. By activation of an amount of 10 g metallic zinc during 5 hours and counting the activity in a well-type NaI-scintillation counter, 17.4 counts per sec. per 10 g Zn were obtained. This activity is practically entirely due to the 13.8 h.⁶⁹Zn, the 52-mn isotope being a pure-emitter.By activation of indium in the same conditions the¹¹⁶In, 54-mn isotope, gives a counting rate of 28.9 counts per second per 10 mg metal, so that it was possible to determine amounts of indium in zinc, using 10 g samples varying from 0.004% to 0.16% with a mean error of 2.3%, without chemical separation. To determine trace amounts of Indium in Gallium by activation at the same conditions as described above, it was necessary to carry out a chemical separation. 1 g metallic Ga gave indeed rise to an activity of 115 counts per second, mainly due to the 14.1-h.⁷²Ga. The activation of the Ga-In samples was therefore carried out in an aqueous solution of their sulfates. After activation, potassium iodide and sulfuric acid were added as to obtain a 2 M solution of HI. The indium iodide was then extracted with diethyl ether and the ethereal solution introduced in a vial fitting the well-type crystal. Using 0.5-g Ga samples it was possible to determine indium amounts down to 0.2 mg, with a mean error of about 5%.

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Zusammenfassung Eine Methode zur Bestimmung kleiner Mengen Indium in Zink und in Gallium durch Aktivierungsanalyse wurde unter Verbindung von 1 g Ra-Be als thermische Neutronenquelle entwickelt. Nach Aktivierung von 10 g metallischem Zink durch 5 Stunden und Bestimmung der Aktivität in einem becherförmigen NaJ-Szintillationszähler wurden 17,4 Stöße pro Sekunde pro 10 g Zn beobachtet. Diese Aktivität kommt praktisch völlig dem⁶⁹Zn von der Halbwertszeit 13,8 Stunden zu, da das Isotop mit der Halbwertszeit 52 Minuten ein reiner-Strahler ist.Durch Aktivierung von Indium unter den gleichen Bedingungen gibt¹¹⁶In mit der Halbwertszeit 54 Minuten 28,9 Stöße pro Sekunde für 10 mg Metall, so daß es möglich war, unter Verwendung von 10 g Zink Indiummengen zwischen 0,004% und 0,16% mit einem mittleren Fehler von 2,3% ohne vorhergehende chemische Trennung darin zu bestimmen. Zur Bestimmung von Indiumspuren in Gallium durch Aktivierung unter den gleichen Bedingungen war es notwendig, eine chemische Trennungsmethode auszuarbeiten. 1 g metallisches Gallium zeigte tatsächlich einen Anstieg der Aktivität auf 115 Stöße pro Sekunde pro 1 g, die vor allem dem⁷²Ga der Halbwertszeit 14,1 Stunden zukommt. Die Aktivierung der Ga-In-Proben wurde daher in einer wäßrigen Lösung ihrer Sulfate durchgeführt. Nach der Aktivierung wurde Kaliumjodid und Schwefelsäure bis zu 2-m Konzentration an Jodwasserstoff zugesetzt. Das Indiumjodid wurde dann mit Diäthyläther extrahiert und die ätherische Lösung in eine dem becherförmigen Kristall angepaßte Schale gebracht. Unter Verwendung von 0,5 g Gallium war es möglich, Indiummengen bis herab zu 0,2 mg mit einem mittleren Fehler von etwa 5% zu bestimmen.

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Résumé On a mis au point une méthode de microdosage de 1'indium dans le zinc et le gallium par radioactivation à l'aide d'une source de neutrons thermiques de 1 g de Ra-Be. Après irradiation de 10 g de zinc métallique pendant 5 heures, on a compté 17,4 coups par seconde lors de la mesure de l'activité dans un compteur à scintillations à cristal creux d'iodure de sodium. Pratiquement, cette activité est entièrement due au⁶⁹Zn de période 13,8 h, son isotope de période 52 mn étant un émetteur-pur.Lorsqu'on active l'indium dans les mêmes conditions, l'isotope¹¹⁶In de période 54 mn donne au compteur 28.9 coups par seconde pour 10 mg de métal de sorte qu'il est possible de déterminer la teneur en indium du zinc sur des échantillons de 10 g pour des valeurs variant de 0,004% à 0 16%, avec une erreur moyenne de 2,3% et sans séparation chimique. Pour effectuer le dosage de traces d'indium dans le gallium par application de la même méthode d'activation, il est nécessaire d'effectuer une séparation chimique. 1 g de gallium métallique donne en effet naissance à une activité de 115 coups par seconde qui sont principalement dûs à l'isotope⁷²Ga de période 14,1 h. En conséquence, l'activation des échantillons de Ga-In a été effectuée dans une solution aqueuse des sulfates de ces métaux. Après activation, on ajoute de l'iodure de potassium et de l'acide sulfurique de façon à obtenir une solution 2 M d'acide iodhydrique. L'iodure d'indium est alors extrait dans l'éther diéthylique et la solution éthérée est introduite dans une fiole s'ajustant dans le cristal creux. En employant des échantillons de gallium de 0,5 g, il a été possible de déterminer des quantités d'indium de 0,2 mg avec une erreur moyenne d'environ 5%.

     

Analysis of vibronic intensities in the phosphorescence spectrum of dimethylbenzaldehydes in durene

An attempt is reported to explain the main intensity patterns in the phosphorescence spectra of 2,4-, 2,5- and 3,4-dimethyl-benzaldehyde-1h₁ and -1d₁, observed previously. The analysis is based on CNDO and MINDO calculations of (transition) dipole moments, spin-orbit couplings, vibronic couplings, state energies, normal coordinates and vibrational frequencies. Where possible these quantities are empirically checked and corrected. Additional information, especially about the separation of the closely spaced T₁(³ππ^*) and T₂(³nπ^*) states, is obtained from phosphorescence excitation spectra reported here for all six isomers. The phosphorescence spectra consist of two components, an “allowed” component of ³ππ^* and a “forbidden” component of ³nπ^* symmetry. It is concluded that the allowed component is partly induced by the crystal field. The forbidden component is vibronically induced by out-of-plane vibrations among which the aldehydic CH(CD)-wag mode is the most active. The observed intensity patterns for this component are ascribed to interference between two mechanisms, one involving vibronic coupling between S₀ and S₁(¹nπ^*) and spin-orbit coupling between S₁ and T₁, the other involving vibronic coupling between T₁ and T₂ and spin-orbit coupling between S₀ and T₂. Within the groups of either 1h₁ or 1d₁ isomers, the main changes in the spectrum are shown to be due to the change in T₁–T₂ energy separation. The changes observed upon deuterium substitution in the aldehyde group involve, in addition to changes in the T₁–T₂ gap, changes in vibronic coupling due to normal-coordinate mixing. All these spectral changes are reproduced by calculations based on a mixture of theoretical and empirical input parameters, derived from, or at least consistent with, other observations, including excitation spectra, dipole moments and zero-field splittings. It is concluded that the mechanisms underlying these calculations offer a satisfactory explanation of the observed intensity patterns in the phosphorescence spectra of dimethylbenzaldehydes.     

Molecular-mass-distribution of oligomers in the products of tetrafluoroethylene telomerization in various solvents

The possibility of using differential thermogravimetry (DTG) for determination of the molecularmass-distribution (MMD) of oligomers in polymerization products has been experimentally and theoretically substantiated. The technique is based on the assumptions that the increase in the boiling temperature of oligomers with the increasing chain length is described by the additivity rule and the shape of DTG curves obeys the equation of mass transfer in the stationary convective flow created by evaporation. The results have been confirmed by gel-permeation chromatography and ¹⁹F NMR data. It has been shown that the chain length of oligomers produced via tetrafluoroethylene (TFE) telomerization in carbon tetrachloride, chloroform, acetone, and ethyl acetate reaches about 20–25 C₂F₄ units at an initial TFE concentration of C ₀ ≈ 0.5 mol/l. The MMD includes a low-molecular-mass component (n ≤ 5) in an amount that decreases with increasing C ₀ and a high-molecular-mass component, whose maximum shifts toward higher values of n with an increase in C ₀. The bimodality of MMD is explained in terms of decrease in the propagation rate constant with the accumulation of long oligomers.     

Chaos in oscillatory sorption of hydrogen in palladium

Aperiodic oscillations in the sorption of hydrogen and deuterium in palladium have been observed. An expression relating the square of a function, with the derivative and integral with variable upper limit of the same function has been proved and proposed to be used as a base for a chaos-vs.-random test. The result of one “branch” of the test is a real number \(D \in [0,2]\) ; close to zero for the deterministic and smooth datasets, and approaching two for the random or discrete datasets. Another “branch” of the test, based on the same mathematical relation, produces two functions that appear to be convergent for deterministic and smooth datasets, but run totally divergent for random or discrete ones. The \(D\) -values yielded by deterministic time series, recorded in the periodic and quasiperiodic sorptions of H \(_{2}\) or D \(_{2}\) in Pd, are around 0.001. On the other hand, the databases that were presumably random or non-smooth yielded the test results from \(D= 0.2\) to \(D= 1.9\) . Against these benchmarks, the experimental, aperiodic oscillations scored around 0.003 in \(D\) , which is much closer to the deterministic than to a random manner.     

Reactivity of N-alkyl derivatives of hydroxylamine in decomposition of 4-nitrophenyl diethylphosphonate in water and in cetyltrimethylammonium bromide micelles

Neutral forms of hydroxylamine, N-methylhydroxylamine, and N,N-dimethylhydroxylamine are typical α-nucleophiles in water. In comparison with aryl anions of similar basicity their rate of reaction in the decomposition of 4-nitrophenyl diethylphosphonate is increased by about 10² times. Decomposition of the substrate is accelerated in cetyltrimethylammonium bromide micelles (about 4 to 30 fold). Hydroxylamine and its N-alkyl derivatives are the most effective low basicity nucleophiles. The sole factor responsible for the micellar effects is the concentration of the reagent in the surfactant micelles. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 4, pp. 231–236, July–August, 2007.     

Evaluation of As,Se and Zn in octopus samples in different points of sales of the distribution chain in Brazil

Three CRMs of different matrix composition were analysed, representing an environmental matrix sample (BCR–320R Channel Sediment), a botanical matrix sample (SRM 1547 Peach Leaves) and a zoological matrix sample (SRM 1566b Oyster Tissue). The element mass fractions were obtained using the KayWin program. Analytical measurement uncertainty was determined by two approaches: (1) the routine procedure applying combination of the overall uncertainty u(m) = 3.5 % and statistical uncertainty of the peak area determination and (2) the procedure applying the dedicated ERON program for calculating uncertainty. Performance of altogether 31 certified values was tested by means of calculating E _n numbers. For the remaining 52 non-certified values, comparison between uncertainties obtained by the two approaches was made. When using the first approach, the E _n number showed satisfactory performance in 28 cases; by using the second approach, the E _n number showed satisfactory performance in 27 cases. None of the unsatisfactory performances (E _n  > 1) appeared to be of systematic nature. The uncertainties obtained by applying the two approaches revealed a big extent of consistency. As the present nuclear database lacks lot of data that serve as input to the ERON program, in particular uncertainties of Q ₀ factors, estimates need to be introduced for the missing values, emphasising the urgent need to upgrade the database with missing data.     

Calculations of enthalpies of formation of carbenes in the ground state in the gas phase

Known enthalpies of formation (Δ_f H ^o) of carbenes in the ground state in the gas phase were analyzed; the prospects for the theoretical evaluation of (Δ_f H ^o) were considered. The (Δ_f H ^o) values of carbenes were calculated by the group-addition method, developed previously for free radicals, as well as by the AM1 and PM3 quantum-chemical methods; these methods were compared. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 57–63, January, 1997.     

Dielectric study of dipolar association in dilute solutions of nitrobenzene in benzene

The correlation factors R_p and R_s are determined for the dielectric polarization and the non-linear dielectric effect in dilute solutions of nitrobenzene in benzene. Assuming dipole association of the nitrobenzene molecules to be restricted to dimerization, we determined the concentration x₂ of dimers, their dipole moment μ_dim, and the equilibrium constant K_x and Gibbs energy ΔG of the dimerization process.     

Determination of chromium by GFAAS in slurries of fish feces to estimate the apparent digestibility of nutrients in feed used in pisciculture

This paper presents a simple, fast and sensitive method to determine chromic oxide (used as a biological marker of fish feed) in samples of fish feces by GFAAS through the direct introduction of slurries of the samples into the spectrometer's graphite tube. The standard samples of feces and of fish feed containing 0.10-1.00 mg kg⁻¹ of Cr₂O₃ were pre-frozen for 1 min in liquid nitrogen and then ground a cryogenic mill for 2 min, which reduced the samples’ grain size to less than 60 μm. The standard slurries were prepared by mixing 20 mg of standard samples of fish feed or feces with 1 mL of a solution containing 0.05% (v/v) of Triton X-100 and 0.50% (v/v) of suprapure HNO₃ directly in the spectrometer's automatic sampling glass. The final concentrations of Cr₂O₃ present in the standard slurries were 2, 4, 8, 16 and 20 μg L⁻¹. After sonicating the mixture for 20 s, 10 μL of standard slurries were injected into the graphite tube, whose internal wall was lined with a metallic palladium film that acted as a permanent chemical modifier. The limits of detection (LOD) and quantification (LOQ) calculated for 20 readings of the blank of the standard slurries (2%, m/v of feces or feed devoid of minerals) were 0.81 and 2.70 μg L⁻¹ of Cr₂O₃ for the standard feces slurries, 0.84 and 2.83 μg L⁻¹ of Cr₂O₃ for the standard feed slurries. The proposed method was applied in studies of nutrient digestibility of different fish feeds and its results proved compatible with the results obtained from samples pre-mineralized by acid digestion.     

Analysis of intermetallic particles in aluminium by dissolution of the sample in butanol

Summary A new method for the quantitative analysis of intermetallic particles in aluminium has been developed. 0.3–5 g samples are dissolved in absolute 1-butanol. The content, the chemical composition, the structure, the shape and the size distribution of the undissolved particles have been determined by means of a series of methods including weight measurements, X-ray fluorescence, inductively coupled argon plasma spectrometry, Coulter Counter analysis and X-ray diffraction. The materials investigated were samples of 99.999 wt% aluminium, 99.5 wt% aluminium and aluminium — 0.4 wt% magnesium — 0.4 wt% silicon — 0.2 wt% iron alloy. Cast samples of the latter alloy contained mainly -AlFeSi and samples homogenized at 580°C - AlFeSi and 1-AlFe(Ni,Cu)Si. Al₁₃Fe₄-particles were dominant in the intermetallic phase present in the 99.5 wt% aluminium samples investigated. The results have been compared and found in agreement with emission spectrometric measurement of the alloys' chemical composition, transmission electron microscopy of the intermetallic phases of thin foils and light microscopy analysis of particles in polished samples.

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Analyse intermetallischer Partikel in Aluminium durch Auflösung der Probe in Butanol

Zusammenfassung Zur Analyse wurden 0,3–5 g der Probe in absolutem 1-Butanol gelöst. Gehalt, chemische Zusammensetzung, Struktur, Form und Größenverteilung der ungelösten Partikel wurden mit Hilfe verschiedener Methoden bestimmt (Gewichtsmessungen, Röntgenfluorescenzanalyse, ICP, Coulter Counter-Analyse, Röntgendiffraktion). Die untersuchten Proben waren 99,999%iges Al, 99,5%iges Al sowie Al-Legierung mit 0,4% Mg, 0,4% Si und 0,2% Fe. Gußproben dieser Legierung enthielten hauptsächlich -AlFeSi, bei 580° C homogenisierte Proben -AlFeSi und 1-AlFe(Ni,Cu)Si. In der intermetallischen Phase der 99,5%- igen Al-Probe überwogen Al₁₃Fe₄-Partikel. Die erhaltenen Ergebnisse stimmen überein mit emmissionsspektrometrischen Bestimmungen der chemischen Zusammensetzung, mit transmissions-elektromikroskopischen Messungen der intermetallischen Phasen dünner Folien sowie der lichtmikroskopischen Analyse der Partikel in polierten Proben.

     

On the use of nitrite in the determination of halogen in organic compounds

Summary A few properties of nitrite are cited which are useful for the determination of halogens and perhaps also of sulfur in organic compounds. Procedures using this reagent for the determination of chlorine and bromine in ordinary organic compounds and compounds containing mercury, using flask combustion, and a procedure for microdetermination of chlorine and bromine using combustion and subsequent hydrogenation are described.

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Zusammenfassung Einige Eigenschaften des Nitrits werden erwähnt, die es für die Bestimmung der Halogene und möglicherweise auch des Schwefels in organischen Verbindungen geeignet erscheinen lassen. Arbeitsvorschriften für die Verwendung dieses Reagens bei der Bestimmung von Chlor und Brom in gewöhnlichen organischen Verbindungen und Organo-Quecksilberverbindungen mit Hilfe der Kolbenverbrennung werden beschrieben. Ebenso wird auch ein Verfahren zur Mikrobestimmung von Chlor und Brom durch Verbrennung und nachfolgende Hydrierung angegeben.

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Résumé L'auteur cite quelques propriétés des nitrites qui sont utiles pour la détermination des halogènes et peut être également du soufre dans les composés organiques. Il décrit des techniques de détermination du chlore et du brome dans les composés organiques courants et dans les composés contenant du mercure par combustion en fiole, et une technique de microdosage du chlore et du brome par combustion suivie d'hydrogénation, dans lesquelles ce réactif est utilisé.

     

Interpretation of spin relaxation in polyisobutylene in terms of specific motions

Porton and carbon spin-lattice relaxation times T₁ and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional ¹H and ¹³C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole–dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T₁ for the methylene and methyl carbons with increasing molecular weight in solution and increase of T₁ of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three-bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three-bond jump in a 5% (wt/vol) solution in CCI₄ at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl-group rotation about the threefold symmetry axis. The methyl-group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI₄ at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl-group rotation.     

Polymerization of acrylamide in various solvents in the presence of Lewis acids

The radical polymerization of acrylamide in various solvents in the presence of Lewis acids has been investigated. Considerable effects of LiBr, LiCl and CaCl₂ on the total reaction rate and the values of k_p and k₁ for polymerization in DMSO or THF have been shown. For the polymerization of acrylamide in aqueous solution, addition of the salts does not affect the kinetic behaviour of the process. The observed effect of salts arises from complexation between the salt and the monomer and/or the propagating radicals.     

Time-resolved CIDNP effects in the reaction of hydrogen atom transfer in photolysis of benzaldehyde in solution

We have studied the dependence of CIDNP effects on the concentration of the starting material in photolysis of a solution of benzaldehyde in cyclohexane-D₁₂ and in benzene-D₆. Using an excimer laser (=308 nm), we have investigated the time evolution of the CIDNP signals with time resolution 1 sec. We have determined the rate constant k₁ for transfer of a hydrogen atom from the hydroxybenzyl radical to the ground-state benzaldehyde molecule and also the rate constant for recombination of two hydroxybenzene radicals.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 3, pp. 324–329, May–June, 1988.The authors thank Doctor of Chemical Sciences L. N. Krasnoperov for useful discussions.