Characterization of water-soluble,cationic polyelectrolytes as exemplified by poly(acrylamide-co-trimethylammoniumethylethacryate chloride) and the establishment of structure-property relationships

The cationic copolymerization products of poly (acrylamide-co-trimethylammoniumethylmethacrylate chloride (PTMAC) having cationic monomer percentages of 8%, 25%, and 50% as well as the cationic homopolymer, were characterized with respect to their molecular dimensions. The light-scattering and viscometric measurements were carried out for molecular weights ranging from 200 000 to 12 800 000 g/mol in 1 M NaCl solution at 25°C. It was possible to establish a relationship between the molecular weight and the two parameters: intrinsic viscosity and radius of gyration, for all four polymers.Rheological investigations of the flow properties in 1 M NaCl solution were also carried out using the polymer with a cationic monomer of 50% (PTMAC 50). Structure-property relationships were formulated which made it possible to describe and predict the shear viscosity, both in the zero-shear region (Newtonian region) and in the shear-dependent region (non-Newtonian region) as a function of the polymer concentration, the molecular weight, and shear rate.Abbreviations a exponent of the []-M relationship - A ₂ 2^nd virial coefficient/mol·cm³·g^–2 - AAm acrylamide - b slope of the flow-curve in the shear-rate dependent region - c concentration/g·cm^–3 - dn/dc refractive index increment/cm³·g^–1 - f function - K constant of the []-M relationship/cm³·g^t-1 - m _c proportion of cationic monomers/mol % - M molecular weight/g·mol^–1 - M _w weight-average molecular weight/g·mol^–1 - M _n number-average molecular weight/g·mol^–1 - NaCL sodium chloride - PAAm polyacrylamide - PS polystyrene - PTMAC poly(acrylamide-co-trimethylammoniumethylme thacrylate chloride) - R_G ^20.5 radius of gyration/nm - TMAC trimethylammoniumethylmethacrylate chloride - shear rate/s^–1 - critical shear rate/s^–1 - viscosity/Pa·s - 0 zero-shear viscosity/Pa·s - _s solvent viscosity/Pa·s - _sp specific viscosity - [] intrinsic viscosity/cm³·g^–1 - relaxation time/s     

Synthesis,characterization and charge-transfer photochemistry of trans-aquo azido-N,N′-trimethylenebis(naphthylideneiminato)chromium(III)

A new Cr^III complex, viz. trans-[Cr(naphprn)(H₂O)₂]ClO₄·2H₂O, (1) {naphprn=N,N-trimethylenebis(naphthylideneimine)} has been synthesized and characterized. Aquo ligand substitution of ( 1 ) by the azide ligand gave rise to trans-[Cr(naphprn)(N₃)(H₂O)], ( 2 ). Irradiation of ( 2) in DMF gave nitrido(naphprn)chromium(V) ( 3 ). Solutions of ( 3 ) showed e.p.r. spectra at room temperature (g _iso=1.9865). The i.r. spectra showed disappearance of a band at 2067cm^–1 showing the breakdown of NN and appearance of a new band at 1074cm^–1which is assigned to the Cr¹⁴N, stretching frequency indicating the formation of a nitrido chromium(V) complex, ( 3). The u.v.–vis. spectrum of complex ( 3 ) exhibited a d–d band maximum at 553nm (=120M^–1cm^–1). The rate of formation of ( 2 ) was found to be 5.0×10^–3M^–1s^–1 in an aqueous acidic medium at [Cr^III]=0.5×10^–3M; [N₃ ^–]=0.01–0.15M; [H⁺]=0.001M and I=0.2M (LiClO₄). The rate of photo-decomposition of ( 2 ) to give rise to ( 3 ) was found to be 0.15×10^–3s^–1 in DMF.     

Chlorine loss from polyvinylchloride under neutron irradiation

PVC samples were irradiated for 1 hour with a thermal neutron flux of _th =4.71·10¹¹n·cm^–2·s^–1 and the chlorine lost during irradiation was measured by -ray spectrometry. About 15% of loss of chlorine has been observed for untreated samples while samples heated to temperatures of 60 and 80°C for one minute before irradiation have been found to loose about 8% and 3%, respectively. The results indicate an influence of the polymer structure on the release of chlorine.     

Complex formation followed by internal electron transfer: The reaction between cysteine and iron(III)

Summary A kinetic study of the anaerobic oxidation of cysteine (H₂ L) by iron(III) has been performed over thepH-range 2.5 to 12 by use of a stopped-flow high speed spectrophotometric method. Reaction is always preceded by complex formation. Three such reactive complex species have been characterized spectrophotometrically: FeL ⁺ (_max=614 nm, =2 820 M^–1cm^–1); Fe(OH)L (_max=503 nm; shoulder at 575 nm, =1 640 M^–1cm^–1); Fe(OH)L ₂ ^2– (_max=545 nm; shoulder at 445 nm, =3 175 M^–1 cm^–1). Formation constants have been evaluated from the kinetic data: Fe³⁺+L ^2– FeL ⁺: logK ₁ ^M =13.70±0.05; Fe(OH)²⁺+L ^2– Fe(OH)L: logK ₁ ^MOH =10.75±0.02; Fe(OH)L+L ^2– Fe(OH)L ₂ ^2– ; logK ₂ ^MOH =4.76±0.02. Furthermore the hydrolysis constant for iron(III) was also obtained: Fe(OH)²⁺+H⁺ Fe _aq ³⁺ : logK ^FeOH=2.82±0.02). Formation of the mono-cysteine complexes, FeL ⁺ and Fe(OH)L, is via initial reaction of Fe(OH)²⁺ with H₂ L (k=1.14·10⁴M^–1s^–1), the final product depending on thepH. FeL ⁺ (blue) formed at lowpH decomposes following protonation with a second-order rate constant of 1.08·10⁵M^–1s^–1. Fe(OH)L (purple) decomposes with an apparent third order rate constant ofk=3.52·10⁹M^–2s^–1 via 2 Fe(OH)L+H⁺ products, which implies that the actual (bimolecular) reaction involves initial dimer formation. Finally, Fe(OH)L ₂ ^2– (purple) is remarkably stable and requires the presence of Fe(OH)L for electron transfer. A rate constant of 8.36·10³M^–1s^–1 for the reaction between Fe(OH)L and Fe(OH)L ₂ ^2– is evaluated.Dedicated to Prof. Dr. mult. Viktor Gutmann on the occasion of his 70th birthday     

Multinuclear macromolecule metal complexes 2. Preparation and characterization of Prussian blue and its analogs bonded to pofy(vinylamine hydrochloride)

Prussian blue and its analogs bonded to poly(vinylamine hydrochloride) (PVAm · HCl) containing Fe^II or Fe^III and M²⁺ (M=Fe, Co, Cu) in a 11 molar ratio were obtained by the reaction of [Fe(CN)₆] ^n– (n=3,4) with M²⁺ ion-PVAm · HCl mixture in aqueous solution. Under a limited polymer concentration (T_VAm/T_Fe over 10), these polymer complexes thus obtained were stable and soluble in water. By casting these solutions, colored films can be produced. The formation of Prussian blue and its analogs bonded to PVAm · HCl was also investigated by the Benesi-Hildebrand method. The molar extinction coefficients of intervalence charge transfer (Fe^IIFe^III, Co^IIFe^III, Fe^IICu^II) band for MFe(CN)₆]^(n–2)– bound to PVAm · HCl (M=Fe, Co, Cu) were found to be 10,100–9601 · mol^–1 · cm^–1 at 25 C. The formation constants were found to be in the range of 10⁷ to 10¹⁰ M^–1. The changes of enthalpy (H) and entropy (S) were found to be in the range of –10.4 to –22.5 kJ · mol^–1 and 5.7 to 52.9 J · K^–1 mol^–1 respectively, at 25C.     

Synthesis and magnetic properties of trinuclear chromium(III)palladium(II)-chromium(III) complexes bridged by extended dioximato groups

Summary Heterotrinuclear Cr^III-Pd^II-Cr^III complexes of formulae [Cr(salen)-Pd(dmg)₂-Cr(salen)]·H₂O (1), [Cr(salen)-Pd(-BD) ₂-Cr(salen)]·H₂O (2) and [Cr(salen)-Pd(-FD) ₂-Cr(salen)]·2H₂O (3) [dmg^2- =dimethyl-glyoximato, (-BD)^2/2- = -benzyldioximato, (-FD)^2/2- = -furildioximato and salen^2– = N,N-ethylenebis(salicylideneiminate)] have been prepared and characterized by elemental analysis, i.r. and electronic spectroscopies, and molar conductances. These complexes are thought to contain extended diomixato bridges. The magnetic properties of complex (1) has been investigated over the 80–300 K range and corresponds to what is expected for an antiferromagnetic Cr^III-Cr^IIIi pair with S _Cr = 3/2 and S _Pd = 0 (Pd²⁺ is a diamagnetic in a square-planar environment) local spins. The exchange integral (J) was evaluated as -3.38cm^–1 using the spin Hamiltonians = -2J _{A B}(S _A = S _B = 3/2).     

Kinetics and mechanism of the oxidation of hydrogen peroxide by the octacyanotungstate(V) ion in alkaline aqueous media

Summary The oxidation of H₂O₂ by [W(CN)₈]^3– has been studied in aqueous media between pH 7.87 and 12.10 using both conventional and stopped-flow spectrophotometry. The reaction proceeds without generation of free radicals. The experimental overall rate law, , strongly suggests two types of mechanisms. The first pathway, characterized by the pH-dependent rate constant k _s, given by , involves the formation of [W(CN)₈· H₂O₂]^3–, [W(CN)₈· H₂O₂·W(CN)₈]^6– and [W(CN)₈· HO]^3– intermediates in rapid pre-equilibria steps, and is followed by a one-electron transfer step involving [W(CN)₈·HO]^3– (k _a) and its conjugate base [W(CN)₈·O]^4– (k _b). At 25 °C, I = 0.20 m (NaCl), the rate constant with H _a =40±6kJmol^–1 and S _a =–151±22JK^–1mol^–1; the rate constant with H _b =36±1kJmol^–1 and S _b =–136±2JK^–1mol^–1 at 25 °C, I = 0.20 m (NaCl); the acid dissociation constant of [W(CN)₈·HO]^3–, K ₅ =(5.9±1.7)×10^–10 m, with and is the first acid dissociation constant of H₂O₂. The second pathway, with rate constant, k _f, involves the formation of [W(CN)₈· HO₂]^4– and is followed by a formal two-electron redox process with [W(CN)₈]^3–. The pH-dependent rate constant, k _f, is given by . The rate constant k ₇ =23±6m ^–1 s ^–1 with and at 25°C, I = 0.20 m (NaCl).     

Kinetics and mechanism of chromium(VI) oxidation of L-methionine

The kinetics and mechanism of chromium(VI) oxidation of L-methionine in acidic medium have been studied spectrophotometrically. The reaction proceeds via the formation of a transient intermediate (_max = 410–420 nm) which decomposes by a proton catalyzed pathway. The rate law is:

Study of a hollow cathode arc discharge in the presence of chromium oxide

A hollow cathode arc discharge in hydrogen has been used for the purpose of chromium oxide reduction, the solid oxide being placed inside the anode. Mass transport from the oxide to the gas phase and excitation conditions in the plasma have been investigated. The results show that a substantial amount of oxide is transferred to the gas phase with subsequent reduction and deposition inside the cathode cavity, in the form of a pure metal. The residual part condenses on the discharge chamber wall as an amorphous substance, containing 50–60% of Cr metal, and on the anode surface under the form of a mixture of chromium oxide and metal crystals (10%). From spectroscopic investigations it follows that, inside the anode zone, total Cr concentration in the gas phase is of the order of 10¹⁴ cm^–3, the excitation temperature of the atoms and ions being 4500 and 5500 K, respectively, and the ionization temperature being about 6000 K.Notation I absolute spectral line intensity (W cm^–2 sr^–1) - emission coefficient (W cm^–3 sr^–1) - A relative absorption - absorption coefficient (cm^–1) - L plasma diameter (mm) - f _tk oscillator strength - _D full Doppler width (cm^–1) - S( ₀ L) Ladenburg-Levy function - wave number (cm^–1) - k _pl mass transport rate (mol cm^–2 s^–1) - k _th thermal reduction rate (mol cm^–2 s^–1) - u ion mobility (mm V^–1 s^–1 ) - E electric field strength (V mm^–1) - drift velocity (cm s^–1)     

Chromium(VI), chromium(V) and chromium(IV) oxidation of 12-tungstocobaltate(II)

The reaction between Cr^VI and 12-tungstocobaltate(II) was carried out in 2.0 mol dm^–3 HCl and followed a simple second order rate law. The reaction was catalysed by hydrogen ion due to the formation of active H₂CrO₄ and was inhibited by chloride ion as, in its presence, conversion of the active species into inactive chlorochromate occurs. Chromium(V) and chromium(IV) were generated in situ by the use of Cr^VI—V^IV or Cr^VI—2-ethyl-2-hydroxybutyric acid and Cr^VI—i-PrOH reactions respectively, and the oxidation of 12-tungstocobaltate(II) by these atypical oxidation states, was also studied. The rate constants for the oxidation of 12-tungstocobaltate(II) by Cr^VI, Cr^V and Cr^IV were found to be in the ratio 1:1.2:5.2 respectively. The ionic strength did not affect the reaction, while decrease in the solvent polarity increased the rate of the reaction. The activation parameters were also determined and the values H , G and S were found to be 52.4 ± 6 kJ mol^–1, 100.8 ± 7 kJ mol^–1, –151.7 ± 10 J K^–1 mol^–1 respectively, supporting the mechanism proposed.     

Preparation and reactivity of metal-containing monomers

Thermal transformations (at 340 to 390 °C) of coprecipitates of iron and cobalt acrylates, [Fe₃O(CH₂CHCOO)₆OH][Co(CH₂CHCOO)₂]_2.4 (1) and [Fe₃O(CH₂CHCOO)₆OH][Co(CH₂CHCOO)₂]_1.5·3H₂O (2), are studied. The dependence of the degree of gas evolution () on time is described by the equation () wherek ₁=2.3 · 10¹² · exp[–49500/(RT)] s^–1,k ₂=6.0 · 10⁶ · exp[–33000/(RT)] s^–1 andk ₁=2.6 · 10¹² · exp[–49000/(RT)] s^–1,k ₂=6.6 · 10⁵ · exp[–30000/(RT)] s^–1 for cocrystallizates1 and2, respectively. The coefficient ₁ decreases as the temperature increases. The value of ₁ for compound1 is higher than that for compound2. The composition of products of the transformations of1 and2 are studied. The main solid state products of the decomposition are nanometer-sized particles of cobalt ferrite, CoFe₂O₄, with a narrow size distribution stabilized by the polymeric matrix. The thermal transformations of cocrystallizates1 and2 include dehydration, thermal decomposition, copolymerization in the solid state, and decarboxylation of the metallocarboxylate groups of the polymer. The effect of the ratio between the Fe clusters and the Co-containing fragments on the process of thermal transformation is analyzed.For Part 40, seeRuss. Chem. Bull., 1994,43, 2020.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 885–893, May, 1995.The authors are grateful to A. N. Titkov for optical microscopic and electron microscopic studies.     

Preparation and characterization of a series of poly(acrylamide-co-acrylates), with a copolymer composition between 0–96.3 mol-% acrylate units with the same degree and distribution of polymerization

A series of linear poly(acrylamide-co-acrylates) (PAAm/AAcNa) has been prepared covering a copolymer composition between 0 and 96.3 mol% acrylate units, which have the same degrees of polymerization and chain length distributions. Measurements of viscosity and light scattering have proven that maximum coil dimensions of PAAm/ AAcNa in salt solutions are achieved at about 67 mole-% AAcNa. This so-called maximum behaviour was researched by measuring the radius of gyration, second virial coefficient, molecular weight, preferential solvation, viscosity and absorption bands of the copolymer series. Thus, an increase in the possible ways of arranging AAcNa-AAm-AAcNa units (via H-bonds) will lead to extended coil dimensions and therefore influence the viscosity. In addition, it can therefore be concluded from all these results that the maximum behaviour is real and not influenced by the different distributions of the samples. The copolymer composition can be easily determined by infra-red spectroscopy by use of a proposed relation.Abbreviations A₂ second virial coefficient (mole · cm³ · g^–2) - AAm acrylamide - AAcH acrylic acid - AAcNa sodium acrylate - c polymer concentration (g · cm^–3) - salt concentration (g · cm^–3), (Val · cm^–3) - C _LS critical concentration obtained by light scattering (g · cm^–3) - d _[] viscosity equivalent diameter of a sphere (nm) - E extinction - FW _s formula weights of salt - g _s gram of salt - g _p gram of polymer - GuaCl guanidinium chloride - h ^21/2 root mean square end-to-end distance (nm) - K optical constant for unpolarized incident light (mole · cm² · g^–2) - M molarity (mole · 1^–1) - M _w weight average molecular weight (g · mole^–1) - N _L Avogadro constant 6.023 · 10²³ mole^–1 - P _n number average degree of polymerization - P _w weight average degree of polymerization - PAAm poly(acrylamide) - PAAcH poly(acrylic acid) - PAAcNa poly(sodium acrylate) - PAAm/AAcNa poly(acrylamide-co-sodium acrylate) - R _[] Rayleigh ratio of the scattering at angle (cm^–1) - R _G ² _Z ^1/2 root mean square average radius of gyration (nm) - R _[] viscosity equivalent radius of a sphere (nm) - T temperature (°C), (K) - u excluded volume (cm³ · g^–1) - V molar volume (cm³ · mole^–1) - V _s partial specific volume - X mole fraction - (NH₂) oscillation of deformation - extinction coefficient - ₀ zero shear viscosity (Pa · s), (mPa · s) - _red reduced viscosity (cm³ · g^–1) - [] intrinsic viscosity (cm³ · g^–1) - _a constant of preferential solvation (g · g^–1) - ₀ wavelength of light in vacuo (nm) - chemical potential - v _as stretching vibration - scattering angle (°)     

MD Simulation of an Infinitely Dilute Aqueous Solution of Formamide. Study of Thermodynamic, Structural, Dynamic, and Spectroscopic Properties

A molecular dynamics simulation of an infinitely dilute aqueous solution of formamide was carried out using an MP2-CP ab initio potential to describe the solute–solvent interaction. Various static and dynamic properties were calculated using this potential obtained by fitting the formamide–water interaction energies to a 12-6-1 type function. These energies were calculated with the supermolecular approach by considering the MP2 correlation and the CP superposition. The values presented for the thermodynamic functions (H _S–W = –25.5 kcal-mol^–1 and G _S–W = –15.9 kcal-mol^–1), the structure of the first hydration layer (with 5 to 6 solvent molecules bonded to the solute), the solute's translational (D= 1.50 × 10^–5 cm²-s^–1) and rotational ( = 6.6 ps) mobility in the surrounding medium, and the positions of the H···O hydrogen bond spectral bands corresponding to these motions (_i = 92, 246, 379, and 636 cm^–1), are in agreement with the available results for this and other similar systems. In addition, the results are compared with those obtained by using parameters transferred from other systems. We observed that these values depend strongly on the potential used and concluded that it is advisable to avoid the use of such parameters.     

Heterobinuclear copper(II)–lanthanoid(III) complexes bridged by N,N′-oxamidobis(benzoato)cuprate(II)

Eight new -oxamido-bridged copper(II)–lanthanoid(III) heterobinuclear complexes described by the overall formula Cu(obbz)Ln(Me-phen)₂NO₃ (Ln = Y, La, Nd, Eu, Gd, Tb, Ho, Er), where obbz denotes the oxamidobis(benzoato) and Me-phen represents 5-methyl-1,10-phenanthroline (Me-phen), have been synthesized and characterized by the elemental analyses, spectroscopic (i.r., u.v., e.s.r.) studies, magnetic moments (at room temperature) and by molar conductivity measurements. The temperature dependence of the magnetic susceptibility of Cu(obbz)Gd(Me-phen)₂NO₃ has also been measured over the 4.2 300 K range. The least-squares fit of the experimental susceptibilities based on the spin Hamiltonian operator, = –2 J ₁ · ₂, yielded J = + 2.18 cm^–1. The observed Gd^III–Cu^II coupling is ferromagnetic. A plausible mechanism for a ferromagnetic coupling between Gd^III–Cu^II is discussed in terms of spin-polarization.     

Spin topology and ferromagnetic coupling: synthesis and magnetic properties of [CuII3CrIII] tetranuclear complexes of [14]N4 macrocyclic oxamides

Three novel tetranuclear macrocyclic complexes, [(CuL¹)₃Cr](ClO₄)₃·3H₂O (1), [(CuL²)₃Cr](ClO₄)₃·3H₂O (2) and [(CuL³)₃Cr](ClO₄)₃·3H₂O (3) [L¹, L² and L³ are the dianions of three [14]N₄ and [15]N₄ macrocyclic oxamides, namely 2,3-dioxo-5,6:13,14-dibenzo-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene,2,3-dioxo-5,6:13,14-dibenzo-9-methyl-7,12-bis(ethoxycarbonyl)-1,4,8,11-tetraazacyclotetradeca-7,11-diene and 2,3-dioxo-5,6:14,15-dibenzo-7,13-bis(ethoxycarbonyl)-1,4,8,12-tetraazacyclotetradeca-7,12-diene, respectively], have been prepared and characterized. These complexes are the first examples of Cu₃Cr species exhibiting spin topology with all the spins parallel in the ground state. Cryomagnetic studies on (1) (2–300 K) and (3) (77–300 K) revealed that the Cu^II and Cr^III ions interact ferromagnetically through the oxamido bridge, with the exchange integral J = 6.7 cm^–1 for (1) and J = 6.3 cm^–1 for (3) based on = –2J _{i j} . The ferromagnetic interaction has been rationalized in terms of strict orthogonality of the magnetic orbitals. The oxamido bridge is also more efficient than the oxalato bridge at propagating the ferromagnetic interaction.     

Formation,properties, and thermal decomposition of bisarene chromium(i) and molybdenum(i) fullerides

Fullerides [(⁶-Ph₂)₂Cr]⁺[C₆₀]^·–, [(⁶-C₁₀H₁₂)₂Cr]⁺[C₆₀]^·– (C₁₀H₁₂ is tetralin), and [(⁶-PhCH₃)₂Mo]⁺[C₆₀]^·– were synthesized. The molecular structure of [(⁶-Ph₂)₂Cr]⁺[C₆₀]^·– was established. In this compound at 100 K, radical anions C₆₀ ^–· are linked by an ordinary bond to form dimers, whereas at 293 K they are disordered and do not form dimers. The [(⁶-tetralin)₂Cr]⁺[C₆₀]^·– fulleride is stable in vacuo (10^–2 Torr) below 429 K, and [(⁶-toluene)₂Mo]⁺[C₆₀]^·– is stable below 581 K.Based on the materials presented at the International Conference Modern Trends in Organoelement and Polymer Chemistry (Moscow, May 30–June 4, 2004) dedicated to the 50th anniversary of the A. N. Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1973–1976, September, 2004.     

Neutron scattering by hydrogen in cold neutron prompt gamma-activation analysis

The effects of neutron scattering by hydrogen within targets for cold neutron prompt -ray activation analysis (CNPGAA) have been characterized. For most targets studied, the probability for neutron absorption, and hence CNPGAA sensitivities (counts·s^–1·mg^–1), decrease with increasing H content and with target thickness. Comparisons with results from thermal neutron PGAA indicate that the effects of cold neutron scattering differ from those of thermal neutron scattering. CNPGAA sensitivities for l/v nuclides show similar sensitivity decreases, while Sm sensitivities show smaller decreases.     

On the mechanism of racemisation of dichlorobis(ethylenediamine)-metal chlorides [metal = cobalt(III) or chromium(III)] in the solid state

Summary In the solid state l-cis-[M(en)₂Cl₂]Cl [M=cobalt(III) or chromium(III)] undergoes thermal racemisation smoothly at 158 °C without anycis-trans interconversion. The values of k_rac, H and S are 6 × 10^–6s^–1, 218 kJM^–1 and 156.1 JK^–1M^–1 for the cobalt(III) complex and 3.5 × 10^–5s^–1, 229.7 kJM^–1 and 197.9 JK^–1M^–1 for the chromium(III) complex, respectively. The results are only in accord with a rhombic twist mechanism of the type originally proposed by Ray and Dutt for [M(AA)₃] complexes.     

Novel dioximato-bridged chromium(III)-copper(II)-chromium(III) trinuclear complexes with ferromagnetic exchange interactions

Summary Two new dioximato-bridged trinuclear Cr^II-Cu^II-Cr^III complexes, [Cr(salen)-Cu(-BD)₂-Cr(salen)] (1) and [Cr(salen)-Cu(-FD)₂-Cr(salen)]-H₂O (2), have been prepared and characterized [salen^2– = N,N-ethylene- bis (salicylideneiminate), (-BD)^2– = -benzyldioximato and (-FD)^2– = -furildioximato]. Magnetic susceptibility measurements in the 4.2–300 K range demonstrated the operation of a ferromagnetic interaction between the adjacent Cr^III and Cu^II ions through oximato bridges in both (1) and (2). Based on spin Hamiltonians =–2J(₁₂+₂₃)(S₁=S₃=3/2,S₂=1/2) the exchange integrals (J) were evaluated as 3.19 and 5.38 cm^–1 for (1) and (2), respectively.     

Pulse radiolysis investigations on the reactions of primary radiolytic species of water with atropine

On pulse radiolysis of N₂O saturated aqueous solutions of atropine, an optical absorption band (_max at 320 nm,e=2.81·10³ dm³·mol^–1·cm^–1) was observed, which is assigned to the product of reaction of OH radicals with the solute. This absorption decayed following second order kinetics with a rate constant of 4.5·10⁸ dm³·mol^–1·s^–1. The rate constant for the reaction of OH radicals with atropine as estimated by following the build-up kinetics is 2.7·10⁹ dm³·mol^–1·s^–1. The H atoms also reacted with this compound to produce a transient absorption band behaving similarly to the one observed in the case of reaction with OH radicals. The transient species formed in both cases is assigned to a radical derived by H atom abstraction by H/OH radicals from the parent compound. This radical was unreactive towards 2-mercaptoethanol. e _aq ^– was found to react with atropine forming a transient band with _max at 310 nm (=3.55·10³ dm³·mol^–1). Its decay was also second order with a rate constant of 1.64·10⁹ dm³·mol^–1·s^–1. The bimolecular rate constant for the reaction of e _aq ^– with atropine as estimated from the decay of e _aq ^– absorption at 720 nm is 3.9·10⁹ dm³·mol^–1·s^–1. Specific one-electron oxidizing and reducing agents (such as Cl ₂ ^– , Tl²⁺, SO ₄ ^– and (CH₃)₂COH, CO ₂ ^– , respectively) failed to oxidize or reduce this compound in aqoues solutions. The radical anion of atropine formed by its reaction with e _aq ^– was found to reduce thionine and methyl viologen with bimolecular rate constant of 3.8·10⁹ and 3.2·10⁹ dm³·mol^–1·s^–1, respectively.