Mode of initiation in ceric salt initiated aqueous polymerization of methylmethacrylate

Summary The basic reaction for the production of initiating radicals in Ceric salt initiated polymerization of methylmethacrylate is strongly dependent on the acidity of the medium and independent of the nature of the anion associated' with the ceric ion. In moderately acid medium the primary reaction is the formation of hydroxyl radicals by ceric ion oxidation of water. When ceric sulfate is used as the initiator these hydroxyl radicals initiate the polymerization and appear as hydroxyl endgroups in the polymers. On the other hand, when ammonium ions are present, as in case of ceric ammonium sulfate initiator or ceric sulfate initiator in the presence of ammonium sulfate, some of the hydroxyl radicals generated in the primary reaction, react with the ammonium ions producing ammonium radicals and both hydroxyl and ammonium radicals act as the initiator giving rise to both hydroxyl and amine endgroups in the polymers. In strongly acid medium the basic initiating reaction changes into one in which the monomer transfers an electron to the ceric ion producing monomer radicals which initiate the polymerization and polymers with no endgroups are formed.

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Zusammenfassung Die Grundreaktion zur Erzeugung von Startradikalen aus Cersalz-initiierter Polymerisation von Methylmethacrylat ist von der Aciditäat des Mediums stark abhängig und unabhängig von der Natur des Anions, das mit den Cerionen assoziiert ist. Im mäßig sauren Medium besteht die primäre Reaktion in der Bildung von Hydroxylradikalen durch das Cerion auf Basis der Oxidation von Wasser. Wenn Cersulfat als Initiator verwendet wird, starten die Hydroxylradikale die Polymerisation und erscheinen als Kettenendgruppen. Andererseits, bei Gegenwart von Ammonium, wie im Falle des Cerammoniumsulfats oder Cersulfats in Gegenwart von Ammoniumsulfat, reagieren einige der Hydroxylradikale in primärer Reaktion mit den Ammoniumionen und erzeugen Ammoniumradikale, und darn geben beide-Hydroxyl-und Ammoniumradikale - als Initiatoren Anlaß für Hydroxyl-und Aminendgruppen der Hydroxylketten. In stark saurem Medium verändert sich die Startreaktion in eine andere, in der Monomere ein Elektron an das Cerion transferieren und hierdurch Monomerradikale erzeugen, die die Polymerisation starten und Polymere ohne Endgruppen bilden.

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With 5 tables     

荷移分光光度法测定双酚S的研究

该文研究了电子供体硼砂与双酚S荷移络合物的光谱性质,建立了简单快速测定双酚S(BPS)含量的荷移紫外分光光度法。结果表明:荷移络合物的最大吸收波长为291 nm,表观摩尔吸光系数ε为1.92×104L·mol-1·cm-1。双酚S的质量浓度在0.7~7 mg/L范围内符合比尔定律,相关系数为0.999 6,检出限为0.195 mg/L。该方法用于测定塑料中双酚S的含量,加标回收率为99.8%~100.4%,相对标准偏差不大于0.5%。     

Charge transfer in photoacids observed by stark spectroscopy

The charge redistribution upon photoexcitation is investigated for a series of pyrene photoacids to better understand the driving force behind excited-state proton-transfer processes. The changes in electric dipole for the lowest two electronic transitions ( (1)L b and (1)L a) are measured by Stark spectroscopy, and the magnitudes of charge transfer of the protonated and deprotonated states are compared. For neutral photoacids studied here, the results show that the amount of charge transfer depends more upon the electronic state that is excited than the protonation state. Transitions from the ground state to the (1)L b state result in a much smaller change in electric dipole than transitions to the (1)L a state. Conversely, for the cationic (ammonium) photoacid studied, photoexcitation of a particular electronic state results in much smaller charge transfer for the protonated state than for the deprotonated state.     

利用电荷迁移反应分光光度法测定头孢唑林钠的研究

研究了π受体试剂四氯苯醌与头孢唑林钠的电荷迁移反应。发现在乙酰丙酮乙二醇聚乙二醇２００体系中，两者形成稳定的橙色络合物。络合物比为１∶１，λｍａｘ＝４５２ｎｍ。药物质量浓度在２０～８００ｍｇ／Ｌ范围呈线性。用该法测量试样含量与药典法一致。相对标准偏差１．０％（ｎ＝１０），加标回收率９７％以上。     

Charge transfer between quasi-zero-dimensional nanostructures

In the present paper, we show the main features of the theoretical formula allowing us to understand the irreversible transfer of electrons or holes, as it may be observed in some electrically conducting (conjugated) polymers. The formula reported here is derived with the use of the nonequilibrium quantum transport theory. The key role in the formula is played by the electron–phonon interaction which is included in an approximation going beyond the limits of the finite order of the perturbation calculation. The transfer formula is developed for a simple model of the stacked conjugated polymer, which is represented here by two interacting quantum dots. The numerical calculations show the dependence of the charge carrier mobility on the charge carrier concentration and on the lattice temperature. A comparison with organic field-effect transistor experiments and with molecular-scale modeling on conjugated polymers is promising.     

Charge transfer complexes of hexamethylphosphoramide chalcogenides

Charge transfer complexes between iodine and hexamethylphosphoramide chalcogenides have been investigated spectrophotometrically. The equilibrium constant increases on passing from O to Se but not proportionally to the ionization potential of the atoms. A linear correlation was found between ΔG (or ΔS) and ΔH. The structure of the complexes is discussed.     

Charge transfer emission of ytterbium-doped oxyborates

The ultraviolet spectroscopic properties of trivalent ytterbium have been studied at low temperature in one borate and two oxyborates in the ternary diagram Li(2)O-Y(2)O(3)-B(2)O(3). The UV luminescence was detected in the two ytterbium-doped oxyborates. The evolution of these emissions was studied as a function of the temperature. A determination of the configurational coordinate diagrams based on the Struck and Fonger model is proposed to calculate the position in energy of the charge transfer band afforded by the simulation of spectral distribution of these excitation and emission bands. The strong correlation between the luminescent properties and the environments of the rare earth is pointed out.     

Charge transfer in the Cl-CO cluster induced by core ionization

Ab initio calculations of core-ionization spectra of the anion-molecule Cl-CO cluster are performed. Particular attention is paid to the investigation of charge-transfer screening processes accompanying core ionization of the CO molecule in the cluster. The charge-transfer processes are very efficient and favored by the presence of a low-lying unoccupied pi* orbital in CO capable of accepting an electron from Cl-. The O1s(-1) and C1s(-1) core-ionization spectra are calculated and compared. Both reveal a breakdown of the quasiparticle picture of core ionization caused by the charge-transfer processes. Remarkable differences between these two spectra are found which manifest themselves in distinct intensity distributions in the prominent low-energy spectral bands. The underlying reason for these differences is elucidated and linked with the preference of the pi* orbital to localize mainly on carbon. Core-ionization spectra of anion-molecule clusters are very sensitive to the type of the molecule involved as the comparative analysis of the O1s(-1) core-ionization spectra of the Cl-CO and Cl-H(2)O clusters show.     

Charge effects on oxygen atom transfer

The rhenium(V) complex [(HCpz3)ReOCl2]+ ([1]+), the tris(pyrazolyl)methane analogue of the known tris(pyrazolyl)borate complex (HBpz3)ReOCl2 (2), has been prepared. The two complexes are strikingly similar, as are the phosphine oxide adducts [(HCpz3)ReCl2(OPPh3)]Cl ([3]Cl) and (HBpz3)ReCl2(OPPh3) (4), which have been characterized by X-ray crystallography. Comparison of the bimolecular reduction of [1]BF4 and 2 by triarylphosphines reveals a pronounced charge effect, with the cationic species being reduced by PPh3 about 1,000 times faster than its neutral analogue in CH2Cl2 at room temperature. Ligand substitution of the adducts [3]+ and 4 is dissociative, with the cationic complex dissociating phosphine oxide about 56 times more slowly than the neutral compound. The relative impact of charge on ground and transition states in atom transfer reactions is discussed.     

Charge transfer through a protein-nano junction

We address the problem of charge transfer (CT) between a nanosized inorganic system and a protein from a theoretical and numerical perspective. The CT process is described on an atomistic level by applying an electronic Hamiltonian that takes into account the chemical bond, vibronic coupling effects, and polarization degrees of freedom. As a structurally well-characterized example, we consider a complex of C60 and its antibody. For this system, we find a novel efficient protein CT mechanism; through-space superexchange is mediated by stacked pi orbital systems. The predicted rates are comparable to those obtained for short-range electron tunneling through covalent bonds, the fastest ground-state CT process known for proteins.     

Charge transfer in the TCNQ-sexithiophene complex

Molecular crystals from thiophene molecules can be doped with TCNQ-F4 molecules for use in all-organic optoelectronic and semiconductor devices. The charge transfer and the molecular orbital energy level formation in between these two organic molecules are investigated here by density functional theory calculations. The isolated molecules are calculated nonbonded and bonded together, forming a charge transfer complex (CTC). The relaxed structure of the complex shows essentially coplanar and centered molecules with the alpha-sexithiophene rings tilted alternatingly by 4.8 degrees. The bond formation of these molecules results in a charge transfer of approximately 0.4 e from the alpha-sexithiophene to the TCNQ-F4 molecule. The highest occupied molecular orbital-lowest unoccupied molecular orbital gap width is reduced as compared to the isolated molecules due to the newly formed orbitals in the CTC. Upon adsorption on a Au(111) surface, electrons are transferred onto the molecule complex, thereby causing the molecular levels to align asymmetric with respect to the charge neutrality level. The theoretical results for the single molecule and CTC layer are compared to experimental photoemission and scanning tunneling spectroscopy results.     

Charge transfer complexes of N-ethylcarbazole and poly-N-vinylcarbazole

Poly-N-vinylcarbazole and its monomeric analog, i.e., N-ethylcarbazole, act as donors in charge transfer complexes with such electron acceptors as iodine, tetracyanoethylene, and tetracyanoquinodimethane. Poly-N-vinylcarbazole and N-ethylcarbazole are also capable of accepting electrons from an alkali metal such as sodium. A study of the spectral properties of both types of complexes showed that the monomer can both accept and donate electrons to a greater extent than the corresponding unit segment of the polymer chain. Equilibrium constants are presented for both cases, and estimates of the ionization potential of N-ethylcarbazole and related compounds are made from the characteristic charge transfer frequencies. Good agreement between these values and those calculated from molecular orbital theory is outlined.     

Charge transfer complexes of N-substituted 2-pyrrolidinones

The complex formation of 1-ethyl-2-pyrrolidinone, 1-benzyl-2-pyrrolidinone and 1-phenyl-2-pyrrolidinone with iodine, iodine monobromide and iodine monochloride has been studied by u.v. and visible spectroscopic methods in carbon tetrachloride, dichloromethane, 1,2-dichloroethane, n-heptane and cyclohexane. The results show the equilibrium constants (K), complexation enthalpies (ΔH) and the wavelengths of maximum absorption bands (λ_max) of the complexes to vary markedly with the solvent. The decrease in the K values with increasing acceptor number (AN) of the solvent may be due to the competition of the solvent and the halogen molecule for the amide; for halogenated hydrocarbon solvents can act as weak electron acceptors. The complex formation ability of the electron donors decreases in the order 1-ethyl-2-pyrrolidinone ⪢ 1-benzyl-2-pyrrolidinone ⪢ 1-phenyl-2-pyrrolidinone, and the electron acceptor properties decrease in the order iodine monochloride ⪢ iodine monobromide ⪢ iodine.     

Charge transfer interactions in liquid crystalline polymers probed by fluorescence spectroscopy

Rigid-rod aromatic LC polyester with long alkyl side chains and two thermotropic LC polyesters (PET40/OBA60 and PB-10) were studied by fluorescence spectroscopy to investigate their charge transfer interactions corresponding to LC configuration and changes during phase transition.     

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed. Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.     

Charge transfer driven by electron correlation: a non-Dyson propagator approach

A hole charge created in a molecular system, for instance, by ionization, can migrate through the system solely driven by electron correlation. This charge transfer due to electron correlation is referred to as charge migration. We introduce in this work a new ab initio method analyzing charge migration due to electron correlation in molecules. This method, a third-order "non-Dyson" propagator approach, aims in the long run, in particular, at the calculation of charge migration in relatively large molecules such as oligopeptides. First results of the new non-Dyson method are compared with a previously used propagator approach.