Spectrophotometric Determination of Cimetidine through Charge-transfer Reaction with 1,5-Dichloroanthraquinone as a π-Electron Acceptor

Cimetidine reacting with 1,5-dichloroanthraquinone in acetone solution can produce a charge-transfer complex that shows a strong absorption peak at 343 nm. The absorption value at 343 nm increased with cimetidine concentration in the range of 0.01—0.5 μg/mL, with regression coefficient of 0.9995 and detection limit of 0.006 μg/mL. This simple and sensitive method has been successfully applied to determine cimetidine in tablets and capsules, with average recovery of (98.47±0.92)% and (97.07±1.16)%, respectively. Furthermore, the mole ratio of the complex between cimetidine and 1,5-dichloroanthraquinone is 2∶1, and the mechanism of charge-transfer reaction is explored.     

Solvent effect on standard electrode potential: Part III. Silver-silver chloride electrode in methanol-water mixtures

From measurements of the electromotive force of the Pt, H₂ (gas, 1 atm); HCl (m), X% methanol, Y% water; AgCl, Ag cells at nine temperatures from 15 to 55°C at 5° intervals, the standard potential of the silver-silver chloride electrode has been determined over a broad range of methanol concentrations (0–90 wt. % methanol). The standard molal potential in the various solvent mixtures has been expressed as a function of temperature. The primary medium effects of various media on hydrochloric acid, and the standard thermodynamic quantities accompanying the transfer of HCl from water to the respective solvent media have been computed. The results have been discussed both in terms of the acid-base behaviour of the solvent mixtures and also their structural effects on the transfer process.     

Anomalous solubility of polyacrylamide prepared by dispersion (precipitation) polymerization in aqueous tert‐butyl alcohol

Polyacrylamide prepared by dispersion (precipitation) polymerization in an aqueous t‐butyl alcohol (TBA) medium is only partially soluble when the TBA concentrations in the polymerization media are in the range 82 vol % < TBA < 95 vol %. Independent experiments with a soluble (linear) sample of polyacrylamide show that the polymer swells sufficiently in the aforementioned media to lower the glass‐transition temperature of the polymer below the polymerization temperature (50 °C). The anomalous solubility has been attributed to the crosslinking of polymer chains that occurs during the solid‐phase polymerization of acrylamide in the swollen polymer particles. It is postulated that some of the radical centers shift from the chain end to the chain backbone during solid‐phase polymerization by chain transfer to neighboring polymer molecules, and when pairs of such radicals come into close vicinity, crosslinking occurs. However, dispersion (precipitation) polymerization in other media such as aqueous methanol and aqueous acetone yields polymers that are soluble. This result has been attributed to the fact that the polymer radical undergoes a chain‐transfer reaction with these solvents at a much faster rate than with TBA, which overcomes the effect of the polymer‐transfer reaction. Even the addition of as little as 5% methanol to a TBA–water mixture (TBA:water = 85:10) gives rise to a soluble polymer. The chain‐transfer constants for acetone, methanol, and TBA have been determined to be 9.0 × 10^?6, 6.9 × 10^?6, and 1.48 × 10^?6, respectively, at 50 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3434–3442, 2001     

Polymerization of diethylene glycol bis(allyl carbonate) by means of di-sec-butyl peroxydicarbonate

The initial stages of the free radical polymerization of diethylene glycol bis(allyl carbonate) at temperatures of 35–65°C have been studied. The polymer is unsaturated and cyclization to give a 16-membered ring occurs only to a small extent. The kinetic order with respect to the initiator, di-sec-butyl peroxydicarbonate, has an average value of 0.79; the order increases slightly with peroxydicarbonate concentration over the range 0.018–0.22M. The molecular weight of the polymer isolated after 3% polymerization is close to 19,000. It shows no significant dependence on initiator concentration or on temperature. The dominant feature of the bulk polymerization, as in free radical polymerization of the other allyl and diallyl monomers, is degradative chain transfer in which the growing polymer radical abstracts a hydrogen atom from a monomer unit to give a relatively unreactive allylic radical. The dependence of rate on initiator concentration is rationalized if some of these allylic radicals are able to reinitiate polymerization. The transfer constant to monomer is 0.014 at 50°C, assuming that the main termination step involves mutual termination of allylic radicals. Carbon tetrachloride is an active transfer agent with a transfer constant of 0.20 ± 0.04 at 50°C. Toluene, which is less active, has a transfer constant of 0.0064 at 50°C and also retards the polymerization. Some kinetic studies have been made with other initiators, including di-2-methyl-pentanoyl peroxide which initiates polymerization at temperatures as low as 13°C.     

THE MECHANISM OF THE 9,10-DIBROMOANTHRACENE MEDIATED TRIPLET-SINGLET ENERGY TRANSFER IN THE TETRAMETHYL-1,2-DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*

Abstract— The ternary chemiluminescent system consisting of tetramethyl-dioxetane (TMD), 9 ,10-dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (³K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines-cence involves triplet-singlet (TS) energy transfer from ³K to DBA, followed by singlet-singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of k^TS_K.DBA= (1.4 ± 0.4) ± 10⁹M^-1s^-1 and an efficiency of ø^TS_K.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. k^SS_DBARU= 1.5 ± 10¹⁰ M^-1 and (2.2 ± 0.2) ± 10¹⁰M^-1s^-1, respectively.     

Study on the time-dependent simulation and input parameter sensitivity of spent nuclear fuel electrorefining

A computer program for the simulation of spent nuclear fuel electrorefining has been developed based on general Butler–Volmer kinetics and mass transport within a diffusion layer model. The effect of a solid electrode area change due to the dissolution and deposition, the solubility of the element in the liquid Cd, and a volume change due to the development of metallic compounds were considered in this program. The program has been verified through Tomczuk et al.’s experiment, and the results show a good agreement of within 4 and 2 % for U amount in the anode and cathode, respectively. The sensitivity of several input parameters such as the standard electrode potential, activity coefficient, diffusion coefficient, diffusion layer thickness, and transfer coefficient has been tested. It was found that the standard electrode potential is very sensitive, as a 3 % variation leads to a U amount change of more than 30 and 50 % in the anode and molten salt, respectively. The sensitivity of the other input parameters is much less than the standard electrode potential, but significant within the data difference with the other references, except for the transfer coefficient. This result is useful for understanding the effectiveness of each input parameters on the simulation results.     

ENERGY TRANSFER FROM CAROTENOID POLYENES TO PORPHYRINS: A LIGHT-HARVESTING ANTENNA

Carotenoid to porphyrin singlet-singlet energy transfer has been observed in a new covalently linked carotenoid-porphyrin ester. Nuclear magnetic resonance studies reveal that the relatively high energy transfer efficiency (? 25%) is a result of a stacked conformation in which the 26 π electron carotenoid chromophore resides ?4–5 Å above the mean porphyrin plane. Substantial quenching of porphyrin fluorescence was also observed. Implications for the mechanism of energy transfer and possible applications to synthetic solar energy conversions systems are discussed.     

Thiourea as a transfer agent in the radical polymerization of methyl methacrylate in aqueous solution at 42

Chain transfer involving thiourea in radical polymerization of methyl methacrylate in acidic aqueous media has been studied by polymer endgroup analysis using the dye-partition technique. Thiourea has feeble reactivity in chain transfer, the transfer constant with respect to poly (methyl methacrylate) radicals being 1.21 × 10^?4 at 42°. This chain transfer study led to the development of a new method for studying the tautomeric equilibrium between the thione and thiol forms of thiourea. The equilibrium is pH dependent and the equilibrium constant at 42° is 232. The ratios of the equilibrium concentrations of the thiol to thione forms of thiourea at various pH's have been calculated. The thiol form is responsible for the chain transfer reactivity; it predominates in strongly acidic media and is almost absent above pH 3.5. This new method may be used for studying the thione-thiol tautomerism of other thiourea derivates.     

Polymerization and copolymerization of trioxane: Factors influencing molecular weight and end groups

In bulk polymerization and copolymerization of trioxane with ethylene oxide, it has been shown that p-chlorophenyldiazonium hexafluorophosphate is a superior catalyst as compared to boron trifluoride dibutyl etherate (BF₃ · Bu₂O). Polymers and copolymers of significantly higher molecular weight have been obtained. The higher molecular weight has been attributed primarily to less inherent chain transfer during propagation, which in turn can be attributed to the superior gegenion PF₆^?. The polymerization proceeds via a clear period followed by sudden solidification. Faster polymerization and higher molecular weight polymers have been observed for homopolymerization than for copolymerization. The polymer yield obtained after solidification is determined by both rate of polymerization and rate of crystallization of polymers. These rates, in turn, are dependent on the catalyst concentration. The molecular weight is determined both by polymer yield and extent of inherent chain transfer. In the range of monomer to catalyst mole ration [M]/[C] = (0.5–20) × 10⁴ investigated, it has been found that in the higher range, the polymer yield is independent of the catalyst concentration and the extent of inherent chain transfer is inversely proportional to the half power of catalyst concentration: [M]/[C] = (0.5–8) × 10⁴ for homopolymerization and (0.5–3) × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. In the lower range, the yield decreases with catalyst concentration and the extent of inherent chain transfer is inversely proportional to higher power of catalyst concentration. The dependence of molecular weight of polymers on catalyst concentration has been shown to be a complex one. The molecular weight goes through a maximum as the catalyst concentration is decreased. The maximum molecular weights have been obtained at [M]/[C] ≈ 8 × 10⁴ for homopolymerization and ～3 × 10⁴ for copolymerization with 4.2 mole % ethylene oxide. Prior to reaching maximum the molecular weight is inversely proportional to the half power of catalyst concentration indicating it is primarily controlled by inherent chain transfer. Upon further decrease of catalyst, molecular weight decreases as a result of both a decrease in polymer yield and an increase in inherent chain transfer. In copolymerization of trioxane and ethylene oxide, it has been ascertained that methylene chloride exhibits a favorable solvating effect. Although higher inherent chain transfer takes place in copolymerization than in homopolymerization, the extent of chain transfer is independent of ethylene oxide concentration. The difference in polymer yield and molecular weight a t different ethylene oxide concentrations is attributed primarily to the difference in k_p/k_t ratio. It also has been demonstrated that end capping of polymer chains can be accomplished by the use of a chain transfer agent—methylal.     

Cinetique de polymerisation du styrene en presence de peroxyde de benzoyle p,p′ bis-bromomethyle synthese de polymeres peroxydes

The free radical polymerization of styrene has been studied by using p,p′-bisbromomethyl benzoyl peroxide as initiator containing a chain transfer group. The rate constant of decomposition (k_d) of this peroxide has been determined at various temperatures, as well as the efficiency factor f and the transfer constant to initiator C₁. At 60°, f = 0·70 ± 0·05 and C₁ = 0·5. Polystyrene containing peroxide groups has been prepared by using this initiator. The highest yield in polymeric peroxide has been obtained for polymerization in emulsion at 40°.     

Diffusion-limited energy transfer from Dy3+ to Ho3+ in dimethyl sulfoxide

Diffusion-limited energy transfer has been studied from Dy³⁺ to Ho³⁺ in dimethyl sulfoxide. The value of the diffusion constant has been calculated to be 4.65 × 10⁻¹⁴ cm² sec⁻¹ at 300 K. A temperature-dependent study of energy transfer has also been carried out. The probabilities of energy transferP_da and transfer efficiencyη_T have been calculated.     

Effect of volume concentration and temperature on viscosity and surface tension of graphene–water nanofluid for heat transfer applications

In the present study, the effect of volume concentration (0.05, 0.1 and 0.15 %) and temperature (10–90 °C) on viscosity and surface tension of graphene–water nanofluid has been experimentally measured. The sodium dodecyl benzene sulfonate is used as the surfactant for stable suspension of graphene. The results showed that the viscosity of graphene–water nanofluid increases with an increase in the volume concentration of nanoparticles and decreases with an increase in temperature. An average enhancement of 47.12 % in viscosity has been noted for 0.15 % volume concentration of graphene at 50 °C. The enhancement of the viscosity of the nanofluid at higher volume concentration is due to the higher shear rate. In contrast, the surface tension of the graphene–water nanofluid decreases with an increase in both volume concentration and temperature. A decrement of 18.7 % in surface tension has been noted for the same volume concentration and temperature. The surface tension reduction in nanofluid at higher volume concentrations is due to the adsorption of nanoparticles at the liquid–gas interface because of hydrophobic nature of graphene; and at higher temperatures, is due to the weakening of molecular attractions between fluid molecules and nanoparticles. The viscosity and surface tension showed stronger dependency on volume concentration than temperature. Based on the calculated effectiveness of graphene–water nanofluids, it is suggested that the graphene–water nanofluid is preferable as the better coolant for the real-time heat transfer applications.     

Gold nanoparticles and a glucose oxidase based biosensor: an attempt to follow-up aging by XPS

Amperometric biosensors are widely used for clinical, food industry and environmental control. A universal platform allowing immobilization of different enzymes could provide a fast and easy way to design new sensors, but the main drawback effect with oxidase based biosensors is the production of hydrogen peroxide. The direct electron transfer is a way to limit the H₂O₂ production. A modified electrode described by Zhao et al. (Bioelectrochemistry, 69(2):158, 2006), based on immobilization of glucose oxidase/colloidal gold nanoparticles on a glassy carbon electrode by Nafion film, has been used. Its sensitivity is 0.4 μA mM^?1 cm^?2, reproducibility is 3.0%, detection limit is 0.37 mM, response to glucose is linear up to 20 mM; limit of detection is 0.37 mM and response time is about 1.5 min. This sensor displays a formal redox potential compatible with a direct electron transfer, and has been tested for its response in time and GOx denaturation by X-ray photoelectron spectroscopy. Vanishing of disulphide bonds of GOx has been observed after a period in a saturating solution of glucose but this does not appear determinant in loss of enzyme activity.     

Thermal profiles of förster energy transfer preliminary studies of luminescent probes of protein dynamics in transferrin and calmodulin

Fluorescence energy transfer, the transfer of energy from a donor to an acceptor via a dipole/induced dipole mechanism, has long been used to measure distances between donors and acceptors in proteins and other macromolecules. Because the transfer can occur over time scales larger than protein bending and breathing modes, multiple conformational states can be sampled. The analysis of these states is weighted by the donor-acceptor distance; shorter distances carry more weight, because the energy transfer depends on the inverse sixth power of the distance. The usefulness of fluorecence energy transfer in probing these large amplitude protein motions is studied here. The method involves measuring the nergy transfer efficiency while perturbing the protein conformation with heat. As the temperature increases, the amplitudes of vibrations increase, and fluorescence energy transfer should also increase if the donor and acceptor are in flexible region of the protein. This hypothesis was tested in two different protein systems; calmodulin, a calcium- activated regulatory protein, and transferrin, a blood serum iron shuttle. The preliminary studies show a differential sensitivity of the transfer efficiency to heat for the systems. Normalized energy transfer over 10 Å in calmodiulin from a tyrosine donor to a Tb(III) acceptor increases 40% from 297 to 322 K. Normalized energy transfer over 42 Å in transferrin from a Tb(III) donor to an Fe(III) acceptor increase 35% over the same temperature range. In marked contrast to these systems, energy transfer from tyrosine to a chelated Tb(III) shows anomalously high temperature- dependence.     

Fast pyrolysis (ultrapyrolysis) of cellulose

A fast pyrolysis process, termed ultrapyrolysis, has been developed at the University of Western Ontario in order to exploit the high heating rates, short residence times high temperatures and rapid quenching, which are required to produce valuable non-equilibrium intermediates (i.e. ethylene and acetylene) from finely divided biomass. Hot solids(Thermo-for) are used to carry and transfer heat to the biomass particles in a very turbulent vortical contactor (Thermovortactor). This turbulence creates an ideal environment for fast thorough mixing and extremely rapid heat transfer. Cold solids (Cryofor) are then used to quickly quench the products. Trials with cellulose were conducted at temperatures between 750 and 900°C and residence times between 250 and 450 ms. Ethylene yields, expressed as a mass fraction of the product gas, varied from 6.8 to 8.2% for temperatures ranging from 750 to 900°C. The total hydrocarbon yield, also expressed as amass fraction of the product gas, was 18.8% at 900°C. The conversion of cellulose to a permanent non-condensible gaseous product was estimated to be 98% by mass at 900°C.     

Muonic hydrogen and deuterium in H-D mixture and muon transfer in excited states

The deexcitation of µp and µd atoms in hydrogen-deuterium mixtures has been studied with a new kinetics model that takes the energy dependence of the cascade processes into account. The X-ray yields, the populations of atomic states, and the muon transfer from hydrogen to deuterium during the cascade have been calculated as functions of density and isotope fractions. The evolution of the kinetic energy distribution during the cascade is shown to play an important role in the transfer kinetics. The atomic energy distribution in the ground state is significantly changed by the transfer. The calculated X-ray yields and the muon transfer probabilities are in fair agreement with experimental data provided the current theoretical transfer rates are reduced by a factor of about 2.     

Chain transfer to solvent in the radical polymerization of N‐isopropylacrylamide

Chain transfer to solvent has been investigated in the conventional radical polymerization and nitroxide‐mediated radical polymerization (NMP) of N‐isopropylacrylamide (NIPAM) in N,N‐dimethylformamide (DMF) at 120 °C. The extent of chain transfer to DMF can significantly impact the maximum attainable molecular weight in both systems. Based on a theoretical treatment, it has been shown that the same value of chain transfer to solvent constant, C_tr,S, in DMF at 120 °C (within experimental error) can account for experimental molecular weight data for both conventional radical polymerization and NMP under conditions where chain transfer to solvent is a significant end‐forming event. In NMP (and other controlled/living radical polymerization systems), chain transfer to solvent is manifested as the number‐average molecular weight (M_n) going through a maximum value with increasing monomer conversion. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Long-distance electron transfer from a triplet excited state

Electron transfer from the triplet excited state of N,N,N',N'-tetramethylphenylene diamine to phthalic anhydride has been monitored by phosphorescence emission decay. The kinetics of the transfer process were observed directly and the rate constant depends exponentially on the reacting distance, k(r) = 1 × 10⁴ exp(−0.58r) s⁻¹. The electron transfer rate has been found to be invariant over the temperature interval 77–143 K.     

Thermal properties and interactions of l-proline in aqueous solutions of NaCl or KCl at different temperatures

The enthalpies of solution of l-proline in aqueous electrolyte solutions within the electrolyte molality range up to 4.9 mol kg^?1 of NaCl and up to 4.0 mol kg^?1 of KCl at 288, 298 and 313 K have been measured by the calorimetric method. Enthalpies of transfer of l-proline from water to aqueous electrolyte solutions up to saturation have been derived at 273–348 K. The enthalpic and heat capacity parameters of pair and triplet interaction of l-proline with electrolyte in water have been evaluated. Enthalpic parameters of pair interaction at 298 K have been compared to similar parameters for glycine and l-alanine. The temperature changes of reduced enthalpy, and also the change of entropy and reduced Gibbs energy of transfer of l-proline from water to aqueous electrolyte solution at temperature rise from 273 to 323 K have been determined. It has been shown that the entropy–enthalpy compensation takes place for transfer processes.     

Spectrophotometric,Thermodynamic and Density Functional Studies of Charge Transfer Complex Between Benzhydryl Piperazine and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone

The charge transfer complex of benzhydryl piperazine as donor with the π-acceptor 2,3-dichloro-5,6-dicyano-p-benzoquinone has been studied spectrophotometrically in acetonitrile medium at different temperatures. On mixing the donor with acceptor, a reddish brown colored charge transfer complex is formed. Electronic absorption spectra of the complex show charge transfer bands at 587, 546 and 457 nm. The molecular composition of the complex was studied by applying Job’s continuous variation and spectrophotometric titration methods. These results support the formation of the complex in a 1:2 ratio. The Benesi–Hildebrand equation has been applied to compute the formation constant and molecular extinction coefficient. Thermodynamic parameters of the charge transfer complexation reaction (standard entropy, standard enthalpy and standard Gibbs free energy) have been calculated. The results of the spectrophotometric study demonstrated that the charge transfer complex formation is endothermic. The computational studies of the charge transfer complex were performed by using the Gaussian 09 W package of programs. The bond lengths, bond angles, dihedral angles, Mulliken atomic charges, molecular electrostatic potential maps and characterization of the highest occupied molecular orbital and lowest unoccupied molecular orbital surfaces of charge transfer complex were computed.