Mole Sec Research Articles

Synthesis Via Beta-Cyclodextrin of Graphene Supported Platinum Nanoparticles for Application in a Hydrogen Evolution Reaction

Carbon-based fuels are currently being consumed at an unsustainable rate.1 The increase in energy consumption of the modern world has created a demand for alternative fuel sources, and the need has never been greater.2 With mounting economic and environmental concerns, the time for the switch to a clean, reliable alternative is prime. Hydrogen gas is a popular choice due to its low greenhouse gas emissions however, pure hydrogen gas is problematic due to its high flammability. Hydrogen feedstock materials are currently being explored due to their ability to store substantial amounts of hydrogen gas in a stable and safe way.2-3 NaBH4 is a common hydrogen feedstock material because of its high percentage of hydrogen (over 10% by weight). This reaction occurs very slowly without catalytic assistance.4 Transition metal catalysts have demonstrated efficiency in the oxidation of sodium borohydride resulting in an increased release rate of hydrogen gas.4 Platinum nanoparticles have demonstrated potential as a catalyst for this reaction. Nanoparticles must be stabilized on a support system for them to achieve maximum catalytic efficiency through reduced agglomeration and by maintaining the particle shape and size distribution.2-4 Graphene and graphene oxide scaffolds may be used as a support system for platinum nanoparticles in this reaction.5 Overall, platinum nanoparticles showed the highest reaction rate of 0.0022 mol-1 sec-1 with a standard concentration of NaBH4, at a pH of 7 subjected to an increased temperature at 30°C. References Retnamma, R.; Novais, A.Q.; Rangel, C.M. Kinetics of hydrolysis of sodium borohydride for hydrogen production in fuel cell applications: a review. Int J Hydrogen Energy 2011, 36, 9772-9790.Huff, C.; Long, J.; Aboulatta, A.; Heyman, A.; T. Abdel-Fattah, Silver Nanoparticle/Multi-Walled Carbon Nanotube Composite as Catalyst for Hydrogen Production. ECS J Solid State Sci Technol. 2017, 6, M115-118.Tian, Z. Q.; Jiang, S. P.; Liang, Y. M.; Shen, P. K. Synthesis and Characterization of Platinum Catalysts on Multiwalled Carbon Nanotubes by Intermittent Microwave Irradiation for Fuel Cell Applications. The Journal of Physical Chemistry B 2006, 110(11), 5343–5350.Pena-Alonsa R, Sicurelli A, Callone E, Carturan G, Raj R. A picoscale catalyst for hydrogen generation from NaBH4 for fuel cells. J Power Sources 2007; 165:315-23.Kochkar, H., Aouine, Ghorbel, A.,Berhault, G. Shape-Controlled Synthesis of Silver and Palladium Nanoparticles Using β-Cyclodextrin. Journal of Physical Chemistry 2011, 115, 11364-11373.

Beta-Cyclodextrin Mediated Synthesis of Graphene Supported Gold Nanoparticles for Application in a Hydrogen Generation Reaction

The fast-paced economic climate of the world today has prompted a more thorough investigation into the field of alternative fuels. Increasing energy demands coupled with the crippling environmental and economic costs of carbon-based fuels, has aided in bringing this issue to a global level.1 Hydrogen gas is among the most favorable of candidates being pursued in the search for a viable alternative to gasoline. Hydrogen is renewable in nature and produces no harmful emissions.2 Current methods of hydrogen generation are limited in their efficiency due to the difficulties of harnessing and storing pressurized gas. Solid chemical storage in the form of metal hydrides, known for their hydrogen releasing capabilities, have been proposed as an alternative to these methods.3 Sodium borohydride (NaBH4) is among the most favorable of metal hydrides for its high hydrogen content (10.8% wt) and superior energy density.1-4 When coupled with water, sodium borohydride can generate up to 4 moles of dihydrogen gas per mole of NaBH4 via a hydrolysis reaction. However, the oxidation of aqueous sodium borohydride is a slow process and the use of a catalyst is necessary for the reaction to procced at an appreciable rate. Transition metal catalysts, in particular Au, have been implemented in this reaction however, many suffer from oxidation degradation, therefore, the use of a support system is necessary.5 For this experiment, gold nanoparticles coupled with graphene and graphene oxide supports were used as the catalytic material for hydrogen evolution reactions. Overall, gold nanoparticles showed the highest reaction rate of 0.0018 mol-1 sec-1 at a standard concentration of NaBH4, standard pH 7 and an increased temperature at 30°C. References Dunn, S. Hydrogen futures: toward a sustainable energy system. International Journal of Hydrogen Energy 2002, 27, 235–264.Haryanto, A.; Fernando, S.; Murali, N.; Adhikari, S. Current Status of Hydrogen Production Techniques by Steam Reforming of Ethanol: A Review. Energy Fuels 2005, 19, 2098–2106.Dicks, A.L. Hydrogen generation from natural gas for the fuel cell systems of tomorrow. J. Power Sources 1996, 61, 113-124.Huff, C.; Dushatinski, T.; Barzanjii, A.; Abdel-Fattah, N.; Barzanjii, K.; Abdel-Fattah, T.M. Pretreatment of gold nanoparticle multi-walled carbon nanotube composites for catalytic activity toward hydrogen generation reaction. ECS J Solid State Sci Technol 2017, 6, M69-M71.Kochkar, H., Aouine, Ghorbel, A.,Berhault, G. Shape-Controlled Synthesis of Silver and Palladium Nanoparticles Using β-Cyclodextrin. Journal of Physical Chemistry 2011, 115, 11364-11373.

Hydrogen Generation Reaction of Sodium Borohydride Catalyzed By Gold and Platinum Nanoparticles

The increasing energy demands of the world today have prompted a more thorough investigation into alternative fuels. The renewable nature of hydrogen gas and its environmentally-benign byproducts when produced by the hydrolysis reaction of water and sodium borohydride have identified this as a viable method of production for the alternative fuel. Gold and platinum nanoparticles were synthesized using beta-cyclodextrin for applications in hydrogen evolution reactions from sodium borohydride (NaBH4). The resulting homogenous metal nanoparticles were characterized using Ultraviolet- visible spectroscopy and Transmission Electron Microscope (TEM). Catalytic activity of the hydrogen evolution reactions was measured using a previously described gravimetric water displacement system [1,2]. The data collected shows an increase in the efficiency of the hydrogen generation reaction with the addition of gold and platinum nanoparticles when compared to the un-catalyzed reaction. Overall, gold nanoparticles showed the highest reaction rate of 0.0016 mol-1 sec-1 at a standard concentration of NaBH4, standard pH 7 and an increased temperature at 30 °C. The platinum nanoparticle catalyzed reaction preformed best with a standard concentration of NaBH4 and a standard pH 7 solution producing a rate constant of 0.0021 mol-1 sec-1. All reaction rates were determined to be second order kinematic reactions.

Combined spectroscopies and molecular docking approach to characterizing the binding interaction of enalapril with bovine serum albumin.

The binding interaction between bovine serum albumin (BSA) and enalapril (ENPL) at the imitated physiological conditions (pH=7.4) was investigated using UV-vis absorption spectroscopy (UV-vis), fluorescence emission spectroscopy (FES), synchronous fluorescence spectroscopy (SFS), Fourier transform infrared spectroscopy (FT-IR), circular dichroism (CD) and molecular docking methods. It can be deduced from the experimental results from the steady-state fluorescence spectroscopic titration that the intrinsic BSA fluorescence quenching mechanism induced by ENPL is static quenching, based on the decrease in the BSA quenching constants in the presence of ENPL with increase in temperature and BSA quenching rates >1010 Lmol-1 sec-1 . This result indicates that the ENPL-BSA complex is formed through an intermolecular interaction of ENPL with BSA. The main bonding forces for interaction of BSA and ENPL are van der Waal's forces and hydrogen bonding interaction based on negative values of Gibbs free energy change (ΔG0 ), enthalpic change (ΔH0 ) and entropic change (ΔS0 ). The binding of ENPL with BSA is an enthalpy-driven process due to |ΔH°|>|TΔS°| in the binding process. The results of competitive binding experiments and molecular docking confirm that ENPL binds in BSA sub-domain IIA (site I) and results in a slight change in BSA conformation, but BSA still retains its α-helical secondary structure.

Effect of Sacoglottis gabonensis and Alstonia boonei on the kinetics of Saccharomyces cerevisiae isolated from palm wine

Sacoglottis gabonensis and Alstonia boonei are botanicals used for the preservation of palm wine in Southern Nigeria. This study investigated the effect of S. gabonensis (0.625%) and A. boonei (0.50%) on the kinetics of Saccharomyces cerevisiae isolated from palm wine (PW). Concentrations of the preservatives used in this study were optimal concentrations of the preservatives that had preservative effect on fermenting palm sap. The fermentation rate constant, k, of 2.79 × 10-4mol-1 s-1 obtained for untreated PW was higher than the k values for PW treated with A. boonei (1.7 × 10-4 mol-1 s-1) and S. gabonensis (1.1 × 10-4 mol-1 sec-1). Both preservatives enhanced yeast growth. The specific growth rates (µmax) for the yeast were 0.43, 0.76 and 0.88 for the control, samples treated with A. boonei andS. gabonensis, respectively. However, the sedimentation rate of the yeast was reduced by both preservatives, but A. boonei produced the greatest effect. The utilization of these botanicals for industrial fermentations involving yeast is promising. Key words: Palm wine, preservation, Saccharomyces cerevisiae, fermentation kinetic, growth kinetic, sedimentation rate, Sacoglottis gabonensis, Alstonia boonei.

Avian IgY Binds to a Monocyte Receptor with IgG-like Kinetics Despite an IgE-like Structure

An ancestor of avian IgY was the evolutionary precursor of mammalian IgG and IgE, and present day chicken IgY performs the function of human IgG despite having the domain structure of human IgE. The kinetics of IgY binding to its receptor on a chicken monocyte cell line, MQ-NCSU, were measured, the first time that the binding of a non-mammalian antibody to a non-mammalian cell has been investigated (k(+1) = 1.14 +/- 0.46 x 10(5) mol(-1)sec(-1), k(-1) = 2.30 +/- 0.14 x 10(-3) s(-1), and K(a) = 4.95 x 10(7) m(-1)). This is a lower affinity than that recorded for mammalian IgE-high affinity receptor interactions (Ka approximately 10(10) m(-1)) but is within the range of mammalian IgG-high affinity receptor interactions (human: Ka approximately 10(8)-10(9) m(-1) mouse: Ka approximately 10(7)-10(8) m(-1). IgE has an extra pair of immunoglobulin domains when compared with IgG. Their presence reduces the dissociation rate of IgE from its receptor 20-fold, thus contributing to the high affinity of IgE. To assess the effect of the equivalent domains on the kinetics of IgY binding, IgY-Fc fragments with and without this domain were cloned and expressed in mammalian cells. In contrast to IgE, their presence in IgY has little effect on the association rate and no effect on dissociation. Whatever the function of this extra domain pair in avian IgY, it has persisted for at least 310 million years and has been co-opted in mammalian IgE to generate a uniquely slow dissociation rate and high affinity.

Content of antioxidants in plant extracts obtained by supercritical extraction

The content of natural antioxidants in extracts of medicinal plants, fruits, and seeds obtained by supercritical fluid extraction was determined by a microcalorimetric technique using the model reaction of induced cumene oxidation. All tested extracts can be divided into two groups according to their antioxidant activity. The first group includes extracts containing strong antioxidants with high inhibition rate constants; the second group includes preparations containing week antioxidants capable of reducing the oxidation rate. Among the preparations studied, the maximum concentrations of antioxidants were found in the extracts of sage (10.0 × 10−2 mole/kg), rosemary (5.3 × 10−2 mole/kg), cranberry (1.4 × 10−2 mole/kg), and carrot (1.2 × 10−2 mole/kg). The rate constants of reactions between antioxidants and peroxide radicals were calculated (k 7 = (0.4 − 9.0) × 104 liter/(mole sec)). With respect to this value, several types of natural antioxidants can be distinguished in each extract. The most active antioxidants are those contained in the rosemary extract, their reaction rate constants being about 2.3 × 105 liter/(mole sec). It is suggested that the most active components are tocopherols, polyphenols, and quinones.

KINETICS OF ALKALINE HYDROLYSIS OF ISOAMYLACETATE

ABSTRACT The theory of mass transfer accompanied by chemical reaction has been used to determine the kinetics of alkaline hydrolysis of isoamylacetate. The rate constant for the alkaline hydrolysis is around 9.52 cm3/(mole)(sec). This is much lower than the rate constant for alkaline hydrolysis of n-amyl acetate, which is about 85 cm3/(mole)(sec). The presence of an electrolyte like sodium chloride in the aqueous phase reduced the rate of extraction to some extent. The rates of extraction with sodium chloride in the aqueous phase and the corresponding rate constant values have been reported.

Scavenging of the one-electron reduction product from nisoldipine with relevant thiols: electrochemical and EPR spectroscopic evidences.

To determine the formation of the one-electron reduction product from nisoldipine and its reactivity with relevant thiols in mixed medium. Cyclic voltammetry (CV) and electron paramagnetic resonance (EPR) techniques were used to determine the one-electron reduction product corresponding to the nitro radical anion. CV was employed to assess both the rate constants corresponding to the decay of the radicals and its interaction with relevant thiols. The nisoldipine radical anion follows second order kinetics, with an association rate constant of 283+/-16 l mol(-1) sec(-1). Nitro radical anion from nisoldipine significantly reacted with thiol compounds. This reactivity was significantly higher than the natural decay of the radical in mixed medium. EPR spectra recorded in situ using DMF/ 0.1 N NaOH (pH 13) confirmed the formation of the nitro radical anion, giving a well-resolved spectra in 35 lines using 0.1 G modulation. Electrochemical and EPR data indicated that all the tested thiols scavenged the nitro radical anion from nisoldipine. The following tentative order of reactivity towards the thiols can be proposed: cysteamine approximately glutathione > N-acetylcysteine > captopril > penicillamine.

Radical polymerization of dicyclohexyl fumarate and its derivatives as studied by electron spin resonance spectroscopy

The radical polymerization of dicyclohexyl fumarate (DCHF) and its derivatives was carried out with dimethyl 2,2′-azobisisobutyrate in benzene at 60 °C. The propagation and termination rate constants ( k p and k t ) were determined by electron spin resonance spectroscopy. The k p and k t values were 0.48−0.91 l mol sec and 14−23,000 l mol sec , depending on the DCHF concentration ( 0.1−1.5 mol l ). It has been revealed that the alkyl substituents on the cyclohexyl ring have important effects on the polymerization reactivity of the DCHF derivatives. The 2-substituted cyclohexyl derivatives showed a lower polymerization reactivity because of the decrease in k p . The propagation manner of the 2-substituted derivatives is discussed, based on the results of the investigation of the tacticity of the polymer in comparison with those of non- or 4-substituted derivatives.

Chemically modified cardiac Na+ channels and their sensitivity to antiarrhythmics: Is there a hidden drug receptor?

Elementary Na+ currents were recorded at 19 degrees C in inside-out patches from cultured neonatal rat cardiocytes. In analyzing the sensitivity of chemically modified Na+ channels to several class 1 antiarrhythmic drugs, the hypothesis was tested that removal of Na+ inactivation may be accompanied by a distinct responsiveness to these drugs, open channel blockade. Iodate-modified and trypsin-modified cardiac Na+ channels are noninactivating but strikingly differ from each other by their open state kinetics, a O1-O2 reaction (tau open(1) 1.4 +/- 0.3 msec; tau open(2) 5.4 +/- 1.1 msec; at -40 mV) in the former and a single open state (tau open 3.0 +/- 0.5 msec; at -40 mV) in the latter. Lidocaine (150 mumol/liter) like propafenone (10 mumol/liter), diprafenone (10 mumol/liter) and quinidine (20 mumol/liter) in cytoplasmic concentrations effective to depress NPo significantly can interact with both types of noninactivating Na+ channels to reduce the dwell time in the conducting configuration. Iodate-modified Na+ channels became drug sensitive during the O2 state. At -40 mV, for example, lidocaine reduced tau open(2) to 62 +/- 5% of the control without detectable changes in tau open(1). No evidence could be obtained that these inhibitory molecules would flicker-block the open Na+ pore. Drug-induced shortening of the open state, thus, is indicative for a distinct mode of drug action, namely interference with the gating process. Lidocaine proved less effective to reduce tau open(2) when compared with the action of diprafenone. Both drugs apparently interacted with individual association rate constants, a(lidocaine) was 0.64 x 10(6) mol-1 sec-1 and a(diprafenone) 13.6 x 10(6) mol-1 sec-1. Trypsin-modified Na+ channels also appear capable of discriminating among these antiarrhythmics, the ratio a(diprafenone)/a(lidocaine) even exceeded the value in iodate-modified Na+ channels. Obviously, this antiarrhythmic drug interaction with chemically modified Na+ channels is receptor mediated: drug occupation of such a hypothetical hidden receptor that is not available in normal Na+ channels may facilitate the exit from the open state.

Differential response of DPI-modified cardiac Na+ channels to antiarrhythmic drugs: no flicker blockade by lidocaine.

Elementary Na+ currents were recorded in cell-attached patches from short-time cultured neonatal cardiocytes in order to test the hypothesis whether the open state of DPI-modified, noninactivating cardiac Na+ channels is basically sensitive to blocking drug molecules such as antiarrhythmics. Lidocaine (300 mumol/liter) effectively reduced the open probability of cardiac Na+ channels and, at a stimulation rate of 1 Hz, depressed the reconstructed macroscopic peak INa to 40 +/- 3.5% of the predrug value. The same drug concentration failed to influence DPI-modified Na+ channels. Their open state proved almost insensitive to lidocaine. tau open decreased only slightly to 85 +/- 2%. Still more importantly, the number of transitions between the conducting and a nonconducting configuration did not increase. At -40 mV, lidocaine may interfere with the open state with an association rate constant of 1.3 x 10(5) mol-1 sec-1 which is about two orders of magnitude smaller than the rate constant obtained with propafenone or prajmalium. Moreover, propafenone (10-20 mumol/liter) or prajmalium (30 mumol/liter) led to a tremendous increase in the number of transitions between the open and a nonconducting configuration. Lidocaine also failed to evoke a fast flicker blockade with reaction kinetics in the microsecond range. It is concluded that DPI-modified cardiac Na+ channels discriminate between lidocaine and other antiarrhythmic drugs. As a tentative explanation, this might be indicative for multiple binding sites for those drugs in cardiac Na+ channels.

Responsiveness of cardiac Na+ channels to antiarrhythmic drugs: the role of inactivation.

Elementary Na+ currents were recorded at 9 degrees C in inside-out patches from cultured neonatal rat heart myocytes. In characterizing the sensitivity of cooled, slowly inactivating cardiac Na+ channels to several antiarrhythmic drugs including propafenone, lidocaine and quinidine, the study aimed to define the role of Na+ inactivation for open channel blockade. In concentrations (1-10 mumol/liter) effective to depress NPo significantly, propafenone completely failed to influence the open state of slowly inactivating Na+ channels. With 1 mumol/liter, tau open (at -45 mV) in cooled, (-)-DPI-modified, noninactivating Na+ channels proved to be drug resistant and could not be flicker-blocked by 10 mumol/liter propafenone. The same drug concentration induced in (-)-DPI-modified Na+ channels a discrete block with association and dissociation rate constants of 16.1 +/- 5.3 x 10(6) mol-1 sec-1 and 675 +/- 25 sec-1, respectively. Quinidine, known to have a considerable affinity for activated Na+ channels, in lower concentrations (5 mumol/liter) left tau open unchanged or reduced, in higher concentrations (10 mumol/liter) tau open only slightly to 81% of the predrug value whereas NPo declined to 30%, but repetitive blocking events during the conducting state could never be observed. Basically the same drug resistance of the open state was seen in cardiac Na+ channels whose open-state kinetics had been modulated by the cytoplasmic presence of F- ions. But in this case, propafenone reduced reopening and selectively abolished a long-lasting open state. This drug action is unlikely related to the inhibitory effect on NPo since hyperpolarization and the accompanying block attenuation did not restore the channel kinetics. It is concluded that cardiac Na+ channels cannot be flicker-blocked by antiarrhythmic drugs unless Na+ inactivation is removed.

The kinetics of dissolution of UO 2 under reducing conditions and the influence of an oxidized surface layer (UO 2+x): Application of a continuous flow-through reactor

We have studied the kinetics of dissolution of uranium dioxide, UO 2(s), under strongly reducing conditions (H 2(g)/Pd). We have investigated the dependence of the rate of dissolution as a function of critical geochemical parameters: pH, pCO 2, and carbonate concentration. By using a stirred batch reactor, the kinetics of dissolution of an UO 2+x surface layer and the subsequent precipitation of UO 2 have also been studied. Although the initial UO 2 is pretreated before starting the experiments, it seems to be very difficult to avoid the formation of the oxidized surface layer. For this reason we have developed a thin layer continuous flow-through reactor in order to study the kinetics of dissolution of pure UO 2(s). The dependence of the rate of dissolution of these solids on the proton concentration of the solution may be expressed according to the following equations: r diss ( UO 2)(mol sec −1 m −2) = 1.4(±0.3) × 10 −8[ H +] 0.53 ± 0.08 (3 ⩽ pH ⩽ 7) r diss ( UO 2)(mol sec −1 m −2) = 1.9(±0.8) × 10 −12 (7⩽ pH⩽ 11) r diss ( UO 2+ x )(mol sec −1 m −2) = 1.1(±0.3) × 10 −12 [ H +] −0.30 ± 0.02 (3 ⩽ pH ⩽ 9) mechanism of dissolution of these solids is surface controlled. rate of dissolution of UO 2 in acidic solutions may be described in terms of an integer dependence on the activity of the protonated surface complexes: r diss ( UO 2)(mol sec −1 m −2) = 1.11 × 10 13 {> UOH 2 +} + (2 ⩽ pH ⩽ 6)

Observations of formaldehyde in comet Machholz (1988j)

The VLA was used in September 1988 to detect the 1 11−1 10 transition of formaldehyde (H 2CO) in emission at 6-cm wavelength (4829.659-MHz rest frequency) from Comet Machholz, a new comet. The cometary line had a small blueshift of −0.76 ± 0.40 km sec −1, which is consistent with the anisotropic outgassing of the nucleus in the solar direction and very similar to the blueshift observed in January 1986 with the VLA for the H 2CO emission line from Comet Halley. The derived H 2CO production rate for Comet Halley was 1.5 × 10 28 mol sec −1, and for Comet Machholz it was about an order of magnitude larger, 2 × 10 29 mol sec −1. Comet Machholz faded considerably only days after these H 2CO observations, which suggests that it fell apart. Indeed, the Comet Machholz H 2CO line is ≈2.5 times wider than the Comet Halley H 2CO line, which may indicate that the comet had started to come apart during these VLA observations.

Binding characteristics of 125I-labelled human FSH to granulosa cells from Booroola ewes which were homozygous, heterozygous or non-carriers of a major gene(s) influencing their ovulation rate

At 37 degrees C 125I-labelled human (h) FSH (NIAMDD-hFSH-I-3) bound rapidly to granulosa cells from Booroola and Romney ewes with 50% maximum binding achieved after 3 min and equilibrium being reached within 45 min, irrespective of whether the cells were obtained from the FF, F+ or ++ Booroola genotypes or from Romney ewes. Binding of 125I-labelled FSH followed second order kinetics and there was no effect of follicle diameter (1-2.5 mm vs greater than or equal to 3 mm). Irrespective of breed, genotype or follicle size, the mean (+/- s.e.m.) calculated association rate constant, (ka) was 7.3 (+/- 0.8) x 10(5) litres mol-1 sec-1 (n = 12). Dissociation of receptor bound 125I-labelled hFSH was less than 5% after 30 min and low but variable (i.e. between 0 and 30%) after 2-6 h irrespective of breed, genotype or follicle size. No gene-specific differences were noted in binding specificity between F+ and ++ genotypes: studies were not performed with cells from FF ewes because of insufficient cells. The binding of 125I-labelled hFSH could be displaced with sheep FSH (NIH-FSH-S16; 10% cross-reaction) and FSH-P (2.5% cross-reaction) but other sheep pituitary hormones and hCG showed little or no cross-reaction (less than or equal to 0.1%). The calculated binding capacities (Bmax) and equilibrium dissociation constants (Kd) for 125I-labelled hFSH binding to granulosa cells did not differ between the Booroola genotypes or between Booroola or Romney follicles of different diameter (i.e. 1-2.5 mm; or greater than or equal to 3 mm). The overall mean +/- s.e.m. (n = 24) Bmax and Kd values were 16.7 +/- 0.8 fm/mg protein (i.e. approximately 800 available receptor binding sites/cell) and 1.1 +/- 0.1 nM respectively. Collectively, these findings suggest that the earlier maturation of follicles in FF or F+ ewes compared to ++ ewes is unlikely to be due to gene-specific differences in the FSH binding characteristics of the granulosa cells.

Pulse Radiolysis Studies of the Interactions of the Sulfhydryl Compound Dithiothreitol and Sugars

Pulse radiolysis studies of the hydrogen atom transfer ("repair") reaction from the sulfhydryl-containing (RSH) compound dithiothreitol (DTT) to the DNA sugar deoxyribose and to several related sugars have been undertaken. The H transfer reaction is measured by monitoring the transient absorbance of the radical-anion RSSR-. The H atom transfer reactions for some sugars were fitted by a single time exponential function, but other sugars exhibited both a fast and a slow component (approximately 10-fold difference in rates) to the reaction. The reaction rates for the slow stage of the reaction between DTT and the sugars ranged from 0.5 X 10(7) dm3 mole-1 sec-1 for ribose-5-phosphate to 9 X 10(7) dm3 mole-1 sec-1 for 2-deoxyglucose. The maximum extent of total repair varied from 60% for ribose-5-phosphate to 100% for 2-deoxyglucose. The rate of repair, the extent of repair, and the appearance of more than one component of repair seem to depend on several factors: The occurrence of radical-radical reactions in the system is indicated by the demonstration of a dose dependence of the reaction kinetics, and this affects the observed rate of formation of RSSR-. Sugars with a deoxy group on the 2-carbon atom seem to have enhanced rates and extents of repair and to exhibit both fast and slow components to the reaction. The presence of a phosphate group on the sugar causes a decrease in the rate and extent of repair. The biological relevance of the reactions studied herein is discussed and the rates obtained are compared with rates for repair of damage in certain radiobiological systems.

The Radical Ions and Photoionization of Bile Pigments

The semireduced, semioxidized, and OH(.)-adduct radicals of bilirubin (BR) and biliverdin (BV) have been characterized using pulse radiolysis techniques. Laser flash photolysis (265-nm) of these pigments led to monophotonic photoionization with quantum yields of 0.08 for BR and 0.03 for BV. No evidence for triplet formation or for photoisomerization was found after 265-nm laser excitation. However, 347-nm excitation of BR in chloroform led to simultaneous photoisomerization and radical formation, but the radicals are thought to have originated from a pathway other than photoionization. The relevance of these observations to BR photoreactivity is discussed. BR radical ions in alkaline solution did not react with tryptophan (TrpH), but the semioxidized TrpH radical oxidized BR with k = 4.3 X 10(8) dm3 mole-1 sec-1. When human serum albumin (HSA) was oxidized using radiolytically generated azide radicals, a radical transformation involving TrpH and TyrOH residues occurred with k = 3.8 X 10(3) sec-1. When BR was complexed with the protein the transformation rate was reduced to 1.6 X 10(3) sec-1. This was interpreted in terms of a conformational change in the protein. Identification of the probable residues involved provided information about the primary BR binding site which was consistent with an earlier report.

Pulse Radiolytic Study of the Interaction of Thiols and Ascorbate with OH Adducts of dGMP and dG: Implications for DNA Repair Processes

Using the technique of pulse radiolysis, the interaction of .OH radicals with 2'-deoxyguanosine (dG) and dG-5'-monophosphate (dGMP) has been shown to result in the production of intermediates with different redox properties as demonstrated by their reactions with tetranitromethane (TNM) and N,N,N',N'-tetramethyl-p-phenylenediamine. The ratio of the yields of oxidizing to reducing-type .OH radical adducts of dGMP was determined to be about 1:1 and independent of pH (6-11). The nature of the intermediates produced on reaction of .OH with dGMP are discussed. The thiols, cysteine, glutathione, mercaptoacetic acid, and ascorbate have been shown to interact with those .OH adducts of dGMP and dG with oxidizing properties preferentially via an electron transfer process (k approximately 3 X 10(7)-1.4 X 10(9) dm3 mole-1 sec-1) as implied from the pH dependence of the rate constants. It is further demonstrated that oxygen and TNM do not interact with those .OH adducts of the purines with oxidizing properties. The implications of these findings are discussed with reference to the mechanistic aspects of radioprotection and especially of radiosensitization.

Metallkomplexe der Liganden 1.4.7-Triazacyclononan-N.N′.N″ -tris-2-ethansulfonat (TES) und 1.4.7-Triazacyclononan-N.N′.N″ -trisethylacetat (TEA). Die Kristallstrukturen von Na[Ni(TES)(H2O)]·5H2O und Na[Cu(TES)]·3H2O / Transition Metal Complexes Containing the Ligands 1,4,7-Triazacyclononane-N,N′,N″-tris-2-ethanesulfonate (TES) and 1,4,7-Triazacyclononane-N,N′,N″-tris-ethylacetate (TEA). The Crystal Structures of Na[Ni(TES) (H2O)]·5H2O and of Na[Cu(TES)]·3H2O

The syntheses of two new, potentially hexadentate ligands with an N3O3 donor set is reported: 1,4,7-triazacyclononane-N,N′,N″-tris-2-ethanesulfonate (TES) and 1,4,7-triazacyclononane- N,N′,N″-tris-ethylacetate (TEA). Complexes of the divalent transition metals Co(II), Ni(II), Cu(II) containing these ligands have been prepared. The kinetics of the reactions of [Con(TEA)H2O]2+ and [CoII(TCTA)]-(TCTA= 1,4,7-triazacyclononane- N,N′N″-tris-acetate) with [FeIII(CN)6]3-, respectively, have been measured. A stable binuclear [Co(TEA)(CN)6Fe]- species has been characterized in solution whereas the reaction of [Co(TCTA)]- with [Fe(CN)6]3- yields [CoIIITCTA] and [Fe(CN)6]4- via an outer-sphere electron transfer reaction (k = 5,9 × 103 1 mol-1 sec-1; 25 °C, I = 0,26 M). Na[Ni(TES)H2O]·5H2O crystallizes in the triclinic space group P1̄ (Ci 1-No 2) with cell constants a = 806,7(4), b = 1468,4(8), c = 2317,9(8) pm, α = 72,36(4)°, β = 83,48 (3)°, γ = 81,99(4)°, and Z = 4. The nickel(II) center is in a distorted octahedral environment of a pentadentate TES ligand (N3O2) and a coordinated H2O. Na[Cu(TES)] 3H2O crystallizes in the triclinic space group P1̄ (Ci 1-No 2) with cell constants a = 747,3(3), b - 1082,6(5), c = 1459,3(9) pm, α = 81,13(5)°, β = 84,75(4)°, γ = 79,39(3)°, and Z = 2. The copper(II) center is in a distorted quadratic pyramidal environment of a pentadentate TES ligand. Each of the complex anions contains one uncomplexed CH2-CH2-SO3-group.