The formation and properties of the melatonin radical: a photolysis study of melatonin with 248 nm laser light

The photolysis of melatonin in aqueous solution has been studied spectrometrically with a 248 nm laser. The formation of hydrated electrons in a monophotonic process has been confirmed in neutral solution with a quantum yield of 0.22. Two main absorption bands at 340 and 460 nm plus an absorption shoulder resulted from the counterpart of the ejected electron, a melatonin radical, in solution. The big difference for the relative intensity of the absorption peaks under various pH conditions reveals that the melatonin radical exists in the solution through an acid-base equilibrium. In support from the pH dependence of the spectrum of the intermediate, the pKa1 for the doubly-protonated melatonin radical against the mono-protonated melatonin cation radical was estimated to be -0.95 and the pKa2 for the mono-protonated melatonin cation and melatonin neutral radical was 4.5 +/- 0.5. This work will benefit the basic understanding about melatonin as a UV-light protector, as a light receptor and the antioxidation functions of melatonin.     

Dissolution of copper phthalocyanine and fabrication of its nano-structure film

The mono-protonated and di-protonated forms of copper phthalocyanine (CuPc) were obtained by increasing concentrations of trifluoroacetic acid (TFA) solution to a fixed concentration of CuPc solutions. UV-Vis spectrum shows that the Q bands of these two derivatives split and shift to the red, which means successive protonation happened and caused the two derivatives to lose their symmetry. After the protonation step, the solubility of protonated CuPc in organic solvent increased 60 times. The CuPc film was fabricated by the electrophoretic deposition (EPD) method from the protonated CuPc dissolved in nitromethane containing TFA. Scanning electron microscopy (SEM) showed that the deposited CuPc film on the indium tin oxide (ITO) substrate is composed of thread-like nanobelts with diameters between 100 nm and 200 nm. Furthermore, the CuPc film is in α phase with stacking direction (b-axis) parallel to the substrate, which was detected by X-ray diffraction.     

Synthesis and Characterization of New Phthalocyanines Peripherally Fused to Four 13-Membered Tetrathiamacrocycles

The new metal-free phthalocyanine 5 and phthalocyaninatometals 6–8 (M=Co, Ni, or Zn) fused in peripheral positions with four 13-membered tetrathiamacrocycles were prepared by cyclotetramerization of 2, 3, 6, 7, 9, 10-hexahydro-5H-[1, 4, 8, 11]benzotetrathiacyclotridecine-13, 14–dicarbonitrile in the presence of a suitable metal salt or a strong organic base. In contrast to the aza- or oxamacrocycle-fused analogs, the solubility of these phthalocyanines is very low. Complexation of the tetrathiamacrocycles of 7 and 8 with Pd^II or Ag^I to form pentanuclear products was accomplished from their suspensions.     

地开石热分解过程及非等温动力学研究

Fourier-transform infrared emission spectroscopy was used to study the dehydroxylation behavior of the thermal decomposition of dickite from Chenxi, Hunan Province, China. Dehydroxylation of dickite was followed by a loss of intensity of the 3620.73, 3695.34 cm-1 OH-stretching bands and 916.06, 1009.33 cm-1 OH bending bands. The thermal decomposition was investigated by thermogravimetric analysis (TGA). A good agreement is found with TG curves of dickite and the mass loss is 13.7% (close to the theoretical value). The non-isothermal kinetics of the thermal decomposition of dickite was studied in TG-DTG curves over the temperature range from 298 K to 1123 K by thermogravimetry and differential thermal analysis in air. Mathematical analysis of TG-DTG data using the integral methods (Coats-Redfern equation, HM equation, MKN equation) and differential method (Achar equation) shows that the thermal decomposition of dickite accords F2 mechanism. The kinetic parameters such as the activation energy (E=131.62 kJ/mol), pre-exponential factor (A=108.30 s-1) and reaction order (n=2.1) are reported. The Ozawa method was used to analyse the activation energy of the same sample at different heating rate and gave 133.07 kJ/mol. The kinetic parameters calculated from different equation are rather close to each other.     

Thermal decomposition of liebigite

Summary A combination of high resolution thermogravimetric analysis coupled to a gas evolution mass spectrometer has been used to study the thermal decomposition of liebigite. Water is lost in two steps at 44 and 302°C. Two mass loss steps are observed for carbon dioxide evolution at 456 and 686°C. The product of the thermal decomposition was found to be a mixture of CaUO₄ and Ca₃UO₆. The thermal decomposition of liebigite was followed by hot-stage Raman spectroscopy. Two Raman bands are observed in the 50°C spectrum at 3504 and 3318 cm^-1 and shift to higher wavenumbers upon thermal treatment; no intensity remains in the bands above 300°C. Three bands assigned to the υ₁ symmetric stretching modes of the (CO₃)^2- units are observed at 1094, 1087 and 1075 cm^-1 in agreement with three structurally distinct (CO₃)^2- units. At 100°C, two bands are found at 1089 and 1078 cm^-1. Thermogravimetric analysis is undertaken as dynamic experiment with a constant heating rate whereas the hot-stage Raman spectroscopic experiment occurs as a staged experiment. Hot stage Raman spectroscopy supports the changes in molecular structure of liebigite during the proposed stages of thermal decomposition as observed in the TG-MS experiment.     

The polymerization of ethylene with a soluble titanium-aluminium complex

The reaction between biscyclopentadienyl titanium dichloride and aluminium alkyls and alkyl chlorides has been examined by ESR spectroscopy, and by the abilities of the various resulting complexes to initiate the polymerization of ethylene at 1 atm and ambient temperature. In general, it is concluded that the active initiating species is a Ti(IV) complex, and not the paramagnetic Ti(III) complexes. Accordingly, the development of an ESR spectrum is accompanied by a fall off in initiating efficiency, decrease in polymerization rate and increased molecular weight of the polymers produced. The reduction of Ti(IV) to Ti(III) during the polymerization accounts for the fall in rate with conversion; addition of an oxidizing agent (1:2-dichloroethane) to the polymerization converts Ti(III) to Ti(IV), as observed by the disappearance of the ESR signal, and increases the efficiency of the polymerization. Block copolymers of ethylene with propylene and butadiene have been prepared with this initiator; the efficiency in producing blocks has been used to study the decomposition of the active sites by a first order reduction process.     

Studies on the kinetics of decomposition of diacyl peroxides: III. Kinetics and mechanism of decomposition of 3, 5, 5-trimethylhexanoyl peroxide in benzene

The kinetics of decomposition of 3,5,5-trimethylhexanoyl peroxide (1) in benzene at 30, 40, and 50°C respectively have been studied and the cage effect, main products and the products obtained in scavenging experiment with galvinoxyl determined and characterized. The results show that the decomposition of 1, with initial concentration between 0.04 to 0.43 mol. L^?1, followed first plus three halves order kinetics with cage effect of 0.6, and the mechanism of decomposition is basically the same as previously proposed for lauroyl peroxide (2).⁴ In comparison with 2, the decomposition of 1 at the same temperature showed a faster rate for spontaneous decomposition, a larger cage effect and lesser induced decomposition, which is attributed to the branching in molecule of 1, especially to the presence of β-methyl group, which caused a larger entropy increase between the peroxide molecule and the transition state for decomposition.     

Cs NMR study of the cryptand-222-Cs complex in binary solvent mixtures

The formation constants of the cryptand-222 complex with the cesium ion were studied by ¹³³Cs NMR measurements in four binary solvent systems: acetonedimethylsulfoxide (Me₂Co---Me₂SO), acetonitrile (MeCN)---Me₂SO, propylene carbonate(PC)---Me₂SO and PC-dimethylformamide (DMF). In the neat solvents the formation constant increases in the order Me₂SO < DMF < Me₂CO < PC < MeCN, which is the inverse order of their solvating abilities as given by the Gutmann donor number. In binary mixtures the stabilities varied monotonically with the decomposition. As expected, there is no correlation between the stabilities of the complexes and the dielectric constant of the medium. It seems that, for aprotic solvents with similar Pearson basicities and in the absence of ion pair formation, the donor ability of a binary solvent mixture can be qualitatively predicted from the donicities of the two solvents and the composition of the mixture.     

Studies on azotetrazolate based high nitrogen content high energy materials potential additives for rocket propellants

This paper reports the synthesis, characterisation and thermolysis studies of a series of azotetrazolate salts, viz., ammonium/guanidinium/triaminoguanidinium [azotetrazolate]. TG-DTA and DSC results of these compounds exhibited their thermal stability up to 180°C. DSC indicated the highest heat release (2804 J g^–1) for guanidinium azotetrazolate salt during exothermic decomposition. FTIR of the decomposition products of azotetrazolate salts showed bands at 3264 and 2358 cm^–1 which may be attributed to gaseous species such as NH₃ and HCN or NH₂CN. The sensitivity data suggests low vulnerability of ammonium and guanidinium salts. In cyclic voltammetric studies all the salts showed similar response in reduction reactions. Triamino guanidinium azotetrazolate (TAGAZ) was incorporated into solid propellant formulations in order to establish the compatibility of this class of compounds. DSC results revealed that it does not have adverse effect on thermal stability of double base matrix. The burning rate data obtained indicated that TAGAZ acts as an efficient energetic additive in composite modified double base (CMDB) propellant formulations in high-pressure region.The authors are grateful to Dr. Haridwar Singh, Outstanding Scientist and Director, HEMRL for constant encouragement to carry out this work. Authors also thankful to Dr. R. S. Satpute, Dr. A. N. Nazare and Dr. C. N. Divekar for their assistance in propellant processing.     

Thermal decomposition behavior of mono-aminimides and their application to polymerization of epoxide

Mono-aminimide compounds [N,N-dimethyl-N-(2-hydroxypropyl)-amine-N′-propionimide ( 1 ), trimethylamine valerimide ( 2 ), and trimethylamine benzimide ( 3 )] were found to exhibit different thermal decomposition behaviors and polymerization efficiencies for an epoxide (phenyl glycidyl ether, PGE). The thermal decomposition rate of aminimides at 150°C decreased in the order 1 > 2 > 3 . It seemed that hydrogen bonding enchanced the decomposition rate, and the resonance effect induced by the phenyl group suppressed the decomposition. 1 was thermolyzed to give isocyanate and tertiary aminoalcohol, which subsequently reacted with each other to give isocyanate and tertiary aminoalcohol, which subsequently reacted with each other to give urethane. When 2 was heatted, the isocyanurate generated from 2 remained intact. On heating of 3 , we observed the formation of triphenyl isocyanurate. PGE reacted with those aminimides and gave different products depending on their thermolyzed products. Equimolar mixtures of isocyanate, tertiary amine, PGE were used in the model reactions, and the thermal reaction between the expected decompostion products of aminimides was investigated in the presence and absence of PGE. The rate of PGE consumption was in the order PGE + 2 > PGE + 1 > PGE + 3 . It is clear that the formation of urethanes and oxazolidone derivatives affects the polymerization process.     

从TPD谱图求解Ed、ko的等脱附速率法

提出了一种简便的TPD谱图处理法——等脱附速率法。此法与查表法相结合, 有助于确定脱附反应动力学级数。实验证明, 该法适用于从一级或二级脱附反应TPD谱求解脱附活化能E_d和指前因子k_o值。     

INVARIABLE TRAPPING TIMES IN PHOTOSYSTEM I UPON EXCITATION OF MINOR LONG-WAVELENGTH-ABSORBING PIGMENTS

The primary charge separation in photosystem (PS) I was measured on stacked pea thylakoids using the light-gradient photovoltage technique. Upon 532 nm excitation with picosecond flashes, a trapping time of 80 ± 10 ps for PS I was found, which is in close agreement with literature data. In the wavelength range between 700 nm and 717 nm the trapping time was essentially the same although there was an indication for a slight decrease. To further analyze the data we performed a spectral decomposition of PS I with Chi a and b solvent spectra. This procedure yielded bands at around 682 nm, 690 nm, 705 nm and 715 nm. According to this decomposition, a selective excitation of long-wavelength antenna pigments at wavelengths Λ > 710 nm is possible, because the direct excitation of the main 682 nm band is small compared to the excitation of the two most red-shifted bands. The invariability of the trapping time of the excitation wavelength suggests thermal equilibration of the excitation energy among all antenna pigments according to their excited state energy levels and their abundance. Hence, we conclude that trapping in PS I is essentially rate-limited by the primary charge separation much as it is the case in PS II. Then, according to our spectral decomposition in a time constant of2–3 ps is predicted for the primary charge separation in PS I.     

Selective catalytic reduction of NO with hydrocarbon on Cu2+-exchanged pillared clay: An IR study of the NO decomposition mechanism

In an earlier study, it has been found that Cu²⁺ ion-exchanged pillared clay (Cu-PILC) has a substantially higher activity for the selective catalytic reduction of NO by ethylene over Cu-ZSM-5. Moreover, it is not significantly deactivated by water vapor and SO₂. In this study, the activity for direct NO decomposition in the presence of O₂ on Cu-PILC was studied and an in situ IR study for the key intermediates and the reaction mechanism was made. The direct NO decomposition activities for Cu-PILC and Cu-ZSM-5 were similar. Under in situ NO and O₂ reaction conditions at temperatures up to 300°C, IR absorption bands at well-defined peak positions are identified. The band at 1699 cm⁻¹ is assigned to a dinitrosyl species on Cu⁺. The bands with peaks at 1609, 1530–1480 and in the region of 1440–1335 cm⁻¹ are assigned to bidentate nitrate, monodentate nitrate and nitro species bonded to Cu²⁺. A redox mechanism is proposed for NO decomposition. The limiting step is thought to be the N–N coupling between surface nitrate and gaseous nitric oxide to form nitrogen. The existence of substantial amounts of nitrate formed from NO alone indicates the important role of the large amount of lattice oxygen that is available on Cu-PILC. As a result, the role of external oxygen supply is only to replenish the consumed lattice oxygen. The proposed NO decomposition mechanism suggests that the redox property of Cu-PILC is crucial for this reaction.     

Quantitation of Cu+‐catalyzed Decomposition of S‐Nitrosoglutathione Using Saville and Electrochemical Detection: a Pronounced Effect of Glutathione and Copper Concentrations

S‐nitrosothiols (RSNOs) are composed of nitric oxide (NO) bound to the sulfhydryl group of amino acids of peptides or proteins. There is a great interest for their quantitation in biological fluids as they have a crucial impact on physiological and pathophysiological events. Most analytical methodologies for quantitation of RSNOs are based on their decomposition followed by the detection of the released NO. In order to obtain the optimal sensitivity for each detection method, the total decomposition of RSNOs is highly desired. The decomposition of RSNOs can be obtained by using catalytically active metal ions, such as Cu⁺, obtained from CuSO₄ in presence of a reducing agent such as glutathione (GSH) that is naturally present in biological environment. In this work, we have re‐investigated the decomposition of S‐nitrosoglutathione (GSNO) which is the most abundant in vivo low molecular weight RSNO, with a special emphasis on the effect of CuSO₄, GSH, and GSNO concentrations and of their ratio. To this aim, GSNO decomposition optimization was performed by both indirect (Griess assay) and direct (real time electrochemical detection of NO at NO‐microsensor) quantitation methods. Our results show that the ratio between CuSO₄, GSH and GSNO should be adjusted to tune the highest decomposition rate of GSNO and the most efficient electrochemical detection of released NO; also it shows the deleterious effect of very high GSH concentration on the detection of GSNO.     

Exchange and decomposition reactions of isobutyl iodide with iodine

In the presence of elementary iodine, isobutyl iodide (2-methyl-1-iodopropane) undergoes isotopic exchange and also decomposes with production of additional iodine. Both reactions are approximately first order in isobutyl iodide and half order in iodine molecules. In degassed hexachlorobutadiene at 160°, the rate constants for exchange and decomposition are 7.5 × 10^?6 and 11.4 × 10^?6 (liter/mole)^1/2sec^?1, respectively. The decomposition is probably initiated by iodine atom abstraction of a β hydrogen atom, but comparison with rates for related compounds indicates that this hydrogen abstraction does not contribute significantly to the mechanism of exchange.     

High resolution electronic spectroscopy of p-vinylphenol in the gas phase

A recent controversy regarding the proper assignment of two closely spaced bands in the S₁ ← S₀ electronic transition of trans-p-coumaric acid (pCA) has been addressed by recording their spectra at full rotational resolution. The results show unambiguously that the carrier of these two bands is p-vinylphenol (pVP), a thermal decomposition product of pCA. The two bands belong to two conformers of pVP; trans-pVP at 33,207.3 cm⁻¹ and cis-pVP at 33,211.8 cm⁻¹.     

Excited electronic state decomposition of furazan based energetic materials: 3,3'-diamino-4,4'-azoxyfurazan and its model systems, diaminofurazan and furazan

We report the first experimental and theoretical study of gas phase excited electronic state decomposition of a furazan based, high nitrogen content energetic material, 3,3'-diamino-4,4'-azoxyfurazan (DAAF), and its model systems, diaminofurazan (DAF) and furazan (C2H2N2O). DAAF has received major attention as an insensitive high energy explosive; however, the mechanism and dynamics of the decomposition of this material are not clear yet. In order to understand the initial decomposition mechanism of DAAF and those of its model systems, nanosecond energy resolved and femtosecond time resolved spectroscopies and complete active space self-consistent field (CASSCF) calculations have been employed to investigate the excited electronic state decomposition of these materials. The NO molecule is observed as an initial decomposition product from DAAF and its model systems at three UV excitation wavelengths (226, 236, and 248 nm) with a pulse duration of 8 ns. Energies of the three excitation wavelengths coincide with the (0-0), (0-1), and (0-2) vibronic bands of the NO A 2Sigma+<--X 2Pi electronic transition, respectively. A unique excitation wavelength independent dissociation channel is observed for DAAF, which generates the NO product with a rotationally cold (20 K) and a vibrationally hot (1265 K) distribution. On the contrary, excitation wavelength dependent dissociation channels are observed for the model systems, which generate the NO product with both rotationally cold and hot distributions depending on the excitation wavelengths. Potential energy surface calculations at the CASSCF level of theory illustrates that two conical intersections between the excited and ground electronic states are involved in two different excitation wavelength dependent dissociation channels for the model systems. Femtosecond pump-probe experiments at 226 nm reveal that the NO molecule is still the main observed decomposition product from the materials of interest and that the formation dynamics of the NO product is faster than 180 fs. Two additional fragments are observed from furazan with mass of 40 amu (C2H2N) and 28 amu (CH2N) employing femtosecond laser ionization. This observation suggests a five-membered heterocyclic furazan ring opening mechanism with rupture of a CN and a NO bond, yielding NO as a major decomposition product. NH2 is not observed as a secondary decomposition product of DAAF and DAF.     

Thermal study of decomposition of selected biomass samples

Fears of climate change and increasing concern over the global warming have prompted a search for new, cleaner methods for electricity power generation. Technologies based on utilising biomass are attracting much attention because biomass is considered to be CO₂ neutral. Co-firing of biomass fuels with coal, for example, is presently being considered as a mean for reducing the global CO₂ emissions. Biomass is also applied in thermal conversion processes to produce fuels with higher calorific values and adsorbents. In any case, thermal decomposition is essential stage where volatiles and tars are evolved followed by consequent heats of reactions. In this work sawdust biomass samples were selected in order to study their thermal conversion behaviour. Heats of decomposition for each sample were measured during continuous heating at a prescribed heating rate under inert atmospheric conditions. The decomposition generally commenced in all samples at 150°C and was completed at 460°C in a series of endo and exothermic reactions influenced by its lignin and cellulosic content. Single biomass sample was subjected to heating rates ranging from 10 to 1000°C min^-1 and the effect of heating rate on decomposition was studied. The origin of reactions for each thermal sequence is herein discussed in detail. This revised version was published online in July 2006 with corrections to the Cover Date.     

The kinetics and mechanism of induced thermal decomposition of peroxomonosulphate by phase transfer catalysts

The kinetics of induced decomposition of potassium peroxomonosulphate (PMS) by the phase transfer catalysts (PTC), viz. tetrabutylammonium chloride [TBAC] and tetrabutylphosphonium chloride [TBPC] have been investigated. The effect of [PMS], [PTC], ionic strength of the medium and temperature on the rate of decomposition of PMS was studied. The rate of decomposition of PMS was monitored under pseudo-first-order condition at a constant temperature (50 ± 0.1 °C). The rate of decomposition was first order with respect to PMS for TBAC and half order for TBPC. The order with respect of PTC was found to be unity for TBAC and half order for TBPC. A suitable kinetic scheme has been proposed to account for the experimental data and its significance is discussed.     

p-Benzyne

A noble gas matrix at low temperature was used to investigate the photochemical behavior of diacetyl terephthaloyl diperoxide and dipropionyl terephthaloyl diperoxide as well as 1,4-diiodobenzene. All three photoreactions formed small quantities of a compound with IR absorption bands at 725 and 980 cm⁻¹, which disappeared when the matrix was annealed. These bands correspond to the most intense of the calculated bands (B3LYP) for 1,4-didehydrobenzene (p-benzyne) ( 1 ). That decomposition of the peroxides in fact leads to 1 is confirmed by vapor-phase pyrolysis experiments in which (Z)- 2 was obtained in high yield.