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61.
A phytochemical investigation in plantlets of the Brazilian medicinal tree Virola surinamensis resulted in the isolation and structural determination of four new compounds: 3-hydroxy-4-methyl-2-(11'-piperonyl-n-undecyl)-butenolide; 3-hydroxy-4-methyl-2-(7'-piperonyl-n-heptyl)-butanolide; 9'-(3,4-methylenedioxy-phenyl)-nonanoic acid and 13'-(3,4-methylene-dioxyphenyl)-tridecanoic acid. Thirteen compounds previously isolated from seeds and adult plants were also reported. 相似文献
62.
In this paper we consider the essential electronic excited states in parallel chains of semiconducting polymers that are currently being explored for photovoltaic and light-emitting diode applications. In particular, we focus upon various type II donor-acceptor heterojunctions and explore the relation between the exciton binding energy to the band offset in determining the device characteristic of a particular type II heterojunction material. As a general rule, when the exciton binding energy is greater than the band offset at the heterojunction, the exciton will remain the lowest-energy excited state and the junction will make an efficient light-emitting diode. On the other hand, if the offset is greater than the exciton binding energy, either the electron or hole can be transferred from one chain to the other. Here we use a two-band exciton to predict the vibronic absorption and emission spectra of model polymer heterojunctions. Our results underscore the role of vibrational relaxation and suggest that intersystem crossings may play some part in the formation of charge-transfer states following photoexcitation in certain cases. 相似文献
63.
Elisabeth Seguin Michel Koch Evelyne Chenu Marcel Hayat 《Helvetica chimica acta》1980,63(5):1335-1346
Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and Tubulosine Pseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described. 相似文献
64.
Vera R. L. Constantino Luiz F. C. de Oliveira Paulo S. Santos Henrique E. Toma 《Transition Metal Chemistry》1994,19(1):103-107
Summary The synthesis, spectra and electrochemistry of [Ru(bipy)2-(picOH)]+ and -picO-[Ru(bipy)2]2
2+ (bipy = 2,2-bipyridine and picOH = 3-hydroxypicolinate ion) are described. The spectroscopic properties in the visible region are dominated by the intense Ru bipy chargetransfer transitions. In the binuclear complex, the two [Ru(bipy)2L]2+ moieties are nonequivalent, exhibiting E
1/2 = 0.69 and 1.20 V versus s.h.e. The partially oxidized species exhibits a weak intervalence transfer band at 1085 nm, and is consistent with a Robin-Day class II mixed valence complex. 相似文献
65.
Luciana B.O. dos Santos 《Analytica chimica acta》2005,528(1):21-27
This paper describes the development of a sequential injection analysis method to automate the determination of atrazine by square wave voltammetry exploiting the concept of monosegmented flow analysis to perform in-line sample conditioning and standard addition. To perform these tasks, an 800 μL monosegment is formed, composed by 400 μL of sample and 400 μL of buffer/standard solution. To obtain an efficient homogenization, the sample solution is divided in five zones intercalated by four zones of the Britton-Robinson buffer (pH 2.0) in presence of appropriate concentration of NaNO3 and varying atrazine standard concentrations. This mixture zone is isolated from the carrier solution by two 100 μL air bubbles. After homogenization in an auxiliary reaction coil the mixture zone is injected toward the flow cell, which is adapted to the capillary of a hanging drop mercury electrode, at a flow rate of 50 μL s−1. After a suitable delay time, the potential is scanned from −0.5 to −1.2 V versus Ag/AgCl using a frequency of 300 Hz and pulse height of 25 mV. The linear dynamic range is observed for atrazine concentrations between 1.16 × 10−7 and 2.32 × 10−6 mol L−1, obeying the linear equation ip = (−6.91 ± 0.07) × 108[atrazine] + (4 ± 8), with r2 = 0.9996, for which the slope is given in nA L mol−1. The detection and quantification limits of the method are 2.1 × 10−8 and 7.0 × 10−8 mol L−1, respectively. The sampling frequency is 37 h−1, when the standard addition protocol is followed. This frequency can be increased to 42 h−1 if the protocol to obtain in-line calibration curve is used for quantification. The method was applied for determination of atrazine in spiked river water samples and its accuracy was evaluated by comparison with the batch standard addition approach, which revealed that there is no evidence of statistically significant differences between the two methods. 相似文献
66.
Santos E Schühle DT Jones H Schmickler W 《Langmuir : the ACS journal of surfaces and colloids》2005,21(14):6406-6421
The nonlinear optical properties of self-assembled monolayers obtained from bonding two different alpha-functionalized terthiophenes (alpha-T3) to (111) silver electrode surfaces have been investigated using second harmonic generation (SHG). The two (alpha-T3) compounds used were functionalized with alkane chains of different lengths (C8 and C4), and each was terminated with a thiol anchoring group. A nitrile group was attached to the terminal thiophene ring of the (alpha-T3) compound with the C4 chain. The orientation of the polarization of the incident beam was changed systematically and gradually between "p" and "s" orientation and the SH signal (isotropic and anisotropic contributions) analyzed in both directions ("P" and "S"). The symmetry of the system was reduced by the presence of the adlayers from C3v to C3. The dependence on the applied potential and the incident wavelength has also been studied. The relative magnitudes and phases of the various second-order tensor elements have been estimated and compared with the values for a bare surface. A resonance process in the (alpha-T3) pi moiety has been investigated, and from this, the effective "band-gap" energies of the organic semiconductor SAMs (i.e., the energy difference between the pi-pi bands) have been estimated. 相似文献
67.
M. J. L. Santos A. F. Rubira R. M. Pontes E. A. Basso E. M. Girotto 《Journal of Solid State Electrochemistry》2006,10(2):117-122
Much effort has been made to synthesize novel compounds and enhance the optical properties of poly(terthiophenes). The electrochromic
properties of poly(4,4′′-dimetoxy-3′-methyl-2′-5′,2′′-terthiophene) (PDMMT) and poly(4,4′′-dipentoxy-3′-methyl-2′-5′,2′′-terthiophene)
(PDPMT) have been studied focusing on the differences in the alkoxy-group length. Theoretical calculations were employed to
elucidate the structural and thermodynamic stability of the monomers and dimmers. The results showed that in this type of
thiophenes large alkoxy chains assist positive charge dispersion through hyperconjugative effect. Thus, PDPMT is thermodynamically
more stable than PDMMT in the oxidized state, leading to better electrochromic stability and optical memory. 相似文献
68.
L. L. M. Santos J. A. Osso S. G. Araujo 《Journal of Radioanalytical and Nuclear Chemistry》1995,200(3):227-232
The development of an automated water target for the production of18F is described. The system was fully fested and shown to be reliable and secure. The chemical separation of18F was carried out using an anionexchange resin and K2CO3 as eluent. The18F production yields were, on average, (4.81±0.42) MBq/Ah and the specific activity was higher than 6.623×105 MBq/mmol. Heat transfer measurements and calculations were made. 相似文献
69.
The reaction between copper (II) and azide has been studied spectrophotometrically at four wavelengths, at 25 degrees , and ionic strength 4.00M (sodium perchlorate). The formation constants beta(2) and beta(3) found are 2.90 +/- 0.08 x 10(4) and 3.02 +/- 0.07 x 10(6) respectively. The results obtained from potentiometric measurements with a solid-state electrode disagree with those calculated from the spectrophotometric data. Causes of the discrepancy are discussed. 相似文献
70.
Ladislaus Szekeres und Elisabeth Sugár 《Fresenius' Journal of Analytical Chemistry》1960,172(1):35-38
Zusammenfassung Zur Bestimmung von Sulfit und Thiosulfat nebeneinander wird folgendes Verfahren beischrieben: In einem aliquoten Teil der zu untersuchenden Lösung wird mit elementarem Jod oxydiert, wobei die Sulfitionen zwei Äquivalente, die Thiosulfationen ein Äquivalent Jod je Mol verbrauchen. In einem zweiten aliquoten Teil der zu untersuchenden Lösung werden die Ionen mit — aus KBrO3 + KBr hergestelltem — NaOBr oxydiert; die Sulfitionen verbrauchen dabei zwei Äquivalente, die Thiosulfationen acht Äquivalente Brom je Mol. 相似文献