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991.
Reza Behjatmanesh-Ardakani 《Theoretical chemistry accounts》2007,118(4):799-805
In some works on the lattice Monte Carlo simulation of amphiphilic systems additional peaks in the cluster size distribution
has been interpreted as a clue for the phase or shape transition of micellar aggregates. On the other hand, some other works
showed that the additional peaks are a result of finite size of the lattice box. In this paper using calculating energy-auto-correlation
function and statistical error in correlated data, it is shown that how these apparently contradictory results are the same.
To do this, we have simulated a pure system containing amphiphile and water molecules. A simple model of potential containing
the main feature for these systems (the hydrophobicity of surfactant molecules) that cause the aggregates to be formed is
considered to avoid any synthetic results due to additional non-real parameters. To relax the initial configuration faster,
configurational bias Monte Carlo move is used in addition to reptation move. Periodic boundary condition and self-avoiding
walks are used as former published works in this field. It is shown that the additional peaks is a result of the statistical
errors for averaged cluster size distribution and can not be interpreted as a clue for shape or phase transition. 相似文献
992.
N. A. Mohamed Farook 《Journal of solution chemistry》2007,36(3):345-356
The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each
of the 4-oxoacids, NCSA and H+. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition
state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA
with 4-oxoacids. 相似文献
993.
Electroactive conducting copolymers of aniline (ANI) and o-aminophenol (OAP) and two-layered poly(o-aminophenol) (POAP)/polyaniline (PANI) composites were prepared in aqueous acidic solution by electrode potential cycling.
Copolymerization was carried out at different feed concentrations of OAP and ANI on a gold electrode. A strong inhibition
of electropolymerization was found at a high molar fraction of OAP in the feed. The copolymers showed good adherence on the
electrode surface and gave a redox response up to pH=10.0. Two transitions were observed in the in situ conductivities of
the copolymers (as with PANI), but the conductivities were lower by 2.5–3 orders of magnitude as compared to PANI. Electrosynthesis
of PANI on POAP modified electrodes showed copolymer formation after reaction initiation and finally formation of a PANI layer
at the copolymer/solution interface. The ‘memory effect’ of the bilayer structures of both polymers was discussed in terms
of protonation/deprotonation and anion consumption taking place during redox processes of both polymers. 相似文献
994.
我们已对O(~3p)原子和酮类分子化学反应速率常数进行了系列测定,分析讨论了羰基对O(~3p)抽提氢原子反应速率的影响,关于O(~3p)与醛类分子反应速率的测定也有报道。本文用流动微波放电-化学发光光子计数方法测定O(~3p)原子与丙醛和正丁醛化学反应速率常数及其与温度的关系,并由动力学数据对醛基中C—H键的离解能进行了讨论。 相似文献
995.
In this paper, a sensitive and rapid chromatographic procedure using a selective analytical detection method (electrospray ionization-mass spectrometry in selected-ion monitoring mode) in combination with a simple and efficient sample preparation step is first presented for the determination of zaleplon in human plasma. The separation of the analyte, internal standard, and possible endogenous compounds are accomplished on a phenomenex Luna 5-microm C8(2) column (250- x 4.6-mm i.d.) with methanol-water (75:25, v/v) as the mobile phase. In order to optimize the mass detection of zaleplon, several parameters such as ionization mode, fragmentor voltage, m/z ratios of ions monitored, type of organic modifier, and eluent additive in the mobile phase are discussed. An internal standard is selected to guarantee the quantitative accuracy. Each analysis takes less than 6 min. The calibration curve of zaleplon in the range of 0.1-60.0 ng/mL in plasma is linear with a correlation coefficient of > 0.9992, and the detection limit (s/n = 3) is 0.1 ng/mL. The within- and between-day variations (relative standard deviation) in the zaleplon plasma analysis are less than 2.4% (n = 15) and 4.7% (n = 15), respectively. The application of this method is demonstrated for the analysis of zeleplon plasma samples in a Phase-I human pharmacokinetic study. 相似文献
996.
Gamil A. Al-Hazmi Mohammed S. El-Shahawi Ahmed A. El-Asmy 《Transition Metal Chemistry》2005,30(4):464-470
The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical CuI and CuIIIspecies stable only in the voltammetric time scale, The effects of substituents on E1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N1[H, CH3 or C6H5] and/or N4H [H, C2H5, C6H5 or pClC6H4] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E1/2 for the complexes due to remote substituent effects could be related to changes in basicity of N4H.Thus, variation in N41-J has more influence on E1/2 than changes in C=N1. The correlation between E1/2 of the complexes and pKa of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals. 相似文献
997.
Shinsaku Fujita 《Theoretical chemistry accounts》2007,117(3):353-370
Planted three-dimensional (3D) trees, which are defined as a 3D version of planted trees, are enumerated by means of Fujita’s
proligand method formulated in Parts 1–3 of this series [Fujita in Theor Chem Acc 113:73–79, 80–86, 2005; Fujita in Theor
Chem Acc 115:37–53, 2006]. By starting from the concepts of proligand and promolecule introduced previously [Fujita in Tetrahedron
47:31–46, 1991], a planted promolecule is defined as a 3D object in which the substitution positions of a given 3D skeleton are occupied by a root and proligands.
Then, such planted promolecules are introduced as models of planted 3D-trees. Because each of the proligands in a given planted
promolecule is regarded as another intermediate planted promolecule in a nested fashion, the given planted promolecule is
recursively constructed by a set of such intermediates planted promolecules. The recursive nature of such intermediate planted
promolecules is used to derive generating functions for enumerating planted promolecules or planted 3D-trees. The generating
functions are based on cycle indices with chirality fittingness (CI-CFs), which are composed of three kinds of sphericity
indices (SIs), i.e., a
d
for homospheric cycles, c
d
for enantiospheric cycles, and b
d
for hemispheric cycles. For the purpose of evaluating c
d
recursively, the concept of diploid is proposed, where the nested nature of c
d
is demonstrated clearly. The SIs are applied to derive functional equations for recursive calculations, i.e., a(x), c(x
2), and b(x). Thereby, planted 3D-trees or equivalently monosubstituted alkanes as stereoisomers are enumerated recursively by counting
planted promolecules. The resulting values are collected up to 20 carbon content in a tabular form. Now, the enumeration problem
initiated by mathematician Cayley [Philos Mag 47(4):444–446, 1874] has been solved in such a systematic and integrated manner
as satisfying both mathematical and chemical requirements. 相似文献
998.
Robin Zuluaga Jean-Luc Putaux Adriana Restrepo Iñaki Mondragon Piedad Gañán 《Cellulose (London, England)》2007,14(6):585-592
Cellulose microfibrils have been prepared from banana rachis using a combination of chemical and mechanical treatments. The
morphology and structure of the samples were characterized using transmission electron microscopy, atomic force microscopy,
and X-ray diffraction. Fourier-transformed infrared spectroscopy (FTIR) was used to characterize the chemical modifications
of the samples after each treatment. Suspensions of bundled or individualized 5-nm-wide microfibrils were obtained after homogenization
(PH) whereas an organosolv (PO) treatment resulted in shorter aggregates of parallel cellulose microcrystallites. The sharper
rings in the X-ray diffraction pattern of the PO-treated sample suggest a higher crystallinity due to a more efficient removal
of hemicelluloses and dissolution of amorphous zones by the acid treatment. Both microfibrils and microcrystals prepared by
both methods can be used as reinforcing filler in nanocomposite materials. 相似文献
999.
Standardising quality of measurements at both the national and international level results in a unity in measurement that
may be regarded a synonym of traceability. In gas analysis, the key issue in achieving this aim is production of gaseous reference
materials. Establishing a network of secondary measurement standards at gaseous CRM producers’ sites in Ukraine might be interesting
for those involved in gas analysis activities. Inevitably, problems concerning the recognition of measuring capabilities of
both national metrological institutes and local CRM producers are now an international issue. Thus, the problems of national
adoption of international standards, as well as harmonisation between different international documents are currently relevant,
and Ukrainian experience may be useful to others in this field.
Presented at the 3rd International Conference on Metrology, November 2006, Tel Aviv, Israel. 相似文献
1000.
A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of CeO2 powders produced from dissolved cerium nitrate salts. The conical reactor minimized particle recirculation and provided a
highly symmetrical and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of CeO2 powders. Both a calorimetric study of the reactor and a thermodynamic analysis of CeO2 formation were conducted. The sampling probe is described and near-isokinetic sampling was achieved. The sampled particles
were collected using a miniature wet collection system, i.e. a mist atomizer and a custom-made spray chamber. A numerical
simulation of the velocity and temperature fields of the plasma gas in the reactor was done using Fluent. A comprehensive
droplet-to-particle formation mechanism presented elsewhere is revisited and expanded based on calorimetry, thermodynamics
of CeO2 formation, numerical simulations and collected particles. No traces of other oxidation states other than CeO2 were found. 相似文献