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61.
A novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and yE(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized. 相似文献
62.
The kinetics of the reaction of the CH3CHBr, CHBr2 or CDBr2 radicals, R, with HBr have been investigated in a temperature-controlled tubular reactor coupled to a photoionization mass spectrometer. The CH3CHBr (or CHBr2 or CDBr2) radical was produced homogeneously in the reactor by a pulsed 248 nm exciplex laser photolysis of CH3CHBr2 (or CHBr3 or CDBr3). The decay of R was monitored as a function of HBr concentration under pseudo-first-order conditions to determine the rate constants as a function of temperature. The reactions were studied separately from 253 to 344 K (CH3CHBr + HBr) and from 288 to 477 K (CHBr2 + HBr) and in these temperature ranges the rate constants determined were fitted to an Arrhenius expression (error limits stated are 1σ + Student’s t values, units in cm3 molecule−1 s−1, no error limits for the third reaction): k(CH3CHBr + HBr) = (1.7 ± 1.2) × 10−13 exp[+ (5.1 ± 1.9) kJ mol−1/RT], k(CHBr2 + HBr) = (2.5 ± 1.2) × 10−13 exp[−(4.04 ± 1.14) kJ mol−1/RT] and k(CDBr2 + HBr) = 1.6 × 10−13 exp(−2.1 kJ mol−1/RT). The energy barriers of the reverse reactions were taken from the literature. The enthalpy of formation values of the CH3CHBr and CHBr2 radicals and an experimental entropy value at 298 K for the CH3CHBr radical were obtained using a second-law method. The result for the entropy value for the CH3CHBr radical is 305 ± 9 J K−1 mol−1. The results for the enthalpy of formation values at 298 K are (in kJ mol−1): 133.4 ± 3.4 (CH3CHBr) and 199.1 ± 2.7 (CHBr2), and for α-C–H bond dissociation energies of analogous compounds are (in kJ mol−1): 415.0 ± 2.7 (CH3CH2Br) and 412.6 ± 2.7 (CH2Br2), respectively. 相似文献
63.
Interlaboratory comparisons for the analysis of mineral oil in polluted soil using the GC–FID method indicate that extraction
and cleanup conditions have significant effects on the analytical results. In this investigation a ruggedness test was performed
on the extraction and cleanup method for the determination of total petroleum hydrocarbons in soil. A two-level Plackett–Burman
design was utilized to study the effect of 11 different method parameters on the extraction recovery of total petroleum hydrocarbons
(TPH) in soil. Both qualitative and quantitative factors were investigated. The results indicate that total petroleum hydrocarbons
can be relatively reliably monitored through strict implementation of the ISO and CEN draft standards. However, variation
in certain method parameters readily affects the validity of the results. The most critical factors affecting TPH recovery
were the solvent and co-solvent used for extraction, the extraction time, adsorbent and its weight and sample TPH concentration.
Because adaptation of the draft standards especially with respect to these factors easily leads to TPH recoveries higher than
200% or lower than 70%, the validity of the adapted method should always be verified. A proper estimate of the expanded uncertainty
should also be appended to TPH results, because only then can the reliability of the results be guaranteed and further justification
is gained to support the end-use of the data. This also supports the credibility of the analytical services and prevents the
data end-users from drawing misleading conclusions concerning the environmental risks and potential remediation requirements. 相似文献
64.
Dr. Stefan H. A. M. Leenders René Becker Dr. Tatu Kumpulainen Prof. Dr. Bas de Bruin Dr. Tomohisa Sawada Taito Kato Prof. Dr. Makoto Fujita Prof. Dr. Joost N. H. Reek 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(43):15468-15474
There is broad interest in molecular encapsulation as such systems can be utilized to stabilize guests, facilitate reactions inside a cavity, or give rise to energy‐transfer processes in a confined space. Detailed understanding of encapsulation events is required to facilitate functional molecular encapsulation. In this contribution, it is demonstrated that Ir and Rh‐Cp‐type metal complexes can be encapsulated inside a self‐assembled M6L4 metallocage only in the presence of an aromatic compound as a second guest. The individual guests are not encapsulated, suggesting that only the pair of guests can fill the void of the cage. Hence, selective co‐encapsulation is observed. This principle is demonstrated by co‐encapsulation of a variety of combinations of metal complexes and aromatic guests, leading to several ternary complexes. These experiments demonstrate that the efficiency of formation of the ternary complexes depends on the individual components. Moreover, selective exchange of the components is possible, leading to formation of the most favorable complex. Besides the obvious size effect, a charge‐transfer interaction may also contribute to this effect. Charge‐transfer bands are clearly observed by UV/Vis spectrophotometry. A change in the oxidation potential of the encapsulated electron donor also leads to a shift in the charge‐transfer energy bands. As expected, metal complexes with a higher oxidation potential give rise to a higher charge‐transfer energy and a larger hypsochromic shift in the UV/Vis spectrum. These subtle energy differences may potentially be used to control the binding and reactivity of the complexes bound in a confined space. 相似文献
65.
Jorma K. Merikoski 《Czechoslovak Mathematical Journal》2016,66(3):1027-1038
Consider the n×n matrix with (i, j)’th entry gcd (i, j). Its largest eigenvalue λn and sum of entries sn satisfy λn > sn/n. Because sn cannot be expressed algebraically as a function of n, we underestimate it in several ways. In examples, we compare the bounds so obtained with one another and with a bound from S.Hong, R.Loewy (2004). We also conjecture that λn > 6π?2nlogn for all n. If n is large enough, this follows from F.Balatoni (1969). 相似文献
66.
Viitala T Hautala JT Vuorinen J Wiedmer SK 《Langmuir : the ACS journal of surfaces and colloids》2007,23(2):609-618
The adsorption of anionic phospholipids on silica was investigated by the dissipative quartz crystal microbalance (QCM) technique. Liposomes composed of 1 mM 80:20 mol % of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC)/phosphatidic acid, POPC/phosphatidylglycerol, or POPC/phosphatidylserine in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) buffer at pH 7.4 (with or without 3 mM of CaCl2) were examined. We have previously demonstrated that similar phospholipid coatings can be used in capillary electrochromatography as a stationary phase for the separation of analytes. In this work, we focus on the formation of the coatings and on the type of lipid structure formed on silica. The QCM investigation comprised qualitative results based on changes in frequency and resistance, and quantitative modeling of the obtained results. The latter was performed using the dissipative QCM, which measures the quartz crystal impedance, combined with equivalent circuit analysis. A previously developed coating and cleaning procedure for phospholipid-coated fused silica capillaries was adopted in this study, and the same silica-coated crystal was used throughout the QCM study. We will demonstrate in this work that the type of lipid structure formed on silica, that is, a rather rigid supported lipid bilayer or a viscoelastic supported vesicle layer (SVL), is highly dependent on the lipid and solvent composition. We also show for the first time that the modeling of the dissipative QCM data can be used to extract a more quantitative picture of an adsorbed SVL, because, so far, published studies have merely used the QCM data in a qualitative sense. 相似文献
67.
A Comparative Study of Pyrolysis Liquids by Slow Pyrolysis of Industrial Hemp Leaves,Hurds and Roots
Ayobami Salami Jorma Heikkinen Laura Tomppo Marko Hyttinen Timo Keklinen Janne Jnis Jouko Vepslinen Reijo Lappalainen 《Molecules (Basel, Switzerland)》2021,26(11)
This study assessed the pyrolysis liquids obtained by slow pyrolysis of industrial hemp leaves, hurds, and roots. The liquids recovered between a pyrolysis temperature of 275–350 °C, at two condensation temperatures 130 °C and 70 °C, were analyzed. Aqueous and bio-oil pyrolysis liquids were produced and analyzed by proton nuclear magnetic resonance (NMR), gas chromatography–mass spectrometry (GC-MS), and atmospheric pressure photoionization Fourier transform ion cyclotron resonance mass spectrometry (APPI FT-ICR MS). NMR revealed quantitative concentrations of the most abundant compounds in the aqueous fractions and compound groups in the oily fractions. In the aqueous fractions, the concentration range of acetic acid was 50–241 gL−1, methanol 2–30 gL−1, propanoic acid 5–20 gL−1, and 1-hydroxybutan-2-one 2 gL−1. GC-MS was used to compare the compositions of the volatile compounds and APPI FT-ICR MS was utilized to determine the most abundant higher molecular weight compounds. The different obtained pyrolysis liquids (aqueous and oily) had various volatile and nonvolatile compounds such as acetic acid, 2,6-dimethoxyphenol, 2-methoxyphenol, and cannabidiol. This study provides a detailed understanding of the chemical composition of pyrolysis liquids from different parts of the industrial hemp plant and assesses their possible economic potential. 相似文献
68.
The first synthetic route to amaminol A with use of an organocatalytic intramolecular Diels-Alder reaction is reported. The absolute stereochemistry is proven with a crystallographic image of a cyclic carbamate of amaminol A. 相似文献
69.
Detlev?Sülzle Marcus?Bauser Thomas?Frenzel Gregor?Jost Hubertus?Pietsch Martina?Sch?fer Markus?BergerEmail author Jorma?Hassfeld Heribert?Schmitt-Willich 《Journal of Cluster Science》2015,26(1):111-118
In recognition of the seminal contributions of F. A. Cotton and A. Bino to the field of aqueous chemistry of organometallic, trinuclear cluster compounds of tungsten, we describe their modifications and use as contrast agents for X-ray computed tomography. To enable their fundamental work for an advantageous diagnostic application in medicine a new generation of polydentate W3O2 complexes with improved hydrolytical stability has been synthesized and characterized. The applicability as new metal based contrast agent has been demonstrated in a computed tomography angiography animal study with increased signal intensity. Especially the bis tridentate W3O2 complexes with their reduced stereochemical complexity represent a promising new class in the field of X-ray contrast agents. 相似文献
70.
Jorma Roine Matti Murtomaa Markko Myllys Jarno Salonen 《Journal of Electrostatics》2012,70(5):428-437
The feasibility of electroencapsulation of mesoporous silicon (PSi) micro- and nanoparticles as a method to seal the PSi particles in mechanically processable solid units, and to facilitate time and site specific drug release from the pores of PSi particles, is of interest in the present work. Suitable microcapsules and micromatrix particles were produced in a single-step process using a setup with two electrospraying nozzles kept at high electric potentials of opposite polarities. The structures of the produced particles were analyzed by microscope and X-ray micro- and nanotomography imaging, and optimization of the electroencapsulation process production efficiency is discussed. 相似文献