四氟乙烯齐聚体的反应 四氟乙烯四、五聚体和芳香胺的反应

前已报道四氟乙烯四聚体(全氟-3,4-甲基己烯-3)(1)、五聚体(全氟-3,4-二甲基-4-乙基己烯-2)(2)和脂肪烷氧以及脂肪胺的亲核反应.本文报道化合物1,2和芳香胺如苯胺、β-萘胺的反应.由于烯烃1、2双键处于分子中间,因而当亲核试剂进攻时,双键容易发生重排,生成的末端基烯烃更具反应性,故导致一取代、二取代、三取代以及环化降解等复杂产物.     

Modeling of the pseudo-colloids migration for multi-member decay chains with a arbitrary flux boundary condition in a fractured porous medium

A deep geologic disposal is the prime option for the long-term isolation of high-level radioactive waste (HLW) in many countries. For deeply located repositories, a radionuclide released from a failed waste container moves through the engineered and natural barriers before it reaches a biosphere. The pseudo-colloid which a radionuclide is adsorbed on a moving natural humic or fulvic colloid can be generated in a fractured porous medium. The size of a colloid is in general in the order of a hundred nanometer so that its migration velocity in a fracture is higher than that of a radionuclide due to the hydrochromatic effect. A large colloid cannot diffuse easily into a surrounding rock. Also, there are many kinds of actinides and these actinides have decay chains. In this analysis, the canonical form solution is derived for a pseudo-colloid and a solute in a fracture and a surrounding rock with a realistic inlet boundary condition with multi-member decay chains. It is used the Fortran based a computational code which uses a special subroutine for the inversion of Laplace transform. Consequently, the role of the pseudo-colloid in the fractured porous medium is important and also their decay chains aren’t neglected in the performance assessment of the HLW.     

PHOTOCHEMISTRY OF QUINOLYLMETHYLISOTHIORONIUM SALTS. GUANINE SELECTIVE DNA PHOTOCLEAVAGE REAGENTS

Quinolylmethylisothioronium salts (1a and 4a) cleave DNA upon irradiation. The cleavage is more than 10-fold enhanced by piperidine treatment and subsequently shows a high preference for guanines. Photolysis of 1a, 2a and 4a in water at lambda greater than 300 nm resulted in photoheterolysis. Irradiation of 1a in 2-propanol gave only products from photohomolysis, irradiation of 1a in methanol and 2a and 4a in 2-propanol resulted in products from both photoheterolysis and photohomolysis. Quantum yields for the disappearance of 1a in water and 2-propanol were determined. The presence or absence of oxygen had no effect in water, whereas oxidation products were observed upon irradiation in methanol and 2-propanol in the presence of oxygen. The guanine specific DNA photoreaction is proposed to take place by alkylation at N7 via the quinolylmethyl carbocation and thus to represent a photoalkylation.     

Regularities of binary condensation of vapors when one of them is undersaturated

Simple analytical expressions are derived for the stationary concentration of a binary solution in a markedly supercritical droplet growing exothermically in diffusion or free-molecular regimes in mixed vapors when one of condensing vapors is supersaturated and present in a small amount and another vapor is slightly undersaturated and present in a large amount. The condensation of sulfuric acid and water vapors on a droplet under the conditions of Earth atmosphere is considered as an example of practical importance. Under isothermic conditions, analytical expressions are obtained for the time of establishing a power law for variations in a droplet radius with time under the diffusion and free-molecular regimes of the droplet growth. The power laws are derived in an explicit form under these regimes, which describe the rapid establishment of a stationary concentration of a solution in a growing droplet.     

Fast choice of separation conditions for analyses by capillary zone electrophoresis using an information system Xemic

An information system Xemic applicable in analytical chemistry is described and its use in capillary electrophoresis for searching suitable separation conditions is demonstrated. This system is capable to provide suitable separation conditions even for analytes for which no electrophoretic experiments have been published so far. The system works with a database of components of anionic character the analyses of which have been performed, published in reviewed scientific journals, and included into a database created by an expert. Moreover, the system learned to search also in abstracts or complete scientific articles to find articles dealing with the determination of a substance in a given sample matrix. When no experiments have been published so far for a defined substance in a specific matrix, Xemic shows the separation conditions for determination of the substance regardless of the matrix. When no response can be found for the analyte of interest at all, the system Xemic works like an expert in the field and searches chemically similar substances and offers a series of substances the physicochemical properties of which are close to the followed analyte with respect to the behavior in the electric field, and shows working conditions for their analysis. Thus, the analyst puts only the order in the form of a given analyte in a given matrix and obtains a recommendation of a separation system that should enable to perform a successful separation. The system is not rigid and enables the operator to change the importance of individual attributes used in similarity search so as to obtain a broader or narrower group of similar components. With a certain probability the analyte of interest can be successfully analyzed under separation conditions that suited for the analysis of the most similar substances in the given matrix.     

Real-time monitoring of brain energy metabolism in vivo using microelectrochemical sensors: the effects of anesthesia

Rats were implanted in the striatum with a Pt/Ir electrode for measurement of regional cerebral blood flow (rCBF) (H(2) clearance technique), a carbon paste electrode for monitoring tissue oxygen and a glucose biosensor for monitoring extracellular glucose. Changes in all three parameters were recorded in response to the intraperitoneal (i.p.) administration of the anesthetics chloral hydrate (350 mg/kg), sodium pentobarbitone (60 mg/kg) and ketamine (200 mg/kg). An i.p. injection of normal saline, given as a control for the injection of the anesthetics, produced a parallel increase in rCBF and tissue oxygen accompanied by a brief decrease in extracellular glucose. Changes in tissue oxygen reflected the changes in rCBF; there was a decrease in both after sodium pentobarbitone, a decrease followed by a rebound after ketamine and a transient increase after chloral hydrate. All three anesthetics produced a decrease in extracellular glucose. The disparity between the changes in glucose and the changes in rCBF and oxygen suggests that during anesthesia, the reduction in extracellular glucose is not due to a reduction in the direct delivery of glucose from the blood vascular system. These results also indicate that levels of enzymatic substrates and mediators, which are intrinsic to the design and operation of amperometric biosensors, are clearly altered in a complex manner by anesthesia and suggest that caution should be exercised in extrapolating data from acute anesthetized experiments to normal physiology.     

Polarization curve of partially degraded catalyst layer

A model of a partially degraded catalyst layer (CL) in a fuel cell is reported. The degradation is modeled as a lowering of the exchange current density in a sub-layer at the membrane/CL interface. Degradation of 30 to 40% of the CL thickness may dramatically increase the polarization voltage. At a large current density, the voltage loss in such a two-layer system is close to the loss in a fully degraded CL. Estimates of this effect for a PEMFC cathode and a DMFC anode are performed.     

Characteristics of atomic vibrational motion in a one-component defective crystal

Vibrations of atoms in a defective argon crystal are considered. Frequencies are calculated in the harmonic approximation and Mie and Einstein approximations. The vibrations are calculated for a set of local clusters differing in the position of a vacancy at different distances from a selected atom. Probabilities for these clusters are calculated within a quasichemical approximation of the lattice gas model. It is shown that when combined contributions from lateral interactions and vibrational motions are allowed for in the free crystal energy, there is an increase in the lattice constant upon a rise in temperature in all approximations. It is found that the frequencies calculated using the Mie model become closer to the frequency distribution in the harmonic approximation as the degree of crystal defectiveness increases.     

CSTR和批式反应器中酶法拆分萘普生的比较

比较了批式反应器和连续流动搅拌反应器中酶动力学拆分萘普生的不同之处。从宏观反应器平衡角度,推导出了在ＣＳＴＲ中不同于在批式反应器中的酶立体选择性,产物对映体过量值和反应转化率的定量关系式,并通过脂肪酶催化的萘一甲酯的不对称水解反应得到了证实。     

Droplet formation in a thin layer of a two-component solution under the thermal action of laser radiation

Droplet growth in thin layers of water-alcohol solutions under the effect of a concentration-induced capillary flow, which is governed by a laser electromagnetic radiation, is investigated. It is established that an increase in water concentration in a solution accelerates the droplet growth. In low-concentrated solutions, a droplet may reach a quasi-steady state, in which its diameter is no larger than the diameter of the light beam projection onto the layer. A rise in the radiation power above an optimal magnitude decelerates the droplet growth. In low-concentrated solutions, this deceleration results from a decrease in the flow that feeds the droplet, while in high-concentrated solutions, it is due to a droplet constriction and an increase in its curvature radius.     

Guest-induced assembly of tetracarboxyl-cavitand and tetra(3-pyridyl)-cavitand into a heterodimeric capsule via hydrogen bonds and CH-halogen and/or CH-pi interaction: control of the orientation of the encapsulated guest

The guest- or solvent-induced assembly of a tetracarboxyl-cavitand 1 and a tetra(3-pyridyl)-cavitand 2 into a heterodimeric capsule 1.2 in a rim-to-rim fashion via four intermolecular CO(2)H.N hydrogen bonds has been investigated both in solution and in the solid state. In the (1)H NMR study, a 1:1 mixture of1a and 2a (R = (CH(2))(6)CH(3)) in CDCl(3) gave a mixture of various complicated aggregates, whereas this mixture in CDCl(2)CDCl(2) or p-xylene-d(10) exclusively produced the heterodimeric capsule 1a.2a. It was found that an appropriate 1,4-disubstituted-benzene is a suitable guest for inducing the exclusive formation of 1a.2a in CDCl(3). The ability of a guest to induce the formation of guest-encapsulating heterodimeric capsule, guest@(1a.2a), increased in the order p-ethyltoluene < 1-ethyl-4-methoxybenzene < or = 1-ethyl-4-iodobenzene < or = 1,4-dibromobenzene < 1-iodo-4-methoxybenzene < or= 1,4-dimethoxybenzene < or = 1,4-diiodobenzene. The (1)H NMR study revealed that a CH-halogen interaction between the inner protons of the methylene-bridge rims (-O-H(out)CH(in)-O-) of the 1a and 2a units and the halogen atoms of 1,4-dihalobenzenes and a CH-pi interaction between the methoxy protons of 1,4-dimethoxybenzene and the aromatic cavities of the 1a and 2a units play important roles in the formation of 1,4-dihalobenzene@(1a.2a) and 1,4-dimethoxybenzene@(1a.2a), respectively. A preliminary single-crystal X-ray diffraction analysis of guest@(1b.2b) (R = (CH(2))(2)Ph; guest = 1-iodo-4-methoxybenzene or p-xylene) confirmed that the guest encapsulated in 1b.2b is oriented with the long axis of the guest along the long axis of 1b.2b and that the iodo and the methoxy groups of the encapsulated 1-iodo-4-methoxybenzene are specifically oriented with respect to the cavities of the 2b and 1b units, respectively.     

Quantification of the effect of nonphotochemical quenching on the determination of in vivo chl a from phytoplankton along the water column of a freshwater reservoir

Nonphotochemical quenching (NPQ) is a well-known collection of different photoprotective mechanisms of plants and algae to avoid photodamage under an excess of light energy. In order to evaluate the overall effect of NPQ processes on the fluorometric determination of in vivo Chl a from a phytoplankton community dominated by diatoms, we compared the results obtained by two different fluorometric field devices with the total concentration of extracted Chl a measured by HPLC ( in vitro Chl a ). A different set of measurements were made to assess the performance of these fluorometers at high, moderate and low irradiance conditions. The Fbbe fluorometer, which is capable of distinguishing different algal groups according to their pigment content, allowed a better determination of in vivo Chl a under high irradiance conditions, with only a 10% mean difference from the in vitro Chl a concentration. In turn, the FMII fluorometer underestimated by as much as 50% the in vitro Chl a concentration under the same light conditions. As data from both fluorometers were in accordance with the in vitro Chl a values at moderate irradiance levels, the differences observed at high irradiances were attributed to the decrease in the yield of Chl a fluorescence caused by photoprotective NPQ processes. Accordingly, we estimated the effect of NPQ processes on the in vivo Chl a determination and the results allow us to provide an equation to correct this effect when in situ fluorometric measurements are carried out under high irradiance regimes. Our results demonstrate that under certain circumstances NPQ seriously compromises the results obtained by in situ fluorometric probes and highlight the need for a cautious interpretation of field data under such environmental conditions.     

Study of the direct detection of crosslinks in hydrocarbons by 13C-NMR. I. Preparation and characterization of model compound 1,1,2,2-tetra(tridecyl) ethane

The present series of papers is the commencement of a study aimed at the direct detection and quantification of crosslinking in hydrocarbons with the ultimate objective of a precise study of radiation-induced crosslinking in polyethylene. The subject of the present paper is the synthesis of a model compound containing a crosslink in a well-defined position sufficiently remote from the chain ends to be representative of an average crosslink in polyethylene. Such a compound in the form of 1,1,2,2-tetra(tridecyl) ethane has been synthetized and isolated in pure form in the course of the present work. Melting points and x-ray spacings of the new compound have been determined, and a comparison with the corresponding linear paraffins has been made. Effects are noted relating to the influence of molecular shape on the GPC elution volume, in which context an observation on a cyclic paraffin is also quoted.     

Hydrogen-bond-assisted control of H versus J aggregation mode of porphyrins stacks in an organogel system

To obtain insights into a correlation relationship between the structure and the aggregation mode in an organogel system, we synthesized gelators 2a-4a bearing a porphyrin moiety as a one-dimensional aggregation unit and amide groups as peripheral hydrogen-bonding sites. Gelators 3a and 3b bearing the amide groups at the 4-position of the meso-phenyl groups are classified as versatile gelators, gelating 10 and 14 solvents, respectively, among 23 solvents tested herein. In contrast, gelators 2a and 4a bearing the amide groups at the 3,5-positions and 3-position, respectively, are classified as poor gelators. Examination by spectroscopic methods (UV-vis, ATR-FTIR, XRD, etc.) revealed that in the organogel phase porphyrins in 3a adopt the H aggregation mode whereas those in 2a and 4a adopt the J aggregation mode. X-ray analysis of the single crystals established that in fact 3b features a columnar stack of porphyrin moieties that can be classified as the H-aggregate, whereas 2a results in a two-dimensional a-b plane, in which porphyrin moieties are arranged in the J-aggregate. Very interestingly, the difference in the H versus J aggregation mode is well-reflected by the difference in the macroscopic aggregate morphology observed by SEM: 3a + cyclohexane gel results in a one-dimensionally aggregated fibrillar structure, whereas 2a + cyclohexane gel results in a two-dimensional sheetlike structure. These findings indicate that the H versus J aggregation mode of porphyrin stacks can be controlled by the peripheral hydrogen-bonding interactions and the microscopic hydrogen-bonding network structure is well-reflected by the macroscopic SEM-observed structure.     

Multiple Li positions inside oxygen octahedra in lithiated TiO2 anatase

Intercalation of Li in TiO2 anatase results in a phase separation in a Li-poor and a Li-rich phase. The local lithium configuration in the coexisting crystallographic phases is resolved by detailed analysis of neutron diffraction data. In each of the phases, two distinct positions within the octahedral interstices are found, with a temperature-dependent occupancy. A combination of quasi-elastic neutron scattering and force field molecular dynamics simulations shows that Li is hopping on a picosecond time scale between the two sites in the octahedral interstices. The results also suggest a specific Li arrangement along the crystallographic a direction, albeit without long range order. It is likely that multiple discrete Li sites within a distorted oxygen octahedron occur not only in intercalated TiO2 anatase but also in other (transition metal) oxides.     

Study of the electrochemical reduction of dioxygen in acetonitrile in the presence of weak acids

The electrochemical reduction of dioxygen has been studied in acetonitrile at glassy-carbon electrodes. The initial step is the reversible one-electron reduction to form superoxide. In the presence of hydrogen-bond donors (water, methanol, 2-propanol), the superoxide forms a complex with the donor resulting in a positive shift in the potential that can be analyzed to obtain formation constants for these complexes. Stronger acids result in protonation of the superoxide followed by reduction to produce HO2-. In the absence of hydrogen-bond donors, the reduction of superoxide occurs at very negative potentials, and this second reduction peak is very much drawn-out along the potential axis, indicating a small value of the transfer coefficient, alpha. The addition of hydrogen-bond donors, HA, brings about a positive shift in this peak, without a noticeable change in shape. The reaction occurring at the second peak is a concerted proton and electron transfer (CPET) in which the electron is transferred to superoxide and a proton is transferred from HA to the superoxide, forming HO2- and A- in a concerted process. An estimation of the standard potential for this reaction shows that the second reduction always occurs at a high driving force, which explains the small value of alpha that is observed. Consistent with a CPET, a kinetic isotope effect, HA versus DA, was detected for the three hydrogen-bond donors. The increasing positive shift of the second peak with increasing water concentration has been interpreted as being a consequence of the change in the formal potential, as water is both a reactant in the process and a participant through the hydrogen-bond stabilization of the anions.     

Orbital signatures of methyl in L-alanine

Molecular orbital signatures of the methyl substituent in L-alanine have been identified with respect to those of glycine from information obtained in coordinate and momentum space, using dual space analysis. Electronic structural information in coordinate space is obtained using ab initio (MP2/TZVP) and density functional theory (B3LYP/TZVP) methods, from which the Dyson orbitals are simulated based on the plane wave impulse approximation into momentum space. In comparison to glycine, relaxation in geometry and valence orbitals in L-alanine is found as a result of the attachment of the methyl group. Five orbitals rather than four orbitals are identified as methyl signatures. That is, orbital 6a in the core shell, orbitals 11a and 12a in the inner valence shell, and orbitals 19a and 20a in the outer valence shell. In the inner valence shell, the attachment of methyl to glycine causes a splitting of its orbital 10a' into orbitals 11a and 12a of L-alanine, whereas in the outer valence shell the methyl group results in an insertion of an additional orbital pair of 19a and 20a. The frontier molecular orbitals, 24a and 23a, are found without any significant role in the methylation of glycine.     

TDP-mycaminose biosynthetic pathway revised and conversion of desosamine pathway to mycaminose pathway with one gene

Analysis of the tylosin gene cluster in Streptomyces fradiae uncovered an ORF, tyl1a, homologous to a hexose 3,4-isomerase found in Aneurinibacillus thermoaerophilus. Inclusion of the tyl1a gene along with other mycaminose biosynthetic genes (tylB, tylM1, tylM2, tylM3) identified in previous studies in an in vivo expression system successfully reconstituted the mycaminose pathway. Expression of tyl1a alone in the S venezuelae KdesI mutant converted a desosamine pathway to a mycaminose pathway. These results strongly support the role of Tyl1a as a TDP-4-keto-6-deoxy-d-glucose 3,4-isomerase.