Evaporation rate from aerosol OT-water-n-heptane inverse micellar systems

The evaporation rate of aerosol OT-water-n-heptane inverse micellar systems was studied. The evaporation behavior of solutions was strongly affected when compared with pure heptane. The changes are related to the structure of the micelles and the properties of the water molecules dissolved in the micelles. The initial rate of evaporation reaches a maximum when the surfactant head groups are hydrated with three water molecules, a minimum when the first hydration shell of Na⁺ ions is completed, and then rises and stabilizes until the second hydration shell is completed. The presence of free water when the ratio water molecules to surfactant molecules exceeds 12 produces a new rise of the initial evaporation rate, which is always higher than that of puren-heptane.     

Modeling of Decay Rates for Molecules at an Island Surface

The decay rates for molecules at rough surfaces are studied via an island surface model, with particular emphasis on the effect due to the distribution of surface roughness. Two extreme cases are studied when the surface islands distribute themselves evenly and when they coalesce to form local clusters at the molecule-substrate interface. The optical properties of the interfacial layer in these two cases are described by the Maxwell-Garnett and the fractal-cluster models, respectively. Among other results, it is found that both enhancement and suppression of the surface-induced decay rates are possible due to the presence of roughness, with more dramatic suppression taking place when the surface islands coalesce to form clusters.     

Comparing Dichromate Oxidation and Size Exclusion Chromatography of Dissolved Carbohydrates

Standardised methods are used to characterise the pulp or cellulosic material for its alkali resistance and alkali solubility. Today, pulp is usually characterised by its solubility in sodium hydroxide. The characterisation test was based on the treatment of pulp with sodium hydroxide solution of a defined concentration, according to a specified procedure. The dissolved organic matter was then determined by dichromate oxidation. The results obtained by size exclusion chromatography showed that both the amount and the molecular weight of the dissolved carbohydrates vary when investigating solubility and α-cellulose content of pulps. The results show further that S₁₈ values obtained by dichromate oxidation are overestimated when characterising pulps containing higher amounts of hemicellulose and/ or short chain cellulose, compared with results obtained by the SEC method. On the contrary, S₁₀ values are overestimated when determined by dichromate oxidation in higher alpha pulps.     

Regression models with process variables and parallel blocks of raw material measurements

The topic of this paper is regression models based on designed experiments, where additional spectroscopic measurements are also available. This particular case describes a situation with two spectral blocks with no natural order: The blocks are parallel. Three methods are described, which combine least squares regression of the design variables with PCA or PLS on the spectra. The methods properties are explored in two simulation studies based on real experiments. The results show that the methods are equal when it comes to prediction, but interpretability varies. One of the methods, LS‐ParPLS, is especially interesting when it comes to interpretability because it splits the spectral information into two parts; information that is common in both blocks and information that is unique for each block. Copyright © 2008 John Wiley & Sons, Ltd.     

Electrophilic aromatic fluorination with fluorine: meta-Directed fluorination of anilines

Anilines are mainly or selectively fluorinated in the meta-position with F₂ when dissolved in triflic acid, sometimes in the presence of small quantities of antimony pentafluoride. The regioselectivity is increased when an electron-donating substituent is present at the para-position.     

掩膜诱导的光敏性三组分聚合物混合体系的自组装

采用含时金兹堡-朗道理论(time-dependent Ginzburg-Landau theory)研究了二维体系中光敏性三组分聚合物混合体系在掩膜诱导下的相行为.详细探讨了光化学反应速率、聚合物组分比和掩膜长宽比对相分离行为的影响.获得了不同条件下体系形貌结构的相图,通过对这些相图的分析得到了岛状、网络状、层状等有序结构形成的条件.研究表明,固定掩膜的长宽比(L:d=6:4),当C组分的浓度?C0.35和光化学反应速率Γ1×10~(-5)时,体系形成岛状结构;当?C0.4和Γ1×10~(-5)时,体系主要形成层状和网状结构.固定光化学反应速率(Γ=1×10~(-3)),当6:5≤L:d≤6:1和?C0.35时,体系形成岛状结构;当6:6≤L:d≤6:1和?C0.4时,体系主要形成层状和网状结构.固定C组分的浓度(?C=0.45),当Γ≥5×10~(-4)和6:6≤L:d≤6:1时,体系主要形成层状和网状结构.稳定性分析表明这些有序结构在去掉掩膜之后仍能稳定存在.     

5‐Aza‐7‐deazaguanine DNA: Recognition and Strand Orientation of Oligonucleotides Incorporating Anomeric Imidazo[1,2‐a]‐1,3,5‐triazine Nucleosides

The base‐pairing properties of oligonucleotides containing the anomeric 5‐aza‐7‐deazaguanine 2′‐deoxyribonucleosides 1 and 5 are described. The oligonucleotides were prepared by solid‐phase synthesis, employing phosphoramidite or phosphonate chemistry. Stable `purine'⋅purine duplexes with antiparallel (aps) chain orientation are formed, when the α‐D ‐anomer 5 alternates with the β‐D ‐anomeric 2′‐deoxyguanosine ( 2 ) within the same oligonucleotide chain. Parallel (ps) oligonucleotide duplexes are observed, when the β‐D anomer 1 alternates with 2 . A renewed reversal of the chain orientation (ps→aps) occurs when compound 1 pairs with 2′‐deoxyisoguanosine ( 6 ). In all cases, it is unnecessary to change the orientation within a single strand when α‐D units alternate with their β‐D counterparts. Heterochiral base pairs of 5 (α‐D ) with 2′‐deoxyisoguanosine (β‐D ) are well accommodated in duplexes with random base composition and parallel chain orientation. Base pairs of 5 (α‐D ) with 2′‐deoxyguanosine (β‐D ) destabilize duplexes with antiparallel chains.     

Highly Conducting and Flexible Radical Crystals

Together with high conductivity, high flexibility is an important property required for next generation organic electronic components. Both properties are difficult to achieve together especially when the components are crystalline because of the intrinsic high brittleness of organic molecular crystals. We report an organic radical crystal system that has both high flexibility and high conductivity. The crystal consists of 9,10‐bis(phenylethynyl)anthracene radical cation ( BPEA^.+ ) units, and shows flexibility under pressure with high conductivity in ambient condition exhibiting average conductivity of 2.68 S cm^?1 when normal linear shape, as well as 2.43 S cm^?1 when bent. The structural analysis reveals that both a short π–π distance (3.290 Å) between BPEA^.+ units that are aligned along the crystal length direction, and the presence of PF₆^? counter ions induce flexibility and high electrical conductivity.     

The effect of active component distribution in a porous structure of supported catalyst

The catalytic process in supported catalyst with nonuniform distribution of active component among the pores of different size is considered. Some previous as well as new estimates are presented. The limit value of diffusivity in small pores (D _L < 10^?8 cm²/s) is established, at which the distribution can takes an effect. That is possible in the case of capillary condensation, when micro-pores are filled with liquid while macro-pores are filled with gas. Such diffusivity is also observed at configuration or surface diffusion in zeolite channels. Then the distribution may influence the pellet effectivity when the activity of active component inside zeolite crystals is higher than that on its external surface.     

Improvement of Weyl’s Inequality

Consider the construction of an operator from the sum of two component operators. Weyl’s inequality gives a lower bound to an eigenvalue of the constructed operator using a single eigenvalue from each of the component operators. Using such minimal information gives a poor bound, however, and when the eigenvectors that correspond to the said eigenvalues of the component operators are known, Weyl’s inequality can be significantly improved by considering the overlap of the two eigenvectors. This improvement can sometimes be further improved when several eigenvectors of each component operator are known so that the overlap of sub-eigenspaces are considered instead. The improvement is best when there is minimal overlap and Weyl’s inequality returns when the overlap is complete. An example with the hydrogen molecular ion is presented which illustrates the superiority over Weyl’s inequality when eigenvector or sub-eigenspace information is utilized.     

Fluorescent photoionic devices with two receptors and two switching mechanisms: applications to pH sensors and implications for metal ion detection

Two leading designs of fluorescent sensors are combined to yield the novel hybrid system of the ‘Fluorophore-Receptor₁-Spacer-Receptor₂’ format. We use 4-(dialkylaminoalkylamino)-7-nitrobenzo-2-oxa-1,3-diazoles as examples. The emission from internal charge transfer excited states in the present instances are highly responsive to N-H deprotonation as well as being quenched by intramolecular tertiary amine groups via photoinduced electron transfer (PET). When applied to pH sensing, this leads in favourable cases to two steps in the fluorescence-pH profile which can be viewed as a multi-stable photoionic device, even though single steps are more usual. The former situation is favoured when the two proton-associated equilibria are sufficiently separated on the pH scale and when the PET process is of moderate efficiency. These systems have the added feature of excitation/emission wavelengths in the visible region. As a secondary theme, we point out that caution is required when designing sensors for transition metal ions from systems with intrinsically proton-sensitive fluorescence due to receptors either integrated with or spaced from the fluorophore.     

On the oximation of diaryl-β-diketones

The reaction of asymmetrically substituted β-diketones with hydroxylamine to give 3,5-diarylisoxazoles has been re-investigated, and has been found to occur with a low degree of site-selectivity unless steric effects are operating. The isoxazole that has the more electron-deficient aryl group in position 3 is formed preferentially when the reactions are run with hydroxylamine hydrochloride. When the reactions are performed in a neutral medium, a reversed site-selectivity is observed. Steric effects have a much stronger influence on the selectivity of the reaction: when a substituent is present in the ortho position(s) of the phenyl ring, the heterocycle bearing the ortho-substituted phenyl group in position 5 is obtained as the sole product both in acidic and in neutral medium.     

单取代苯分子中的电荷分布与定位效应

本文报道了一种简便计算一元取代苯分子中碳原子电荷分布的新方法,找出了判断定位效应的经验规则。     

A+B2表面催化反应相变及自振荡的蒙特卡罗模拟

用MonteCarlo法研究了脱附和E－R机理对不可逆催化氧化反应A＋1／2B2→AB的相交和自振荡的影响、结果表明，（1）催化剂表面A的脱附使ZGB模型中的一级相变点消失，但对二级相交点的影响很小；当有E－R机理参与时，二级相交点消失，且E－R过程的几率对一级相交点的影响较大；当A的脱附和E－R过程同时起作用时，上述反应不存在相交（2）在ZGB模型中的二级相变点附近，反应速率随时间的变化具有明显的振荡现象，在其它位置主要表现为噪音。引入A的脱附后在二级相交点附近明显的自振荡现象依然存在；当E-R过程起作用时，随着二级相交点的消失，明显的振荡现象亦随之消失．（3）A的脱附和E－R过程对上述反应相变的影响与A的表面扩散对相变的影响有着本质的区别，因为后者只能改变相变点的位置而不能改变相变点的存在状况．     

On the evolution and application of the concept of electrochemical polarization

This paper yields an overview on the evolution of the concept of polarization applied to electrochemical systems, ranging from electrodes to cells. The historical discussion starts at the early phase of the development of electrochemistry when current-controlled measurements were possible only, and when the early definitions of polarization, depolarization and depolarizer were created. A number of contemporary handbooks, recommendations and other reference resources are listed in which these concepts are represented in various ways, from conservative definitions to attempts of redefining them. The traditional definitions are confronted with the everyday use of professional language, drawing attention to the fact that the widespread application of potential-controlled electrochemical measurements led to new meanings. Some suggestions are made that open room for the application of the term of polarization in accord with the modern methodologies, without compromising the traditional introduction of the term. Polarization-related phenomena in biological membranes are not dealt with in the present work.

     

Slater orbital molecular integrals with numerical fourier transform methods. I. (coplanar) multicenter exchange integrals over 1s orbitals

Slater orbital r₁₂^?1 integrals are calculated with a numerical Fourier-transform method based on a formulation first given by Bonham, Peacher and Cox. Spherical wave expansions are introduced that decouple the Feynman integrations for the charge distribution Fourier transforms. The Feynman integrals are evaluated semianalytically, and their properties are analyzed in detail. The final computational step involves a numerical integration over charge distribution quantities. Results for (coplanar) multicenter exchange integrals over 1s orbitals are given. As long as the charge distributions are overlapping considerably, the method gives good results, even when these distributions are highly asymmetric. The method as presently implemented fails when highly disconnected charge distributions are involved.     

Structural transformations in macromolecules of synthetic nonionogenic polymers and DNA in salt-containing aqueous solutions

The influence of salt additives on structural transformations in macromolecules of synthetic polymers free of ionogenic groups and DNA molecules has been determined with the use of the nanosecond dynamics luminescent method. When polyvalent metal salts are added, a coil-globule transition is observed in macromolecules of poly(N-n-propylmethacrylamide), while structural transformations occur in DNA macromolecules in aqueous solutions, processes that are accompanied by the passage of low-molecular-mass organic cations intercalated into DNA into solution. These transformations make themselves evident when polyvalent metal ions are added in an amount of one Mt³⁺ ion per ten phosphate groups of DNA. The same effect takes place when salts of polycations are added to solutions of DNA-polycation interpolyelectrolyte complexes.     

Some aspects of graft polymerization of vinyl monomers onto cellulose with the use of tetravalent cerium. V

The presence of occluded air lowers the ceric consumption between the beginning and end of the reaction time, decreases the grafting parameters, and increases the copper number. Grafting reactions carried out in presence of organic solvents show parameters that are lower than those obtained when the reactions are carried out in water. Solvents with high chain-transfer constants cause a marked decrease in the yield relative to the solvents of low chain-transfer constants. Conversion percentages are similarly influenced. However, the donor alcohols enhance polymer formation with the acceptor monomers; this is attributed to the ability of ceric salt solution to oxidize alcohol and hence initiate polymerization reaction. Scavenging of the free radicals by certain alcohols and competition between alcohol and cellulose for the ceric consumption are responsible for the low grafting yields achieved. The order of reactivity of monomers may change when solvents are used; it follows the relative differences in the chaintransfer constant of solvent with the different monomers. Pseudografting and complex formation, when they occur, interfere with the results achieved.     

New transformations involving squarate esters. Multi-channel rearrangement options available to 2-(dimethoxy-methyl)-1-cycloalken-1-yl adducts

The Vilsmeier-Haack reaction of cyclic ketones with PBr₃ and DMF is an effective means for generating β-bromo-α,β-unsaturated aldehydes, which are readily transformed into their dimethyl acetals. These bromides are conveniently amenable to halogen-metal exchange in the presence of tert-butyllithium. The resultant organometallic intermediates, when treated with an equimolar amount of diisopropyl squarate, undergo 1,2-addition to deliver α-hydroxy ketone adducts that have proven to be sensitive to different rearrangements when in the presence of silica gel or boron trifluoride etherate. Although both processes involve net ring expansion of the cyclobutene ring with loss of methanol, the similarity stops there. In the first instance, spirocyclic diketones are produced by 1,2-shift of either of two ring carbons. In the second, extensively conjugated lactones are generated. The behavior of the adduct originating from a lithiated quinone bisketal has also been scrutinized.     

Changes of vibrational lifetimes with minor structural modification of small polyatomic molecules

Substantial changes of population lifetimes of CH-stretching modes are observed when two atoms are exchanged in CH₂CCl₂ to form trans CHClCHCl and when three deuterons are substituted in C₆H₆ to form 1,3,5.-C₆H₃D₃. The measured lifetimes are in good agreement with estimates based on Fermi resonance-mixing which is inferred from infrared and Raman spectra.