二聚体系常数的计算方法

本文对计算二聚常数的方程组成求解法进行了改进，用改进方法计算了二磺化酞菁锌（Ｓ２ＰｃＺｎ）二聚常数。结果表明，Ｓ２ＰｃＺｎ的二聚常数随着ｐＨ的增大而减小，随离子强度的增大而增大。     

Chemical and electrochemical dimerization of BODIPY compounds: electrogenerated chemiluminescent detection of dimer formation

The electrochemistry of several difluoroboradiaza-s-indacene (BODIPY) compounds lacking substituent groups in the meso (8)- and/or 3 (α)-positions was investigated. Chemical and electrochemical dimerization was demonstrated, and the dimerization depended on the character of substitution. The chemical dimerization was achieved by oxidative coupling using FeCl(3) in CH(2)Cl(2) at 0 °C. The electrochemical dimerization proceeded via anodic oxidation to the radical cation and monitored by both cyclic voltammetry (CV) and electrogenerated chemiluminescence (ECL). An available open 3-position was important for the formation of the dimer. The resulting 3,3'-dimer produced a second peak in the CV oxidation and also the appearance of a longer wavelength ECL peak at 656 nm, which is considerably shifted from the parent peak at 532 nm. No dimerization was seen for BODIPY molecules in which only the meso 8-position was unsubstituted, either by chemical or electrochemical means, demonstrating that dimerization occurs at position 3.     

Theoretical comparison of ketene dimerization in the gas and liquid phase

We present the first theoretical comparison between ketene dimerization in gas phase and ketene dimerization in solution. Density functional theory (DFT) calculations on the ketene dimerization were carried out considering the following product dimers: diketene (d-I), 1,3-cyclobutanedione (d-II), 2,4-dimethylene-1,3-dioxetane (d-III), and 2-methyleneoxetan-3-one (d-IV). All structures were optimized at the PW86x+PBEc/DZP level of theory. Based on these geometries, a total of 58 meta and hybrid functionals were used to evaluate the heat of dimerization. The MPW1K functional was found to fit the experimental data best and subsequently used in the final analyses for all energy calculations. It was found on both kinetic and thermodynamic grounds that only d-I and d-II are formed during ketene dimerization in gas phase and solution. In gas phase, d-I is favored over d-II by 2 kcal/mol. However, the dimerization barrier for d-I is 1 kcal/mol higher than for d-II. Solvation makes dimerization more favorable. On the enthalpic surface this is due to a favorable interaction between the dimer dipole moment and solvent molecules. The dimer is stabilized further on the Gibbs energy surface by an increase of the dimerization entropy in solution compared to gas phase. The species d-I remains the most stable dimer in solution by 1 kcal/mol. Kinetically, the dimerization barriers for the relevant species d-I and d-II are cut in half by solvation, due to both favorable dimer-dipole/solvent interactions (DeltaH++, DeltaG++) and an increase in the activation entropies (DeltaS++). While the dimerization barrier for d-II is lowest for the gas phase and toluene, the barrier for d-I formation becomes lowest for the more polar solvent acetone by 1 kcal/mol as d-I dimerization has the most polar transition state.     

Modeling a reaction path by molecular mechanics: Dimerization of carbon free radicals

A variable force field model for radical dimerization was developed. It uses MM2 force constants for most atoms and new parameters only for the core atoms involved in bonding changes. The change in hybridization from sp² to sp³ is modeled using distance-dependent switch functions. The validity of the model has been tested by calculating the minimum energy path of the dimerization of di-tert-butylmethyl radicals. The calculated and experimental values for the enthalpy of activation of both dimerization of the radicals and dissociation of the dimer are in excellent agreement. The model has also been successfully applied to the stereoselective dimerization of 1-phenylneopentyl radicals: The form of the potential energy surface yields an explanation for the observed stereoselectivity. Another common feature in radical dimerization seems to be the formation of adsorption complexes prior to dimerization that can lead to increased reactivity. The results suggest that it is important to analyze the whole reaction path and not only the transition state alone.     

Phosphorylinitrile oxides. 7. Quantum chemical study of the dimerization of nitrile oxides

A semiempirical MNDO calculation was carried out for the singlet potential energy surface for the dimerization of acetonitrile oxide leading to dimethylfuroxane. The dimerization of nitrile oxides proceeds by a two-step mechanism. The rate-limiting step is formation of a dinitrosoethylene intermediate. A semiempirical AMI calculation was carried out to study the effect of phosphoryl substituents on formation of the transition state of the rate-limiting step in the dimerization of dimethoxyphosphorylnitrile oxide. Independently of the initial orientation of the two phosphorylnitrile oxide molecules, a gauche-oriented dimerica species is formed in the first step in the dimerization. There is hardly any specific effect ofthe phosphoryl substituents in the first step of phosphorylnitrile oxide dimerization.Communication 6, see ref. [1].Kazan State Technological University, 420015 Kazan, and Institute of Physiologically Active Compounds, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1269–1273, September, 1994. Original article submitted August 5, 1994.     

Dimerization of some substituted benzoic acids in aqueous solution from conductance measurements

Precision molar conductances of benzoic, o-toluic, 2,6-dimethylbenzoic, 2,3,6-trimethylbenzoic, and, o-fluorobenzoic acids have been determined in aqueous solution as a function of temperature and of concentration up to near saturation (<0.035 M). At the higher concentrations molar conductances are found to be less than anticipated for the simple dissociation of a 1-1 electrolyte. Although the deviations are only 1% or less they have been interpreted to show that these acids are dimerized in solution. The interpretation includes an assumption that the dimer ionizes to produce a triple ion. Increasing numbers of methyl groups lead to increasing dimerization. For those acids with two ortho groups the dimerization increases with increasing temperature while the other three show decreasing dimerization with increasing temperature. Temperature functions have been determined for the dimerization constants and from these functions standard changes in enthalpy, entropy, and heat capacity have been determined. Comparisons are made with dimerization studies in non-aqueous solvents. From these as well as the behavior of benzene in water it is concluded that a major factor driving the dimerization is hydrophobic interaction. To provide a limiting conductance of the triple ion needed in the dimerization calculations a conductance study was also made for o-Phenylbenzoic acid on the assumption that its anion provides an approximate model of the triple ion.     

The roles of cysteines in the heme domain of human soluble guanylate cyclase

Soluble guanylate cyclase(sGC) is a critical heme-containing enzyme involved in NO signaling.The dimerization of sGC subunits is necessary for its bioactivity and its mechanism is a striking and an indistinct issue.The roles of heme domain cysteines of the sGC on the dimerization and heme binding were investigated herein.The site-directed mutations of three conserved cysteines(C78A,C122A and C174S) were studied systematically and the three mutants were characterized by gel filtration analysis,UV-vis spectroscopy and heme transfer examination.Cys78 was involved in heme binding but not referred to the dimerization,while Cys174 was demonstrated to be involved in the homodimerization.These results provide new insights into the cysteine-related dimerization regulation of sGC.     

Selective dimerization of ethylene to but-1-ene under the conditions of industrial process. II. Selection of a solvent for the process of ethylene to but-1-ene dimerization

A comparative economical analysis of reasons for application the solvents of various type in the process of ethylene to but-1-ene dimerization and of technological schemes of rectification of the products of ethylene dimerization with use of different solvents. The optimal solvent for the currently working industrial process of ethylene to but-1-ene dimerization is hexane fraction forming in the process of ethylene dimerization.     

Design of dimerization inhibitors of HIV-1 aspartic proteinase: A computer-based combinatorial approach

Inhibition of dimerization to the active form of the HIV-1 aspartic proteinase (HIV-1 PR) may be a way to decrease the probability of escape mutations for this viral protein. The Multiple Copy Simultaneous Search (MCSS) methodology was used to generate functionality maps for the dimerization interface of HIV-1 PR. The positions of the MCSS minima of 19 organic fragments, once postprocessed to take into account solvation effects, are in good agreement with experimental data on peptides that bind to the interface. The MCSS minima combined with an approach for computational combinatorial ligand design yielded a set of modified HIV-1 PR C-terminal peptides that are similar to known nanomolar inhibitors of HIV-1 PR dimerization. A number of N-substituted 2,5-diketopiperazines are predicted to be potential dimerization inhibitors of HIV-1 PR.     

离子液体体系中1－丁烯二聚反应的研究

 研究了在强酸性AlCl3／Et2AlCl／［BMIM］Cl型离子液体体系中过渡金属化合物对1－丁烯二聚反应的催化作用．结果表明，［BMIM］Cl对强酸性AlCl3／Et2AlCl催化剂催化1－丁烯高聚反应有明显的阻聚作用，并显著提高了1－丁烯二聚的选择性．在过渡金属化合物中，含镍化合物对1－丁烯二聚反应有最好的催化效果．在最佳反应条件下，1－丁烯的转化率可达95．1％，二聚产物C8烯的选择性为85．8％．同时，对1－丁烯二聚反应的机理进行了初步探讨．     

Acid-catalyzed Dimerization Reaction of Pyrroles to Synthesize Hexaaryl-4,8-dihydropyrrolo[2,3-f]indoles

Pyrroloindoles, as a kind of promising small-melecular hole injetion materials, have attracted wide attention. Herein, we described a simple metal-free method for the synthesis of 4,8-dihydropyrrolo[2,3-f]indole compounds through the acid-catalyzed dimerization reaction of pyrroles. The structures of target 4,8-dihydropyrrolo-[2,3-f]indoles were confirmed by NMR spectrum and X-ray single crystal diffraction. Notably, pyrrole substrates were synthesized conveniently starting from available biological dipeptides. cis-Configuration was preferred when bulky p-toluene sulfonic acid(TsOH) was employed. Excessive aicds empoyed in dimerization would lead to the formation of quantitative pyrrolium chloride intermediate, restraining further conversion to target compounds. Furthermore, the dimerization process was monitored by ¹H NMR spectrum, proving that it followed a second-order kinetics, providing significant insight to the mechanism of dimerization reaction.     

Theoretical Insight into the Effect of Fluorine-Functionalized Metal-Organic Framework Supported Palladium Single-Site Catalyst in the Ethylene Dimerization Reaction

Ethylene dimerization reaction is one of the most common mechanisms for the production of 1-butene. Recently, metal–organic frameworks (MOFs) have received extensive attention in this area since they combine all the advantages of homogeneous and heterogeneous catalysts in a single compound. Here a computational mechanistic study of MOF-supported palladium single-site catalyst for ethylene dimerization reaction is reported. Catalytic systems with both biphenyl-type backbone as organic ligand and its fluorine-functionalization have been investigated to reveal the origin of ligand effects on the catalytic activity and selectivity. The calculations revealed that the nonfluorinated palladium MOF catalyst undergoes dimerization over isomerization reaction. Then the influence of the fluorine-functionalized organic ligand was compared in the dimerization catalytic cycle, which was strongly favored in terms of activity and selectivity. Catalyst-substrate interactions were analyzed by energy decomposition analysis revealing the critical role of ligand backbone functionalization on the activity. This theoretical analysis identified three chemically meaningful dominant effects on these catalysts; steric, electrostatic and charge transfer effects. The steric effects promote nonfluorinated MOF catalyst, whereas the electrostatic effects are the dominant factor that promotes its fluorinated counterpart. This theoretical study provides feedback with future experimental studies about the role of fluorine ligand functionalization in palladium MOF catalysts for ethylene dimerization reaction.     

酸性分子筛催化乙烯二聚反应

应用密度泛函理论(DFT), 采用5T簇模型来模拟分子筛催化剂的酸性位, 在B3LYP/6-311+G(3df, 2p)的条件下通过理论计算研究了乙烯在酸性分子筛上的二聚反应. 对反应各驻点进行了全局优化, 经过零点能校正后, 计算得出乙烯二聚反应的活化能. 研究表明, 乙烯在分子筛上的二聚反应分三步进行: 单个乙烯分子化学吸附→第二个乙烯分子的物理吸附→两乙烯分子二聚反应. 乙烯化学吸附生成的烷氧化合物与物理吸附的乙烯分子发生二聚反应生成新的C—C键同时生成新的烷氧化合物. 计算得到的乙烯化学吸附和二聚反应的反应能垒分别为108和149 kJ·mol-1. 反应的逆过程也就是1-丁烯在酸性分子筛表面的1-丁基烷氧化合物发生β分裂反应, 计算所得相应的1-丁烯β分裂反应的能垒为217 kJ·mol-1, 远高于相应的乙烯二聚反应能垒. 此外还进一步研究了所用基组对计算结果的影响.     

The effect of the short wavelength ultraviolet radiation. An extension of biological dosimetry to the UV-C range

Polycrystalline uracil thin layer can be used as biological dosimeter for assessing exposure to UV radiation. The dimerization and reversion efficiency of the ultraviolet radiation in the UV-B and the UV-C range were quantified on polycrystalline uracil thin layers irradiated with quasi-monochromatic radiation using interference filters of 10nm bandwidth. The dimer formation and monomerization (reversion) dose-effect relations were determined by optical spectroscopy. The decrease of the OD value of the uracil thin layer at 288 nm was taken as a measure of the dimer formation, while the increase of the OD of a completely irradiated (until reaching the saturation level) uracil layer was taken as the sign of the monomerization. The two processes in the UV-B and the UV-C range take place simultaneously, the individual characterization of the dimerization efficiency was performed from the initial slope of the dimerization dose-effect function and an action spectrum for dimerization was constructed in the UV-C range too. The reversion efficiency was found to be practically the same with all of the investigated wavelengths: 200 nm, 210 nm, 220 nm, 230 nm, 240 nm The possible biological relevance of the reversion of dimers are discussed.     

Products and mechanism of acene dimerization. A computational study

The high reactivity of acenes can reduce their potential applications in the field of molecular electronics. Although pentacene is an important material for use in organic field-effect transistors because of its high charge mobility, its reactivity is a major disadvantage hindering the development of pentacene applications. In this study, several reaction pathways for the thermal dimerization of acenes were considered computationally. The formation of acene dimers via a central benzene ring and the formation of acene-based polymers were found to be the preferred pathways, depending on the length of the monomer. Interestingly, starting from hexacene, acene dimers are thermodynamically disfavored products, and the reaction pathway is predicted to proceed instead via a double cycloaddition reaction (polymerization) to yield acene-based polymers. A concerted asynchronous reaction mechanism was found for benzene and naphthalene dimerization, while a stepwise biradical mechanism was predicted for the dimerization of anthracene, pentacene, and heptacene. The biradical mechanism for dimerization of anthracene and pentacene proceeds via syn or anti transition states and biradical minima through stepwise biradical pathways, while dimerization of heptacene proceeds via asynchronous ring closure of the complex formed by two heptacene molecules. The activation barriers for thermal dimerization decrease rapidly with increasing acene chain length and are calculated (at M06-2X/6-31G(d)+ZPVE) to be 77.9, 57.1, 33.3, -0.3, and -12.1 kcal/mol vs two isolated acene molecules for benzene, naphthalene, anthracene, pentacene, and heptacene, respectively. If activation energy is calculated vs the initially formed complex of two acene molecules, then the calculated barriers are 80.5, 63.2, 43.7, 16.7, and 12.3 kcal/mol. Dimerization is exothermic from anthracene onward, but it is endothermic at the terminal rings, even for heptacene. Phenyl substitution at the most reactive meso-carbon atoms of the central ring of acene blocks the reactivity of this ring but does not efficiently prevent dimerization through other rings.     

The role of the methylene blue and toluidine blue monomers and dimers in the photoinactivation of bacteria

The interactions between the phenothiazine dyes, methylene blue (MB) and toluidine blue (TB), and bacteria (Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis, Hemophilus influenzae, Escherichia coli and Pseudomonas aeruginosa) were studied spectrophotometrically. This demonstrated that a metachromatic reaction took place between the dyes and bacteria. Furthermore, bacteria induced additional dimerization of MB and TB. The effective dimerization constants of MB and TB were evaluated in the presence of each bacterial strain at a concentration of 10(8) CFU/ml. The analysis of the effective dimerization constants for MB and TB in the presence of bacteria indicated that the ability to form dimers was greater for TB than for MB. Gram-negative bacteria induced the dye dimerization more intensely than gram-positive bacteria. There was a correlation between the ability of each dye to form dimers in the presence of bacteria and the relative photobactericidal efficacy of each dye against these bacteria. These results provide evidence confirming the essential role of the dye dimers in bacterial photodamage.     

Determination of the dimerization constant of pinacyanol: role of the thermochromic effect

Pinacyanol (PIN), as other cyanine dyes, has demonstrated a unique ability to form associates such as dimers, and H- and J-aggregates. This association is strongly favoured in water, and even at low dye concentrations, dimers and superior order aggregates are present. As a consequence, the determination of the dimerization constant involves sometimes a significant error when these aggregates are neglected. As an increase in temperature shifts the equilibrium among the different species towards the lowest order aggregates, we have obtained the spectra of PIN at several temperatures. By extrapolating some spectral characteristics at high temperatures, a spectrum of the dimer without any contribution of other aggregates was obtained. From this spectrum and that of the monomer, the dimerization constant was calculated, as well as the Gibbs energy change associated to the reaction. The enthalpy and entropy changes of the dimerization were determined from the dependence of the dimerization constants on the temperature. From these results it can be inferred that the driving force of the dimerization is of enthalpic origin.     

Aspects of the photodimerization mechanism of 2,4-dichlorocinnamic acid studied by kinetic photocrystallography

Photoinduced structural variations in single crystals of 2,4-dichloro-trans-cinnamic acid (C9H6Cl2O2, DiClCA) have been investigated using X-ray diffraction (photocrystallography) and optical spectroscopic methods. During UV irradiation, which initiates the irreversible dimerization reaction, a loss of the long-range order of the reactant single crystal was found, i.e., that the dimerization is a heterogeneous one. This unexpected result emphasizes the still-existing problem of predicting changes or of remaining periodicity during chemical reactions in the solid state. On the basis of the experimental results, we propose a qualitative kinetic reaction scheme for DiClCA heterogeneous dimerization reaction.     

异丁烯二聚反应

由于甲基叔丁基醚(MTBE)对水源的污染,它作为汽油添加剂的应用受到环保限制,并对其生产和应用前景带来消极影响。MTBE经裂解、二聚和加氢生产异辛烷成为国外现有MTBE装置转产的主要途径。本文对异丁烯二聚催化剂、反应活性位、机理及动力学研究成果进行了综述,试图解释在异丁烯二聚时,加入的叔丁醇对二聚反应选择性提高的作用机理,为今后二聚反应的研究提供参考。     

tert-Butyl nitrite induced radical dimerization of primary thioamides and selenoamides at room temperature

A simple and efficient method for the dimerization of primary thioamides into 1,2,4-thiadiazoles using tert-butyl nitrite is described. The optimized condition was also found to be suitable for the dimerization of benzoselenoamides into 1,2,4-selenadiazoles. All the reactions proceed smoothly at room temperature and gave the desired products in excellent yields in a short span of time.