Competition and coadsorption of di-acids and carboxylic acid solvents on HOPG

The self-assemblies of di-acids HOOC-(CH(2))(n)-COOH (n = 20, 18, 16, 14, 12, 10) in three solvents hexanoic acid, octanoic acid, and decanoic acid on highly oriented pyrolytic graphite (HOPG) were studied with scanning tunneling microscopy (STM). In the solvent hexanoic acid, solvent molecules coadsorb with HOOC-(CH(2))(n)-COOH (n = 20, 18, 16) via formation of hydrogen bonds. The solvent octanoic acid coadsorbs with HOOC-(CH(2))(n)-COOH (n = 20, 18). Decanoic acid only coadsorbs with HOOC-(CH(2))(20)-COOH. In each solvent, the trend of coadsorption between solvent molecules and di-acid molecules decreases with decreasing chain-length of di-acid molecules. These systematic investigations suggest that coadsorption of solvent molecules with di-acid solute molecules is mainly dependent on the relative hydrogen-bond densities in the formed monolayer. This is consistent with the maximization of adsorption heat of the self-assembled monolayers of di-acids dissolved in solvents of carboxylic acids.     

Solid-state preparation of hybrid organometallic-organic macrocyclic adducts with long chain dicarboxylic acids

The supramolecular macrocyclic adducts of general formula {[Fe(eta5-C5H4-C5H4N)2].[HOOC(CH2)nCOOH]}2 with n = 4 (adipic acid), n = 6 (suberic acid), n = 7 (azelaic acid) and n = 8 (sebacic acid) have been obtained quantitatively by kneading powdered samples of the crystalline organometallic and organic reactants with drops of MeOH (for n = 4, 6 and 7) and by direct crystallization from MeOH for n = 8, while the adduct with n = 5 represents an isomeric open chain alternative to the macrocycle.     

ω-氯氟烷基醇,烯烃及环氧化物的合成

全氟烷基碘的加成反应一直活跃在氟化学中,即使近来也依然受到注意,这是因为由它们出发可做许多有用的中间体,其中氟烷基取代的醇可做织物表面处理剂,氟烷基取代的环氧化合物可做润滑剂。我们曾用引发剂,使ψ—碘代全氟烷基磺酰氟与多键类化合物在较温和条件下进行加成。黄维垣教授等用NaHCO_3—K_3[Fe(CN)_6]引发Cl(CF_2)_(4.6)I与烯丙醇顺利加成。     

Solvent effect on self-assembled structures of 3,8-bis-hexadecyloxy-benzo[c]cinnoline on highly oriented pyrolytic graphite

3,8-Bis-hexadecyloxy-benzo[c]cinnoline (BBC16) self-assembled into two structures at highly oriented pyrolytic graphite (HOPG) surface: one was formed by molecules with a V-like configuration (C2v symmetry) and the other by molecules with a Z-like configuration (C(s) symmetry). The self-assembled structures could be tweaked by the solvents used. In the self-assembled monolayers (SAMs) on HOPG, the BBC16 molecule adopted the V-like configuration in polar solvents and the Z-like configuration in nonpolar solvents. Moreover, the solvent viscosity, solvent dissolvability of BBC16, and substrate temperature also played some roles in tuning the two-dimensional self-assembled structures.     

碳苷研究XXVI:异黑豆素类似物的合成

本文首次报道了异黑豆素类似物, 6-非环糖基-4',7一二羟基黄酮的合成, 以2,4-二羟基苯甲酸为原料, 溴化和脱羧后以苄基作为羟基保护基, 通过Grignarcl反应获得具有各种不同侧链的中间体7,7氢解脱除苄基再用Fries重排或Frieclel-Crafts反应得到了C-Z酰化产物, 接着用碱缩合生成查尔酮, 经I2/H2SO4/DM SO氧化环合得到目标产物。     

Ag(I)-based tectons for the construction of helical and meso-helical hydrogen-bonded coordination networks

The new ligand 4-(3-(2-pyridyl)pyrazol-1-ylmethyl)benzoic acid (L) has been prepared and characterized. This bifunctional ligand incorporates both a chelating region, with two nitrogen donors, suitable for chelating to soft transition metal ions, and a self-complementary hydrogen-bonding region which can facilitate intermolecular association of ligands or ligand-based complexes. X-ray structural analysis of the ligand shows it to adopt a one-dimensional helical polymeric structure, with adjacent ligands hydrogen bonded to each other. Reaction of L with silver(I) salts (AgOTf (1, 1.1.5H(2)O), AgNO(3) (2), AgPF6 (3.CH(3)OH), and AgClO(4) (4.CH(3)OH)) results in the formation of complexes with 2:1 stoichiometries. X-ray structural analysis of these complexes shows that, in each case, one-dimensional chain structures are obtained where chiral AgL(2) tectons are hydrogen bonded together, either directly or mediated by anions or solvent. Structures with either helical or meso-helical structures are observed.     

Hydrogen bonding versus van der Waals interactions: competitive influence of noncovalent interactions on 2D self-assembly at the liquid-solid interface

The structures of the self-assembled monolayers of various 4-alkoxybenzoic acids physisorbed at the liquid-solid interface were established by employing scanning tunnelling microscopy (STM). This study has been essentially undertaken to explore the competitive influence of van der Waals and hydrogen-bonding interactions on the process of two-dimensional self-assembly. These acid derivatives form hydrogen-bonded dimers as expected; however, the dimers organise themselves in the form of relatively complex lamellae. The characteristic feature of these lamellae is the presence of regular discommensurations or kinks along the lamella propagation direction. The formation of kinked lamellae is discussed in light of the registry mechanism of the alkyl chains with the underlying graphite substrate. The location of the kinks along a lamella depends on the number (odd or even) of carbon atoms in the alkyl chain. This result indicates that concerted van der Waals interactions of the alkyl chain units introduce the odd/even chain-length effect on the surface-assembled supramolecular patterns. The odd/even effects are retained even upon complexation with a hydrogen-bond acceptor. However, as the solvent is changed from 1-phenyloctane to 1-octanoic acid, the kinked lamellae as well as the odd/even effects disappear. This solvent-induced convergence of supramolecular patterns is attained by means of co-crystallisation of octanoic acid molecules in the 2D crystal lattice, which is evident from high-resolution STM images. The solvent co-adsorption phenomenon is discussed in terms of competing van der Waals and hydrogen-bonding interactions.     

基于磷钼酸和2-(2-羟基苯)苯并咪唑复合物的晶体结构和质子导电性(英文)

以磷钼酸和2-(2-羟基苯)苯并咪唑(L)为原料制备了具有质子导电性的有机-无机化合物[H3L2(PMo12O40)·7H2O·4CH3OH]n(1).单晶X射线衍射分析结果表明化合物1具有基于磷钼酸、2-(2-羟基苯)苯并咪唑及溶剂甲醇分子的二维氢键网络结构;质子导电性能测试结果表明该化合物在100℃、相对湿度为98%时的电导率达到10-4 S·cm-1.     

New oligophosphines and (hydroxymethyl)phosphonium chlorides

The new oligophosphines [H2P(CH2)2]2PH, [H2P(CH2)2P(H)CH2]2, and{[(H2P(CH2)2]2PCH2}2 have been made by hydrophosphination of diethyl vinylphosphonate (2) with H2P(CH2)2PH2 (1), using different ratios of 2/1, followed by LiAlH4 reduction of the phosphonate intermediates; the three phosphonate precursors were obtained as oils of varying purity (approximately 90-95%) in low (approximately 20%) to almost quantitative yield. The tri-, tetra-, and hexaphosphines were then treated with formaldehyde in the presence of hydrochloric acid to generate the corresponding water-soluble (hydroxymethyl)phosphonium chlorides {(HOCH2)3P[(CH2)2P(CH2OH)2]n(CH2)2P(CH2OH)3}Cl m (n = 1, m = 3; n = 2, m = 4) and {[(HOCH2)3P(CH2)2]2P(CH2OH)CH2}2Cl6 that were characterized by NMR spectroscopy and elemental analysis. The known (hydroxymethyl)bisphosphonium chloride [(HOCH2)3P(CH2)2]2Cl2 was similarly prepared from H2P(CH2)2PH2, and the determined crystal structure revealed strong hydrogen bonding between the chloride anions and the hydrogen atoms of the hydroxymethyl groups.     

Single molecular insight into steric effect on C-terminal amino acids with various hydrogen bonding sites

Amino acids are basic units to construct a protein with the assistance of various interactions. During this building process, steric hindrance derived from amino acid side groups or side chains is a factor that could not be ignored. In this contribution, adsorption behaviors of C-terminal amino acid derivatives with amino acid residues fused in 3,4,9,10-perylenetetracarboxylic dianhydride were investigated by scanning tunneling microscopy (STM) and density functional theory (DFT) calculations at various liquid/solid interfaces. STM results at 1-phenyloctane/HOPG interface show that N,N'-3,4,9,10-perylenedicarboximide (GP) and N,N'-methyl-3,4,9,10-perylenedicarboximide (AP) formed linear and herringbone structures, respectively. The driving force could be attributed to different H-bonding sites induced by steric hindrance at side groups. N,N'-Benzyl-3,4,9,10-perylenedicarboximide (PP) generates both linear and herringbone structures because steric hindrance changes the H-bonding sites between PP molecules, whereas N,N'-isopropyl-3,4,9,10-perylenedicarboximide (LP) failed to be imaged because of strong steric hindrance coming from larger side group. To further investigate the impact of steric hindrance, we utilized octanoic acid (OA) as solvent to capture the adsorption details of LP and PP. We found that OA molecules drag PP and LP molecules in a different direction to generate linear structure, impeding the molecular rotation. The structure–solvent relationship shows that the steric hindrance is brought by the large side group, which makes it easier to recognize OA molecules at the interface. These results demonstrate that steric effect plays a significant role in altering interaction sites of the compounds during the adsorption process at the liquid/solid interface.     

Hydrogen bonded arrays: the power of multiple hydrogen bonds

Hydrogen bond interactions in small covalent model compounds (i.e., deprotonated polyhydroxy alcohols) were measured by negative ion photoelectron spectroscopy. The experimentally determined vertical and adiabatic electron detachment energies for (HOCH(2)CH(2))(2)CHO(-)(2a), (HOCH(2)CH(2))(3)CO(-) (3a), and (HOCH(2)CH(2)CH(OH)CH(2))(3)CO(-) (4a)reveal that hydrogen-bonded networks can provide enormous stabilizations and that a single charge center not only can be stabilized by up to three hydrogen bonds but also can increase the interaction energy between noncharged OH groups by 5.8 kcal mol(-1) or more per hydrogen bond. This can lead to pK(a) values that are very different from those in water and can provide some of the impetus for catalytic processes.     

Effect of hydrogen bonds on pKa values: importance of networking

The pK(a) of an acyclic aliphatic heptaol ((HOCH(2)CH(2)CH(OH)CH(2))(3)COH) was measured in DMSO, and its gas-phase acidity is reported as well. This tertiary alcohol was found to be 10(21) times more acidic than tert-butyl alcohol in DMSO and an order of magnitude more acidic than acetic acid (i.e., pK(a) = 11.4 vs 12.3). This can be attributed to a 21.9 kcal mol(-1) stabilization of the charged oxygen center in the conjugate base by three hydrogen bonds and another 6.3 kcal mol(-1) stabilization resulting from an additional three hydrogen bonds between the uncharged primary and secondary hydroxyl groups. Charge delocalization by both the first and second solvation shells may be used to facilitate enzymatic reactions. Acidity constants of a series of polyols were also computed, and the combination of hydrogen-bonding and electron-withdrawing substituents was found to afford acids that are predicted to be extremely acidic in DMSO (i.e., pK(a) < 0). These hydrogen bond enhanced acids represent an attractive class of Br?nsted acid catalysts.     

Theoretical mechanistic study on the radical-molecule reaction of CH2OH with NO2

The complex singlet potential energy surface for the reaction of CH2OH with NO2, including 14 minimum isomers and 28 transition states, is explored theoretically at the B3LYP/6-311G(d,p) and Gaussian-3 (single-point) levels. The initial association between CH2OH and NO2 is found to be the carbon-to-nitrogen approach forming an adduct HOCH2NO2 (1) with no barrier, followed by C-N bond rupture along with a concerted H-shift leading to product P1 (CH2O + trans-HONO), which is the most abundant. Much less competitively, 1 can undergo the C-O bond formation along with C-N bond rupture to isomer HOCH2ONO (2), which will take subsequent cis-trans conversion and dissociation to P2 (HOCHO + HNO), P3 (CH2O + HNO2), and P4 (CH2O + cis-HONO) with comparable yields. The obtained species CH2O in primary product P1 is in good agreement with kinetic detection in experiment. Because the intermediate and transition state involved in the most favorable pathway all lie blow the reactants, the CH2OH + NO2 reaction is expected to be rapid, as is confirmed by experiment. These calculations indicate that the title reaction proceeds mostly through singlet pathways; less go through triplet pathways. In addition, a mechanistic comparison is made with the reactions CH3 + NO2 and CH3O + NO2. The present results can lead us to deeply understand the mechanism of the title reaction and may be helpful for understanding NO2-combustion chemistry.     

Exceptional kinetic propensity of hydroxymethyl phosphanes toward Rh(III) stabilization in water

The reactions of (HOCH2)2P(C6H4)P(CH2OH)2 (HMPB) and P(CH2OH)3 (THP) with RhCl3.xH2O in aqueous media gave water-soluble complexes cis-[RhCl2{eta2-(HOCH2)2P(C6H4)P(CH2OH)2}2]Cl (3) and fac-[RhCl3(P(CH2OH)3)3] (4) respectively in good yields, X-ray crystal structures of 3 and 4 confirmed their molecular constitution. These reactions provide the first examples demonstrating the kinetic propensity of hydroxymethyl phosphanes to stabilize Rh in +3 oxidation state in water.     

Brønsted acidic ionic liquids and their zwitterions: synthesis, characterization and pKa determination

Imidazolium chlorides with one or two carboxylic acid substituent groups, 1-methyl-3-alkylcarboxylic acid imidazolium chloride, [Me[(CH2)nCOOH]im]Cl (n=1, 3), and 1,3-dialkylcarboxylic acid imidazolium chloride, [[(CH2)nCOOH]2im]Cl (n=1, 3), have been synthesized via their corresponding acid esters. Deprotonation of the carboxylic acid functionalized imidazolium chlorides with triethylamine affords the corresponding zwitterions [Me[(CH2)nCOO]im] (n=1, 3) and [[(CH2)nCOOH][(CH2)nCOO]im] (n=1, 3). Subsequent reaction of the zwitterions with strong acids gives the new imidazolium salts [Me[(CH2)nCOOH]im]X (n=1, 3; X=BF4, CF3SO3) and [[(CH2)nCOOH]2im]X (n=1, 3; X=BF4, CF3SO3), which exhibit melting points as low as -61 degrees C. The solid-state structures of two of the carboxylic acid functionalized imidazolium salts have been determined by single-crystal X-ray diffraction analysis. Extensive hydrogen bonding is present between the chloride and the imidazolium, with eight Cl.H interactions below 3 A. The pK(a) values of all the salts, determined by potentiometric titration, lie between 1.33 and 4.59 at 25 degrees C.     

Self-assembly and odd-even effects of cis-unsaturated carboxylic acids on highly oriented pyrolytic graphite

The self-assembly of several cis-unsaturated carboxylic acids of the structure cis-CH3(CH2)p-1CH=CH(CH2)m-1COOH on highly oriented pyrolytic graphite (HOPG) was studied. The impact of the interior cis-CH=CH group and the molecular chain length on their self-assembled structures was considered. Due to the cis conformation of the -HC=CH- group in the interior of these molecules, they display self-assembled structures significantly different from saturated acids with all-trans configurations. As an example of the class of molecules cis-CH3(CH2)p-1CH=CH(CH2)2n-1COOH (p not equal 2n) (p=8, n=7), cis-CH3(CH2)7CH=CH(CH2)13COOH self-assembles into two kinds of enantiomer domains with opposite 2-D chirality. Due to the steric restriction of the interior cis-HC=CH group, all chains with acid groups are packed at the same side of a lamella, a head-to-head arrangement which is different from the head-to-tail packing of saturated all-trans acids. However, cis-CH3(CH2)7CH=CH(CH2)8COOH, considered as one example of the group cis-CH3(CH2)p-1CH=CH(CH2)2n-2COOH (p not equal 2n-1) (p=8, n=5), does not form any stable self-assembled domain, consistent with the molecular arrangement model. This difference in self-assembly behavior between cis-CH3(CH2)p-1CH=CH(CH2)2n-1COOH (p not equal 2n) and cis-CH3(CH2)p-1CH=CHC2n-2COOH (p not equal 2n-1) shows an odd-even chain-length effect of cis-CH3(CH2)p-1CH=CH(CH2)m-1COOH (p not equal m, m=2n or 2n-1). For another category of molecules, cis-unsaturated acids with equal numbers of all-trans carbon atoms on both sides of the cis-CH=CH group, cis-CH3(CH2)m-1CH=CH(CH2)m-1COOH (m=2n or 2n-1), display another odd-even effect. cis-CH3(CH2)7CH=CH(CH2)7COOH, one example of cis-CH3(CH2)2n-1-CH=CH(CH2)2n-1COOH (n=4), is predicted to form both an enantiomer and a nonchiral racemic structure, which is in accordance with the experimental observation of its self-assembled monolayer. However, cis-CH3(CH2)2n-2CH=CH(CH2)2n-2COOH does not form a stable self-assembled domain due to the same steric repulsion as that seen in the cis-CH3(CH2)7CH=CH(CH2)8COOH structure. These odd-even effects demonstrate that molecular self-assembly can be significantly tailored by slightly changing the molecular chain length.     

Influence of the boron atom on the solvatochromic properties of 4-nitroaniline-functionalized boronate esters

Para-nitroaniline derivatives with peripheral 1,2- and 1,3-diol functionalities [O(2)N-C(6)H(4)-NR(1)-CH(2)CH(OH)CH(2)OH; O(2)N-C(6)H(4)-NR(1)-CH(CH(2)OH)(2); R(1) = -H, -CH(3)] covalently bonded to the amino group are esterified with various para-substituted phenylboronic acids [R(2)-C(6)H(4)-B(OH)(2); R(2) = -OCH(3), -CH(3), -H, -Br, -CHO, -NO(2), -B(OH)(2)], and the solvatochromic properties of these esters are investigated in 33 solvents of different polarity. To interpret the solvent effects, the established linear solvation energy (LSE) multiparameter equations of Kamlet-Taft and the improved Catalán scales are used. Although the boron atom is separated by two or three sp(3)-hybridized carbon atoms from the actual chromophore, solvation effects have a significant positive solvatochromic effect on the nitroaniline unit (R(1) = -CH(3)) as result of the solvent acting as a donor at the boron atom. The influence of the substituent R(2) on the coefficient b of the LSE relationship according to Kamlet-Taft and Catalán, which reflects the quantitative influence of the hydrogen-bonding acceptor or the electron-pair donor capacity of the solvent on the position of the UV-vis absorption maximum, can be determined via a linear Hammett relationship [b = f(σ(p))]. The interpretation of the effects is based on the electronic influence of the solvated boronic acid ester unit on the 4-nitroaniline group, predominantly through inductive interactions.     

正十八烷醇在HOPG上形成自组装膜的吸附特性

研究了正十八烷醇在高定向热解石墨(HOPG)上形成自组装膜的吸附特性, 正十八烷醇在室温下从溶液中吸附至HOPG上形成整齐定向排列的单层自组装膜. 通过扫描隧道显微镜(STM)、接触角测量和X射线光电子能谱(XPS)分析了正十八烷醇单层自组装膜在HOPG上的结构. 实验结果表明, 正十八烷醇自组装膜在基底上成平铺或直立形态, 由于分子在基底上覆盖程度的不同, 会导致它在基底上排列的方式有所不同.     

Investigation of the radical product channel of the CH3COO2 + HO2 reaction in the gas phase

The reaction of CH(3)C(O)O(2) with HO(2) has been investigated at 296 K and 700 Torr using long path FTIR spectroscopy, during photolysis of Cl(2)/CH(3)CHO/CH(3)OH/air mixtures. The branching ratio for the reaction channel forming CH(3)C(O)O, OH and O(2) (reaction ) has been determined from experiments in which OH radicals were scavenged by addition of benzene to the system, with subsequent formation of phenol used as the primary diagnostic for OH radical formation. The dependence of the phenol yield on benzene concentration was found to be consistent with its formation from the OH-initiated oxidation of benzene, thereby confirming the presence of OH radicals in the system. The dependence of the phenol yield on the initial peroxy radical precursor reagent concentration ratio, [CH(3)OH](0)/[CH(3)CHO](0), is consistent with OH formation resulting mainly from the reaction of CH(3)C(O)O(2) with HO(2) in the early stages of the experiments, such that the limiting yield of phenol at high benzene concentrations is well-correlated with that of CH(3)C(O)OOH, a well-established product of the CH(3)C(O)O(2) + HO(2) reaction (via channel (3a)). However, a delayed source of phenol was also identified, which is attributed mainly to an analogous OH-forming channel of the reaction of HO(2) with HOCH(2)O(2) (reaction ), formed from the reaction of HO(2) with product HCHO. This was investigated in additional series of experiments in which Cl(2)/CH(3)OH/benzene/air and Cl(2)/HCHO/benzene/air mixtures were photolysed. The various reaction systems were fully characterised by simulations using a detailed chemical mechanism. This allowed the following branching ratios to be determined: CH(3)C(O)O(2) + HO(2)--> CH(3)C(O)OOH + O(2), k(3a)/k(3) = 0.38 +/- 0.13; --> CH(3)C(O)OH + O(3), k(3b)/k(3) = 0.12 +/- 0.04; --> CH(3)C(O)O + OH + O(2), k(3c)/k(3) = 0.43 +/- 0.10: HOCH(2)O(2) + HO(2)--> HCOOH + H(2)O + O(2), k(17b)/k(17) = 0.30 +/- 0.06; --> HOCH(2)O + OH + O(2), k(17c)/k(17) = 0.20 +/- 0.05. The results therefore provide strong evidence for significant participation of the radical-forming channels of these reactions, with the branching ratio for the title reaction being in good agreement with the value reported in one previous study. As part of this work, the kinetics of the reaction of Cl atoms with phenol (reaction (14)) have also been investigated. The rate coefficient was determined relative to the rate coefficient for the reaction of Cl with CH(3)OH, during the photolysis of mixtures of Cl(2), phenol and CH(3)OH, in either N(2) or air at 296 K and 760 Torr. A value of k(14) = (1.92 +/- 0.17) x 10(-10) cm(3) molecule(-1) s(-1) was determined from the experiments in N(2), in agreement with the literature. In air, the apparent rate coefficient was about a factor of two lower, which is interpreted in terms of regeneration of phenol from the product phenoxy radical, C(6)H(5)O, possibly via its reaction with HO(2).     

Controlled self-assembly of filled micelles on nanotubes

We have used coarse-grained molecular dynamics simulations to show that hydrated lipid micelles of preferred sizes and amounts of filling with hydrophobic molecules can be self-assembled on the surfaces of carbon nanotubes. We simulated micelle formation on a hydrated (40,0) carbon nanotube with an open end that was covered with amphiphilic double-headed CH(3)(CH(2))(14)CH(((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(2)H)(2) or single-headed CH(3)(CH(2))(14)CH(2)((CH(2)OCH(2)CH(2))(2)(CH(2)COCH(2)))(4)H lipids and filled with hexadecane molecules. Once the hexadecane molecules inside the nanotube were pressurized and the lipids on its surface were dragged by the water flowing around it, kinetically stable micelles filled with hexadecane molecules were sequentially formed at the nanotube tip. We investigated the stability of the thus-formed kinetically stable filled micelles and compared them with thermodynamically stable filled micelles that were self-assembled in the solution.