Polymer-centered theory in comparison with surfactant-centered theory: a lattice Monte Carlo study

Lattice Monte Carlo simulation is used to study micellization of both pure and surfactant-polymer mixture, with an emphasis on cluster size distribution. The amphiphile molecule is of the type H(4)T(4) where the H (head) monomers like the solvent molecules and the T (tail) monomers are solvophobic. To compare polymer- and surfactant-centered theories, copolymers with the structure of (H(4)T(4))(5) are used instead of homopolymers. Since above copolymer molecules have the structural unit like the structure of surfactant molecules, it is possible to study the competition between the binding of surfactant molecules to the copolymer and the micellization in a copolymer-free solution. Results show that, first, surfactant molecules bind to the copolymer molecules, and not until copolymers are saturated do micelles form. Furthermore, it is shown that for the model used in this paper, the polymer-centered theory is more appropriate than the surfactant-centered theory, and finally the cooperative nature of cluster formation on copolymers is also discussed.     

From Sponges to Nanotubes: A Change of Nanocrystal Morphology for Acute‐Angle Bent‐Core Molecules

The crystalline (B₄) phase made of acute‐angle bent‐core molecules (1,7‐naphthalene derivatives), which exhibits an unusual, highly porous sponge‐like morphology, is presented. However, if grown in the presence of low‐weight mesogenic molecules, the same crystal forms nanotubes with a very high aspect ratio. The nanotubes become unstable upon increasing the amount of dopant molecules, and the sponge‐like morphology reappears. The phase is optically active, and the optical activity is an order of magnitude smaller than in the B₄ phase made of conventional bent‐core molecules. The optical activity is related to the spatial inhomogeneity of the layered structure and is reduced due to the low apex angle and low tilt of the molecules. The arrangement of molecules within the layers was deduced from the bathochromic absorption shift in the B₄ phase.     

Complex orientational ordering of C60 molecules on Au(111)

The orientation and adsorption site for C(60) molecules on Au(111) has been studied using low temperature scanning tunneling microscopy. A complex orientational ordering has been observed for molecules inside the "in-phase" (R0°) domain. A 7-molecule cluster consisting a central molecule sitting atop of a gold atom and 6 tilted surrounding molecules is identified as the structural motif. The 2√3 × 2√3-R30° phase consists of molecules bonding to a gold atomic vacancies with a preferred azimuthal orientation. The quasi-periodic R14° phase is composed of groups of similarly oriented molecules with the groups organized into a 4√3 × 4√3-R30° like super-lattice unit cell.     

Carbonate and oxalate dianions as prolific hydrogen-bond acceptors in supramolecular assembly

In the new inclusion compound [(C2H5)4N+]2 x CO3(2-) x 7(NH2)2CS, the carbonate ion is surrounded by twelve convergent NH donor groups from six thiourea molecules to form a hydrogen-bonded aggregate shaped like two concave three-leaved propellers sharing a common core, whereas in [(n-C3H7)4N+]2 x C2O4(2-) x 4(NH2)2CS the oxalate ion serves as a hub for binding four thiourea molecules to generate a cross-shaped structural motif.     

Cyclotrimerization‐Induced Chiral Supramolecular Structures of 4‐Ethynyltriphenylamine on Au(111) Surface

Cyclotrimerization‐induced chiral supramolecular structures of 4‐ethynyltriphenylamine (ETPA) have been synthesized on the Au(111) surface through alkyne‐based reactions. Whereas the ETPA molecules adsorbed on the Au(111) surface remain inert and form a close‐packed self‐assembled structure at room temperature, the combination of scanning tunneling microscopy observations and theoretical calculations unambiguously reveal that the ETPA molecules cyclotrimerize to form new trimer‐like species—1,3,5‐tris[4‐(diphenylamino)phenyl]benzene (TPAPB)—after annealing at 323 K. Further annealing drives these cyclotrimerized TPAPB molecules to form chiral hexagonal supramolecular structures with an extraordinary self‐healing ability.     

Dielectric spectroscopy of unsymmetrical liquid crystal dimers showing wide temperature range TGBA and TGBC* phases

The electrical properties of frustrated twist grain boundary (TGB) phase are a matter of curiosity. Some studies have indicated the existence of soft and Goldstone modes in TGBA and TGBC* phases respectively. However, the experimental results are still not very conclusive. In the present work, we report dielectric studies of wide temperature range TGBA and TGBC* phases of an optically active dimeric compound 4‐n‐decyloxy‐4′‐(cholesteryloxycarbonyl‐1‐butyloxy) chalcone in the frequency range of 1 Hz to 35 MHz for the planar and homeotropic anchoring of the molecules. Two different relaxation processes have been detected for the planar anchoring of molecules in the TGBA and TGBC^* phases. The soft mode like behaviour is obtained due to tilt fluctuation of molecules in the megahertz region for both TGBA and TGBC* phases. Goldstone mode like behaviour due to phase fluctuation of molecules has been detected for the TGBC* phase in the low frequency region (～200–300 Hz). Activation energies for DC conductivity have also been determined for various phases of the material.     

Breaking Parallel Orientation of Rods via a Dendritic Architecture toward Diverse Supramolecular Structures

Self‐assembled nanostructures of rod‐like molecules are commonly limited to nematic or layered smectic structures dominated by the parallel arrangement of the rod‐like components. Distinct self‐assembly behavior of four categories of dendritic rods constructed by placing a tri(hydroxy) group at the apex of dendritic oligo‐fluorenes is observed. Designed hydrogen bonding and dendritic architecture break the parallel arrangement of the rods, resulting in molecules with specific (fan‐like or cone‐like) shapes. While the fan‐shaped molecules tend to form hexagonal packing cylindrical phases, the cone‐shaped molecules could form spherical motifs to pack into various ordered structures, including the Frank–Kasper A15 phase and dodecagonal quasicrystal. This study provides a model system to engineer diverse supramolecular structures by rod‐like molecules and sheds new light into the mechanisms of the formation of unconventional spherical packing structures in soft matter.     

Methane—the Promising Career of a Humble Molecule

Methane, CH4, here represents natural gas (NG) of which it is the main constituent. Routes ofchemical utilisation of NG — as opposed to energy usage — are discussed. A main step is the conversion of NG to synthesis gas, a mixture of CO and H2. Simple molecules derived from synthesis gas, like methanol,can be further reacted to longer-chained hydrocarbons like propylene and other olefins and even to gasoline and diesel.     

New examples of metalloaromatic Al-clusters: (Al4M4)Fe(CO)3 (M = Li, Na and K) and (Al4M4)2Ni: rationalization for possible synthesis

Ab initio calculations reveal that all-metal antiaromatic molecules like Al4M4 (M = Li, Na and K) can be stabilized in half sandwich (Al4M4)Fe(CO)3 and full sandwich (Al4M4)2Ni complexes. The formation of the full sandwich complex [(Al4M4)2Ni] from its organometallic precursor depends on the stability of the organic-inorganic hybrid (C4H4)Ni(Al4Li4).     

DNA碱基与高氯酸根共吸附行为的表面增强拉曼光谱研究

共吸附有助于实现弱吸附分子或离子的高灵敏表面增强拉曼光谱(SERS)检测.本文研究了四种脱氧核糖核酸(DNA)碱基,即腺嘌呤、鸟嘌呤、胞嘧啶、胸腺嘧啶与高氯酸根(ClO4-)在金纳米粒子表面的共吸附行为,并考察了吸附能力、电位、共存阴离子等因素的影响.研究发现四种碱基在质子化后都可以与ClO4-发生共吸附,但在金表面吸附能力弱的胸腺嘧啶与ClO4-共吸附所获得的ClO4-信号最弱.另外,负电位下电极的排斥作用,以及较正电位下基底SERS增强效应减小等因素都会导致ClO4-信号衰减.此外,Cl-、NO3-、SO24-等阴离子可以与ClO4-发生可逆动态竞争共吸附,同时引起ClO4-信号减弱.以上结果将为提高共吸附法检测弱吸附离子的灵敏度提供重要参考.     

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] and copolymers prepared by reaction‐induced crystallization during polymerization

Morphosynthesis of poly[4‐(1,4‐phenylene)oxyphthalimide] (POPI) and poly[4‐(1,4‐phenylene)oxyphthalimide‐co‐4‐phthalimide] (POPI‐PPI) was examined by using the crystallization during the polymerization. The POPI fibrillar crystals were obtained as precipitates with the formation of spherical aggregates of plate‐like crystals. Some of the POPI fibrillar crystals were longer than 15 μm. They possessed high crystallinity and the molecules aligned perpendicular to the long direction of the fibers. On the other hand, one‐dimensional structures of POPI‐PPI such as ribbon, cone, rod, and fiber were obtained as precipitates by the copolymerization. The copolymer molecules might align along the long direction of the cone‐like crystals. The morphology of these poly(ether‐imide)s could be controlled by not only the polymerization condition but also with the aid of copolymerization. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Pyridine-containing versatile gelators for post-modification of gel tissues toward construction of novel porphyrin nanotubes

Low molecular weight gelators have recently been used as a template to construct novel kind of composite materials of different shape or structures such as helix, fibers, tape or tube through the electrostatic interaction between gelators and the intermediate molecules. In this article, we intricately apply the non-electrostatic interaction between gelator and fluorescent molecules to fabricate the gel fibers. To achieve our goal, we have intentionally designed pyridine containing cholesterol-based gelators 1-3 by keeping one thing in our mind that during the formation of the stacking column the pyridine moieties will be arranged like a spiral staircase around the cholesterol column. The gelation properties of these three gelators are tested in different solvents including sublimable solvents like naphthalene and the gelator 1 has emerged as a ‘supergelator’. The morphologies strongly depend on the process of solvent removal from the gel state and the stabilities of gel have been tuned by the added metal ions like Ag(I) by using metal-ligand interaction. Lastly, we have decorated the gel fibers obtained from gelator 1 with fluorescent molecules like tetraphenyl porphyrin Zn(II) [4·H and 4·Zn] having photopolymerizable unit at the end of tether groups and the modified fibers are well characterized by UV-vis absorption spectroscopy, confocal laser scanning microscopy as well as transmission electron microscopy. This is a novel example of decoration of gel fibers with fluorescent molecules and the process will offer an alternate application in photochemical and electrochemical devices.     

String-like propagation of the 5-coordinated defect state in supercooled water: molecular origin of dynamic and thermodynamic anomalies

We find that at low temperature water, large amplitude (~60°) rotational jumps propagate like a string, with the length of propagation increasing with lowering temperature. The strings are formed by mobile 5-coordinated water molecules which move like a Glarum defect (J. Chem. Phys., 1960, 33, 1371), causing water molecules on the path to change from 4-coordinated to 5-coordinated and again back to 4-coordinated water, and in the process cause the tagged water molecule to jump, by following essentially the Laage-Hynes mechanism (Science, 2006, 311, 832-835). The effects on relaxation of the propagating defect causing large amplitude jumps are manifested most dramatically in the mean square displacement (MSD) and also in the rotational time correlation function of the O-H bond of the molecule that is visited by the defect (transient transition to the 5-coordinated state). The MSD and the decay of rotational time correlation function, both remain quenched in the absence of any visit by the defect, as postulated by Glarum long time ago. We establish a direct connection between these propagating events and the known thermodynamic and dynamic anomalies in supercooled water. These strings are found largely in the regions that surround the relatively rigid domains of 4-coordinated water molecules. The propagating strings give rise to a noticeable dynamical heterogeneity, quantified here by a sharp rise in the peak of the four-point density response function, χ(4)(t). This dynamics heterogeneity is also responsible for the breakdown of the Stokes-Einstein relation.     

Dynamics of the barium-molecule system within large argon clusters

The effects of adding molecules on the LIF at 540 nm of a barium atom at the surface of an argon cluster (average size 420) has been investigated. We showed that molecules like ethanol,n-hexane and O₂ from stable complexes with ground state barium. In the case of molecules like N₂, CH₄ and SF₆, the collisional quenching of solvated Ba(¹ P) is observed. The large quenching rates obtained are interpreted by a surface mobility of the collisional partners. Moreover, we showed that this collisional quenching leads to the ejection of free Ba(³ P ₁).     

Solvation of tetraalkylammonium chlorides in acetonitrile-water mixtures: mass spectrometry and molecular dynamics simulations.

The solvation of tetramethylammonium chloride (Me4NCl) and tetra-n-butylammonium chloride (Bu4NCl) in water-acetonitrile mixtures was investigated by mass spectrometry of clusters isolated from the solution. As far as the positive ions are concerned, clusters composed of alkylammonium ions and acetonitrile molecules only were observed, even for mixtures with high water content. In contrast, for the negative ions, clusters composed of chloride with both water and/or acetonitrile molecules were observed. For the smaller system (Me4NCl) we performed quantum chemical calculations and molecular dynamics simulations. It was found that even though water is present in the solvation shell of Me4N+, only acetonitrile has a strong electrostatic interaction with the cation. Water molecules around Me4N+ form hydrogen bonds with other water molecules, and they interact with Me4N+ mainly via dispersive interactions. These results indicate that Me4N+ behaves like a hydrophobic solute. On the other hand, the interaction of Cl- with water and acetonitrile is of comparable strength and, in both cases, the electrostatic interaction dominates. Herein we demonstrate experimentally and theoretically that positive and negative ions give rise to characteristic solvation structures in mixed solvents: even a relatively small organic cation, such as Me4N+, exhibits a hydrophobic-like solvation shell.     

Variable-energy photoelectron spectroscopy of substituted rhenium and manganese pentacarbonyls: molecular orbital assignments and the interatomic resonant effect

High-resolution variable-energy photoelectron spectra of M(CO)5X [M = Re, X = Re(CO)5, Cl, Br, and I; and M = Mn, X = Mn(CO)5 and Br] are reported. Tunable synchrotron radiation is used to distinguish the Re 5d and Br 4p orbital based peaks for the controversial Re(CO)5Br. Our results provide firm molecular orbital assignments for all of these molecules. The valence orbital in the ordering of ionization energies for M(CO)5Cl (M = Mn and Re) and Mn(CO)5Br is a 1(M-X) > e(X) > b2(M) > e(M); but for M(CO)5I (M = Mn and Re) and Re(CO)5Br the ordering is a1(M-X) > e(M) > b2(M) > e(X). The crossover of the HOMO in the Re molecules due to the change in the halogen electronegativities occurs at Re(CO)5Br. The metal np-->nd resonance is observed for all of these molecules. For molecules like M2(CO)10 (M = Re and Mn) and Mn(CO)5Br, the observation of this np-->nd resonance is useful in assigning the metal nd based orbitals in their valence level spectra. However, for molecules like Re(CO)5X (X = Br and Cl), a np-->nd type resonance is observed on bands arising from both Re 5d and halogen mp based orbitals. This new resonant effect on the ligand-based orbitals is shown to be mainly due to the interatomic resonant effect. The core and valence level chemical shifts of these compounds are treated using Jolly's approach to confirm the assignments for the valence level spectra of some of these molecules. The high-resolution inner valence and core level spectra of these compounds are reported. Broadening of Re 4f, Br 3d, and I 4d core level spectra is discussed. The Auger peaks are observed in the high-resolution, high-intensity Br 3d of Re(CO)5Br and I 4d of Re(CO)5I spectra.     

Self-assembly of 5,11,17,23-tetranitro-25,26,27,28-tetramethoxythiacalix[4]arene with neutral molecules and its use for anion recognition

Methylation of 5,11,17,23-tetranitrothiacalix[4]arene with diazomethane leads to the tetramethoxy derivative, which was studied using single-crystal X-ray crystallography. It revealed that this compound, albeit in the 1,3-alternate conformation, can form the inclusion complexes with various solvent molecules possessing acidic methyl groups (ethyl acetate, nitromethane, acetone, acetonitrile) and creates interesting infinite channels filled with solvent molecules. The subsequent transformation of nitro groups into the ureido moieties gave receptors capable of anion recognition even in a highly HB-competitive solvent like DMSO.     

分子团簇的量子化学研究

采用Hartree-Fock方法、密度泛函(DFT)方法(BLYP、B3LYP)和MP2方法对Se4分子团簇的各种可能构型进行了结构优化和频率分析, 结果表明有5种构型是势能面上的稳定驻点, 同时对上述4种量子化学方法计算结果的差异进行了分析。并对这5种构型的结构稳定性、几何构型、前线分子轨道、Mulliken布局分析和偶极矩进行了分析, 根据分析结果对Se4分子的某些物理和化学性质进行了预测。     

Real‐Time Scanning Force Microscopy of Macromolecular Conformational Transitions

Summary: Comb‐like macromolecules were adsorbed on mica and imaged by scanning force microscopy in real time as they underwent a transition from an extended worm‐like conformation to globuli and vice versa. The conformational transition was effected by coadsorption of ethanol and water molecules. Coadsorption of the small molecules allowed manipulation of the adherence and spreading of the macromolecules, thus effecting the reptation like stretching and collapse of the single molecules.

SFM images of three individual PMA‐g‐PnBuA brush molecules on mica 27 min (left, first collapse cycle) and 18 min (right, second collapse cycle) after injection of ethanol into the sample space.     

Pyrazine control of the solid-state supramolecular chemistry of zinc phthalocyanine

Crystals of monoaxially coordinated T-shaped and H-shaped supramolecular zinc(II) phthalocyaninato complexes with pyrazine are obtained. In both types of molecules the central Zn atom of ZnPc complexes with pyrazine exhibits 4 + 1 coordination. The Zn atom is equatorially coordinated by four isoindole N atoms of Pc macrocycle and axially by N atom of pyrazine molecule. The interaction of the central Zn atom of ZnPc with the axial N atom of pyrazine leads to a deviation of Zn from the centre of cavity by 0.371(2) Å in the T-shaped complex and by 0.296(2) Å in the H-shaped complex. Thermogravimetric analysis of the crystals exhibits three slopes down, corresponding to the loss in succession of solvated pyrazine molecules, than the loss of ligated pyrazine molecules from the T-shaped complex and the finally the loss of the bridged pyrazine molecule from the H-shaped complex. Finally the thermal processing leads to the β-ZnPc as residue. The UV–Vis spectrum taken in solution shows the batochromic shift in the polar solvent like α-chloronaphthalene in relation to the spectrum in non-polar solvent like benzene.