Self-assembly of alkanols on Au(111) surfaces

Self-assembled monolayers (SAMs) of alkanols (1-C(N)H(2N+1)OH) with varying carbon-chain lengths (N = 10-30) have been systematically studied by means of scanning tunneling microscopy (STM) at the interfaces between alkanol solutions (or liquids) and Au(111) surfaces. The carbon skeletons were found to lie flat on the surfaces. This orientation is consistent with SAMs of alkanols on highly oriented pyrolytic graphite (HOPG) and MoS2 surfaces, and also with alkanes on reconstructed Au(111) surfaces. This result differs from a prior report, which claimed that 1-decanol molecules (N = 10) stood on their ends with the OH polar groups facing the gold substrate. Compared to alkanes, the replacement of one terminal CH3 group with an OH group introduces new bonding features for alkanols owing to the feasibility of forming hydrogen bonds. While SAMs of long-chain alkanols (N > 18) resemble those of alkanes, in which the aliphatic chains make a greater contribution, hydrogen bonding plays a more important role in the formation of SAMs of short-chain alkanols. Thus, in addition to the titled lamellar structure, a herringbone-like structure, seldom seen in SAMs of alkanes, is dominant in alkanol SAMs for values of N < 18. The odd-even effect present in alkane SAMs is also present in alkanol SAMs. Thus, the odd N alkanols (alkanols with an odd number of carbon atoms) adopt perpendicular lamellar structures owing to the favorable interactions of the CH3 terminal groups, similar to the result observed for odd alkanes. In contrast to alkanes on Au(111) surfaces, for which no SAMs on an unreconstructed gold substrate were observed, alkanols are capable of forming SAMs on either the reconstructed or the unreconstructed gold surfaces. Structural models for the packing of alkanol molecules on Au(111) surfaces have been proposed, which successfully explain these experimental observations.     

Thermotropic Liquid Crystals Formed by Intermolecular Hydrogen Bonding Interactions

The role of hydrogen bonding in the formation or stabilization of liquid crystalline phases has only recently been appreciated. Following the first, wellestablished examples of liquid crystal formation from the dimerization of aromatic carboxylic acids, through hydrogen bonding, several classes of compounds have recently been synthesized, the liquid crystalline behavior of which is also dependent on intermolecular hydrogen bonds between similar or dissimilar molecules. In this review the main classes of compounds exhibiting liquid crystallinity due to hydrogen bonding are presented to show the diversity of organic compounds that can be used as building elements in liquid crystals. The molecules are either of the rigid-rod anisotropic or amphiphilic types such as molecules appropriately functionalized with pyridyl and carboxyl groups, whose interaction leads to the formation of liquid crystals; amphiphilic carbohydrates and amphiphilic and bolaamphiphilic compounds with multiple hydroxyl groups whose dimerization or association is indispensable for the formation of liquid crystals; and certain amphiphilic carboxylic acids with monomeric or polymeric mesogens and amphiphilic-type compounds bearing different moieties, whose interaction may lead to the formation of mesomorphic compounds. Associated with the macroscopic display of liquid crystalline phases is the supramolecular structure, and therefore rather extended discussion of these structures are included in this review.     

Morphology controlled self-assembled nanostructures of sandwich mixed (phthalocyaninato)(porphyrinato) europium triple-deckers. Effect of hydrogen bonding on tuning the intermolecular interaction

A series of five novel sandwich-type mixed (phthalocyaninato)(porphyrinato) europium triple-decker complexes with different numbers of hydroxyl groups at the meso-substituted phenyl groups of porphyrin ligand 1-5 have been designed, synthesized, and characterized. Their self-assembly properties, in particular the effects of the number and positions of hydroxyl groups on the morphology of self-assembled nanostructures of these triple-decker complexes, have been comparatively and systematically studied. Competition and cooperation between the intermolecular pi-pi interaction and hydrogen bonding in the direction perpendicular to the pi-pi interaction direction for different compounds were revealed to result in nanostructures with a different morphology from nanoleafs for 1, nanoribbons for 2, nanosheets for 3, and curved nanosheets for 4 and to spherical shapes for 5. The IR and X-ray diffraction (XRD) results reveal that, in the nanostructures of triple-decker 2 as well as 3-5, a dimeric supramolecular structure was formed through an intermolecular hydrogen bond between two triple-decker molecules, which as the building block self-assembles into the target nanostructures. Electronic absorption spectroscopic results on the self-assembled nanostructures reveal the H-aggregate nature in the nanoleafs and nanoribbons formed from triple-deckers 1 and 2 due to the dominant pi-pi intermolecular interaction between triple-decker molecules, but the J-aggregate nature in the curved nanosheets and spherical shapes of 4 and 5 depending on the dominant hydrogen bonding interaction in cooperation with pi-pi interaction among the triple-decker molecules. Electronic absorption and XRD investigation clearly reveal the decrease in the pi-pi interaction and increase in the hydrogen bonding interaction among triple-decker molecules in the nanostructures along with the increase of hydroxyl number in the order of 1-5. The present result appears to represent the first effort toward realization of controlling and tuning the morphology of self-assembled nanostructures of sandwich tetrapyrrole rare earth complexes through molecular design and synthesis.     

Poly(hydroxyether of phenolphthalein) and its blends with poly(ethylene oxide)

Poly(hydroxyether of phenolphthalein) (PPH) was synthesized through the polycondensation of phenolphthalein with epichlorohydrin. It was characterized by Fourier transform infrared (FTIR) spectroscopy, NMR spectroscopy, and differential scanning calorimetry (DSC). The miscibility of the blends of PPH with poly(ethylene oxide) (PEO) was established on the basis of the thermal analysis results. DSC showed that the PPH/PEO blends prepared via casting from N,N‐dimethylformamide possessed single, composition‐dependent glass‐transition temperatures. Therefore, the blends were miscible in the amorphous state for all compositions. FTIR studies indicated that there were competitive hydrogen‐bonding interactions with the addition of PEO to the system, which were involved with OH…O?C〈, ? OH…? OH, and ? OH vs ether oxygen atoms of PEO hydrogen bonding, that is both intramolecular and intermolecular, between PPH and PEO). Some of the hydroxyl stretching vibration bands significantly shifted to higher frequencies, whereas others shifted to lower frequencies, and this suggested the formation of hydrogen bonds between the pendant hydroxyls of PPH and ether oxygen atoms of PEO, which were stronger than the intramolecular hydrogen bonding between hydroxyls and carbonyls of PPH. The FTIR spectra in the range of carbonyl stretching vibrations showed that the hydroxyl‐associated carbonyl groups were partially set free because of the presence of the competitive hydrogen‐bonding interactions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 466–475, 2003     

Phosphonyl/hydroxyl hydrogen bonding–induced miscibility of poly(arylene ether phosphine oxide/sulfone) statistical copolymers with poly(hydroxy ether) (phenoxy resin): Synthesis and characterization

High molecular weight bisphenol A or hydroquinone‐based poly(arylene ether phosphine oxide/sulfone) homopolymer or statistical copolymers were synthesized and characterized by thermal analysis, gel permeation chromatography, and intrinsic viscosity. Miscibility studies of blends of these copolymers with a (bisphenol A)‐epichlorohydrin based poly(hydroxy ether), termed phenoxy resin, were conducted by infrared spectroscopy, dynamic mechanical analysis, and differential scanning calorimetry. All of the data are consistent with strong hydrogen bonding between the phosphonyl groups of the copolymers and the pendent hydroxyl groups of the phenoxy resin as the miscibility‐inducing mechanism. Complete miscibility at all blend compositions was achieved with as little as 20 mol % of phosphine oxide units in the bisphenol A poly(arylene ether phosphine oxide/sulfone) copolymer. Single glass transition temperatures (T_g) from about 100 to 200°C were achieved. Replacement of bisphenol A by hydroquinone in the copolymer synthesis did not significantly affect blend miscibilities. Examination of the data within the framework of four existing blend T_g composition equations revealed T_g elevation attributable to phosphonyl/hydroxyl hydrogen bonding interactions. Because of the structural similarities of phenoxy, epoxy, and vinylester resins, the new poly(arylene ether phosphine oxide/sulfone) copolymers should find many applications as impact‐improving and interphase materials in thermoplastics and thermoset composite blend compositions. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1849–1862, 1999     

FT-IR studies of solvent and temperature effects on poly(diglycidal ether of bisphenol A) (epoxy)

The infrared spectra of poly(diglycidal ether of bisphenol A) (epoxy) were studied in solutions of chloroform, benzene, and carbon tetrachloride separately to investigate the solvent effect through the behavior of the hydroxyl stretching band. The effect of temperature on the epoxy resin was also studied in this region. The results indicate that there is a varying degree of the weakening of the hydrogen bonding of the hydroxyl group in the epoxy, depending on the solvent. There is evidence also for the formation of hydrogen bonding between chloroform and the hydroxyl group of the epoxy and to a lesser extent between epoxy and benzene.     

Simulation of Polymer Aggregates as a Method to Investigate the Solvent Effect on Blend Complexation and the Relative Strength of H‐Bonding Groups in Blends

Simulations of polymer‐solvent and polymer‐polymer aggregates, in which the study of hydrogen bonding plays an important role, have been carried out with two blend systems. The aim was to examine the influence of the solvent on blend complexation and to compare the strength of different hydrogen bonds in a blend system. We quantified the strength of one hydrogen bond in the blend environments. For this we used the EVOCAP software, developed by our institute. It allows the building of large molecular aggregates with realistic and homogeneous densities, with an implemented positioning algorithm of the molecules under consideration and their excluded volume, and a charge equilibration method for the partial charge calculation. In the simulated aggregates the specific interaction energy of the hydrogen atom forming the hydrogen bond was a useful indicator for our studies. Through a direct correlation of this specific‐interaction energy with the strength of the hydrogen bond, we supported the experimental result that, in toluene, complex formation between poly(methyl methacrylate) (PMMA) and PSOH, a hydroxyl‐modified polystyrene, is possible, but not in tetrahydrofuran. Varying the proton‐donor polymer, also a hydroxyl‐modified polystyrene, in blends of poly(vinyl methyl ether) (PVME) with groups of different donor strength, we reconstructed the experimental row of increasing hydrogen‐bond strengths.     

The behavior of cellulose molecules in aqueous environments

Molecular motions of cellulose chains in aqueous environments were investigated by comparison with those in non-aqueous environments using molecular simulation techniques. The cellulose chains under non-aqueous conditions approached each other closely and then made tight aggregates that were formed by direct hydrogen bonding. Those in aqueous environments, such as in a bio-system, were separated from each other by water molecules and did not have direct hydrogen bonding between the cellulose chain molecules. Folded-chain structures were not found in either aqueous or non-aqueous environments that were somewhat crowded. In the aqueous system, the water molecules around the cellulose chains restricted their molecular motions and interrupted formation of direct, interchain hydrogen bonds. In the non-aqueous system, the cellulose chains approached each other closely and then made a tight cluster before the chain molecules could wind and bend. It was concluded that a very dilute solution of cellulose molecules in appropriate solvents is necessary to create folded-chain or random-coiled structures. We also confirmed that the driving force for making tight clusters of cellulose molecules in highly concentrated solutions is the energy of the hydrogen bonding created directly between the hydroxyl groups of the cellulose chains. These results strongly suggest that hydrogen bonding plays a very important role in the characteristics of cellulose molecules.     

Intramolecular hydrogen bonding (P=O--H) stabilizes the chair conformation of six-membered ring phosphates

[reaction: see text] Six-membered cyclic phosphates (2-phenoxy-2-oxo-1,3,2-dioxaphosphorinanes) bearing an internal protected or unprotected hydroxyl group were designed, synthesized, and studied by NMR and computational methods. Selective opening of O-isopropylidene-protected 1,2-diols at the primary site was achieved with either triethylsilane or trimethylallylsilane in the presence of BF3.OEt2. Applied to 5,6-O-isopropylidenepentofuranosides, this reaction gave rise to the formation of the corresponding 1,3-diol precursors for the six-membered ring phosphates containing an O-isopropyl or O-1,1-dimethyl-3-butenyl functional group at C-6. The O-1,1-dimethyl-3-butenyl protecting group was efficiently removed after the phosphorylation with BF3.OEt2, and the six-membered cyclic phosphates containing free hydroxyl groups were obtained. A cyclic phosphate with a free hydroxyl group oriented cis to the phosphoryl group shows a vicinal coupling constant 3J(HP) that is in accordance with the chair conformation. This is due to the formation of a seven-membered intramolecular hydrogen-bonded ring structure that stabilizes the chair conformation. Thus, the strong tendency of the phenoxy group to be in an axial position is diminished by the internal hydrogen bonding interaction. Computational studies provided strong support for the experimental observation.     

大孔交联聚(对乙烯基苄基苯胺)树脂对苯酚的吸附

由氯甲基化聚苯乙烯合成了大孔交联聚(对乙烯基苄基苯胺)树脂, 测定了其对正己烷和水中苯酚的吸附等温线, 计算了吸附焓. 结果表明, 苯胺基树脂主要是通过氢键吸附正己烷中苯酚的, 树脂负载的功能基氮原子和苯环都作为氢键受体与苯酚的羟基氢原子形成氢键, 而其对水中苯酚的吸附是基于氢键和疏水作用.     

Effect of intermolecular hydrogen bonding on low-surface-energy material of poly(vinylphenol)

We discovered that poly(vinylphenol) (PVPh) possesses an extremely low surface energy (15.7 mJ/m2) after a simple thermal treatment procedure, even lower than that of poly(tetrafluoroethylene) (22.0 mJ/m2) calculated on the basis of the two-liquid geometric method. Infrared analyses indicate that the intermolecular hydrogen bonding of PVPh decreases by converting the hydroxyl group into a free hydroxyl and increasing intramolecular hydrogen bonding after thermal treatment. PVPh results in a lower surface energy because of the decrease of intermolecular hydrogen bonding between hydroxyl groups. In addition, we also compared surface energies of PVPh-co-PS (polystyrene) copolymers (random and block) and their corresponding blends. Again, these random copolymers possess a lower fraction of intermolecular hydrogen bonding and surface energy than the corresponding block copolymers or blends after similar thermal treatment. This finding provides a unique and easy method to prepare a low-surface-energy material through a simple thermal treatment procedure without using fluoro polymers or silicones.     

Hydrogen bonding interactions and miscibility between phenolic resin and octa(acetoxystyryl) polyhedral oligomeric silsesquioxane (AS‐POSS) nanocomposites

We have synthesized a polyhedral oligomeric silisesquioxane (POSS) derivative containing eight acetoxystyryl functional groups [octa(acetoxystyryl)octasilsesquioxane (AS‐POSS)] and then blended it with phenolic resin to form nanocomposites stabilized through hydrogen bonding interactions between the phenolic resin's hydroxyl group and the AS‐POSS derivative's carbonyl and siloxane groups. One‐ and two‐dimensional infrared spectroscopy analyses provided positive evidence for these types of hydrogen bonding interactions. In addition, we calculated the interassociation equilibrium constant, based on the Painter–Coleman association model (PCAM), between phenolic resin and POSS indirectly from the fraction of hydrogen‐bonded carbonyl groups; quantitative analyses indicate that the hydroxyl–siloxane interassociation from the PCAM is entirely consistent with the classical Coggesthall and Saier (C and S) methodology. From a thermal analysis, we observed that the miscibility between phenolic and AS‐POSS occurs at a relatively low AS‐POSS content, which characterizes this mixture as a polymer nanocomposite system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 673–686, 2006     

The study of the miscibility and morphology of poly(styrene‐co‐4‐vinylphenol)/poly(propylene carbonate) blends

Blends of poly(propylene carbonate) (PPC) with copolymer poly(styrene‐co‐4‐vinyl phenol) (STVPh) have been studied by electron spin resonance (ESR) spin probe method and Raman spectroscopy. The ESR results indicated that the nitroxide radical existed in a PPC‐rich and an STVPh‐rich micro domain in the blends, corresponding to the fast‐motion and slow‐motion component in the ESR spectra, respectively. And in the temperature dependence composite spectra, the fast‐motion fraction increased with increasing the hydroxyl group content in copolymer STVPh. Moreover, the ESR parameter T_5mT, rotational correlation times (τ_c) and activation energies (E_a) showed similar dependence on the hydroxyl group content as the fast‐motion fraction. It resulted from the enhancement of the hydrogen‐bonding interaction between the hydroxyl groups in STVPh and the carboxyl groups and ether oxygen in PPC. However, the distinct band shift and intensity change among the Raman spectra of pure polymer components and those of the blends were observed. In the carboxyl‐stretching region, the band shifted to lower frequency with increasing the hydroxyl groups. Furthermore, the phase morphologies of the blends were obtained by optical microscopy. All could be concluded that the hydrogen‐bonding interaction between the two components was progressively favorable to the mixing process and was the driving force for the miscibility enhancement in the blends. Copyright © 2004 John Wiley & Sons, Ltd.     

Spectroscopic Observation of the Hydroxy Position in Butanol Hydrates and Its Effect on Hydrate Stability

In this study, we investigate the crystal structures and phase equilibria of butanols+CH₄+H₂O systems to reveal the hydroxy group positioning and its effects on hydrate stability. Four clathrate hydrates formed by structural butanol isomers are identified with powder X‐ray diffraction (PXRD). In addition, Raman spectroscopy is used to analyze the guest distributions and inclusion behaviors of large alcohol molecules in these hydrate systems. The existence of a free OH indicates that guest molecules can be captured in the large cages of structure II hydrates without any hydrogen‐bonding interactions between the hydroxy group of the guests and the water‐host framework. However, Raman spectra of the binary (1‐butanol+CH₄) hydrate do not show the free OH signal, indicating that there could be possible hydrogen‐bonding interactions between the guests and hosts. We also measure the four‐phase equilibrium conditions of the butanols+CH₄+H₂O systems.     

Nanoscale-confined crystallization in epoxy resin and polyethylene-block-poly(ethylene oxide) diblock copolymer blends

In this paper, the nanoscale-confined crystallization behavior and crystallization kinetics in blends of double-crystalline polyethylene-block-poly(ethylene oxide) (PE-b-PEO) diblock copolymer with diglycidyl ether of bisphenol A epoxy resin were investigated. The results showed that there appeared three crystallization regimes related to the crystallization of the PE block within three different microenvironments in the epoxy resin/PE-b-PEO blends. The Avrami index n is around 1.8–2.4, suggesting PE block of the copolymer in the blends exhibited nanoscale-confined crystallization behavior by homogeneous nucleation. The PE block nanoscale-confined crystallization is ascribed to the formation of the strong intermolecular hydrogen bonding interaction between hydroxyl groups of amine-cured epoxy and ether oxygen atoms of PEO, as seen from Fourier transform infrared spectroscopy spectra.     

Theoretical investigations on chalcogen-chalcogen interactions: what makes these nonbonded interactions bonding?

To understand the intermolecular interactions between chalcogen centers (O, S, Se, Te), quantum chemical calculations on pairs of model systems were carried out. For the oxygen derivatives, one of the components of the supermolecules consists of dimethyl ether, while the second component is either dimethyl ether (1) or ethynyl methyl ether (2) or methyl cyanate (3). The model calculations were also extended to the sulfur (4-6), selenium (7-9), and tellurium congeners (10-12). The MP2/SDB-cc-pVTZ, 6-311G level of theory was used to derive the geometrical parameters and the global energies of the model systems. A detailed analysis based on symmetry adapted perturbation theory (SAPT) reveals that induction and dispersion forces contribute to the bonding in each case. For 1-3 the electrostatic energy also contributes to the intermolecular bonding, but not for 4-12. The NBO analysis reveals that the interaction in the dimers 1-3 is mainly due to weak hydrogen bonding between methyl groups and chalcogen centers. Similar hydrogen bonding is also found in the case of 4 and to a lesser extent in 5 and 7. For the aggregates with heavier centers the chalcogen-chalcogen interaction dominates, and hydrogen bonding only plays a minor role. Electron-withdrawing groups on the chalcogen centers increase the interaction energy and reduce the intermolecular distance dramatically. The one-electron picture of an interaction between the lone pair of the donor and the chalcogen carbon sigma orbital allows a qualitatively correct reproduction of the observed trend.     

Weak calcium-mediated interactions between Lewis X-related trisaccharides studied by NMR measurements of residual dipolar couplings

The Lewis X (LeX) determinant, a trisaccharide with the carbohydrate sequence Galbeta(1-->4)[Fucalpha(1-->3)]GlcNAcbeta, is believed to be responsible for Ca2+-mediated cell-cell interactions. In partly oriented phases composed of mixtures of penta(ethyleneglycol)monododecyl ether HO(CH2CH2O)5C12H25 and n-hexanol in the presence of Ca2+ ions, the variation of the residual dipolar couplings 1DCH of various CiHi vectors in LeX as a function of the concentration of the trisaccharide demonstrates the existence of very weak LeX-Ca2+-LeX complexes in solution. Synthetic 3-, 4-, and 6-deoxy-LeX variants were also shown to form complexes in the presence of calcium ions, despite the replacement of one of their hydroxyl groups by hydrogen atoms. This is the first direct observation in solution of a calcium-mediated interaction between LeX molecules.     

The role of charge transfer in the hydrogen bond cooperative effect of cis-N-methylformamide oligomers

Two accumulating molecular systems have been designed to investigate the cooperative effect of hydrogen bonding in theory. The first system included a series of linear oligomers of cis-N-methylformamide (c-NMF) molecules. Substantial cooperative effect has been confirmed in the electronic structures and energies of the hydrogen bonds in them as shown by the results obtained using the B3LYP method at the level of cc-pVTZ basis sets. Such a cooperative effect gradually increases with the growth of the c-NMF oligomer. The second system included a series of modified c-NMF trimers whose central c-NMF molecules contained insertion fragments of varying structural and electrical compositions. On the basis of an examination of the structures and charge populations of the c-NMF oligomers in these two systems, a mechanism of the cooperative effect of hydrogen bonding in these systems based on charge flow in the c-NMF molecules is proposed. The results from the second system of c-NMF trimers were particularly instrumental in formulating this mechanism, because the charge flows between the C=O and N-H groups in the modified c-NMF molecule of these trimers were dampened by the various molecular insertions. A clear correlation between the degree of charge flow dampening from each inserted fragment and the magnitude of the cooperative effect of hydrogen bonding was observed. On the basis of an analysis of the electronic structural characteristics of the molecular fragments, we conclude that the charge flow between the hydrogen bond donor and acceptor groups in the c-NMF molecule is the most important factor inducing the cooperative effect of hydrogen bonding.     

Molecular tectonics. Porous hydrogen-bonded networks built from derivatives of pentaerythrityl tetraphenyl ether

The symmetric four-armed geometry of pentaerythrityl tetraphenyl ether (5) makes it a valuable starting point for building complex molecular and supramolecular structures. In particular, it provides a core to which multiple sites of attractive intermolecular interaction can be attached, thereby creating compounds predisposed to form complex networks by association. To facilitate exploitation of the pentaerythrityl tetraphenyl ether core in such ways, we have prepared more than 20 new derivatives by efficient methods. Of special interest are compounds 3 and 4, which incorporate four diaminotriazine groups attached to the meta and para positions of the pentaerythrityl tetraphenyl ether core. Crystallization of compounds 3 and 4 from DMSO/dioxane is directed by hydrogen bonding of the diaminotriazine groups according to well-established motifs, thereby producing three-dimensional networks. In forming these networks, each molecule of compound 3 forms a total of 12 hydrogen bonds with six others, whereas each molecule of compound 4 forms a total of 16 hydrogen bonds with four others. Both networks are highly porous and define significant interconnected channels for the inclusion of guests. In crystals of compounds 3 and 4, the fraction of the volume accessible to guests is 66% and 57%, respectively. In both cases, the pentaerythrityl tetraphenyl ether cores adopt conformations that deviate substantially from tetrahedral geometry. It is noteworthy that the inherent flexibility of the core does not favor the formation of close-packed guest-free structures.