Metal ion coordination with an asymmetric fan-shaped dendrimer at the air-water interface

Metal coordination to monolayers of 4-{10-[4-(3,5-bis-benzyloxy)-phenyl]-anthracen-9-yl}-benzoic acid ([G1-An]-CO(2)H, G1) and 4-(10-{4-[3,5-bis-(3,5-bis-benzyloxy)-benzyloxy]-phenyl}-anthracen-9-yl)-benzoic acid ([G2-An]-CO(2)H, G2) at the air-water interface and to Langmuir-Blodgett (LB) films was investigated using surface pressure-area isotherms, ultraviolet-visible (UV-vis) spectroscopy, atomic force microscopy (AFM), and X-ray reflectivity (XRR). Surface pressure-area isotherms show that G1 and G2 have different limiting areas according to the type of subphase. The limiting area of G1 and G2 increased more with Al(3+) than with Eu(3+) in the subphase. This result indicates that the hydrophilic core group is anchored to ions in the water via bidentate chelates with the carboxylate oxygen atoms of G1 and G2. Circular domains and aggregates were observed for the LB film. The different behavior of Eu(3+) and Al(3+) complexes is originated from the intrinsic nature of the ion, i.e., coordination number.     

Influence of interfacial features in the supramolecular assembly of 3,5-dihydroxybenzylalcohol based dendrimers on Si/SiO2 surfaces

Self-organization of 3,5-dihydroxybenzylalcohol (DHBA) based dendrimers of generations 0-3 (G0-G3) on bare and functionalized single crystal silicon (Si/SiO2) surfaces has been examined. The underlying monolayer plays a significant role in the supramolecular assembly leading to ordered structures of DHBA (G0) and generation 1-3 (G1-G3) dendrimers at interfaces. Ordered hyperbranched structures are formed on surfaces containing self-assembled monolayers with complimentary features to the assembling molecules, whereas no such organized assemblies are observed on unfunctionalized surfaces.     

Synthesis and characterization of chiral azobenzene dye functionalized Janus dendrimers

Eight bischromophoric bisMPA based polyester Janus dendrimers emanating from a pentaerythritol core were synthesized and their properties evaluated. 4-((4-(Ethyl(2-(2-(6-methoxynaphthalen-2-yl)propanoyloxy)ethyl)amino)-phenyl)diazenyl)-benzoic acid and 4-((4-(ethyl(2-(2-(6-methoxynaphthalen-2-yl)propanoyloxy)-ethyl)-amino)phenyl)diazenyl)-3-nitrobenzoic acid were attached to the dendritic polyester skeleton to make chiral dendrimers up to the second generation. The structures and the purity of the molecules were verified with ¹H NMR, ¹³C NMR, ESI TOF mass spectrometry, and elemental analysis. Spectral properties were evaluated with UV-vis and CD spectrometer. The compounds displayed broad absorption maxima in the visible region. The CD spectra confirmed the optical purity of the compounds. The thermal properties were evaluated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC).     

Langmuir-Blodgett-Kuhn and self-assembled films of asymmetrically substituted poly(paraphenylene)

Asymmetrically substituted poly(paraphenylene) (PhPPP) with hydrophilic and hydrophobic side chains was investigated. The polymer behavior at the air-water interface was studied on the basis of surface pressure-area (pi-A) isotherms and compression/expansion hysteresis measurements. PhPPP can form stable monolayers with an area per repeat unit of A=0.20+/-0.02 nm2 and a collapse pressure in the range of pi=25 mN/m. Then, Langmuir-Blodgett-Kuhn (LBK) films of PhPPP were prepared by horizontally and vertically transferring the Langmuir monolayers onto hydrophilic solid substrates at pi=12 mN/m. Cross-section analysis of the AFM tapping-mode topography images of a single transferred monolayer reveals a thickness of d0=0.9+/-0.1 nm. Taking into account the obtained monolayer thickness, curve-fitting calculations of angular scan data of LB monolayers measured using surface plasmon resonance (SPR) spectroscopy lead to a value for the refractive index of n=1.78+/-0.02 at lambda=632.8 nm. Next, the spontaneous formation of a PhPPP monolayer by adsorption from solution was studied ex situ by atomic force microscopy and UV-vis spectroscopy and in situ by using SPR spectroscopy. Stable self-assembled monolayers of PhPPP can be formed on hydrophilic surfaces with a thickness similar to that of the monolayer obtained using the LB method. The characterization results confirmed the amphiphilic character and the self-assembly properties of PhPPP, as well as the possibility of preparing homogeneous monolayer and multilayer films.     

多枝[1,3,4]-噁二唑衍生物的双光子吸收和光功率限幅特性

采用非线性透过率法测定了多枝[1,3,4]-噁二唑衍生物的双光子吸收性质. 测定了化合物的单光子荧光光谱和双光子荧光光谱, 在800 nm波长的激光激发下, 9-乙基-3,6-双{5-(4-叔丁基苯基)-[1,3,4] 噁二唑-2-苯乙烯基}-咔唑(3)和三-{5-(4-叔丁基苯基)-[1,3,4] 噁二唑-2-苯乙烯基-4-苯基}-胺(4)能够发出很强的蓝色和黄绿色双光子上转换荧光, 荧光峰分别位于485和547 nm. 这些多枝结构化合物的双光子吸收截面较大(数值超过104 GM), 并具有很强的光限幅效应. 多枝分子中重复单元的推拉电子结构和协同效应有效地增强了分子的双光子吸收性质.     

Lateral and vertical nanophase separation in Langmuir-Blodgett films of phospholipids and semifluorinated alkanes

It has recently been found that monodisperse surface micelles (hemimicelles) were formed in Langmuir monolayers of the semifluorinated alkane C8F17C16H33 (F8H16) after transfer onto silicon wafers. Grazing incidence X-ray diffraction studies have demonstrated that compression of mixed Langmuir monolayers made from combinations of dipalmitoyl phosphatidylethanolamine (DPPE) and diblock F8H16 in various molar ratios resulted in the complete expulsion of the diblock molecule at high surface pressure. F8H16 then formed a second layer on top of a DPPE-only monolayer, demonstrating a novel type of reversible, pressure-induced, vertical phase separation. Using atomic force microscopy and X-ray reflectivity, we show now that mixed DPPE/F8H16 (1:1.3) Langmuir-Blodgett films transferred onto silicon wafers below 10 mN m(-1) are laterally phase separated and consist of domains of F8H16 surface micelles in coexistence with a monolayer of DPPE. The density of the network of F8H16 surface micelles increases when the surface pressure of transfer increases. Around 10 mN m(-1), the F8H16 surface micelles start to glide on the DPPE monolayer, progressively overlying it, until total coverage is achieved.     

Sum frequency generation spectroscopic studies on phase transitions of phospholipid monolayers containing poly(ethylene oxide) lipids at the air-water interface

Vibrational sum frequency generation (SFG) spectroscopy was applied to study the phase transitions of the mixed monolayers of l-alpha-distearoyl phosphatidylethanolamine (DSPE) and DSPE covalently coupled with poly(ethylene oxide) at the amino head group (DSPE-EO(45), DSPE with 45 ethylene oxide monomers) at the air-water interface. The SFG spectra were measured for the mixed monolayers with the mole fractions of DSPE-EO(45) of 0, 1.3, 4.5, 9.0, 12.5, and 16.7% at the surface pressures of 5, 15, and 35 mN/m. The monolayer compression isotherms indicated that the mixed monolayers at 5, 15, are 35 mN/m are mainly in the so-called "pancake", "mushroom", and "brush" states, respectively. The SFG spectra in the OH stretching vibration region give rise to SFG bands near 3200 and 3400 cm(-1). The mean molecular amplitude of the former band due to the OH stretching of the "icelike" water molecules associated mainly with the hydrophilic poly(ethylene oxide) (PEO) chains, exhibits appreciable decrease on compression of the mixed monolayers from 5 to 15 mN/m. The result corroborates the model for the pancake-mushroom transition, which presumes the dissolution of the PEO chains from the air-water interface to the water subphase. Further compression of the mixed monolayers to 35 mN/m causes a slight decrease of the line amplitude, which can be explained by considering a squeezing out of water molecules from the hydrophilic groups of DSPE-EO(45) in the brush state, where the PEO chains strongly interact with each other to form a tight binding state of the hydrophilic groups. The relative intensities of the SFG bands due to the CH3 asymmetric and symmetric vibrations were used to estimate the tilt angles of the terminal methyl group of DSPE, indicating that the angle increases with increasing the mole fraction of DSPE-EO(45). The angles almost saturate at the mole fraction larger than 10%, the saturation angle being nearly 90 degrees at 5 mN/m, ca. 60 degrees at 15 mN/m, and ca. 47 degrees at 35 mN/ m. Then, the introduction of the hydrophilic PEO head group causes a large tilting of the alkyl groups of DEPE in the mixed monolayers.     

2,4和8-支噁二唑衍生物的三光子吸收和三光子上转换荧光

用飞秒Ti:sapphire激光测定了3个对称噁二唑衍生物4-{N,N-双[4-(4-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2]苯乙烯基)苯基]氨基}苯甲醛(Bis-oxa)、2,5-双{4-[2-N,N-双(4-{4-[5-(4-叔丁基苯基)-1,3,4-噁二唑-2]苯乙烯基}苯基)氨基苯乙烯基]苯基}-1,3,4-噁二唑(Quadri-oxa)和2,5-双(4-{2-N,N-双[({3,5-二[5-(4-叔丁基苯基)-1,3,4-噁二唑-2]苯基}乙烯基)苯基]氨基苯乙烯基}苯基)-1,3,4-噁二唑(Octu-oxa)的三光子吸收谱和三光子荧光光谱. 在1260 nm飞秒激光激发下, 2,4和8-支噁二唑衍生物的三光子吸收系数分别为5.0×10^-5, 10.0×10^-5和10.0×10^-5 cm³/GW², 三光子频率上转换荧光发射波长分别为533, 544和551 nm. 研究了多支化合物线性吸收和透过、单光子荧光及量子产率、荧光寿命、多光子荧光光谱和三光子吸收系数谱. 对称多支噁二唑衍生物具有很强的三光子吸收和上转换荧光性质.     

Degradation behaviors of polyester monolayers at the air/water interface: Alkaline and enzymatic degradations

The degradation kinetics of Langmuir monolayer films of a series of biodegradable polyesters has been studied to investigate the effect of degradation medium, alkalinity and enzymes. The degradation behavior of polyester monolayers strongly depended on both degradation medium and surface pressure. As the surface pressure was increased, the degradation rates of poly(l-lactide) (PLLA) and poly[(R)-3-hydroxybutyrate] (P(3HB)) increased in both degradation media. When monolayers were exposed to an alkaline subphase, the degradation of PLLA monolayers occurred at relatively low surface pressures; the PLLA monolayers were hydrolyzed at pH 10.5 regardless of surface pressure, while the alkaline degradation of P(3HB) monolayer occurred over a constant surface pressure of 7 mN/m at pH 11.8. These results have been explained by the difference in hydrophilic/hydrophobic balance of the polymers; PLLA is more hydrophilic than P(3HB). In contrast, the enzymatic degradations of both polymer monolayers occurred at higher constant surface pressures than those of the alkaline treatment; 7 mN/m for PLLA and 10 mN/m for P(3HB). This behavior was attributed to the enzymes being much larger than the alkaline ions: the enzymes need a larger contact area with the submerged monolayers to be activated.     

Novel first-generation dendrimers on calix[4]resorcinol core equipped with multiple triazole units

Novel first-generation dendrimers on the calix[4]resorcinol core with four branches each containing multiple 1,2,3-triazole units have been synthesized in one-step by acid catalyzed condensation of resorcinols with a new aldehyde dendron, namely, 4-{3,5-bis[(1-benzyl-1H-1,2,3-triazol-4-yl)- methoxy]benzyloxy}benzaldehyde (obtained by alkyne–azide cycloaddition). The reaction proceeds stereoselectively to form rccc-diastereoisomers in high yields.     

Fabrication of metal nanoparticle monolayers on amphiphilic poly(amido amine) dendrimer Langmuir films

A newly designed 1.5th generation poly(amido amine) dendrimer with an azacrown core, hexylene spacers, and octyl terminals was spread on gold nanoparticle (Au-NP) suspension. The surface pressure-area isothermal curves indicated that the molecular area of dendrimer on Au-NP suspension was significantly smaller than that on water, indicating the formation of dendrimer/Au-NP composites. The dendrimer Langmuir films on the Au-NP suspension were transferred to copper grids at various surface pressures and observed by transmission electron microscopy. The transferred films consisted of a fractal-like network of nanoparticles at low surface pressure and of a defect-rich monolayer of nanoparticles at high surface pressure. From these results, it was suggested that the dendrimers bind Au-NPs, and dendrimer/Au-NP composites formed networks or monolayers at the interface. From the intensity decrease of the Au plasmon band of Au-NP suspension after the formation of composite, it was estimated that some (approximately 14) dendrimer molecules bind to one Au-NP. Furthermore, neutron reflectivity at the air/suspension interface and X-ray reflectivity of the film transferred on a silicon substrate revealed that the dendrimer molecules are localized on the upper-half surface of Au-NP. Metal affinity of azacrown, flexibility of hexylene spacer, and amphiphilicity of dendrimer with octyl terminals played important roles for the formation of dendrimer/Au-NP hybrid films. The present investigation proposed a new method to fabricate the self-assembled functional polymer/nanoparticle hybrid film.     

Synthesis, photoluminescence, and adsorption of CdS/dendrimer nanocomposites

CdS/dendrimer nanocomposites can be synthesized from methanolic Cd(2+) and S(2-) with amine-terminated polyamidoamine dendrimers of generation 8 (G8NH(2)) as stabilizers. By controlling the preparation conditions, nanoparticles with diameters < or = 2 nm can be obtained with a narrow size distribution. They show blue photoluminescence at approximately 450 nm. We studied the effects of various additives on the photoluminescence and elucidated its mechanism. Stable aggregates of two to three G8NH(2) molecules with several CdS nanoparticles form; the particles are located at the surface of the G8NH(2) molecules. The adsorption of the CdS/G8NH(2) nanocomposites on flat substrate surfaces is determined by the substrate chemistry. The hydrophilic nature of G8NH(2) results in weak affinity to graphite but strong affinity to hydroxy-terminated substrates such as mica, oxidized silicon wafers, and carboxylate-terminated monolayers. Patterning of nanocomposites on these hydrophilic substrates is achieved by the microcontact printing method. We propose to use only one molecule, a large dendrimer, to control the nanoparticle formation and also the immobilization of the synthesized nanoparticle/dendrimer composites.     

Some chemical transformations of alkyl (4-aminophenyl)carbamates

Azo coupling of diazonium salts derived from alkyl (4-aminophenyl)carbamates with ethyl α-methylacetoacetate gave ethyl 5-alkoxycarbonylamino-1H-indole-2-carboxylates. The condensation of aminophenylcarbamates with aromatic aldehydes in ethanol afforded the corresponding Schiff bases. Cyclohexyl {4-[(4-methoxyphenyl)methylidene]aminophenyl}carbamate reacted with chloroacetyl chloride in dioxane in the presence of triethylamine to produce cyclohexyl {4-[3-chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl]phenylcarbamate, and the reaction of benzyl {4-[(4-nitrophenyl)methylidene]aminophenyl}carbamate with sulfanylacetic acid in DMF led to the formation of benzyl {4-[2-(4-nitrophenyl)-4-oxo-1,3-thiazolidin-3-yl]-phenyl}carbamate.     

Investigation of negative differential resistance properties of self-assembled dipyridinium using STM

Recently, research on conducting molecules containing thiol functional groups such as benzenethiol has been progressing [X. Xiao, B. Xu, N.J. Tao, Nano Lett. 4 (2004) 267]. This conducting molecule is applicable to the study of the negative differential resistance (NDR) and switching properties of logic device. The 4-{4[4-(4-{1-[4-(4-acetylsulfanyl-phenylethynyl)-phenyl]-2,6-diphenyl-pyridinium-4-yl}-phenyl)-2,6-diphenyl-pyridinium-1-yl]-phenylethynyl}-phenylthioacetate (dipyridinium) molecule contains thiol functional groups such as benzenethiol. Thus, we have studied an NDR property of a dipyridinium molecule using the self-assembly method in scanning tunneling microscopy (STM). The Au substrate was exposed to a 1 mM solution of 1-dodecanethiol in ethanol for 24 h to form a monolayer. After thorough rinsing of the sample, it was exposed to a 0.1 μM solution of dipyridinium in dimethylformamide (DMF) for 30 min. After the assembly, we measured the electrical properties of the self-assembly monolayers (SAMs) using ultra high vacuum scanning tunneling microscopy (UHV-STM) and scanning tunneling spectroscopy (STS). As a result, we confirmed the properties of NDR in a negative region at −1.67 V and a positive region at 1.78 V. The energy gap (E_g) was found to be 3.12 eV [C. Arena, B. Kleinsorge, J. Robertson, W.I. Milne, M.E. Welland, J. Appl. Phys. 85 (1999) 1609]. This molecule is applicable to the fabrication of molecular junctions.     

Thermodynamic characteristics and Langmuir-Blodgett deposition behavior of mixed DPPA/DPPC monolayers at air/liquid interfaces

The role of dipalmitoylphosphatic acid (DPPA) as a transfer promoter to enhance the Langmuir-Blodgett (LB) deposition of a dipalmitoylphosphatidylcholine (DPPC) monolayer at air/liquid interfaces was investigated, and the effects of Ca2+ ions in the subphase were discussed. The miscibility of the two components at air/liquid interfaces was evaluated by surface pressure-area per molecule isotherms, thermodynamic analysis, and by the direct observation of Brewster angle microscopy (BAM). Multilayer LB deposition behavior of the mixed DPPA/DPPC monolayers was then studied by transferring the monolayers onto hydrophilic glass plates at a surface pressure of 30 mN/m. The results showed that the two components, DPPA and DPPC, were miscible in a monolayer on both subphases of pure water and 0.2 mM CaCl2 solution. However, an exception occurs between X(DPPA)=0.2 and 0.5 at air/CaCl2-solution interface, where a partially miscible monolayer with phase separation may occur. Negative deviations in the excess area analysis were found for the mixed monolayer system, indicating the existence of attractive interactions between DPPA and DPPC molecules in the monolayers. The monolayers were stable at the surface pressure of 30 mN/m for the following LB deposition as evaluated from the area relaxation behavior. It was found that the presence of Ca2+ ions had a stabilization effect for DPPA-rich monolayers, probably due to the association of negatively charged DPPA molecules with Ca2+ ions. Moreover, the Ca2+ ions may enhance the adhesion of DPPA polar groups to a glass surface and the interactions between DPPA polar groups in the multilayer LB film structure. As a result, Y-type multilayer LB films containing DPPC could be fabricated from the mixed DPPA/DPPC monolayers with the presence of Ca2+ ions.     

Preparation of ordered films containing a phenylene ethynylene oligomer by the Langmuir-Blodgett technique

This paper reports the fabrication and characterization of Langmuir and Langmuir-Blodgett (LB) films incorporating an oligo(phenylene-ethynylene) (OPE) derivative, namely, 4-[4-(4-hexyloxyphenylethynyl)-phenylethynyl]-benzoic acid (HBPEB). Conditions appropriate for deposition of monolayers of HBPEB at the air-water interface have been established and the resulting Langmuir films characterized by a combination of surface pressure and surface potential versus area per molecule isotherms, Brewster angle microscopy, and ultraviolet reflection spectroscopy. The Langmuir films are readily transferred onto solid substrates, and one-layer LB films transferred at several surface pressures onto mica substrates have been analyzed by means of atomic force microscopy, from which it can be concluded that 14 mN/m is an optimum surface pressure of transference, giving well-ordered homogeneous films without three-dimensional defects and a low surface roughness. The optical and emissive properties of the LB films have been determined with significant blue-shifted absorption spectra indicating formation of two-dimensional H aggregates and a Stokes shift illustrating the effects of the solid-like environment on the molecular chromophore.     

Parallel synthesis of 2-substituted 6-(5-oxo-1-phenylpyrrolidin-3-yl)pyrimidine-5-carboxamides

A library of 24 6-(5-oxo-1-phenylpyrrolidin-3-yl)pyrimidine-5-carboxamides 10{1,2; 1-12} was prepared by a parallel solution-phase approach. The synthesis comprises a five-step transformation of itaconic acid (11) into 1-methyl and 1-phenyl substituted 6-(5-oxo-1-phenylpyrrolidin-3-yl)pyrimidine-5-carboxylic acids 17{1,2} followed by parallel amidation of 17{1,2} with a series of 12 aliphatic amines 18{1-12} to afford the corresponding carboxamides 10 in good overall yields and in 80-100% purity.     

Synthesis and Molecular Structure of 3-[N-Acetyl(3,5-dimethylphenyl)amino]-5,7-di(tert-butyl)-2-{5,8-dimethyl-4-[(3,5-dimethylphenyl)amino]quinolin-2-yl}tropone

Russian Journal of General Chemistry - Acylation of 5,7-di(tert-butyl)-2-{5,8-dimethyl-4-[(3,5-dimethylphenyl)amino]quinolin-2-yl}-3-[(3,5-dimethylphenyl)amino]tropone leads to...     

Synthesis of Some New Thiazoles and Pyrazolo[1,5-a]pyrimidines Containing an Antipyrine Moiety

Ethyl 2-{2-[4-(2,3-dimethyl-5-oxo-1-phenyl-3-(pyrazolin-4-yl)]-2-cyano-1-(phenylamino)vinylthio}-acetate, 2-[4-(2,3-dimethyl-5-oxo-1-phenyl-(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]2-(4-oxo-3-phenyl-(1,3-thiazoilidin-2-ylidene))ethanenitrile, 2-[4-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]-2-(4-methyl-3-phenyl(1,3-thiazolin-2-ylidene))ethanenitrile, 2-(5-acetyl-4-methyl-3-phenyl(1,3-thiazolin-2-ylidene))-2-[4-(2,3-dimethyl-5-oxo-1-phenyl(3-pyrazolin-4-yl))(1,3-thiazol-2-yl)]ethanenitrile, and ethyl 2-(cyano(4-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)methylene)-2,3-dihydro-4-methyl-3-phenylthiazole-5-carboxylate were synthesized by treatment of 2-(4-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-yl)thiazol-2-yl)-3-mercapto-3-(phenylamino)-acrylonitrile with appropriate halo ketones or halo esters. Also, 4-{2-[5,7-dimethyl-2-(phenylamino)(7a-hydropyrazolo[1,5-a]pyrimidin-3-yl](1,-thiazol-4-yl)}-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one derivatives were synthesized via reaction of 4-{2-[5-amino-3-(phenylamino)pyrazolin-4-yl](1,3-thiazol-2-yl)}-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one with β-diketone or β-keto ester. All synthesized compound were established by elemental analysis, spectral data, and alternative synthesis whenever possible.     

Correlation between the structure and wettability of photoswitchable hydrophilic azobenzene monolayers on silicon

Photoresponsive monolayers of hydrophilically substituted azobenzenes have been prepared by reaction on aminosilane monolayers on silicon surfaces. Grafting densities in the 0.2-1.0 molecule/nm(2) range were determined by X-ray reflectometry. The monolayers exhibit reversible photoisomerization, switching from a more hydrophilic trans state to a less hydrophilic cis state upon UV irradiation, in contrast with the usual behavior of most azobenzene monolayers that switch from a less to a more hydrophilic state. This indicates that the wettability is not dominated by the change in the dipole moment of the azobenzene moiety but originates from variations in the composition of the outer surface of the monolayers resulting from the reorientation of the substituent groups. The light-driven change in the water contact angle correlates linearly with the grafting density but remains small. However, the wettability contrast can be increased by forcing the molecules to stand in an improved vertical orientation, either by densifying the underlying aminosilane monolayer or by filling the voids left at the bottom of the layer of grafted azobenzene molecules.