Trans-zigzag Conformation Research Articles

A trial to clarify a cause of forming physical gels: Morphology of syndiotactic polystyrene in n-alkylbenzene

We dissolved low concentration of syndiotactic polystyrene (SPS) in serial n-alkylbenzenes (NB: C6H5–CNH2N+1 (N = 1–10)) at high temperatures and observed the morphology and structure after cooling by SEM, IR, DSC, and WAXD. The morphology of SPS in NB changes with N: (I) N = 1–3, SPS/NB forms a gel with fibril structure networking three-dimensionally, (II) N = 4–6, SPS/NB produces paste-like state where SPS chains with 21-helix conformation gather together to form SPS γ crystalline phase, and (III) N = 7–10, SPS/NB produces sherbet-like state where SPS chains with trans zigzag conformation gather together to form SPS β crystalline phase. We have discussed a cause of forming physical gels of SPS together with the reason why the morphology of SPS/NB depends on N.

N-Butylpyridine-4-thiocarboxamide

In the title mol­ecule, C10H14N2S, the n-butyl chain assumes a trans zigzag conformation. The dihedral angle between the pyridine ring and the thio­amide plane is 23.38 (8)°. The mol­ecules in the crystal structure are linked by an inter­molecular N—H⋯N hydrogen bond.

Molecular Orientation and Structure in LB Films of a Liquid Crystal MPUOPM Investigated by UV-Vis and IR Spectroscopy

Langmuir monolayers and LB films of 4-((s)-2-methylbutoxy)phenyl-(4-(10-undecen-1-oyloxy)phenyl) methylenimine (MPUOPM) were investigated by ultraviolet-visible, polarized infrared spectroscopy. -A isotherms showed well-defined Langmuir monolayers were formed at an air/water interface for the MPUOPM and their mixture with SA. An inflection point at 13 mN/m appeared on the isotherm, which was due to the transition from the monolayer to multilayer. The polarized IR spectra of LB films of MPUOPM had provided new insight into the molecular orientation and structure. In LB films, the tilted angle between the alkyl chain and the normal line of the substrate was 48, the tilted angle between the dipole moment of C=N and the normal line of the substrate was 51. The alkyl chains assumed a trans-zigzag conformation but it included a few gauche conformers. The C=N groups were almost in one plane in the LB films.

Crystallization process of poly(ɛ-caprolactone)–poly(ethylene oxide)–poly(ɛ-caprolactone) investigated by infrared and two-dimensional infrared correlation spectroscopy

The crystallization of poly(ɛ-caprolactone)–poly(ethylene oxide)–poly(ɛ-caprolactone) (PCL–PEO–PCL) triblock copolymer was studied using FTIR and 2D FTIR spectroscopies. The weight ratio of PCL/PEO in the investigated sample was about 20:1. Although it is such a low amount of PEO that it cannot form any crystals, the PEO block undergoes some structural change in the cooling process. It was established that the PCL constituent crystallized quickly, and then forced the noncrystallizable PEO constituent to form a tighter structure (helical conformation) from the trans zigzag conformation. Besides, through the 2D IR analysis, more exact and detailed assignments of the overlapped CH 2 bands have been made – the 1193 cm −1 band is attributed to methylene next to the carbonyl group, whereas the 1162 cm −1 and 1295 cm −1 bands are assigned to other common methylenes.

Ordered Arrays of Organometallic Iridium Complexes with Long Alkyl Chains on Graphite

Iridium(III) fac-tris(2-phenylpyridine) fac-[Ir(ppy)3] complexes equipped with long alkyl chains were prepared to examine their capability to form organized arrays on the surface of highly oriented pyrolytic graphite (HOPG). The molecules form lamellar arrays at the 1-phenyloctane/HOPG interface. From the analysis of the STM images, it was concluded that the molecules align with alkyl chains being interdigitated. Similar lamellar arrays were also obtained at the air/HOPG interface upon drop-casting of toluene solutions. The lamellar structure at the molecular level leads to rectangular two-dimensional crystalline domains a few hundred nanometers long (nanoslips). Infrared external reflection spectroscopy suggested that the adsorbed alkyl chains adopt the trans-zigzag conformation in the nanoslip, although the orientations of the zigzag plane of the alkyl groups are mixed. Cyclic voltammetry indicates fast electron transfer between the adsorbed molecules and the substrate and significant intermolecular electronic interactions. It was found that annealing at high temperatures is an effective method to prepare ordered assemblies more than a few micrometer scale (microslips). The orientations of the nanoslips prepared from the racemic mixture exhibited an apparent 12-fold symmetry, while its optically active enantiomer resulted in more irregular domains with a six-fold symmetry, implying an important role of chirality on packing at the molecular level and on the orientation of the domains at larger scales. When drop-cast from more concentrated solutions than a few hundreds of micromolar, multilayers were obtained, in which the alkyl chains in the molecules are more or less perpendicular to the surface. This structure can be transformed into the nanoslips upon standing.

Langmuir−Blodgett Films of a Novel Cellulose Derivative with Dihydrophytyl Group: The Ability to Anchor β-Carotene Molecules

A novel cellulose derivative, 6-O-dihydrophytylcellulose (DHPC), was first synthesized via a ring-opening polymerization and allowed to self-assemble onto an air-water interface. Langmuir-Blodgett (LB) films were characterized with atomic force microscope (AFM), UV-vis spectroscopy, and Fourier transform infrared spectroscopy. The surface pressure-area (pi-A) isotherms for DHPC and beta-carotene (betaC) mixture indicated strong interaction between these compounds to pack well. Thus, DHPC has the ability to anchor betaC in the monolayer. It was proved that a betaC-DHPC monolayer was transferred successfully onto a substrate, yielding Y-type LB films by UV spectroscopic analysis. The transmission and reflection-absorption IR spectra (RAS) indicated that the dihydrophytyl chains had almost trans-zigzag conformation and were oriented nearly perpendicular to the substrate. AFM section analysis revealed the thickness per layer to be 2.32 nm. Consequently, DHPC was found to be an appropriate matrix to fabricate the mixed LB films containing betaC.

Preparation, characterization and crystalline transitions of odd–even polyamides 11,12 and 11,10

The novel odd–even polyamides 11,12 (P11, 12) and 11,10 (P11, 10) were synthesized via step-heating melting-polycondensation of 1,11-diaminoundecane with dodecanedioic acid and decanedioic acid, respectively. Their chemical structures were confirmed by various spectroscopic techniques (FTIR, Raman, NMR). The thermal properties of the polyamides under consideration were measured by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). The crystalline transitions of the prepared polyamides were studied by wide angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR). The variable temperature WXRD results indicated that P11,10 undergoes the Brill transition during the heating process before melt while P11,12 does not. From the real time FTIR spectra of P11,10, it was found that the intensity of hydrogen bond becomes weak, and the twisting of the C–CO and C–N bonds becomes enhanced. The vibration of the methylene units strengthens and the trans-zigzag conformation decreases. The ordered stacking of the methylene segments becomes gradually disordered by insertion of the gauche conformation during the crystalline transition process.

Surface phase behavior in Langmuir monolayers of diethylene glycol mono-n-hexadecyl ether at the air-water interface

The surface phase behavior of condensed-phase domains formed during a first-order phase transition in Langmuir monolayers of diethylene glycol mono-n-hexadecyl ether at the air-water interface has been investigated by Brewster angle microscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). A variety of two-dimensional (2D) structures are observed just after the appearance of the phase transition at different temperatures. At 10 and 15 degrees C, the domains are found to be small nuclei of irregular structures. Spiral structures are observed at 20 and 22 degrees C, while striplike structures at 24 degrees C. The spiral domains attain increasingly compact shape with increasing temperature, and finally become circular at >or=26 degrees C. Increases in temperature result in dehydration in the ethylene oxide chain, which increases the hydrophobicity, and impart to the molecules a longer-chain-like character. As a result line tension increases with increasing temperature, which probably outweighs the dipole-dipole repulsions showing circular domains at higher temperatures. The PM-IRRAS measurement reveals that the nu(as)(CH(2)) mode moves to lower wave numbers indicating that the LE-LC (liquid expanded-liquid condensed) phase transition during the compression of the monolayer involves changes in the conformational order of the molecules with a preferential increase in the planner trans zigzag conformation of the hydrocarbon chains. The nu(as)(CH(2)) mode in the LC region of the isotherm shows a constant value around 2917.8 cm(-1) indicating a stable state of the monolayer with an almost all-trans conformation of the hydrocarbon chains. The downward band at 1124 cm(-1) assigned to the nu(as)(C-O-C) mode indicates that the corresponding transition dipole moment is oriented perpendicular to the water surface.

Packing mode and conformational transition of alkyl side chains in N-alkylated poly( p-benzamide) comb-like polymer

A series of rigid-rod poly( p-benzamide) polymers (PBA) with different length of flexible alkyl side chains, denoted as PBA( n)Cs, have been prepared by N-alkylation method. The alkyl side chain lengths varied from decyl ( n=10) to octadecyl ( n=18), with an interval of two carbon atoms. The packing mode and conformational transition of the alkyl side chains of the prepared PBA derivatives were characterized by wide-angle X-ray diffraction (WAXD), differential scanning calorimertry (DSC), and Fourier transform infrared spectroscopy (FTIR). WAXD results revealed that the derivatives form layered structure in which the distance between the backbones depends on the length of alkyl side chains. DSC studies indicated that melting transition temperature of PBA( n)Cs increases accordingly with increasing the alkyl chain length of the substituents. Meanwhile, DSC results proved that as the carbon atom number of the side group exceeds 14, alkyl side chains in PBA( n)Cs tend to crystallize FTIR spectroscopic investigation showed that the all- trans zigzag conformation is the most stable state for the alkyl side chain in PBA18C comb-like polymer. Temperature variation caused the reversible transition between trans and gauche conformational states of the side octadecyl group, and in turn made the molecular chain packing mode of PBA18C comb-like polymer undergo an reversible transformation from ordered packing to disordered packing.

Structures and dynamics of dodecyldimethylamine oxide intercalated into RUB-18

A new proton-conducting intercalation system of a layered polysilicate compound, octosilicate (RUB-18), was synthesized by exchanging Na + ion with half- and full-ionized dodecyldimethylamine oxides. RUB-18 intercalated by half-ionized dodecyldimethylamine oxide was shown to contain alkyl chains of the trans zigzag conformation by powder X-ray diffraction and 13C CP-MAS NMR measurements. The DC electrical conductivity and the distribution factor β of the relaxation time were determined to be 6.4×10 −6 S m −1 and 0.67, respectively, from Cole–Cole plots of the complex impedance measured at room temperature under the relative humidity of 100%.

LB film structure of poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)- p-phenylene vinylene) studied by spectroscopy

A PPV derivative, poly(2-methoxy,5-(8-methoxy-3,6-dioxa-1-undecoxy)- p-phenylene vinylene), has been synthesized by the Gilch route to study the influence of a long alkyl side chain and a di(ethylene oxide) methyl ether group on the multilayer structure obtained by Langmuir–Blodgett (LB) technique. UV–visible, PL, and FTIR spectra are applied to study the conformation and orientation of the MMDU-PPV molecules in multilayer organization. MMDU-PPV is apt to form a transferable monolayer film, in which the plane of its π system is perpendicular to the air–water interface. The adjacent conjugated main chains of MMDU-PPV in LB films are aligned in parallel fashion and packed with the plane of its π system approximately perpendicular to the layer plane and not organized to compact π-stacking structure for introducing di(ethylene oxide) methyl ether (DEOM) side chains to conjugated main chains. The long alkyl side chains are characterized by all trans-zigzag conformation and average tilt angle of 36±1.5°. The layer-by-layer multilayer of MMDU-PPV obtained by Langmuir–Blodgett technique exhibits some in-plane anisotropy and more pure photoluminescence than that of the dilute MMDU-PPV solution.

Synthesis of Gold Nanoparticles in a Winsor II Type Microemulsion and Their Characterization

Dodecanethiol-capped nanospherical gold metal particles have been synthesized using a biphasic Winsor II type microemulsion of diethyl ether/aerosol-OT/water. The reduction of gold(III) chloride in the presence of dodecanethiol results in the formation of stable, organically soluble nanoparticles of 4±0.6 nm average diameter. The UV–vis plasmon absorption band and transmission electron microscopic (TEM) analysis confirmed the formation and size of the particles. TEM morphology shows a two-dimensional array of these particles with an average spacing between gold cores of about 1.8 nm onto hydrophobic carbon surfaces. Elemental analysis results and the similarity of the Fourier transform infrared (FT-IR) spectrum of free dodecanethiol to that of composite material reveal the encapsulation of gold particles by dodecanethiol. The detailed analysis of FT-IR spectra of our composite material and its comparison with literature reports disclose that a Winsor II type system is superior for the synthesis of nanoparticles bounded by a three-dimensional self-assembled monolayer of alkanethiol with a close-packed all trans zigzag conformation. 1H NMR spectroscopic observations suggest the absence of free thiols. X-ray photoelectron spectroscopic analysis supports that the oxidation state of gold is zero (Au 0). Thermogravimetric and differential thermal analysis indicates an interaction between thiol group and gold surfaces and thiol molecule per nearly three gold atoms in the composite particles.

Polarization Modulation Infrared Reflection Absorption Spectroscopy of Gibbs Monolayer at the Air/Water Interface

Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was applied to investigate Gibbs monolayers of ethylene glycol mono-n-dodecyl ether (EGDE), spontaneously adsorbed at the interface of air andaqueous EGDE subphase. Brewster angle microscopic images reveal that the EGDE monolayer forms circular domains in a condensed state. The PM-IRRAS measurements reveal a ν a s (CH 2 ) band at 2918.2 cm - 1 and a δ(CH 2 ) band at 1469.2 cm - 1 , indicating respectively the planar trans zigzag conformation and crystalline packing of the -(CH 2 ) 1 1 - chain. The ν a s (C-O-C) mode gives a negative band, implying that the ether linkage preferentially stands up in the Gibbs monolayer. The Gibbs monolayer was successfully transferred onto solid substrates such as Au and CaF 2 , using the conventional Langmuir-Blodgett technique. Infrared transmission and reflection measurements of the transferred monolayer were applied to obtain the anisotropic complex refractive indexes. Using these indexes, the PM-IRRAS spectrum of the EGDE monolayer at the air/subphase interface was simulated and compared to the experimental one. It is concluded that the -(CH 2 ) 1 1 - chain is tilted at 21° with respect to the surface normal and twisted at 56° on the aqueous subphase. The physical act of LB transfer onto solid substrates has caused reorientation of the -(CH 2 ) 1 1 - chain and the ether linkage as well as deterioration of the chain conformational order.

Surface Micelles of F(CF2)m(CH2)22COOH on the Aqueous Cadmium Acetate Solution Investigated in Situ and ex Situ by Infrared Spectroscopy

Partially fluorinated alkanoic acids F(CF2)m(CH2)22COOH (m = 8, 6, and 4) spontaneously formed monodispersed nanometer-sized two-dimensional micelles on the aqueous cadmium acetate subphase in a Langmuir trough, according to the atomic force microscope images. Normal transmission and grazing incidence reflection infrared spectroscopy were applied to investigate the single monolayer deposited on solid substrates by the Langmuir−Blodgett (LB) method. Polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) was applied to investigate the monolayer in situ. PM-IRRAS simulation was performed for the first time to determine molecular orientation at the air/water interface. The hydrocarbon chain takes a planar trans zigzag conformation on the subphase surface, largely inclined at 43∼40° and twisted at 66∼61°, packing in a pseudotriclinic way. By contrast, the simple CH3(CH2)20COOH spontaneously forms micrometer-sized domains on the aqueous Cd2+ subphase, with the hydrocarbon chain verticall...

Monolayer Behavior and LB Film Structure of Poly(2-methoxy-5-(n-hexadecyloxy)-p-phenylene vinylene)

A PPV derivative, poly(2-methoxy, 5-(n-hexadecyloxy)-p-phenylenevinylene) (MH−PPV), has been synthesized by the Gilch route to study the influence of long alkyl side chains on the organization behavior of film at the air−water interface and multilayer structure obtained by Langmuir−Blodgett technique. The π−A isotherm, hysteresis, and film stability are used to characterize the behavior of a monolayer film at the air−water interface. Small-angle X-ray diffraction (SAXRD), UV−visible spectra, and FTIR are applied to study the conformation and orientation of the MH−PPV molecules in multilayer organization. MH−PPV is apt to form a stable and transferable monolayer film. The adjacent conjugated main chains of MH−PPV in LB films are aligned in side-by-side parallel fashion and packed with the plane of its π system approximately perpendicular to the layer plane (H-aggregate structure). The long alkyl side chains are characterized by all trans-zigzag conformation and average tilt angle (26.5 ± 1.5°) obtained by means of both FTIR and SAXRD. The LB films of MH−PPV are well ordered with layer-by-layer structure and a d-space of 49.9 Å.

Phase Behavior of Heptaethylene Glycol Dodecyl Ether and Its Aqueous Mixture Revealed by DSC and FT-IR Spectroscopy

The phase behavior of heptaethylene glycol dodecyl ether (C12E7) and its aqueous mixture was investigated by means of differential scanning calorimetry (DSC) and Fourier transform infrared (FT-IR) spectroscopy in the temperature range from −20 to 70 °C. Phase boundaries among various phases including mesomorphic phases were determined on the basis of DSC thermograms, from which the binary phase diagram of this mixture system was constructed. According to the phase diagram, the mixture with the composition of 31 wt % H2O exhibits the following phase sequence with increasing temperature: solid → H1 (normal hexagonal) → V1 (normal bicontinuous-type cubic) → Lα (lamellar) → liquid. FT-IR measurements for the mixture with this composition revealed the following features concerning the conformational structure of the C12E7 molecule and the interaction between the surfactant and D2O in each phase. In the solid phase, the polyoxyethylene (POE) chain of the surfactant molecule has a rather extended structure with a trans-rich conformation, in contrast to the case of pure C12E7, in which a helical structure is dominant. When the solid phase transforms to the H1 phase, the hydrogen-bond interaction between C12E7 molecules and between C12E7 and water are both weakened, and the fraction of gauche-conformer in the POE chain increases, whereas the alkyl chain adjacent to the POE chain remains, taking a rather trans-zigzag conformation. The enhanced fraction of gauche-conformer in the POE chain suggests that the POE chain has a helical structure in this phase. The increase in temperature within the H1 region causes a conformational change in both the POE chain and the alkyl chain of the surfactant to a more disordered structure. Among the phases of V1, Lα, and liquid, no significant difference is seen in the conformational structure and interaction with water molecules of the surfactant.

Adsorption and Reaction of 4-Nitrobenzoic Acid on ω-Functionalized Alkanethiol Monolayers on Powdered Silver: Infrared and Raman Spectroscopy Study

We have investigated the stability of ω-functionalized alkanethiol monolayers anchored on 2 μm-sized silver particles by means of infrared and Raman spectroscopy. Although the alkyl chains of dodecanethiol (DDT) monolayers were deduced to have a trans-zigzag conformation by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), those of 11-mercapto-1-undecanol (11-MUD) and 12-mercapto-1-dodecylamine (12-MDA) monolayers seemed to assume strongly disordered conformations on the powdered silver surface. We also found by DRIFTS that 4-nitrobenzoic acid (4-NBA) can be incorporated nearly equally into the hydrophilic (11-MUD and 12-MDA) and hydrophobic (DDT) group-terminated monolayers by forming Ag−COO- bond(s). This seemed to be best understood by presuming that the hydrophobic interchain interaction is less optimal on a microscopically rough surface than on a smooth surface when monolayers of 11-MUD and 12-MDA are assembled on Ag. It was also found by surface-enhanced Raman scattering (SERS) t...

Influence of Length of Alkyl Chains Used To Passivate Silver Sulfide Nanoparticles on Two- and Three-Dimensional Self-Organization

Silver sulfide Ag2S nanocrystals have been synthesized in reverse micelles and coated with thioalkyl chains with different lengths. With short chains (≤C8) and very long ones (≥C16) the particles cannot be extracted from micelles. For short alkyl chains, this is due to disorder at the interface. For longer chains it is attributed to the highly hydrophobic character of the alkyl chains. For alkyl chains varying from C8 to C14, the long-range order of 2D self-assembly depends on the number of particles deposited on the support; at low concentration, rings are formed and then disappear by increasing the number of particles. When the thiol alkyl chain length is increased, an increase in the average distance between two adjacent particles is observed. It is correlated with the change in the chain conformation and defects, which depend on the chain length. When particles are self-organized in 2D, the distance between adjacent particles centers varies linearly with the particle radius. This indicates that the interparticle distance does not change with the particle size and varies with the length of the alkyl chain. For short chains (≤C6), the gauche defects prevent attachment to the surface, and self-organization in 2D is prevented. Hence, by using short chains, the distance between particles cannot be markedly reduced. By the increase of the particle concentration, 3D superlattices are obtained. The best faceted and largest fcc crystals are formed with the largest particles and densest chain packing. When the chain length is too long (C14) end-gauche defects occur, which show an edge−edge core spacing smaller than one chain length in the all trans zigzag conformation. This prevents the 3D growth.

Electrostatic Interactions and Conformations of Zwitterionic Pyridinium Alkanoates

Conformations of flexible zwitterionic ω-pyridinium alkanoates (PBn) with n methylene units in the tether and their hydrates and hydrochlorides are studied in the solid state by X-ray diffraction, in aqueous solution by FT-IR and 1H,13C, and 14N NMR spectroscopies, and in the gas phase by PM3, SAM1, and DFT calculations. PB1 and PB1·H2O in crystals have a conformation with the N+···O intramolecular distance of ca. 2.7 Å, while PB3·2H2O and PB10·3H2O have a trans-zigzag conformation and are arranged antiparallel. Structures of isolated molecules of ω-pyridinium alkanoates (PBn) and their dihydrates (PBn·2H2O) and hydrochlorides (PBn·HCl) optimized using the PM3, SAM1, and DFT methods are significantly different from those observed in the crystals. In crystals, when n ≥ 2, as a result of electrostatic interactions in the crystal lattice, the positively charged center (N+ atom) interacts with negative carboxyl groups, water molecules, or chloride ions of the neighboring molecules (intermolecular charge compensation), while in the gas phase only with their own (intramolecular charge compensation). In aqueous solutions, similarly as in the crystalline state, distances between the charged centers increase monotonically with increasing number of methylene units in the tether. The 1H and 13C NMR data suggest that polymethylene chains in PBn contain more folded (gauche) conformations than do sodium salts of carboxylic acids without a charged N+ atom. The SCRF calculations predict slightly longer N+···Cc distances than those derived by Chevalier and Perchec for trimethylammonium carboxylates from 13C NMR spectra. This suggests that the SCRF model underestimates contribution of the gauche conformers in aqueous solutions.

Molecular Orientation and Aggregation in the Langmuir-Blodgett Films of 4-[4′-(4″-Decyloxy Phenylazo) Naphthloxy] Butyl Trimethylammonium Dextran Sulfate Studied by Ultra-Violet and Infrared Spectroscopy

Infrared transmission, Reflectance-Absorption (RA) and Ultra-Violet (UV) spectra were measured for mono-and multi-layers Langmuir-Blodgett (LB) films of 4-[4′-(4″-decyIoxy phenylazo)naphthloxy] butyl trimethylammonium bromide formed with SDS to study the molecular orientation and aggregation. The results indicate that the compound do not aggregate in the LB films, and the alkyl tail is nearly perpendicular to the substrate surface and the chromorphore part adopts trans-zigzag conformation. These results also suggest that the molecular orientation and aggregation are not depend upon the number of monolayers The comparison of infrared transmission and RA spectra indicates that the hydrocarbon chain is nearly perpendicular to the substrate surface, but the two rings in the chromophore part are tilted considerably from the surface normal.