Self-Assembly Behavior of Diacetylenic Acid Molecules upon Vapor Deposition: Odd–Even Effect on the Film Morphology

A series of linear carboxylic acids containing diacetylenic units at different positions along the chain (C₁₂H₂₅(C≡C)₂(CH₂)_nCOOH, n=7–11) were vacuum-deposited on clean silica substrates. The morphologies of the initial films after UV irradiation were studied. A clear odd–even effect on the morphology of the initial film was observed in that, depending on the spacer length between the diacetylenic unit and carboxyl head group, rings or dendrites of acid dimer layers were obtained. A molecular dynamic simulation of the aggregation process suggests that two competing intermolecular interactions and thus aggregation directions are involved and modulated by the odd or even carbon chain length. Further modulation of the interaction by substitution of a phenyl group at the terminus of the chain or by changing the carboxyl head group to an amidobenzoic acid head group led to a similar odd–even effect but with different dimensions or trends, which can be rationalized similarly. These results give the opportunity to create aligned conjugated polymer chains of different dimensions through self-assembly for applications in molecular/organic electronics.     

Lipophilic peptide nucleic acids containing a 1,3-diyne function: synthesis, characterization and production of derived polydiacetylene liposomes

Adenine-, cytosine- and thymine-containing peptide nucleic acid (PNA) monomers have been synthesized in which either diacetylenic or stearoyl moieties are attached to the N-or C-terminus; the diacetylenic group is embedded within a long hydrocarbon chain. A range of analogous lipophilic functionalized PNA oligomers have been prepared using either solid phase synthesis or a post-synthetic solution phase procedure following cleavage of the PNA oligomer from the solid support. Selected functionalized PNA monomers and oligomers have been incorporated into liposomal polydiacetylenes and characterized by UV-vis absorption spectroscopy. Preliminary investigations show that blue PDA-liposomes containing thymine-based PNAs can be formed and that production of liposomes with other PNA systems are viable.     

Unusual Attractive Au–π Interactions in Small Diacetylene‐Modified Gold Clusters

It is well known that alkynes act as π‐acids in the formation of complexes with metals. We found unprecedented attractive Au–π interactions in diacetylene‐modified [core+exo]‐type [Au₈]⁴⁺ clusters. The 4‐phenyl‐1,3‐butadiynyl‐modified cluster has unusually short Au–C_α distances in the crystal structure, revealing the presence of attractive interactions between the coordinating C≡C moieties and the neighboring bitetrahedral Au₆ core, which is further supported by IR and NMR spectra. Such weak interactions are not found in mono‐acetylene‐modified clusters, which indicates that they are specific for diacetylenic ligands. The attractive Au–π interactions are likely associated with the low energy of the π* orbital in the diacetylenic moieties, into which the valence electrons of the gold core may be back donated. The [Au₈]⁴⁺ clusters show clear red‐shifts of >10 nm with respect to the corresponding mono‐acetylenic clusters in UV/Vis absorption bands, which indicates substantial electronic perturbation effects of the Au–π interactions.     

Preparation and Characterization of Amine Modified Porous Polymer for Rplc

Abstract

The retention behaviour and selectivity of various aromatic compounds, including halobenzenes and a IkyIbenzenes, were examined on the stationary phase of chloromethylated polystyrene(CMS) beads, of which the chloride group was substituted by the alkylamines: n-hexyl(C₆), n-octyl(C₈), n-decyl (C₁₀),n-dodecyl (C₁₂), n-tetradecyl (C₁₄) or n-hexadecy1 (C₁₆). Changes in the distribution coefficients of benzene derivatives are demonstrated not only by the changes of the eluent compositions but also by the changes of chain length in the stationary phase. In general, a longer alkyl chain in the stationary phase gives longer retention time and different selectivity. The effects of MeOH/H₂O ratios on retention and selectivity was also demonstrated on the C₁₄ stationary phase. Good separations of halobenzenes and alkyIbenzenes were obtained with C₁₄ stationary phase. Moreover, the retention time for samples was shortened by about a half compared to polystyrene stationary phase. These results show the chemical modification of CMS gel with long chain alkyl amines decreases tailing and provides new supports with different selectivities.     

Crystal polymorphs of 6‐[(phenylcarbamoyl)oxy]hexa‐2,4‐diyn‐1‐yl isonicotinate

The title compound, C₁₉H₁₄N₂O₄, was found to have two crystal polymorphs, in which the molecular structures of the diacetylenic compound are broadly similar. The main structural difference between the polymorphs concerns the intermolecular hydrogen‐bonding motifs adopted, namely a one‐dimensional zigzag polymer linked by N—H…N(py) (py is pyridine) interactions in polymorph I and a centrosymmetric dimeric motif formed by N—H…O=C interactions in polymorph II. The diacetylene cores of the molecules stack along the a and b axes in polymorphs I and II, respectively. It was found that only the molecular arrangement in polymorph II satisfies Baughman's criterion to afford polydiacetylenes (PDAs) by thermal annealing or irradiation with light. This predicted polymerization activity was confirmed by experiment.     

Direct and initiated halogenation of carbon nanomaterials at low temperatures

Cryochemical reactions of the direct and initiated (by photolysis and radiolysis) halogenation of carbon nanomaterials (C₆₀ fullerene, nanotubes, and nanofibers) at 77–240 K were investigated by the ESR, IR spectroscopy, and elemental analysis techniques. A high reactivity of C₆₀ in reactions with fluorine and chlorine with the formation of corresponding derivatives was shown. High concentrations of radical intermediates indicating the radical chain halogenation of C₆₀ were detected (the kinetic chain length for the chlorination process reaches 10⁴–10⁶ units). The amount of chlorine attached to fullerene is ～35% and practically does not depend on the initiation mode (UV or γ-irradiation at doses up to 350 kGy). The mechanism of the cryochemical halogenation of C₆₀ is considered within the limits of the model of multicenter synchronous transitions in a molecular complex consisting of several reactant molecules including molecular fluorine or chlorine and ensuring a net exothermic effect. The amount of chlorine added to nanotubes and nanofibers did not exceed 2.5–8%, thereby indicating a low reactivity of these materials under cryogenic conditions.     

Synthesis and polymerisation of lipophilic peptide nucleic acids derived from stearic acid and pentacosa-10,12-diynoic acid

The adenine, cytosine and thymine peptide nucleic acid (PNA) monomers and PNA T₁₀ oligomers bearing either a diacetylenic or stearoyl moiety at the N- or C-terminus have been successfully prepared. The resulting thymine monomeric and T₁₀-mer derivatives have been subsequently incorporated into polydiacetylene-containing liposomes.     

Thermal and thermo-oxidative degradation of high density polyethylene/fullerene composites

Fullerene (C₆₀)/high density polyethylene (HDPE) composites were studied in order to understand for their behaviors on thermal and thermo-oxidative degradation. Under different atmosphere, the influences of C₆₀ on the thermal stability of HDPE are different. Thermogravimetric analysis coupled to Fourier transform infrared spectroscopy (TG-FTIR) and pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) demonstrate that in N₂ the addition of C₆₀ increases the onset decomposition temperature by about 10 °C with more heavy compounds (more than 34 carbon). Also the thermal stability of HDPE in air is remarkably improved with the addition of C₆₀. When the content of C₆₀ is 2.5 wt% the onset decomposition temperature increases by about 91 °C. The results of viscoelastic behavior and gel content reveal that C₆₀ can trap the alkyl radicals and alkyl peroxide radicals to inhibit hydrogen abstraction to suppress the chain scission and preserve the long chain structure. However, in the absence of C₆₀ or with low C₆₀ concentration, hydrogen abstraction occurs, resulting in the formation of a series of alkyl radicals and alkyl peroxide radicals, which accelerates the chain scission and plays a leading role in the thermal oxidative degradation.     

Mesomorphic and fluorescence properties of methyl 4-(4-alkoxystyryl)benzoates

A series of methyl 4-(4-alkoxystyryl)benzoates was synthesised and studied for liquid crystalline and fluorescence properties. The peculiarity of the reaction scheme involved condensation between 4-alkoxybenzaldehyde and 4-(methoxycarbonyl)benzyltriphenyl phosphonium bromide in dichloromethane without any phase separation. The compounds were found thermally stable up to 200°C. The banded or arced focal-conic fan texture of CrE phase was exhibited on cooling the compounds (with chain length > C₄) below the SmA phase. It was observed that increasing chain length up to C₁₀ enhances mesophase stability. No LC behaviour was manifested by small (up to C₃) and branched small chain (up to C₄) members of the series.     

The Influence of Reversed-Phase n-Alkyl Chain Length on Protein Retention,Resolution and Recovery: Implications for Preparative HPLC

Abstract

High-performance liquid chromatography (HPLC) of proteins on reversed-phase columns of varying n-alkyl chain length (C₂ to C₂₂ was studied using a trifluoroacetic acid/2-propanol mobile phase system. Protein resolution was influenced by chain length but retention times for proteins, unlike those of small molecules, were relatively constant, independent of chain length or carbon loading. Loading capacities were found to be affected by chain length, and aspects of protein interaction with stationary phase are discussed.     

Elasticity and structure of chemically crosslinked polyurethanes

A combination of electron-microscopy, light-scattering, and stress-birefringence studies on chemically crosslinked polyurethanes point toward the existence of rodlike regions (“bundles”), approximately 3000–8000 Å in length and involving about 5% of the volume, in which molecular orientations are correlated. The elastic behavior of these networks—as indeed that of most rubberlike networks—deviates substantially from the Gaussian behavior. The empirical representation of the data in Mooney-Rivlin plots yields C₁ and C₂ constants which depend on the type of imposed strain. It is thus impossible to identify C₁ with the Gaussian behavior and C₂ with the deviation there-from. Instead, it is found that the elastic behavior can be adequately described if it is assumed that, as a result of the bundle structure, about 5% of the segments of each chain are not free to assume the normal random-walk configurations. The determination of the number of chains in the network from the elastic behavior remains ambiguous, however, and the behavior upon swelling is not (yet) adequately reproduced by the theory. It is conceivable that in many cases deviations from Gaussian elasticity behavior may be caused by an intermolecular structuring effect, rather than by various minor deficiencies in the Gaussian model for the single chain statistics or by anisotropic excluded volume effects, as has been proposed in the past. In the present case, the amount of bundle structure, as well as the C₂/C₁ values, increase with the number of urethane couplings per chain, and this suggests that the interaction of the highly polar urethane couplings is responsible for the structuring. In other networks one often finds a dependence of C₂/C₁ on the previous history of the sample, which suggests that an accidentally trapped order may be responsible for the elastic behavior.     

Analysis of high molecular weight esters and ketones in thymus

A crystalline mixture of esters from Thymus chamaedris is analyzed by mass spectrometry, and after hydrolysis, by gas chromatography. Two series of straight chain even aliphatic acids from C₁₆ to C₂₆, and from C₄₀ to C₄₈, and a series of straight chain even saturated primary alcohols, from C₈ to C₃₀, are its main constituents. Another crystalline mixture, isolated from Thymus caespititius, is shown by mass spectrometry and gas chromatography to be composed of a straight chain series of aliphatic ketones, from C₂₅ to C₃₇.     

Improved in Vitro Permeation of Nabumetone across Rat Skin from 1‐O‐Alkylglycerol/Lecithin Stabilized o/w Nanoemulsions

In vitro permeation of nabumetone across rat skin from nanoemulsions of soybean oil in 2.5% aqueous glycerol stabilized with a blend of lecithin and 1‐O‐alkylglycerol (C₁₀, C₁₂, C₁₄, or C₁₆ chain length) was studied. The mean droplet size of the emulsions was in the range of 214 to 280 nm. 1‐O‐Alkylglycerol stabilized emulsions showed significant enhancement in permeation of nabumetone. This enhancement is attributed to the interaction of 1‐O‐alkylglycerol with the skin lipids, fluidizing the lipid matrix and bringing about disordering effect. The extent of interaction appears to depend on chain length of 1‐O‐alkylglycerol. 1‐O‐Decylglycerol stabilized emulsion showed highest flux in the first four hours and did not exhibit any lag time. The other emulsions showed increase in lag time with increase in the chain length of 1‐O‐alkylglycerol. Control nabumetone solution exhibited highest overall flux, but it showed lower flux than nanoemulsions stabilized by 1‐O‐decylglycerol for the initial four hours and a significantly higher flux thereafter. This appears to be due to slow extraction of skin lipid by the solvent action of control solution and consequent permeabilization of the skin.     

Effects of alkyl chain length on properties of 1-alkyl-3-methylimidazolium fluorohydrogenate ionic liquid crystals

A series of 1‐alkyl‐3‐methylimidazolium fluorohydrogenate salts (C_xMIm(FH)₂F, x=8, 10, 12, 14, 16, and 18) have been characterized by thermal analysis, polarized optical microscopy, IR spectroscopy, X‐ray diffraction, and anisotropic ionic conductivity measurements. Liquid crystalline mesophases with a smectic A interdigitated bilayer structure are observed from C₁₀ to C₁₈, showing a fan‐like or focal conic texture. The temperature range of the mesophase increases with the increase in the alkyl chain length (from 10.1 °C for C₁₀MIm(FH)₂F to 123.1 °C for C₁₈MIm(FH)₂F). The distance between the two layers in the smectic structure gradually increases with increasing alkyl chain length and decreases with increasing temperature. Conductivity parallel to the smectic layers is around 10 mS cm^?1 regardless of the alkyl chain length, whereas that perpendicular to the smectic layers decreases with increasing alkyl chain length because of the thicker insulating sheet with the longer alkyl chain.     

Shorter Alkyl Chains Enhance Molecular Diffusion and Electron Transfer Kinetics between Photosensitisers and Catalysts in CO2-Reducing Photocatalytic Liposomes

Covalent functionalisation with alkyl tails is a common method for supporting molecular catalysts and photosensitisers onto lipid bilayers, but the influence of the alkyl chain length on the photocatalytic performances of the resulting liposomes is not well understood. In this work, we first prepared a series of rhenium-based CO₂-reduction catalysts [Re(4,4’-(C_nH_2n+1)₂-bpy)(CO)₃Cl] ( ReC_n ; 4,4’-(C_nH_2n+1)₂-bpy=4,4’-dialkyl-2,2’-bipyridine) and ruthenium-based photosensitisers [Ru(bpy)₂(4,4’-(C_nH_2n+1)₂-bpy)](PF₆)₂ ( RuC_n ) with different alkyl chain lengths (n=0, 9, 12, 15, 17, and 19). We then prepared a series of PEGylated DPPC liposomes containing RuC_n and ReC_n , hereafter noted C_n , to perform photocatalytic CO₂ reduction in the presence of sodium ascorbate. The photocatalytic performance of the C_n liposomes was found to depend on the alkyl tail length, as the turnover number for CO (TON) was inversely correlated to the alkyl chain length, with a more than fivefold higher CO production (TON=14.5) for the C₉ liposomes, compared to C₁₉ (TON=2.8). Based on immobilisation efficiency quantification, diffusion kinetics, and time-resolved spectroscopy, we identified the main reason for this trend: two types of membrane-bound RuC_n species can be found in the membrane, either deeply buried in the bilayer and diffusing slowly, or less buried with much faster diffusion kinetics. Our data suggest that the higher photocatalytic performance of the C₉ system is due to the higher fraction of the more mobile and less buried molecular species, which leads to enhanced electron transfer kinetics between RuC₉ and ReC₉ .     

Synthesis and study of hydrazones of 17α-hydroxyprogesterone and 17α-hydroxypregna-4,6-diene-3,20-dione and their 17α-acylated derivatives

It has been shown that under mild conditions the reactions of 17α-hydroxy 3,20-diones of the pregnane series with acid hydrazides lead to the formation of 3-monohydrazones, while under severe conditions 3,20-dihydrazones are formed regardless of whether a C₄–C₅ ethylenic bond or a chain of conjugation of C₄–C₅ and C₆–C₇ ethylenic bonds is present in the steroid molecule. The reaction of 17α-acetoxy 3,20-diketones of the pregnane series with acid hydrazides takes place only with the formation of 3-monohydrazones. An investigation of the gestagenic action of some of the compounds synthesized has shown that the presence of a 3-keto group in the steroids of the pregnane series is not necessary for the retention of this effect. The replacement of the keto group at carbon atom 3 by an azomethine group does not abolish the gestagenic action.     

Dependence of the dispersion behavior of [60]fullerene in aqueous media on the chain length of poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide) as a dispersing agent

We have investigated the effect of the chain length of temperature-sensitive poly(N-isopropylacrylamide) (PIPAAm) on the dispersion of [60]fullerene (C₆₀) in aqueous media through an interaction between PIPAAm and C₆₀ below the lower critical solution temperature (LCST) of PIPAAm. UV–vis absorption spectral measurements showed that the saturated amount of the dispersed C₆₀ increased in proportion to the chain length of the PIPAAm. Additionally, an absorption band at around 430 nm was observed in the dispersed C₆₀ solution and was assigned to a C₆₀/PIPAAm complex. The complex formed an amorphous molecular assembly between C₆₀ molecules and PIPAAm chains, the structure of which was confirmed in a transmission electron microscopy image. Dynamic light scattering measurements indicated that the particle size of the C₆₀/PIPAAm complex increased with the chain length of the PIPAAm. From electrophoretic laser light scattering measurements, the zeta potential of the C₆₀/PIPAAm complex was found to be shifted from a negative value to zero with an increase in the chain length of PIPAAm. Longer PIPAAm chains, however, gave rise to a higher dispersion stability of the complex. Similar to the dispersion behavior of PIPAAm-C₆₀ conjugates in aqueous solutions, the aqueous C₆₀ dispersion with PIPAAm exhibited rapid, and reversible dispersion–aggregation changes in response to temperature alternation across the LCST.     

Steric effect on the formation of columnar phases in β-diketonate copper(II) complexes

A systematic study of the mesomorphic properties of three series of copper(II) complexes based on β-diketonate ligands containing branched side chains is reported. These disc-like compounds have four, six and eight flexible alkoxy side chains appended to the central core, in which two or four side chains were substituted by bulkier secondary alkoxy groups: 1-methylbutyloxy R ' = C₅(2°) or 1-methylheptyloxy R ' = C₈(2°). The mesomorphic results indicated that at least eight side chains are required to form stable columnar mesophases; other compounds with four or six side chains are not mesogenic regardless of the combination of the carbon length on the alkoxy or secondary alkoxy groups of the side chains. The compounds 3 with shorter R ' = C₅(2°) side chains were all non-mesogenic regardless of the carbon length of three alkoxy side chains (R = C₈, C₁₀, C₁₂) used. However, when the longer 1-methylheptyloxy side chain R ' = C₈(2°) was substituted, the compounds 3b-3e with various alkoxy groups (R = C₆, C₇, C₈, C₁₀, C₁₂) exhibited columnar phases. The mesophases were characterized and identified as columnar hexagonal phases (Col_h), as expected, by thermal analysis and optical polarized microscopy. The presence of the introduced secondary alkoxy groups apparently appeared to influence the formation of columnar phases. The clearing points were relatively lower than other similar copper(II) compounds not substituted by secondary alkoxy side chains.     

New Fluorous Reversed Phase Silica Gels for HPLC Separations of Perfluorinated Compounds

Two new perfluoroalkyl-modified stationary phases were prepared and compared with two commercially available perfluorinated stationary phases (Fluophase RP and Fluophase Pentafluorophenyl) and a C₁₈-RP column with respect to retention times of an array of perfluoroalkyl-tagged and untagged molecules. A few highly lipophilic compounds were also included in the study. They showed high retention times on C₁₈-RP columns, but not on perfluorinated support materials. Perfluoroalkyl-tagged compounds revealed a weak interaction with the pentafluorophenyl-modified support. The interaction between perfluoroalkyl-tagged compounds and perfluoroalkyl-modified stationary phases was strong, and dependent on the chain length of the perfluoro tags. Surprisingly, there was only a small difference between the retention times of perfluorinated compounds on C₁₈-RP and C₆F₁₃-modified support. Fluorous-fluorous interactions became prevalent only with C₈F₁₇-tagged compounds on C₈F₁₇ functionalized silica gel. Compounds with two perfluoro tags showed a drastic increase in retention time, which might be due to a cooperative effect. These results demonstrate the uniqueness of fluorous-fluorous interactions based on linear perfluoroalkyl chains and open up possibilities for the design of new perfluoro tags for purifications and noncovalent attachments of catalysts or biomolecules on perfluorinated solid supports.     

Spectral properties of hemicyanine dye in confinement by helical amylose

Hemicyanine dye structure is modified with a C₁₆-alkyl chain to amino-head and a C_1, C₈ or C₁₆ alkyl to pyridinium-tail. Spectral properties of the dyes in supramolecular inclusion complexation with amylose are studied in order to assess the mono-functional polarity sensing activity of the pyridinium cations in DMSO-H₂O mixtures. Inclusion complexation brings the γ_max of C₁₆DASPC₁ dye to a blue-shift (relative to that of the free dye state) while that of C₁₆DASP(C₈ and C₁₆) dyes remains almost unchanged.