Number Of Methylene Groups Research Articles

Theoretical insight into the minor role of paring mechanism in the methanol-to-olefins conversion within HSAPO-34 catalyst

Insight into the structure of hydrocarbon pool species and its effect on the catalytic activity and selectivity are urgently required in methanol-to-olefins (MTO) conversion. The fundamental issue is the understanding of its reaction mechanism. Previously, we have elucidated a complete catalytic cycle of side chain hydrocarbon pool mechanism. In this paper, paring hydrocarbon pool mechanism for different methylbenzenes (MBs) in HSAPO-34 zeotype catalyst is comprehensively investigated by periodic density functional theory calculations. The complete catalytic cycle involves a sequence of elementary steps that include methylation, ring contraction, shift of proton or methyl group, elimination of side alkyl groups, and regeneration of MBs. The major bottleneck is identified as the regeneration of MBs from five-membered ring cations. The intermediate cations having five-membered ring structure and the transition states featuring primary carbocations are unstable in the paring route. The overall energy barriers of different MBs depend strongly on the number of methyl groups. By comparing the kinetics of the paring route and the side chain route, we demonstrate that the full paring mechanism exhibits a higher barrier, and which is a minor route in the MTO conversion.

Insights into the Atmospheric Pressure Plasma‐Enhanced Chemical Vapor Deposition of Thin Films from Methyldisiloxane Precursors

AbstractThis work describes the plasma‐enhanced chemical vapor deposition of thin films at atmospheric pressure using dielectric barrier discharges fed with argon, oxygen and different methyldisiloxanes, i.e., hexamethyldisiloxane, pentamethyldisiloxane, and 1,1,3,3‐tetramethyldisiloxane. The influence of the methyldisiloxane chemical structure and of the oxygen/methyldisiloxane feed ratio is investigated in order to provide insights into the organosilicon plasma chemistry at atmospheric pressure. As expected the FT‐IR and XPS analyses show that the carbon content of the coatings depends on the number of methyl groups in the precursor molecule; in the case of coatings obtained with PMDSO and TMDSO carbon removal seems to be further enhanced by the presence of SiH bonds. Gaschromatography‐mass spectrometry analyses of the exhaust gas allow to assess the precursor depletion and to perform the quali‐quantitative determination of by‐products (e.g., silanes, siloxanes, silanols) formed by plasma activation. The results are exploited to rise hypotheses on the contribution of the different reaction pathways on the deposition mechanism.magnified image

Degradation of methyl-phenanthrene isomers during bioremediation of soil contaminated by residual fuel oil

Phenanthrene and methyl-phenanthrenes are major aromatic pollutants originating in particular from fuel oil. Phenanthrene is usually degraded faster than methyl-phenanthrenes under geological and environmental conditions. Here, we report a preferential and accelerated biodegradation of methyl-phenanthrenes versus phenanthrene in soil contaminated by fuel oil. The polluted soil was mixed with sawdust and sand to form a homogenized biopile. The biopile was continuously sprayed with microbial consortia isolated from crude oil–contaminated soil and treated by biosurfactants and nutritive substances for biostimulation. During a 6-month bioremediation experiment, a steady increase in the relative abundance of phenanthrene compared to methyl-phenathrenes was observed by gas chromatography–mass spectrometry. The increase was the highest for trimethyl-phenanthrenes, with a phenanthrene/trimethyl-phenanthrenes ratio increasing from 0.42 to 2.45. By contrast, the control, non-stimulated samples showed a ratio decrease from 0.85 to 0.11. Moreover, the results showed that the level of degradability depends on the number of methyl groups.

Novel building units in the construction of materials of the oxomolybdate–organodiphosphonate/copper(II)–dipodal-organonitrogen ligand system: Structural influences of dipodal ligand tether length and flexibility

The hydrothermal reactions of copper(II) acetate, MoO3, 1,4-butylenediphosphonic acid and a ligand of the N,N,N′,N′-tetrakis(pyridine-2-ylmethyl)alkyl-α,ω-diamine (Ln, where n is the number of methylene groups) in the presence of HF provided crystals of [{Cu2(L7)(H2O)2}Mo5O15{O3P(CH2)4PO3}]·2H2O (1·2H2O) and [{Cu2(L5)}Mo6O18(H2O){O3P(CH2)4PO3}]·14H2O (2·14H2O). Compound 1 contains the common pentanuclear cluster building block {Mo5O15(O3PR)2}4−, extending into one-dimensional chains through the alkyl tethers of the diphosphonate ligand. Each pentanuclear subunit bonds to four copper(II) sites of the {Cu2(L7)(H2O2)}4+ subunits that serve to link each chain to five adjacent chains to propagate the structure in three dimensions. The Cu/Mo/P/O inorganic substructure which arises from this juxtaposition of building motifs is a one-dimensional {Cu2Mo5O15(O3P−)2} unit consisting of clusters linked through Cu(II) sites. The alkyl arms of the diphosphonate and nitrogen ligands radiate outward to link to adjacent chains and propagate the structure in three-dimensions. In contrast, compound 2 exhibits a hexanuclear building unit {Mo6O18(H2O)(O3P−)2}4−, which again extends into a chain through the tethering diphosphonate ligands. Each cluster bonds to four Cu(II) centers to generate one-dimensional inorganic substructures of the type {Cu2Mo6O18(H2O)(O3P−)2}n. In contrast to 1, the {Cu2(L5)}4+ subunits of 2 associate with a single chain, rather than radiating outward to link to adjacent chains. Consequently, the three-dimensional expansion is effected through the diphosphonate tethers.

Sucrose Monoester Micelles Size Determined by Fluorescence Correlation Spectroscopy (FCS)

One of the several uses of sucrose detergents, as well as other micelle forming detergents, is the solubilization of different membrane proteins. Accurate knowledge of the micelle properties, including size and shape, are needed to optimize the surfactant conditions for protein purification and membrane characterization. We synthesized sucrose esters having different numbers of methylene subunits on the substituent to correlate the number of methylene groups with the size of the corresponding micelles. We used Fluorescence Correlation Spectroscopy (FCS) and two photon excitation to determine the translational D of the micelles and calculate their corresponding hydrodynamic radius, Rh. As a fluorescent probe we used LAURDAN (6-dodecanoyl-2-dimethylaminonaphthalene), a dye highly fluorescent when integrated in the micelle and non-fluorescent in aqueous media. We found a linear correlation between the size of the tail and the hydrodynamic radius of the micelle for the series of detergents measured.

Isothermal titration calorimetry and molecular dynamics study of ion-selectivity in mixtures of hydrophobic polyelectrolytes with sodium halides in water

Aliphatic x,y-ionenes are polyelectrolytes in which x and y denote the numbers of methylene groups separating quaternary ammonium ions. They represent useful model substances for studying hydrophobic and charge effects in aqueous solutions. We used isothermal titration calorimetry to measure the enthalpies of mixing, ΔH(mix), of 3,3- and 6,6-ionene fluorides and bromides with low molecular weight salts (NaF, NaCl, NaBr, and NaI) at 298 K in water. The signs and magnitudes of the measured enthalpies depend on the hydrophobicity of the ionene and on the nature of the added salt. For example, addition of sodium fluoride to solutions of 3,3- and 6,6-ionene fluorides produced endothermic effects, while addition of sodium bromide to 3,3-ionene bromide resulted in a strong exothermic effect. Interestingly, mixing of 6,6-ionene bromide and NaBr solutions in water gave a small exothermic heat effect. Polyelectrolyte theories, based on continuum-solvent models, predict enthalpies of mixing to be positive (endothermic) for all the solutions examined in this work. The ion-specific effect is more strongly expressed in ionene solutions with higher charge density (3,3-ionene). The most important result of this work is the finding that the enthalpy of mixing of 3,3- (and of 6,6-ionene) fluorides with sodium halides can be expressed as a linear function of the enthalpy of hydration of the halide counterions. The experimental results were complemented with an explicit water molecular dynamics simulation of solutions of oligoions modelling 3,3- and 6,6-ionenes. The computer simulation results for various nitrogen-counterion pair distribution functions were in most cases consistent with the enthalpy measurements.

Liquid crystalline and photocrosslinkable poly(4,4′‐stilbeneoxy) alkylarylphosphates

AbstractThree series of liquid crystalline and photocrosslinkable poly(4,4′‐stilbeneoxy) alkylarylphosphates were synthesized from various 4,4′‐bis(m‐hydroxyalkyloxy)stilbenes (m = 2, 4, 6, 8, 10) and arylphosphorodichloridates in chloroform by solution polycondensation method. Polarized optical microscope (POM) and differential scanning calorimetry (DSC) observations revealed that polymers containing less than four methylene spacer groups did not exhibit liquid crystalline (LC) texture, possibly due to smaller microdomain and restricted movement of the mesogen. In contrast, polymers containing more than four methylene spacer group established LC texture, which has been attributed to the larger monodomain and free movement of mesogens. Thermogravimetric analysis (TGA) data indicated that thermal stability and char yield decreased with increasing flexible methylene spacer groups, increased significantly for biphenyloxy and 1‐naphthyloxy containing polymers than that of phenyloxy containing polymers ascribed to increasing aromaticity, size, and number of aromatic rings. Photocrosslinking of stilbene containing polymers has been shown to proceed via 2π‐2π cycloaddition reaction by Ultra‐violet (UV) and fluorescence. The rate photocrosslinking has been found to increase with increasing number of methylene group in the main chain. The aromaticity of the side chain also increases the rate of crosslinking. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Kinetics and products of the reactions of ozone with toluene and its derivatives in acetic anhydride

The reactions of ozone with toluene and its derivatives in acetic anhydride were studied. It was found that competing parallel reactions of ozone with the aromatic ring and substituents occurred in the ozone-arene-acetic anhydride system. The ratio between these reaction paths depended on the arene structure and reaction conditions. The selectivity of the oxidation of toluene and its derivatives at the methyl group varied from 0 to 40%. The fraction of aromatic products decreased as the number of methyl groups at the ring was increased. Tri- and tetramethylbenzenes were oxidized only at the aromatic ring. The stability of an aromatic system increased upon the introduction of electron-acceptor substituents into the benzene ring. Aminotoluenes and hydroxytoluenes were oxidized with ozone mainly at the NH2 and HO groups; however, as in the case of toluene, the aromatic ring and methyl group became the main directions upon their acylation. The oxidation of the methyl group in acetic anhydride in the presence of sulfuric acid was finished at the step of the formation of the acylated derivatives of benzyl alcohols and benzaldehydes, which are resistant to the action of ozone.

Heterogeneous Reactions of Alkylamines with Ammonium Sulfate and Ammonium Bisulfate

The heterogeneous reactions between alkylamines and ammonium salts (ammonium sulfate and ammonium bisulfate) have been studied using a low-pressure fast flow reactor coupled to an ion drift-chemical ionization mass spectrometer (ID-CIMS) at 293 ± 2 K. The uptake of three alkylamines, i.e., monomethylamine, dimethylamine, and trimethylamine, on ammonium sulfate shows a displacement reaction of ammonium by aminium, evidenced by the release of ammonia monitored using protonated acetone dimer as the reagent ion. For the three alkylamines, the initial uptake coefficients (γ(0)) range from 2.6 × 10(-2) to 3.4 × 10(-2) and the steady-state uptake coefficients (γ(ss)) range from 6.0 × 10(-3) to 2.3 × 10(-4) and decrease as the number of methyl groups on the alkylamine increases. A different reaction mechanism is observed for the uptake of the three alkylamines on ammonium bisulfate, which is featured by an acid-base reaction (neutralization) with irreversible alkylamine loss and no ammonia generation and occurs at a rate limited by diffusion of gaseous alkylamines to the ammonium bisulfate surface. Our results reveal that the reactions between alkylamines and ammonium salts contribute to particle growth and alter the composition of ammonium sulfate and bisulfate aerosols in the atmosphere.

Haemolytic action of N-alkylpolymethylenediamines.

The haemolytic action of various N-alkyl derivatives (lauryl; C12H25-, myristyl; C14H29-, palmityl; C16H33-) of 1,3-diaminopropane, 1,4-diaminobutane, 1,5-diaminopentate, 1,6-diaminohexane, 1,7-diaminoheptane, 1,8-diaminooctane was examined using rabbit red blood cells. The activities of the various derivatives were compared with those of antiplaque agents commonly used as mouthwashes; cetylpyridinium chloride (CP) and chlorhexidine acetate (CH). The haemolytic activities of these agents were dependent on the length of the N-alkyl chain, whereas the number of methylene groups between the nitrogen atoms had little effect. The order of potency was CP, N-palmityl derivatives, N-myristyl derivatives greater than N-lauryl derivatives greater than CH which was similar to the order of the antiplaque effect evaluated in-vitro.

Assessment and prediction of thermal transport at solid–self-assembled monolayer junctions

Self-assembled monolayers (SAMs) have recently garnered much interest due to their unique electrical, chemical, and thermal properties. Several studies have focused on thermal transport across solid-SAM junctions, demonstrating that interface conductance is largely insensitive to changes in SAM length. In the present study, we have investigated the vibrational spectra of alkanedithiol-based SAMs as a function of the number of methylene groups forming the molecular backbone via Hartree-Fock methods. In the case of Au-alkanedithiol junctions, it is found that despite the addition of nine new vibrational modes per added methylene group, only one of these modes falls below the maximum phonon frequency of Au. In addition, the alkanedithiol one-dimensional density of normal modes (modes per unit energy per unit length) is nearly constant regardless of chain length, explaining the observed insensitivity. Furthermore, we developed a diffusive transport model intended to predict interface conductance at solid-SAM junctions. It is shown that this predictive model is in an excellent agreement with prior experimental data available in the literature.

Synthesis and characterization of ionic charged water soluble arginine-based poly(ester amide)

A family of water soluble and positively charged L-arginine based poly(ester amide)s (Arg-PEAs) was synthesized and characterized. These biodegradable polymers consist of three nontoxic building blocks: L-arginine, diols, and dicarboxylic acids. The Arg-PEAs were prepared by solution polycondensation reaction of tetra-p-toluenesulfonic acids salts of bis-(L-arginine) α, ω-alkylene diesters and di-p-nitrophenyl esters of dicarboxylic acids. Optimal conditions of the monomers and polymers synthesis were investigated, and the monomers and Arg-PEAs were chemically characterized. Arg-PEAs were found to have good solubility in water and many other polar solvents. Structure-function relationship of the Arg-PEAs revealed that changing the number of methylene groups in the diol or/and diacid segment could finely tune the hydrophobic and cationic properties of the Arg-PEAs. MTT assay showed that all the prepared Arg-PEAs were non-toxic to the cell lines even at very large doses. Arg-PEAs with double bond functionality could be photo-crosslinked with polyethylene glycol diacrylate to form cationic hybrid hydrogels.

Ex Vivo Proton NMR Analysis and Characterization of Thymus Lipid Metabolites and their Variation with Age in C57BL/6 Mice

Application 1H NMR spectroscopy techniques to the ex vivo study of thymus of 0.5-24 month-old C57BL/6 mice allowed the identification, the quantification and the estimation of some structural parameters (length and unsaturation) of various lipids in the thymus and their changes with age. An initial decrease of lipid metabolites in the thymus from 0.5 to 1 month of age was followed by large raises on further ageing, with 14, 8, and 4 fold increases for the total lipid content, fatty acids and glycerides, respectively, which correlated positively with age and negatively with thymus involution. The estimated average number of methylene groups per lipid chain essentially doubled its value from approximately 4-5 for the youngest mice to around 8 for the elderly, while the values obtained for the average number of double bonds per chain decreased with age from about 1-0.9 at 0.5/1 months of age to 0.6-0.7 for 18/24 months-old mice. The combination of NMR and histological data allowed studying the age-associated changes of the contribution of adipose- derived lipids to the total lipid content of the thymus and the amount of adipose tissue infiltrating the thymus. Both parameters initially showed a decrease from 0.5 months of age to (the adipose-free thymus at) 1 month of age. Afterwards, a continuous increase was observed on ageing: at 2 months about 55% of the lipids in the thymus were adipose-derived, while at 24 months they amounted to as much as about 95% of the total lipid content; for the same age-period, the estimated minimum adipose lipid content in the thymus changed from about 0.26% to 4.5%. Keywords: Aging, adipose tissue, 1H NMR, spectroscopy, lipids, mice, thymus involution, fatty acids, glycerides, methylene, adipose- derived lipids, T cells, thymopoiesis, thymectomy, homeostasis, epithelial cells, connective tissue, stem cells, mesenquimal stem cells, chemokines, stroma cell, adipocyte, sodium tetradeuterated trimethylsilylpropionate, homogenization, resonance, apodization, WET scheme, spin-locking scheme, Normalized thymus signals, Relative thymus signals, metabolite, hematoxylin-eosin, Pearson correlation test, correlation coefficient, TOCSY spectra, acylglyceride, puberty, significant correlation, immunocompetency, atrophy, esterified, non-esterified, glucose, hypothalamicpituitary-adrenal (HPA), hypothalamic-pituitary-gonadal (HPG), palmitic acid, lipodystrophies

Ex Vivo Proton NMR Analysis and Characterization of Thymus Lipid Metabolites and their Variation with Age in C57BL/6 Mice

Application (1)H NMR spectroscopy techniques to the ex vivo study of thymus of 0.5-24 month-old C57BL/6 mice allowed the identification, the quantification and the estimation of some structural parameters (length and unsaturation) of various lipids in the thymus and their changes with age. An initial decrease of lipid metabolites in the thymus from 0.5 to 1 month of age was followed by large raises on further ageing, with 14, 8, and 4 fold increases for the total lipid content, fatty acids and glycerides, respectively, which correlated positively with age and negatively with thymus involution. The estimated average number of methylene groups per lipid chain essentially doubled its value from approximately 4-5 for the youngest mice to around 8 for the elderly, while the values obtained for the average number of double bonds per chain decreased with age from about 1-0.9 at 0.5/1 months of age to 0.6-0.7 for 18/24 months-old mice. The combination of NMR and histological data allowed studying the age-associated changes of the contribution of adipose- derived lipids to the total lipid content of the thymus and the amount of adipose tissue infiltrating the thymus. Both parameters initially showed a decrease from 0.5 months of age to (the adipose-free thymus at) 1 month of age. Afterwards, a continuous increase was observed on ageing: at 2 months about 55% of the lipids in the thymus were adipose-derived, while at 24 months they amounted to as much as about 95% of the total lipid content; for the same age-period, the estimated minimum adipose lipid content in the thymus changed from about 0.26% to 4.5%.

Compensation of the Odd−Even Effects in Araliphatic Self-Assembled Monolayers by Nonsymmetric Attachment of the Aromatic Part

The integrity, chemical identity, packing density, and molecular orientation in SAMs formed by anthracene-substituted alkanethiols (Ant-n) with a variable number of methylene groups (n) in the aliphatic linker on Au(111) and Ag(111) substrates were studied by a combination of several complementary experimental techniques. The Ant-n molecules were found to form well-defined and highly ordered SAMs on these substrates, with very small inclination of the anthracene backbone. In addition, the Ant-n SAMs exhibited odd−even effects, that is, dependence of the molecular orientation and packing density on the length of the aliphatic linker, with the parity of n being the decisive parameter. While the direction (sign) of this odd−even behavior on gold and silver is the same as for SAMs of biphenyl- and terphenyl-substituted alkanethiolates and -alkaneselenolates, suggesting a common reason behind this phenomenon, the presence of a strong substrate−headgroup−C bending potential, the extent of the odd−even effects i...

Hydrophobic Molecules Slow Down the Hydrogen-Bond Dynamics of Water

We study the spectral and orientational dynamics of HDO molecules in solutions of tertiary-butyl-alcohol (TBA), trimethyl-amine-oxide (TMAO), and tetramethylurea (TMU) in isotopically diluted water (HDO:D(2)O and HDO:H(2)O). The spectral dynamics are studied with femtosecond two-dimensional infrared spectroscopy and the orientational dynamics with femtosecond polarization-resolved vibrational pump-probe spectroscopy. We observe a strong slowing down of the spectral diffusion around the central part of the absorption line that increases with increasing solute concentration. At low concentrations, the fraction of water showing slow spectral dynamics is observed to scale with the number of methyl groups, indicating that this effect is due to slow hydrogen-bond dynamics in the hydration shell of the methyl groups of the solute molecules. The slowing down of the vibrational frequency dynamics is strongly correlated with the slowing down of the orientational mobility of the water molecules. This correlation indicates that these effects have a common origin in the effect of hydrophobic molecular groups on the hydrogen-bond dynamics of water.

Effect of Chain Length on the Assembly of Mercaptoalkanoic Acid Multilayer Films Ligated through Divalent Cu Ions

The structural stability of alkenthiolate monolayers assembled on gold surfaces is a result of the well-defined organization of the individual molecules within the film. The formation of three-dimensional films assembled by stacking multiple molecular monolayers is substantially more challenging because the correct organization of the molecular components is required not only within the individual monolayers but also between the monolayers of the film. In this paper we examine the structure of multilayer films based on mercaptoalkanoic acid monolayers in which ligation between adjacent monolayers is achieved using the interaction of carboxylic acid and thiol groups with a divalent Cu ion. Using contact angle analysis and atomic force microscopy, we show that the use of Cu(2+) has profound implications on the properties and structure of the multilayer film. In particular, the divalent ions effectively prohibit the complete assembly of the next monolayer. For multilayer SAMs assembled from short alkane chains with six methylene groups, we find that molecules in the incomplete adlayer organize themselves randomly over the underlying monolayer. However, as the number of methylene groups increases (11 and 16 methylene groups), the upper layer tends to fracture into discrete islands which cover around 50% of the surface. The height of these islands is found to be equal to that expected for a complete, well-ordered monolayer assembled from the equivalent mercaptoalkanoic acid molecules. This relationship between chain length and island growth results from the migration of molecules into ordered aggregates driven by the reduction of free energy associated with maximizing intermolecular interactions.

The effect of the head-group spacer length of 12- s-12 gemini surfactants in the host–guest association with β-cyclodextrin

NMR spectroscopy has been used to study and characterize the interactions in solution between β-CD and alkyl-α,ω-bis(dodecyldimethyl ammonium bromide) gemini surfactants with the following head-group spacer lengths: 2, 4, 6, 8, and 10. The application of the method of continuous variation gives as a result that 1:1 and 2:1 (β-cyclodextrin-gemini) complexes are formed; the association stoichiometry is dependent on the spacer chain length, varying from 1.5 (for s = 2) to 1.8 (for s = 10). Assuming a two-step mechanism, the binding constants have been computed. In general, the overall binding constant slightly increases with an increase of the number of methylene groups in the spacer. The 1H NMR spectra of the N-(CH 3) 2 groups in β-cyclodextrin/gemini mixed solutions are split into two peaks for 12-10-12, suggesting that the gemini spacer can thread the β-cyclodextrin so that the latter is positioned between the gemini head-groups. Inspection of the ROESY spectra allowed the establishment of several spatial proximities between the protons from the β-CD and the gemini and for a spacer length of 10, the data indeed indicate that complexes are formed with the CD molecule positioned between the two charged head groups with the spacer passing through the CD molecule.

Photoswitching properties of photonic crystals infiltrated with polymer liquid crystals having azobenzene side chain groups with different methylene spacers

Photo-tunable photonic crystals were prepared by infiltrating a photoresponsive material into SiO 2 inverse opal films. Azobenzene-containing polymer liquid crystals, including poly(X-(4-methoxy-4′-oxy-azobenzene) alkyl acrylate), or PMAzXAc, where X is the number of methylene groups in the side chains (3, 6 and 11), were used as the photoresponsive material. PMAzXAc polymers were infiltrated in a spherical void of SiO 2 inverse opal films to give photo-tunable photonic crystals that showed a photonic band gap. The photonic band gap of the photonic crystals could be controlled by irradiation with linearly and circularly polarized lights, leading to a reversible change in reflection from the photonic crystals. The change in the reflection band was found to be dependent on the methylene spacer length of the PMAzXAc. PMAz6Ac showed the largest shift of the reflection band (25 nm), while very little shift was observed for PMAz11Ac.

New difunctional mediators based on 4-amino-TEMPO derivatives for controlling free radical polymerization of styrene

Summary — The free radical polymerization of styrene in the presence of a number of freshly newly synthesized bifunctional mediators differing in the number of methylene groups serving as a link between two functional 4-amino-TEMPO radicals has been investigated. It was found, that the activity of a nitroxide group in the biradicals in controlling radical polymerization of styrene differs from that of the TEMPO radical. Mediators with a lower number of connecting methylene groups between the two TEMPO rings give a higher conversion in the same reaction time. However, no simple correlation between the number of methylene groups in spacer chain and polymerization rate was observed, namely unexpectedly, high rate of polymerization was found for C4 . The formation of single-arm (P) and double-arm (P-P) macromolecules containing binitroxide at the core was observed.