Polymethylene Groups Research Articles

Dielectric relaxation of thermotropic liquid crystalline polyesters based on α,ω-alkylene-di-4-hydroxybenzoates and 4,4′-alkylenedioxy-dibenzoic acid

Two structurally isomeric homologous series of semiflexible thermotropic liquid crystalline polyesters were analysed by dielectric spectroscopy in temperature intervals varying from 253 to 403 K. Each series is characterised by a well-distinct behaviour of the dielectric loss versus temperature with a minor diffuse and a more confined relaxation occurring at lower and higher temperatures, respectively. Extrapolations from semilog plots of frequency (f) versus reciprocal absolute temperature (1/T) indicated that the principal relaxation is related to the glass transition temperature as defined by DSC. The analysis of data according to WLF equation indicated that the size and the kind of the polymethylene groups influence the apparent activation energy. A parity effect, connected to the length of polymethylene segments within each series, was finally detected on the relative position of the maximum relaxation, the odd numbers showing in any case higher temperature values.

Comb-like ionic complexes of pectinic and alginic acids with alkyltrimethylammonium surfactants

Ionic coupling of both polygalacturonic and alginic acids with alkyltrimethyl ammonium surfactants containing 18, 20 and 22 carbon atoms in the alkyl side chain was conducted in water solution to prepare non-soluble comb-like complexes. These amphiphilic complexes are arranged in a biphasic layered structure with the paraffinic phase made of alkyl side chains alternating with the hydrophilic phase made of polyuronic chains. The complexes displayed the thermal behaviour typical of comb-like systems carrying long polymethylene groups, which melt at temperatures between 40 and 80°C without significant disruption of the layered arrangement. Melting temperature, crystallinity and thermal stability were slightly higher for the polygalacturonic complexes and all they increased almost steadily with the length of the alkyl chain within each series. The melting-crystallization process was followed by combined WAXS/SAXS and 13C CP-MAS NMR, which revealed that the transition involves an expansion-contraction of the structure that may attain up to 20% of the original dimension. The transition takes place without large conformational changes and is not fully reversible.

Fluorescence Ratiometric Selective Recognition of Cu2+ Ions by Dansyl−Naphthalimide Dyads

Chimeric dyads 1a and 1b based on dansyl and naphthalimide units linked through the polymethylene group were synthesized, and their photophysical and interactions with various metal ions were investigated under different conditions. These dyads showed dual emission centered at around 375 and 525 nm, respectively, due to the locally excited state of the naphthalimide chromophore and energy-transfer-mediated emission (FRET) from the dansyl moiety. When titrated with various metal ions, these systems exhibited unusual selectivity for Cu(2+) ions as compared to Na(+), Li(+), K(+), Zn(2+), Pb(2+), Hg(2+), Co(2+), Fe(2+), Cd(2+), Mg(2+), and Ba(2+) ions and signaled the binding event through inhibition of FRET mediated emission at 525 nm with concurrent enhancement in the emission intensity of the naphthalimide chromophore at 375 nm. The uniqueness of these dyads is that they form stable 2:1 stoichiometric complexes involving sulfonamide functionality and act as visual fluorescence ratiometric probes for the selective recognition of Cu(2+) ions.

Investigating the Role of Mineral-Bound Humic Acid in Phenanthrene Sorption

Contaminant-soil interaction studies have indicated that physical conformation of organic matter atthe solid-aqueous interface is important in governing hydrophobic organic compound (HOC) sorption. To testthis, organo-clay complexes were constructed by coating montmorillonite and kaolinite with peat humic acid (PHA) in Na+ or Ca2+ dominated solutions with varying pH and ionic strength values. The solution conditions encouraged the dissolved PHA to adopt a "coiled" or "stretched" conformation prior to interacting with the clay mineral surface. Both kaolinite and montmorillonite organo-clay complexes exhibited higher phenanthrene sorption (Koc values) with decreasing pH, indicating that the coiled configuration provided more favorable sorption conditions. Evidence from 1H high-resolution magic angle spinning (HR-MAS) nuclear magnetic resonance (NMR) indicated that polymethylene groups were prevalent at the surface of the organo-clay complexes and may enhance sorptive interactions. Preferential sorption of polymethylene groups on kaolinite and aromatic compounds on montmorillonite may also contribute to the difference in phenanthrene sorption by PHA associated with these two types of clay. This study demonstrates the importance of solution conditions in the sorption of nonionic, hydrophobic organic contaminants and also provides evidence for the indirect role of clay minerals in sorption of contaminants at the soil-water interface.

Mononuclear and binuclear ruthenium(II) heteroleptic complexes based on 1,10-phenanthroline ligands. Part II: Spectroscopic and photophysical study in the presence of DNA

Photophysical and photochemical properties of a series of mononuclear and binuclear ruthenium(II) complexes of phen (phen = 1,10-phenanthroline), in the absence or in the presence of calf-thymus DNA have been investigated by steady-state as well as time-resolved methods. The complexes of this series (see Fig. 1) are [Ru x (phen) 2 x (L)] 2 x+ ( x = 1 or 2) type, where L is a bpy (4,4′-dimethyl-2,2′-bypiridine, with x = 1) or a bis-bpy covalently linked by flexible chains including either polymethylene groups or polyamine functions (with x = 2). Upon addition of DNA, the most important increasing luminescence and change of emission maxima wavelength are observed for the bimetallic compounds having amine functions in their spacer. A biexponential decay in luminescence is found with emission lifetimes of the complexes upon binding to DNA. Moreover, these complexes induce efficient photocleavage of DNA by irradiation at 450 nm. This efficiency is particularly important when the binuclear complexes include amino groups. Topoisomerization experiments have pointed out a similarity between the DNA cleaving ability of these complexes and their intercalation into DNA. Scavenging experiments have shown that the oxidative species involved in DNA cleavage was mainly 1O 2, via a type II mechanism.

Unusually High Fluorescence Enhancement of Some 1,8-Naphthalimide Derivatives Induced by Transition Metal Salts

Three-component systems, 1a−c and 2a,b, comprising 1,8-naphthalimide and 4-methoxy-1,8-naphthalimide as fluorophore, a dimethylamino moiety as guest binding site and a polymethylene group as spacer, have been synthesized and the fluorescence behavior of these systems has been studied in the absence and in the presence of the salts of several transition metal ions. The systems are found to be very weakly fluorescent compared to their constituent fluorophores (3 and 4) and this observation has been ascribed to photoinduced intramolecular electron transfer (PIET) between the electron rich amino moiety (donor) and relatively electron deficient fluorophore component (acceptor). Spectral and electrochemical data indicate the thermodynamic feasibility of PIET (exergonic free energy changes) in these multicomponent systems and PIET is found to be most efficient in systems where the fluorophore and the amino moiety are separated by two methylene groups. Fluorescence decay behavior of the systems suggest that PIET ...

Solvent Extraction of Silver Using Bis(O-butylxanthato)alkane Derivatives

New xanthic acid derivatives containing the bisbutyl polymethylene group were used for silver extraction in 0.1M NaClO4. Solvent extraction results showed that silver extraction was established through 1:2 (silver:ligand) complexes. The stabilities of the extractable complexes were determined based the length of the polymethylene chain between the donor atoms and the presence of a neighboring functional group within the structure of the ligands, as revealed by the Kex values. The probable extraction mechanism (extraction and back-extraction) and interferences are also discussed.

THE VIBRATIONAL SPECTRA OF COBALT AND IRON CYCLIDENE DIOXYGEN COMPLEXES AND THEIR RELATION TO MOLECULAR GEOMETRY

Abstract Infrared spectra were obtained for dioxygen adducts of a series of cobalt(II) and iron(II) cyclidene complexes with 1-methylimidazole as the axial base. The v o-o bands were located in the range 1137–1163 cm−1, and their identity was confirmed by 18O2 isotopic substitution. The frequency was found to be insensitive of the metal ion but dependent on both the σ and π electron donating properties of the cyclidene ligands. There is no apparent correlation between v o-o and the oxygen affinity; v o-o alternates with the even or odd number of carbon atoms in the bridging polymethylene group because of a symmetry effect on the π electron system of the ligand.

Steric effects of polymethylene chain length on the liquid-liquid extraction of Be(II), Sc(III) and Y(III) with bis(4-acylpyrazol-5-one) derivatives

The liquid-liquid extraction of Be(II) and rare earth metal ion, Sc(III) and Y(III), compounds with two 4-acylpyrazol-5-one subunits linked by a polymethylene group of varying length (H 2BP n )( n=2–8, 10, 20, where n is the number of methylene groups) is described. The results demonstrate that the extracted species with H 2BP n are Be(BP n)( n=2–8, 10, 20), Sc(BP n)(HBP n)( n=3–8, 10, 20), Sc(HBP n) 3 ( n=2), Y(BP n(HBP n)( n=5–8, 10, 20) and Y(BHP n) 3 ( n=3, 4). The relationship between the acidity constants and the extraction constants of chemical species of the same composition ratio shows that the metal ions can be divided into two groups, one including Be(II), Y(III), Ni(II) and Zn(II) and the other Sc(III) and Cu(II).

Chromatographic Optical Resolution of Enantiomers on Polyamides Containing 1,2-Disubstituted Cyclohexane Moiety as a Chiral Residue

Optically active polyamides having (−)-1,2-trans-diaminocyclohexane [(−)-DA] or (+)-1,2-trans-cyclohexane dicarboxylic acid [(+)-CDA] residue in main chain were synthesized by polycondensation. Polyamides with a p-phenylene group in main chain showed better resolution for several racemic compounds than the polyamides with a polymethylene group [ –(–CH2–)–n– (n=2–7)] in main chain. Among the polyamides with a polymethylene group in main chain, the polyamides with a shorter polymethylene group showed better chiral recognition abilities than the polyamides with a longer polymethylene group. Polyamides derived from (−)-trans-3,6-endomethylene-1,2,3,6-tetrahydrophtharic acid [(−)-ETHF] showed low chiral recognition ability. CD spectra of these polyamides showed characteristic patterns. Odd-even effect was observed in CD spectra of the polyamides having a series of a polymethylene group.

Anionic Surfactants with Divalent Counterions of Separate Electric Charge. III. Proton NMR Study

Abstract The proton NMR spectra of 1-tetradecanesulfonates whose cationic counterion, the 1,1′-polymethylenedipyridinium ion (with even-numbered methylene groups up to 14), is divalent with separate electric charge, were measured. From the chemical shifts the pyridine rings were found to move about in quite hydrophilic environment of micellar surface region, leading to a downfield shift of methylene groups next to head group of surfactant ion. The chemical shifts of methylene groups of micellized counterions with more than eight methylene groups are different from those of corresponding counterions in aqueous environment and are similar to those of methylene group in hydrophobic micellar interior. These results strongly support the previous conclusion that the polymethylene group with more than eight methylene groups folds and penetrates micellar interior in their micellized state.

Dependence of Liquid Crystalline Properties of Esters on the Central (CH2)nBridge

Abstract Effects of the central polymethylene group (CH2)n on the liquid crystalline properties displayed by cyanobiphenyl esters of ω-phenyl and cyclohexylalkanic acids were studied.

Formation of light gases and aromatic species during the rapid pyrolysis of coal

Light gases, long chain aliphatic species and aromatic hydrocarbons produced by the rapid pyrolysis of a sub-bituminous coal in a fluid-bed reactor have been determined as a function of temperature in the range 400–1050°C for residence times of the order of 1 s. The species released from the coal at the lowest temperatures (400–600°C) were predominantly large, complex molecules, with the exception of small quantities of aliphatic material that had been physically trapped in the microporous structure of the coal. At temperatures above 550–600°C long-chain polymethylene groups decomposed to form light olefins, predominantly ethylene and propylene. A significant proportion of the polymethylene groups appear to have been chemically bound to aromatic nuclei. Coincident with the polymethylene decomposition, yields of simple one- and two-ringed aromatic species increased significantly above 600°C. The more stable of these, benzene and naphthalene, continued to increase to 1050°C but the alkyl substituted species began to decrease at 800–850°C. Phenolic compounds also increased in yield between 600–800°C but decomposed at higher temperatures by decarbonylation to produce CO. At the highest temperatures studied, polycyclic aromatic hydrocarbons became increasingly important components of the tar, demonstrating that it is possible to form these species solely from coal pyrolysis reactions. Significant yields of phenylacetylene, styrene and indene, identified as important intermediates in the formation of polycyclic aromatic hydrocarbons in previous flame studies, were also observed in tars produced above 700°C.

Coal flash pyrolysis: secondary cracking of tar vapours in the range 870–2000 K

Tar free from influences of the original coal or char was cracked in two reaction systems, one using tar vapour in tubular quartz reactors at 900–1400 K and reactor residence times of ≈ 0.2 and ≈ 1 s, the other using tar aerosol in a shock tube at 1100–2000 K and residence time ≈ 1 ms. In the latter system the aerosol evaporated rapidly after passage of the shock front and the tar behaved kinetically as a vapour. Yields of light hydrocarbons including C 6H 6 and CO from tar cracking were determined as a function of temperature. Maximum yields of individual species agreed well between the two reactors but the temperatures of maximum yield depended on residence time. Hydrocarbon yields on a daf coal basis were very similar to those obtained previously by direct flash pyrolysis of the same coal at 870–1270 K. Kinetic analyses of the formation of C 2H 4, C 3H 6 and C 2H 2 gave activation energies of 220–260 kJ mol −1, similar to those for formation of the same hydrocarbons from n-hexadecane. The precursors of the alkenes could be polymethylene groups in the tar. CH 4, C 6H 6 and CO all had low activation energies of formation, reflecting the many different functional groups capable of eliminating these molecules.

Heats of Solution of Bolaform Electrolytes in Water. II. Polymethylenebis(trimethylammonium) Dibromides

Abstract The heats of solution of polymethylenebis(trimethylammonium) dibromides [(CH3)3N(CH2)nN-(CH3)3]Br2 (n=3–6, 8, 10, and 12) and alkyltrimethylammonium bromides CnH2n+1N(CH3)3Br (n=2–6) in water were measured at 15, 25, and 35 °C. The hydrophobic character of the polymethylene groups was compared with that of alkyl groups on the basis of the changes in the heat capacity for dissolution, which were obtained from the relation between the heats of solution and the temperature.

Relationship between structure and antiplaque and antimicrobial activities for a series of bispyridines

A series of bispyridines were examined for their bactericidal activities against in vitro, preformed, pure-culture plaques of selected oral plaque-forming bacteria. The antimicrobial activities of these agents were examined in relation to their molecular configurations. These studies demonstrated that the length of the interpyridine polymethylene group bridge and the length of the alkyl side chain were important determinants of antiplaque and antimicrobial efficacy. The most potent compounds of the bispyridine series were studied to determine the minimal conditions (concentration, duration, and frequency) of treatment required for likely clinical efficacy.

Five coordinate nickel(II) isothiocyanato and chloro complexes of triazacycloalkanes

The new nickel(II) complexes [Ni(pqr-cy)(NCS) 2], [Ni(pqr-cy)Cl]ClO 4, and Ni 2(pqr-cy) 3(ClO 4) 4·nH 2O (n = 4 or 5) have been prepared, where pqr-cy is a triazacycloalkane, NH(CH 2) pNH(CH 2) qNH(C H 2) r (p,q = 2,3; r = 2–6). The isothiocyanato complexes are six-coordinate, NCS-bridged octahedral when t (= p + q + r) is small (t≦9). but they are five-coordinate when t is large (t≧9). The five-coordination is peculiar and its origin is attributable to blocking of a coordination site by the backbone polymethylene groups of the pqr-cy ligands. Only the ligands with t=9 and 10 form the chloro complexes, which are Cl-bridged dimers and are also five-coordinate because of the same steric hindrance. It is worth noting that these five-coordinate nicke(II) complexes are isolated from aqueous solutions. The 2:3 perchlorate complexes are octahedral and available only for the ligands with t=9.

Preparation and Stereochemistry of the Cobalt(III) Complexes with N,N′-Polymethylenedi(salicylideneamine) and Its Related Compounds

Abstract Preparation of two series of the cobalt(III) complexes, Na[Co(CN)2(SB)] and [Co(acac)(SB)], was carried out. CN, acac and SB respectively refer to cyanide anion, acetylacetonate anion and the quadridentate Schiff base anion, N,N′-polymethylenedi(salicylideneamine), N,N′-polymethylenedi(α-methylsalicylideneamine) or N,N′-polymethylenedi(2-hydroxy-1-naphthylmethyleneamine). Efforts to obtain Na[Co(CN)2(SB)] only containing the last Schiff base were unsuccessful. It was concluded from their PMR spectra that, for the dicyano complexes, the structure changes from a trans-form to a cis-one via a distorted trans-form, whereas for the acetylacetonato complexes, it changes from a distorted cis-β-form to an undistorted one with an increase in the length of carbon chain in the bridged polymethylene group of the Schiff bases.

Fragmentation of 13C Labelled methylcyclohexanes under electron‐impact

AbstractThe methylcyclohexanes labelled with carbon‐13 in the five possible positions have been synthesised and their mass spectra recorded. By comparison of these spectra with those of the corresponding deuterated molecules, it was possible to accurately determine the nature and the contribution of the various fragmentation paths. More than ninety percent of the fragment ions formed from methylcyclohexane result from the rupture, at one stage or another, of one of the CC bonds attached to the tertiary carbon atoms. Besides the elemination of a polymethylene group from the ring, in either one or two steps, the two major fragmentation pathways involve the prior formation of a cyclohexyl or a cyclopentyl ion.

Influence of glycol type on the progress of condensation telomerization. Hardening kinetics and properties of hardened oligo-ester acrylates

EARLIER reports [1, 2] had shown the effect of adding a monofunc~ional telogen and, correspondingly, the effect of all the starting components of condensation telomerization on the properties of the telomer homologues and polymers formed. The present work, which continues the study of the connection between the structure of the oligo-ester acrylate (CA) and the properties of the polymers produced from them, deals with the effect of the type of glycol on the synthesis, polymerization and properties of the oligo-ester acrylates and some of the properties o f the hardening products. Alkanediols with different numbers of polymethylene groups were used to synthesize tetrafnnctional OA; their general formula was HO(CH2)~OH, but we also used glycols containing oxyethylene groups, of general formula H0(CH2CH20)nH.