Ring-chain interconversion in high-performance polymer systems. 3. Cyclodepolymerization of poly(m-phenylene isophthalamide) (Nomex) and entropically driven ring-opening polymerization of the macrocyclic oligomers so produced

A homologous series of macrocyclic oligoamides has been prepared in high yield by reaction of isophthaloyl chloride with m-phenylenediamine under pseudo-high-dilution conditions. The products were characterized by infrared and H-1 NMR spectroscopies, matrix assisted laser desorption-ionization time-of-flight mass spectrometry, and gel permeation chromatography (GPC). A series of linear oligomers was prepared for comparison. The macrocycles ranged in size from the cyclic trimer up to at least the cyclic nonamer (90 ring atoms). The same homologous series of macrocyclic oligomers was prepared in high yield by the cyclodepolymerization of poly(m-phenylene isophthalamide) (Nomex). Cyclodepolymerization was best achieved by treating a 1% w/v solution of the polymer in dimethyl sulfoxide containing calcium chloride or lithium chloride with 3-4 mol % of sodium hydride or the sodium salt of benzanilide at 150 degreesC for 70 h. Treatment of a concentrated solution of the macrocyclic oligomers (25% w/v) with 4 mol % of sodium hydride or the sodium salt of benzanilide in a solution of lithium chloride in dimethyl sulfoxide at 170 degreesC for 6 h resulted in efficient entropically driven ring-opening polymerizations to give poly(m-phenylene isophthalamide), characterized by infrared and H-1 NMR spectroscopies and by GPC. The molecular weights obtained were comparable with those of the commercial polymer.

Influence of sodium chloride on seed germination and seedling root growth of cotton (Gossypium hirsutum L.)

Response of cotton (Gossypium hirsutum L. cv. NIAB-78) to salinity, in terms of seed germination, seedling root growth and root Na+ and K+ content was determined in a laboratory experiment. Cotton seeds were exposed to increasing salinity levels using germination water with Sodium chloride concentrations of 0, 50, 100, 150 and 200 mM, to provide different degrees of salt stress. Germinated seeds were counted and roots were harvested at 24, 48, 72 and 96 h after the start of the experiment. It appeared that seed germination was only slightly affected by an increase in salinity (in most cases the differences between treatment were non-significant), whereas root length, root growth rate, root fresh and dry weights were severely affected, generally highly significant differences in these variables were found for comparisons involving most combinations of salinity levels, in particular with increased incubation period. K+ contents decreased with increasing salinity levels, although differences in K+ content were only significant when comparing the control and the 4 salinity levels. Na+ content of the roots increased with increasing levels of NaCl in the germination water, suggesting an exchange of K+ for Na+. The ratio K+/Na+ strongly decreased with rising levels of salinity from around 4.5 for the control to similar to 1 at 200 mM NaCl.

Vibrational intensities VIII: CH3- and CD3- chloride, bromide and iodide

Absolute intensity measurements have been made on the fundamental vibrations of methyl chloride, bromide, and iodide, and their fully deuterated derivatives, by integrating the optical density over the absorption bands. The bands were fully pressure broadened by using up to 80 atmos of foreign gas. Band separations were made graphically. The results are analyzed in terms of the dipole moment derivatives with respect to symmetry coordinates in the molecule, (∂p/∂Si). The data on the different isotopic species are shown to yield consistent results, and this requirement of consistency has also been used as an aid in the analysis. In the E‐class vibrations the signs of the dipole moment derivatives have been determined unambiguously by assuming the permanent dipole to be directed CH3+☒X—.

The fundamental vibration-rotation band of hydrogen chloride

The fundamental vibration-rotational absorption band of hydrogen chloride near 3 45,t has been remeasured using higher resolving power than previously. The wave-lengths of the absorption lines have been determined more precisely, and the isotopic splitting of lines has been completely resolved. The results have provided new and more satisfactory values for the rotational constants Bi, and the centrifugal stretching constants Di, and their relative values for the two isotopic species agree closely with what is to be expected for the difference in mass. The positions of the lines in the pure rotational absorption spectrum have been calculated from the derived data, and agree closely with those recently observed. The bond lengths re for each isotopic species H35C1 and H37C1 is found to be 1-2744A.

In situ observation of lithium hydride hydrolysis by DRIFT spectroscopy

Polycrystalline LiH was studied in situ using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy to investigate the effect water vapour has on the rate of production of the corrosion products, particularly LiOH. The reaction rate of the formation of surface LiOH was monitored by measurement of the hydroxyl (OH) band at 3676 cm(-1). The initial hydrolysis rate of LiH exposed to water vapour at 50% relative humidity was found to be almost two times faster than LiH exposed to water vapour at 2% relative humidity. The hydrolysis rate was shown to be initially very rapid followed by a much slower, almost linear rate. The change in hydrolysis rate was attributed to the formation of a coherent layer of LiOH on the LiH surface. Exposure to lower levels of water vapour appeared to result in the formation of a more coherent corrosion product, resulting in effective passivation of the surface to further attack from water. Crown Copyright (c) 2007 Published by Elsevier B.V. All rights reserved.

Synthesis and characterization of carbamoyl methyl pyrazole(CMPz) compounds of palladium(II) chloride: the crystal and molecular structure of [PdCl2{(C3H3N2CH2CONBu2)-Bu-i}(2)]

Carbamoyl methyl pyrazole compound of palladium(II) chloride of the type [PdCl2L2] (where L = C5H7N2CH2CON(C4H9)(2), C5H7N2CH2CON((C4H9)-C-i)(2), C3H3N2CH2CON(C4H9)(2), or C3H3N2CH2CON((C4H9)-C-i)(2)) has been synthesized and characterized by IR and H-1 NMR spectroscopy. The structure of the compound [PdCl2{(C3H3N2CH2CONBu2}2)-Bu-i] has been determined by single crystal X-ray diffraction and shows that the ligands are bonded through the soft pyrazolyl nitrogen atom to the palladium(II) chloride in a trans disposition. (c) 2007 Elsevier B.V. All rights reserved.

Effects of calcium chloride and sodium hexametaphosphate on certain chemical and physical properties of soymilk

Soymilks with sodium hexametaphosphate (SHMP) (0% to 1.2%) and calcium chloride (12.50, 18.75, and 25.00 mM Ca),were analyzed for total Ca, Ca ion concentration, pH, kinematic viscosity, particle diameter, and sediment after pasteurization. Higher added Ca led to significant (P <= 0.05) increases in Ca ion concentration and significant (P <= 0.05) decreases in pH. At certain levels of SHMP, higher concentrations of added Ca significantly increased (P <= 0.05) kinematic viscosity, particle diameter, and sediment. Increasing SHMP concentration reduced Ca ion concentration, particle diameter, and dry sediment content, but reduced kinematic viscosity of samples (P <= 0.05). Adding SHMP up to 0.7% influenced pH of soymilk in different ways, depending on the level of Ca addition. When the pH of Ca-fortified soymilk was adjusted to a higher level, ionic Ca decreased as pH increased. Ihere was a negative linear relationship between the logarithm of ionic Ca concentration and the adjusted pH of the soymilk. Ionic Ca appeared to be a good indicator of thermally induced sediment formation, with little sediment being produced if ionic Ca was maintained below 0.4 mM.

Mucoadhesive interactions of amphiphilic cationic copolymers based on [2-(methacryloyloxy)ethyl]trimethylammonium chloride

Three series of water-soluble cationic copolymers have been synthesised by free-radical copolymerisation of [2-(methacryloyloxy)ethyl]-trimethylammonium chloride (MADQUAT) with methyl acrylate (MA), butyl acrylate (BA) and butyl methacrylate (BMA). The interactions between these copolymers and porcine stomach mucin have been studied in aqueous solutions using dynamic light scattering, zeta-potential measurements, turbidimetric titration and transmission electron microscopy (TEM). It was demonstrated that mixing aqueous dispersions of mucin with solutions of the cationic copolymers results in significant changes in size distribution and zeta-potential of its particles. It was found that an increase in the content of hydrophobic groups in copolymers leads to more efficient adsorption of macromolecules on the surface of mucin particles, which evidences the importance of hydrophobic effects in mucoadhesion. The efficiency of mucoadhesive interactions was found to be significantly dependent on pH, which affects the surface charge and aggregation stability of mucin. (C) 2007 Elsevier B.V. All rights reserved.

Molecular dynamics simulations of threadlike cetyltrimethylammonium chloride micelles: effects of sodium chloride and sodium salicylate salts

We use atomistic molecular dynamics simulations to probe the effects of added sodium chloride (NaCl) and sodium salicylate (NaSal) salts on the spherical-to-threadlike micelle shape transition in aqueous solutions of cetyltrimethylammonium chloride (CTAC) surfactants. Long threadlike micelles are found to be unstable and break into spherical micelles at low concentrations or NaCl, but remain stable for 20 ns above a threshold value of [NaCl] approximate to 3.0 M, which is about 2.5 times larger than the experimental salt concentration at which the transition between spherical and rodlike micelles occurs. The chloride counterions associate weakly oil the surface of the CTAC micelles with the degree of counterion dissociation decreasing slightly with increasing [NaCl] on spherical micelles, but dropping significantly on the threadlike micelles tit high [NaCl]. This effect indicates that the electrolyte ions drive the micellar shape transition by screening the electrostatic repulsions between the micellar headgroups, The aromatic salicylate counterions, on the other hand, penetrate inside the micelle with their hydrophilic groups staying in the surfactant headgroup region and the hydrophobic groups partially embedded into the hydrophobic core of the micelle. The strong association of the salicylate ions with the surfactant headgroups leads to dense packing of the surfactant molecules, which effectively reduces the surface area per surfactant, and increases intramicellar ordering of the surfactant headgroups, favoring the formation of long threadlike micelles. Simulation predictions of the geometric and electrostatic properties of the spherical and threadlike micelles are in good agreement with experiments.

Coordination behavior of pyridylmethylthioether system with cupric chloride and cupric bromide: CS bond cleavage and crystal structures

The coordination behavior of pyridylmethylthioether type of organic moieties having N2S2 donor set [L-1=1,2-bis(2-pyridylmethylthio)ethane, L-2 = 1,3-bis(2-pyridylmethyl-thio)propane and L-3 = 1,4-bis(2-pyridylmethylthio)butane] with copper(II) chloride and copper(II) bromide have been studied in different chemical environments. Copper(II) chloride assisted C-S bond cleavage of the organic moieties leading to the formation of copper(II) picolinate derivatives, whereas, under similar experimental conditions, no C-S bond cleavage was observed in the reaction with copper(II) bromide. The resulted copper(II) complexes isolated from the different mediums have been characterized by spectroscopic and X-ray crystallographic tools.

Lithium and oxygen adsorption at the b-MnO2 (110) surface

The adsorption and co-adsorption of lithium and oxygen at the surface of rutile-like manganese dioxide(b-MnO2), which are important in the context of Li–air batteries, are investigated using density functional theory. In the absence of lithium, the most stable surface of b-MnO2, the (110), adsorbs oxygen in the form of peroxo groups bridging between two manganese cations. Conversely, in the absence of excess oxygen, lithium atoms adsorb on the (110) surface at two different sites, which are both tricoordinated to surface oxygen anions, and the adsorption always involves the transfer of one electron from the adatom to one of the five-coordinated manganese cations at the surface, creating (formally) Li+ and Mn3+ species. The co-adsorption of lithium and oxygen leads to the formation of a surface oxide, involving the dissociation of the O2 molecule, where the O adatoms saturate the coordination of surface Mn cations and also bind to the Li adatoms. This process is energetically more favourable than the formation of gas-phase lithium peroxide (Li2O2) monomers, but less favourable than the formation of Li2O2 bulk. These results suggest that the presence of b-MnO2 in the cathode of a nonaqueous Li–O2 battery lowers the energy for the initial reduction of oxygen during cell discharge.

Effects of aluminium chloride and aluminium chlorohydrate on DNA repair in MCF10A immortalised non-transformed human breast epithelial cells

Use of underarm aluminium (Al)-based antiperspirant salts may be a contributory factor in breast cancer development. At the 10th Keele meeting, Al was reported to cause anchorage-independent growth and double strand DNA breaks in MCF10A immortalised non-transformed human breast epithelial cells. We now report that exposure of MCF10A cells to Al chloride or Al chlorohydrate also compromised DNA repair systems. Longterm (19–21 weeks) exposure to Al chloride or Al chlorohydrate at a 10−4 M concentration resulted in reduced levels of BRCA1 mRNA as determined by real-time RT-PCR and BRCA1 protein as determined by Western immunoblotting. Reduced levels of mRNA for other DNA repair genes (BRCA2, CHK1, CHK2, Rad51, ATR) were also observed using real-time RT-PCR. Loss of BRCA1 or BRCA2 gene function has long been associated with inherited susceptibility to breast cancer but these results suggest that exposure to aluminium-based antiperspirant salts may also reduce levels of these key components of DNA repair in breast epithelial cells. If Al can not only damage DNA but also compromise DNA repair systems, then there is the potential for Al to impact on breast carcinogenesis.

Chemoselective and stereoselective lithium carbenoid mediated cyclopropanation of acyclic allylic alcohols

The reaction of geraniol with different lithium carbenoids generated from n-BuLi and the corresponding dihaloalkane has been evaluated. The reaction occurs in a chemo and stereoselective manner, which is consistent with a directing effect from the oxygen of the allylic moiety. Furthermore, a set of polyenes containing allylic hydroxyl or ether groups were chemoselectively and stereoselectively converted into the corresponding gemdimethylcyclopropanes in one single step in moderate to good yields mediated by a lithium carbenoid generated in situ by reaction of n-BuLi and 2,2-dibromopropane.