Polyamide synthesis by the direct polycondensation with phenylphosphonic dichloride in pyridine

The direct polycondensation of isophthalic acid (IPA) and aromatic diamines with a new phosphorus compound, phenylphosphonic dichloride (PPDC), was studied. PPDC could actually react with nearly a two molar amount of carboxyl groups, but more than 75 mol % PPDC with respect to the carboxyl groups of IPA were satisfactorily used in the polycondensation. The initial reaction of IPA with PPDC in pyridine at room temperature and then at 120°C was needed to complete the activation, and the subsequent aminolysis at 120°C for 3 h was most effective. The polyamides of high inherent viscosity were obtained even from weakly basic aromatic diamines, and their values were more than those obtained by the conventional method. In their thermal properties determined by the DTA, they showed T_gs and T_ms higher than those reported before.     

THE RELATIONSHIP BETWEEN CARCINOGENIC ACTIVITIES OF POLYCYCLIC AROMATIC HYDROCARBONS AND THEIR SINGLET, TRIPLET, AND SINGLET-TRIPLET SPLITTING ENERGIES AND PHOSPHORESCENCE LIFETIMES

Abstract— The energies of the lowest excited singlet, E_s, and triplet, E_t, states, and singlet-triplet splitting energies, ΔE_s,t, were determined on 18 carcinogenic and 31 noncarcinogenic polycyclic aromatics. A highly significant correlation was found between carcinogenic activity and the energy of the excited singlet state. Compounds with an E_s < 312 kJ/mol were 4.8 times more likely to be carcinogens than those compounds with E_s 312 kJ/mol (P= 0.015). Compounds whose singlet energies fell within the narrow range of 297 ≤E_s≤ 310 kJ/mol were 22.8 times more likely to be carcinogens than those compounds which fell outside this range (P= 0.00006). A significant correlation between carcinogenic activity and E_t energies was not found, while the correlation involving ΔE_s,t energies was intermediate between the E_s and E_t correlations. The phosphorescence lifetimes, τ_p, of the 18 carcinogenic aromatics and 27 of the noncarcinogenic aromatip were determined, and were shown not to be correlated with carcinogenic activity. When either the E_t or ΔE_s,t energies were plotted as a function of E_s it was found that the carcinogens tended to form in an elliptical cluster. Compounds whose E_s and E_t energies placed them within the ellipse were 9.7 times more likely to be carcinogens than those compounds which fell outside the ellipse (P= 0.002), while with the E_s, ΔE_s,t ellipse, compounds which fell inside were 20.6 times more likely to be carcinogens than those which fell outside (P= 0.0004). E_s, E_t, ΔE_s,t and τ_p values were also determined on 12 carcinogenic and 4 noncarcinogenic alkyl substituted benz[a]anthracenes. There was no significant difference between the carcinogens and noncarcinogens and the “elliptical” correlation predicted both the carcinogens and noncarcinogens to be carcinogenic. The results suggest that either some property(ies) of the lowest excited singlet state, but not its energy, or some molecular property(ies) which runs parallel to singlet state energies may be important in determining carcinogenic activity in polycyclic aromatics.     

The Theoretical and Experimental Studies on Oxidation of Straight Chain Amino Acids in Moderately Concentrated Sulfuric Acid Medium

The kinetics of the permanganic oxidation process of some straight chain amino acids in moderately concentrated sulfuric acid medium have been investigated using a spectrophotometric technique. Conclusive evidences have proven autocatalytic activity of Mn(II) for these reactions. It is determined that even and odd effects of the number carbon atom in a carbon chain are annihilated when it's the number of carbon atoms is increased more than of three in a noncatalytic oxidation pathway. Thus, rate constants belonging to glycine, l ‐α‐amino‐n‐butyric acid, l ‐norleucine, and l ‐α‐amino‐n‐heptanoic acid satisfy Taft's equation involving the induction factor in the noncatalytic pathway, whereas l ‐α‐amino‐n‐heptanoic acid has an odd number of carbon atom in its chain carbon. On the other hand, in the catalytic pathway, rate constants satisfy Taft' equation including inductive and steric factors, when rate constants belonging to amino acids with an even number of carbon atoms are separated from those with an odd number of carbon atoms. The oxidation process of amino acids in the noncatalytic pathway and those with the even number of carbon atoms in the carbon chain in the catalytic pathway speeds up by an increase in the length of chain that is accompanied with an increase in the carbon chain's electron‐donating characteristic. On the other hand, an increase in the length of the carbon chain is accompanied with more steric hindrance, which counteracts its electron‐donating character, thereby decreasing reaction rate in the catalytic pathway. Finally, amino acid–Mn(II) complexes were studied using a density functional theory method. Results obtained show that such a complex is less stable than reactants, namely it is formed in an endothermic reaction. The number and strength of hydrogen bonding belonging to amino acid is more than those of the amino acid–Mn(II) complex. Besides, it has been illustrated that natural bond orbital analysis and molecular orbital calculations satisfy the findings.     

Thermodynamic properties of peptide solutions. Part 15. Partial molar isentropic compressibilities of some glycyl dipeptides in aqueous solution at 15 and 35°C

The partial molar isentropic compressibilities at infinite dilution,K _s,2 ^o , have been obtained for eight glycyl dipeptides of sequence gly-X (X is an amino acid) in aqueous solution at the temperatures 15 and 35°C. The results have been combined with those obtained at 25°C, that were reported earlier, to evaluate the temperature dependences ofK _s,2 ^o for the dipeptides in the temperature range 15 to 35°C. TheK _s,2 ^o values for all the dipeptides are negative and increase (become more positive) with an increase in temperature. The slopes of the temperature dependences ofK _s,2 ^o for the dipeptides with typically hydrophobic side-chains are significantly larger than those for dipeptides with hydrophilic side-chains.     

The production and properties of a new xylose reductase from fungus

Neurospora crassa XI was found to ferment xylose and glucose simultaneously. Xylose was the appropriate inducer for the production of xylose reductase that had two isoenzymes designated as EI and EII. Both EI and EII, which were purified by affinity chromatography, had NADPH-dependent xylose reductase activities. EII also had NADH-dependent activity, and EI is the only xylose reductase found so far without any NADH-dependent activity. EI and EII had MWs of 30 kDa and 27 kDa, and pIs of 5.6 and 5.2, respectively. The specifities of EI and EII against triose, pentoses, and hexoses were studied. The K_ms against xylose for EI and EII were 2.3 mM and 1.1 mM respectively, which were much lower than those of the xylose reductase from yeast.     

Radiation-induced solid-state polymerization of methacrylic acid. I. Crystalline transition of the monomer

The anomalous crystalline transition of methacrylic acid found by broad-line NMR measurements was studied in connection with the build-up and decay of trapped radicals. The build-up of radicals is smaller and the decay rate of the trapped radicals is faster in the low-temperature range (phase II), which gave the narrower maximum slope distance ΔH_msl of the NMR spectrum, than those in the higher temperature range (phase I), which gave the broader ΔH_msl. From these experiments it was concluded that in phase I the crystals have a more closely packed structure, resulting in a more rigid matrix for the trapped radicals than those in phase II. This interpretation is consistent with the temperature dependence of the ESR spectrum of the trapped propagating radicals previously reported. The existence of the crystalline transition was also confirmed by DSC measurements, and the effects of the crystallization conditions on the transition were investigated and were discussed with reference to the results of broad line NMR measurements.     

A comparative study of effective core potential and full-electron calculations in Mo compounds. I. An analysis of topological properties of bond charge distribution

Effective core potential (ECP) and full-electron (FE) calculations for MoS₄^?2, MoO₄^?2, and MoOCl₄ compounds were analyzed. Geometry parameters, binding energies, charge distributions, and topological properties of the electronic density were studied for Mo? L bonds (L = S, O, Cl). Results clearly indicate that those approaches that include valence plus 4s and 4p electrons (ECP2 methods) are able to reproduce the topological properties of Mo? L bonds, charge distributions, and geometries with respect to those obtained by FE methods. ECP methods that consider only the 4d and 5s valence electrons (ECP1) fail in the calculation of molecular properties. The use of 5p functions in ECP1 approaches produces a negative Mulliken charge on Mo. Bader's charges give more consistent results than Mulliken's ones. A new parameter for measuring the degree of ionicity is proposed. © 1994 by John Wiley & Sons, Inc.     

Melting behavior of ethylene oxide–propylene oxide (sym-PEP) block copolymers

Melting points and lamellar thicknesses have been measured for ethylene oxide–propylene oxide block copolymers (sym-PEP) with central poly(ethylene oxide) block lengths of 70–100 chain units and end poly(propylene oxide) block lengths of 0–30 chain units. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by an amount (up to 15°C) which increases as the poly(propylene oxide) block length increases. Most samples have more than one melting transition, which can be assigned to variously folded chain crystals. End interfacial free energies σ_e for the various crystals have been estimated by use of Flory's theory of melting of block copolymers. For a given crystal type (e.g., once-folded-chain) σ_e is higher the longer the chain length of the end poly(propylene oxide) blocks. For a given copolymer σ_e is lower, the more highly folded the poly(ethylene oxide) chain.     

The synthesis of bis(benzo-crown ether)s and their incorporation into potassium-selective PVC membrane electrodes

Five bis(benzo-15-crown-5) derivatives connected with different bridge chains were synthesized as neutral carriers in K⁺-selective electrodes. Potassium ion-selective PVC membrane electrodes based on these bis(crown ether)s were prepared using dibutyl phthalate (DBP) and dioctyl phthalate (DOP) as plasticizers of the PVC membrane. The selectivity coefficients (K _M ⁿ⁺:K _K+) for various alkali and alkaline-earth metal ions were measured. The electrodes based on the bis(crown ether)s are more selective for K⁺ than those based on monomeric crown ethers. The selectivity of one of the prepared potassium selective electrodes was higher than that of the electrode based on valinomycin and three of them were stable over a wide pH range.     

Effect of Titanium on Fluxional Behavior of Unbridged Metallocene Catalysts

Summary: Thanks to the use of a ligand consisting of a saturated ring fused to the cyclopentadienyl moiety, which sensibly increases the stability of titanocenes, it was possible to investigate the oscillating behavior of titanium catalysts in propylene polymerization for the first time. The titanium‐based catalysts yield poly(propylene)s with new and interesting microstructures. Indeed, in spite of the significantly lower isotactic pentad content [mmmm], the average lengths of the isotactic blocks (N_iso) are similar or even higher than that obtained with the zirconium‐based homologues. Accordingly, differential scanning calorimetry (DSC) analysis shows melting peaks which are more evident than those obtained with the zirconium homologues. The study of the microstructure of the poly(propylene)s obtained with these catalysts allowed us to participate in the still open discussion on the oscillating mechanism of unbridged metallocenes.

The titanium‐based catalysts employed in this study.     

Synthesis of macrocyclic bis(phenylbenzoxazole) derivatives via tandem claisen rearrangement and their fluorescence behavior

Novel macrocyclic bis(phenylbenzoxazole) derivatives were easily synthesized from macrocyclic isobutenyl bis(amide‐ether)s by tandem Claisen rearrangement and subsequent intramolecular cyclization of the amide‐phenol intermediates. The position of substitution of the oligoethylene glycol moiety on the phenylamido groups of the macrocycles did not have a large effect on the yields of the bis(benzoxazole)s for the meta and para derivatives. The fluorescence quantum yields of most of the macrocyclic bis(benzoxa‐zole)s were lower than those of the corresponding nonmacrocyclic bis(benzoxazole) model compounds. The quantum yields of the para‐substituted macrocyclic bis(benzoxazole)s were clearly lower than those of the model compounds and decreased with increasing length of the oligoethylene chain.     

A systematic preparation of new contracted Gaussian- type orbital sets. VII. MINI-3, MINI-4, MIDI-3, and MIDI-4 sets for transition metal atoms

Two minimal contracted Gaussian-type orbital (CGTO ) sets are developed for the transition metal atoms. The expansion terms for the first set, MINI -3, are 4, 3, 3, and 3 for s-type CGTO s and others are all three. The abbreviation would be (4333/33/3) where the slash divides symmetry. The expansion terms for the other set, MINI -4, is (4333/43/4). The split-type basis sets, MIDI -3 and MIDI -4, are derived directly from MINI -3 and MINI -4, MINI -3 and MIDI -3 provide the outer-shell orbital energies which are far better than those by single-zeta (SZ ) STO s. MINI -4 and MIDI -4 provide the outer-shell orbital energies which are almost as good as those by double-zeta (DZ ) STO s. The total energies given by the present sets are better than those of SZ except for MINI -3 for Sc and Ti: the energies by MINI -4 and MIDI -4 are only 0.8–1.7 a.u. higher than DZ . The basis sets were tested on the Cu₂ molecule, where a large basis set was also used.     

A Panel of Cytochrome P450 BM3 Variants to Produce Drug Metabolites and Diversify Lead Compounds

Herein we demonstrate that a small panel of variants of cytochrome P450 BM3 from Bacillus megaterium covers the breadth of reactivity of human P450s by producing 12 of 13 mammalian metabolites for two marketed drugs, verapamil and astemizole, and one research compound. The most active enzymes support preparation of individual metabolites for preclinical bioactivity and toxicology evaluations. Underscoring their potential utility in drug lead diversification, engineered P450 BM3 variants also produce novel metabolites by catalyzing reactions at carbon centers beyond those targeted by animal and human P450s. Production of a specific metabolite can be improved by directed evolution of the enzyme catalyst. Some variants are more active on the more hydrophobic parent drug than on its metabolites, which limits production of multiply‐hydroxylated species, a preference that appears to depend on the evolutionary history of the P450 variant.     

Sorption and transport of water vapor in alginic acid,sodium alginate,and alginate-cobalt complex films

The sorption and the transport of water vapor in films of alginic acid (G1), sodium alginate (G1Na), and alginate-cobalt complex (G1Co) were studied at 30°C by employing the weighing method. Sorption isotherms for all films of G1, G1Na, G1Co were of type II in the Brunauer's classification. The integral absorption from, and desorption to, zero pressure were non-Fickian type for all films studied. The mean permeability coefficient P , which was determined by the cup method, increased with the increase of vapor pressure, especially in the low vapor pressure region. P for G1Na was much higher than that for G1, which mainly reflects more hygroscopic nature of G1Na than that of G1. The values of P for G1Co were lower than those for G1 at lower pressures and then approached those for G1 at higher vapor pressures. Integral diffusion coefficient D evaluated as P /S, where the solubility coefficient S was evaluated from sorption isotherms, increased rapidly with increasing water concentration and then leveled off. In the concentration region studied, the magnitude of D and its dependence on concentration for H₂O-G1Na system did not differ much from those for H₂O-G1 system. D for H₂O-G1Co system was much lower than that for H₂O-G1 system. © 1994 John Wiley & Sons, Inc.     

Shift reagents in ion mobility spectrometry: the effect of the number of interaction sites,size and interaction energies on the mobilities of valinol and ethanolamine

Overlapping peaks interfere in ion mobility spectrometry (IMS), but they are separated introducing mobility shift reagents (SR) in the buffer gas forming adducts with different collision cross‐sections (size). IMS separations using SR depend on the ion mobility shifts which are governed by adduct's size and interaction energies (stabilities). Mobility shifts of valinol and ethanolamine ions were measured by electrospray‐ionization ion mobility‐mass spectrometry (MS). Methyl‐chloro propionate (M) was used as SR; 2‐butanol (B) and nitrobenzene (N) were used for comparison. Density functional theory was used for calculations. B produced the smallest mobility shifts because of its small size. M and N have two strong interaction sites (oxygen atoms) and similar molecular mass, and they should produce similar shifts. For both ethanolamine and valinol ions, stabilities were larger for N adducts than those of M. With ethanolamine, M produced a 68% shift, large compared to that using N, 61%, because M has a third weak interaction site on the chlorine atom and, therefore, M has more interaction possibilities than N. This third site overrode the oxygen atoms' interaction energy that favored the adduction of ethanolamine with N over that with M. On the contrary, with valinol mobility shifts were larger with N than with M (21 vs 18%) because interaction energy favored even more adduction of valinol with N than with M; that is, the interaction energy difference between adducts of valinol with M and N was larger than that between those adducts with ethanolamine, and the third M interaction could not override this larger difference. Mobility shifts were explained based on the number of SR's interaction sites, size of ions and SR, and SR–ion interaction energies. This is the first time that the number of interaction sites is used to explain mobility shifts in SR‐assisted IMS. Copyright © 2016 John Wiley & Sons, Ltd.     

Investigation on nonisothermal crystallization kinetics of the high‐flow nylon 6 by differential scanning calorimetry

The crystallization kinetics of the high‐flow nylon 6 containing polyamidoamine (PAMAM) dendrimers units in nylon 6 matrix was investigated by differential scanning calorimetry. The Ozawa and Mo equations were used to describe the crystallization kinetics under nonisothermal condition. The values of Avrami exponent m and the cooling crystallization function F(T) were determined from the Ozawa plots, which showed bad linearity, and were divided into three sections depending on different cooling rates. The plots of the m and log F(T) values versus crystallization temperatures were obtained, which indicated that the actual crystallization mechanisms might change with the crystallization temperatures. The high‐flow nylon 6 has higher values of m and log F(T) than those of pure nylon 6, which implied that the high‐flow nylon 6 had more complicated crystallization mechanisms and slower crystallization rate than those of pure nylon 6. The good linearity of the Mo plots verified the success of this combined approach. The activation energies of the high‐flow nylon 6 ranged from 157 to 174 kJ/mol, which were determined by the Kissinger method. The ΔE values were lower than those of pure nylon 6, and the ΔE values were affected by both the generation and the content of PAMAM units in the nylon 6 matrix. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2201–2211, 2008     

Stability Constants for 1:1 Complexes Formed between2-hydroxypropyl-β-Cyclodextrin with an Average Substitution Degree of 4.4 and Benzene and Alkylbenzenes as Guests by Modified Static Head-Space Gas Chromatography Method

Modified static head-space gas chromatography method (M-SHSGC method) was used to determine the stability constants of benzene and alkylbenzenes with 2-hydroxypropyl-β-cyclodextrin inclusion complexes. The 1:1 stability constants were in agreement with those obtained by conventional SHSGC method. The M-SHSGC method precludes the necessity of the calibration curve by the use of Henry’s law constant of guest. Consequently, it is more advantageous than conventional SHSGC method because the time required to determine the stability constant is markedly reduced.     

Energetics and structure of the hydrated gaseous halide anions

Energetics and geometries for the hydrated gaseous halide anions have been computed from a simple model in which the molecular dipole of water was composed of two parts, one due to a lone pair on oxygen (60%) and the rest to formal charges on the nuclei. The calculations were made for both the symmetric and nonsymmetric structures. A variety of structures were used to compute potential energies and distances with up to six water molecules. The total energy consisted of a sum of electrostatic, polarization, dispersion, and repulsion terms. Various sets of repulsive potential parameters, ranging from those determined from molecular beam experiments to those determined using experimental ion–water distances or energies, have been employed to compute repulsive interaction energies. It was found that the range parameters play a significant role in deciding the magnitudes of the distances and energies, as the latter are most sensitive to them. It was also shown that with a simple correlation scheme the consistency of the experimental energies and distances can be tested separately without using repulsive potential parameters from other sources. It also suggests that a range of parameters can be used to compute repulsion energies. Despite the fact that the model is greatly simplified, the agreement of both the predicted ion-oxygen distances and energies with both experiment and other calculations is excellent. A detailed analysis of our calculation suggests that the negative ion clusters with one to three water molecules contain symmetric orientation of water molecules, while those with more than three may contain asymmetric orientations of water molecules or a mixture of both. From the log–log plots of hydration energies versus (R + radius of water molecule), we have proposed empirical expressions of the type ΔE_n?1,n = 10·0^x (R + 1.38)^?y with both Pauling's and Ladd's radii for univalent ions with which stepwise hydration energies of the latter can be predicted if we know thier radii. The values predicted for the alkali cations are in excellent agreement with the experimental and theoretical values, indicating the consistency of the simple model.     

Investigation of catalytic property in the t-butylation of 1,2-dihydroxybenzene using FT-IR and XPS study

Catalytic properties of HZSM-5s with three different Na⁺ ion-exchange levels and SiO₂ /Al₂O₃ ratios used in tert-butylation of DHB (1,2-dihydroxybenzene) are interpreted through pyridine adsorbed FT-IR and XPS study. The DHB conversion decreases as increment of degree of Na⁺ ion-exchange level and of Si content in HZSM-5. Catalytic properties with respect to Na amount in ZSM-5 are more sensitive than those of HZSM-5s with different SiO₂/Al₂O₃ ratios. But selectivity for 4-TBC (4-t-butylcatechol) is not changed significantly. Acidic properties, i.e. acid strength and acid density are characterized by pyridine adsorbed FT-IR and XPS study. Based on FTIR and XPS analyses, DHB conversion and selectivities for DTBC (3,5-di-t-butylcatechol) and 3-TBC (3-t-butylcatechol) depend on type and strength of acid sites, with the result that strong Brønsted acid rather than weak Brønsted or Lewis acid sites are more closely related to the conversion. Furthermore, t-butyl alcohol is selectively adsorbed on the Brønsted acid site of FT-IR band at 3612 cm^-1, which signifies that the Brønsted acid site is the active site. The mechanism for t-butylation of DHB is suggested based on the FT-IR results of adsorption/desorption of reactants.     

Polystyrene/thermoplastic starch blends with different plasticizers

Conventional plastics has a large impact in increasing the environment’s pollution. That’s why the interest has turned towards novel partially and completely biodegradable polymers. In this work, blends of polystyrene and thermoplastic starch with glycerol and Buriti (Mauritia flexuosa L.) oil as plasticizers were prepared. Samples were analyzed using TG/DTG and DSC techniques. The TG results indicated that the blends with Buriti oil are thermally more stable than those with glycerol. The DSC analysis that Buriti oil provides a higher degree of plasticization of PS, compared to the blends plasticized using glycerol under the studied conditions.