Infrared spectra and molecular structure: Part II. N-methyl- and N,N-dimethylaminobenzoic acids

Infrared spectra of N-methyl- and N,N-dimethylaminobenzoic acids have been investigated. All the acids except N,N-dimethylanthranilic acid showed neutral structures in the solid state. The N,N-dimethylanthranilic acid, however, exhibited a dipolar structure with strong intramolecular hydrogen bonding in the solid state while in solution it is neutral.     

The orthosomycin family of antibiotics—I : The constitution of flambamycin

The antibiotic, flambamycin, is shown to have the novel oligosaccharide structure (1) associated with two orthoester linkages. It is proposed that flambamycin (1), the everninomicins (28), curamycin, avilamycin, destomycin A (29a), destomycin C (29b), destomycin B (30), hygromycin B (29c), the antibiotics A-396-I (29d) and SS-56C (29e), belong to a new family of antibiotics called the orthosomycins.     

Thermal and rheological behaviour of some random aromatic polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological behaviour of seven random Cl-ended aromatic PES/PEES copolymers (M_n ≈ 9500 g mol⁻¹), at various PES/PEES repeating unit ratios, was studied. The glass transition temperatures (T_g), determined by DSC experiments, showed a dependence on copolymer composition significantly different from the ideal linear behaviour expected on the basis of Fox equation. Degradations were carried out in the scanning mode, under flowing nitrogen, in the temperature range 35-650 °C and a single degradation stage was observed for all copolymers. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosity (η^∗) of molten copolymers was determined in experimental conditions of linear viscoelasticity. T_i, T_1/2, E_a, and η^∗ values were depending on copolymer composition, showing a trend similar to that of T_g values. The results obtained were discussed and interpreted.     

Characterization of some commercial poly (styrene-divinylbenzene) copolymers for reversed-phase HPLC1

Summary The properties of the poly(styrene-divinylbenzene) copolymers PRP-1 and PLRP-S have been studied by infrared spectroscopy and chromatographic techniques. The following results were obtained: PRP-1 and PLRP-S are spectroscopically very similar. Their surfaces are chemically neither homogeneous nor stable during use. Retained nonpolar solutes should be eluted with a mobile phase containing tetrahydrofuran. Uncharged acids and anions can be chromatographed without difficulty. Cations of amines should be chromatographed only with a mobile phase of low pH. Uncharged amino-alcohols cannot be chromatographed without the addition of a competitor. Presented at the 16th International Symposium on Chromatography, Paris, France, September 1986     

Thermal and rheological behaviours of some random aromatic amino-ended polyethersulfone/polyetherethersulfone copolymers

The thermal and rheological characterizations of seven random, low molecular weight (M_n ≅ 9500 g mol⁻¹), H₂N-ended polyethersulfone/polyetherethersulfone (PES/PEES) copolymers, at various PES/PEES ratios, were performed. The glass transition temperatures (T_g) were determined by DSC. Degradations were carried out in a thermobalance, under flowing nitrogen, in dynamic heating conditions from 35 °C to 650 °C. The initial decomposition temperatures (T_i) and the half decomposition temperatures (T_1/2) were directly determined by TG curves, while the apparent activation energies of degradation (E_a) were obtained by the Kissinger method. In addition, the complex viscosities (η^∗) of the molten polymers were determined in experimental conditions of linear viscoelasticity. T_g, E_a and η^∗ values increased linearly with PES% content, while T_i and T_1/2 values showed opposite behaviour. In every case both PES and PEES homopolymers felt outside linearity. The results obtained are discussed and interpreted, and compared with those of corresponding Cl-ended copolymers previously studied.     

Structure and properties of blends containing ethylene-methacrylate copolymers

The preparation, melting point, degree of crystallinity, mechanical properties, and morphology of a family of blends composed of a transition-metal-neutralized carboxylate semicrystalline ionomer (metal-neutralized ethylene-methacrylate copolymer) and an amorphous copolymer (styrene-4-vinyl pyridine copolymer) are described. These polymeric materials contain low levels (≤ 10.0 mol %) of interacting groups which are capable of forming interpolymeric complexes. These interactions are best described as transition metal-pyridine coordination complexes. A general characteristic of these blend systems is that the mechanical properties and morphology are directly influenced by the nature of the counterion and the specific composition ratio of amorphous to semicrystalline component. A nontransition metal counterion (sodium) is weakly interacting at best, while a transition metal counterion (zinc) is strongly interacting. Morphological studies (polarized-light microscopy and small-angle light-scattering measurements) confirm that the glassy component, if nonassociating, resides primarily in the interspherulite region, while the associating species will behave in a similar manner only after the stoichiometric ratio is reached. The morphology directly influences the stress-strain behavior of these blends. It is noteworthy that the spherulite size remains unchanged with nonassociating blends while a 50% reduction is noted in the associating blends. Thermal and wide-angle x-ray scattering measurements confirm the lamellar structure is unaffected by these associations. © 1992 John Wiley & Sons, Inc.     

Vibrational study in the low frequency region (700—100 cm−1) of phosphine monosubstituted group VI B metal carbonyls

IR, FIR and Raman data in the low-frequency region (700-100 cm^?1) are presented for a number of Cr, Mo and W carbonyls of the type R₃PM(CO)₅, with the ligands (CH₃)₃P, (C₂H₅)₃P, (C₆H₅)₃P and (X—C₆H₄)₃P (X = F, Cl, CH₃), and for three further chromium carbonyls LCr(CO)₅, with the ligands PCl₃, C₆H₅PCl₂ and (C₆H₅)₂PCl. The observed δ(MCO) modes are assigned together with all ν(MC) and ν(MP) fundamentals. The behavior of these modes is discussed in relation to the different ligands and in comparison with known ν(CO) data. The dependence of ν(MP) on σ and π properties of the ligands is investigated.     

Trends in the CNDO/2 molecular orbital study of electronic structure in some neurotransmitter drugs

An investigation of electronic structure in some neurotransmitter drugs has been made using the CNDO/2 semi-empirical molecular orbital method.The electronic structure has been conveniently characterized by the electronic parameters nett atomic population (NAP) and bond index (BI). A variation of these electronic parameters with respect to conformation has been studied and has been found unlikely to exceed 0.1 e in most. cases. Further, the useful extent to which the electronic parameters of some commonly occurring functional groups may be regarded as conformationally invariant has been demonstrated. Also presented are (i) a discussion on the intramolecular close-approach of functional groups — the interaction between terminal —COO^? and ?NH₃⁺ groups of α-ω anaino acids is explicitly considered; (ii) an enquiry into the extension of ‘standard’ (idealized) geometry models in the elucidation of electronic structure.The implication of the results and observations presented here are briefly discussed with reference to classical and quantum structure-activity studies of drug molecules.     

Comprehensive thermal analysis of random copolymers of ethylene and 1-olefins

Random copolymers of ethylene and propylene, butene-1 and hexene-1 were characterised by measurements of heat capacity in the temperature interval 140–480 K and specific volume of the melt in the temperature interval 330–490 K and in the range of pressures 27.8–100 MPa. Analysis of the composition dependences, of the degree of crystallinity, melting and glass transition temperatures, as well as of thermodynamic and thermophysical properties of the melt led to the conclusion about the microblock structure of macromolecules of all series at molar ethylene contentF ₁ > 0.8. In this range of compositions the properties of copolymers in the melt seem to be independent of the chemical nature of a comonomer, contrary to the solid state where at identical molar compositions, the degree of crystallinity diminishes and the melting temperature decreases, as the molecular structure of the comonomer becomes more complex. This effect becomes weaker asF ₁ decreases, so that in the composition rangeF ₁ < 0.8 the properties of copolymers of all series are additive.

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Zusammenfassung Durch Messungen der Wärmekapazität im Temperaturintervall 140–480 K und des spezifischen Volumens im Temperaturintervall 330–490 K und im Druckbereich 27.8–100 MPa wurden Random-Kopolymere von Ethylen und Propylen, Buten-1 und Hexen-1 charakterisiert. Die Analyse der Abhängigkeit des Kristallinitätsgrades, der Schmelz- und Glasumwandlungspunkte sowie der thermodynamischen und thermophysikalischen Eigenschaften der Schmelzen führte zu einem Schluß über die Mikroblock-Struktur von Makromolekülen aller Serien bei einem molaren Ethylengehalt vonF ₁>0.8. In diesem Zusammensetzungsintervall scheinen die Eigenschaften des Kopolymers unabhängig von der chemischen Natur des Komonomers zu sein, im Gegensatz zum festen Zustand, wo bei einer ähnlichen molaren Zusammensetzung sich der Kristallinitätsgrad verringert und die Schmelztemperatur sinkt, wenn die Molekülstruktur des Komonomers komplexer wird. Dieser Effekt wird kleiner, wennF ₁ abnimmt, so daß im Zusammensetzungsbereich mitF ₁<0.8 die Eigenschaften der Kopolymere aller Serien additiv sind.

     

Dynamic mechanical and gas transport properties of blends and random copolymers of bisphenol-A polycarbonate and tetramethyl bisphenol-A polycarbonate

Dynamic mechanical and gas transport properties for homogeneous homopolymer blends and random copolymers of bisphenol-A and tetramethyl bisphenol-A polycarbonates (PC-TMPC) were determined. The gas transport measurements were performed at 35°C for the gases He, H₂, O₂, Ar, N₂, CH₄, and CO₂. The results show that the copolymers have lower permeability, apparent diffusion, and solubility coefficients than the blends. Permeability coefficients for blends follow a semilogarithmic ideal mixing rule while copolymers exhibit negative deviations from this. Specific volume measurements show that the free volume available for gas transport is slightly larger in copolymers than in blends of the same composition. These apparently contradictory results may relate to the differences in local mode chain motions observed for the copolymer and blend series. The γ relaxation processes in PC and TMPC seem to operate independently in the blends (no intermolecular coupling) while there is clear evidence for intramolecular coupling in the copolymers. © 1992 John Wiley & Sons, Inc.     

One-dimensional and two-dimensional nanomaterials for the detection of multiple biomolecules

The complexity of biological samples determines that the detection of a single biomolecule is unable to satisfy actual needs. Moreover, the “false positives” results caused by a single biomolecule detections easily leads to erroneous clinical diagnosis and treatment. Thus, it is important for the homogenous quantification of multiple biomolecules in not only basic research but also practical application. As a consequent, a large number of literatures have been exploited to monitor multiple biomolecules in homogenous solution, enabling facilitating the development of the disease diagnosis, treatment as well as drug discovery. One-dimensional nanomaterials and two-dimensional nanomaterials have special physical and chemical properties, such as good electrochemical properties, stable structure, large specific surface area, and biocompatibility, which are widely used in electrochemical and fluorescent detection of biomolecules. This tutorial review highlights the recent development for the detection of multiple biomolecules by using nanomaterials including one-dimensional materials (1DMs) as well as two-dimensional materials (2DMs).     

Ab initio Study on Structures and Isomerization of Magnesium Fluorosilylenoid H2SiFMgF

The structures and isomerization of magnesium fluorosilylenoid H2SiFMgF were investigated by ab initio molecular orbital theory. Four equilibrium structures and three isomeric transition states were located and fully optimized at the B3LYP/6-31G(d,p) and G3MP2B3 levels, respectively. Based on the B3LYP/6-31G(d,p) optimized geometries, harmonic frequencies of various structures were obtained and 29Si chemical shifts were calculated. The solvent effects were investigated by means of the polarizable continuum model using THF as a solvent at B3LYP/6-31G(d,p) level. Isomerization paths for isomers were confirmed by intrinsic reaction coordinate calculations. The calculated results show that tetrahedral structure has the lowest energy and is the most stable; tetrahedral, three-membered ring, and p-complex structures are suggested to be the experimentally detectable ones; and σ-complex structure has the highest energy and will not exist.     

Thermal property changes of poly(N-isopropylacrylamide) microgel particles and block copolymers

Investigation of the thermo-reversible properties of different poly(N-isopropyl acrylamide) samples, including microgels and block copolymers, with a combination of methods such as electron microscopy, dynamic light scattering, analytical ultracentrifugation, electrophoresis and ultrasound resonator technology allows comprehensive characterisation of the phase transition. By the combination of methods, it was possible to show that the precipitated polymer phase contains at 40 °C between 40 and 50 vol.% of water. Besides free bulk water, there is also bound water that strongly adheres to the N-isopropyl acrylamide units (about 25 vol.%). Ultrasound resonator technology, which is a non-sizing characterisation method, revealed for the microgel particles two more temperatures (at about 35 and between 40 °C and 50 °C depending on the chemical nature) where characteristic changes in the ultrasound attenuation take place. Moreover, the experimental data suggest that the phase transition temperature is related to surface charge density of the precipitated particles.     

Enthalpies and entropies of fusion of some substituted dipeptides

Enthalpies and temperatures of fusion or transition for four substituted dipeptides (Nacetylamides of glycyl-L-alanine (NAGAA),L-alanyl-L-alanine (NAA₂A),L-prolyl-glycine (NAPGA) andL-leucyl-L-proline monohydrate (NALPA·H₂O)) were determined by differential scanning calorimetry and the entropies of fusion derived. The results obtained have been compared with those of the corresponding substituted aminoacids and some of their racemic crystalline mixtures. The enthalpies and entropies of fusion of some substituted aminoacids have been redetermined. The results are discussed in comparison with crystal structural data, which has been reported in the literature or determined recently by some of the authors. Rationalization of the fusion parameters was attempted mainly on the basis of the number of intramolecular hydrogen bonds and the packing densities in the crystals.This work was carried out with the financial support from the Italian C.N.R. (Rome) and from the Ministry of University and Scientific and Technological Research.     

Structure and properties of sequentially polymerized propylene-b-[ethylene-co-propylene]-b-propylene copolymers

The structure and properties of presumed block copolymers of polypropylene (PP) with ethylene-propylene random copolymers (EPR), i.e., PP-EPR and PP-EPR-PP, have been investigated by viscometry, transmission electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, gel permeation chromatography, wide-angle x-ray diffraction, and other techniques testing various mechanical properties. PP-EPR and PP-EPR-PP were synthesized using δ-TiCl₃-Et₂-AlCl as a catalyst system. The results indicate that the intrinisic viscosity of these polymers increases with each block-building step, whereas the intrinsic viscosity of those prepared by chain transfer reaction (strong chain-transfer reagent hydrogen was introduced between block-building steps during polymerization) hardly changes with the reaction time. Compared with PP/EPR blends, PP-EPR-PP block copolymers have lower PP and polyethylene crystallinity, and lower melting and crystallization temperatures of crystalline EPR. Two relaxation peaks of PP and EPR appear in the dynamic spectra of blends. They merge into a very broad relaxation peak with block sequence products of the same composition, indicating good compatibility between PP and EPR in the presence of block copolymers. Varying the PP and EPR content affects the crystallinity, density, and morphological structure of the products, which in turn affects the tensile strength and elongation at break. Because of their superior mechanical properties, sequential polymerization products containing PP-EPR and PP-EPR-PP block copolymers may have potential as compatibilizing agents for isotactic polypropylene and polyethylene blends or as potential heat-resistant thermoplastic elastomers.     

Normal coordinates and potential energy distributions of methyl acetylene and some halogen substituted analogues

The normal coordinates and potential energy distributions of methyl acetylene, methyl-d₃ acetylene and some halogen substituted analogues (CH₃CCX; X = H, D, Cl, Br, I) have been calculated using previously determined force fields. For methyl chloro-acetylene, the chlorine-35,37 isotope frequency splitting has been calculated. In addition, for methyl acetylene, the harmonic frequencies were obtained and plotted for hypothetical molecules in which the mass of X varied from 1 to 1000 a.m.u. The frequencies for these molecules are compared and discussed.     

Calculation of molecular polarizabilities: the indo method applied to some aromatic hydrocarbons1

Molecular polarizabilities calculated by the all valence electron INDO method are reported for benzene, naphthalene, anthracene, phenanthrene, biphenyl and p-terphenyl. For these molecules INDO is better than other semi-empirical methods at predicting the polarizability anisotropy.