Determination of Kinetic Parameters from GPC-Data

Abstract

The molecular weight distribution and its first moments of selected polymers were experimentally determined through GPC-investigations with additional molecular weight detection. In on-line operation discontinuously functioning Ubbelohde-viscometer was used for the determination of degree of polymerization in dependence on elution volume.

The relation between the experimentally determined values and relative kinetic parameters were derived for some polymers prepared by radical mechanism. The relative constants which determines the branching structure in polymer can be now calculated.

From the investigated polymers the effect of chemical nature of monomer units for the branching formation was determined.     

A Per-O-Isoprofylidene Derivative of (1→4)-β-D-Mannan

Abstract

Isopropylidene acetals of carbohydrates are important as intermediates for the synthesis of other sugar derivatives. The isopropylidenation reaction is generally applied to only low molecular weight carbohydrates. However in 1982, we applied the reaction to a polysaccharide² and demonstrated that (1→3)-β-D-glucan was isopropylidenated at the 4- and 6-hydroxyl groups of the D-glucose units. These results suggested that some chemical modification at the unprotected 2-hydroxyl groups might be possible. Consequently, (1→3)-β-D-glucomannan^3,4 was derived from (1→3)-β-D-glucan through inversion of the 2-hydroxyl groups.     

Ab initio studies of NMR chemical shifts for calix[4]arene and its derivatives

Ab initio calculations are performed for the calix[4]arene (1) and its derivatives (2 and 3), in this study. ¹H and ¹³C NMR measured spectral data given in our previous work are used to elucidate the structures of the prepared calix[4]arenes (1–3). The molecular geometry and chemical shift are calculated by using ab initio calculations based on the Hartree-Fock (HF) and the density functional theory (DFT) in the ground state. The results obtained from both methods are in agreement with the experimental results. The results of molecular geometry and chemical shifts show that DFT approach is closer to the experimental data than HF method.     

H Nmr Spectra of Oligosaccharide Substituted Cyclodextrins

ABSTRACT

¹H NMR spectra of some oligosaccharide substituted cyclodextrins composed of only α-D-glucose units are analysed. Chemical shifts of protons of each glucosyl group of the chain were determined by experiments with the HOHAHA pulse technique. In spite of the similar kinds of protons, dispersion of chemical shifts is observed. The most dispersed proton is the anomeric proton, and the largest change in the chemical shifts is 0.5 ppm.     

The effect of acetyl on the electronic communication of carbon-bridged diferrocene

Diferrocenylmethane (1) and 2-acetyl(diferrocenyl)methane (2) were synthesized and characterized by elemental analysis, FT-IR, and NMR. The molecular structures of 1 and 2 were determined using X-ray single crystal diffraction. The effect of acetyl group on electronic communication between two ferrocenyl units of 2 was investigated through cyclic voltammetry and density functional theory calculation. The acetyl did not influence electronic communication between two ferrocenyl units. The key factor that effected electronic communication of carbon-bridged diferrocenyl derivatives was charge density of the bridged carbon.     

Corrections for Instrumental and Secondary Broadening in the Chromatographic Analysis of Linear Copolymers

Abstract

The effects of instrumental broadening and of polymer/solvent/packing interactions (secondary broadening) are separately investigated in the context of chromatography experiments, for the characterization of linear copolymers with two types of repeating units. The problems associated to the estimation of: a) the joint molecular weight distribution - chemical composition distribution (MWD-CCD) through orthogonal chromatography; and of b) the average MWD - average CCD through standard size exclusion chromatography (SEC) with dual detection are considered. The main difficulty with the secondary broadening correction, is the calibration for this effect. In the case of standard SEC with dual detection, a simple solution was found to the instrumental broadening problem, that involves a direct extension of the calibration and deconvolution techniques developed for linear homopolymers and mass detectors.     

Properties of composite solid polymer electrolyte using hyperbranched polymer with ether-linkage

The cross-linked composite solid polymer electrolytes composed of poly(ethylene oxide), lithium salt (LiN(SO₂CF₃)₂), and a hyperbranched polymer whose repeating units were connected by ether-linkage (hyperbranched polymer (HBP)-2) were prepared, and their ionic conductivity, thermal properties, electrochemical stability, mechanical property, and chemical stability were investigated in comparison with the non-cross-linked or cross-linked composite solid polymer electrolytes using hyperbranched polymers whose repeating units were connected by ester-linkage (HBP-1a, 1b). The cross-linked composite solid polymer electrolyte using HBP-2 exhibited higher ionic conductivity than the non-cross-linked and cross-linked composite solid polymer electrolytes using HBP-1a and HBP-1b, respectively. The structure of the hyperbranched polymer did not have a significant effect on the thermal properties and electrochemical stability of the composite solid polymer electrolytes. The tensile strength of the cross-linked composite solid polymer electrolyte using HBP-2 was lower than that of the cross-linked composite solid polymer electrolyte using HBP-1b, but higher than that of the non-cross-linked composite solid polymer electrolyte using HBP-1a. The HBP-2 with ether-linkage showed higher chemical stability against alkaline hydrolysis compared with HBP-1a with ester-linkage.     

13-NMR Analysis of Branched Polyethyleneimine

A commercial, branched polyethyleneimine was analyzed by ¹³C-NMR. The chemical shift assignments for the eight principal peaks were compared to the calculated chemical shifts using an additivity relationship developed for low molecular weight acyclic aliphatic amines. The change in carbon chemical shift induced by H/D exchange at nearby nitrogens was examined for this polymer and low molecular weight model compounds. The direction and magnitude of the shift are determined by the number and proximity of exchangeable NH' and are described by a simple formula. The spin lattice relaxation times for the various methylenes indicate the usual decreasing mobility for units at chain ends, internal units, and units close to branch points in that order. The integrated spectrum, under equilibrium conditions, is not consistent with the reorted amine distribution, 1°:2°:3° = 1:2:1. Our results indicate 38k l°, 36% 2°, and 26% 3°.     

Chemical bonding in ternary magnesium hydrides

The electronic structure of various alkali and alkaline–earth magnesium‐based hydrides was investigated in detail. These types of crystalline compounds show MgH₄ or MgH₆ units ordered within a light‐metal framework. We investigated the nature of the chemical bonding in these units by means of quantum chemical calculations of several related clusters. The properties of the charge density of the clusters, within the framework of the theory of atoms in molecules, was analyzed. A further set of computations of the band structure of the solid hydrides was conducted using a state‐of the‐art density functional‐based method and the mechanism of stabilization of the Mg? H units is discussed. It was found that the properties obtained at the molecular level correlate well with those of the solid crystals, indicating the molecular nature of the extended systems in which the units MgH_x, x = 4, 6, are stabilized by means of Mg? H closed‐shell interactions. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 150–164, 2003     

Spectroscopic and structural studies of 6,6′-bis(N-methylhydrazine)-2,2′-bipyridine and its mononuclear copper(II) complex

The tetradentate ligand, 6,6′-bis(N-methylhydrazine)-2,2′-bipyridine (L) and its mononuclear copper(II) complex [Cu(L)](ClO₄)₂] (1) have been synthesized and characterized. The crystal structures of L and 1 have been determined by single-crystal X-ray diffraction. Both crystallize in the centrosymmetric monoclinic space group with crystallographic inversion symmetry. The ligand adopts a planar transoid configuration in the solid state. In 1, the Cu(II) is six-coordinate octahedral, defined by N₄O₂ donors from ligand and two perchlorates. The molecular units are connected by intermolecular H-bonds between the hydrazino group of the one unit and coordinated perchlorate of the neighboring two units via N–H ··· O to furnish a 2-D network. Coordinated perchlorates also form an intramolecular H-bond with hydrazine influencing the crystal packing.     

Side chain cholesteric liquid crystalline elastomers: synthesis and phase behaviour

A series of new side chain cholesteric liquid crystalline elastomers (P-2–P-6) containing the nematic crosslinking monomer 4-(10-undecen-1-yloyloxy)benzoyl-4′-allyloxybenzoyl-p-benzenediol bisate (M-1) and the cholesteric monomer 4-cholesteryl 4-(10-undecen-1-yloyloxy)benzoate (M-2) were synthesized. The chemical structures of the monomers and elastomers obtained were confirmed by FTIR and ¹H NMR spectroscopy. Their liquid crystalline properties and phase behaviour were investigated by differential scanning calorimetry, polarizing optical microscopy and X-ray diffraction. The effect of the crosslinking units on phase behaviour is discussed. Elastomers containing less than 20?mol?% of the crosslinking units showed elasticity, reversible phase transitions and cholesteric Grandjean texture. The experimental results demonstrated that the glass transition and isotropization temperatures of P-2–P-6 increased with the increasing concentration of crosslinking unit M-1.     

A GPC Method for Analysis of Low Molecular Weight Drugs

Abstract

Gel permeation chromatography has been shown as a versatile method for the analysis of low molecular weight drugs. Aspirin and its hydrolysis product, salicylic acid, which differ in a molecular weight of 42 units have been efficiently separated by a retention time difference of 3.25 minutes. Qualitative idea of other impurities is also obtained.     

Insights into the Lattice Structure of Cellulose II From the High Resolution CP/MAS Solid State 13C NMR Spectrum of Cellotetraose

Abstract

The chemical shifts and multiplicities of the high-resolution ¹³C CP/MAS NMR spectrum of cellulose II are quite diagnostic of the lattice structure of this polymorph. Particularly important is the chemical shift of C-1 and its clear splitting into two lines of equal intensity. Similar chemical shifts and multiplicities are seen in the spectrum of cellotetraose. Thus cellotetraose is considered to be a good model for the lattice structure of the polymer. A detailed investigation of the multiplicity of the C-1 resonance of cellotetraose shows that the two peaks are of equal intensity in this case also. Because of the limited number of repeat units in the tetramer, this observation implies that the unit cell contains two independent chains rather than a “double” repeat unit. This gives support for a similar lattice structure, with two independent chains, for cellulose II itself.     

New thermally stable condensation polymers containing central ketal moieties derived from malonaldehydetetramethyl acetal and dihydroxyaromatic compounds

Abstract

A number of new condensation polymers with acetal units in the main chain and having linear and ladder-form structure and high thermal stability were synthesized by solution polycondensation of dihydroxyaromatic compounds with malonaldehydetetramethyl acetal as a reactive protected 1,3-dicarbonyl compound. Optimal conditions for polycondensation were obtained via study of the model compounds. In order to obtain high molecular weight polymers, general investigations on the influence of reaction conditions, such as monomer concentration and reaction temperature were carried out. All polymers were obtained in high yields and moderate inherent viscosity ranging from 0.25 to 0.41?dL/g. The proposed chemical structures of condensation polymers were confirmed by ¹H-NMR, ¹³C-NMR, FTIR spectroscopies, TGA, and DSC. Thermal analysis indicated that these polymers are stable up to 360?°C, and a 10% weight loss (T₁₀) were recorded on the TG curves in the temperature range of 381–411?°C in nitrogen atmosphere, indicating their good thermal stability.     

Strategies for protein-based nanofabrication: Ni-NTA as a chemical mask to control biologically imposed symmetry

Background: Technologies that improve control of protein orientation on surfaces or in solution, through designed molecular recognition, will expand the range of proteins that are useful for biosensors, molecular devices and biomaterials. A limitation of some proteins is their biologically imposed symmetry, which results in indistinguishable recognition surfaces. Here, we have explored methods for modifying the symmetry of an oligomeric protein that exhibits useful self-assembly properties.Results:Escherichia coli glutamine synthetase (GS) contains 24 solvent-exposed histidines on two symmetry-related surfaces. These histidines drive a metal-dependent self-assembly of GS tubes. Immobilization of GS on the affinity resin Ni²⁺-NTA followed by on-column modification with diethyl pyrocarbonate affords asymmetrically modified GS that self-assembles only to the extent of ‘short’ dimeric GS tubes, as demonstrated by electron microscopy, dynamic light scattering and atomic force microscopy. The utility of Ni²⁺-NTA as a chemical mask was also demonstrated for asymmetric modification of engineered cysteines adjacent to the natural histidines.Conclusions: Current genetic methods do not provide distinguishable recognition elements on symmetry-related surfaces of biologically assembled proteins. Ni²⁺-NTA serves as a mask to control chemical modification in vitro of residues within symmetry-related pairs, on proteins containing functional Histags. This strategy may be extended to modification of a wide range of amino acids with a myriad of reagents.     

Syntheses,crystal structures,and properties of two molecular double-supporting polyoxotungstates

Two molecular double-supporting polyoxotungstates [SiW₁₂O₄₀{M(phen)₂H₂O}₂] · nH₂O (phen = 1,10′-phenanthroline, M = Mn 1, n = 2; M = Co 2, n = 3) were synthesized hydrothermally and characterized by elemental analyses, IR, TG, and X-ray single-crystal diffraction. The variable-temperature magnetic susceptibilities were measured at 2–300 K. The double-supporting polyoxotungstate molecule consists of a Keggin-type dodecatungstosilicate anion and a pair of transition metal complex fragments which are covalently linked to opposite sides of the Keggin anion. The transition metal ion locates in the center of a distorted octahedron. Multiple H-bonding interactions are observed between the coordinated waters of the transition metal complex fragments and terminal oxygen atoms of Keggin units and also between the bridging oxygen atoms of Keggin units and the lattice waters, which creates one-dimensional chains or two-dimensional layers. Between the layers or chains there are weak CH···O hydrogen bonding interactions and van der Waals forces. The molecular double-supporting polyoxotungstosilicate begins to decompose at ca. 500 °C. The variable-temperature magnetic behavior of 1 shows weak antiferromagnetic characteristics with a small value of θ = −0.289 K.     

Synthesis and NMR Characterization of Multi‐hydroxyl End‐groups PEG and PLGA‐PEG Barbell‐like Copolymers

Multi‐hydroxyl end‐groups poly(ethylene glycol) (PEG) was prepared from PEG and epichlorohydrin. Then, PEG‐supported poly(lactic‐ran‐glycolic acid) (PLGA)_n‐PEG‐(PLGA)_n (n=1, 2, 4) linear‐dendritic barbell‐like copolymers were synthesized through direct polycondensation under bulk condition from the multi‐hydroxyl end‐groups PEG, lactic acid and glycolic acid. Arm numbers were varied, with 2, 4 and 8, by using bis‐, tetra‐, and octa‐hydroxyl end‐groups PEG, respectively. The chemical structures, absolute number‐average molecular weight, the monomer units per single arm and the molar ratio of hydroxyl acid monomer units of the (PLGA)_n‐PEG‐(PLGA)_n barbell‐like copolymers were analyzed by NMR spectroscopy. The result indicated that the structures of the multi‐hydroxyl end‐groups PEG and (PLGA)_n‐PEG‐(PLGA)_n barbell‐like copolymers were consistent with design. Compared with the theoretical values, molecular weights determined by ¹H‐NMR end‐group analysis gave reasonably consistent values, but the values determined by gel permeation chromatography (GPC) were considerably less than theoretical values. The results indicated that (PLGA)_n‐PEG‐(PLGA)_n copolymers have linear‐dendritic structures.     

The novel rufigallol-based liquid crystals with cholesterol units: synthesis,mesomorphic and photophysical properties

Three novel rufigallol derivatives with four alkyl chains and two cholesteric units 6a, 6b and 6c were prepared in yields of 83–88%. The mesomorphic properties were investigated by DSC, POM and XRD analysis, suggesting that compounds 6a, 6b and 6c possess the ordered hexagonal columnar mesophase. The long alkyl chains contribute to the low phase transition temperature. Sample 6c with four dodecyl chains and two cholesterol units is a room temperature liquid crystal between 31°C and 87°C. Compounds 6a, 6b and 6c also have good fluorescence emission between 400 nm and 500 nm. The studies on CD spectra implied that the chiralities of cholesterol moieties are successfully transferred to the liquid crystalline core. Samples 6a, 6b and 6c are the first fluorescence liquid crystal based on rufigallol core with chiral cholesterol units.