Addition Of Side Chains Research Articles

Conjugate addition of amino acid side chains to dyes containing alkynone, alkynoic ester and alkynoic amide linker arms

Derivatives of fluorescein, 7-hydroxycoumarin, Sudan 1 and dansyl chloride with linker arms containing a conjugated terminal alkyne have been prepared. The Michael addition of the sulfanyl group of protected cysteine, the hydroxyl group of protected serine and the ϵ-amino group of protected lysine to the conjugated alkyne gave the expected heterosubstituted vinyl products.

Low‐Melting, Liquid‐Crystalline Metalloporphyrins

The type of mesophase can be controlled by the addition of side chains to porphyrins bearing several long terminal chains (see, for instance, 1). Either columnar phases or those characteristic of rodlike molecules are formed, whose transition temperatures are lower than those found in the parent systems.

Effects of Acylation and Crosslinking on the Material Properties and Cadmium Ion Adsorption Capacity of Porous Chitosan Beads

Abstract Chitosan is a novel glucosamine biopolymer derived from the shells of marine organisms. This biopolymer is very attractive for heavy metal ion separations from wastewater because it is selective for toxic transition metal ions over less toxic alkali or alkane earth metal ions. Highly porous, 3-mm chitosan beads were prepared by an aqueous phase-inversion technique for casting gel beads followed by freeze drying. In the attempt to simultaneously improve material properties and adsorption capacity, chitosan was chemically modified by 1) homogeneous acylation of amine groups with nonanoyl chloride before bead casting, and 2) heterogeneous crosslinking of linear chitosan chains with the bifunctional reagent glutaric dialdehyde (GA) after bead casting but before freeze drying. The random addition of C8 hydrocarbon side chains to about 7% of the amine groups on uncrosslinked chitosan beads via N-acylation improved the saturation adsorption capacity from 169 to 216 mg Cd2+/g-bead at saturation (pH 6.5, ...

Microstructure and water transport in spin cast films of poly(hexylmethacrylate azobenzene-sulfone)

Spin cast films of poly(hexylmethacrylate azobenzene-sulfone) (PHMA-AS) with a thickness of 7.5 μm were studied at 25 °C by Fourier transform infrared attenuated total reflectance spectroscopy before and after annealing at 140 °C, and before and after contact with water vapor or liquid. Spectral analysis of the hydrocarbon and water bands was used to probe the changes in the film microstructure after these treatments. Slight orientation changes were detected in the hydrocarbon region after hydration. No changes were observed, however, in the dichroic ratios of the carbonyl and the chromophore groups of the PHMA-AS films. These groups had average tilt angles of 62 ° and 69 °, respectively, from the surface normal. The addition of side chains consisting of a spacer and a chromophore group to the backbone of PMMA makes the film a better barrier material for water, as it absorbs less water vapor and less liquid water. The density of the sorbed water at 89% relative humidity was estimated to be 0.006 g per cm3 of polymer. Initially water permeated fast, as non-bulk-like water, through film defects before diffusing more slowly, as bulk-like water, throughout the film. The estimated total density of liquid water absorbed by the film was 0.05 g per cm3 of polymer. The in-situ transport data suggest transport mechanisms more complex than the one-dimensional Fickian diffusion, evidently due to the complex microporous structure of the films.

Human neutrophil gelatinase: a marker for circulating blood neutrophils. Purification and quantitation by enzyme linked immunosorbent assay.

Human neutrophil gelatinase was purified to apparent homogeneity. The N-terminal amino-acid sequence of the purified enzyme could be aligned to an internal part of the cDNA-derived amino-acid sequence of 92-kDa type IV collagenase from SV 40-transfected human lung fibroblasts and from a TPA differentiated monocytic cell line, U937. Total amino-acid composition of U937 and neutrophil gelatinases was identical. Gelatinase was susceptible to treatment with o- and n-glycanase, indicating that posttranslational addition of oligosaccharide side chains occurs. An enzyme-linked immunosorbent assay for gelatinase was developed using specific polyclonal rabbit antibodies. The assay was specific, sensitive, accurate, and reproducible. Ninety percent range for plasma gelatinase from normal subjects was 17.3 to 102.9 ng/ml. In patients treated with cytostatic agents for non-Hodgkin's lymphoma, there was a parallel drop in plasma gelatinase and peripheral granulocyte count. This indicates that plasma gelatinase is a marker for circulating neutrophils. Plasma gelatinase does not seem to reflect bone marrow cellularity.

Complexation of 6-ACYL-O-β-Cyclodextrin derivatives with steroids - effects of chain length and substitution degree

This study was designed to test a hypothesis that the esterification of the primary 6-hydroxyl groups on β-cyclodextrin (β-CD) may disrupt its crystallinity, thereby enhancing its aqueous solubility and increasing its ability to solubilize water-insoluble compounds. 6-acyl-o-β-CD derivatives with different chain length and substitution degree were synthesized by esterifying the primary hydroxyl groups at 6-position of β-CD with various acyl chlorides. X-ray diffraction patterns confirmed the existence of 6-acyl-o-β-CD derivatives as amorphous solid. Effects of chain length and substitution degree of the acyl groups on 6-acyl-o-β-CD/steroid complexation and solubilization were investigated with the phase solubility method. The results indicated that the solubilities of 6-acyl-o-β-CD derivatives were significantly higher than that of β-CD itself, which resulted in an increase in their ability to solubilize poorly water-soluble drugs such as steroids. The addition of side chains to β-CD did not change the stoichiometric ratio (2:1) of β-CD/steroid complexes. The increase in chain length can enhance the association of 6-acyl-o-β-CDs with steroids as it was evidenced from the apparent stability constants. A solubility study utilizing different combinations of 6-acyl-o-β-CDs, α-CD and 2,6- dimethyl-o-β-CD suggested a competitive complexation process among the family of acyl-β-CD derivatives. A non-competitive steroid complexation between 6-acyl-o-β-CDs and α-CD and between 6-acyl-o-β-CDs and 2,6-dimethyl-o-β-CD was observed.

Uncoupling of chondroitin sulfate glycosaminoglycan synthesis by brefeldin A.

Brefeldin A has dramatic, well-documented, effects on the structural and functional organization of the Golgi complex. We have examined the effects of brefeldin A (BFA) on the Golgi-localized synthesis and addition of chondroitin sulfate glycosaminoglycan carbohydrate side chains. BFA caused a dose-dependent inhibition of chondroitin sulfate glycosaminoglycan elongation and sulfation onto the core proteins of the melanoma-associated proteoglycan and the major histocompatibility complex class II-associated invariant chain. In the presence of BFA, the melanoma proteoglycan core protein was retained in the ER but still acquired complex, sialylated, N-linked oligosaccharides, as measured by digestion with endoglycosidase H and neuraminidase. The initiation of glycosaminoglycan synthesis was not affected by BFA, as shown by the incorporation of [6-3H]galactose into a protein-carbohydrate linkage region that was sensitive to beta-elimination. The ability of cells to use an exogenous acceptor, p-nitrophenyl-beta-D-xyloside, to elongate and sulfate core protein-free glycosaminoglycans, was completely inhibited by BFA. The effects of BFA were completely reversible in the absence of new protein synthesis. These experiments indicate that BFA effectively uncouples chondroitin sulfate glycosaminoglycan synthesis by segregating initiation reactions from elongation and sulfation events. Our findings support the proposal that glycosaminoglycan elongation and sulfation reactions are associated with the trans-Golgi network, a BFA-resistant, Golgi subcompartment.

Temporal expression of HIV-1 envelope proteins in baculovirus-infected insect cells: Implications for glycosylation and CD4 binding

Three different human immunodeficiency virus type I (HIV-1) envelope derived recombinant proteins and the full length human CD4 polypeptide were expressed in Spodoptera frugiperda (Sf9) cells. DNA constructs encoding CD4, gp120, gp160, and gp160Δ (full length gp160 minus the transmembrane and cytoplasmic region of gp41) were cloned into the baculovirus expression vector pVL941 or a derivative and used to generate recombinant viruses in a contransfection with DNA from Autographa californica nuclear polyhedrosis virus (AcMNPV). Western blotting of cell extracts of the recombinant HIV-1 proteins showed that for each construct two major bands specifically reacted with anti-HIV-1 envelope antiserum. These bands corresponded to glycoslated and nonglycosylated versions of the HIV proteins as determined by 3H-mannose labeling and tunicamycin treatment of infected cells. A time course of HIV envelope expression revealed that at early times post-infection (24 hours) the proteins were fully glycosylated and soluble in nonionic detergents. However, at later times postinfection (48 hours), expression levels of recombinant protein reached a maximum but most of the increase was due to a rise in the level of the nonglycosylated species, which was largely insoluble in nonionic detergents. Thus, it appears that Sf9 cells cannot process large amounts of glycosylated recombinant proteins efficiently. As a measure of biological activity, the CD4 binding ability of both glycosylated and nonglycosylated recombinant HIV envelope proteins was tested in a coimmunoprecipitation assay. The results showed that CD4 and the glycosylated versions of recombinant gp120 or gp160Δ specifically associated with one another in this analysis. Nonglycosylated gp120 or gp160Δ proteins from tunicamycin-treated cultures did immunoprecipitate with anti-HIV-1 antiserum but did not interact with CD4. We conclude that production of native HIV envelope proteins, as measured by addition of carbohydrate side chains and ability to bind CD4, peaks early after infection in baculovirus-infected insect cells.

Addition of carbohydrate side chains at novel sites on influenza virus hemagglutinin can modulate the folding, transport, and activity of the molecule.

We have constructed and expressed a series of mutant influenza virus hemagglutinins, each containing a new consensus site for glycosylation in addition to the seven sites found on the wild-type protein. Oligosaccharide side chains were added with high efficiency at four of the five novel sites, located on areas of the protein's surface that are not normally shielded by carbohydrate. Investigations of the structure, intracellular transport, and biological activities of the mutant hemagglutinin molecules indicated that (a) supernumerary carbohydrate side chains can be used to shield or disrupt functional epitopes on the surface of hemagglutinin, and (b) the presence of an additional oligosaccharide may cause temperature-dependent defects in the transport of the glycoprotein. We discuss the addition of supernumerary oligosaccharides as a general tool for shielding chosen areas of the surface of proteins that enter or traverse the secretory pathway.

Characterization of a supported liquid membrane for macrocycle-mediated selective cation transport

Macrocycle-mediated cation transport has been studied using aqueous phases separated by a liquid membrane supported on a microporous polypropylene film. A macrocycle-containing organic phase was incorporated into the pores of the film. In this system, phenylhexane was found to be superior to chloroform, toluene and 1,2-dichlorobenzene as a membrane solvent in maintaining membrane integrity due to its lower water solubility and higher boiling point. Transport experiments using a bis (1-hydroxyheptyl) derivative of dicyclohexano-18-crown-6 (DC18C6) as carrier gave the selectivity sequecnes K + > Rb + > Cs + >Na + > Li + and Sr 2+ > Ba 2+ > Ca 2+. Furthermore, the addition of t-butyl or hydroxyheptyl side-chains to DC18C6 improved cation transport over that observed with DC18C6 due to the decreased distribution of the ligand from the membrane to the adjacent water phases. Cation flux was found to be independent of the rate of stirring of the water phases and to be a direct function of carrier concentration in the membrane.

Effect of Oil Composition on Minimum Miscibility Pressure—Part 1: Solubility of Hydrocarbons in Dense CO2

Summary This paper examines the effect of oil composition on the phase behavior of CO2/hydrocarbon mixtures and, hence, on the development of miscibility in a CO2 flood. Results of component-partitioning measurements are reported for mixtures of CO2 with five synthetic oil systems: normal alkanes, branched alkanes, naphthenes, aromatics, and a mixture of all four molecular types. The results of the experiments indicate that unsubstituted ring structures are less soluble in dense CO2 than branched or normal alkanes with the same number of carbon atoms, but that the addition of alkyl side chains to ring structures improves their solubility. Also reported are component-partitioning measurements for mixtures of CO2 with three crude oils: Rock Creek (paraffinic), Maljamar (more aromatic), and Rock Creek plus 15 wt% of a mixture of aromatic components. The experimental results suggest that of the many factors that influence extraction of hydrocarbons by dense CO2, the distribution of molecular weights present in the oil is the most important.

Biosynthesis and processing of a variant surface glycoprotein from Trypanosoma brucei brucei

Iowa trypanosome antigen type (IaTat) 1.2 variant surface glycoprotein (VSG) is synthesized in vitro as a M r 54,000 preprotein that contains a 31-amino-acid signal peptide. Translation of mRNA in the presence of either dog pancreas or trypanosome microsomal membranes results in cotranslational cleavage of the signal peptide and addition of core oligosaccharide side chains to the protein. Analysis of these products on sodium dodecyl sulfate (SDS)-gels indicates that removal of the signal peptide ( M r 3200) is almost exactly compensated for by an increase in molecular weight due to carbohydrate addition. Pulse-chase experiments in cultures of isolated trypanosomes indicate that two IaTat 1.2 VSG species ( M r 58,000 and 60,000) occur in vivo. When glycosylation is inhibited by incubation of trypanosomes with tunicamycin, a single M r 50,000 polypeptide is immunoprecipitated. The multiple protein species, therefore, arise from heterogeneity in carbohydrate side chains whose synthesis and transfer to the protein are tunicamycin sensitive. Sequence analysis verified that both species of VSG contain identical amino-terminal sequences. Further post-translational processing of IaTat 1.2 VSG includes addition of phosphate and myristic acid residues, both of which have been shown to be located in the immunologically cross-reactive determinant at the carboxyl terminus of the protein. Exposure of this attachment site requires posttranslational proteolytic removal of a 17-amino-acid peptide from the carboxyl terminus of an intermediate form of VSG.

7] Nylon-encapsulated pharmaceuticals

This chapter discusses the properties of Nylon Microcapsules. Nylon 610, the most popular and perhaps the most extensively studied polyamide, is prepared by the interfacial polymerization reaction between 1,6-hexamethylenediamine (HMD) and sebacoyl chloride (SC). An attractive feature of the nylon polyamides is that slight monomer structural changes such as carbon chain length, addition of side chains, or cross-linking agents may alter the properties of the microcapsule wall. The wide range of drug diffusion rates from nylon microcapsules is reported as a function of the drug itself, the core material, and the properties of the nylon membrane. By encapsulating drugs in various matrix materials, drug release may be carefully controlled from the dense, free-flowing microcapsules. In addition to controlled-release, these microparticulates offer several other pharmaceutical advantages, including taste masking, separation of incompatible drugs, and improved drug stability. For nylon microcapsules to be useful as an oral delivery system, the stability of the membrane in gastrointestinal fluids must be characterized.

Arabinoglucuronoxylans of the stems ofFagopyrum sagittatum andPolygonum wegrichii

The primary structures of the arabinoglucuronoxylans of the stems of common buckwheat andPolygonum weyrichii have been established. It has been shown that the polysaccharides differ by their degrees of branching and also by the nature of the addition of certain side chains.

Synthesis of a nitrobenzeneboronic acid substituted polyacrylamide and its use in purifying isoaccepting transfer ribonucleic acids.

Highly purified isoaccepting species of transfer ribonucleic acid (tRNA) were prepared by use of a polyacrylamide substituted with nitrobenzeneboronic acid functional groups. This method exploits the well-known ability of boronic acids to complex with RNA cis-diols. tRNA isoacceptors were obtained by enzymatically acylating a mixture of tRNA species with a single amino acid and passing the mixture over a solid-state nitrobenzeneboronic acid at pH 6.5 or 7.0. Pure aminoacyl-tRNA eluted at the column liquid volume, and unacylated tRNA species were bound. The bound species were recovered by lowering the pH of the eluant to 4.5. This procedure is uncomplicated, rapid, and applicable to nearly all tRNA isoacceptors. It does not chemically modify the tRNA(s) of interest or adversely affect their ability to be aminoacylated. Since boronic acids must be ionized to complex with cis-1,2-diols, boronic acid derivatives were prepared which ionize at a pH compatible with the stability of the aminoacyl bond. Two isomeric benzeneboronic acids with pKas of 6.8 and 7.4 were synthesized by introducing electron-withdrawing nitro groups into the aromatic ring. The addition of succinyl side chains permitted the nitrobenzeneboronic acids to be coupled to aminoethylpolyacrylamide. The properties of the nitrobenzeneboronic acid substituted acrylamide were illustrated by enriching phenylalanyl-tRNA at pH 7.0 to greater than 95% purity (1.63 nmol of phenylalanine accepted per A260 unit of tRNA) and seryl-tRNA isoacceptors at pH 6.5 to essentially theoretical purity (1.58 nmol of serine accepted per A260 unit of tRNA.

A carbohydrate-containing form of immunoreactive calcitonin in transplantable rat medullary thyroid carcinomas.

Extracts of transplantable rat medullary thyroid carcinomas were fractionated by concanavalin A-agarose chromatography and SDS-polyacrylamide gel electrophoresis. While tumor extracts contained mostly (greater than 90%) native calcitonin, 4 distinct larger calcitonin species (Mr = 27,000, 17,000, 13,700, and 9,600) were also observed. Glycoprotein fractions from lectin-affinity chromatography of the tumor extracts contained 0.3-1.5% of the total immunoreactive calcitonin. Gel electrophoresis of the pooled glycoprotein fractions demonstrated that the predominant forms of immunoreactive calcitonin were larger than calcitonin monomer. One high molecular weight species (Mr = 9,600), isolated in sufficient quantity from the polyacrylamide gels for reapplication to concanavalin A-agarose, was specifically eluted from the lectin, indicating that it was a glycoprotein. These results are the first evidence that intact C-cells contain at lest one high molecular weight glycoprotein form of immunoreactive calcitonin and suggest that addition and removal of carbohydrate side chains occur during processing of calcitonin precursors to the native hormone.

An organic ‘metal’?

LITTLE1 has proposed a mechanism by which an electron–electron (e–e) interaction in certain organic polymers and macromolecules might result in a high superconducting transition temperature. This e–e mechanism requires a combination of two systems consisting of a conducting or semiconducting polymeric compound forming a spine, with highly polarisable side chains attached to the spine. According to Little, the addition of such side chains can increase the e–e attraction in the spine to the point where it becomes energetically favourable to enter the superconducting state. This e–e mechanism of superconductivity has led to lively discussions, primarily concerned with superconductivity in quasi one and two-dimensional systems2,3, and the magnitude of the e–e attraction4,5. It has been shown theoretically3 that, depending on, the nature of the interaction between the electrons, a quasi one-dimensional system may exist in different states: metallic, dielectric, antiferromagnetic and superconducting. It has also been shown experimentally that the organic charge transfer salt N-methyl-pehnazinium tetracyanoqui-nodimethan has ‘metallic’ properties at temperatures above 200 K with a continuous transition to a small-band-gap insulator below 200 K (ref. 6).

Ion Binding by Synthetic Macrocyclic Compounds

The existence of synthetic macrocyclic molecules with hydrophilic cavities containing multiple binding atoms and with hydrophobic exteriors gives rise to extraordinary possibilities with respect to the design and synthesis of molecules with specific cation and anion binding properties. The preparation of many new macrocyclic compounds has recently been reported, but few practical applications for them have been suggested. From the information available, it is becoming clear that it should be possible to synthesize macrocycles that will have specified, or selected, ion binding properties. Cavity size can be varied to accommodate only those cations or anions within a specified narrow band of sizes. Numbers and types of coordinating atoms can be chosen to give essentially electrostatic or covalent bonding or a combination of the two in a metalmacrocycle complex. The metal ligand bond appears to be predominantly ionic in the case of the cyclic polyethers but the covalent character increases on substitution of sulfur or nitrogen for oxygen donor atoms. The essential hydrophobic exteriors of the macrocycles can be modified by the addition of side chains and groups to facilitate the solution of anions and cations in organic solvents. The structures of many macrocycles can be made to approximate naturally occurring molecules, that is, cyclic polyethers similar to macrocyclic antibiotics of the valinomycin and nonactin types and cyclic polyamines similar to porphyrins. Macrocycles are also useful as model compounds for the study of metal interactions with biological systems. The synthetic macrocycles thus represent an intriguing new area of coordination chemistry, the systematic study of which should lead to many interesting and useful chemical applications in the field of metal complexation in solution.