Amount Of Charged Groups Research Articles

Modular synthesis of non-charged and ionic xylan carbamate derivatives from xylan carbonates

Novel non-charged and ionic xylan carbamate (XC) derivatives were synthesized in a modular approach from xylan phenyl carbonates (XPC) as reactive intermediates. XPC with varying degrees of substitution (DS) from 0.5 to 1.9 were converted with different non-ionic primary and secondary amines in different molar ratio to obtain the corresponding XC with high conversion rates of up to 100%. In a similar way, ionic amines were employed for the aminolysis of XPC to obtain charged XC. The XC were characterized by NMR- and infrared spectroscopy. XPC proofed to be highly versatile building blocks for the preparation of ionic xylan derivatives. The type and amount of charged groups could be tuned efficiently. Moreover, high DS values of up to 1.4 for cationic and 1.8 for anionic XC derivatives could be achieved, which is higher than reported previously for comparable ionic xylan derivatives that were prepared by “conventional” esterification and etherification reactions.

Effects of Temperature and pH on the Contraction and Aggregation of Microgels in Aqueous Suspensions

Chemically cross-linked poly(N-isopropylacrylamide) (PNIPAM) microgels and PNIPAM with different amounts of acrylic acid groups (PNIPAM-co-PAA) were synthesized and the temperature-induced aggregation behaviors of aqueous suspensions of these microgels were investigated mainly with the aid of dynamic light scattering (DLS) and turbidimetry. The DLS results show that the particles at all conditions shrink at temperatures up to approximately the lower critical solution temperature (LCST), but the relative contraction effect is larger for the microgels without acid groups or for microgels with added anionic surfactant (SDS). A significant depression of the cloud point is found in suspensions of PNIPAM with very low concentrations of SDS. The compression of the microgels cannot be traced from the turbidity results, but rather the values of the turbidity increase in this temperature interval. This phenomenon is discussed in the framework of a theoretical model. At temperatures above LCST, the size of the microgels without attached charged groups in a very dilute suspension is unaffected by temperature, while the charged particles (pH 7 and 11) continue to collapse with increasing temperature over the entire domain. In this temperature range, low-charged particles of higher concentration and particles containing acrylic acid groups at low pH (pH 2) aggregate, and macroscopic phase separation is approached at higher temperatures. This study demonstrates how the stabilization of microgels can be affected by factors such as polymer concentration, addition of ionic surfactant to particles without charged acid groups, amount of charged groups in the polymer, and pH.

Microstructure of N-Isopropylacrylamide−Acrylic Acid Copolymer Gels Having Different Spatial Configurations of Weakly Charged Groups

Gel microstructure formation according to spatial configuration of charged groups in gel network has been investigated using macroscopic swelling measurements and microscopic small-angle neutron scattering. Three types of gel consisting of hydrophobic N-isopropylacrylamide (NIPAm) and weakly charged acrylic acid (AAc) copolymers were prepared with different distributions of AAc monomer units in the network. The first type was a NIPAm/AAc copolymer gel in which NIPAm and AAc were randomly copolymerized in monomer units using the redox method. The second type was a UV-cross-linked NIPAm/poly-AAc copolymer gel in which NIPAm was copolymerized with polymer units of AAc. The third type was a NIPAm/poly-AAc polymer gel prepared using the redox method in which poly-AAc was not cross-linked but physically entrapped in the NIPAm polymer network. These three types of gel contained the same amount of charged groups but with different spatial configurations. The differences in spatial and topological distribution of ...

Carbohydrate-containing components of biofilms producedin vitroby some staphylococcal strains related to orthopaedic prosthesis infections

The capacity of coagulase-negative staphylococci to colonize implanted medical devices is generally attributed to their ability to produce biofilms. Biofilm of the model strain of Staphylococcus epidermidis RP62A was shown to contain two carbohydrate-containing moieties, a linear poly-beta-(1-->6)-N-acetyl-D-glucosamine (PNAG) and teichoic acid. In the present study, we investigated several biofilm-producing staphylococci isolated from infected orthopaedic implants and characterized the composition of the laboratory-grown biofilms using chemical analysis and 1H nuclear magnetic resonance spectroscopy. Extracellular teichoic acid was produced by all strains studied. Some of the clinical strains were shown to produce biofilms with compositions similar to that of the model strain, containing a varying amount of PNAG. The chemical structure of PNAG of the clinical strains was similar to that previously described for the model strains S. epidermidis RP62A and Staphylococcus aureus MN8m, differing only in the amount of charged groups. Biofilms of the strains producing a substantial amount of PNAG were detached by dispersin B, a PNAG-degrading enzyme, while being unsusceptible to proteinase K treatment. On the other hand, some strains produced biofilms without any detectable amount of PNAG. The biofilms of these strains were dispersed by proteinase K, but not by dispersin B.

Assembly modulates dissociation: electrokinetic experiments reveal peculiarities of the charge formation at monolayer films

Self-assembled monomolecular films of alkanethiols chemisorbed on gold were used as a two-dimensional model system to study the effects of spatial confinement of surface functional groups on their acid-base behaviour; reduction of the surface charge density by mixed assemblies revealed an increase of the acidity of carboxy groups; surfaces with low amounts of charged groups show the interplay of dissociation of functional groups and preferential adsorption of ions in terms of surface charge formation.

STABILIZATION OF LIPID BILAYERS ON SURFACES THROUGH CHARGED POLYMERS

ABSTRACT It is our concept to use a polymer as a hydrophilic cushion to stabilize a lipid bilayer on a solid support. This can be accomplished by using polyacrylamides with disulfides and DMPE anchors as a hydrophilic cushion. These polymers have the additional functionalities to chemisorb on gold surfaces through the disulfides and to bind a lipid bilayer on it through the insertion of the lipid anchors into the lipid bilayer. This paper shows that a polymer with the additional functionality of charged groups increases the attraction of vesicles to form a tethered supported lipid bilayer. By varying the amount of charged groups in the polymer, we are able to control the hydrophilic behavior of the polymer and therefore are able to change the wetting on a surface. This was examined by measuring the contact angles. Using the technique of the surface plasmon spectroscopy, we are able to monitor the process of vesicle fusion on the polymer support.

Miscibility enhancement of polymers in polar media by incorporation of a small amount of charged groups into the polymer chains

Miscibility enhancement of polymers in polar media by incorporation of a small amount of charged groups into the polymer chains

Alkaline phosphatases from hen's egg yolk, liver, blood plasm and intestinal mucosa: Affinity chromatographic purification and comparison

1. 1. Alkaline phosphatases from hen's egg yolk, liver, blood plasm, and intestinal mucosa were purified with, as main purification step, affinity chromatography on 4-( p-amino-phenylazo)-phenylarsonic acid-epoxy-Sepharose 4B. Specific activities up to 50 U/mg were obtained. 2. 2. Yolk alkaline phosphatase is composed of two identical inactive subunits with Mg 68,800 ± 1700. The active enzyme monomer has a Mg 150,400 ± 2100. Comparable values were obtained for the predominant liver and blood plasm enzymes. The active monomer from intestinal mucosa has a M R 120,000. 3. 3. All alkaline phosphatases are mixtures of enzyme forms, differing in glycoprotein content and/or amount of charged groups. 4. 4. The concept that yolk proteins are synthesized in the liver, and transported through the blood plasm to the growing egg yolk, is not invalidated. The heterogeneity of the blood plasm alkaline phosphatase originates likely from the presence of liver, intestinal mucosa, and bone alkaline phosphatases.

Effect of pH and counter ions on the zeta-potential of oral streptococci

The ζ-potentials of 10 different strains of Streptococcus mutans, Streptococcus sanguis and Streptococcus salivarius were determined in the pH range 2.5–8.0 and after incorporation of counter ions in the running media, using a standardized particle microelectrophoretic technique. The results indicate that the surface potentials of oral streptococci are pH-dependent and that this dependence is related to the microbial strain. The effects are probably caused by presence of different kinds as well as different amounts of charged groups on the bacterial surfaces. Anions did not have noticeable influence on the ζ-potential of the microorganisms but multivalent cations decreased it. Some of these were even able to change the potential of the streptococci to positive. Generally speaking, the variations of the ζ-potentials were in accord with accepted colloid and surface chemical laws and phenomena.

Reversible inhibition of enzymes by interaction with synthetic polysaccharide macroanions

Charged polyglucose derivatives, such as polyglucose sulfates, with different molecular weights, branching, and degree of substitution precipitated basic proteins, such as lysozyme, ribonuclease, protamine, thymus peptide, polymyxin B, an ACTH preparation, cytochrome c, and serum albumin from aqueous solution at low pH and salt concentration. Enzymic activity of lysozyme, ribonuclease (both on ribonucleic acid and on a cyclic phosphate), and hyaluronidase was inhibited in solution. The inhibition required macromolecular size and polyanionic structure and depended on the type and amount of charged groups on the synthetic polysaccharide derivative. Highly substituted sulfates were the most effective inhibitors, while sulfates with similar molecular size but lower charge density or derivatives with weaker dissociating anionic groups (carboxyls) had less inhibitory activity. The inhibition appears to be due to electrostatic interaction forces between the oppositely charged macromolecules and can be reversed by a polymeric cation stronger than the substrate.