Cross-linking Of Side Chains Research Articles

Novel active ester-bridged copolynorbornene materials containing terminal functional hydroxyl, amino, methacryloyl, or ammonium groups via ring-opening metathesis polymerization

Several random and block copolynorbornenes with side chains containing terminal hydroxyl, amino, methacryloyl or ammonium groups were derived from the functional alkyl ester-containing norbornenes by ring-opening metathesis polymerization (ROMP). The main chain of ROMP-type polynorbornene had a more important role for glass-transition temperature in comparison with vinyl addition polymerization. There is little effect on glass-transition temperature (about −39 °C) of polynorbornenes with different length of alkyl side chain. The organosoluble copolynorbornenes with active crosslinkable methylacryloyl side chains derived from functional hydroxyl group were prepared to improve the thermal stability of poly(methyl methacrylate) [decomposition temperature (Td)10% = 325 °C in nitrogen] by forming networked AB crosslinked polymer (T = 367 °C in nitrogen). The sizes of nanometer-scale polymeric micelles of block copolymers having hydrophobic alkyl ester and hydrophilic ammonium groups were measured in the range of 11–25 nm by scanning electron microscopy. These polymeric materials with various functional groups or amphiphilic architectures are accessible by ROMP, whose topology makes them particularly attractive for application potential such as biomedical and photoelectric materials. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4233–4247, 2005

Tertiary structure of bacterial murein: the scaffold model.

Although the chemical structure and physical properties of peptidoglycan have been elucidated for some time, the precise three-dimensional organization of murein has remained elusive. Earlier published computer simulations of the bacterial murein architecture modeled peptidoglycan strands in either a regular (D. Pink, J. Moeller, B. Quinn, M. Jericho, and T. Beveridge, J. Bacteriol. 182: 5925-5930, 2000) or an irregular (A. Koch, J. Theor. Biol. 204: 533-541, 2000) parallel orientation with respect to the plasma membrane. However, after integrating published experimental data on glycan chain length distribution and the degree of peptide side chain cross-linking into this computer simulation, we now report that the proposed planar network of murein appears largely dysfunctional. In contrast, a scaffold model of murein architecture, which assumes that glycan strands extend perpendicularly to the plasma membrane, was found to accommodate published experimental evidence and yield a viable stress-bearing matrix. Moreover, this model is in accordance with the well-established principle of murein assembly in vivo, i.e., sequential attachment of strands to the preexisting structure. For the first time, the phenomenon of division plane alternation in dividing bacteria can be reconciled with a computer model of the molecular architecture of murein.

Polyelectrolyte Networks Based on Poly(Para-phenylene)s: Synthesis, Preparation of Thin Films, and Swelling Behavior

The preparation of poly(para-phenylene) (PPP) derivatives with sulfonate groups and photo cross-linkable side chains is described. These statistical copolymers are used to construct molecularly reinforced polyelectrolyte networks. Their swelling behavior as thin films with covalent attachment to a solid substrate is investigated by multiangle null-ellipsometry in a total internal reflection geometry (TIRE). Different mixtures of water, tetrahydrofurane, and added sodium chloride as well as a variation of the network structure show that the behavior of the networks is mainly determined by the balance of hydrophobic and hydrophilic groups of the polyelectrolyte. Increasing degree of swelling on addition of salt to water/THF mixtures suggests a preferential solvation of the organic compound in the network.

Polynorbornene with Cross-Linkable Side Chains via Ring-Opening Metathesis Polymerization

The ring-opening metathesis polymerization (ROMP) of 5-(methyl methacryloyl isocyanate)bicyclo[2.2.1]hept-2-ene [i.e., norbornene containing methacryloyl isocyanate (NBMMAI)] having cyclic olefin and terminal double bond was investigated in order to produce novel polymers with cross-linkable side chains under ligand exchange with MMA by using {RuCl2(CHPh)[P(C6H11)3]2} (II) as catalyst. Results of infrared spectra, 1H NMR, and 13C NMR showed that poly(NBMMAI) contains polynorbornene backbone ring structure and methacryloyl side chains. The 1H NMR spectrum of poly(NBMMAI) showed new vinyl protons as a broad signal between 5.15 and 5.37 ppm in the ratio of 0.4 and 2.8, corresponding to the vinyl protons of the cis and trans double bond of the ring-opened polymer, respectively. Gel formation was still observed in the polymerization of NBMMAI using ruthenium catalyst II with 20 mol % p-methoxyphenol (MEHQ). An increase in bulkiness of the ligand reduced the cross metathesis reaction and led to reduced activity...

Synthesis and Controlled Cross-Linking of Polymers Derived from Ring-Opening Metathesis Polymerization (ROMP)

The ROMP of 5-methacryloyl-1-cyclooctene and the copolymerization of this monomer with cyclooctadiene were investigated to produce polymers with cross-linkable side chains. The impact of concentration, monomer to catalyst ratio, and the amount of inhibitor in the polymerization was examined. These polymers were cross-linked through the methacrylate side chains with either thermal or photochemical initiation, and the incorporation of these polymers into poly(methyl methacrylate) (PMMA) to produce AB cross-linked materials was accomplished. A comparison of the physical properties of PMMA and these new materials demonstrated that these materials had higher thermal stability and solvent resistance than pure PMMA.

Design, synthesis and properties of molecular composites of rod‐like polymers

AbstractProcessing and performance of fiber reinforced polymers suffer from problems related to the heterogeneous nature of the composites. The strong impact of the nature of the interface between fibers and matrix adds to the complication of the field. Consequently many attempts have been made to reduce the cross‐section of the reinforcing fibers to molecular dimensions and to increase the compatibility between the rod‐like molecules or bundles of molecules and the isotropic matrix of ordinary flexible polymers. All such attempts have failed, mainly for reasons of thermodynamics which predict immiscibility of rods and coils on the molecular level. A possibility to create structures in which molecular rods are embedded in a continuous matrix of flexible chain segments exists nevertheless.1 Rod‐like backbone structures decorated with a skin of flexible side chains of moderate length in terms of the number of carbon atoms (typically C6 ‐ C18‐side chains) have been synthesized and tested for the spontaneous formation of molecular composites. Some of the materials built along this principle can be processed by solution casting or even melt extrusion. The academically more interesting materials can be built up layerwise by a modified Langmuir‐Blodgett technique. The latter process gives rise to monodomain textures which allow for straight‐forward testing of the mechanical properties by optical means (Brillouin‐spectroscopy) and by piezoquartz‐techniques.Hairy‐rod macromolecules can also be synthesized which contain crosslinkable side chains. Thus, after formation of layered, oriented structures, these can be crosslinked photochemically or by curing. The result is a network, which is unidirectionally reinforced by the rod‐like macromolecules. These novel types of networks can serve as membranes by which size exclusion is achieved via control of the distance between adjacent backbone molecules in the matrix. Recent synthetic advances in the field have concentrated on hairy‐rod macromolecules based on cellulose alkyl ethers and on derivatives of poly‐(p‐phenylene). The latter materials serve as examples of systems which can be processed by casting and extrusion processes. Due to their excellent thermal stability relevant data on the rheological and mechanical‐dynamical data have become available. These data serve to document the unique behavior of the hairy‐rod macromolecules as bulk materials.

Fluorescence Study on Dynamics and Structure of Polymer Chain II. Dependence of Intra-macromolecular Photo-crosslinking Reaction of Polymers with Anthryl and Eosinyl Moieties on Number of Crosslinkable Side Chains

Fluorescence Study on Dynamics and Structure of Polymer Chain II. Dependence of Intra-macromolecular Photo-crosslinking Reaction of Polymers with Anthryl and Eosinyl Moieties on Number of Crosslinkable Side Chains

24] Transition-metal complexes as spectroscopic probes for selective covalent labeling and cross-linking of proteins

Publisher Summary A good reagent for covalent labeling and cross-linking of amino acid side chains should be selective in reactions with proteins under mild conditions, easily detected and quantitated, stable yet removable, and noninvasive. Well-chosen transition-metal complexes can meet all of these requirements. Because much is known about substitution reactions of metal complexes, their selectivity toward side chains of certain types or in certain regions of the protein surface can be controlled according to principles of coordination chemistry and stereochemistry. The methods described in this chapter are developed in experiments with different species of cytochrome c , a prototypical electron carrier, and with papain, chymotrypsin, and a-lytic protease, prototypical proteinase enzymes. A metal complex with two open coordination sites or a precursor to such a complex may in principle serve as a cross-linking reagent. Procedures in this chapter are described in sufficient detail to enable relatively easy optimization for other proteins, especially metalloproteins.

The modulus of randomly-crosslinked poly(dimethylsiloxane) networks

In several published studies, randomly crosslinked networks were prepared from poly(dimethylziloxane) by the selective crosslinking of vinyl side chains with a silicon-hydride crosslinking agent. Stress-strain measurements on these elastomers gave values of the elongation modulus in the limits of small and large deformations which exceeded those predicted by the Flory-Erman theory. Although these unexpectedly large values at the small-strain limit have frequently been attributed to contributions from trapped entanglements, the present analysis interprets them as simply arising from contributions from short chains inadvertently introduced from the silicon-hydride crosslinking agent. In this interpretation there is a bimodal distribution of network chain lengths and, possibly, of crosslink functionalities as well. The present analysis gives results in good agreement with experiment.

The interfaces of actin and Acanthamoeba actobindin. Identification of a new actin-binding motif

Actobindin is an 88-amino acid polypeptide, containing two almost identical repeated domains of 33 and 34 residues. Depending on the molar ratios in which they are mixed, actobindin binds either one or two actin molecules. We cross-linked actobindin and actin in the 1:1 complex, using the zero-length cross-linker 1-ethyl-3(3-dimethylaminopropyl)carbodiimide. The cross-linked peptides were purified after consecutive CNBr cleavage and trypsin and Staphylococcus protease V8 digestions, and the cross-linked side chains were identified by amino acid sequencing. Isopeptide linkages were formed between residues Glu-100 of actin and Lys-16 of actobindin. In addition, we found a connection between one or more of the acidic residues 1,2, or 3 of actin and Lys-16 and Lys-52 of actobindin. The cross-linked regions in actobindin contain Leu-Lys-His-Ala-Glu-Thr motifs, similar to sequences observed in several other actin-binding proteins.

Effect of side chain length and crosslinking on the ac conductivity of oligo (ethyleneoxide) comb-branch polymer-salt mixtures

Linear and crosslinked comb-branch polymers have been prepared from the macromonomers CH 2 = CH-O-(CH 2CH 2O) nCH 3 where n=3, 5, and 6 7 . Comparable ionic conductivity levels could be achieved in both linear and branched system when mixed with several salts, if the crosslink density was kept ∼5%. The conductivity-temperature behaviour for the crosslinked systems mixed with LiClO 4, LiSO 3CF 3, LiBF 4 and NaClO 4 was examined as a function of the length of the oligo (ethylene oxide) side chain. It was found that the maximum conductivities of σ=10 −4−1.58×10 −3 for T=303–373 K were achieved when n=5 for a 5% crosslinked sample mixed with LiClO 4 at the composition [Li +] [EO] =0.05 .

Linear, uncross-linked peptidoglycan secreted by penicillin-treated Bacillus subtilis. Isolation and characterization as a substrate for penicillin-sensitive D-alanine carboxypeptidases.

Incubation of growing Bacillus subtilis with penicillin G led to the secretion of a peptidoglycan-related polymer and a nonglycan-bound pentapeptide into the culture medium. The secreted polymer was isolated and characterized as a linear cell wall glycan strand substituted predominantly by uncross-linked pentapeptide side chains. Polymer formation and secretion are most likely the result of continued synthesis and elongation of nascent glycan strands in the absence of subsequent processing by peptidoglycan transpeptidase or D-alanine carboxypeptidase enzymes. The nonglycan-bound pentapeptide, L-Ala-D-iso-Glu-meso-diaminopimelic acid-D-Ala-D-Ala, was probably formed by an N-acetylmuramyl-L-alanine amidase active on the peptide side chains of The uncross-linked polymer. The uncross-linked peptidoglycan polymer was shown to be a good substrate for penicillin-sensitive D-alanine carboxypeptidases purified from membranes of B. subtilis, Bacillus stearothermophilus, and Escherichia coli. D-alanine release was not, however, coupled to the cross-linking of peptide side chains, suggesting that these enzymes do not function as peptidoglycan transpeptidases in vivo. No transpeptidase or D-alanine carboxypeptidase activity was detected in mixtures of high molecular weight penicillin-binding proteins from B. subtilis, B. stearothermophilus, or Staphylococcus aureus. Possible reasons for the inability to demonstrate these activities are discussed. In addition, an N-acetylmuramyl-L-alanine amidase activity which copurifies with penicillin-binding proteins from B. subtilis, S. aureus, and E. coli was partially characterized.

Synthesis of Epoxide Polymers of Steroidal Compounds

A series of twenty ethylene oxide and propylene oxide addition polymers of ursolic acid and some of its derivatives have been made and characterized. In addition, an ethylene oxide and propylene oxide polymer of cholic acid and ethylene oxide polymers of vitamin A, vitamin D 2 , vitamin E, cortisone, estradiol, and testosterone are reported. Attempts to prepare steroidal polymers with highly branched or crosslinked side chains by using glycidol and epichlorhydrin were unsuccessful. The most acceptable structures as determined from molecular weight and solubility data were determined. Percentage polyalkylene oxide content, solubilities, and molecular weight or chain length distributions are presented.

Some observations on peptide chain models in relation to crystallographic data for gramicidin B and insulin

As chemical data for protein molecules accumulate, it becomes clear that any theory of the configuration of protein chains has to be integrated with evidence of considerable chemical complexity, both in side-chain distribution, interaction and cross-linking. We have recently considered chain models in relation to two crystal structures, gramicidin B and insulin, for both of which chemical and crystallographic evidence is more than usually detailed. Gramicidin B is interesting as a cyclic peptide of size intermediate between amino-acids and proteins (Dubos 1939; Gregory & Craig 1948). A combination of chemical and crystallographic data (see table 8) suggests that the molecule has a weight 3800 and contains about 32 residues, two of which are ethanolamine and some of which are D-amino acid residues. Further, the intensity distribution of X-ray reflexions from crystals of this peptide strongly suggests that the molecule consists of two chains, anti-parallel with one another and linked end to end, these molecules being packed in a roughly hexagonal array. This is illustrated by the calculation of two possible electron density projections shown in figure 39. The chain structures seen here have dimensions corresponding to chain folding of the same order of magnitude as that proposed in α -keratin, 14 to 15 residues in about 22 Å, or 1 residue in 1⋅4 to 1⋅6 Å. It is possible to construct models of molecules with these dimensions, based either on the α -helix model proposed by Pauling, Corey & Branson (1951), or folded chains of the Astbury type (1941), provided that considerable deviations are allowed for residues linking the two chains and for the ethanolamine residues. Such deviations do not apparently prevent the structure from having a marked similarity, from an X-ray scattering point of view, to α -folded synthetic peptides (figure 40).