HYDROPHOBICALLY ASSOCIATING POLYACRYLAMIDES MODIFIED BY A NOVEL SELF-ASSOCIATIVE CATIONIC MONOMER

A series of hydrophobically associating polyacrylamides modified by small amounts （〈 3 mol%） of a self- associative cationic monomer 4-（2-（acryloyloxy） ethoxy） benzyl tri-ethyl ammonium bromide （AEBA） as hydrophobe were synthesized by radical copolymerization in aqueous solutions without external surfactants. The resulting eopolymers containing a multiblock structure exhibited a high tendency for hydrophobic association and a high thickening capacity. Solution properties and aggregation structures were investigated by viscometry and fluorescence technique. The high viscosity enhancement was found as the polymer concentration beyond a critical value c＊ and strongly depended on the copolymer microstructures. The number and length of hydrophobic microblocks within the copolymer backbones could be controlled by changing the AEBA concentration in copolymerization system. Addition of salt induced more hydrophobic association and viscosity enhancement. The synthesis method used was simple and environmentally friendly without any external surfactant contamination in comparison with the conventional micellar copolymerization.

STUDIES ON SELF-ASSOCIATIVE BEHAVIOR OF A NOVEL CATION AMPHIPHILIC POLYMER

A novel associating polymer P(AEBA) was synthesized by radical polymerization of the cationic amphiphilic monomer,4-(2-(acryloyloxy)ethoxy)benzyl tri-ethyl ammonium bromide(AEBA),in aqueous solutions.P(AEBA) displays a strong tendency for self-association in aqueous solutions and is sensitive to the external stimulation such as added salt.The associative properties and morphologies of P(AEBA) were studied by fluorescnece probe technique,viscometry and TEM.In dilute salt-free solutions P(AEBA) behaves as pol...

A NOVEL INTERPRETATION OF CONCENTRATION DEPENDENCE OF VISCOSITY OF DILUTE POLYMER SOLUTION

The concentration dependence of the reduced viscosity of dilute polymer solution is interpreted in the light of a new concept of the self-association of polymer chains in dilute solution. The apparent self-association constant is defined as the molar association constant divided by the molar mass of individual polymer chain and is numerically interconvertible with the Huggins coefficient. The molar association constant is directly proportional to the effective hydrodynamic volume of the polymer chain in solution and is irrespective of the chain architecture. The effective hydrodynamic volume accounts for the non-spherical conformation of a short polymer chain in solution and is a product of a shape factor and hydrodynamic volume. The observed enhancement of Huggins coefficient for short chain and branched polymer is satisfactorily interpreted by the concept of self-association. The concept of self-association allows us to predict the existence of a boundary concentration C-s(dynamic contact concentration) which divides the dilute polymer solution into two regions.

The Photochemical Study of HSA and BSA with Resonance Light Scattering and Fluorescence Spectra

The resonance light-scattering (RLS) of human serum albumin (HSA) and bovine serum albumin (BSA) is reported for the first time, and applied to study photochemical reaction of HSA and BSA. The fact of photocrosslinking self-association effect in HSA and BSA solutions is identified by the enhancement of RLS. The fluorescence quenching at about 350 nm and 700 nm proves that tryptophan (Trp) residues are one of the photochemical activity sites in HSA and BSA molecules. The Rayleigh scattering (RS) spectra of HSA and BSA that were neglected in fluorescence spectra before are found at about 296 nm, 592 nm and 888 nm for the first time, and are of adventageous to studying the aggregation of HSA or BSA. The possible photochemical reaction mechanism is also proposed.

Non-Isothermal Degradation Kinetics of Hybrid Copolymers Containing Thermosensitive and Polypeptide Blocks

Novel, self-associating hybrid copolymers were synthesized via controlled ring-opening polymerization of N-carboxyanhydride of Z-L-lysine (Z-L-Lys-NCA), initiated by amino-functional macroinitiators. A poly(N-isopropylacry-lamide) (PNIPAm)-based macroinitiator containing 10 mol% of polyoxyethylene grafts and a terminal primary amine group in the form of ammonium hydrochloride (PNIPAm-g-PEО) was synthesized and used to initiate the ammonium- mediated ring-opening polymerization of NCA described by Dimitrov and Schlaad [1]. Thus, hybrid copolymers ((PNIPAm-g-PEO)-b-PLys) with controlled molar-mass characteristics and functionality were obtained. The potential applications of PNIPAm-based copolymers in the systems for controlled drug release, immobilization of enzymes and protein purification have aroused great interest in the studies of their properties and behaviour. The thermal stability and thermodynamic properties of the copolymers obtained were studied. The differential thermal analysis of polyfunctional hybrid copolymers (PNIPAm-g-PEO)-b-PLys) showed that thermooxidative destruction occurs in two stages: primary, of the unstable fragments (grafted chains of PEO);and secondary, of the main polymer chains of poly(N-isopropylacry-lamide) and poly(L-lysine). The kinetics of thermal degradation was evaluated and the values of the activation energy of the degradation process, changes of Gibbs free energy, enthalpy and entropy for the formation of the activated complex were also calculated.

Length-regulation in the self-association of actin and the effect of platinum complexes

The evidence on the length-regulation in the self-association of actin is conflicting andits interpretation relies heavily on the character of the measurement method. By quasi-elastically light scattering (QELS) measurements. the change of the polymerlength as a function of time and the effect of ATP have been studied. QELS studies re-vealed that there is a length-regulation stage in self-association of actin which is not in-

NLR immune receptor RB is differentially targeted by two homologous but functionally distinct effector proteins

Plant nucleotide-binding leucine-rich repeat(NLR)receptors mediate immune responses by directly or indirectly sensing pathogen-derived effectors.Despite significant advances in the understanding of NLR-mediated immunity,the mechanisms by which pathogens evolve to suppress NLR activation triggered by cognate effectors and gain virulence remain largely unknown.The agronomically important immune receptor RB recognizes the ubiquitous and highly conserved IPI-O RXLR family members(e.g.,IPI-O1)from Phytophthora infestans,and this process is suppressed by the rarely present and homologous effector IPIO4.Here,we report that self-association of RB via the coiled-coil(CC)domain is required for RB activation and is differentially affected by avirulence and virulence effectors.IPI-O1 moderately reduces the self-association of RB CC,potentially leading to changes in the conformation and equilibrium of RB,whereas IPIO4 dramatically impairs CC self-association to prevent RB activation.We also found that IPI-O1 associates with itself,whereas IPI-O4 does not.Notably,IPI-O4 interacts with IPI-O1 and disrupts its self-association,therefore probably blocking its avirulence function.Furthermore,IPI-O4 enhances the interaction between RB CC and IPI-O1,possibly sequestering RB and IPI-O1 and subsequently blocking their interactions with signaling components.Taken together,these findings considerably extend our understanding of the underlying mechanisms by which emerging virulent pathogens suppress the NLR-mediated recognition of cognate effectors.

On Some n-C2 and Strongly C2 Extensions

Let R be a ring and n be a positive integer.Then R is called a left n-C2-ring(strongly left C2-ring)if every n-generated(finitely generated)proper right ideal of R has nonzero left annihilator.We discuss some n-C2 and strongly C2 extensions,such as trivial extensions,formal triangular matrix rings,group rings and[D,C].