A Polymer/Peptide Complex‐Based Sensor Array That Discriminates Bacteria in Urine

A negatively charged poly(para ‐phenyleneethynylene) (PPE) forms electrostatic complexes with four positively charged antimicrobial peptides (AMP). The AMPs partially quench the fluorescence of the PPE and discriminate fourteen different bacteria in water and in human urine by pattern‐based fluorescence recognition; the AMP‐PPE complexes bind differentially to the components of bacterial surfaces. The bacterial species and strains form clusters according to staining properties (Gram‐positive and Gram‐negative) or genetic similarity (genus, species, and strain). The identification and data treatment is performed by pattern evaluation with linear discriminant analysis (LDA) of the collected fluorescence intensity data.     

Conjugated Polyelectrolyte‐Induced Self‐Assembly of Alkynylplatinum(II) 2,6‐Bis(benzimidazol‐2′‐yl)pyridine Complexes

Water‐soluble cationic alkynylplatinum(II) 2,6‐bis(benzimidazol‐2′‐yl)pyridine (bzimpy) complexes have been demonstrated to undergo supramolecular assembly with anionic polyelectrolytes in aqueous buffer solution. Metal–metal‐to‐ligand charge transfer (MMLCT) absorptions and triplet MMLCT (³MMLCT) emissions have been found in UV/Vis absorption and emission spectra of the electrostatic assembly of the complexes with non‐conjugated polyelectrolytes, driven by Pt???Pt and π–π interactions among the complex molecules. Interestingly, the two‐component ensemble formed by [Pt(bzimpy‐Et){C?CC₆H₄(CH₂NMe₃‐4)}]Cl₂ ( 1 ) with para‐linked conjugated polyelectrolyte (CPE), PPE‐SO₃^?, shows significantly different photophysical properties from that of the ensemble formed by 1 with meta‐linked CPE, mPPE‐Ala. The helical conformation of mPPE‐Ala allows the formation of strong mPPE‐Ala– 1 aggregates with Pt???Pt, electrostatic, and π–π interactions, as revealed by the large Stern–Volmer constant at low concentrations of 1 . Together with the reasonably large Förster radius, large HOMO–LUMO gap and high triplet state energy of mPPE‐Ala to minimize both photo‐induced charge transfer (PCT) and Dexter triplet energy back‐transfer (TEBT) quenching of the emission of 1 , efficient Förster resonance energy transfer (FRET) from mPPE‐Ala to aggregated 1 molecules and strong ³MMLCT emission have been found, while the less strong PPE‐SO₃^?– 1 aggregates and probably more efficient PCT and Dexter TEBT quenching would account for the lack of ³MMLCT emission in the PPE‐SO₃^?– 1 ensemble.     

Conformational study of papain in the presence of sodium dodecyl sulfate in aqueous medium

The interactions between a globular protein, papain and the anionic surfactant, sodium dodecyl sulfate (SDS) have been investigated in aqueous medium using fluorimetric, circular dichroism, Fourier transform infra-red, UV-vis spectrophotometric, dynamic light scattering, and nuclear magnetic resonance techniques. The conformational change of papain in aqueous solution has been studied in the presence of SDS. The results show the high alpha-helical content and unfolded structure of papain in the presence of SDS due to strong electrostatic repulsion leading to a "necklace and bead model" in protein-surfactant complexes.     

聚合物主体中纳米CdTe的光致发光与电致发光性质

利用紫外和荧光光谱技术研究了共轭聚合物PPE4+分别在溶液和薄膜中与纳晶CdTe间的能量传递现象。通过静电层层组装技术制备了混杂有纳晶CdTe的PPE4+薄膜发光二极管,并测试了其电致发光性质。结果表明在溶液和薄膜中共轭聚合物PPE4+与纳晶CdTe间均能发生有效的能量转移,而共轭聚合物PPE4+在能量传递过程中起到分子天线的作用。     

Polymeric Membranes Containing Phosphorus in the Chain for Solid Polymer Electrolytes

Abstract

Two new series of solid polymer electrolytes (SPEs) based on phosphorus containing (co)polyesters (PPE) and Lithium triflate were obtained. PPEs are composed of phosphonate moeties (cyclohexyldichlorophosphonate (CHDP)) as linking agent and two diols: PEG (6000) and poly(tetramethylene glycol) (PTMG) in PPE I, and PEG (6000) and 4,4′-cyclohexylidenebisphenol (bisphenol Z, BZ) in PPE II. Polycondensation was carried out in solution in the presence of triethylamine (TEA) as scavenger of HCl side product (PPE I–IIa) and in the absence of any acid acceptor (PPE I–IIb). The Limiting Oxygen Index (LOI) and thermal analysis were performed both on polymers and membranes. The ionic conductivity of SPE membranes based on PPE-salt complexes, with various salt concentrations, was investigated at different temperature and ionic transference numbers were determined. Optimum composition was obtained for the polymer which contains in structure only alkyl units and 15% Lithium triflate.     

Gelation of native beta-lactoglobulin induced by electrostatic attractive interaction with xanthan gum

The mechanism and kinetics of the electrostatic gelation of native beta-lactoglobulin-xanthan gum mixtures in aqueous solution is reported. The total biopolymer concentration at which gelation was obtained was extremely low (0.1 wt %) compared to the usually tested concentrations for protein-polysaccharide mixed gels (4-12 wt %). This is, to our knowledge, the first time that oppositely charged proteins and polysaccharides are reported to form a gel without applying any treatment to denature the protein (e.g. heating, enzymatic hydrolysis) and at such low concentrations. Static light-scattering and viscoelastic measurements allowed determination of the gelation kinetics. It was found that the gelation process initiated following a similar path as that of an associative phase separation process, i.e., with the formation of primary and interpolymeric electrostatic complexes. However, interpolymeric complexes were able to form clusters and junction zones that resulted in the freeze-in of the whole structure at the point of gelation. The formed gel is therefore a coupled-gel, that is, a gel that has junction zones involving two different molecules. The structuration of xanthan gum, even at these low concentrations, may have played a role in the structuration process. Due to the electrostatic nature of the gels, there was an optimum pH and macromolecular ratio at which the stability of the gels was maximal. This was related to the existence of a stoichiometric electrical charge equivalence pH, where molecules carry equal but opposite charges and protein-polysaccharide interactions are at their maximum.     

Quantum Dots Arrangement and Energy Transfer Control via Charge‐Transfer Complex Achieved on Poly(Phenylene Ethynylene)/Schizophyllan Nanowires

Assemblies of organic and inorganic compounds in the nanoscale region have contributed to the development of novel functional materials toward future applications, including sensors and opto‐electronics. We succeed in fabricating hybrid nanowires composed of a conjugated polymer and semiconductor quantum dots (QDs) by a supramolecular assembly technique. The 1‐D fashion of the nanowire structure is obtained by the polymer wrapping of cationic poly(phenylene ethynylene) (PPE) with helix‐forming polysaccharide schizophyllan (SPG). The electrostatic interaction between cationic PPE and anionic QDs affords the nanowires decorated with QDs. Upon addition of an acceptor molecule, tetranitrofluorenone (TNF), the charge‐transfer (CT) complex between PPE and TNF is formed, resulting in energy transfer from the QDs to PPE arising from the induced spectral overlap. Furthermore, the employment of the conjugated polymer allows highly sensitive quenching of the QD’s emission by raising the transmission efficiency to the CT complexed electron deficient sites along the polymer backbone.     

Anthryl-doped conjugated polyelectrolytes as aggregation-based sensors for nonquenching multicationic analytes

The fluorescence-based detection of nonquenching, multicationic small molecules has been demonstrated using a blue-emitting, polyanionic poly(p-phenylene ethynylene) (PPE) doped with green-emitting exciton traps (anthryl units). Multicationic amines (spermine, spermidine, and neomycin) were found to effectively induce the formation of tightly associated aggregates between the polymer chains in solution. This analyte-induced aggregation, which was accompanied by enhanced exciton migration in the PPE, ultimately led to a visually noticeable blue-to-green fluorescence color change in the solution. The aggregation-based sensor exhibited poor sensitivity toward dicationic and monocationic amines, demonstrating that a conjugated polyelectrolyte sensor relying on nonspecific, electrostatic interactions may still attain a certain level of selectivity.     

Nonspecific interactions of a carboxylate-substituted PPE with proteins. A cautionary tale for biosensor applications

Two carboxylate-substituted, fluorescent (Phi = 0.08), water-soluble poly(p-phenyleneethynylene)s (PPE) and a water-soluble model compound were exposed to a series of proteins and bovine serum. While the anionic PPEs do not have any specific binding sites, they form stable complexes with histone, lysozyme, myoglobin, and hemoglobin. The complex formation was evidenced by fluorescence quenching. Bovine serum albumin does not quench the fluorescence of the PPEs but enhances it, probably due to its surfactant character. These results imply that the use of charged conjugated polymers as biosensors, while an attractive proposition, has to take into account strong nonspecific interactions between conjugated polymers and the host of proteins that is found in cells and complex biological fluids.     

利用水相合成的量子点标记木瓜蛋白酶的研究

利用半导体纳米粒子 (也称半导体量子点 ,Quantum Dots,以下简称 QDs)和表面修饰技术制备的半导体荧光探针具有极其优良的光谱特征和光化学稳定性 [1] .自 1 997年以来 ,随着量子点制备技术的不断提高 ,量子点在生物医学方面已有应用 . 1 998年 ,Alivisatos[1] 和 Nie[2 ] 两个研究小组分别将结合了生物分子的 QDs作为荧光探针应用于生物体系 ,开创了纳米粒子应用的新领域 .最近 Nie等 [3 ]在利用量子点编码生物分子的研究中取得了突破性进展 .目前 ,纳米粒子与生物分子的连接以共价键方式相结合最为常见 [1,2 ,4 ,5] ,而且在这些应用中…     

Significance of grafting in curing processes initiated by UV, excimer and ionising radiation sources

The grafting of a typical methacrylate monomer (MMA) to polypropylene (PPE) and cellulose initiated by UV and ionising radiation is reported. The effect of additives which constitute components in radiation curing on the grafting process is examined. Additives studied include photoinitiators (PIs), multifunctional acrylates and methacrylates and acrylate oligomers. Synergistic effects when these additives are combined in the same solution are reported. The photografting studies have been extended to include grafting with charge transfer (CT) complexes involving donor/acceptor (DA) monomers to PPE, cellulose and wool. The importance of this work in conventional and PI free curing is discussed, particularly the significance of concurrent grafting during curing.     

Destructive effect of polystyrene sulfonate on the structure of hemoproteins

The mechanism of the destruction of horse heart hemoglobin (Hb) and spermwhale muscle myoglobin (Mb), two hem-containing proteins, by polystyrene sulfonate, an anionic polyelectrolyte, was studied. Measurements of the optical absorption of the prostetic group of the hem in the visible spectrum and of the circular dichroism in the absorption bands of the peptide groups and aromatic amino acid residues demonstrated that the compact structure of both proteins experiences destruction in the presence of polystyrene sulfonate (PSS) at PSS concentrations ten times as low as that of the protein (in wt %) and that the content of α-helix structure in Hb and Mb decreases from 81% in the native state to 43% in their complexes with PSS. The distinctions in the mechanisms of the destruction of Hb and Mb by PSS were found to be as follows: (1) in contrast to Mb, Hb forms insoluble complexes with PSS at low PSS concentrations and (2) Mb-PSS solutions at Mb-to-PSS ratios >1 were found to contain free hems (that absorb at 397 nm), a feature not observed for Hb; the kinetics of the destruction of both the proteins by the polyelectrolyte was demonstrated to be a two-stage process. The first stage of the destruction of Hb (τ ≈ 24.5 s) was found to be four times as slow as that of Mb (τ ≈ 6 s); the second (slow) stage had a halftime of ～6 h for both the proteins under study. To determine the localization of regions at the protein molecule surface that are capable of binding polyelectrolyte molecules, the distribution of the electrostatic potential over the surface of the Hb and Mb molecules was numerically calculated with the help of the Poisson-Boltzmann equation at pH 6.2 and an ionic strength of 100 mmol/l. Based on experimental and theoretical studies of the mechanism of the interaction of the polyelectrolyte with the proteins, the structural-functional properties of proteins responsible for their destruction by the polyelectrolyte are determined.     

Resonance light-scattering spectrometric study of interaction between enzyme and MPA-modified CdTe nanoparticles

This paper described a novel assay of enzyme based on the measurement of enhanced resonance light-scattering (RLS) signals resulting from the electrostatic and coordination interaction of functionalized CdTe nanoparticles with enzyme. The CdTe nanoparticles which were modified with 3-mercaptocarboxylic acid (MPA) have abundant carboxylic groups (COOH). So the nanoparticles are water-soluble, stable and biocompatible. At pH 8.3 phosphate buffered saline (PBS), the RLS signals of functionalized nano-CdTe are greatly enhanced by bromelain and papain in the region of 220-800 nm characterized by the peak around 318-314 nm, respectively. The optimization conditions of the reaction were also examined and selected. Under the selected conditions, the enhanced RLS intensity is linearly proportional to the concentration of bromelain and papain. The liner range is (0.09-0.9) x 10(-6)mol/L for bromelain and (0.048-0.702) x 10(-6)mol/L for papain. The influences of some foreign substances were also examined. This method can be applied to the determination of enzyme.     

Adsorption behaviour of lactoferrin in oil-in-water emulsions as influenced by interactions with beta-lactoglobulin

Oil-in-water emulsions (pH 7.0 or pH 3.0) containing 30 wt% soya oil and various concentrations of lactoferrin were made in a two-stage valve homogenizer. The average droplet size (d32), the surface protein coverage (mg/m2) and composition, and the zeta-potential of the emulsions were determined. The value of d32 decreased with increasing lactoferrin concentration up to 1%, and then was almost independent of lactoferrin concentration beyond 1% at both pH 7.0 and pH 3.0. The surface protein coverage of the emulsions made at pH 7.0 increased almost linearly with increasing lactoferrin concentration from 0.3 to 3%, but increased only slightly in emulsions made at pH 3.0 at lactoferrin concentrations >1%. The surface protein coverage of the emulsions made at pH 3.0 was lower than that of the emulsions made at pH 7.0 at a given protein concentration. The emulsion droplets had a strong positive charge at both pH 7.0 and pH 3.0, indicating that stable cationic emulsion droplets could be formed by lactoferrin alone. When emulsions were formed with a mixture of lactoferrin and beta-lactoglobulin (beta-lg) (1:1 by weight), the charge of the emulsion droplets was neutralized at pH 7.0 suggesting the formation of electrostatic complexes between the two proteins. The composition of the droplet surface layer showed that both proteins were adsorbed, presumably as complexes, from the aqueous phase at pH 7.0 in equal proportions, whereas competitive adsorption occurred between lactoferrin and beta-lg at pH 3.0. At this pH, beta-lg was adsorbed in preference to lactoferrin at low protein concentrations (1%), whereas lactoferrin appeared to be adsorbed in preference to beta-lg at high protein concentrations.     

Controlling the charge and organization of anionic lipid bilayers: effect of monovalent and divalent ions

It is shown that the organization of lipid bilayers containing phosphatidic acid (PA) and phosphatidlycholine (PC) can be controlled by altering the monovalent and divalent ion concentrations. At high pH and/or calcium concentration, 1:1 Ca(2+)-PA(2-) complexes form; these complexes demix, and PA-rich and PC-rich regions are observable with epifluorescence microscopy. The results are compared with predictions from electrostatic theory. It is noted that the complex formation correlates in a roughly linear fashion with the monovalent/divalent ion ratio, a parameter that cells adjust.     

Emulsion stabilisation using polysaccharide–protein complexes

There is a great deal of interest in the Food Industry in the use of polysaccharides and proteins to stabilise oil-in-water emulsions and there is a particular interest nowadays in the use of polysaccharide–protein complexes. There are three classes of complexes namely; (a) naturally-occurring complexes in which protein residues are covalently attached to the polysaccharide chains as is the case, for example, with gum Arabic; (b) Maillard conjugates, which are formed by interaction of the reducing end of a polysaccharide with an amine group on a protein forming a covalent bond; and (c) electrostatic complexes formed between a polysaccharide and a protein with opposite net charge. This review sets out our current understanding of the nature of these different polysaccharide–protein complexes and their ability to stabilise oil-in-water emulsions.     

A Comparative Study of the Direct Calorimetric Determination of the Denaturation Enthalpy for Lysozyme in Sodium Dodecyl Sulfate and Dodecyltrimethylammonium Bromide Solutions

The complexes of lysozyme with the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB) have been investigated by isothermal titration calorimetry at pH=7.0 and 27 °C in a phosphate buffer. A new direct calorimetric method was applied to follow the protein denaturation and study the effect of surfactants on the stability of proteins. The extended solvation model was used to represent the enthalpies of lysozyme + SDS interaction over the whole range of SDS concentrations. The solvation parameters recovered from the new equation are attributed to the structural change of lysozyme and its biological activity. At low SDS concentrations, the binding is mainly electrostatic with some simultaneous interaction of the hydrophobic tail with nearby hydrophobic regions of lysozyme. These initial interactions presumably cause some protein unfolding and expose additional hydrophobic sites. The induced enthalpy of denaturation of lysozyme by SDS is 160.81±0.02 kJ⋅mol⁻¹. The lysozyme-DTAB complexes behave very differently from those of the lysozyme-SDS complexes. SDS induces a stronger unfolding of lysozyme than DTAB. The induced enthalpy of lysozyme denaturation by DTAB is 86.46±0.02 kJ⋅mol⁻¹.     

Antioxidant and anti-inflammatory effects of pomegranate peel extracts on bovine mammary epithelial cells BME-UV1

Abstract

Pomegranate peel extracts (PPE) were tested for the first time on BME-UV1, a valid cellular model to study the bovine mammary epithelial metabolism, to evaluate the effects on the oxidative stress and inflammatory status. Based on the statistical analysis of MTT data, PPE at 0.1, 1.0 and 10?μg/mL resulted not cytotoxic after 24?h, 48?h and 7 days of treatment. At the same concentrations, PPE induced a reduction of ROS production elicited by the addition of hydrogen peroxide or lipopolysaccharide evidencing an antioxidant effect confirmed also by a decrease of malondialdehyde. At 10?μg/mL, PPE reduced pro-inflammatory cytokines expressions showing an anti-inflammatory effect on BME-UV1 treated with lipopolysaccharide. Although in vivo experiments are necessary, the results of this study are promising for future applications of PPE as feed supplement for dairy cattle, in particular around calving, when the animals are more subject to oxidative stress and inflammatory diseases.     

Absorption,Fluorescence and Resonance Rayleigh Scattering Spectra of Interaction of Papain with Calf Thymus DNA

In weak acidic medium, interaction between papain and calf thymus DNA (ctDNA) resulted in absorption spectral change, fluorescence quenching of papain and remarkable enhancement of resonance Rayleigh scattering (RRS). The interaction types and binding modes were discussed by characteristics of RRS, absorption, fluorescence and circular dichroism spectra combining thermodynamic data. Four interaction types include electrostatic attraction, hydrophobic force, hydrogen bonding and aromatic stacking interaction. Papain interacted with the major groove of ctDNA. Aromatic stacking interaction is the main reason of change of absorption spectrum and fluorescence quenching of papain. Surface enhanced scattering effect, resonance energy transfer effect, increase of molecular volume and conformational change make contribution to RRS enhancement. The enhanced RRS intensity (ΔI) is directly proportional to the concentration of ctDNA or papain. The detection limit (3σ) is 5.2 ng·mL^?1 for ctDNA and 5.6 ng·mL^?1 for papain. This creates conditions for determination of papain and ctDNA.     

Electrostatic interactions between a protein and oppositely charged micelles

Micellar solutions made of a fully fluorinated surfactant, LiPFN, form water-soluble complexes with lysozyme in a wide concentration range. Such complexes are stabilized by electrostatic and, very presumably, double-layer interactions. The mixtures were investigated by combining electrophoretic mobility, DLS, and dielectric relaxation methods. The former gives information on the surface charge density of protein-micelle complexes and indicates that the resulting adducts retain a negative charge (i.e., charge neutralization is incomplete). The double-layer thickness of proteins, micelles, and protein-micelle complexes is also connected to the dielectric relaxation frequency. Changes in particle size (inferred by DLS), charge density, and double-layer thickness are closely interrelated to each other. A model was developed to quantify such properties.