Interaction of dissolved proteins with spherical polyelectrolyte brushes

We consider the adsorption of bovine serum albumin (BSA) on spherical polyelectrolyte brushes (SPB). The SPB consist of a solid polystyrene core of 100nm diameter onto which linear polyelectrolyte chains (poly(acrylic acid), (PAA)) are grafted. The adsorption of BSA is studied at a pH of 6.1 at different concentrations of added salt and buffer (MES). We observe strong adsorption of BSA onto the SPB despite the effect that the particles as well as the dissolved BSA are charged negatively. The adsorption of BSA is strongest at low salt concentration and decreases drastically with increasing amounts of added salt. The adsorbed protein can be washed out again by raising the ionic strength. The various driving forces for the adsorption are discussed. It is demonstrated that the main driving force is located in the electrostatic interaction of the protein with the brush layer of the particles. All data show that the SPB present a new class of carrier particles whose interaction with proteins can be tuned in a well-defined manner.     

Preparation of Au/Ag multilayers via layer-by-layer self-assembly in spherical polyelectrolyte brushes and their catalytic activity

Spherical polyelectrolyte brushes(SPBs) consisting of polystyrene(PS) core and poly(2-aminoethyl methacrylate hydrochloride)(PAEMH) shell were prepared by photo-emulsion polymerization. Au nanoparticles(Au-NPs) with controlled size and size distribution were synthesized in situ using SPBs as nanoreactors. Via layer-by-layer deposition technique on the surface of SPBs, nano-composite particles with Au/Ag-NPs bilayer and Au/Ag/Au-NPs trilayer were prepared. The structures of the as-prepared Au/Ag multilayer SPBs were characterized by UV-Vis spectroscopy, TEM, ICP-AES and DLS. The charge reversal of the nano-composite particles observed by zeta potential confirmed the success of layer-by-layer assembly. The Au/Ag-NPs bilayer nano-composite particles showed high catalytic efficiency with an apparent activation energy of about 41.2 k J/mol in the reduction reaction of 4-nitrophenol to 4-aminophenol in the existence of sodium borohydride monitored. The catalytic activity of Au/Ag-NPs multilayer SPBs close to that of Au-NPs SPBs and much higher than that of Ag-NPs SPBs reveals its potential applications in cost-effective catalysts with high-performance.     

Distribution of magnetic nanoparticles in spherical polyelectrolyte brushes as observed by small-angle X-ray scattering

Magnetic nanoparticles (MNPs) with a size of about 2 nm are prepared in nanoreactors of spherical polyelectrolyte brushes (SPBs) consisting of a solid polystyrene (PS) core and a shell of linear poly(acrylic acid) (PAA) chains densely grafted onto the core by one end. The synthesized MNP are strongly adhered to PAA chains due to the intense interaction of chemical coordination with the carboxyl groups. The generation of MNP in SPB layer is legibly revealed by small-angle X-ray scattering (SAXS) due to the significant increase in electron density. The radial distribution of MNP in SPB is built by fitting SAXS data. Most of MNP are found to locate nearby the surface of PS core. Compared to dynamic light scattering and transmission electron microscopy, SAXS can observe the generation and distribution of MNP in SPB as well as the changes upon changing pH and salt concentration in real time. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1681–1688     

A theoretical investigation on the pH-induced switching of mixed polyelectrolyte brushes

A theoretical investigation on the pH-induced switching of mixed polyelectrolyte brushes was performed by using a molecular theory. The results indicate that the switching properties of mixed polyelectrolyte brushes are dependent on the pH values. At low pH, negatively charged chains adopt a compact conformation on the bottom of the brush while positively charged chains are highly stretched away from the surface. At high pH values, the inverse transformation takes place. The role of pH determining the polymer chains conformation and charge behavior of mixed polyelectrolyte brushes was analyzed. It is found that there exists a mechanism for reducing strong electrostatic repulsions： stretching of the chains. The H＋ and OH- units play a more important role as counterions of the charged polymers do. The collapse of the polyelectrolyte chains for different pH values could be attributed to the screening of the electrostatic interactions and the counterion-mediated attractive interaction along the chains.     

Monomer volume fraction profiles in pH responsive planar polyelectrolyte brushes

Spatial dependencies of monomer volume fraction profiles of pH responsive polyelectrolyte brushes were investigated using field theories and neutron reflectivity experiments. In particular, planar polyelectrolyte brushes in good solvent were studied and direct comparisons between predictions of the theories and experimental measurements are presented. The comparisons between the theories and the experimental data reveal that solvent entropy and ion‐pairs resulting from adsorption of counterions from the added salt play key roles in affecting the monomer distribution and must be taken into account in modeling polyelectrolyte brushes. Furthermore, the utility of this physics‐based approach based on these theories for the prediction and interpretation of neutron reflectivity profiles in the context of pH responsive planar polyelectrolyte brushes such as polybasic poly(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA) and polyacidic poly(methacrylic acid) (PMAA) brushes is demonstrated. The approach provides a quantitative way of estimating molecular weights of the polymers polymerized using surface‐initiated atom transfer radical polymerization. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 956–964     

Recent advances in the use of the quartz crystal microbalance with dissipation for the study of the collapse of polyelectrolyte brushes

The combination of Quartz Crystal Microbalance and ellipsometry to quantify polyelectrolyte brush hydration and how this impacts on the study of brush collapse is discussed here. Recent articles study collapse after quantifying hydration of poly (2-methacryloyloxy ethyl trimethyl ammonium chloride) (PMETAC) and poly(potassium sulfo propyl methacrylate). Water lost increases with ionic strength but only a 50% of their water content is lost at 1 M NaCl. For PMETAC brushes the exchange of Cl⁻ by ClO₄⁻ is more effective, causing 50% lost at 0.05 M. The hydration and water lost for PMETAC brushes synthesized from thiol monolayers with variable density of initiators from 1 to 100% show that the freely entrapped water of the brushes is around a 10%. Irrespectively of initiator percentage the brush does not lose at 1 M NaCl more than 50% of the original water content. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013, 51, 1068–1072     

A Sharp Thermal Transition of Fast Aromatic‐Ring Dynamics in Ubiquitin

Aromatic amino acid side chains have a rich role within proteins and are often central to their structure and function. Suitable isotopic‐labelling strategies enable studies of sub‐nanosecond aromatic‐ring dynamics using solution NMR relaxation methods. Surprisingly, it was found that the three aromatic side chains in human ubiquitin show a sharp thermal dynamical transition at approximately 312 K. Hydrostatic pressure has little effect on the low‐temperature behavior, but somewhat decreases the amplitude of motion in the high‐temperature regime. Therefore, below the transition temperature, ring motion is largely librational. Above this temperature, a complete ring‐rotation process that is fully consistent with a continuous diffusion not requiring the transient creation of a large activated free volume occurs. Molecular dynamics simulations qualitatively corroborate this view and reinforce the notion that the dynamical character of the protein interior has much more liquid‐alkane‐like properties than previously appreciated.     

Surface potential of spherical polyelectrolyte brushes in the presence of trivalent counterions

We consider the ζ-potential and the effective charge of spherical polyelectrolyte brushes (SPBs) in aqueous solution in the presence of trivalent europium ions. The SPB consists of a polystyrene core of ca. 250 nm diameter onto which long chains of the strong polyelectrolyte poly(styrene sulfonate) are grafted (contour length: 82 nm). At low concentration of EuCl₃ the chains are stretched to nearly full length. If the concentration of the trivalent ions is raised, the surface layer of the polyelectrolyte chains collapses. The ζ-potential of the SPB is calculated from the electrophoretic mobilities measured at different concentrations of EuCl₃. At the collapse, ζ decreases by the partial neutralization of the charges by the trivalent ions. The experimental ζ-potential thus obtained agrees with the theoretical surface potential Ψ_theo calculated for the effective shear plane by a variational free energy model of the SPB.     

近红外光谱法研究升温导致的尼龙1010结晶区域的变化

采用近红外光谱技术和二维相关分析法研究尼龙1010膜在升温过程中的结构变化. 为了排除非晶区域酰胺基团的影响, 事先对尼龙1010的样品膜进行了氘代, 并测量了其最终氘代率. 结果证明, 尼龙1010的结晶区域在升温过程中被逐渐破坏, 首先是其主链碳氢结构发生调整, 进一步影响到结合酰胺, 导致氢键作用减弱并最后生成自由胺基.     

Structural Transformation of Bovine Serum Albumin Induced by Dimethyl Sulfoxide and Probed by Fluorescence Correlation Spectroscopy and Additional Methods

Determining the structure of a protein and its transformation under different conditions is key to understanding its activity. The structural stability and activity of proteins in aqueous–organic solvent mixtures, which is an intriguing topic of research in biochemistry, is dependent on the nature of the protein and the properties of the medium. Herein, the effect of a commonly used cosolvent, dimethyl sulfoxide (DMSO), on the structure and conformational dynamics of bovine serum albumin (BSA) protein is studied by fluorescence correlation spectroscopy (FCS) measurements on fluorescein isothiocyanate (FITC)‐labeled BSA. The FCS study reveals a change of the hydrodynamic radius of BSA from 3.7 nm in the native state to 7.0 nm in the presence of 40 % DMSO, which suggests complete unfolding of the protein under these conditions. Fluorescence self‐quenching of FITC has been exploited to understand the conformational dynamics of BSA. The time constant of the conformational dynamics of BSA is found to change from 35 μs in its native state to 50 μs as the protein unfolds with increasing DMSO concentration. The FCS results are corroborated by the near‐UV circular dichroism spectra of the protein, which suggest a loss of its tertiary structure with increasing concentration of DMSO. The intrinsic fluorescence of BSA and the fluorescence response of 1‐anilinonaphthalene‐8‐sulfonic acid, used as a probe molecule, provide information that is consistent with the FCS measurements, except that aggregation of BSA is observed in the presence of 40 % DMSO in the ensemble measurements.     

Nonempirical analysis of nature of catalytic effects in ribonuclease A active site

The physical nature of the catalytic activity exerted by various ribonuclease A active site constituents is analyzed in terms of the differential transition state stabilization approach in which activation barrier changes induced by the molecular environment are expressed by additive components defined in the theory of intermolecular interactions. Electrostatic multipole contributions seem to approximate total catalytic activity well for residues separated by contacts longer than 2.7 Å whereas at shorter distances the remaining exchange and delocalization terms are not negligible. Depending on the reaction step, the same residue may exhibit catalytic or inhibitory activity. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 432–445, 2000     

Infrared spectroscopic and thermal analytical investigations on the polymorphism of N-arylsulphonyl isothioureas

34 compounds containing the SO₂-N-C-N-moiety are investigated by means of infrared spectroscopy and differential scanning calorimetry to study problems of polymorphic species. There are arguments for different crystalline solids of 16 sulphonyl derivatives. The phenomenon of polymorphism can be discussed both in terms of different hydrogen bonding and conformational effects. Although two tautomers are thinkable for the compounds being investigated the sulphonylimino structure is assumed to yield the most stable state.     

A molecular simulation study of the structure and tribology of polymer brushes: Comparison of behavior in theta and good solvents

Implicit solvent Brownian dynamics simulations of the structure and tribology of opposing polymer-brush covered surfaces have been carried out as a function of surface separation and solvent quality. Consistent with experiment, shear forces were found to be greater under theta solvent conditions than in a good solvent at equal relative separations (normalized by the respective height of the brushes in theta and good solvents). Much higher relative compression is required before the onset of significant shear forces in good solvent compared to theta solvent. The dependence of shear force for a given relative separation on solvent quality can be accounted for by differences in interpenetration of the brushes. When compared as a function of absolute surface separation, greater interpenetration and greater shear force are observed at large separations for the brushes in good solvent than in theta solvent, consistent with the greater brush height in good solvent. At shorter separations, corresponding to moderate to high compression, brush-brush interactions result in significant deformation of the brushes. In this regime, greater interpenetration and greater shear forces are observed in theta solvent at a given separation, in qualitative agreement with experiment.     

Molecular Recognition in Glycolaldehyde,the Simplest Sugar: Two Isolated Hydrogen Bonds Win Over One Cooperative Pair

Carbohydrates are used in nature as molecular recognition tools. Understanding their conformational behavior upon aggregation helps in rationalizing the way in which cells and bacteria use sugars to communicate. Here, the simplest α-hydroxy carbonyl compound, glycolaldehyde, was used as a model system. It was shown to form compact polar C₂-symmetric dimers with intermolecular O–H⋅⋅⋅O=C bonds, while sacrificing the corresponding intramolecular hydrogen bonds. Supersonic jet infrared (IR) and Raman spectra combined with high-level quantum chemical calculations provide a consistent picture for the preference over more typical hydrogen bond insertion and addition patterns. Experimental evidence for at least one metastable dimer is presented. A rotational spectroscopy investigation of these dimers is encouraged, also in view of astrophysical searches. The binding motif competition of aldehydic sugars might play a role in chirality recognition phenomena of more complex derivatives in the gas phase.     

Conformation and Counterion Distribution of Polyelectrolyte in Solution as Viewed from Dielectric Approach

Polyelectrolyte solutions are more variable than uncharged macromolecule due to electrical interaction between charged molecules and surrounding counterions.Therefore,the subject of polyelectrolyte solutions has attracted a wide range of interests in both basic and applied research,and has also been extensively explored.However,the understanding of the molecular dynamics and conformation of polyelectrolytes in solution remains to be deepened,and universal consensus on some key issues have not been reached.Many methods have contributed to solving the above problems in different ways,including dielectric relaxation spectroscopy(DRS).In this perspective,we briefly reviewed the his-tory of dielectric spectroscopic research on polyelectrolyte solution,with emphasis on summarizing our efforts.In particular,we expound the characteristics of DRS and its ability to obtain the internal information of the system of interest.Finally,we evaluate the advantages and limita-tions of the dielectric method and discussed future prospects of this field.     

A comparative study of the dehydroxylation process in untreated and hydrazine-deintercalated dickite

A dickite from Tarifa (Spain) was used to study the influence of the intercalation and the later deintercalation of hydrazine on the dehydroxylation process. The dehydroxylation of the untreated dickite occurs through three overlapping endothermic stages whose DTA peaks are centred at 586, 657 and 676°C. These endothermic effects correspond, respectively, to the loss of the inner-surface, the inner hydroxyl groups, and the loss of the water molecules, product of dehydroxylation process, which has been trapped in the framework of the dehydroxylated dickite. The intercalation of hydrazine in the interlayer space of dickite and the later deintercalation affect the dehydroxylation process. It occurs through only two endothermic stages which DTA peaks are centred at 575 and 650°C. The first corresponds to the simultaneous loss of both the inner and the inner-surface hydroxyl groups, whereas the second one is analogous to that at 676°C observed in the DTA curve of untreated dickite. These effects appear shifted to lower temperatures compared to those observed in the untreated dickite.     

A differential scanning calorimetric study on the irreversible thermal unfolding of concanavalin A

A differential scanning calorimetry study on the thermal denaturation of concanavalin A at pH 5.2 where it exists in the dimeric form was carried out. The calorimetric transitions were observed to be irreversible and the transition temperature of the protein increased with increasing scan rate, indicating that the thermal denaturation process is under kinetic control. The thermal unfolding, and its scan rate dependence could be explained according to the kinetic scheme with k as first-order kinetic constant whose change with temperature is given by the Arrhenius equation. Using this model, rate constant as a function of temperature and activation energy of the process have been calculated. The average activation energy of the kinetic process using different approaches is 129±10 kJ mol⁻¹. The differential scanning calorimetric results on transition temperatures and calorimetric enthalpies supported by intrinsic fluorescence indicate that the irreversibility in the calorimetric transitions of concanavalin A includes a combination of post-transition aggregation, chain separation and loss of cofactor.     

Mechanism of generation of photoelastic birefringence in methacrylate polymers for optical devices

We clarified the birefringence properties of poly(methyl methacrylate), poly(ethyl methacrylate), poly(isobutyl methacrylate), poly(cyclohexyl methacrylate), poly(isopropyl methacrylate), and poly(tert‐butyl methacrylate). We demonstrated that the conformational change in polymer molecules that causes orientational birefringence differs from that causing photoelastic birefringence. Orientational birefringence depends mainly on the orientation of the main chains of the methacrylate polymers above T_g. On the other hand, photoelastic birefringence in elastic deformation below T_g depends mainly on the orientation of the side chains while the main chains are scarcely oriented. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2029–2037, 2010