The Experts below are selected from a list of 153 Experts worldwide ranked by ideXlab platform

Daniela Zanchet - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Weight, Osmotic Second Virial Coefficient, and Extinction Coefficient of Colloidal CdSe Nanocrystals
    2014
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet, D. Gerion, D. Milliron, A. P. Alivisatos
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31-45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this short-range potential, shows two-body repulsion or attraction, depending on the sample and on solution conditions

  • molecular weight osmotic second virial coefficient and extinction coefficient of colloidal cdse nanocrystals
    Journal of Physical Chemistry B, 2002
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31−45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this sho...

Alberto Striolo - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Weight, Osmotic Second Virial Coefficient, and Extinction Coefficient of Colloidal CdSe Nanocrystals
    2014
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet, D. Gerion, D. Milliron, A. P. Alivisatos
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31-45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this short-range potential, shows two-body repulsion or attraction, depending on the sample and on solution conditions

  • molecular weight osmotic second virial coefficient and extinction coefficient of colloidal cdse nanocrystals
    Journal of Physical Chemistry B, 2002
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31−45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this sho...

Nikos Hadjichristidis - One of the best experts on this subject based on the ideXlab platform.

  • synthesis of well defined second g 2 and third g 3 generation dendritic polybutadienes
    Macromolecules, 2006
    Co-Authors: Katerina Orfanou, Hermis Iatrou, David J Lohse, Nikos Hadjichristidis
    Abstract:

    A series of well-defined second (G-2) and third (G-3) generation dendritic polybutadienes (PBd) were synthesized by the coupling of the living G-2 and G-3 dendrons with methyltrichlorosilane, using anionic polymerization high-vacuum techniques. The synthetic approach of the living G-2 dendrons involves (a) the synthesis of an in-chain double-bond PBd by selective replacement of the two chlorines of 4-(dichloromethylsilyl)diphenylethylene (DCMSDPE), a novel linking reagent with dual functionality, with PBd by titration with PBdLi, (b) addition of s-BuLi to the double bond, and finally (c) polymerization of butadiene from the newly created anionic site. The synthesis of the G-3 dendrons requires the repetition of the aforementioned procedure with the exception of the addition of the living G-2 dendron, instead of PBdLi, to DCMSDPE. Intermediate and final products were characterized via size exclusion chromatography, Membrane Osmometry, size exclusion chromatography equipped with a two-angle laser light scat...

  • model mono di and tri omega functionalized three arm star polybutadienes synthesis and association in dilute solutions by Membrane Osmometry and static light scattering
    Macromolecules, 1995
    Co-Authors: Marinos Pitsikalis, Nikos Hadjichristidis
    Abstract:

    Three-arm polybutadienes with one, two, and three functional end groups were prepared by anionic polymerization using [3-(dimethylamino)propyl]lithium and sec-butyllithium as initiators and methyltrichlorosilane as linking agent. Characterization carried out on the dimethylamine-capped polymers by SEC, in THF, low-angle laser light scattering (LALLS) in THF, and Membrane Osmometry (MO) in toluene indicates a high degree of molecular and structural homogeneity. The 1,2 content, determined by NMR spectroscopy, of the arms having the functional groups was higher (12-32%) than that of the arms without the functional groups (7-10%), owing to the tertiary amine group of the initiator. The dimethylamine end groups were transformed to the highly polar sulfozwitterionic ones by reaction with cyclopropanesultone. Association of the different ω-functionalized star polybutadienes was studied in dilute solutions of cyclohexane by MO and LALLS. It was found that although the dimethylamine-capped polybutadienes do not associate, the corresponding zwitterionic species associate strongly in this solvent. At fixed molecular weight of the arms, the degree of association increases with decreasing number of functional groups and, for the same number of functional groups, with decreasing molecular weight of the arms. The trifunctional species form gels at concentrations needed for MO experiments. Comparison with linear ω-zwitterionic polybutadienes in cyclohexane shows that the stars associate less strongly, maybe due to the sterically hindered star structure (monofunctional species) and to intramolecular interactions (di- and trifunctional species)

Andrew L Zydney - One of the best experts on this subject based on the ideXlab platform.

  • the osmotic pressure of highly concentrated monoclonal antibody solutions effect of solution conditions
    Biotechnology and Bioengineering, 2014
    Co-Authors: Elaheh Binabaji, Suma Rao, Andrew L Zydney
    Abstract:

    The behavior of monoclonal antibodies at high concentrations is important in downstream processing, drug formulation, and drug delivery. The objective of this study was to evaluate the osmotic pressure of a highly purified monoclonal antibody at concentrations up to 250 g/L over a range of pH and ionic strength, and in the presence of specific excipients, using Membrane Osmometry. Independent measurements of the second virial coefficient were obtained using self-interaction chromatography, and the net protein charge was evaluated using electrophoretic light scattering. The osmotic pressure at pH 5 and low ionic strength was >50 kPa for antibody concentrations above 200 g/L. The second virial coefficients determined from the oncotic pressure (after subtracting the Donnan contribution) were in good qualitative agreement with those determined by self-interaction chromatography. The second virial coefficient decreased with increasing ionic strength and increasing pH due to the reduction in intermolecular electrostatic repulsion. The third virial coefficient was negative under all conditions, suggesting that multi-body interactions in this system are attractive. The virial coefficients were essentially unaffected by addition of sucrose or proline. These results have important implications for the analysis of protein-protein interactions in downstream processing at high protein concentrations.

  • improved method for evaluating the dead volume and protein protein interactions by self interaction chromatography
    Analytical Chemistry, 2013
    Co-Authors: Elaheh Binabaji, Suma Rao, Andrew L Zydney
    Abstract:

    Self-interaction chromatography (SIC) is a well-established method for studying protein-protein interactions. The second virial coefficient in SIC is evaluated directly from the measured retention coefficient for the protein using a column packed with resin on which the same protein has been immobilized on the pore surface. One of the challenges in determining the retention coefficient is the evaluation of the dead volume, which is the retention volume that would be measured for a noninteracting solute with the same effective size as the protein of interest. Previous studies of SIC have used a "dead column" packed with the same resin but without the immobilized protein to evaluate the dead volume, but this creates several experimental and theoretical challenges. We have developed a new approach using a dextran standard with effective size equal to that of the protein (as determined by size exclusion chromatography). The second virial coefficient was evaluated for a monoclonal antibody over a range of buffer conditions using this new approach. The data were in good agreement with independent measurements obtained by Membrane Osmometry under conditions dominated by repulsive interactions. The simplicity and accuracy of this method should facilitate the use of self-interaction chromatography for quantifying protein-protein interactions.

Wolfgang J Parak - One of the best experts on this subject based on the ideXlab platform.

  • Molecular Weight, Osmotic Second Virial Coefficient, and Extinction Coefficient of Colloidal CdSe Nanocrystals
    2014
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet, D. Gerion, D. Milliron, A. P. Alivisatos
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31-45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this short-range potential, shows two-body repulsion or attraction, depending on the sample and on solution conditions

  • molecular weight osmotic second virial coefficient and extinction coefficient of colloidal cdse nanocrystals
    Journal of Physical Chemistry B, 2002
    Co-Authors: Alberto Striolo, J Ward, John M Prausnitz, Wolfgang J Parak, Daniela Zanchet
    Abstract:

    Membrane Osmometry is used to measure osmotic pressures of dilute solutions containing quasispherical CdSe nanocrystals covered with polymer brushes in toluene in the range 31−45 °C. Osmotic-pressure data, as a function of nanocrystal concentration, yield the molecular weight and the osmotic second virial coefficient of the nanocrystals; the latter is related to the potential of mean force between two nanocrystal particles in dilute solution. Coupled with molecular-weight data, extinction coefficients and oscillator strengths are also obtained for nanocrystals of various sizes in toluene. CdSe nanocrystal sizes were obtained either from transmission electron microscopy or from correlations between the wavelength of the absorbing peak and nanocrystal size. Osmotic-pressure data are reduced with a simple perturbed-hard-sphere equation of state; the perturbation is due to long-range (London dispersion) attraction and a short-range interaction potential. The only adjustable parameter, the strength of this sho...