Effective Pore Diffusivity Research Articles

Adsorption equilibrium and kinetics of Immunoglobulin G on a mixed-mode adsorbent in batch and packed bed configuration

It is commonly accepted that efficient protein separation and purification to the desired level of purity is one bottleneck in pharmaceutical industries. MabDirect MM is a new type of mixed mode adsorbent, especially designed to operate in expanded bed adsorption (EBA) mode. In this study, equilibrium and kinetics experiments were carried out for the adsorption of Human Immunoglobulin G (hIgG) protein on this new adsorbent. The effects of ionic strength and pH are assessed. Langmuir isotherms parameters are obtained along with the estimation of the effective pore diffusion coefficient (Dpe) by fitting the batch adsorption kinetics experiments with the pore diffusion model. The maximum adsorption of the IgG protein on the MabDirect MM adsorbent, 149.7±7.1mg·gdry−1, was observed from a pH 5.0 buffer solution without salt addition. Adding salt to the buffer solution, and/or increasing pH, decreases the adsorption capacity which is 4.7±0.4mg·gdry−1 for pH 7.0 with 0.4M NaCl in solution. Regarding the Dpe estimation, a value of 15.4×10−6cm2·min−1 was obtained for a pH 5.0 solution without salt. Increasing the salt concentration and/or the pH value will decrease the effective pore diffusion, the lowest Dpe (0.16×10−6cm2·min−1) value being observed for an IgG solution at pH 7.0 with 0.4M NaCl. Fixed bed experiments were conducted with the purpose to validate the equilibrium and kinetic parameters obtained in batch. For a feed concentration of 0.5 g·L−1 of IgG in pH 5.0 buffer solution with 0.4M NaCl, a dynamic binding capacity at 10% of breakthrough of 5.3mg·gwet−1 (15.4mgIgG·mLresin−1) was obtained, representing 62% of the saturation capacity. As far as the authors know, this study is the first one concerning the adsorption of hIgG on this type of mixed mode chromatography adsorbent.

Insight into effects of pore diffusion on smoldering kinetics of coal using a 4-step chemical reaction model

Pore diffusion plays a crucial role in coal smoldering fires, however, its effects have been inadequately investigated. This paper aims to study influences of pore diffusion of oxygen (O2) on chemical reaction and apparent reaction rate of coal smoldering. Non-isothermal thermogravimetric (TG) tests for two bituminous coal samples at three heating rates (2, 5 and 10 K/min) were conducted, and a 4-step decomposition scheme was constructed. The decomposition schemes contained two competing paths: Coal oxidation → β-Char oxidation → Ash (Path One), and Pyrolysis → α-Char oxidation → Ash (Path Two). A number of kinetic triplets (reaction order, pre-exponential factor and activation energy) and stoichiometric coefficients of the developed decomposition schemes were optimized by a Genetic Algorithm (GA) tool. Emphasis was put on influences of pore diffusion on chemical reactions (e.g. pyrolysis, coal matrix's and chars' oxidation) and on competing paths. Research results show that Knudsen diffusion plays a dominant role in pore diffusion that retards coal oxidation and its successive char oxidation on the Path One, but basically enhances char oxidation on the Path Two. Pore diffusion may exert ignorable influence on pyrolysis as it takes place without O2. The investigation is beneficial for understanding mechanism of smoldering of coal piles and coal dust layers.

Performance of Pt/ZrO2–TiO2–Al2O3 and coke deposition during methylcyclohexane catalytic cracking

Three groups of ZrO2–TiO2–Al2O3 catalysts with and without Pt addition were prepared to comparatively investigate the coke performance during pyrolysis of supercritical methylcyclohexane at 650°C and 4.0MPa. From the data of gas chromatography-mass spectrometer, it was observed that the contents of alkenes in liquid products over Pt-loaded catalysts have higher values than those on pure supports. But for the aromatics, e.g., benzene and toluene, the yields over Pt-loaded samples are obviously less than those on pure supports. It revealed that the addition of Pt to the metal oxides supports prevented the formation of aromatics. With the characterization of XPS and TPO, the coke formed over pure supports was more ordered with a higher dehydrogenation extent than those produced on the Pt-loaded samples. According to our coke formation model, the results of product distribution could be owing to the Pt-loaded catalysts, which restrained the generation and polymerization of coke intermediates. PT3 obtained the best coke inhibition effect, which attributes to the reduced polymerization rate by Pt effect and pore diffusion effect. The acid and pore property have an influence on both the coke amount and the nature of coke, moreover, less amount of coke and easier-oxidized coke were obtained with Pt addition.

On the Initial Rate of Fluid–Solid Reactions

It is argued in this paper that the initial rate should not be used for the measurement or analysis the kinetics of a fluid–solid reaction, especially for a reaction in which the effect of pore diffusion starts appearing even moderately as the reaction proceeds. Even in the absence of external mass transfer effects, it is shown in this work by rigorous mathematical analysis that the range of conditions where the initial rate represents the intrinsic kinetics is very narrow. For an initially non-porous solid in the absence of external mass transfer effects, the very initial rate should mathematically be the intrinsic rate even when pore diffusion becomes important as the reaction proceeds. However, even in this case, the range of conditions for this statement is very limited. For the reaction of an initially porous solid, the rate at time zero is already affected by pore diffusion unless its effect is negligible over the entire range of conversion. Furthermore, the initial reaction rates of porous solids reacting under large values of k/De ratio (chemical reactivity is much greater than the capacity for pore diffusion) have an apparent rate constant of \( \sqrt {k \cdot D_{\text{e}} } \) and thus pore diffusion alone does not control the initial rate no matter how large the effect of pore diffusion is overall.

Adsorption of Human Serum Albumin (HSA) on a mixed-mode adsorbent: equilibrium and kinetics

The adsorption equilibrium and kinetics of Human Serum albumin (HSA) onto a novel high particle density multimodal adsorbent were studied by batch adsorption experiments. MabDirect MM, from Upfront Chromatography A/S, is an agarose-tungsten carbide composite adsorbent with an anionic mixed mode ligand. The effects of ionic strength (by addition of salt) and of pH are assessed. Langmuir isotherms parameters are obtained along with pore diffusivity values by fitting the batch experiments using a pore diffusion model. Under the studied conditions for pH 5.0, without salt, it was obtained the largest adsorption capacity (36.0 ± 3.5 mg·gadsorbent,dry −1) a typical behavior for a mixed mode adsorbent. Effective pore diffusivity (Dpe) was estimated as (2.2 ± 0.1) × 10−6 cm2·min−1 for this condition. Additionally, the lowest adsorption capacity (8.6 ± 2.1 mg·gadsorbent,dry −1) and an estimation of Dpe equal to (2.4 ± 0.6) × 10−6 cm2·min−1 were obtained for pH 7.0 without salt. An alternative method of Dpe estimation is used and validate the results obtained by simulations. Furthermore, several experiments were carried out in a fixed bed column with the aim to understand the kinetics and hydrodynamics, and to validate the batch adsorption results. For a feed concentration of ±0.92 g·L−1, pH 5.0, without salt, for cleaned and fresh adsorbent, fixed bed dynamic binding capacities of 13.84 and 14.37 mg·gadsorbent,dry −1 were obtained, respectively, representing near 50% of saturation capacity.

Adsorption behavior of levulinic acid onto microporous hyper-cross-linked polymers in aqueous solution: Equilibrium, thermodynamic, kinetic simulation and fixed-bed column studies

The recovery of levulinic acid (LA) from aqueous solution and actual biomass hydrolysate by a microporous hyper-cross-linked polymer, SY-01, was investigated for the first time under batch and fixed-bed column conditions. The results showed that the optimum pH should be in the acidic range (pH < 3.0) without adjusting the pH. In the single-component system equilibrium study, the Langmuir isotherm model fits the LA adsorption onto SY-01 resin better than the Freundlich isotherm model, indicating that LA adsorption onto SY-01 resin under the concentration range studied is a monolayer homogeneous adsorption process. The maximum adsorption capacity of LA onto SY-01 resin decreased with increasing temperature, ranging from 103.74 to 95.70 mg/g. The obtained thermodynamic parameters suggested that the adsorption of LA on SY-01 was spontaneous (ΔG0<−3.788 kJ/mol), and exothermic (ΔH0 = −11.764 kJ/mol). For kinetic study, the adsorption of LA onto SY-01 resin at various operating conditions follows the pore diffusion model and the intraparticle diffusion is the rate-limiting step for the adsorption of LA onto SY-01 resin. The effective pore diffusivity was dependent upon temperature, but independent of initial LA concentration, and were 3.306 × 10−10, 5.274 × 10−10 and 7.707 × 10−10 m2/s at 298, 318 and 338 K, respectively. In desorption process, the recovery efficiency of LA from SY-01 resin was 99.39%, and LA concentration in the eluent was raised 2.97-fold. In conclusion, our results show that the SY-01 resin has potential application in product recovery of LA from biomass hydrolysate.

A simplified technique to determine intraparticle diffusivity of macro-reticular resins

Abstract Both resins and activated carbons are commonly used as adsorbents in water and wastewater treatment. In general, intraparticle diffusion mechanisms within macro reticular resin particles (such as XAD-2000) are different from those in activated carbon particles. Currently, completely mixed batch reactor (CMBR) technique can be used to determine the intraparticle diffusivity for phenolic compounds adsorbed onto activated carbon systems. However, the technology cannot determine the intraparticle diffusivity accurately if the fluid-film resistance is significant, such as synthetic macro-reticular resins. Therefore, this study develops a technique to determine the intraparticle diffusivities of XAD-2000 resin. This paper characterized the concentration decay curves of para-nitrophenol in CMBR to determine effective pore diffusivity (D P ) of the resin. The obtained mean and standard deviation of D P are about 1.1 × 10 −5 and 3.2 × 10 −6 (cm 2 s −1 ), respectively. The technology developed in this study has the advantages of significant chemical saving and easy operation.

Adsorption rate of Reactive Black 5 on chitosan based materials: geometry and swelling effects

The overall adsorption rate of Reactive Black 5 dye (RB5) on chitosan based materials was elucidated using diffusional models. Fundamental aspects, such as, geometry of the adsorbents and swelling effects were considered. Chitosan based materials (powder and film) were prepared from shrimp wastes and characterized regarding to the fundamental features for adsorption. Experimental decay curves were obtained under different conditions of stirring rate and initial dye concentration. The data were modeled according to the external mass transfer and diffusional models. The kL (external mass transfer coefficient), Dep (effective pore diffusion coefficient) and Ds (surface diffusion coefficient) values were estimated. For both adsorbents, it was found that the surface diffusion was the intraparticle diffusion mechanism governing the adsorption rate of RB5, since its contribution was higher than 92 % regardless the position and time. The Ds values ranged from 2.85 × 10−11 to 5.78 × 10−11 for chitosan powder and from 4.15 × 10−11 to 12.12 × 10−11 cm2 s−1 for chitosan films. The RB5 adsorption was faster when chitosan powder was used, mainly at higher stirring rates and initial dye concentrations. The swelling effect was most pronounced for the chitosan films, where, provided an increase of about 65 times in the Ds value.

Poly(glycidyl methacrylate)-grafted hydrophobic charge-induction agarose resins with 5-aminobenzimidazole as a functional ligand.

Hydrophobic charge-induction chromatography is a new technology for antibody purification. To improve antibody adsorption capacity of hydrophobic charge-induction resins, new poly(glycidyl methacrylate)-grafted hydrophobic charge-induction resins with 5-aminobenzimidazole as a functional ligand were prepared. Adsorption isotherms, kinetics, and dynamic binding behaviors of the poly(glycidyl methacrylate)-grafted resins prepared were investigated using human immunoglobulin G as a model protein, and the effects of ligand density were discussed. At the moderate ligand density of 330 μmol/g, the saturated adsorption capacity and equilibrium constant reached the maximum of 140 mg/g and 25 mL/mg, respectively, which were both much higher than that of non-grafted resin with same ligand. In addition, effective pore diffusivity and dynamic binding capacity of human immunoglobulin G onto the poly(glycidyl methacrylate)-grafted resins also reached the maximum at the moderate ligand density of 330 μmol/g. Dynamic binding capacity at 10% breakthrough was as high as 76.3 mg/g when the linear velocity was 300 cm/h. The results indicated that the suitable polymer grafting combined with the control of ligand density would be a powerful tool to improve protein adsorption of resins, and new poly(glycidyl methacrylate)-grafted hydrophobic charge-induction resins have a promising potential for antibody purification applications.

The role of pore diffusion in determining NH3 SCR active sites over Cu/SAPO-34 catalysts

Cu/SAPO-34 catalysts have been extensively investigated recently for NOx selective catalytic reduction (SCR) reactions. Due to the small pore size (4.3Å) of the zeolites, it is a natural concern that the reaction rates might be dictated by the pore diffusion regime rather than the intrinsic kinetics. In this work, a series of Cu/SAPO-34 catalysts, with identical Cu ion active site loadings but varying zeolite particle sizes (1–9μm), were evaluated. A variety of characterization techniques (XRD, BET, H2 TPR, and NH3 TPD) have confirmed that the same copper species and surface chemistry existed in these samples despite the different SAPO-34 particle sizes. While the Thiele modules governing the pore diffusion effects were vastly different, up to nine times, these samples shared a similar turnover frequency (TOF) and apparent activation energy (44.8±3.0kJ/mol) for the NH3 SCR reaction. These results unequivocally conclude that under the representative SCR reaction conditions investigated in this work, the reaction rates on Cu/SAPO-34 powder catalysts are kinetically controlled and pore diffusion plays little role in disguising the intact intrinsic activity per single-site copper.

A novel polymer-grafted hydrophobic charge-induction chromatographic resin for enhancing protein adsorption capacity

Hydrophobic charge-induction chromatography (HCIC) is a developing technology for antibody purification. To enhance the protein adsorption capacity, a novel polymer-grafted HCIC resin was developed, in which the surface-initiated activator generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) was explored as a controlled polymerization technique to reconstruct matrix structure and ligand distribution. Using poly(glycidyl methacrylate, GMA) as grafting polymer and 2-mercapto-1-methyl-imidazole (MMI) as functional ligand, poly(GMA)-grafted HCIC resins were prepared with series of grafting and ligand densities. Adsorption behaviors of human immunoglobulin G (hIgG) on the prepared resins demonstrated the necessity of controlling grafting and ligand density. Saturated adsorption capacity (Qm) and effective pore diffusivity (De) reached the maximum under medium ligand density when the grafting density was kept constant. The highest Qm and De values were found under the highest grafting density, which were 73% and 7.17times higher than the non-grafted resin, respectively. Column breakthrough tests indicated that the dynamic binding capacity of the resin with optimized grafting density and ligand density was up to 34.6mg/g when linear velocity was 300cm/h, which was 86.3% higher than dextran-grafted resin. The resin was then used to separate hIgG from a protein mixture (hIgG/human serum albumin=1:4), high purity (>99%) and recovery (>90%) of hIgG were found with 50-cycle reuses, which verified the selectivity and robustness of G-MMI resin prepared. In general, the surface-initiated AGET ATRP provides a controlled grafting strategy to improve protein binding capacity for chromatographic separation, and new resins developed have great potential in large-scale protein purification applications.

Adsorption of cationic and anionic azo dyes on sepiolite clay: Equilibrium and kinetic studies in batch mode

In the present work, sepiolite clay adsorptive properties were investigated for textile azo dyes in aqueous solution. The clay (78wt.% sepiolite) was characterized in terms of physical, textural, chemical and mineralogical properties. Basic Red 46 and Direct Blue 85 azo dyes were selected as adsorbates. Adsorption equilibrium data were successfully fitted to Freundlich and Langmuir equations. For Basic Red, the maximum adsorption capacities, predicted by the Langmuir model, were 110mg/g (at 25°C) and 310mg/g (at 35°C). The value obtained at 25°C, matched perfectly the cation exchange capacity of the clay. For Direct Blue, the adsorption capacity was 332mg/g. Adsorption equilibrium was also evaluated for Direct Blue dye in a synthetic effluent, containing salt and auxiliary dyeing chemicals. In this mixture, the amount of dye adsorbed by sepiolite decreased, but very considerable values were still reached (106mg/g). Adsorption kinetics was studied and modeled. Homogeneous solid diffusion coefficient and effective pore diffusivities were calculated for both dyes. Sepiolite clay showed to be an advantageous adsorbent in terms of price and versatility, being effective under a wide pH range, for both anionic and cationic dyes. Its use as adsorbent does not require further purification or chemical modifications, which is beneficial for the environment and for the economy of the treatment.

Carbon Dioxide Adsorption in Nanopores of Coconut Shell Chars for Pore Characterization and the Analysis of Adsorption Kinetics

The uptake data of CO2 adsorption at 273 K by coconut shell chars prepared at various carbonization temperatures from 250 to 550°C were used for characterizing pore texture of chars as well as the analysis of CO2 adsorption kinetics. The equilibrium isotherms were used to determine the porous texture of chars, employing the DR equation and GCMC simulation. It was found that all the test chars contain micropores of a size range from 0.8 to 2.2 nm with the pore size distribution becoming wider for char prepared at a higher carbonization temperature. Porous properties of chars, including surface area, total pore volume, and the average pore size, appear to increase with an increasing carbonization temperature. The analysis of CO2 uptake during the transient measurement of isotherms revealed that the kinetics of CO2 adsorption is governed by the internal diffusional transport of the adsorptive molecules. The effective pore diffusivity characterizing this transport process increases with increasing CO2 loading and passes through a maximum at a certain loading. This maximum pore diffusivity shifts to a higher value as the carbonization temperature is increased. A semiempirical equation was developed to correlate the effective pore diffusivity of CO2 with the equilibrium adsorption loading and its predictive capability is satisfactory.

Impact of natural organic matter properties on the kinetics of suspended ion exchange process

Removal kinetics of four standard organic matter isolates under the application of strongly basic ion exchange resins (IEX) in suspended mode was studied under commercial application conditions. Suwannee River natural organic matter (SRNOM), SR fulvic acid (SRFA), and Pony Lake fulvic acid (PLFA) were greatly removed (>90%) and highly preferred by IEX resins (α > 5, over Cl−, and HCO3−) while SR humic acid (SRHA) was the least preferred organic structure among the four isolates studied (α ≈ 1). Moreover, the efficacy of removal for fulvic acids (i.e., SRFA, PLFA) was consistent over consecutive reuse of IEX resins (i.e., loading cycles) whereas it decreased for SRNOM and SRHA over the course of operation. The stoichiometric correlation between the chloride released from the resins as a result of organic molecules uptake indicated that ion exchange was the dominant mechanism. Results obtained indicated that molecular weight and charge density of isolates played a major role in the performance of ion exchange process for organic matter removal. Furthermore, various empirical and physical models were evaluated using the experimental data and pore diffusion was found to be the rate-liming step during the uptake of organic matters; hence, it was used as the appropriate model to predict the kinetics of removal. Consequently, free liquid diffusivities and effective pore diffusion coefficients of organic molecules were estimated and findings were in agreement with the literature data that were obtained from spectrophotometric methods.

Protein adsorption to poly(ethylenimine)-modified Sepharose FF: V. Complicated effects of counterions

In the previous studies on protein adsorption to poly(ethylenimine) (PEI)-grafted Sepharose FF resins, a critical ionic capacity (600mmol/L) of PEI-Sepharose resins was found for the adsorption of bovine serum albumin (BSA), above which both protein capacity and uptake rate increased drastically. In this work, the influence of counterions on the PEI-Sepharose resin with an ionic capacity of 683mmol/L (FF-PEI-L680) was investigated with sodium salts of SCN−, Cl−, HPO42− and SO42−. Linear gradient elution, batch adsorption and breakthrough experiments showed that counterion preference, effective pore diffusion coefficient (De) and dynamic binding capacity (DBC) values increased in the order of SCN−, Cl−, HPO42− and SO42−, while static adsorption capacity decreased in this order. It is considered that higher counterion preference of the ion exchange groups resulted in lower protein binding strength and adsorption capacity, while the De value increased due to the enhanced “chain delivery” effect (a kind of surface diffusion). Besides, the DBC value was mainly dependent on De value. In particular, SO42− was the most favorable counterion for the PEI-Sepharose resin, which gave rise to the highest De value (De/D0=1.17, D0 is protein diffusivity in free solution) and DBC value (118mg/mL at a residence time of 2min). Moreover, the effects of counterions on BSA adsorption to DEAE Sepharose FF and Q Sepharose FF, which were non-grafted resins, were also studied for comparisons. It was found that the counterion preferences of the two non-grafted resins were different from each other and also different from that of FF-PEI-L680. The different counterion preferences were attributed to the differences in the ion-exchange ligand chemistries. In addition, the De values for DEAE Sepharose FF and Q Sepharose FF kept unchanged. The low counterion sensitivity of De values could be interpreted as the lack of “chain delivery” effect for the non-grafted resins. The results indicate that protein adsorption and chromatographic performance with PEI-Sepharose can be improved by proper counterions. For the four counterions tested, SO42− was the most favorable for providing the best adsorption and elution outcomes with FF-PEI-L680.

Comparison of two numerical modelling approaches to a field experiment of unsaturated radon transport in a covered uranium mill tailings soil (Lavaugrasse, France)

Uncertainties on the mathematical modelling of radon (222Rn) transport in an unsaturated covered uranium mill tailings (UMT) soil at field scale can have a great impact on the estimation of the average measured radon exhalation rate to the atmosphere at the landfill cover. These uncertainties are usually attributed to the numerical errors from numerical schemes dealing with soil layering, and to inadequate modelling of physical processes at the soil/plant/atmosphere interface and of the soil hydraulic and transport properties, as well as their parameterization. In this work, we demonstrate how to quantify these uncertainties by comparing simulation results from two different numerical models to experimental data of radon exhalation rate and activity concentration in the soil-gas measured in a covered UMT-soil near the landfill site Lavaugrasse (France). The first approach is based on the finite volume compositional (i.e., water, radon, air) transport model TOUGH2/EOS7Rn (Transport Of Unsaturated Groundwater and Heat version 2/Equation Of State 7 for Radon; Saâdi et al., 2014), while the second one is based on the finite difference one-component (i.e., radon) transport model TRACI (Transport de RAdon dans la Couche Insaturée; Ferry et al., 2001). Transient simulations during six months of variable rainfall and atmospheric air pressure showed that the model TRACI usually overestimates both measured radon exhalation rate and concentration. However, setting effective unsaturated pore diffusivities of water, radon and air components in soil-liquid and gas to their physical values in the model EOS7Rn, allowed us to enhance significantly the modelling of these experimental data. Since soil evaporation has been neglected, none of these two models was able to simulate the high radon peaks observed during the dry periods of summer. However, on average, the radon exhalation rate calculated by EOS7Rn was 34% less than that was calculated by TRACI, and much closer to the measured one for physically-based soil radon diffusion models. Unlike TRACI, EOS7Rn was able to simulate qualitatively seasonal variations of both radon exhalation and concentration. These results show that EOS7Rn produces less numerical errors than TRACI, and can be considered as a promising model for predicting radon transport in the landfill, if soil evaporation is modelled and its numerical inversion for parameter estimation is realized.

Characterization of immunoglobulin adsorption on dextran-grafted hydrophobic charge-induction resins: Cross-effects of ligand density and pH/salt concentration

Hydrophobic charge-induction chromatography (HCIC) is a promising technology for antibody purification. New HCIC resins MMI-B-XL with dextran-grafted agarose gel as the matrix and 2-mercapto-1-methyl-imidazole (MMI) as the functional ligand were prepared with different ligand densities. The adsorption behaviors (static adsorption equilibrium and adsorption kinetics) of human immunoglobulin G (hIgG) on series of MMI-B-XL resins at varying pHs and salt concentrations were investigated. The cross-effects of solid phase property (ligand density) and liquid phase conditions (pH and salt concentration) were focused. The results showed that the new resins had typical pH-dependent and salt-tolerant characteristics for hIgG adsorption, but differences were found for the resins with different ligand densities. For MMI-B-XL resins with higher ligand density, an obvious higher saturated adsorption capacity (Qm) and effective pore diffusivity (De) could be obtained, which were less affected at pH 7.0∼8.9 but dropped drastically at pH 5.0. Salt addition had less influence on protein adsorption onto MMI-B-XL with higher ligand density. Qm and De both reached minimum values at 0.2mol/L NaCl for all MMI-B-XL resins tested. The results of dynamic binding in the column demonstrated that MMI-B-XL with higher ligand density had better performance for hIgG adsorption, especially under high linear velocities. The mechanism of the cross-effects of ligand density and pH/salt concentration on IgG adsorption was discussed, which provides new insights into protein adsorption and mass transport for dextran-grafted HCIC resins.

The enantioselective hydrogenation of (E)-α-phenylcinnamic acid: Role of TiO2 coated on Al2O3 as a novel support for cinchonidine-modified Pd catalysts

The TiO2-coated Al2O3 composites with various TiO2 wt.% loadings were synthesized by the sol–gel method and were used as supports for the Pd-based catalysts to evaluate the enantiomeric excess (ee) of the hydrogenation of (E)-α-phenylcinnamic acid. The physicochemical properties of the composites and the Pd-based catalysts were characterized. The results reveal the strong influence of the TiO2 wt.% loading on the ee value, which is attributed to the effect of pore diffusion. The 5%TiO2/Al2O3 support, which can diminish most of small mesopores in Al2O3 template while remain most of large mesopores, exhibits the highest ee. Our results demonstrate the promising application of mixed oxides as novel supports to improve ee values of the asymmetric hydrogenation of unsaturated prochiral compounds.

The quantitative impact of the mesopore size on the mass transfer mechanism of the new 1.9 μm fully porous Titan-C18 particles II – Analysis of biomolecules

The kinetic performances of 3.0×100mm columns packed with 1.9μm Titan-C18 particles with average mesopore sizes of 80Å and 120Å were investigated quantitatively for the analysis of biomolecules. Large mesopores are expected to speed up the rate of diffusivity of high-molecular-weight compounds across the stationary phase and to generate higher plate counts at high velocities. The mass transfer mechanism of bradykinin acetate salt (1060Da) and insulin (5733Da) was determined over a range of flow rates from 0.025 to 1.0mL/min. The pore diffusivities of these two biomolecules were accurately measured from the peak parking method.Even though the gain in column efficiency was not found significant for small molecules such as valerophenone (162Da), enlarging the average pore size from 80 to 120Å induces a measurable diminution of the reduced plate height, h, of bradykinin (from 17 to 11 or −35% at a reduced velocity of 50) and a significant reduction for insulin (from 43 to 12 or −72% at a reduced velocity of 90). Remarkably, while the increase of the column efficiency for bradykinin is consistent with a faster diffusivity of bradykinin across the 120Å Titan-C18 particles, the higher column efficiencies measured for insulin are mostly due to a faster absorption kinetics into the 120Å than that into the 80Å Titan-C18 particles. This result is supported by the fact that the effective pore diffusivity of insulin is even slightly smaller across the 120Å than that across the 80Å 1.9μm Titan-C18 particles.

Toward improving selectivity in affinity chromatography with PEGylated affinity ligands: the performance of PEGylated protein A.

Chemical modification of macromolecular affinity chromatography ligands with polyethylene glycol chains or "PEGylation" can potentially improve selectivity by sterically suppressing non-specific binding interactions without sacrificing binding capacity. For a commercial protein A affinity media and with yeast extract (YE) and fetal bovine serum (FBS) serving as mock contaminants, we found that the ligand accounted for more than 90% of the media-associated non-specific binding, demonstrating an opportunity for improvement. The IgG static binding affinity of protein A mono-PEGylated with 5.0 and 20.7 kDa poly(ethylene glycol) chains was found to be preserved using a biomolecular interaction screening platform. Similar in situ PEGylations of the commercial protein A media were conducted and the modified media was functionally characterized with IgG solutions spiked with YE and FBS. Ligand PEGylation reduced the mass of media-associated contaminants by a factor of two to three or more. Curiously, we also found an increase of up to 15% in the average recovery of IgG on elution after PEGylation. Combined, these effects produced an order of magnitude increase in the IgG selectivity on average when spiked with YE and a two- to three-fold increase when spiked with FBS relative to the commercial media. Dynamic binding capacity and mass-transfer resistance measurements revealed a reduction in dynamic capacity attributed to a decrease in IgG effective pore diffusivity and possibly slower IgG association kinetics for the PEGylated protein A ligands. Ligand PEGylation is a viable approach to improving selectivity in affinity chromatography with macromolecular ligands.