Protein adsorption on novel acrylamido-based polymeric ion exchangers. II. Adsorption rates and column behavior

Uptake kinetics and breakthrough behavior were determined for bovine serum albumin (BSA) and alpha-chymotrypsinogen (alphaCHY) in new polymeric ion-exchange media based on acrylamido monomers. Two anion exchangers and a cation exchanger were investigated. As shown in Part I of this work, the two anion exchangers have different morphologies. The first one, BRX-Q, comprises a low-density gel with a matrix of denser polymeric aggregates. While this material has a very low size-exclusion limit for neutral probes, it exhibits an extremely high binding capacity for BSA. The second anion exchanger, BRX-QP, comprises large open pores but has a very low binding capacity. The cation exchanger, BRX-S, also comprises large open pores but exhibits an intermediate capacity; likely as a result of the presence of smaller pores. Dynamic protein uptake experiments showed that the highest mass transfer rates are obtained with BRX-Q. The apparent diffusivity is also highest for this material and increases substantially as the protein concentration is reduced. For these particles, the external film resistance is dominant at very low protein concentrations. Much lower rates and apparent diffusivities are obtained for BRX-QP. Finally intermediate rates and apparent diffusivities are found with BRX-S. The concentration dependence of the apparent pore diffusivity is much less pronounced in this case. The apparently paradoxical result that mass transfer rates are highest for the material with the smallest neutral-probe size-exclusion limit can be explained in terms of a general conceptual model where parallel pore and adsorbed-phase diffusion paths exist in these particles. In the first case, adsorbed phase diffusion in gel pores is dominant, while in the second transport is dominated by diffusion in a macroporous network. In the third case, both contributions are important. The conceptual model provides an accurate prediction of the breakthrough behavior of columns packed with these media using independently determined rate parameters. Dynamic binding capacities of 80-140 mg/ml were observed for BSA on BRX-Q in ca. 1.5 cm columns operated at 300-900 cm/h in agreement with theoretical predictions.     

On the homology spectral sequence for topological Hochschild homology

Marcel Bökstedt has computed the homotopy type of the topological Hochschild homology of using his definition of topological Hochschild homology for a functor with smash product. Here we show that easy conceptual proofs of his main technical result of are possible in the context of the homotopy theory of -algebras as introduced by Elmendorf, Kriz, Mandell and May. We give algebraic arguments based on naturality properties of the topological Hochschild homology spectral sequence. In the process we demonstrate the utility of the unstable ``lower' notation for the Dyer-Lashof algebra.

     

Laser desorption of DNA oligomers larger than one kilobase from cooled 4-nitrophenol

A unique matrix system consisting mostly of 4-nitrophenol has shown to be very effective for matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of large DNA oligomers when a cooled sample stage was used to prevent the sublimation of this matrix under vacuum. Using this 4-nitrophenol matrix with UV laser desorption, detection of picomole quantities of DNA oligomers containing up to approximately 800 nucleotides was routinely achieved. The effectiveness of this matrix was further demonstrated by the observation of a double-stranded DNA oligomer larger than 1000 base pairs, seen as a denatured single-stranded species, with a molecular ion mass exceeding 300 000 Da. The potential applications of 4-nitrophenol as a matrix for DNA sizing are discussed.     

Synthesis and photochemistry of a new class of photocleavable protein cross-linking reagents

A new series of photocleavable protein cross-linking reagents based on bis(maleimide) derivatives of diaryl disulfides have been synthesised. They have been functionalised with cysteine and transient absorption spectra for the photolysis reaction have been recorded by using the pump-probe technique with a time resolution of 100 femtoseconds. Photolysis of the disulfide bond yields the corresponding thiyl radicals in less than a picosecond. There is a significant amount of geminate recombination, but some of the radicals escape the solvent cage and the quantum yield for photocleavage is 30 % in water.     

Aggregation of iron colloids in estuaries: a heterogeneous kinetics study using continuous mixing of river and sea waters

The kinetics of iron colloid aggregation in estuaries have been simulated with a model estuary in which seawater is continuously pumped into a reservoir initially containing river water. Profiles of colloidal Fe concentration versus salinity produced in this apparatus closely resembled field data for actual estuaries. Synthetic Fe colloids prepared by peptising Fe(OH)₃ with humic acid and phosphate showed very similar kinetic behaviour. Aggregation rate was found to be almost independent of velocity shear rate, implying that most aggregations are induced by brownian interparticle collisions. A heterogeneous kinetic model is proposed to explain the kinetic behaviour of Fe colloids during seawater-induced aggregation. This model describes kinetic behaviour in terms of a log-normal distribution of rate constants characterised by a mean value k and a standard deviation γ. Experiments showed that k is linearly related to the rate constant for salinity increase during mixing. This coupling of salinity changes and aggregation rate leads to Fe-salinity profiles that are nearly independent of the rate of salinity change, but which are dependent on γ.     

SPECTRA AND EXTINCTION COEFFICIENTS OF NEAR-INFRARED ABSORPTION BANDS IN MEMBRANES OF Rhodobacter sphaeroides MUTANTS LACKING LIGHT-HARVESTING AND REACTION CENTER COMPLEXES

Abstract— Membranes from Rhodobacter (formerly Rhodopseudomonas) sphaeroides mutant strains that lack one or more of the bacteriochlorophyll a (BChl)-protein complexes were used to obtain spectra and molar extinction coefficients of the near-IR absorption bands. The strains examined were NF57 which lacks the B875 light-harvesting and reaction center complexes, and M21 which lacks the B800–850light-harvesting complex. The extinction coefficients obtained for the B800, B850 and B875 bands were 226 ± 10, 170 ± 5, and 118 ± 5 m M ^-1cm^-1, respectively, in reasonable agreement with values reported for detergent-isolated complexes (Clayton, R. K. and B. J. Clayton, Proc. Natl. Acad. Sci. USA 78 ,5583–5587, 1981). The results also demonstrated that detergent solubilization altered the spectra, causing a band broadening on the blue side of the B875 and B800 peaks. The data obtained from the analysis of the mutant strains were used for deconvolution of the BChl species in membranes of the wild-type. A short BASIC computer program for performing this deconvolution is included.     

De novo enantioselective syntheses of galacto-sugars and deoxy sugars via the iterative dihydroxylation of dienoate

An efficient route to various sugar lactones has been developed. Key to the overall transformation is the sequential osmium-catalyzed dihydroxylation of 2,4-dienoates. The simplest (one-step/racemic) example of this reaction occurs when the dihydroxylation is performed with aqueous NMO in MeOH. When the first dihydroxylation is performed using the AD-mix procedure, an enantioselective variant results. When a matched AD-mix procedure is used for the second dihydroxylation, an exceedingly diastereo- and enantioselective synthesis of galacto-1,4-lactone results. [Reaction: see text]     

Preparation and characterization of acrylates and polyacrylates having variable fluorine contents and distributions

Five acrylic esters having different fluorine contents and distributions in their side-groups (i.e., CH₂=CHC(O)OR, where R = ? C(CH₃)₂C₆F₄H, ? C(CH₃)₂C₆F₅, ? C(CF₃)₂C₆F₅, ? C(CF₃)₂C₆H₅, and ? C(CH₃)₂C₆H₅) have been prepared from the reactions of the lithium salts of their corresponding alcohols with acryloyl chloride. These monomers are polymerized under identical conditions by the radical initiator AIBN and five polyacrylates were prepared having the structure of ? [ ? CH₂CHC(O)OR? ]_n? . These addition polymers were compared and fully characterized by GPC, VPO, DSC, TGA, NMR, IR, and UV-visible spectroscopies, and they showed potential for practical applications. Significant differences in their thermal stabilities were found with respect to fluorine contents and distributions in these polyacrylates, and the highest stability arises from CF₃ substitutions in the side-chains of the polymers. © 1994 John Wiley & Sons, Inc.     

The hydrogen bonding properties of cytosine: a computational study of cytosine complexed with hydrogen fluoride, water, and ammonia

Density functional theory is used to study the hydrogen bonding pattern in cytosine, which does not contain alternating proton donor and acceptor sites and therefore is unique compared with the other pyrimidines. Complexes between various small molecules (HF, H(2)O, and NH(3)) and four main binding sites in (neutral and (N1) anionic) cytosine are considered. Two complexes (O2(N1) and N3(N4)) involve neighboring cytosine proton acceptor and donor sites, which leads to cooperative interactions and bidendate hydrogen bonds. The third (less stable) complex (N4) involves a single cytosine donor. The final (O2-N3) complex involves two cytosine proton acceptors, which leads to an anticooperative hydrogen bonding pattern for H(2)O and NH(3). On the neutral surface, the anticooperative O2-N3 complex is less stable than those involving bidentate hydrogen bonds, and the H(2)O complex cannot be characterized when diffuse functions are included in the (6-31G(d,p)) basis set. On the contrary, the anionic O2-N3 structure is the most stable complex, while the HF and H(2)O N3(N4) complexes cannot be characterized with diffuse functions. B3LYP and MP2 potential energy surface scans are used to consider the relationship between the water N3(N4) and O2-N3 complexes. These calculations reveal that diffuse functions reduce the conversion barrier between the two complexes on both the neutral and anionic surfaces, where the reduction leads to a (O2-N3) energy plateau on the neutral surface and complete (N3(N4)) complex destabilization on the anionic surface. From these complexes, the effects of hydrogen bonds on the (N1) acidity of cytosine are determined, and it is found that the trends in the effects of hydrogen bonds on the (N1) acidity are similar for all pyrimidines.