Unique selectivity windows using selective displacers/eluents and mobile phase modifiers on hydroxyapatite

A detailed study was carried out to combine the unique selectivity of ceramic hydroxyapatite (CHA) with the separation power of selective displacement chromatography. A robotic liquid handling system was employed to carry out a parallel batch screen on a displacer library made up of analogous compounds. By incorporating positively charged, metal chelating and/or hydrogen bonding groups into the design of the displacer, specific interaction sites on CHA were targeted, thus augmenting the selectivity of the separation. The effect of different mobile phase modifiers, such as phosphate, sulfate, lactate and borate, were also investigated. Important functional group moieties and trends for the design of CHA displacers were established. Selective batch separations were achieved between multiple protein pairs which were unable to be resolved using linear gradient techniques, demonstrating the applicability of this technique to multiple protein systems. The specific interaction moieties used on the selective displacer were found to dictate which protein was selectively displaced in the separation, a degree of control not possible using a mono-interaction type resin in displacement chromatography. Mobile phase modifiers were also shown to play a crucial role, augmenting the selectivity of a displacer in a synergistic fashion. Column separations were carried out using selective displacers and mobile phase modifiers identified in the batch experiments, and baseline separation of the previously unresolved protein pairs was achieved. Further, the elution order in these systems was able to be reversed while still maintaining baseline separations. This work establishes a new class of separations which combine the selectivities of multi-modal resins, displacers/eluents, and mobile phase modifiers to create unique selectivity windows unattainable using traditional modes of operation.     

Rhodium(I)‐Catalyzed Enantioselective Activation of Cyclobutanols: Formation of Cyclohexane Derivatives with Quaternary Stereogenic Centers

The activation of carbon–carbon σ bonds is a complementary method to access uncommon and difficult‐to‐prepare organometallic species. Herein, we describe the activation of tert‐cyclobutanols through an enantioselective insertion of a chiral rhodium(I) complex into the C? C σ bond of the cyclobutane, forming a quaternary stereogenic center and an alkyl‐rhodium functionality that initiates ring‐closure reactions. This technology provides access to a variety of substituted cyclohexane derivatives with quaternary stereogenic centers. The formation of different product families can be controlled by the employed set of reaction conditions and additives. In general, high yields and excellent enantioselectivities of up to 99 % ee are obtained.     

Effects of urea induced protein conformational changes on ion exchange chromatographic behavior

Urea is widely employed to facilitate protein separations in ion exchange chromatography at various scales. In this work, five model proteins were used to examine the chromatographic effects of protein conformational changes induced by urea in ion exchange chromatography. Linear gradient experiments were carried out at various urea concentrations and the protein secondary and tertiary structures were evaluated by far UV CD and fluorescence measurements, respectively. The results indicated that chromatographic retention times were well correlated with structural changes and that they were more sensitive to tertiary structural change. Steric Mass Action (SMA) isotherm parameters were also examined and the results indicated that urea induced protein conformational changes could affect both the characteristic charge and equilibrium constants in these systems. Dynamic light scattering analysis of changes in protein size due to urea-induced unfolding indicated that the size of the protein was not correlated with SMA parameter changes. These results indicate that while urea-induced structural changes can have a marked effect on protein chromatographic behavior in IEX, this behavior can be quite complicated and protein specific. These differences in protein behavior may provide insight into how these partially unfolded proteins are interacting with the resin material.     

Emergence of information transmission in a prebiotic RNA reactor

A poorly understood step in the transition from a chemical to a biological world is the emergence of self-replicating molecular systems. We study how a precursor for such a replicator might arise in a hydrothermal RNA reactor, which accumulates longer sequences from unbiased monomer influx and random ligation. In the reactor, intra- and intermolecular base pairing locally protects from random cleavage. By analyzing stochastic simulations, we find temporal sequence correlations that constitute a signature of information transmission, weaker but of the same form as in a true replicator.     

Time-humidity-superposition principle in electrical conductivity spectra of ion-conducting polymers

We analyze the scaling properties of the ac conductivity spectra of ion-conducting polyelectrolyte complexes of different compositions. Spectra were taken at ambient temperature but at different relative humidities. For the first time, we report on a scaling principle for conductivity spectra termed "time-humidity-superposition principle" in analogy with the well-known time-temperature-superposition principle. This model-free scaling holds for different materials over several decades in frequency. It implies that the hydration is activating ion motion over short and long distances in a similar general way, a concept so far only established for thermal energy.     

Zur Analyse der ätherischen Öle

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Über eine quantitative Reaction des Lignins

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