Secondary deuterium kinetic isotope effects in irreversible additions of allyl reagents to benzaldehyde

The competitive kinetics of additions of allyl to benzaldehyde-h and -d from allyltributyl tin, from diisopropyltartrylallyl boronate, and from allyl bromide and zinc dust in aqueous tetrahydrofuran have inverse secondary deuterium kinetic isotope effects, SDKIEs. These inverse SDKIEs are in contrast to the normal SDKIEs that were obtained with allyl lithium and allyl Grignard, suggesting rate-determining single-electron transfer in these cases. By various MO calculations the transition state for addition of allyl boronate occurs with substantial B-O bond formation and little C-C bond formation. The magnitudes of the SDKIEs with the other two allylating reagents, when compared with reasonable equilibrium isotope effects for the addition, suggest transition states with substantial C-C bond formation.     

Automated multi-attribute method sample preparation using high-throughput buffer exchange tips

Rationale

The multi-attribute method (MAM) has become a valuable mass spectrometry (MS)-based tool that can identify and quantify the site-specific product attributes and purity information for biotherapeutics such as monoclonal antibodies (mAbs) and fusion molecules in recent years. As we expand the use of the MAM at various stages of drug development, it is critical to enhance the sample preparation throughput without additional chemical modifications and variability.

Methods

In this study, a fully automated MAM sample preparation protocol is presented, where rapid desalting in less than 15 minutes is achieved using miniaturized size-exclusion chromatography columns in pipette tips on an automated liquid handler. The peptide samples were analyzed using an electrospray ionization (ESI) orbitrap mass spectrometer coupled to an ultra-high-performance liquid chromatography (UHPLC) system with a dual column switching system.

Results

No significant change was observed in product attributes and their quantities compared with manual, low-artifact sample preparation. The sample recovery using the buffer exchange tips was greatly enhanced over the manual spin cartridges while still demonstrating excellent reproducibility for a wide variety of starting sample concentrations. Unlike a plate desalting system, the individual columns provide flexibility in the number of samples prepared at a time and sample locations within plates.

Conclusions

This automated protocol enables the preparation of up to 96 samples with less “at-bench” time than the manual preparation of a smaller batch of samples, thereby greatly facilitating support of process development and the use of the MAM in quality control.

     

Excess enthalpy and entropy of aqueous tetramethylguanidinium methanesulfonate and trifluoromethanesulfonate solutions

Relative apparent molal heat contents, φ_L, are reported for the tetramethylguanidinium salts of methanesulfonic (MS) and trifluoromethanesulfonic (TFMS) acids. Relative partial molal heat contents, L?₂, are calculated and combined with previously reported activity coefficient data, to yield excess entropies. It is found that the values of L?₂ make the principal contribution to the excess entropies of Me₄GuMS solutions while the excess free energies, as calculated from activity coefficients, make the greatest contribution to the excess entropies of Me₄GuTFMS solutions.     

Characterization of anthocyanin extracts from maize kernels

The aim of the present work is to characterize the pigments present in the kernel of four native maize varieties related to the races Arrocillo, Cónico, Peruano, and Purepecha to determine their possible use as natural dyes. Total anthocyanin content is determined by a conventional spectrophotometric method, and anthocyanin analysis is done by high-performance liquid chromatography. The stability of the pigment at pH is also evaluated. The four maize samples contained anthocyanin in both the pericarp and aleurone layer. Total anthocyanin content among samples ranged from 54 mg/100 g of sample to 115 mg/100 g of sample. Anthocyanin profiles are almost the same among the four samples. Differences are observed only in the relative percentage of each anthocyanin. The anthocyanins identified are cyanidin-3-glucoside, pelargonidin- 3-glucoside, peonidin-3-glucoside, cyanidin-3-(6" malonylglucoside), and cyanidin-3-(3",6"-dimalonylglucoside). Anthocyanin extracts showed similar behavior in solutions with different pH. From pH 1-6 lambdamax values are maintained almost constant; however, above this pH value, a marked increase is observed in the bathochromic shifts, but the bluish color did not continue to change above pH 8.     

Sequestering of Eu(III) by a GAAA RNA tetraloop

The site-specific binding of metal ions maintains an important role in the structure, thermal stability, and function of folded RNA structures. RNA tetraloops of the "GNRA" family (where N = any base and R = any purine), which owe their unusual stability to base stacking and an extensive hydrogen bonding network, have been observed to bind metal ions having different chemical and geometric properties. We have used laser-induced lanthanide luminescence and isothermal titration calorimetry (ITC) to examine the metal-binding properties of an RNA stem loop of the GNRA family. Previous research has shown that a single Eu(III) ion binds the stem loop fragment in a highly dehydrated site with a K(d) of approximately 12 microM. Curve-fitting analysis of the broad luminescence excitation spectrum of Eu(III) upon complexation with the tetraloop fragment indicates the possibility of two microenvironments that do not differ in hydration number. Binding of Eu(III) to the loop was accompanied by positive enthalpic changes, consistent with energetic cost of removal of water molecules and suggesting that the binding is entropically driven. By comparison, binding of Mg(II) or Mn(II) to the RNA loop, or Eu(III) to the DNA analogue of the loop, was associated with exothermic changes, consistent with predominantly outer-sphere coordination. These results suggest specific binding, most probably involving ligands on the 5' side of the loop.     

Composition-controlled synthesis of bimetallic gold-silver nanoparticles

This paper reports findings of an investigation of the synthesis of monolayer-capped binary gold-silver (AuAg) bimetallic nanoparticles that is aimed at understanding the control factors governing the formation of the bimetallic compositions. The synthesis of alkanethiolate-capped AuAg nanoparticles was carried out using two related synthetic protocols using aqueous sodium borohydride as a reducing agent. One involves a two-phase reduction of AuCl(4)(-), which is dissolved in organic solution, and Ag(+), which is dissolved in aqueous solution. The other protocol involves a two-phase reduction of AuCl(4)(-) and AgBr(2)(-), both of which are dissolved in the same organic solution. AuAg nanoparticles of 2-3 nm core sizes with different compositions in the range of 0-100% Au have been synthesized. The two synthetic routes were compared in terms of bimetallic composition and size properties. Our new findings have allowed us to establish the correlation between synthetic feeding of metals and metal compositions in the bimetallic nanoparticles, which have important implications to the exploration of gold-based bimetallic nanoparticles for constructing sensing and catalytic nanomaterials.     

An experimental study of the effects of three-dimensionality on the near wall turbulence structures using flow visualization

The effects of three-dimensionality on the turbulence producing near-wall structures over a rotating disk are examined using hydrogen bubble visualization. Laser Doppler anemometry measurements of the tangential and radial velocities indicate the flow to resemble that of an infinite disk. It was found that the crossflow acts to reduce vertical mixing during the turbulence ejection events, thus reducing the efficiency of the boundary layer in producing shear stress.This research has been sponsored by the Department of Energy Office of Basic Energy Sciences through Grants DE-FG03-86ER13608 and DE-FG03-93ER12309.     

Chiral environments for asymmetric hydrogenation of model didehydro-amino acid residues

Dedicated to Professor John C. Sheehan on the occasion of his sixty-fifth birthday Nmr and glc analysis of diastereoisomeric mixtures of dipeptides has been used to study the asymmetric hydrogenation of model benzoyldidehydro- and trifluoroacetyldidehydro-dipeptide methyl esters. Chiral enhancement of one isomeric form appears to be independent of the N-terminal acyl group, but is significantly influenced by the choice of amino-acid in the C-terminal position. C-Terminal aromatic amino-acids and their derivatives give the best chiral enhancement during hydrogenation of a neighbouring dehydroamino-acid residue.     

Single-run analysis of retinal isomers, retinol and photooxidation products by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) procedure was developed to allow the rapid separation, in a single run, of a mixture of the main retinal isomers (all-trans, 13-cis, 9-cis), all-trans-retinol, and of the two major photooxygenated photoproducts (5,8-peroxyretinal and 5,6-epoxyretinal). The mixture was separated by HPLC on an octadecyl (ODS) column with 16% (v/v) diethyl ether in hexane as mobile phase and anthracene as the internal standard. A commercial type cosmetic formulation containing 0.05% all-trans-retinal was analyzed successfully for this analyte.     

Slurry sampling for graphite furnace atomic absorption spectrometry

Summary Slurry preparations are an effective way to introduce solids into the graphite furnace. Ultrasonic agitation keeps samples mixed prior to analysis. Several aspects of the ultrasonic slurry sampling approach are discussed including contamination concerns, analyte partitioning, and the effect of particle size. In addition, sample preparation strategies for slurry preparations of non-powdered materials are reviewed. The suitability of this method for assessing homogeneity is demonstrated.