Modular assembly of a preorganised, ditopic receptor for dicarboxylates

Two types of calix[4]arene derived hosts for anions with, respectively, 1,3-alternate and cone conformations have been prepared; the 1,3-alternate system binds dicarboxylate anions in a ditopic manner while the cone compounds are deprotonated by carboxylates.     

The errors of our ways: taking account of error in computer-aided drug design to build confidence intervals for our next 25 years

The future of the advancement as well as the reputation of computer-aided drug design will be guided by a more thorough understanding of the domain of applicability of our methods and the errors and confidence intervals of their results. The implications of error in current force fields applied to drug design are given are given as an example. Even as our science advances and our hardware become increasingly more capable, our software will be perhaps the most important aspect in this realization. Some recommendations for the future are provided. Education of users is essential for proper use and interpretation of computational results in the future.     

Photokinetic,Biochemical and Structural Features of Chimeric Photoactive Yellow Protein Constructs

Of the 10 photoactive yellow protein (PYPs) that have been characterized, the two from Rhodobacter species are the only ones that have an additional intermediate spectral form in the resting state (λ_max = 375 nm), compared to the prototypical Halorhodospira halophila PYP. We have constructed three chimeric PYP proteins by replacing the first 21 residues from the N‐terminus (Hyb1PYP), 10 from the β4–β5 loop (Hyb2PYP) and both (Hyb3PYP) in Hhal PYP with those from Rb. capsulatus PYP. The N‐terminal chimera behaves both spectrally and kinetically like Hhal PYP, indicating that the Rcaps N‐terminus folds against the core of Hhal PYP. A small fraction shows dimerization and slower recovery, possibly due to interaction at the N‐termini. The loop chimera has a small amount of the intermediate spectral form and a photocycle that is 20 000 times slower than Hhal PYP. The third chimera, with both regions exchanged, resembles Rcaps PYP with a significant amount of intermediate spectral form (λ_max = 380 nm), but has even slower kinetics. The effects are not strictly additive in the double chimera, suggesting that what perturbs one site, affects the other as well. These chimeras suggest that the intermediate spectral form has its origins in overall protein stability and solvent exposure.     

Separation of Natural Food Pigments in Saponified and Un-Saponified Paprika Oleoresin by Ultra High Performance Supercritical Fluid Chromatography (UHPSFC)

The natural pigments in paprika were rapidly and efficiently separated by ultra high performance supercritical fluid chromatography. The separation of both un-saponified and saponified mixtures of paprika oleoresin were optimized, with run times of 10.6 min. Three different C18 columns, a cyano, silica and diol column, all 3 × 100 mm, with 1.8 μm particles were compared. The best separation for the un-saponified sample was found with an SB-C18 column, while the saponified samples were best separated on a bare silica, RX-Sil column. A SB-CN column allowed near optimum separation of both the unsaponified, and saponified samples, with similar run times. The best mobile phase was carbon dioxide (CO₂) modified with isopropyl alcohol (IPA), with a composition gradient. Fingerprints of several commercial pepper products indicated that one appeared to be colored with artificial dyes, while the color of a chili powder may have been enhanced with a paprika extract. Spectra, using CO₂ with IPA as modifier, produced a single maximum at 453 nm, which appears to represent up to a 30 nm solvatochromic shift from the maxima in most organic solvents. Acetonitrile (ACN) as modifier produced spectra with two maxima and a similar solvatochromic shift. These results appear to be the first on saponified paprika oleoresin samples using SFC. It is also the first detailed report on the separation of un-saponified samples. The results are up to six times faster than comparable results by HPLC. It appears that SFC is a viable, superior alternative to HPLC for the analysis of this important commercial product, without using ACN, or chlorinated solvents.

     

Preparation of polymandelide by reaction of α-bromophenylacetic acid and triethylamine

Polymandelide was prepared in 77% yield by reaction of α-bromophenylacetic acid and triethylamine. The product was characterized by ¹H- and ¹³C-NMR and IR spectra and isolation and identification of mandelic acid from hydrolysis of the polymer. The NMR spectra indicate the presence of tacticity at CH in the polymer. Molecular weights were determined by GPC and viscosity measurements; n values of 12–20 are comparable to those reported for polymandelides prepared by other methods. The x-ray powder diffraction pattern showed the product to be completely amorphous. Thermal decomposition was studied using DSC.     

Sensitivity-enhanced quantitative 13C NMR spectroscopy via cancellation of 1J(CH) dependence in DEPT polarization transfers

A scheme has been developed to eliminate virtually all signal intensity dependence on 1JCH in polarization transfers between 1H and 13C nuclei, reducing differences in signal intensity to only 1.5% over the entire natural 1JCH range. The scheme relies on the summation of time-domain data acquired with four suitably selected Delta delays so that the J dependence is essentially canceled in the final, signal-averaged free-induction decay. These Delta delays have been incorporated into the DEPT pulse sequence to create sensitivity-enhanced experiments for collecting quantitative 13C{1H} spectra. Four experiments, each with unique read pulse angles, give quantitative spectra with 200-300% more sensitivity than conventional 13C spectra acquired with inverse-gated 1H decoupling. The experiments are ideal for recording spectra with improved quantitative information or for substantially reducing the long acquisition times indicative of quantitative 13C experiments. The ability of the experiments to provide quantitative spectra was demonstrated with a simple ethylbenzene solution, however, they can easily be adapted to various applications for analysis of complex mixtures.     

Rapid, Direct Quantitation of the Preservatives Benzoic and Sorbic Acid (and Salts) Plus Caffeine in Foods and Aqueous Beverages Using Supercritical Fluid Chromatography

The preservatives benzoate and sorbate, plus caffeine were rapidly separated and quantified, in just over 2 min, in a wide range of beverages and foods, using supercritical fluid chromatography (SFC). Fifteen beverages and 10 semi-liquid foods were evaluated. The benzoate and sorbate were originally present in the samples as the acid, or the sodium, or potassium salt. The aqueous samples were diluted 3:1 with acidified methanol, to insure the acids were protonated, then directly injected. The solutes were isocratically eluted from a 4 × 250 mm, 5 μm Diol column with 3.5 mL min^?1 of 8.5 % methanol containing 0.3 % acetic acid at 50 °C and a column outlet pressure of 150 bar. The real samples exhibited remarkably little interference. All the beverages were accurately labeled. However, many of the foods, such as salad dressings, mustard, etc., were mislabeled. The method was linear over a wide range with correlation coefficients for all three solutes >0.999. RSD’s were generally less than 1 %. The results agreed with the caffeine content on the labels within a few percent. Surprisingly, this appears to be the first published separation of benzoic and sorbic acid preservatives in food, and beverages using SFC, and one of a very few SFC applications where aqueous samples were simply diluted and injected. Compared to published references, the SFC method was found to be up to 7 times faster than HPLC, and eliminated the use of acetonitrile.