In Situ global method for measurement of oxygen demand and mass transfer

Two aerobic microorganisms,Saccharomycopsis lipolytica andBrevibacterium lactofermentum, have been used in a study of mass transfer and oxygen uptake from a global perspective, using a closed gas system. Oxygen concentrations in the gas and liquid were followed using oxygen electrodes; the results allowed for easy calculation of in situ oxygen transport. The cell yields on oxygen forS. lipolytica and B.lactofermentum were 1.01 and 1.53 g/g, respectively. The mass transfer coefficient was estimated as 10/h at 500 rpm for both fermentations. The advantages with this method are noticeable, since the use of model systems may be avoided, and thein situ measurements of oxygen demand assure reliable data for scale-up. Managed by Lockheed Martin Energy Research Corp. for the US Department of Energy under contract DE-AC05-96OR22464     

MS–MS Fragmentation Patterns of Cholesterol Oxidation Products

Summary. This study was aimed at analyzing the daughter ion spectra of 7 toxicologically relevant cholesterol oxidation products (COPs) i.e. cholestanetriol (cholestane-3β,5α,6β-triol), 7-ketocholesterol (cholest-5-en-3β-ol-7-one), 7α-hydroxycholesterol (cholest-5-en-3β,7α-diol), 7β-hydroxycholesterol (cholest-5-en-3β,7β-diol), 25-hydroxycholesterol (cholest-5-en-3β,25-diol), α-epoxycholesterol (cholestane-5α,6α-epoxy-3β-ol) and β-epoxycholesterol (cholestane-5β,6β-epoxy-3β-ol). In addition, 19-hydroxycholesterol (cholest-5-en-3β,19-diol) was analyzed as this serves as internal standard in COPs determination by HPLC-MS. Mass spectrometry was performed using a triple quadrupol mass spectrometer that was equipped with an APCI ion source. Our results indicate a common fragmentation pattern for COPs. The main breaking sites identified were in the sterol ring system between the carbon atoms with the position numbers 11–12, 12–13, and 8–14. Typical daughter ions of m/z = 81, 95, and 195 were used for multiple reaction monitoring analysis.     

Glycosylidene Carbenes. Part 31

The diastereoselectivity of the addition of NH₃ and MeNH₂ to glyconolactone oxime sulfonates and the structures of the resulting N‐unsubstituted and N‐methylated glycosylidene diaziridines were The ¹⁵N‐labelled glucono‐ and galactono‐1,5‐lactone oxime mesylates 1* and 9* add NH₃ mostly axially (>3 : 1; Scheme 4), while the ¹⁵N‐labelled mannono‐1,5‐lactone oxime sulfonate 19* adds NH₃ mostly equatorially (9 : 1; Scheme 7). The ¹⁵N‐labelled mannono‐1,4‐lactone oxime sulfonate 30* adds NH₃ mostly from the exo side (>4 : 1; Scheme 9). The configuration of the N‐methylated pyranosylidene diaziridines 17, 18, 28 , and 29 suggests that MeNH₂ adds to 1, 9, 19 , and 23 mostly to exclusively from the equatorial direction (>7 : 3; Schemes 5 and 8). The mannono‐1,4‐lactone oxime sulfonate 30 adds MeNH₂ mostly from the exo side (85 : 15; Scheme 10), while the ribo analogue 37 adds MeNH₂ mostly from the endo side (4 : 1; Scheme 10). Analysis of the preferred and of the reactive conformers of the tetrahedral intermediates suggests that the addition of the amine to lactone oxime sulfonates is kinetically controlled. The diastereoselectivity of the diaziridine formation is rationalized as the result of the competing influences of intramolecular H‐bonding during addition of the amines, steric interactions (addition of MeNH₂), and the kinetic anomeric effect. The diaziridines obtained from 2,3,5‐tri‐O‐benzyl‐D ‐ribono‐ and ‐D ‐arabinono‐1,4‐lactone oxime methanesulfonate ( 42 and 48 ; Scheme 11) decomposed readily to mixtures of 1,4‐dihydro‐1,2,4,5‐tetrazines, pentono‐1,4‐lactones, and pentonamides. The N‐unsubstituted gluco‐ and galactopyranosylidene diaziridines 2, 4, 6, 8 , and 10 are mixtures of two trans‐substituted isomers ( S / R ca. 19 : 1, Scheme 2). The main, (S,S)‐configured isomers S are stabilised by a weak intramolecular H‐bond from the pseudoaxial NH to RO? C(2). The diaziridines 12 , derived from GlcNAc, cannot form such a H‐bond; the (R,R)‐isomer dominates ( R / S 85 : 15; Scheme 3). The 2,3‐di‐O‐benzyl‐D ‐mannopyranosylidene diaziridines 20 and 22 adopt a ⁴C₁ conformation, which does not allow an intramolecular H‐bond; they are nearly 1 : 1 mixtures of R and S diastereoisomers, whereas the ^OH₅ conformation of the 2,3:5,6‐di‐O‐isopropylidene‐D ‐mannopyranosylidene diaziridines 24 is compatible with a weak H‐bond from the equatorial NH to O? C(2); the (R,R)‐isomer is favoured ( R / S ≥7 : 3; Scheme 6). The mannofuranosylidene diaziridine 31 completely prefers the (R,R)‐configuration (Scheme 9).     

Small-angle X-ray scattering, light scattering, and NMR study of PEO-PPO-PEO triblock copolymer/cationic surfactant complexes in aqueous solution

The formation of triblock copolymer/surfactant complexes upon mixing a nonionic Pluronic polymer (PEO-PPO-PEO) with a cationic surfactant, hexadecyltrimethylammonium chloride (CTAC), has been studied in dilute aqueous solutions using small-angle X-ray scattering, static and dynamic light scattering, and self-diffusion NMR. The studied copolymer (denoted P123, EO(20)PO(68)EO(20)) forms micelles with a radius of 10 nm and a molecular weight of 7.5 x 10(5), composed of a hydrophobic PPO-rich core of radius 4 nm and a water swollen PEO corona. The P123/CTAC system has been investigated between 1 and 5 wt % P123 and with varying surfactant concentration up to approximately 170 mM CTAC (or a molar ratio n(CTAC)/n(P123) = 19.3). When CTAC is mixed with micellar P123 solutions, two different types of complexes are observed at various CTAC concentrations. At low molar ratios (>/=0.5) a "P123 micelle-CTAC" complex is obtained as the CTAC monomers associate noncooperatively with the P123 micelle, forming a spherical complex. Here, an increased interaction between the complexes with increasing CTAC concentration is observed. The interaction has been investigated by determining the structure factor obtained by using the generalized indirect Fourier transformation (GIFT) method. The interaction between the P123 micelle-CTAC complexes was modeled using the Percus-Yevick closure. For the low molar ratios a small decrease in the apparent molecular weight of the complex was obtained, whereas the major effect was the increase in electrostatic repulsion between the complexes. Between molar ratios 1.9 and 9 two coexisting complexes were found, one P123 micelle-CTAC complex and one "CTAC-P123" complex. The latter one consists of one or a few P123 unimers and a few CTAC monomers. As the CTAC concentration increases above a molar ratio of 9, the P123 micelles are broken up and only the CTAC-P123 complex that is slightly smaller than a CTAC micelle exists. The interaction between the P123/CTAC complexes was modeled with the hypernetted-chain closure using a Yukawa type potential in the GIFT analysis, due to the stronger electrostatic repulsion.     

The binding of human carbonic anhydrase II by functionalized folded polypeptide receptors

Several receptors for human carbonic anhydrase II (HCAII) have been prepared by covalently attaching benzenesulfonamide carboxylates via aliphatic aminocarboxylic acid spacers of variable length to the side chain of a lysine residue in a designed 42 residue helix-loop-helix motif. The sulfonamide group binds to the active site zinc ion of human carbonic anhydrase II located in a 15 A deep cleft. The dissociation constants of the receptor-HCAII complexes were found to be in the range from low micromolar to better than 20 nM, with the lowest affinities found for spacers with less than five methylene groups and the highest affinity found for the spacer with seven methylene groups. The results suggest that the binding is a cooperative event in which both the sulfonamide residue and the helix-loop-helix motif contribute to the overall affinity.     

Intersystem crossing versus electron transfer in porphyrin-based donor-bridge-acceptor systems: influence of a paramagnetic species

We have investigated how the spin state of an acceptor influences the photophysical processes in a donor-bridge-acceptor (D-B-A) system. The system of choice has zinc porphyrin as the electron donor and high- or low-spin iron(III) porphyrin as the acceptor. The spin state of the acceptor porphyrin is switched simply by coordinating imidazole ligands to the metal center. The D-A center-center distance is 26 A, and the bridging chromophore varies from pi-conjugated to a sigma-bonded system. The presence of a high-spin iron(III) porphyrin in such systems has previously been shown to significantly enhance intersystem crossing in the remote zinc porphyrin donor, whereas no significant electron transfer to the iron porphyrin acceptor was observed, even though the thermodynamics would allow for photoinduced electron transfer. Here, we demonstrate that by switching the acceptor to a low-spin state, the dominating photophysical process is drastically changed; the low-spin system shows long-range electron transfer on the picosecond time-scale, and intersystem crossing occurs at its "normal" rate.     

DLVO interactions of tungsten oxide and cobalt oxide surfaces measured with the colloidal probe technique

We have investigated the DLVO surface forces of oxidized tungsten and cobalt surfaces using the atomic force microscope (AFM) colloidal probe technique. It was shown by X-ray photoelectron spectroscopy (XPS) and electrokinetic measurements that this model system is representative of industrial tungsten carbide (WC) and cobalt powders used in the production of hard metals. We found that the attractive van der Waals forces are well described by Hamaker constants, calculated from optical data for WO(3) and CoOOH. The repulsive electrostatic double layer forces between WO(3) surfaces increase with increasing pH due to an increasingly negative surface potential. This surface potential decreases with increasing ionic strength at pH 7.5. The electrostatic interaction between WO(3) and CoOOH is attractive at pH 10, suggesting a positively charged CoOOH surface.     

Rapid Analysis of Cell–Nanoparticle Interactions using Single‐Cell Raman Trapping Microscopy

Iron oxide nanoparticles have been used in preclinical studies to label stem cells for non‐invasive tracking and homing. The search continues for novel particle candidates that are suitable for clinical applications. Since standard analyses to investigate cell–particle interactions and safety are labor‐intensive, an efficient procedure is required to guide future particle development and to exclude adverse health effects. The application of combined Raman trapping microscopy with fluidic chips is reported for the analysis of single cells labeled with different types of aminated iron oxide particles. Multivariate data analysis revealed Raman signal differences that could be clearly assigned to cell–particle interactions and cytotoxicity, respectively. A validation dataset verified that more than 95 % of the spectra were correctly classified. Thus, our approach enables rapid discrimination of non‐hazardous from cytotoxic nanoparticles as a prerequisite for safe clinical applications.     

Concerted Catalysis by Adjacent Palladium and Gold in Alloy Nanoparticles for the Versatile and Practical [2+2+2] Cycloaddition of Alkynes

A Pd‐Au alloy efficiently catalyzed the [2+2+2] cycloaddition of substituted alkynes. Whereas monometallic Pd and Au catalysts were totally ineffective, Pd‐Au alloy nanoparticle catalysts with a low Pd/Au molar ratio showed high activity to give the corresponding polysubstituted arenes in high yields. A variety of substituted alkynes participated in various modes of cycloaddition under Pd‐Au alloy catalysis. The Pd‐Au alloy catalysts exhibited high air tolerance and reusability.     

Synthesis of boroxifen, a nido-carborane analogue of tamoxifen.

A nido-carborane analogue of tamoxifen, the widely employed breast cancer therapy agent, was prepared as an archetype of a potential new class of antiestrogen and boron neutron capture therapy agent in which the carborane is incorporated within the framework of the parent compound. The carborane was introduced through the reaction of 6,9-bis(acetonitrile)decaborane with a unique and highly conjugated ene-yne, which was prepared stereoselectively. NMR spectroscopy and a crystal structure of a key intermediate, the carborane analogue of chloro-tamoxifen, demonstrated the structural similarities between the tamoxifen carboranes and their corresponding phenyl analogues.