Continuous flow stable isotope methods for study of delta(13)C fractionation during halomethane production and degradation

Gas chromatography/mass spectrometry/isotope ratio mass spectrometry (GC/MS/IRMS) methods for delta(13)C measurement of the halomethanes CH(3)Cl, CH(3)Br, CH(3)I and methanethiol (CH(3)SH) during studies of their biological production, biological degradation, and abiotic reactions are presented. Optimisation of gas chromatographic parameters allowed the identification and quantification of CO(2), O(2), CH(3)Cl, CH(3)Br, CH(3)I and CH(3)SH from a single sample, and also the concurrent measurement of delta(13)C for each of the halomethanes and methanethiol. Precision of delta(13)C measurements for halomethane standards decreased (+/-0.3, +/-0.5 and +/-1.3 per thousand) with increasing mass (CH(3)Cl, CH(3)Br, CH(3)I, respectively). Given that carbon isotope effects during biological production, biological degradation and some chemical (abiotic) reactions can be as much as 100 per thousand, stable isotope analysis offers a precise method to study the global sources and sinks of these halogenated compounds that are of considerable importance to our understanding of stratospheric ozone destruction.     

Mass Activated Droplet Sorting (MADS) Enables High‐Throughput Screening of Enzymatic Reactions at Nanoliter Scale

Microfluidic droplet sorting enables the high‐throughput screening and selection of water‐in‐oil microreactors at speeds and volumes unparalleled by traditional well‐plate approaches. Most such systems sort using fluorescent reporters on modified substrates or reactions that are rarely industrially relevant. We describe a microfluidic system for high‐throughput sorting of nanoliter droplets based on direct detection using electrospray ionization mass spectrometry (ESI‐MS). Droplets are split, one portion is analyzed by ESI‐MS, and the second portion is sorted based on the MS result. Throughput of 0.7 samples s^?1 is achieved with 98 % accuracy using a self‐correcting and adaptive sorting algorithm. We use the system to screen ≈15 000 samples in 6 h and demonstrate its utility by sorting 25 nL droplets containing transaminase expressed in vitro. Label‐free ESI‐MS droplet screening expands the toolbox for droplet detection and recovery, improving the applicability of droplet sorting to protein engineering, drug discovery, and diagnostic workflows.     

Visible-Light Switching of Metallosupramolecular Assemblies**

A photoswitchable ligand and palladium(II) ions form a dynamic mixture of self-assembled metallosupramolecular structures. The photoswitching ligand is an ortho-fluoroazobenzene with appended pyridyl groups. Combining the E-isomer with palladium(II) salts affords a double-walled triangle with composition [Pd₃L₆]⁶⁺ and a distorted tetrahedron [Pd₄L₈]⁸⁺ (1 : 2 ratio at 298 K). Irradiation with 410 nm light generates a photostationary state with approximately 80 % of the E-isomer of the ligand and results in the selective disassembly of the tetrahedron, the more thermodynamically stable structure, and the formation of the triangle, the more kinetically inert product. The triangle is then slowly transformed back into the tetrahedron over 2 days at 333 K. The Z-isomer of the ligand does not form any well-defined structures and has a thermal half-life of 25 days at 298 K. This approach shows how a thermodynamically preferred self-assembled structure can be reversibly pumped to a kinetic trap by small perturbations of the isomer distribution using non-destructive visible light.     

N-donor ligand complexes of nickel,zinc and copper: Comparisons with tetradentate N-donor ligands derived from Schiff bases

The nickel and zinc complexes of 2-aminomethylaniline (AMA) are reported. Both metals form the octahedral complex [M(AMA)₂(ONO₂)₂] (M = Ni, Zn) where the aromatic ligands lie in the meridial plane with the anilino donors trans to one another. The remaining nitrates coordinate axially. A simple comparison with the nitrogen donor disposition (cis/trans) in nickel complexes of tetradentate N₄ donor ligands derived from symmetric Schiff base ligands is presented. The discussion is extended to interrogate the bonding motifs of the nitrate ligands viz –ONO₂ in the nickel complexes of AMA compared to the two motifs (viz O₂NO and ONO₂) that are isolated for the nickel complexes of the macrocycle hexamethyltetraazacyclotetradecane.     

Regulatory problems caused by contamination, a frequently overlooked cause of veterinary drug residues

The occurrence of violative residues of veterinary medicines and other, unauthorised, drugs in food of animal origin is an issue of popular concern within the European Union. Violations can occur as a result of improper use of a licensed product or through the illegal use of an unlicensed substance. However, a "violative" analytical result does not necessarily mean that abuse has occurred. Contamination of animal feedingstuffs, environmental contamination and animal-to-animal transfer of drugs can also cause residue violations. This paper reviews these inadvertent causes of residues violations in food, and includes data generated using chromatographic and non-chromatographic methods of analysis.     

Enantiospecific and regioselective rhodium-catalyzed allylic alkylation: diastereoselective approach to quaternary carbon stereogenic centers

The enantiospecific and regioselective rhodium-catalyzed allylic alkylation of a series of chiral nonracemic allylic carbonates, followed by ozonolysis and reductive lactonization, provides a convenient route to optically active gamma-lactones. Sequential alkylation and reductive alkylation furnished the alpha-quaternary-beta-ternary substituted gamma-lactone derivative as a >/=10:1 mixture of diastereoisomers.     

Engineering quadrupole magnetic flow sorting for the isolation of pancreatic islets

Quadrupole magnetic flow sorting (QMS) is being adapted from the separation of suspensions of single cells (<15 μm) to the isolation of pancreatic islets (150–350 μm) for transplant. To achieve this goal, the critical QMS components have been modeled and engineered to optimize the separation process. A flow channel has been designed, manufactured, and tested. The quadrupole magnet assembly has been designed and verified by finite element analysis. Pumps have been selected and verified by test. Test data generated from the pumps and flow channel demonstrate that the fabricated channel and peristaltic pumps fulfill the requirements of successful QMS separation.