New fluorimetric method of liquid chromatography for the determination of the neurotoxin domoic acid in seafood and marine phytoplankton

Domoic acid (DA) is a neurotoxic amino acid that is responsible for the human toxic syndrome, amnesic shellfish poisoning (ASP). A new rapid, sensitive liquid chromatographic (LC) method has been developed for the determination of DA in various marine samples. DA in marine biological materials was derivatised with 4-fluoro-7-nitro-2,1,3-benzoxadiazole (NBD-F) and analysed using isocratic reversed-phase LC with fluorimetric detection. The calibration, based on standard DA solutions, was linear in the range 0.04-2 microg/ml (r2=0.998) and the detection limit (3:1, signal/noise) was better than 1 ng/ml. Using the certified reference material (MUS-1B), recoveries of DA from shellfish tissue were >95% (n=5). When a strong anion exchange SPE cartridge was used for sample clean-up the detection limit was 6 ng DA/g mussel tissue. Good reproducibility was achieved with RSD values ranging from 3% for 8 microg DA/g (n=5), to 5% for 0.04 microg DA/g (n=5). This new method was successfully applied to the determination of DA in naturally contaminated shellfish and in marine phytoplankton cultures of Pseudonitzschia sp.     

(E)-1-alkyl-4-

(E)-1-Alkyl-4-[2-(alkylsulfonyl)-1-ethenyl]pyridinium salts were synthesized in two steps. These sulfones were stable at pH 7.3 and underwent a nucleophilic vinylic substitution (S(N)V) with mercaptans, including thiouracile, to give the corresponding 4-(thiovinyl)-pyridinium salts. The X-ray diffraction structure of (E)-1-methyl-4-[2-(ethylsulfanyl)-1-ethenyl]pyridinium iodide indicated conjugation of the sulfur with the pyridinium ring. (Z)-1-Methyl-4-[2-(methylsulfanyl)-1-ethenyl]pyridinium iodide, prepared from the corresponding thioether by reaction with methyl iodide in diethyl ether, underwent isomerization to the E isomer in a first-order reaction in deuterated [D6]DMSO with an activation energy of 14 kcalmol(-1). At pH 7, the (E)-1-methyl-4-[2-(methylsulfonyl)-1-ethenyl]pyridinium iodide (19) reacted specifically with thiols. The reaction of this sulfone with glutathione in a TES buffer at pH 7 was a second-order reaction (k = 4,100 M(-1)s(-1) at 30 degrees C) and gave the corresponding substitution product with an intense long wavelength absorption band (lambdamax=360 nm, epsilon = 27,500 M(-1)cm(-1)). The modification of different enzymes of known structure with 19 showed the high selectivity of this reagent towards thiol groups and its usefulness in the quantitative determination of free thiol groups in proteins.     

Immobilizing a Fluorescent Dye Offers Potential to Investigate the Glass/Resin Interface

Silane coupling agents are commonly applied to glass fibers to promote fiber/resin adhesion and enhance durability in composite parts. In this study, a coupling agent multilayer on glass was doped with trace levels of the dimethylaminonitrostilbene (DMANS) fluorophore. The fluorophore was immobilized on the glass surface by tethering the molecule to a triethoxy silane coupling agent, creating the DMANS/silane coupling agent molecule (DMSCA). DMSCA was then diluted with commonly used coupling agents and grafted to a glass microscope coverslip to create a model composite interface. A 53-nm blue shift in fluorescence from the immobilized DMSCA can be followed during cure of an epoxy resin overlayer, giving this technique potential to monitor the properties of the fiber/resin interface during composite processing. Contact angle measurements on these coupling agent layers were similar in the presence or absence of the DMSCA molecule, suggesting that trace levels of the fluorescent probe did not affect the structure of the layer. The immobilized DMSCA molecule behaved similarly to the DMANS precursor in solution. Both showed longer wavelength fluorescence in more polar environments. Copyright 2000 Academic Press.     

Chemical Proteomics and Phenotypic Profiling Identifies the Aryl Hydrocarbon Receptor as a Molecular Target of the Utrophin Modulator Ezutromid

Duchenne muscular dystrophy (DMD) is a fatal muscle‐wasting disease arising from mutations in the dystrophin gene. Upregulation of utrophin to compensate for the missing dystrophin offers a potential therapy independent of patient genotype. The first‐in‐class utrophin modulator ezutromid/SMT C1100 was developed from a phenotypic screen through to a Phase 2 clinical trial. Promising efficacy and evidence of target engagement was observed in DMD patients after 24 weeks of treatment, however trial endpoints were not met after 48 weeks. The objective of this study was to understand the mechanism of action of ezutromid which could explain the lack of sustained efficacy and help development of new generations of utrophin modulators. Using chemical proteomics and phenotypic profiling we show that the aryl hydrocarbon receptor (AhR) is a target of ezutromid. Several lines of evidence demonstrate that ezutromid binds AhR with an apparent K_D of 50 nm  and behaves as an AhR antagonist. Furthermore, other reported AhR antagonists also upregulate utrophin, showing that this pathway, which is currently being explored in other clinical applications including oncology and rheumatoid arthritis, could also be exploited in future DMD therapies.     

Antibody-recruiting protein-catalyzed capture agents to combat antibiotic-resistant bacteria

Antibiotic resistant infections are projected to cause over 10 million deaths by 2050, yet the development of new antibiotics has slowed. This points to an urgent need for methodologies for the rapid development of antibiotics against emerging drug resistant pathogens. We report on a generalizable combined computational and synthetic approach, called antibody-recruiting protein-catalyzed capture agents (AR-PCCs), to address this challenge. We applied the combinatorial protein catalyzed capture agent (PCC) technology to identify macrocyclic peptide ligands against highly conserved surface protein epitopes of carbapenem-resistant Klebsiella pneumoniae, an opportunistic Gram-negative pathogen with drug resistant strains. Multi-omic data combined with bioinformatic analyses identified epitopes of the highly expressed MrkA surface protein of K. pneumoniae for targeting in PCC screens. The top-performing ligand exhibited high-affinity (EC₅₀ ∼50 nM) to full-length MrkA, and selectively bound to MrkA-expressing K. pneumoniae, but not to other pathogenic bacterial species. AR-PCCs that bear a hapten moiety promoted antibody recruitment to K. pneumoniae, leading to enhanced phagocytosis and phagocytic killing by macrophages. The rapid development of this highly targeted antibiotic implies that the integrated computational and synthetic toolkit described here can be used for the accelerated production of antibiotics against drug resistant bacteria.

Antibody-recruiting protein-catalyzed capture agent (AR-PCCs) are a new class of all-synthetic and highly targeted antibiotics that recruit endogenous immune responses to eliminate drug-resistant microbes.     

Outer-sphere effects on ligand-field excited-state dynamics: solvent dependence of high-spin to low-spin conversion in [Fe(bpy)3]2+

In condensed phase chemistry, the solvent can have a significant impact on everything from yield to product distribution to mechanism. With regard to photo-induced processes, solvent effects have been well-documented for charge-transfer states wherein the redistribution of charge subsequent to light absorption couples intramolecular dynamics to the local environment of the chromophore. Ligand-field excited states are expected to be largely insensitive to such perturbations given that their electronic rearrangements are localized on the metal center and are therefore insulated from so-called outer-sphere effects by the ligands themselves. In contrast to this expectation, we document herein a nearly two-fold variation in the time constant associated with the ⁵T₂ → ¹A₁ high-spin to low-spin relaxation process of tris(2,2′-bipyridine)iron(ii) ([Fe(bpy)₃]²⁺) across a range of different solvents. Likely origins for this solvent dependence, including relevant solvent properties, ion pairing, and changes in solvation energy, were considered and assessed by studying [Fe(bpy)₃]²⁺ and related derivatives via ultrafast time-resolved absorption spectroscopy and computational analyses. It was concluded that the effect is most likely associated with the volume change of the chromophore arising from the interconfigurational nature of the ⁵T₂ → ¹A₁ relaxation process, resulting in changes to the solvent–solvent and/or solvent–solute interactions of the primary solvation shell sufficient to alter the overall reorganization energy of the system and influencing the kinetics of ground-state recovery.

Time-resolved spectroscopic measurements of ground-state recovery for [Fe(bpy)₃]²⁺ reveal that the solvent can induce an outer-sphere reorganization energy effect on excited-state dynamics involving metal-centered ligand-field electronic states.     

An efficient preparation of vinamidinium hexafluorophosphate salts

Substituted acetic acids or acetyl chlorides react with phosphorus oxychloride in DMF to yield the vinamidinium salts 3a-j in moderate to excellent recrystallized yields (28-90%). The cations are conveniently isolated as their hexafluorophosphate salts, which are easily handled nonhygroscopic solids. The nitro compound 3l is prepared in 91% yield by nitration of the parent vinamidinium 3k. The X-ray crystal structure is reported for the 2-phenyl isomer 3e and displays minimal overlap of the two pi-systems.     

Thermodynamically controlled synthesis of a chiral tetra-cavitand nanocapsule and mechanism of enantiomerization

The dynamic covalent synthesis, structure and conformational dynamics of a chiral polyimine nanocapsule 1a are reported. Reaction of four tetraformyl cavitands and eight H(2)N(CH(2))(2)NH(2) yields quantitatively 1a, which has a compact, asymmetrically folded, pseudo-C(2)-symmetric structure, as determined by X-ray crystallography, and encapsulates four CHCl(3) and three CH(3)OH guests in the solid state. In solution, 1a enantiomerizes by passing over a barrier of ΔG(298)(double dagger) = 21.5 ± 0.7 kcal mol(-1) via a refolding process.     

Electrospun Nanofibers Sorbents for Pre-Concentration of 1,1-dichloro-2,2 bis-(4-chlorophenyl)ethylene with Subsequent Desorption by Pressurized Hot Water Extraction

Electrospun polystyrene (PS) nanofibers (130–500 nm) incorporating a potassium salt of imidazole-1-carbodithioate were evaluated as potential sorbents for the pre-concentration of a model organochlorine pesticide; 1,1-dichloro-2,2bis-(4-chlorophenyl)ethylene (DDE). The efficiencies of DDE (0.25–1.0 μg L^?1) adsorption by the nanofiber sorbent followed by desorption employing pressurized hot water extraction (PHWE) were investigated and monitored using gas chromatography with electron capture detection (GC-ECD). Parameters such as time, temperature and pressure of extraction, sample volume, DDE concentration and sorbent mass were optimized. The maximum adsorption of DDE (0.50 μg L^?1) on electrospun PS and carbodithioate incorporated PS nanofibers was at 43.7 and 94.6%, respectively, in 20 min. Incorporation of carbodithiote doubled the adsorption efficiency of PS and achieved LOD of 0.000234 μg L^?1 for DDE. The optimal DDE desorption on the PHWE system was 93.8% in 10 min. It would seem that the use of electrospun nanofibers as sorbent material with subsequent desorption by PHWE has great potential and thus warrants further investigations. This approach as it uses water as an extraction solvent for an organochlorine pesticide provides an opportunity to eliminate organic solvents, especially for procedures aimed at monitoring organic pollutants in the environment.