Reusable optical bioassay platform with permeability-controlled hydrogel pads for selective saccharide detection

A reusable optical bioassay platform using permeability-controlled hydrogel pads for selective saccharide detection has been developed. An optical glucose detection assay based on fluorescence resonance energy transfer (FRET) between dye-labeled dextran and Concanavalin A (ConA) was incorporated into hydrogel pads by entrapment. The hydrogel pads are constructed from hemispherical hydrogel attached onto hydrophobic surfaces of a microtiter plate. The resulted hemispherical hydrogel pads entrapping the sensing biological materials were further surface coated with polyelectrolyte multilayers through a Layer-by-Layer (LbL) self-assembly process to create a permeability-controlled membrane with nanometer thickness. The selective permeable LbL film deposited on the hydrogel surface allows small molecular weight analytes to diffuse into the hydrogel pads while the large molecular weight sensing biological molecules are immobilized. An encapsulation efficiency of 75% for the ConA/Dextran complex within the coated hydrogel pads was achieved and no significant leakage of the complex was observed. Glucose calibration curve with linear range from 0 to 10 mM glucose was obtained. Selective permeability of the hydrogel pads has been demonstrated by measurement of saccharides with various molecular weights. The LbL hydrogel pads could selectively detect monosaccharides (glucose, MW = 180) and disaccharides (sucrose, MW = 342) while polysaccharides (dextran, MW ∼ 70 kDa) cannot diffuse through the LbL layer and are excluded. LbL hydrogel pads allow regeneration of the FRET system with good signal reproducibility of more than 90% to construct a reusable and reagentless optical bioassay platform.     

Electrophilic S‐Trifluoromethylation of Cysteine Side Chains in α‐ and β‐Peptides: Isolation of Trifluoro‐methylated Sandostatin® (Octreotide) Derivatives

The new electrophilic trifluoromethylating 1‐(trifluoromethyl)‐benziodoxole reagents A and B (Scheme 1) have been used to selectively attach CF₃ groups to the S‐atom of cysteine side chains of α‐ and β‐peptides (up to 13‐residues‐long; products 7 – 14 ). Other functional groups in the substrates (amino, amido, carbamate, carboxylate, hydroxy, phenyl) are not attacked by these soft reagents. Depending on the conditions, the indole ring of a Trp residue may also be trifluoromethylated (in the 2‐position). The products are purified by chromatography, and identified by ¹H‐, ¹³C‐, and ¹⁹F‐NMR spectroscopy, by CD spectroscopy, and by high‐resolution mass spectrometry. The CF₃ groups, thus introduced, may be replaced by H (Na/NH₃), an overall Cys/Ala conversion. The importance of trifluoromethylations in medicinal chemistry and possible applications of the method (spin‐labelling, imaging, PET) are discussed.     

Sandwich-type tetranuclear lanthanide complexes with cucurbit[6]uril: from molecular compounds to coordination polymers

Sandwich-type lanthanide complexes with macrocyclic ligand cucurbit[6]uril (C 36H 36N 24O 12, CB[6]) were synthesized under hydrothermal conditions from aqueous solutions of lanthanide(III) bromides, CB[6], and 4-cyanopyridine. According to X-ray analysis (Ln = La, Pr, Dy, Ho, Er, and Yb), the compounds with different structural types of lanthanide cores have a common fragment where the tetranuclear hydroxo complex is sandwiched between two macrocycles {(IN@CB[6])Ln 4(mu 3-OH) 4(IN@CB[6])} (6+) (IN = isonicotinate). The photoluminescence (for Ln = Eu) and Fourier transform ion cyclotron resonance mass spectra (for Ln = Pr, Dy, and Er) were studied. The compounds are used for the first time as precursors for the synthesis of lanthanide-silver heterometallic coordination polymers. The chainlike crystal structure of polymers (Ln = La, Pr, and Dy) is constituted by the sandwich complexes linked via the coordination of IN nitrogen atoms to the silver atoms.     

Facile Recoding of Selenocysteine in Nature

Selenocysteine (Sec or U) is encoded by UGA, a stop codon reassigned by a Sec‐specific elongation factor and a distinctive RNA structure. To discover possible code variations in extant organisms we analyzed 6.4 trillion base pairs of metagenomic sequences and 24 903 microbial genomes for tRNA^Sec species. As expected, UGA is the predominant Sec codon in use. We also found tRNA^Sec species that recognize the stop codons UAG and UAA, and ten sense codons. Selenoprotein synthesis programmed by UAG in Geodermatophilus and Blastococcus, and by the Cys codon UGU in Aeromonas salmonicida was confirmed by metabolic labeling with ⁷⁵Se or mass spectrometry. Other tRNA^Sec species with different anticodons enabled E. coli to synthesize active formate dehydrogenase H, a selenoenzyme. This illustrates the ease by which the genetic code may evolve new coding schemes, possibly aiding organisms to adapt to changing environments, and show the genetic code is much more flexible than previously thought.     

Bioorthogonal Probes for the Study of MDM2‐p53 Inhibitors in Cells and Development of High‐Content Screening Assays for Drug Discovery

To study the behavior of MDM2‐p53 inhibitors in a disease‐relevant cellular model, we have developed and validated a set of bioorthogonal probes that can be fluorescently labeled in cells and used in high‐content screening assays. By using automated image analysis with single‐cell resolution, we could visualize the intracellular target binding of compounds by co‐localization and quantify target upregulation upon MDM2‐p53 inhibition in an osteosarcoma model. Additionally, we developed a high‐throughput assay to quantify target occupancy of non‐tagged MDM2‐p53 inhibitors by competition and to identify novel chemical matter. This approach could be expanded to other targets for lead discovery applications.     

Synthesis and Characterization of Diorganocobalt Chlorides by Aliphatic Vinylic C–Cl Bond Activation

Three diorganocobalt chlorides [CoClMe(PMe₃)₂–{(C₅H₆)–CH=O}] ( 4 ), [CoClMe(PMe₃)₂–{(C₆H₈)–CH=O}] ( 5 ), and [CoClMe(PMe₃)₂–{(C₆H₇Memeta)–CH=O}] ( 6 ) were synthesized through cyclometalation reactions with aldehyde as an anchoring group involving aliphatic vinylic C–Cl bond activation. Complexes 4 – 6 were characterized by IR and NMR spectroscopy. The crystal and molecular structures of complexes 4 and 5 were determined by single‐crystal X‐ray diffraction. Complexes 4 – 6 are stable in solution at room temperature, but they decompose at above 30 °C affording C,C‐couplings products with the formation of [Co(PMe₃)₃Cl]. The results of this work will be important for people to deepen the understanding of the C–Cl bond activation mechanism.     

Clara Haber,nee Immerwahr (1870–1915): Life,Work and Legacy

We examine the life, work, and legacy of Clara Haber, nee Immerwahr, who became the first woman to earn a doctorate from the University of Breslau, in 1900. In 1901 she married the chemist Fritz Haber. With no employment available for female scientists, Clara freelanced as an instructor in the continued education of women, mainly housewives, while struggling not to become a housewife herself. Her duties as a designated head of a posh household hardly brought fulfillment to her life. The outbreak of WWI further exacerbated the situation, as Fritz Haber applied himself in extraordinary ways to aid the German war effort. The night that he celebrated the “success” of the first chlorine cloud attack, Clara committed suicide. We found little evidence to support claims that Clara was an outspoken pacifist who took her life because of her disapproval of Fritz Haber's involvement in chemical warfare. We conclude by examining “the myth of Clara Immerwahr” that took root in the 1990s from the perspective offered by the available scholarly sources, including some untapped ones.     

Ca2+‐complex stability of GAPAGPLIVPY peptide in gas and aqueous phase,investigated by affinity capillary electrophoresis and molecular dynamics simulations and compared to mass spectrometric results

Strong, sequence‐specific gas‐phase bindings between proline‐rich peptides and alkaline earth metal ions in nanoESI‐MS experiments were reported by Lehmann et al. (Rapid Commun. Mass Spectrom. 2006, 20, 2404–2410), however its relevance for physiological‐like aqueous phase is uncertain. Therefore, the complexes should also be studied in aqueous solution and the relevance of the MS method for binding studies be evaluated. A mobility shift ACE method was used for determining the binding between the small peptide GAPAGPLIVPY and various metal ions in aqueous solution. The findings were compared to the MS results and further explained using computational methods. While the MS data showed a strong alkaline earth ion binding, the ACE results showed nonsignificant binding. The proposed vacuum state complex also decomposed during a molecular dynamic simulation in aqueous solution. This study shows that the formed stable peptide–metal ion adducts in the gas phase by ESI‐MS does not imply the existence of analogous adducts in the aqueous phase. Comparing peptide–metal ion interaction under the gaseous MS and aqueous ACE conditions showed huge difference in binding behavior.