Fluorescently Labeled Substrates for Monitoring α1,3‐Fucosyltransferase IX Activity

Fucosylation is often the final process in glycan biosynthesis. The resulting glycans are involved in a variety of biological processes, such as cell adhesion, inflammation, or tumor metastasis. Fucosyltransferases catalyze the transfer of fucose residues from the activated donor molecule GDP‐β‐L ‐fucose to various acceptor molecules. However, detailed information about the reaction processes is still lacking for most fucosyltransferases. In this work we have monitored α1,3‐fucosyltransferase activity. For both donor and acceptor substrates, the introduction of a fluorescent ATTO dye was the last step in the synthesis. The subsequent conversion of these substrates into fluorescently labeled products by α1,3‐fucosyltransferases was examined by high‐performance thin‐layer chromatography coupled with mass spectrometry as well as dual‐color fluorescence cross‐correlation spectroscopy, which revealed that both fluorescently labeled donor GDP‐β‐L ‐fucose‐ATTO 550 and acceptor N‐acetyllactosamine‐ATTO 647N were accepted by recombinant human fucosyltransferase IX and Helicobacter pylori α1,3‐fucosyltransferase, respectively. Analysis by fluorescence cross‐correlation spectroscopy allowed a quick and versatile estimation of the progress of the enzymatic reaction and therefore this method can be used as an alternative method for investigating fucosyltransferase reactions.     

Langmuir and Langmuir-Blodgett films of multifunctional, amphiphilic polyethers with cholesterol moieties

Langmuir films of multifunctional, hydrophilic polyethers containing a hydrophobic cholesterol group (Ch) were studied by surface pressure-mean molecular area (π-mmA) measurements and Brewster angle microscopy (BAM). The polyethers were either homopolymers or diblock copolymers of linear poly(glycerol) (lPG), linear poly(glyceryl glycidyl ether) (lPGG), linear poly(ethylene glycol) (lPEG), or hyperbranched poly(glycerol) (hbPG). Surface pressure measurements revealed that the homopolymers lPG and hbPG did not stay at the water surface after spreading and solvent evaporation, in contrast to lPEG. Because of the incorporation of the Ch group in the polymer structure, stable Langmuir films were formed by Ch-lPG(n), Ch-lPGG(n), and Ch-hbPG(n). The Ch-hbPG(n), Ch-lPEG(n), Ch-lPEG(n)-b-lPG(m), Ch-lPEG(n)-b-lPGG(m), and Ch-lPEG(n)-b-hbPG(m) systems showed an extended plateau region assigned to a phase transition involving the Ch groups. Typical hierarchically ordered morphologies of the LB films on hydrophilic substrates were observed for all Ch-initiated polymers. All LB films showed that Ch of the Ch-initiated homopolymers is able to crystallize. This strong tendency of self-aggregation then triggers further dewetting effects of the respective polyether entities. Fingerlike morphologies are observed for Ch-lPEG(69), since the lPEG(69) entity is able to undergo crystallization after transfer onto the silicon substrate.     

Simultaneous analysis of select pharmaceuticals and personal care products in fish tissue using pressurized liquid extraction combined with silica gel cleanup

Analytical improvements were developed and validated for measuring select personal care products (PCPs) and two pharmaceuticals in fish tissue. The method was validated using fortified fillet tissue for twelve PCPs including fragrance materials, alkylphenols, photo initiators, and triclosan as well as two pharmaceuticals including carbamazepine (anti-seizure) and diazepam (anti-convulsant). The analytical method utilized pressurized liquid extraction (PLE) combined with silica gel cleanup, gel permeation chromatography, and gas chromatography ion-trap tandem mass spectrometry. Silica gel cleanup was combined with the PLE to produce one automated extraction/cleanup technique. This analytical improvement served to reduce the incurred cost, time, and loss of potential target analytes associated with independent cleanup steps. The combined extraction/cleanup technique resulted in an average increase of 10% in analyte recoveries. Average triplicate recoveries and relative standard deviations for the entire method, using 2.5 g of fish fillet tissue, were 92 ± 9% (recoveries ranged from 64 to 131%). The sensitivity of the analytical methods was improved by optimizing the resonant collision induced dissociation energy to the hundredths place (0.01 V). Improvements in ion production range from 24 to 122% for six of the 12 PCPs. Statistically derived method detection limits (MDLs) were also lowered on average by a factor of 8 and ranged from 1.2 to 38 ng/g wet weight. MDLs for carbamazepine and diazepam were 18 and 3.7 ng/g wet weight, respectively. Galaxolide and tonalide were measured in an environmental sample at concentrations of 81 and 5.5 ng/g wet weight, respectively.     

Acetylene-expanded dendralene segments with exotopic phosphaalkene units

Bis-TMS protected C,C-diacetylenic phosphaalkene (A(2)PA) 1 (Mes*P=C(C≡CTMS)(2); Mes* = 2,4,6-tBu(3)Ph) has been used as a building block for the construction of butadiyne-expanded dendralene fragments in which phosphaalkenes feature as exotopic double bonds. Treatment of 1 with CuCl gives rise to a Cu(I) acetylide that is selectively formed at the acetylene trans to the Mes* group. The cis-TMS-acetylene engages in similar chemistry, albeit at higher temperatures and longer reaction times. The differentiation between the two acetylene termini of 1 allows for the controlled synthesis of the title compounds by a variety of different Cu- and Pd-catalyzed oxidative acetylene homo- and heterocoupling protocols. Crystallographic characterization of A(2)PA 1 and dimeric Mes*P=C(C≡CR(1))C(4)(R(2) C≡C)C=PMes* (3b, R(1) = R(2) = Ph; 6, R(1) = R(2) = TMS), and 10 (R(1) = R(2) = C≡CPh) verifies that the stereochemistry across the P=C bond is conserved during the coupling reactions, whereas spectroscopic evidence reveals cis/trans isomerization in an iodo-substituted A(2)PA intermediate 4 (Mes*P=C(C≡CTMS)(C≡CI). UV/Vis spectroscopic and electrochemical studies reveal that efficient π conjugation operates through the entire acetylenic phosphaalkene framework, even in the cross-conjugated dimeric structures. The P centers contribute considerably to the frontier molecular orbitals of the compounds, thereby leading to smaller HOMO-LUMO gaps than in all-carbon-based congeners. Phenyl- and/or ethynylphenyl substituents at the A(2)PA framework influence the HOMO and LUMO to a varying degree depending on their relationship to the Mes* group, thus enabling a fine-tuning of the frontier molecular orbitals of the compounds.     

Between imide,imidyl and nitrene – an imido iron complex in two oxidation states

Imidyl and nitrene metal species play an important role in the N-functionalisation of unreactive C–H bonds as well as the aziridination of olefines. We report on the synthesis of the trigonal imido iron complexes [Fe(NMes)L₂]^0,− (L = –N{Dipp}SiMe₃); Dipp = 2,6-diisopropyl-phenyl; Mes = (2,4,6-trimethylphenyl) via reaction of mesityl azide (MesN₃) with the linear iron precursors [FeL₂]^0,−. UV-vis-, EPR-, ⁵⁷Fe Mössbauer spectroscopy, magnetometry, and computational methods suggest for the reduced form an electronic structure as a ferromagnetically coupled iron(ii) imidyl radical, whereas oxidation leads to mixed iron(iii) imidyl and electrophilic iron(ii) nitrene character. Reactivity studies show that both complexes are capable of H atom abstraction from C–H bonds. Further, the reduced form [Fe(NMes)L₂]⁻ reacts nucleophilically with CS₂ by inserting into the imido iron bond, as well as electrophilically with CO under nitrene transfer. The neutral [Fe(NMes)L₂] complex shows enhanced electrophilic behavior as evidenced by nitrene transfer to a phosphine, yet in combination with an overall reduced reactivity.

A pair of trigonal imido iron complexes ([Fe(NMes)L₂]^0,−) in two oxidation states is reported. The anionic complex K{crypt.222}[Fe(NMes)L₂] is best described as an iron(ii) imide.     

In Situ Spectroscopic Detection of Large-Scale Reorientations of Transmembrane Helices During Influenza A M2 Channel Opening**

Viroporins are small ion channels in membranes of enveloped viruses that play key roles during viral life cycles. To use viroporins as drug targets against viral infection requires in-depth mechanistic understanding and, with that, methods that enable investigations under in situ conditions. Here, we apply surface-enhanced infrared absorption (SEIRA) spectroscopy to Influenza A M2 reconstituted within a solid-supported membrane, to shed light on the mechanics of its viroporin function. M2 is a paradigm of pH-activated proton channels and controls the proton flux into the viral interior during viral infection. We use SEIRA to track the large-scale reorientation of M2’s transmembrane α-helices in situ during pH-activated channel opening. We quantify this event as a helical tilt from 26° to 40° by correlating the experimental results with solid-state nuclear magnetic resonance-informed computational spectroscopy. This mechanical motion is impeded upon addition of the inhibitor rimantadine, giving a direct spectroscopic marker to test antiviral activity. The presented approach provides a spectroscopic tool to quantify large-scale structural changes and to track the function and inhibition of the growing number of viroporins from pathogenic viruses in future studies.     

The Influence of Water in the Vapor-Assisted Conversion Synthesis of UiO-67 MOF Thin Films

Water is known to play an important role for the crystallization and stability of Zr-based metal-organic frameworks (MOFs). This work investigates its effect on the vapor-assisted conversion (VAC) synthesis of UiO-67 MOF thin films on Au-coated Si substrates. We demonstrate the equilibration processes taking place during the VAC procedure, confirming the gradual equilibration of all solutions upon heating. The presence of water affects the vapor phase composition but does not significantly impact the acetic acid equilibration rate. However, the preparation of UiO-67 thin films by VAC is highly sensitive to the water content in the reaction. Some water is required for the formation of the zirconium clusters, but excessive water in the reaction vial yields poorly crystalline materials. Atmospheric water that is taken up by the vapor source can be sufficient to reduce crystallinity dramatically. This complication can be partially overcome by increasing the amount of acetic acid in the vapor source.     

Front Cover: A Dibismuthane with Olefin Functional Groups: Towards Tridentate Hybrid Chalcogen/Olefin Ligands (Eur. J. Inorg. Chem. 32/2023)

Bis[dibenzobismepine], a dibismuthane composed of two bismepine units (R₂Bi−BiR₂), was synthesized and fully characterized (R₂=(C₆H₄CH)₂). Reactions of this dibismuthane with diphenyl dichalcogenides, dibenzoylperoxide, and elemental chalcogens have been investigated. All products of these reactions have been isolated and fully characterized, including a series of compounds R₂Bi−E−BiR₂ (E=O−Te). These species contain two olefin units of the bismepine moieties and a chalcogen atom as potential coordination sites. The potential of these species to act as hybrid tridentate chalcogen/olefin ligands with bismuth atoms as structure-determining elements in the backbone has been investigated by theoretical approaches, aiming at the complexation of Co^I, Rh^I, Ir^I and Ni⁰, Pd⁰, Pt⁰. The analytical techniques applied in this work include heteronuclear and 2D NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, and DFT calculations.