Extended Reaction Scope of Thiamine Diphosphate Dependent Cyclohexane‐1,2‐dione Hydrolase: From CC Bond Cleavage to CC Bond Ligation

ThDP‐dependent cyclohexane‐1,2‐dione hydrolase (CDH) catalyzes the C? C bond cleavage of cyclohexane‐1,2‐dione to 6‐oxohexanoate, and the asymmetric benzoin condensation between benzaldehyde and pyruvate. One of the two reactivities of CDH was selectively knocked down by mutation experiments. CDH‐H28A is much less able to catalyze the C? C bond formation, while the ability for C? C bond cleavage is still intact. The double variant CDH‐H28A/N484A shows the opposite behavior and catalyzes the addition of pyruvate to cyclohexane‐1,2‐dione, resulting in the formation of a tertiary alcohol. Several acyloins of tertiary alcohols are formed with 54–94 % enantiomeric excess. In addition to pyruvate, methyl pyruvate and butane‐2,3‐dione are alternative donor substrates for C? C bond formation. Thus, the very rare aldehyde–ketone cross‐benzoin reaction has been solved by design of an enzyme variant.     

Water Vapor Sorption in Cementitious Materials—Measurement,Modeling and Interpretation

The rate and extent of uptake and release of moisture are critical in controlling the behavior of cementitious materials ranging from fluid transport to hygral deformations. While classically determined using an equilibrium (static) salt solution method (Baroghel-Bouny in Cem Concr Res 37:414–437, 2007), advanced capabilities offered by gravimetric dynamic vapor sorption (DVS) analyzers, are now permitting acquisition of sorption spectra at microgram ( $\upmu \hbox {g}$ ) resolution on the order of a few weeks. This work highlights new multicycle determinations of adsorption/desorption isotherms, acquired using a custom-built DVS analyzer for well-hydrated alite and ordinary portland cement pastes over a range of water-to-solid ratios ( $w/s$ , mass basis). Special focus is paid to describe measurement aspects relevant to acquiring reliable spectra, and their interpretation. Sorption isotherms are used to assess transport properties, and sorption hysteresis and its irreversibility following first drying. Based on an optimization-based criterion, the Young-Nelson model is selected to simulate sorption evolutions, including the effects of hysteresis. Sensitivity analyses carried out using this model are used to understand the role of parameters, including porosity and $w/s$ , on the hysteresis that develops from the first to subsequent sorption cycles.     

One-pot formation of piperidine- and pyrrolidine-substituted pyridinium salts via addition of 5-alkylaminopenta-2,4-dienals to N-acyliminium ions: application to the synthesis of (±)-nicotine and analogs

Addition of 5-alkylaminopenta-2,4-dienals onto N-acyliminium ions, generated in situ from α-hydroxycarbamates derived from pyrrolidine or piperidine, in the presence of zinc triflate, followed by dehydrative cyclization, allowed the formation of pyridinium salts substituted at their 3-position by a five- or six-membered nitrogen heterocycle. Subsequent N-dealkylation of the pyridinium moiety and deprotection of the secondary amine or reduction of the carbamate function led to (±)-nicotine and analogs.     

Analysis of cocaine and benzoylecgonine in urine by using multisyringe flow injection analysis‐gas chromatography‐mass spectrometry system

In this paper, a method was described to determine cocaine (COC) and benzoylecgonine (BZE) in human urine samples by GC‐MS detection. The extraction of analytes from urine samples was achieved in an Oasis hydrophilic–lipophilic balance column (20 mm×3.9 mm id, dp=25 μm; Waters, USA), incorporated in a multisyringe flow injection system, used for the sample treatment. Finally, to improve the volatility of the BZE, an in‐line derivatization reaction with N,O‐bis (trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane was made microwave‐assisted in order to reduce the reaction time. The results showed that the proposed method is a good alternative for the analysis of COC and BZE in urine samples because it offers advantages compared with those described in the literature, which include simplicity in the sample treatment, the sensitivity and selectivity necessary to determine the analytes of interest at low levels in the urine and high sample throughput.     

Gold nanoclusters protected by conformationally constrained peptides

The preparation and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The peptides were devised to form 0-3 C=O...H-N intramolecular hydrogen bonds, as required by their 3(10)-helical structure. The monolayer-protected clusters (MPCs) were prepared, using a modified version of the two-phase Brust-Schiffrin preparation, and fully characterized with (1)H NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The MPCs were obtained with core diameters in the range of 1.1-2.3 nm, depending on the reaction conditions. Structured peptides formed smaller clusters. The smallest MPC obtained is in agreement with the average formula Au(38)Pep(18). The results showed that the chemical integrity of the peptide is maintained upon monolayer formation and that the average number of peptide ligands per gold cluster is typically 75-85% the value calculated for alkanethiolate MPCs of similar sizes. The IR and NMR spectra indicated that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds.