Identifying Enantiomers in Mixtures of Chiral Molecules with Broadband Microwave Spectroscopy

Chirality‐sensitive broadband microwave spectroscopy was performed on mixtures of carvone enantiomers and conformers to distinguish enantiomers, measure enantiomeric excesses, and determine the absolute configurations of the enantiomers. This method uses microwave three‐wave mixing and is inherently well‐suited to the analysis of mixtures—a unique advantage over other techniques. In contrast to conventional microwave spectroscopy, the phase of the received signal is also exploited. This phase depends upon the signs of the molecules’ dipole‐moment components and is used to identify the excess enantiomer. The measured signal amplitude determines the size of the excess. The broadband capabilities of the spectrometer were used to simultaneously excite and measure two conformers of carvone, demonstrating the analysis of a sample with multiple chiral species. Employing quantum chemical calculations and the measured phases, the absolute configurations of the enantiomers are determined.     

Protease Probes that Enable Excimer Signaling upon Scission

Peptide‐based probes that fluoresce upon proteolytic cleavage are invaluable tools for monitoring protease activity. The read‐out of protease activity through pyrene excimer signaling would be a valuable asset because the large Stokes shift and the long lifetime of the excimer emission facilitate measurements in autofluorescent media such as blood serum. However, proteolytic cleavage abolishes rather than installs the proximity relationships required for excimer signaling. Herein, we introduce a new probe architecture to enable the switching on of pyrene excimer emission upon proteolytic scission. The method relies on hairpin‐structured peptide nucleic acid (PNA)/peptide hybrids with pyrene units and anthraquinone‐based quencher residues positioned in a zipper‐like arrangement within the PNA stem. The excimer hairpin peptide beacons afforded up to a 50‐fold enhancement of the pyrene excimer emission. Time‐resolved measurements allowed the detection of matrix metalloprotease 7 in human blood serum.     

Multifunctional Redox Polymers: Electrochrome,Polyelectrolyte, Sensor,Electrode Modifier,Nanoparticle Stabilizer,and Catalyst Template

Simple “click” polycondensation metallopolymers of redox‐robust bis(ethynyl)biferrocene (biFc) and di(azido) poly(ethylene glycol) (PEG400 and PEG1000) were designed for multiple functions including improvement of water solubility and biocompatibility, the introduction of mixed valency and sensing capabilities, and as nanoparticle stabilizers for catalysis.     

A 1,1‐Carboboration Route to Bora‐Nazarov Systems

Hydroboration of the conjugated enynes 1 a and 1 b with Piers’ borane [HB(C₆F₅)₂] gave the respective dienylboranes trans‐ 2 c and trans‐ 2 d . Their photolysis resulted in the formation of the dihydroborole products 3 c and 3 d . Both were converted to their pyridine adducts 5 c and 5 d , respectively. Compounds 3 c and 5 c,d were characterized by X‐ray diffraction. The reaction of the bis(enynyl)boranes 6 a and 6 b with B(C₆F₅)₃ resulted in the formation of the dihydroboroles 7 a and 7 b , respectively. This reaction is thought to proceed by 1,1‐carboboration of one of the enynyl substituents at boron to generate the dienylborane intermediates 8 a / 8 b , followed by thermally induced bora‐Nazarov ring‐closure and subsequent stabilizing 1,2‐pentafluorophenyl group migration from boron to carbon. Compound 7 a was characterized by X‐ray diffraction and solid‐state ¹¹B NMR spectroscopy.     

Peak assignment in multi-capillary column–ion mobility spectrometry using comparative studies with gas chromatography–mass spectrometry for VOC analysis

Over the past years, ion mobility spectrometry (IMS) as a well established method within the fields of military and security has gained more and more interest for biological and medical applications. This highly sensitive and rapid separation technique was crucially enhanced by a multi-capillary column (MCC), pre-separation for complex samples. In order to unambiguously identify compounds in a complex sample, like breath, by IMS, a reference database is mandatory. To obtain a first set of reference data, 16 selected volatile organic substances were examined by MCC-IMS and comparatively analyzed by the standard technique for breath research, thermal desorption–gas chromatography–mass spectrometry. Experimentally determined MCC and GC retention times of these 16 compounds were aligned and their relation was expressed in a mathematical function. Using this function, a prognosis of the GC retention time can be given very precisely according to a recorded MCC retention time and vice versa. Thus, unknown MCC-IMS peaks from biological samples can be assigned—after alignment via the estimated GC retention time—to analytes identified by GC/MS from equivalent accomplished data. One example of applying the peak assignment strategy to a real breath sample is shown in detail.     

Salen-type compounds of calcium and strontium

Salen complexes of the heavy alkaline-earth metals, calcium and strontium, were prepared by the reaction of various salen(t-Bu)H(2) ligands with the metals in ethanol. Six new calcium and strontium compounds, [Ca(salen(t-Bu))(HOEt)(2)(thf)] (1), [Ca(salen(t-Bu))(HOEt)(2)] (2), [Ca(salpen(t-Bu))(HOEt)(3)] (3), [Ca(salophen(t-Bu))(HOEt)(thf)] (4), [Sr(salen(t-Bu))(HOEt)(3)] (5), and [Sr(salophen(t-Bu))(HOEt)(thf)(2)] (6), were formed in this way with the quatridentate Schiff-base ligands N,N'-bis(3,5-di-tert-butylsalicylidene)ethylenediamine (salen(t-Bu)H(2)), N,N'-bis(3,5-di-tert-butylsalicylidene)-1,3-propanediamine (salpen(t-Bu)H(2)), and N,N'-o-phenylenebis(3,5-di-tert-butylsalicylideneimine (salophen(t-Bu)H(2)). Initially, ammonia solutions of the metals were combined with the salen(t-Bu)H(2) ligands, and in the reaction of strontium with salen(t-Bu)H(2), the unusual tetrametallic cluster [(OC(6)H(2)(t-Bu)(2)CHN(CH(2))(2)NH(2))Sr(mu(3)-salean(t-Bu)H(2))Sr(mu(3)-OH)](2) (7) was produced (salean(t-Bu)H(4) = N,N'-bis(3,5-di-tert-butyl-2-hydroxybenzyl)ethylenediamine). In this compound, the imine bonds of the salen(t-Bu)H(2) ligand were reduced to form the known ligands salean(t-Bu)H(4) and (HO)C(6)H(2)(t-Bu)(2)CHN(CH(2))(2)NH(2). Compounds 1, 5, 6, and 7 were structurally characterized by single-crystal X-ray diffraction. Crystal data for 1 (C(44)H(74)CaN(2)O(6)): triclinic space group P(-)1, a = 8.3730(10) A, b = 14.8010(10) A, c = 18.756(2) A, alpha = 72.551(10) degrees, beta = 81.795(10) degrees, gamma = 78.031(10) degrees, Z = 2. Crystal data for 5 (C(38)H(64)SrN(2)O(5)): monoclinic space group P2(1)/c, a = 23.634(3) A, b = 8.4660(10) A, c = 24.451(3) A, beta = 101.138(10) degrees, Z = 4. Crystal data for 6 (C(46)H(67)N(2)O(5)Sr): orthorhombic space group P2(1)2(1)2(1), a = 10.5590(2) A, b = 16.2070(3) A, c = 26.7620(6) A, Z = 4. Crystal data for 7 (C(98)H(156)N(8)O(8)Sr(4)): triclinic space group P(-)1, a = 14.667(1) A, b = 15.670(1) A, c = 18.594(2) A, alpha = 92.26(1) degrees, beta = 111.84(1) degrees, gamma = 117.12(1) degrees, Z = 4.     

Ln(III) methyl and methylidene complexes stabilized by a bulky hydrotris(pyrazolyl)borate ligand

The reaction of Ln(AlMe(4))(3) with bulky hydrotris(pyrazolyl)borate (Tp(t)(Bu,Me))H proceeds via a sequence of methane elimination and C-H bond activation, affording unprecedented rare-earth metal ligand moieties including Ln(Me)[(micro-Me)AlMe(3)] and X-ray structurally characterized "Tebbe-like" Ln[(micro-CH(2))(2)AlMe(2)].     

Simultaneous determination of a spectrum of trichothecene toxins out of residuals of biogas production

A sensitive and selective method for the simultaneous determination of a spectrum of trichothecenes in residuals of biogas production has been developed. It comprises sample clean-up by liquid/liquid partition for digested manure and solid phase extraction for digested solid phase. Quantification of A- and B-type trichothecenes as their trifluoroacetyl derivatives is performed by gas chromatography mass spectrometry (GC/MS), that of B-type trichothecenes alternatively by high-performance liquid chromatography (HPLC). Fluorescence detection (FLD) after post-column derivatisation using methylacetoacetate and ammonium acetate after alkaline decomposition of toxins was applied. Detection limits in digestates were between 1 and 30 microg/l and 20 and 50 microg/l for GC/MS and HPLC/FLD, respectively. Recovery rates were between 52 and 129% for GC/MS detection with the exception of T-2 tetraol with 22%, and between 56 and 123% for HPLC/FLD.     

Reactivity of stoichiometric titanium oxide cations

We present the results of a reactivity study of titanium cationic clusters towards CO, C(2)H(2), C(2)H(4) and C(3)H(6) based on guided-ion-beam mass spectrometry and DFT calculations. We identified Ti(2)O(4)(+) and to a lesser extent TiO(2)(+) species which preferentially undergo oxidation reactions. An oxygen centered radical of Ti(2)O(4)(+) is responsible for selective oxidation. Energy profiles and MD simulations reveal the mechanisms of the reactions. Regeneration of the oxygen centered radical was achieved experimentally and theoretically through the reaction of N(2)O with Ti(2)O(3)(+).     

Tuning Single‐Molecule Dynamics in Functionalized Mesoporous Silica

Diffusion of single molecules of a substituted terrylene diimide dye in functionalized mesoporous silica films was monitored by single‐molecule fluorescence microscopy. By varying the chemical nature and density of the functional groups, the diffusion dynamics of the dye molecules can be controlled precisely. The picture shows a sketch of a dye molecule in a pore, diffusion data for different phenyl functionalization densities, and the trajectory of one molecule in a cyanopropyl‐functionalized film.