The NMR reciprocity theorem for arbitrary probe geometry

It is shown that the NMR reciprocity theorem is a variant of a problem considered by Lorentz in 1895. This formulation is quite general and applies to electric-dipole-based as well as coil-based or resonator-based magnetic resonance probes. The reasoning is related to, but different from, the proof of the reciprocity theorem for radiofrequency networks and for transmit/receive antenna systems in telecommunications. The signal-to-noise ratio of the NMR experiment is also discussed in very general terms.     

Fluorescence A 4.3 μm en fonction de la pression dans un laser CO2 supraatmospherique

We have observed the 4.3 μm fluorescence signal produced by a superatmospheric double-discharge CO₂ laser, up to a pressure of 5 atm. The evolution of the signal amplitude with pressure reveals an unusual behaviour which we associate to the hot bands. Moreover, we have deduced the V-V relaxation times of CO₂ in mixtures CO₂:N₂:He of (10:5:85) and CO₂:He of (9:91).     

The vibration-rotation spectrum of D12CP in the region of the ν2 band: The spectroscopic constants for the states 0000, 0110, 0200, and 0220 and the bond lengths of the molecule

The vibration-rotation spectrum of DCP has been recorded with a resolution of 0.004 cm^?1 in the spectral region extending from 575 to 475 cm^?1. The fundamental band ν₂ and the “hot” bands from the vibrational level (01¹0) to the levels (02⁰0) and (02²0) have been identified and analyzed. A total of 347 infrared transitions have been measured and their wavenumbers together with 13 microwave or millimeter-wave frequencies have been fit simultaneously to obtain 15 spectroscopic constants including those arising from l-type doubling and l-type resonance. The agreement between the calculated and measured wavenumbers of nonblended lines is usually within 1 × 10^?4 cm^?1. These constants, used in conjunction with the ones previously obtained for the molecule, allow the calculation of the anharmonicity constants x₂₂ and g₂₂ and of the second-order vibration-rotation interaction constants γ₂₂ and γ₁₁. Although many of the γ's are still missing because an insufficient number of bands have been analyzed, the equilibrium bond lengths for the molecule have been recalculated using the improved set of first-order vibration-rotation interaction constants: r_e(CH) = 1.06596(11)Å and r_e(CP) = 1.540452(18)Å.     

Umpolung of Methylenephosphonium Ions in Their Manganese Half‐Sandwich Complexes and Application to the Synthesis of Chiral Phosphorus‐Containing Ligand Scaffolds

Half‐sandwich manganese methylenephosphonium complexes [Cp(CO)₂Mn(η²‐R₂P?C(H)Ph)]BF₄ were obtained in high yield through a straightforward reaction sequence involving a classical Fischer‐type manganese complex and a secondary phosphine as key starting materials. The addition of various nucleophiles (Nu) to these species took place regioselectively at the double‐bonded carbon center of the coordinated methylenephosphonium ligand R₂P⁺?C(H)Ph to produce the corresponding chiral phosphine complexes [Cp(CO)₂Mn(κ¹‐R₂P? C(H)(Ph)Nu)], from which the phosphines were ultimately recovered as free entities upon simple irradiation with visible light. The synthetic potential of this umpolung approach is illustrated herein by the preparation of novel chiral pincer‐type phosphine–NHC–phosphine ligand architectures.     

The Kalimantacin Polyketide Antibiotics Inhibit Fatty Acid Biosynthesis in Staphylococcus aureus by Targeting the Enoyl‐Acyl Carrier Protein Binding Site of FabI

The enoyl‐acyl carrier protein reductase enzyme FabI is essential for fatty acid biosynthesis in Staphylococcus aureus and represents a promising target for the development of novel, urgently needed anti‐staphylococcal agents. Here, we elucidate the mode of action of the kalimantacin antibiotics, a novel class of FabI inhibitors with clinically‐relevant activity against multidrug‐resistant S. aureus. By combining X‐ray crystallography with molecular dynamics simulations, in vitro kinetic studies and chemical derivatization experiments, we characterize the interaction between the antibiotics and their target, and we demonstrate that the kalimantacins bind in a unique conformation that differs significantly from the binding mode of other known FabI inhibitors. We also investigate mechanisms of acquired resistance in S. aureus and identify key residues in FabI that stabilize the binding of the antibiotics. Our findings provide intriguing insights into the mode of action of a novel class of FabI inhibitors that will inspire future anti‐staphylococcal drug development.     

Azavinylidenephosphoranes: A Class of Cyclic Push–Pull Carbenes

The synthesis of a novel family of cyclic push–pull carbenes, namely, azavinylidene phosphoranes, is described. The methodology is based on a formal [3+2] cycloaddition between terminal alkynes and phosphine–imines followed by an oxidation/deprotonation step. Carbenes 6 , obtained by simple deprotonation, exhibit typical transient carbene reactivity like the intramolecular C?H insertion reaction and a pronounced ambiphilic character exemplified by [2+1] cycloaddition with electron‐poor methyl acrylate. Owing to the cyclic structure, carbenes 6 also exhibit an excellent coordination ability toward transition metals. Rh^I complex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X‐ray crystallography. The corresponding Rh^I–carbonyl complex was also prepared; this indicates that carbenes 6 belong to the strongest σ‐donating ligands to date. DFT calculations confirmed the high σ‐donation ability of 6 and their classification as push–pull carbenes with a relatively small singlet–triplet energy gap of 23.2–24.3 kcal mol^?1.     

Electronic Tuning of a Carbene Center via Remote Chemical Induction,and Relevant Effects in Catalysis

The present report develops the idea that an N‐heterocyclic carbene incorporating a remote anionic functionality—here, a malonate group—as a backbone component of its heterocyclic framework, can be “post‐functionalized” directly from its transition‐metal complexes, upon simple addition of a variety of electrophiles interacting directly with the malonate group in the outer coordination sphere. From a palette of selected electrophilic reagents, it was thus possible to modulate the electronic donor properties of the carbene center over a rather broad range. Both the zwitterionic complex [Rh{malo‐NHC}(cod)] and the cationic derivatives [Rh{malo‐NHC^E}(cod)]⁺ (where “malo‐NHC^E” represents the ligand modified by a selected electrophile “E”) were used as pre‐catalysts in two types of catalytic reactions, namely, the polymerization of phenylacetylene and the hydroboration of styrene. The results indicate that, in both cases, the zwitterionic species is by far the best catalyst, whereas a decrease in the ligand donicity induced by the added electrophile results in a concomitant reduction of catalytic activity. Apparent deviations to such a trend in the case of the hydroboration of styrene were rationalized in terms of an interaction between the reactive catecholborane substrate and the remote functionality of the N‐heterocyclic carbene leading to an in situ modification of the nature of the active species. These observations serve as a useful basis to define the scope and limitations of the present conceptual approach in catalysis.     

Tributyltin determination in marine sediments: A comparative study of methods

Two independent speciation methods have been applied to the determination of tributyltin (TBT) in marine sediments: (1) acetic acid leaching/hydride generation/cold trapping/GC/quartz furnace AA; and (2) toluene–tropolone extraction/HPLC/GFAA. TBT determines in a typically moderately polluted sediment (Porto Vecchio Bay, Corsica, France) are in very good agreement, as also are the determination of total recoverable tin by the first method and by a direct one using strong acid leaching followed by GFAA. These cross-verifications lead one to conclude that both speciation methods are convenient and allow for valid determination of TBT in marine sediments, with no loss of TBT. Method-induced modification of tin speciation has not been observed.