NMR Structure Determination of Saccharose and Raffinose by Means of Homo‐ and Heteronuclear Dipolar Couplings

Residual dipolar couplings have dramatically improved the accuracy and precision of high‐resolution NMR structures during the last years. This was first demonstrated for proteins. In this article, we describe, with raffinose and saccharose as examples, that dipolar couplings improve the precision of structures of carbohydrates for which usually very few structural parameters are available. The relative orientation as well as the dynamics of the monosaccharide moieties with respect to each other can be determined with the help of ¹³C,¹H and ¹H,¹H dipolar couplings, which can easily be measured. Significant differences between the solution and the X‐ray crystal structure exist. These results indicate that residual dipolar‐coupling data may provide a more complete and dynamic model of carbohydrates in particular, and small molecules in general.     

Aminoderivate von α‐P4S3, α‐P4Se3 und P3Se4 – Daten und Analyse der 31P‐NMR‐Spektren in Lösungen

Amino Derivatives of α‐P₄S₃, α‐P₄Se₃, and P₃Se₄; Data and Analyses of their ³¹P NMR Spectra in Solution α‐P₄S₃I₂, α‐P₄Se₃I₂, and P₃Se₄I were reacted with primary and secondary amines in CS₂. The reaction yields exo‐exo isomeres of α‐P₄S₃L₂ and α‐P₄Se₃L₂, the N‐bridged compounds α‐P₄S₃L′ and P₃Se₄L, with L = NHR¹, NPhR², THC (R¹ = ^tBu, Ad, Ph, Flu, TPMP; R² = Me, Et, ⁱPr), and L′ = NR¹. The ³¹P NMR data of the compounds in CS₂ solution were measured. By the reaction of α‐P₄Se₃I₂ with primary amines NH₂^tBu and NH₂Ad in CS₂ an asymmetric isomer α‐P₄Se₃I_endo(NHR¹)_exo was observed for the first time in the ³¹P NMR spectra. The influence of the ligands L on the ³¹P NMR parameter of α‐P₄S₃L₂, α‐P₄Se₃L₂, and P₃Se₄L is discussed.     

Zwei neue Phosphorsulfide

Two New Phosphorus Sulfides Jason [1] prepared by the reaction of triphenylantimony sulfide with α-P₄S₅ and α-P₄S₇ new phosphorus sulfides. The application of this method on α-P₄S₄ yielded the main product γ-P₄S₅ which was assumed to appear in low concentration in phosphorus-sulfur melts by Bjorholm and Jakobsen [2]. In addition the new isomers δ-P₄S₆ and ϵ-P₄S₆ were identified by ³¹P-NMR spectroscopy. Furtheron the sulfurization of α-P₄S₅ and β-P₄S₅ was studied. Reaction paths are suggested. In all cases the primary reaction is an exocyclic addition of phosphorus, followed by insertion or further addition.     

Synthese und Kristallstruktur von [Fe(MeCN)6][Fe2OCl6]

Synthesis and Crystal Structure of [Fe(MeCN)₆][Fe₂OCl₆] [Fe(MeCN)₆][Fe₂OCl₆] ( 2 ) is obtained by passing dry air through a solution of FeCl₂ in acetonitrile in almost quantitative yield. 2 crystallises in the trigonal space group R 3 [a = b = 12.121(1), c = 29.875(6) Å, Z = 6]. The oxygen atom in the Fe₂OCl₆ anion occupies the 3 position and causes therefore an Fe–O–Fe angle of 180°. The refinement in the triclinic space group P1 leads to a slightly bent arrangement of the Fe–O–Fe fragment.     

Laser Diffraction Spectroscopy: Influence of Particle Shape and a Shape Adaptation Technique

The evaluation algorithm employed in laser diffraction spectroscopy is usually based on the Fraunhofer diffraction theory for spheres. As this evaluation theory is limited to spheres only, the measurement of irregularly shaped particles results in errors in the evaluated particle size distribution. To determine the influence of the particle shape, measurements of arbitrarily shaped particles were simulated, evaluated and compared with results for spherical particles of the same projected area. The detailed investigations showed that the particle's microstructure, i.e. its surface roughness, has almost no or only a negligible effect on the measurement result. In contrast to this advantageous outcome, the particle's microstructure, i.e. its axis ratio, affects the measurement result greatly and must be taken into account in the evaluation method. Based on these results, particles were considered to be ellipsoids with specific (but negligible) surface structures and a mathematical adaptation method was developed by extending the evaluation theory from spheres to randomly in space oriented ellipsoids. Simulations and experiments with reticles verified the need for this adaptation technique and its efficiency when applied.     

Platin(0)‐Komplexe mit amino‐substituierten Alkinen: Neue Metallorganische Bausteine für supramolekulare Architekturen und „Kristall‐Engineering”︁

Platinum(0) Complexes with Amino‐Substituted Alkynes: Novel Organometallic Building Blocks for Supramolecular Architectures and “Crystal Engineering” Homoleptic Bis(alkyne)platinum(0) compounds containing either NH₂‐ or NH₂‐/OH‐substituents are formed by reaction of Pt(cod)₂ with alkynes as stable compounds. They can be used as variable building blocks for supramolecular networks. The crystal structure analyses of Bis(2‐amino‐2,5dimethyl‐5‐hydroxy‐hex‐3‐yne)platinum(0) ( 1 ) and of Bis(1(3‐amino‐3‐methyl‐but‐1‐inyl)‐cyclohexane‐1‐ol)platinum(0) ( 2 ) exhibit that the low‐valent Pt atom is tetrahedrally surrounded by the four sp‐hybridizated carbonatoms of the alkynes. Despite the fact that the bond lengths and ‐angles of the PtC₄ units are equal, the supramolecular structures are different. While in 1 polymer strands are formed in which the bis(alkyne)‐Pt⁰ units are connected by (OH)₂(NH₂)₂‐ tetrahedrons, 2 yields only a dimer containing a network of four OH‐ and two NH₂‐groups. Platinum(0) complexes with cationic alkynes bearing ammonium substituents can be isolated as thermal stable compounds. The X‐ray structures of [Cl( FH ⁺)Pt(cod)]₄ ( 8 ) reveals that four molecular units form a cube with both four NH₃⁺ groups and Cl^– at the corners connected by hydrogen bridges. In the bis(alkyne)Pt⁰ complex [Cl_1.5( FH ⁺)_1.5( F )_0.5Pt] ( 9 ) only 1,33 of two NH₂ groups are protonated and a hydrogen bridged network connects four bis(alkyne)Pt⁰ units (cod: cycloocta‐1.5‐diene, F : 1‐(trimethylsilylethinyl)‐1‐amino‐cyclohexane).     

The Strengths of Some Violations of Covering

We consider two models V₁, V₂ of ZFC such that V₁ ⊆ V₂, the cofinality functions of V₁ and of V₂ coincide, V₁ and V₂ have that same hereditarily countable sets, and there is some uncountable set in V₂ that is not covered by any set in V₁ of the same cardinality. We show that under these assumptions there is an inner model of V₂ with a measurable cardinal κ of Mitchell order κ⁺⁺. This technical result allows us to show that changing cardinal characteristics without changing cofinalities or ω‐sequences (which was done for some characteristics in [13]) has consistency strength at least Mitchell order κ⁺⁺. From this we get that the changing of cardinal characteristics without changing cardinals or ω‐sequences has consistency strength Mitchell order ω₁, even in the case of characteristics that do not stem from a transitive relation. Hence the known forcing constructions for such a change have lowest possible consistency strength. We consider some stronger violations of covering which have appeared as intermediate steps in forcing constructions.     

A Practical One-Pot Synthesis of Positron Emission Tomography (PET) Tracers via Nickel-Mediated Radiofluorination

Invited for this months cover picture is the group of Professor Bernd Neumaier at the Institute of Radiochemistry and Experimental Molecular Imaging at the University Clinic of Cologne. The cover picture shows the differences in brain metabolism of a healthy young and a healthy old subject, as well as a patient suffering from Parkinsons disease (left to right) uncovered by 6-[¹⁸F]FDOPA-positron emission tomography (PET). Morbus Parkinson occurs when nerve cells that produce dopamine begin to die. The shortage of dopamine leads to movement problems in affected individuals. 6-[¹⁸F]FDOPA is extensively used to evaluate the progression of Parkinsons disease. Bold stick projections of this PET tracer, as well as a neuronal network, are seen in the background. Unfortunately, conventional procedures to produce 6-[¹⁸F]FDOPA are cumbersome. Thus, several recent developments aim at the simplification of this radiosynthesis. In our work, we studied the applicability of the recently reported Ni-mediated radiofluorination approach for daily routine production of 6-[¹⁸F]FDOPA. For more details, see the Full Paper on p. 457 ff.     

Irreversible electrostatic deposition of Prussian blue from colloidal solutions

Prussian blue (PB) can be deposited from colloidal solutions (5.4 × 10⁻³ mol_PB L⁻¹, 0.01 mol L⁻¹ KNO₃) on glassy carbon, either by potential cycling or potentiostatically, provided that the deposition potential is more positive than −0.2 V vs. Hg/Hg₂Cl₂. Depending on the deposition potential, the PB particles form either a single layer of Everitt’s salt, of PB, or multilayers of Berlin green. Also depending on the electrode potential, the deposition was accompanied by currents which were either only of capacitive nature, or represent the sum of capacitive and faradaic currents. The currents were always limited by the diffusion of the colloidal particles to the electrode surface, i.e., they obeyed the Cottrell equation. The PB layers were characterized by in situ atomic force microscopy.