Periodic Behavior of Lanthanide Coordination within Reverse Micelles

Trends in lanthanide(III) (Ln^III) coordination were investigated within nanoconfined solvation environments. Ln^III ions were incorporated into the cores of reverse micelles (RMs) formed with malonamide amphiphiles in n‐heptane by contact with aqueous phases containing nitrate and Ln^III; both insert into pre‐organized RM units built up of DMDOHEMA (N,N′‐dimethyl‐N,N′‐dioctylhexylethoxymalonamide) that are either relatively large and hydrated or small and dry, depending on whether the organic phase is acidic or neutral, respectively. Structural aspects of the Ln^III complex formation and the RM morphology were obtained by use of XAS (X‐ray absorption spectroscopy) and SAXS (small‐angle X‐ray scattering). The Ln^III coordination environments were determined through use of L₃‐edge XANES (X‐ray absorption near edge structure) and EXAFS (extended X‐ray absorption fine structure), which provide metrical insights into the chemistry across the period. Hydration numbers for the Eu species were measured using TRLIFS (time‐resolved laser‐induced fluorescence spectroscopy). The picture that emerges from a system‐wide perspective of the Ln? O interatomic distances and number of coordinating oxygen atoms for the extracted complexes of Ln^III in the first half of the series (i.e., Nd, Eu) is that they are different from those in the second half of the series (i.e., Tb, Yb): the number of coordinating oxygen atoms decrease from 9 O for early lanthanides to 8 O for the late ones—a trend that is consistent with the effect of the lanthanide contraction. The environment within the RM, altered by either the presence or absence of acid, also had a pronounced influence on the nitrate coordination mode; for example, the larger, more hydrated, acidic RM core favors monodentate coordination, whereas the small, dry, neutral core favors bidentate coordination to Ln^III. These findings show that the coordination chemistry of lanthanides within nanoconfined environments is neither equivalent to the solid nor bulk solution behaviors. Herein we address atomic‐ and mesoscale phenomena in the under‐explored field of lanthanide coordination and periodic behavior within RMs, providing a consilience of fundamental insights into the chemistry of growing importance in technologies as diverse as nanosynthesis and separations science.     

3‐[2,6‐Bis­(diethyl­carbamoyl)­pyridin‐4‐yl]‐N‐(tert‐butoxy­carbonyl)­alanine methyl ester: a chiral tridentate ligand that causes a diastereomeric excess of its lanthanide complexes in solution

L⁴, or 3‐[2,6‐bis­(diethyl­carbamoyl)­pyridin‐4‐yl]‐N‐(tert‐but­oxy­car­bonyl)­alanine methyl ester, C₂₄H₃₈N₄O₆, crystallizes in neat [010] laths stabilized by abundant intra‐ and intermolecular hydrogen bonds. The strongest of these form [010] chains of mol­ecules, thus rationalizing the fastest growth direction, while the slowest direction coincides with the normal to the (110) layers, which are linked by very weak hydrogen bonds. There exist two independent mol­ecules, the distances and bond angles of which differ in a random manner only. The torsion and dihedral angles, however, differ so as to achieve optimal packing. The influence of the chiral group in the 4‐position of the pyridine ring on the helical wrapping and on the ensuing diastereomeric induction is briefly discussed.     

Protection and Labelling of Thymidine by a Fluorescent Photolabile Group

A fluorescent photolabile group including coumarin and MeNPOC moieties was synthesized to protect 5′‐OH terminal function of thymidine (T). Its photochemical and photophysical properties were studied, in particular the photocleavage (photodeprotection under a 365‐nm irradiation) is only lowered by a factor of two by addition of the fluorophore. Fluorescence properties of the coumarin probe are not changed upon irradiation, which is satisfactory for the application required, i.e., in situ synthesis of DNA microarrays.     

Affinity of human thrombin for insoluble polystyrene substituted with sulfonate,n-hydroxyethylsulfamoyl and n-substituted amidine functions

A new polymeric material was prepared from polystyrene beads with N-substituted amidines and rendered hydrophilic with sulfonate and N-hydroxyethylsulfamoyl groups. It was synthesized by reacting the p-chlorosulfonyl polystyrene with ethanolamine followed by the Michael-like addition of the terminal OH of the polymer (PSEa) to N-t-butyl-N'-phenylpropenamidine 1 thus leading to the final polymer PSEaAm. Its affinity constant for human α-thrombin calculated from the Langmuir adsorption isotherms was about 10⁶ M⁻¹, a value comparable to the one estimated for polystyrene modified with L-arginine methyl ester. This new material was used as stationary phase in affinity chromatography of thrombin confirming a strong and specific interaction between the positively charged amidinium groups and the enzyme at pH = 7.4 and desorption at pH = 10 and high ionic strength.     

Properties of GeSi Nanocrystals Embedded in Hexagonal SiC

In this paper high‐resolution electron microscopy investigations and molecular dynamics simulations of GeSi nanocrystals buried in 4H‐SiC are performed, showing that the experimentally observed shapes of the GeSi nanocrystals are strongly correlated with their orientational relationships. Measurements of the lattice spacing suggest that the nanocrystals are strained. Quantum confinement in selected nanocrystals has been detected using spatially‐resolved electron energy loss spectroscopy performed in conjunction with atomic resolution annular dark‐field scanning TEM.     

Temperature behaviour of optical properties of Si+-implanted SiO2

Silicon nanocrystals were prepared by Si⁺-ion implantation and subsequent annealing of SiO₂ films thermally grown on a c-Si wafer. Different implantation energies (20-150 keV) and doses - cm ^-2 ) were used in order to achieve flat implantation profiles (through the thickness of about 100 nm) with a peak concentration of Si atoms of 5, 7, 10 and 15 atomic%. The presence of Si nanocrystals was verified by transmission electron microscopy. The samples exhibit strong visible/IR photoluminescence (PL) with decay time of the order of tens of μs at room temperature. The changes of PL in the range 70-300 K can be well explained by the exciton singlet-triplet splitting model. We show that all PL characteristics (efficiency, dynamics, temperature dependence, excitation spectra) of our Si⁺-implanted SiO₂ films bear close resemblance to those of a light-emitting porous Si and therefore we suppose similar PL origin in both materials. Received 1st September 1998 and Received in final form 7 September 1999     

Lowering of magnetic field intensity at the surfaces of α-Fe2O3 and FeBO3 single crystals

Depth-selective conversion electron Mössbauer spectroscopy was used to study magnetic properties of the thin surface layers of the α-Fe₂O₃ and FeBO₃ single crystals. An analysis of the experimental spectra indicates that the magnetic properties of the layers at a depth of more than ～100 nm from the surface are similar to the properties of crystal bulk, and the corresponding spectra consist of narrow lines. The lines gradually broaden as the crystal surface is approached. The spectra of the ～10-nm-thick surface layers consist of broad lines, indicating a wide distribution δ=2.1 T of the effective magnetic field about its mean value of 32.2(4) T. The experimental spectra were used to determine the effective magnetic fields (H _eff) for the iron ions situated in the surface layers of thickness ～100 nm. The effective fields in these layers were found to gradually decrease at room temperature (291 K) as the crystal surface was approached. The H _eff values in the 2.4(9)-nm-thick surface layer of the α-Fe₂O₃ crystal and 4.9(9)-nm layer of FeBO₃ are 0.7(2) and 1.2(3)%, respectively, smaller than for the nuclei of the ions in the bulk of these crystals.     

Reduction—complexation des sulfures de phosphines par les fer-carbonyles

1-Phenyl-3,4-dimethylphosphole (L) yields the classic σ complex LFe(CO)₄ with Fe₂(CO)₉ and the unsual σ,π complex LFe₂(CO)₇ with Fe₃(CO)₁₂, whereas 1-t-butyl-3,4-dimethylphosphole (L′) with Fe₃(CO)₁₂ yields L′Fe₂(CO)₆ which belongs to a type already described in the literature. With Fe₂(CO)₉ at 85°C, the phosphole sulfide LS yields the two σ and σ,π complexes directly by reduction—complexation. This Fe₂(CO)₉ reduction—complexation process works only with phosphole and phospholene sulfides. However, with Fe(CO)₅ in great excess at 150°C, a general phosphine sulfide reduction—complexation procedure takes place. A study of the displacement of 1-phenyl-3,4-dimethyl-3-phospholene (L″) from its σ complex L″Fe(CO)₄ by trimethylphosphite has shown that L″ has a greater complexing ability toward iron than the phosphite, contrary to what could be expected from the work of Tolman on nickel complexes.     

The evolution of the brabender farinograph

The importance of the consistency of wheat flour dough in baking is defined. This is normally determined with the aid of a recording dough mixer.Such a mixer was first patented byHogarth, a Scottish miller in 1889 but proved inadequate. About 40 years laterHankóczy a Hungarian cereal chemist initiated the line of recording dough mixers which are used today.His andBrabender's work are reviewed which led from a factory mixer fitted with an ammeter, via the early torque recording laboratory instruments to the modern Farinograph. The basic unit is described in some detail.Slides of the various attachments are shown which allow application to grinding and high speed mixing both on a batch and continuous basis.The use of the system for the testing of cereal products, fats, rubber, filler and plastics is described.The theoretical significance of the results obtained is briefly discussed. The lecture is illustrated by 14 slides.Paper presented at the Conference on Experimental Rheology, University of Bradford, April 17–19, 1968. — Original paper unpublished.     

Evidence for non-cubic magnetostriction in epitaxial bubble garnets

Epitaxial bubble garnet films grown on non-magnetic garnet substrates exhibit a dominant growth or stress induced uniaxial anisotropy, which is responsible for the stripe and bubble domain structures, and the intrinsic cubic magnetocrystalline anisotropy which can affect bubble device performance. The anisotropy constants have been deduced from measurements of stripe domain nucleation in the garnet films. We extend this measurement technique and its interpretation so that it also yields values of the magnetoelastic interactions.The measurement is based on observing the details of the topography of the nucleating domain structure, specifically the orientation of the nucleating stripe domains as a function of the orientation and magnitude of the applied magnetic field.The interpretation is based on a micromagnetic analysis of the conditions for homogeneous second order stripe domain nucleation. The contributions to the phenomena of the cubic anisotropy and of the magnetostriction are included in the analysis as perturbations.The theory produces predictions which are compatible with qualitative earlier experiments reported in the literature. It provides a satisfactory quantitative account of systematic new observations we have made on a GdTmY bubble garnet film with the specific objective of measuring magnetostriction.Analysis of the experimental data yields strong evidence for a non-cubic component of the magnetostriction possibly associated with the same growth-kinetic mechanism that gives rise to the non-cubic anisotropy. The sign and magnitude of the macroscopic non-cubic magnetoelastic constant is estimated from the experimental results.