Search

Complexation by small organic ligands controls the bioavailability of contaminants and influences their mobility in the geosphere. We have studied the interactions of Cm3+, as a representative of the trivalent actinides, and Eu3+, as an inactive homologue, with glucuronic acid (GlcA) a simple sugar acid. Time-resolved laser-induced luminescence spectroscopy (TRLFS) shows that complexation at pH 5.0 occurs only at high ligand to metal ratios in the form of 1:1 complexes with standard formation constants log β0 = 1.84 ± 0.22 for Eu3+ and log β0 = 2.39 ± 0.19 for Cm3+. A combination of NMR, QMMM, and TRLFS reveals the structure of the complex to be a half-sandwich structure wherein the ligand binds through its carboxylic group, the ring oxygen, and a hydroxyl group in addition to five to six water molecules. Surprisingly, Y3+, which was used as a diamagnetic reference in NMR, prefers a different coordination geometry with bonding through at least two hydroxyl groups on the opposite side of a distorted GlcA molecule. QMMM simulations indicate that the differences in stability among Cm, Eu, and Y are related to ring strain induced by smaller cations. At higher pH a stronger complex was detected, most likely due to deprotonation of a coordinating OH group.

Seit 01.01.2021 werden die durch Kältemittel verursachten CO2-Emissionen auf Basis der F-Gase-Verordnung erneut deutlich reduziert. Damit die vorgegebenen Werte erreicht werden können, müssen alte Kältemittel vom Markt verschwinden. Wasser als Kältemittel stellt in diesem Zusammenhang eine ökologisch und ökonomisch nachhaltige Alternative für die Kühlung von Gebäuden, Rechenzentren und einer Vielzahl industrieller Prozesse dar. Ein Überblick.

Structural investigations of three actinide(IV) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(IV), U(IV), Np(IV)) and their cerium(IV) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(IV) complex shows that dependent on the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(IV) metal centre to bi-capped trigonal prismatic. Further, single crystal analyses of the La(III) and Ce(III) complexes show that the ligand can also act as a neutral ligand by protonation of the pyrazolyl moiety. All complexes were comprehensively characterized by NMR, IR and Raman spectroscopy. A single resonance in each of the 31P NMR spectra for the La(III), Ce(III), Ce(IV), Th(IV) and Np(IV) complex indicates the formation of highly symmetric complex species in solution. Extended X-ray absorption fine structure (EXAFS) investigations provide evidence for the same local structure of the U(IV) and Np(IV) complex in toluene solution, confirming the observations made in the solid state.

The synthesis of three complex series of the form [AnCl2(salen)(Pyx)2] (H2salen=N,N′‐bis(salicylidene)ethylenediamine; Pyx=pyridine, 4‐methylpyridine, 3,5‐dimethylpyridine) with tetravalent early actinides (An=Th, U, Np, Pu) is reported with the goal to elucidate the affinity of these heavy elements for small neutral N‐donor molecules. Structure determination by single‐crystal XRD and characterization of bulk powders with infrared spectroscopy reveals isostructurality within each respective series and the same complex conformation in all reported structures. Although the trend of interatomic distances for An−Cl and An−N (imine nitrogen of salen or pyridyl nitrogen of Pyx) was found to reflect an ionic behavior, the trend of the An−O distances can only be described with additional covalent interactions for all elements heavier than thorium. All experimental results are supported by quantum chemical calculations, which confirm the mostly ionic character in the An−N and An−Cl bonds, as well as the highest degree of covalency of the An−O bonds. Structurally, the calculations indicate just minor electronic or steric effects of the additional Pyx substituents on the complex properties., Th–PuIV salen complexes: A series of monosalen complex with Th–PuIV has been synthesized and characterized in the solid state and with quantum chemical (QC) calculations. They reveal the salen's potential to provide a fixed binding pocket to AnIV, allowing a facile exchange of pyridine‐based solvents in the labile positions. Differences in binding strength explain the findings: all AnIV−N are of mostly ionic nature but AnIV−O have a significant covalent contribution.

Two series of isostructural tetravalent actinide amidinates [AnX((S)-PEBA)3] (An = Th, U, Np; X = Cl, N3) bearing the chiral (S,S)-N,N’-bis-(1-phenylethyl)benzamidinate ((S)- PEBA) ligand have been synthesized and thoroughly characterized in solid and in solution. This study expands the already reported tetravalent neptunium complexes to the lighter actinides thorium and uranium. Furthermore, a rare Ce(IV) amidinate [CeCl((S)-PEBA)3] was synthesized to compare its properties to those of the analogous tetravalent actinide complexes. All compounds were characterized in the solid state using single crystal XRD and infrared spectroscopy and in solution using NMR spectroscopy. Quantum chemical bonding analysis including also the isostructural Pa and Pu complexes was used to characterize the covalent contributions to any bond involving the metal cation. Th shows the least covalent character throughout the series, even substantially smaller than for the Ce complex. For U, Np, and Pu similar covalent bonding contributions are found, but a natural population analysis reveals different origins. The 6d participation is the highest for U and decreases afterwards, whereas the 5f participation increases continuously from Pa to Pu.

Sodium silicate is one of the main depressants against calcite and fluorite in the scheelite flotation industry. In the first part of this article, the authors acidified sodium silicate (AWG) with three acids (sulfuric, oxalic and hydrochloric) to improve its performance. Results showed that acidified water glass outperforms alkaline water glass in terms of selectivity: it increases mainly the grade by further depressing silicates and calcium-bearing minerals. In most cases, AWG requires lower dosages to do so. The effect of acidified water glass is evaluated through Mineral Liberation Analysis (MLA), froth analysis, Raman and Nuclear Magnetic Resonance (NMR) spectroscopy in order to hypothesize its mechanism. MLA shows that AWG affects silicates and sulfides more intensely than semi-soluble salt-type minerals. Froth observations indicate other species in solution associated to the acid having an impact on the flotation results. Raman spectroscopy and NMR measurements indicate that the solution undergoes deep depolymerization when water glass is acidified. Lower molecular weight silica species, specifically Si-O monomers such as SiO(OH)3- will be responsible for the depression of the gangue minerals and are the drivers of the selectivity of AWG, more than orthosilicic acid. Depolymerization is more or less effective depending on the mass ratio of the acid to water glass and depending on the acid.

This book chapter covers all aspects of nuclear magnetic resonance spectroscopy observing actinides and nuclei in actinide-containing compounds with this spectroscopic technique.

Six mononuclear tetravalent actinide complexes (1-6) have been synthesized using a new Schiff base ligand 2-methoxy-6-(((2-methyl-1-(pyridin-2-yl)propyl)imino)methyl)phenol (HLpr). The HLpr is treated with tetravalent actinide elements in varied stoichiometry to afford mononuclear 1:1 complexes [MCl3-Lpr∙nTHF] (1-3) and 2:1 complexes [MCl2-Lpr2] (4-6) (M = Th4+ (1 and 4), U4+ (2 and 5) and Np4+ (3 and 6)). All complexes are characterized using different analytical techniques such as IR, NMR, and absorption spectroscopy as well as crystallography. UV-vis spectroscopy revealed more red-shifted absorption spectra for 2:1 complexes as compared to 1:1 complexes. 1H NMR of Th(IV) complexes exhibit diamagnetic spectra whereas U(IV) and Np(IV) complexes revealed paramagnetically shifted 1H NMR. Interestingly, NMR signals are paramagnetically shifted between -70 to 40 ppm in 2 and 3, but are confined within -35 to 25 ppm in 2:1 complexes 5 and 6. Single crystal structures for 1:1 complexes revealed an eight-coordinated Th(IV) complex (1) and seven-coordinated U(IV) (2) and Np(IV) (3) complexes. Whereas, all 2:1 complexes 4-6 were isolated as eight-coordinated isostructural molecules. The geometry around the Th4+ center in 1 is found to be trigonal dodecahedral and, capped trigonal prismatic around U(IV) and Np(IV) centers in 2 and 3, respectively. Whereas, An4+ centers in 2:1 complexes are present in dodecahedral geometry. Importantly, 2:1 complexes exhibit increased bond distances in comparison to their 1:1 counterparts as well as interesting bond modulation w.r.t. ionic radii of An(IV) centers. Cyclic voltammetry displays an increased oxidation potential of the ligand by 300 to 500 mV, after coordination with An4+. CV studies indicates Th(IV)/Th(II) reduction beyond −2.3 V whereas attempts were made to identify redox potentials for U(IV) and Np(IV) centers. Spectroscopic binding studies reveal that complex stability in 1:1 stoichiometry follows the order Th4+≈ U4+ > Np4+.

Die meisten fluorierten Kältemittel, die als ultimative Lösung für das Herunterfahren der Treibhausgaspotenziale dieser Kältemittel gelten, bergen auf den zweiten Blick Umweltrisiken. Natürliche Kältemittel hingegen sind die einzig wahre Alternative. Eine bayrische Firma treibt die Verwendung von Wasser voran.

A series of tetradentate N2O2-type Schiff base complexes with tetravalent 4f- and 5f-block metals, [M(salpn)2] (H2salpn = N,N′-disalicylidene-1,3-diaminopropane; M = Ce, Th, U, Np, and Pu), were prepared to systematically investigate their solid state structure, and their complexation behaviour in solution with the goal to investigate the subtle differences between 4f- and 5f-elements. X-ray diffraction revealed that all investigated metal cations form [M(salpn)2] complexes. All the complexes show the same ligand arrangement with meridional conformation, amongst which only Ce(IV) exhibits unique behaviour upon crystallisation. [Ce(salpn)2] crystallises in two less symmetric systems (P or P21/n), whilst all the other [M(salpn)2] crystallise in a more symmetric orthorhombic system (Pban). Quantum chemical calculations suggest that the observed structural peculiarity of Ce(IV) stems from the geometrical flexibility due to the more “ionic” nature of bonds to the 4f element. 1H NMR measurements revealed that [M(salpn)2] forms two different species in solution with and without an additional solvent molecule, where the relative distribution of the two species depends mainly on the ionic radius of the metal centre. Again, Ce(IV) behaves differently from the tetravalent actinides with a higher ratio of the solvent-molecule-coordinated species than the ratio expected from its ionic radius. Hence, this study is successful in observing subtle differences between 4f- (i.e. Ce) and 5f-elements (actinides; Th, U, Np, and Pu) both in the solid state and in solution on an analytically distinguishable level, and in relating the observed subtle differences to their electronic structure.

Over recent decades there has been a great deal of interest and associated research into aspects of the f-block (lanthanide and actinide) metal chemistry of naturally-occurring ligands, such as proteins, peptides, porphyrins and related tetraaza derivatives as well as synthetically modified natural ligands and solely synthetic ligand systems incorporating bio-relevant functional groups. In this review, we present a wide-ranging overview of published work spanning the above areas, with emphasis on selected biological, medical and environmental aspects. Systems capable of discriminating between metal ions from within, or between, the lanthanide and actinide groups are also discussed including the design and synthesis of biomimetic radionuclide chelators and radionuclide decorporation agents as well as solid adsorbent materials for the uptake of radionuclides from the environment and elsewhere. Thus, the interaction of the f-group elements with a range of biopolymers, including systems based on cellulose, chitin, chitosan, humic substances as well as a range of synthetic model systems is also presented. Other applications include the synthesis of new luminescent materials, including luminescent probes and luminescent metal coordination polymers exhibiting unusual photophysical properties as well as systems showing potential for use in the development of new MRI imaging agents.

Structural investigations of three actinide(iv) 4-phosphoryl 1H-pyrazol-5-olate complexes (An = Th(iv), U(iv), Np(iv)) and their cerium(iv) analogue display the same metal coordination in the solid state. The mononuclear complexes show the metal centre in a square antiprismatic coordination geometry composed by the two O-donor atoms of four deprotonated ligands. Detailed solid state analysis of the U(iv) complex shows that dependent on the solvent used altered arrangements are observable, resulting in a change in the coordination polyhedron of the U(iv) metal centre to bi-capped trigonal prismatic. Further, single crystal analyses of the La(iii) and Ce(iii) complexes show that the ligand can also act as a neutral ligand by protonation of the pyrazolyl moiety. All complexes were comprehensively characterized by NMR, IR and Raman spectroscopy. A single resonance in each of the 31P NMR spectra for the La(iii), Ce(iii), Ce(iv), Th(iv) and Np(iv) complex indicates the formation of highly symmetric complex species in solution. Extended X-ray absorption fine structure (EXAFS) investigations provide evidence for the same local structure of the U(iv) and Np(iv) complex in toluene solution, confirming the observations made in the solid state.

A series of tetradentate N2O2-type Schiff base complexes with tetravalent 4f- and 5f-block metals, [M(salpn)2] (H2salpn = N,N'-disalicylidene-1,3-diaminopropane; M = Ce, Th, U, Np, and Pu), were prepared to systematically investigate their solid state structure, and their complexation behaviour in solution with the goal to investigate the subtle differences between 4f- and 5f-elements. X-ray diffraction revealed that all investigated metal cations form [M(salpn)2] complexes. All the complexes show the same ligand arrangement with meridional conformation, amongst which only Ce(iv) exhibits unique behaviour upon crystallisation. [Ce(salpn)2] crystallises in two less symmetric systems (P1[combining macron] or P21/n), whilst all the other [M(salpn)2] crystallise in a more symmetric orthorhombic system (Pban). Quantum chemical calculations suggest that the observed structural peculiarity of Ce(iv) stems from the geometrical flexibility due to the more "ionic" nature of bonds to the 4f element. 1H NMR measurements revealed that [M(salpn)2] forms two different species in solution with and without an additional solvent molecule, where the relative distribution of the two species depends mainly on the ionic radius of the metal centre. Again, Ce(iv) behaves differently from the tetravalent actinides with a higher ratio of the solvent-molecule-coordinated species than the ratio expected from its ionic radius. Hence, this study is successful in observing subtle differences between 4f- (i.e. Ce) and 5f-elements (actinides; Th, U, Np, and Pu) both in the solid state and in solution on an analytically distinguishable level, and in relating the observed subtle differences to their electronic structure.

The synthesis of a tetravalent neptunium amidinate [NpCl((S)‐PEBA)3] (1) ((S)‐PEBA=(S,S)‐N,N′‐bis‐(1‐phenylethyl)‐benzamidinate) is reported. This complex represents the first structurally characterized enantiopure transuranic compound. Reactivity studies with halide/pseudohalides yielding [NpX((S)‐PEBA)3] (X=F (2), Br (3), N3 (4)) have shown that the chirality‐at‐metal is preserved for all compounds in the solid state. Furthermore, they represent an unprecedented example of a structurally characterized metal–organic Np complex featuring a Np−Br (3) bond. In addition, 4 is the only reported tetravalent transuranic azide. All compounds were additionally characterized in solution using para‐magnetic NMR spectroscopy showing an expected C 3‐symmetry at low temperatures., Enantiopure transuranic complexes: The first structurally characterized enantiopure complexes of neptunium have been synthesized. Starting from a chloro tris(amidinate) complex unprecedented neptunium(IV) fluoro, ‐bromo and ‐azido compounds could be yielded and characterized in solution and in the solid state (see scheme).

Cellulosic materials present as tissue, paper, wood, or filter materials in low and intermediate level waste will degrade under alkaline conditions if water ingresses in a cementitious backfilled repository. The main degradation product is isosaccharinic acid. Complex formation with isosaccharinic acid may adversely affect the retention of radionuclides by the sorption or formation of solid phases. Hence, this compound is of particular concern in the context of nuclear waste disposal. Structural information of complexes is limited to spherical metal centers and little is known about the interaction of uranyl (UVIO22+) with isosaccharinic acid. Therefore, the interaction of UO22+ with α-isosaccharinate (ISA) was studied under acidic conditions focusing particularly on the structural characterization of the formed complexes. Attenuated total reflection Fourier-transform infrared (ATR-FTIR), nuclear magnetic resonance (NMR), UV-Vis, extended X-ray absorption fine structure (EXAFS) spectroscopy and electrospray-ionization mass spectrometry (ESI-MS) were combined with theoretical calculations to obtain a process understanding on the molecular level. The dominant binding motifs in the formed complexes are 5- and 6-membered rings involving the carboxylic group as well as the α- or β-hydroxy group of ISA. Two concentration dependent complex formation mechanisms were identified involving either mono- ([UO2(ISA)(H2O)3]+) or binuclear ([(UO2)2(ISA)(H2O)6]3+) species. Furthermore, this study unveils the interaction of UO22+ with the protonated α-isosaccharinic acid (HISA) promoting its transformation to the corresponding α-isosaccharinate-1,4-lactone (ISL) and inhibiting the formation of polynuclear UO22+-ISA species. Future studies on related systems will benefit from the comprehensive knowledge concerning the behavior of ISA as a complexing agent gained in the present study.

A comprehensive molecular analysis of a simple aqueous complexing system. U(VI) acetate. selected to be independently investigated by various spectroscopic (vibrational, luminescence, X-ray absorption, and nuclear magnetic resonance spectroscopy) and quantum chemical methods was achieved by an international round-robin test (RRT). Twenty laboratories from six different countries with a focus on actinide or geochemical research participated and contributed to this scientific endeavor. The outcomes of this RRT were considered on two levels of complexity: first, within each technical discipline, conformities as well as discrepancies of the results and their sources were evaluated. The raw data from the different experimental approaches were found to be generally consistent. In particular, for complex setups such as accelerator-based X-ray absorption spectroscopy, the agreement between the raw data was high. By contrast, luminescence spectroscopic data turned out to be strongly related to the chosen acquisition parameters. Second, the potentials and limitations of coupling various spectroscopic and theoretical approaches for the comprehensive study of actinide molecular complexes were assessed. Previous spectroscopic data from the literature were revised and the benchmark data on the U(VI) acetate system provided an unambiguous molecular interpretation based on the correlation of spectroscopic and theoretical results. The multimethodologic approach and the conclusions drawn address not only important aspects of actinide spectroscopy but particularly general aspects of modern molecular analytical chemistry.

Gallium (Ga) is a critical element in developing renewable energy generation and energy efficient systems. The supply of Ga is at risk and needed recycling technologies for its availability in future. This study demonstrated the recovery of Ga3+ from low gallium concentrated wafer fabrication industry wastewaters using the siderophores desferrioxamine B (DFOB) and desferrioxamine E (DFOE). The complexation of Ga3+ by DFOB and DFOE was through hydroxamate group as demonstrated by infrared spectroscopy, nuclear magnetic resonance and density functional theory calculations. The high selectivity of DFOB/E towards Ga3+ was observed due to the formation of highly stable complex. Indeed, due to the formation of such high stability complex, the DFOB and DFOE were able to successfully complex 100% Ga in the two different wastewater from wafer fabrication industry. For the recovery of the siderophores, a high rate of decomplexation of Ga (>90%) was achieved upon addition of 6 times excess of ethylenediaminetetraacetic acid (EDTA) at pH of 3.5. More than 95% of Ga-DFOB and Ga-DFOE complex were recovered with purity (% of Ga moles in comparison to total moles of metals) of 70.4 and 94.9%, respectively by application of a C18 reversed-phase chromatography column. A preliminary cost-calculation demonstrated that acetonitrile consumption and desferrioxamines are major cost input for the technology. This study, for the first time, demonstrated a technical solution to the recovery of Ga3+ from the low concentrated wastewater based on siderophores and reversed-phase chromatography. A German patent application had been filed for this technology.

C5-BPP is a highly efficient N-donor ligand for the separation of trivalent actinides, An(III), from trivalent lanthanides, Ln(III). The molecular origin of the selectivity of C5-BPP and many other N-donor ligands of the BTP-type is still not entirely understood. We present here the first NMR studies on C5-BPP Ln(III) and An(III) complexes. C5-BPP is synthesized with 10% 15N labeling and characterized by NMR and LIFDI-MS methods. 15N NMR spectroscopy gives a detailed insight into the bonding of C5-BPP with lanthanides and Am(III) as a representative for trivalent actinide cations, revealing significant differences in 15N chemical shift for coordinating nitrogen atoms compared to Ln(III) complexes. The temperature dependence of NMR chemical shifts observed for the Am(III) complex indicates a weak paramagnetism. This as well as the observed large chemical shift for coordinating nitrogen atoms show that metal–ligand bonding in Am(C5-BPP)3 has a larger share of covalence than in lanthanide complexes, confirming earlier studies. The Am(C5-BPP)3 NMR sample is furthermore spiked with Cm(III) and characterized by time-resolved laser fluorescence spectroscopy (TRLFS), yielding important information on the speciation of trace amounts of minor complex species.

Gallium (Ga) is a critical element for the electronic industry, however, its long-term supply is not assured. Thus, the recovery of Ga from industrial wastewaters is important. Selective sorption is a recommended technology for the recovery of Ga from industrial wastewaters, however, selective sorbents are elusive. Desferrioxamine B (DFOB), a hydroxomate siderophore that is known to be highly selective towards Fe3+, is tested for its ability to complex Ga. This study demonstrated that DFOB forms 1:1 complex with Ga and the maximum Qe-Ga is 124.4 mg of Ga complexed per g of DFOB. Further, the complexation mechanism of Ga3+ and Fe3+ with DFOB is similar, as indicated by NMR, suggesting that the selectivity of DFOB towards Fe3+ will be extended to Ga3+ as well. Thus, DFOB seems to be a suitable candidate for the sorption of Ga from industrial wastewaters.

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross-linking of the polymer with accelerated electrons provides an alignment medium with different properties. However, PU exhibits a number of undesired polymer signals in corresponding spectra, which ideally have to be removed spectroscopically. Within this context, we demonstrate the applicability of diffusion-filtered experiments for removal of the polymer signals. Example spectra for the usefulness of PU alignment media are provided for the common test molecules strychnine and norcamphor.

i-SANEX is a process for separating actinides(III) from used nuclear fuels by solvent extraction: Actinides(III) and lanthanides(III) are co-extracted from a PUREX raffinate followed by selective back extraction of actinides(III) from the loaded organic phase. This step requires a complexing agent selective for actinides(III). A hydrophilic sulfonated bis triazinyl pyridine (SO3-Ph-BTP) was synthesized and tested for selective complexation of actinides(III) in nitric acid solution. When co-extracting Am(III) and Eu(III) from nitric acid into TODGA, adding SO3-Ph-BTP to the aqueous phase suppresses Am(III) extraction while Eu(III) is extracted. Separation factors in the range of 1000 are achieved. SO3-Ph-BTP remains active in nitric acid up to 2 mol/L. As a result of this performance, buffering or salting-out agents are not needed in the aqueous phase; nitric acid is used to keep the lanthanides(III) in the TODGA solvent. These properties make SO3-Ph-BTP a suitable candidate for i-SANEX process development.

Lgt1 is one of the glucosyltransferases produced by the Gram-negative bacterium Legionella pneumophila. This enzyme modifies eukaryotic elongation factor 1A (eEF1A) at serine 53, which leads to inhibition of protein synthesis and death of target cells. Here we studied the region of eEF1A, which is essential for substrate recognition by Lgt1. We report that the decapeptide 50GKGSFKYAWV59 of eEF1A is efficiently modified by Lgt1. This peptide covers the loop of the helix-loop-helix region formed by helices A* and A′ of eEF1A and is part of the first turn of helix A′. Substitution of either serine 53, phenylalanine 54, tyrosine 56, or tryptophan 58 by alanine abolished or severely decreased glucosylation. Lgt1 modified the decapeptide 50GKGSFKYAWV59 with a higher glucosylation rate than full-length eEF1A purified from yeast, suggesting that a specific conformation of eEF1A is the preferred substrate of Lgt1. A GenBankTM search on the basis of the substrate decapeptide for similar peptide sequences retrieved heat shock protein 70 subfamily B suppressor 1 (Hbs1) as a target for glucosylation by Lgt1. Recombinant Hbs1 and the corresponding fragment (303GKASFAYAWV312) were gluco syl a ted by Lgt1. NMR studies with the gluco syl a ted eEF1A-derived decapeptide identified an α-anomeric structure of the glucose-serine 53 bond and characterize Lgt1 as a retaining glucosyltransferase.

Lactobacillus reuteri TMW 1.106, a dominant type II sourdough bacterium, produces glucan from sucrose in vitro and in situ. Exopolysaccharides positively affect the texture and mouth feel of foods and their in situ production in fermented foods could be an alternative to the addition of hydrocolloids from plants or non-GRAS microorganisms. The aim of this study was to elucidate a probable function of the EPS for the bacterium. Lb. reuteri TMW 1.106 harbors two glucosyltransferases, Gtf106A and Gtf106B and produces a dextran. Gtf106B exhibited hydrolysis but no transferase activity. Enzymatic production of dextran with the heterologously expressed, N-terminally truncated ΔN Gtf106A was highest at a pH of 4.0, whereas dextran formation in pH static fermentations was optimal between pH 4.7 and 5.4. The dextran synthesised at these pH values had the highest molecular mass (1.2 × 107) and 15% α–(1–4) linkages. A protective effect of this EPS on Lb. reuteri TMW 1.106 against low pH, explaining the low pH-produc...

Bistriazinyl-pyridine type ligands are important extracting agents for separating trivalent actinide ions from trivalent lanthanides. The alkyl substituents on the lateral triazine rings have a significant effect on the stability of the ligand against hydrolysis and radiolysis. Furthermore they influence solubility, extraction behaviour and selectivity. TRLFS and extraction studies suggest differences in complexation and extraction behaviour of BTP ligands bearing iso-propyl or n-propyl substituents, respectively. As NMR studies allow insight into the metal-ligand bonding, we conducted NMR studies on a range of 15N-labelled nPrBTP and iPrBTP Ln(III) and Am(III) complexes. Our results show that no strong change in the metal-ligand bonding occurs, thus excluding electronic reasons for differences in complexation behaviour, extraction kinetics and selectivity. This supports mechanistic reasons for the observed differences.

Room temperature detection of neptunyl(VI) LMCT emission in a coordination compound and in the presence of uranyl(VI) is reported for the first time. Differences in the excitation profiles of the complexes enable spectral editing so either exclusively neptunyl(VI) or uranyl(VI) emission is observed or a sum of the two.

The molecular origin of the selectivity of N-donor ligands, such as alkylated bis-triazinyl pyridines (BTPs), for actinide complexation in the presence of lanthanides is still largely unclear. NMR investigations of an Am(nPrBTP)3(3+) complex with a (15)N labelled ligand showed that it exhibits large differences in (15)N chemical shift for coordinating N-atoms in comparison to both lanthanide(III) complexes and the free ligand. The temperature dependence of NMR chemical shifts observed for this complex indicates a weak paramagnetism. This fact and the observed large chemical shift for bound nitrogen atoms allow us to conclude that metal-ligand bonding in the reported Am(III) N-donor complex has a larger share of covalence than in lanthanide complexes. This may account for the observed selectivity.

Several rare earth coordination compounds and the first actinide coordination compound of the recently introduced multifunctional ligand (S)P[N(Me)NC(H)Py]3 (1, Py = pyridyl) have been synthesized and characterized. The electronic and structural properties of these complexes were probed by X-ray diffraction analysis, X-ray absorption fine structure (XAFS), and advanced nuclear magnetic resonance (NMR) spectroscopy. Pulsed field-gradient spin-echo (PGSE) diffusion measurements and 1H,19F heteronuclear Overhauser spectroscopy (HOESY) revealed that the degree of ion pairing of the trivalent rare earth complexes [Ln(1)(OTf)3] (Ln = Y (2), La (3), Sm (4), and Lu (5); [OTf]− = [O3SCF3]−) depends on their metal cation ionic radii and decreases in acetonitrile solution for the smaller lanthanides. The plutonium(III) complex 6 exhibits, however, a significantly different behavior in solution and has a much stronger tendency to form solvent-separated ion pairs.

With polyurethane (PU), a novel alignment medium for organic solvents is introduced and characterized, which is very robust and easy to produce on a large scale. Linear PU already constitutes an elastomer gel with several solvents based on its ability to form hydrogen bonds. Covalent cross-linking of the polymer with accelerated electrons provides an alignment medium with different properties. However, PU exhibits a number of undesired polymer signals in corresponding spectra, which ideally have to be removed spectroscopically. Within this context, we demonstrate the applicability of diffusion-filtered experiments for removal of the polymer signals. Example spectra for the usefulness of PU alignment media are provided for the common test molecules strychnine and norcamphor.

Lgt1 is one of the glucosyltransferases produced by the Gram-negative bacterium Legionella pneumophila. This enzyme modifies eukaryotic elongation factor 1A (eEF1A) at serine 53, which leads to inhibition of protein synthesis and death of target cells. Here we studied the region of eEF1A, which is essential for substrate recognition by Lgt1. We report that the decapeptide (50)GKGSFKYAWV(59) of eEF1A is efficiently modified by Lgt1. This peptide covers the loop of the helix-loop-helix region formed by helices A* and A' of eEF1A and is part of the first turn of helix A'. Substitution of either serine 53, phenylalanine 54, tyrosine 56, or tryptophan 58 by alanine abolished or severely decreased glucosylation. Lgt1 modified the decapeptide (50)GKGSFKYAWV(59) with a higher glucosylation rate than full-length eEF1A purified from yeast, suggesting that a specific conformation of eEF1A is the preferred substrate of Lgt1. A GenBank search on the basis of the substrate decapeptide for similar peptide sequences retrieved heat shock protein 70 subfamily B suppressor 1 (Hbs1) as a target for glucosylation by Lgt1. Recombinant Hbs1 and the corresponding fragment ((303)GKASFAYAWV(312)) were gluco syl a ted by Lgt1. NMR studies with the gluco syl a ted eEF1A-derived decapeptide identified an alpha-anomeric structure of the glucose-serine 53 bond and characterize Lgt1 as a retaining glucosyltransferase.

A DNA system consisting of pyrene-modified oligonucleotides and nitrobenzoate (Nb)-modified DNA-binding tripeptides has been applied to study electron-transfer processes through the DNA-peptide interface. 5-(Pyren-1-yl)-2'-deoxyuridine (Py-dU) has been used as the photoinducible charge generator. Upon excitation at 350 nm, a pyrene-like excited state (Py-dU) is formed which undergoes an electron transfer yielding the charge-separated state which is the contact ion pair Py(*)(+)-dU(*)(-). The subsequent electron shift from dU(*)(-) into the base stack competes with charge recombination and can be probed chemically by trapping the electron at the 5-bromo-2'-deoxyuridine (Br-dU) group leading to strand cleavage which can be quantified by HPLC analysis. Several Nb-modified DNA-binding tripeptides influence these DNA-mediated electron-transfer processes as shown by fluorescence spectroscopy experiments. Fluorescence quenching can occur primarily through a reductive electron-transfer process in which the Nb group traps the electron thermodynamically from the contact ion pair Py(*)(+)-dU(*)(-). Moreover, our results indicate that, once the negative charge has been trapped on the peptide, oxidative processes from Py(*)(+) take place resulting in an enhanced and nonspecific strand degradation of the Py-dU-modified duplexes. The latter type of strand cleavage can be inhibited by the presence of tryptophane or tyrosine as part of the peptides. Most remarkably, DNA-binding tripeptides, which bear both the Nb and the tryptophan/tyrosine moiety, are able to trap both the negative and the positive charge from the contact ion pair Py(*)(+)-dU(*)(-).