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The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites. This work is focussed on the competition effect of Al(III) on complexation of Tb(III) or Eu(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. Whilst the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived "diffusion theory'' turned out to be inapplicable, since it cannot explain an increase in competition for the "initial'' sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.
Formation of a Eu(III) borate solid species from a weak Eu(III) borate complex in aqueous solution
(2014)
In the presence of polyborates (detected by B-11-NMR) the formation of a weak Eu(III) borate complex (lg beta(11) similar to 2, estimated) was observed by time-resolved laser-induced fluorescence spectroscopy (TRLFS). This complex is a precursor for the formation of a solid Eu(III) borate species. The formation of this solid in solution was investigated by TRLFS as a function of the total boron concentration: the lower the total boron concentration, the slower is the solid formation. The solid Eu(III) borate was characterized by IR spectroscopy, powder XRD and solid-state TRLFS. The determination of the europium to boron ratio portends the existence of pentaborate units in the amorphous solid.
We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1–10 mM by measuring reversible fluorescence decay time changes.
We report a 1,2,3-triazol fluoroionophore for detecting Na+ that shows in vitro enhancement in the Na+-induced fluorescence intensity and decay time. The Na+-selective molecule 1 was incorporated into a hydrogel as a part of a fiber optical sensor. This sensor allows the direct determination of Na+ in the range of 1-10 mM by measuring reversible fluorescence decay time changes.
A highly K+-selective two-photon fluorescent probe for the in vitro monitoring of physiological K+ levels in the range of 1-100 mM is reported. The two-photon excited fluorescence (TPEF) probe shows a fluorescence enhancement (FE) by a factor of about three in the presence of 160 mM K+, independently of one-photon (OP, 430 nm) or two-photon (TP, 860 nm) excitation and comparable K+-induced FEs in the presence of competitive Na+ ions. The estimated dissociation constant (K-d) values in Na+-free solutions (K-d(OP)=(28 +/- 5) mM and K-d(TP)=(36 +/- 6) mM) and in combined K+/Na+ solutions (K-d(OP)=(38 +/- 8) mM and K-d(TP)=(46 +/- 25) mM) reflecting the high K+/Na+ selectivity of the fluorescent probe. The TP absorption cross-section (sigma(2PA)) of the TPEF probe+160 mMK(+) is 26 GM at 860 nm. Therefore, the TPEF probe is a suitable tool for the in vitro determination of K+.
The effect of cellulose-based polyelectrolytes on biomimetic calcium phosphate mineralization is described. Three cellulose derivatives, a polyanion, a polycation, and a polyzwitterion were used as additives. Scanning electron microscopy, X-ray diffraction, IR and Raman spectroscopy show that, depending on the composition of the starting solution, hydroxyapatite or brushite precipitates form. Infrared and Raman spectroscopy also show that significant amounts of nitrate ions are incorporated in the precipitates. Energy dispersive X-ray spectroscopy shows that the Ca/P ratio varies throughout the samples and resembles that of other bioinspired calcium phosphate hybrid materials. Elemental analysis shows that the carbon (i.e., polymer) contents reach 10% in some samples, clearly illustrating the formation of a true hybrid material. Overall, the data indicate that a higher polymer concentration in the reaction mixture favors the formation of polymer-enriched materials, while lower polymer concentrations or high precursor concentrations favor the formation of products that are closely related to the control samples precipitated in the absence of polymer. The results thus highlight the potential of (water-soluble) cellulose derivatives for the synthesis and design of bioinspired and bio-based hybrid materials.
Britholite group minerals (REE,Ca)(5)[(Si,P)O-4](3)(OH,F) are widespread rare-earth minerals in alkaline rocks and their associated metasomatic zones, where they usually are minor accessory phases. An exception is the REE deposit Rodeo de los Molles, Central Argentina, where fluorbritholite-(Ce) (FBri) is the main carrier of REE and is closely intergrown with fluorapatite (FAp). These minerals reach an abundance of locally up to 75 modal% (FBri) and 20 modal% (FAp) in the vein mineralizations. The Rodeo de los Molles deposit is hosted by a fenitized monzogranite of the Middle Devonian Las Chacras-Potrerillos batholith. The REE mineralization consists of fluorbritholite-(Ce), britholite-(Ce), fluorapatite, allanite-(Ce), and REE fluorcarbonates, and is associated with hydrothermal fluorite, quartz, albite, zircon, and titanite. The REE assemblage takes two forms: irregular patchy shaped REE-rich composites and discrete cross-cutting veins. The irregular composites are more common, but here fluorbritholite-(Ce) is mostly replaced by REE carbonates. The vein mineralization has more abundant and better-preserved britholite phases. The majority of britholite grains at Rodeo de los Molles are hydrothermally altered, and alteration is strongly enhanced by metamictization, which is indicated by darkening of the mineral, loss of birefringence, porosity, and volume changes leading to polygonal cracks in and around altered grains. A detailed electron microprobe study of apatite-britholite minerals from Rodeo de los Molles revealed compositional variations in fluorapatite and fluorbritholite-(Ce) consistent with the coupled substitution of REE3+ + Si4+ = Ca2+ + P5+ and a compositional gap of similar to 4 apfu between the two phases, which we interpret as a miscibility gap. Micrometer-scale intergrowths of fluorapatite in fluorbritholite-(Ce) minerals and vice versa are chemically characterized here for the first time and interpreted as exsolution textures that formed during cooling below the proposed solvus.
By varying reaction parameters for the syntheses of the hydrogen-bonded metal-imidazolate frameworks (HIF) HIF-1 and HIF-2 (featuring 14 Zn and 14 Co atoms, respectively) to increase their yields and crystallinity, we found that HIF-1 is generated in two different frameworks, named as HIF-1a and HIF-1b. HIF-1b is isostructural to HIF-2. We determined the gas sorption and magnetic properties of HIF-2. In comparison to HIF-1a (Brunauer-Emmett-Teller (BET) surface area of 471m(2) g(-1)), HIF-2 possesses overall very low gas sorption uptake capacities [BET(CO2) surface area=85m(2) g(-1)]. Variable temperature magnetic susceptibility measurement of HIF-2 showed antiferromagnetic exchange interactions between the cobalt(II) high-spin centres at lower temperature. Theoretical analysis by density functional theory confirmed this finding. The UV/Vis-reflection spectra of HIF-1 (mixture of HIF-1a and b), HIF-2 and HIF-3 (with 14 Cd atoms) were measured and showed a characteristic absorption band centered at 340nm, which was indicative for differences in the imidazolate framework.