| 1. |
- Aas, Wenche, et al.
(författare)
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Equilibria and dynamics in binary and ternary uranyl oxalate and acetate/fluoride complexes
- 1999
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Ingår i: Journal of the Chemical Society - Dalton Transactions. - : Royal Society of Chemistry (RSC). - 0300-9246 .- 1364-5447. ; :8, s. 1311-1317
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Tidskriftsartikel (refereegranskat)abstract
- The formation of ternary UO2(ac)pFq2-p-q (p = 1 or 2 and q = 1-3) complexes, and their equilibrium constants were investigated by potentiometric titrations and 19F NMR spectroscopy. The equilibrium constants have been determined from the emf data in a NaClO4 medium at constant sodium concentration, [Na+] = 1.00 M at 25°C, except for the UO2(ac)F32- complex where 19F NMR at -5°C was used. The magnitude of the equilibrium constant for the stepwise addition of fluoride indicates that prior co-ordination of acetate has only a small effect on the subsequent bonding of fluoride. The acetate exchange in the ternary UO2(ac)F32- complex was studied using 19F NMR. Through magnetisation transfer experiments, it was possible to confirm the provisional mechanism from a previous study and also the consistency of the rate constants for the five different exchange pathways required to describe the fluoride exchange. The exchange takes place via the intermediate UO2F3(H2O)2-, indicating that the acetate exchange follows an interchange mechanism with solvent participation in the transition state. The rates and mechanisms of the ligand exchange reactions in UO2(ox)2(H2O)2- and UO2(ac)2(H2O) have been studied using 13C NMR techniques at -5°C. The rate law is v = k-[complex][ligand], and the second order rate constant and the activation parameters for both systems have been determined. The reactions most likely take place through an Eigen-Wilkins type of mechanism, where the first step is a pre-equilibrium of an outer-sphere complex followed by a rate determining exchange of water. The rate constants for the water exchange reactions are very similar to that in UO2(H2O)52+. The information from the binary oxalate system rules out the formation of UO2(ox)2(H2O)2- as an intermediate in the exchange reactions in the previously studied UO2(ox)2F3-, also in this case confirming a previously suggested exchange mechanism. The H+/D+ isotope effects and a linear free energy relationship suggest that the main catalytic effect of H+ on ligand exchange rates is due to the formation of a protonated precursor. Hence, the catalytic effect depends on the basicity of the ligand and the site for the proton attack.
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| 2. |
- Agfors, Gunnar, et al.
(författare)
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KEMI : den gränslösa vetenskapen
- 2011
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Bok (populärvet., debatt m.m.)abstract
- Kemi – handlar inte det bara om farliga ämnen och onödiga tillsatser? Det är kanske bildenmånga har av kemi, men faktum är att utan kemi skulle vi inte ha det höga välstånd vi har i dag.Tack vare kemisk kunskap har vi tillgång till läkemedel som botar sjukdomar och lindrar smärta– med hjälp av syntetiska antibiotika kan infektionssjukdomar som tidigare var dödliga botas,magsår kan behandlas utan dyra och plågsamma operationer och många cancerformer kanframgångsrikt behandlas med syntetiska preparat. Konstgödsel och medel som hindrar skadeinsektergör att skördar kan ökas och svälten i världen därigenom begränsas. Tack vare kemin harvi även tillgång till alla de material vi behöver för att tillverka allt från kläder, rengöringsprodukteroch kosmetika till bilar, TV-apparater och reservdelar till kroppen. Det är genom kemisk syntes vikan framställa dessa och alla de övriga produkter vi behöver för vårt dagliga liv och det är keminsom visar vägen till hållbar produktion som utnyttjar förnybara råvaror och ger minimala mängderavfall. Kemisk kunskap är också oumbärlig för utveckling av nanoteknik och medicinskdiagnostik och andra till kemin angränsande områden. Kemin bidrar alltså till att finna lösningartill många av de komplexa globala problem vi står inför: hälsa, klimat, brist på råvaror, utnyttjandetav nya energikällor och tillgång till livsmedel för att föda jordens ökande befolkning. DET ÄR OM ALLT DETTA DEN HÄR BOKEN HANDLAR.
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| 3. |
- Buehl, Michael, et al.
(författare)
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Binding modes of oxalate in UO(2)(oxalate) in aqueous solution studied with first-principles molecular dynamics simulations. Implications for the chelate effect
- 2011
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; 40:42, s. 11192-11199
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Tidskriftsartikel (refereegranskat)abstract
- Car-Parrinello molecular dynamics simulations are reported for aqueous UO(2)(H(2)O)(n)(C(2)O(4)) (n = 3, 4), calling special attention to the binding modes of oxalate and the thermodynamics of the so-called chelate effect. Based on free energies from thermodynamic integration (BLYP functional), the kappa(1),kappa(1')-binding mode of the oxalate (with one O atom from each carboxylate coordinating) is more stable than kappa(2) (2 O atoms from the same carboxylate) and kappa(1) forms by 23 and 39 kJ mol(-1), respectively. The free energy of binding a fourth water ligand to UO(2)(H(2)O)(3)(kappa(1)-C(2)O(4)) is computed to be low, 12 kJ mol(-1). Changes of the hydration shell about oxalate during chelate opening are discussed. Composite enthalpies and free energies, obtained from both experiment and quantum-chemical modeling, are proposed for the formation of monodentate UO(2)(H(2)O)(4)(kappa(1)-C(2)O(4)). These data suggest that the largest entropy change in the overall complex formation occurs at this stage, and that the subsequent chelate closure under water release is essentially enthalpy-driven.
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| 4. |
- Elding, Lars Ivar, et al.
(författare)
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Ido Leden - banbrytande kemist : -
- 2006
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Ingår i: Kemivärlden, Biotech, Kemisk tidskrift. - 1653-5596. ; 2006:3, s. 46-46
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Tidskriftsartikel (populärvet., debatt m.m.)abstract
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| 5. |
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| 6. |
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| 7. |
- Macak, Peter, et al.
(författare)
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A theoretical study of the fluoride exchange between UO2F+(aq) and UO22+(aq)
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :30, s. 3638-3646
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data on the thermodynamics and reaction mechanism of the inner-sphere. uoride exchange reaction (UO22+)-O-17 + UO2F+ reversible arrow (UO2F+)-O-17 + UO22+ have been compared with different intimate reaction mechanisms using quantum chemical methods. Two models have been tested that start from the outer sphere complexes, (H2O)[UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)] and [UAO2F(OH2)(4)(+)] center dot center dot center dot [UBO2(OH2)(5)(2+)]; the geometry and energies of the intermediates and transition states along possible reaction pathways have been calculated using different ab initio methods, SCF, B3LYP and MP2. Both the experimental data and the theoretical results suggest that the. uoride exchange takes place via the formation and breaking of a U - F - U bridge that is the rate determining step. The calculated activation enthalpy Delta H-not equal = 30.9 kJ mol(-1) is virtually identical to the experimental value 31 kJ mol(-1); however this agreement may be a coincidence as we do not expect a larger accuracy than 10 kJ mol(-1) with the methods used. The calculations show that the. uoride bridge is formed as an insertion of UAO2F(OH2)(4)(+) into UBO2(OH2)(5)(2+) followed by a subsequent transfer of water from the first to the second coordination sphere of U-B.
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| 8. |
- Mizuoka, K, et al.
(författare)
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Structural and kinetic studies on uranyl(V) carbonate complex using C-13 NMR spectroscopy
- 2005
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 44:13, s. 4472-4474
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Tidskriftsartikel (refereegranskat)abstract
- We have measured C-13 NMR spectra of uranyl(V) carbonate complex in D2O solution containing 1.003 M Na-2 (CO3)-C-13 at various temperatures. Two singlet signals corresponding to free and coordinated CO32- were observed at 169.13 and 106.70 ppm, respectively. From the peak area ratio, the structure of the uranyl(V) carbonate complex was determined as [(UO2)-O-V(CO3)(3)](5-). Furthermore, kinetic analyses of the exchange reaction of free and coordinated CO32- in [(UO2)-O-V(CO3)(3)](5-) were carried out using 13C NMR line-broadening. As a result, the first-order rate constant at 298 K and the activation parameters for CO32- exchange reaction in [(UO2)-O-V(CO3)(3)](5-) were evaluated as 1.13 x 10(3) s(-1) and Delta H-not equal = 62.0 +/- 0.7 KJ(.)mol(-1), Delta S-not equal = 22 +/- 3 J(.)mol(-1.)K(-1), respectively. We suggest that the exchange follows a dissociative mechanism as in the corresponding [(UO2)-O-VI(CO3)(3)](4-) complex.
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| 9. |
- Palladino, Giuseppe, et al.
(författare)
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Structure, equilibrium and ligand exchange dynamics in the binary and ternary dioxouranium(VI)-ethylenediamine-N,N '-diacetic acid-fluoride system : a potentiometric, NMR and X-ray crystallographic study
- 2006
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Ingår i: Dalton Transactions. - : Royal Society of Chemistry (RSC). - 1477-9226 .- 1477-9234. ; :43, s. 5176-5183
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Tidskriftsartikel (refereegranskat)abstract
- The structure, thermodynamics and kinetics of the binary and ternary uranium(VI)-ethylenediamine- N,N'-diacetate (in the following denoted EDDA) fluoride systems have been studied using potentiometry, H-1, F-19 NMR spectroscopy and X-ray diffraction. The UO22+ - EDDA system could be studied up to - log[H3O+] = 3.4 where the formation of two binary complexes UO2(EDDA)(aq) and UO2(H(3)EDDA)(3+) were identified, with equilibrium constants log beta(UO(2)EDDA) = 11.63 +/- 0.02 and log beta(UO(2)H(3)EDDA(3+)) = 1.77 +/- 0.04, respectively. In the ternary system the complexes UO2(EDDA) F-, UO2(EDDA)(OH)(-) and (UO2)(2)(mu-OH)(2)(HEDDA)(2)F-2(aq) were identified; the latter through F-19 NMR. H-1 NMR spectra indicate that the EDDA ligand is chelate bonded in UO2(EDDA)(aq), UO2(EDDA) F- and UO2(EDDA)(OH)(-) while only one carboxylate group is coordinated in UO2(H(3)EDDA)(3+). The rate and mechanism of the fluoride exchange between UO2(EDDA) F- and free fluoride was studied by F-19 NMR spectroscopy. Three reactions contribute to the exchange; (i) site exchange between UO2(EDDA) F- and free fluoride without any net chemical exchange, (ii) replacement of the coordinated fluoride with OH- and (iii) the self dissociation of the coordinated fluoride forming UO2(EDDA)(aq); these reactions seem to follow associative mechanisms. H-1 NMR spectra show that the exchange between the free and chelate bonded EDDA is slow and consists of several steps, protonation/deprotonation and chelate ring opening/ring closure, the mechanism cannot be elucidated from the available data. The structure (UO2)(2)(EDDA)(2)(mu-H(2)EDDA) was determined by single crystal X-ray diffraction and contains two UO2( EDDA) units with tetracoordinated EDDA linked by H(2)EDDA in the zwitterion form, coordinated through a single carboxylate oxygen from each end to the two uranium atoms. The geometry of the complexes indicates that there is no geometric constraint for an associative ligand substitution mechanism.
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| 10. |
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