An official website of the United States government
Abstract Affinities of six anions (mesylate, acetate, trifluoroacetate,p‐toluenecarboxylate,p‐toluenesulfonate, and perfluorooctanoate) for three related Pt2+‐linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M6L312+(1b) and M4L28+(2) composition (M=(en)Pt2+, L=(3‐py)4porphyrin) were prepared in a one‐pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N−H hydrogen‐bond donor ability. Comparisons of isostructural hosts that differ in hydrogen‐bonding ability were made between1band a related M6L312+nanoprism (1a, M=(tmeda)Pt2+) that lacks N−H groups. Considerable variation in association constants (K1=1.6×103 M−1to 1.3×108 M−1) and binding mode (exovs.endo) were found for different host–guest combinations. Strongest binding was seen betweenp‐toluenecarboxylate and1b, but surprisingly, association of this guest with1awas only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity betweenp‐toluenecarboxylate and1acould be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host.
more »
« less
On the Replicability of the Thermodynamic Modeling of Spectroscopic Titration Data in the Nickel(II) En System
ABSTRACT Characterizing complicated solution phase systems in situ requires advanced modeling techniques to capture the intricate balances between the many chemical species. Due to the error inherent in any scientific measurement, a spectrophotometric titration experiment with nickel(II) and ethylenediamine (en) was repeated six times using an autotitrator to test the replicability of the data and the consistency of the resulting thermodynamic model. All six datasets could be modeled very tightly (R2 > 99.9999%) with the following eight complexes: [Ni]2+, [Ni2en]4+, [Nien]2+, [Ni2en3]4+, [Nien2]2+, [Ni2en5]4+, [Nien3]2+, and [Nien6]2+. The logK values for the stepwise associative reactions agree with existing literature values for the majority species ([Nienn = 1–3]2+) and matched expectations for the minority species; 95% confidence intervals for each logK value were determined via bootstrapping, which quantifies the variability in the binding constant value that is supported by a given dataset. The repeated experiments, which could not be successfully concatenated together, demonstrate that replication is crucial to capturing all the variability in the logK values. Conversely, bootstrapped confidence intervals across multiple experiments can be readily combined to generate an appropriate range for an experimentally determined binding constant.
more »
« less
- Award ID(s):
- 2004005
- PAR ID:
- 10551412
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Journal of Chemometrics
- Volume:
- 38
- Issue:
- 12
- ISSN:
- 0886-9383
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The structure of Ni(3-amino-4,4′-bipyridine)[Ni(CN)4] (or known as Ni-BpyNH2) in powder form was determined using synchrotron X-ray diffraction and refined using the Rietveld refinement technique (R= 8.8%). The orthorhombic (Cmca) cell parameters were determined to bea= 14.7218(3) Å,b= 22.6615(3) Å,c= 12.3833(3) Å,V= 4131.29(9) Å3, andZ= 8. Ni-BpyNH2forms a 3-D network, with a 2-D Ni(CN)4net connecting to each other via the BpyNH2ligands. There are two independent Ni sites on the net. The 2-D nets are connected to each other via the bonding of the pyridine “N” atom to Ni2. The Ni2 site is of six-fold coordination to N with relatively long Ni2–N distances (average of 2.118 Å) as compared to the four-fold coordinated Ni1–C distances (average of 1.850 Å). The Ni(CN)4net is arranged in a wave-like fashion. The functional group, –NH2, is disordered and was found to be in them-position relative to the N atom of the pyridine ring. Instead of having a unique position, N has ¼ site occupancy in each of the fourm-positions. The powder reference diffraction pattern for Ni-BpyNH2was prepared and submitted to the Powder Diffraction File (PDF) at the International Centre of Diffraction Data (ICDD).more » « less
-
Abstract In an effort to reconcile the various interpretations for the cation components of the 2p3/2observed in x-ray photoelectron spectroscopy (XPS) of several spinel oxide materials, the XPS spectra of both spinel alloy nanoparticles and crystalline thin films are compared. We observed that different components of the 2p3/2core level XPS spectra, of these inverse spinel thin films, are distinctly surface and bulk weighted, indicating surface-to-bulk core level shifts in the binding energies. Surface-to-bulk core level shifts in binding energies of Ni and Fe 2p3/2core levels of NiFe2O4thin film are observed in angle-resolved XPS. The ratio between surface-weighted components and bulk-weighted components of the Ni and Fe core levels shows appreciable dependency on photoemission angle, with respect to surface normal. XPS showed that the ferrite nanoparticles NixCo1−xFe2O4(x= 0.2, 0.5, 0.8, 1) resemble the surface of the NiFe2O4thin film. Surface-to-bulk core level shifts are also observed in CoFe2O4and NiCo2O4thin films but not as significantly as in NiFe2O4thin film. Estimates of surface stoichiometry of some spinel oxide nanoparticles and thin films suggested that the apportionment between cationic species present could be farther from expectations for thin films as compared to what is seen with nanoparticles.more » « less
-
Abstract MorphDeCage (2‐(4‐methoxy‐3‐nitrophenyl)‐2‐morpholinoacetic acid) and PyrDeCage (2‐(4‐methoxy‐3‐nitrophenyl)‐2‐(methyl(pyridin‐2‐ylmethyl)amino)acetic) are Zn2+photocages that utilize photodecarboxylation of the methoxy derivative ofmeta‐nitrophenylacetic acid as the release mechanism. Isothermal titration calorimetry (ITC) was used an alternative to usual approaches to measure the Zn2+binding affinities of these new compounds owing to unsuccessful measurement by competitive titration with 4‐(2‐pyridylazo)resorcinol (PAR). MorphDeCage forms a 1 : 1 ligand‐metal complex with a 106 μM Kdvalue. PyrDeCage forms both a 1 : 1 and 1 : 2 metal: ligand complexes with 3.2 and 21.7 μM Kdvalues respectively. To further demonstrate the efficacy of the ITC methodology and provide a comparison to direct UV‐vis titrations data, two photocages based on Sanger's reagent (SRPs) were prepared. The Kdvalues of the SRPs measured by UV‐vis titration and ITC were internally consistent and support the retraction of the original report (J. Am. Chem. Soc.2020,142, 3806–3813), which was withdrawn due to errors in binding affinity measurements.more » « less
-
Abstract We have been interested in the development of rubisco‐based biomimetic systems for reversible CO2capture from air. Our design of the chemical CO2capture and release (CCR) system is informed by the understanding of the binding of the activator CO2(ACO2) in rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase). The active site consists of the tetrapeptide sequence Lys‐Asp‐Asp‐Glu (or KDDE) and the Lys sidechain amine is responsible for the CO2capture reaction. We are studying the structural chemistry and the thermodynamics of CO2capture based on the tetrapeptide CH3CO−KDDE−NH2(“KDDE”) in aqueous solution to develop rubisco mimetic CCR systems. Here, we report the results of1H NMR and13C NMR analyses of CO2capture by butylamine and by KDDE. The carbamylation of butylamine was studied to develop the NMR method and with the protocol established, we were able to quantify the oligopeptide carbamylation at much lower concentration. We performed a pH profile in the multi equilibrium system and measured amine species and carbamic acid/carbamate species by the integration of1H NMR signals as a function of pH in the range 8≤pH≤11. The determination of ΔG1(R) for the reaction R−NH2+CO2R−NH−COOH requires the solution of a multi‐equilibrium equation system, which accounts for the dissociation constantsK2andK3controlling carbonate and bicarbonate concentrations, the acid dissociation constantK4of the conjugated acid of the amine, and the acid dissociation constantK5of the alkylcarbamic acid. We show how the multi‐equilibrium equation system can be solved with the measurements of the daughter/parent ratioX, the knowledge of the pH values, and the initial concentrations [HCO3−]0and [R‐NH2]0. For the reaction energies of the carbamylations of butylamine and KDDE, our best values are ΔG1(Bu)=−1.57 kcal/mol and ΔG1(KDDE)=−1.17 kcal/mol. Both CO2capture reactions are modestly exergonic and thereby ensure reversibility in an energy‐efficient manner. These results validate the hypothesis that KDDE‐type oligopeptides may serve as reversible CCR systems in aqueous solution and guide designs for their improvement.more » « less
