1
|
Bengs C, Dagys L, Moustafa GAI, Whipham JW, Sabba M, Kiryutin AS, Ivanov KL, Levitt MH. Nuclear singlet relaxation by chemical exchange. J Chem Phys 2021; 155:124311. [PMID: 34598559 DOI: 10.1063/5.0066182] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The population imbalance between nuclear singlet states and triplet states of strongly coupled spin-1/2 pairs, also known as nuclear singlet order, is well protected against several common relaxation mechanisms. We study the nuclear singlet relaxation of 13C pairs in aqueous solutions of 1,2-13C2 squarate over a range of pH values. The 13C singlet order is accessed by introducing 18O nuclei in order to break the chemical equivalence. The squarate dianion is in chemical equilibrium with hydrogen-squarate (SqH-) and squaric acid (SqH2) characterized by the dissociation constants pK1 = 1.5 and pK2 = 3.4. Surprisingly, we observe a striking increase in the singlet decay time constants TS when the pH of the solution exceeds ∼10, which is far above the acid-base equilibrium points. We derive general rate expressions for chemical-exchange-induced nuclear singlet relaxation and provide a qualitative explanation of the TS behavior of the squarate dianion. We identify a kinetic contribution to the singlet relaxation rate constant, which explicitly depends on kinetic rate constants. Qualitative agreement is achieved between the theory and the experimental data. This study shows that infrequent chemical events may have a strong effect on the relaxation of nuclear singlet order.
Collapse
Affiliation(s)
- Christian Bengs
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| | - Laurynas Dagys
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| | - Gamal A I Moustafa
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| | - James W Whipham
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| | - Mohamed Sabba
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| | | | | | - Malcolm H Levitt
- School of Chemistry, University of Southampton, Southampton, United Kingdom
| |
Collapse
|
2
|
Rodriguez J, Elola MD. Molecular Dynamics Simulations of Ibuprofen Release from pH-Gated Silica Nanochannels. J Phys Chem B 2014; 119:8868-78. [DOI: 10.1021/jp505585g] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Affiliation(s)
- Javier Rodriguez
- Departamento
de Física, Comisión Nacional de Energía Atómica, Avenida Libertador 8250, 1429 Buenos Aires, Argentina
- ECyT, UNSAM, Martín de Irigoyen 3100, 1650 San Martín, Provincia de Buenos Aires, Argentina
| | - M. Dolores Elola
- Departamento
de Física, Comisión Nacional de Energía Atómica, Avenida Libertador 8250, 1429 Buenos Aires, Argentina
| |
Collapse
|
3
|
Pomata MHH, Sonoda MT, Skaf MS, Elola MD. Anomalous Dynamics of Hydration Water in Carbohydrate Solutions. J Phys Chem B 2009; 113:12999-3006. [DOI: 10.1021/jp904019c] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Matías H. H. Pomata
- Departamento de Física, Comisión Nacional de Energía Atómica-CNEA, Avenida Gral. Paz 1499 (1650) San Martín, Buenos Aires, Argentina
| | - Milton T. Sonoda
- Universidade Federal de Uberlandia, Avenida Jose Joao Dib, 2545 Ituiutaba, MG, 38302-000 Brazil
| | - Munir S. Skaf
- Institute of Chemistry, State University of Campinas—UNICAMP, P. O. Box 6154, Campinas, SP, 13084-862 Brazil
| | - M. Dolores Elola
- Departamento de Física, Comisión Nacional de Energía Atómica—CNEA, Avenida Libertador 8250, (1429) Buenos Aires, Argentina
| |
Collapse
|
4
|
Krienke H, Schmeer G. Hydration of Molecular Anions with Oxygen Sites – a Monte Carlo Study. ACTA ACUST UNITED AC 2008. [DOI: 10.1524/zpch.218.6.749.33456] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Abstract
Equilibrium properties of molecular model water (in pure phase and in electrolyte solutions) are calculated with the help of spatial pair correlation functions, starting from classical molecular pair interactions. Simulations were performed for a new simple water model derived from combined quantum-mechanical and statistical calculations in a SCF/SSOZ scheme.
Ion hydration of molecular anions with oxygen sites such as nitrate and perchlorate ions is of special interest when compared with hydration structures of spherical atomic anions like the halide ions. The water structure around the different solutes, and their influence on solution properties, is discussed.
Collapse
|
5
|
Idrissi A. The hypothetical signature of self aggregation in the low frequency response of aqueous solutions: A molecular dynamics simulation analysis. J Mol Liq 2007. [DOI: 10.1016/j.molliq.2006.12.020] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
|
6
|
Kritayakornupong C. The Jahn-Teller effect of the Cr2+ ion in aqueous solution:Ab initio QM/MM molecular dynamics simulations. J Comput Chem 2007; 29:115-21. [PMID: 17551971 DOI: 10.1002/jcc.20771] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The hydration structure of Cr(2+) has been studied using molecular dynamics (MD) simulations including three-body corrections and combined ab initio quantum mechanical/molecular mechanical (QM/MM) MD simulations at the Hartree-Fock level. The structural properties are determined in terms of radial distribution functions, coordination numbers, and several angle distributions. The mean residence time was evaluated for describing ligand exchange processes in the second hydration shell. The Jahn-Teller distorted octahedral [Cr(H(2)O)(6)](2+) complex was pronounced in the QM/MM MD simulation. The first-shell distances of Cr(2+) are in the range of 1.9-2.8 A, which are slightly larger than those observed in the cases of Cu(2+) and Ti(3+). No first-shell water exchange occurred during the simulation time of 35 ps. Several water-exchange processes were observed in the second hydration shell with a mean residence time of 7.3 ps.
Collapse
Affiliation(s)
- Chinapong Kritayakornupong
- Department of Chemistry, Faculty of Science, King Mongkut's University of Technology Thonburi, Bangkok, Thailand.
| |
Collapse
|
7
|
Idrissi A, Longelin S, Damay P, Krishtal S, Kiselev M. Analysis of the transverse and the longitudinal pseudodiffusion of CO2 in sub- and supercritical states: a molecular-dynamics analysis. J Chem Phys 2006; 125:224501. [PMID: 17176143 DOI: 10.1063/1.2400855] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
We have performed molecular-dynamics simulations of CO(2) system along the gas-liquid coexistence curve and on the isochore 94.22 cm(3) mol(-1) (which corresponds to the critical isochore). The calculation has been carried out in order to analyze the diffusion of CO(2) and particularly to figure out how the diffusion coefficient may be decomposed along the molecular axes. This makes it possible to analyze the anisotropy of the diffusion along these axes and to shed light on the microscopic changes which accompany such behavior. This anisotropy is traced back to the effect of the translation-rotation coupling (TRC) along the molecular axes. Along the liquid-gas coexistence curve, the pseudolongitudinal diffusion is found to be more rapid than the transverse one. The opposite trend is found along the isochore 94.22 cm(3) mol(-1). The role of the local structure was explored by calculating intermediate scattering function and the autocorrelation functions for the forces acting along the molecular axes. It is shown that the strength of the TRC effect is correlated to the difference between the relaxation times of the local structure, that of the reorientation along the molecular axes, and that of the translational motion. The analysis of the correlation time and the average mean square force along the longitudinal and transverse directions confirms the anisotropy of the local environment that determines the translational dynamics of a molecule.
Collapse
Affiliation(s)
- A Idrissi
- Laboratoire de Spectrochimie Infrarouge et Raman (UMR CNRS A8516), Centre d'Etudes et de Recherches Lasers et Applications, Université des Sciences et Technologies de Lille, 59655 Villeneuve d'Ascq Cedex, France.
| | | | | | | | | |
Collapse
|
8
|
de Oliveira CIR, de Oliveira LFC, Dias Filho FA, Messaddeq Y, Ribeiro SJL. Spectroscopic investigation of a new hybrid glass formed by the interaction between croconate ion and calcium polyphosphate. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2005; 61:2023-8. [PMID: 15911387 DOI: 10.1016/j.saa.2004.01.036] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/07/2003] [Accepted: 01/13/2004] [Indexed: 05/02/2023]
Abstract
In this work, a new organic-inorganic hybrid material has been synthesized by the incorporation of croconate ion into a calcium polyphosphate coacervate. The hybrid so obtained was characterized by means of electronic and vibrational spectroscopies. The material is a homogeneous mixture described by a structural model, which includes helical chains of polyphosphate ions, where the calcium ion occupies the internal vacancies of the structure. The croconate ion appears to be occupying the regions outside the polymeric structure, surrounded by several water molecules. The electronic spectrum of the incorporated material shows a broad band peaking at the same wavelength region (363 nm) observed for the aqueous solution of croconate ion, and manifesting the Jahn-Teller effect as evidenced by the doublet structure of the band. The infrared spectrum is widely dominated by the absorption bands of the polyphosphate ion and the appearance of the carbonyl stretching band at ca. 1550 cm(-1) indicates the presence of croconate ion incorporated in the structure. The Raman spectrum of the material shows several vibrational bands related to the oxocarbon moiety; most of them are shifted in comparison with the free ion. These shifts can be understood in terms of strong hydrogen bonding interactions between water molecules and the oxocarbon moiety. The low temperature methodology proposed here can be well used in the preparation of new phosphate glasses containing organic moieties opening the route to an entirely new class of hybrid glasses.
Collapse
Affiliation(s)
- Carlos Ivan R de Oliveira
- Núcleo de Espectroscopia e Estrutura Molecular, Departamento de Química, Instituto de Ciências Exatas, Universidade Federal de Juiz de Fora, Campus Universitário, Juiz de Fora, MG 36036-330, Brazil
| | | | | | | | | |
Collapse
|
9
|
Lam CK, Cheng MF, Li CL, Zhang JP, Chen XM, Li WK, Mak TCW. Stabilization of D5hand C2vvalence tautomers of the croconate dianion. Chem Commun (Camb) 2004:448-9. [PMID: 14765252 DOI: 10.1039/b312545a] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The non-benzenoid aromatic D(5h) and enediolate C(2v) form of C5O5(2-) have been stabilized by hydrogen bonding with urea and 1,3-dimethylurea, respectively, in the host lattices of two novel crystalline inclusion compounds.
Collapse
Affiliation(s)
- Chi-Keung Lam
- Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, P. R. China
| | | | | | | | | | | | | |
Collapse
|
10
|
Cavalcante AO, Ribeiro MCC. Raman band shape analysis of a low temperature molten salt. J Chem Phys 2003. [DOI: 10.1063/1.1611871] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
|
11
|
Abstract
A set of novel oligomeric polycyclic neutral oxocarbons has been computed at the B3LYP level of density functional theory. On the basis of the calculated dissociation enthalpies, the most stable structures are C(9)O(9) and C(12)O(12) with benzene-like central ring, in agreement with the experimental finding, and the enhanced stability is due to their aromaticity. Several other oxocarbons also have been identified as stable and are targets for further experimental investigations.
Collapse
Affiliation(s)
- Haijun Jiao
- Department of Chemistry, Shanxi Normal University, Linfen, Shanxi, 041004, China.
| | | |
Collapse
|