An Ab Initio Investigation of the Structure and Alkali Metal Cation Selectivity of 18-Crown-6

Glendening, Eric D.; Feller, David; Thompson, M. A.

doi:10.1021/ja00102a035

Cited by 377 publications

(457 citation statements)

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“…Here the apparent threshold is about 6 eV, whereas analysis performed using eq 10 (without kinetic shifts) gives a threshold of 7.37 Ϯ 0.24 eV. Using eq 11 (with kinetic shifts) yields a threshold of 3.07 Ϯ 0.20 eV, which can be favorably compared with results from ab initio theory of 3.44 eV [74]. (Indeed, at the level of theory used, the bond energies of Na ϩ to other simple ethers, where kinetic shifts should not be influential, are systematically overestimated by 12 Ϯ 8%, which corresponds to a shift of 0.37 Ϯ 0.25 eV in the 18 -crown-6 system [73].)…”

Section: Kinetic Shiftsmentioning

confidence: 85%

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Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

Armentrout

2002

J. Am. Soc. Mass Spectrom.

172

180

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Guided ion beam tandem mass spectrometry has proved to be a robust tool for the measurement of thermodynamic information. Over the past twenty years, we have elucidated a number of factors necessary to make such thermochemistry accurate. Careful attention must be paid to the reduction of the raw data, ion intensities versus laboratory ion energies, to a more useful form, reaction cross sections versus relative kinetic energy. Analysis of the kinetic energy dependence of cross sections for endothermic reactions can then reveal thermodynamic data for both bimolecular and collision-induced dissociation (CID) processes. Such analyses need to include consideration of the explicit kinetic and internal energy distributions of the reactants, the effects of multiple collisions, the identity of the collision partner in CID processes, the kinetics of the reaction being studied, and competition between parallel reactions. This work provides examples illustrating the need to consider this multitude of effects along with details of the procedures developed in our group for handling each of them. ( W hen does a mass spectrometer become an ion beam instrument? Is this defined by the instrument, by whether the operator is an analytical or physical chemist, or by the experiments done? All mass spectrometers utilize ion beams, but the unspoken definition of an ion beam instrument is an apparatus that can be used to make quantitative physical measurements. In this regard, the capabilities of the instrumentation and the intent and training of the operator are all important factors. Whereas a mass spectrometer is often used as an identification tool through the use of mass spectral patterns, by taking advantage of the ability to easily change the kinetic energy of ions, it can also be a powerful instrument for the determination of thermodynamic data.In this article, I lay down some of the founding principles behind our use of tandem mass spectrometry, and in particular, so-called guided ion beam mass spectrometry to elucidate thermochemical information. This is achieved primarily by examining the kinetic energy dependence of endothermic ion-molecule reactions and determining their energy thresholds.Although many types of instruments have been used to perform such measurements, the link between such studies and guided ion beam techniques is a strong one. Indeed, the NIST Webbook [1] states in its section on Determinations of Reaction Endothermicity that "more commonly a so-called guided-beam apparatus is utilized for such determinations." Considering that there are only about a dozen such laboratories worldwide, this is a testament to the ability of this particular kind of apparatus to provide a plethora of high quality information. However, such information requires attention to myriad details, which are outlined in this article.Two fundamental types of reactions can be used to acquire thermodynamic information: Bimolecular exchange reactions, process 1, and collision-induced dissociation (CID), process 2.Reactions 1 can be either ex...

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Section: Kinetic Shiftsmentioning

confidence: 85%

“…The full line shows this model convoluted with the kinetic and internal energy distributions of the reactants. Arrows indicate the bond energies for this complex measured using eq 10 (no RRKM, which excludes lifetime effects), using eq 11 (with RRKM), and calculated (theory) [74]. …”

Section: Competitive Shiftsmentioning

confidence: 99%

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

Armentrout

2002

J. Am. Soc. Mass Spectrom.

172

180

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“…For the Rb ϩ and Cs ϩ complexes, geometry optimizations and frequency analyses were performed using a hybrid basis set in which the effective core potentials (ECPs) and valence basis sets of Hay and Wadt (HW) were used to describe the alkali metal cation [43], while the all-electron 6-31G* basis sets were used for the C, H, P, and O atoms. As suggested by Glendening et al [44], a single polarization (d) function was added to the Hay-Wadt valence basis set for Rb and Cs, with exponents of 0.24 and 0.19, respectively. The calculated vibrational frequencies were scaled by a factor of 0.9804 [45] and are listed in the Supporting Data, Table 1S (which can be found in the electronic version of this article).…”

Section: Theoretical Calculationsmentioning

confidence: 99%

A simple model for metal cation-phosphate interactions in nucleic acids in the gas phase: Alkali metal cations and trimethyl phosphate

Ruan

Huang

Rodgers

2008

J. Am. Soc. Mass Spectrom.

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Threshold collision-induced dissociation techniques are employed to determine the bond dissociation energies (BDEs) of complexes of alkali metal cations to trimethyl phosphate, TMP. Endothermic loss of the intact TMP ligand is the only dissociation pathway observed for all complexes. Theoretical calculations at the B3LYP/6-31G* level of theory are used to determine the structures, vibrational frequencies, and rotational constants of neutral TMP and the M ϩ (TMP) complexes. Theoretical BDEs are determined from single point energy calculations at the B3LYP/6-311ϩG(2d,2p) level using the B3LYP/6-31G* optimized geometries. The agreement between theory and experiment is reasonably good for all complexes except Li ϩ (TMP hosphate esters are integral parts of many biologically active molecules ranging from nucleic acids, lipids, and ATP to pesticides and nerve agents [1][2][3]. Serving as link components in nucleic acids, phosphate esters connect thousands of base pairs to form large molecules that contain the genetic information. These phosphate groups are deprotonated under physiological conditions. The resulting negative charges along the phosphate backbone are stabilized and neutralized by the binding of metal cations. Metal cations can and often do exert a significant influence on nucleic acid structure and genetic information transfer [4]. Metal cation binding reduces the repulsion between neighboring nucleotide units, and therefore influences the stabilization and structural dynamics of nucleic acids and lipids in membranes. For example, alkali and alkaline earth metal cations, including the most biologically important of these cations, Na ϩ and Mg 2ϩ , prefer to bind to a phosphate group rather than to the nucleobases or sugar moieties [5]. Mg 2ϩ is found to increase the melting temperature of DNA [6]. Metal cations may also be involved in the functioning of nucleic acids, e.g., metal cations are required for the proper functioning of all ribozymes [7]. Metal cation-nucleic acid interactions are currently of great interest because metal cations and metal cation-ligand complexes bind to DNA and regulate gene expression, act as drugs, or can be used as tools for molecular biology studies [8]. Hendry and Sargeson studied metal cation-promoted phosphate ester hydrolysis and found that the rate of hydrolysis is modulated by the size of the metal cation and the ease of formation of a four-membered chelate ring [9]. Dempcy and Bruice found a pentacoordinate intermediate for the catalysis of alkyl phosphate diesters [10]. Schneider and Kabelac et al. [11] studied the distribution of five metal cations (i.e., Na, and Zn 2ϩ ) and water around a negatively charged phosphate group from various crystal structures, and found that all of the cations prefer asymmetric monodentate coordination over bidentate coordination. Their ab initio calculations suggest that bidentate binding of these metal cations to an isolated phosphate group is preferred, but that the presence of even a single water molecule alters this preference. Ab...

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“…21,22 On the other hand, in recent years, hydration of the crown ether molecules and complexes has been also studied by both the theoretical [23][24][25][26][27][28][29][30][31] and experimental [32][33][34][35][36][37] approaches, but most of these studies were in aqueous solution. Studies concerning hydration in the wet-organic solvents for the crown ether system are scarce.…”

Section: Introductionmentioning

confidence: 99%

Hydration to Benzo-15-crown-5, Benzo-18-crown-6 and the Benzo-18-crown-6-Potassium Ion Complex in the Low-Polar Organic Solvents

2001

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The water in the organic solvents sometimes exerts quite a large effect on the equilibria, the existing state and the structure of solutes. [1][2][3][4][5][6][7][8][9][10] Particularly, in the solvent extraction study, since the solutes in the water-saturated organic solution are discussed, hydration of the solutes in the organic phase is a very important subject. It has been demonstrated that the water molecules are coextracted with the metal ions, 11-14 the metal complexes, [14][15][16][17] and the inorganic anions 2,3,[18][19][20] into the organic solvents, and the mean hydration numbers of these solutes in the organic phase were determined.There have been numerous studies about the ion-pair extraction of the crown ether complexes; extractability and selectivity of the metal ions have been discussed by using the overall extraction equilibrium constant and its component equilibrium constants. 21,22 On the other hand, in recent years, hydration of the crown ether molecules and complexes has been also studied by both the theoretical 23-31 and experimental [32][33][34][35][36][37] approaches, but most of these studies were in aqueous solution. Studies concerning hydration in the wet-organic solvents for the crown ether system are scarce.Iwachido et al. 14 reported on the hydration number of the alkali and alkaline earth metal ions and of those complexes with several crown ethers or cryptands in the water-saturated NB. We reported on the hydration number of the alkali metal ions and barium ion complexes with the non-cyclic poly-(oxyethylene) compounds (POE compounds) or 18-crown-6 (18C6) in the water-saturated 1,2-DCE. 17 However, the information for hydration in the wet-organic solvents for the crown ether system is still insufficient, and particularly information is lacking about hydration in various organic solvents. Therefore, in this study, we have investigated the coextraction of water with B15C5, B18C6 and the B18C6-K + complex into seven relatively low-polar solvents which are usually employed for the extraction study of crown ethers. The mean hydration number and hydration equilibrium in the solvents saturated with water are discussed. Experimental ReagentsB15C5 and B18C6 were purchased from Tokyo Kasei, and were used without further purification. Organic solvents (Wako Pure Chemicals): CTC, CF, DCM, 1,2-DCE, BZ, CB and o-DCB, were washed three times with distilled water. Potassium picrate was prepared from its hydroxide and picric acid (Wako), and was recrystallized twice from distilled water. Other chemicals were of analytical reagent grade. ProcedureFor distribution of free crown ethers, a portion of an organic solution (20 ml) containing B18C6 (0 -0.06 mol dm -3 ) or B15C5 (0 -0.1 mol dm -3 ) was shaken with an equal volume of water in a centrifuge tube (50 ml) in a thermostated water bath for 1 h at 25.0 ± 0.1˚C. After centrifugation, the water concentration of the organic phase was determined by the coulometric Karl-Fischer titration (Kyoto Electronics MKC-210).For distribution of potassium picrate ...

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An Ab Initio Investigation of the Structure and Alkali Metal Cation Selectivity of 18-Crown-6

Cited by 377 publications

References 0 publications

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

Mass spectrometry—Not just a structural tool: The use of guided ion beam tandem mass spectrometry to determine thermochemistry

A simple model for metal cation-phosphate interactions in nucleic acids in the gas phase: Alkali metal cations and trimethyl phosphate

Hydration to Benzo-15-crown-5, Benzo-18-crown-6 and the Benzo-18-crown-6-Potassium Ion Complex in the Low-Polar Organic Solvents

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