Symmetric dissociation of the water molecule with truncation energy error. A benchmark study

2019 ◽  
Vol 21 (9) ◽  
pp. 4953-4964 ◽  
Author(s):  
César X. Almora-Díaz ◽  
Alejandro Ramírez-Solís ◽  
Carlos F. Bunge
Keyword(s):  
Water Molecule ◽  
Equilibrium Geometry ◽  
Energy Error ◽  
Benchmark Study ◽  
Triple Zeta ◽  
The Difference

We use selected CI with truncation energy error to study the symmetric dissociation of H2O with two triple zeta quality bases. In both cases, the difference between CBS energy errors at the equilibrium geometry and dissociation is larger than 10 mH thus chemically accurate NPE values do not guarantee a chemically accurate PES.

scholarly journals Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference

Molecules ◽  
2021 ◽  
Vol 26 (6) ◽  
pp. 1524
Author(s):  
Ferenc K. Kálmán ◽  
Viktória Nagy ◽  
Rocío Uzal-Varela ◽  
Paulo Pérez-Lourido ◽  
David Esteban-Gómez ◽  
...  
Keyword(s):  
Water Molecule ◽  
Metal Ion ◽  
Macrocyclic Ligand ◽  
Relaxation Dispersion ◽  
Metal Exchange ◽  
Relaxation Rates ◽  
Exchange Reactions ◽  
Biologically Relevant ◽  
The Difference ◽  
Nuclear Magnetic

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A2−) or piperidineacetamide (tO2DO2AMPip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H2O)]·2H2O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A2− ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H2O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AMPip)(H2O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A2− is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using 17O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and 1H nuclear magnetic relaxation dispersion (NMRD) profiles.

scholarly journals Revisiting the Role of Charge Transfer and Local Excitations in Thermally Activated Delayed Fluorescence

2022 ◽  
Author(s):  
Leonardo Evaristo de Sousa ◽  
Piotr de Silva
Keyword(s):  
Charge Transfer ◽  
Excited States ◽  
Delayed Fluorescence ◽  
Equilibrium Geometry ◽  
Thermally Activated Delayed Fluorescence ◽  
Thermally Activated ◽  
Model Hamiltonian ◽  
The Difference ◽  
Triplet Excitons

Thermally activated delayed fluorescence (TADF) is a phenomenon that relies on the upconversion of triplet excitons to singlet excitons by means of reverse intersystem crossing (rISC). It has been shown both experimentally and theoretically that the TADF mechanism depends on the interplay between charge transfer and local excitations. However, the difference between the diabatic and adiabatic character of the involved excited states is rarely discussed in the literature. Here, we develop a diabatization procedure to implement a 4-state model Hamiltonian to a set of TADF molecules. We provide physical interpretation for the Hamiltonian elements and show their dependence on the electronic state of the equilibrium geometry. We also demonstrate how vibrations affect TADF efficiency by modifying the diabatic decomposition of the molecule. Finally, we provide a simple model that connects the diabatic Hamiltonian to the electronic properties relevant to TADF and show how such relationship translates into different optimization strategies for rISC, fluorescence and overall TADF performance.

scholarly journals IR spectra of paracetamol

2021 ◽  
Vol 56 (4) ◽  
pp. 255-262
Author(s):  
U Habiba ◽  
A Alam ◽  
S Rahman ◽  
SUD Shamim ◽  
AA Piya
Keyword(s):  
Ir Spectra ◽  
Molecular Crystals ◽  
Equilibrium Geometry ◽  
Experimental Ir ◽  
Crystal Forms ◽  
Spectrum Interpretation ◽  
Free Molecules ◽  
The Difference ◽  
Structure Of Molecular Crystals

Paracetamol is a very popular medication used to treat pain and fever. IR spectra of paracetamol have been measured for powder crystals. Ab initio calculations of its equilibrium geometry and vibrational spectra were carried out for spectrum interpretation. Differences between the experimental IR spectra of crystalline samples have been analyzed. Variations of molecular structure from the isolated state to molecular crystal were estimated based on the difference between the optimized molecular parameters of free molecules and the experimental bond lengths and angles evaluated for the crystal forms of the title compounds. The role of hydrogen bonds in the structure of molecular crystals of paracetamol is investigated. Bangladesh J. Sci. Ind. Res.56(4), 255-262, 2021

scholarly journals VERY LOW H–O–H BENDING FREQUENCIES. VI. VIBRATIONAL SPECTRA OF CdCl2·H2O

2017 ◽  
Vol 38 (1) ◽  
pp. 91
Author(s):  
Viktor Stefov ◽  
Metodija Najdoski ◽  
Bernward Engelen ◽  
Zlatko Ilievski ◽  
Adnan Cahil
Keyword(s):  
Hydrogen Bonds ◽  
Water Molecule ◽  
Gas Phase ◽  
Raman Spectra ◽  
Structural Data ◽  
Liquid Nitrogen Temperature ◽  
Water Molecules ◽  
Deuterium Content ◽  
Infrared And Raman Spectra ◽  
The Difference

The infrared and Raman spectra of CdCl2·H2O as well as those of a series of its partially deuterated analogues were recorded at room and at liquid-nitrogen temperature (RT and LNT, respectively). The combined results from the analysis of the spectra were used to assign the observed bands. In the difference IR spectrum of the compound with low deuterium content (≈ 4 % D) recorded at RT, one broad bands is observed at around 2590 cm–1 while in the LNT spectrum two bands appear (at 2584 cm–1 and 2575 cm–1). The appearance in the LNT spectrum of these two bands which are due to the stretching OD modes of the isotopically isolated HDO molecules points to the existance of two crystallographically different hydrogen bonds and is in accordance with the structural data for this compound. In the LNT infrared and Raman spectra of the protiated compound, one band, at 1583 cm-1, is observed in the region of the bending НОН vibrations with a frequency that is decreasing with lowering the temperature. An interesting finding related to this band is that its frequency is lower than that for the water molecule in the gas phase (1594 cm–1). In the RT and LNT IR spectra, only one strong band (at 560 cm–1) is observed in the region of the librations of water molecules (700 cm–1 – 400 cm–1).

scholarly journals Research on the Hydrophilicity of Non-Coal Kaolinite and Coal Kaolinite from the Viewpoint of Experiments and DFT Simulations

Symmetry ◽  
2020 ◽  
Vol 12 (7) ◽  
pp. 1199
Author(s):  
Peng Xi ◽  
Ruixin Ma ◽  
Wenli Liu
Keyword(s):  
Contact Angle ◽  
Hydrogen Atom ◽  
Oxygen Atom ◽  
Water Molecule ◽  
Density Functional ◽  
Physical Adsorption ◽  
Key Factor ◽  
The Difference ◽  
Kaolinite Surface ◽  
Single Water Molecule

Coal is often coated by coal kaolinite in flotation, resulting in an increase in concentrate ash. The natural hydrophilicity of minerals is the key factor to determining its flotation behavior. The results of studies on the contact angle of non-coal kaolinite and coal kaolinite samples found that the contact angle of coal kaolinite was bigger than that of non-coal kaolinite and the hydrophilicity of the latter was stronger. To investigate the mechanism of the hydrophilic difference between non-coal kaolinite and coal kaolinite, the adsorption of a single water molecule on non-coal kaolinite and coal kaolinite (100) and (00 1 ¯ ) surfaces was calculated with the first principle method of the density functional theory (DFT). The calculation results showed that hydrogen bonds were formed between the hydrogen atom and the oxygen atom of the surface and the hydrogen atom and the oxygen atom of the water molecule after the water molecule was adsorbed on the kaolinite (100) and (00 1 ¯ ) surface. The adsorption process of water molecules on the kaolinite surface was physical adsorption with Van der Waals force existing between them. Regardless of whether the kaolinite (001) surface or the kaolinite (00 1 ¯ ) surface was doped with a carbon atom, the adsorption of a single water molecule was weakened, with a weaker hydrogen bond formed. The calculated results explained the difference of hydrophilicity between non-coal kaolinite and coal kaolinite samples from the molecular and atomic viewpoint.

scholarly journals Hexa-μ-acetato-chlorido(μ-N,2-dioxodobenzene-1-carboximidato)-μ3-oxido-tetrairon(III)–water (1/1) and hexa-μ-acetato-(μ-N,2-dioxodobenzene-1-carboximidato)fluorido-μ3-oxido-tripyridinetetrairon(III)–pyridine–water (1/1/0.24)

2021 ◽  
Vol 77 (10) ◽  
Author(s):  
Cassandra L. Ward ◽  
Matthew J. Allen ◽  
Jacob C. Lutter
Keyword(s):  
Acetic Acid ◽  
Water Molecule ◽  
Intermolecular Interactions ◽  
Self Assembly ◽  
Ligand Field ◽  
Coordination Environment ◽  
Halide Salt ◽  
Salicylhydroxamic Acid ◽  
Space Groups ◽  
The Difference

The title compounds, [Fe4(C2H3O2)6(C7H4O3)FO(C5H5N)3]·C5H5N·0.24H2O (1-F) and [Fe4(C2H3O2)6(C7H4O3)ClO(C5H5N)3]·H2O (1-Cl) were synthesized using a self-assembly reaction in methanol and pyridine with stoichiometric addition of salicylhydroxamic acid (H3shi), acetic acid (HOAc), and the appropriate ferric halide salt. The compounds crystallize as solvates, where 1-F has one pyridine molecule that is disordered about a twofold axis and one water molecule with an occupancy of 0.24 (2); and 1-Cl has one water molecule that is disordered over two sites with occupancies of 0.71 (1) and 0.29 (1). The space groups for each analog differ as 1-F crystallizes in Fdd2 while 1-Cl crystallizes in P21. The difference in packing is due to changes in the intermolecular interactions involving the different halides. The two molecules are mostly isostructural, differing only by the torsion of the pyrine ligands and slight orientation changes in the acetate ligands. All of the iron(III) ions are in six-coordinate octahedral ligand field geometries but each one exhibits a unique coordination environment with various numbers of O (four to six) and N (nought to two) atom donors. Bond-valence sums confirm each iron is trivalent. The hydroximate ligand is bound to three iron(III) ions using a fused chelate motif similar to those in metallacrown compounds.

COMPUTATIONAL DESIGN OF NORBORNANE-BASED HIV-1 PROTEASE INHIBITORS

2010 ◽  
Vol 09 (02) ◽  
pp. 471-485 ◽  
Author(s):  
DAWEI ZHANG ◽  
LIU ZE YU ◽  
PHILIP LIN HUANG ◽  
SYLVIA LEE-HUANG ◽  
JOHN Z. H. ZHANG
Keyword(s):  
Free Energy ◽  
Water Molecule ◽  
Interaction Energy ◽  
Binding Free Energy ◽  
Computational Design ◽  
Free Energies ◽  
Structural Water ◽  
Linear Interaction ◽  
The Difference ◽  
Hiv 1

A series of norbornane-based HIV-1 protease (PR) inhibitors are designed theoretically to displace the tetrahedrally coordinated internal water molecule that bridges inhibitor to flaps via hydrogen bonds. These designed inhibitors use the norbornenone oxygen atom to mimic this structural water molecule and contain diols to interact with the carboxylate oxygens of catalytic aspartates. The binding free energies were estimated by modified linear interaction energy approach [Zoete H, Michielin O, Karplus M, J Comput Aided Mol Des17:861, 2003], in which the binding free energy is written as a linear combination of the electrostatic interaction energy between PR and the ligand, E elec , the van der Waals interaction energy between PR and the ligand, E vdW , and the difference of the solvation free energies of the complex, the receptor, and the isolated ligand, ΔG solv . The equation obtained in previous work [Da W. Zhang, Philip Lin Huang, Sylvia Lee-Huang, John Z. H. Zhang, J Theor Comput Chem7:485, 2008] is applied directly to calculate the binding free energy of designed norbornane-based HIV-1 PR inhibitors.

scholarly journals Syn and anti conformers of diammonium aquabis(malonato)oxidovanadate(IV) in an anhydrate crystal

2018 ◽  
Vol 74 (5) ◽  
pp. 664-667
Author(s):  
Keiji Ohno ◽  
Takumi Yoshida ◽  
Akira Nagasawa ◽  
Takashi Fujihara
Keyword(s):  
Hydrogen Bonding ◽  
Water Molecule ◽  
Complex Anion ◽  
Octahedral Geometry ◽  
The Other ◽  
Distorted Octahedral Geometry ◽  
Asymmetric Unit ◽  
Distorted Octahedral ◽  
The Difference ◽  
Complex Anions

The asymmetric unit of the title anhydrate compound, (NH4)2[VO(C3H2O4)2(H2O)], consists of two independent complex anions and four ammonium cations. In the complex anions, the VIV atoms are each coordinated by two malonate ligands, one water molecule and one oxide O atom in a distorted octahedral geometry. The equatorial plane is formed by the malonate O atoms, while the axial positions are occupied by water and oxide O atoms. The difference between the two independent complexes is the relative conformation of the malonate ligands. The two ligands in one complex anion are in a syn conformation, while in the other they adopt an anti conformation. In the crystal, the complex anions interact with the counter-cations and adjacent anions through O—H...O, N—H...O and C—H...O hydrogen bonds. Stacks of alternating layers consisting of either anti or syn isomers, formed with the aid of the hydrogen bonding, are observed. DFT calculations for the anti and syn isomers show a similar thermodynamic stability to each other. The crystal used for this analysis was an inversion twin with the ratio of the twin components being 0.270 (13):0.730 (13).

The Origin of the Moon

1962 ◽  
Vol 14 ◽  
pp. 149-155 ◽  
Author(s):  
E. L. Ruskol
Keyword(s):  
Chemical Composition ◽  
Solar System ◽  
The Moon ◽  
The Earth ◽  
The Difference ◽  
Origin Of The Moon

The difference between average densities of the Moon and Earth was interpreted in the preceding report by Professor H. Urey as indicating a difference in their chemical composition. Therefore, Urey assumes the Moon's formation to have taken place far away from the Earth, under conditions differing substantially from the conditions of Earth's formation. In such a case, the Earth should have captured the Moon. As is admitted by Professor Urey himself, such a capture is a very improbable event. In addition, an assumption that the “lunar” dimensions were representative of protoplanetary bodies in the entire solar system encounters great difficulties.

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