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1.
Following our recent study on triazane, we present a follow-up study on the thermodynamic properties of triazane’s unsaturated
analog, triazene. We predict optimized structural parameters, vibrational frequencies, enthalpies of formation, enthalpies
of combustion, specific enthalpies of combustion, and proton affinities. Our results indicate that the cis form of triazene
has a specific enthalpy of combustion of −15.2 kJ g−1 and the trans form has a specific enthalpy of combustion of −14.7 kJ g−1.
Figure Structures of cis- and trans-triazane, N3H3 相似文献
2.
Setzer WN 《Journal of molecular modeling》2008,14(5):335-342
The energetics of the Cope rearrangement of 17 germacrane sesquiterpenoids to their respective elemane forms have been calculated
using both density functional theory (B3LYP/6-31G*) and post Hartee-Fock (MP2/6-31G**) ab initio methods. The calculations are in qualitative agreement with experimentally observed Cope rearrangements, but the two methods
give slightly different results. MP2 calculations generally show more favorable elemene energies compared to the respective
germacrenes (by around 3–4 kcal mol−1) and smaller activation energies (by 2–3 kcal mol−1). Additionally, neither method is accurate enough to consistently reproduce the germacrene/elemene equilibrium. Apparently,
the generally small energy differences between the two forms in these sesquiterpenoids cannot be adequately reproduced at
these levels of calculation.
Figure The Cope rearrangement of the germacrane sesquiterpenoid bacchascandon to the elemane shyobunone 相似文献
3.
A series of [XN5]− (X=O, S, Se, Te) compounds has been examined with ab initio and Density Functional Theory (DFT) methods. The five-membered nitrogen ring series of structures are global minima and may exist or be characterized due to their significant dissociation barriers (29.7–32.7 kcal mol−1). Nucleus-independent chemical shifts (NICS) criteria and the presence of (4n+2) π-electrons confirmed that the five-membered nitrogen ring in their structures exhibits characteristics of aromaticity. Thus, the strong stability of the five-membered nitrogen ring structures may be attributed partially to their aromaticity.
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4.
Nongnit Morakot Wandee Rakrai Somchai Keawwangchai Chatthai Kaewtong Banchob Wanno 《Journal of molecular modeling》2010,16(1):129-136
The thiourea based receptor containing naphthalene groups (1), has been successfully designed and synthesized for application as an oxalate receptor. A density functional theory at B3LYP/6-31G(d,p)
level of theory has been applied to predict the binding ability between 1 and selected anions, i.e., oxalate, malonate, succinate, glutarate, dihydrogen phosphate, and hydrogen sulphate. Calculation results point out that
receptor 1 shows the strongest interaction to oxalate ion with the binding free energy of 172.48 kcal mol−1. The recognition ability of 1 to the selected anions has been also investigated by means of the absorption and emission techniques. Experimental results
are in excellent agreement with the calculation data in which receptor 1 shows highly selective for oxalate ion over the other anions with logβ of 3.82 (0.02) M−1 by means of the size of binding cavity.
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5.
Stewart JJ 《Journal of molecular modeling》2007,13(12):1173-1213
Several modifications that have been made to the NDDO core-core interaction term and to the method of parameter optimization
are described. These changes have resulted in a more complete parameter optimization, called PM6, which has, in turn, allowed
70 elements to be parameterized. The average unsigned error (AUE) between calculated and reference heats of formation for
4,492 species was 8.0 kcal mol−1. For the subset of 1,373 compounds involving only the elements H, C, N, O, F, P, S, Cl, and Br, the PM6 AUE was 4.4 kcal
mol−1. The equivalent AUE for other methods were: RM1: 5.0, B3LYP 6–31G*: 5.2, PM5: 5.7, PM3: 6.3, HF 6–31G*: 7.4, and AM1: 10.0 kcal
mol−1. Several long-standing faults in AM1 and PM3 have been corrected and significant improvements have been made in the prediction
of geometries.
Figure Calculated structure of the complex ion [Ta6Cl12]2+ (footnote): Reference value in parenthesis
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
In this paper, we proposed a new method for the determination of either human serum albumin (HSA) or 5-Aminosalicylic acid
(5-ASA) by synchronous fluorescence spectra and examined the interaction between them using the molecular modeling method
under simulative physiological conditions. The optimum conditions of synchronous fluorometric determination of HSA were investigated
and the method was successfully applied to the determination of 5-ASA added to serum, urine, and saliva samples. The linear
range of the determination of HSA and 5-ASA were 1.60 – 414 μg mL−1 and 0.76 –22.95 μg mL−1, the detection limits were 0.552 μg mL−1 and 0.38 μg mL−1, respectively. In addition, the effect of various common ions on the determination of HSA with 5-ASA was also discussed at
room temperature.
Figure The salicylic acid moiety is located within the binding pocket. The ring of 5-ASA was inserted in the hydrophobic cavity of
site I, and it is important to note that the residue ARG-218 and the trptophan residue of HSA (Trp214) are in close proximity
to the ring of 5-ASA suggesting the existence of hydrophobic interaction between them. 相似文献
7.
The ONIOM2 (B3LYP/6–31G (d, p): PM3) and B3LYP/6–31G (d, p) methods were applied to investigate the interaction between STI-571 and abelson tyrosine kinase binding site. The complex of N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)- phenyl]-benzamide (part of STI-571) and related 16 amino acid residues were found at B3LYP/6–31G (d, p) level to have hydrogen bonds and π....π stacking interaction,
their binding energy via HAF optimization was −20.4 kcal mol−1. The results derived from this study agreed well with the reported observation.
Figure Optimized structure of STI-571 and Thr315 in abelson tyrosine kinase based on ONIOM2 method 相似文献
8.
The structure and stability of endohedral X@C20F20 complexes (X = H−, F−, Cl−, Br−, H, He) have been computed at the B3LYP level of theory. All complexes in I
h symmetry were found to be energy minimum structures. H−@C20F20 and F−@C20F20 complexes have negative inclusion energies, while other complexes have positive inclusion energies. Similarity between C20F20 and C20H20 has been found for X = H and He. On the basis of the computed nucleus independent chemical shift values at the cage center,
both C20F20 and C20F20 are aromatic.
Figure Endohedral X@C20F20 complexes 相似文献
9.
Haripal PK Raval HK Raval MK Rawal RM Biswal B Biswal UC 《Journal of molecular modeling》2006,12(6):847-853
A three-dimensional model of the PsbS protein was built with the help of homology-modeling methods. This protein is also known as CP22 and is associated with the protection of photosystem II of thylakoid from excess quanta of light energy absorbed by the photosynthetic apparatus. PsbS is reported to bind two molecules of zeaxanthin at low pH (<5.0) and is believed to be essential for rapid nonphotochemical quenching (qE) of chlorophyll a fluorescence in photosystem II. An attempt was made to explain the pH modulation of the conformation of protein through salt-bridges Glu−(122)-Lys+(113) and Glu−(226)-Lys+(217). Binding of two molecules of zeaxanthin in the three-dimensional model of PsbS is postulated. The molecular mechanism of photoprotection by PsbS is explained through the model.
1 Backbone structure of the PsbS protein with two molecules of all trans zeaxanthin (ZEX). Residues Glu 90, 122, 194, 226 and Lys 113, 217 are shown. The figure is drawn with RASMOL (Molecular Visualization Program, RasMol V2.6, Roger Sayle, Glaxo Wellcome Research and Development, Stevenage, Hertfordshire, UK)
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
10.
A theoretical analysis of the nature of the interactions in dibenzo[24]crown-8 (DB24C8)-n-dibutylammonium (DBM)—pseudorotaxane complex at the MP2 and DFT levels shows that the main contribution to the binding energy is the electrostatic interaction with moderate (20–25%) correlation stabilization. The total binding energy in the DB24C8-DBM complex represents a sum of the binding energies of two NH–O and one CH–O hydrogen bonds and the latter constitutes about 25% of the total interaction energy, giving the total binding energy of −41.2 kcal mol−1 at the BHandHLYP/6-311++G** level. Deprotonation of the DB24C8-DBM complex reduces the binding energy by some 50 kcal mol−1, giving metastable complexes DB24C8-DBA-1 or DB24C8-DBA-2, which will dissociate to give free crown ether and n-dibutylamine because of the strong exchange repulsion that prevails in neutral complexes.
Figure
Formation of DB24C8-DBM pseudorotoxane complex 相似文献
11.
Semiempirical molecular orbital theory has been used for a systematic scan of the binding positions for a Mg2+ ion with 5a,6–anhydrotetracycline taking both conformational flexibility and possible different tautomeric forms into account. The magnesium ion has been calculated alone and with four or five complexed water molecules in order to simulate the experimental situation more closely. The results are analyzed by comparing the behavior of the title compound with that of tetracycline itself and possible causes for the stronger induction of the Tetracycline Receptor (TetR) by 5a,6–anhydrotetracycline than by tetracycline are considered.
Energetically favored 3D -structure of the zwitteranionic 5a,6-anhydrotetracycline magnesium complex in solution
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
12.
13.
As a follow-up study to our study on tetrazane (N4H6), we present computed thermodynamic properties of triazane (N3H5). Calculated properties include optimized geometries, infrared vibrations, enthalpy of formation, enthalpy of combustion,
and proton affinities. We have also mapped the potential energy surface as the molecule is rotated about the N-N bond. We
have predicted a specific enthalpy of combustion for triazane of about -20 kJ g−1.
Figure Schematic diagram of the dielectric barrier discharge (left) and typical temporal profiles of voltage and current, as obtained
from the simulations (right) 相似文献
14.
49Ti chemical shifts for a total of 20 titanium complexes are reported, and several levels of theory are evaluated in order to identify a reliable approach for the calculation of titanium NMR data. The popular B3LYP/6–31G(d)//B3LYP/6–31G(d) proves to give very good agreement with experimental data over a range from 1,400 to −1,300 ppm. The MP2/6–31G(d)//MP2/6–31G(d) level computes even smaller average deviations but fails for TiI4. This behavior together with its huge demand for computational resources requires careful handling of this theoretical level. In addition, NMR data for five titanium fulvene (or related) complexes are given.
Dedicated to Professor Dr. Paul von Ragué Schleyer on the occasion of his 75th birthday 相似文献
15.
The conformational stability of the extended antiparallel dimer structure of Met-enkephalin in water was analyzed by examining the hydration structure of enkephalin using molecular dynamics simulations. The result shows that, despite of the hydrophicility of the terminal atoms in the pentapeptide, the main contributor for the stability of the dimer in water is the four intermolecular hydrogen bonds between the Gly2 and Phe4 groups. The three-dimensional model of the δ-opioid pharmacophore for this dimer structure was also established. Such a model was demonstrated to match the δ-opioid pharmacophore query derived from the non-peptides SIOM, TAN-67, and OMI perfectly. This result thus strongly supports the assumption that the dimer structure of Met-enkephalin is a possible δ-receptor binding conformation.
Figure Schematic model of the extended antiparallel dimer structure of Met-enkephalin 相似文献
16.
Aminophosphine oxides and aminophosphonates are, in general, very stable compounds. However, following phosphorus–carbon bond
cleavage in aqueous acidic media these compounds sometimes decompose to phosphonic acids derivatives (PIII). Despite some controversy in the literature, careful analysis supported by theoretical studies leads to the conclusion that
decomposition to PIII derivatives proceeds via an elimination reaction.
Figure The decomposition of α-aminophosphine oxides to phosphonic acid derivatives (PIII) 相似文献
17.
Orvinols are potent analgesics that target opioid receptors. However, their analgesic mechanism remains unclear and no significant preference for subtype opioid receptor has been achieved. In order to find new orvinols that target the κ-receptor, comparative 3D–QSAR studies were performed on 26 orvinol analogs using comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA). The best predictions for the κ-receptor were obtained with the CoMFA standard model (q
2=0.686, r
2=0.947) and CoMSIA model combined steric, electrostatic, hydrophobic, and hydrogen bond donor/acceptor fields (q
2=0.678, r
2=0.914). The models built were further validated by a test set made up of seven compounds, leading to predictive r
2 values of 0.672 for CoMFA and 0.593 for CoMSIA. The study could be helpful for designing and prepare new category κ-agonists from orvinols.
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18.
σ-Hole bonding is a noncovalent interaction between a region of positive electrostatic potential on the outer surface of a
Group V, VI, or VII covalently-bonded atom (a σ-hole) and a region of negative potential on another molecule, e.g., a lone
pair of a Lewis base. We have investigated computationally the occurrence of increased vibration frequencies (blue shifts)
and bond shortening vs decreased frequencies (red shifts) and bond lengthening for the covalent bonds to the atoms having the σ-holes (the σ-hole
donors). Both are possible, depending upon the properties of the donor and the acceptor. Our results are consistent with models
that were developed earlier by Hermansson and by Qian and Krimm in relation to blue vs red shifting in hydrogen bond formation. These models invoke the derivatives of the permanent and the induced dipole moments
of the donor molecule.
Figure Computed electrostatic potential on the molecular surface of Cl-NO2. Color ranges, in kcal mol−1, are: red, greater than 25; yellow, between 10 and 25; green, between 0 and 10; blue, between −4 and 0; purple, more negative
than −4. The chlorine is facing the viewer, to the right. Note the yellow region of positive potential on the outer side of
the chlorine, along the extension of the N–Cl bond. The blue region shows the sides of the chlorine to have negative potentials.
The calculations were at the B3PW91/6–31G(d,p) level. 相似文献
19.
We have carried out B3PW91 and MP2-FC computational studies of dimethyl sulfoxide, (CH3)2SO, and dimethyl sulfone, (CH3)2SO2. The objective was to establish quantitatively the basis for their high polarities and boiling points, and their strong solvent
powers for a variety of solutes. Natural bond order analyses show that the sulfur–oxygen linkages are not double bonds, as
widely believed, but rather are coordinate covalent single S+→O− bonds. The calculated electrostatic potentials on the molecular surfaces reveal several strongly positive and negative sites
(the former including σ-holes on the sulfurs) through which a variety of simultaneous intermolecular electrostatic interactions
can occur. A series of examples is given. In terms of these features the striking properties of dimethyl sulfoxide and dimethyl
sulfone, their large dipole moments and dielectric constants, their high boiling points and why they are such good solvents,
can readily be understood.
Figure Dimers of dimethyl sulfoxide (DMSO; left) and dimethyl sulfone (DMSO2; right) showing O S—O -hole bonding and C H—O hydrogen bonding. Sulfur atoms are yellow, oxygens are red, carbons are gray and hydrogens are white 相似文献
20.
Gaucher disease is a lysosomal storage disorder caused by deficiency of human acid β-glucosidase. Recent x-ray structural
elucidation of the enzyme alone and in the presence of its inhibitor was done, which provided an excellent template for further
studies on the binding of substrate, product and inhibitor. To draw correlations between the clinical manifestation of the
disease driven by point mutations, L444P and L444R, and the placement and function of putative S-binding sites, the presented
theoretical studies were undertaken, which comprised of molecular dynamics and molecular docking methods. The obtained results
indicate the D443 and D445 residues as extremely important for physiological functionality of an enzyme. They also show, although
indirectly, that binding of the substrate is influenced by an interplay of E235 and E334 residues, constituting putative substrate
binding site, and the region flanked by D435 and D445 residues.
Figure The binding of an arbitrarily chosen structure of glucosylceramide (A), conduritol-β-epoxide (B), glucose (C) to the active
site D443/D445 (A1, B1, C1) and E320/E340 (A2, B2, C2) of the wild-type structure of human acid-β-glucosidase. A1, B1, C1
blue mask represents the residues D443-D445; red mask represents the residue D444; A2, B2, C2 blue mask represents loop1 (Ser345-Glu349) and loop2 (Val394-Asp399), whereas red mask the residues E235 and 340 相似文献