Conformational polymorphs of 3-cyclopropyl-5-(3-methyl-[1,2,4]triazolo[4,3-a]pyridin-7-yl)-1,2,4-oxadiazole

2021 ◽  
Vol 77 (1) ◽  
pp. 20-28
Author(s):  
Svitlana V. Shishkina ◽  
Irina S. Konovalova ◽  
Svitlana S. Kovalenko ◽  
Lyudmila L. Nikolaeva ◽  
Natalya D. Bunyatyan ◽  
...  
Keyword(s):  
Weak Interactions ◽  
Isoamyl Alcohol ◽  
Lattice Energy ◽  
Relative Energy ◽  
Polymorphic Form ◽  
Structural Motif ◽  
Strong Interactions ◽  
Monoclinic Structure ◽  
Orthorhombic Structure ◽  
Polymorphic Forms

The dipharmacophore compound 3-cyclopropyl-5-(3-methyl-[1,2,4]triazolo[4,3-a]pyridin-7-yl)-1,2,4-oxadiazole, C12H11N5O, was studied on the assumption of its potential biological activity. Two polymorphic forms differ in both their molecular and crystal structures. The monoclinic polymorphic form was crystallized from more volatile solvents and contains a conformer with a higher relative energy. The basic molecule forms an abundance of interactions with relatively close energies. The orthorhombic polymorph was crystallized very slowly from isoamyl alcohol and contains a conformer with a much lower energy. The basic molecule forms two strong interactions and a large number of weak interactions. Stacking interactions of the `head-to-head' type in the monoclinic structure and of the `head-to-tail' type in the orthorhombic structure proved to be the strongest and form stacked columns in the two polymorphs. The main structural motif of the monoclinic structure is a double column where two stacked columns interact through weak C—H...N hydrogen bonds and dispersive interactions. In the orthorhombic structure, a single stacked column is the main structural motif. Periodic calculations confirmed that the orthorhombic structure obtained by slow evaporation has a lower lattice energy (0.97 kcal mol−1) compared to the monoclinic structure.

Concomitant polymorphic forms of 3-cyclopropyl-5-(2-hydrazinylpyridin-3-yl)-1,2,4-oxadiazole

2020 ◽  
Vol 76 (8) ◽  
pp. 836-844 ◽  
Author(s):  
Svitlana V. Shishkina ◽  
Irina S. Konovalova ◽  
Veronika R. Karpina ◽  
Svitlana S. Kovalenko ◽  
Sergiy M. Kovalenko ◽  
...  
Keyword(s):  
Hydrogen Bonds ◽  
Lone Pair ◽  
Lattice Energy ◽  
Structural Motif ◽  
Stacking Interactions ◽  
Centrosymmetric Dimer ◽  
Triclinic Structure ◽  
Isopropanol Solution ◽  
Polymorphic Forms ◽  
Head Type

The dipharmacophore compound 3-cyclopropyl-5-(2-hydrazinylpyridin-3-yl)-1,2,4-oxadiazole, C10H11N5O, was studied on the assumption of its potential biological activity. Two concomitant polymorphs were obtained on crystallization from isopropanol solution and these were thoroughly studied. Identical conformations of the molecules are found in both structures despite the low difference in energy between the four possible conformers. The two polymorphs differ crucially with respect to their crystal structures. A centrosymmetric dimer formed due to both stacking interactions of the `head-to-tail' type and N—H...N(π) hydrogen bonds is the building unit in the triclinic structure. The dimeric building units form an isotropic packing. In the orthorhombic polymorphic structure, the molecules form stacking interactions of the `head-to-head' type, which results in their organization in a column as the primary basic structural motif. The formation of N—H...N(lone pair) hydrogen bonds between two neighbouring columns allows the formation of a double column as the main structural motif. The correct packing motifs in the two polymorphs could not be identified without calculations of the pairwise interaction energies. The triclinic structure has a higher density and a lower (by 0.60 kcal mol−1) lattice energy according to periodic calculations compared to the orthorhombic structure. This allows us to presume that the triclinic form of 3-cyclopropyl-5-(2-hydrazinylpyridin-3-yl)-1,2,4-oxadiazole is the more stable.

scholarly journals Blind crystal structure prediction of a novel second polymorph of 1-hydroxy-7-azabenzotriazole

2006 ◽  
Vol 62 (4) ◽  
pp. 642-650 ◽  
Author(s):  
Harriott Nowell ◽  
Christopher S. Frampton ◽  
Julie Waite ◽  
Sarah L. Price
Keyword(s):  
Crystal Structure ◽  
Structure Prediction ◽  
Structure Refinement ◽  
Lattice Energy ◽  
Polymorphic Form ◽  
Crystal Structure Prediction ◽  
Blind Test ◽  
Coupling Reagent ◽  
Energy Penalty ◽  
Alcohol Solvents

The commercially available peptide coupling reagent 1-hydroxy-7-azabenzotriazole has been shown to crystallize in two polymorphic forms. The two polymorphs differ in their hydrogen-bonding motif, with form I having an R_2^2(10) dimer motif and form II having a C(5) chain motif. The previously unreported form II was used as an informal blind test of computational crystal structure prediction for flexible molecules. The crystal structure of form II has been successfully predicted blind from lattice-energy minimization calculations following a series of searches using a large number of rigid conformers. The structure for form II was the third lowest in energy with form I found as the global minimum, with the energy calculated as the sum of the ab initio intramolecular energy penalty for conformational distortion and the intermolecular lattice energy which is calculated from a distributed multipole representation of the charge density. The predicted structure was sufficiently close to the experimental structure that it could be used as a starting model for crystal structure refinement. A subsequent limited polymorph screen failed to yield a third polymorphic form, but demonstrated that alcohol solvents are implicated in the formation of the form I dimer structure.

New Ternary Phosphide La7Pd17P12: Preparation and Crystal Structure

2002 ◽  
Vol 57 (12) ◽  
pp. 1409-1413 ◽  
Author(s):  
S. Budnyk ◽  
Yu. Prots ◽  
Yu. Kuz’ma ◽  
Yu. Grin
Keyword(s):  
Crystal Structure ◽  
Temperature Region ◽  
Large Family ◽  
Structural Features ◽  
Structural Motif ◽  
Crystal Data ◽  
Monoclinic Structure ◽  
X Ray ◽  
Data Space ◽  
Metal Ratio

The title compound was prepared from elements by sintering in the temperature region between 1073 and 1473 K. The monoclinic structure of La7Pd17P12 was solved and refined from X-ray single crystal data: space group C2/m, a = 24.519(1), b = 4.0859(5), c = 13.6106(8)Å , β = 112.129(3)°, Z = 2, RF = 0.025 for 1065 unique of 4877 measured reflections and 112 refined parameters. Main structural motif of the new phosphide are condensed blocks of trigonal prisms around phosphorus atoms connected to infinite chains via lanthanum atoms. The structural features of La7Pd17P12 are discussed in comparison with some representatives of a large family of structures with metal / non-metal ratio close to 2 : 1.

scholarly journals The Nature of Triel Bonds, a Case of B and Al Centres Bonded with Electron Rich Sites

Molecules ◽  
2020 ◽  
Vol 25 (11) ◽  
pp. 2703 ◽  
Author(s):  
Sławomir J. Grabowski
Keyword(s):  
Lewis Acids ◽  
Weak Interactions ◽  
Lewis Base ◽  
Basis Set ◽  
Strong Interactions ◽  
Orbital Method ◽  
Covalent Bonds ◽  
Moller Plesset ◽  
Intermolecular Distances ◽  
Base Units

The second-order Møller–Plesset perturbation theory calculations with the aug-cc-pVTZ basis set were performed on complexes of triel species: BCl3, BH3, AlCl3, and AlH3 acting as Lewis acids through the B or Al centre with Lewis base units: NCH, N2, NH3, and Cl− anion. These complexes are linked by triel bonds: B/Al⋅⋅⋅N or B/Al⋅⋅⋅Cl. The Quantum Theory of ´Atoms in Molecules´ approach, Natural Bond Orbital method, and the decomposition of energy of interaction were applied to characterise the latter links. The majority of complexes are connected through strong interactions possessing features of covalent bonds and characterised by short intermolecular distances, often below 2 Å. The BCl3⋅⋅⋅N2 complex is linked by a weak interaction corresponding to the B⋅⋅⋅N distance of ~3 Å. For the BCl3⋅⋅⋅NCH complex, two configurations corresponding to local energetic minima are observed, one characterised by a short B⋅⋅⋅N distance and a strong interaction and another one characterised by a longer B⋅⋅⋅N distance and a weak triel bond. The tetrahedral triel structure is observed for complexes linked by strong triel bonds, while, for complexes connected by weak interactions, the structure is close to the trigonal pyramid, particularly observed for the BCl3⋅⋅⋅N2 complex.

Electroweak Interactions and W, Z Boson Properties

2020 ◽  
Author(s):  
Maarten Boonekamp ◽  
Matthias Schott
Keyword(s):  
Standard Model ◽  
Weak Interaction ◽  
Top Quark ◽  
Quantum Electrodynamics ◽  
Weak Interactions ◽  
Higgs Field ◽  
Nuclear Research ◽  
Strong Interactions ◽  
Weak Boson ◽  
The Standard Model

With the huge success of quantum electrodynamics (QED) to describe electromagnetic interactions in nature, several attempts have been made to extend the concept of gauge theories to the other known fundamental interactions. It was realized in the late 1960s that electromagnetic and weak interactions can be described by a single unified gauge theory. In addition to the photon, the single mediator of the electromagnetic interaction, this theory predicted new, heavy particles responsible for the weak interaction, namely the W and the Z bosons. A scalar field, the Higgs field, was introduced to generate their mass. The discovery of the mediators of the weak interaction in 1983, at the European Center for Nuclear Research (CERN), marked a breakthrough in fundamental physics and opened the door to more precise tests of the Standard Model. Subsequent measurements of the weak boson properties allowed the mass of the top quark and of the Higgs Boson to be predicted before their discovery. Nowadays, these measurements are used to further probe the consistency of the Standard Model, and to place constrains on theories attempting to answer still open questions in physics, such as the presence of dark matter in the universe or unification of the electroweak and strong interactions with gravity.

A NEW THEORY OF ELECTROMAGNETIC, WEAK AND STRONG INTERACTIONS

2002 ◽  
Vol 11 (03) ◽  
pp. 177-210 ◽  
Author(s):  
SOKRATES T. PANTELIDES
Keyword(s):  
Weak Interactions ◽  
Structure Constant ◽  
Fine Structure Constant ◽  
Strong Interactions ◽  
Gauge Bosons ◽  
Lepton Pairs ◽  
Mixing Angle ◽  
Yang Mills ◽  
Photon Field ◽  
New Interpretation

The Higgs mechanism for imparting masses to gauge bosons and matter particles is obviated by showing that Yang–Mills gauge bosons have intrinsic nonzero masses (rest-frame energies) from self-interactions. Electroweak (EW) mixing is ruled out because it produces a photon field that is massive, carries EW charge, and does not satisfy Maxwell's equations. Other fundamental difficulties of the Standard Model are identified. A new gauge theory of electromagnetic, weak and strong interactions is derived from the Dirac equation with no other postulates and no free parameters. The three forces are intrinsically unified, the photon field is Maxwellian, weak interactions derive from spin (not isospin), and the weak and strong bosons are naturally massive and chiral. Charge is naturally quantized to integral values. Three generations of lepton pairs and elementary-hadron pairs, all with integral charges, are predicted, contradicting the phenomenology of fractional quark charges, but in full accord with experimental data on weak and strong processes and composite hadrons. Neutrinos are massive. The Dirac masses, the fine structure constant, neutrino oscillations and Cabibbo mixing are shown to have a common origin in the gravitational field. The new theory leads to a new interpretation of "negative energies" with cosmological implications. Finally, it is shown that key expressions of the EW formalism agree with those of the new theory and with experiments only if the mixing angle θ is given by sin 2 θ = 0.25, which accounts for the EW model's successes.

Unification of Strong-Weak Interactions and Possible Unified Scheme of Four-Interactions

2020 ◽  
Vol 8 (5) ◽  
Author(s):  
Yi-Fang Chang
Keyword(s):  
Particle Physics ◽  
Short Range ◽  
Weak Interactions ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Coupling Constants ◽  
Strong Interactions ◽  
Main Character ◽  
Unified Theories ◽  
Three Dimensional Space

First, various known unified theories of interactions in particle physics are reviewed. Next, strong and weak interactions are all short-range, which should more be unified. Except different action ranges their main character is: strong interactions are attraction each other, and weak interactions are mutual repulsion and derive decay. We propose a possible method on their unification, whose coupling constants are negative and positive, respectively. Further, we propose a figure on the unification of the four basic interactions in three-dimensional space, and search some possible tests and predictions, for example, strong-weak interactions transform each other, some waves may be produced. Finally, based on the simplest unified gauge group GL(6,C) of four-interactions, a possible form of Lagrangian is researched. Some relations and equations of different interactions are discussed.

Two new polymorphic forms of combretastatin A-4, an antitumour agent

2020 ◽  
Vol 76 (10) ◽  
pp. 958-964
Author(s):  
Anita M. Grześkiewicz ◽  
Tomasz Stefański ◽  
Zbigniew Dutkiewicz ◽  
Daria Buśko ◽  
Maciej Kubicki
Keyword(s):  
Weak Interactions ◽  
Topological Analysis ◽  
Monoclinic Form ◽  
Colchicine Binding Site ◽  
Biological Studies ◽  
Antitumour Agent ◽  
Conformational Freedom ◽  
Polymorphic Forms

Two new polymorphic forms of combretastatin A-4 {systematic name: 2-methoxy-5-[(E)-2-(3,4,5-trimethoxyphenyl)ethenyl]phenol, C18H20O5, CA-4}, an inhibitor of tubulin polymerization at the colchicine binding site, were identified. A number of crystallization attempts led to the orthorhombic form, with two molecules in the asymmetric part of the unit cell; obtaining a different form required the experiment to be moved to another laboratory. None of the attempts resulted in the monoclinic form described earlier. The three different forms contain molecules of significantly different geometries, which can be related to conformational freedom, postulated as the result of biological studies. In addition, the packing modes in all three forms are basically different. The structural differences at both the molecular and the supramolecular level have also been studied via calculations of energies and a topological analysis of the electron density. The results confirm the role of weak interactions in the determination of crystal architecture and additionally hint at an explanation for the results of crystallization attempts: the new monoclinic form has significantly lower energy than the form reported earlier.

scholarly journals Structure determination and phase transition behaviour of dimethyl sulfate

2006 ◽  
Vol 62 (2) ◽  
pp. 280-286 ◽  
Author(s):  
Richard M. Ibberson ◽  
Mark T. F. Telling ◽  
Simon Parsons
Keyword(s):  
Phase Transition ◽  
Dimethyl Sulfate ◽  
Monoclinic Structure ◽  
Orthorhombic Structure ◽  
X Ray Diffraction ◽  
Coordination Environment ◽  
Space Group ◽  
X Ray ◽  
First Order ◽  
Transition Behaviour

The crystal structures of phase I and phase II of dimethyl sulfate, (CH3O)2SO2, have been determined using complementary high-resolution neutron powder and single-crystal X-ray diffraction techniques. Below its melting point of 241 K dimethyl sulfate crystallizes in an orthorhombic structure (I) in the space group Fdd2. On cooling below ∼175 K the crystal transforms to a monoclinic structure (II) in the space group I2/a. The molecule is located on a twofold axis (Z′ = 1/2) in both structures. The phase transition is of first order with strong hysteresis. The phase transition results in changes to both the intra- and the intermolecular coordination environment.

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