Molecular invariants: Atomic-group valence

1990 ◽  
Vol 12 (6) ◽  
pp. 765-769 ◽  
Author(s):  
K. C. Mundim ◽  
M. Giambiagi ◽  
M. Segre de Giambiagi
Keyword(s):  
Atomic Group ◽  
Group Valence

scholarly journals Factors Impacting σ- and π-Hole Regions as Revealed by the Electrostatic Potential and Its Source Function Reconstruction: The Case of 4,4′-Bipyridine Derivatives

Molecules ◽  
2020 ◽  
Vol 25 (19) ◽  
pp. 4409
Author(s):  
Carlo Gatti ◽  
Alessandro Dessì ◽  
Roberto Dallocchio ◽  
Victor Mamane ◽  
Sergio Cossu ◽  
...  
Keyword(s):  
Electron Density ◽  
Electrostatic Potential ◽  
Source Function ◽  
Noncovalent Interactions ◽  
Conformational Search ◽  
Atomic Group ◽  
Group Contributions ◽  
Conformational Freedom ◽  
Molecular Patterns ◽  
The Impact

Positive electrostatic potential (V) values are often associated with σ- and π-holes, regions of lower electron density which can interact with electron-rich sites to form noncovalent interactions. Factors impacting σ- and π-holes may thus be monitored in terms of the shape and values of the resulting V. Further precious insights into such factors are obtained through a rigorous decomposition of the V values in atomic or atomic group contributions, a task here achieved by extending the Bader–Gatti source function (SF) for the electron density to V. In this article, this general methodology is applied to a series of 4,4′-bipyridine derivatives containing atoms from Groups VI (S, Se) and VII (Cl, Br), and the pentafluorophenyl group acting as a π-hole. As these molecules are characterized by a certain degree of conformational freedom due to the possibility of rotation around the two C–Ch bonds, from two to four conformational motifs could be identified for each structure through conformational search. On this basis, the impact of chemical and conformational features on σ- and π-hole regions could be systematically evaluated by computing the V values on electron density isosurfaces (VS) and by comparing and dissecting in atomic/atomic group contributions the VS maxima (VS,max) values calculated for different molecular patterns. The results of this study confirm that both chemical and conformational features may seriously impact σ- and π-hole regions and provide a clear analysis and a rationale of why and how this influence is realized. Hence, the proposed methodology might offer precious clues for designing changes in the σ- and π-hole regions, aimed at affecting their potential involvement in noncovalent interactions in a desired way.

Generation of atomic group V materials for the p-type doping of wide gap II–VI semiconductors using a novel plasma cracker

1996 ◽  
Vol 161 (1-4) ◽  
pp. 86-89 ◽  
Author(s):  
H.-J. Lugauer ◽  
A. Waag ◽  
L. Worschech ◽  
W. Ossau ◽  
G. Landwehr
Keyword(s):  
Atomic Group ◽  
Group V ◽  
Wide Gap ◽  
P Type

Impact of fluoride for hydroxide substitution on the magnetic properties of a Co-based single-ion magnet imbedded in the barium apatite crystal lattice

CrystEngComm ◽  
2019 ◽  
Vol 21 (7) ◽  
pp. 1193-1199 ◽  
Author(s):  
Mikhail A. Zykin ◽  
Artem A. Eliseev ◽  
Mariam A. Pogosova ◽  
Lev A. Trusov ◽  
Walter Schnelle ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Crystal Lattice ◽  
Magnetization Reversal ◽  
Energy Barrier ◽  
High Energy ◽  
Apatite Crystal ◽  
Atomic Group ◽  
High Energy Barrier

The atomic group O–Co–O persists in the apatite channel and retains a high energy barrier for magnetization reversal.

scholarly journals From deep TLS validation to ensembles of atomic models built from elemental motions. II. Analysis of TLS refinement results by explicit interpretation

2018 ◽  
Vol 74 (7) ◽  
pp. 621-631 ◽  
Author(s):  
Pavel V. Afonine ◽  
Paul D. Adams ◽  
Alexandre Urzhumtsev
Keyword(s):  
Rigid Body ◽  
Atomic Displacement ◽  
Atomic Group ◽  
Acta Cryst ◽  
Atomic Models ◽  
Atomic Displacement Parameters ◽  
Atomic Parameters

TLS modelling was developed by Schomaker and Trueblood to describe atomic displacement parameters through concerted (rigid-body) harmonic motions of an atomic group [Schomaker & Trueblood (1968), Acta Cryst. B24, 63–76]. The results of a TLS refinement are T, L and S matrices that provide individual anisotropic atomic displacement parameters (ADPs) for all atoms belonging to the group. These ADPs can be calculated analytically using a formula that relates the elements of the TLS matrices to atomic parameters. Alternatively, ADPs can be obtained numerically from the parameters of concerted atomic motions corresponding to the TLS matrices. Both procedures are expected to produce the same ADP values and therefore can be used to assess the results of TLS refinement. Here, the implementation of this approach in PHENIX is described and several illustrations, including the use of all models from the PDB that have been subjected to TLS refinement, are provided.

Specificity of Triamineoxidease

1940 ◽  
Vol 5a (2) ◽  
pp. 187-196 ◽  
Author(s):  
H. L. A. Tarr
Keyword(s):  
Substrate Specificity ◽  
General Structure ◽  
Bacterial Species ◽  
Well Water ◽  
Atomic Group ◽  
Subsequent Reduction

The substrate-specificity of a newly described enzyme common to six bacterial species, comprising five different genera, isolated from such widely divergent sources as decomposing fish, well-water and surface taint butter, was investigated. Of the various substrates studied only trialkylamine oxides having the general structure R3 ≡≡ N = 0 were activated with subsequent reduction, the corresponding volatile base being formed in each case. Betaine, choline, acetylcholine, ergothioneine and stachydrine containing an atomic group similar to the above were not activated. The designation "triamineoxidease" is proposed for this enzyme.

scholarly journals Lightweight causal and atomic group multicast

1991 ◽  
Vol 9 (3) ◽  
pp. 272-314 ◽  
Author(s):  
Kenneth Birman ◽  
André Schiper ◽  
Pat Stephenson
Keyword(s):  
Atomic Group

Single Atomic Group in RNA Helix Needed for Positive and Negative tRNA Synthetase Discrimination

1996 ◽  
Vol 118 (10) ◽  
pp. 2523-2524 ◽  
Author(s):  
Hongjian Liu ◽  
Li-Ping Yap ◽  
Karin Musier-Forsyth
Keyword(s):  
Trna Synthetase ◽  
Atomic Group

scholarly journals Дефекты и некоторые физические свойства номинально чистых и легированных цинком кристаллов ниобата лития

2021 ◽  
Vol 63 (8) ◽  
pp. 1132
Author(s):  
Н.А. Теплякова ◽  
М.В. Смирнов ◽  
Н.В. Сидоров ◽  
М.Н. Палатников
Keyword(s):  
Luminescence Intensity ◽  
Defect Structure ◽  
Zinc Concentration ◽  
Energy Levels ◽  
Visible Region ◽  
Small Energy ◽  
Photoinduced Light Scattering ◽  
Group Valence ◽  
Group Concentration ◽  
The Ideal

The features of defect structure and their influence on the properties of LiNbO3:Zn crystals, doped in a wide concentration range, including two concentration thresholds (at ~ 3.0 and ~ 6.8 mol. % ZnO in the melt), were studied by absorption IR spectroscopy in the region of OH--group valence vibrations, photoluminescence in the visible region of the spectrum, and photoinduced light scattering. In LiNbO3:Zn(0.004-2.01 mol. % ZnO) crystals the increase of zinc concentration led to increasing in the OH--group concentration and decreasing the luminescence intensity of luminescence centers associated with NbLi defects. Apparently, the latter was connected with the formation of small energy levels near the bottom of the conduction band as the zinc atoms displaced niobium atoms from the lithium positions in the ideal structure and the NbLi defect concentration decreased, respectively. In highly doped LiNbO3:Zn crystals (4.46-6.5 mol. % ZnO) and in the LiNbO3stoich(6.0 wt. % K2O) crystal there were lower OH--group concentration, the increase of band gap by 0.3-0.4 eV, and the increase of luminescence intensity in the green region of the spectrum due to the formation of new recombination channels compared to weakly doped crystals. In addition, in such crystals, the increase of proton conductivity was observed due to increasing in the concentration of interstitial hydrogen H+ and, as a result, the formation of many small acceptor levels near the valence band.

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