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1.
Frontispiece: A Multicomponent Conjugation Strategy to Unique N‐Steroidal Peptides: First Evidence of the Steroidal Nucleus as a β‐Turn Inducer in Acyclic Peptides
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2.
The Madelung constant, the electrostatic and repulsive energies of the compounds MAX, with the PbFCI structure (D74h), are calculated and compared with the experimental cohesive energy. This calculation yields a crude estimate of the Van der Waals energy. The special case of CaHBr is discussed. 相似文献
3.
Backbone rearranged cholest-13(17)-enes are obtained quantitatively from cholest-5-ene in the presence of K-10 montmorillonite clay. 相似文献
4.
F. Decremps M. Fischer A. Polian J.P. Itié M. Sieskind 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,9(1):49-57
Compounds belonging to the matlockite family are ionic layered crystals. Some previous experimental studies on these compounds
demonstrated the correlation between the difference in bond strength translating the layered properties and the anisotropic
coordination of the highly polarizable halogen anion. In the present paper, we present a model to estimate the anisotropic
compressibilities of matlockites which could be generalized to other ionic layered compounds. The compressibilities of each
individual polyhedron which built the sheet of an ionic layered crystal are determined from a simple relation based on a semi-empirical
relation obtained by Hazen et al., involving the electrical charge of the ions and the interatomic distances. The electrical charge of the anions are taken
to be direction-dependent and are modulated by the anion polarizability value. Finally, to validate the model, the calculated
compressibilities are compared with previously published data, but also with new high pressure experimental data obtained
by X-ray absorption spectroscopy up to 20 GPa on SrFCl and SrFBr at the K edge of the strontium and by X-ray diffraction up
to 30 GPa on SrFBr and PbFBr. Present estimations give results which differ from the experimental values by less than 15%.
Received 26 October 1998 相似文献
5.
Two general relation between bond orderl and bond distance d (Å) are proposed:
- between atomssp 2-hybridised of second and third row: $$d_{PQ} = \left[ {0,731 + 0,3181\left( {n_P + n_Q } \right) - 0,1477\left( {\zeta _P + \zeta _Q } \right)} \right] - 0,020 + 0,0523\left( {\zeta _P + \zeta _Q } \right)l_{PQ} $$ ,ζ=Z/n,Z=Slater's effective nuclear charge of theπ-orbital).
- between atomssp-hybridised of the second row: $$d_{PQ} = \left[ {1,904 - 0,123\left( {\zeta _P + \zeta _Q } \right)} \right] - \left[ {0,075 + 0,023\left( {\zeta _P + \zeta _Q } \right)} \right]l_{PQ} $$ (l=total bond orderπ+π′).
6.
The synthesis of peptide-furostane conjugates from natural steroidal sapogenins is reported. The approach comprises the introduction of α-oriented amino groups into spirostanic sapogenins followed by reductive opening of the spiroketal chain, thus producing diamino-furostanic scaffolds suitable for further functionalization. Solid and solution-phase coupling processes were utilized for the incorporation of various α-amino acids and peptides into the furostanic skeletons. The attachment position depends on the steroidal sapogenin originally used, i.e., diosgenin or hecogenin. The resulting furostanic skeletons feature a trans A/B-ring fusion and hold the peptides in axial disposition. This characteristic ensures a preorganized alignment of the peptidic motifs, an important structural feature for future applications in molecular recognition and catalysis. A macrocyclic tripeptide-furostane conjugate was also produced by a combination of peptide coupling, Staudinger ligation, and a cyclization protocol. This work constitutes the first report on the use of furostanic sapogenins as scaffolds for positioning natural amino acids and (cyclo)peptides. 相似文献
7.
Effects of colored noise on the dynamics of quantum entanglement of a one-parameter qubit—qutrit system
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Odette Melachio Tiokang Fridolin Nya Tchangnwa Jaures Diffo Tchinda Arthur Tsamouo Tsokeng and Martin Tchoffo 《中国物理 B》2022,31(5):50306-050306
We analyzed the effect of colored noise on the negativity dynamics of a hybrid system consisting of a qubit-qutrit and not interacting, prepared from the start in an entangled one-parameter state and acting with noise in local and non-local environments. In this pink and brown noise we investigated two different situations: in the first situation, the noise is produced by a bistable oscillator with an unknown exchange rate; however, in the second situation, the noise is generated by a set of bistable oscillators. We found that entanglement decreases with time to zero, and undergoes the phenomenon of sudden death and rebirth. The pink noise is more prone to entanglement than the brown noise and the non-local environment is more prone to entanglement than the local one. When the number of fluctuators is increased, entanglement decays faster and finally, for certain parameters of the initial state, the subsystems are not affected by the noise. 相似文献
8.
Johan F. T. van Lieshout Odette N. Pérez Gutiérrez Wietse Vroom Antoni Planas Willem M. de Vos John van der Oost Sotirios Koutsopoulos 《Applied biochemistry and biotechnology》2012,167(7):2039-2053
An intein-driven protein splicing approach allowed for the covalent linkage between the N- and C-termini of a polypeptide chain to create circular variants of the endo-??-1,3-1,4-glucanase, LicA, from Bacillus licheniformis. Two circular variants, LicA-C1 and LicA-C2, which have connecting loops of 20 and 14 amino acids, respectively, showed catalytic activities that are approximately two and three times higher, respectively, compared to that of the linear LicA (LicA-L1). The thermal stability of the circular variants was significantly increased compared to the linear form. Whereas the linear glucanase lost half of its activity after 3?min at 65?°C, the two circular variants have 6-fold (LicA-C1) and 16-fold (LicA-C2) increased half-life time of inactivation. In agreement with this, fluorescence spectroscopy and differential scanning calorimetry studies revealed that circular enzymes undergo structural changes at higher temperatures compared to that of the linear form. The effect of calcium on the conformational stability and function of the circular LicAs was also investigated, and we observed that the presence of calcium ions results in increased thermal stability. The impact of the length of the designed loops on thermal stability of the circular proteins is discussed, and it is suggested that cyclization may be an efficient strategy for the increased stability of proteins. 相似文献
9.
A Multicomponent Conjugation Strategy to Unique N‐Steroidal Peptides: First Evidence of the Steroidal Nucleus as a β‐Turn Inducer in Acyclic Peptides
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Prof. Dr. Daniel G. Rivera Aldrin V. Vasco Radell Echemendía Odette Concepción Prof. Dr. Carlos. S. Pérez Prof. Dr. José A. Gavín Prof. Dr. Ludger A. Wessjohann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(41):13150-13161
Constraining small peptides into specific secondary structures has been a major challenge in peptide ligand design. So far, the major solution for decreasing the conformational flexibility in small peptides has been cyclization. An alternative is the use of topological templates, which are able to induce and/or stabilize peptide secondary structures by means of covalent attachment to the peptide. Herein a multicomponent strategy and structural analysis of a new type of peptidosteroid architecture having the steroid as N‐substituent of an internal amide bond is reported. The approach comprises the one‐pot conjugation of two peptide chains (or amino acid derivatives) to aminosteroids by means of the Ugi reaction to give a unique family of N‐steroidal peptides. The conjugation efficiency of a variety of peptide sequences and steroidal amines, as well as their consecutive head‐to‐tail cyclization to produce chimeric cyclopeptide–steroid conjugates, that is, macrocyclic lipopeptides, was assessed. Determination of the three‐dimensional structure of an acyclic N‐steroidal peptide in solution proved that the bulky, rigid steroidal template is capable of both increasing significantly the conformational rigidity, even in a peptide sequence as short as five amino acid residues, and inducing a β‐turn secondary structure even in the all‐s‐trans isomer. This report provides the first evidence of the steroid skeleton as β‐turn inducer in linear peptide sequences. 相似文献
10.
Dr. Daniel G. Rivera Fredy León Odette Concepción Fidel E. Morales Prof. Dr. Ludger A. Wessjohann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6417-6428
The success of multi‐armed, peptide‐based receptors in supramolecular chemistry traditionally is not only based on the sequence but equally on an appropriate positioning of various peptidic chains to create a multivalent array of binding elements. As a faster, more versatile and alternative access toward (pseudo)peptidic receptors, a new approach based on multiple Ugi four‐component reactions (Ugi‐4CR) is proposed as a means of simultaneously incorporating several binding and catalytic elements into organizing scaffolds. By employing α‐amino acids either as the amino or acid components of the Ugi‐4CRs, this multiple multicomponent process allows for the one‐pot assembly of podands bearing chimeric peptide–peptoid chains as appended arms. Tripodal, bowl‐shaped, and concave polyfunctional skeletons are employed as topologically varied platforms for positioning the multiple peptidic chains formed by Ugi‐4CRs. In a similar approach, steroidal building blocks with several axially‐oriented isocyano groups are synthesized and utilized to align the chimeric chains with conformational constrains, thus providing an alternative to the classical peptido‐steroidal receptors. The branched and hybrid peptide–peptoid appendages allow new possibilities for both rational design and combinatorial production of synthetic receptors. The concept is also expandable to other multicomponent reactions. 相似文献