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31.
During past several years we have been engaged in the synthesis of phosphono peptides, peptide analogues with phosphonic acid replacing C-terminal or N-terminal carboxylate moiety. These compounds are of interest not only because of their promise of direct practical applications1,2 but also as a source of information about mechanisms of enzymatic reactions. 1,3–5 Esters of N-blocked 1 -aminoalkylphosphonic and phosphinic acids are popularly used as starting substrates in multistep syntheses of phosphono peptides.6–9 Although several methods for their preparation have been described 6,10–13 the search for the new and useful methods of their synthesis is still in progress. In this paper we report that the use of complexes of potassium 1-(N- benzyloxycarbonylamiuo)alkylphosphonates and phosphates with 18-crown-6 as nucleophiles in the reaction with alkyl halides afforded the desired esters in good yields. 相似文献
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Motzkin numbers are derived from a special case of Random Domino Automaton – recently proposed a slowly driven system being a stochastic toy model of earthquakes. It is also a generalisation of 1D Drossel–Schwabl forest-fire model. A solution of the set of equations describing stationary state of Random Domino Automaton in inverse-power case is presented. A link with Motzkin numbers allows to present explicit form of asymptotic behaviour of the automaton. 相似文献
34.
Małgorzata T. Kaczmarek Renata Jastrząb Wanda Radecka-Paryzek 《Journal of solution chemistry》2013,42(1):18-26
Formation of complexes between the lanthanide ions and N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand was studied in solution by pH potentiometry. The potentiometric titration was performed at 25.00 °C in 0.1 mol·dm?3 NaClO4 ionic strength and in DMSO:water (30:70 v:v) solvent mixture. N,N′-bis(salicylidene)-4-methyl-1,3-phenylenediamine ligand (H2L) occurs in three forms: fully or partially deprotonated and unionized. Computer analysis of potentiometric data indicated that in solution the lanthanide (Ln) complexes exist as LnL2, Ln(HL)2 and Ln(H2L)2 species. This observation appears to be in contrast to the solid-state behavior of these complexes prepared in a self-assembly process and structurally defined. Stability constants for La3+, Eu3+, Gd3+, Tb3+, Ho3+ and Lu3+ (Ln3+) complexes were determined. The order of stabilities of LnL2 species in terms of metal ions is La3+ > Eu3+ ≈ Gd3+ = Tb3+ < Ho3+ < Lu3+ with a prominent “gadolinium break”. 相似文献
35.
Dr. Renata Kaczmarek Samuel Ward Dipra Debnath Taisiya Jacobs Alexander D. Stark Dariusz Korczyński Prof. Dr. Anil Kumar Prof. Dr. Michael D. Sevilla Dr. Sergey A. Denisov Dr. Viacheslav Shcherbakov Dr. Pascal Pernot Prof. Dr. Mehran Mostafavi Prof. Dr. Roman Dembinski Prof. Dr. Amitava Adhikary 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(43):9495-9505
The directionality of the hole-transfer processes between DNA backbone and base was investigated by using phosphorodithioate [P(S−)=S] components. ESR spectroscopy in homogeneous frozen aqueous solutions and pulse radiolysis in aqueous solution at ambient temperature confirmed initial formation of G.+-P(S−)=S. The ionization potential of G-P(S−)=S was calculated to be slightly lower than that of guanine in 5′-dGMP. Subsequent thermally activated hole transfer from G.+ to P(S−)=S led to dithiyl radical (P-2S.) formation on the μs timescale. In parallel, ESR spectroscopy, pulse radiolysis, and density functional theory (DFT) calculations confirmed P-2S. formation in an abasic phosphorodithioate model compound. ESR investigations at low temperatures and higher G-P(S−)=S concentrations showed a bimolecular conversion of P-2S. to the σ2-σ*1-bonded dimer anion radical [-P-2S 2S-P-]− [ΔG (150 K, DFT)=−7.2 kcal mol−1]. However, [-P-2S 2S-P-]− formation was not observed by pulse radiolysis [ΔG° (298 K, DFT)=−1.4 kcal mol−1]. Neither P-2S. nor [-P-2S 2S-P-]− oxidized guanine base; only base-to-backbone hole transfer occurs in phosphorodithioate. 相似文献
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Juan Amaro-Gahete Prof. Anna M. Kaczmarek Prof. Dolores Esquivel Prof. César Jiménez-Sanchidrián Prof. Pascal Van Der Voort Prof. Francisco J. Romero-Salguero 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(27):6823-6830
Graphene-based materials exhibit outstanding physical properties and so are potentially applicable in a great variety of fields. Unlike their corresponding oxides, graphite and graphene are not prone to functionalization. Diels–Alder reactions are among the scarce reactions that they can occur without disrupting their conjugated sp2 systems. Herein, the reaction between graphite and 3,6-di(2-pyridyl)-1,2,4,5-tetrazine under different conditions affords several graphene-based materials consisting of dipyridylpyridazine-functionalized few-layer graphene, multilayer graphene and graphite, the sheets of which act as ligands for the grafting of a europium complex. These three materials show strong red emission under 365 nm UV radiation. Their emitting particles can be visualized by confocal microscopy. The rich coordination chemistry of dipyridylpyridazine ligands has potential novel properties for similarly functionalized graphene-based materials grafted with other metal complexes. 相似文献
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Mariusz Urbaniak Agnieszka Pedrycz Barbara Gawdzik Alicja Wzorek 《Supramolecular chemistry》2013,25(12):777-781
The conditions for synthesis of mono-, di- and trifunctionalised resorcinarenes by catalysed Mannich reaction are described. A series of these compounds are functionalised with different functional groups. 相似文献
39.
Khaled D. Khalil Sayed M. Riyadh Mariusz Jaremko Thoraya A. Farghaly Mohamed Hagar 《Molecules (Basel, Switzerland)》2021,26(12)
Recently, the development of nanocatalysts based on naturally occurring polysaccharides has received a lot of attention. Chitosan (CS), as a biodegradable and biocompatible polysaccharide, is considered to be an excellent template for the design of a hybrid biopolymer-based metal oxide nanocomposite. In this case, lanthanum oxide nanoparticles doped with chitosan at different weight percentages (5, 10, 15, and 20 wt% CS/La2O3) were prepared via a simple solution casting method. The prepared CS/La2O3 nanocomposite solutions were cast in a Petri dish in order to produce the developed catalyst, which was shaped as a thin film. The structural features of the hybrid nanocomposite film were studied by FTIR, SEM, and XRD analytical tools. FTIR spectra confirmed the presence of the major characteristic peaks of chitosan, which were modified by interaction with La2O3 nanoparticles. Additionally, SEM graphs showed dramatic morphological changes on the surface of chitosan, which is attributed to surface adsorption with La2O3 molecules. The prepared CS/La2O3 nanocomposite film (15% by weight) was investigated as an effective, recyclable, and heterogeneous base catalyst in the synthesis of pyridines and pyrazoles. The nanocomposite used was sufficiently stable and was collected and reused more than three times without loss of catalytic activity. 相似文献
40.
Over the last years, scientific interest in noncovalent interactions based on the presence of electron-depleted regions called σ-holes or π-holes has markedly accelerated. Their high directionality and strength, comparable to hydrogen bonds, has been documented in many fields of modern chemistry. The current review gathers and digests recent results concerning these bonds, with a focus on those systems where both σ and π-holes are present on the same molecule. The underlying principles guiding the bonding in both sorts of interactions are discussed, and the trends that emerge from recent work offer a guide as to how one might design systems that allow multiple noncovalent bonds to occur simultaneously, or that prefer one bond type over another. 相似文献