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771.
772.
Ivana Jarak Grace Karminski‐Zamola Gordana Pavlovi Zora Popovi 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(2):o98-o100
The title compound, C10H16N·Cl−·C2H6O, is an important intermediate in the convergent synthesis of amidine‐substituted polycyclic heterocycles, a class of compounds that shows significant anticancer activity. The molecule of (I) is not planar, having a dihedral angle of 25.00 (7)° between the aniline and amidine (–C—NH=C=NH2) groups. The protonation of the amidine molecular fragment is accompanied by delocalized C—N bond distances of 1.320 (2) and 1.317 (2) Å. The cations and chloride anions are involved in a network of hydrogen bonds, resulting in the formation of infinite chains propagating along the b direction. The chains are further grouped within the ab plane, in such a way that the structure is segregated into layers dominated by hydrophobic interactions involving N‐isopropyl residues and layers dominated by N—H⋯Cl [N⋯Cl = 3.275 (2)–3.596 (2) Å], O—H⋯Cl [O⋯Cl = 3.229 (3) Å] and N—H⋯O [N⋯O = 2.965 (3) Å] hydrogen bonds. 相似文献
773.
In this study, parametrically excited purely nonlinear oscillators are considered. Instabilities associated with 2:1, 3:1, and 4:1 subharmonics resonances are analyzed by assuming the solution for motion in the form of a Jacobi elliptic function, the elliptic parameter, and the frequency of which are calculated based on the energy conservation law of the corresponding conservative system. Chirikov??s overlap criterion is used to obtain the approximate critical value of the amplitude of the parametric excitation that causes the transition from local irregular behavior (seen as chaotic) to global chaos. The analytical results derived are compared with numerically results. 相似文献
774.
Ivana Ivancov Radek Pohl Martin Hublek Michal Hocek 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(38):13479-13482
Squaramate‐linked 2′‐deoxycytidine 5′‐O‐triphosphate was synthesized and found to be good substrate for KOD XL DNA polymerase in primer extension or PCR synthesis of modified DNA. The resulting squaramate‐linked DNA reacts with primary amines to form a stable diamide linkage. This reaction was used for bioconjugations of DNA with Cy5 and Lys‐containing peptides. Squaramate‐linked DNA formed covalent cross‐links with histone proteins. This reactive nucleotide has potential for other bioconjugations of nucleic acids with amines, peptides or proteins without need of any external reagent. 相似文献
775.
Sustainability, eco‐efficiency, pollution prevention, industrial ecology, and green chemistry are considering platform‐based approaches to the development of the next generation of products and processes. Recently, renewable alternatives to traditional petroleum‐derived plastics have motivated recent interest in bio‐based composite materials which can contribute to the reduction of the environmental footprint. Lignin is a complex and amorphous biopolymer with a high density of functional groups and high modulus, which makes it potentially promising for material applications. In this sense, lignin can potentially be employed to improve the performance of materials and an economical alternative to convert lignin into high value‐added materials. Two different types of Kraft lignin were incorporated into polypropylene to fabricate composites with high bio‐content. In this study, polypropylene, Kraft lignin, and coupling agent were subjected to reactive extrusion. The composites prepared by melt processing were compared in terms of morphological, mechanical, and thermal characterizations. The results revealed that the incorporation of lignin into polypropylene matrix resulted in composites with properties suitable for various industrial sectors, especially those in which mechanical and thermal properties are crucial, such as the replacement of engineering plastics and polypropylene mineral filled. As a result, this work provides an effective way of using lignin as a low‐cost bio‐renewable resource in the plastics industry. 相似文献
776.
Branislav Milovanović Dr. Ivana M. Stanković Prof. Dr. Milena Petković Prof. Dr. Mihajlo Etinski 《Chemphyschem》2019,20(21):2852-2859
The dynamic aspect of solvation plays a crucial role in determining properties of strong intramolecular hydrogen bonds since solvent fluctuations modify instantaneous hydrogen-bonded proton transfer barriers. Previous studies pointed out that solvent-solute interactions in the first solvation shell govern the position of the proton but the ability of the electric field due to other solvent molecules to localize the proton remains an important issue. In this work, we examine the structure of the O−H⋅⋅⋅O intramolecular hydrogen bond of dibenzoylmethane in methanol solution by employing density functional theory-based molecular dynamics and quantum chemical calculations. Our computations showed that homogeneous electric fields with intensities corresponding to those found in polar solvents are able to considerably alter the proton transfer barrier height in the gas phase. In methanol solution, the proton position is correlated with the difference in electrostatic potentials on the oxygen atoms of dibenzoylmethane even when dibenzoylmethane-methanol hydrogen bonding is lacking. On a timescale of our simulation, the hydrogen bonding and solvent electrostatics tend to localize the proton on different oxygen atoms. These findings provide an insight into the importance of the solvent electric field on the structure of a strong intramolecular hydrogen bond. 相似文献
777.
Ivana B. Campos Sergio Brochsztain 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):207-211
The formation of inclusion complexes between 4-amino-1,8-naphthalimides and cyclodextrins (CDs) was investigated. The naphthalimides used in the study were 4-amino-1,8-naphthalimide (I) and4-(2-phosphonoethylamino)-N-(2-phosphonoethyl)-1,8-naphthalimide,tetraethylester (II). The CDs employed were -CD, -CD, -CD, HP--CD, HP--CD andHP--CD (HP = hydroxypropyl). Evidence for complex formation was obtained from the changes in the fluorescence spectra of the dyes in the presence of increasing amounts of the CDs. The most striking changes were observed with HP--CD and HP--CD. Treatment of the data using Benesi–Hildebrand plotswas consistent with a 1:1 inclusion model. The determined stabilityconstants were (Keq, M-1): 106 (I:HP--CD, pH = 2.0), 193 (I:HP--CD, pH = 7.0), 113 (I:HP--CD, pH = 7.0), 155(II:HP--CD, pH = 2.0), 121 (II:HP--CD,pH = 7.0), 301 (II:HP--CD, pH = 7.0). It can beconcluded that compound I forms a more stable complex with HP--CD than with HP--CD. Compound II, on the other hand, forms a more stable complex with HP--CD than with HP--CD. 相似文献
778.
779.
Cynthia Demicheli Rosemary Ochoa Ivana Silva Lula Fabio C. Gozzo Marcos N. Eberlin Frdric Frzard 《应用有机金属化学》2003,17(4):226-231
Two simple and efficient procedures for the preparation of pentavalent antimony derivatives are described, using either antimony pentachloride (SbCl5) or potassium hexahydroxoantimonate (KSb(OH)6) as sources of antimony(V). These two new methods are evaluated for the synthesis of an important anti‐leishmanial drug: meglumine antimonate. Using elemental (carbon, hydrogen, nitrogen) and thermal analysis, atomic absorption (antimony), proton NMR spectroscopy and high‐resolution positive‐ion electrospray ionization mass spectrometry (ESI(+)‐MS), products for the reaction with N‐methyl‐D ‐glucamine (NMG) using both the SbCl5 and KSb(OH)6 methods were characterized and found to be similar to a commercial sample of the drug. The only notable difference was observed for the ESI‐MS spectrum of the KSb(OH)6 product; it displays the same pattern of ESI‐generated ions as those of both the SbCl5 product and the commercial drug, but with significantly different abundance ratios. NMR data indicate that the NMG molecules coordinate antimony in two different fashions, which suggests either the coexistence of two different complexes or the existence of a single major complex in which two NMG molecules are coordinated with antimony in an asymmetrical geometry. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
780.