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SANS curves for G (3) 7 dendrimers in chloroform-d (1) and in benzene-d6 (2), and for G (4) 7 dendrimers in benzene-d6 (3). w = 4 wt.% (1,2) and 1 wt.% (3).
Source publication
The structural characteristics of polycarbosilane dendrimers with different molecular architecture were determined in solutions by small angle neutron and X-ray scattering. The same linear dimensions were sized up for the dendrimers both in benzene and chloroform. A solvent molecules penetration inside dendrimer structure in amount up to 30 vol.% w...
Citations
... Это ограничивает возможности получать структуры с низким разрешением. Применяя технику сгона на нулевую концентрацию, частично можно избежать влияния этого фактора [3]. ...
This seems to be an automatically translated in English version of our manuscript that we recently published in Russian journal (https://sciencejournals.ru/view-article/?j=biofiz&y=2023&v=68&n=2&a=BioFiz2302009Vlasov). Therefore, there are many incorrect terms and grammar mistakes. Please use the version on the original Russian language that I uploaded here on ResearchGate.
... As for the consistent fundamental approach to the investigation of a new form of polymeric matter, developed by the Russian academic school, it is certainly bearing fruit in understanding the properties of dendrimers as a special type of polymers with a pronounced dualism of properties in macromolecule-particle coordinates. Like classical polymers, they consist of many repeating units, display the propensity to swell and collapse depending on the quality of the solvent [129,145], and their glass transition temperature increases with increasing molecular weight, which tends to a certain limit. However, unlike classical polymers, in solutions they behave like solid spheres impermeable to the solvent [62,73,77]. ...
The emergence of a new type of organization of polymeric matter, namely, dendrimers has led to a change in concepts about the macromolecular world. High and strictly defined functionality, monodispersity, and the cascade principle of molecular structure formation made these systems unique objects, the interest in which has not faded to date. Carbosilane dendrimers are of particular importance owing to the stability and inertness of their molecular backbone, high reactivity of functional groups at the silicon atom, and also the possibility of providing good analytical control over the forming structure. A wide variety of synthetic approaches to the modification of terminal groups allows for considering them as hybrid systems for the elucidation of structure–property relationships. Based on the results of the analysis of a large number of variations of the main strategies for the synthesis of dendrimers, this review highlights the importance of studying the relationships between structure and properties using representative homologous series of new objects as a fundamental basis for exploring the dendritic form of polymeric matter.
... Intensive experimental and theoretical research has demonstrated that the dualism of the dendrimer nature, expressed in its definition as a macromolecule-particle [6,7], has objective grounds. Accordingly, the term particle is associated not only with the early visualization of the dendrimer shape being close to spherical [8,9], but mainly with the viscosity of their dilute solutions that obeys Einstein's equation, depending only on the volume fraction of the solute, but not on its molecular weight [5], as well as SAXS data, which are best described by models of monodisperse spherical objects [10][11][12]. The polymer nature of dendrimers can be traced from purely polymer-like dependences of the glass transition temperature on the dendrimer generation number that reaches a plateau after the third or fourth generation [5,7,[13][14][15][16], and especially from dendrimer swelling and collapse in dilute solutions, which is controlled by the solvent quality [17,18]. ...
A series of carbosilane dendrimers of the 4th, 6th, and 7th generations with a terminal trimethylsilylsiloxane layer was synthesized. Theoretical models of these dendrimers were developed, and equilibrium dendrimer conformations obtained via molecular dynamics simulations were in a good agreement with experimental small-angle X-ray scattering (SAXS) data demonstrating molecule monodispersity and an almost spherical shape. It was confirmed that the glass transition temperature is independent of the dendrimer generation, but is greatly affected by the chemical nature of the dendrimer terminal groups. A sharp increase in the zero-shear viscosity of dendrimer melts was found between the 5th and the 7th dendrimer generations, which was qualitatively identical to that previously reported for polycarbosilane dendrimers with butyl terminal groups. The viscoelastic properties of high-generation dendrimers seem to follow some general trends with an increase in the generation number, which are determined by the regular branching structure of dendrimers.
... In the series of works [30,31,[59][60][61], aimed at investigation of the structure of polyallylcarbosilane dendrimers, the specificities of interactions such nanodisperse objects with solvent and their arrangement inside the solution, some quantitative parameters characteristics were obtained, such as sizes of several generations and average scattering density. Appliance of modern data treatment methods and the usage of good resolution of upgraded spectrometer YuMO allowed characterizing the form of dendrimers of several generations for 3 and 4-functional core. ...
The work is a review of neutronographic investigations of supramolecular structures on upgraded small-angle spectrometer YuMO. Here, key parameters of small-angle spectrometers are considered. It is shown that two-detector system is the basis of YuMO upgrade. It allows to widen the dynamic q-range twice. In result, the available q-range is widened and dynamic q-range and data collection rate are doubled. The detailed description of YuMO spectrometer is given.The short review of experimental researches made on the spectrometer in the polymers field, biology, material science and physical chemistry is given. The current investigations also have a methodological aspect. It is shown that upgraded spectrometer provides advanced world level of research of supramolecular structures.
... Dendrimers are specially class of high-molecular compounds whose molecules are highly ordered spatially hyperbranched topologically completely acyclic compositions with structure of continuously branching tree [1,2]. Liquid-crystalline (LC) dendrimers, which molecules combine structural units (commonly referred to as mesogenic groups) capable to impart the liquidcrystalline properties with amorphous dendritic architecture have attracted progressively growing attention of researchers engaged in the chemistry and physics of liquid crystals, physical chemistry of polymers, and supramolecular chemistry [3][4][5][6][7][8]. This interest is related to the search for new materials for nanotechnology and electronics which need moleculesparticles with a size of several nanometersthat are capable of ordering and changing their properties under application of external fields. ...
... Carbosilane liquid-crystalline dendrimers hold a particular position among a wide scope of studied dendrimers. This is connected with their kinetic and thermodynamic stability and vast possibilities to change their dendritic architecture via specific reactions typical of silicon [3][4][5][6][7][8]. ...
... This significant penetration of solvent molecules inside the dendrimer structure is in agreement with the recent SANS studies on poly(benzyl ether) 27 and polycarbosilane dendrimers. 37 In these experiments the number of solvent molecules inside the dendrimer was calculated from the change in neutron scattering density. In general, a lower relative density leads to a larger solvent content inside the dendritic structure and vice versa. ...
We report various structural and conformational properties of generations 4, 5. and 6 PAMAM (polyamidoamine) dendrimer [EDA (ethylenediamine) core)] at various protonation levels through extensive molecular dynamics (MD) simulations in explicit solvent. The presence of solvent leads to swelling of the dendrimer (by 33% for G5 compared to the case of no solvent). We find that decreasing the solution from high pH (similar to10, no protonation) to neutral (similar to7, only primary amines protonated) to low pH (similar to4, tertiary amines also protonated) changes the radius of gyration of G5 from 21 to 22 to 25 Angstrom respectively. We also report such other structural quantities as radial density, distribution of terminal groups, solvent accessible surface area and volume, shape, and structure factors (to compare. with SAXS and SANS experiments) at various pH conditions. We find. significant back-folding of the outer subgenerations in the interior of the molecules at all levels of pH contrary to original expectations and some SANS experiments but in agreement with other SANS experiments. We find significant water penetration inside the dendrimer, with similar to3 water/tertiary amine for high pH and similar to6 water/tertiary amine for low pH (all for G5). This indicates that the interior of the dendrimer is quite open with. internal cavities available for accommodating guest molecules, suggesting using PAMAM dendrimer for guest-host applications. This estimate of internal waters suggests that sufficient, water is available to facilitate metal ion binding.
Small-angle scattering makes it possible to solve structural biology problems without specific sample preparation, which is typical for methods such as X-ray diffraction of protein crystals or cryo-electron microscopy of proteins. In our review, it is shown how to use small-angle scattering to address biological problems. The use of small-angle scattering is suggested for applications as a tool to control the quality of the assembly of proteins and protein complexes and to test the identity of the structural organization of biological objects in the native state and in prepared samples before measurements by X-ray diffraction or cryo-electron microscopy. This work demonstrates the possibilities of the small-angle neutron scattering spectrometer YuMO based on the IBR-2 pulsed reactor (Laboratory of neutron physics, Joint Institute for Nuclear Research, Dubna, Russia) to solve a whole array of problems, with an eye toward applying these in biophysics, structural biology, and biotechnology. This review presents and discusses the main findings of the studies of various biological systems obtained by using the setup small-angle scattering of neutrons YuMO. The possibilities of development of structural biology methods with the help of small-angle scattering, including protein crystallization, are shown.
New non-functional methylsiloxane dendrimers possessing a sparse structure with a trimethylsiloxy outer layer containing a flexible dimethylsiloxane link between branch points have been synthesized. Two alternative synthetic protocols were employed, namely, a divergent scheme comprising an additional stage of generating a spacer –OSiMe2– group with sodium ethoxy(dimethyl)silanolate, and a hybrid method using monofunctional dendrons with a sparse structure.
Recently developed non-functional derivatives of polymethylsilsesquioxane (PMSSO) dendrimers of the first to fifth generation were characterized by ¹H, ¹³C and ²⁹Si NMR spectroscopy. The self-diffusion and NMR relaxation of PMSSO dendrimers in dilute solutions of toluene and melts were investigated in a wide temperature range (−50–80 °C). The hydrodynamic radii of dendrimers were determined from the self-diffusion coefficients measured in diluted solutions according to the Stokes–Einstein equation. The hydrodynamic radius of PMSSO dendrimers as a function of molecular mass follows a power law with the scaling exponent of 0.32 ± 0.02 in the investigated temperature range. The temperature dependences of the self-diffusion coefficients of dendrimers were described by the Arrhenius-type equation. The activation energies of self-diffusion of dendrimers in diluted toluene solutions are identical for different generations while the dependence of activation energy for dendrimers in melts shows a maximum for the third generation (G3) dendrimer. Taking into account the absence of specific interactions in PMSSO dendrimer melts the observed behavior was ascribed to the manifestation of interpenetration of dendrimer molecules. For low generations (G1 and G2) the short length of the branches does not considerably affect the translational diffusion while for higher generations (G4 and G5) the densification of the structure prevents significant interpenetration.
