Добірка наукової літератури з теми "B20H18 clusters"

Abstract In this work, the cobalt(II) complexation with 1,10-phenanthroline (Phen) in the presence of the [trans-B20H18]2– anion has been studied. At a Co : Phen = 1 : 2 ratio in acetonitrile, a binuclear cobalt(II) complex with bridging chlorine atoms and the boron cluster anion as a counterion [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18] has been isolated. However, during slow crystallization (within a month), spontaneous isomerization of [trans-B20H18]2– into [iso-B20H18]2– is observed. It has been established by X-ray diffraction analysis that in the crystal of the final compound [(Phen)2Co(µ-Cl)2Co(Phen)2][trans-B20H18]1/3[iso-B20H18]2/3, co-crystallization of both isomeric forms of the octadecahydroeicosaborate anion is observed for the first time. The presence of the iso form of the boron cluster anion is also confirmed by IR spectroscopy data: the spectrum of the product shows a band of stretching vibrations of the BHB bridge groups at 1773 cm–1, which is absent in the trans-form of the boron cluster.

Gold(III) complexation with the octadecahydrido-eicosaborate anion [B20H18]2− was studied for the first time. It was found that when gold(III) complexes [Au(L)Cl2]BF4 (L = bipy, phen) reacted with [B20H18]2−, complexes [Au(L)Cl2]2[B20H18] were isolated. The compounds consisted of a cationic gold(III) complex [Au(L)Cl2]+ and the hydridoborate cluster as a counterion. X-ray diffraction studies revealed weak B–H...Au interactions for both compounds. Note that more reactive anions [BnHn]2− (n = 10, 12) in similar reactions with gold(III) complexes resulted in gold mirror reactions.

A new synthesis of the fused macropolyhedral boron cluster B20H16 is described and its molecular structure in solution discussed, based on multi-nuclear NMR spectra, including COSY measurements, in relation to its previously elucidated solid-state structure. To verify the conclusions from the NMR study, experimentally determined chemical shifts are compared with calculated values at the GIAO-B3LYP level with a TZP basis set by Huzinaga. There is a very good agreement between the experimental and computed δ(11B) values, suggesting that the MP2/6-31G* internal coordinates are a reasonable representation of the molecular geometry of this twenty-vertex cluster in solution that is essentially the same as its solid-state structure. A computational analysis of the FMO orbitals of B20H16, in particular of the LUMO, reveals that the four naked boron atoms, common for two shared icosahedral subclusters, are the reactive sites of this D2d-symmetrical molecule.

In the course of the study, nanocrystalline cobalt monoboride was prepared by thermal decomposition of precursors [Co(DMF)6][An], where [An] = [B12H12]2− (1), [trans-B20H18]2− (2) or [B10Cl10]2− (3) in an argon atmosphere. Three new salt-like compounds 1–3 were prepared when Co(NO3)2 was allowed to react with (Et3NH)2[An]. Compound 1 is new; the structures of compounds 2 and 3 have been previously reported. Samples 1–3 were annealed at 900 °C in argon to form samples 1a–3a, which were characterized by single crystal XRD for 1 and powder XRD for 1–3. Powder XRD on the products showed the formation of BN and CoB for 1a in a 1:1 ratio; 2a gave a higher CoB:BN ratio but an overall decreased crystallinity. For 3a, only CoB was found. IR spectra of samples 1a–3a as well as X-ray spectral fluorescence analysis for 3a confirmed these results. The nanoparticular character of the decomposition products 1a–3a was shown using TEM; quite small particle sizes of about 10–15 nm and a quite normal size distribution were found for 1a and 2a, while the decomposition of 3 gave large particles with 200–350 nm and a broad distribution.

Ramalina thrausta (Ach.) Nyl., Ramalina roesleri (Hochst. Ex Schaerer) Hue, and Ramalina dilacerata (Hoffm.) Hoffm. are three common North American species that have not been placed in a phylogeny and are sympatric in their distribution leading to uncertainty about monophyly. Species characters include secondary metabolites (polyketides) in Ramalina that may be both hereditary and influenced by environmental conditions, but little is known about the function of polyketide synthase (PKS) genes. The main goal of this study was to examine the monophyly among some of the more common species in northern North America and secondarily to compare potential PKS gene function with the phylogeny. Nucleotide sequences of two genes, the internal transcribed spacer 1 of ribosomal DNA and the mitochondrial small subunit, were used to infer a phylogeny. Gene function was inferred from three PKS genes by the ratio of nonsynonymous to synonymous substitutions (dN:dS) ratios. Although seven species of Ramalina are highly supported in monophyletic clades, two other species form clusters with low support: Ramalina americana Hale is paraphyletic, and Ramalina pollinaria (Westr.) Ach. is polyphyletic. Three PKS genes were inferred to be functional but were not present in all samples. Functional PKS genes could enable adaptation to new habitats and facilitate species diversification.

AbstractWe communicate the discovery of a new globular cluster in the Galaxy that was first detected on WISE/2MASS images and is now confirmed with VVVX photometry. It is a Palomar-like cluster projected at ℓ = 359.15°, b = 5.73°, and may be related to the bulge. We derive an absolute magnitude of MV ≈ −3.3, thus being an underluminous globular cluster. Our analyses provide a reddening of E(B − V) = 1.08 ± 0.18 and a distance to the Sun d⊙ = 6.3 ± 1 kpc, which implies a current position in the bulge volume. The estimated metallicity is [Fe/H] = −1.5 ± 0.25. It adds to the recently discovered faint globular cluster (Minniti 22) and candidates found with VVV, building up expectations of ≈50 globular clusters yet to be discovered in the bulge. We also communicate the discovery of an old open cluster in the same VVVX tile as the globular cluster. The VVVX photometry provided E(B − V) = 0.62 ± 0.1, d⊙ = 7.6 ± 1 kpc, and an age of 1.5 ± 0.3 Gyr. With a height from the plane of ≈0.8 kpc, it adds to nine Gyr-class clusters recently discovered within 0.8 ⩽ Z ⩽ 2.2 kpc, as recently probed in the single VVV tile b201. We suggest that these findings may be disclosing the thick disk at the bulge, which so far has no open cluster counterpart, and hardly any individual star. Thus, the VVV and VVVX surveys are opening new windows for follow-up studies, to employ present and future generations of large aperture telescopes.

Le développement d'une nouvelle classe de POM hybrides multifonctionnels, désignés sous le nom de "SiW10-B10-Ligand organique”, à partir du précurseur POM-Borate "SiW10-monoB10",a été étudié pour des applications biologiques.Ce dernier résulte de la réaction du groupe carbonyle de l'anion closo-décahydrodécaborate [B10H9CO]- avec l'un des deux groupes amine pendants du lien organique 3-(aminopropyl)triéthoxysilane, qui est attaché de manière covalente au polyoxométalate de type Keggin POM [SiW10O36]2-.L'objectif initiale de cette étude était d'aller plus loin en fonctionnalisant la deuxième fonction amine de SiW10-monoB10.Le composé mono-adduct "SiW10-monoB10" a d'abord été synthétisé avec une bonne pureté et en quantité suffisante,puis caractérisé par une spectrométrie RMN 1H-15N HMQC, ce qui a permis d'examiner la nature de la fonction amine libre et de montrer la présence d'une fraction d'amine non nulle qui ne serait pas impliquée dans l'interaction H-H avec le cluster de déca-borate.Malgré tous nos efforts et différentes stratégies étudiées, les études réalisées montrent que les interactions avec la partie POM et avec les groupements B-H sont préférentielles à la formation des liaisons covalentes espérées.Dans la partie suivante,nous nous sommes intéressés à d'autres POMs hybrides utilisés comme photo-amorceurs. Des dérivés à base d'anthracène, de benzophénone et d'anthraquinone ont été respectivement greffés de manière covalente sur la plateforme de polyoxométalate (POM) [Mo6O19]2-, donnant naissance à des complexes Lindqvist organo-imido: POM-imidoanthraquinone (POM-AQ), POM-imidoanthracène (POM-AC) et POM-imidobenzophénone (POM-AB). Il a été démontré que les photosystèmes combinant la N-méthyldiéthanolamine (MDEA) en tant que donneur d'électrons et ces hybrides POM favorisent la photopolymérisation radicalaire libre de dérivés de monomères acrylates sous irradiation dans le domaine visible,tandis que dans des conditions similaires, aucune polymérisation n'a été observée lorsque l'on ajoutait chacun des clusters d'hexamolybdate ou de l'entité organique seule avec la MDEA et les monomères acrylates. Grâce à la présence du POM,les revêtements préparés à l'aide du photosystème POM-AQ/MDEA/acrylate d'huile de soja époxydée présentent d'excellentes propriétés mécaniques,avec une très bonne flexibilité,et une résistance à la rupture fragile.Dans le dernier chapitre, la préparation de nouveaux complexes d'inclusion closo-borate/CD a été étudiée pour élaborer des systèmes suffisamment forts pour être envisagés pour des applications biologiques. Jouant sur le volume et la charge de [B10H10]2-,on a cherché à augmenter leur caractère chaotrope des clusters de bore et ainsi à augmenter leur affinité de liaison avec les CDs. L'encapsulation des anions [B10H9NCCH3]- et [B20H18]2- dans les CDs a été étudiée en deux parties distinctes.La spectrométrie de RMN ont montré la formation de complexes d'inclusion entre [B10H9NCCH3]- et [B20H18]2- et les beta- et gamma-CDs, tandis que des interactions plus faibles ont été observées avec la alpha-CD,pour laquelle les constantes de liaison ont été déterminées par RMN et ITC.Ces valeurs sont bien supérieures à celles obtenues lors de travaux antérieurs avec [B10H10]2- validant ainsi l'approche suivie dans ce travail de thèse.Une nouvelle approche en chimie du [B20H18]2- a également été étudiée à la fin du travail lié au processus d'échange hydrogène-deutérium en solution aqueuse de [B20H18]2-.La RMN 1H{11B} et 11B{1H} a mis en évidence des processus d'échange de deutérium-proton avec les protons des atomes de bore sur une période de temps en présence de dégradation. Il est intéressant de noter que, par le biais de la RMN de solutions [B20H18]2-/CD dans D2O,il a été démontré que les cyclodextrines beta et gamma protégeraient l'anion de la dégradation après 4 à 5 mois, ouvrant la voie à la conception de médicaments à base de bore offrant une stabilité accrue adaptée à une utilisation médicale
The development of a novel class of multifunctional POM hybrids, denoted as ″SiW10-B10-Organic ligand" starting from the POM-Borate precursor ″SiW10-monoB10", has been investigated for biological applications. The latter resulted from the reaction of the carbonyl group of closo-decahydrodecaborate anion [B10H9CO]- with one of the two pendant amine groups of the organic linker 3-(Aminopropyl)triethoxysilane (APTES), which is covalently attached to the POM Keggin-type polyoxometalate [SiW10O36]2-.Herein, we aimed to go further by functionalizing the second amine function of SiW10-monoB10.The mono-adduct ″SiW10-monoB10” compound was firstly synthesized with good purity and in sufficient quantities, then characterized by atypical 1H-15N HMQC NMR, which allowed the examination of the nature of the free amine function and showed the presence of non-zero amine fraction that would not be involved in the H-H interaction with the decaborate cluster. Consequently, the possibility of new functional groups on this free amino arm of SiW10-monoB10 adduct was tested and followed through 1H and 11B NMR. Despite our best efforts and the various strategies, we have investigated, the studies carried out show that interactions with the POM part and with B-H groups are preferential to the formation of the covalent bonds we had hoped for.In the following section, we turned our attention to other hybrid POMs used as photoinitiators. Anthracene-, benzophenone- and anthraquinone-based derivatives were respectively covalently grafted onto the polyoxometalate (POM) platform [Mo6O19]2-, giving rise to highly colored organo-imido Lindqvist complexes: POM-imidoanthraquinone (POM-AQ), POM-imidoanthracene (POM-AC), and POM-imidobenzophenone (POM-AB). It has been evidenced that photosystems combining N-methyldiethanolamine (MDEA) as electron donor and these hybrid POMs promote free-radical photopolymerization of acrylate monomer derivatives under irradiation in the visible range, while in similar conditions, no polymerization was observed considering when adding each of the hexamolybdate cluster or the organic entity alone with the MDEA and acrylate monomers. Such organo-imido Lindqvist species can represent new, easy-to-synthesize, efficient visible-light photoinitiators. Moreover, due to the presence of the POM, coatings prepared using the POM-AQ/MDEA/Soybean oil epoxidized acrylate photosystem exhibit excellent mechanical properties, with very good flexibility, resistance to brittle fracture, and adherence to the steel.In the last chapter, the preparation of new closo-borate/CD inclusion complexes has been studied to elaborate systems strong enough to be considered for biological application. Playing on the volume and charge of [B10H10]2- was set out to increase their chaotropic character and thus enhance their binding affinity to cyclodextrins. The encapsulation of [B10H9NCCH3]- and [B20H18]2- anions within cyclodextrins has been investigated in two different parts. ESI-MS and NMR evidenced the formation of inclusion complexes between the borate compounds and beta- and gamma-CDs, while weaker interactions are evidenced with alpha-CD, for which the binding constants were determined by NMR and ITC. These constant values are much higher than those obtained in previous work with [B10H10]2- thus validating the approach followed in this thesis work.A new approach in [B20H18]2- chemistry has also been studied at the end of the work related to the Hydrogen-Deuterium exchange process in [B20H18]2- aqueous solution.1H{11B} and 11B{1H} NMR evidenced selective deuterium-proton exchange processes with the protons of equatorial Boron atoms over a period of time with the presence of degradation. Interestingly, it has been shown through NMR of [B20H18]2-/CD solutions in D2O that beta- and gamma-CDs would protect the anion from degradation after 4-5 months, opening the route for designing Boron-based drugs with enhanced stability suitable for medical use