Stabilisation effects of ferrocenylalkyl groups on hydrides of heavier main group elements

New hydrides of heavier p-block main group elements with a ferrocenylalkyl moiety, Fc(CH₂)nEHm (Fc = (CpFeC₅H₄-); E = P, As, Si, Ge or Se; n = 1, 2, 4, 6 or 11; m = 1, 2 or 3) and FcCH₂P(R)H (R = CH₃, C₆H₁₁ or p-CH₂C₆H₄NO₂), have been synthesised and characterised. Although some precursors of the desired hydrides, i.e. Fc(Cl)C=C(SnCl₃)H and (FcCH₂Te)₂, which are also new compounds, could be prepared, the syntheses of the corresponding desired hydrides, FcCH₂EHn, were unsuccessful probably due to their extreme instabilities. Some related primary phosphanes, [CpFeC₅H₃(CH₂OH)(CH₂PH₂)], RcCH₂PH₂ and Fc(CH₂)₆PH₂∙BH₃, phosphane oxide, FcCH₂P(O)H₂, and phosphinic acid, FcCH₂P(O)(OH)H, were also synthesised and reported. The X-ray crystal structures of Fc(CH₂)₆PH₂∙BH3 and FcCH₂SeCN are also presented in the present thesis. The stability of the hydrides of heavier p-block main group elements with a ferrocenyl or ruthenocenylalkyl moiety under ambient conditions has been investigated using NMR and/or IR spectroscopy. Ferrocenylalkyl and ruthenocenylmethyl primary phosphanes, Fc(CH₂)nPH₂ (n = 4, 6 or 11) and RcCH₂PH₂, respectively, exhibited a remarkable stability towards air oxidation in solution, i.e. ~1 year. In contrast, the secondary phosphanes were not as stable as expected, rapidly oxidising over several weeks or months. General trend for the oxidative stability of the secondary phosphanes could not be elucidated on the basis of the electronegativity, size or degree of conjugation of the substituent on the phosphorus. Ferrocenylmethyl primary arsane, FcCH₂AsH₂, was also unexpectedly air-sensitive, having been readily oxidised as a neat liquid or in solution upon the exposure to air. Ferrocenylethyl primary silane, Fc(CH₂)₂SiH₃, was stable both as a neat liquid and also in solution. It could be purified on a TLC plate in air and also stored in solution for up to 7 months. On the other hand, ferrocenylmethyl primary germane, FcCH₂GeH₃, was unstable, almost completely decomposing left overnight in solution, which was indicated by the disappearance of the germane proton NMR signal by ¹H NMR spectroscopy. Ferrocenylalkyl selenols, Fc(CH₂)nSeH (n = 1 or 4), were both found to be unstable as neat liquids or in solution. Handling the compounds in air caused significant oxidation, resulting in the formation of the corresponding diselenides which are the common oxidation products of selenols. Ferrocenylmethyl selenol, FcCH₂SeH, was completely oxidised in solution in air in 5 days while ferrocenylbutyl selenol, Fc(CH₂)₄SeH, in 3 days. The rapid oxidation of the latter was also observed by IR spectroscopy over a period of 10 minutes when exposed to air as a neat liquid. The oxidative stability of the air-sensitive primary phosphanes, PhPH₂ and camphylPH₂, in the presence of ferrocene, FcH, or its derivative, FcCH₂PH₂, in solution, was studied by ³¹P NMR spectroscopy. The study showed that the primary phosphanes could be stabilised by simple addition of FcH or FcCH₂PH₂. The corresponding ³¹P NMR study using known antioxidants, diphenyl picryl hydrazyl (DPPH) or nitrosobutane, in place of the ferrocene species also exhibited that PhPH₂ could be stabilised by addition of an antioxidant. These results suggest that FcH and FcCH₂PH₂ can be used to stabilise air-sensitive primary phosphanes in solution by simply adding them, probably acting as radical scavengers

Studies of Magic-size II-VI Nanoclusters and Surface Exchange on Flat Colloidal Nanocrystals

This dissertation presents the isolation, characterization and reactivity of two magic size clusters, (ZnSe)34 and (CdTe)34, as well as the L-, Z- and X-type ligand exchange on the CdSe QBs or CdS QP surface. The dissertation first reports the spectroscopically observed magic-size nanoclusters (ZnSe)34 and (CdTe)34 are isolable as amine derivatives. The nanoclusters [(ZnSe)34(n-octylamine)29±6(di-n-octylamine)5±4] and [(CdTe)34(n-octylamine)4±3(di-n-pentylamine)13±3] are fully characterized by UV-visible spectroscopy, IR spectroscopy, elemental analysis, and mass spectrometry. Amine derivatives of both (ZnSe)34 and (CdTe)34 are observed to convert to the corresponding (ZnSe)13 and (CdTe)13 derivatives, indicating that the former are kinetic products and the latter thermodynamic products, under the conditions employed. This conversion process is significantly inhibited in the presence of secondary amines. The isolation of the two new nanocluster derivatives adds to a total of nine of twelve possible isolated derivatives in the (II-VI)13 and (II-VI)34 families (II = Zn, Cd; VI = S, Se, Te), allowing comparisons of their properties. The members of these two families exhibit extensive spectroscopic homologies. In both the (II-VI)13 and (II-VI)34 families, linear relationships are established between the lowest-energy nanocluster electronic transition and the band gap of the corresponding bulk semiconductor phase. Then, the research interest expanded from the magic-size clusters to the flat colloidal nanocrystals. The dissertation demonstrates that reaction of n-octylamine-passivated {CdSe[n-octylamine]0.53} QBs with anhydrous metal carboxylates M(oleate)2 (M = Cd, Zn) results in a rapid exchange of the L-type amine passivation to Z-type M(oleate)2 passivation. The cadmium-carboxylate derivative is determined to have the composition {CdSe[Cd(oleate)2]0.19±0.02}. The morphologies and crystal structures of the quantum belts are largely unaffected by the exchange processes. Addition of n-octylamine or oleylamine to the M(oleate)2-passivated quantum belts removes M(oleate)2, and restores the L-type amine passivation. Analogously, reversible surface exchanges are also demonstrated for CdS QPs. The absorption and emission spectra of the QBs and QPs are reversibly shifted to lower energy by M(oleate)2 passivation vs. amine passivation. The largest shift of 140 meV is observed for the Cd(oleate)2-passivated CdSe quantum belts. We establish that changes in strain states, which can be calculated from high-angle XRD patterns, and confinement dimensions contribute roughly equally to the spectral shifts in the Cd(oleate)2-passivated nanocrystals. Notably, addition of Cd(oleate)2, which electronically couples to the nanocrystal lattices, increases the effective thickness of the belts and platelets by approximately a half of a momolayer, thus increasing the confinement dimension. However, these shifts are attributed entirely to changes in the strain states in the Zn(oleate)2-passivated nanocrystals. Last, the dissertation describes facile interchange of neutral-donor amine (L-type) and anionic (X-type) ligation on CdSe QBs. Reaction of n-octylamine-passivated QBs with protic acids HX (X = halide, nitrate, or carboxylate) results in displacement, protonation and liberation of the amines. The newly formed n-octylammonium ions will balance the surface charge of X– anions in the form of surface-bound ion pairs. Addition of n-octylamine to the bound-ion-pair X-type ligation quantum belts restores the L-type amine passivation. These ligand exchanges are readily monitored spectroscopically. The shifts in the lowest-energy feature ranged from 49 meV to 112 meV, depending on the different X– anions. We attribute the red spectral shifts in X-type ligation to negative surface charges and associated dipoles, which slightly increase the energy of the valence-band edge, and decrease the energy of the conduction-band edge

CDSE Quantum Dot Surface Chemistry Thermodynamics via Isothermal Titration Calorimetry: An Emphasis on the Fundamentals

For several decades, the study and development of colloidal semiconductor nanocrystals, or quantum dots (QD), has become a rich field heralding improved integration into applications ranging from photovoltaics and photocatalysis to biomedical imaging and drug delivery. CdxSey is the most extensively studied QD system, however numerous compositional details still confound the nanocrystal field. Although CdSe QDs with native ligand coatings can show high fluorescence quantum yield and may be suitable for some applications, often times these original ligand layers are comprised of long aliphatic chains that preclude incorporation into biological matrices or severely impede charge transfer – depending on the end goal functionality. While the innermost core can be highly crystalline, due to the QD size regime a large fraction of the constituent atoms is found at the surface; the nature of which strongly influences optoelectronic properties. Indeed, the necessary ligand surfactant layer is anything but innocuous; dictating synthetic morphology, determining solubility, quenching or enhancing photoluminescence, or even modulating the nanocrystal’s band gap. A detailed, consistent and unambiguous profile for QD surface composition and thermodynamics would be extremely advantageous toward controlling and improving photophysical properties. This dissertation highlights several caveats for appropriately compiling a thermodynamic profile in situ for the dynamic nature of QD surfaces, and to describe approaches to address them. I have focused on developing commonly employed metrics for investigating CdSe QD surface chemistries. I begin by thoroughly considering how various purification techniques alter the most significant aspects of QD investigations and performance. Among these, I illustrate the gel permeation chromatography (GPC) approach that I helped to establish as a highly effective technique for nanoparticle purification. Finally, I delineate in several fundamental CdSe-based QD systems the capacity of isothermal titration calorimetry as a sensitive and precisely quantitative technique to directly probe reaction thermodynamics in organic phase. Even in cases where common spectroscopic techniques have been of limited use, ITC is employed to elucidate complex binding phenomena. Beginning with the highly reproducible GPC purification technique for a consistent QD starting material, this dissertation depicts my efforts to provide consistent equilibrium thermodynamic data for relevant QD surface chemistry interactions

Smart Nanoplatforms Responding to the Tumor Microenvironment for Precise Drug Delivery in Cancer Therapy

Yujie Wang,1 Tingting Deng,1 Xi Liu,2 Xueyang Fang,1 Yongpan Mo,3 Ni Xie,4 Guohui Nie,1 Bin Zhang,1 Xiaoqin Fan1,4 1Shenzhen Key Laboratory of Nanozymes and Translational Cancer Research, Department of Otolaryngology, Shenzhen Institute of Translational Medicine, The First Affiliated Hospital of Shenzhen University, Shenzhen Second People’s Hospital, Shenzhen, 518035, People’s Republic of China; 2Department of Nephrology, Shenzhen Longgang Central Hospital, Shenzhen, 518116, People’s Republic of China; 3Department of Breast Surgery, The First Affiliated Hospital of Shenzhen University, Shenzhen Second People’s Hospital, Shenzhen, 518035, People’s Republic of China; 4The Bio-Bank of Shenzhen Second People’s Hospital, The First Affiliated Hospital of Shenzhen University, Shenzhen Second People’s Hospital, Shenzhen, Guangdong, 518035, People’s Republic of ChinaCorrespondence: Bin Zhang; Xiaoqin Fan, Email [email protected]; [email protected]: The tumor microenvironment (TME) is a complex and dynamic entity, comprising stromal cells, immune cells, blood vessels and extracellular matrix, which is intimately associated with the occurrence and development of cancers, as well as their therapy. Utilizing the shared characteristics of tumors, such as an acidic environment, enzymes and hypoxia, researchers have developed a promising cancer therapy strategy known as responsive release of nano-loaded drugs, specifically targeted at tumor tissues or cells. In this comprehensive review, we provide an in-depth overview of the current fundamentals and state-of-the-art intelligent strategies of TME-responsive nanoplatforms, which include acidic pH, high GSH levels, high-level adenosine triphosphate, overexpressed enzymes, hypoxia and reductive environment. Additionally, we showcase the latest advancements in TME-responsive nanoparticles. In conclusion, we thoroughly examine the immediate challenges and prospects of TME-responsive nanopharmaceuticals, with the expectation that the progress of these targeted nanoformulations will enable the exploitation, overcoming or modulation of the TME, ultimately leading to significantly more effective cancer therapy. Keywords: tumor microenvironment, stimulus-responsive, drug delivery, cancer therapy, intelligent biomedicin

Electron capture dissociation of diselenides and disulphides

Tesis doctoral inédita. Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química. Fecha de lectura: 10-12-201

Chalcogenol Ligand Toolbox for CdSe Nanocrystals and Their Influence on Exciton Relaxation Pathways

We have employed a simple modular approach to install small chalcogenol ligands on the surface of CdSe nanocrystals. This versatile modification strategy provides access to thiol, selenol, and tellurol ligand sets <i>via</i> the <i>in situ</i> reduction of R₂E₂ (R = ^<i>t</i>Bu, Bn, Ph; E = S, Se, Te) by diphenylphosphine (Ph₂PH). The ligand exchange chemistry was analyzed by solution NMR spectroscopy, which reveals that reduction of the R₂E₂ precursors by Ph₂PH directly yields active chalcogenol ligands that subsequently bind to the surface of the CdSe nanocrystals. Thermogravimetric analysis, FT-IR spectroscopy, and energy dispersive X-ray spectroscopy provide further evidence for chalcogenol addition to the CdSe surface with a concomitant reduction in overall organic content from the displacement of native ligands. Time-resolved and low temperature photoluminescence measurements showed that all of the phenylchalcogenol ligands rapidly quench the photoluminescence by hole localization onto the ligand. Selenol and tellurol ligands exhibit a larger driving force for hole transfer than thiol ligands and therefore quench the photoluminescence more efficiently. The hole transfer process could lead to engineering long-lived, partially separated excited states