Phosphonioalkylthiosulfate zwitterions—new masked thiol ligands for the formation of cationic functionalised gold nanoparticles

Gold nanoparticles functionalized by phosphine oxide derivatives: characterization and influence of ligand structure on their stability

The rapid development of nanotechnology has led to an incredible expansion in the production and use of nanoparticles (NPs). Gold nanoparticles (AuNPs) are one of the most significant types of NPs and have shown outstanding medical applications due to their low toxicity. AuNPs stabilized by phosphine derivatives have extensive applications in sensing, catalysis, and biological imaging. In this work, phosphine oxide ligands were employed to stabilize AuNPs in DMSO with NaBH4 as the reducing agent. These ligands included (3-thioacetyl-N-ethylmethylamine)-diphenylphosphine oxide (10), (3-thioacetylpropyl)-thiodiphenylphosphine oxide (7), (3-thioacetylpropyl)di-(p-tolyl)phosphine oxide (4A), and (3-thioacetylpropyl)-diphenylphosphine oxide (4B). The AuNPs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and UV-Vis spectroscopy. AuNPs stabilized by both 4B and 7 remained stable for five months. However, when 4A and 10 were used, the AuNPs remained stable for three months. Due to their small surface-area-to-volume ratio and good stability, AuNPs are nowadays needed for different applications. Therefore, small, homogenous, and spherical AuNPs were considered herein, where their sizes were 55 ± 13.6 nm, 40 ± 8 nm, 25 ± 6 nm, and 43 ± 7 nm for 4A-AuNPs, 4B-AuNPs, 7-AuNPs, and 10-AuNPs, respectively, based on TEM results. These results aligned with the DLS results, where homogenous AuNPs were produced with no evidence of aggregation.

Study of the Stability of Functionalized Gold Nanoparticles for the Colorimetric Detection of Dipeptidyl Peptidase IV

In this report, we investigated three stabilization strategies of gold nanoparticles and their practical application for the visual detection of dipeptidyl peptidase IV (DPP-IV). Citrate-capped gold nanoparticles (Au NPs) are generally unstable in high-ionic-strength samples. Au NPs are easily tagged with various proteins and biomolecules rich in amino acids, leading to important biomedical applications including targeted drug delivery, cellular imaging, and biosensing. The investigated assays were based on different modes of stabilization, such as the incorporation of polyethylene glycol (PEG) groups, stabilizer peptide, and bifunctionalization. Although all approaches provided highly stable Au NP platforms demonstrated by zeta potential measurements and resistance to aggregation in a high-ionic-strength saline solution, we found that the Au NPs modified with a separate stabilizer ligand provided the highest stability and was the only platform that demonstrated sensitivity to the addition of DPP-IV, whilst PEGylated and peptide-stabilized Au NPs showed no significant response.

Highly stable noble metal nanoparticles dispersible in biocompatible solvents: synthesis of cationic phosphonium gold nanoparticles in water and DMSO

In this work, we report the synthesis of novel cationic phosphonium gold nanoparticles dispersible in water and dimethyl sulfoxide (DMSO) for their potential use in biomedical applications. All the cationic-functionalising ligands currently reported in the literature are ammonium-based species. Here, the synthesis and characterisation of an alternative system, based on phosphonioalkylthiosulfate zwitterions and phosphonioalkylthioacetate were carried out. We have also demonstrated that our phosphonioalkylthiosulfate zwitterions readily disproportionate into phosphonioalkylthiolates in situ during the synthesis of gold nanoparticles produced by the borohydride reduction of gold(III) salts. The synthesis of the cationic gold nanoparticles using these phosphonium ligands was carried out in water and DMSO. UV-visible spectroscopic and TEM studies have shown that the phosphonioalkylthiolates bind to the surface of gold nanoparticles which are typically around 10 nm in diameter. The resulting cationic-functionalised gold nanoparticles are dispersible in aqueous media and in DMSO, which is the only organic solvent approved by the U.S. Food and Drug Administration (FDA) for drug carrier tests. This indicates their potential future use in biological applications. This work shows the synthesis of a new family of phosphonium-based ligands, which behave as cationic masked thiolate ligands in the functionalisation of gold nanoparticles. These highly stable colloidal cationic phosphonium gold nanoparticles dispersed in water and DMSO can offer a great opportunity for the design of novel biorecognition and drug delivery systems.

Gold nanoparticle-enhanced photodynamic therapy: effects of surface charge and mitochondrial targeting

Aim: The authors aimed to further improve the efficiency and selectivity of gold nanoparticle (Au NP)-assisted photodynamic therapy by modulating the surface charge of Au NPs and delivering Au NPs particularly to mitochondria of breast cancer cells. Methods: Solid gold nanospheres (˜50 nm) with negative and positive surface charge were synthesized respectively, and mitochondria-targeting Au NPs were prepared by conjugating with triphenylphosphonium molecules. Conclusion: Positively charged Au NPs were preferably taken up by breast cancer cells. Combination of positive surface charge with mitochondria-targeting domain onto Au NPs allowed their accumulation in the mitochondria of breast cancer cells to significantly elevate reactive oxygen species formation in 5-aminolevulinic-acid-enabled photodynamic therapy and improve selective destruction of breast cancer cells.

Triphenylarsonium-functionalised gold nanoparticles: potential nanocarriers for intracellular therapeutics

Gold nanoparticles functionalised with triphenylarsonium alkylthiolate ligands have been synthesised; both arsonium ligands show comparatively low cytotoxicity in cells.

Radiosynthesis of 11-[(18) F]fluoroundecyltriphenylphosphonium (MitoF) as a potential mitochondria-specific positron emission tomography radiotracer

Changes in the magnitude of the mitochondrial membrane potential occur in a range of important pathologies. To assess changes in membrane potential in patients, we set out to develop an improved mitochondria-targeted positron emission tomography probe comprising a lipophilic triphenylphosphonium cation attached to a fluorine-18 radionuclide via an 11-carbon alkyl chain, which is well-established to effectively transport to and localise within mitochondria. Here, we describe the radiosynthesis of this probe, 11-[(18) F]fluoroundecyl-triphenylphosphonium (MitoF), from no-carrier-added [(18) F]fluoride and a fully automated synthetic protocol to prepare it in good radiochemical yields (2-3 GBq at end-of-synthesis) and radiochemical purity (97-99%).

Mechanism of spontaneous formation of monolayers on gold from alkyl thiosulfates

The kinetics of adsorption of self-assembled monolayers (SAMs) from solutions of hexadecyl thiosulfate in tetrahydrofuran was studied under a variety of experimental conditions to elucidate the mechanism(s) important in this process. Monolayers did not form in the absence of water, which ruled out the direct addition of the alkyl thiosulfate to the gold surface and implicated hydrolysis as a route to surface-active adsorbates. The role of tetrafluoroborate ion, known to inhibit SAM formation in this system, was also examined. These studies, too, were consistent with hydrolysis as an intermediate step in the formation of monolayer films in this system.

Direct synthesis of large water-soluble functionalized gold nanoparticles using Bunte salts as ligand precursors

The widespread use of functionalized gold nanoparticles (AuNPs) in a rapidly increasing number of sensing and biomedical applications has made the development of synthetic methods that combine precise surface chemistry control (functionality) with effective core size control over the range of 1-20 nm crucial. Although a variety of effective methods exist for controlling the core size and functionality during gold nanoparticle synthesis, there is a lack of synthetic methods that permit the direct synthesis of thiol-protected gold nanoparticles with core diameters greater than 5.0 nm. Inspired by previous reports on the use of alkyl thiosulfates (Bunte salts) as ligand precursors, we anticipated that the slow passivation kinetics of these masked thiols would provide a method to synthesize large functionalized AuNPs directly. We found that Bunte salts produce larger AuNPs under the same synthesis conditions than do thiols. We investigated the effect of the ligand/gold ratio, temperature, and reducing agent concentration on the particle diameter and dispersity to understand better how to control particle size. The AuNP core size can be systematically controlled by varying the ratio of ligand precursor/gold (L/Au) and the temperature of the reaction. The synthesis produces functionalized AuNPs ranging from 1.5 to 20.0 nm in diameter. The use of Bunte salts provides a convenient synthetic platform for the synthesis of AuNPs across this size range that possess a variety of surface functionalities, including positive, negative, and neutral functional groups.

Reactions of tertiary phosphines with alcohols in aqueous media

The phosphines R(2)R'P [R = R' = Me, Et, (n)Pr, (i)Pr, (CH(2))(3)OH; Me(2)PhP and MePh(2)P] react with 2- or 4-hydroxybenzyl alcohols, including "lignin-type" vanillyl, syringyl, and alpha-methylvanillyl alcohols, in a 1:1 ratio in aqueous media, to give zwitterionic phosphobetaine products; these on treatment with aq HCl form the corresponding phosphonium chlorides in good to excellent yields. The syringyl derivative [3,5-(OMe)(2)-4-OH-C(6)H(2)CH(2)PEt(3)]Cl was structurally characterized by X-ray analysis. Kinetically, the reactivity of the benzyl alcohols, studied with the water-soluble [HO(CH(2))(3)](3)P, decreases with substituents in the order 2-hydroxy > 4-hydroxy > vanillyl > syringyl > alpha-methylvanillyl, while 3-hydroxybenzyl alcohol is unreactive; the trend is consistent with reactivity requiring the presence of an ortho- or para-OH substituent in the aromatic ring of the alcohol, and that the reactions proceed via a carbocation species stabilized as a quinone methide. Triethylphosphine reacts with coniferyl alcohol at the C=C moiety to give a zwitterionic intermediate that is again converted by aq HCl to a phosphonium chloride; no reaction was observed with cinnamyl alcohol. The effect on a phenolic pK(a) by incorporation of a phosphonium substituent is also measured.

Mitochondria-specific nanotechnology

Mitochondrial research has made an enormous leap since mitochondrial DNA mutations were identified as a primary cause for human diseases in 1988 and the organelle’s crucial role in apoptosis was identified during the 1990s. Considerable progress has been made in identifying the molecular components of the mitochondrial machinery responsible for life and cell death; however, effective therapies for diseases caused by mitochondrial dysfunction remain elusive. An impediment to manipulating, probing and assessing the functional components of mammalian mitochondria within living cells is their limited accessibility to direct physical, biochemical and pharmacological manipulation. Recent advances in nanotechnology hold the promise of helping to overcome these obstacles. New tools will undoubtedly emerge, creating new avenues for the diagnosis and therapy of mitochondrial disorders. This review briefly discusses current efforts to merge nanobiotechnology with mitochondrial medicine.