Antiferromagnetic spin-coupling between MnII and amminium radical cation ligands: models for coordination polymer magnets

One and two electron oxidation of the manganese(II) complex [L2Mn(hfac)2] {L = 4'',4'''-di-tert-butyl-2',2'',2'''trimethoxy-{4-(4'-diphenylaminophenyl)pyridine} were studied by ultra violet/ visible/ near infra red spectroscopy, cyclic voltammetry and magnetometry. A one-electron oxidation converts the triarylamine ligand to its radical cation and gives a complex in which the antiferromagnetic coupling between the spin on the ligand and that on the metal J/kb is -1.5 K. In a dilute frozen matrix and at low temperature this behaves as an S = 2 system. A two electron oxidation gives [L2Mn(hfac)2]2.+ which at low enough temperatures behaves as an S = 3/2 system but the spin-coupling between the metal and the ligand is weaker (J/kb = -0.3 K). The weakness of these spin-couplings mean that MnII/amminium radical cation complexes are not promising systems on which to base coordination polymer magnets. The equivalent copper(II) complex [L2Cu(hfac)2] was also investigated but this decomposes when an attempt is made to oxidise the ligand to its amminium radical cation

Spectrophotometric Analysis and Optimization of 2D Gold Nanosheet Formation

Free-standing, 2D gold nanosheets (AuNS) offer broad potential applications from computing to biosensing and healthcare. Such applications, however, require improved control of material growth. We recently reported the synthesis of AuNS only ∼0.47 nm (two atoms) thick, which exhibited very high catalytic activity. The synthesis is a one-pot, seedless procedure in which chloroauric acid is reduced by sodium citrate in the presence of methyl orange (MO). In this study, we use spectrophotometric analysis and TEM imaging to probe AuNS formation and optimize the procedure. Previously, we suggested that MO acted as the confining agent, directing two-dimensional growth of the gold. Here, we provide the first reported analysis of the HAuCl4 and MO reaction. We show that MO is rapidly oxidized to give 4-diazobenzenesulfonic acid, indicating that a complex interplay between HAuCl4, MO, and other reaction products leads to AuNS formation. Time-resolved studies indicate that synthesis time can be significantly reduced from over 12 to 2-3 h. Decreasing the reaction temperature from 20 to 4 °C improved AuNS yield by 16-fold, and the catalytic activity of the optimized material matches that obtained previously. Our elucidation of AuNS formation mechanisms has opened avenues to further improve and tune the synthesis, enhancing the potential applications of ultrathin AuNS

Maleimide–Thiol Linkages Alter the Biodistribution of SN38 Therapeutic Microbubbles Compared to Biotin–Avidin While Preserving Parity in Tumoral Drug Delivery

Therapeutic microbubbles (thMBs) contain drug-filled liposomes linked to microbubbles and targeted to vascular proteins. Upon the application of a destructive ultrasound trigger, drug uptake to tumour is improved. However, the structure of thMBs currently uses powerful non-covalent bonding of biotin with avidin-based proteins to link both the liposome to the microbubble (MB) and to bind the targeting antibody to the liposome–MB complex. This linkage is not currently FDA-approved, and therefore, an alternative, maleimide–thiol linkage, that is currently used in antibody–drug conjugates was examined. In a systematic manner, vascular endothelial growth factor receptor 2 (VEGFR2)-targeted MBs and thMBs using both types of linkages were examined for their ability to specifically bind to VEGFR2 in vitro and for their ultrasound imaging properties in vivo. Both showed equivalence in the production of the thMB structure, in vitro specificity of binding and safety profiles. In vivo imaging showed subtle differences for thMBs where biotin thMBs had a faster wash-in rate than thiol thMBs, but thiol thMBs were longer-lived. The drug delivery to tumours was also equivalent, but interestingly, thiol thMBs altered the biodistribution of delivery away from the lungs and towards the liver compared to biotin thMBs, which is an improvement in biosafety

A Novel Synthesis of Soluble, Stable Derivatives of the Perchlorinated Trityl Radical

A new approach to the synthesis of derivatives of the perchlorinated tritryl radical is described. It relies on the fact that, under the conditions required to fully chlorinate the ortho positions of a triarylmethane, there is only minimal substitution of aryl fluorine by chlorine and then on the fact that, in the mixed Cl/F substituted triarylmethanes obtained, it is possible to selectively substitute the fluorine-bearing positions using the sodium salt of n-hexanol in n-hexanol/dimethylsulfoxide. The meta-hexyloxy derivatives obtained are much more soluble and photostable than the parent perchlorotrityl radical. For example, the introduction of four meta-hexyloxy substituents gives a radical where, under white light illumination, the lifetime is improved by a factor of almost 104. The photostability of the radical, the lifetime of the excited state and the fluorescence all decrease as the number of meta-hexyloxy substituents is increased. The improvements in solubility and in photostability observed should help in creating a more diverse range of perchlorotrityl radical derivatives and in the development of new applications

New mesophases formed by water soluble discoidal amphiphiles

We present the first examples of lyotropic discotic nematic and columnar (hexagonal) mesophases obtained by dissolution of non-ionic, disk-like amphiphilic mesogens (hexa-polyethyleneoxy derivatives of triphenylene) in water. The phenomenon of « solvent driven aggregation » is shown to be a practicable route to new and novel mesophases with structures and properties intermediate to and encompassing those of the thermotropic and lyotropic-amphiphilic classes of liquid crystals.Nous donnons les premiers exemples de mésophases lyotropes nématiques colonnes hexagonales, préparées par dissolution dans l'eau de mésogènes amphiphiliques non ioniques avec des molécules en forme de disque(dérivés hexa-polyethyleneoxy de triphénylène). Nous montrons que le phénomène « d'agrégation forcée par solvant » est une bonne méthode pour obtenir de nouvelles mésophases, de structures et de propriétés intermédiaires entre celles des cristaux liquides thermotropes et celles de systèmes amphiphiles lyotropes

Self-assembled columns of fullerene

Columnar mesophases based on alternating triphenylene and hexaphenyltriphenylene moieties are exceptionally stable and able to accommodate bulky side-chain substituents within the alkyl chain continuum between the columns. This paper presents a system in which the triphenylene bears a fullerene on its side-chain and the hexaphenyltriphenylene equivalent is the aza-derivative hexakis(4-nonylphenyl)dipyrazino[2,3-f : 2'3'-h] quinoxalene, PDQ9. The mesophase formed was identified as hexagonal columnar (Col(h)) by X-ray diffraction (a = 25.2 angstrom and c = 3.5 angstrom) but, in addition to the expected peaks, there is indication of a two-dimensional hexagonal superlattice with d-spacing 59 angstrom. This superlattice is believed to arise from ordering of the fullerenes within the liquid crystal matrix. It can be explained on the assumption that, to maximise fullerene-fullerene contact, the fullerenes form chains which wrap around the central column in every group of seven columns of the triphenylene : PDQ9 Col(h) array

A simple route to derivatives of benzo[j]fluoranthene

3,6,8,11-Tetramethoxybenzo[j]fluoranthene can be made from 1,6-dimethoxynaphthalene in a one-pot ferric chloride oxidation/methanol reduction procedure. The reaction is tolerant of the presence of substituents in the 7-position of the naphthalene nucleus and provides a quick and easy route to these particular benzo[j]fluoranthenes. The reactions presumably proceed through initial formation of a bond between the 4-positions of two naphthalene molecules followed by closure of the five-membered ring. Indeed in one case some 4,4�-binaphthyl was isolated from the reaction mixture and it was generally found that better yields of the benzo[j]fluoranthrenes were obtained starting from the 4,4�-binaphthyl rather than by using the naphthalene as the starting material. In an analogous manner to the ring-closure of the 4,4�-binaphthyls, starting from a hexakisalkoxyphenylnaphthalene, a hexakisalkoxyfluoranthene could be obtained. © 2013 Elsevier Ltd. All rights reserved