Control of Excitation and Quenching in Multi‐colour Electrogenerated Chemiluminescence Systems through Choice of Co‐reactant

We demonstrate a new approach to manipulate the selective emission in mixed electrogenerated chemiluminescence (ECL) systems, where subtle changes in co‐reactant properties are exploited to control the relative electron‐transfer processes of excitation and quenching. Two closely related tertiary‐amine co‐reactants, tri‐n‐propylamine and N,N‐diisopropylethylamine, generate remarkably different emission profiles: one provides distinct green and red ECL from [Ir(ppy)₃] (ppy=2‐phenylpyridinato‐C2,N) and a [Ru(bpy)₃]²⁺ (bpy=2,2′‐bipyridine) derivative at different applied potentials, whereas the other generates both emissions simultaneously across a wide potential range. These phenomena can be rationalized through the relative exergonicities of electron‐transfer quenching of the excited states, in conjunction with the change in concentration of the quenchers over the applied potential range.     

Click‐Assembled,Oxygen‐Sensing Nanoconjugates for Depth‐Resolved,Near‐Infrared Imaging in a 3 D Cancer Model

Hypoxia is an important contributing factor to the development of drug‐resistant cancer, yet few nonperturbative tools exist for studying oxygenation in tissues. While progress has been made in the development of chemical probes for optical oxygen mapping, penetration of such molecules into poorly perfused or avascular tumor regions remains problematic. A click‐assembled oxygen‐sensing (CAOS) nanoconjugate is reported and its properties demonstrated in an in vitro 3D spheroid cancer model. The synthesis relies on the sequential click‐based ligation of poly(amidoamine)‐like subunits for rapid assembly. Near‐infrared confocal phosphorescence microscopy was used to demonstrate the ability of the CAOS nanoconjugates to penetrate hundreds of micrometers into spheroids within hours and to show their sensitivity to oxygen changes throughout the nodule. This proof‐of‐concept study demonstrates a modular approach that is readily extensible to a wide variety of oxygen and cellular sensors for depth‐resolved imaging in tissue and tissue models.     

Solid polymers doped with rare earth metal salts. I. Complex formation and morphology in the neodymium chloride–poly(ethylene oxide) system

The complex formation and morphology of the NdCl₃?PEO system have been investigated. Peak shifts, peak broadening, and the appearance of new peaks in the 800–1200 cm^?1 range of the infrared (IR) spectra, by comparison with what is observed with pure PEO, unequivocally demonstrates complex formation. Although the NdCl₃?PEO complex is found to be highly hygroscopic, residual moisture can be removed reversibly, thereby permitting the role of water in affecting the morphology of the solid film to be examined. As elucidated with infrared, differential scanning calorimetry, thermogravimetric analysis, and hot-stage polarized optical microscopy, under anhydrous conditions the resultant complex is amorphous at an EO/NdCl₃ ratio approximately less than ca. 8; but above this critical value the PEO in excess of the stoichiometric ratio required for complexation tends to form a separate crystalline phase. Furthermore, water was found to compete with the ethylene oxide unit for complexation with Nd³⁺, resulting in phase-separated PEO with a tendency toward crystallinity. The glass transition temperature of the complex is found to increase sigmoidally with the NdCl₃ content, an observation further substantiating complexation between NdCl₃ and PEO.     

Electrochemical studies of porphyrin-appended dendrimers

The electrochemical properties of porphyrin-appended dendrimers containing 2-, 4-, 8-, 16-, 32- and 64-porphyrin macrocycles in their free-base and zinc(II) forms have been investigated. Both series gave diffusional based voltammetric responses in dichloromethane. There was minimal effect of dendrimer generation on the redox potentials. Multiple pi-cation and anion radicals as well as dications and dianions were formed on the surface of the dendrimers on oxidation or reduction as appropriate, with each cyclic voltammetric wave representing electron transfer to or from multiple non-interacting porphyrin sites. Electrostatic interactions in the higher generation dendrimers result in kinetic effects being observed for the highly charged species generated when each porphyrin unit is doubly or triply oxidised. The number of electrons transferred on reduction or oxidation of the dendrimers was evaluated using steady-state microelectrode voltammetry. For the lower generations of species a good correlation was observed between numbers of electrons transferred and number of porphyrin entities per molecule; for the dendrimers containing 32 and 64 units, however, slight negative deviations were observed, possibly due to electrostatic interactions as the porphyrins become closer packed.     

Exploiting a Bacterial Drug‐Resistance Mechanism: A Light‐Activated Construct for the Destruction of MRSA

A cunning and dangerous plan foiled! An enzyme‐specific molecular construct exploits the overexpression of β‐lactamase in several drug‐resistant bacteria. Specific photodynamic toxicity was detected towards β‐lactam‐resistant methicillin‐resistant Staphylococcus aureus (MRSA), whereby the usual mechanism for antibiotic resistance (cleavage of the β‐lactam ring) releases the phototoxic component from the prodrug (see picture; Q=quencher).

     

Aluminum(I)/Boron(III) Redox Reactions

Reactions between B^III species and the novel nucleophilic cyclopentadienyl‐stabilized Al^I reagent ( 1 ) result in a diversity of complexes bearing different Al/B oxidation states and coordination geometries. With the triarylborane B(C₆F₅)₃, a simple Al^I→B^III adduct is formed. In contrast, a bulky aryldihaloborane undergoes oxidative addition with the formation of a covalent bora‐alane species. With an N‐heterocyclic carbene‐stabilized amino(bromo)borenium ion, a redox reaction was observed, where the product is a borylene‐alane B^I→Al^III complex. Additionally, reaction of 1 with BI₃ results in complete scrambling of all of the Al/B‐bound substituents, and the formation of a cyclopentadienylboron(I)→AlI₃ complex. These latter reactions are the first examples of the reduction of a boron(III) compound to a borylene by a p‐block reagent, and illustrate how subtle changes in the nature of the borane can result in highly divergent reaction outcomes.     

Total synthesis of a diastereomer of the marine natural product clavosolide A

The first total synthesis of the reported structure of the sponge metabolite clavosolide A is described using a Prins cyclisation to assemble the tetrahydropyran core followed by manipulation of the side-chain, dimerisation and finally glycosidation.