We report a modular design of vesicular chemosensors by co-embedding a Tb(III) complex and a receptor-sensitizer conjugate in phospholipid vesicles. The binding of phosphate anions to the vesicle surface in aqueous media is detected by a decrease in Tb(III) phosphorescence. The sensory response can be modulated by a variation in the membrane fluidity.Analyte detection at low concentrations is a key issue in the fields of analytical, biological and medicinal chemistry. Fluorescent chemosensors, with their high sensitivity and fast response times, are frequently employed for this purpose.1 Functionalized artificial membranes/bilayers with embedded fluorescent probes 2 represent a special class of chemosensors. They mimic the functions of biomembranes, known to play pivotal roles in the intracellular signalling pathways. 3 The molecular recognition events at the cellular interface are governed by the self-assembly of membrane lipids and proteins through the formation of domains or clusters. 4 We recently reported the detection of various biological analytes in aqueous buffer (pH = 7.4) by utilizing the interface of functionalized luminescent vesicles. 5 The vesicles were prepared by co-embedding amphiphilic metal complex receptors and amphiphilic fluorescent dyes in synthetic DSPC (1,2-distearoyl-sn-glycero-3-phosphocholine) lipid membranes. The analyte binding at the interface alters the composition of the self-assembled mixed dye/ receptor patches. This results in a partial expulsion of the dyes from these patches, thereby triggering an emission response.In spite of their widespread use, a common drawback of fluorescent probes with short excited state lifetimes is the interference from the background fluorescence, especially for bioanalyte detection and in vivo measurements.6 Therefore, time delayed measurement using long life-time luminescent probes has evolved as a technique. We envisaged that the modular nature of the design of our vesicular chemosensors would allow us to replace the fluorescent dyes with lanthanide based long excited state life-time probes; a modification that would certainly broaden their applicability. In the literature, to the best of our knowledge, the only example of such Ln(III) based vesicular chemosensors is of Kimizuka et al. 12They reported the sensing of ATP and ADP by phosphorescent vesicles made from an amphiphilic, positively charged Tb(III) complex. The binding event was accompanied by an increase in Tb(III) emission, a consequence of the removal of H 2 O molecules from its inner co-ordination sphere. Herein, we report a conceptually different approach by co-embedding a Tb(III) complex, functioning as a phosphorescent reporter, along with a phosphate receptor in the phospholipid vesicles (B100 nm) for the detection of different phosphate analytes. Furthermore, we demonstrate the tuning of the sensitivity of these chemosensors by varying the fluidity of the lipid bilayer.The intra 4f transitions in Ln(III) ions are Laporte forbidden resulting in very weak emissions by their dir...

A series of water‐soluble bis‐ and tetrakis‐ZnII–cyclen complexes with rigid structures was prepared to enhance the carboxylate and phosphate ion binding response in contrast to analogues with less‐confined molecular structures. Boc‐protected 6‐chloro‐1,3,5‐triazine–bis‐cyclen was coupled to different aryl and alkyl moieties in moderate to high yields and subsequently converted into the corresponding bis‐ or tetrakis‐ZnII–cyclen complexes. The bis‐ZnII–cyclen moiety is known for its affinity to anions. Depending on the arene substituent some of the synthesized synthetic receptors are luminescent. They were studied by absorption and emission spectroscopy for their response to the presence of phosphate anions of biological relevance in buffered aqueous solution at neutral pH and for their affinity to the genetically encodable oligoaspartate and glutamate sequences (D4 and E4 tag) recently introduced. The rigid structures of the compounds enhance the electronic coupling between the metal complex binding site and the reporter dye. This leads to an increased anion binding response in homogeneous aqueous solution.

Benzyl cobaloximes, ArCH 2 Co(dioxime) 2 Py, with two different dioximes, glyoxime (gH) and dimesitylglyoxime (dmestgH), have been synthesized and characterized by 1 H and 13 C NMR and UVvis spectroscopy. The dioxy adducts, ArCH 2 (O 2 )Co(dioxime) 2 Py, were prepared by the insertion of molecular oxygen into the Co-C under photochemical conditions. The rate of insertion depends upon the nature of the dioxime and follows the order dmestgH . dpgH > chgH > dmgH > gH. The steric cis influence of the dioximes on the Co-C bond also follows the same order. The study also suggests that the interactions between the axial benzyl group and the dioximes have significant influence on the Co-C bond reactivity. Such interactions are also seen in the molecular structure of [C 6 H 4 CH 2 Co(gH) 2 -(4-t BuPy)] and in the dioxy complexes 4-CN-C 6 H 4 CH 2 (O 2 )Co(dmestgH) 2 Py and 2-naphthylCH 2 -(O 2 )Co(dmestgH) 2 Py. On the basis of the results we have supported the cage mechanism for the oxygen insertion into the Co-C bond.

Self-assembled lipid vesicles with embedded amphiphilic terbium(III) complexes show a strong temperature dependence of their phosphorescence intensity and lifetime in the physiological range.Temperature is a fundamental physical property of matter important in everyday life, in scientific and industrial applications. The methods to measure temperature can be divided into two main techniques: contact thermometry and non-contact thermometry. Contact methods use thermocouples, thermistors, and resistance temperature detectors (RTDs), whereas noncontact methods often use the spectral emittance of a material for readout. 1 Non-contact optical techniques have various advantages in terms of sensitivity and real-time monitoring over a wide range, from femtoseconds to seconds. 2 Among the available optical methods, infrared thermometry that uses the principle of blackbody radiation is flexible and easy to use, but can only measure the temperature of surfaces, thus limiting its applications. 3 Therefore luminescence based optical sensors have attracted much attention, because of their fast response, high spatial resolution, accurate usability even in strong electromagnetic fields 4 and safety of remote handling. 5 Such sensing probes use appropriate luminophores ranging from polycyclic aromatic hydrocarbons to metal complexes. 2 Temperature sensitive probes were incorporated into nanogels for intracellular thermometry, 6 and in sensor films or thermo-sensitive polymers to allow spatially resolved temperature imaging. 7 Recently tripositive lanthanide complexes have been used for optical sensing of temperature. 4,7,8 The use of such lanthanide complexes has several advantages over organic luminophores: (a) they have long emission wavelengths, (b) lanthanide emissions are Laporte forbidden and are therefore characterized by very long luminescence lifetimes, which is useful for applications in biological media by excluding background emission using time delayed detection, (c) 4f electrons of the lanthanides are highly shielded from the chemical environment by the 5s and 5p orbitals thus making them insensitive to the environment. Among the tripositive lanthanides, typically Eu 3+ based complexes have been used as optical temperature sensors, while Tb 3+ complexes are less explored. One reason is their smaller luminescence dependence on temperature. 9 However, the longer luminescence lifetime of the Tb 3+ ion compared to Eu 3+ makes Tb 3+ complexes the favoured systems for the lifetime based optical sensing of temperature. 10 Having this in mind we used the diethylenetriamine pentaacetic acid (DTPA) based amphiphilic Tb 3+ complex (Tb-1) as a probe for the optical sensing of temperature. By embedding the complex [for detailed experimental procedures and analytical data of the prepared compounds, see ESIw] in different phospholipids we obtain reversible thermosensitive luminescent vesicles (Fig. 1) at an adjustable temperature range. The luminescent nanosized vesicles (LNT) with embedded Tb 3+ complexes were prepared by th...

The Co−C bond is activated toward homolysis due to the interactions between axial and equatorial dioxime ligands. Benzylcobaloxime gives an oxygen-inserted product, whereas the alkyl derivative forms air-stable cobalt(II). The stabilization of the axial R group due to the interaction between axial and equatorial ligands causes the reactivity difference.