Chemical tuning

Membranes are also used to separate gases, for example, the production of N2 and O2 from air and the recovery of hydrogen from ammonia plant purge gas. The working principle is a membrane that is chemically tuned to pass a molecular type. 

Lanthanide ions offer several salient properties that make them especially attractive as qubit candidates (i) their magnetic states provide proper definitions of the qubit basis (ii) they show reasonably long coherence times (iii) important qubit parameters, such as the energy gap AE and the Rabi frequency 2R, can be chemically tuned by the design of the lanthanide co-ordination shell and (iv) the same molecular structure can be realized with many different lanthanide ions (e.g. with or without nuclear spin), thus providing further versatility for the design of spin qubits or hybrid spin registers. 

The dimerisation energy for derivatives of 2 (ca. 35 kJ mol-1) is considerable, particularly in relation to the strength of intermolecular forces and some persistence is required in order to isolate derivatives of 2 which do not form 7T —7r dimers in the solid state. A survey of the monomeric derivatives has been published recently.26 Since the spin density distribution in 2 is rather insensitive to chemical tuning, approaches to inhibit dimerisation rely exclusively on structural modifications, which affect the nature of the intermolecular forces. Inclusion of sterically demanding groups, such as 13, 14 and 15 has proved partially successful (in the case of the diradical 14 one ring is involved in formation of a dimer, while the other retains its open shell character). 

P.L. Burn, A.B. Holmes, A. Kraft, D.D.C. Bradley, A.R. Brown, R.H. Friend, and R.W. Cymer, Chemical tuning of electroluminescent copolymers to improve emission efficiency and allow patterning, Nature, 356 47-49, 1992. 

REGULATION OF CATALYSIS BY DESIGN OF ACTIVE STRUCTURES 8.3.1 Chemical Tuning of Active Sites... 

The availability of low-cost laser diodes has expanded the applications of NIR dyes.(34) NIR dyes have been used in analytical applications such as fiber probes(39,79) and the detection of caustic brine.(89) However, most of the NIR dye applications have been in electrophotography for the manufacturing of office products such as laser printers and facsimiles. The wavelength of the lasers is not necessarily matched to the absorbance maxima of the dyes. Therefore, an understanding of the spectroscopic properties of NIR dyes and their ability to be chemically tuned is necessary to further expand the use of these dyes. 

Traditionally, potentiometric sensors are distinguished by the membrane material. Glass electrodes are very well established especially in the detection of H+. However, fine-tuning of the potentiometric response of this type of membrane is chemically difficult. Solid-state membranes such as silver halides or metal sulphides are also well established for a number of cations and anions [25,26]. Their LOD is ideally a direct function of the solubility product of the materials [27], but it is often limited by dissolution of impurities [28-30]. Polymeric membrane-based ISEs are a group of the most versatile and widespread potentiometric sensors. Their versatility is based on the possibility of chemical tuning because the selectivity is based on the extraction of an ion into a polymer and its complexation with a receptor that can be chemically designed. Most research has been done on polymer-based ISEs and the remainder of this work will focus on this sensor type. 

Since then, several studies on the chemical reactivity of endohedral metallofullerenes have been performed in order to understand their basic chemical properties. The endohedral metallofullerenes Gd C82 [137], La2 C80, and Sc2 C84 [138] showed similar behavior towards disilirane, forming the corresponding adducts via C-Si bonds. Also, similar functionalization of La C82 was achieved with digermirane [ 139,140]. However, when diphenyldiazomethane was added to La C82 an exohedral adduct was formed via C-C bonds [ 140,141 ]. This organic functionalization of endohedral metallofullerenes opened the way to chemically tune the electronic properties of the so-produced materials, the degree of charge transfer, and ultimately their electronic properties. 

How can we chemically tune the strength of donors and acceptors, and stabilize their corresponding ion radicals ... 

In the aq/polymer/org situation, the organic solvent typically penetrates the polymer causing it to swell considerably, and the situation is very similar to that of MMLLE. With a fixed composition of the membrane, the possibilities for chemical tuning (such as application of carriers) of the separation process are greatly reduced compared to SLM extraction or MMLLE. Also, as diffusion coefficients in polymers are lower than in liquids, the mass transfer is slower, leading to slower extractions. On the other hand, as the membrane is virtually insoluble, any combination of aqueous and organic liquids can be used, and the entire system becomes very stable. 

In this paper we illustrate with novel examples the considerable impact of POMs in molecular magnetism and molecular materials. In the first part we show that ideal examples of large magnetic clusters can be designed, wherein magnetic exchange interactions can be chemically tuned and physically studied at the molecular level. In the second part we report the synthesis of highly conductive molecular materials based upon polyoxometalates and perylene. In the last section we show the possibilities offered by POMs to obtain multifunctional materials. 

With the exception of ird excited states, detailed analyses of the emission characteristics of d complexes of the second and third transition series have lead to criteria for classifying these states by means of emission spectroscopy (3, 6). Moreover, further investigation revealed that complexes can be engineered to possess a predetermined sequence of excited states with prescribed orbital types 4, 5). This capability, designated chemical tuning, has led to series of molecules whose low lying excited states were chosen specifically and whose spectroscopic properties were ordained as well. 

Terazzi E, Guenee L, Bocquet B, Lemonnier J-P, Daha Favera N, Piguet C. A simple chemical tuning of the effective concentration selection of single-, double-, and triple-stranded binuclear lanthanide helicates. Chem EurJ. 2009 15 12719-12732. 

Bendejacq, D., Ponsinet, V., Joanicot, M., Vacher, A., Airiau, M. Chemical tuning of the microphase separation in diblock copolymers from controlled radical polymerization. 

Burn, P.L., et al. 1992. Chemical tuning of electroluminescent copolymers to improve emission efficiencies and allow patterning. Nature 356 47. 

Holst JR, Stockel E, Adams DJ, Cooper A1 (2010) Chemical tuning of CO2 sorption in robust nanoporous organic polymers. Macromolecules 43 8531-8538... 

Wenger OS, Wermuth M, Gudel HU. Chemical tuning of transition metal upconversion properties. J Alloys Compd 2002 341(l-2) 342. 

---