Bianca H.M. Snellink-Ruël

Uranyl salophenes as ionophores for phosphate-selective electrodes

Anion selectivities of poly(vinylchloride) (PVC) plasticized membranes containing uranyl salophene derivatives were presented. The influence of the membrane components (i.e. ionophore structure, dielectric constant and structure of plasticizer, the amount of incorporated ammonium salt) on its phosphate selectivity was investigated. The highest selectivity for H2PO4− over other anions tested was obtained for lipophilic uranyl salophene III (without ortho-substituents) in PVC/o-nitrophenyl octylether (o-NPOE) membrane containing 20 mol% of tetradecylammonium bromide (TDAB). Ion-selective electrodes (ISEs) based on these membranes exhibited linear response in the range 1–4 of pH2PO4− with a slope of 59 mV/decade. The introduction of ortho-methoxy substituents in ionophore structure decreased the phosphate selectivity of potentiometric sensors.

Durable phosphate-selective electrodes based on uranyl salophenes

Lipophilic uranyl salophenes derivatives were used as ionophores in durable phosphate-selective electrodes. The influence of the ionophore structure and membrane composition (polarity of plasticizer, the amount of incorporated ionic sites) on the electrode selectivity and long-term stability were studied. The highest selectivity for H2PO4− over other anions tested was obtained for lipophilic uranyl salophene III (with t-butyl substituents) in poly(vinylchloride)/o-nitrophenyl octyl ether (PVC/o-NPOE) membrane containing 20 mol% of tetradecylammonium bromide (TDAB). Moreover, phosphate-selective electrodes based on this derivative exhibited the best long-term stability (2 months). The electrode durability can be improved decreasing the amount of the ammonium salt in membrane to 5 mol%.

Ag+ labeling: a convenient new tool for the characterization of hydrogen-bonded supramolecular assemblies by MALDI-TOF mass spectrometry

Herein we describe our results on the characterization of a wide variety of different hydrogen-bonded assemblies by means of a novel matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) technique with Ag+ labeling. The labeling technique with Ag+ ions is extremely mild and provides a nondestructive way to generate charged assemblies that can be detected by mass spectrometry. Up to now more than 25 different single (1(3).2(3)), double (3(3).2(6)), and tetrarosettes (4(3).2(12)) have been successfully characterized by the use of this method. The success of the method entirely depends on the presence of a suitable binding site for the Ag+ ion. A variety of functionalities has been identified that provide strong binding sites for Ag+, either acting in a cooperative way (pi-arene and pi-alkene donor functionalities) or individually (cyano and crown ether functionalities). The method works well for assemblies with molecular weights between 2,000 and 8,000 Da, and most likely far beyond this limit.

Photophysical studies of m-terphenyl-sensitized visible and near-infrared emission from organic 1:1 lanthanide ion complexes in methanol solutions

The luminescence properties of several 11 lanthanide ion (Sm3+, Tb3+, Dy3+, Pr3+, Nd3+, Ho3+, Tm3+ and Yb3+) complexes based on the m-terphenyl-containing ligands 1–3 have been studied in methanol solutions. The organic complexes show their typical luminescence in the visible (Sm3+, Tb3+, Dy3+ and Pr3+) and in the near-infrared (Nd3+, Er3+ and Yb3+) region of the electromagnetic spectrum. The degree of shielding of the lanthanide ions from high-energy quenching modes of the solvent by the acyclic ligand 3 is less than the shielding by the macrocyclic ligands 1 and 2.Not only the high-energy vibrational modes of the solvent quench the luminescent state, but also the C–H modes of the organic ligand, and even O–D and C–D modes can contribute significantly to the quenching. In general, the high-energy vibrational O–H and C–H modes are most efficient in luminescence quenching, but the quenching is strongly dependent on the magnitude of the energy gap between the lowest luminescent state and a lower-lying state. Luminescence at longer wavelengths can be quenched relatively easily because of the smaller energy gaps, rendering all quenching pathways, especially quenching by the remaining C–H modes in the partially deuterated ligand, efficient. When the energy gap is resonant with (an overtone of) a vibrational mode, i.e. O–H, C–H, O–D or C–D, the luminescence is very efficiently quenched by these modes and can even be extinguished. For instance: Ho3+ luminescence was not observed because the 5S25F5 transition is resonant with the C–H vibrational mode, deuteration is less effective than expected for Pr3+ because the energy gap is resonant with the first overtone of the C–D vibration, and Nd3+ is efficiently quenched by the deuterated solvent because the energy gap is resonant with the first overtone of the O–D vibration.

H2PO4 -selective CHEMFETs with uranyl salophene receptors

Abstract Chemically modified field effect transistors (CHEMFETs) with ion-selective membranes which incorporate lipophilic uranyl salophene derivatives exhibit H2PO−4 selectivities strongly deviating from the Hofmeister series. Selectivity is obtained over much more lipophilic anions such as NO−3 ( log K Pot H 2 PO 4 , NO 3 =−1.3 ) and Cl− ( log K Pot H 2 PO 4 , Cl =−1.8 ). Modification of the uranyl salophene derivatives with additional hydrogen bond accepting methoxy substituents results in lowered detection limits and an improved selectivity over Cl−, Br−, SO2−4 and OH−.

Molecular Recognition of Carbonyl Compounds by Uranyl-salophen Based Neutral Receptors Driven by Van Der Waals Forces

The complexation of the salophen-uranyl metallocleft 2 and of its half-cleft analogue 3 with enones and other carbonyl compounds was assessed in chloroform by UV-Vis titration and, occasionally, by FT-IR measurements. Complexes with receptors 2 and 3 are in all cases more stable than those with the control unsubstituted uranyl-salophen 1 , showing that in addition to the primary binding force provided by coordination of the carbonyl oxygen to the uranium, a significant driving force for complexation, typically in the range of 2-3 kcal/mol, results from van der Waals interactions of the guest with the aromatic walls. Replacement of the phenyl group in 3 with larger aromatic residues to give 4 and 5 , led to enhanced complex stabilities, due to more extended contact surfaces between host and guest.

Covalent capture of dynamic hydrogen-bonded assemblies

Covalent linkage of the three calix[4]arene units in hydrogen-bonded assemblies 13(DEB)6via a threefold ring closing metathesis (RCM) reaction quantitatively converts the dynamic assemblies into covalent systems (123-membered macrocycles) that can be easily characterized using MALDI-TOF MS and HPLC.

High hyperpolarizabilities of donor-p-acceptor-functionalized calix[4]arene derivatives by pre-organization of chromophores

A systematic investigation of the conceptofpre-organization of nonlinear optical (NLO) active chromophoric groups in calix[4]arene derivatives and the influence on the absolute second-order nonlinear optical coefficients is reported. Several calix[4]arenes were synthesized by modification of the electron-withdrawing groups at the upper rim of the aromatic and extension of the conjugated system of the pre-organized chromophoric groups. Electrical field induced second harmonic generation (EFISH) experiments showed high (0) values up to 1165·10-48 esu. Compared with the corresponding reference compounds, enhancements of the (0) values varying up to 2.5 times per chromophore were observed which proves the benefit of pre-organization of NLO-active units in a multi-chromophoric system. Another important advantage is that the increase in NLO activity observed for these systems is not accompanied with a shift of the absorption band to longer wavelengths exceeding 20 nm. This makes these calix[4]arene derivatives promising building blocks for the development of stable, NLO-active materials that are suitable for frequency doubling.

Durability of phosphate-selective CHEMFETs

Lipophilic uranyl salophenes derivatives I and II were used as ionophores in membranes of phosphate-selective CHEMFETs. High selectivity for H2PO4− over other anions was obtained for these sensors. The influence of the ionophore structure on the sensor durability was investigated. CHEMFETs based on derivative II exhibited better long-term stability due to the better solvation of this ionophore in the membrane phase. The microsensor durability can be improved decreasing the amount of the ammonium salt in the membrane to 5% mol, with only little decrease of initial selectivity.

Chemically modified field effect transistors with nitrite or fluoride selectivity

Polysiloxanes with different types of polar substituents are excellent membrane materials for nitrite and fluoride selective chemically modified field effect transistors (CHEMFETs). Nitrite selectivity has been introduced by incorporation of a cobalt porphyrin into the membrane; fluoride selectivity has been obtained with a uranyl salophen derivative as the anion receptor. Polysiloxanes with acetylphenoxypropyl or phenylsulfonylpropyl substituents are the best sensing membranes. The nitrite selective CHEMFETs exhibit Nernstian responses and a high selectivity over chloride and bromide (log KPotNO2,j = –2.9 and –2.7 respectively, based on a phenylsulfonylpropyl functionalized polysiloxane). Also the sensitivity and selectivity of the fluoride selective CHEMFETs is better with the polysiloxane membranes than with plasticized PVC membranes. Even in the presence of 0.1 M of the more lipophilic chloride, bromide, or nitrate ions an almost Nernstian response and a detection limit of 0.25 mM is obtained for fluoride (log KF,jPot = –2.5).