Encapsulation of divalent tetrahedral oxyanions of sulfur within the rigidified dimeric capsular assembly of a tripodal receptor: first crystallographic evidence of thiosulfate encapsulation within neutral receptor capsule

A simple tris(2-aminoethyl)amine based meta-chloro substituted tripodal thiourea receptor L has been extensively studied with two divalent oxyanions of sulfur, such as sulfate and thiosulfate, with identical dimensionality. The solid state crystal structure of the anion complexes with L reveal that the anions are encapsulated within the dimeric rigid capsular assembly of the receptor via N-Hanion interactions. To the best of our knowledge this is the first report on the encapsulation of thiosulfate within dimeric capsular assembly of a neutral receptor. The tight capsular sizes for both anion complexes are quite comparable, whereas the coordination mode of the anions and the hydrogen bonding parameters are significantly varied. The three dimensional solid state structural orientations of the capsular complexes are mainly governed by the ClCl (for thiosulfate complex) and ClS (for sulfate complex) halogen bonding interactions. The solution-state binding and encapsulation of oxyanions by N-Hanion hydrogen bonding has also been confirmed by quantitative (1)H NMR titration and 2D NOESY NMR experiments. Both the experiments confirm that in contradiction of 2?:?1 solid state binding, in solution the studied anions are bound within the pseudocavity of the receptor with 1?:?1 binding stoichiometry. Moreover, the change in chemical shifts of thiourea -NH protons and the binding constant values suggest the receptor-sulfate interaction is more energetically favorable compared to the receptor thiosulfate interaction.     

Anion binding in the C3v-symmetric cavity of a protonated tripodal amine receptor: potentiometric and single crystal X-ray studies

Tris(2-aminoethyl)amine (tren) based pentafluorophenyl-substituted tripodal L, tris[[(2,3,4,5,6-pentafluorobenzyl)amino]ethyl]amine receptor is synthesized in good yield and characterized by single crystal X-ray diffraction analysis. Detailed structural aspects of binding of different anionic guests toward L in its triprotonated form are examined thoroughly. Crystallographic results show binding of fluoride in the C(3v)-symmetric cavity of [H(3)L](3+) where spherical anion fluoride is in tricoordinated geometry via (N-H)(+)···F interaction in the complex [H(3)L(F)]·[F](2)·2H(2)O, (3). In the case of complexes [H(3)L(OTs)]·[OTs](2), (4) and [H(3)L(OTs)]·[NO(3)]·[OTs], (5), tetrahedral p-toluenesulphonate ion is engulfed in the cavity of [H(3)L](3+) via (N-H)(+)···O interactions. Interestingly, complex [(H(3)L)(2)(SiF(6))]·[BF(4)](4)·CH(3)OH·H(2)O, (6) shows encapsulation of octahedral hexafluorosilicate in the dimeric capsular assembly of two [H(3)L](3+) units, via a number of (N-H)(+)···F interactions. The kinetic parameters of L upon binding with different anions are evaluated using a potentiometric study in solution state. The potentiometric titration experiments in a polar protic methanol/water (1:1 v/v) binary solvent system show high affinity of the receptor toward more basic fluoride and acetate anions, with a lesser affinity for other inorganic anions (e.g., chloride, bromide, nitrate, sulfate, dihydrogenphosphate, and p-toluenesulphonate).     

Anion binding with a tripodal amine

Binding studies of the tren-based amine, L (N,N',N' '-tris(2-benzylaminoethyl)amine), with inorganic anions and two crystal structures, [H(3)L][H(2)PO(4)](3).H(3)PO(4) and [H(3)L][Br](3), are reported. NMR titration results indicate that the ligand binds H(2)PO(4)(-) and HSO(4)(-) more strongly than NO(3)(-) and halides. In the crystal structure of the phosphate complex, the ligand is triprotonated with the three arms pointing outward in a trigonal-planar-like arrangement. Four phosphate species are associated with the receptor, and have been assigned as three H(2)PO(4)(-) counterions located between each of the tren arms, and an additional H(3)PO(4) molecule above the quasi-planar tren. The structure of the bromide complex is slightly different, although again the tren receptor is triprotonated and quasi-planar, but in this case C(2v)-like symmetry is seen with two of the arms pointed in the same direction with a bromide ion in between. The other two bromides lie outside of the tren arms.     

Carbohydrate recognition of symmetrical tripodal receptor type tris(2-aminoethyl)amine derivatives

Carbohydrate recognition of some bioactive symmetrical tripodal receptor type tris(2-aminoethyl)amine (TAEA) derivatives was investigated. In calorimetric experiments, the highest binding constant (Ka) of compound C (C₃₅H₄₉N₅O₄S) with methyl α-d-mannopyranoside was Ka = 858 M^?1 with 1:1 stoichiometry. Formation of hydrogen bonds in binding between symmetrical tripodal receptor type compound C and sugars was suggested by the large negative values of ?H° (=?34 to ?511 kJ mol^?1). In a comparison of each set of α- and β-anomers of some monosaccharides (methyl α/β-d-galactopyranoside, methyl α/β-d-glucopyranoside, and methyl α/β-l-fucopyranoside), compound C showed that the binding constant of β-anomer was larger than that of the corresponding α-anomer, indicating higher β-anomer selectivity. The calculated energy-minimized structure of the complex of compound C with guest methyl α-d-mannopyranoside is also presented. The experimental results obtained from this work indicated that symmetrical tripodal receptor type TAEA derivative C has a lectin-like carbohydrate recognition property.     

Encapsulation of metal cations and anions within the cavity of bis(1,4,7-triazacyclononane) receptors

The synthesis and characterisation of a new bis([9]aneN3) ligand (L4) containing two [9]aneN3 macrocyclic moieties separated by a 2,6-dimethylenepyridine unit is reported. A potentiometric and 1H NMR study in aqueous solution reveals that ligand protonation occurs on the secondary amine groups and does not involve the pyridine nitrogen. The coordination properties toward Cu(II), Zn(II), Cd(II) and Pb(II) were studied by means of potentiometric and UV spectrophotometric measurements. The ligand can form mono- and binuclear complexes in aqueous solution. In the 1 : 1 complexes, the metal is sandwiched between the two [9]aneN3 moieties and the pyridine N-donor is coordinated to the metal, as actually shown by the crystal structure of the compound [ZnL4](NO3)2.CH3NO2. L4 shows a higher binding ability for Cd(II) with respect to Zn(II), probably due to a better fitting of Cd(II) ion inside the cavity generated by the two facing [9]aneN3 units. The formation of binuclear complexes is accompanied by the assembly of OH-bridged M2(OH)x (x = 1-3) clusters inside the cavity defined by the two facing [9]aneN3 units, and pyridine is not involved in metal coordination. A potentiometric and (1)H NMR study on the coordination of halogenide anions by L4 and its structural analogous L3 in which the two [9]aneN3 units are separated by a shorter quinoxaline linkage, shows that bromide is selectively recognised by L4, while chloride is selectively bound by L3. Such a behaviour is discussed in terms of dimensional matching between the spherical anions and the cavities generated by the two [9]aneN3 units of the receptors.     

Primary aliphatic amine complexes of transition-metal halides

The hexakis(methylamine) complexes of nickel(II)-chloride, -bromide and -iodide have been prepared using-gas phase preparation procedure. The thermal decomposition starts with the release of four moles of the organic ligand. The bis(methylamine) intermediate decomposes in one step to the pure nickel(II) halide in the case of the chloride compound, however one and a half moles of methylamine containing intermediates were identified for the bromide and iodide analogues. The UV/VIS and the far IR spectra of the hexakis complexes show a typical octahedral environment around the central nickel(II) ion.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Modeling of drug molecule orientation within a receptor cavity in the BiS algorithm framework

The BiS algorithm is suggested for modeling the drug molecule orientation within a receptor cavity. It is based on the assumption of complementarity of the field created by biologically active compounds and the field of the responsive receptor. The comparison of predicted orientations of various biologically active compounds on the relevant receptors with the data of X-ray structural studies (Protein Data Bank) reveals that the results obtained with this approach surpasses those reported in the literature. The suggested technique made it possible to elucidate the details of the action mechanism of DNA antimetabolites, dihydrofolate reductase inhibitors. The dependence of the activity on the structural parameters of “ligand-receptor” complexes is determined.     

Encapsulation of TCNQ and the acridinium ion within a bisporphyrin cavity: synthesis, structure, and photophysical and HOMO-LUMO-gap-mediated electron-transfer properties

The encapsulation of tetracyanoquinodimethane (TCNQ) and fluorescent probe acridinium ions (AcH(+)) by diethylpyrrole-bridged bisporphyrin (H(4)DEP) was used to investigate the structural and spectroscopic changes within the bisporphyrin cavity upon substrate binding. X-ray diffraction studies of the bisporphyrin host (H(4)DEP) and the encapsulated host-guest complexes (H(4)DEP?TCNQ and [H(4)DEP?AcH]ClO(4)) are reported. Negative and positive shifts of the reduction and oxidation potentials, respectively, indicated that it was difficult to reduce/oxidize the encapsulated complexes. The emission intensities of bisporphyrin, upon excitation at 560?nm, were quenched by about 65?% and 95?% in H(4)DEP?TCNQ and [H(4)DEP?AcH]ClO(4), respectively, owing to photoinduced electron transfer from the excited state of the bisporphyrin to TCNQ/AcH(+); this result was also supported by DFT calculations. Moreover, the fluorescence intensity of encapsulated AcH(+) (excited at 340?nm) was also remarkably quenched compared to the free ions, owing to photoinduced singlet-to-singlet energy transfer from AcH(+) to bisporphyrin. Thus, AcH(+) acted as both an acceptor and a donor, depending on which part of the chromophore was excited in the host-guest complex. The electrochemically evaluated HOMO-LUMO gap was 0.71 and 1.42?eV in H(4)DEP?TCNQ and [H(4)DEP?AcH]ClO(4), respectively, whilst the gap was 2.12?eV in H(4)DEP. The extremely low HOMO-LUMO gap in H(4)DEP?TCNQ led to facile electron transfer from the host to the guest, which was manifested in the lowering of the CN stretching frequency (in the solid state) in the IR spectra, a strong radical signal in the EPR spectra at 77?K, and also the presence of low-energy bands in the UV/Vis spectra (in the solution phase). Such an efficient transfer was only possible when the donor and acceptor moieties were in close proximity to one another.     

Solid,primary aliphatic amine complexes of transition-metal halides

The thermal decomposition characteristics of the ternary mixed, solid, primary aliphatic amine complexes formed with nickel(II) chloride was investigated by a simultaneous TG-DTG-DTA method.The course of the thermal decomposition is described in detail, results thus obtained are compared with the literature data and contradictions are pointed out.In addition to the complexes described in previous papers some new compounds and thermal intermediates have been prepared by solid-gas phase chemisorption and by freezing-out technique. Thermal intermediates containing two-third mole of the ligands, characteristic of the decomposition of pyridine type complexes of transition-metal halides, were identified during the degradation process.

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Zusammenfassung Mittels simultaner TG-DTG-DTA wurden die Merkmale der thermischen Zersetzung von Nickel(II)-komplexen mit gemischten ternären, festen und primären aliphatischen Aminen untersucht.Der Reaktionsweg der thermischen Zersetzung wird eingehend beschrieben, die so erhaltenen Ergebnisse wurden mit Literaturangaben verglichen und auf Widersprüche hingewiesen.Zusätzlich zu den in vorangehenden Arbeiten beschriebenen Komplexen wurden mittels Feststoff-Gasphasen Chemisorption und Ausfrierungstechnik einige neue Verbindungen und Thermoindermediäre hergestellt. Während des Abbauprozesses wurden Thermointermediäre mit zwei Drittel Mol Liganden beobachtet, die charakteristich für die Zersetzung der Pyridinkomplexe von Übergangsmetallhalogeniden si

     

Chromogenic and fluorescent recognition of iodide with a benzimidazole-based tripodal receptor

A novel 1,3,5-substituted triethylbenzene derivative with a 2-aminobenzimidazole moiety as a binding and signaling subunit was synthesized. The sensor was tested in a buffered CH(3)CN/H(2)O (99:1, v/v) solution and found to be selective for iodide as demonstrated by the photophysical properties obtained through UV-vis absorption and fluorescence spectroscopy analyses.     

Synthesis of a novel tripodal receptor based on 1,8-naphthyridine derivatives

<正>A novel tripodal receptor,1,3,5-tri((5,7-dimethyl-1,8-naphthyridin-2-yl-amino)methyl)-2,4,6-triethylbenzene(1) was synthesized from starting materials 2,6-diamino-pyridine(2) and 1,3,5-triethylbenzene(4) by three steps with an overall yield of 25%,and characterized by ESI-MS,FT-IR and ~1H NMR spectra.Additionally,its absorption and emission spectra were investigated.     

Solid,Primary aliphatic amine complexes of transition metal halides

The thermal decomposition of some new primary aliphatic amine RNH₂ (R=methyl-, ethyl-,n-propyl,i-propyl,n-butyl-,i-butyl-,n-amyl-,i-amyl-, cyclohexyl-andi-allyl-) complexes with cadmium(II) chloride, prepared by solid-gas phase chemisorption, have been investigated by simultaneous TG-DTG-DTA. The enthalpy changes during the degradation were followed by DSC. The course of the thermal decomposition is described in detail. The thermal properties observed were compared to the more recently reported nickel(II) analogues. The changes in thermal parameters in the series of cadmium(II) chloride aliphatic amine complexes are discussed on the basis of the inductive releasing effect of the aliphatic chain and the steric hindrance of the ligands. Part I: J. Thermal Anal. 39 (1993) 333.     

Tunable Encapsulation of Proteins within Charged Microgels

The binding of cytochrome c to pH and thermoresponsive colloidal hydrogels was investigated using multiangle light scattering, measuring loading through changes in particle molar mass and root mean square radius. Loosely cross-linked microgels [composed of a random copolymer of N-isopropylacrylamide (NIPAm) and acrylic acid (AAc)] demonstrated a high loading capacity for protein. Encapsulation was dependent on both the charge characteristics of the network and the salinity of the medium. Under favorable binding conditions (neutral pH, low ionic strength), microgels containing the highest studied charge density (30 mol% AAc) were capable of encapsulating greater than 9.7 × 10(5) cytochrome c molecules per particle. Binding resulted in the formation of a polymer-protein complex and condensation of the polymer. Anionic microgels demonstrated a change in density ~20-fold in the presence of oppositely charged proteins. These studies of cytochrome c encapsulation represent a significant step towards direct measurement of encapsulation efficiency in complex media as we pursue responsive nanogels and microgels for the delivery of macromolecular therapeutic agents.     

Encapsulation of Isolated Luminophores within Supramolecular Cages

The sequestration of luminophores within supramolecular polyhedral compartments of a crystalline zeolite‐like hydrogen‐bonded framework illustrates a unique approach to limiting the self‐quenching ordinarily exhibited at the high concentrations achievable in this framework. A range of differently sized luminescent guests, namely coumarin 1, coumarin 4, fluorescein, [Ru(bpy)₃]Cl₂, and rhodamine B, can be encapsulated in amounts of up to one molecule per cage, equivalent to a concentration of 0.175 m , which is significantly higher than the concentration at which aggregation‐induced quenching occurs in other media. The luminescence spectra of the encapsulated guests are consistent with the presence of isolated monomers and the absence of self‐quenching. The emission color of the single crystals can be tuned readily from blue to red through the choice of guest molecules. These observations promise an approach to organic solid‐state lasing compounds if crystals of sufficient size and quality can be prepared.     

Photophysics of a cyanine dye within cyclodextrin cavity

The modulated photophysical and dynamical behavior of a potent anti-tumor photosensitizer 3,3^/-diethyloxadicarbocyanine iodide (DODCI) following host-guest inclusion complex formation with α-, β- and γ-Cyclodextrins (CDs) has been studied using steady-state and time-resolved spectroscopic methods. The cavity size of the CDs (α-CD <β-CD <γ-CD) is argued to play an instrumental role underlying the formation of the host-guest inclusion complex. While negligible interaction with α-CD is found to be succeeded by prominent quenching of monomeric fluorescence of the dye within β-CD and γ-CD with the degree of quenching being greater within γ-CD. The most appealing fact attained from the experimental results is the anticipation of dimer formation of DODCI within the large cavity of γ-CD which can entrap more than one molecule of DODCI. The steady-state results are found to be adequately corroborated by time-resolved fluorescence decay studies. Such encapsulation of the cyanine dye within the carrier cargo can be designed for targeted delivery inside biological systems.     

Lithium cation enhances anion binding in a tripodal phosphine oxide-based ditopic receptor

A tripodal ditopic receptor presents H-bond donors and a phosphine oxide to potential guests. In the idealized binding conformation, an endohedral P=O functionality provides enhanced halide binding in the presence of lithium with the greatest ΔΔG° observed for bromide, while minimal changes in K(a) are observed in the presence of sodium.