Binding Of Mono Research Articles

Binding of Mono- and Dianions within Silver Thiazolylurea Tweezers and Capsules.

A silver thiazolylurea complex, [Ag(TUTh)2]+, has been used as a host species for geometrically differently shaped mono- and dianions: trigonal planar (NO3-), tetrahedral (SO42-), and octahedral (SiF62-). In the presence of nitrate a 1:1 near-planar tweezer host-guest species is formed, with poor binding in solution despite excellent geometric complementarity being found between the host and the anion in the solid state. In the presence of either SO42- or SiF62- a 2:1 host-guest species is formed, whereby the guest is held in a capsulelike arrangement stabilized by an array of eight NH hydrogen-bond donors, as confirmed by X-ray crystallographic studies. Solution studies in DMSO-d6 support the host-guest stoichiometry seen in the solid state. The binding constant between SO42- and [Ag(TUTh)2]+ was calculated to be K21 = 2511 M-2 and was shown to be the dominant species in solution, in excellent agreement with the solid-state studies. However, upon the addition of SiF62- ions different speciation is observed: H2·G (capsule), H·G (tweezer), and H·G2 during the course of the study.

Thermodynamic Insights into the Binding of Mono- and Dicationic Imidazolium Surfactant Ionic Liquids with Methylcellulose in the Diluted Regime.

Alkylimidazolium salts are an important class of ionic liquids (ILs) due to their self-assembly capacity when in solution and due to their potential applications in chemistry and materials science. Therefore, detailed knowledge of the physicochemical properties of this class of ILs and their mixtures with natural polymers is highly desired. This work describes the interactions between a homologous series of mono- (CnMIMBr) and dicationic imidazolium (Cn(MIM)2Br2) ILs with cellulose ethers in aqueous medium. The effects of the alkyl chain length (n = 10, 12, 14, and 16), type, and concentration range of ILs (below and above their cmc) on the binding to methylcellulose (MC) were evaluated. The thermodynamic parameters showed that the interactions are favored by the increase of the IL hydrocarbon chain length, and that the binding of monocationic ILs to MC is driven by entropy. The monocationic ILs bind more effectively on the methoxyl group of MC when compared to dicationic ILs, and this outcome may be rationalized by considering the structural difference between the conventional (CnMIMBr) and the bolaform (Cn(MIM)2Br2) surfactant ILs. The C16MIMBr interacts more strongly with hydroxypropylcellulose when compared to methylcellulose, indicating that the strength of the interaction also depends on the hydrophobicity of the cellulose ethers. Our findings highlight that several parameters should be taken into account when designing new complex formulations.

Exploring the Binding Ability of Polyammonium Hosts for Anionic Substrates: Selective Size-Dependent Recognition of Different Phosphate Anions by Bis-macrocyclic Receptors

Binding of mono-, di-, and triphosphate, adenosine diphosphate (ADP), and adenosine triphosphatase (ATP) with receptors L1-L3, composed of two [9]aneN(3) units separated by a 2,9-dimethylene-1,10-phenanthroline (L1), a 2,6-dimethylenepyridine (L2), or a 2,3-dimethylenequinoxaline (L3) spacer, has been studied by means of potentiometric titrations, (1)H and (31)P NMR measurements in aqueous solutions, and molecular modeling calculations. In the case of inorganic phosphates, the binding properties of the receptors appear to be determined by their geometrical features, in particular the distance between the two [9]aneN(3) units imposed by the spacer separating the two macrocyclic units. While L1 is able to selectively bind triphosphate over di- and monophosphate, L3 selectively coordinates the smaller monophosphate anion. Finally, L2 shows preferential binding of diphosphate. (1)H and (31)P NMR measurements show that the complexes are essentially stabilized by charge-charge and hydrogen-bonding interactions between the anion and the protonated amine groups of the macrocyclic subunits of the receptors. Molecular dynamics simulations suggest that the larger distance between the two macrocyclic units of L1 allows this receptor to form a larger number of hydrogen-bonding contacts with triphosphate, justifying its selectivity toward this anion. Conversely, in the case of L3, the two facing [9]aneN3 units give rise to a cleft of appropriate dimensions where the small monophosphate anion can be conveniently hosted. Considering nucleotide coordination, L1 is a better receptor for ATP and ADP than L2, thanks to the higher ability of phenanthroline to establish stabilizing π stacking and hydrophobic interactions with the adenine units of the guests.

ChemInform Abstract: Novel Macrocycles with 1,1′-Binaphthyl Substituents for the Recognition of Saccharides.

Novel saccharide-selective receptors 1 and 2 based on a porphyrin with 1,1′-binaphthyl substituents were synthesized and tested for binding of mono-, di- and tri-saccharides; a binding selectivity for di- and tri-saccharides was found.

New Bis-Cresol-Bridged bis(1,4,7-Triazacyclononane) Ligand As Receptor for Metal Cations and Phosphate Anions

The synthesis and characterization of a new bis([9]aneN3) ligand (H2L) containing two [9]aneN3 macrocyclic moieties separated by a 2,2'-methylene-bis-cresol (cresol = 4-methyl-phenol) unit is reported. A potentiometric and (1)H NMR study in aqueous solution reveals that H2L is in a zwitterionic form, and protonation of the cresolate oxygens occurs only with the formation of the highly charged (H5L)(3+) and (H6L)(4+) species at acidic pH values. The coordination properties of H2L toward Cu(II), Zn(II), Cd(II), and Pb(II) were studied by means of potentiometric and UV spectrophotometric measurements. The ligand gives both mono- and binuclear complexes in aqueous solution. At acidic pH values the ligand forms stable binuclear [M2H2L](4+) complexes, where each metal is coordinated by two amine groups of [9]aneN3 and the deprotonated oxygen of the adjacent cresol unit; the remaining amine group is protonated. Deprotonation of the [M2H2L](4+) species at alkaline pH values affords [M2L](2+) complexes, where all amine groups of the [9]aneN3 moieties are involved in metal coordination. Binding of mono-, di- and triphosphate, and adenosine triphosphate (ATP) was studied by means of potentiometric, (1)H and (31)P NMR measurements and by molecular dynamics simulations. The receptor forms stable 1:1 adducts with di-, triphosphate, and ATP, while the interaction with monophosphate is too low to be detected. In the complexes both the [9]aneN3 moieties act cooperatively in the substrate binding process. The stability of the adducts increases in the order diphosphate < triphosphate < ATP. This trend is explained in terms of increasing number of charge-charge interactions between the phosphate chains and the protonated [9]aneN3 subunits and, in the case of ATP, of stacking interactions between the adenine and cresol units.

Comparison of estimates of free energy for binding of mono- and di-substituted benzenes with α-cyclodextrin obtained by single-step perturbation and thermodynamic integration

In this work, the relative free energies of binding individual members of a series of mono- and di-substituted benzenes to α-cyclodextrin in water have been estimated using the single step perturbation methodology (SSP). The computations involved were based on 5 ns molecular dynamics simulations of a judiciously chosen unphysical reference state and its complex with α-CD in water. The thermodynamic integration method (TI) was also used to calculate the relative free energies of binding for comparison purposes. The results of SSP computations were in good agreement with experimental data. The results also show that the SSP technique exhibits a potential alternative to more traditional but more expensive free energy computational methods.

Photoresponsive synthetic receptors: binding properties and photocontrol of catalytic activity

The photoresponsive ditopic receptors 1a,b bearing two adenine binding sites linked by an azobenzene moiety were prepared. Photochromism, binding of mono- and bis-adenine derivatives and template effects on the coupling reaction of aminoadenosine 2 and the adenosine-derived active ester 3 were studied. Photoswitching of the azobenzene linker from the extended E to the folded Z isomer enhances the catalytic activity of the template 1a by a factor of 50. The binding studies provide evidence for the formation of termolecular complexes 1·2·3 and allow for mechanistic considerations. The influence of various adenine derivatives on the rate of the thermal Z→E isomerization of (Z)-1a, b was evaluated and a significant stabilization of the Z isomers by the bis-adenine guest 4 was observed.

Structural and functional studies on the G(o) protein.

Monoclonal antibodies were raised against purified bovine and human brain G-proteins. The epitopes recognized by three monoclonal antibodies (MONO, 3C2, and 3E7) were mapped by expressing defined parts of the bovine G(o) alpha-cDNA in bacteria, followed by immunoblotting. All three antibodies recognize the recombinant bovine alpha o-protein, but at distinct sites. The epitopes of MONO and 3C2 were mapped between alpha o amino acids 80 and 145, and both antibodies recognize alpha o exclusively. Heterotrimeric G(o)-proteins as well as guanosine 5'-3-O-(thio)triphosphate-liganded free alpha o-subunits are readily immunoprecipitated by these monoclonal antibodies. Binding of MONO or 3C2 does not affect ADP-ribosylation of the alpha o-subunit by pertussis toxin. Apparently, the antibodies do not bind to or induce large conformational changes in regions of the alpha o-subunit that are involved in association with beta gamma-subunits or ADP-ribosylation. 3E7 behaves as an anti common alpha-subunit antibody when used in immunoblots. However, under nondenaturing conditions, 3E7 recognizes alpha o exclusively. After binding of 3E7, the pertussis toxin-dependent ADP-ribosylation of alpha o is effectively blocked, while the ADP-ribosylation of the various alpha i-subunits is not affected. The epitope of 3E7 was mapped between alpha o amino acids 13-88, a region which has been implicated in the interaction between alpha- and beta gamma-subunits. Possibly, the inhibitory effect of 3E7 on ADP-ribosylation of G(o) is secondary to the loss of beta gamma-subunits that is observed upon binding of 3E7.

Characterization of binding sites for oxyntomodulin on a somatostatin-secreting cell line (RIN T3).

Oxyntomodulin (OXM), a glucagon-containing peptide extended at its C-terminal end by an octapeptide, is a potent inhibitor of gastric acid secretion in rat and man. OXM appears to act on gastric mucosa at least partially through a stimulation of gastric somatostatin release. We have investigated the effects of OXM on a somatostatin-secreting cell line (RIN T3) derived from a radiation-induced rat insulinoma and characterized specific binding sites for this peptide. OXM increased somatostatin release with an ED50 of 2.3 nM. OXM also stimulated the cAMP accumulation in intact RIN T3 cells and adenylate cyclase activity in RIN T3 cell membranes with ED50 values of 0.5 and 11 nM, respectively. On these parameters, glucagon was 10-30 times less potent than OXM. Forskolin, isobutylmethylxanthine, and 8-bromo-cAMP mimicked the effect of OXM on somatostatin release. Specific binding for mono-[125I]OXM was dependent upon time and membrane concentration. Binding of mono-[125I]OXM was inhibited by OXM and glucagon in a concentration-dependent manner, with dissociation constants (Kd) of 4.5 and 43 nM, respectively. The nonhydrolyzable analogs of GTP (guanosine 5',3-O-(thio)triphosphate and guanosine 5' (beta,gamma-imino)triphosphate decreased the binding of mono-[125I]OXM to its binding sites. Covalent cross-linking of mono-[125I]OXM or mono-[125I]glucagon to RIN T3 cell membranes followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis demonstrated a single radiolabeled band at 63,000 mol wt, which differed from that observed after cross-linking with liver plasma membranes (55,000 mol wt). These results demonstrate the presence of specific high affinity binding sites for OXM in a somatostatin-secreting cell line (RIN T3) and their coupling to adenylate cyclase via guanine nucleotide-binding proteins.

A human melanoma‐derived cell line (IGR39) with a very high number of vasoactive‐intestinal‐peptide (VIP) receptors

Vasoactive intestinal peptide (VIP) stimulated in a dose-dependent manner the accumulation of cAMP in human melanoma-derived cell line IGR39. The maximal effect (about 100 times the basal level) was observed with 10 nM VIP. Half-maximum cAMP production was obtained at 0.78 nM VIP. VIP-related peptides were also potent in stimulating the cAMP production in IGR39 cells. The order of potency was VIP much greater than peptide histidine-methioninamide greater than human growth-hormone-releasing factor(1-44) greater than secretin greater than glucagon. Using the same conditions, IGR37 cells, a metastasic counterpart of IGR39 cells, displayed a weak stimulation of cAMP production. After exposure of IGR39 cells to 10 nM VIP, the cAMP response to a new stimulation by VIP was strongly reduced. This desensitization of IGR39 cells to VIP was rapid (t1/2 less than 2 min) and homologous. Preincubation of IGR39 cells in the presence of native VIP induced disappearance of the VIP-binding sites at the cell surface. This phenomenon was dependent on time and VIP concentration. Maximum effect (loss of 80% of binding capacity) was obtained after exposure of the cells at 37 degrees C with a VIP concentration of 1 microM. The t1/2 of maximum disappearance was less than 2 min and the concentration of VIP giving half-maximum decrease in binding of mono[125I]iodinated VIP (125I-VIP) was 8 nM. This phenomenon was also reversible since 85% of the VIP-binding capacity could be restored in less than 1 h by incubating IGR39 cells in a VIP-free medium. The IGR39 cell line should be a useful model for further study of the structure and function of the human VIP receptor.

Atrial natriuretic factor receptor on cultured Leydig tumor cells: ligand binding and photoaffinity labeling.

Atrial natriuretic factor (ANF) is a peptide hormone discovered recently from the heart atrium that possesses potent natriuretic and vasorelaxant activities. Recently we found that ANF markedly stimulates intracellular cGMP and almost completely inhibits cAMP accumulation in testicular interstitial tumor cells [Pandey, K. N., Kovacs, W. J., & Inagami, T. (1985) Biochem. Biophys. Res. Commun. 133, 800-806]. These actions of ANF suggest the presence of ANF receptors in testicular interstitial cells. In this study, cultured murine Leydig tumor cells have been shown to contain specific binding sites for ANF. Saturation binding studies indicated a single class of binding sites with a Kd of 5 X 10(-9) M at a density of 2 X 10(6) sites/cell. The binding of mono[125I]iodo-ANF (125I-ANF) was competed by unlabeled ANF in a dose-dependent manner. Hormones unrelated to ANF such as angiotensin I, bovine luteinizing hormone, and human chorionic gonadotropin were not able to compete against 125I-ANF. The binding of 125I-ANF was rapid, reaching maximum levels in 15 min at 4 degrees C. At 37 degrees C, the cell-bound 125I label was quickly decreased. Pretreatment of cells with NH4Cl, chloroquine, or NaN3 resulted in significant increases in maximum levels of the cell-bound 125I radioactivity. A photoaffinity reagent for ANF receptor was prepared by reacting ANF with succinimido 4-azidobenzoate, and resultant 4-azidobenzoyl- (AZB-) ANF was purified by high-performance liquid chromatography (HPLC). AZB-ANF was radioiodinated by use of chloramine T and purified again by HPLC.(ABSTRACT TRUNCATED AT 250 WORDS)

51V-n.m.r. analysis of the binding of vanadium(V) oligoanions to sarcoplasmic reticulum.

The binding of mono- and oligo-vanadates to sarcoplasmic reticulum was analysed by 51V-n.m.r. spectroscopy. The observations indicate that, in addition to monovanadate, the di-, tetra- and deca-vanadates are also bound to sarcoplasmic-reticulum membranes with high affinity. The binding of the vanadate oligoanions may explain some of the effects of vanadates on the conformation and crystallization of Ca2+-transport ATPase.

Calcium ion-selective electrode studies: covalent bonding of organic phosphates and phosphonates to polymer matrices

The covalent linking of organophosphates and phosphonates to the copolymer VAGH (a partially hydrolysed copolymer of vinyl chloride and vinyl acetate) is described along with attempts to phosphonate polystyrene by Friedel - Crafts and free-radical processes. The various products obtained have been evaluated for use in calcium ion-selectiv electrode membranes. The best membranes were all based on VAGH, a product from each type being selected for further study for their calcium ion-sensing qualities, namely, VAGH PI, VAGH PII and VAGH PIII.VAGH PI is based on the covalent bonding of monodecylphosphate to VAGH, while VAGH PII resulted from the binding of mono-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate. Viable electrode membranes required additional poly(vinyl chloride) support and dioctyl phenylphosphonate solvent mediator. VAGH PIII was obtained by a synthesis amounting to covalently binding monooctyl phenylphosphonate to VAGH and was used with some additional dioctyl phenylphosphonate solvent mediator and calcium bis{di-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate} sensor in electrode membranes.The VAGH PI electrode matched those based on equivalent ungrafted didecylphosphate sensors, except that calcium ion selectivity was poor in a high sodium ion background. The VAGH PII electrode, on the other hand, did not fulfil the performance of electrodes based on free calcium bis{di-[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate} as ion sensor, and there was less selectivity for calcium over sodium and magnesium. Some loss of selectivity was also characteristic of the VAGH PIII electrode, but its slightly lengthened lifetime was insufficient to warrant synthesis of the phosphonated polymer matrix.

Direct Evidence of a Glucagon-Dependent Regulation of the Concentration of Glucagon Receptors in the Liver

Chronic treatment with exogenous glucagon in the rat results in a reduced concentration of glucagon receptors in the liver. To determine if this is a direct effect of the hormone on its own receptors, the following experimental model in vilro was designed. Cultured rat hepatocytes were exposed to glucagon at 37°C, washed and incubated with mono[125I]iodoglucagon (125I-glucagon), resulting in reduced binding of 125I-glucagon. The magnitude of the diminution in binding was dependent on the concentration of glucagon present as well as on the duration of the exposure. Analysis of the data indicated that the decrease in binding of 125I-glucagon was due to a loss of receptor numbers per cell rather than any change in receptor affinity for the hormone. Degradation of 125I-glucagon during the incubation of cells in the presence or absence of glucagon was studied and did not account for the differences observed in binding. The binding of mono[125I]iodoinsulin of these cells was not affected by glucagon, suggesting specificity of the phenomenon. Although the cells incubated with glucagon incorporate less L-[14C]valine into hepatocyte proteins, this effect was smaller than the reduction in glucagon receptors. Exposure of the cells to cycloheximide (1 μg/ml) produced a progressive loss of glucagon receptors, and this effect was additive to the glucagon-induced receptor loss. This suggests that cycloheximide inhibited receptor synthesis while glucagon accelerated receptor loss. Glucagon-dependent reduction of glucagon receptors closely correlated with the decreased glucagon-stimulated production of CAMP. Furthermore, epinephrine (0.5 μM) stimulation of cyclic AMP production was similar in hepatocytes previously incubated with or without glucagon, indicating a specific role for glucagon in modifying target-cell sensitivity.

New uranyl(VI) complexes: Binding of mono and bidentate ligands to UO 2(tridentate) species

New species of the type UO 2T·D, UO 2T·D·H 2O and UO 2T·DD are described (T = tridentate dianionic Schiff base ligand; D = monodentate donor e.g., H 2O, dmf, dmso, py etc.; DD = bidentate donor e.g., 2,2′-bipyridyl). The infrared, pmr and thermal analyses data of the complexes are reported. The ν 3 frequency of the dioxouranium(VI) moiety is seen in the region 880–925 cm −1. While this frequency is not very sensitive to the nature of D, on the average ν 3 with D = nitrogen donor is smaller than that with D = oxygen donor. Sufficient solubility for NMR work exists only in strongly donor solvents (py or dmso). In such solutions D is displaced by the solvent. On heating, complexes generally lose H 2O, D or DD in one or more steps endothermically. The DD complexes are particularly stable and loss of DD occurs only at relatively high temperatures. It is proposed that the complexes are generally pentagonal bipyramidal. The five coordination positions on the equator are occupied by the combination of T and D, H 2O or DD. In the case of UO 2TD a dimeric T-bridged structure is likely. The dramatic stereochemical difference between UO 2T·D and MoO 2T·D is noted.

Cation binding to membranes: competition between mono-, di- and trivalent cations.

The binding of mono-, di- and trivalent cations to negatively charged surfaces is studied within the framework of a modified Gouy-Chapman equation. For any given combination of ions of the above valences, the existence and uniqueness of the solution for the surface potential is shown. The treatment provides the surface potential and charge density. For a system containing only monovalent and divalent ions, analytical solutions are given. When trivalent ions are also present, a procedure based on numerical integration is described. The distance dependence of the electrostatic potential for planar surfaces is given. The calculations provide the amount of cations tightly bound and the amount trapped in the double layer region. The competition between cations for binding to surfaces is elucidated.

Binding of Mono‐ and Bis‐N‐substituted Benzoquinolinium Halides to Butyrylcholinesterase: Fluorescence Measurements

The dissociation constants (Kdiss) of mono‐ and bis‐N‐substituted benzoquinolinium salts from butyrylcholinesterase were determined by the disappearance of the fluorescence of the free ligand. The Kdissvalue determined by this method agreed closely with the dissociation constants (KI,s) of the free enzyme obtained by steady‐state kinetic studies. The results indicate that theN‐substituted benzoquinolinium salts with a strong binding ability to butyrylcholinesterase also are potent inhibitors of the esterolytic properties of the enzyme. Enzyme binding is favored by the coplanar structure and does not require a high concentration of charge on the onium function. The shape of the hydrophobic structures markedly influences binding.

Chemical synthesis of branched polysaccharides, 6. Binding of Mono‐, Di‐ and oligosaccharides to various carriers via amide linkage

Chemical synthesis of branched polysaccharides, 6. Binding of Mono‐, Di‐ and oligosaccharides to various carriers via amide linkage