Intramolecular Complex Formation Research Articles

Monitoring Antibody Binding Events in Homogeneous Solution by Single-Molecule Fluorescence Spectroscopy

Abstract We demonstrate the potential of modern confocal fluorescence microscopy in combination with quenched peptide-based fluorescence probes for sensitive detection of p53 antibodies directly in homogeneous solution. Single tryptophan (Trp) residues in the sequences of short, synthetic peptide epitopes of the human p53 protein efficiently quench the fluorescence of an oxazine fluorophore attached to the amino terminal ends of the peptides. The fluorescence quenching mechanism is thought to be a photoinduced electron transfer reaction from Trp to the dye enabled by the formation of intramolecular complexes between dye and Trp. Specific recognition of the epitope by the antibody confines the conformational flexibility of the peptide. Consequently, complex formation between dye and Trp is abolished and fluorescence is recovered. Using fluorescence correlation spectroscopy (FCS), antibody binding can be monitored observing simultaneously two parameters: the diffusional mobility of the peptide as well as the quenching amplitude induced by the conformational flexibility of the peptide change significantly upon antibody binding. Furthermore, we demonstrate that the strong fluorescence increase upon binding can also be used to directly detect p53 autoantibodies from human blood serum samples in fluorescence intensity time traces. Our data demonstrate that new refined single-molecule fluorescence techniques in combination with quenched peptide epitopes open new possibilities for the reliable detection of antibody binding events in homogeneous solution.

Self-inclusion properties of C 60-linked calix[5]arene

C 60-linked calix[5]arenes were synthesized and their intramolecular binding properties were investigated. The self-inclusion ratio of the C 60 moiety was determined by using UV–vis spectroscopy, and the ratio depends on chain length, temperature, and solvent. Influence of temperature and solvent was explained by the thermodynamic data of the intramolecular complex formation process.

Prolylpeptide Binding by the Prokaryotic SH3-like Domain of the Diphtheria Toxin Repressor: A Regulatory Switch,

Diphtheria toxin repressor (DtxR) regulates the expression of iron-sensitive genes in Corynebacterium diphtheriae, including the diphtheria toxin gene. DtxR contains an N-terminal metal- and DNA-binding domain that is connected by a proline-rich flexible peptide segment (Pr) to a C-terminal src homology 3 (SH3)-like domain. We determined the solution structure of the intramolecular complex formed between the proline-rich segment and the SH3-like domain by use of NMR spectroscopy. The structure of the intramolecularly bound Pr segment differs from that seen in eukaryotic prolylpeptide-SH3 domain complexes. The prolylpeptide ligand is bound by the SH3-like domain in a deep crevice lined by aliphatic amino acid residues and passes through the binding site twice but does not adopt a polyprolyl type-II helix. NMR studies indicate that this intramolecular complex is present in the apo-state of the repressor. Isothermal equilibrium denaturation studies show that intramolecular complex formation contributes to the stability of the apo-repressor. The binding affinity of synthetic peptides to the SH3-like domain was determined using isothermal titration calorimetry. From the structure and the binding energies, we calculated the enhancement in binding energy for the intramolecular reaction and compared it to the energetics of dimerization. Together, the structural and biophysical studies suggest that the proline-rich peptide segment of DtxR functions as a switch that modulates the activation of repressor activity.

Studies on poly(acrylic acid)/attapulgite superabsorbent composites. II. Swelling behaviors of superabsorbent composites in saline solutions and hydrophilic solvent–water mixtures

AbstractThe effect of the attapulgite content on the swelling for a series of poly(acrylic acid)/attapulgite superabsorbent composites in water was studied. The effects of the temperature and pH values on the water absorbency of the superabsorbent composites were investigated. The swelling behavior of the superabsorbent composites in various saline solutions was also investigated. The water absorbency in various salt solutions decreased with an increase in the ionic strength of the solutions. At a high ionic strength (>1 × 10−3M), the water absorbency in monovalent cationic solutions was higher than that in multivalent cation solutions. This dramatic reduction of the water absorbency in multivalent cationic solutions of high ionic strength may have been due to the complexing ability of the carboxylate groups inducing the formation of intramolecular and intermolecular complexes, which resulted in an increased crosslink density of the network. The swelling behavior of the superabsorbent composites in mixtures of water and hydrophilic solvents, including methanol, acetone, ethanol, and dimethyl sulfoxide (DMSO), was also investigated. The water absorbency decreased with an increase in the concentration of any of the four organic solvents, and two transitions were observed in the superabsorbent composite/hydrophilic solvent–water mixture systems. The main transition for the four hydrophilic solvent–water mixtures was a collapse of the swollen gel (at 50–80% methanol, 30–80% acetone, 50–80% ethanol, and 50–80% DMSO). For the methanol–water system, the magnitudes of the first and second transitions for the poly(acrylic acid)/attapulgite superabsorbent composites containing lower proportions of attapulgite were larger than those for the superabsorbent composites with higher attapulgite contents. The effect of the mixture temperature on the water absorbency of the superabsorbent composites in 10 min was also reported. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1869–1876, 2004

Unprecedented host-induced intramolecular charge-transfer complex formation.

For the first time, host-induced intramolecular charge-transfer complex formation in a guest containing both an electron donor and an electron acceptor is demonstrated in the cucurbit[8]uril cavity, leading to unusual back-folding of the guest molecule.

Face-selective addition to a cation-pi complex of a pyridinium salt: synthesis of chiral 1,4-dihydropyridines.

Selective shielding of one side of the pyridinium face by way of intramolecular cation-pi complex formation enabled nucleophiles to attack only from the non-shielded side, and consequently, chiral 1,4-dihydropyridines were produced stereoselectively with up to 99% de. The structure of the cation-pi complex was elucidated by 1H NMR studies and X-ray analysis.

Intramolecular Complex Formation between Flexible Molecular Tweezers and Weak Electron Acceptor

Intramolecular Complex Formation between Flexible Molecular Tweezers and Weak Electron Acceptor

Complexation in the Nitrolignin-Pectin-Copper Ion System

Potentiometric titration, spectrophotometry, and viscosimetry were used to study complexation of nitrolignin macromolecules, pectin, and their mixture with copper ions. The salt mechanism of formation of intramolecular polymer-metal complexes was established. Stability constants and extinction coefficients of the complexes were measured.

Sandwich-Type Complexes of Alkaline-Earth Metal Cations with a Bisstyryl Dye Containing Two Crown Ether Units

The formation of complexes between a bisstyryl dye containing two benzo-15-crown-5 ether groups, 2, and Mg2+, Ca2+, Sr2+, and Ba2+ ions was studied in acetonitrile solution by using a spectrophotometric approach. In contrast to its monostyryl analogue 1, which shows a rather low cation-binding selectivity, the bisstyryl dye 2 selectively binds the Sr2+ and Ba2+ ions because of formation of intramolecular sandwich complexes. Alkaline-earth metal cations induce substantial blue shifts of the absorption maximum of 1 and 2, particularly in the case of sandwich complex formation. The emission behavior of 1 and 2 and their Ba2+ complexes in acetonitrile solution has also been studied. In both cases, complex formation leads to a blue shift of the fluorescence maximum and a decrease in the emission quantum yield. The fluorescence decay is monoexponential for the complex of 1 and biexponential for that of 2. The longer-lived fluorescence component, which corresponds to the lower-energy band in the steady-state spectrum, is assigned to an intramolecular excimer state.

A new class of poly(1,6-heptadiyne)-based photorefractive materials by metathesis polymerization

We utilized the first metathesis reaction to synthesize a new type of photorefractive polymers that contain both a carbazole moiety as a hole transporter and NLO chromophores. These polymers have a long tail band at above 700 nm, indicating the formation of intramolecular charge transfer complexes between the carbazole groups and the conjugated double bonds in the polymer backbone. Also, these polymers show two maximum values of photocurrent around 350 and 700 nm. The electro-optic coefficient (r 33 ) at the wavelength of 1.3 μm for polymer thin films poled around the 85°C were in the range of 1.6 ∼6.3 pm/V The hyperpolarizabilities, , of the resulting polymers were ca. 2.9 x 10 -32 esu. at the incident wavelength of 1.907 μm.

Intramolecular Complex Formation and Triplet Energy Transfer in Polynorbornenes Incorporating Benzophenone

The photophysical properties of homopolymers (2) and block copolymers (3) prepared by ring-opening metathesis polymerization of norbornenes substituted with benzophenone, naphthalene, and phenanthrene groups (1) have been investigated. When benzophenone is attached to this polynorbornene backbone, its excited state behavior differs from that observed for monomeric benzophenone. A new intramolecular excited state complex can be observed in the transient absorption and emission measurements of the benzophenone-substituted homopolymer. In copolymers bearing benzophenone and naphthalene or phenanthrene substituent blocks, triplet energy transfer from the sensitizer (benzophenone) to the arene is observed. This energy transfer dominates over the intramolecular complexation that characterizes group interactions in the homopolymer. 41 refs., 14 figs., 7 tabs.

Association of Amino-Terminated Polystyrenes. 3. Trifunctional Star Polymers

Amino-terminated three-armed polystyrene stars of narrow molecular weight distribution were prepared by anionic polymerization. The association of these star polymers with a low molecular weight dinitrophenol compound was studied by means of light scattering and ultraviolet−visible spectroscopy in the good solvent 1,4-dioxane and in the ϑ solvent diethyl malonate. The concentration dependence of the scattered intensity was used to derive the increase in weight average molecular weights of the associates Mw(c) where a correction was applied that allowed the separation of the influence of repulsion forces. The experimental molecular weights were found to be smaller than predicted by the Flory−Stockmayer branching theory. Deviations are stronger for star polymers of low molecular weight, which is explained by intramolecular complex formation. No substantial difference was detected between the association in good and ϑ solvents. Gel formation did not occur, and reasons are discussed.

Thermochemistry of heteroatomic compounds. Part 6. Enthalpy of solvation and complex formation of some halides of three-coordinated phosphorus compounds in pyridine

Using previously published values of the enthalpies of solvation of some derivatives of three-coordinated phosphorus compounds, the contributions of the non-specific solvation enthalpies in the general solvation effect in benzene, p-xylene, methanol and pyridine have been calculated. Taking into account the known possibility of intramolecular complex formation between halogenated derivatives of P III and pyridine, the magnitudes of specific interaction enthalpies for PCl 3, PBr 3, (EtO) 2PCl, ▪ PCl and ▪ PBr were determinated. Thermodynamic parameters of complex formation between cyclic chlorophosphites and 1-dimethylamino-3,3-dimethyl-propan-2-one have been obtained and are discussed.

Potential formation of intramolecular inclusion complexes in peptido-cyclodextrins as evidenced by NMR spectroscopy

Investigations of the structure of β- and γ-cyclodextrin derivatives in solution obtained by grafting amino acids or peptides are presented. These compounds are models for vectorization-dedicated molecular carriers. It is shown that for some amino acids, strong intramolecular self inclusion complexes are formed in aqueous solution. This process strongly depends upon the nature and position of the pertinent amino acid in the peptide sequence. Two dimensional NMR experiments are used in conjunction with competition with external guests to evidence and estimate the strength of these auto-inclusion complexes.

Transanular Interactions in Difunctional Medium Rings, 6. Spectroscopic Investigations of Bicyclic Amino Ketones

The endo‐7‐(aminomethyl)bicyclo[3.3.1]nonan‐3‐ones 1–4 with a primary, secondary, or tertiary amino group have been synthesized, and their tendency to form the corresponding tricyclic amino carbinols has been investigated by theoretical (MMX, AM1) and experimental (PE, 13C‐NMR spectroscopy) methods. Comparison of the characteristic spectroscopic properties of 1–4 with those of the isochromophoric monofunctional compounds 7–11 indicates that 1 and 2 form mixtures with the tricyclic isomers 5 and 6, respectively, whereas 3 and 4 show no interactions between the amino and the carbonyl group in the solely present bicyclic structures.

Transanular Interactions in Difunctional Medium Rings, 5. Spectroscopic Investigations of Bicyclic Boraamines

AbstractThe endo‐7‐[(dialkylamino)methyl]‐3‐borabicyclo[3.3.1]nonanes 1 and 2 have been synthesized and their intramolecular complex formation of the corresponding 2‐azonia‐1‐boratatricyclo[4.3.1.14,8]undecanes 3 and 4 has been studied in the gas phase by UV photoelectron spectroscopy and in solution by 11‐NMR spectroscopy. Deviations of the characteristic spectral features from those of the monofunctional bicyclic boranes 5 and amines 6 and 7 indicate that in the gas phase the (dimethylamino)boranes with a B‐alkyl substituent adopt the tricyclic form 3a–c whereas the diethylamino and the B‐methoxy derivatives 1e and 2 prefer the bicyclic structure. In solution some deviations from this behavior are observed.

Inter- versus intramolecular cyclobutadiene complex formation in the reaction of 1,6-cyclodecadiyne derivatives with (.eta.5-Me5C5)Co(C2H4)2

The synthesis of dispiro[2.4.2.4]tetradern-5,12-diyne has been accomplished. X-ray investigations conducted on single crystals of 12 reveal a chair-like 10-membered ring system with a distance of 3.003 œ1 between the triple bonds. In the case of Cp ≡ 8Co(C 2 H 4 ) 2 , an intermolecular reaction occurs exclusively, leading to a new superphane of the cyclobutadiene type stabilized by Cp ≡ 8Co moieties.

1,2-Bis(azacrown)ethanes: Effect of Bridge Substitution and Ring Size on Formation of Sandwich Complexes with Sodium and Potassium Ions

The title problem was investigated potentiometrically using four homologous series of bis(azacrown)s I-IV. A surprisingly large destabilizing effect of bridge substituent was found in the intramolecular sandwich complex formation and ascribed to symmetry violation.

Complex Formation of Poly(acrylic acid) with Mg, Mn, and Pb Ions in Dioxane-Water Mixed Solvents

Abstract Equilibria between poly(acrylic acid) and Mg(II), Mn(II) and Pb(II) ions have been investigated at 25 °C by means of potentiometric and viscometric titrations in dioxane-water mixed solvents containing 0.1 mol dm−3 added salt to maintain a constant ionic strength. The stability constant for the complex formation reaction, M2+ + iA− = MAi2−i, and the equilibrium constant for the reaction, M2+ + iHA = MAi2−i + nH+ (HA denotes a carboxyl group) have been evaluated from the data of pH titration. Although the stability constants, β1 and β2, increased with dioxane content in the mixed solvent and depended on the kinds of added salts, the equilibrium constants, B1 and B2, were almost independent of both factors. The values of B1 for Mg, Mn, and Pb monocarboxylate complexes were 10−3.1, 10−2.5, and 10−1.0 and those of B2 for Mg, Mn, and Pb dicarboxylate complexes were 10−7.6, 10−5.7 and 10−2.1, respectively. From the data of viscometric titrations of poly(acrylic acid) solutions containing Pb(II) ion, it is considered that the contraction of polymer coil is caused by the intramolecular complex formation with two remote carboxylate groups in the range of low degree of neutralization (α′). As α′ increases, the complex is transformed into another form which consists of two adjacent carboxylate groups.

Interactions between betaine-type zwitterionic and anionic surfactants in mixed micelles

The interaction between zwitterionic and anionic mixed surfactants has been investigated by means of surface tension, static and dynamic light-scattering, {sup 1}H NMR spectroscopy, rheological measurement, and probing methods. These systems are N-alkyl-N,N-dimethylbetaine (C{sub 12},DNB; C{sub 14}, TNB) and sodium dodecyl sulfate (SDS) in the presence of 0.01 mol dm{sup {minus}3} NaCl. These systems show a composition dependency in micellar properties. When the molar fraction of DNB and TNB is about 0.6, the cmc values of these systems exhibit minima, whereas the solubilized amount of water-insoluble dye, viscosity, and NMR line widths show maxima. Furthermore, the size of a micelle is found to increase at the same fraction. The viscosity displays a Newtonian flow at all compositions for the DNB-SDS system, while a strong shear dependence is observed at a certain composition for the TNB-SDS system where a sphere-rod transition would occur in micellar shape due to the formation of intramolecular complexes by the electrostatic interaction of oppositely charged head groups between TNB and SDS.