Intramolecular Ion Pair Research Articles

Photorefractivity in Nematic Liquid Crystals Containing Electron Donor−Acceptor Molecules That Undergo Intramolecular Charge Separation

We report photorefractivity in nematic liquid crystals doped with electron donor-acceptor molecules that undergo intramolecular photoinduced charge separation. We show that subsequent intermolecular electron transfer from the intramolecular ion pairs to neutral donor-acceptor molecules is responsible for the charge migration over macroscopic distances that is required to produce photorefractivity. The results are compared to nematic liquid crystals doped with identical unlinked donors and acceptors that can achieve charge separation only through intermolecular electron transfer. We find that the liquid crystals doped with molecules that first undergo intramolecular charge separation exhibit superior photorefractivity when compared to the same liquid crystals doped with unlinked donors and acceptors. The differing mechanisms for charge generation and charge transport in these liquid crystal composites are analyzed. 43 refs., 7 figs., 2 tabs.

Triple helical structures involving inosine: there is a penalty for promiscuity.

Inosine has the ability to act as a "wild-card" binding nonspecifically to both A.T and G.C base pairs. This has obvious implications for the design of oligonucleotide site-directed probes. In this paper we present a series of oligonucleotides with a 5'pur9-pyr9-pyr9 motif which are designed to fold up sequentially into intramolecular triple helices. One or more inosines are incorporated into the Hoogsteen strands in place of T's and/or C's. Once folded into the triplex, the inosine-containing third strand is incorporated in parallel orientation to the purine strand of the duplex. The influence of inosine on the triplex-duplex equilibrium, characterized by the melting temperature (Tm) and on the phase boundaries, as a function of pH and/or ionic strength, has been assessed by means of UV and CD spectroscopy. There are two distinguishable influences of third-strand inosines which affect binding, namely, backbone distortion due to bulkiness (I for T and I for C+) and/or loss of intramolecular ion pairs between protonated cytosines and the backbone phosphates (I for C+). A single thymine replacement drops the Tm by 25.0 (+/- 2.1) degrees C, and replacing a single protonated cytosine drops the Tm by 32.1 (+/- 1.0) degrees C at pH 6.0. On introducing two inosines in place of thymines, the Tm at pH 6.0 of the triple helix to hairpin transition is lowered by 35.5 (+/- 1.4) degrees C; on introducing two inosines in place of cytosines, the Tm drops by 44.5 (+/- 1.0) degree C, and on replacing a cytosine and a neighboring thymine with inosines, the Tm of the same transition is lowered by 29.2 (+/- 1.6) degrees C. Replacing more than two thymines or cytosines, respectively, eliminates the binding of the Hoogsteen strand at room temperature altogether. Under no circumstances does inosine replacement stabilize the triplex helix: it is a poor substitute and its role as a wild-card is limited.

Schiff bases formed between pyridoxal 5′-phosphate and Amino-β-cyclodextrins: Intramolecular remote ion pair interactions of the phosphate with ammonium moieties

Abstract Equilibria involved in the Schiff base formations of pyridoxal 5′-phosphate (PLP) and 5′-deoxypyridoxal with mono-, di-, and peraminocyclodextrins have been studied to determine equilibrium binding constants in aqueous media at several pH values. These results, as well as the circular dichroism study, show that remote electrostatic interactions between the negatively charged 5′-phosphate group and a second ammonium group on the cyclodextrins play a significant role in the complexation.

The rational design and application of new chiral phosphonates for the enantiomeric excess determination of unprotected amino acids. Remarkable pH dependency of the diastereomeric shift differences.

Diastereomeric amide derivatives of chiral phosphorinane 8 and unprotected amino acids are easily prepared in aqueous solutions, showing well separated signals in the 31P NMR spectra allowing accurate enantiomeric excess determination. Moreover, the obtained diastereomeric shift dispersion appears to be highly pH dependent, indicating the influence of intramolecular ion pair formation on the diastereomeric shift dispersion.

Reducing supermolecules to 'pseudo-atoms' and anions: Cryptatium species and C60

Abstract

Thermodynamics of the aggregation phenomenon in associating polymer solutions

The effect of temperature on the extent of aggregation, in dilute solution, of sodium sulfonated polystyrene ionomers in xylene has been determined by using small-angle neutron scattering (SANS). The data are described by using the open association model in which it is assumed that an equilibrium is eventually formed between single chains and aggregates of all sizes. The extent of aggregation was found to be temperature independent which suggests that there is no change in enthalpy on forming aggregates. It was therefore suggested that on aggregation intramolecular ion pair associations are broken and the same number of intermolecular associations formed. Intramolecular ion pair associations in the ionomer solutions were shown to collapse the single-chain radius of gyration (R g ) at infinite dilution to a value less than half the single chain dimension of normal polystyrene in this solvent and also smaller than for polystyrene in θ solvents. The temperature dependence of the second virial coefficient for the ionomers was determined and compared with values for polystyrene. It was also found that 2% by volume of methanol was enough to almost completely solvate all the ionic groups and prevent both inter- and intramolecular ion pair associations in dilute solution. © 1990, American Chemical Society. All rights reserved.

ChemInform Abstract: Charge‐Transfer Interaction Between a Pair of Electronically Excited Moieties: Very Slow Charge Neutralization of Intramolecular Ion Pairs Formed by Biphotonic Excitation of Diarylmethanes

ChemInformVolume 20, Issue 8 Physical Organic Chemistry ChemInform Abstract: Charge-Transfer Interaction Between a Pair of Electronically Excited Moieties: Very Slow Charge Neutralization of Intramolecular Ion Pairs Formed by Biphotonic Excitation of Diarylmethanes S. H. MODIANO, S. H. MODIANO Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this authorR. J. LOCKE, R. J. LOCKE Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this authorE. C. LIM, E. C. LIM Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this author S. H. MODIANO, S. H. MODIANO Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this authorR. J. LOCKE, R. J. LOCKE Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this authorE. C. LIM, E. C. LIM Dep. Chem., Wayne State Univ., Detroit, MI 48202, USASearch for more papers by this author First published: February 21, 1989 https://doi.org/10.1002/chin.198908045Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume20, Issue8February 21, 1989 RelatedInformation

The bell-shaped energy gap dependence of the charge recombination reaction of geminate radical ion pairs produced by fluorescence quenching reaction in acetonitrile solution

In view of the theoretical prediction that the observation of the inverted region in the photoinduced charge separation will be difficult, as it is actually the case in the fluorescence quenching reaction, but the charge recombination of the produced geminate ion pair will show a clear-cut bell-shaped energy gap dependence, we have made systematic studies on the charge recombination processes of geminate ion pairs by directly observing their dynamics with ultrafast laser spectroscopy. We have obtained not only the results for the inverted region, but also the results for the top region as well as normal region, confirming the bell-shaped energy gap dependence of the charge recombination. On the basis of this result, some discussions on the nature of the inter- and intra-molecular ion pairs with respect to the charge recombination processes have been given in the case of some typical exciplexes and porphyrin-quinone systems.

Charge transfer interaction between a pair of electronically excited moieties: Very slow charge neutralization of intramolecular ion pairs formed by biphotonic excitation of diarylmethanes

It is shown that biphotonic excitation of diarylmethanes leads to the formation of ion pairs with extremely long time scale of charge recombination.

Modeling of calcium-induced solubility profiles of casein for biotechnology: Influence of primary structure and posttranslational modification

Molecular biology holds the promise of new tools for the food industry which include proteins with tailor-made functionality. Without a fundamental knowledge of the molecular bases of these properties, implementation will be strictly empirical. For example, the phenomena of salt-induced precipitation of proteins (salting-out) and their resolubilization (salting-in) has heretofore been discussed only qualitatively. A quantitative method, using Wyman's theory of thermodynamic linkage, has been developed and tested on the calcium-induced solubility profiles of the major milk proteins, the caseins. Salting-out was described by a salt-binding constant,k1, andn, the number of moles of salt bound; salting-in was described by the corresponding termsk2 andm. The magnitude of these parameters indicated involvement of protein phosphate groups in binding and precipitation, but enzymatic dephosphorylation showed significant increases ink1 andk2 indicating involvement of carboxylate groups as well. Studies on two genetic variants of αs1-casein indicated the importance of a hydrophobically stabilized intramolecular ion pair in the functionality of the protein. These studies have led to a fuller understanding of the molecular basis for the solubility behavior of caseins and have laid the groundwork for future computer simulation of food protein functionality.

Picosecond time-resolved transient absorption spectral studies of ω-(1-pyrenyl)-α-N,N-dimethylaminoalkanes in acetonitrile

Intramolecular photoinduced electron transfer (ET) and the recombination deactivation of the produced intramolecular ion pair state of (CH 3) 2N(CH 2) n (1-pyrenyl) (1Py nNM; with n = 3,4) in acetonitrile have been studied by means of picosecond laser spectroscopy. The photoinduced ET process was much slower and the recombination deactivation of the ion pair state was much faster in the case of 1Py 3NM in acetonitrile compared with those of p-(CH 3) 2NC 6H 4(CH 2) 3 (1-pyrenyl (P 3), respectively.

Synthesis of chromogenic crown ethers and liquid—liquid extraction of alkaline earth metal ions

New crown ether dyes carrying two pendent anionic side-arms were synthesized for the extraction-spectrophotometry of alkaline earth metal ions. In the extraction of alkaline earth metal ions by these dianionic reagents, size recognition by the crown ether ring was more remarkable than in the case of alkali metal ion extraction by a similar type of monoanionic reagents. Dramatic changes in metal selectivity were observed when the nature of the anionic side-arm was changed while the crown ether skeleton was kept the same. The structure/selectivity relationship is discussed in terms of “chelate” and “intramolecular ion-pair” formation. Typically, when the basicity of the pendent anions was relatively high and a six-membered chelate was structurally possible for the pendent anions and the crown-bound metal, the extraction of calcium was favored by up to a factor of 3000 in the ratio of the Ca/Ba extraction constants for reagents of the diaza-18-crown-6 type. In contrast, the reagents which had pendent anions with only poor coordination ability for metal ions seemed to form complexes of the ion-pair type, and calcium ion was 10 5 times less extractable than barium ion for the same diaza-18-crown-6-skeleton. Strontium ion seemed to be extracted most effectively when the extracted complex assumed properties intermediate between the chelate and intramolecular ion-pair.

Lariat ethers: from cation complexation to supramolecular assemblies

Abstract

Sn .rarw. S1 absorption spectra of 4-(N,N-dimethylamino)benzonitrile in various solvents: confirmation of the intramolecular ion pair state in polar solvent

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTSn .rarw. S1 absorption spectra of 4-(N,N-dimethylamino)benzonitrile in various solvents: confirmation of the intramolecular ion pair state in polar solventTadashi. Okada, Noboru. Mataga, and Wolfram. BaumannCite this: J. Phys. Chem. 1987, 91, 4, 760–762Publication Date (Print):February 1, 1987Publication History Published online1 May 2002Published inissue 1 February 1987https://doi.org/10.1021/j100288a004RIGHTS & PERMISSIONSArticle Views274Altmetric-Citations67LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (372 KB) Get e-Alerts

Peptide models of electrostatic interactions in proteins: NMR studies on two beta-turn tetrapeptides containing Asp-His and Asp-Lys salt bridges.

Two model peptides Boc-Asp-Pro-Aib-X-NHMe [X = His (1) and X = Lys (2)] were synthesized to simulate intramolecular electrostatic interactions between ionizable side chains. Conformational analysis by 270-MHz 1H NMR in (CD3)2SO reveals that the backbone secondary structures of these two peptides are stabilized by two strong intramolecular hydrogen bonds, involving the consecutive carboxy-terminal NH groups. 1H NMR chemical shifts were measured in 1, 2, and a protected derivative, Boc-Asp(OBzl)-Pro-Aib-His-NHMe (3). These shifts were also measured for the model compounds Ac-Lys-NHMe, Boc-Asp-NHMe, and Boc-His-NHMe in their different states of ionization. An analysis of the chemical shifts of the ionization-sensitive reporter resonances suggests the formation of a strong intramolecular salt bridge in the lysyl peptide 2 and a bridge of moderate strength in the histidyl peptide 1. A comparison of the temperature dependence of chemical shifts in peptides 1-3 suggests that intramolecular salt bridge formation results in diminished backbone flexibility. The results establish that proximity effects confer far greater stability to intramolecular ion pair interactions vis-a-vis their intermolecular counterparts. The salt bridge interaction in peptide 1 displays a remarkable sensitivity to the dielectric constant of the solvent medium. The results suggest that these peptides are good simulators of the role of salt bridges in the structural dynamics of proteins.

Chelate and intramolecular ion-pair formation: A guiding concept for structure/selectivity relationships in the liquid-liquid extraction of alkali and alkaline earth metal ions by anionic crown ether derivatives

Crown ether dyes with pendent anionic side-arms were synthesized for extractionspectrophotometry of alkali and alkaline earth metal ions. Dramatic changes in metal selectivity were obtained simply by changing the nature of the anionic side-arm on the same crown ether skeleton. A structure/metal selectivity relationship is discussed in detail in terms of “chelate” and “intramolecular ion-pair” formation. Small metal cations (high charge density) are preferred in the extraction by a crown ether reagent with a charge-localized anionic side-arm through the formation of a “chelate”. Large metal cations (low charge density) are preferred in the extraction by reagents with a charge-delocalized anionic side-arm through the formation of an “intramolecular ion-pair”. Steric restrictions imposed by the side-arm on the metal ion approaching the crown ether are also important factor in controlling the selectivity of these reagents.

Photo-Smiles Rearrangement (IV) Electron-Transfer Mechanism of an Intra-Molecular Aromatic Nucleophilic Substitution

The mechanism of the photo-Smiles rearrangement involves formation of an intra-molecular radical ion-pair and a spiro-type Meisenheimer complex. The complete reaction pathways can be qualitatively ...

Liquid chromatographic separation of enantiomeric alkanolamines via diastereomeric tartaric acid monoesters

A new resolution method for the analytical and preparative separation of enantiomeric alkanolamines into their antipodes is presented. It involves formation of the monoesters of the alkanolamines with optically pure and symmetrically O,O- disubstituted ( R,R)- or ( S,S)-tartaric acids. The derivatization reactions are carried out in aprotic media by reaction with the tartaric acid anhydrides. The amine functions are ionically blocked via ion-pair formation with strong acids, e.g. trichloro-acetic acid. The resulting diastereomeric monoesters are easily separable into their antipodes by reversed-phase liquid chromatographic technique. Relative retention factors,α, up to 4 can be obtained, depending on the structural parameters of the alkanolamines and reagents, as well as on the mobile phase conditions (pH). The monoesters are zwitterions, possibly capable of forming intramolecular ion pairs via a ring structure favoured for ethanolamines.

Intramolecular interactions of amino groups in 13C reductively methylated hen egg-white lysozyme.

Reductive methylation of hen egg-white (HEW) lysozyme with [13C]formaldehyde and NaCNBH3 and subsequent 13C NMR spectroscopy reveal resonances for each of the mono- and dimethyl derivatives of the six lysyl epsilon-amino groups and the NH2 terminus. Each resonance has a unique chemical shift, pKa, and chemical shift change upon deprotonation. The assignment of the resonances arising from the N alpha,N-dimethyl and N alpha-monomethyl NH2 terminus has been made as have resonance assignments for the two lysyl residues which crystallographic studies indicate are involved in ion pair interactions (Imoto, T., Johnson, L. N., North, A. C. T., Phillips, D. C., and Rupley, J. A. (1972) in The Enzymes (Boyer, P. D., ed) 3rd Ed, Vol. 7, pp. 665-868, Academic Press, New York). One resonance, tentatively assigned to the lysine 1 (epsilon NH3+) which forms an ion pair with glutamic acid 7 (gamma COO-), has a highly perturbed chemical shift which shows a biphasic titration curve (N epsilon, N-dimethyl pKa values 10.0 and 2.6). A similar titration curve is observed for a N epsilon-monomethyl lysyl residue. The resonance for lysine 13 (epsilon NH3+), which forms an ion pair with the carboxyl terminus, leucine 129 (alpha COO-), has been assigned by removal of leucine 129 with carboxypeptidase whereupon only one pair of mono- and dimethyl lysyl resonances is greatly perturbed. The pKa of N epsilon,N-dimethyl lysine 13 is 9.3 in des-Arg-Leu-lysozyme in contrast to 9.8 for the intact enzyme. Thus, it appears that both of the intramolecular ion pairs predicted by x-ray crystallography exist in the solution structure of HEW lysozyme.

Ion selective extraction of alkali and alkaline earth metal ions by new crown ether reagents

To understand the mechanism of solvent extraction of alkali and alkaline earth metal ions by crown ether-based reagents, [1–3], new chromogenic crown ethers 1 and 2 were synthesized, and their extraction behavior was studied. 1 is insoluble in water, and its 1, 2-dichloroethane solution extracts selectively alkaline earth metal ions, especially calcium, according to the reaction (1). Potassium is partially extracted when present in high concentration. The reagent 2 extracts potassium ▪ X, Y = H, NO 2, Br, OH, picrylamino, chromophoric groups conjugated with dissociable protons. selectively. The table summarizes the constants K ex. The extraction ability of 1 or 2 is generally higher than the reagent 3 or 4 reported earlier. This probably reflects the difference in the mode of extraction. The extraction by the former reagent is based on the intramolecular ion-pair formation, while in the latter the adoption of chelate-type structure t001 Extraction constants; 1, 2-dichloroethane, 25 °C. Mg Ca Sr Ba 1a < 1 × 10 −18 1.0 × 10 −15 6.3 × 10 −18 2.5 × 10 −18 1b « 1 × 10 −16 2.9 × 10 −13 3.1 × 10 −14 7.3 × 10 −16 with less charge separation within the extracted complex facilitates the transfer of the complex into the organic solution. ▪