Ionic Hydrogen Bonds Research Articles

Hydrothermal synthesis of a new layered inorganic–organic hybrid cobalt(II) phosphite: (C2H10N2)[Co3(HPO3)4]: Crystal structure and spectroscopic and magnetic properties

The (C2H10N2)[Co3(HPO3)4] phosphite templated by ethylenediamine has been prepared by hydrothermal synthesis. It crystallizes in the triclinic space group P-1 with the parameters: a=5.351(2), b=5.347(4), c=14.010(6) Å, α=80.98(5), β=85.66(4), γ=60.04(4)°, V=343.0(3) Å3 and Z=1. The compound shows a layered structure stacked along the c-axis. The ethylenediammonium cations are placed between the sheets. Ionic interactions and hydrogen bonds are present between the ethylenediammonium cations and the inorganic layers. The layers are formed by Co3O12 trimeric entities which contain face-sharing CoO6 octahedra interconnected by (HPO3)2− tetrahedral phosphite anions. The spectroscopic study by diffuse reflectance allowed us to obtain the Dq=725 cm−1 and the Racah parameters, B=880 and C=3950 cm−1 for the high spin octahedral Co(II) ions. Magnetic measurements reveal the presence of antiferromagnetic exchange interactions in the trimeric units of (C2H10N2)[Co3(HPO3)4].

Phosphorylation disrupts the central helix in Op18/stathmin and suppresses binding to tubulin.

Protein phosphorylation represents a ubiquitous control mechanism in living cells. The structural prerequisites and consequences of this important post-translational modification, however, are poorly understood. Oncoprotein 18/stathmin (Op18) is a globally disordered phosphoprotein that is involved in the regulation of the microtubule (MT) filament system. Here we document that phosphorylation of Ser63, which is located within a helix initiation site in Op18, disrupts the transiently formed amphipathic helix. The phosphoryl group reduces tubulin binding 10-fold and suppresses the MT polymerization inhibition activity of Op18's C-terminal domain. Op18 represents an example where phosphorylation occurs within a regular secondary structural element. Together, our findings have implications for the prediction of phosphorylation sites and give insights into the molecular behavior of a globally disordered protein.

Proton Transfer to CpRuH(CO)(PCy3) Studied by Low-Temperature IR and NMR Spectroscopy

The interaction of the ruthenium hydride complex RuH ≡ CpRuH(CO)(PCy3) (1) with various proton donors AH ≡ CF3CH2OH (2a), (CF3)2CHOH (2b), (CF3)3COH (2c), CF3COOH (2d), and HBF4 (2e) has been studied by variable-temperature IR spectroscopy using hexane and CH2Cl2 as solvents of different polarity. A low-temperature NMR study of the interaction of 1 with 2c was performed using [D8]methylcyclohexane, CD2Cl2, and a liquefied mixture of CDF2Cl/CDF3 (2:1). The first stage of the proton transfer process was found to be the formation of hydrogen-bonded complexes of the type RuH···HA. The hydrogen bonds in these complexes are of medium strength (−ΔH° = 5.3−7.6 kcal mol−1). The second stage is the slow conversion of the H-complex to a dihydrogen complex to which a hydrogen-bonded ion-pair structure [Ru(η2-H2)]+···A− was assigned. The kinetics of this unusually slow proton transfer reaction was monitored in the case of 2c at 200 K in CH2Cl2. Fast protonation of 1 by 2d leads additionally to a species assigned as the free cationic complex [Ru(η2-H2)]+, whose formation is driven by the formation of the homoconjugated anionic complex [AHA]−. At temperatures above 220 K both the hydrogen-bonded ion pair and the free cationic complex easily release dihydrogen, producing RuA.

Infrared spectra of the H-bound and π-bound isomers of the phenol–argon cation

Infrared photodissociation spectra of the phenol–argon cation (Ph +–Ar) are recorded in the vicinity of the O–H stretch vibration ( ν 1) of bare Ph +. Two isomers are identified by their characteristic complexation-induced frequency shifts, Δ ν 1. In H-bound Ph +–Ar, the Ar atom forms an ionic hydrogen bond with the O–H group of Ph + leading to a significant red shift, Δ ν 1∼−70 cm −1. In the π-bound Ph +–Ar isomer, the Ar atom is attached to the π-electron system of Ph +, resulting in a much smaller shift, Δ ν 1∼+2 cm −1. The Ph +–Ar complexes are produced in an electron impact ion source. The relative ν 1 band intensities of both isomers depend strongly on the source conditions and reveal that H-bound Ph +–Ar is the global minimum, while the π-bound structure is a local minimum. Ab initio calculations at the UMP2/6-311G(2df,2pd) level predict binding energies of D e∼660 and ∼400 cm −1 for the H-bound and π-bound minima, with an isomerization barrier of V b∼150 cm −1 from π-bound toward H-bound Ph +–Ar.

The bond properties and electronic structure of uronium sulfate [CO(NH 2) 2H] 2SO 4

A recent crystallographic report on uronium sulfate made studies of its electronic structure possible. The properties of the UV spectrum and photoelectron spectroscopy reveal a novel chemical bonding in this compound. The mechanism of formation, based on the combination of the proton of sulfuric acid with the carbonyl group of the urea molecule, has been established. An ionic bond, coordination bond, conjugate bond, covalent bond, and hydrogen bond are all present in this small molecule. An analysis of its electronic structure and properties is proved to be significant.

Variation in the coordination mode of arenedisulfonates to copper(II): synthesis and structural characterization of six copper(II) arenedisulfonate complexes

Six copper(II) arenedisulfonate complexes with the general formula Cu(N4)(nds/bpds)·nH2O (nds = naphthalenedisulfonate, bpds = biphenyldisulfonate) have been synthesized in aqueous solution and structurally characterized by X-ray single crystal diffraction, IR and UV spectroscopies, TGA and DSC. In Cu(en)2(1,5nds)·2H2O 1, Cu(N-meen)2(2,6nds)·2H2O 2 (N-meen = N-methylethylenediamine), Cu(dpn)2(bpds) 3 (dpn = 2,3-diaminopropane), and Cu(cylam)(1,5nds) 4 the SO3− group coordinates monodentately to the axial position of Cu2+ which is equatorially coordinated by four amino nitrogens. In 1 and 4 intramolecular hydrogen bonds are formed between the SO3− oxygens and amino hydrogens which reinforce interaction between the SO3− group and Cu2+ complex cation. In Cu(dpn)2(1,5nds)·2H2O 5 and Cu(N,N′-meen)2(1,5nds)·3H2O 6 (N,N′-meen = N,N′-dimethylethylenediamine), due to the steric hindrance caused by the methyl substitution of the amino ligands and the rigidity of the naphthalene ring, water molecules, instead of the bulky SO3− group, coordinate to the axial position of Cu2+. Structures 1–4 represent the first synthesis and structural characterization of polymeric 1-dimensional structures constructed by arenedisulfonates and divalent transition metals. Also, 1 crystallizes in the enantiomorphic space group P41212 and displays interesting chiral grids constructed by ionic hydrogen bonds. The coordination geometries of Cu2+, as well as the coordination modes of arenedisulfonates, are discussed in detail.

Structure-based chimeric enzymes as an alternative to directed enzyme evolution: phytase as a test case

Thermostability is a key feature for commercially attractive variants of the fungal enzyme phytase. In an initial set of experiments, we restored ionic interactions and hydrogen bonds on the surface of Aspergillus terreus phytase, which are present in the homologous but more thermostable enzyme from A. niger. Since these mutations turned out to be neutral, we replaced — in the same region and based on the crystal structure of A. niger phytase — entire secondary structure elements. The replacement of one α-helix on the surface of A. terreus phytase by the corresponding stretch of A. niger phytase resulted in an enzyme with improved thermostability and unaltered enzymatic activity. Surprisingly, the thermostability of this hybrid protein was very similar to that of A. niger phytase, although the fusion protein contained only a 31 amino acid stretch of the more stable parent enzyme. This report provides evidence that structure-based chimeric enzymes can be used to exploit the evolutionary information within a sequence alignment. We propose this method as an alternative to directed enzyme evolution if due to expression constraints the screening of large mutant populations is not feasible.

Hydrogen/Deuterium-Isotope Effects on NMR Chemical Shifts and Symmetry of Homoconjugated Hydrogen-Bonded Ions in Polar Solution

ADVERTISEMENT RETURN TO ISSUEPREVCommunicationNEXTHydrogen/Deuterium-Isotope Effects on NMR Chemical Shifts and Symmetry of Homoconjugated Hydrogen-Bonded Ions in Polar SolutionParwin Schah-Mohammedi, Ilja G. Shenderovich, Carsten Detering, Hans-Heinrich Limbach, Peter M. Tolstoy, Sergei N. Smirnov, Gleb S. Denisov, and Nikolai S. GolubevView Author Information Institut für Chemie der Freien Universität Berlin Takustrasse 3, D-14195, Berlin, Germany Institute of Physics, St. Petersburg State University 198904 St. Petersburg, Russia Cite this: J. Am. Chem. Soc. 2000, 122, 51, 12878–12879Publication Date (Web):December 27, 2000Publication History Received22 May 2000Revised5 October 2000Published online27 December 2000Published inissue 1 December 2000https://doi.org/10.1021/ja0017615Copyright © 2000 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1072Altmetric-Citations92LEARN 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 Read OnlinePDF (36 KB) Get e-AlertsSUBJECTS:Hydrogen,Ions,Isotope effects,Noncovalent interactions,Peptides and proteins Get e-Alerts

Microsolvation of the Water Cation in Argon: I. Ab Initio and Density Functional Calculations of H2O+−Arn (n = 0−4)

The intermolecular interaction and microsolvation process of the water cation in its 2B1 ground electronic state with up to four Ar ligands are investigated with quantum chemical ab initio and density functional calculations at the unrestricted HF, MP2, and B3LYP levels of theory using a basis set of aug-cc-pVTZ quality. The intermolecular potential energy surface (PES) of the H2O+−Ar dimer calculated at the MP2 level features a planar proton (H)-bound HOHAr global minimum. The slightly translinear ionic hydrogen bond is characterized by a binding energy, D0 ∼ 2200 cm-1, an H−Ar separation, Re ∼ 1.92 Å, and a bond angle, φe ∼ 176°. The p-bound structure, with the Ar atom attached in a T-shaped fashion to the partially filled 2py orbital of oxygen, is a local minimum with D0 ∼ 1300 cm-1 and an O−Ar separation, Re ∼ 2.47 Å. The attraction in the H-bound structure is dominated by induction forces, whereas charge transfer from Ar to the 2py orbital of H2O+ provides a significant contribution to the stabilization energy of the p-bound isomer. In the most stable structures of H2O+−Arn (n = 1−4) the first two Ar ligands occupy H-bound sites and the next two ligands are located at the p-bound sites leading to geometries with Cs (n = 1,3) and C2v symmetry (n = 2,4), respectively.

A gold(I) mononuclear complex and its association into binuclear and cluster compounds by hydrogen bonding or metal ion coordination.

The mononuclear Au(I) complex, Au(Spy)(PPh2py) (1), has been synthesized and characterized structurally. The complex possesses the expected linear coordination geometry with a S-Au-P bond angle of 176.03(6) degrees and no evidence of aurophilic interactions between nearest neighbor Au(I) ions in the solid state. Protonation of the pendant pyridyl groups of 1 leads to the formation of the H-bonded dimer [(Au(SpyH)(PPh2py))2](PF6)2 (2), which has also been structurally characterized. A linear coordination geometry at the Au(I) ions in 2 with a S-Au-P bond angle of 173.7(2) degrees is augmented by evidence of a strong aurophilic interaction with a Au...Au distance of 2.979(1) A. The pendant pyridyl groups of 1 have also been used to bind Cu(I) by reactions with [Cu(NCMe)4](PF6) and Cu(P(p-tolyl)3)2(NO3) leading to the formation of the heterobimetallic complexes [(AuCu(mu-Spy)(mu-PPh2py))2](PF6)2 (3) and [AuCu(P(p-tolyl)3)2(mu-Spy)(mu-PPh2py)](NO3) (4), respectively. A structure determination of 3 reveals a tetranuclear complex composed of two AuCu(mu-Spy)(mu-PPh2py)+ units held together by bridging thiolate ligands. A strong metal-metal interaction is noted between the two different d10 ions with nearest Au-Cu distances averaging 2.6395 A. The S-Au-P bond angles in 3 deviate slightly from linearity due to the Au...Cu interactions, while the coordination geometries at Cu(I) are distorted tetrahedral consisting of the two pyridyl nitrogen atoms, a bridging thiolate sulfur, and the interacting Au(I) ion. While mononuclear complex 1 is only weakly emissive in the solid state and in fluid solution, complexes 2-4 show stronger photoluminescence in the solid state and rigid media at 77 K, and in fluid solution. The emission maxima for 2-4 in ambient temperature fluid solution are 470, 635, and 510 nm, respectively. A tentative assignment of the emitting state as a S(p pi)-->Au LMCT transition is made on the basis of previous studies of Au(I) thiolate phosphine complexes. Shifts of lambda em result from the influence of H bonding or Cu(I) coordination on the filled thiolate orbital energy, or on the effect of metal-metal interaction on the Au(I) acceptor orbital energy. Crystal data for Au(Spy)(PPh2py) (1): triclinic, space group P1 (No. 2), with a = 8.3975(4) A, b = 11.0237(5) A, c = 12.4105(6) A, alpha = 98.6740(10) degrees, beta = 105.3540(10) degrees, gamma = 110.9620(10) degrees, V = 995.33(8) A3, Z = 2, R1 = 3.66% (I > 2 sigma(I)), wR2 = 9.04% (I > 2 sigma(I)) for 2617 unique reflections. Crystal data for [(Au(SpyH)(PPh2py))2](PF6)2 (2): triclinic, space group P1 (No. 2), with a = 14.0284(3) A, b = 14.1093(3) A, c = 15.7027(2) A, alpha = 97.1870(10) degrees, beta = 96.5310(10) degrees, gamma = 117.1420(10) degrees, V = 2692.21(9) A3, Z = 2, R1 = 7.72% (I > 2 sigma(I)), wR2 = 15.34% (I > 2 sigma(I)) for 5596 unique reflections. Crystal data for [(AuCu(mu-Spy)(mu-PPh2py))2](PF6)2 (3): monoclinic, space group P2(1)/c (No. 14), with a = 19.6388(6) A, b = 16.3788(4) A, c = 17.2294(5) A, beta = 91.48 degrees, V = 5540.2(3) A3, Z = 4, R1 = 3.99% (I > 2 sigma(I)), wR2 = 8.38% (I > 2 sigma(I)) for 10,597 unique reflections.

Unimolecular decay of hydrogen-bonded cluster ions

The unimolecular decay of the hydrogen-bonded phenol(H2O)4+ cluster ion was studied both experimentally and theoretically. The ion is formed by resonant two-color two-photon ionization of the neutral cluster. If the second color exceeds the dissociation threshold of the ion, fragmentation occurs on a microsecond time scale. By analyzing the time-of-flight (TOF) signal of the metastable ions at different excess energies the dependence of the fragmentation rate on the excess energy can be deduced. These experimental rates are compared to microcanonical decay constants k(E) calculated from Rice–Ramsperger–Kassel–Marcus (RRKM) theory based on ab initio data solely.

Design of Layered Crystalline Materials Using Coordination Chemistry and Hydrogen Bonds

The supramolecular chemistry and crystal structures of five bis(imidazolium 2,6-pyridinedicarboxylate)M(II) trihydrate complexes, where M = Mn2+, Co2+, Ni2+, Cu2+, or Zn2+ (1−5, respectively), are reported. These complexes serve as supramolecular building blocks that self-assemble when crystallized to generate a single, well-defined, predictable structure in the solid state. 2,6-Pyridinedicarboxylate anions and imidazolium cations form strong ionic hydrogen bonds that dominate crystal packing in compounds 1−5 by forming two-dimensional networks, or layers of molecules. This layer motif serves as a platform with which to control and predict molecular packing by design for engineering the structures of crystals. Moreover, compounds 1−5 create a robust organic host lattice that accommodates five different transition metals without significantly altering molecular packing. Growth of crystals from solutions that contain two or more different metal complexes produces mixed crystals in which mixtures of the different metal complexes are incorporated in the same relative molar ratio present in solution. Epitaxial growth of crystals from one metal complex on the surface of a seed crystal that contains a second metal complex generates composite crystals in which the different metal complexes are segregated into different regions of the crystals. Compounds 1−5 form crystalline solids that represent a new class of modular materials in which the organic ligands serve as a structural component that defines a single packing arrangement that persists over a range of structures, and in which the metal serves as an interchangeable component with which to vary the physical properties of the material.

The Effect of Electrolyte Concentration on the Chemical Force Titration Behavior of ω-Functionalized SAMs: Evidence for the Formation of Strong Ionic Hydrogen Bonds

The chemical force titration behavior of carboxylic and phosphonic acid-functionalized tips and substrates has been found to be very strongly dependent on electrolyte concentration. Under low electrolyte concentration conditions, these force titrations take the form of peaks, which change to monotonic sigmoidal curves with a concomitant shift to lower pH as the electrolyte concentration of the buffer is increased. The appearance of a peak in the low electrolyte concentration force titrations is attributed to the formation of strong hydrogen bonds between neutral and ionized species on the tip and substrate, which is prevented in the case of high electrolyte concentration by the formation of an electric double layer. There is strong evidence that the measured pK1/2(which corresponds to the pH of the bulk solution at which half of the surface groups are ionized) of these acid groups lies at the position of the peak of the low electrolyte concentration titration curves (carboxylic acid, pKa = 8; phosphonic acid, pKa1 = 4.6, pKa2 = 8.4) and cannot be measured under high electrolyte concentration conditions by this adhesion method. JKR theory of contact mechanics cannot be used to describe the low electrolyte concentration force titration data of these acid SAMs. The shapes of the force titration curves are described very well at all electrolyte concentrations by a simple model in which strong ionic and weak neutral hydrogen bonds contribute to the total adhesion force, which strongly supports our hypothesis. The results of fitting the force titration data to this model indicate that the strong ionic hydrogen bonds are on the order of 16 times stronger than a neutral hydrogen bond, which agrees well with theoretical predictions.

Potential energy surface and infrared spectrum of the Ar–H2Cl+ ionic complex

The infrared photodissociation spectrum of the Ar–H2Cl+ dimer has been recorded in the vicinity of the Cl–H stretch fundamentals of bare H2Cl+. Eleven Q branches of a strong perpendicular transition of a (near) prolate symmetric top are observed. The position and rotational structure of the band are consistent with an assignment to the free Cl–H stretch fundamental of a proton-bound Ar–HClH+ dimer. The global minimum on the intermolecular potential energy surface of Ar–H2Cl+, calculated at the MP2/aug-cc-pVTZ# level of theory, corresponds to the proton-bound structure with an intermolecular separation of Re=1.97 Å and a well depth of De=1860 cm−1. The slightly nonlinear ionic hydrogen bond is directional with large barriers (Vb) for internal rotation of H2Cl+ via planar transition states with C2v symmetry: Vb∼750 and 1330 cm−1 for the bridged (Re=3.45 Å, De=1107 cm−1) and chlorine-bound (Re=3.38 Å, De=531 cm−1) structures. The molecular constants of the observed transition, ν0=2663.1 cm−1 and A=10.35 cm−1, are in good agreement with the values calculated for the proton-bound equilibrium geometry, ν0=2665.4 cm−1 and Ae=10.28 cm−1.

Apolipoprotein E–low density lipoprotein receptor interaction: influences of basic residue and amphipathic α-helix organization in the ligand

Conserved lysines and arginines within amino acids 140–150 of apolipoprotein (apo) E are crucial for the interaction between apoE and the low density lipoprotein receptor (LDLR). To explore the roles of amphipathic α-helix and basic residue organization in the binding process, we performed site-directed mutagenesis on the 22-kDa fragment of apoE (amino acids 1–191). Exchange of lysine and arginine at postions 143, 146, and 147 demonstrated that a positive charge rather than a specific basic residue is required at these positions. Consistent with this finding, substitution of neutral amino acids for the lysines at positions 143 and 146 reduced the binding affinity to about 30% of the wild-type value. This reduction corresponds to a decrease in free energy of binding of ~600 cal/mol, consistent with the elimination of a hydrogen-bonded ion pair (salt bridge) between a lysine on apoE and an acidic residue on the LDLR. Binding activity was similarly reduced when K143 and K146 were both mutated to arginine (K143R + K146R), indicating that more than the side-chain positive charge can be important.Exchanging lysines and leucines indicated that the amphipathic α-helical structure of amino acids 140–150 is critical for normal binding to the low density lipoprotein receptor.

Three-Dimensional Hexagonal Structures from a Novel Self-Complementary Molecular Building Block

Nitrilotri(methylphosphonic acid), 1H6, exists as a zwitter ion in its pure form and reveals a complex three-dimensional structure with no predictable structural patterns. However, when acid 1H6 is reacted with 1,7-phenanthroline, 2, 1,10-phenanthroline, 3, acridine, 6, and tripropylamine, 8, in a 1:1 molar ratio, monodeprotonation of 1H6 triggers a prototypal self-complementary 3D hexagonal architecture in complexes 9 (1H5·H·2H2O), 10 (1H5·3H), 11 (1·5H)·(5)0.5, and 12 (1·8H). The networks are stabilized by very strong ionic hydrogen bonds and offer a viable new strategy for the design of stable and predictable 3D open organic networks. However, monodeprotonation of acid 1H6 with quinoline, 6, does not lead to the expected open hexagonal structure in 13 (1·6H) as quinolinium cations cannot effectively fill the void space if open hexagonal open structures were formed. The unique three-dimensional connectivity of these open networks does not permit interweaving, and template effects play a critical role in...

Isolation of immunoglobulin from egg yolk by anionic polysaccharides.

Isolation conditions of immunoglobulin in egg yolk (IgY) were optimized by the addition of various levels of Na-alginate (Alg), lambda-carrageenan (lambda-Cg), Na-carboxymethyl cellulose (CMC), and pectin (PC) to 6-fold diluted yolk. The mixtures were then reacted at pH 4.0-6.0 for 30 min. The optimal isolation conditions of IgY for Alg, lambda-Cg, and CMC were at the 0.1% level and at pH 5.0, while those for PC were at the 0.15% level and at the same pH. The remaining lipid and remaining protein in the supernatants thus obtained was 0.5-3.8% and 10-17%, respectively, and more than 90% of lipoproteins were precipitated. The IgY recovery was determined to be 33-74% by means of single radial immunodiffusion method when IgY was isolated under the optimal conditions. PC showed the best recovery of IgY, while lambda-Cg provided the least. The interactions between polysaccharides and lipoproteins were mainly ionic bonds, hydrophobic interactions, and hydrogen bonds as determined by the addition (0-2.0 M) of NaSCN or urea to the polysaccharide-lipoprotein precipitates.

Inframolecular protonation process of 6-modified myo-inositol 1,4,5-tris(phosphates): substitution effects on the cooperativity between the phosphate groups

The protonation process of the individual functional groups of four analogues of (±)-myo-inositol 1,4,5-tris(phosphate) [Ins(1,4,5)P3], modified at position 6, were studied by 31P- and 1H-NMR titration experiments in order to gain insight into the reasons for the particular importance of OH6 for the binding of Ins(1,4,5)P3 to its receptor. The fluorinated derivative (2) was studied to evaluate the H-bond donor or acceptor ability of OH6. Compounds 3 and 4 should explain the presence and the configuration of OH6, respectively, whereas the amino analogue (5) was considered to delineate the effect of a positively charged group of about the same size as OH6 on the vicinal phosphates P1 and P5. The 31P-NMR curves look alike for compounds 2–4 and differ from that of Ins(1,4,5)P3 , as the initial downfield shift of P1 upon protonation is no longer observed. In the 1H-NMR titration curves, the wrongway shift found for H2 of Ins(1,4,5)P3 is observed for H6 in compounds 3 and 4. In addition, both phosphorus and proton resonances of compound 5 are influenced by the protonation of the neighbouring NH2 group. By considering the protonation constants it is shown that the log K1 values decrease in the order 6-F-Ins(1,4,5)P3>6-deoxy-Ins(1,4,5)P3>Ins(1,4,5)P3> epi-Ins(1,4,5)P3>6-NH2-Ins(1,4,5)P3, indicating that the substitution effect is the consequence of the lipophilicity of the substituents, the basicity order following the order of the hydrophobic π constants. Consideration of the microprotonation constants, calculated for all the studied compounds, leads to the conclusion that hydration effects and hydrogen bond donor ability of the equatorial OH6 hydroxyl should mainly account for the differences observed between compounds 2–4 and Ins(1,4,5)P3. The amino derivative 5 remains in a zwitterionic form over almost the entire pH range studied (2.5<pH<11.5). Through the presence of an intramolecular hydrogen-bonded ion pair interaction the basicity of all three phosphates is decreased whereas the basicity of the amine increases. The strength of the hydrogen-bonded ion pair appears to be of the same order of magnitude as that of the recently published monoammonium phosphate complexes.

Infrared spectra of hydrogen-bonded ion–radical complexes: I−⋅HCH2 and Br−⋅HCHBr

We report the preparation and infrared spectra of the CH3I− and CH2Br2− anions formed by argon cluster-mediated electron attachment to the neutral molecular precursors. Infrared predissociation spectra were acquired for both the bare and argon-solvated species in the C–H stretching region. Partial rotational structure was recovered in the CH3I− system, consistent with the hydrogen-bonded, C2v structure suggested in an earlier analysis of its photoelectron spectrum [J. Kim et al., J. Am. Soc. Mass Spectrom. 10, 810 (1999)]. The spectrum and photofragmentation pattern confirm that this species is trapped in a very weakly bound ion–methyl radical form (I−⋅HCH2) involving a single ionic H bond. The CH2Br2− anion displays a similar spectrum, where one CH stretch is significantly redshifted, again signaling the single H-bonding motif.

Spectroscopic and ab initio studies of ionic hydrogen bonds: the O–H stretch vibration of SiOH +–X dimers (X=He, Ne, Ar, N 2)

Infrared photodissociation spectra of SiOH +–X dimers with X=He, Ne, Ar, and N 2 are analyzed in the vicinity of the O–H stretch ( ν 1) vibration of SiOH +. The observed complexation-induced red-shifts, Δ ν 1=−8.4(3.0), −35.7(6), −217.42(1), and −517.1(5) cm −1, are consistent with the linear proton-bound global minimum structures predicted by ab initio calculations at the MP2 level of theory. Empirical relations between the magnitude of Δ ν 1 and the interaction strength of the ionic hydrogen bond are discussed.