Strong Hydrogen Bridge Research Articles

Self-assembly dynamics and effect on synthetic nanobio-optical properties by hybrid monocolored silica nanoparticle labeling of Escherichia coli

The deposition of silica nanoparticles on Escherichia coli bacteria was investigated. The noncovalent interaction between the silanized surfaces and polar components of the biomembrane resulted in a nanobiostructure. This hybrid architecture showed stable conformation characteristics evaluated with different microscopy techniques, such as bright field confocal microscopy and transmission electron microscopy (TEM). Nanobioarchitectures were detected within colloidal dispersions and in the absence of aqueous media. Nanobiointeractions were related to strong polar and hydrogen bridges’ noncovalent interactions. Thus, well-constituted and defined nanobiostructures were observed by bright field confocal microscopy and TEM after their preparation in optimal conditions. However, to evaluate their stability and internanobiostructure interactions, size distributions within variable periods were determined. Variable nanobioaggregate sizes were recorded according to nanoparticles and bacteria concentrations. From single nanolabeled E. coli with well dispersible properties, low bacteria concentrations were observed. In intermediate and high concentrations, different distributions of nanobiostructures were observed in different periods. It was observed that the incorporation of silica nanoparticles into E. coli increased their dispersibility; however, their modified E. Coli membranes with silanized nanosurfaces augmented their internanobiostructure interactions through time. Here, we discuss the dynamics and nanobio-optics properties of E. coli. Their nanobiostructures could not be considered to be static systems; their interactions are regarded as important factors for dispersibility, stability, and effects against additional chemical agents such as antibiotics.

Stabilization of a Snub Bisphenoidal Environment of Strontium in Bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)‐2H‐pyrazole]strontium Bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)pyrazolate] by Strong Hydrogen Bridges

AbstractMetalation of 3‐(1‐naphthyl)‐5‐(2‐pyridyl)‐2H‐pyrazole (1) with [(thf)2Sr{N(SiMe3)2}2] in toluene and recrystallization from tetrahydrofuran and diethyl ether yields ether‐free bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)‐2H‐pyrazole]strontium bis[3‐(1‐naphthyl)‐5‐(2‐pyridyl)pyrazolate] (2). This complex contains an octa‐coordinate central strontium atom in a snub bisphenoidal coordination sphere. Intramolecular N···H···N hydrogen bridges between pyrazolyl groups stabilize the large coordination number of the alkaline earth metal. Short N···N contacts of 272.5 and 274.5 pm verify the existence of strong hydrogen bridges; the chemical shift of δ = 19.7 for these protons underlines their extremely acidic character.

Anodic Behavior of Aluminum in Glycine Aqueous Solutions at Various pH Values

At the present work, it was investigated aluminum (Al 99.99%) anodic behavior in glycine aqueous solutions (in the concentration range from 10–4 to 10–1M) at various pH values (pH 4.8 - 8.4). Reliability of the obtained experimental results was confirmed by use of a complex of independent physic-chemical methods (voltammetry, chronoamperometry, optical microscopy (МBS-2 (x7) and МIМ-7 (x500)), scanning electronic microscopy (SEM, x1000) with JEOL-6380LV and energy-dispersive X-ray analysis (EDXA) with INCA Energy-250).The received data have shown that depending on the pH, the amino acid exhibits a dual effect. On the one hand, glycine zwitter-ions (pH 4.8–5.8) conducts one’s self like an inhibitor slowing down the anodic process and aluminum is in a stable passive state at these pH values in the vicinity of the isoelectric point of the investigated amino acid. Under this the probable reason of the observed effect consists of strong intermolecular hydrogen bridges which are formed between the amino and carboxy groups in the amino acid zwitter-ions predominate over it’s interactions with the oxidized aluminum surface. It follows from this that glycine zwitter-ions do not participate in the anodic process on aluminum, and the passive film on aluminum surface is formed upon metal–water interaction according to the following scheme because of a high chemical affinity of aluminum to oxygen:Al + yH2O → [Al (H2O)y]ads (1)On the other hand, it has been shown that the glycine anions formed at pH = 8.4 stimulate pit formation (PF) on oxidazed aluminum surface in these solutions (pit depth was 6 μm at 10-1 M). The choice of this pH value was caused by two reasons. In the first place, at pH = 8.4 the system contains both inactive zwitter-ions and active glycine anions. Secondly, solutions with higher pH might cause intense general corrosion of aluminum. The data about aluminum anodic behavior in glycine solutions (pH = 8.4) were analyzed on the basis of the nucleophilic substitution theory, according to which PF observed on aluminum involves nucleophilic substitution of ligands of adsorbed surface complexes by corrosive solution components with subsequent hydrolysis of a compound formed. Generalization of experimental data and literature data [1-3] allowed us to suggest the following multistage mechanism of the PF process:Al + yOH- = [Al(OH)y]z1-y ads + z1e- (2) [Al(OH)y]z1-yads → [Al(OH)y-k]z1´-y ads + k OH- (3)[Al(OH)y-k]z1´-y ads + Gly- = [Al(OH)y-kGly]z2-y ads (4)[Al(OH)y-kGly]z2-y ads = Alz3 + Gly- + (y – k) OH- + (z2-z3)e- (5)According to the kinetic analysis data obtained in the present investigation, the limiting stage of the PF process studied is dissociation of the initial complex at equation (3).This fact is confirmed by independence of the PF process rate from activator –glycine anions. ReferencesT.A. Borisenkova, S.A. Kaluzhina // Int. J. Corros. Scale Inhib., 2, 122 (2013)T.A. Borisenkova, S.A. Kaluzhina // Condensed matter and interphases, 13, 136 (2011).T.A. Borisenkova, S.A. Kaluzhina // ECS of the 218th Meeting, Las Vegas, №1227 (2010).

A Ditopic Catechol Phosphane as Building Block for Selective Construction of Heterometallic Complexes with Early and Late Transition Metal Centers

Base-assisted reaction of catechol phosphane 2 (H2L) with [M′Cl2(cod)] (cod = 1, 5-cyclooctadiene, M′ = Pd, Pt) yielded chelate complexes [M′(HL)2] (7a, b). Spectroscopic and single-crystal X-ray diffraction studies revealed that both complexes feature cis-configuration of the P- and O-donor atoms in solution and in the solid state. Reaction of 7a, b with acetylacetonato or alkoxide complexes [MO2(acac)2] (M = Mo, W), [VO(acac)2], [{Ti(μ-O)(acac)2}2], or Ti(OiPr)4 gave good to excellent yields of early-late heterometallic complexes [MOn(μ-L)2M′] (MOn = MoO2, WO2, VO; 8a, b–10a, b) or [Ti(RO-1κO)2(μ-L-1κ2O, O'-2κ2P, O)2Pd] (R = Me, iPr; 11a, b), which were inaccessible via other synthetic routes. Spectroscopic and single-crystal X-ray diffraction studies revealed that the early metal centres in 8a, b, 9b and in 11b feature distorted octahedral coordination spheres with rigid transoid alignment of the catechol ring planes. Vanadium complexes 10a, b exhibit a square-pyramidal coordination sphere with cisoid alignment of the catechol ring planes and evidence for intermolecular pairing via weak VO···Pd contacts in the solid state; complexes 8, 9 do not undergo conformational inversion on the NMR time-scale. The molecular structure of Ti complex 11a is characterized by a different orientation of the catechol moieties, which can be envisaged to picture an intermediate state during a configuration inversion process, and a strong hydrogen bridge between a terminally coordinated catecholato-oxygen atom and a solvent molecule (MeOH). Solution NMR studies indicate that the (MeO)2Ti(μ-L)2M' framework is in this case conformationally labile and that the MeO ligands undergo intermolecular dynamic exchange with the solvent.

Total Synthesis and Detection of the Bilirubin Oxidation Product (Z)-2-(3-Ethenyl-4-methyl-5-oxo-1,5-dihydro-2H-pyrrol-2-ylidene)ethanamide (Z-BOX A)

The selective total synthesis of the pure Z-isomer of BOX A (8a), a product of oxidative heme degradation with significant physiological impact, was achieved in four to six steps starting from 3-bromo-4-methylfuran-2,5-dione (1). Z-BOX A forms a strong hydrogen bridge framework in the crystalline state. LC-MS techniques allow identification and characterization of isomeric forms of BOX A.

Anodic behavior of aluminum in α-alanine aqueous solutions at various pH values

The effect of α-alanine on aluminum anodic behavior in its solutions with pH values from 4.2 to 8.5 has been studied. It has been found that, depending on the pH, the amino acid exhibits a dual effect. On the one hand, α-alanine zwitter-ions (pH 4.2–5.6) behaving like an inhibitor slow down the anodic process, so aluminum is in a stable passive state at these pH values in the vicinity of the isoelectric point of the amino acid. The probable reason of the observed effect is that strong intermolecular hydrogen bridges that are formed between the amino and carboxy groups in the amino acid zwitter-ions predominate over interactions with the oxidized aluminum surface. On the other hand, it has been shown that the αalanine anions formed at pH = 8.5 stimulate pit formation on aluminum surface in these solutions. Based on literature and experimental data, a dissociative mechanism of pit formation on aluminum in the systems in question is suggested.

The stability of the acetic acid dimer in microhydrated environments and in aqueous solution

The thermodynamic stability of the acetic acid dimer conformers in microhydrated environments and in aqueous solution was studied by means of molecular dynamics simulations using the density functional based tight binding (DFTB) method. To confirm the reliability of this method for the system studied, density functional theory (DFT) and second order Møller-Plesset perturbation theory (MP2) calculations were performed for comparison. Classical optimized potentials for liquid simulations (OPLS) force field dynamics was used as well. One focus of this work was laid on the study of the capabilities of water molecules to break the hydrogen bonds of the acetic acid dimer. The barrier for insertion of one water molecule into the most stable cyclic dimer is found to lie between 3.25 and 4.8 kcal mol(-1) for the quantum mechanical methods, but only at 1.2 kcal mol(-1) for OPLS. Starting from different acetic acid dimer structures optimized in gas phase, DFTB dynamics simulations give a different picture of the stability in the microhydrated environment (4 to 12 water molecules) as compared to aqueous solution. In the former case all conformers are converted to the hydrated cyclic dimer, which remains stable over the entire simulation time of 1 ns. These results demonstrate that the considered microhydrated environment is not sufficient to dissociate the acetic acid dimer. In aqueous solution, however, the DFTB dynamics shows dissociation of all dimer structures (or processes leading thereto) starting after about 50 ps, demonstrating the capability of the water environment to break up the relatively strong hydrogen bridges. The OPLS dynamics in the aqueous environment shows--in contrast to the DFTB results--immediate dissociation, but a similar long-term behavior.

Air‐Stable Platinum and Palladium Complexes Featuring Bis[2,4‐bis(trifluoromethyl)phenyl]phosphinous Acid Ligands

Secondary phosphane oxides, R(2)P(O)H, are commonly used as preligands for transition-metal complexes of phosphinous acids, R(2)P-OH (R=alkyl, aryl), which are relevant as efficient catalysts in cross-coupling processes. In contrast to previous work by other groups, we are interested in the ligating properties of an electron-deficient phosphinous acid, (R(f))(2)P-OH, bearing the strongly electron-withdrawing and sterically demanding 2,4-bis(trifluoromethyl)phenyl group towards catalysis-relevant metals, such as palladium and platinum. The preligand bis[2,4-bis(trifluoromethyl)phenyl]phosphane oxide, (R(f))(2)P(O)H, reacts smoothly with solid platinum(II) dichloride yielding the trans-configured phosphinous acid platinum complex trans-[PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)]. The deprotonation of one phosphinous acid ligand with an appropriate base leads to the cis-configured monoanion complex cis-[PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H](-), featuring the quasi-chelating phosphinous acid phosphinito unit, (R(f))(2)P-O-H···O=P(R(f))(2), which exhibits a strong hydrogen bridge substantiated by an O···O distance of 245.1(4) pm. The second deprotonation step is accompanied by a rearrangement to afford the trans-configured dianion trans-[PtCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)](2-). The reaction of (R(f))(2)P(O)H with solid palladium(II) dichloride initially yields a mononuclear palladium complex [PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)], which condenses under liberation of HCl to the neutral dinuclear palladium complex [Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(2)]. The equilibrium between the mononuclear [PdCl(2)({2,4-(CF(3))(2)C(6)H(3)}(2)POH)(2)] and dinuclear [Pd(2)(μ-Cl)(2){({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H}(2)] palladium complexes is reversible and can be shifted in each direction by the addition of base or HCl, respectively. Treatment of palladium(II) hexafluoroacetylacetonate, [Pd(F(6)acac)(2)], with a slight excess of (R(f))(2)P(O)H yields the complex [Pd(F(6)acac)({2,4-(CF(3))(2)C(6)H(3)}(2)PO)(2)H]. The quasi-chelating phosphinous acid phosphinito unit, which is formed by the liberation of HF(6)acac, is characterized by a O···O distance of 244.1(3) pm. These transition metal complexes are stable towards air and moisture and can be stored for months without any evidence of decomposition.

Synthesis of a Water‐Stable 2, 4‐Bis(trifluoromethyl)phenyl‐Substituted Phosphonous Acid Palladium Complex and its Catalytic Activity in Cross‐Coupling Reactions

AbstractThis manuscript describes the selective synthesis of2, 4‐bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH.Reaction of chlorobis(diethylamino)phosphane with a mixture of 2, 4‐(CF3)2C6H3Li and 2, 6‐(CF3)2C6H3Li results in the formation of 2, 4‐bis(trifluoromethyl)phenylbis(diethylamino)phosphane, (Rf)P(NEt2)2. The following in situ reaction with gaseous HBr leads to the cleavage of the phosphorus nitrogen bonds resulting in the selective formation of the corresponding dibromophosphane (Rf)PBr2.2, 4‐Bis(trifluoromethyl)phenylphosphinic acid is available via two different synthetic strategies starting from the dibromophosphane (Rf)PBr2. Reduction of the dibromophosphane with tributyltin hydride affords selectively the phosphane (Rf)PH2. The following oxidation to the phosphinic acid (Rf)P(O)(H)OH, however, only proceeds in moderate yields. A more efficient synthesis is achieved via the hydrolysis of the dibromophosphane (Rf)PBr2 in dichloromethane solution. 2, 4‐bis(trifluoromethyl)phenylphosphinic acid, (Rf)P(O)(H)OH, is surprisingly stable towards air and water. The water soluble phosphinic acid reacts sluggishly with a 30 % H2O2 solution, yielding only 23 % of the corresponding phosphonic acid (Rf)P(O)(OH)2 after seven days at ambient temperature.In principle a tautomerization of the phosphinic acid (Rf)P(O)(H)OH to the corresponding phosphonous acid (Rf)P(OH)2 – analogously to the phosphane oxide (Rf)2P(O)H and the phosphinous acid (Rf)2POH – is conceivable. However, the phosphonous acid could not be detected with spectroscopic methods. The energy difference between the phosphinic acid and the phosphonous acid is calculated by quantum chemical calculations at the B3LYP/6‐311+G(2df, p) level of theory to 30.1 kJ·mol–1. This high value explains why the phosphonous acid tautomer could not be detected by spectroscopic methods so far.As transition metal complexes featuring phosphonous acid ligands are of significant interest for the application as homogeneous catalysts we studied the coordination chemistry of the related phosphinic acid in more detail. The preligand 2, 4‐bis(trifluoromethyl)phenylphosphinic acid reacts smoothly with palladium dichloride in THF to the dinuclear complex [Pd2(μ‐Cl)2{[2, 4‐(CF3)2C6H3P(OH)O]2H}2], featuring a phosphonous acid phosphonato unit, with a strong hydrogen bridge substantiated by an O···O distance of 247.7(3) pm. The dinuclear phosphonous acid palladium complex exhibits a high catalytic activity in the Suzuki cross‐coupling. Alternatively, the phosphinic acid can be used as preligand for the in situ formation of a phosphonous acid palladium complex. These compounds combine catalytic activity with a very high stability towards air and water.

The Protonation of HSO3F: Preparation and Characterization of Fluorodihydroxyoxosulfonium Hexafluoroantimonate [H2SO3F]+[SbF6]−

Sulfurtrioxide reacts with the superacidic solutions XF/SbF(5) (X=H, D) to form the corresponding salts [X(2)SO(3)F](+)[SbF(6)](-), which are the protonated forms of fluorosulfuric acid. The salts have been characterized by vibrational spectroscopy and a single-crystal structure analysis. [H(2)SO(3)F](+)[SbF(6)](-) crystallizes in the monoclinic space group P2(1)/n (no. 14) with four formula units in the unit cell. The crystal structure possesses a distorted tetrahedral O(3)SF skeleton of the cations, which are linked with two strong hydrogen bridges to [SbF(6)](-) anions and forms a one-dimensional chain. The crystal structure and the vibrational spectra are compared to the quantum-chemical-calculated free [H(2)SO(3)F](+) cation. Additionally, an [H(2)SO(3)F(HF)(2)](+) unit was calculated at the RHF/6-311(++)G(d,p) level to simulate HF hydrogen bridges found in the solid state.

Complexation of Cs+, K+ and Na+ by norbadione A triggered by the release of a strong hydrogen bond : nature and stability of the complexes

Norbadione A (NBA) is a pigment present in edible mushrooms which is presumed to selectively complex Cs(+) cations. Due to a very uncommon complexation mechanism, we used a combination of several experimental techniques, including (1)H-NMR, (133)Cs-NMR, isothermal calorimetric, potentiometric titrations and molecular dynamics MD simulations to determine the nature of the complexed species, as well as their stability constants for the NBA-M(+) systems (M(+) = Cs(+), K(+), Na(+)) in methanol:water 80:20 solutions at 25.0 degrees C. We show that almost no complexation occurs below pH 7.5, as long as a proton, involved in a strong hydrogen bond, bridges both carboxylic and enolic groups of each pulvinic moiety of NBA. Thus, neutralization of that proton is necessary to both set free potential coordination sites and to trigger a conformational change, two conditions needed to bind successively a first, then a second metallic cation. The stability constants determined in this study are in good agreement with each other, leading to the stability order Cs(+) > K(+) > Na(+) for both mono- and bimetallic complexes, which is the reversed order to the one generally observed for low molecular weight carboxylic ligands in water. According to MD simulations in solution, complexation involves a mixture of Z/E isomers and conformers of NBA with a broad diversity of binding modes. Some pH and environment dependent aggregation phenomena are considered to also contribute to the binding process, and to possibly explain the accumulation of radionuclides in mushrooms.

Probing the Intramolecular Hydrogen Bond of 2-(2-Hydroxyphenyl)benzotriazoles in Polar Environment: A Photophysical Study of UV Absorber Efficiency

An in-depth photophysical study is presented for a series of 2-(2-hydroxyphenyl)benzotriazoles (HBzTs); the structural characteristic of all these photostabilizers is their strong intramolecular hydrogen bridge (IMHB). Tinuvin P (TIN P, 11a) and six other HBzTs, with no substituent in the 3'-position ortho to the hydroxy function, show pronounced phosphorescence already in the dark (at 77 K in a polar glass). Upon irradiation, the phosphorescence intensity rises further until an equilibrium value is attained (up to 1.5 fold the dark value). A kinetic model is given which excellently reproduces this phosphorescence evolution: it demonstrates phosphorescence to arise from open conformers where the IMHB has been broken. Phosphorescence excitation spectra match the absorption spectra of the open conformer and also that of the O-methyl homologue 11A which cannot form an IMHB. Fluorescence spectra likewise prove the equilibrium between the closed and open conformer for these HBzTs. In unpolar glasses as well as in the crystalline state, TIN P displays a long-wavelength (red) fluorescence (with an enormous Stokes shift of approximately 10.000 cm-1) which is associated with the excited singlet state of the closed form after proton transfer within the IMHB, S1'(C). In polar matrixes, on the other hand, a blue fluorescence is observed (with a regular Stokes shift) for all those HBzTs which have no 3'-substituent shielding the IMHB against being opened by the polar solvent. This blue fluorescence, just as the characteristic phosphorescence evolution for these compounds, is associated with the open conformer. For HBzTs with an (alkyl) group ortho to the bridging OH group, however, a long-wavelength (red) fluorescence is again observed. The shielding effect of the 3'-substituent shows a fine gradation, cumyl >/= 1,1,3,3-tetramethylbutyl (isooctyl) > t-butyl >/= methyl.

Tritium/Protium Fractionation Near and Inside DNA

The fractionation factor of tritium between water and DNA as well as between water and the first hydration shell of DNA is determined. For this purpose the sublimation kinetics of water from DNA dissolved in water were determined at -200 °C and tritium was measured in the remaining water free DNA. The last sublimating water fractions showed a tritium level of about 1.4, the residual water free DNA about 1.9 units above the bulk water. The tritium accumulation inside and near DNA is attributed to the thermodynamic triton-proton exchange isotope effect existing between the strong hydrogen bridges of water and weaker hydrogen bridges as well as inside DNA as between the first hydration shell and DNA.

Synthese und Charakterisierung von kronenetherstabilisierten Platin(IV)- Komplexen mit Aminosäureliganden / Synthesis and Characterization of Amino Acid Complexes of Platinum(IV) Stabilized by Crown Ethers

Abstract Crown ether complexed pentachloro(aqua)platinic acid, (H3O)[PtCl5(H2O)]·2(18-cr-6)·6H2O (1) reacts with glycine, L-alanine, and DL-2-aminobutyric acid to give cis-[PtCl4(O-glyH)(H2O)]·(18-cr-6)·H2O (4a)1 and cis-[PtCl4(O-amacH)(H2O)]·(18-cr-6) (amacH = alaH 4b, abuH 4c), respectively, as well as (amacH2)2[PtCl6]·2(18-cr-6) (amacH = glyH 5a, alaH 5b, abuH 5c). The crown ether complexed hexachloroplatinic acid, (H3O) 2[PtCl6]·2(18-cr-6) (2), reacts with glycine to afford (glyH2)[PtCl4(N,O-gly)]·2(18-cr-6)·1.25H2O (6). The structures of 4b and 6 were determined by X-ray diffraction. The alanine ligand in 4b is a zwitterion that is coordinated to platinum by one oxygen atom of the carboxylate group only. The other oxygen atom is engaged in a strong hydrogen bond to the ds-coordinated aqua ligand. The glycinato ligand in 6 is N, O-coordinated at platinum forming an anion [PtCl4(N,O-gly)]- . The other oxygen atom of the carboxylate group is involved in a strong hydrogen bridge to the cation (glyH2)+. In both complexes hydrogen bridges are formed between the -N+H3 and -NH2 groups of the amino acid ligands and the oxygen atoms of the crown ether molecules.

Nuclear magnetic resonance studies of surface interactions between trifluoromethanesulfonic acid and silica

The nature of the interaction between trifluoromethanesulfonic acid (triflic acid) and the surface groups of silica as a support has been investigated by1H and19F-NMR studies. The19F-NMR spin-lattice relaxation time (T1) dependence on temperature suggests that the dominant relaxation mechanism for19F is a combination of spin-rotation (SR) interactions, one of which seems to be quenched by cage-like structures. This mechanism is activated by the treatment followed to stabilize the acid on silica. Hydrogen proton relaxation seems instead to be driven by dipolar interactions and the formation of hydrogen bridges. Activation energies have been estimated for various cases, assuming an Arrhenius-type temperature dependence for the correlation times of molecular motion. A linear dependence of1H chemical shift on inverse temperature was also found, which is interpreted as thermal weakening of hydrogen bonding. The results support the conclusion that the stability of triflic acid on silica is due to the formation of strong hydrogen bridges between the sulfonic groups of triflic acid and the silica surface hydroxyls, provided a network structure similar to that observed for pure acid is obtained in which strong interactions between acid molecules occur. The acid seems to be organized as solid-like “drops” on the silica surface, which accounts for the long residence time on the silica surface.

Theory for the solvation of alkali metal atoms in clusters of polar molecules. Many-body polarization interactions

We present a theory for the binding energy of clusters of polar molecules (ammonia or water) and an alkali metal atom (Na, Cs). The metal atom dissociates into a positive ion and a separate valence electron, which has the role of an excess electron. The positive ion and the electron have strong electromagnetic interactions with the molecules of the cluster. It is shown that the resulting polarization energy contains important many-body terms and that it is not possible to use a pair-potential approximation for the electronic potential. We propose a model for the ionization potential, including both-initial and final state effects. Our results for the ionization potential of metal-ammonia clusters agree well with recent experiments, indicating that a size-dependent transition from a single-center structure of small clusters to a fully solvated two-center structure for large clusters occurs. Spherically symmetric model structures do not yield a good agreement with experimental results for Na(H 2O) n clusters. Thus these clusters either have a distinct asymmetric shape because of strong hydrogen bridge bonding or an autoionizing resonance might have been observed in the experiment instead of the true ionization threshold.

Molybdenum carbonyl complexes of diphenylphosphinous acid and diphenylphosphinous acid derivatives. Crystal and molecular structures of [Et 4N][Mo(CO) 4(PPh 2O) 2H]·0.37 CH 2Cl 2, Mo(CO) 4(PPh 2OH)(PPh 2OCH 2CH 2NMe 2)·H 2O and Mo(CO) 4(PPh 2SPPh 2)

Crystal and molecular structures for the three complexes [Et 4N][Mo(CO) 4(PPh 2O) 2H]·0.37CH 2Cl 2 ( 1), [Mo(CO) 4(PPh 2OH)(PPh 2OCH 2CH 2NMe 2]·H 2O ( 2) and [Mo(CO) 4(PPh 2SPPh 2] ( 3) are reported. The octahedral coordination sphere at molybdenum consists of four carbonyl groups and two cis oriented phosphorus donor ligands. The unlocated hydrogen atom in 1 forms a strong hydrogen bridge between the two Ph 2PO − ligands as evidence by a short OO distance of 2.415(4) Å. In complex 2, the acidic proton of the PPh 2OH ligand forms a strong hydrogen bond to the tertiary amine with a NO distance of 2.77 Å. Complex 3 has essentially C 2v symmetry; the PSP bond angle is 86.9°. The PMP angles are 88.06(4)°, 86.36(7)° and 72.02(7)° for 1, 2 and 3, respectively. The average MC distance over all these compounds is 2.010(6) Å; the MP distances range from 2.487(2) to 2.563(2) Å and average to 2.51(1) Å. Compound 1 crystallizes in space group P 1 with a = 12.456(2) Å, b = 13.757(3) Å, c = 11.892(3) Å, α = 95.51(2)° β = 108.30(2)°, γ = 91.91(1)°, V = 1922(2) Å 3, Z = 2. Compound 2 crystallizes in space group Pbca with a = 20.901(3) Å, b = 16.032(3) Å, c = 19.686(5) Å, V = 6597(2) Å 3, Z = 8. Compound 3 crytallizes in space group P2 12 12 1 with a = 11.014(1) Å, b = 14.244(2) Å, c = 17.233(1) Å, V = 27041(1) Å 3, Z = 4.

Acenaphthenequinonedioxime as an analytical reagent: Determination of nickel in mixtures

The titled reagent (ANDO) has been used as a reagent for gravimetric determination of nickel and for its separation from common cations and anions. Nickel (II) precipitates quantitatively by ANDO within the pH range 6.8–8.4. After drying the precipitate at 110°, its composition corresponds to the formula Ni(C12H7O2N2)2. Many commonly associated ions, except Fe(III), Co(II) and Cu(II), do not interfere. Solvent-extraction techniques have been utilized to separate Cu(II) and Co (II) from the binary mixture. For masking Fe(III) excess citrate ion has been used. Elemental analysis confirms 1∶2 metal-ligand ratio. The complex is approximately diamagnetic (μ eff=0.95 B. M.) and gives typical d-d spectral bands as generally observed in square planar complexes involving d8 electronic configuration. Electronic spectra of the metal chelate in pyridine are discussed and results of thermo gravimetric analysis are also presented. I. R. and far I. R. spectral analysis indicate the involvement of strong hydrogen bridges and metal-nitrogen bond.

Crystal and molecular structure of (E)-5-(2-bromovinyl-2'-deoxyuridine).

(E)-5-(2-bromovinyl-2'-deoxyuridine) crystallizes in the space group P2(1) with a = 12.976(1), b = 4.800(1), c = 20.385(2) A, beta = 96.88(1) degrees, Z = (two molecules a and b in the asymmetric unit). The structure has been determined by the use of 2400 diffractometer reflexions and refined by least-squares to R of 0.053. Conformational features of both molecules a and b resemble those of thymidine. The ribofuranose rings assume the rare C(3')-exo form observed also in thymidine. Similarly, the torsion angles around the glycosidic bonds (mean = 40(1) and 56(1) degrees fall in the anti range. In each molecule the best plane of the 2-bromovinyl moiety is bent out of the least-squares plane of the pyrimidine base by 6 degrees, so that the positively charged C(8)-H(8) group can donate an intramolecular hydrogen bond to 0(4) atom. Eight strong and weak intermolecular hydrogen bridges are built up between the symmetry independent and related molecules forming a complicated three dimensional hydrogen bond network.

ChemInform Abstract: THE CHEMISTRY OF SMALL RING COMPOUNDS PART 25, 1‐ACETOXYCYCLOPROPANOL, A CONVENIENT PRECURSOR FOR CYCLOPROPANONE

AbstractDie Acetoxygruppe in der Titelverbindung (I) kann leicht durch verschiedene Nucleophile substituiert werden, wie die dargestellten Verbindungen (II) demonstrieren.