Soft Lewis Base Research Articles

Light-stable and antimicrobial active silver(I) complexes composed of triphenylphosphine and amino acid ligands: Synthesis, crystal structure, and antimicrobial activity of silver(I) complexes constructed with hard and soft donor atoms ( n∞{[Ag(L)(PPh 3)] 2} with L = α-ala − or asn − and n = 1 or 2)

Three novel silver(I) complexes consisting of both hard Lewis bases (O and N atoms) and one soft Lewis base (P atom) (( dl-α-alaninato)(triphenylphosphine)silver(I) ( 1), ( dl-asparaginato) (triphenylphosphine)silver(I) ( 2) and ( l-asparaginato) (triphenylphosphine)silver(I) ( 3)) were prepared from stoichiometric reactions of amino acid–silver(I) complexes with PPh 3 in a 1:1 molar ratio in a mixed organic solvent. These silver(I) complexes were soluble in organic solvents but insoluble in water; they are also more light-stable as compared to the corresponding precursors, amino acid–silver(I) complexes. Their solid-state and solution structures were unequivocally characterized using elemental analysis, TG/DTA, FTIR, X-ray structure analysis, solution ( 1H, 13C, and 31P) NMR and solid-state 31P CPMAS NMR spectroscopy. The X-ray structure analysis of complexes 1 and 2 revealed that these complexes were dimers with an inversion center. Each silver(I) atom was coordinated in a distorted four-coordinate environment containing an AgNO 2P core. Complexes 1 and 2 formed 1D and 2D networks in the crystal through intermolecular hydrogen bonding networks that can be described as ∞{[Ag( dl-α-ala)(PPh 3)] 2 · 2H 2O} and 2 ∞{[Ag( dl-asn)(PPh 3)] 2 · 2H 2O · 2EtOH}, respectively. Complexes 1– 3 showed moderate to modest antimicrobial activities against selected bacteria and yeasts in a water-suspension system.

The Cadmium Transport Sites of CadA, the Cd2+-ATPase from Listeria monocytogenes

CadA, the Cd(2+)-ATPase from Listeria monocytogenes, belongs to the Zn(2+)/Cd(2+)/Pb(2+)-ATPase bacterial subfamily of P(1B)-ATPases that ensure detoxification of the bacteria. Whereas it is the major determinant of Listeria resistance to Cd(2+), CadA expressed in Saccharomyces cerevisiae severely decreases yeast tolerance to Cd(2+) (Wu, C. C., Bal, N., Pérard, J., Lowe, J., Boscheron, C., Mintz, E., and Catty, P. (2004) Biochem. Biophys. Res. Commun. 324, 1034-1040). This phenotype, which reflects in vivo Cd(2+)-transport activity, was used to select from 33 point mutations, shared out among the eight transmembrane (TM) segments of CadA, those that affect the activity of the protein. Six mutations affecting CadA were found: M149A in TM3; E164A in TM4; C354A, P355A, and C356A in TM6; and D692A in TM8. Functional studies of the six mutants produced in Sf9 cells revealed that Cys(354) and Cys(356) in TM6 as well as Asp(692) in TM8 and Met(149) in TM3 could participate at the Cd(2+)-binding site(s). In the canonical Cys-Pro-Cys motif of P(1B)-ATPases, the two cysteines act at distinct steps in the transport mechanism, Cys(354) being directly involved in Cd(2+) binding, while Cys(356) seems to be required for Cd(2+) occlusion. This confirms an earlier observation that the two equivalent Cys of Ccc2, the yeast Cu(+)-ATPase, also act at different steps. In TM4, Glu(164), which is conserved among P(1B)-ATPases, may be required for Cd(2+) release. Finally, analysis of the role of Cd(2+) in the phosphorylation from ATP and from P(i) of the mutants suggests that two Cd(2+) ions are involved in the reaction cycle of CadA.

Rh2[MTPA]4, a dirhodium complex as NMR auxiliary for chiral recognition

The dirhodium complex Rh(+II)2[(+)-MTPA]4 is introduced as an NMR auxiliary for enantiodifferentiation. As a soft Lewis acid, it is particularly useful for the recognition of soft Lewis base molecules. The donor properties of ligands can be divided into several categories and are exemplified by various classes of phosphorus-containing functionalities. In addition, the thermodynamics of the underlying ligand-complex equilibria are discussed and stereochemical implications demonstrated. The extension of the dirhodium method to absolute configuration determination is evaluated. The outlook for future applications with further non-phosphorus ligands is presented.

Dynamics and equilibrium for the formation of fluorescent Lewis acid-base exciplexes and triplexes between 9-aminophenanthrene and aliphatic amines.

The excited singlet states of 9-aminophenanthrene and its N-aminoalkyl derivatives are strongly fluorescent in cyclohexane. Addition of low concentrations of Et(3)N, Pr(2)NH, or PrNH(2) results in a red shift of the emission maximum and moderately decreased fluorescence intensity. Analysis of the fluorescence behavior using a combination of singular value decomposition with self-modeling and kinetic analysis provides evidence for the sequential formation of 1 : 1 (exciplex) and 1 : 2 (triplex) complexes between the excited 9-aminophenanthrene and ground-state alkylamine, both of which are strongly fluorescent. Both the formation and decay of the exciplex and triplex are dependent upon the extent of amine N-alkylation. Rate constants and equilibrium constants for complex formation follow the order 1 degree approximately 2 degree > 3 degree, analogous to that for the formation of ground-state complexes between amines and the soft Lewis base HgBr(2). Similarly, N-aminoalkyl derivatives of 9-aminophenanthrene form intramolecular exciplexes. Excited-state complex formation is attributed to a Lewis acid-base interaction between the excited aminophenanthrene (lone-pair acceptor) and ground-state amine (lone-pair donor). The factors which determine the stability of excited-state Lewis acid-base complexes are characteristic of the specific excited-state acceptor. No universal scale of lone-pair donor strength can be expected to describe the formation of such complexes.

Polymeric Membrane Ion-Selective Electrodes Based on Molecular Asterisk Ionophores

Ion-selective electrodes (ISEs) have been developed that incorporate a novel supramolecular class of ionophores called molecular asterisks. These ionophores are constructed with “arms” of repeating phenylene sulfide units that radiate outward from a core of either benzene or coronene. The flexibility of the arms, as well as the open exterior geometry and multiple soft Lewis base functionalities make these molecules potential candidates as ionophores for ISEs particularly for soft Lewis acids like transition metals. Studies with molecular asterisk-based ISEs show that these ionophores display a high selectivity relative to ion-exchanging ionophores toward Ag+ over a number of other cations. According to theoretical prediction, these ISEs demonstrate a super-Nernstian region of response toward silver from 10−6 to 10−5 M with a Nernstian response above 10−5 M, when primary ion is absent from the internal filling solution. Additionally, it was determined that both the nature of the core entity and the length (or generation) of the arms play a role in governing selectivity of these ionophores.

Ligand Properties of Thioamides and Their N- and N,N'-Derivatives

A series of nonempirical calculations by the Hartree-Fock method with full geometry optimization for a number of N- and N,N'-derivatives of thioamides which are potential functional groups for sorbents for extraction of platinum metals from technological solutions. The ligands all prefer to coordinate to platinum metal ions by the sulfur atom (soft Lewis base) at an angle to the sulfur-oxygen bond.

Effect of Inorganic Additives on Solutions of Nonionic Surfactants

The effect of salts on the nonionic surfactant octoxynol 9 was studied by the changes they produced in its cloud point (CP): CP increases indicate salting in. The temperatures by which the sodium salts of water structure-breaking (chaotropic) anions increased the CP of 2.0% octoxynol solutions were measured as a function of salt concentration. The curves representing changes in CP versus salt molality rose to a maximum in a parabolic fashion, followed by steep decreases. Their ascending branches, corresponding to salting in, were caused by a disruption of the water structure due to the chaotropic effect of the anions combined with the effect of elevated CP temperatures. The descending branches were due to salting out by Na+. The net CP increases due to the chaotropic effect of the anions were calculated at each concentration by subtracting the CP decrease due to Na+from the observed CP increase of the respective Na+salts. With the exception of ClO4−, the plots of CP changes produced by the chaotropic anions rose in a nearly linear fashion to a maximum and then levelled off. The levelling off occurred at the salt concentration and CP temperature leading to the maximum disruption of the water structure of which each anion was capable. The chaotropic anions were ranked in the following order according to their capacity for increasing the CP: SCN−> I−> [Fe(CN)5NO]2−> ClO4−> BF4−. Even though the thiosulfate anion is a very soft Lewis base, it lowered the CP in direct proportion to its molality; i.e., it enhanced the structure of water and promoted salting out at all concentrations.

CUPROUS DITHIOCARBAMATES. SYNTHESES AND REACTIVITY

Abstract Thiuram disulfides react with copper metal in organic solvents to afford copper(I) dithiocarbamates which are characterized by infrared, proton magnetic resonance and ESCA spectroscopies, as well as room temperature magnetic susceptibility measurements. These compounds react with some soft Lewis bases such as triphenylphosphine to give the bis-adducts, which are also isolated and characterized.

ChemInform Abstract: Tungsten Pentacarbonyl as a Potential Protecting Group for Soft Lewis Base Centres in Alkylation of Multifunctional Molecules.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Tungsten pentacarbonyl as a potential protecting group for soft lewis base centres in alkylation of multifunctional molecules

Reaction of W(CO) 6 or (PhNH 2)W(CO) 5 with the molecules which possess both diphenylphosphanyl- and dialkylamino group or nitrogen — containing hetcrocyclic ring proceeds selectively through “soft” Lewis base groups and can be used for the protection of the groups from alkylalion. As a rule, the diphenylphosphanyl group participates in the co-ordination, but in some cases an sp 2-hybridized nitrogen was shown to be the preferable co-ordination site. The new synthesized compounds have been characterized by NMR, IR spcctroscopy, and elemental analysis.

Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γsd) is about 90 mJ·m−2 at 25 °C and the acid-base contribution to the free energy of adsorption (ΔGaAB) for Lewis bases is higher than 8 kJ·mol−1. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago's EA, CA, EB and CB parameters. Whilst EA and CA are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the EB and CB values suggest that PPyTos is a very soft Lewis base.

Coordination of (CH 3) 2X (X  O, S, and Se) to borane: an ab initio molecular orbital study

The mechanism of coordination of (CH 3) 2X (X = O, S, and Se), i.e. dimethyl ether, dimethyl sulfide, and dimethyl selenide, to BH 3 as well as free (CH 3) 2X itself has been studied by ab initio molecular orbital methods. In all cases coordination occurs through σ-donation from (CH 3) 2X to BH 3. Both (CH 3) 2Se and (CH 3) 2S coordinate to BH 3 with their local C 2-like axis tilting largely from the local C 3-like axis of BH 3 while (CH 3) 2O coordinates to BH 3 with moderate tilting. These trends can be rationalized in terms of orbital interaction stabilization energy. The orbital interaction stabilization energy term is large for (CH 3) 2Se and (CH 3) 2S while the electrostatic energy term is almost the same for the three complexes. All these features support the general idea that both (CH 3) 2Se and (CH 3) 2S are soft Lewis bases and (CH 3) 2O is a hard Lewis base.

Stability of ternary amino acid complexes and its computer simulation under physiological conditions

AbstractThe binary and ternary formation constants of mixed amino acid complexes with Zn(II), Cu(II), Ni(II) and Cd(II) have been potentiometrically determined under physiological conditions. The symbiosis of HSAB does play a role in the formation of ternary amino acid complexes. Comparing with Zn(II), as a softer Lewis acid Ni(II) shows its preference to softer Lewis bases cysteinate and histidinate. These soft Lewis bases more likely gather together in the mixed amino acid complexes. It is expected that the ternary amino acid complexes are overwhelming in the distribution of complex species especially at biological conditions. In the case of zinc, differring from previous study the alaninate‐containing mixed complexes become the predominant species formed in the region of pH 7.4.

Crown Thioether Complexes of AgI and CuI: The Crystal Structures of [{Ag3L3}AgL{AgL2}](ClO4)4 and [LCuI] (L = 1, 4, 7‐Trithiacyclononane)

A crown thioether molecule as bridging ligand and two types of cations in the molecule are the most striking features of the silver complex [Ag4L5](ClO4)4 (L = 1,4,7‐trithiacyclononane). In the cation [AgL2]⊕, Ag⊕ is surrounded by six S atoms, in the cation [Ag3L3]3⊕ by four. One S atom of each of the three ligands in [AgL,]3⊕ is bound to two Ag⊕. In contrast, the soft Lewis base I⊕ in [LCuI] competes with the S atoms for coordination positions. In the resulting monomeric units, Cu⊕ is coordinated in a distorted tetrahedral fashion by three S atoms and one I⊕.

Infrared matrix isolation study of the interaction of sulfur trioxide with soft Lewis bases

Infrared spectroscopy has been coupled with the matrix isolation technique for a study of the molecular complexes formed between SO/sub 3/ and soft Lewis bases (phosphorus and sulfur bases). Each 1:1 complex was characterized by a significant shift of the antisymmetric stretching mode of the SO/sub 3/ subunit as well as by the perturbation of certain base vibrational modes. The shifts observed in this study were substantially larger than those seen in previous studies of the complexes of SO/sub 2/ with oxygen and nitrogen bases. This is in disagreement with predictions based on the proton affinity of the base, but fits well with the principles of hard/soft acid/base theory. The data are also in good agreement with the extensive data on HF complexes of similar bases.

Chemisorption bond energies of Lewis acids and bases on oxygen modified Mo(100) surfaces

The acid-base properties of three molybdenum (100) surfaces chemically modified by 1.5, 1.2, and 1.0 monolayers (ML) of atomic oxygen were investigated by thermal desorption spectroscopy using a series of molecular Lewis bases. The molecules used in this study were of three types, hard Lewis bases, ammonia and dimethylether, soft Lewis bases, phosphine, ethene and propene, and two π acids, carbon monoxide and 3,3,3-trifluoropropene. The trends in desorption energies are consistent with the expectation that the molecules would adsorb at localized, acidic surface sites. The desorption energies are correlated with proton affinities, and the 1.5 ML oxygen modified surface was found to most resemble a gas phase proton.

ChemInform Abstract: ON THE TRAIL OF DICHLORODINITROSYLTUNGSTEN: A TALE OF TWO REACTIONS

AbstractPolymeres [W(NO)2CI2]" (I) kann bei Beachtung experimenteller Einzelheiten nach zwei prä‐ parativen Methoden dargestellt werden." Im ersten Verfahren wird WCl6 in CH2Cl2 mit NO im Überschuß behandelt und das Nebenprodukt ClNO vollständig aus dem System entfernt; die Ausb. beträgt 47%.

An EELS study of N 2O adsorption on Pt(111)

At 78 K, N 2O adsorbs on a Pt(111) surface in an end-on configuration through the terminal N atom and inclined at an angle to the surface estimated at 35°. N 2O is a soft Lewis base with adsorption occurring by donor bond formation and without significant back donation into the unoccupied 3π antibonding orbital. Adsorption is accordingly weak with an initial heat of adsorption of 5.6 kcal mol −1 which increased to 6.05 kcal mol −1 at saturation by attractive lateral interactions. No evidence for decomposition was seen. A multilayer state, adsorbed approximately parallel to the surface, desorbed near 86 K with a heat of vaporization estimated at 5.24 kcal mol −1.

Reactions of methylmercuric chloride with soft lewis bases in anhydrous media

Reactions of methylmercuric chloride with soft lewis bases in anhydrous media