Anionic Substituents Research Articles

Self-assembly of cinchonine quaternary salts: Effect of substituents and halogen anions on supramolecular architecture

Four cinchonine quaternary salts organic salts of formulations [C 25H 34N 3O 2] +X − (X=Cl ( 1), Br ( 2), I ( 3)), and [C 21H 26N 3O 2] +I − ( 4), have been synthesized and characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, 1H NMR. Single crystal X-ray diffraction analysis shows that compound 1 is isostructural with 2. 1D supramolecular helix assembled from O–H⋯X − and C–H⋯X − ((X=Cl ( 1), Br ( 2)) hydrogen bonds are observed in 1 and 2; however, a two-dimensional (2D) hydrogen bonds grids in 3 due to effect of halogen anions. Compound 4 possesses novel hydrogen-bonded three-dimensional (3D) network, in which unusual 1D hydrogen-bonded organic double-stranded helical chains assembled from wrapping of two single-stranded helical chains around each other via aromatic π–π stacking interactions. The role of the weak C–H⋯X −, C–H⋯O hydrogen bonding and the effects of substituents of quinuclidine and halogen anions on supramolecular architecture have also been discussed.

The participation of the anion and alkyl substituent of diaryliodonium salts in photo-initiated cationic polymerization reactions

The photo-initiated cationic polymerization (PCP) of epoxides using diaryliodonium salt photoacid generators (PAGs) bearing alkyl groups and anions was investigated. The properties and reactivities of a series of iodonium salts containing various cations and anions were compared in the context of a PCP reaction. The products from the decomposition of the cations of these salts were analyzed using gas chromatography-mass spectrometry (GC-MS) spectra. The relationship between the molecular structure of the salts and their reaction mechanism in the PCP reaction was investigated. Based on the results of the investigation, it was concluded that the structures of the cations and anions of theiodonium salts affect the PCP reaction rate, which was controlled by the products from the diaryliodonium salts. As part of an additional investigation, the diaryliodonium salts-epoxide materials were applied to 254 nm-photo-patterning. Copyright © 2006 John Wiley & Sons, Ltd.

VARIATIONS IN THE SUBSTITUTED 3‐LINKED MANNANS CLOSELY ASSOCIATED WITH THE SILICIFIED WALLS OF DIATOMS1

The polysaccharides from cleaned frustules of the diatoms Pinnularia viridis (Nitzsch) Ehrenberg, Craspedostauros australis Cox, Thalassiosira pseudonana Hasle et Heimdal, and Nitzschia navis‐varingica Lundholm et Moestrup were extracted with hot alkali that dissolved the silica and were characterized by constituent sugar and linkage analyses. The polysaccharides from P. viridis were investigated further by permethylation, partitioning according to solubility, desulfation, and CD3I‐methylation. Yields of carbohydrate in the hot alkali extracts ranged from 0.9% to 1.8% w/w based on the dry weight of the silica. Mannose was the dominant sugar in the polysaccharides from all four species (54–69 mol% of constituent sugars), although 14 other monosaccharides, including neutral sugars (glucose, galactose, xylose, arabinose, rhamnose, fucose), acidic sugars (glucuronic acid, galacturonic acid, 2‐O‐methylglucuronic acid), and O‐methylated neutral sugars (2‐O‐methylrhamnose, 3‐O‐methylrhamnose, 2,3‐di‐O‐methylrhamnose, 3‐O‐methylxylose, 4‐O‐methylxylose) were also detected in varying proportions among the four samples. The polysaccharides were predominantly composed of a 3‐linked mannopyranose backbone with a prevalence of linkage and/or substitution at O‐2 of the 3‐linked mannopyranosyl residues, and they were polyanionic, bearing uronic acid residues and/or sulfate esters. There were, however, species‐specific differences in the degree and position of substitution on the mannan backbone, the type and substitution patterns of the anionic substituents, and the type and linkage patterns of sugars other than mannose. Although definitive functions for these polysaccharides in diatom biology remain uncertain, a possible role in biosilicification is discussed.

Open Shell Dianions Likely To Be Stable in the Gas Phase with Respect to Autoionization.

We address the challenge set by Dreuw and Cederbaum [Dreuw, A.; Cederbaum, L. S. Chem. Rev. 2002, 102, 181-200] to develop a set of "small" open shell stable dianions. We offer two families of such species, based on a central diradical center with attached anionic sites. Both families achieve dianion stabilization through alternating zones of positive and negative charge. First, quasi-linear systems such as NB(C2)n-Q-(C2)nBN become diradical dianions stable to autoionization in two cases: (a) for Q a divalent (carbene) carbon when n is two or greater and (b) for Q a C4 ring diradical when n is one or greater. Second, carbenes with certain anionic aromatic substituents can be stable with respect to autoionization. π-Acid substituted carbenes (A2Q) have triplet ground states generally. If A is cyclopentadienyl anion stabilized by cyano substitution, the resulting triplet dianion is stable with respect to autoionization. In bisphenyl carbenes the triplet is relatively stabilized when ortho substituents force the system toward D2d symmetry. The dianion of bis(orthochlorophenyl) carbene produced by para-substitution with BN retains the triplet preference and is stable with respect to autoionization. These results obtained first by density functional calculations in a small basis, B3LYP/6-31G(d), are confirmed and extended by ROMP2 and CCSD calculations in a more flexible basis, 6-31+G(d). DFT has a systematic bias against systems with excess electrons, which is paradoxically a virtue in the screening of candidate dianions since the DFT calculation does not make false predictions of stability.

Influence of Host's Substitution on the Orientation of the Guest: Pseudo-rotaxanes of Charged Cyclodextrins with Methyl Orange in Solution

Methyl Orange (MO), an azo-dye molecule with an inherent dipole moment, has been used as a probe to explore the influence of anionic or cationic substituents of cyclodextrins (CDs) on the mode of insertion to form pseudorotaxanes, using NMR spectroscopy. MO is oriented in a single mode inside the βCD cavity, with the dimethylamino group localized at the secondary side. This orientation is completely reversed when MO enters the anionic sodium heptakis[6-deoxy-6-(3-thiopropionate)]-βCD (βpsp) cavity, whereas inside the cationic heptakis(6-deoxy-6-amino)-βCD hydrochloride, MO flips once more, to adopt the same orientation as in βCD. In the latter case the water solubility of MO is significantly lowered. The disposition of the guest in βCD and in each βCD derivative in a single mode was attributed principally to anti-parallel dipole-dipole stabilization. In the wider γCD, the availability of more cavity space leads to 1:2 and 2:2 host/guest stoichiometries and the effect of dipoles is of secondary significance. In the anionic sodium octakis[6-deoxy-6-(3-thiopropionate)]-γCD, MO is positioned as in βpsp, but a 1:2 adduct is also detected. Finally, MO does not dissolve in octakis(6-deoxy-6-amino)-γCD hydrochloride solution.

Electrostatic Contributions to Cyanine Dye Aggregation on Peptide Nucleic Acid Templates

A symmetrical benzothiazole-based dicarbocyanine dye with anionic propylsulfonate substituents was synthesized in order to assess the importance of electrostatic forces in the assembly of helical dye aggregates on peptide nucleic acid (PNA) templates (Smith, J. O.; Olson, D. A.; Armitage, B. A. J. Am. Chem. Soc. 1999, 121, 2686−2695). UV−vis and circular dichroism spectroscopy demonstrate effective aggregation of the dye on a 10 base pair PNA−PNA duplex but weak aggregation on the analogous PNA−DNA duplex. The CD spectra are consistent with a left-handed helical morphology for the dye aggregate, as expected for the left-handed PNA−PNA double helical template. Continuous variations analysis indicates formation of a 6:1 aggregate of the dye on a 10 base pair PNA−PNA duplex. An analogous dye bearing two cationic side chains and a net charge of +3 does not aggregate on the PNA−PNA duplex but can be recruited into a mixed aggregate with the anionic dye due to partial charge neutralization. Finally, charged gro...

Electronic Absorption and Resonance Raman Signatures of Hyperporphyrins and Nonplanar Porphyrins

We have carried out a broad survey of tetraphenylporphyrin derivatives in relation to their possible hyperporphyrin character. The majority of the free-base tetraphenylporphyrins studied, i.e., TArPH2; Ar = p-X−C6H4, where X = CH3, H, F, CF3, and NO2, when dissolved in trifluoroacetic acid (i.e. when centrally diprotonated), exhibit red-shifted “hyperporphyrin” spectra. The “hyper” features are attributable to phenyl-to-porphyrin charge-transfer transitions. However, certain free-base tetraphenylporphyrins with extremely electron-deficient phenyl groups, such as TPFPPH2, do not exhibit hyperporphyrin spectra in trifluoroacetic acid solution. Certain anionic tetraphenylporphyrin derivatives such as T(p-OH−P)PH2 or Ni[T(p-OH−P)P] dissolved in methanolic Bu4NOH also qualify as hyperporphyrins. The hyper transitions in these cases involve charge transfer from anionic phenolate substituents to the neutral porphyrin core. This study also presents a first systematic resonance Raman spectroscopic exploration of h...

Concerted rearrangement versus heterolytic cleavage in anionic [2,3]- and [3,3]-sigmatropic shifts. A DFT study of relationships among anion stabilities, mechanisms, and rates.

The anionic [2,3] sigmatropic Wittig rearrangements of deprotonated 4-hetera-1-pentenes and the anionic [3,3] sigmatropic Cope rearrangements of 3-substituted-1,5-hexadienes were explored by using density functional theory calculations. While the deprotonated anionic 3-hydroxy-1,5 hexadiene (2a), 3-thiohydroxy-1,5-hexadiene (2c), and 3-formamidyl-1,5-hexadiene (2d) Cope substrates undergo concerted rearrangements, the deprotonated anionic 3-amino-1,5-hexadiene (2b) and 3-methyl-1,5-hexadiene (2e) Cope substrates follow nonconcerted cleavage/recombination pathways. We have also found that the gas-phase Wittig (1a), aza-Wittig (1b), and carba-Wittig (1c) reactions proceed via nonconcerted cleavage/recombination pathways. These results are compared with previous results on the Cope rearrangements of deprotonated anionic 3-hydroxy-1,5-hexadiene and 3-amino-1,5-hexadiene anions. A previously established model that heterolytic and homolytic bond dissociation energies can be used to predict how anionic amino- and oxy-Cope substrates will react is generalized to account for the reactivity of other Cope substrates as well as for the Wittig rearrangements. There is also a relationship between the basicity of the anionic substituent in the Cope rearrangement and the reaction pathway: the more basic the substituent anion, the less stable it is, and the more likely it is that cleavage will occur. A first step toward studying these reactions in solution was also taken by calculating energetics for some of the rearrangements with a lithium counterion present.

Thiols as classical and slow-binding inhibitors of IMP-1 and other binuclear metallo-beta-lactamases.

The inhibitory effect of a variety of thiol compounds on the function of binuclear metallo-beta-lactamases, with a particular focus on IMP-1 from Pseudomonas aeruginosa, has been investigated. Thiol inhibitors, depending on their structural features, fall into two categories, one in which inhibition at neutral pH was instantaneous and the other in which inhibition was time-dependent. While mercaptans with anionic substituents in the vicinity of their SH groups exhibited the former type of inhibition, neutral thiols appear to induce a slow, time-dependent isomerization of the initially formed EI complex to a tighter EI complex. Kinetic parameters describing the latter process were obtained by fitting progress curves of substrate hydrolysis using standard and numerical procedures. The failure of charged thiols to exhibit slow binding is suggested to be due to a rapid isomerization of the initial EI complex. Slow binding in the case of neutral thiols was observed only below pH 8. Studies on the pH dependence of catalysis by IMP-1 revealed that (i) enzyme inactivation at low pH is a slow process with presumably two groups with a pK(a) of approximately 5.2 in the protein being responsible for the loss of activity, (ii) inhibition by thiols is independent of pH between pH 5 and 9, and (iii) an apparent enhancement of the catalytic activity of IMP-1 by thiols occurs at pH <5. The last mentioned phenomenon is explained by a model in which mercaptans retard the proton-dependent isomerization of the enzyme. Studies on the thiol-mediated inhibition of the binuclear forms of Bacteroides fragilis (CcrA) and Bacillus cereus (BcII strain 5/B/6) metallo-beta-lactamase have revealed that while CcrA was instantaneously albeit moderately inhibited by mercaptans, BcII mimicked IMP-1 in its interaction with thiols. These differences are proposed to be due partly to the structural divergence of these proteins in the vicinity of Zn2.

Synthesis and Structure of Solvated Protons Incorporating Weakly Coordinating Anions. Precursors of Superacids†

AbstractSix new solvated proton salts of highly halogenated carborane anions, [H(solvent),] [carborane] (carborane = 1‐R‐CB11‐Y5X6‐(R=H, Me; X, Y=CI, Br, I), 1‐H‐CB9Br9−) were prepared from the salt metathesis reaction of Ag(carborane) and HO in high yields. Single‐crystal X‐ray analyses show that they are all discrete molecules in the solid‐state. The number of the solvated molecules surrounding H+ ion can not be determined with the knowledge of the size and substituents of the carborane anions. These salts provide convenient weighable sources of Brønsted acid reagents having a wide range of acidities and good thermal stabilities. TGA results indicate that the solvated molecules (water or organic molecules) in the cations [H(solvent)n]+ can be removed under high temperature and high vacuum conditions to give superacidic materials H(carborane) which can protonate olefin.

Supramolecular assemblies of photochromic benzodithia-18-crown-6 ethers in crystals, solutions, and monolayersElectronic supplementary information (ESI) available: crystal data, data collection, and structure solution and refinement parameters. See http://www.rsc.org/suppdata/nj/b1/b110630a/

We studied the assembly of dithiacrown ether styryl dye (CSD) molecules in crystals, solutions, and films in the presence of metal cations. X-Ray diffraction data allowed us to conclude that the anion affects the supramolecular architecture of CSDs in the crystal, specifically, the type of stacking of the dye molecules. In solution, in the presence of Pb2+, CSD molecules with the betaine structure spontaneously form dimeric complexes consisting of two dye molecules and two metal cations, with a fixed mutual arrangement of the double bonds. The dimer complex is stable due to coordination between the anion substituent of one molecule and the metal cation located in the crown ether cavity of the other molecule. Irradiation of the dimer complexes leads to regio- and stereoselective [2 + 2]-cycloaddition, giving only one cyclobutane derivative of the eleven theoretically possible products. The other photoreaction studied for CSDs is reversible Z–E isomerization. Due to its specific structure, the betaine-type CSD is able to form the ‘anion-capped’ Z-isomer. Intramolecular coordination in the ‘anion-capped’ isomer enhances its stability and causes a sharp deceleration of its dark Z–E isomerization. The amphiphilic CSD forms relatively stable monolayers on distilled water and various aqueous salt subphases. The results obtained indicate that it is possible to distinguish between two types of the dye monolayer structures based on the presence of alkali or heavy metal cations in the aqueous subphase.

Synthesis and X-ray Crystal Structure Analysis of a Cp-Substituted Phosphaferrocene

At 140 °C in THF, a 2,3,4,5-tetramethyl-1-cyclopentadienylide anionic substituent migrates from phosphorus to the α-carbon of the corresponding P-substituted 3,4-dimethylphosphole 2. The resulting 2-cyclopentadienyl-3,4-dimethylphospholide ion (3) reacts with a [CpFe]+ source to give the corresponding 2-cyclopentadienyl-3,4-dimethyl-1-phosphaferrocene (5) as a mixture of two diastereomers, one of which has been characterized by X-ray crystal structure analysis.

Carbonium ion salts. Part 16. Molecular orbital study of tropylium ions with borane anion and carborane substituents (hemiousene compounds)

We have extended our ab initio study of substituted tropylium ions to examine several known and postulated hemiousene compounds where the ring has a substituent derived from a polyhedral borane anion, carborane, or carborane anion. Tropyliumyl derivatives of the borane anions closo-B 10H 10 2−, closo-B 12H 12 2−, and closo-CB 9H 10 − are Type III substituted tropylium ions with substituent to ring charge-transfer in the HOMO–LUMO (HL) transition. An additional boron electron pair of the closo-cage in 2-C 7H 6–B 10H 9 − and C 7H 6–B 12H 11 − is completely delocalized over cage and ring. Tropyliumyl derivates of the carborane and carborane anions closo-C 2B 10H 12 and closo-CB 11H 12 − are Type II substituted tropylium ions with polarization of ring π-system by substituent and little if any charge-transfer HL interaction. The tropyliumyl derivative of nido-C 2B 9H 12 − is in a class by itself; however both theory and experiment demonstrate that it has strong HL charge-transfer like a Type III ion.

27] Extracellular polymers of microbial communities colonizing ancient limestone monuments

Publisher Summary This chapter discusses the extracellular polymers of microbial communities colonizing ancient limestone monuments. Biofilms are layered microbial communities growing on inert and livingsurfaces in a variety of terrestrial and aquatic environments, including submerged artificial substrata, invertebrate teguments, sediments, soils, and rock surfaces. The exopolymers, mainly composed of polysaccharides, are an important component of such biofilm communities and their functional roles in terms of attachment, nutrient absorption, and protection against desiccation and antimicrobial agents. Given the anionic substituents that these compounds may have, they can interact actively with dissolved ions in aqueous environments and with framework elements in mineral matrices. The implications of such interactions among exopolysaccharides (EPS) and minerals may also include cation mobilization in soils, solubilization of toxic metals, and the dissolution of minerals. On other hand, studies carried out in Mayan archaeological sites (Yucatan, Mexico) have shown that thick microbial biofilms dominated by cyanobacterial populations contributed to the biodegradation of these buildings by supporting growth of organic acid-producing microorganisms and through active boring. These microbial exopolymers may contribute directly to the deterioration processes by interacting through their polysaccharide fraction with metal cations, which could lead to the complexation of soluble calcium, sequestering it from the limestone matrix. This chapter describes procedures to extract and characterize the polysaccharidic fraction of naturally occurring microbial exopolymers associated with epilithic biofilms.

Isokinetic relationships for nucleophilic substitution reactions at the saturated carbon atom. Reactions in aqueous solutions

An isokinetic relationship (IKR) with the parametersT iso=6145 K and logk iso=10.622 is valid for nucleophilic substitution reactions at the saturated carbon atom with the participation of anionic nucleophiles in aqueous solutions. The IKR describes the rate constants of the reactions with different anionic nucleophiles, leaving groups, and substituents at the electrophilic reaction center. Similar reactions with neutral nucleophiles, which follow another mechanism, are described by a separate IKR withT iso=−1232 K and logk iso=16.226. The reactions of haloforms with hydroxide ion, which proceed by a specific mechanism involving the haloform ionization equilibrium followed by α-elimination of the halide ion, are described by yet another IKR withT iso=−1463 K and logk iso=21.057.

A computational examination of Diels–Alder reactions with 1,3-cyclopentadienes bearing anionic and cationic substituents at C-5

Ab initio calculations predict that deprotonation and protonation of 5-heterosubstituted 1,3-cyclopentadienes would significantly modify their facial selectivities in Diels–Alder additions. Anionic substituents enhance syn-addition, and cationic substituents promote anti-addition, relative to the neutral dienes. Stereoelectronic and steric effects together determine the facial selectivity of ionic dienes.

Ganglioside GD1α analogues as high-affinity ligands for myelin-associated glycoprotein (MAG)

The first systematic synthesis of ganglioside GD1α analogues carrying N-acetyldeoxyneuraminic acids linked to C-6 of the GalNAc residue was accomplished. The suitably protected GM1b pentasaccharide derivative was regioselectively glycosylated with the phenyl 2-thioglycosides of 7-deoxy, 8-deoxy, and 9-deoxy- N-acetylneuraminic acid promoted by N-iodosuccinimide (NIS)–trifluoromethanesulfonic acid (TfOH) in acetonitrile, and the resulting hexasaccharides were converted to the target GD1α analogues. All of the analogues retained excellent efficiency in supporting the adhesion to myelin-associated glycoprotein (MAG), raising the possibility that the internal sialic acid linked to the GalNAc residue may be replaced by other anionic substituents, in contrast to the terminal sialic acid, which is essential for MAG binding.

Inhibition of protease-resistant prion protein formation by porphyrins and phthalocyanines.

A central aspect of pathogenesis in the transmissible spongiform encephalopathies or prion diseases is the conversion of normal protease-sensitive prion protein (PrP-sen) to the abnormal protease-resistant form, PrP-res. Here we identify porphyrins and phthalocyanines as inhibitors of PrP-res accumulation. The most potent of these tetrapyrroles had IC50 values of 0.5-1 microM in scrapie-infected mouse neuroblastoma (ScNB) cell cultures. Inhibition was observed without effects on protein biosynthesis in general or PrP-sen biosynthesis in particular. Tetrapyrroles also inhibited PrP-res formation in a cell-free reaction composed predominantly of hamster PrP-res and PrP-sen. Inhibitors were found among phthalocyanines, deuteroporphyrins IX, and meso-substituted porphines; examples included compounds containing anionic, neutral protic, and cationic peripheral substituents and various metals. We conclude that certain tetrapyrroles specifically inhibit the conversion of PrP-sen to PrP-res without apparent cytotoxic effects. The inhibition observed in the cell-free conversion reaction suggests that the mechanism involved direct interactions of the tetrapyrrole with PrP-res and/or PrP-sen. These findings introduce a new class of inhibitors of PrP-res formation that represents a potential source of therapeutic agents for transmissible spongiform encephalopathies.

Million-Fold Acceleration of a Diels−Alder Reaction due to Combined Lewis Acid and Micellar Catalysis in Water

The effect of micelles of sodium dodecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB), dodecyl heptaoxyethylene ether (C12E7), and copper and zinc didodecyl sulfate (M(DS)2) on the Diels−Alder reaction of 3-(para-substituted phenyl)-1-(2-pyridyl)-2-propen-1-ones 1a−g, containing neutral, cationic, or anionic substituents, with cyclopentadiene (2) has been studied. In the absence of catalytically active transition-metal ions, micelles invariably retard the reaction. This can be rationalized on the basis of different binding locations of the reaction partners in the micelle. These binding sites have been probed using solubilizate-induced aromatic shifts in the 1H NMR spectrum of the surfactant and paramagnetic counterion-induced relaxation enhancements of the 1H NMR signals of the solubilizate. In contrast to SDS, CTAB, and C12E7, Cu(DS)2 micelles catalyze the Diels−Alder reaction between 1 and 2 with extremely high efficiency, leading to rate enhancements up to 1.8 × 106 compared to the uncatalyzed...

Transmission of electronic effects by icosahedral carboranes; skeletal carbon-13 chemical shifts and ultraviolet–visible spectra of substituted aryl-p-carboranes (1,12-dicarba-closo-dodecaboranes)

A series of para-carboranes (1,12-dicarba-closo-dodecaboranes) substituted at one or both carbon atoms by phenyl groups bearing a range of electron-releasing or -withdrawing substituents (X = NMe2, NH2, OH, OMe, Me, CF3 or NO2), principally at the para positions, has been prepared. The carbon-13 NMR shifts of the monoaryl compounds (4-XC6H4)CB10H10CH showed a linear increase in shielding of the unsubstituted (antipodal) cage carbon, C12, and a linear decrease at the substituted position, C1, with increasing electron-donating power of the substituent represented by its Hammett σP value. Purely inductive, σI, or resonance σR, parameters gave less satisfactory plots. The diaryl series of 4-nitrophenyl derivatives showed the same relationships. Calculations of electron densities showed that the 13C NMR shifts correspond with charge density in the tangential p orbitals. The UV absorptions of the monoaryl p-carboranes have substantial red-shifts compared with the corresponding substituted benzenes, while those of the 4-nitrophenyl compounds having 4-dimethylamino or 4-oxide anion substituents in the second phenyl group extend into the visible. The colour is attributed to changes in the nitro n → π* absorption rather than conjugation or intermolecular charge transfer. Two anhydrous polymorphs and a hydrate of the (18-crown-6)potassium salt of this nitrophenoxide have been identified (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane). The results establish that p-carborane transmits electronic effects, perhaps as a formally unsaturated system or possibly in a similar manner to the staffanes (bicyclo[1.1.1]pentanes) and other formally saturated hydrocarbon linkages.