Anionic Substituents Research Articles

Cl– Complexation Induced H- and J-Aggregation of meso-Tetrakis(4-sulfonatothienyl)porphyrin Diacid in Aqueous Solution

Various porphyrin diacids are known to show controlled self-assembly by inorganic anions. Following the unexpected finding that meso-tetrakis(4-sulfonatothienyl)porphyrin diacid shows Cl(-) specific aggregation in spite of having the anionic substituents, the aggregation behavior of the diacid in aqueous solution with Cl(-) was investigated in detail. We found that Cl(-) induces the H-aggregate, followed by the transformation into the J-aggregate with increasing Cl(-) concentration. For the J-aggregate formation, negatively charged sulfonic acid groups were suggested to be of minor influence. The J-aggregate forms nanoscale macrostructures composed of highly oriented molecules on substrate. To our knowledge, this is the first report of both H- and J-type aggregate formation of a porphyrin diacid in the presence of an aqueous inorganic anion. These results would open the gate for controlling the chromophore packing structure of a porphyrin diacid complexed with an inorganic anion by varying the composition.

“Crowned” Univalent Indium Complexes as Donors? Experimental and Computational Insights on the Valence Isomers of EE′X4 Species

The use of the univalent indium reagent [In([18]crown-6)][OTf] as a donor is investigated by its reactions with acceptors including InX(3) (X=Cl, Br, I). The donor-acceptor complexes of the form [X([18]crown-6)In-InX(3)] obtained in this manner represent the first new isomeric form of indium(II) halides identified for at least five decades. The formation of such complexes appears to be particularly favorable and they are isolated as products in many reactions involving low-valent indium, a halide source, and [18]crown-6. A convenient solution-phase synthesis of In[ECl(4)] salts is reported. This facile and direct syntheses of In[ECl(4)] (E=Al, Ga, In) salts allows for the in situ preparation and isolation of crown-ether complexes of the form [In([18]crown-6)][ECl(4)], whose existence had been postulated but never confirmed. Solution-phase and solid-state NMR experiments reveal that these compounds can exist as either donor-acceptor complexes or ionic salts, depending on the phase of the system, the nature of the solvent employed, and the identity of the metalate anion involved. Similar investigations into the effect of a smaller crown ether allow for the isolations of salts containing the cation [In([15]crown-5)](+). Computational investigations into the nature of the crowned univalent indium donor fragments, and on the donor-acceptor complexes produced, demonstrate the influence of anionic substituents on the reactivity of lone pair of electrons of the In(I) center. Natural bond orbital (NBO) analysis of donor-acceptor models shows that the composition of the E-E bond MO should provide the ability to predict which models should form stable complexes.

The influence of benzoate anion substituents on the crystal packing and hydrogen-bonding network of 9-aminoacridinium salts

As a continuation of our recent work, we discuss the crystal structures of a series of salts with the 9-aminoacridinium cation and 3-chlorobenzoate, 4-chlorobenzoate and 3-hydroxybenzoate anions. The crystal structure of [2(C 13H 11N 2 +)·C 7H 5O 3 −·Cl −·2(H 2O)] is the first of all the known 9-aminoacridinium salts where mixed salts were obtained. Analysis of the hydrogen bonds in the crystal lattices of the title compounds shows that the ions are linked via N(amino)–H⋯O(carboxy) hydrogen bonds forming R 2 2(8) or R 2 4(16) hydrogen bond ring motifs. In the packing, there are also two kinds of hydrogen bond chain motif. The first, C 4 2(16), in which 9-AA cations, a Cl − anion and a water molecule are interlinked, and the second, C(7), in which aromatic carboxylic acid anions are connected directly. We also observed the influence of the different anions on the packing of the acridine skeletons in the crystal lattice.

Zwitterionic Iridium Complexes with P,N‐Ligands as Catalysts for the Asymmetric Hydrogenation of Alkenes

Several zwitterionic iridium complexes based on chiral P,N-ligands with imidazoline or oxazoline donors and anionic tetraarylborate or aryltrifluoroborate substituents have been synthesized. The corresponding cationic analogues have also been prepared, to evaluate the effect of the covalent linkage between the anion and the cationic metal complex in catalytic reactions. The respective pairs of structurally analogous precatalysts have been compared for their efficacies in the asymmetric hydrogenation of unfunctionalized olefins. In most cases, the anionic derivatization has virtually no influence on the asymmetric induction of the iridium complex. This is in accordance with X-ray structural studies, which have shown that the chiral environment of the cationic metal center is not affected by the anionic substituent. Depending on the nature of the counterion employed, the zwitterionic catalysts proved to be significantly more reactive than their cationic counterparts in nonpolar solvents.

Amino acid-based ionic liquids: using XPS to probe the electronic environment via binding energies

Here we report the synthesis and characterisation by X-ray photoelectron spectroscopy (XPS) of eight high purity amino acid-based ionic liquids (AAILs), each containing the 1-octyl-3-methylimidazolium, [C(8)C(1)Im](+), as a standard reference cation. All expected elements were observed and the electronic environments of these elements identified. A fitting model for the carbon 1s region of the AAILs is reported; the C aliphatic component of the cation was used as an internal reference to obtain a series of accurate and reproducible binding energies. Comparisons are made between XP spectra of the eight AAILs and selected non-functionalised ionic liquids. 1-octyl-3-methylimidazolium acetate was also studied as a model of the carboxyl containing amino acid anion. The influence of anionic substituent groups on the measured binding energies of all elements is presented, and communication between anion and cation is investigated. This data is interpreted in terms of hard and soft anions and compared to the Kamlet-Taft hydrogen bond acceptor ability, β, for the ionic liquids. A linear correlation is presented which suggests that the functional side chain, or R group, of the amino acid has little impact upon the electronic environment of the charge-bearing moieties within the anions and cations studied.

ChemInform Abstract: A Computational Examination of Diels-Alder Reactions with 1,3-Cyclopentadienes Bearing Anionic and Cationic Substituents at C-5.

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Density Prediction of Ionic Liquids at Different Temperatures and Pressures Using a Group Contribution Equation of State Based on Electrolyte Perturbation Theory

Based on the electrolyte perturbation theory, a group contribution equation of state that embodies hard-sphere repulsion, dispersive attraction, and ionic electrostatic interaction energy was established to calculate the density of ionic liquids (ILs). According to this method, each ionic liquid is divided into several groups representing cation, anion, and alkyl substituents. The performance of the model was examined by describing the densities of a large number of imidazolium-based ILs over a wide range of temperatures (293.15−414.15 K) and pressures (0.1−70.43 MPa). A total number of 202 data points of density for 12 ILs and 2 molecular liquids (i.e., 1-methylimidazole and 1-ethylimidazole) were used to fit the group parameters, namely, the soft-core diameter σ and the dispersive energy e. The resulting group parameters were used to predict 961 data points of density for 29 ILs at varying temperatures and pressures. The model was found to estimate well the densities of ionic liquids with an overall ave...

Torquoselectivity Studies in the Generation of Azomethine Ylides from Substituted Aziridines

Aziridines are useful precursors to the azomethine ylide family of 1,3-dipoles whose cycloaddition chemistry has been extensively exploited in the synthesis of heterocyclic targets. The torquoselectivity of aziridines that lack a plane of symmetry was investigated as an essential component of the calculation of the overall relative reaction rates and in prediction of the stereochemistry of the 2,3-trans compounds in 1,3-dipolar cycloaddition chemistry. It has been found at the MP2(Full)/6-311++G(d,p)//MP2(Full)/6-31+G(d) level that outward rotation is preferred for electronegative or anionic substituents while electropositive and cationic substituents favor inward rotation. After consideration of frontier molecular orbital theory, inductive, resonance, and electrostatic effects, an explanation of the preferred direction of rotation during ring cleavage that is based on substituent electron-withdrawing ability by means of a polar effect is presented.

Identification of the Mesorhizobium loti gene responsible for glycerophosphorylation of periplasmic cyclic β-1,2-glucans

Periplasmic cyclic beta-1,2-glucans play a crucial role in symbiosis as well as in hypo-osmotic adaptation for rhizobia. These glucans are modified in many species by anionic substituents such as glycerophosphoryl and succinyl ones, but their role remains to be examined. In this work, the cgmA homolog is shown to be responsible for glycerophosphorylation of cyclic beta-1,2-glucans in Mesorhizobium loti. The mutation in cgmA converted most anionic glucans into neutral ones, leaving a small amount of succinylated ones. An additional mutation in opgC, which encodes a succinyltransferase homolog, abolished the residual succinyl substituents in the cgmA-mutant background. The double mutant in cgmA and opgC did not show any significant phenotypic differences from the wild type during both vegetative growth and symbiosis. It is concluded that the anionic substituents make a minor contribution, if any, to the effectiveness of cyclic beta-1,2-glucans in M. loti.

Substituent effects on the thermodynamic stability of imines formed from glycine and aromatic aldehydes: implications for the catalytic activity of pyridoxal-5'-phosphate.

Equilibrium constants for addition of glycine to substituted benzaldehydes to form the corresponding imines and pK(a)'s for ionization of the iminium ions were determined by (1)H NMR analysis in D(2)O. The introduction of a phenoxide anion substituent into the aromatic ring of benzaldehyde leads to a substantial increase in the pK(a) of the iminium ion from 6.3 to 10.2 for p-hydroxybenzaldehyde and to 12.1 for salicylaldehyde. An analysis of the differential effect of ortho- versus para-substitution shows that the iminium ion to salicylaldehyde is stabilized by an intramolecular hydrogen bond in aqueous solution, with an estimated energy ca. 3 kcal/mol larger than can be accounted for by a simple electrostatic interaction. A comparison of the o-O(-) substituent effect on the acidity of the iminium ions of glycine to benzaldehyde and 4-pyridine-carboxaldehyde provides evidence for the existence of an internal hydrogen bond of similar strength in pyridoxal 5'-phosphate (PLP) iminium ions in water. The effects of other ring substituents on the stability of PLP iminium ions are discussed.

1.1]Ferrocenophane‐1,12‐dione as a Precursor of 1,12‐Di(cyclopenta‐2,4‐dienylidene)‐[1.1]ferrocenophane, a Doubly Bridged Difulvene

Abstractmagnified imageAn improved synthesis of [1.1]ferrocenophane‐1,12‐dione (2) by oxidation of [1.1]ferrocenophane with 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ) is presented. The syn conformer of dione 2 is structurally characterized. The compound undergoes various addition reactions at the bridging carbonyl groups. Attempts to add 1,1′‐dilithioferrocene result, however, in the diadduct 9, not in the symmetric trinuclear diol 8. Reaction of 2 with sodium cyclopentadienide in the presence of aluminium trichloride (AlCl3) gives the respective difulvene 11 in excellent yield. The dynamic behavior of 11 is investigated by variable temperature 1H NMR measurements (VT‐NMR). The cyclovoltammogram of 11 indicates two reversible oxidation steps. Reduction of difulvene 11 with lithium aluminium hydride (LiAlH4) results in the formation of [1.1]ferrocenophane 12 with cyclopentadienyl anion substituents at either one of the two bridges. While attempts to generate a third ferrocene moiety by reaction with iron(II) choride (FeCl2) have failed so far, the formation of 12 is established by protonolysis and methylation reactions.

Synthesis of hydrophilic conjugated porphyrin dimers for one-photon and two-photon photodynamic therapy at NIR wavelengths

We report the synthesis of a series of hydrophilic butadiyne-linked conjugated zinc porphyrin dimers, designed as photodynamic therapy (PDT) agents. These porphyrin dimers exhibit exceptionally high two-photon absorption cross sections (delta(max) approximately 8,000-17,000 GM) and red-shifted linear absorption spectra (lambda(max) approximately 700-800 nm) making them ideal candidates for one-photon and two-photon excited photodynamic therapy. Four polar triethyleneglycol substituents are positioned along the sides of each dimer, but, on their own, these TEG chains do not confer sufficient solubility in aqueous physiological media for reproducible delivery into live cells. Charged cationic (methylpyridinium and trimethylammonium) and anionic (sulfonate and carboxylate) substituents have been appended to the meso-positions of porphyrin dimers using three synthetic strategies: 1) Suzuki coupling, 2) Sonogashira coupling, and 3) nucleophilic Senge arylation. Approaches 1 and 3 both allow attachment of aromatic substituents directly to the meso-positions of porphyrins. Approach 2 provides a route to hydrophilic porphyrin dimers with an ethyne link between the porphyrin and the polar aromatic substituent. The palladium-catalysed approaches 1 and 2 allow the synthesis of a broader range of meso-capped porphyrins, as many aryl halides are available. However the synthesis of the intermediate required for these routes necessitates a statistical reaction step, which decreases the overall yield. On the other hand, Senge-arylation provides highly regioselective nucleophilic aromatic substitution, and offers higher overall yield than the other routes. All these charged dimers exhibit good solubility in polar solvents (e.g. methanol) and aqueous solvent mixtures (aqueous DMSO or DMF).

On the modeling of arginine‐bound carboxylates: A case study with Pyruvate Formate‐Lyase

High level ab initio and density functional calculations have been employed to determine the most appropriate manner in which to truncate an arginine-bound carboxylate motif, using the substrate mechanism of Pyruvate Formate-Lyase as a case study. The results show that, both qualitatively and quantitatively, a neutral carboxylic acid provides a more realistic approximation to the salt bridge arrangement than does a bare anionic carboxylate substituent.

METALLOPHILIC INTERACTIONS IN DOUBLE SALTS: TOWARD 1D METAL ATOM CHAINS

A new family of double salts has been developed that can display infinite one-dimensional chains of metallophilic interactions in the solid state. These salts are composed of cationic and anionic components that are designed to participate in metallophilic interactions with one another. These building blocks incorporate Au(III), Au(I), and Pt(II) atoms in the forms [L3PtX]+, [L2AuX2]+, [AuX4]−, and [AuX2]−. Five different metallophilic structural motifs have been observed in these double salts and their monomeric precursors. The particular structure observed is affected by metal oxidation state, the electronic nature of the neutral (L) and anionic (X) substituents, the synthetic conditions employed, as well as the solvent present.

Arginine Binding Motifs: Design and Synthesis of Galactose-Derived Arginine Tweezers as Galectin-3 Inhibitors

Anionic O2 derivatives of methyl 3-deoxy-3-(4-methylbenzamido)-1-thio-beta-D-galactopyranoside have been synthesized as inhibitors against galectin-3. The sulfate, H-phosphonate, and benzyl phosphate derivatives showed an increased affinity as compared to the parent unsubstituted galactopyranoside. Modeling revealed arginine-144 being pinched by the C3 benzamide and O2 anionic substituents in that the benzamide stacked face-to-face and the anionic O2 substituent ion-paired with the guanidinium moiety.

Indiscriminate Binding by Orotidine 5‘-Phosphate Decarboxylase of Uridine 5‘-Phosphate Derivatives with Bulky Anionic C6 Substituents

Orotidine 5'-phosphate (OMP) decarboxylase appears to act upon its substrate without the intervention of metals or other cofactors and without the formation of covalent bonds between the enzyme and the substrate. Crystallographic information indicates that substrate binding forces the substrate's scissile carboxylate group into the neighborhood of several charged groups at the active site. It has been proposed that binding might result in electrostatic stress at the substrate's C6 carboxylate group in such a way as to promote decarboxylation by destabilizing the enzyme-substrate complex in its ground state. If that were the case, one would expect uridine 5'-phosphate (UMP) derivatives with bulky anionic substituents at C6 to be bound weakly compared with UMP, which is unsubstituted at C6. Here, we describe the formation of anionic 5,6-dihydro-6-sulfonyl derivatives by spontaneous addition of sulfite to UMP and to OMP. These sulfite addition reactions, which are slowly reversible and are not catalyzed by the enzyme, result in the appearance of one (or, in the case of OMP, two) bulky anionic substituents at the 6-carbon atom of UMP. These inhibitors are bound with affinities that surpass the binding affinity of UMP. We are led to infer that the active site of OMP decarboxylase is remarkably accommodating in the neighborhood of C6. These are not the properties that one would expect of an active site with a rigid structure that imposes sufficient electrostatic stress on the substrate to produce a major advancement along the reaction coordinate.

Layering in cinnamate structures: The role of cations and anion substituents

Four materials have been used to investigate the effect of the cation and ring substituent on crystal packing. In potassium 3-bromo- trans-cinnamate ( 1), potassium 3-chloro- trans-cinnamate ( 2) and sodium 3-chloro- trans-cinnamate ( 3), the cations are accommodated in continuous two-dimensional layers formed by the interaction between cations and anions. The C C double bonds in 1 and 2 are parallel with optimal geometry for photochemical reaction, whereas 3 is disordered. The identity of the halogen substituent influences the structure through halogen-halogen contacts. In the structure of calcium di- trans-cinnamate ( 4), calcium-anion coordination leads to the formation of ribbons rather than two-dimensional layers.

Synthesis and Characterization of Water-Soluble Silver and Palladium Imidazol-2-ylidene Complexes with Noncoordinating Anionic Substituents

Zwitterionic imidazolium salts have been synthesized bearing alkylsulfonate and alkylcarboxylate substituents and used as precursors to water-soluble metal−carbene complexes. Reaction of the zwitterionic imidazolium compounds with Ag2O gave bis(imidazol-2-ylidene)silver complexes. These compounds have been characterized spectroscopically and by electrospray mass spectrometry. A DMSO solvate of bis[1-(2,6-diisopropylphenyl)-3-(3-sulfonatopropyl)imidazol-2-ylidene]silver sodium salt has been structurally characterized. In the solid state, this complex exists as a coordination polymer in which the sodium ions bridge the sulfonate groups from two bis(imidazol-2-ylidene)silver moieties. Diiodobis[1-mesityl-3-(3-sulfonatopropyl)imidazol-2-ylidene]palladium disodium salt has also been prepared in low yield and characterized by NMR spectroscopy and electrospray mass spectrometry.

Lysozyme refolding with cyclodextrins: structure–activity relationship

Cyclodextrins (CDs), in the presence or absence of detergents, have been reported to suppress aggregate formation during the refolding of a number of proteins. A structure–activity relationship study between CD chemistry and refolding of lysozyme was performed and compared to carbonic anhydrase, in order to better understand the mechanism of CD-assisted protein refolding and to identify CDs that could function as good protein folding agents. Among the natural CDs, which have only hydroxyl groups, alpha-CD, with a smaller cavity size was more effective than the oligosaccharide with a larger cavity, gamma-CD. Replacement of the hydroxyls with other functional groups did not improve, but could seriously interfere, with the lysozyme refolding ability of alpha-CD. In case of gamma-CD, substitution of its hydroxyls with other groups either enhanced or diminished its refolding capability towards lysozyme. In general, neutral CDs were better refolding agents than the charged sugars. The presence of anionic substituents like carboxyl and phosphate groups actually promoted aggregate formation and completely abolished the sugar's refolding ability. This effect was more pronounced with lysozyme than with carbonic anhydrase. CDs with cationic functional groups did not show any significant effects on lysozyme refolding. The presence of both anionic and cationic substituents on the same CD molecule was found to partially restore its renaturation ability. Electrophoresis data indicate that CDs, which promoted lysozyme refolding, arrested aggregation at the stage of smaller soluble aggregates. Interestingly, the structure–activity relationship observed with lysozyme was quite similar to that reported for a non-disulfide protein, carbonic anhydrase. These results suggest that the effects of CDs on protein refolding are attributed to their ability to suppress aggregation of proteins. CDs may show properties similar to chaotropic agents, which may help explain their anti-aggregation and protein refolding ability. Besides alpha-CD, a number of other neutral CDs were found to be effective protein folding aids.

Supramolecular Switches Based on the Guanine–Cytosine (GC) Watson–Crick Pair: Effect of Neutral and Ionic Substituents

We have theoretically analyzed Watson-Crick guanine-cytosine (GC) base pairs in which purine-C8 and/or pyrimidine-C6 positions carry a substituent X = NH(-), NH(2), NH(3) (+) (N series), O(-), OH, or OH(2) (+) (O series), using the generalized gradient approximation (GGA) of density functional theory at the BP86/TZ2P level. The purpose is to study the effects on structure and hydrogen-bond strength if X= H is substituted by an anionic, neutral, or cationic substituent. We found that replacing X = H by a neutral substituent has relatively small effects. Introducing a charged substituent, on the other hand, led to substantial and characteristic changes in hydrogen-bond lengths, strengths, and hydrogen-bonding mechanism. In general, introducing an anionic substituent reduces the hydrogen-bond-donating and increases the hydrogen-bond-accepting capabilities of a DNA base, and vice versa for a cationic substituent. Thus, along both the N and O series of substituents, the geometric shape and bond strength of our DNA base pair can be chemically switched between three states, thus yielding a chemically controlled supramolecular switch. Interestingly, the orbital-interaction component in some of these hydrogen bonds was found to contribute to more than 49 % of the attractive interactions and is thus virtually equal in magnitude to the electrostatic component, which provides the other (somewhat less than) 51 % of the attraction.