Anionic Ring Research Articles

Systematic Modulation of a Bichromic Cyclometalated Ruthenium(II) Scaffold Bearing a Redox-Active Triphenylamine Constituent

The syntheses and physicochemical properties of nine bis-tridentate ruthenium(II) complexes containing one cyclometalating ligand furnished with terminal triphenylamine (TPA) substituents are reported. The structure of each complex conforms to a molecular scaffold formulated as [Ru(II)(TPA-2,5-thiophene-pbpy)(Me(3)tctpy)] (pbpy = 6-phenyl-2,2'-bipyridine; Me(3)tctpy = trimethyl-4,4',4''-tricarboxylate-2,2':6',2''-terpyridine), where various electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) are installed about the TPA unit and the anionic ring of the pbpy ligand. It is found that the redox chemistry of the Ru center and the TPA unit can be independently modulated by (i) placing EWGs (e.g., -CF(3)) or EDGs (e.g., -OMe) on the anionic ring of the pbpy ligand (substituted sites denoted as R(2) or R(3)) and/or (ii) installing electron-donating substituents (e.g., -H, -Me, -OMe) para to the amine of the TPA group (i.e., R(1)). The first oxidation potential is localized to the TPA unit when, for example, EDGs are placed at R(1) with EWGs at R(2) (e.g., the TPA(•+)/TPA(0) and Ru(III)/Ru(II) redox couples appear at +0.98 and +1.27 V vs NHE, respectively, when R(1) = -OMe and R(2) = -CF(3)). This situation is reversed when R(3) = EDG and R(1) = -H: TPA-based and metal-centered oxidation waves occur at +1.20 and +1.11 V vs NHE, respectively. The UV-vis spectrum for each complex is broad (e.g., absorption bands are extended from the UV region to beyond 800 nm in all cases) and intense (e.g., ε ∼ 10(4) M(-1)·cm(-1)) because of the overlapping intraligand charge-transfer and metal-to-ligand charge-transfer transitions. The information derived from this study offers guiding principles for modulating the physicochemical properties of bichromic cyclometalated ruthenium(II) complexes.

Design and Development of Functionalized Cyclometalated Ruthenium Chromophores for Light-Harvesting Applications

The syntheses and the electrochemical spectroscopic properties of a suite of asymmetrical bistridentate cyclometalated Ru(II) complexes bearing terminal triphenylamine (TPA) substituents are reported. These complexes, which contain structural design elements common to both inorganic and organic dyes that exhibit superior power conversion efficiencies in the dye-sensitized solar cell (DSSC), are broadly formulated as [Ru(II)(L-2,5'-thiophene-TPA-R(1))(L-R(2))](+) [L = tridentate chelating ligand (e.g., 2,2':6',2''-terpyridine (tpy); deprotonated forms of 1,3-di(pyridin-2-yl)benzene (Hdpb) or 6-phenyl-2,2'-bipyridine (Hpbpy)); R(1) = -H, -Me, -OMe; R(2) = -H, -CO(2)Me, -CO(2)H]. The following structural attributes were systematically modified for the series: (i) electron-donating character of the terminal substituents (e.g., R(1) = -H, -Me, -OMe) placed para to the amine of the "L-2,5'-thiophene-TPA-R(1)" ligand framework; (ii) electron-withdrawing character of the tridentate chelate distal to the TPA-substituted ligand (e.g., R(2) = -H, -CO(2)Me, -CO(2)H); and (iii) position of the organometallic bond about the Ru(II) center. UV-vis spectra reveal intense and broad absorption bands arising from a collection of metal-to-ligand charge-transfer (MLCT) and TPA-based intraligand charge-transfer (ILCT) transitions that, in certain cases, extend beyond 800 nm. Electrochemical data indicate that the oxidative behavior of the TPA and metal chelate units can be independently modulated except in cases where the anionic phenyl ring is in direct conjugation with the TPA unit. In most cases, the anionic character of the cyclometalating ligands renders a metal-based oxidation event prior to the oxidation of the TPA unit. This situation can, however, be reversed with an appropriately positioned Ru-C bond and electron-rich R(1) group. This finding is important in that this arrangement confines the highest occupied molecular orbital (HOMO) to the TPA unit rather than the metal, which is optimal for sensitizing TiO(2); indeed, a remarkably high power conversion efficiency (η) in the DSSC (i.e., 8.02%) is measured for the TPA-substituted pbpy(-) chelate where R(1) = -OMe. These results provide a comprehensive strategy for improving the performance of bistridentate Ru sensitizers devoid of NCS(-) groups for the DSSC.

Enzymatic- and temperature-sensitive controlled release of ultrasmall superparamagnetic iron oxides (USPIOs)

BackgroundDrug and contrast agent delivery systems that achieve controlled release in the presence of enzymatic activity are becoming increasingly important, as enzymatic activity is a hallmark of a wide array of diseases, including cancer and atherosclerosis. Here, we have synthesized clusters of ultrasmall superparamagnetic iron oxides (USPIOs) that sense enzymatic activity for applications in magnetic resonance imaging (MRI). To achieve this goal, we utilize amphiphilic poly(propylene sulfide)-bl-poly(ethylene glycol) (PPS-b-PEG) copolymers, which are known to have excellent properties for smart delivery of drug and siRNA.ResultsMonodisperse PPS polymers were synthesized by anionic ring opening polymerization of propylene sulfide, and were sequentially reacted with commercially available heterobifunctional PEG reagents and then ssDNA sequences to fashion biofunctional PPS-bl-PEG copolymers. They were then combined with hydrophobic 12 nm USPIO cores in the thin-film hydration method to produce ssDNA-displaying USPIO micelles. Micelle populations displaying complementary ssDNA sequences were mixed to induce crosslinking of the USPIO micelles. By design, these crosslinking sequences contained an EcoRV cleavage site. Treatment of the clusters with EcoRV results in a loss of R2 negative contrast in the system. Further, the USPIO clusters demonstrate temperature sensitivity as evidenced by their reversible dispersion at ~75°C and re-clustering following return to room temperature.ConclusionsThis work demonstrates proof of concept of an enzymatically-actuatable and thermoresponsive system for dynamic biosensing applications. The platform exhibits controlled release of nanoparticles leading to changes in magnetic relaxation, enabling detection of enzymatic activity. Further, the presented functionalization scheme extends the scope of potential applications for PPS-b-PEG. Combined with previous findings using this polymer platform that demonstrate controlled drug release in oxidative environments, smart theranostic applications combining drug delivery with imaging of platform localization are within reach. The modular design of these USPIO nanoclusters enables future development of platforms for imaging and drug delivery targeted towards proteolytic activity in tumors and in advanced atherosclerotic plaques.

Density functional study on ionic liquid of 1-propyl-4,5-dibromo-3-methylimidazolium bromide

The density functional method and DNP basis set were employed to study 1-pair, 2-pair, and 3-pair of cation–anion interactions of 1-propyl-4,5-dibromo-3-methylimidazolium bromides. The calculated results reveal that H 2 atoms of 1-propyl-4,5-dibromo-3-methylimidazolium form hydrogen bondings with Br −. The natural bond orbital (NBO) and atoms in molecules (AIM) analyzes show that halogen bondings between Br − anion and imidazolium ring substituted bromine atoms were formed in the gas phase, in agreement with the crystal phase of 1-propyl-4,5-dibromo-3-methylimidazolium bromide which is governed by both hydrogen bondings and halogen bondings.

A ferrocene functionalized rotaxanehost system capable of the electrochemical recognition of chloride

A ferrocene appended rotaxane is prepared by chloride anion templation and ring closing metathesis. Upon removal of the chloride template, the rotaxane is demonstrated to be selective for chloride over more basic oxoanions by (1)H NMR spectroscopy and electrochemistry, in marked contrast to an acyclic analogue--the first example of a solution based redox-active interlocked host system capable of the electrochemical recognition of anions.

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

Crystal structures of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates and their solvent-free salts are determined. p-Semiquinone anion radical reveals enhanced aromaticity of the ring compared to the quinone. A pair of π-stacked radical anion (p-semiquinone) rings occurs in crystal structures of potassium and rubidium salts of tetrachlorosemiquinone anion acetone solvates and their potassium tetrabromo analogue. The ring centroid separation distances are about 3.2 A and carbon–carbon contacts between the contiguous rings are 0.3 A shorter than the sum of van der Waals radii. The spin-coupling of the two unpaired electrons between the two anion radical rings (forming a stacked dimer) correlates with the diamagnetic property of the crystals. Magnetic properties of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates were examined by electron paramagnetic resonance spectroscopy.

Di-μ-aqua-bis{triaqua[5-(1-oxopyridin-4-yl)tetrazol-1-ido]sodium}

In the title compound, [Na2(C6H4N5O)2(H2O)8], the NaI atom is in a distorted octahedral environment defined by six O atoms, one from the 5-(1-oxopyridin-4-yl)tetra­zolide anion and five from water mol­ecules. Two water mol­ecules act as bridging ligands, resulting in the formation of dimeric units organized around inversion centers. In the organic anion, the pyridine and tetra­zole rings are nearly coplanar, forming a dihedral angle of 4.62 (1)°. The dimeric units and organic anions are connected by O—H⋯O and O—H⋯N hydrogen bonds, leading to the formation of a three-dimensional network.

ChemInform Abstract: General Method for the Synthesis of Substituted Phenanthridin‐6(5H)‐ones Using a KOH‐Mediated Anionic Ring Closure as the Key Step.

AbstractThe cyclization proceeds with both 2′‐fluorobiphenyl‐2‐carbonitriles bearing electron‐withdrawing and electron‐donating groups.

Thecyclo-tetraphosphate Cd2P4O12, a member of the isotypic seriesM2P4O12(M= Mg, Mn, Fe, Co, Ni, Cu)

The title compound, Cd2P4O12, dicadmium cyclo-tetra­phosphate, crystallizes isotypically with the members of the series M II 2P4O12, where M = Mg, Mn, Fe, Co, Ni or Cu. Two CdO6 octa­hedra, one with 2 and one with symmetry, share corners with the centrosymmetric P4O12 4− ring anion that is built up from four corner-sharing PO4 tetra­hedra. The isolated ring anions are arranged in layers parallel to (10) with the CdO6 octa­hedra situated between these layers. The main difference between the individual M II 2P4O12 structures pertains to the different sizes of the MO6 octa­hedra whereas the geometric parameters of all cyclo-P4O12 4− anions are very similar.

Novel in situ polydimethylsiloxane-sepiolite nanocomposites: Structure-property relationship

A series of novel in situ polydimethylsiloxane (PDMS)-sepiolite nanocomposites were synthesized by anionic ring opening polymerization of octamethylcyclotetrasiloxane. These nanocomposites were characterized by Attenuated Total Reflection-Fourier Transform Infrared Spectroscopy, Wide Angle X-Ray Diffraction (WAXD), Transmission Electron Microscopy (TEM), mechanical and dynamic mechanical properties and thermogravimetry. This paper highlights the structure-property relationship of in situ PDMS-sepiolite nanocomposites and a way to improve the mechanical, dynamic mechanical and thermal properties of silicone rubber. Comparison of these physico-mechanical properties with those of the ex situ nanocomposites reflects greater degree of filler dispersion for the in situ nanocomposites. Increasing amount of the filler reduced the size of the crystalline domains in PDMS matrix, which was evident from the X-Ray and the dynamic mechanical analysis. However, the polymer-filler interaction was even more prominent to negate the effect of the deterioration of the properties due to decrease in size of the microcrystallites. The polymer-filler interaction was reflected in the improved mechanical and thermal properties which were the consequences of proper dispersion of the filler in the polymer matrix. The modulus improvement of the rubber-clay nanocomposites was examined by using Guth and Halpin-Tsai model. The temperature of maximum degradation was raised by 167 °C and improvement of 210% in tensile strength and 460% in modulus at 100% elongation was observed. These results were correlated with the data obtained from WAXD and TEM studies.

ChemInform Abstract: Effect of Silicate Ratio on the Distribution of Silicate and Aluminosilicate Anions in TPA Aluminosilicate Solutions.

{sup 29}Si and {sup 27}Al spectroscopies were used to characterize dilute, highly alkaline tetrapropylammonium (TPA) aluminosilicate solutions. The solution compositions ranged from 0.1 to 2 mol % SiO{sub 2}, silicate ratios (R = (SiO{sub 2})/((TPA){sub 2}O)) from 0.05 to 1, and Si/Al molar ratios from 0.25 to 5. {sup 29}Si NMR resonances were observed for Al incorporation into the dimer, linear trimer, cyclic trimer, branched cyclic trimer, double three-membered ring (D3R), and double four-membered ring (D4R) anions. In aluminosilicate solutions with 2 mol % SiO{sub 2}, silicate ratios of less than 1.5 lead to the stabilization of D3R(1Al) anions. The addition of DMSO to TPA aluminosilicate solutions provides the solutions with a high concentration of D3R(1Al) and D4R(1Al) anions. Semiempirical quantum mechanical calculations were performed to calculate the partial charges on Si atoms in silicate and aluminosilicate anionic structures. A correlation between the Si atom partial charge and its experimentally observed chemical shift assists in the assignment of {sup 29}Si NMR peaks due to soluble aluminosilicates.

ChemInform Abstract: Radical Anion Ring Opening Reactions via Photochemically Induced Electron Transfer.

ChemInform 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.

ChemInform Abstract: Diphosphiranes: Formation and Ionic Ring Opening, a Theoretical Approach.

The process of addition of methylene to diphosphene was studied theoretically using ab initio theory (SCF+CI level). Two possible mechanisms (addition to the π system and addition to the lone pair of phosphorus) were analyzed. The preferential process corresponds to a π addition leading to the diphosphirane ring. The cationic and anionic ring opening processes of the diphosphirane have been investigated at the same level of theory (ab initio SCF+CI). The results were analyzed by comparison with those of cyclopropane and in terms of the Woodward-Hoffmann rules

ChemInform Abstract: Interconversions in Cyclosilazanes and Their Application to SiN- Ceramics.

Abstract Rearrangements occur very frequently in reactions of cyclosilazanes. We have found an equilibrium between the eight-, six-, and four-membered ring anions, which is strongly dependent on thermal and kinetic effects, the choice of substituents and the properties of the attacking group. Knowledge of the interconversion mechanisms has enabled us to prepare silyl-bridged and coupled cyclosilazanes of high molecular weight. These coumpounds are useful precursors of SiN-ceramics.

Effects of transesterification and degradation on properties and structure of polycaprolactone–polylactide copolymers

Ester bonds of biodegradable polymers, such as poly (α-hydroxy esters), synthesized by the coordinated anionic ring opening polymerization (CAROP), are subject to transesterification during synthesis. In this work, a series of poly(ɛ-caprolactone)-poly( l-lactide) (PCL-PLA) block and random copolymers with targeted molar mass of 10,000 Da was synthesized to study the mechanism of transesterification reactions via NMR and MALDI-TOF. Polylactide segments are more vulnerable to transesterification compared to polycaprolactone. As a result, the actual quantity of l-lactide in the polymers was less than the target for all studied copolymers because of the decarboxylation and consequent CO elimination from fragments of macromolecules after transesterification. The presence of decarboxylation during transesterification was confirmed analytically and was reflected in the MALDI-TOF and 13C NMR spectra. An analysis of the polymer structure pointed to dehydration reactions that led to the formation of cyclic structures and double bonds with possible crosslinking.

Synthesis, crystal structure, and characterization of dimeric tetraorganodistannoxane and two tricyclohexyltin carboxylates

Three diorganotin(IV) series and triorganotin(IV) complexes, [(C6H11)2Sn]4(L1)2O2(OH)2 (1), (C6H11)3Sn(HL2) (2), and (C6H11)3SnL3 (3) (where HL1 is 2-(4-isopropyl benzoyl) benzoic acid, H2L2 is phthalic acid and HL3 is 2-benzoyl benzoic acid), were synthesized and their crystal structures were determined. There are four crystallographically unique Sn centers in the structure of 1, which consists of a Sn4O2(OH)2 ladder unit, and the ladder consists of four tins held together by two µ3-oxygens and two µ2-oxygens. The supermolecular motif of 1 is a 2-D structure linked by O–H ··· O hydrogen bonds. The asymmetric unit of 2 contains two crystallographically independent monomers. The supramolecular architecture of 2 is a 2-D layer structure linked by face-to-face π–π interactions between phenyl rings of adjacent L2 anions. The structure of 3 contains one tricyclohexyltin cation and one L3 anion. The Sn ··· O interactions lead the whole structure to a supramolecular chain. Elemental analysis, infrared, and 1H NMR of 1–3 were investigated and discussed.

ChemInform Abstract: X-Ray Powder Structure Determination of Li6P6O18×3H2O.

Abstract Preparation, characterization by X-ray diffraction, IR absorption, DTA-GTA analysis and ab-initio crystal structure determination are reported for a new lithium cyclohexaphosphate hydrate Li6P6O18·3H2O. It crystallizes in a trigonal (rhomboedral) cell (space group R 3¯m No 166, Z = 6) with a = 15.7442(2) A, c = 12.5486(2) A. X-ray powder diffraction pattern data was refined by Rietveld profile technique and lead to RBragg = 0.09. The crystal structure of Li6P6O18·3H2O is built up from [P6O18]6- ring anions, having the 3m symmetry, alternating along the 3¯ axis with rings made of six LiO4 tetrahedra and six LiO5 pseudo square pyramids sharing common edges.

Dipotassium dialuminium cyclooctaphosphate

Single crystals of the title compound, K2Al2P8O24, were obtained by solid-state reaction. The monoclinic structure is isotypic with that of the GaIII analogue and is built of eight-membered phosphate ring anions P8O24 8− (2/m symmetry) isolated from each other and further linked by isolated AlO6 octa­hedra ( symmetry) by sharing corners. Each AlO6 octa­hedron is linked to four P8O24 8− rings in such a way that two rings are linked through bidentate diphosphate groups attached in the cis positions on two opposite parallel edges of the octa­hedron. The two other rings are linked via corner-sharing to the two remaining corners in the trans positions of the AlO6 octa­hedron. Each P8O24 8− ring anion is linked to eight AlO6 octa­hedra. More accurately, each ring anion is linked to four AlO6 octa­hedra through bidentate diphosphate groups attached in the cis positions to the AlO6 octa­hedron and to the four remaining octa­hedra by sharing corners. This three-dimensional linkage delimits channels running parallel to [001] in which the ten-coordinated K+ cations (2 symmetry) are distributed over two columns. These columns alternate with empty octa­gonally-shaped channels expanding through the P8O24 8− ring anions.

Synthesis and biological evaluation of novel benzoxazinic analogues of ellipticine

Original 1,4-benzoxazine analogues of ellipticine were prepared using a general synthetic route that relied on an anionic ring annulation as the key transformation. The interest of this approach lies on the possibility of an easy entrance to a wide range of derivatives from the phenol intermediate. In addition, this synthetic strategy offers a smart access to diverse structurally related heteroaryl annulated carbazole analogues of ellipticine just by replacing the starting heterocyclic core. Antiproliferative activities of newly synthesized derivatives were evaluated toward tumor cell lines.

General method for the synthesis of substituted phenanthridin-6(5 H)-ones using a KOH-mediated anionic ring closure as the key step

Substituted phenanthridin-6(5 H)-ones were obtained in a two-step procedure involving a Suzuki cross-coupling reaction followed by a KOH-mediated anionic ring closure. The influence of the nature and the position of the substituents on the cyclization step were studied. This methodology offers a general and practical route to diversely substituted phenanthridin-6(5 H)-ones.