Solution-state Studies Research Articles

Investigation of Zinc Dimercaptothiadiazole as a Corrosion Inhibitor for Steel

The mechanism of corrosion inhibition of zinc dithiomercaptothiadiazole (Zn(DMcT)2) has been known and elucidated. The efficacy of (Zn(DMcT)2) as used in primer coatings for corrosion inhibition on steel alloys such as 1010 steel and 4130 high strength steel under neutral pH conditions was investigated by accelerated corrosion testing methodologies. Solution-state studies and surface elemental analyses were conducted to determine the possible mechanism of corrosion inhibition. Solution state experiments showed a correlation between increasing Zn(DMcT)2 amounts and increased polarization resistance, but DMcT on its own did not show this relationship. Under neutral pH conditions, it was determined that Zn(II) species such as Zn(OH)2, Zn(DMcT)2, and possibly ZnO were deposited on the steel surface, providing corrosion protection.

Solution and solid state study of copper(II) ternary complexes with some dipeptides presence in Aβ-42 peptide and methionine

The ternary complexes of Cu(II) with some dipeptides and methionine were studied both in aqueous solution and in solid state. The formation constants of copper(II) ternary complexes were calculated by potentiometric titration at 25°C and μ=0.1molL−1. The values of the constants for CuL1L2 species (L1=GlyGly, GlyVal, GlyLeu or GlyPhe; L2=Met) were 15.66, 15.75, 15.69 and 16.31, respectively. The complexes [Cu(GlyGly)Met]K (1), [Cu(GlyVal)Met]K·2H2O (2), [Cu(GlyLeu)(Met)(H2O)2]K·H2O (3) and [Cu(GlyPhe)(Met)(H2O)]K·2H2O (4) were isolated in pH around 7 and characterized through microanalyses, thermogravimetry, UV–Vis, infrared and EPR spectroscopies. The presence of the sulfur noncoordinated to metal in these ternary complexes can exert reduction action in biological systems under stress conditions.

Comparative study on MnII, NiII and CuII supramolecular complexes obtained from a proton transfer methodology: solid- and solution-state studies

In this study, the solution chemistry and solid-state structures of a novel proton transfer compound, (pipzH2)(pyc)2·H2O 1, and three metal–organic complexes of [Mn(pyc)2(H2O)2]2·2H2O 2, [Ni(pyc)2(H2O)2]·H2O 3 and [Cu(pyc)2H2O] n 4, (pyc = pyridine-2-carboxylate, pipz = piperazine) were investigated. On the basis of crystallographic data, each MII ion is coordinated to pyridine-2-carboxylate as bidentate ligand. Furthermore, these complexes form a three-dimensional structure by a variety of noncovalent interactions such as extensive O–H···O, O–H···N, N–H···O, N–H···N, C–H···O hydrogen bonds, C–H···π and C–O···π interactions. The equilibrium constants for the binary pyc-pipz proton transfer system, the stoichiometry and stability of complexation of this system with Mn2+, Ni2+ and Cu2+ ions in aqueous solution were investigated by potentiometric pH titration method. In each case, the stoichiometry of the dominant metal complex species in solution was compared with that obtained from the crystal structure.

Commercial Abuse-Deterrent Dosage Forms: Clinical Status

Abuse of prescription medications is being combated with the advent of novel formulations designed to prevent or discourage tampering and misuse. The ability of these abuse-deterrent and tamper-resistant formulations to impact abuse, and the test methods used to determine their lowered abuse potential is becoming more important. There are three main reasons for the need to access these formulations, a) to determine if a formulation itself can impact abuse of a product, b) for standardized methods that can be used to support product labeling, and c) to evaluate both new and generic products for tamper-equivalence. The object of this review is to provide an overview and evaluation of the various types of premarketing tamper and abuse studies performed both in-vitro and by experienced abusers when evaluating a product’s deterrence to abuse. To find and assess abuse liability studies of FDA approved products, a database search using Medline and Google Scholar with keywords “abuse deterrent”, and “tamper resistant” was used along with information obtained from product innovator websites and regulatory documents from the FDA regarding each product. Results from our investigation revealed that studies evaluating of a products abuse deterrent properties could be separated into three main categories based on the state the product is in during the study. The three main categories are 1) solid state studies, 2) solution state studies, and 3) aerosol state studies. For each category, various study examples are discussed and assessed for factors that will have significant impact on the way the study is evaluated.

Reactivity of 1-aminoazetidine-2-carboxylic acid during peptide forming procedures: observation of an unusual variant of the hydrazino turn

Peptide formation on the N-terminal of 1-aminoazetidine-2-carboxylic acid is rendered problematic due to a ring opening reaction. However C-terminal development is possible and two diastereomeric mixed hydrazino dipeptides were prepared. Solution-state studies of these compounds suggest the presence of intramolecular hydrogen bonding, consistent with a hydrazino turn, and the crystal structure of one of these compounds shows a horse-shoe conformation, centered around what appears to be a hydrazino turn involving three hydrogen bond acceptors.

Synthesis and characterization of vinylimidazolium salts: Solution state study to realize the influence of different anions

New vinylimidazolium salts, [9,10-bis{(N-vinylimidazolium)methyl}anthracene] bistetrafluoroborate (2) and [9,10-bis{(N-vinylimidazolium)methyl}anthracene] bishexafluorophosphate (3) have been prepared by the N alkylation of 9,10-bis(chloromethyl)anthracene with 1-vinylimidazole in 1,4-dioxane at 70°C followed by the anion exchange reaction between [9,10-bis{(N-vinylimidazolium)methyl}anthracene] dichloride (1) and ammonium salt of tetrafluoroborate (for 2) or hexafluorophosphate (for 3). The interaction of tribromide anion with 1–3 has been studied with the help of 1H NMR and fluorescence spectra. Notably, the tribromide anion exhibits very strong fluorescent quenching effects towards 2 than 1 and 3. Similarly, 2 shows very strong fluorescent quenching effect in the presence of tribromide anion compare to bromide anion. Moreover the proton of imidazolium cation, NCHN in 2 undergoes considerable downfield shift in the presence of tribromide anion, while the vinyl group depicts strong upfield shift due to the possible interaction of tribromide with vinylimidazolium unit.

Resorcinarene Bis-Thiacrowns: Prospective Host Molecules for Silver Encapsulation

Mixed-donor atom tetramethoxy resorcinarene bis-thiacrown hosts, in which the crown unit contains both hard oxygen and soft sulfur donor atoms, were synthesized for soft metal cation binding. The binding properties were investigated both in solution and in the solid state by NMR spectroscopy and X-ray crystallography. It was found that the resorcinarene bis-thiacrowns were able to complex silver cations with remarkable affinity forming readily 1:2 host-guest complexes in solution. The solid state structures also revealed that the bis-thiacrowns form silver complexes in an unanticipated endo- and exo-cavity fashion within the same host molecule. Both the solution and solid state studies indicated the sulfur atoms to be the major contributing donor atoms in forming the binding interactions with silver cations.

Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry – 2: Homocysteine with aspartate, glutamate or methionine

Alzheimer’s disease is characterized by the loss of synapses and by the presence of extra-cellular amyloid β-peptide (Aβ) plaques, and it has been associated to copper metabolism. The plasma of patients with Alzheimer’s disease presents higher levels of the amino acid homocysteine (hCys).In this study, three new ternary complexes of copper(II) with homocysteine and three amino acids of Aβ (aspartate, glutamate or methionine) were studied both in solution (pH-potentiometry and UV–Vis) and in the solid state (CHNS, AAS, TGA, EPR, and FT-IR). Molar conductance and electrochemical (CV) measurements were carried out as well. The binary complex [Cu(hCys)2] was also synthesized and characterized.For the ternary complexes, the values of the stability constants (log β equal to 25.62 for CuAsphCys, 23.53 for CuGluhCys, and 18.61 for CuMethCys) are similar to those of the cysteine-containing ternary complexes CuAspCys and CuGluCys, recently reported by us, indicating a related N2OS coordination.The results found in the solid state are in agreement with the data found in solution studies whereby methionine, aspartic, and glutamic acids coordinate to copper(II) ion through the nitrogen atom of the amino group and one oxygen atom of the α-carboxylate group, and homocysteine coordinates through nitrogen and sulfur atoms. EPR data suggest that, in solution, the complexes are in a distorted tetrahedral geometry.

Highly Efficient Near-Infrared-Emitting Lanthanide(III) Complexes Formed by Heterogeneous Self-Assembly of AgI, LnIII, and Thiacalix[4]arene-p-tetrasulfonate in Aqueous Solution (LnIII = NdIII, YbIII)

Heterogeneous self-assembly of thiacalix[4]arene-p-tetrasulfonate (TCAS), Ag(I), and Ln(III) (= Nd(III), Yb(III)) in aqueous solutions conveniently afforded ternary complexes emitting Ln(III)-centered luminescence in the near-infrared (NIR) region. A solution-state study revealed that the Ag(I)-Nd(III)-TCAS system gave a complex Ag(I)(4)·Nd(III)·TCAS(2) in a wide pH range of 6-12. In contrast, the Ag(I)-Yb(III)-TCAS system gave Ag(I)(2)·Yb(III)(2)·TCAS(2) at a pH of around 6 and Ag(I)(2)·Yb(III)·TCAS(2) at a pH of approximately 9.5. The structures of the Yb(III) complexes were proposed based on comparison with known Ag(I)-Tb(III)-TCAS complexes that show the same self-assembly behavior. In Ag(I)(2)·Yb(III)(2)·TCAS(2), two TCAS ligands sandwiched a cyclic array of a Ag(I)-Ag(I)-Yb(III)-Yb(III) core. In Ag(I)(2)·Yb(III)·TCAS(2), Yb(III) was accommodated in an O(8) cube consisting of eight phenolate O(-) groups from two TCAS ligands linked by two S-Ag-S linkages. Crystallographic analysis of Ag(I)(4)·Nd(III)·TCAS(2) revealed that the structure was similar to Ag(I)(2)·Yb(III)·TCAS(2) but that it had four instead of two S-Ag-S linkages. The number of water molecules coordinating to Ln(III) (q) estimated on the basis of the luminescent lifetimes was as follows: Ag(I)(4)·Nd(III)·TCAS(2), 0; Ag(I)(2)·Yb(III)(2)·TCAS(2), 2.4; and Ag(I)(2)·Yb(III)·TCAS(2), 0. These findings were compatible with the solution-state structures. The luminescent quantum yield (Φ) for Ag(I)(4)·Nd(III)·TCAS(2) was 4.9 × 10(-4), which is the second largest value ever reported in H(2)O. These findings suggest that the O(8) cube is an ideal environment to circumvent deactivation via O-H oscillation of coordinating water. The Φ values for Ag(I)(2)·Yb(III)(2)·TCAS(2) and Ag(I)(2)·Yb(III)·TCAS(2) were found to be 3.8 × 10(-4) and 3.3 × 10(-3), respectively, reflecting the q value. Overall, these results indicate that the ternary systems have the potential for a noncovalent strategy via self-assembly of the multidentate ligand, Ln(III), and an auxiliary metal ion to obtain a highly efficient NIR-emissive Ln(III) complex that usually relies on elaborate covalent linkage of a chromophore and multidentate ligands to expel coordinating water.

What drives the precipitation of long-chain calcium carboxylates (soaps) in aqueous solution?

The interaction of sodium octanoate, decanoate or dodecanoate with calcium(ii) in aqueous solutions has been studied using turbidity, conductivity and potentiometric measurements. These show a marked alkyl chain length dependence on the behaviour. At the calcium concentration used (1.0 mM), there is little interaction with the octanoate, the decanoate shows initially formation of a 1:1 complex, followed by precipitation, while the dodecanoate precipitates at low surfactant concentrations. The solid calcium carboxylates were prepared, and show lamellar, bilayer structures with planes of calcium(II) ions coordinated to carboxylate groups through bidentate chelate linkages. Thermogravimetry and elemental analyses indicate the presence of coordinated water with the calcium decanoate but not with longer chain carboxylates. The results of both the solution and solid state studies suggest that precipitation of long-chain carboxylates depends on a balance between hydration effects and hydrophobic (largely van der Waals') interactions. Electrostatic effects make little energetic contribution but play the important structural role of ordering the carboxylate anions before precipitation. Differences are observed in the interactions between calcium(II) and long chain alkylcarboxylates and alkylsulfates, and are interpreted in terms of stronger binding to the metal of the carboxylate group. A general mechanism is proposed for calcium carboxylate precipitation from aqueous solution based on this and previous studies.

Thiol-ene “click” networks from amphiphilic fluoropolymers: full synthesis and characterization of a benchmark anti-biofouling surface

The synthesis of heterogeneous, amphiphilic crosslinked networks from photo-initiated thiol-ene chemistry and full characterization of the physicochemical, anti-biofouling, mechanical, and thermal properties of this system are reported. Although interest in coatings that present heterogeneous surface features is increasing, anti-biofouling performance is typically compared to homogeneous biocidal- or non-toxic polydimethylsiloxane-based paints, for the advancement of commercial and novel systems, which leaves a need for a benchmark to compare highly complex, heterogeneous composites with similar complexities. This system has been generated and rigorously analyzed to understand how microscopic and nanoscopic disorder, resistance to protein adsorption and surface mechanical properties can be fine-tuned and optimized through oligomer selection, blend ratios and process conditions. Solution-state studies of individual and blended constituents probed the relative fluorescence intensities based on concentration and neighboring species that were used to identify microscopic disorder on the surface. Incubation of a fluorescently labelled protein on the benchmark surface showed 42% and 72% less adsorption than on model surfaces that largely expressed a single component. The extent of reaction and the identification of unconsumed functionalities were found through infrared spectroscopy. The benchmark surface had a Young's modulus of approximately 0.5 GPa, 7 to 35 times higher than model surfaces, with 50 times the variation in modulus. Nanoscale surface adhesion force variation and bulk wettability and bulk thermal stability are also reported. This study provides an extensive list of metrics to be used for the development of complex, heterogeneous, anti-biofouling coatings, appropriate to both surface optimization and mechanical tunability, for implementation in real-world applications.

Switching azonaphthols containing a side chain with limited flexibility. Part 1. Synthesis and tautomeric properties

A series of azo dyes, possessing amide fragments with restricted flexibility tethered to 4-(phenyldiazenyl)naphthalen-1-ol, was obtained from 1-hydroxy-2-naphthoic acid by subsequent conversion to amides and diazo coupling. It was shown that the position of the tautomeric equilibrium in solution strongly depends on the solvent in both UV and NMR concentration scale. The compounds exist as pure enol forms in chloroform and hydrocarbons, while in polar solvents (acetone, acetonitrile, alcohols) a tautomeric mixture is observed. According to the quantum-chemical calculations the aggregation of the keto tautomer is the possible reason for this shift in the position of the tautomeric equilibrium. To support the theoretical predictions, it was found that from acetone the keto form crystallizes as a dimer with hydrogen bonding between N 1– H in the one molecule and amide C O in the other forming a three-dimensional structure. The importance of the side-chain nitrogen atom on the dimer formation was confirmed by solution and solid state study of 4-(phenyldiazenyl)-2-acetylnaphthalen-1-ol. The results indicate that the new azo-dyes obtained could be suitable candidates for switching and sensing applications in non-polar solvents.

Fluorenyl Hexa-peri-hexabenzocoronene-Dendritic Oligothiophene Hybrid Materials: Synthesis, Photophysical Properties, Self-Association Behaviour and Device Performance

Apart from molecular properties, intermolecular forces play a vital role in defining the performance of organic electronic devices. This is particularly relevant in bulk heterojunction (BHJ) solar cells in which the arrangement of electron-donor and -acceptor materials into distinct crystalline phases of ideal size and distribution can lead to better power conversion efficiencies. In this study, a series of fluorenyl hexa-peri-hexabenzocoronenes (FHBC) decorated with thiophene dendrons (DOT) of variable size was obtained by using a convergent synthetic approach. With such variety of molecular sizes and shapes in hand, the objective of this study is to highlight the relationships between molecular properties, bulk properties and device performance. Correlations between π-π stacking ability and dendrimer generation were established from self-organisation studies in solution and solid state. The synergistic combination of molecular organisation at the nanoscale and photophysical characteristics derived from the FHBC and DOT moieties leads to a notable improvement of the photovoltaic performance.

The structure of human ubiquitin in 2-methyl-2,4-pentanediol: a new conformational switch.

A new crystal structure of human ubiquitin is reported at 1.8 Å resolution. Compared with the other known crystal structure or the solution NMR structure of monomeric human ubiquitin, this new structure is similar in its overall fold but differs with respect to the conformation of the backbone in a surface-exposed region. The conformation reported here resembles conformations previously seen in complex with deubiquinating enzymes, wherein the Asp52/Gly53 main chain and Glu24 side chain move. This movement exposes the backbone carbonyl of Asp52 to the exterior of the molecule, making it possible to engage in hydrogen-bond contacts with neighboring molecules, rather than in an internal hydrogen bond with the backbone of Glu24. This particular crystal form of ubiquitin has been used in a large number of solid state NMR studies. The structure described here elucidates the origin of many of the chemical shift differences comparing solution and solid state studies.

Structure-property relationships in conjugated donor–acceptor systems functionalized with tetrathiafulvalene

The properties of two donor–acceptor compounds tetrathiafulvalene-acenaphtho[1,2-b] quinoxaline (1) and tetrathiafulvalene-3-nitro-acenaphtho[1,2-b]quinoxaline (2) have been investigated by solution-state studies (electrochemistry, absorption, self-assembly) and theoretical calculations (DFT, TD-DFT). The electrochemical studies indicate the nitro-substituted effect on their redox properties is negligible. Both compounds show effective intramolecular charge transfer (ICT) transitions in the UV-Visible range in solution. Compared with compound 1, compound 2 has a bathochromic shift in the absorption spectra, the λmax−ICT has been extended from 20 800 cm−1 to 19 700 cm−1 (480 nm to 507 nm). In addition, when the nitro group is employed, the self-assembly characteristics of the two compounds are substantially changed from ribbon-like nanostructures to root-like nanostructures. Density functional theory (DFT) calculations provide insights into their molecular geometries, electronic structures, and physico-chemical properties.

Photophysical Properties of Dipeptides Containing Substituted 3-(Quinoxalin-6-yl) Alanine. Spectroscopic Studies and Theoretical Calculations

The photophysical properties of excited states of two hybrid dipeptides [N-(3-(2,3-diphenylquinoxaline-6-ylo)alanylo) glycine], Pe-DPhQ, and [N-(3-(2,3 (pirydine-2-ylo) quinoxaline-6-ylo)alanylo) glycine], Pe-DPiQ, have been investigated by a combined solution-state study (absorption, emission) and quantum-mechanical (ab initio, DFT) calculations. The RHF and DFT B3LYP/6-31G (d,p) computations of the ground-state isomers of Pe-DPiQ dipeptide (open, half-closed, and closed) indicate that the most stable is the "open"-type structure with approximately equal (-44.43 degrees , -43.05 degrees ) dihedral angles describing rotation of the aromatic side rings with respect to the quinoxaline framework. This agrees with the literature findings that synthetic peptides are mostly unfolded. The experiments show that emission of Pe-DPiQ dipeptide is strongly temperature dependent, and at ambient and elevated temperatures the fluorescence is prevailing while the phosphorescence dominated emission spectra are observed at 77 K. On the basis of the decay curves that in the broad temperature range (rt-77 K) are biexponential (2 and 9 ns), it was concluded that at least its two major excited-state conformations may interconvert on the nanosecond time scale. The third component, of a small amplitude (10%) and a long time constant (25 ns), appears only in a new fluorescence band (570 nm) that grows up with the temperature increase. Analysis of the CIS/6-31G(d,p) results of the excited-state isomers of Pe-DPiQ supports the interpretation of experimental emission spectra and enables one to assign two excited-state conformations, demonstrating a tendency to keep one of their two side rings coplanar relative to the central quinoxaline plane, as Pe-DPiQ-I* (41.9 degrees , 6.3 degrees ) and Pe-DPiQ-II* (40.1 degrees , 4.5 degrees ) isomers contributing to the room temperature (403 nm) and 363 K (570 nm) fluorescence bands, respectively. The calculations also explain the electronic character of the corresponding S(1)<-->S(0) transitions and show that the state ordering of Pe-DPiQ resembles that of other diazines where the first singlet is of the npi* character while the S(2) and T(1) are the pipi* states. The reason for a strong phosphorescence is assigned to an effective spin-orbit coupling of appropriate singlet and triplet states that leads to ISC transitions and in result to population of the T(1) state and a phosphorescence from the T(1) state. From the present study, it was concluded that incorporation of quinoxaline moiety into the model peptides does not change the useful spectroscopic properties of the fluorophore and allows one to design its new analogues with improved activity and specificity.

Solution and solid state study of copper(II) ternary complexes containing amino acids of interest for brain biochemistry – 1: Aspartic or glutamic acids with methionine or cysteine

Four new ternary complexes of Cu(II) containing aspartic or glutamic acids and methionine or cysteine as ligands were studied both in solution and in solid state. The solution study was performed using potentiometry, UV–Vis spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and electrochemistry. The stability constants of the ternary complexes were determined by potentiometry. The order of the values for the stability constants was CuGluMet (complex 4) < CuAspMet (complex 2) < CuGluCys (complex 3) < CuAspCys (complex 1), with complex 1 ≈ complex 3 ≫ complex 2 ≈ complex 4. This behavior was confirmed by the electronic spectra, EPR parameters and cyclic voltammetry. The compounds were synthesized in the solid state and characterized by thermogravimetry as well as vibrational and EPR spectroscopy. The results found in solid state are in agreement with the data found in solution studies where methionine, aspartic and glutamic acids coordinate to the copper(II) ion using the nitrogen atom of the amino group and one oxygen atom of the carboxylate group and cysteine coordinates through the nitrogen and sulfur atoms. The EPR data suggest that the complexes are square planar and that the complexes with cysteine as one of the ligands have some distortion.

Thiomethoxychalcone-Functionalized Ferrocene Ligands as Selective Chemodosimeters for Mercury(II): Single-Crystal X-ray Structural Signature of the [Hg8(μ8-S)(SCH3)12]2+ Cluster

Thiomethoxychalcone-based ligands bis[3,3-bis(methylsulfanyl)]-1,1'-eta(5)-ferrocenyl-2-propen-1-one (L(1)), 3,3-bis(methylsulfanyl)-1-eta(5)-ferrocenyl-2-propen-1-one (L(2)), and 3-methylsulfanyl-3-sulfanyl-1-eta(5)-ferrocenyl-2-propen-1-one (L(3)) have been synthesized on the ferrocene backbone by varying the number of chalcone arms and thiomethoxy substitutents. The single-crystal X-ray crystallographic analyses of all three ligands are reported in which crystals of L(1) were obtained as both syn and anti conformers and showed the conformational freedom of the two cyclopentadienyl (Cp) units. L(1)-L(3) are studied extensively toward their applicability in the colorimetric sensing of metal ions in solution. The solution-state study of mono- and bis(thiomethoxy)ferrocenylchalcone-functionalized ligands L(1) and L(2) showed selective colorimetric sensing for Hg(2+) over Li(+), Na(+), Ca(2+), Mg(2+), Cr(2+), Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), and Au(3+) in acetonitrile. In both cases, a selective color change from orange to purple was observed with Hg(2+) and the resultant solution showed the appearance of a new peak at 565 nm (epsilon = 3920 M(-1) cm(-1)) for L(1) and 600 nm (epsilon = 1140 M(-1) cm(-1)) for L(2) in the UV/vis experiments. The UV/vis titration profiles of L(1) and L(2) indicate the formation of 2:1 (L(1)/Hg(2+)) and 1:1 (L(2)/Hg(2+)) initial complexations in solution. On the other hand, L(3) with thiomethoxy- and thiol-functionalized ferrocenylchalcone showed no appreciable color change with Hg(2+) under the same experimental conditions. Attempts were made to isolate single crystals of the resulting purple solution obtained in the cases of L(1) and L(2) with Hg(2+). In both cases, crystals suitable for a single-crystal X-ray diffraction study were isolated in very low yield by a layer diffusion technique. The single-crystal structural investigations demonstrated the formation of a sulfide-encapsulated mercury thiolate cuboctahedron cluster, [Hg(8)S(SCH(3))(12)](2+), upon a selective chemodosimetric desulfurization reaction between Hg(2+) and L(1) or L(2). Cyclic voltammetric studies also support the Hg(2+)-induced cleavage of thiomethoxy groups.

Synthesis and anion binding of 2-arylazo-meso-octamethylcalix[4]pyrroles

2-Arylazo-5,5,10,10,15,15,20,20-octamethylcalix[4]pyrroles (azo-OMCPs) have been synthesised by the reaction of calix[4]pyrrole with aryldiazonium chloride in 15–45% yields. The solution-state binding studies of the synthesised hosts were investigated by absorption spectroscopy and 1H NMR in DMSO and CDCl3, respectively. These receptors, appended with electron-donating and electron-withdrawing groups, displayed enhanced affinity and selectivity for fluoride anion. Well-defined colour change in the visible region of the spectrum was observed upon addition of fluoride ion in DMSO solution of azo-OMCPs. Detailed NMR studies in CDCl3 revealed that azo-OMCPs with nitro and chloro groups have higher binding affinity for fluoride ion.

A systematic investigation of the CuCl 2/H 2mal/phen reaction system (H 2mal = malonic acid): Solution and solid state studies of its products

The systematic investigation of the parameter space of the CuCl 2/H 2mal/phen reaction system in MeOH resulted in the isolation of seven different complexes either as mixtures or in pure form, six of which have been structurally characterized. The molar ratios of the reactants and the crystallization methods have been systematically varied, leading to the isolation of compounds [Cu(H 2O)(phen)(mal)] ( 1), [Cu(MeOH)(phen)(mal)] ( 2), [Cu 2Li 2Cl 2(phen) 2(mal) 2(MeOH) 4] ( 3), [Cu 2(phen) 4(mal)][CuCl(phen)(mal)](OH) ( 4), [CuCl(phen) 2]Cl ( 5), and [CuCl(phen)(mal)][CuCl(phen) 2][Cu(phen) 2(Hmal)]Cl ( 6). The coordination versatility of the malonato ligand has been confirmed by the presence of three different coordination modes and its two deprotonation states in compounds 1– 6. Solution studies on methanolic solutions of 2– 4 and 6 by mass spectrometry revealed the absence of parent ion peak and the presence of fragment ions of low relative abundance not previously found in their crystal structure, thus indicating decomposition and rearrangement/reorganization of the complexes in solution and confirming the dynamic character of their solutions. Compounds 3 and 4 have been also studied in the solid state by EPR spectroscopy and magnetic measurements.