Polymer-nanoparticle complexes: from dilute solution to solid state

We report on the formation and the structural properties of "supermicellar" aggregates made from mineral nanoparticles and polyelectrolyte-neutral block copolymers in aqueous solutions. The mineral particles put under scrutiny are ultrafine and positively charged yttrium hydroxyacetate nanoparticles. Combining light, neutron, and X-ray scattering experiments, we have characterized the sizes and the aggregation numbers of the organic-inorganic complexes. We have found that the hybrid aggregates have typical sizes in the range of 100 nm and exhibit a remarkable colloidal stability with respect to ionic strength and concentration variations. Solid films with thicknesses up to several hundreds of micrometers were cast from solutions, resulting in a bulk polymer matrix in which nanoparticle clusters are dispersed and immobilized. It was found in addition that the structure of the complexes remains practically unchanged during film casting.     

Physicochemical characterization of terbinafine-cyclodextrin complexes in solution and in the solid state

Terbinafine (TB) is an allylamine derivative used as oral and topical antifungal agent. The physicochemical properties of the complexes between TB and different cyclodextrins (CDs): α-CD, β-CD, hydroxypropylβ-CD, methylβ-CD and γ-CD, have been studied in pH 12 aqueous solutions at 25 °C and in the solid state. Different phase solubility profiles of TB in the presence of CDs have been obtained: A_L type for TB with hydroxypropylβ-CD and γ-CD, A_P type for the complexes with methylβ-CD and α-CD, while a B_S profile was found for TB-β-CD. The apparent stability constants of the complexes were calculated at 25 °C from the phase solubility diagrams. The higher increase of TB solubility, up to 200-fold, together with the higher value of the stability constant were found for the complex with methylβ-CD. Solid systems of 1:1 drug:CD molar ratio were prepared and characterised using X-ray diffraction patterns, thermal analysis and FTIR spectroscopy. The coevaporation method can be considered the best method in preparing these solid complexes. The complexes of TB with natural CDs, except with α-CD, were crystalline, whereas the methyl and hydroxypropyl derivatives gave rise to amorphous phases. Dissolution rate studies have been performed with TB-β-CD and TB-HPβ-CD complexes, showing a positive influence of complexation on the drug dissolution.     

Studies on some novel Schiff-base complexes in solution and solid state

In solution Schiff-base complexes of stoichiometry MAB, MAB₂ or MA₂B₂ have been detected in the Co(II), Ni(II), Cu(II) and Zn(II)-o-vanillin (o-van) [A]-L-valine (val), L-glutamine (gln) and L-histidine (his)(B) systems. The results suggest that in the M-o-van-val/gln systems, the Schiff-base ligand (AB) is tridentate in M(AB) complexes, while (AB) is tetradentate in his systems. MAB₂ species can be represented as M(AB)(B), where the mode of coordination of (AB) would be similar to that in the M(AB) species. The MA₂B₂ complex can be represented as M(AB)₂, where (AB) is tridentate in all the systems. The stabilities of complexes follow the Irwin–Williams order of stability. MAB complexes were isolated and conformed by characterization data. Conductance studies indicate that all complexes are non-ionic. Magnetic susceptibility and electronic spectral data suggest a tetrahedral structure in Co(II) and Ni(II)-o-van-val/gln and Ni(II)-o-van-his systems and square-planar structure in Co(II)-o-van-his and Cu(II)-o-van-val/gln/his systems for the MAB species. The IR spectral data indicate the tri and tetradentate binding of (AB) in the M(AB) complexes, respectively, in M(II)-o-van-val/gln and M(II)-o-van-his systems. Antimicrobial activity of the ligand and its Cu(II) complexes has been studied; Cu(II) complexes have higher activity than that of the ligand and control.     

Ruthenium(II) complexes containing tetrazolate group: electrochemiluminescence in solution and solid state

In this work, we report the results about the solution and solid-state phosphorescence emission properties of six Ru(II) complexes containing various 5-substituted tetrazolate ligands. The photo- and electrochemiluminescence spectra of all compounds revealed a red shifted emission with respect to the Ru(bpy)(3)(2+). Significant changes to the light emission energy and to the efficiency and sensitivity to oxygen were also determined by varying the nature of the substituent ring of the tetrazolate ligand. Light-emitting solid devices with active layers containing solid films of the same complexes were prepared, and preliminary studies of their electroinduced emission properties were performed. The electrochemiluminescence (ECL) emission intensity of two of the six complexes was of the same order of magnitude as the reference Ru(bpy)(3)(2+).     

Preparation and spectroscopic studies of an inclusion complex of adenine with beta-cyclodextrin in solution and in the solid state

The interaction between adenine and beta-CD has been investigated in solution and in the solid state by several analytical techniques, primarily by 1H-NMR, 2D ROESY and fluorescence spectra, and secondarily by other important techniques, for example, Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC). The association constant and 1:1 nature of the complex between adenine and beta-CD in solution were determined by fluorescence spectroscopy. A spatial configuration for the complex in solution is proposed from analysis of the 1H-NMR and 2D ROESY data. The Fourier transform infrared spectroscopy (FT-IR) and differential scanning calorimetry (DSC) data are consistent with the formation of an inclusion complex. In addition, a solid inclusion complex of adenine with beta-CD was synthesized by the coprecipitation method.     

Lanthanide nitrate complexes of tri-isobutylphosphine oxide: solid state and CD2Cl2 solution structures

The complexes Ln(NO(3))(3)L(3) between Ln(NO(3))(3) and (i)Bu(3)PO (=L) have been prepared for Ln = La-Lu (excluding Pm). The isolated complexes have been characterized by infrared spectroscopy, mass spectrometry, and elemental analysis. The single crystal X-ray structures have been determined for representative complexes across the series Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb and show the coordination geometry around the metal to be the same with 9-coordinate lanthanide ions and bidentate nitrates. Subtle changes in the coordination of the nitrate ligand occur from Sm onward. Changes in the infrared spectra correlate well with changes in the X-ray structures. Solution properties have been examined by variable temperature multinuclear ((1)H, (13)C, (15)N, and (31)P) NMR spectroscopy in CD(2)Cl(2). The spectra of complexes of the early lanthanides are consistent with the presence of a single species in solution while those of the heavier lanthanides show that more than one complex is present in solution and that two inequivalent phosphorus environments are observable at low temperature. The fluxional behavior is lanthanide dependent with smaller ions giving static structures at higher temperature. Complexes with tricyclohexylphosphine oxide show that the dynamic NMR behavior is also related to the size of the ligand. Analysis of the lanthanide induced shifts indicates minor changes in solution structure occur from Sm onward which correlate well with the solid state structures.     

Diels-Alder reaction volumes in the solid state and solution

The densities of anthracene, tetracyanoethylene, maleic anhydride, N-phenylmaleineimide, trans, trans-1,4-diphenylbuta-1,3-diene, and their Diels-Alder adducts were measured in the solid state and in solution at 25 °C. The reaction volumes in the solid state were calculated from the difference in molar volumes. They turned out to be low, close to each other (–4 to –11 cm³ mol^–1), and slightly different from the reaction volumes (–8±1 cm³ mol^–1) calculated from the van der Waals radii. The reaction volumes in solutions (–15 to –32 cm³ mol^–1) were found from the difference in partial molar volumes of the reactants in dioxane, acetonitrile, and 1,2-dichloroethane, The experimental Diels-Alder reaction volumes in solution are determined not only by the formation of new bonds in an adduct: a considerably higher contribution (to 75%) is made by a change in the volume of intermolecular empty spaces in solution on going from reactants to adducts.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2386–2390, November, 2004.     

Composition and solution properties of fluorinated block copolymers and their surface structures in the solid state

A series of diblock copolymers composed of methyl methacrylate and 2-perfluorooctylethyl methacrylate (PMMA₁₄₄-b-PFMA _n ) with various PFMA block lengths were prepared by atom transfer radical polymerization (ATRP). The surface structures and properties of these polymers in the solid state and in solution were investigated using contact angle measurement, X-ray photoelectron spectroscopy (XPS), sum frequency generation (SFG) vibrational spectroscopy, surface tension and dynamic laser light scattering (DLS). It was found that with increasing PFMA block length, water and oil repellency decreased, the ratio of F/C increased with increasing film depth, and the degree of ordered packing of the perfluoroalkyl side chains at the surface decreased. When the number of PFMA block units reached 10, PMMA segments were detected at the copolymer surface, which was attributed to the PFMA block length affecting molecular aggregation structure of the copolymer in the solution and the interfacial structure at the air/liquid interface, which in turn affects surface structure formation during solution solidification. The results suggest that copolymer solution properties play an important role in structure formation on the solid surface. Supported by the National Natural Science Foundation of China (Grant Nos. 50573069 and 20704038) and Program for Changjiang Scholars and Innovative Research Team in University (Grant No.IRT 0654)     

H-Bonded complexes of adenine with Rebek imide receptors are stabilised by cation-pi interactions and destabilised by stacking with perfluoroaromatics

A series of Rebek imide receptors with naphthalene or heteroaromatic platforms attached by amide or ester linkers have been prepared from the corresponding acyl chloride or anhydride; the X-ray crystal structure of the receptor-derived anhydride reveals a supramolecular H-bonded helix formation in the crystal; the complexes of adenine bound to the receptors by Hoogsteen H-bonding are found to be stabilised by stacking with a methylquinolinium ion, but destabilised by stacking with a perfluorinated naphthalene.     

4-Aminobenzimidazole-1-methylthymine: a model for investigating Hoogsteen base-pairing between adenine and thymine

We report the infrared spectrum of the 4-aminobenzimidazole-1-methylthymine (4ABI:1MT) heterodimer, detected by femtosecond multiphoton ionization. Based on calculations of both the harmonic and the anharmonic frequencies, the observed vibrational spectrum is assigned to a structure that mimics the Hoogsteen base pairing of adenine and thymine. A notable observation made in the course of this study is that there is a significant imbalance in the observed strengths of the H-bonds. While the N···H-N bond reveals a large red shift of >700 cm(-1) for the NH stretch frequency, the N-H···O bond is characterized by only a 50 cm(-1) shift. The importance of this observation in the formation of Hoogsteen duplexes by thymine-based oligonucleotides is discussed.     

Protonation of leucoemeraldine in the solid state and in solution

The protonation of leucoemeraldine in power form and in N-methylpyrrolidinone (NMP) solution by HCIO₄ and HBF₄ has been studied by x-ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)-visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO₄, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O₂ content of the solutions. © 1993 John Wiley & Sons, Inc.     

Solid state and solution nitrate photochemistry: photochemical evolution of the solid state lattice

We examined the deep UV 229 nm photochemistry of NaNO(3) in solution and in the solid state. In aqueous solution excitation within the deep UV NO(3)ˉ strong π → π* transition causes the photochemical reaction NO(3)ˉ → NO(2)ˉ + O·. We used UV resonance Raman spectroscopy to examine the photon dose dependence of the NO(2)ˉ band intensities and measure a photochemical quantum yield of 0.04 at pH 6.5. We also examined the response of solid NaNO(3) samples to 229 nm excitation and also observe formation of NO(2)ˉ. The quantum yield is much smaller at ～10(-8). The solid state NaNO(3) photochemistry phenomena appear complex by showing a significant dependence on the UV excitation flux and dose. At low flux/dose conditions NO(2)ˉ resonance Raman bands appear, accompanied by perturbed NO(3)ˉ bands, indicating stress in the NaNO(3) lattice. Higher flux/dose conditions show less lattice perturbation but SEM shows surface eruptions that alleviate the stress induced by the photochemistry. Higher flux/dose measurements cause cratering and destruction of the NaNO(3) surface as the surface layers are converted to NO(2)ˉ. Modest laser excitation UV beams excavate surface layers in the solid NaNO(3) samples. At the lowest incident fluxes a pressure buildup competes with effusion to reach a steady state giving rise to perturbed NO(3)ˉ bands. Increased fluxes result in pressures that cause the sample to erupt, relieving the pressure.     

Vanadate complexes bearing an imidazolidine-bridged bis(aryloxido) ligand: synthesis and solid state and solution structure

A new imidazolidine-bridged bis(aryloxido) ligand precursor (H(2)L) [H(2)L = 2,2'-(imidazolidine-1,3-diylbis(methylene))bis(4-(1,1,3,3-tetramethylbutyl-2-yl)phenol)] was prepared in a relatively high yield (～60%) via a single-step Mannich condensation of 4-(1,1,3,3-tetramethylbutyl)phenol, ethylenediamine and paraformaldehyde at 2:1:3 molar ratio and characterized by chemical and physical techniques including X-ray crystallography. Reactions of H(2)L with [VO(OEt)(3)] at 1:1 and 1:2 molar ratios in toluene afforded [V(L-κ(3)O,N,N,O)(O)(OEt)] (1) and [V(2)(μ-L-κ(4)O,N,N,O)(μ-OEt)(2)(O)(2)(OEt)(2)] (2), respectively. Alcoholysis of 1 with EtOH enables elimination of one molecule of H(2)L and the formation of 2. Compounds 1 and 2 were characterized by IR and NMR spectroscopy as well as ES-MS experiments. The definitive molecular structure of 2 was provided by a single-crystal analysis and revealed its dinuclear nature, featuring two octahedral vanadium centres bridged by both OEt groups and the L ligand. The (51)V, (1)H and (13)C NMR spectra as well as ES-MS showed that 2 does not stay intact in solution and undergoes dissociation to give 1 and [VO(OEt)(3)].     

Coordination chemistry of phosphanyl amino acids: solid state and solution structures of neutral and cationic rhodium complexes

Copper phosphide or arsenide complexes, [Cu(EPh(2))(neo)] (E = P, As, neo = 2,9-dimethyl-1,10-phenanthroline; trivial name: neocuprine) react selectively with the N-protected brominated serine derivatives, 2-(S)-(alkoxycarbonylamino)-3-bromomethylpropionates ((ROCO)SerBr, : R = PhCH(2), : tBu, : Me) to give the corresponding phosphanylated or arsanylated amino acids, (ROCO)SerPhos (: Phos = PPh(2)) and (Z)SerArs (Ars = AsPh(2), Z = PhCH(2)OCO). The dipeptide (Z)AlaSerPhos was likewise prepared. The phosphanes , and the arsane reacted cleanly with [Rh(2)(micro-Cl)(2)(cod)(2)] to give the rhodium(I) complexes [RhCl(cod)((Z)SerPhos)] , [RhCl(cod)((Boc)SerPhos)] (Boc = tBuOCO), [RhCl(cod)((Z)AlaSerPhos)] , and [RhCl(cod)((Z)SerArs)] which were characterized by X-ray diffraction studies. A common structural feature is an intramolecular (N)H[dot dot dot]Cl(Rh)-hydrogen bridge which according to NMR investigations remains intact in solution. The abstraction of chloride from the coordination sphere of Rh(I) in or has a profound structural impact. While in and , the ligands bind in a monodentate fashion, via the phosphorus atom only, they serve as bidentate ligands via the phosphorus centre and the peptidic C=O group in [Rh(cod)(kappa(2)-(Z)SerPhos)]PF(6) and [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6). This causes also the amino acid residue structures to change from alpha-helix type in and to a beta-sheet type in both. Addition of chloride to and fully re-establishes the structures of both. The complexes [RhCl(cod)((Z)SerPhos)] and [RhCl(cod)((Boc)SerPhos)] show good activities in homogeneously catalyzed hydrogenations of olefins while the dipeptide complex is less active. Phosphane addition to greatly diminishes the catalytic activity. The cationic complex [Rh(cod)(kappa(2)-(Z)AlaSerPhos)]PF(6) shows low activity which, however, is greatly increased by addition of one equivalent of phosphane.     

Isomerization of cyclobutane ligands in the solid state and solution

Cyclobutane compounds are a class of compounds that can be conveniently synthesized in the solid state by employing crystal engineering principles. The rctt-isomer (or the syn-dimer) is the most common form of any cyclobutene compound that is obtained in the solid state by the photochemical [2 + 2] cycloaddition reactions. However, these rctt-isomers can be converted to other less accessible forms, under some special conditions. Isomerization of cyclobutane compounds thus plays an important role in synthetic chemistry. Such isomerization of cyclobutane compounds have been reported in organic salts, metal complexes, coordination polymers and metal-organic frameworks. In this review, these fascinating examples of isomerization that occur both in the solid state and solution phase have been discussed.     

Spectroscopic studies of iron(III) complexes of D-saccharose and D-glucose in the solid state and in solution

Iron(III) complexes of D-saccharose and D-glucose were prepared. The compositions of the complexes were determined by standard analytical methods. The Mössbauer spectra reflected the presence of high-spin iron(III) in the polynuclear species. EPR spectroscopy demonstrated antiferromagnetically coupled iron(III) centers within the solid complexes. The¹³C NMR spectra indicated the presence of a mixture of coordination isomers of iron(III) complexes containing the sugar ligand in differently bound forms.This work is dedicated to the memory of Dr. L. Korecz.     

Cyclodextrin solubilization of celecoxib: solid and solution state characterization

The low aqueous solubility of celecoxib (CCB) hampers its oral bioavailability and permeation from aqueous environment through biological membranes. The aim of this study was to enhance the aqueous solubility of CCB by complexation with cyclodextrin (CD) in the presence of water-soluble polymer. The effects of different CDs (αCD, βCD, γCD, 2-hydroxypropyl-β-cyclodextrin and randomly methylated β-cyclodextrin (RMβCD)) and mucoadhesive, water-soluble polymers (hydroxypropyl methylcellulose (HPMC), chitosan and hyaluronic acid) were investigated. The phase solubility profiles and CCB/CD complex characteristics were determined. RMβCD exhibited the greatest solubilizing effect of the two CDs tested. However, γCD was also selected for further investigations due to its safety profile. Addition of polymer to the aqueous CD solutions enhanced the CD solubilization. Formation of CCB/RMβCD/HPMC and CCB/γCD/HPMC ternary complexes resulted in 11 and 19-fold enhancement in the apparent complexation efficiency in comparison to their CCB/CD binary complex, respectively. The size of ternary complex aggregates in solution were determined to be from about 250 to about 350 nm. The data obtained from Fourier transform infra-red, differential scanning calorimetry and powder X-ray diffraction indicated presence of CCB/CD inclusion complexes in the solid state. Proton nuclear magnetic resonance data demonstrated that CCB was partially and totally inserted into the hydrophobic central cavities of RMβCD and γCD.     

The structure of hydantoins in solution and in the solid state

The results of NMR spectroscopic and X-ray crystallographic studies are critically discussed with respect to the structure of hydantoins, their tautomerism, and their acidity. The imide NH proton of the preferred, nearly planar 2,4-imidazolidine-dione tautomer proved to be more acidic than the corresponding amide NH proton. Phenyl substituents at the ring nitrogen atoms and at C-5 are twisted from the plane of the hydantoin ring; in case ofortho substituents restricted rotation about the N-aryl bond was found and the barrier to rotation determined by dynamic NMR spectroscopy. For 5-benzyl substituents, afolded conformation of the two rings, due to intramolecular interactions, was found and for 5-exo-methylene substituted hydantoins the relevant E/Z isomerism at theexo-cyclic C, C double bond was studied. In addition, the¹H and¹³C chemical shifts of the hydantoins proved to excellently indicate the electronic distribution along the hydantoin ring moiety. Finally, the mass spectrometric fragmentation of the hydantoins is critically discussed.Dedicated to Prof. Rolf Borsdorf on the occasion of his 65th birthday.     

Study of tolbutamide-hydroxypropyl-gamma-cyclodextrin interaction in solution and solid state

Tolbutamide-hydroxypropyl-gamma-cyclodextrin (TBM-HPGCD) interaction has been investigated in an aqueous environment and in the solid state. The solubility of TBM was increased in accord with the amount of HPGCD added to the aqueous medium forming a soluble inclusion compound. The phase solubility diagram obtained was of A(L) type. Physical mixtures and kneaded systems of the drug and cyclodextrin derivative were prepared in 1:1 and 1:2 drug/cyclodextrin mol/mol ratio. All solid binary systems were characterised by hot-stage microscopy (HSM), differential scanning calorimetry (DSC), thermogravimetry (TG) and X-ray powder diffractometry (XRD). An inclusion complex was formed in both of the kneaded systems. In the 1:2 kneaded system, the entire drug was included in the cyclodextrin cavity, while, in the 1:1 kneaded system only a part of the drug formed an inclusion complex with the cyclodextrin. A significant improvement in the dissolution of the drug was obtained from the kneaded systems in comparison with that of the pure TBM and physical mixtures. However, there was no significant difference between the dissolution profiles of the two kneaded systems. The study suggests that an inclusion complex was obtained both in aqueous solution and in solid state.