Study of ordered structures of syndiotactic poly(methyl methacrylate) in solution and in the solid state

From analysis of infrared spectra it was found that in syndiotactic (s) poly(methyl methacrylate) (PMMA) in solution, long s sequences contain an increased population of diads with a skeletal conformation tt (in the staggered approximation). Self-aggregation of s-PMMA in solution leads to a further increase of the fraction of long s sequences in the extended chain conformation, and to an ordering of easter groups. When solid s-PMMA is isolated from a solution in which it exists in the aggregated state, these characteristics are preserved in the solid. The polymer appears partially crystalline by x-ray scattering, and it exhibits fibrillar morphology under the electron microscope. Ordered structures of s-PMMA melt at temperatures about 150°C, while the presence of residual solvent decreases the temperature of melting. Solid s-PMMA obtained from solutions in which aggregation of the polymer does not take place, like s-PMMA which did not come into contact with solvent, contains a higher proportion of syndiotactic diads with a skeletal conformation tg; these samples are amorphous and morphologically structureless. Analogies between the structure of ordered s-PMMA and the structure of the PMMA stereocomplex are also discussed.     

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.     

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.     

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.     

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.     

The structure and chemical and acid-base state of the surface of solid solutions and binary components in the InSb-CdS system

The surface physicochemical properties, including microstructure, chemical composition, and acid-base surface properties, of solid solutions and binary components in the InSb-CdS system obtained for the first time were studied. Films of all the components had a polycrystalline structure with a nonuniform character of the distribution of crystallites, which associated into agglomerates. The chemistry of the surface was mainly determined by adsorbed H₂O and CO₂ molecules, OH⁻ groups, and, to a lesser extent, oxygen and hydrogen carbon compounds. The strength, concentration, and nature of acid centers were determined. Coordination-unsaturated In and Cd atoms, adsorbed water molecules, and OH-groups were responsible for acid-basic centers. Changes in the acid-base properties of the surface of InSb-CdS system components caused by composition variations were studied. They correlated with the “specific conductivity-composition” dependence, reflected the special features of donor-acceptor interactions in solid solutions, and could be used to predict adsorption-catalytic properties.     

Structure formation of sulfonated polyphenylquinoxalines in solution and in the solid state

Sulfonated polyphenylquinoxalines with different content of sulfo groups have been synthesized by polymer analogous reactions under different conditions. The rheological properties of these polymers in Nmethylpyrrolidone have been studied. The mechanical properties of films based on sulfonated polyphenylquinoxalines under uniaxial tension have been measured. The structures of the polymers have been examined by AFM.     

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.     

Electronic transitions of vanadyl phthalocyanine in solution and in the solid state

The electronic absorption and luminescence of vanadyl phthalocyanine (Pc) in dilute solution. and solids at 300 K were measured and analyzed qualitatively with the Ake and Gouterman(AG) mode [1] and the exciton in molecular crystal model [2]. Good agreement between the group theoretical predictions and the observed spectra was found. The presence of trace aggregates in VOPc dilute solutions was clearly illustrated by their characteristic O-O fluoreseences. The dimer fluoresces on the high energy side of the monomer, whereas the signal from the heavier aggregates appears on the low energy side. The presence of an unpaired electron in the monomer results in a much smaller fluorescence yield as compared to the dimeric form in which the odd electrons are paired. The absorption and fluorescence vibronic progressions suggest that the monomer is quite stable upon optical excitation to the first excited singlet. Our spectra show that there are at least two crystal forms in the phase I solid in agreement with Griffiths et al.`s calorimetric observation [3]. One of the two forms is dimeric as proposed by Griffiths et al. and confirmed by us. The extremely low radiative yield of the dimeric form is attributed to ultrafast exciton migration and to the intrinsic low yield of the molecules. In the phase II crystal, two prominent electronic absorptions were predicted and assigned. The low luminescence yield of this phase is ascribed to the rapid ²Q ? ²T₁ relaxation which also leads to the greatly red shifted luminescence (i.e. ²T₁ → ²T) relative to the absorption, ²T → ²Q. Molecules in this phase are treated as monomeric rather than dimeric as in one of the phase I forms. Thus, the characteristics of the unpaired electron of the single molecule are preserved in the phase II crystal.     

Asymmetric synthesis of the allocolchicinoid natural product N-acetylcolchinol methyl ether (suhailamine), solid state and solution phase conformational analysis

An asymmetric synthesis of the allocolchicinoid N-acetylcolchinol methyl ether (NCME) from 3-methoxybenzaldehyde is reported. Comparison of ¹H and ¹³C NMR spectroscopic data obtained for this sample of NCME provide further evidence for the assertion that this compound is congruous with the natural product that has been dubbed suhailamine, establishing NCME as a naturally-occurring allocolchicinoid. The single crystal X-ray diffraction structure of NCME is also reported for the first time, revealing a preference for adoption of the (7S,R_a,Z) form—i.e., describing the orientation of the biaryl axis and the amide N–CO bond as well as the configuration of the stereocenic centre—in the solid state. A preference for the same form in DMSO-d₆ solution is revealed upon analysis by a range of NMR spectroscopic techniques, whilst an interconverting 69:24:7 mixture of the (7S,R_a,Z), (7S,S_a,Z) and (7S,R_a,E) forms is observed in CDCl₃.     

Cyclodextrin complexation improves aqueous solubility of the antiepileptic drug,rufinamide: solution and solid state characterization of compound-cyclodextrin binary systems

Rufinamide (RUF) was characterized in terms of cyclodextrin (CD) complexation in order to improve its aqueous solubility. Binary systems of RUF with three CDs—β-cyclodextrin (β-CD), randomly methylated-β-cyclodextrin (RAMEB) and sulfobutylether-β-cyclodextrin (SBE-β-CD)—were characterized with a wide variety of analytical techniques. Liquid state characterization was carried out by complementary techniques such as nuclear magnetic resonance spectroscopy (NMR), capillary electrophoresis (CE), mass spectrometry (MS) and phase solubility studies. The latter revealed that the stability of the complexes decreased in the order of RAMEB?>?β-CD?>?SBE-β-CD. A_L-type diagrams were obtained in all cases, characteristic of 1:1 stoichiometry, with a maximum of over 15-fold increase in RUF solubility, when complexed with RAMEB. NMR Job plot and MS studies confirmed phase solubility results, regarding the binding stoichiometry. ¹H NMR and 2D ROESY investigations revealed the inclusion of the triazole moiety of RUF, confirmed by molecular modeling. Solid state complexation in 1:1 molar ratio was carried out by kneading method and investigated by differential scanning calorimetry (DSC) and infrared spectroscopy (IR). Comparative dissolution studies indicated an over two-fold improvement in dissolution efficacy of the kneaded products, when compared to the pure drug. Results of the present study might pave the way for a drug formulation with improved bioavailability.     

Self-association and self-assembly of molecular clips in solution and in the solid state

Clip molecules based on diphenylglycoluril form well-defined dimeric structures in chloroform solution and in the solid state. In solution the dimerization process is based on favourable π-π interactions and cavity filling effects. A combination of favourable π-π interactions and crystal packing forces determine the self-assembly of clips in the solid state. The geometry that the clip molecules adopt in solution and in a series of X-ray crystal structures is compared with favourable geometries predicted by molecular modelling calculations.     

Unprecedented synthesis of 1,3-dimethylcyclobutadiene in the solid state and aqueous solution

Cyclobutadiene ( CBD ), the smallest cyclic hydrocarbon bearing conjugated double bonds, has long intrigued chemists because of its chemical characteristics. The question of whether the molecule could be prepared at all has been answered, but the parent compound and its unperturbed derivatives have eluded crystallographic characterization or synthesis “in water”. Different approaches have been used to generate and to trap cyclobutadiene in a variety of confined environments: a) an Ar matrix at cryogenic temperatures, b) a hemicarcerand cage enabling the characterization by NMR spectroscopy in solution, and c) a crystalline guanidinium–sulfonate–calixarene G₄C matrix that is stable enough to allow photoreactions in the solid state. In the latter case, the 4,6‐dimethyl‐α‐pyrone precursor, Me₂1 , has been immobilized in a guanidinium–sulfonate–calixarene G₄C crystalline network through a combination of non‐covalent interactions. UV irradiation of the crystals transforms the entrapped Me₂1 into a 4,6‐dimethyl‐Dewar‐β‐lactone intermediate, Me₂2 , and rectangular‐bent 1,3‐dimethylcyclobutadiene, Me₂CBD^R , which are sufficiently stable under the confined conditions at 175 K to allow a conventional structure determination by X‐ray diffraction. Further irradiation drives the reaction towards Me₂3&Me₂CBD^S /CO₂ (63.7 %) and Me₂CBD^R (37.3 %) superposed crystalline architectures and the amplification of Me₂CBD^R . The crystallographic models are supported by additional FTIR and Raman experiments in the solid state and by ¹H NMR spectroscopy and ESI mass spectrometry experiments in aqueous solution. Amazingly, the 4,6‐dimethyl‐Dewar‐β‐lactone, Me₂2 , the cyclobutadiene‐carboxyl zwitterion, Me₂3 , and 1,3‐dimethylcyclobutadiene, Me₂CBD , were obtained by ultraviolet irradiation of an aqueous solution of G₄C{Me₂1} . 1,3‐Dimethylcyclobutadiene is stable in water at room temperature for several weeks and even up to 50 °C as demonstrated by ¹H NMR spectroscopy.     

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.     

Properties of solid solutions in the KCl-NaCl system

Conditions for the decomposition of solid solutions in the KCl-NaCl system and their electrophoretic properties were studied. Compositions based on the KCl-NaCl system can be used for producing temperature sensors.     

Spectral and photophysical studies on cruciform oligothiophenes in solution and the solid state

The photophysical and spectroscopic properties of a new class of oligothiophene derivatives, designated as cruciform oligomers, have been investigated in solution (room and low temperature) and in the solid state (as thin films in Zeonex matrixes). The study comprises absorption, emission, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation) and lifetimes. The overall data allow the determination of the rate constants for all decay processes. From these, several conclusions are drawn. First, in solution, the main deactivation channels for the compounds are the radiationless processes: S(1) --> S(0) internal conversion and S(1) --> T(1) intersystem crossing. Second, in general, in the solid state, the fluorescence quantum yields decrease relative to solution. A comparison is made with the analogous linear alpha-oligothiophenes, revealing a lower fluorescence quantum efficiency and, in contrast to the normal oligothiophenes, that internal conversion is an important channel for the deactivation of the singlet excited state. Replacement of thiophene by 1,4-phenylene units in the longer-sized cruciform oligomer increases the fluorescence efficiency. The highly efficient generation of singlet oxygen through energy transfer from the triplet state (S(Delta) approximately 1) provides support for the measured intersystem crossing quantum yields and suggests that reaction with this may be an important pathway to consider for degradation of devices produced with these compounds.