Photolysis of water/dicyanoacetylene complexes: an infrared matrix isolation and theoretical study

The structure and energy of the 1:1 complexes formed between dicyanoacetylene and water (D₂O) in argon matrix are investigated using FTIR spectroscopy and ab initio calculations at the B3LYP/6-31g** level of theory. Two types of 1:1 complexes are observed. The first one corresponds to the NH structure characterized by a hydrogen bond between H₂O and one of the nitrogen of dicyanoacetylene. The second corresponds to the CO form which involves a van der Waals interaction between the Cβ of dicyanoacetylene and the oxygen of water.

These complexes were irradiated with an Hg–Xe lamp at 10 K. Two products were observed by FTIR spectroscopy. The first one corresponds to the Isonitrile:H₂O complexes formation. The second one, resulting from the reaction of water on the photolyzed dicyanoacetylene, corresponds to the cyanoketene:HCN complex formation.     

Competitive processes associated to the interaction of a cavitand derivative with caffeic acid

Abstract

The interaction of caffeic acid and a newly synthesised cavitand derivative was investigated by UV–vis and fluorescence spectroscopy in tetrahydrofuran–water matrix. The temperature dependence of the equilibrium constants was determined first, then the thermodynamic parameters were calculated using the van’t Hoff equation. Absorption measurements highlighted entropy-controlled formation of cavitand–caffeic acid complexes with 1:2 stoichiometry. It was proved by fluorescence measurements that caffeic acid dimerisation is followed by the formation of cavitand–caffeic acid complexes with 1:2 stoichiometry. It was also shown that both the caffeic acid dimerisation and the formation of 1:2 complexes are controlled by the entropy gain. PL signal is preferred to use for analytical application in this particular case.     

Formation of Water Complexes with Organic Compounds in Solid Matter. IR Manifestation and DFT Study

In terms of FTIR study it was estimated that water forms the complexes with furan, thiophene, dichloromethane, tribromomethane in low temperature films at 90–150 K interval and with benzene in KBr matrix at ambient temperature. The mechanism of intermolecular interaction was simulated by ab initio calculation using DFT method. It was shown that complex formation occurs due to arising of hydrogen bond between hydronium ion of water cluster or single water molecule with organic components.     

Physicochemical characterization of finasteride:PEG 6000 and finasteride:Kollidon K25 solid dispersions, and finasteride: ��-cyclodextrin inclusion complexes

Finasteride is a practically insoluble in water drug that belongs to the Class II of the BCS (poor solubility and high permeability). Solid dispersions are solid products consisting of at least two different components, generally a hydrophilic matrix and a hydrophobic drug. Solid dispersions are a successful strategy to improve drug release of poorly water-soluble drugs such as finasteride. Natural cyclodextrins are doughnut-shaped molecules with an internal hydrophobic cavity and a hydrophilic external surface. The lipophilic cavity enables cyclodextrins to form non-covalent inclusion complexes with a wide variety of poorly water-soluble drugs such as finasteride. The aim of this study was to investigate the formation of finasteride:PEG 6000 and finasteride:Kollidon K25 solid dispersions and finasteride:??-cyclodextrin inclusion complexes by solvent evaporation method using a mixture of water:ethanol (1:1). The formation of finasteride:PEG 6000 and finasteride:Kollidon K25 solid dispersions and finasteride:??-cyclodextrin inclusion complexes was investigated and characterized by differential scanning calorimetry (DSC), infrared (IR) spectroscopy, and dissolution studies from capsules containing a quantity equivalent to 5 mg of finasteride. The DSC thermograms revealed the transformation of finasteride into the amorphous state in solid dispersions with PEG 6000 and Kollidon K25, and in inclusion complexes with ??-cyclodextrin. The IR spectra demonstrated molecular interaction in solid dispersions of finasteride with PEG 6000, and in inclusion complexes with ??-cyclodextrin. Dissolution rate of solid dispersions and inclusion complexes was significantly greater than that of corresponding physical mixtures and pure drug, indicating that the formation of solid dispersions and inclusion complexes increased the solubility of the poorly soluble drug, finasteride.     

Infrared matrix isolation and quantum chemical studies of the nitrous acid complexes with water

The 1:1 and 2:1 complexes between water and trans- and cis-isomers of nitrous acid have been isolated in argon matrices and studied using FTIR spectroscopy and DFT(B3LYP) calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra indicate that 1:1 complexes trapped in solid argon involve very strong hydrogen bond in which acid acts as the proton donor and water as the proton acceptor. The perturbed OH stretches are −248, −228 cm⁻¹ red shifted from their free-molecules values in complexes formed by trans- and cis-HONO isomers, respectively. The calculated spectral parameters for the two complexes are in good agreement with experimental data. The calculations also predict stability of two more 1:1 weakly bound complexes formed by each isomer. In these the water acts as the proton donor and one of the two oxygen atoms of the acid as the acceptor. The experimental spectra demonstrate also formation of 2:1 complex between water and trans-HONO isomer in an argon matrix. The performed calculations indicate that the complex involves a seven-membered ring in which OH group of HONO forms very strong hydrogen bond with the oxygen atom of one water molecule and nitrogen atom acts as a weak proton acceptor for the hydrogen atom of the second water molecule of the water dimer. The observed perturbations of the OH stretch of trans-HONO (750 cm⁻¹ red shift) is much larger than that predicted by calculations (556 cm⁻¹ red shift); this difference is attributed to strong solvation effect of argon matrix on very strong hydrogen bond.     

Intermolecular interactions as controlling factor for water sorption into polymer membranes

A multidisciplinary approach was used for delineating the mechanisms controlling water sorption into modified block co-poly-(ether/amide) (PEBAX) membranes. In particular, incorporation of aromatic sulfonamide (KET) into the polymer matrix led to a nonlinear increase of water sorption in the membrane. The modification in sorption was accompanied by a nonlinear behavior in membrane surface energies. Infrared analysis revealed a different availability and accessibility of free polar groups supporting the formation of hydrogen bonding as a function of modifier concentration. A combination of both experimental and theoretical procedures was used to analyze the molecular processes of water sorption on PEBAX membranes. Molecular dynamics (MD) and quantum chemical (QC) calculations demonstrated that the formation of KET-KET dimers in the polymeric matrix led to a decrease in the interaction energy between water and modifiers. In addition, no variations in the dipole moments of water-dimer structures were found in comparison to a single KET and water-KET molecule. The formation of water-dimer complexes at higher concentration of modifier decreases the number of the dipole moment, thus preventing the polarization of polymer chains.     

Sol–gel technology and template synthesis in thin gelatin films

Processes of sol–gel technology of template synthesis of 3d-element metal macrocyclic complexes that occurs in thin films of metalhexacyanoferrate(II) gelatin-immobilized matrix implants under their contact with water solutions containing various (N,O,S)-donor atomic and (C=O) containing organic compounds, have been discussed. It was noted that, in a series of cases, sol–gel technology of template synthesis in the given specific conditions allows to realize such metal macrocyclic complexes formation processes that are not typical at the complexing in solutions or solid phase.     

Intra- and intermolecular hydrogen bonding in formohydroxamic acid complexes with water and ammonia: infrared matrix isolation and theoretical study

The complexes of formohydroxamic acid with water and ammonia have been studied using FTIR matrix isolation spectroscopy and MP2 calculations with a 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the HCONHOH/H₂O(NH₃)/Ar matrixes indicates formation of strongly hydrogen-bonded complexes in which the NH group of formohydroxamic acid acts as a proton donor toward the oxygen atom of water or the nitrogen atom of ammonia. The NH stretching vibration of formohydroxamic acid exhibits 150 cm⁻¹ red shift in the complex with water and 443 cm⁻¹ red shift in the complex with ammonia as compared to the NH stretch of the HCONHOH monomer. The theoretical calculations indicate stability of five isomers for the water complex and three isomers for the ammonia complex. The most stable are the cyclic structures in which the water or ammonia molecules are inserted within the intramolecular hydrogen bond of the formohydroxamic acid molecule and act as proton donors for the CO group and proton acceptors for the OH group of the formohydroxamic acid molecule. In spite of their stability the cyclic structures have not been observed in the matrixes which indicates high energy barrier for their formation, the reaction of complex formation is under kinetic and not thermodynamic control.     

Residual water in polyvinyl alcohol

The state of sorbed water molecules in the matrix of polyvinyl alcohol is investigated via the methods of static sorption, DSC, TGA, IR Fourier spectroscopy, ¹H NMR spectroscopy, and quantum-chemical simulation. It is shown that the sorption of water by polyvinyl alcohol characterized by an S-shaped isotherm is described by the double-sorption model. It is established that the low diffusion coefficients and extremely low rates of desorption processes observed in the range of low activities are determined by a shift of the equilibrium toward the formation of hydrogen-bonded complexes of water molecules with hydroxy groups of the polymer. A mechanism for the behavior of residual water in hydrophilic polymers is suggested. It implies that differences between polymers are determined only by the quantity of residual water immobilized in “traps” and the energy of hydrogen-bond formation.     

Infrared spectroscopic and photochemical study of water-ozone complexes in solid argon

Infrared spectroscopy has been coupled with the matrix isolation technique, firstly for a study of the molecular complexes between ozone and water, secondly to investigate the mechanism of the water photooxidation by ozone at 15 K by UV light. The 1:1, 1:2 and 2:1 complexes are isolated and mainly characterized by a shift in the infrared absorption of the H₂O (D₂O) submolecule. Force field calculations involving anharmonicity corrections allows us to conclude into the non-equivalence of the two OH oscillators within the 1:1 complex. This result suggests the formation of a very weak hydrogen bond of the type HOH...OO₂. By photolysis of the water-ozone mixture in solid argon (λ < 310 nm), formation of H₂O₂ with very small amounts of O₂H and OH is observed. This process occurs through the reaction between the O(¹D) atom generated by photodissociation of O₃ belonging to the one H₂O: O₃ pair and the water molecule of the same pair, without diffusion of the oxygen atom.     

DNA-lipid interactions in vitro and in vivo

The data on lipid-nucleic interactions and their role in vitro and in vivo are presented. The results of study of DNA-lipid complexes in absence and in presence of divalent metal cations (triple complexes) are discussed. The triple complexes represent the generation of cellular structures such as pore complexes of eucaryotes and "Bayer's junctions" of procaryotes. The participation of triple complexes in the formation of structure of bacterial and eucaryotic nucleoid and nuclear matrix is analysed. A model of formation of triple complexes and cellular structures and their role in DNA-lipid interactions are discussed.     

Matrix isolation infrared and ab initio study of the hydrogen bonding between formic acid and water

The infrared spectra of the formic acid-water complexes isolated in argon matrices are reported. Both supersonic jet expansion and a conventional effusive source followed by trapping in solid argon at 10K are used to obtain the matrices. The experimental IR spectra are compared to the data obtained from high level ab initio (MP2) and DFT (B3LYP) calculations with 6-311++G(d,p) and aug-cc-pVTZ basis sets. The complex formation results in red shifts in the C=O and O-H stretching vibrations and a blue shift in the C-O stretching vibration of formic acid. The O-H stretching modes of water also exhibit pronounced red shifts. Both the MP2 and B3LYP calculations located three minima corresponding to cyclic HCOOH...H2O complexes with two hydrogen bond interactions. The binding energies are -10.3, -5.1, and -3.5 kcal mol(-1), respectively, for the three complexes at the MP2/ aug-cc-pVTZ level, corrected for the basis set superposition error (BSSE) using the Boys-Bernardi counterpoise scheme. Comparison of the calculated frequencies of the three complexes with the matrix IR spectrum reveals that the lowest energy complex is formed. In addition, a complex of formic acid with two water molecules is observed.     

Complexes of atmospheric alpha-dicarbonyls with water: FTIR matrix isolation and theoretical study

The complexes of glyoxal (Gly), methylglyoxal (MGly), and diacetyl (DAc) with water have been studied using Fourier transform infrared (FTIR) matrix isolation spectroscopy and MP2 calculations with 6-311++G(2d,2p) basis set. The analysis of the experimental spectra of the Gly(MGly,DAc)/H2O/Ar matrixes indicates formation of one Gly...H2O complex, three MGly...H2O complexes, and two DAc...H2O ones. All the complexes are stabilized by the O-H...O(C) hydrogen bond between the water molecule and carbonyl oxygen as evidenced by the strong perturbation of the O-H, C=O stretching vibrations. The blue shift of the CH stretching vibration in the Gly...H2O complex and in two MGly...H2O ones suggests that these complexes are additionally stabilized by the improper C-H...O(H2) hydrogen bonding. The theoretical calculations confirm the experimental findings. They evidence the stability of three hydrogen-bonded Gly...H2O and DAc...H2O complexes and six MGly...H2O ones stabilized by the O-H...O(C) hydrogen bond. The calculated vibrational frequencies and geometrical parameters indicate that one DAc..H2O complexes, two Gly...H2O, and three MGly...H2O ones are additionally stabilized by the improper hydrogen bonding between the C-H group and water oxygen. The comparison of the theoretical frequencies with the experimental ones allowed us to attribute the calculated structures to the complexes present in the matrixes.     

IR spectroscopy and photosensitivity of the H2OLi complex trapped in a krypton matrix

The reaction of lithium atoms with water has been studied using infrared matrix isolation spectroscopy. H/D and ⁶Li/⁷Li isotopic substitutions and irradiation effects in both visible and IR regions allow us to identify two kinds of complexes: after deposition a 1-1 species, of charge transfer type, characterized by rather small frequency shifts but strong intensity changes of the water bands: after irradiation either in the near IR or in the visible formation of the LiOH molecule identified by two absorptions below 1000 cm^?1: theLiOH stretching mode around 900 cm^?1 and the bending mode at 257 cm^?1. Vibrational calculations on both frequencies and intensities of these complexes allow us to analyse the charge transfer effect in the 1-1 complex and to conclude that the structure of the LiOH molecule is linear.     

Nuclear magnetic resonance study of speciation of water at low concentrations in hydrogen bond acceptor solvents

Equilibrium constants for the formation of 1:1 and 1:2 complexes of monomeric water with twelve hydrogen bond acceptor solvents were evaluated from the chemical shifts of the water protons in ternary mixtures containing a low concentration of water and varying proportions of the acceptor solvent and carbon tetrachloride. Formation constants of the 1:1 complexes (with the exception of those of dioxane and dimethoxyethane) correlate well with Kamlet-Taft -parameters. A good correlation is also obtained with Gutmann donor numbers if nitromethane and pyridine are excluded. Stepwise formation constants of the 1:2 complexes vary relatively little; this is attributed to a leveling effect of first hydrogen bond formation.     

Impact of phase composition on water adsorption on inorganic hybrids "salt/silica"

The effect of a "guest-host" interaction on the phase composition and sorption properties of the composite sorbents "salt in a porous host matrix" has been studied. The matrix was a mesoporous silica of KSK type, while the confined salts were CaCl(2), CuSO(4), MgSO(4), and Na(2)SO(4). Both structure and properties of the composites were studied by X-ray diffraction, titration in the pH range of 2-9, differential dissolution, and TG techniques. Chemical interaction between the silica surface and the salt during preparation results in the formation of the salt surface complexes and stabilization of the dispersed salt in two phases, namely, a crystalline phase and an X-ray amorphous phase. The water sorption properties of the composites depend on the phase composition and can be intently modified by using variation of the preparation conditions.     

Binary,ternary and microencapsulated celecoxib complexes with β-cyclodextrin formulated via hydrophilic polymers

Cyclodextrins are cyclic oligosaccharides, capable of forming inclusion complexes with many active substances. This way, the aqueous solubility and rate of dissolution of active substances can be changed. For this research we have selected celecoxib as the model active substance, due to its low water solubility, high lipophilicity, and high intestinal permeability. Usually, the amount of cyclodextrin complex that can be incorporated into a pharmaceutical dosage form is limited. The usage of hydrophilic polymers can overcome this problem. In this study, we wanted to point out the potential of various types of hydrophilic polymers for enhancing the complex formation efficiencies, and to highlight the possible use of alginate as a solubility stabilizer/enhancer and as a microsphere matrix polymer. The phase solubility investigation showed greater stability constants (> 250 M^?1) in ternary complexes than in the binary complex, which is a good indicator of the complex formation enhancer properties of these hydrophilic polymers. The relative solubilizing efficiency decreased in the next order: PVP K25 (6.49) > Sodium alginate (6.26) > PEG 6000 (5.72) > without polymer (4.81). The DSC curves showed that all samples that were prepared with β-cyclodextrin (both complexes and physical mixtures) had lower melting endotherms at 160 °C than pure celecoxib. XRD confirmed the complex formation by partial celecoxib amorphisation. The dissolution studies of the prepared microspheres revealed that all samples had different release rates (shown by the similarity factor f₂, which was 36.37, 42.46 and 38.11 % respectively) and that the use of β-cyclodextrin increased the dissolution rate of celecoxib from alginate microspheres in a controlled manner. We concluded that sodium alginate could act as a complex stabilizing/enhancing agent and as a microsphere matrix polymer, at the same time.     

Cellulose-Monomer Interaction and a Revised Mechanism for Graft Copolymerization

Graft copolymerization of electron acceptor acrylic monomers on cellulose involves cellulose-monomer complexation. Cellulose acts as a matrix promoting high localized concentrations of donor-acceptor complexes in which uncomplexed monomer, normally an electron acceptor, behaves as a donor relative to the complexed monomer which has been converted to a stronger acceptor. The cellulose-monomer complexation influences both homopolymerizability and grafting efficiency, e. g. acrylonitrile (AN) and methacrylonitrile (MAN) in the presence of a catalyst and methyl methacrylate (MMA) in the absence of a catalyst. The presence of water, cupric ion, aldehydes, and CCU influence the course of the uncatalyzed reaction. When a donor monomer is present, equimolar alternating rather than random, grafted and ungrafted copolymers are produced, e. g., styrene or butadiene with MMA, MAN, or AN, as a result of the formation of an ordered array of donor-acceptor complexes on the cellulose. The revised mechanism of polymerization involves the homopolymerization of the donor-acceptor complexes, irrespective of the nature of the initiator, and grafting results from termination of the propagating chains by coupling with radicals on the cellulose.     

Water complexes of styrene and 4-fluorostyrene: a combined electronic, vibrational spectroscopic and ab-initio investigation

The binary complexes of water with styrene and fluorostyrene were investigated using LIF and FDIR spectroscopic techniques. The difference in the shifts of S 1 <-- S 0 electronic transitions clearly points out the disparity in the intermolecular structures of these two binary complexes. The FDIR spectra in the O-H stretching region indicate that water is a hydrogen bond donor in both complexes. The formation of a single O-H...pi hydrogen-bonded complex with styrene and an in-plane complex with fluorostyrene was inferred based on the analysis of the FDIR spectra in combination with ab initio calculations. The in-plane complex with fluorostyrene is characterized by the presence of O-H...F and C-H...O hydrogen bonds, leading to formation of a stable six-membered ring. The synergistic effect of O-H...F and C-H...O hydrogen bonds overwhelms the O-H...pi interaction in fluorostyrene-water complexes.     

Supramolecular self-assembly of inclusion complexes of a multiarm hyperbranched polyether with cyclodextrins

A new class of crystalline inclusion complexes of a multiarm hyperbranched polyether combined with various cyclodextrins (CDs) was successfully prepared. Using self-condensing ring-opening polymerization, a kind of multiarm polyether with a hyperbranched poly(3-ethyl-3-oxetanemethanol) core and multiple linear poly(ethylene glycol) (PEG) arms was obtained. It has been found that this kind of hyperbranched polyether can be dissolved in water. Adding alpha-CDs to the multiarm hyperbranched polyether solution, molecular recognition results in the formation of crystalline inclusion complexes based on the noncovalent interactions between the linear PEG arms of the polyether particles and the alpha-CDs. These multiarm polyether inclusion complexes have been well characterized. Interestingly, quite different from inclusion complexes of CDs and linear polymeric guests, the complexes of the multiarm hyperbranched polyether with alpha-CDs show a novel lamellar morphology. The experimental results validate that the resultant lamellar crystals have a juxtaposed structure. In addition, the formation mechanism of these inclusion complexes of a multiarm polyether with alpha-CDs has also been well described. Besides the role of displacement of associated water molecules and the presence of hydrogen bonding between CDs in channel structure CD inclusion complexes, the noncovalent intermolecular forces between CDs and polymers also play an important role in the formation of complex architectures.