Computational modeling and experimental infrared spectroscopy of hydrogen bonding interactions in polyvinyl alcohol-starch blends

This study aims to investigate the hydrogen bonding interactions in polyvinyl alcohol (PVOH)-starch blends. Semi-empirical AM1 (Austin Model 1) and PM3 (Parameterized Austin Model 3) methods were employed to model the blending. Binding energies, vibrational frequencies and solubility parameters results were used to analyze the compatibility and stability of the blends. Besides that, experimental infrared spectroscopy was also conducted to validate the modeling results. The computed negative binding energies justified the stability of the blending. On the other hand, the solubility parameters of PVOH and starch modeling complexes have been found close to each other. This confirms that PVOH and starch are compatible blends. In addition, vibrational frequency analysis of these molecular complexes has exhibited that the hydroxyl group shifts to lower wavenumbers due to formation of hydrogen bonds. Findings from the experimental infrared spectroscopy have shown agreement with computational vibrational frequency results. The wavenumbers of the specimens increase is dependent on the ratios of PVOH in the blends. Such increment indicates that PVOH and starch interact in a harmonize manner and the blending is compatible.     

Theoretical Studies on PNMFIW by AM1 and PM3 Methods

AM1 and PM3 semi‐empirical methods were used to conduct theoretical studies on possible polymorphs of pentanitromonoformylhexaazaisowurtzitane (PNMFIW), and a close link between PNMFIW and Hexanitrohexaazaisowurtzitane (HNIW), especially in sensitivity, is shown. The optimized geometries of possible polymorphs of PNMFIW are similar to those of HNIW. PNMFIW in ε‐HNIW prepared from tetraacetyldiformylhexaazaisowurtzitane is predicted to have a D‐form. The average N N bond lengths of PNMFIW computed by AM1 and PM3 methods are shorter than those of HNIW. The differences in energy and thermochemistry values between PNMFIW and HNIW are insignificant except molecular energies 255.75 kJ⋅mol⁻¹ for D‐form PNMFIW and 460.36 kJ⋅mol⁻¹ for ε‐HNIW. Based on a Mulliken population analysis of the N N bonds, the impact sensitivities of A‐, B‐, C‐ and D‐forms of PNMFIW are estimated to be lower than those of the corresponding polymorphs of HNIW. Taking into account all N N bond lengths and overall molecule size, the shock sensitivities of all forms PNMFIW are predicted to be almost the same, and lower than those of HNIW.     

Influence of metal coordination on conductivity behavior in poly(butadiene-acrylonitrile)-CoCl2 system

The metal complex formation and the electrical properties of amorphous solid polymer electrolytes, based on poly(butadiene-acrylonitrile) copolymer (PBAN) and CoCl₂, have been studied over the homogeneity region of the system limited by the CoCl₂ concentration of 1.89 mol kg⁻¹. It has been found that ionic conductivity is carried out by the unipolar anion transfer at lower CoCl₂ concentrations (up to 0.10 mol kg⁻¹). As the CoCl₂ concentration increases, electronic conductivity appears in addition to ionic conductivity, and the former becomes dominant, starting from 0.38 mol kg⁻¹. It has been shown that the nature of charge carriers is determined by the composition of metal complexes formed by CoCl₂ and the macromolecular solvent PBAN. At lower concentrations, the [Co₂L₂Cl₄]⁰ dimers are the predominant species (L being macromolecule side groups CN), and their dissociation is followed by the formation of mobile Cl⁻ anions and immobile binuclear [Co₂Cl₃]⁺ complexes. As CoCl₂ concentration increases, polynuclear [Co_nL₂Cl_2n]⁰ (n > 2) complexes appear (L being CN and CC groups of PBAN). Specific features of chemical bonds in π-complexes of transition metals result in the appearance of electronic charge carriers. The abrupt increase in conductivity observed at the highest CoCl₂ concentration is connected with the formation of a percolation network of polynuclear [Co_nL₂Cl_2n]⁰ complexes.     

Raman microspectroscopy study of structure, dispersibility, and crystallinity of poly(hydroxybutyrate)/poly(l-lactic acid) blends

The structure, dispersibility, and crystallinity of poly(3-hydroxybutyrate) (PHB) and poly(l-lactic acid) (PLLA) blends are investigated by using Raman microspectroscopy. Four kinds of PHB/PLLA blends with a PLLA content of 20, 40, 60, and 80 wt% were prepared from chloroform solutions. Differences in the Raman microspectroscopic spectra between the spherulitic and nonspherulitic parts in the blends mainly lie in the CO stretching band and C-O-C and C-C skeletal stretching bands of PHB and PLLA. In addition to such bands, the Raman spectra of spherulitic structure in the blends show a band due to the CH₃ asymmetric stretching mode at an unusually high frequency (3009 cm⁻¹), suggesting the existence of a C-H?OC hydrogen bond of PHB in the spherulite. The existence of C-H?OC hydrogen bond is one of the unambiguous evidence for the crystallization of PHB component in the blends. Therefore, it is possible to distinguish Raman bands due to each component in the spectra of blends. Raman spectra of the spherulitic structure in the blends are similar to a Raman spectrum of pure crystalline PHB, while those of the nonspherulitic parts in the blends have each component peak of PHB and PLLA. The present study reveals that the PHB component is crystallized in the blends irrespective of the blend ratio, and that both components are mixed in the nonspherulite parts. The crystalline structure of PHB and the nonspherulitic parts of PLLA in the blends are characterized, respectively, by the unique band of C-H?OC hydrogen bond at 3009 cm⁻¹ and CCO deformation bands near 400 cm⁻¹.     

Adsorption mechanism and property of novel composite material PMAA/SiO2 towards phenol

In this paper, functional macromolecule poly(methacrylic acid) (PMAA) was grafted on the surface of silica gel particles using 3-methacryloxypropyl trimethoxysilane (MPS) as intermedia, and the grafted particle PMAA/SiO₂ with strong adsorption ability for phenol was prepared. The adsorption mechanism and properties of PMAA/SiO₂ for phenol were researched by static and dynamic methods. The experimental results showed that PMAA/SiO₂ possesses strong adsorption ability for phenol with interaction of three kinds of hydrogen bonds including peculiar O–Hπ hydrogen bond (aromatic hydrogen bond) and O–HOC π hydrogen bond. The saturated adsorption amount could reach up to 162.88 mg g⁻¹. The empirical Freundlich isotherm was found to describe well the equilibrium adsorption data. pH and temperature were found to have great influence on the adsorption amount. Finally, PMAA/SiO₂ was observed to possess excellent reusability properties as well.     

Complexes of starch polysaccharides and poly(ethylene co-acrylic acid): Structural characterization in the solid state

The structural characterization of model complexes of amylose (AM) and amylopectin (AP) with poly(ethylene-co-acrylic acid) (EAA) was undertaken in order to better understand the interactions that occur between the polysaccharides and EAA in starch-EAA-polyethylene films. X-ray diffraction and CP/MAS ¹³C-NMR studies showed that precipitates from solution mixtures of AM and EAA form crystalline, helical V -type inclusion complexes. The proportion of AM forming the V -type complex in the EAA/AM blends, estimated from shifts in the C1 resonance of AM, increased with increasing EAA/AM ratio, reaching a value of about 80% at EAA/AM = 0.5 (w/w). Similar measurements for EAA/AP complexes showed < 10% V structure. Approximately 80% of the AM and 4% of the AP in these blends was resistant to amylase digestion, in good agreement with their V -structure contents as determined above. Resonances at 184 and 181 ppm were observed for the carboxyl carbon of EAA in the EAA/AM and EAA/AP complexes. The resonance at 181 ppm, which was not observed in pure EAA, probably reflects greater shielding of the carboxyl inside the polysaccharide helix as well as changes in hydrogen bonding. The intensity of this peak was 2–3 times larger for the EAA/AM than for the EAA/AP complexes. FTIR experiments suggest that most (> 50%) of the EAA carboxyl groups were hydrogen bonded to polysaccharide hydroxyl groups in both AM and AP complexes when EAA/polysaccharide < 1.     

Innovative spectral investigations on the thermal-induced poly(aspartic acid)

Two-dimensional (2D) correlation FTIR spectroscopy was used to investigate the dynamic mechanism of poly(aspartic acid) during the heating process. According to the 2D asynchronous correlation spectra, the CO vibration band of Amide I was separated into three peaks at 1637, 1645 and 1677 cm⁻¹, assigned to α helical, random coil and β antiparallel conformation, respectively. And α helical structure would transform into the more ordered and stable conformation of β antiparallel in heating. In the region of 3700-2700 cm⁻¹, the H-contained groups were analyzed; the loosening of hydroxyl is found to change prior to the NH-related hydrogen bonds and the conformational reorganization of hydrocarbon chains.     

3D supramolecular network constructed by intermolecular interactions in mixed ligand complex of zinc

New complex [Zn(quin-2-c)₂(Him)₂] (quin-2-c = quinoline-2-carboxylate ion, Him = imidazole) was synthesized by self assembly and its structure was determined by X-ray analysis. The compound crystallizes in P21/c space group. Four independent molecules of complex are present in the structure. Strong hydrogen bonds create three different 1D chains which are collected in two different layers. The alternately packed layers form the 3D supramolecular structure. The interchain and interlayer contacts are of the C–HO, ππ and C–Hπ type. The influence of strong hydrogen bond on the vibrational characteristics of the monodentately coordinated carboxylate group in zinc complexes with quin-2-c ion is discussed.     

Spectroelectrochemical study of perchloroethylene reduction at copper electrodes in neutral aqueous medium

The potential-dependent chemical reaction of perchloroethylene (PCE) on copper in neutral noncomplexing aqueous media is explored by means of surface-enhanced Raman spectroscopy (SERS), linear sweep voltammetry and preparative electrolysis at controlled potential. Voltammetric peaks associated with copper oxide reduction in Na₂SO₄ solution in the presence and the absence of Cl⁻ are correlated with simultaneously acquired SER spectra. Perchloroethylene undergoes a dechlorination process at potentials at E ≤ −0.3 V vs. Ag/AgCl/KCl (3 M), as shown by the emergence of an intense CuCl stretching band at 290 cm⁻¹ and a CH stretching band together with the presence of Cl⁻ in the catholyte. In the potential region between 0 and −0.9 V vs. Ag/AgCl/KCl (3 M) a broad band assigned to CC structures is observed in the triple-bond region (∼1900 cm⁻¹, FWHM = 180 cm⁻¹). In addition, dichloroethylene (DCE) is detected (but not trichloroethylene (TCE)) in this potential region during preparative electrolysis. At potentials lower than −1 V vs. Ag/AgCl/KCl (3 M) carbon residues are the main product, detected on the copper surface by SERS (and confirmed by XPS), whereas in solution higher levels of dichloroethylene and trichloroethylene are detected with a DCE/TCE ratio below 1.     

Enhance the performances of dye-sensitized solar cell by a new type of sensitizer to co-sensitize zinc oxide photoelectrode with ruthenium complex

We designed a new type of sensitizer for dye-sensitized solar cells based on ZnO photoelectrode. Three five-coordinate transition metal complexes [2,6-(ArNCMe)₂C₅H₃NMCl₂·nCH₃CN] (MZn, Cd, Hg) (named as Zn1, Cd1, Hg1), have been synthesized. In all complexes, the metal center is tridentately chelated by the ligand and further coordinated by two chlorine atoms, resulting in distorted trigonal bipyramidal geometry. The improvement in conversion efficiency of dye-sensitized solar cell was achieved by the complexes (M) and N719 co-sensitizing ZnO photoelectrode. In the tandem structure of M/N719/ZnO, the M forms a re-organization of energy level due to its single-crystal structure, which is advantageous to the electron injection and the hole recovery. The result demonstrates the M/N719 co-sensitized solar cell exhibited excellent photovoltaic performances with the short-circuit photocurrent density of 8.943 mA cm⁻², the open-circuit photovoltage of 591 mV and the fill factor of 0.639 under standard global AM 1.5 solar irradiation conditions.     

Microstructural studies on BaCl2 doped poly(vinyl alcohol)

We have studied the effect of BaCl₂ dopant on the optical and microstructural properties of a polymer poly(vinyl alcohol) (PVA). Pure and BaCl₂ doped PVA films were prepared using solvent casting method. These films were characterized using FTIR, UV-visible, XRD and DSC techniques. The observed peaks around 3425 cm⁻¹, at 1733 cm⁻¹ and 1640 cm⁻¹ in the FTIR spectra were assigned to O-H, CC stretching and acetyle CO group vibrations, respectively. In the doped PVA shift in these bands can be understood on the basis of intra/inter molecular hydrogen bonding with the adjacent OH group of PVA. The UV-visible spectra shows the absorption bands around 196 nm and shoulders around 208 nm with different absorption intensities for doped PVA, which are assigned to n→π* transition. This indicates the presence of unsaturated bonds mainly in the tail-head of the polymer. Optical band energy gap is estimated using UV-visible spectra and it decreases with increasing dopant concentration. The powder XRD shows an increase in crystallinity in the doped PVA, which arises due to the interaction of dopant with PVA causing a molecular rearrangement within the amorphous phase of polymer. These modifications also influence the optical property of the doped polymer. The DSC study also supports increasing crystalline thickness and degree of crystallinity due to doping.     

Two novel 3D bimetallic oxide framework with 16-membered wheel clusters based on {Mo5O16} ribbon-like chains

Two hybrid compounds based on {Mo₅O₁₆} ribbon-like chains, [M(3-pt)₂(Mo₅O₁₆)]·H₂O (M = Co, Mn) (1 and 2) {3-pt = 5-(3-pyridyl)-tetrazole}, have been hydrothermally synthesized and characterized by single crystal X-ray diffraction. Three-dimensional Mo/O/M^II/tetrazole frameworks of the title compounds are constructed from 1D infinite ribbon-like [Mo₅O₁₆]²⁻ chains covalently linked through [M(3-ptz)]²⁺ fragments via OM and NMo coordinate bonds. It is noteworthy that the isostructural compounds contain an unprecedented 3D bimetallic oxide network with 16-membered wheel clusters in which two parallel interdigitated stacks of 3-pt ligands are trapped. Remarkably, the title complexes represent the first two examples of the solid materials containing {Mo₅O₁₆} ribbon-like chains.     

Ionic conductivity, infrared and Raman spectroscopic studies of 1-methyl-3-propylimidazolium iodide ionic liquid with added iodine

Polyiodides (I_x⁻, x = 3 and 5) and 2I⁻…I₂ adducts were established from the Raman spectra study of 1-methyl-3-propylimidazolium iodide (MPIm⁺I_x⁻; 1 ≤ x ≤ 5) ionic liquids containing various amounts of iodine (0 mol ≤ I₂ ≤ 2 mol). The existence of I₃⁻ and 2I⁻…I₂ was established for 1 ≤ x ≤ 2.5, symmetric I₃⁻ ions for x = 3, while linear and discrete I₅⁻ was substantiated for 3 ≤ x ≤ 5. The presence of polyiodide species in MPIm⁺I_x⁻ (1 ≤ x ≤ 5) was correlated with an enhanced ionic conductivity, attributed to the established relay-type Grotthus mechanism. Two-step conductivity increase was also reflected in decrease of the hydrogen bond interactions between the CH ring groups and polyiodides. While in the concentration range 1 ≤ x ≤ 3 (triiodides and tetraiodides) IR bands changed only slightly in intensity, in the concentration range x > 3 the CH stretching bands (3040-3170 cm⁻¹) split and the new band at 1585 cm⁻¹ appeared in the IR spectra beside the already existing Im⁺ ring stretching mode at 1566 cm⁻¹.     

Computational Study on the Conformation and Vibration Frequencies of β-Sheet of ?-Polylysine in Vacuum

Two oligomers, each containing 3 l-lysine residues, were used as model molecules for the simulation of the β-sheet conformation of ɛ-polylysine (ɛ-PLL) chains. Their C terminals were capped with ethylamine and N terminals were capped with α-l-aminobutanoic acid, respectively. The calculations were carried out with the hybrid two-level ONOIM (B3LYP/6-31G:PM3) computational chemistry method. The optimized conformation was obtained and IR frequencies were compared with experimental data. The result indicated that the two chains were winded around each other to form a distinct cyclohepta structure through bifurcated hydrogen bonds. The groups of amide and α-amidocyanogen coming from one chain and the carbonyl group from the other chain were involved in the cyclohepta structure. The bond angle of the bifurcated hydrogen bonds was 66.6°. The frequency analysis at ONIOM [B3LYP/6-31G (d):PM3] level showed the IR absorbances of the main groups, such as the amide and amidocyanogen groups, were in accordance with the experimental data.     

The influence of hydrogen pressure on the heterogeneous hydrogenation of β-myrcene in a CO2-expanded liquid

This paper presents the second part of work on the effect of hydrogen partial pressure on the hydrogenation of a terpene in a CO₂-expanded liquid. The effect of hydrogen partial pressure on the hydrogenation of β-myrcene possessing three CC bonds catalysed by alumina-supported ruthenium and rhodium was studied. Experiments were performed at various hydrogen pressures in the range from 2.0 up to 4.5 MPa at a fixed total pressure of 12.5 MPa. In all the conditions the reaction proceeded in two phases (liquid + gas), that is, the total pressure was below the critical pressure of the CO₂ + β-myrcene + H₂ system. The liquid phase volume is expanded in relation to the initial volume of β-myrcene in a fashion that is strongly dependent on the hydrogen and carbon dioxide pressures. An increase of H₂ pressure concomitantly diminishes carbon dioxide pressure, which leads to the enhancement of the liquid phase in hydrogen and a terpene. It does not direct to straightforward higher reaction rate, but surprisingly the effect of higher concentrations either hydrogen or β-myrcene is opposite. It is attributed to the fact that the hydrogenation of β-myrcene rate-controlling factor turns out to be the hydrogen to β-myrcene ratio which decreases as the hydrogen pressure increases. These unexpected appealing results present that lower pressures of hydrogen guide to higher hydrogen/β-myrcene ratios in the liquid phase, but on the other hand they also amplify the initial reaction rate constant. The obtained results are opposite to the results achieved for effect of hydrogen pressure on the Pd-catalysed hydrogenation of limonene consisting of two CC double bonds.     

Synthesis of poly(aniline-co-o-anisidine)-intercalated graphite oxide composite by delamination/reassembling method

Aniline/o-anisidine copolymer (P(An-co-oAs))-intercalated GO composite was synthesized by the delamination/reassembling method in N-methyl-2-pyrrolidone (NMP) solvent, and was characterized by FTIR, XRD, DSC, SEM, TGA, conductivity and cyclic voltammetry. XRD and FTIR spectra indicate that the P(An-co-oAs) exists as a monolayer of outstretched chains in the gallery of GO due to the hydrogen bonds between -NH, N- and -OCH₃ groups of P(An-co-oAs) and the oxygen functional groups of the GO layers. The results of thermal analysis show that no de-intercalation of P(An-co-oAs) from GO occurred during heating. Its electrical conductivity has reached 1.9 × 10⁻² S/cm, which is by 3 orders of magnitude higher than that of GO. The intercalation of P(An-co-oAs) also has a pronounced effect on the stabilization of electrochemical response in relation to the GO matrix and P(An-co-oAs).     

FTIR investigation of the influence of diisocyanate symmetry on the morphology development in model segmented polyurethanes

Novel segmented polyurethanes with hard segments based on a single diisocyanate molecule with no chain extenders were prepared by the stoichiometric reactions of poly(tetramethylene oxide)glycol (M_n=1000 g/mol) (PTMO-1000) and 1,4-phenylene diisocyanate (PPDI), trans-1,4-cyclohexyl diisocyanate (CHDI), bis(4-isocyanatocyclohexyl)methane (HMDI) and bis(4-isocyanatophenyl)methane (MDI). Time dependent microphase separation and morphology development in these polyurethanes were studied at room temperature using transmission FTIR spectroscopy. Solvent cast films on KBr discs were annealed at 100 °C for 15 s and microphase separation due to self organization of urethane hard segments was followed by FTIR spectroscopy, monitoring the change in the relative intensities of free and hydrogen-bonded carbonyl (CO) peaks. Depending on the structure of the diisocyanate used, while the intensity of free CO peaks around 1720-1730 cm⁻¹ decreased, the intensity of H-bonded CO peaks around 1670-1690 cm⁻¹, which were not present in the original samples, increased with time and reached saturation in periods ranging up to 5 days. Structure of the diisocyanate had a dramatic effect on the kinetics of the process and the amount of hard segment phase separation. While PPDI and CHDI based polyurethanes showed self-organization and formation of well ordered hard segments, interestingly no change in the carbonyl region or no phase separation was observed for MDI and HMDI based polyurethanes. Quantitative information regarding the relative amounts of non-hydrogen bonded, loosely hydrogen bonded and strongly hydrogen bonded and ordered urethane hard segments were obtained by the deconvolution of CO region and analysis of the relative absorbances in CO region.