Change with temperature of the ESR spectra of methacrylic acid radicals

In order to elucidate the structure of methacrylic acid radicals, the change with observation temperature of the ESR spectrum of free radicals trapped in solid methacrylic acid γ-irradiated at ?196°C was studied. Below ?80°C, we found a 9-line spectrum, which is similar to the ordinary 9-line spectrum observed in irradiated poly(methacrylic acid) or poly(methyl methacrylate), but which differs in the stronger intensity of the so-called 4-line component. Our 9-line spectrum changes reversibly into a 13-line spectrum above ?80°C. With broad-line NMR measurements of methacrylic acid, it was found that there is such an unusual crystalline transition around ?30°C that the line width is narrower in the lower-temperature region (phase II) than that in the higher-temperature region (phase I). The change of the ESR spectrum can be interpreted in terms of the exchange of the two β-protons due to the hindered oscillation around the C_α? C_β bond of the single radical ···C_βH₂C_α(CH₃)COOH if one assumes the gradual change of the hindering potential barrier caused by the crystalline transition and the lower barrier in phase II. The modified Bloch treatment gave the hindering potential barrier to be 7.2 kcal/mole in phase I and 1.5 kcal/mole in phase II. The difference between our 9-line spectrum and the ordinary one with the very weak 4-line component comes from the difference of the surrounding matrix.     

Formation of free radicals in photoirradiated cellulose. VII. Radical decay

The ESR spectra of untreated and photosensitized celluloses irradiated with three different ultraviolet light sources, i.e., λ > 2537 Å, λ > 2800 Å, λ > 3400 Å, at 77°K under vacuum were studied. Based on the warm-up process, that is, warming the sample from 77°K to 273°K for a certain time and recorded at 77°K, the decay behavior of free radicals of celluloses was examined for changes of the pattern and the intensities of ESR spectra. For the untreated samples irradiated with light of λ > 2537 Å and λ > 2800 Å, beside the two doublet spectra originating from hydrogen atoms (508 gauss splitting) and formyl radicals (129 gauss splitting), the observed sevenline spectrum was resolved to be a superposition of a singlet (ΔH_msl = 16 gauss), a doublet (24 gauss splitting), a triplet (34 gauss splitting), and a quartet (overall width, 88 gauss) spectrum. For the photosensitized samples irradiated with light of λ > 3400 Å, the 1:1:1 three-line spectrum was resolved to be a superposition of a singlet (ΔH_msl = 27 gauss), a doublet (43 gauss splitting), and a triplet (34 gauss splitting) spectrum. The five-line spectra of the photosensitized samples irradiated with light of λ > 2537 Å and λ > 2800 Å were resolved to be a superposition of a singlet (ΔH_msl = 27 gauss), a doublet (43 gauss splitting), and a triplet (34 gauss splitting) spectrum. Based on these findings, the conclusion was drawn that at least six kinds of spectra, generated from six kinds of radical species, were formed in cellulose irradiated with ultraviolet light under appropriate experimental conditions.     

NMR Investigations of Temperature-Induced Phase Transition in Aqueous Polymer Solutions

The different dynamics of polymer segments forming phase-separated globular structures in aqueous (D₂O) solutions affects both the shape of NMR spectra and NMR relaxation times of polymer and solvent. Two types of the approach are discussed. The first one is based on the reduction of integrated intensities of polymer NMR lines in high-resolution NMR spectra in the system undergoing the coil-globule phase transition. The fraction p of phase-separated units (units with significantly reduced mobility) and subsequently, e.g., thermodynamic parameters ΔH and ΔS characterizing the coil-globule phase transition can be determined. The second approach is based on measurements of ¹H NMR relaxation times of water (HDO) which provide information on behaviour of water during phase transition. The power of both approaches is demonstrated on results obtained with solutions of several thermoresponsive homopolymers and copolymers.     

Plastic deformation of poly(tetramethylene oxide). II. Molecular orientation as measured by x-ray diffraction and NMR measurements

The orientation of the crystalline and amorphous phases in uniaxially drawn samples of polytetramethylene oxide has been studied by x-ray and NMR methods. Pole figure measurements give the orientation of the crystalline phase. Its dependence on the draw ratio does not obey the pseudoaffine model. The crystalline fraction is derived from NMR measurements at temperatures between T_g and T_m, where the free induction decay (FID) of the unoriented sample can be analyzed in terms of a rigid (crystalline), a constrained, and an amorphous phase. Low temperature (T < T_g) measurements of the NMR second-moment anisotropy in protonated and deuterated samples give a mean orientation of the chains higher than that corresponding to the crystalline phase. The lack of anisotropy in the tail of the FID at temperatures between T_g and T_m indicates no appreciable anisotropy in the truly amorphous interlamellar phase. From this and from the ratio of the P₄/P₂ orientations, factors which obey the “most probable distribution,” it is concluded that the amorphous orientation is due to the layer of constrained chains at the surface of the lamellae.     

ESR single-crystal study of radical and radical-pair formation in some γ-irradiated vinyl monomers

Single crystals of methyl methacrylate (MMA), methyl acrylate (MA), and acrolein (A) have been prepared by a low-temperature technique. After irradiation with γ-rays at 77°K the paramagnetic species were identified by ESR spectroscopy. MMA gave a seven-line single spectrum from radicals formed by hydrogen addition. The hyperfine coupling constants are slightly anisotropic with a mean value of 22 G. Radical pairs were observed as ΔM_s = 1 and ΔM_s = 2 transitions; the hyperfine coupling was 11 G. From the strongly anisotropic dipolar interaction, upper limits for the distances between the pair components were calculated to be 5.45 Å and 6.3 Å. MA gave a five-line main spectrum with the same hyperfine coupling values and two radical pairs, one with a distance 5.9 Å between the components. In a there was also a strongly anisotropic interaction. The hyperfine coupling of the ΔM_s = 2 transition was 9.8 G. The number of radical pairs compared to the total number of radicals increases only slightly with the radiation dose. This makes it likely that pair formation occurs in the spurs and blobs formed by the γ-radiation. At an increased temperature the radical pairs disappeared; the spectrum of MMA changed to that characteristic of propagating polymer radicals.     

Radiation-induced solid-state polymerization of methacrylic acid. III. Post-polymerization

The post-polymerization of methacrylic acid in the solid state was studied. The decay of the trapped radicals was also observed by ESR measurements. The decay of trapped radicals is a first-order reaction below 0°C but a second-order reaction at + 10°C. The results of the post-polymerization were compared with the results of radical decay measurements. A kinetic scheme was proposed for the post-polymerization of methacrylic acid. The effect of conditions of monomer crystallization on the polymer yield was also investigated. Fine crystals gave a greater limiting conversion than large crystals. The addition of water to the monomer increased the polymer yield. The change in the ESR spectrum during post-polymerization was interpreted in terms of the change in the matrix which surrounds the propagating radicals.     

Preparation,characterization of some transition metal complexes of hydrazone derivatives and their antibacterial and antioxidant activities

A new series of metal complexes of Pd(II), Cd(II) and Cu(II, I) of polydentate Schiff base ligand (H₂L), namely ((Z)-2-(phenylamino)-N'-(thiophen-2-ylmethylene) acetohydrazide) have been prepared. The ligand and its metal complexes have been characterized based on various physicochemical studies as elemental analyses, molar conductance, spectral (UV–Vis, MS, IR, ¹H NMR, ¹³C NMR and XRD), magnetic moment measurements and thermal studies (TG, DTG). In the view of previous studies, the ligand (H₂L) acts as polydentate one and coordinates with metal ions to form all metal complexes. The kinetic and thermodynamic parameters of decomposition process (ΔG, ΔH, ΔS) were calculated. The possible structures of the metal complexes have been computed using the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The calculations are performed to obtain the optimized molecular geometry. The antibacterial study of the selected compounds was assayed against two pathogenic bacteria. Moreover, the complexes (Cu II, I), Cd(II), Pd(II)) and the ligand revealed excellent antioxidant properties and could be useful in fighting the free radicals which occur in close connection with cancerous cells. It was remarkable that the two complexes (Cu II, I) demonstrated stronger antioxidant effects than their parent compounds. It is clear that the new complexes are good active compounds for use in a variety of applications.     

Halbsandwichkomplexe mit stickstoffliganden: II. Cyclopentadienyl-diazadien-kobalt(I)-komplexe

Cyclopentadienyl- and pentamethylcyclopentadienyl-cobalt(I) complexes, [(C₅H₅)Co(dad)] (II) and [(C₅Me₅)Co(dad)] (IV) (dad = 1,4-diaza-1,3-diene, RN=CR′CR′=NR), can be prepared via substitution and reduction reactions. These complexes, which are thermally stable but extremely sensitive to oxidation, show a pseudo-C_2ν symmetry in their room temperature NMR spectra; at 205 K different conformers can be detected in the NMR spectrum of IIf (dad If: R = i-C₃H₇, R′ = CH₃), indicating steric hindrance, which prevents, in spite of low ionization energies (IE₁ for IIa 6.17 eV), typical “base reactions” of the metal, e.g. addition of methyl iodide. The unusually small half-width of the main transition in the electronic spectra, characteristic of complexes II, is better described as a complex π →- π^★ transition than as a CT transition. Together with NMR and electron spectroscopic data the electrochemical behaviour and photoelectron spectroscopic results for IIa and other electron-rich dad complexes are included in the discussion and the comparison with tetraazadiene analogues.     

Lamellar thickness of crystallizable ethene runs in ethene-propene copolymers by solid state NMR

Crystallizable runs of ethene in ethene-propene copolymers can be identified in ¹³C CPMAS NMR spectra as a resonance at 33 ppm. In the absence of spin diffusion, the variation in intensity of this resonance with a ¹H spin lock will reflect the intrinsic T^H_1ρ. Spin diffusion leads to a more complex relaxation decay, which reflects the local polymer morphology. Simulations of the spin diffusion process have been carried out for a simplified two-phase model for the morphology with the aim of determining whether the lamellar thickness of the crystalline and amorphous regions can be found from the T^H_1ρ observed via the ¹³C NMR spectrum. Calculations covering the expected range of the input parameters, namely the spin diffusion coefficients, domain lengths, and intrinsic relaxation times, show that, providing the intrinsic relaxation time in the amorphous phase is known, an accurate estimate of the crystalline and amorphous lamellar thicknesses can be made. Analysis of simulated T^H_1ρ decays indicate that, in general, the time constant of the fastest decaying component can be identified with the intrinsic relaxation time of the amorphous phase. © 1994 John Wiley & Sons, Inc.     

Disproportionation reactions between alkyl and fluoroalkyl radicals. V. Perfluoro-n-propyl and ethyl radicals revisited

A redetermination of the disproportionation/combination ratio for n–C₃F₇ and C₂H₅ radicals gives a value of Δ(n–C₃F₇, C₂H₅) = 0.13 ± 0.01, independent of the temperature. The radicals were produced by the photolysis of n–C₃F₇COC₂H₅. The previous determinations of this ratio are discussed and are found to be largely incorrect. The values for Δ(CF₃, C₂H₅) and Δ(C₂F₅, C₂H₅) are also re-evaluated, and the recommended values are 0.10 ± 0.02 and 0.12 ± 0.02, respectively. Systems involving perfluoroalkyl and ethyl radicals are complicated due to rapid perfluororadical addition to the ethylene formed in the disproportionation process. The extent of this reaction, and its consequences, are discussed and evaluated. The role of the propionyl (C₂H₅CO) radical in the room temperature photolysis is also assessed. However, it is found that the Δ values determined by the intercept method used in this work are not affected by the secondary reactions that occur. It is concluded that high cross-combination ratios are general to perfluoroalkyl-alkyl radical interactions. For C₃F₇ and C₂H₅ radicals the ratio is 2.7–2.8. Above 100°C ratios exceed 3 due to secondary reactions.     

Synthesis and magnetic,spectral and thermal eukaryotic DNA studies of some 2-acetylpyridine- [N-(3-hydroxy-2-naphthoyl)] hydrazone complexes

Complexes of Ni(II), Co(II), Cu(II), Zn(II), Cd(II), Hg(II) and U(VI)O₂ with 2-acetylpyridine-[N-(3-hydroxy-2-naphthoyl)] hydrazone (H₂APHNH) have been prepared and characterized by elemental analysis, molar conductance, thermal (TG, DTG), spectral (¹H NMR, IR, UV–Vis, ESR) and magnetic measurements. ¹H NMR spectrum of the ligand suggests the presence of intramolecular hydrogen bonding. IR spectra show that H₂APHNH is a bidentate, tridentate and/or tetradentate ligand. Thermal decomposition of some complexes ended with metal oxide as a final product. ESR spectra gave evidence for the proposed structure and the bonding for some Cu(II) complexes. Biological activity measurements were carried out.     

Phase diagrams and phase structures of identical and mixed chain lithium di-n-alkyl phosphate-water binary systems. Asymmetric molecular shape effect

Lithium salts of di-n-pentyl (DPP),n-butyl(n-hexyl) (BHP),n-propyl(n-hexyl) (PHP) and ethyl(n-octyl) (EOP) phosphates were synthesized and the phase diagrams of the lithium phosphate-water binary systems were determined. The phase diagrams of the DPP-, BHP- and PHP-water systems contain three regions (I, II and III) in common, which correspond to a homogeneous transparent one-phase solution, and lyotropic liquid crystalline and coagel phases, respectively. However, the EOP-H₂O system contains an additional hard gel phase (region IV). ³¹P NMR spectra suggest that region I is a monomermicelle equilibrium phase and region II is a lamellar phase. X-ray diffraction results show that for the DPP-, BHP-and PHP-water systems the twon-alkyl chains are closely packed in the lamellar phase in a manner which alternatively combines short and long chains, while in EOP-water system the two long chains are loosely packed. Furthermore, it may be assumed from³¹P NMR spectra and x-ray diffraction results that region IV in the EOP-water system is a cubic phase.Thermotropic properties for these DAP-water systems were also investigated by DSC temperature profile curves. From the H variation upon the III thermal transition, we assumed that stability of the aggregate structure in the liquid crystalline state increases in the order EOP相似文献   

Über Tellurhalogenide des Kupfers mit hoher lonen-Teilleitfähigkeit. III. Zur Phasenumwandlung von CuTeBr und zur Struktur der Hochtemperaturphase

Telluride Halides of Copper with High Ionic Partial Conductivity. III. On the Phase Transition of CuTeBr and the Structure of the High Temperature Phase Copper telluride bromide, CuTeBr, exhibits a reversible sudden change of the electric conductivity. From caloric data a first order phase transition at 345 K can be concluded with ΔH_u = 76.8 cal/g-mol and ΔS_u = 0.222 cal/g-mol K. X-ray measurements show a sudden change of the lattice parameters and the disappearance of the — orthorhombic — superstructure at the transition. Single crystal determinations of the HT-phase yield the tetragonal main structure (space group I 4₁/amd); simultaneously a rearrangement of the statistical population of the Cu sites is observed. The results are discussed on the basis of a displacive transition.     

Pyrolysis mass spectrometry and gas chromatography of plasma-polymerized benzene and xylene

Pyrolysis mass spectra and gas chromatograms of plasma-polymerized benzene (PPB) and p-xylene (PPX) have been studied. Both polymers gave mass spectra that indicated the presence of disubstitution in an aromatic ring and of product molecules, such as biphenyl and ethylbenzene, trapped in the polymer matrix. The PPB spectrum showed fragments originating from ? C₆H_{4? n} structures and the PPX spectrum fragments originated from ? CH₂C₆H₄CH_{2? n} structures. Both the pyrolysis mass spectrum and chromatogram contained peaks that distinguished PPX from commercial polystyrene samples. A chain mechanism which involves H abstraction reactions under plasma activation is proposed. The highly crosslinked structures of the polymers are attributed to the subsequent addition of free radicals to the double bonds of a fragmented chain formed as a result of the scission of the C? C aromatic bond(s).     

Complexes derived from some biologically active ligands

Complexes derived from ampicillin (L1) and amoxicillin (L2) with (Mg(II), Ca(II), Zn(II), Cu(II), Ni(II), Co(II), Ce(III), Nd(III), UO₂(VI), Th(IV)) were prepared and characterized by elemental analysis, electrical conductivity measurements, magnetic susceptibility, IR, UV/Vis, and thermogravimetry. The formed complexes can be formulated as (ML(H₂O)₃(NO₃) _n ) except for Ce(III) which gave (CeL(H₂O)₃(Cl)₂). The ¹H NMR spectra of the Zn(II) complexes are compared to spectra of the ligands. The shift (δ) gave information about the chelating center of the ligands. The ligands and the synthesized complexes, derived from some alkali earth and transition metal ions, were tested as antibacterial reagents. The formed complexes had enhanced activity.     

SMALL ANGLE LIGHT SCATTERING MEASUREMENT OF THE ISOTROPIC TO NEMATIC TRANSITION OF A SIDE CHAIN NEMATIC POLYMETHACRYLATE*

The kinetics of I→N transition of a side chain nematic polymethacrylate has been studied by small angledepolarized light scattering intensity measurements using a charge coupled device linear image sensor. The polymer showsthe transition temperatures K52N79I in ℃. The H_v scattering intensity J(q,t) during the transition I (at 80.2℃)→N (at75.8℃) shows that J(q) is independent of q for all t, and during the initial stage (in 6 s) J(t) increases exponentially with t.In the later stage of the transition J(t) approaches a saturation value in 2 min. This experimental result indicates that the I→Ntransition of a liquid crystalline polymer is a spinodal type of phase transition mediated by orientation fluctuation.     

Structural characterization, thermal, dielectric, vibrational properties and molecular motions in

[C₃N₂H₅]₆[Bi₄Br₁₈] has been synthesized and characterized by the X-ray (at 293 and 110 K), calorimetric, dilatometric and dielectric measurements. At room temperature it crystallizes in the monoclinic space group, C2/m. A crystal structure consists of disordered imidazolium cations and ordered discrete tetramers of [Bi₄Br₁₈]^6-. This compound reveals a rich polymorphism in a solid state. It undergoes three solid–solid phase transitions: from phase I to II at 426/423 K (heating–cooling), II→III at 227 K and III→IV at 219.5/219 K. A clear dielectric relaxation process is found in the room temperature phase II. Infrared studies of the polycrystalline [C₃N₂H₅]₆[Bi₄Br₁₈] showed that the ν(N–H), δ(ring) and δ(C–H) modes of the imidazolium cations appeared to be very sensitive to the IV→III phase transition. ¹H NMR measurements confirmed a key role of the imidazolium cations in the phase transitions mechanisms at low temperatures.     

Component analysis of proton NMR spectra of linear polyethylene in the α-transition temperature range and phase distribution

Broad-line ¹H NMR spectra of linear polyethylene at temperatures in the α-transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n-C₃₂H₆₆ or n-C₄₄H₉₀ prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α-transition range.     

Pyrolysis of 2-phenylethylamines heats of formation of aminomethyl radicals R2NCH2 · (R = H,CH3)

A kinetic study of the very low-pressure pyrolysis of ethylbenzene (I), 2-phenylethylamine (II), and N,N-dimethyl 2-phenylethylamine (III) above 900 K yields the heats of formation of aminomethyl (A) and N,N-dimethylaminomethyl (B) radicals: ΔH_{?, 300 K}(A) = 30.3 and ΔH_{?, 300 K}(B) = 27.5 kcal/mol. The difference of stabilization energies E_s, (relative to methyl radicals): Δ = E_s(B) ? E_s(A) = (2 ± 1) kcal/mol, conforms to similar effects in methyl substituted alkyl and amino free radicals.     

NMR and DSC study of temperature-induced phase transition in aqueous solutions of poly(N-isopropylmethacrylamide-co-acrylamide) copolymers

Combination of ¹H NMR spectroscopy and differential scanning calorimetry (DSC) was used to investigate temperature-induced phase transition in D₂O solutions of poly(N-isopropylmethacrylamide-co-acrylamide) random copolymers. Both the NMR and DSC data showed dependence on the acrylamide (AAm) content in the copolymer; with increasing AAm content, the phase transition is shifted to higher temperatures, and both phase-separated fractions determined by NMR and change of the enthalpy determined by DSC decrease faster than the content of thermosensitive N-isopropylmethacrylamide (NIPMAm) units in the copolymer. NMR data were used to construct van't Hoff plots, and changes of the enthalpy ΔH and entropy ΔS, characterizing the phase transition, were determined. As it follows from comparison of NMR and DSC thermodynamical parameters (ΔH values), the size of the cooperative units (domains), undergoing the transition as a whole, decreases with increasing AAm content in the copolymer since the NIPMAm collapsed domains are separated by regions with hydrated AAm and surrounding NIPMAm sequences.