Microstructure of poly(methyl methacrylate-co-isopropyl acrylate) studied by 13C NMR

The distribution of configurational–compositional sequences of poly(methyl methacrylate-co-isopropyl acrylate) (PMMA/iPrA) has been determined from the carbonyl and β-CH₂ signals in the 100?MHz ¹³C NMR spectra of the copolymer. The carbonyl signal provided information on configurational–compositional sequences up to heptads, whereas β-CH₂ signals offered complementary information on even sequences up to hexads. The assignment of the sequences to the respective signals was based on a comparison with the spectra of respective homopolymers, that is, PMMA and PiPrA followed by a computer simulation applying an incremental calculation of chemical shifts of the individual sequences.     

Sequence Distribution of Poly(methyl acrylate) by Incremental Calculation

The carbonyl signal in the 100 MHz ¹³C NMR spectra of poly(methyl acrylate) (PMA) recorded in benzene-d₆ exhibits configurational sensitivity up to pentads, and the signal of backbone β-CH₂ carbons shows splitting up to configurational hexads with traces of octads. Assignment of the sequences to respective signals was confirmed by computer simulation of both carbonyl and methylene signals applying a method of incremental calculation of chemical shifts of individual sequences and second-order Markov statistics for sequence probabilities.     

Sequence distribution of PMMA/iBuA copolymer by incremental calculation of 13C NMR spectra

An incremental method for characterizing triad and pentad distribution by ¹³C NMR spectroscopy was applied to the poly(methyl methacrylate-co-isobutyl acrylate) copolymer. Calculation of the intensity of individual lines was performed applying Bernoulli statistics, while the chemical shifts for each sequence were calculated by an incremental method. Based on these data, the carbonyl signal was simulated yielding good agreement at the triad and pentad level.     

Poly(isobornyl methacrylate‐co‐methyl acrylate): Synthesis and stereosequence distribution analysis by NMR spectroscopy

Copolymerization of isobornyl methacrylate and methyl acrylate ( I/M ) is performed by atom transfer radical polymerization using methyl‐2‐bromopropionate as an initiator and PMDETA/CuBr as catalyst under nitrogen atmosphere at 70 °C. The copolymer compositions determined from ¹H NMR spectra are used to determine reactivity ratios of the monomers. The reactivity ratio determined from linear Kelen–Tudos method and non‐linear error‐in‐variable method, are r_I = 1.25 ± 0.10, r_M = 0.84 ± 0.08 and r_I = 1.20, r_M = 0.82, respectively. 1D, distortion less enhancement by polarization transfer and 2D, heteronuclear single quantum coherence, and total correlation spectroscopy NMR experiments are employed to resolve highly overlapped and complex ¹H and ¹³C{¹H} NMR spectra of the copolymers. The carbonyl carbon of I and M units and methyl carbon of I unit are assigned up to triad compositional and configurational sequences, whereas β‐methylene carbons are assigned up to tetrad compositional and configurational sequences. Similarly, methine carbon of I unit is assigned up to triad level. The couplings of carbonyl carbon and quaternary carbon resonances are studied in detail using 2D hetero nuclear multiple bond correlation spectra. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Examination of miscibility at molecular level of poly(hydroxyether of bisphenol A)/poly(N-vinyl pyrrolidone) blends by cross-polarization/magic angle spinning 13C nuclear magnetic resonance spectroscopy

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) and poly(N-vinyl pyrrolidone) (PVP) was investigated by differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) techniques. The DSC studies showed that the phenoxy/PVP blends have a single, composition-dependent glass transition temperature (T_g). The S-shaped T_g-composition curve of the phenoxy/PVP blends was reported, which is indicative of the strong intermolecular hydrogen-bonding interactions. To examine the miscibility of the system at molecular level, high-resolution solid-state ¹³C nuclear magnetic resonance (NMR) technique was employed. Upon adding phenoxy to system, the chemical shift of carbonyl carbon resonance of PVP was observed to shift downfield by 1.6 ppm in the ¹³C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) spectra when the concentration of phenoxy is 90 wt %. The observation was responsible for the formation of intermolecular hydrogen bonding. The proton spin-lattice relaxation time T₁(H) and the proton spin-lattice relaxation time in the rotating frame T_1ρ(H) were measured as a function of the blend composition. The T₁(H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogeneous on the scale of 20 ∼ 30 nm. The six results of T_1ρ(H) further indicated that the blends were homogeneous on the scale of 40 ∼ 50Å. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2291–2300, 1998     

The State of NaOH in NaOH/Poly(Sodium Acrylate) Composite

NaOH/poly(sodium acrylate) composites were prepared by in situ polymerization of acrylic acid with an overneutralization level by adding excess NaOH. The composites were studied by XRD, IR and ²³Na MAS NMR spectroscopy. The results showed that the high neutralization degree (>100%) may lead to a complete polymerization. Both XRD and ²³Na MAS NMR spectra did not show any peaks of phase-separated NaOH or Na₂CO₃ until the neutralization degree was up to 217.5%. It can be presumed that the aggregates of Na⁺ ions can contain approximately two Na⁺ units for every carboxyl group before the phase separation.     

Copolymers of 4‐(3′,4′‐Dimethoxycinnamoyl)phenyl Acrylate and MMA: Synthesis,Characterization, Photocrosslinking Properties,and Monomer Reactivity Ratios

Abstract

4‐(3′,4′‐Dimethoxycinnamoyl)phenyl acrylate (DMCPA) containing pendant chalcone moiety was copolymerized with methyl methacrylate (MMA) by radical polymerization in ethyl methyl ketone at 70°C under a nitrogen atmosphere using benzoyl peroxide (BPO) as a free radical initiator. The prepared polymer was characterized by UV, FT‐IR, ¹H‐NMR, and ¹³C‐NMR spectra. The composition of the copolymer was determined using ¹H‐NMR analysis. The monomer reactivity ratios of copolymerization were determined using conventional linearization methods such as Fineman–Ross (r ₁ = 0.26 and r ₂ = 0.61), Kelen–Tudos (r ₁ = 0.26 and r ₂ = 0.61), and Ext. Kelen–Tudos (r ₁ = 0.23 and r ₂ = 0.59), and a non‐linear error‐in‐variables model (EVM) method using the computer program RREVM (r ₁ = 0.2541 and r ₂ = 0.6094). The molecular weights (M _w and M _n) of the copolymers were determined by gel permeation chromatography. Thermogravimetric analysis of the polymers in air reveals that the stability of the copolymers decreases with an increase in the mole fraction of MMA in the copolymers. The solubility of the polymers was tested in various polar and non‐polar solvents. The glass transition temperature of the copolymers was determined as a function of copolymer composition. The copolymers were sensitive to UV light and became crosslinked after irradiation with 254 nm light.     

A.c. impedance behaviour of processes involving adsorption and reactivity of guanidonium-type cations at Pt(1 0 0) surface

The present paper reports a.c. impedance spectroscopic studies on adsorption of guanidonium (G⁺) and N,N-dimethylguanidonium (DMG⁺) resonant cations at Pt(1 0 0) single-crystal surface. The resulted information provided confirmation of the role of electrosorption of the above-mentioned molecule–ions through evaluation of the associated charge-transfer resistances and capacitances for the Pt(1 0 0) plane in 0.5 M H₂SO₄. These results also provided support for the interfacial ion-pairing mechanism that had been based on the voltammetric and in situ FTIR spectroscopic results published earlier.     

Interaction and Scale of Mixing in Cellulose Acetate/Poly(<Emphasis Type="Italic">N</Emphasis>-vinyl Pyrrolidone-co-vinyl Acetate) Blends

Binary blends and pseudo complexes of cellulose acetate (CA) with vinyl polymers containing N-vinyl pyrrolidone (VP) units, poly(N-vinyl pyrrolidone) (PVP) and poly(N-vinyl pyrrolidone-co-vinyl acetate) [P(VP-co-VAc)], were prepared, respectively, by casting from mixed polymer solutions in N,N-dimethylformamide as good solvent and by spontaneous co-precipitation from solutions in tetrahydrofuran as comparatively poor solvent. The scale of miscibility and intermolecular interaction were examined for the blends and complexes by solid-state ¹³C-NMR spectroscopy. It was revealed that the formation of complexes was due to a higher frequency of hydrogen-bonding interactions between the residual hydroxyl groups of CA and the carbonyl groups of VP residues in the vinyl polymer component. From measurements of CP/MAS spectra and proton spin-lattice relaxation times (T_1ρ^H) in the NMR study, the existence of the hydrogen-bonding interaction was also confirmed for the miscible blends and the homogeneity of the mixing was estimated to be substantially on a scale within a few nanometers.     

Solid state N and C NMR study of dioxomolybdenum (VI) complexes of Schiff bases derived from trans-1,2-cyclohexanediamine

The ¹³C, ¹⁵N CP MAS NMR and FT-IR spectra of dioxomolybdenum (VI) complexes of trans-N,N′-bis-(R-salicylidene)-1,2-cyclohexanediamine (R=H, R=3,5-diCl, R=3,5-diBr, R=4,6-diOCH₃), trans-N,N′-bis-(2-OH-naphthylidene)-1,2-cyclohexanediamine and trans-N-(salicylidene)-N′-(2-OH-naphthylidene)-1,2-cyclohexanediamine have been measured. Comparative analysis of the NMR and IR spectra of the complexes with those of the corresponding ligands has shown that the complexation of the di-Schiff bases leads to changes in the conformation of the ligands and the charge redistribution. The asymmetric structure and non-planar structure of the complexes have been suggested.     

Synthesis of regioselectively O-labelled chlorophyll derivatives at the 3- and/or 13-positions through one-pot exchange of carbonyl oxygen atoms

3¹- and/or 13¹-¹⁸O-oxo-labelled methyl pyropheophorbides (84-90% ¹⁸O atoms at each position) were prepared by exchanging carbonyl oxygen atoms under biphasic conditions of acidic H₂¹⁸O (ca. 95% ¹⁸O) and dichloromethane. The (un)labelling occurred more rapidly at less sterically hindered (13-CO possessing 13²-COOCH₃>13-CO lacking it) or more reactive carbonyl groups (formyl>keto group), and not at any hydroxy groups. Reduction of a carbonyl to carbinol group was useful for preparation of regioselectively ¹⁸O-labelled chlorophyll derivatives. Following the labelling procedure, 13¹-¹⁸O-pheophytin-a and 3¹-¹⁸O-pheophytin-d were obtained. All the synthetic ¹⁸O-labelled compounds were characterized by their FAB-mass, ¹³C NMR and IR spectra. Especially, ¹⁸O-labelling induced 0.02 (¹³C-O) and 0.04-0.05 ppm high field shifts (¹³CO) in ¹⁸O-attached carbon resonances and about 30 cm⁻¹ down-shifts in ¹⁸O-labelled carbonyl stretching vibrational bands.     

Structures of Rydberg transitions in the absorption spectra of methyl-substituted derivatives of bis(η6-benzene)chromium

The effect of methylation of ligands in bis(η⁶-benzene)chromium (1) on the structure of Rydberg transitions in absorption spectra has been studied. A detailed analysis and interpretation of all Rydberg elements of the vapor-phase spectra of bis(η⁶-benzene)chromium (2), bis(η⁶-o-xylene)chromium (3), bis(η⁶-m-xylene)chromium (4), and bis(η⁶-mesitylene)chromium (5) was carried out. The vapor-phase electronic absorption spectrum of bis(η⁶-p-xylene)chromium (6) was measured, and the assignment of the Rydberg bands was made for the first time. The first ionization potentials of complexes 2–5 were refined. The energy of detachment of the 3d_z ² electron and the parameters of the Rydberg excitations for molecule 6 were determined. The vibronic components of the 3d_z ²→R4p _x,y transition in the spectra of complexes 2 and 6 were assigned. The differences in the Rydberg structure of the spectra of compounds 2–6 were analyzed in terms of the selection rules for optical transitions in the corresponding symmetry groups. The vapor-phase spectra correspond to conformers with the symmetry groupsC _2v andC ₂ for complexes 2–4, with the symmetry groupsD _3h andD ₃ for compound 5, and with the symmetry groupD _2d for complex 6. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 897–903, May, 1998.     

Metal complexes of the third generation quinolone antibacterial drug sparfloxacin: preparation,structure, and microbial evaluation

The interactions of yttrium chloride, zirconium chloride, and uranium nitrate with sparfloxacin (SPAR) in ethanol, methanol, and acetone were studied. The isolated solid complexes were characterized by elemental analysis, infrared, ¹H-NMR and electronic spectra, and thermogravimetric analysis. The results support the formation of [Y(SPAR)₂Cl₂]Cl ? 12H₂O, [ZrO(SPAR)₂Cl]Cl ? 15H₂O, and [UO₂(SPAR)₃](NO₃)₂ ? 5H₂O. Infrared spectra of the isolated solid complexes indicate that SPAR is bidentate through the ring carbonyl oxygen and one oxygen of carboxylate. The calculated bond length and force constant, F(U=O), in the uranyl complex are 1.747 Å and 655.29 Nm^?1, respectively. The antimicrobial activities of the ligand and metal complexes have been tested against bacteria Staphylococcus aureus (S. aureus), Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) and fungi Penicillium rotatum (P. rotatum) and Trichoderma sp., showing that the complexes exhibit higher antibacterial activity than SPAR.     

CONFORMATIONAL AND ELECTRONIC INTERACTION STUDIES OF α-SUBSTITUTED CARBONYL COMPOUNDS. XV. α-(ARYLSULFINYL)-p-SUBSTITUTED ACETOPHENONES

Abstract

The v_CO IR analysis of α-(p-phenylsulfinyl)-p-substituted acetophenones X-φC(O)CH₂S(O)φ-Y 1–8, being X and Y = NO₂, H and OMe substituents, supported by ab initio calculations of the α-methylsulfinyl/acetophenone (model compound) along with the X-ray geometrical data for 1,7 and 8, indicates the existence of the cis ₂ and gauche rotamers for compounds 1-4 and 6. Compounds 5,7 and 8 present another less stable and more polar cis ₁ rotamer. The cis ₂ rotamer concentration for 4 (ca. 97% in CCl₄) is reduced to ca. 50% for 2,3,5-7 and to ca. 20% for 1 and 8. This behavior is discussed in terms of O^δ- _(CO—S^δ+ _(SO) charge transfer and Coulombic interactions, which stabilize the cis ₁ rotamer, and the π*_CO/δ_C-S, π_CO/n_s and π*_CO/δ_C-S orbital interactions, which stabilize the gauche rotamers. The progressive more negative carbonyl cis ₂ shifts (Δv_c), when X varies from NO₂ to H and to OMe for the same Y, along with the unexpected NAE values of the α-methylene carbon chemical shifts for compounds 1–8 give further support for the existence of a strong intramolecular complex betwen C=O and S=O dipoles which stabilizes the cis ₂ rotamer. The progressive more negative carbonyl gauche shifts (Δv_g), when X varies from NO₂ to H and to OMe for the same Y, is in line with the higher contibution of the interaction π_CO/δ*_C-S, which stabilizes the gauche rotamer of the title compounds.     

Solid state13C NMR spectra of metal carbonyl clusters

The solid state¹³C NMR spectra of four¹³CO enriched carbonyl clusters having a tri-iron metallic core have been analyzed to provide structural and dynamic information. In Fe₃(CO)₁₂ (1), the high temperature spectra suggest the occurrence of large amplitude motions of the CO groups around their position at the vertexes of the coordination polyhedron in addition to the motion involving the Fe₃-triangle previously detected in the VT-¹³C MAS spectra.¹³C and³¹P NMR data of Fe₃(CO)₁₁PPh₃ (2) indicates the presence of one molecule in the asymmetric unit in apparent disagreement with the previously reported X-ray data. Furthermore, we show that structural information can be obtained from the chemical shift tensor components readily available from the analysis of the spinning sideband manifold.     

Analysis of a stacked-triangular platinum carbonyl cluster dianion, [Pt3(CO)6] 3 2− by252Cf-Plasma Desorption Mass Spectrometry

²⁵²Cf-Plasma Desorption Mass Spectrometry (²⁵²Cf-PDMS) has been used to investigate the [(Ph₃PCH₂C₅H₄)Fe(C₅H₅)]⁺ salt of the prototype dianionic, platinum carbonyl cluster, [Pt₃(CO)₃(₂-CO)₃] ₃ ^2– . An envelope of singly charged [Pt₉(CO) _x ]^– ions with the principal peak centered atx=8 was observed in the negative ion mass spectrum as a result of successive losses of the carbonyl ligands from the intact platinum core. Another feature of the negative ion spectrum was the prominent occurrence of other envelopes of multiple peaks which conform to Pt₁₂, Pt₁₅, Pt₁₈, Pt₂₁, and Pt₂₄ singly charged metal cores. An unexpected observation was the presence of singly charged positive ions of the dianionic cluster which were formed without incorporation of the counterion. A similar but, largely unresolvable, broad envelope of singly charged ions containing the Pt₉ core resulted with a peak maximum corresponding closely to the completely carbonylated cluster. The peak distribution extended from the fully decarbonylated cluster to well beyond the mass of the fully carbonylated cluster. Analogous peaks attributable to singly charged positive ions of the Pt₁₂, Pt₁₅, and Pt₁₈ clusters were also evident. Very little fragmentation was observed below the molecular ion in either the positive or negative ion mass spectra except for ions associated with the counterion. A detailed analysis of the mass spectra, including the types of ions observed and correlations with the molecular architecture are described.     

1H, 13C, 15N NMR and 13C, 15N CPMAS studies of cobalt(III)-chloride-pyridine complexes, spontaneous py → Cl substitution in trans-[Co(py)4Cl2]Cl, and a new synthesis of mer-[Co(py)3Cl3]

trans-[Co(py)₄Cl₂]Cl·6H₂O, mer-[Co(py)₃Cl₃] and mer-[Co(py)₃(CO₃)Cl] were studied by UV-Vis, far-IR and ¹H, ¹³C, ¹⁵N NMR. The formation of Co-N bonds lead to variable in sign and magnitude changes of ¹H NMR chemical shifts, heavily dependent on proton position, coordination sphere geometry and character of auxiliary ligands. ¹³C nuclei were deshielded upon Co(III) coordination, while ¹⁵N NMR studies exhibited ca. 85–110 ppm shielding effects (ca. 15–25 ppm more expressed for nitrogens trans to N than trans to Cl or O). ¹³C and ¹⁵N CPMAS spectra revealed a slight inequivalency of formally identical Co-py bonds in trans-[Co(py)₄Cl₂]Cl·6H₂O and mer-[Co(py)₃Cl₃], suggesting for the latter complex an existence of distortion isomers. In chloroform, a spontaneous trans-[Co(py)₄Cl₂]Cl → mer-[Co(py)₃Cl₃] + py reaction was monitored by ¹H NMR and UV-Vis. This process of py → Cl substitution allowed the design of a more convenient and efficient method of mer-[Co(py)₃Cl₃] preparation.      

MACROBICYCLIC D-METAL TRIS-DIOXIMATES OBTAINED BY CROSS-LINKING WITH P-BLOCK ELEMENTS. PART VI. PREPARATION,MOLECULAR STRUCTURE AND MÖSSBAUER (57FE, 119SN) PARAMETERS OF AN IRON(II) COMPLEX WITH A MACROBICYCLIC TIN-CONTAINING TRIS-NIOXIMATE LIGAND

Abstract

The tin-containing clathrochelate complex of Fe(II) with cyclohexanedione-1,2-dioxime (nioxime, H₂Nx), [FeNx₃(SnCl₃)₂]^2- · (Et₂NH⁺ ₂)₂ · Et₂NH₂ ⁺ · Cl^? · 2Prⁱ OH was prepared by slowly adding diethylamine to a solution containing the macrobicyclic [FeNx₃(SnCl₃)₂]^2- anion. The structure of the complex has been determined by X-ray methods. Crystal data: monoclinic, space group P2₁/c, a = 10.565(2), b = 25.413(5), c = 20.198(4)Å, β=95.40(3)°, Z = 4. The iron atoms is encapsulated by the clathrochelate ligand and surrounded by a distorted trigonal antiprismatic coordination sphere comprising by six nitrogen atoms of three dioxime residues. The experimental value of the distortion angle (ca 37.5°) is close to that predicted by the Mössbauer (⁵⁷Fe) parameters (ca 40°). The average Fe-N bond length of 1.923Å is somewhat greater than that in boron-containing analogues. The Sn atoms have a slightly distorted octahedral coordination, which also correspond to Mössbauer (¹¹⁹Sn) spectroscopic data. The six-membered carbocycles in the dioxime fragments have a half-chair conformation with both β-carbons displaced to the opposite sides of the mid-plane of the remaining atoms. All the active hydrogen atoms of the structure are involved in a hydrogen bond system.

The possibilities of use of Mössbauer parameters and their temperature dependences to determine the geometry of iron(II) tris-dioximates and the sign of Δ in Mössbauer (⁵⁷Fe) spectra are discussed.     

High-Resolution Solid-State NMR Characterization of Morphology in Annealed Polylactic Acid

Single-pulse ¹³C NMR spectra and spin-lattice relaxation times T₁(¹H), detected indirectly via ¹³C carbons, and T₁(¹³C) were measured at 31°C for virgin pelletized and annealed polylactic acid (PLA) samples using the magic-angle spinning technique. The structural relaxation resulting in more regular crystals with narrower conformation distribution and increase in the lamellae thickness and crystallinity brought about by annealing at 100°C was deduced from the narrowing of the ¹³C NMR lines and proton spin-lattice relaxation times T₁(¹H). The spin-lattice relaxation times T₁(¹³C) related to the respective carbons of the α-polymorph of PLA are also discussed in the study.     

Synthesis of a rhodium(I) carbonyl complex with a chiral aminodiphosphine ligand and its immobilization onto aminopropyl functionalized silica gel

The reaction of [Rh(CO)₂(µ-Cl)]₂ with two molar equivalents of a chiral ligand, (R)-N,N-bis(2-diphenylphosphinoethyl)-1-phenylethylamine(PNP*) yield a mono-carbonyl complex, [Rh(CO)Cl(η²-P,P-PNP*)] (1), in which the potentially tridentate PNP* ligand coordinates in a bidentate fashion through P,P bonding. The complex was characterized by elemental analysis, FAB mass, IR, UV-Vis, ¹H- and ³¹P{¹H}-NMR spectroscopy. Variable temperature (223–298 K) ³¹P{¹H}-,NMR spectra of 1 showed a mixture of cis and trans isomers in the solution with the trans predominating at room temperature and the cis at lower temperature. Complex 1 was immobilized on silica through axial coordination of amine from 3-aminopropyltriethoxysilane functionalized silica. The immobilized materials were characterized by elemental analysis (N₂), FTIR, DTA–TGA, N₂-adsorption, XRD, and SEM analysis.