Dimerisation and complexation of 6-(4′-t-butylphenylamino)naphthalene-2-sulphonate by β-cyclodextrin and linked β-cyclodextrin dimers

This study shows that stereochemical factors largely determine the extent to which 6-(4′-t-butylphenylamino)-naphthalene-2-sulphonate, BNS^?  and its dimer, (BNS^? )₂, are complexed by β-cyclodextrin, βCD, and a range of linked βCD dimers. Fluorescence and ¹H NMR studies, respectively, show that BNS^?  and (BNS^? )₂ form host–guest complexes with βCD of the stoichiometry βCD.BNS^?  (10^? 4 K ₁ = 4.67 dm³ mol^? 1) and βCD.BNS₂ ^2 ?  (10^? 2 K ₂′ = 2.31 dm³ mol^? 1), where the complexation constant K ₁ = [βCD.BNS^? ]/([βCD][BNS^? ]) and K ₂′ = [βCD. (BNS^? )₂]/([βCD.BNS^? ][BNS^? ]) in aqueous phosphate buffer at pH 7.0, I = 0.10 mol dm³ at 298.2 K. (The dimerisation of BNS^?  is characterised by 10^? 2 K _d = 2.65 dm³ mol^? 1.) For N,N-bis((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)succinamide, 33βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂su, N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)succinamide, 66βCD₂su, N-((2^AS,3^AS)-3^A-deoxy-3^A-β-cyclodextrin)-N′-(6^A-deoxy-6^A-β-cyclodextrin)urea, 36βCD₂ur, and N,N-bis(6^A-deoxy-6^A-β-cyclodextrin)urea, 66βCD₂ur, the analogous 10^? 4 K ₁ = 11.0, 101, 330, 29.6 and 435 dm³ mol^? 1 and 10^? 2 K ₂′ = 2.56, 2.31, 2.59, 1.82 and 1.72 dm³ mol^? 1, respectively. A similar variation occurs in K ₁ derived by UV–vis methods. The factors causing the variations in K ₁ and K ₂ are discussed in conjunction with ¹H ROESY NMR and molecular modelling studies.     

Structural investigation of cellulose Iα and Iβ by 2D RFDR NMR spectroscopy: determination of sequence of magnetically inequivalent d-glucose units along cellulose chain

In our previous studies of the crystal structure of native cellulose (cellulose I) by solid-state two-dimensional (2D) ¹³C–¹³C INADEQUATE, it was revealed that cellulose I_α contains two kinds of β-d-glucose residues (A and A′) in the unit cell and that cellulose I_β contains another two kinds of residues (B and B′). In the present study, the sequence of residues A and A′ along the same chains in cellulose I_α and that of residues B and B′ in I_β were investigated by 2D ¹³C–¹³C rotor-synchronized radiofrequency-driven recoupling (RFDR) experiments using, respectively, uniformly ¹³C₆-labeled (U−¹³C₆) bacterial cellulose and the same [U−¹³C₆] cellulose sample after thermal treatment at 260 °C. The RFDR spectra recorded with a short mixing time (1.0 ms) showed dipolar-coupled ¹³C spin pairs of only the neighboring carbon of the both phases, while those recorded with a longer mixing time (3.0–15 ms) provided correlations between weakly coupled ¹³C spin pairs as well as strongly coupled ¹³C spin pairs such as neighboring carbon nuclei. In the RFDR spectrum of the [U−¹³C₆] cellulose recorded with a mixing time of 15 ms, the inter-residue ¹³C–¹³C correlation between C4 of residue A and C2 of residue A′ and that between C3 of residue A and C4 of residue A′ were clearly observed. In the case of cellulose I_β, however, inter-residue ¹³C–¹³C correlations between residues B and B′ could not be detected in the series of RFDR spectra recorded with different mixing times of annealed [U−¹³C₆] cellulose. From these findings, that cellulose I_α was revealed to have the –A–A′– repeating units along the cellulose chain. For cellulose I_β, it was revealed that the respective residues B and B′ are composed of independent chains (–B–B– and –B′–B′– repeating units) and that there are no –B–B′– repeating units in the chain.     

Darstellung von μ-Schwefeldisulfoniumsalzen [(CH3)2S?Sx?S(CH3)2]2+2A− (x = 1–3, A− = AsF6−, SbF6−, SbCl6−). Über die Analogie im Reaktionsverhalten zwischen Sulfanen und Sulfoniumsalzen

Preparation of μ-Sulfurdisulfonium Salts [(CH₃)₂S? S_x? S(CH₃)₂]²⁺2A^? (x = 1–3, A^? = AsF₆^?, SbF₆^?, SbCl₆^?). On the Analogy of the Reactivity of Sulfanes and Sulfonium Salts The preparation of the μ-sulfurdisulfonium salts [(CH₃)₂S? S_x? S(CH₃)₂]²⁺(A^?)₂ with x = 1–3 and A^? = AsF₆^?, SbF₆^?, SbCl₆^? is reported. The salts are formed by reaction of (CH₃)₂SH⁺A^? and (CH₃)₂SSH⁺A^? with SCl₂ and S₂Cl₂, resp. They are characterized by vibrational spectroscopic measurements. [(CH₃)₂S? S₂? S(CH₃)₂]²⁺(SbF₆^?)₂ crystallizes in the space group C2/c with a = 1 884.5(7) pm, b = 1 302.8(5) pm, c = 1 477.2(5) pm, β = 98.62(3)° und Z = 8.     

Reactions with Oleum under Harsh Conditions: Characterization of the Unique [M(S2O7)3]2− Ions (M=Si,Ge, Sn) in A2[M(S2O7)3] (A=NH4, Ag)

The reactions of group 14 tetrachlorides MCl₄ (M=Si, Ge, Sn) with oleum (65 % SO₃) at elevated temperatures lead to the unique complex ions [M(S₂O₇)₃]^2?, which show the central M atoms in coordination with three chelating S₂O₇^2? groups. The mean distances M? O within the anions increase from 175.6(2)–177.5(2) pm (M=Si) to 186.4(4)–187.7(4) pm (M=Ge) to 201.9(2)–203.5(2) pm (M=Sn). These distances are reproduced well by DFT calculations. The same calculations show an increasing positive charge for the central M atom in the row Si, Ge, Sn, which can be interpreted as the decreasing covalency of the M? O bonds. For the silicon compound (NH₄)₂[Si(S₂O₇)₃], ²⁹Si solid‐state NMR measurements have been performed, with the results showing a signal at ?215.5 ppm for (NH₄)₂[Si(S₂O₇)₃], which is in very good agreement with theoretical estimations. In addition, the vibrational modes within the [MO₆] skeleton have been monitored by Raman spectroscopy for selected examples, and are well reproduced by theory. The charge balance for the [M(S₂O₇)₃]^2? ions is achieved by monovalent A⁺ counter ions (A=NH₄, Ag), which are implemented in the syntheses in the form of their sulfates. The sizes of the A⁺ ions, that is, their coordination requirements, cause the crystallographic differences in the crystal structures, although the complex [M(S₂O₇)₃]^2? ions remain essentially unaffected with the different A⁺ ions. Furthermore, the nature of the A⁺ ions influences the thermal behavior of the compounds, which has been monitored for selected examples by thermogravimetric differential thermal analysis (DTA/TG) and XRD measurements.     

Hyperbranched thermolabile polycarbonates derived from a A2+B3 monomer system

Hyperbranched polycarbonates were synthesized successfully via the A₂ + B₃ route by the reaction of a bis(carbonylimidazolide) with triethanolamine. These polymers containing the carbonate group as thermolabile moiety are decomposing into volatile products at around 200°C. The polymers were characterized with ¹H/¹³C NMR spectroscopy, SEC, DSC and TGA techniques.     

Crystal structure and NMR study of a bisperoxovanadium complex [NH4][VO(O2)2(ima)]

A novel bisperoxovanadium complex, [NH₄][VO(O₂)₂(ima)] (1) (ima = imidazole-4-carboxamide), was synthesized by the reaction of NH₄VO₃ and ima in the presence of H₂O₂, and the structure was characterized by single-crystal X-ray technology. The adjacent [NH₄][VO(O₂)₂(ima)] monomers further constructed a 3-D supramolecular framework through intra- and intermolecular hydrogen bonding interactions. The composition of the title complex solution was explored using a combination of multinuclear (¹H, ¹³C and ⁵¹V) magnetic resonance, heteronuclear single quantum coherence (HSQC), and variable temperature NMR in a 0.15 mol L^?1 NaCl/D₂O solution that mimics physiological conditions. According to NMR experimental results, a pair of isomers (Isomers A and B) are observed in aqueous solution, which are attributed to different types of coordination modes between the metal center and the ligands; Isomer B (the main product) has the same coordination structure as the crystal structure of [NH₄][VO(O₂)₂(ima)]. The ⁵¹V NMR experiment together with single-crystal X-ray diffraction results indicated that Isomer A is the hexa-coordinated peroxovanadium species while Isomer B is the hepta-coordinated species.     

Effect of methoxyl groups on the NMR spectra: configuration and conformation of natural and synthetic indanic and tetralinic structures

Here, we studied the influence of the methoxyl groups attached at C‐7 and C‐2′ of natural and synthetic 1‐arylindanes on the chemical shift of the signal of bibenzylic hydrogen and carbon atoms and J_1,2 coupling constants. This influence was also analysed in natural 1‐aryltetralins and related compounds that possess methoxyl and/or hydroxyl groups bound at C‐8 and C‐2′. The methoxyl groups attached at C‐7 in indanes or at C‐8 in tetralins produce a deshielding signal at H‐1 and shield at C‐1 and a strong decrease in the value of J_1,2 due to the pseudoequatorial location adopted by the aryl group bound at C‐1, avoiding an ‘A^1,3 strain’. Furthermore, compounds with hydroxyl or methoxyl groups in C‐2′, in the absence of substituents of C‐7 or C‐8, present a strong deshielding signal at H‐1, strong shield of the C‐1 signal and a decrease in the value of J_1,2. This is attributed to the stereoelectronic effects of the methoxyl or hydroxyl groups, which we have called ‘Asarone effect’. NOESY experiments were conducted to confirm the configuration and conformation of some of the compounds included in this work. This study shows that both effects, A^1,3 strain and Asarone effect, must be taken into account when the structure of natural indanes and tetralins is analysed by using ¹H‐NMR and ¹³C‐NMR spectra. Copyright © 2016 John Wiley & Sons, Ltd.     

Kinetic Investigations of Self-Condensing Group Transfer Polymerization

Hyperbranched methacrylates were synthesized by Self-Condensing Group Transfer Polymerization (SCGTP) of 2-(2-methyl-1-triethylsiloxy-1-propenyloxy)ethyl methacrylate (MTSHEMA) and characterized by multi-detector SEC as well as quantitative ¹³C-NMR. Kinetic measurements revealed that side reactions limit the molecular weights and lower the polydispersity. A maximum degree of branching of DB ≈ 0.4 and a reactivity ratio, r = k _A/k _B = 18 ± 5, was determined.     

From the SmA to the Hexatic,Including the SmC*, SmC*A and SmC*re Phases: A 2H NMR Relaxation Study

The molecular dynamics of a ferroelectric liquid crystal, denoted ZLL 7/* , is investigated by means of ²H NMR relaxation. The spin–lattice (T_1Q and T_1Z) and spin–spin (T₂) relaxation times of two isotopomers of ZLL 7/* , labeled on the phenyl and biphenyl fragments, are measured and their behavior upon passing from the SmA to the hexatic phase, through the ferroelectric SmC*, antiferroelectric SmC*_A, and re‐entrant ferroelectric SmC*_re phases, is discussed. A comparison between the measured T₂ and T₂*, directly related to the experimental linewidth, provides information on the heterogeneity of the system, thus allowing confirmation of previous hypotheses concerning the structural and ordering properties of the SmC*_A and SmC*_re phases. The possibility to look at different sites of the core of the ZLL 7/* smectogen reveals a peculiar sensitivity of the phenyl moiety with respect to the biphenyl fragment, which may be justified by its vicinity to the chiral centers. Interestingly, the trend of the longitudinal relaxation times is characterized by a minimum that corresponds to the SmC*_A and SmC*_re phases, which is reproducible for the two isotopomers and at several Larmor frequencies. A quantitative analysis of T_1Q and T_1Z is performed in the SmA and SmC* phases, for which the narrowing regime approximation is valid. A multifrequency approach is applied to self‐consistently determine the diffusion coefficients for the overall molecular motions, namely spinning and tumbling, and the internal rotations around the para axes of the phenyl and biphenyl fragments. The effect of the magnetic field in unwinding the helical structure of the SmC* phase (for H>9 T) allows observation of a sensitive change in the rotational diffusion coefficients in the frustrated unwound SmC* phase with respect to the SmC* phase.     

187Os subspectra in 1H and 31P{1H} spectra of triosmium carbonyl clusters

A survey of the use of ¹⁸⁷Os satellite subspectra in ¹H and ³¹P{¹H} spectra of triosmium carbonyl clusters is reported. By varying evolution delays in HMQC spectra of [Os₃(µ‐H)₂(CO)₁₀] we have selectively extracted the values for ¹J(Os,H) and ²J(Os,H), respectively. An analysis of the principal modes of phosphine coordination in triosmium clusters demonstrates that ³¹P{¹H}¹⁸⁷Os satellite subspectra are diagnostic for equatorial coordination [¹J(Os,P) = 211–223 Hz] or for axial coordination (perpendicular to the plane of the cluster) [¹J(Os,P) ≈ 147 Hz]. Chelating and bridging diphosphines yield ¹⁸⁷Os satellite subspectra which are the sum of A₂X and AA′X spin systems. If significant P–P coupling is present, the AA′X component requires simulation. All observed ²J(Os,P) trans‐equatorial couplings fall in the range 38–65 Hz. Copyright © 2001 John Wiley & Sons, Ltd.     

Synthesis of model polycyclohexylene/polyethylene miktoarm star copolymers with three and four arms

The synthesis of well‐defined 3‐ and 4‐miktoarm star copolymers of the A₂B and A₃B types is described, where A is 1,4‐polybutadiene and B is poly(1,3‐cyclohexadiene). The synthetic approach involves the reaction of poly(1,3‐cyclohexadienyl)lithium with an excess of methyltrichlorosilane or tetrachlorosilane followed, after the removal of excess silane, by a small excess of polybutadienyllithium. Characterization was carried out by size exclusion chromatography, low‐angle laser light scattering, laser differential refractometry, and NMR spectroscopy. The complete heterogeneous catalytic hydrogenation of the A₂B and A₃B miktoarm stars, with a calcium carbonate‐supported palladium catalyst, leads to the formation of A₂B and A₃B miktoarm stars with one amorphous polycyclohexylene arm with an extremely high glass‐transition temperature and two or three crystalline polyethylene arms. Differential scanning calorimetry was used to determine the glass‐transition temperature of the amorphous blocks of the starting and hydrogenated stars and the melting temperature of polyethylene. Solid‐state ¹³C NMR spectroscopy was performed to ensure the complete saturation of the polycyclohexadiene and polybutadiene arms. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2575–2582, 2002     

Anomalous lattice parameter increase in alkali earth aluminium substituted tungsten defect pyrochlores

The structures of the defect pyrochlores AAl_0.33W_1.67O₆ where A=K, Rb or Cs have been investigated using X-ray and neutron powder diffraction methods as well as the ab initio modelling program VASP. The three cubic pyrochlores exhibit a non-linear increase in lattice parameter with respect to ionic radius of the A cation as a consequence of displacive disorder of the A-type cations. Solid state ²⁷Al MAS NMR studies of this pyrochlore system reveal shifts in the δ∼21-22 ppm range that are indicative of pseudo-5 coordinate Al environments and emanate from distorted Al octahedral with one abnormally long Al-O bond. Solid state ³⁹K, ⁸⁵Rb, ⁸⁷Rb and ¹³³Cs MAS and static NMR studies reflect the local cation disorder demonstrated in the structural studies.     

Disulfide-Containing Detergents (DCDs) for the Structural Biology of Membrane Proteins

Disulfide-containing detergents (DCDs) are introduced, which contain a disulfide bond in the hydrophobic tail. DCDs form smaller micelles than corresponding detergents with linear hydrocarbon chains, while providing good solubilization and reconstitution of membrane proteins. The use of this new class of detergents in structural biology is illustrated with solution NMR spectra of the human G protein-coupled receptor A_2AAR, which is an α-helical protein, and the β-barrel protein OmpX from E. coli.     

Isolation and characterisation of both the first fluoroxyfluorofullerene C60F17OF and oxahomofluorofullerenol C60F17O.OH

The first fluoroxyfluorofullerene C₆₀F₁₇OF (A) has been isolated from the fluorination of [60]fullerene with a mixture of MnF₃ and K₂NiF₆ at 480 °C. This compound has a shorter HPLC retention time than the isomeric fluorofullerene ethers (oxahomofullerenes) and is less stable towards EI mass spectrometry. It fragments by losing OF as a single entity and shows no formation of C₆₀O as a fragment ion. By contrast, the ethers fragment by first losing a number of F atoms and then CO, and ultimately show also the presence of C₆₀O, whilst epoxides lose CO as a main fragmentation step and do not give C₆₀O. The first oxahomofluorofullerenol C₆₀F₁₇O.OH (B) has been isolated from the UV-irradiation of a toluene solution of C₆₀F₁₈ in air during 65 h and readily eliminates HF due to adjacent F and OH groups during EI mass spectrometry. The structures of both the compounds have been deduced from 1D and 2D NMR spectroscopy. Just as oxygen inserts into FCCF bonds of C₆₀F₁₈ to give ethers, so insertion into a CF bond gives A. The oxahomofluorofullerenol B is produced by S_N2′ substitution of F by OH, followed by oxygen insertion into a 6:5-bond (αβ to the OH group) giving a motif not seen previously in fluorofullerenes.     

Configurational assignment in alkyl‐branched sugars via the geminal C,H coupling constants

The measurement of the magnitude and sign of ²J(C,H) couplings offers a reliable way to determine the absolute configuration at a carbon center in a fixed cyclic system. A decrease of the dihedral angle ? in the O—C_A—C_B—H fragment always leads to a change of the ²J(C_A,H_B) coupling to more negative values, independent of the type and position of substituents at the two carbon centers. The orientations of the two substituents at C‐3 of the epimeric pair 1 and 2 were determined unambiguously through the measurement of the geminal coupling constants between C‐3 and the hydrogen atoms at C‐2 and C‐4. In particular, ²J(C‐3,H‐2ax) with ?1.5 Hz, ? = 174° in 1 and ?6.6 Hz, ? = 47° in 2 , and ²J(C‐3,H‐4) with +1.5 Hz, ? = 175° in 1 and ?4.7 Hz, ? = 49° in 2 showed the greatest differences between the two epimers. Both couplings therefore allow the determination of the absolute configuration at C‐3. It should be noted, however, that the size of the coupling constants can be different for dihedral angles of nearly identical size, when there are different numbers of electronegative substituents on the two coupling pathways, i.e. no O‐substituent at C‐2, but one axial O‐substituent at C‐4. It becomes clear that it is not sufficient to measure the magnitude of ²J coupling constants only, but that the sign of the geminal coupling is needed to identify the absolute configuration at a chiral center. The coupling of C‐3 with H‐2eq is not useful for the determination of the configuration at C‐3, as the similarity of the dihedral angles ? (O—C‐3—C‐2—H‐2eq) (57° in 1 and 70° in 2 ) leads to identical coupling constants (?6.1 Hz) for both epimers. Copyright © 2003 John Wiley & Sons, Ltd.     

Ternary Alkali Metal Transition Metal Acetylides

The first alkali metal transition metal acetylides of general composition A₂M⁰C₂ (A = Na ? Cs, M⁰ = Pd, Pt) were obtained by solid state reactions of alkali metal acetylides with palladium and platinum. They are characterized by chains, which are separated by alkali metal ions. Analogous chains also separated by alkali metal ions are the characteristic structural feature of acetylides of composition AM^IC₂, which are accessible by reacting AC₂H with M^II in liquid ammonia (A = Li ? Cs, M^I = Cu, Ag, Au). Despite their structural similarities they possess different properties, as acetylides of composition A₂M⁰C₂ are semiconductors with very small indirect band gaps and slightly extended C–C distances compared to a C–C triple bond, whereas acetylides of composition AM^IC₂ show a typical salt‐like behavior with C–C distances close to the expected value for a C–C triple bond of 120 pm. But with the help of simple chemical models these differences can be made plausible. Furthermore, it is shown that only by a combination of different methods (powder diffraction with X‐rays and neutrons, solid state NMR spectroscopy, Raman spectroscopy) it was possible to characterize this new class of compounds structurally and chemically.     

Reaction of oligoalcohols with diepoxides: An easy,one‐pot way to star‐shaped,multibranched polymers. II. Poly(ethylene oxide) stars—synthesis and analysis by size exclusion chromatography triple‐detection method

An Erratum has been published for this article in Journal of Polymer Science Part A: Polymer Chemistry (2004) 42(10) 2575‐2576 Starlike, highly branched (A_xB_yA_z) macromolecules having from a few to 100 arms and molar masses up to 10⁵ were prepared in three stages with the one‐pot, arms‐core‐arms method (B_y stands for y molcules of former diepoxides introduced into the core). Oligoalcohols, at least partially converted into their alcoholate counterpart states, reacted with diepoxy compounds giving star‐shaped, highly branched macromolecules. With the properly chosen conditions, complete conversion of both starting components was achieved. In this article homostars built with the first and second generation of poly(ethylene oxide) arms (A_x and A_z, respectively) are described. The number of arms (f) was determined either by direct measurements of the number‐average molcular weight (M_n) of the first and second stars (M_n of arms A_x and A_z is known) or by calculating f from branching indices g and g′ determined from the radius of gyration and the limited viscosity number measured with size exclusion chromatography (SEC) triple detection with TriSEC software. For a few samples, M_n was measured with high‐speed membrane osmometry. The progress of the stars' formation was monitored by ¹H NMR, SEC, and matrix‐assisted laser desorption/ionization time‐of‐flight methods. Functionalization of the ? OH end groups in the second generation of arms was observed by ¹H and/or ³¹P NMR. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1576–1598, 2004     

Multiple quantum1H-NMR of ferrocene in isotropic solution

Summary Excitation of multiple quantum coherence in the C₅ symmetrical A₅-spin system of ferrocene was possible by multiexponential relaxation of degenerated NMR transitions. The mechanism of the excitation was analyzed by means of a tensor operator formalism. Symmetry selection rules were postulated for the relaxation pathways.Dedicated to Professor Dr. Karl Schlögl on occasion of his 65th birthday     

NMR Crystallography Reveals Carbonate Induced Al-Ordering in ZnAl Layered Double Hydroxide

Layered double hydroxides (LDHs) serve a score of applications in catalysis, drug delivery, and environmental remediation. Smarter crystallography, combining X-ray diffraction and NMR spectroscopy revealed how interplay between carbonate and pH determines the LDH structure and Al ordering in ZnAl LDH. Carbonate intercalated ZnAl LDHs were synthesized at different pH (pH 8.5, pH 10.0, pH 12.5) with a Zn/Al ratio of 2, without subsequent hydrothermal treatment to avoid extensive recrystallisation. In ideal configuration, all Al cations should be part of the LDH and be coordinated with 6 Zn atoms, but NMR revealed two different Al local environments were present in all samples in a ratio dependent on synthesis pH. NMR-crystallography, integrating NMR spectroscopy and X-ray diffraction, succeeded to identify them as Al residing in the highly ordered crystalline phase, next to Al in disordered material. With increasing synthesis pH, crystallinity increased, and the side phase fraction decreased. Using ¹H−¹³C, ¹³C−²⁷Al HETCOR NMR in combination with ²⁷Al MQMAS, ²⁷Al-DQ-SQ measurements and Rietveld refinement on high-resolution PXRD data, the extreme anion exchange selectivity of these LDHs for CO₃²⁻ over HCO₃⁻ was linked to strict Al and CO₃²⁻ordering in the crystalline LDH. Even upon equilibration of the LDH in pure NaHCO₃ solutions, only CO₃²⁻ was adsorbed by the LDH. This reveals the structure directing role of bivalent cations such as CO₃²⁻ during crystallization of [M²⁺₄M³⁺₂(OH)₂]²⁺[A²⁻]₁⋅yH₂O LDH phases.