Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

Multinuclear (11B, 31P) MAS NMR spectroscopy of borophosphates

¹¹B and ³¹P MAS NMR spectroscopy of three borophosphates was used to monitor their phase composition via the isotropic chemical shifts. CaBPO₅ and BPO₄ represent nearly pure samples, SrBPO₅ contains β-Sr₂P₂O₇ as well as BPO₄ as impurities. The anisotropic chemical shift data provide additional information on the geometry and connectivity of the BO₄ and PO₄ building units. Received: 25 July 1996 / Revised: 19 August 1996 / Accepted: 23 August 1996     

A proton NMR study on aggregation of cationic surfactants in water: effects of the structure of the headgroup

 ¹H NMR chemical shifts of solutions of the following cationic surfactants in D₂O were determined as a function of their concentrations: cetyltrimethylammonium chloride, CTACl, a 1 : 1 molar mixture of CTACl and toluene, cetylpyridinium chloride, CPyCl, cetyldimethylphenylam-monium chloride, CDPhACl, cetyldimethylbenzylammonium chloride, CDBzACl, cetyldimethyl-2-phenylethylammonium chloride, CDPhEtACl, and cetyldimethyl-3-phenylpropylammonium chloride, CDPhPrACl. Plots of observed chemical shifts versus [surfactant] are sigmoidal, and were fitted to a model based on the mass-action law. Satisfactory fitting was obtained for the discrete protons of all surfactants. From these fits, we calculated the equilibrium constant for micelle formation, K, the critical micelle concentration, CMC and the chemical shifts of the monomer, δ_mon and the micelle δ_mic. ¹H NMR-based CMC values are in excellent agreement with those which we determined by surface tension measurements of surfactant solutions in H₂O, allowing for the difference in structure between D₂O and H₂O. Values of K increase as a function of increasing the size of the hydrophilic group, but the free energy of transfer per CH₂ group of the phenylalkyl moiety from bulk water to the micellar interface is approximately constant, 1.9±0.1 kJ mol^-1. Values of (δ_mic–δ_mon) for the surfactant groups at the interface, e.g., CH₃–(CH₂)₁₅–N+(CH₃)₂ and within the micellar core, e.g., CH₃–(CH₂)₁₅–N⁺ were used to probe the (average) conformation of the phenyl group in the interfacial region. The picture that emerges is that the aromatic ring is perpendicular to the interface in CDPhACl and is more or less parallel to it in CDBzACl, CDPhEtACl, and CDPhPrACl. Received: 23 February 1996 Accepted: 29 August 1996     

Analysis of nitrophenols and other polar nitroaromatic compounds in ammunition wastewater by high-field proton nuclear magnetic resonance (1H-NMR) spectroscopy and chromatographic methods

 It is shown that by using high-field proton nuclear magnetic resonance (¹H-NMR) spectroscopy it is possible, without prior separation, to analyse nitrophenols and other acidic nitroaromatic compounds in the “pH 2 extract” of ammunition wastewater. The ¹H-NMR chemical shifts data of a variety of reference compounds are presented. Two groundwater samples from the former ammunition plant in Elsnig (Saxony) were analysed by ¹H-NMR and also by chromatographic methods (GC/MS, HPLC). The results are compared and discussed. Received: 17 January 1996/Revised: 15 May 1996/Accepted: 17 May 1996     

Analysis of nitrophenols and other polar nitroaromatic compounds in ammunition wastewater by high-field proton nuclear magnetic resonance (1H-NMR) spectroscopy and chromatographic methods

 It is shown that by using high-field proton nuclear magnetic resonance (¹H-NMR) spectroscopy it is possible, without prior separation, to analyse nitrophenols and other acidic nitroaromatic compounds in the “pH 2 extract” of ammunition wastewater. The ¹H-NMR chemical shifts data of a variety of reference compounds are presented. Two groundwater samples from the former ammunition plant in Elsnig (Saxony) were analysed by ¹H-NMR and also by chromatographic methods (GC/MS, HPLC). The results are compared and discussed. Received: 17 January 1996/Revised: 15 May 1996/Accepted: 17 May 1996     

Theoretical investigation into structures and magnetic properties of smaller fullerenes and their heteroanalogues

The smaller fullerenes, C₂₀, C₂₄, C₂₈, C₃₂, C_36, C₄₀ and C₅₀, their hydrogenation products and selected B-, N- and P-doped analogues have been investigated systematically at the B3LYP/6-31G* density functional level of theory. The degree of spherical electron delocalization is evaluated by using the computed nucleus-independent chemical shifts ( NICS) at the cage center and the individual ring centers of interest. The calculated NMR chemical shifts and the NICS values at the cage center, which can be accessed by endohedral ³He chemical shifts, should provide a basis for further experimental characterization of these compounds. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

Endohedral chemical shifts in higher fullerenes with 72–86 carbon atoms

For all isolated pentagon isomers of the fullerenes C₆₀–C₈₆ with nonzero HOMO–LUMO gap and for one nonclassical C₇₂ isomer (C_{2 v} ), endohedral chemical shifts have been computed at the GIAO-SCF/3-21G level using B3LYP/6-31G* optimized structures. The experimental ³He NMR signals are reproduced reasonably well in cases where assignments are unambiguous (e.g. C₆₀, C₇₀ and C₇₆). On the basis of the calculated thermodynamic stability order and the comparison between the computed and experimental ³He chemical shifts, the assignments of the observed ³He NMR spectra are discussed for all higher fullerenes, and new assignments are proposed for one C₈₂ and one C₈₆ isomer (C₈₂:3 and C₈₆:17). The calculated helium chemical shifts also suggest the reassignment of the δ(³He) resonances of two C₇₈ isomers. Received: 26 March 2001 / Accepted: 10 May 2001 / Published online: 11 October 2001     

13C- and 1H-NMR and FTIR spectroscopic evidence for aggregate formation of organosilanes in toluene

 Changes in the ¹³C and ¹H NMR chemical shifts of the silane coupling agent (3-aminopropyltri-ethoxysilane, APTS) in toluene, which were detected as the concentration of APTS increased, have been interpreted in terms of the formation of micelles and the presence of a critical micelle concentration (CMC) equal to ca. 0.47 mol 1^-1. For the protons of the n-propyl segment, ¹H NMR splitting patterns have been analyzed and conformations of the propyl segment have been discussed. Plots of relative absorbance of the two NH₂ stretch IR bands at 3324 and 3384 cm^-1 against concentration provided an inflection point (corresponding to the CMC) at a value equal to 0.46 mol 1^-1. Thus, consideration of the interaction of APTS with a surface must take into account the presence of both APTS aggregates as well as APTS monomers. Received: 16 August 1996 Accepted: 26 September 1996     

1H NMR study of the reduced nickel-octaethylporphyrin complex

The behavior of the proton chemical shifts due to the addition of an extra electron to the starting diamagnetic complex of Ni(II)-octaethylporphyrin is studied. The isotropic shifts are analyzed, and it is concluded that the reduction affords Ni(I)-octaethylporphyrin. The electronic configuration of nickel is (d_xy)²(d_xz, d_yz)⁴(d_z ²)²(d_x ²-_y ²)¹. The density of the unpaired electron is transferred from the Ni(I) ion to the orbitals of the porphyrin ligand; the transfer includes both the σ- and π^* (back binding). Institute of Molecular and Atomic Physics, Belarus Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 3, pp. 507–513, May–June, 1996.     

29Si NMR investigations on oligosilane dendrimers

Starting with the high functionalized trisilane SiClMe(SiCl₂Me)₂ and tetrasilane SiMe(SiCl₂Me)₃ several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the ²⁹Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by ²⁹Si NMR. Received: 3 June 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

Assignment of E/Z isomers in Schiff bases of 3-acyltetramic acids with ethylenediamine by 1H and 13C NMR spectroscopy

The reaction of ethylenediamine with an equivalent mixture of diversely substituted 3-acyltetramic acids leads to Z/Z, Z/E, E/Z and E/E isomers. The E/Z isomerisation is slow in the NMR time scale of the ¹H and ¹³C chemical shifts; therefore at room temperature and in deuterochloroform all isomers of the new synthesized asymmetric compounds N,N′-ethylene-(1-ethyl-5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) a, N,N′-ethylene-(5,5-dimethyl-1′,5′,5′-trimethyl-3,3′-acetyltetramic acid) b and, N,N′-ethylene-(1,5,5-trimethyl-1′,5′,5′-trimethyl-3-acetyl-3′-formyl-tetramic acid) c could be found in the corresponding spectra. To assign the ¹³C NMR signals we used two-dimensional ¹³C-¹H one-bond (HMQC) and ¹³C-¹H multibond (HMBC) correlated spectroscopy and the empirical rule that CO signals involved in hydrogen bonds are shifted to a lower field. The relative stability of isomers depending on substitution pattern could be estimated from the composition of the equilibria. b crystallizes as Z/Z isomer from ethanolic solution. The X-ray structural analysis of b has shown two CH-O hydrogen bonds. Received: 31 May 1996 / Revised: 26 June 1996 / Accepted: 1 July 1996     

Di-tert-butyl(N-pyrrolyl)phosphane,-sulfide, and-selenide, studied by multinuclear magnetic resonance

 Di-tert-butyl(N-pyrrolyl)phosphane (1),-sulfide (2) and-selenide (3) were studied by ¹H, ¹³C, ¹⁵N, ³¹P and ⁷⁷Se NMR spectroscopy in solution. Restricted rotation about the P–N bond was observed for 1 (ΔG^≠ _C≈58.5 kJ/mol) and 2, 3 (ΔG^≠ _C≈45 kJ/mol) by ¹H and ¹³C NMR at variable temperature. The fairly high pyrrolyl rotation barrier in 1 is ascribed to the expected steric effects exerted by the tert-butyl groups and to repulsion between the lone pairs of electrons at the phosphorus and nitrogen atoms. These repulsive forces are reduced in 2 or 3, or in di-tert-butyl(phenyl) phosphane (ΔG^≠ _C≈44 kJ/mol). Signs of coupling constants ⁿJ(³¹P, ¹³C) and ⁿ⁺¹J(³¹P, ¹H) (n=2, 3) were determined by two-dimensional (2D) ¹³C/¹H heteronuclear shift correlations. The preferred orientation of the pyrrolyl group in 1 is evident from the coupling constants ²J(³¹P, ¹³C(2))=+35.4 Hz and ²J(³¹P, ¹³C(5))=−9.3 Hz, typical of C(2) in syn and C(5) in anti position with respect to the assumed axis of the phosphorus lone pair. Hahn-echo extended (HEED) polarization transfer pulse sequences served for measuring ¹J(³¹P, ¹⁵N) and isotope induced chemical shifts ¹Δ^15/14N(³¹P) from ³¹P NMR spectra. Received: 4 April 1996/Revised: 6 May 1996/Accepted: 11 May 1996     

Di-tert-butyl(N-pyrrolyl)phosphane,-sulfide, and-selenide, studied by multinuclear magnetic resonance

 Di-tert-butyl(N-pyrrolyl)phosphane (1),-sulfide (2) and-selenide (3) were studied by ¹H, ¹³C, ¹⁵N, ³¹P and ⁷⁷Se NMR spectroscopy in solution. Restricted rotation about the P–N bond was observed for 1 (ΔG^≠ _C≈58.5 kJ/mol) and 2, 3 (ΔG^≠ _C≈45 kJ/mol) by ¹H and ¹³C NMR at variable temperature. The fairly high pyrrolyl rotation barrier in 1 is ascribed to the expected steric effects exerted by the tert-butyl groups and to repulsion between the lone pairs of electrons at the phosphorus and nitrogen atoms. These repulsive forces are reduced in 2 or 3, or in di-tert-butyl(phenyl) phosphane (ΔG^≠ _C≈44 kJ/mol). Signs of coupling constants ⁿJ(³¹P, ¹³C) and ⁿ⁺¹J(³¹P, ¹H) (n=2, 3) were determined by two-dimensional (2D) ¹³C/¹H heteronuclear shift correlations. The preferred orientation of the pyrrolyl group in 1 is evident from the coupling constants ²J(³¹P, ¹³C(2))=+35.4 Hz and ²J(³¹P, ¹³C(5))=−9.3 Hz, typical of C(2) in syn and C(5) in anti position with respect to the assumed axis of the phosphorus lone pair. Hahn-echo extended (HEED) polarization transfer pulse sequences served for measuring ¹J(³¹P, ¹⁵N) and isotope induced chemical shifts ¹Δ^15/14N(³¹P) from ³¹P NMR spectra. Received: 4 April 1996/Revised: 6 May 1996/Accepted: 11 May 1996     

29Si NMR investigations on oligosilane dendrimers

Starting with the high functionalized trisilane SiClMe(SiCl₂Me)₂ and tetrasilane SiMe(SiCl₂Me)₃ several octa- and decasilane dendrimers containing directly neighboured branchings were prepared. In these compounds the ²⁹Si NMR chemical shifts of the different silyl groups are shifted towards lower field compared with those of analogous groups in tetra- or hexasilanes. This observation is a helpful tool for the characterization of further dendritic oligomers by ²⁹Si NMR. Received: 3 June 1996 / Revised: 3 July 1996 / Accepted: 9 July 1996     

Application of derivative UV spectrophotometry to the simultaneous determination of nitrate and nitrite ions in bath solutions for alkaline black-oxidation of steel

Second order derivative spectrophotometry was applied to the determination of nitrite and nitrate ions in bath solutions for alkaline black-oxidation of steel. The measurements were directly taken after dilution of the samples at λ = 336.4 nm for NO₃ ^– and λ = 390 nm for NO₂ ^–. The method was checked on artificial mixtures and applied to real samples containing approximately 5.5% NaNO₂ and 6% NaNO₃. The results agree well with those obtained by the standard manganometric method. Received: 8 July 1996 / Revised: 24 September 1996 / Accepted: 28 September 1996     

Analysis of the interaction of ethidium bromide with a DNA octamer 5’-d(GpApCpApTpGpTpC) in aqueous solution using1H NMR data

Complexation of a phenanthridine dye ethidium bromide with a desoxyoligonucleotide 5’-d(GpApCpAp-TpGpTpC) in aqueous salt solution is studied by one- and two-dimensional¹H NMR spectroscopy. Two-dimensional correlated homonuclear PMR spectroscopy (2D-TOCSY and 2D-N0ESY) was used for complete assignment of the proton signals of molecules in solution and for qualitative analysis of the character of interaction between ethidium bromide and desoxyoctanucleotide. The concentration dependences of the proton chemical shifts of the molecules were measured at three temperatures (T₁ = 298 K, T₂ = 308 K, and T₃ = 318 K); the temperature dependences were measured in the temperature range 278–358 K. Different schemes of dye complexation with an octamer duplex involving different molecular associates in solution are considered. The equilibrium constants of the reactions, the corresponding thermodynamic parameters (δH⁰, δS₀), and the limiting values of the chemical shifts of ethidium bromide protons in the complexes are determined. The relative contents of complexes of different types in solution (dye complexes with desoxyoctanucleotide in duplex form) are analyzed, and peculiarities of the dynamic equilibrium depending on the ratio of dye and octamer concentrations and temperature are established. The most probable structures of the 1:2 and 2:2 intercalated complexes corresponding to dye intercalation into the pyrimidine-purine sites of the desoxyoctanucleotide duplex are derived using the calculated values of the induced proton chemical shifts of ethidium bromide and two-dimensional PMR data. Translated fromZhurnal Strukturnoi Khimii, Vol.40, No. 2, pp. 265–275, March–April, 1999.     

Simultaneous comparison of δ31P and 1JPN for the assignment of E/Z-stereochemistry of the phosphorus-nitrogen double bond in iminophosphines R-P=N-R′

 The analysis of ³¹P and ¹⁵N NMR data of a series of 40 iminophosphines R-P=N-R′ reveals that the E/Z-stereochemistry of the PN double bond can be predicted on the basis of a simultaneous comparison of the values of δ³¹P and ¹J_PN. Received: 31 May 1996/Revised: 2 July 1996/Accepted: 5 July 1996     

Identification of reaction products of mild oxidation of H2S in solution and in solid state by UV-VIS spectroscopy

 UV-VIS spectroscopic investigations were carried out on several sulphur-compounds to attribute the absorption bands (290, 302, 330 nm) observed by in-situ reflectance spectroscopy to particular S_xO^2- _y and S^2- _x species. It was possible to assign the absorption bands to S₂O^2- ₃, S^2- ₂ and S₂O^2- ₄. These species are relevant in the catalytic oxidation of H₂S over alumina. Received: 11 January 1996/Revised: 4 April 1996/Accepted: 9 April 1996     

Simultaneous comparison of δ31P and 1JPN for the assignment of E/Z-stereochemistry of the phosphorus-nitrogen double bond in iminophosphines R-P=N-R′

 The analysis of ³¹P and ¹⁵N NMR data of a series of 40 iminophosphines R-P=N-R′ reveals that the E/Z-stereochemistry of the PN double bond can be predicted on the basis of a simultaneous comparison of the values of δ³¹P and ¹J_PN. Received: 31 May 1996/Revised: 2 July 1996/Accepted: 5 July 1996     

Determination of trace elements in AR grade alkali salts after preconcentration by column solid-phase extraction on TiO2 (anatase)

 Column solid-phase extraction using TiO₂ (anatase) as a solid sorbent was applied to preconcentrate traces of Cd, Co, Cu, Fe, Mn, Ni and Pb from AR grade alkali salts prior to their measurements by atomic absorption spectrometry (AAS). Multi-element preconcentration was achieved from NaCl, KCl, KNO₃, NaNO₃, CH₃COONa, NaHCO₃ and Na₂CO₃ solutions, whereas the sorption of trace elements from phosphates and sulfates is not quantitative. Optimal conditions (recoveries of the analytes >95%) for solid-phase co-extraction of the most common heavy metal ions are proposed. The conditions for quantitative and reproducible elution and subsequent AAS are established. A method of determination of trace elements in different salts is proposed. It is characterized by precision, reproducibility and a high preconcentration factor. The solid-phase extraction by TiO₂, combined with ETAAS allows the determination of 0.1 ng g^-1 Cd, 2 ng g^-1 Co, 1 ng g^-1 Cu and Ni, 0.5 ng g^-1 Mn and 0.4 ng g^-1 Pb. Received: 1 April 1996/Revised: 24 June 1996/Accepted: 9 July 1996