Critical comments on accuracy of quantitative determination of natural humic matter by solid state (13)C NMR spectroscopy

Structural information of natural organic matter (NOM) at the molecular level is very essential in understanding their nature and reactivity. Nuclear magnetic resonance (NMR) is an excellent tool for estimating the gross chemical composition of the very complex humic matter (HM). A well-known fact is that the solid state ¹³C NMR spectral analysis is very parameter-sensitive especially in the study of the heterogenous HM (e.g. baseline corrections, different pulse techniques and spinning rates of the rotor vs. different disruptive sidebands in the spectra). This being the case, it has been emphasized the importance of qualitative and quantitative analyses for generating as real spectra as possible by means of different pulse and polarization techniques, sampling spinning rates as well as certain correction factors. In the present study a practical accuracy for quantitative determination of NOM type material by solid state ¹³C NMR spectroscopy was assessed using a known HM sample. Different magnetic-field strengths, sampling spinning rates, single and ramped amplitude cross polarization techniques and TOSS pulse sequence were applied for obtaining a more reliable insight into the disruptive effect of the chemical shift anisotropy (CSA), especially the most disturbing first order spinning side bands (SSB). The results demonstrated that the SSB problem is not so significant as sometimes stated, at least in the context of HM samples and in the light of the overall reproducibility and uncertainty connected with the sample itself.     

Structural Characterisation of the Coloured Organic Matter from an Eucalyptus Bleached Kraft Pulp Mill Effluent

Abstract

XAD-8 and XAD-4 resins in tandem were used to isolate and fractionate the coloured organic matter from an eucalyptus bleached Kraft pulp mill effluent which is discharged into river Vouga (Portugal) near the lagoon that exists in its terminal part. The composition of the isolated organic matter was investigated by FTIR and CPMAS-¹³C-NMR and compared to that of humic matter isolated before from the same river at a non-polluted site and a site very contaminated with the effluent of a sulphite pulp mill. The results put into evidence that the organic matter from both kinds of effluent is more aromatic and contains more lignin derived structural units than the humic matter from the unpolluted site. However, the organic matter from the sulphite pulp mill effluent is more soluble due to its content of sulphonic functional groups.     

Advanced CPMAS-13C NMR techniques for molecular characterization of size-separated fractions from a soil humic acid

A humic acid extracted from a volcanic soil was subjected to preparative high-performance size-exclusion chromatography (HPSEC) to reduce its molecular complexity and eleven different size fractions were obtained. Cross-polarization magic-angle spinning ¹³C NMR (CPMAS ¹³C NMR) analysis performed with variable contact-time (VCT) pulse sequences showed that the largest molecular-size fractions contained aromatic, alkyl, and carbohydrate-like components. The carbohydrate-like content and the alkyl chain length seemed to decrease with decreasing molecular size. Progressive reduction of aromatic carbon atoms was also observed with decreasing molecular size of the separated fractions. Mathematical treatment of the results from VCT experiments enabled cross polarization (T _CH) and proton spin–lattice relaxation () times to be related to structural differences among the size fractions. The conformational distribution indicated that the eleven size fractions could be allocated to two main groups. The first group, with larger nominal molecular sizes, was characterized by molecular domains with slower local molecular motion. The second group of size fractions, with smaller nominal molecular sizes, was characterized by a larger number of molecular domains with faster local molecular motion. The T _CH and values suggested that either condensed or strongly associated aromatic systems were predominant in the size fractions with the largest apparent molecular dimensions.     

Polymerization of Bis(Pyridine)bis-(2,4,6-tribromophenoxo)copper(II) Complex (Py2Cu(TBrP)2) by Electrooxidation and Structural Characterization by 1H-NMR, 13C-NMR,and FTIR Spectroscopies

Abstract

Electroinitiated polymerization of bis(2,4,6-tribromophenoxo)- bis(pyridine)copper(II) complex was achieved in dimethylformamide-tetrabutylammonium tetrafluoroborate solvent-electrolyte couple under air or nitrogen at room temperature by constant potential electrolysis. Polymerization conditions were based on the peak potentials measured by cyclic voltammetry. The structural analyses of the polymers were done by ¹H-NMR, ¹³C-NMR, and FTIR spectral analyses along with molecular weight measurements by cryoscopy. The poly(dibromo phenylene oxide)s obtained only at oxidation potentials in either atmosphere were found to be highly linear, indicating mainly 1,4-catenation was taking place.     

An Au(III) complex of glycyl- S -serine: a linear polarized IR and 1H- and 13C-NMR investigation

The structure of a mononuclear Au(III) complex of the dipeptide glycyl-S-serine (Gly-Ser) has been predicted using solid-state linear dichroic IR (IR-LD) spectroscopy, based on an orientation technique in a nematic liquid crystal suspension. Results are compared with data from ¹H- and ¹³C-NMR, MS, elemental analysis, thermogravimetry and differential scanning calorimetry. The metal ion is coordinated as a tridentate through NH₂, N (from deprotonated amide) and O (COO^?) groups to form [Au(C₅H₉N₂O₄)Cl], with the fourth position of the square-planar coordination sphere being completed by a Cl^? ion.     

Chemical Composition of the Essential Oils of <Emphasis Type="Italic">Bunium elegans</Emphasis> and <Emphasis Type="Italic">Bunium caroides</Emphasis>

Analyses of the essential oils of Bunium elegans (Fenzl) Freyn and B. caroides (Boiss.) Hausskn. ex Bornm., using GC, GC/MS, and¹³ C-NMR spectroscopy resulted in identification of their chemical constituents. The oils of both species contain mainly the sesquiterpene hydrocarbons germacrene-D and E-caryophyllene, which amounted to 24.1% and 38% for B. elegans and 22.1% and 26.6% for B. caroides respectively. The oil of B. caroides contained the monoterpenes α-pinene and Z-β-ocimene in 4.1 and 5.9% respectively, while traces of monoterpenes were detected for B. elegans. On the other hand, in B. caroides the phenylpropanoid derivatives asaricin (7.5%) and dillapiole (10.2%) were among the major constituents. __________ Published in Khimiya Prirodnykh Soedinenii, No. 4, pp. 335–336, July–August, 2005.     

Synthesis and structural characterization of a new polymeric zinc(II) complex with thiophene-2-carboxylic acid

A new polymeric zinc(II) complex with thiophene-2-carboxylic acid (α-tpc) of composition [Zn₂(C₂₀H₁₂O₈S₄)] _n was obtained and structurally characterized by X-ray diffraction, thermal analysis, nuclear magnetic resonance (NMR), and infrared spectroscopies. Upfield shift in the ¹H-NMR spectrum is explained by the crystalline structure, which shows the thiophene rings overlapping each other in parallel pairs. The compound crystallizes in the monoclinic system, space group P2₁/c, with a = 9.7074(4) Å, b = 13.5227(3) Å, c = 18.9735(7) Å, β = 95.797(10)°, and Z = 4. Three α-tpc groups bridge between two Zn(II) ions through oxygens and the fourth one bridges between one of these ions and the third one, symmetry related by a twofold screw axis. This arrangement gives rise to infinite chains along the crystallographic a direction. The metal atoms display an approximate tetrahedral configuration. The complex is insoluble in water, ethanol, and acetone, but soluble in dimethyl sulfoxide.     

FTIR and NMR studies of bis(oxaalkyl) sulphates(IV) and their complexes with proton and some metal cations

The complexation of Li⁺ and Na⁺ cations by three bis(oxaalkyl) sulphates(IV) was studied by FTIR and NMR on ¹H, ¹³C, ⁷Li and ²³Na nuclei. The NMR results have proved the formation of complexes and the fluctuation of Li⁺ and Na⁺ cations in respective circular arrangements. In the FTIR spectra of protonated sulphates intense continuous absorptions were observed indicating fast fluctuation of the protons in the respective multiminima potentials. The continuous absorptions in the far infrared region of the FTIR spectra of Li⁺ or Na⁺ complexes with three bis(oxaalkyl) sulphates(IV) indicate fast fluctuations of Li⁺ or Na⁺ cations between O-atoms of the oxaalkyl chains. The independence of the shape of the continua on the length of the oxaalkyl chains, i. e. the number of minima in the multiminima potential, demonstrates that the fluctuation of cations occurs in the respective circular arrangements.     

NMR spectroscopic study of the (Z)/(E)-isomerism of 1-aryl-3-arylamino-2-propen-1-ones in solution and in the crystalline state

Summary ¹H,¹³C, and CP/MAS¹³C NMR spectra of sixp-substituted 1-aryl-3-arylamino-2-propen-1-ones in solution and in the solid state are reported and discussed. In the proteon-accepting solvent dimethylsulfoxide, electronegative substituents shift the isomeric equilibrium to the (E)-isomer. Bulky substituents promote crystallization of the (Z)-form.

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NMR-Spektroskopische Untersuchung der (Z)/(E)-Isomerie von 1-Aryl-3-arylamino-2-propen-1-onen in Lösung und im Kristallzustand (Kurze Mitt.)

Zusammenfassung ¹H-,¹³C- und CP/MAS-¹³C-NMR Spektren von sechsp-substituierten 1-Aryl-3-arylamino-2-propen-1-onen in gelöstem und festem Zustand werden berichtet und diskutiert. In protonenakzeptierendem Dimethylsulfoxid verschieben elektronegative Substituenten das Gleichgewicht zum (E)-Isomer. Große Substituenten begünstigen die Kristallisation in der (Z)-Form.

     

Crystal structure,optical and magnetic properties of the bis(perchlorate) of 3,4-diaminopyridine

3,4-diaminopyridinium bis(perchlorate) has been synthesized and its crystal structure has been solved by single crystal X-ray diffraction. The optical and magnetic properties of the N1, N4 protonated 3,4-diaminopyridinium dication have been elucidated in solution and in the solid-state by means of linear-polarized solid state IR-spectroscopy (IR-LD), UV-spectroscopy, TGA, DSC, and positive and negative ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data, and electronic spectra of the dication. The studied compound crystallizes in the noncentrosymmetric space group Cc and exhibits infinite molecular chains formed by 3,4-diaminopyridinium dications and ClO ₄ ^? anions along the c-axis by moderate intermolecular NH ₃ ⁺ ···OClO ₃ ^? interactions with bond lengths of 3.031, 3.024, 2.825, and 2.875 Å. The NH group participates in intermolecular NH···OClO ₃ ^? contacts with bond lengths of 3.220 and 3.172 Å, respectively. The effect of N1, N4 diprotonation on the optical and magnetic properties of the 3,4-diaminopyridinium dication is discussed.     

Structural determination of Zn and Cd-DTPA complexes: MS, infrared, (13)C NMR and theoretical investigation

The joint application of MS, infrared and (13)C NMR techniques for the determination of metal-DTPA structures (metal=Zn and Cd; DTPA=diethylenetriaminepentacetic acid) is reported. Mass spectrometry allowed determining the 1:1 stoichiometry of the complexes, while infrared analysis suggested that both nitrogen and carboxyl groups are sites for complexation. The (13)C NMR spectrum for the cadmium-containing complex evidenced the existence of free and complexed carboxyl groups, due to a straight singlet at 179.0 ppm (free carboxylic (13)C) and to two broad singlets or a broad doublet at 178.3 ppm (complexed carboxylic (13)C, (2)J(Cd-C(=O))=45.2 Hz). A similar interpretation might be given for the zinc derivative and, with the aid of DFT calculations, structures for both complexes were then proposed.     

ENZYMATICALLY SYNTHESIZED POLYANILINE IN THE PRESENCE OF A TEMPLATE POLY(VINYLPHOSPHONIC ACID): A SOLID STATE NMR STUDY

Template guided enzymatic synthesis of conducting polyaniline (PANI) is a one-step reaction and more importantly, it is an environmentally friendly process. Understanding of the reaction and coupling mechanism at the molecular level is of paramount significance to improve its processability and conductivity. Solid-state NMR techniques are useful to investigate molecular structures of enzymatically synthesized polyaniline (PANI). The PANI sample in three different forms i.e., (a) as-synthesized, self-doped conducting form; (b) dedoped, base form and; (c) redoped, conducting form, are investigated by solid-state ¹³C and ¹⁵N CP/MAS NMR techniques. Solid-state NMR data analysis shows that the structural features of enzymatically synthesized PANI are similar to that of chemically synthesized PANI. The solid-state ¹³C CP/MAS NMR spectrum of the base form of PANI confirmed that benzenoid-quinoid repeating units are present in the backbone of the PANI polymer chain. The poly(vinylphosphonic acid) (PVP) template provides charge compensation during the chain growth of linear polyaniline. After the completion of template-guided synthesis of PANI, it is now possible that the PVP template can be completely removed from the complex by dedoping with aqueous NH₄OH. The detached PANI from the PANI-PVP complex can then be redoped to conducting form without the presence of the template. The conductivity of the PANI and PANI-PVP complex are of the same order of magnitude. The solid-state ¹⁵N CP/MAS NMR chemical shifts are sensitive to charge distribution on the nitrogens in the backbone. The solid-state ¹⁵N CP/MAS NMR spectrum of the base form of the enzymatically derived PANI sample showed the clear signature for benzenoid-quinoid repeating units in the polymer backbone.

     

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.     

Comparability of composition of carbon functional groups in humic acids between inverse-gated decoupling and cross polarization/magic angle spinning 13C nuclear magnetic resonance techniques

To find a certain relation between the composition of carbon functional groups of humic acids derived from liquid state ¹³C nuclear magnetic resonance (NMR) spectra acquired with inverse-gated decoupling (IGD), known as a quantitative pulse sequence, and that by solid-state ¹³C NMR with cross polarization/magic angle spinning (CPMAS) techniques, fifteen soil humic acid samples with a wide range of aromaticity were analyzed. Relationships between the proportions of humic acid carbon as alkyl, O-alkyl, and aromatic carbon assessed by the two methods could be regressed to y = ax (r = 0.932-0.956; P < 0.005), respectively. The contents of alkyl, O-alkyl, and aromatic carbon assessed by CPMAS method were larger than those found by IGD method. However, the differences between the two methods were small and exclusive regression to y = x was also significant (r = 0.775-0.941; P < 0.005). Aromaticity calculated from ¹³C CPMAS NMR data also did not differ significantly from those computed from ¹³C NMR spectra with IGD. These observations indicated the comparability of the relative content of carbon functional groups in humic acids except for carboxyl and carbonyl carbon.     

Synthesis and Hydrolysis of Hybridized Silicon Alkoxide: Si(OEt)x(OBut)4-x. Part I: Synthesis and Identification of the Si(OEt)x(OBut)4-x

Using silicon tetrachloride (SiCl₄), tert-butanol (t-BuOH), ethanol (EtOH) and NH₃, the hybridized silicon ethoxide 3-tert-butoxide (Si(OEt)_x(OBu^t)_4-x) was synthesized and the configuration of the material was investigated by FT-IR,¹ H and ¹³C NMR and gas chromatogram/mass spectrum (GC/MS) techniques. The results confirm that both the ethoxy and the tert-butoxy groups have been attached to silicon atoms. Furthermore, the alkoxy group types and their relative amounts in the alkoxide were also determined by ¹H and ¹³C NMR and GC/MS.     

Poly(DMI-1, 2-Diazinediylethene-l, 2-Diols)

Oligomers of 2 to 9 units having a diazinediylethene-1, 2-diol repeating unit have been prepared by a cyanide ion-catalyzed self-condensation of pyridazine-3, 6-, pyrazine-2, 5-, or pyrimidine-4, 6-dialdehyde. These are the first known representatives of a class of conjugated polymeric enediol materials derivable specifically from these three structurally related diazine dialdehydes. The oligomers, isolated as their potassium salts, are soluble in acid and base with an isoelectric point at pH 6.5. In base, they give dark red-brown solutions whose color, attributable to their semidione ion radical form, is rapidly discharged by oxygen (air) or by the addition of ferric ion, which gives an immediate precipitation of the black chelate. Of several possible methods evaluated for the preparation of the free dialdehydes, only that involving ozonization of the distyryldiazines was found to be of preparative value.     

Formation of dihydroperoxide derivatives during the oxidation of cyclohexene and tetralin by dioxygen

¹H- and¹³C-NMR investigations revealed that prolonged oxidation of unsubstituted cyclohexene and tetralin, containing symmetrical and weak allylic and benzylic CH bonds, results in the formation of both mono- and dihydroperoxo derivatives.     

Structural and spectral studies of 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one and its diorganotin(IV) complexes

Two diorganotin(IV) complexes of the general formula R₂Sn[Ph(O)CCH-C(Me)N-C₆H₄(O)] (R = Ph, 1a; R = Me, 1b) have been synthesized from the corresponding diorganotin(IV) dichlorides and the ligand, 3-(2-hydroxyphenylimino)-1-phenylbutan-1-one (1) in methanol at room temperature in presence of triethylamine. Both compounds have been characterized by elemental analyses, IR and ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn NMR spectra. The structures of the free ligand and the complexes have been confirmed by single crystal X-ray diffraction. There are three independent molecules in the crystal structure of the ligand 1 and in all three the O-bound proton is transferred to the imine nitrogen and makes an intramolecular N-H?O hydrogen bond with the carbonyl oxygen. In turn this makes an intermolecular hydrogen bond with the phenolic H atom. The crystal structure of 1 is trigonal and a new polymorph; triclinic and monoclinic forms have already been published. In 1a, the central tin atom adopts distorted trigonal-bipyramidal coordination geometry whereas in dimeric 1b it is distorted octahedral when including the intermolecular Sn-O(phenolic) bond [2.7998(20) Å]. The δ (¹¹⁹Sn) values for the complexes 1a and 1b are −306.6 and −127.9 ppm, respectively, thus indicating penta-coordinated Sn centres in solution.     

A multinuclear NMR study in the solid state and in solution of thallium(I) tris-(pyrazol-1-yl)borates (thallium scorpionates)

The ¹H, ¹³C and ¹⁵N NMR spectroscopic properties of six thallium tris-(pyrazol-1-yl)borates, including a tetrakis derivative, were determined. The results in solution were necessary to understand those, more complicated, in the solid state. A collection of ²⁰⁵Tl-¹⁵N and ²⁰⁵Tl-¹³C couplings was measured in the latter state. Among those, a very large coupling constant (between 194 and 282 Hz) has been measured on the carbon at the position 4 of the pyrazole ring in several compounds and particularly for the cyclobutyl derivative [Tl(Tp^Cbu)]. It has been assigned to a direct interaction of the 4-C-H ? Tl type and related to the X-ray structures, when available.     

Structure and spectroscopy of diorganotin(IV) complexes derived from N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide

Three new diorganotin(IV) complexes of the general formula R₂Sn[3-(OMe)-2-OC₆H₃CHN-NC(O)Ph] (R = Ph, Ia; R = Me, Ib; R = n-Bu, Ic) have been synthesised from the corresponding diorganotin(IV) dichlorides and the ligand, N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide in methanol at room temperature in the presence of trimethylamine. All the complexes have been characterized by elemental analysis, IR and ¹H, ¹³C, ¹⁵N, ¹¹⁹Sn NMR spectra, and their structures have been confirmed by single crystal X-ray diffraction analysis of one representative compound Ia. Complex Ia crystallises in the orthorhombic system, space group Pna2₁ with a = 12.424(5), b = 9.911(5), c = 18.872(5) Å; Z = 4. The ligand N′-(2-hydroxy-3-methoxybenzylidene)benzohydrazide (H₂L) coordinates to the metal centre in the enolate form via the phenolic O, imino N and enolic O atoms. In Ia, the central tin atom adopts a distorted trigonal bipyramidal coordination geometry with the oxygen atoms in axial positions, while the imino nitrogen atom of the Schiff base and the two phenyl groups occupy the equatorial sites. The δ(¹¹⁹Sn) values for the complexes Ia, Ib and Ic are −327.3, −151.7 and −187.2 ppm, respectively, thus indicating penta-coordinated Sn centres in solution.