The analysis of indigoid dyes as leuco forms by NMR spectroscopy*

¹H and ¹³C NMR spectra of halogen- and alkoxy-substituted indigoid dyes (indigotins), and of some unknown deuterated indigotins as leuco forms (i.e., reduced forms or ‘vats’), in deuterium oxide are recorded and discussed. NMR spectroscopy is a useful technique for the identification and characterisation of this traditional class of vat dyes.     

The analysis of indigoid dyes by mass spectrometry

High–resolution mass spectrometry provides an expeditious technique for positively identifying indigoid dyes of molluscan origin. Indigoids on modern and ancient textile fibres, as well as indigoid mixtures produced by reactions, are discussed. Steam treatment of the fibre or isolation of the dye by solvent extraction permits the analysis by mass spectrometry of dyes which bind more tightly to fibres, such as 6, 6′-dibromoindigotin (C. I. 75800, Natural Vat Dye). The demonstration of the stepwise photolytic denomination of the leuco base of 6, 6′-dibromoindigotin may be of more far-reaching significance in distinguishing between natural and intentional mixtures of indigotin and its dibromo derivative.     

Identification of different hydrogen-reduced titania crystallographic forms by1H NMR spectroscopy

¹H NMR spectra are presented as a function of temperature where hydrogen associated with both crystal modifications of hydrogen-reduced titania can be resolved. In addition, further fine-structure can be resolved as a doublet on both of the two main signals. These doublets are of low intensity and may correspond to hydrogen in two different isolated and dynamically static interstitial sites in each crystal lattice.     

HPLC analysis of the natural scale insect,madder and indigoid dyes

A linear gradient elution method has been applied to the HPLC analysis of plant and scale insect red anthraquinonoid mordant dyes and molluscan blue and red-purple indigoid vat dyes. The method enables the use of the same elution program for the determination of different chemical classes of dyes. In addition, it significantly shortens the retention times of natural anthraquinonoid dyes over those previously published. For the first time a new dye, probably dibromoindirubin, has been detected in the Murex trunculus sea snail. The dye families investigated include the ones most often found on ancient textiles and shards from dyeing vessels in Israel and other regions.     

Novel symmetrical and asymmetrical disaryl hydrazono sulphur-containing direct dyes as possible alternatives for benzidine-based dyestuffs

Two novel series of disaryl azo 2-(thiadiazin-2-yl)-1,2,4-benzothiadiazine-based direct dyes have been synthesized. The produced dyes, being accommodating solubilizing functions, are likely to undergo oxidation and/or hydrolysis to soluble metabolites thus ensure lack of carcinogenicity and in turn, might satisfy the basic requirements for a satisfactory replacement of the prohibited benzidine-based dyes.The assigned structures for the hitherto prepared dyes were confirmed on the basis of elemental analysis and spectral data and, whenever possible, by alternative synthetic routes. Moreover, the predominant tautomeric forms for these highly colored dyes were tested and discussed on the basis of different spectral investigations.     

Stabilizer insights by NMR spectroscopy

During the past decade, advances in both hardware and software have made NMR spectroscopy an enormously powerful analytical technique. In this paper, the author presents examples of the use of NMR in support of vinyl stabilizer research; he also covers representative practical applications of proton, carbon, phosphorus, and tin NMR.     

The chemical composition of the indigoid dyes derived from the hypobranchial glandular secretions of Murex molluscs

The composition of the indigoid dyes and their precursors derived from the hypobranchial glandular secretions of Murex trunculus and Murex brandaris have been determined by high-resolution mass spectrometry. M trunculus secretions yielded three dyes: 6,6′-dibromoindigotin (DBI; CI 75800), indigotin (Cl Natural Blue 1; Cl 75780) and 6-bromoindigotin (MBI), the latter reported here for the first time. Indirubin (Cl Natural Blue 1; Cl 75790) constituted a relatively small amount of the final dye product. No statistically significant sexual differentiation in the final dye colorations was observed when the secretions were fully developed in light. When developed in the dark, male glandular secretions were more purple than those of pseudohermaphroditic females, implying that male glands contain less of the unsubstituted indoxyl precursors, which oxidatively couple in air to form blue indigotin and MBI. M brandaris yielded solely DBI and its precursor the 6-bromo-2-methylthioindoxyl (tyrindoxyl); no methylsulphone precursor was observed, although reported by earlier investigators. Moreover, exposure to light was found to be critical for the formation of the greenish-coloured intermediate 2,2′-bis-substituted 6,6′-dibromo-2,2′-di-indoxyl, not only for the latter's decomposition to DBI.     

Analysis of oxidized moiety of partially periodate-oxidized cellulose by NMR spectroscopy

Periodate-oxidized celluloses (S-100, S-70, S-50) with different degrees of oxidation were prepared. It is presented in this article that oxidized moieties of partially periodate-oxidized cellulose are determined from analyses of ¹H and ¹³C nuclear magnetic resonance (NMR) spectra of those reduction products and the corresponding polytriacetates.     

The curing of an epoxy resin as followed by carbon-13 NMR spectroscopy

Variable-temperature carbon-13 NMR spectroscopy was used to examine the curing reaction of DGEBPA with piperidine. An initial adduct was directly observed and the disappearance of monomer could be conveniently followed. Unreacted epoxide carbons were detectable in cured samples.     

Strain-induced crystallization of natural rubber as studied by high-resolution solid-state C NMR spectroscopy

A series of high-resolution solid-state ¹³C NMR experiments were performed on both unstretched and in situ stretched natural rubber samples. From the ¹³C CP/MAS spectra, it was found that natural rubber does form small crystals at room temperature though the degree of crystallinity is very small. Furthermore, from the ¹³C DD/MAS spectra, the crystalline signals were found to increase with the increase of draw ratio. ¹³C spin-lattice relaxation time (T₁) and ¹H spin-spin relaxation time (T₂) of in situ stretched natural rubber were measured for the first time, which provided further evidences for the conclusion that there exist crystals in both stretched and unstretched natural rubber samples. Quantitative ¹³C NMR measurements indicated that strain-induced crystallization occurs when the draw ratio reaches about 2.0 and the maximum crystallinity of our natural rubber samples can be as high as 19.3% upon stretching.     

Crystallization of magnesium substituted aluminophosphate of type-36 as studied by solid-state NMR spectroscopy

The crystallization process of aluminophosphate molecular sieve MgAPO-36 is characterized by the evolution of intermediate gels. Multinuclear solid-state NMR techniques in combination with powder X-ray diffraction (PXRD) and scanning electron microscopy (SEM) reveal in detail the nature of the intermediate gels and their evolution into crystalline structure. The long-range ordering of the aged as well as heated intermediate gels are probed by PXRD, showing that the crystallization of the framework begins after heating the gels at 423 K for 1.5 h. ³¹P NMR indicated that the structural Al–O–P and Mg–O–P units from the ATS framework are formed at the same time. More information about the local ordering of the gels is obtained from two-dimensional ²⁷Al → ³¹P HETCOR and ¹H → ³¹P CP/MAS experiments. Two types of microstructure regions could be differentiated by partially and fully condensed P species, in which five types of P(nAl) (n = 2–4) units are identified by ³¹P/²⁷Al double-resonance experiments. A possible evolution mechanism consisting of three stages is proposed for the crystallization process.     

Analysis of Lignins as Propionate Derivatives by NMR Spectroscopy

Lignin propionates were prepared by treating lignin samples with propionic anhydride in pyridine solution and the derivatives obtained were examined by NMR spectroscopic methods. ¹H NMR spectroscopy of lignin propionates offers a possibility to determine the number of hydroxyl groups based on the methyl proton signal (δ ～ 1.2) as well as the methylene proton signal (δ ～ 2.5) of the propionate groups. It was found to be advantageous to use propionate derivatives for the analysis of hydroxyl groups in lignin products exhibiting signals (from >CH- and -CH₂- groups) that interfere with the acetate group signals. Analysis of ester groups by ¹³C NMR spectroscopy gave practically the same results as those earlier reported for acetate derivatives.     

Electrokinetic transport of water and methanol in Nafion membranes as observed by NMR spectroscopy

Electrophoretic NMR (eNMR) and pulsed-field-gradient NMR (PFG-NMR) methods were used to study transport processes in situ and in a chemically resolved manner in the electrolyte of an experimental direct methanol fuel cell (DMFC) setup, constituted of several layers of Nafion 117. The measurements were conducted at room temperature for membranes fully swollen by methanol-water mixtures over a wide concentration interval. The experimental setup and the experimental protocol for the eNMR experiments are discussed in detail. The magnitude of the water and methanol self-diffusion coefficients show a good agreement with previously published data while the ratio of the two self-diffusion coefficients may indicate an imperfect mixing of the two solvent molecules. On the molecular level, the drag of water and methanol molecules by protons is roughly of the same magnitude, with the drag of methanol molecules increasing with increasing methanol content. The electro-osmotic drag defined on mass-flow basis increased for methanol from a low level with increasing methanol concentration while that of water remained roughly constant.     

Characterization by solid state V NMR spectroscopy

The fresh catalyst V₂O₅–WO₃/TiO₂ and catalyst used in SCR for 9000 h have been studied by the solid state ⁵¹V NMR spectroscopy in static and MAS conditions. According to ⁵¹V NMR in both samples the majority of vanadium sites are in a distorted octahedral environment similar to that in V₂O₅. There is a strong interaction between vanadium oxide and the support, but the concentration of vanadium atoms strongly bound to the surface is very small and can be detected only in MAS NMR experiments or after removing the excess of V₂O₅. There is no influence of WO₃ additives on the structure of the particles of V₂O₅, whereas the influence on the structure of strongly bounded V cannot be excluded. Combination of static (wide line) and MAS NMR techniques permit the characterization of not only the structure of the vanadium species but also small changes in their local environment. Hence these experiments show that there are some distortions of the local environment of vanadium sites of the vanadium oxide particles compared with the polycrystalline V₂O₅; treatment by SCR increases these distortions.     

Gasoline composition determined by H NMR spectroscopy

A fast and simple ¹H NMR spectroscopic method was developed for the concentration measurement of aromatic, olefinic and aliphatic fractions in gasoline samples. Simultaneously, individual components such as benzene, methyl tert-butyl ether and several dienes could be determined. The method relies on only a few, well-established assumptions about the molecular compositions and is therefore applicable to a broad range of gasolines. It is well suited for laboratories with high sample throughput since measurement time is short and all concentrations are determined within one NMR experiment. The method was applied to commercial gasolines and samples used in European round robin tests. Comparisons of NMR and round robin test results showed excellent agreement.     

Analysis of sequence distribution in methyl methacrylate-methyl acrylate copolymers by C NMR spectroscopy

Methyl methacrylate (MMA)-methyl acrylate (MA) copolymers, prepared in bulk at 50 °C using AIBN as initiator, were characterized by 150 MHz ¹³C NMR spectroscopy, including use of the Distortionless Enhancement by Polarization Transfer (DEPT) experiment to obtain methylene and methine carbon resonances as subspectra. Dyad, triad, tetrad and partial pentad distributions were measured from the α-methyl, methine and methylene carbon resonances. These were in good agreement with distributions calculated for the copolymers based on monomer feed compositions, conversions and reactivity ratios of 2.60 and 0.27 for methyl methacrylate and methyl acrylate, respectively.     

Spin labels as a tool to identify and characterize protein-ligand interactions by NMR spectroscopy

NMR spectroscopy based discovery and optimization of lead compounds for a given molecular target requires the development of methods with maximum sensitivity and robustness. It is shown here that organic nitroxide radicals ("spin labels") can be used to boost the sensitivity of NMR spectroscopic screening in drug discovery research. The concept of utilizing spin labels in NMR spectroscopy is summarized, examples for successful first-site and second-site NMR spectroscopic screens are given, and guidelines for linker design are presented.     

NMR spectroscopy of RNA

NMR spectroscopy is a powerful tool for studying proteins and nucleic acids in solution. This is illustrated by the fact that nearly half of all current RNA structures were determined by using NMR techniques. Information about the structure, dynamics, and interactions with other RNA molecules, proteins, ions, and small ligands can be obtained for RNA molecules up to 100 nucleotides. This review provides insight into the resonance assignment methods that are the first and crucial step of all NMR studies, into the determination of base-pair geometry, into the examination of local and global RNA conformation, and into the detection of interaction sites of RNA. Examples of NMR investigations of RNA are given by using several different RNA molecules to illustrate the information content obtainable by NMR spectroscopy and the applicability of NMR techniques to a wide range of biologically interesting RNA molecules.