The characterisation of synthetic sulphonate and phenate detergents by nuclear magnetic resonance and infrared spectroscopy

Sulphonate and phenate detergents are used in many modern oil formulations. Overbased sulphonates form micelles, whereas in overbased phenates the excess metal carbonate is incorporated in the molecule as a carbonate chain. This is the cause of broad unresolved peaks in the NMR spectra of these detergents. Hydrolysis removes the excess metal carbonate and converts the sulphonates and phenates to sulphonic acids and phenols respectively. Especially in the ¹H- and ¹³C-NMR spectra, a substantial resolution enhancement is achieved after hydrolysis. These spectra reveal much more structural information. One of the features that can be calculated from the ¹³C-NMR spectra is the mean alkyl chain length. In this study a number of commercially available sulphonate and phenate detergents have been investigated. For the sulphonates the alkyl chain length was found to range from 17–22 carbon atoms, and for the phenates the alkyl chain length proved to be approximately 9–12 carbon atoms. The phenate alkyl chains showed significantly more branching than those in the sulphonates. In the ¹H-NMR spectra, the position of the acidic proton signals is influenced by the measurement temperature, water concentration and solvent. The effect of these parameters was studied in detail. A combination of sample preparation techniques, such as dialysis, and hydrolysis and spectroscopic techniques, such as IR and NMR, can be used successfully to characterise detergents in terms of their molecular structure.     

Study of additive‐additive interactions in a lubricant system by NMR,ESCA, and thermal techniques

Engine oil lubricants are formulated with a variety of additive components at different dosages to obtain the desired physico‐chemical characteristics. Antiwear, friction modification/energy efficiency, dispersancy, and detergency properties are normally achieved by the use of zinc dialkyldithiophosphate (ZDDP), molybdenum dithiocarbamate (MoDTC) and ashless alkyl phosphorodithioate, polyisobutylene succinimide (PIBS), and metal sulphonates / phenates, respectively. It has been reported that these additives interact with each other and affect the overall performance of a lubricant system. The additive‐additive interactions have been studied by nuclear magnetic resonance (NMR) and infrared spectroscopic techniques, where attention has been mainly focused on the ZDDP‐PIBS additive system in the presence or absence of other additives. The results have been used to relate the synergistic or antagonistic effects of such interactions to the overall performance of a lubricant. Recently, MoDTC has found wider application in lubricants as a friction modifier and energy‐efficient additive. However, no studies of the additive‐additive interactions of the PIBS‐MoDTC‐ZDDP additive system using analytical techniques have been reported. The present paper covers the fundamental and mechanistic aspects of additive‐additive interactions of ZDDP, MoDTC, PIBS, and sulphonate / phenate additives present in a lubricant system as studied by ³¹P NMR, electron spectroscopy for chemical analysis (ESCA), and thermogravimetric analysis (TGA) techniques. ESCA, which is a surface analytical technique, has been used to provide basic evidence for the formation of various complexes through interactions occurring in the electronic binding energies of orbitals of various atoms of the additives. The ESCA studies have also revealed the actual atomic sites of interaction between the additives responsible for the formation of adducts or complexes. The differential scanning calorimetry profiles of blends have verified the interactions among the additives and shown that the stability of the additive system is quite different from that of the additives alone. The shifts in the ³¹P NMR signals, the changes in the binding energies of the s, p, and d orbitals of additive elements, and the multistage decomposition profiles in the TGA thermograms of interacting systems due to complexion and adduct formation have enabled a mechanism of interaction to be proposed.     

Sulphur-phosphous components in gear oils: part 1, oxidation stability studies by P-NMR spectroscopic techniques

In the present investigations, the mechanism of oxidation stability of sulphur and phosphorus-based additives such as S-alkyl O,O-dialkyl phosphorodithioate, alkyl amine salt of dialkyl dithiophosphoric acid, dialkyl hydrogen phosphite and zinc dialkyl dithiophosphate used in lubricants has been studied by liquid and solid state ³¹P/^lH-NMR spectroscopic techniques. These techniques have enabled to monitor the complex changes that occur during oxidation at different intervals during long duration oxidation tests and provide qualitative and quantitative information of products formed during degradation of S–P based additives. The nature of both soluble and insoluble products of decomposition has been /determined. The studies have revealed few important aspects regarding thermal stability of these additives. The ashless S-alkyl O,O-dialkyl phosphorodithioate have better thermal oxidative stability and retain their identity for longer period compared to other similar ashless additives and zinc dialkyl dithiophosphates. The loss of additives during oxidation is 12% in case of S-alkyl O,O-dialkyl phosphorodithioate compared to other mentioned additives (40–100%) during 64 h of heating at 165 °C in the presence of air and catalyst. The decomposed products are also solublised in case of S-alkyl O,O - dialkyl phosphorodithioate and dialkyl hydrogen phosphite, and small amount of solids are formed compared to other additives. During oxidation the main components are being converted into more complex insoluble polyphosphates. The nature of soluble and insoluble products of decomposition as a result of thermal degradation are similar irrespective of the types of additive used. The mechanism of degradation and subsequent composition and structure of products formed has been discussed in detail. These studies will facilitate correlation of the structure and performance of these additives in lubricants.     

Molecular spectroscopic studies of the effect of base oils on additive—additive interactions

The effect of different types of base oil of API Groups I to V, such as mineral based (solvent refined, hydrofinished, hydro‐cracked/ wax isomerised) and synthetic based (polyalphaolefin and ester), on the interaction of zinc dialkyldithiophosphate (ZDDP) with polyisobutylene succinimide (PIBS) has been studied by variable‐temperature (VT) IR and ³¹P NMR spectro‐scopic techniques. Since ZDDPs are known to exist in monomeric and polymeric forms and as neutral and basic salts, and their functioning is temperature dependent, the structural changes observed in the NMR and IR spectra of the ZDDP—PIBS system in different base oils have been addressed with this in mind. The strength and composition of ZDDP—PIBS complexes has been explained in terms of the degree of solvation provided by the medium (base oil) in which they are present, and thermodynamic parameters ΔH and ΔS estimated from the VT IR spectra. The results indicate that the complexes are stronger and stable in polar base oils, such as from Groups I and V. The equilibrium shifts towards the neutral form of ZDDP in polar base oils. The results have been substantiated by correlating the variation in the shift and width of IR and ³¹P NMR signals to the stability of the complexes and low values of ΔH and ΔS. Polar solvents, such as methanol and tetrahydro‐furan, also favour the formation of the neutral form of ZDDP and stronger complexes between PIBS and ZDDP, in a manner similar to that observed for polar base oils.     

Study of biodegradation properties of phthalate esters in aqueous culture conditions

Several kinds of esters are widely used in synthetic lubricants. The evaluation of their influence on the environment is a matter of considerable interest. This paper studies the ultimate aerobic biodegradation of several phthalates, such as dimethyl phthalate (DMP), diethyl phthalate (DEP), di‐n‐butyl phthalate (DBP), di‐n‐octyl phthalate (DOP) and di(2‐ethylhexyl) phthalate (DEHP), and their degrading kinetics by quantitative assessment of the carbon dioxide produced. The production of CO₂ was chosen as the evaluation parameter to determine the biodegradability of phthalates in aqueous solution. A kinetic model was established to describe the biodegradation process of phthalates. The results indicated that biodegradation of phthalates followed the first‐order kinetic equation; the rate constant (k_b) of biodegradation decreased as the carbon number of the alkyl chain increased, and linear phthalates had better biodegradability than branch phthalate. When the initial concentration was over 200 mg/L, a lag phase was evident during the degradation of phthalates, which was prolonged with increased carbon number in the alkyl chain. Easily biodegradable organics, such as glucose, had a favorable effect on the aerobic biodegradation of phthalates. Copyright © 2006 John Wiley & Sons, Ltd.     

Spectral Data Analyses and Structure Elucidation of Sedative‐Hypnotic Zopiclone

Abstract

The infrared spectrum, ultraviolet spectrum, mass spectrum, and nuclear magnetic resonance spectrum of the sedative‐hypnotic zopiclone were reported and interpreted comprehensively. All the ¹H and ¹³C NMR chemical shifts were assigned by means of ¹H‐¹H and ¹³C‐¹H correlation spectroscopy, and correlation spectroscopy via long range coupling. The main characteristic fragmentations in mass spectra, vibrations of functional groups in infrared spectrum, and electron transition in ultraviolet spectrum of zopiclone were also discussed.     

Investigation of the torque capacity of automatic transmission fluids with various oil additives

A slip‐controlled lock‐up clutch system is very efficient in improving the fuel economy of automatic transmission‐equipped vehicles. However, a special automatic transmission fluid (ATF), which combines anti‐shudder properties with a high torque capacity, is required for such a system. An ATF with various oil additives was formulated, the torque capacity of which was evaluated. The results show that certain additives, especially sulphur‐containing extreme‐pressure and antiwear additives, have an important effect on the torque capacity. Analyses by X‐ray photoelectron spectroscopy of the steel surfaces tested clearly reveal the presence of the elements carbon, sulphur (S²⁻, S⁶⁺), oxygen, nitrogen, phosphorus, boron, and calcium. Among them, sulphur and phosphorus have the more important effects on the torque capacity of the ATF, while the presence of nitrogen is important with regard not only to torque capacity but also to antiwear characteristics.     

Ultrastructural and electron spectroscopic analyses of cyanobacteria and bacteria

The extracellular sheath material and some intracellular cell components of cyanobacteria and phosphate-accumulating sewage bacteria were analysed by electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS). The specimens were embedded in water-soluble Nanoplast resin without any previous fixation and ultrathin sections were examined in a Zeiss CEM 902 microscope. A high sulphur content was detected in the inner sheath of the cyanobacterium Gloeothece. The elemental composition of some cell components and inclusion bodies, such as carboxysomes and cyanophycin, was determined by ESI and EELS. In addition, the phosphate content in specific granules of phosphate-accumulating sewage bacteria was estimated by EELS and nuclear magnetic resonance spectroscopy.     

Automated focusing in bright-field microscopy for tuberculosis detection

Pulsed‐laser atom‐probe tomography is used to compare the field‐evaporation mass spectrum and spatial distribution of molecular fragments from various poly(3‐alkylthiophene) films deposited on sharpened aluminium specimen carriers using two different deposition methods. Films deposited via a modified solution‐cast methodology yield small fragments with a uniform structural morphology whereas films deposited via an electrospray ionization methodology yield a wide range of fragments with a very non‐uniform structural morphology. The main field‐evaporated chemical species identified for both deposition types were, in order of typical relative abundance, C₂H₅⁺, CH₃⁺, C₂H₄⁺, followed by C₃H_7,8⁺/SC⁺ and SCH⁺. Thick electrospray depositions allowed investigation of the influence of laser‐pulse energy on the analysis. Evidence is presented supporting the presence of a critical laser‐pulse energy whereby changes in film morphology are signalled by the appearance of a new mass fragment at 190 Da.     

Studies on additive-additive interactions: Effects of dispersant and antioxidant additives on the synergistic combination of overbased sulphonate and ZDDP

A strong synergism between overbased sulphonate (OBS) and zinc dialkyldithiophosphate (ZDDP) in a proven diesel engine oil formulation has been reported in an earlier communication.¹ In continuation of these studies, the effect of different types of dispersant, of varying nitrogen content, and an antioxidant, on a synergistic combination of OBS-ZDDP has been investigated. Both detergency and dispersancy of the optimised formulation were improved with high nitrogen-content dispersants, which also increased strongly the wear tendencies. The antioxidant, though it improved detergency, did not show any positive effect on antiwear performance. Detailed IR and ³¹p-NMR spectroscopic analyses on interactive additive pairs, namely, ZDDP-PIBS and ZDDP-antioxidant, indicated the formation of association complexes and hydrogen bonding respectively.     

Molecular dynamics studies of a lubricant system by NMR spectroscopic techniques

The present studies highlight the applications of NMR spectroscopic techniques for unravelling the unique structural features present in base oils responsible for imparting lubricant properties. The viscosity—temperature and viscosity—pressure properties of base oils of API groups I—IV, such as viscosity, viscosity index, pour point, elastohydrodynamic film thickness, and pressure—viscosity coefficient, have been correlated with the detailed hydrocarbon composition of base oils with an emphasis on the various types of methyl branched structures. Molecular dynamics parameters, such as diffusion coefficient and energy of activation, estimated from the NMR spectral studies have provided evidence of the factors responsible for the different viscosity—temperature or viscosity—pressure characteristics of base oils.     

Molecular features of sulfonic acids used for synthesis of overbased detergent additives

Overbased calcium sulfonates are used in many modern oil formulations to provide cleaning action and to neutralize the organic acids formed during combustion, preventing corrosion. The performance of detergents is related to their molecular structure, which is generally known only as a chemical category. In the present work, nuclear magnetic resonance (NMR) spectroscopy and electrospray ionization mass spectrometry are used to analyze the molecular structure of three alkyl‐benzene sulfonic acids in detail. Some important molecular features were obtained by elaborating the NMR signal intensities, such as the number and positions of alkyl substituents on the benzene ring, the distribution of alkyl chain lengths and the mole fraction of 1‐phenyl isomers (synthesized by alkylation of benzene with α‐olefin). Ion‐trap mass spectrometry is used to obtain the mass spectrometry/mass spectrometry (MS²) spectra of the principal molecular ions. By choosing suitable molecular ions, MS² spectra can ascertain the presence of different substituted benzene isomers within a mixture because the MS² spectra show specific fragments due to the number of alkyl substituents on the aromatic ring. Copyright © 2006 John Wiley & Sons, Ltd.     

Detailed characterisation of heavy alkylated benzene fluids by multipulse one‐ and two‐dimensional NMR spectroscopy

In this paper, the results of a characterisation of heavy alkylated benzenes (HAB) using multipulse NMR spectroscopy are presented. Four commercial samples of heavy alkylated benzene have been characterised in detail in terms of various structural parameters, such as percentage aromatic carbon (Ca), degree of aromatic substitution, average alkyl chain length, type of alkyl chain and their proportions. Three of the HAB samples were very similar in structure, whereas, in the fourth, the structures present were entirely different. The latter had an abundance of 2‐phenyl alkane‐type structures, and did not contain methyl substituted tetralin or naphthalene type molecules. The influence of the structures on lubricating oil properties, including viscosity index, pour point, and viscosity, as well as Freon^TM floc point, are also discussed.     

Temperature‐dependent effects in base oils: Carbon‐13 NMR spin‐lattice relaxation time and viscometry studies

Carbon‐13 NMR spin‐lattice relaxation time (T₁) data have been used to study the molecular dynamic aspects of base oils with different physical properties. Relaxation time measurements have been carried out on a few model compounds and a number of mineral base oils at various temperatures (273–373 K). Effective correlation time (°_C) and rotational mobility data obtained for the model compounds and base oils have provided evidence of relationships between molecular flexibility and the temperature dependence of viscosity. It is possible to determine the average carbon alkyl chain lengths and the molecular weights of the base oils from the ratio of the T₁ values of C_β and C_int carbons and the optimised value of the microviscosity factor (f_r), respectively. A qualitative correlation between Arrhenius energies (E_a) for microscopic motion and macroscopic bulk properties such as viscosity and viscosity‐temperature characteristics has been observed. Base fluids having better viscosity‐temperature characteristics were also associated with lower values of E_a for micro‐ as well as macroscopic processes.     

Investigations on calcium carboxylate and sulfonate additive incompatibilities in a preservation oil

Severe quality defects of a well‐established preservation oil ranging from improper viscosity values to the formation of calcium carboxylate precipitates led to detailed investigations on the origin of these failures. Chemical analyses employing spectroscopic and chromatographic techniques focusing on the product's additives were performed. Thereupon, a mechanism for precipitate formation based on a delicate interaction between solubilizer, carboxylates, sulfonates and calcium ions was proposed. For this mechanism, ligand properties of sulfonates play a vital role: In contrast to monosulfonates, disulfonates seem to impede precipitation of calcium carboxylates. Copyright © 2014 John Wiley & Sons, Ltd.     

Advances on the compositional analysis of glycosphingolipids combining thin‐layer chromatography with mass spectrometry

Glycosphingolipids (GSLs), composed of a hydrophilic carbohydrate chain and a lipophilic ceramide anchor, play pivotal roles in countless biological processes, including infectious diseases and the development of cancer. Knowledge of the number and sequence of monosaccharides and their anomeric configuration and linkage type, which make up the principal items of the glyco code of biologically active carbohydrate chains, is essential for exploring the function of GSLs. As part of the investigation of the vertebrate glycome, GSL analysis is undergoing rapid expansion owing to the application of novel biochemical and biophysical technologies. Mass spectrometry (MS) takes part in the network of collaborations to further unravel structural and functional aspects within the fascinating world of GSLs with the ultimate aim to better define their role in human health and disease. However, a single‐method analytical MS technique without supporting tools is limited yielding only partial structural information. Because of its superior resolving power, robustness, and easy handling, high‐performance thin‐layer chromatography (TLC) is widely used as an invaluable tool in GSL analysis. The intention of this review is to give an insight into current advances obtained by coupling supplementary techniques such as TLC and mass spectrometry. A retrospective view of the development of this concept and the recent improvements by merging (1) TLC separation of GSLs, (2) their detection with oligosaccharide‐specific proteins, and (3) in situ MS analysis of protein‐detected GSLs directly on the TLC plate, are provided. The procedure works on a nanogram scale and was successfully applied to the identification of cancer‐associated GSLs in several types of human tumors. The combination of these two supplementary techniques opens new doors by delivering specific structural information of trace quantities of GSLs with only limited investment in sample preparation. © 2009 Wiley Periodicals, Inc. Mass Spec Rev 29:425‐479, 2010     

Rapid and Highly Sensitive Method for Protein Determination in Biological Samples with m‐Nitrophenylfluorone‐Mo(VI) Complex as a Spectral Probe

Abstract

A simple, rapid, highly sensitive, and selective method for detecting protein in biological samples has been developed, which is based on the interaction between protein and m‐nitrophenylfluorone‐Mo(VI) complex as a spectral probe. The optimum condition for the reaction is investigated. Bovine serum albumin (BSA) obeys Beer's law up to 10 µg · mL^?1, having a molar absorption coefficient of 8.51×10⁶ L · mol^?1 · cm^?1 at 535 nm. Many amino acids and metal ions do not interfere. The results of determination for biological samples are comparable to those obtained by the Bradford method. Meanwhile, the binding number is also determined.     

Negative ion cleavages of (M–H)− anions of peptides. Part 3. Post‐translational modifications

It is now 25 years since we commenced the study of the negative‐ion fragmentations of peptides and we have recently concluded this research with investigations of the negative‐ion chemistry of most post‐translational functional groups. Our first negative‐ion peptide review (Bowie, Brinkworth, & Dua, 2002) dealt with the characteristic backbone fragmentations and side‐chain cleavages from (M–H)^? ions of underivatized peptides, while the second (Bilusich & Bowie, 2009) included negative‐ion backbone cleavages for Ser and Cys and some initial data on some post‐translational groups including disulfides. This third and final review provides a brief summary of the major backbone and side chain cleavages outlined before (Bowie, Brinkworth, & Dua, 2002) and describes the quantum mechanical hydrogen tunneling associated with some proton transfers in enolate anion/enolate systems. The review then describes, in more depth, the negative‐ion cleavages of the post‐translational groups Kyn, isoAsp, pyroglu, disulfides, phosphates, and sulfates. Particular emphasis is devoted to disulfides (both intra‐ and intermolecular) and phosphates because of the extensive and spectacular anion chemistry shown by these groups. © 2016 Wiley Periodicals, Inc. Mass Spec Rev     

Chromatographic and non‐chromatographic characterization of poly‐α‐olefins

Both chromatographic and non‐chromatographic techniques were used in the characterization and identification of poly‐α‐olefins. Synthetic base oils, although produced from the same raw material, exhibit different physico‐chemical properties. Their mutual miscibility and behaviour in final engine oils may be predicted from data collected through classical physico‐chemical analysis, simulated distillation chromatography as well as inverse gas chromatography. Copyright © 2007 John Wiley & Sons, Ltd.     

EELS Spectrum‐Imaging for Boron Detection in Biological Cryofixed Tissues

Abstract

Boron imaging at the subcellular level in tissues is of prime importance to understand boron neutron capture therapy (BNCT) effects and to suggest ways to improve the efficiency of the treatments. In this paper, we present boron imaging in cryofixed biological tissues by electron energy loss spectroscopy (EELS), using the spectrum‐imaging acquisition mode. We performed boron imaging in tissues of mice who received boron compounds. We analysed cryosections of tumours, livers, and kidneys of infused mice. Our results point out the relevance of EELS for boron imaging and, particularly, in order to detect small accumulation areas. The data also point out the limitations of the technique and its complementarity with other imaging techniques. We discuss and illustrate the possibility for misinterpretation of EELS or electron spectroscopic imaging (ESI) data. We particularly focus on the problem of phosphorus for boron imaging.