‘Wax bloom’ on beeswax cultural heritage objects: Exploring the causes of the phenomenon

The term ‘wax bloom’ is used to describe a thin whitish crystalline layer that develops on the surface of beeswax objects under specific conditions. This phenomenon is undesirable, especially in the cases of objects with aesthetic or informational value, such as wax sculptures or historical seals. A combination of solid‐state NMR and FTIR measurements allowed to obtain fairly detailed insight into the problem and to suggest a probable mechanism of its development. Secondary crystallization of unsaturated hydrocarbons from beeswax was determined as a primary cause. After the macroscopic solidification of beeswax from the melt, these molecules remain for months in a highly mobile, liquid‐like state. This facilitates their diffusion to the surface, where they eventually crystallize, forming the ‘wax bloom’ effect. Although these results are of particular interest with respect to the conservation of beeswax artifacts, they are relevant to this material in general and help with understanding its unique properties. Copyright © 2015 John Wiley & Sons, Ltd.     

First results on headspace-solid phase microextraction-gas chromatography/mass spectrometry of volatile organic compounds emitted by wax objects in museums

Sampling volatile organic compounds (VOCs) emitted by a large variety of materials is nowadays a very useful technique for analytical purpose. In the field of cultural heritage, it can be applied to identify some constituents of museum artefacts off-gassing VOCs without sampling on the object itself. In this study, we focused on objects made of wax. First volatiles emitted by a reference beeswax were trapped and identified by headspace-solid phase microextraction (HS-SPME)-gas chromatography and mass spectrometry (GC/MS). This allowed to identify numerous volatile biomarkers, namely saturated n-alkanes from C(10) to C(21), saturated n-carboxylic acids containing 6-12 carbon atoms, benzene and cinnamic derivatives that may be considered as volatile biomarkers of beeswax. The SPME strategy was then performed at the Orsay museum (Paris) in a showcase containing a wax sculpture "Le Mineur de la Loire" by J.-J. Carriès. The use of beeswax in this sculpture was unequivocally confirmed by the VOCs concentrated in the showcase, together with a set of characteristic molecular compounds identified by HT-GC/MS. HS-SPME-GC/MS thus appears to be a powerful in situ and non-invasive analytical technique that allows to identify natural substances in the field of cultural heritage without any sampling of solid matter from the object. The results obtained are promising for orientating the strategy of preventive conservation related to works of art characterised by important emission of VOCs.     

Determination of Microcrystalline Wax in a Butadiene-Styrene Copolymer by Turbidimetry

Abstract

A method is described for the determination of microcrystalline wax in butadiene-styrene copolymer pellets at levels ranging from 0.10 to 0.55 wt. %. Polymer pellets are contacted with hot isooctane. The mixture is cooled and the solvent decanted. Following further cooling, the turbidity of the extracted solution is measured. The amouit of microcrystalline wax is calculated using a calibration curve derived from prepared standards. The limit of detection is 0.1% microcrystalline wax, due to sample background turbidity.     

Determination of beeswax and some impurities by IR spectroscopy

Summary Analysis of the IR spectra of waxes isolated from samples of paints from paintings dating from the Ist to VIIth centuries of our era and fragments of archaeological antique murals has shown that in some cases the wax isolated is pure beeswax and in others it contains as impurities what are presumably resin acids, and also salts of fatty acids. The IR spectrum of pure beeswax extracted from a fragment buried for 2000 yr is absolutely identical with the spectrum of modern beeswax, which shows the extreme chemical stability of the wax.All-Union Central Scientific-Research Laboratory for Conservation and Restoration, Moscow. Scientific-Research Institute of Organic Intermediates and Dyes, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 271–275, March–April, 1977.     

Characterisation of beeswax in works of art by gas chromatography-mass spectrometry and pyrolysis-gas chromatography-mass spectrometry procedures

Pyrolysis (Py) with in situ derivatisation with hexamethyldisilazane-gas chroma-break tography-mass spectrometry (GC-MS) and a gas chromatography-mass spectrometry procedure based on microwave-assisted saponification were used to identify the organic components in small sized beeswax samples. With the latter procedure quantitative recoveries can be made and hydrocarbons, alcohols and omega-1-diols in the neutral fraction, and fatty acids and omega-1-hydroxy acids in the acidic fraction can be efficiently separated and detected. Both procedures were used to characterise a wax anatomic sculpture "The Plague" (1691-1694) by Gaetano Zumbo, resulting in the identification of beeswax and a Pinaceae resin. The GC-MS analysis brought to light some essential differences in beeswax composition between the raw material and the old modelled wax thus giving some clear indications about the recipe used by the sculptor.     

Analytical characterization of natural waxes employing pyrolysis–gas chromatography–mass spectrometry

Three natural waxes (bleached beeswax, lanolin, yellow carnauba wax) were investigated by means of pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS). Pyrograms were obtained showing very characteristic signal patterns. Mass spectrometric detection enabled the structural identification of the pyrolytically formed fragments. For a more detailed investigation of the thermal degradation behaviour of waxy materials, relevant model compounds were selected. Hexadecylpalmitate, cholesterylstearate, heptadecanoic acid and 1-hexacosanol were examined under identical Py–GC–MS conditions. From the resulting product distribution general statements were able to be derived according to the thermal degradation pathways of typical wax constituents. The findings obtained from the model compounds were then applied to the interpretation of the real wax pyrograms. As a result, conclusions according to their origin from corresponding wax constituents were drawn for the majority of pyrolysis products. Thus, the extended potential of the method for the compositional analysis of natural waxes is demonstrated.     

Characterization of wax manufactures of historical and artistic interest

Purpose of this scientific research is the physic and chemical characterization of two historical wax manufactures, made at the end of XIX century by Francesco Bianchi, a papal engraver. The chemical and analytical investigation was necessary to complete and to confirm the restorer's work. The IR Spectroscopy, X-Ray and GC-MS, the best technique to characterise wax, allowed us to obtain the following results. The two manufactures were made with commercial beeswax: in fact, the relative chromatograms showed unchanged peaks about esters of palmitic acid with C24 to C32 alcohol molecules; using standard beeswax we determined the same amount of hydrocarbons present in the wax manufactures. We found several hydrocarbons in these beeswax materials so that it is reasonable to think about successive modifications. ZnO (white zinc), a pigment, was added, probably due to its colour and covering capacity. Sb2S3, Anthimoniun vermilion, a red-orange pigment, was added to these manufactures to give them a soft pink-orange colour. By all used techniques we determined some modifications in the original beeswax; surely they were made to get a more malleable, mouldable, and then more able to be modelled wax.     

Lipidic Matrixes Containing Clove Essential Oil: Biological Activity,Microstructural and Textural Studies

Clove essential oil (CEO) is known for having excellent antioxidant and antimicrobial properties, but the poor stability of its components to light and temperature compromise this activity. The aim of this study is to evaluate the textural, antioxidant, antimicrobial and microstructural properties of matrixes produced with representative natural waxes and CEO. Thus, waxy emulsifiers, such as beeswax, candelilla wax, carnauba wax, and ozokerite wax, were employed to create such matrixes. The thermal, microstructural, textural, wetting, antioxidant, antimicrobial and infrared characteristics of the matrixes were then studied. The diverse chemical composition (long-chain wax esters in carnauba wax and short-chain fatty acids and hydrocarbons in beeswax and ozokerite wax, respectively) explained the differences in wetting, texture, melting, and crystallization characteristics. Crystal forms of these matrix systems varied from grainy, oval, to needle-like shape, but keeping an orthorhombic allomorph. The alignment and reorganization of beeswax and ozokerite wax into needle-like crystals increased the matrix strength and adhesion force compared to those of carnauba and candelilla matrixes, which showed weak strength and grainy morphology. The former two waxes and their matrixes also showed the largest plasticity. These lipidic matrixes show potential use for topical applications having acceptable antioxidant and textural properties.     

Screening Metal–Organic Frameworks for Separation of Binary Solvent Mixtures by Compact NMR Relaxometry

Metal–organic frameworks (MOFs) have great potential as an efficient alternative to current separation and purification procedures of a large variety of solvent mixtures—a critical process in many applications. Due to the huge number of existing MOFs, it is of key importance to identify high-throughput analytical tools, which can be used for their screening and performance ranking. In this context, the present work introduces a simple, fast, and inexpensive approach by compact low-field proton nuclear magnetic resonance (NMR) relaxometry to investigate the efficiency of MOF materials for the separation of a binary solvent mixture. The mass proportions of two solvents within a particular solvent mixture can be quantified before and after separation with the help of a priori established correlation curves relating the effective transverse relaxation times T_2eff and the mass proportions of the two solvents. The new method is applied to test the separation efficiency of powdered UiO-66(Zr) for various solvent mixtures, including linear and cyclic alkanes and benzene derivate, under static conditions at room temperature. Its reliability is demonstrated by comparison with results from ¹H liquid-state NMR spectroscopy.     

Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids

This paper describes the first coupling of a commercial capillary HPLC system with a diode array spectrophotometric detector and a custom-built nuclear magnetic resonance (NMR) flow microprobe. The eluent from a 3-microm diameter C18 HPLC column is linked to a 500 MHz 1H-NMR microcoil probe with an observe volume of 1.1 microl. The separation and structurally-rich detection of a mixture of terpenoids under both isocratic and gradient solvent elution conditions is presented. The lowest limits of detection yet reported for capillary HPLC on-line measurement (i.e., 37 ng for alpha-pinene) are achieved with this system. The complementary nature of diode array and NMR detection allows stopped-flow data collection from analytes which would otherwise go unnoticed in continuous-flow NMR. Moreover, stopped-flow NMR data is presented for the detection of a trace (sub-nmol) impurity in the sample mixture. Since NMR signals degrade and shift during solvent gradients, flow injection analysis studies are conducted with injected solvent plugs differing in mobile phase composition. The NMR signal degradation accompanying these injections is largely due to the variance in chemical shift with the solvent composition rather than to changes in magnetic susceptibility of the solvent. Characterization of such effects enables the development of improved NMR probes for the coupling of capillary HPLC and NMR.     

13C nuclear magnetic resonance spectroscopy for determining the different components of epicuticular waxes of olive fruit (Olea europaea) Dritta cultivar

¹³C nuclear magnetic resonance spectroscopy (NMR) was applied to determine the different components of apolar and polar fractions which were isolated by column chromatography from the crude chloroform-soluble waxes of olive fruits (Olea europaea) Dritta cultivar.¹³C NMR enabled the determination in the wax apolar fraction, of aliphatic aldehydes, and of benzyl, alkyl and glyceryl esters. In particular, the fatty acid composition of alkyl esters, comprising saturated and unsaturated oleic and linoleic acids, was determined. Acyl chain composition and the chain composition of 1,3- and 2-glycerol positions were also determined for triacylglycerols of olive fruit waxes.Oleanolic and maslinic acids were confirmed to be the major components of wax polar fraction. Complete assignments of ¹³C NMR chemical shifts of oleanolic and maslinic acids as a mixture were achieved by using homonuclear correlation spectroscopy with gradient (g-COSY), attached proton test (APT), inverse-detected heteronuclear single-quantum coherence with gradient (g-HSQC), high-resolution heteronuclear correlation spectroscopy (HETCOR) for C-H directly attached pairs and C-H long-range-coupled experiments.     

Dynamic assembly of porphyrin wires trapped on a highly oriented pyrolitic graphite surface

Carefully designed porphyrin building blocks assemble through selective imidazole binding in various solvents to form linear multiporphyrin objects. From a dynamic mixture of monomers, dimers, and oligomers, linear objects were observed on a highly oriented pyrolitic graphite (HOPG) surface. On the surface, the objects' morphology clearly depended on the solvent used for deposition and was modified upon heating.     

Efficient Separation of Dolaproine Stereoisomers by Optimization of a Three Component Chromatographic Solvent System

Abstract

A solvent system composed of n-hexane-chloroform-acetone was selected (by TLC) for resolving a difficult to separate mixture of protected dolaproine stereoisomers. A set of points representing solvent ratios was generated by an application of statistical methods. From thin layer chromatography data semifinal solvent ratios were selected. By applying simplex optimization, the solvent ratio was found to be 32.3 : 53.4 : 14.3 respectively for the preceding solvent system.     

In situ and frontal polymerization for the consolidation of porous stones: a unilateral NMR and magnetic resonance imaging study

Consolidation treatment of porous materials was performed by in situ and frontal polymerization of acrylic monomers inside a porous stone. To study the penetration of the polymer inside the stone and its consolidating effects we used water as a contrast agent, detecting its penetration using unilateral NMR and magnetic resonance imaging. All data obtained on differently treated stones were compared with corresponding ones obtained analyzing both untreated stones and stones simply painted with a well-known polymeric protective agent. In situ polymerization of acrylic monomers inside porous stones has been demonstrated to be an extremely powerful consolidating method, whereas thermally initiated frontal polymerization seems less efficient. In both cases the optimal choice of monomers is still open and requires further study. Our data indicate that unilateral NMR represents an inexpensive and simple technique for the non-invasive observation of the water uptake and of the effect of consolidation procedures in porous materials.     

Molecular interactions in polystyrene cosolvent systems

Studied here are miscible binary cosolvents for polystyrene, for which polystyrene is insoluble in either of the individual solvents. Polymer-solvent interactions in solutions of atactic polystyrene in acetone/diethyl ether and in methylcyclopentane (MCP)/acetone binary cosolvents have been investigated using nuclear magnetic resonance (NMR) spectroscopy. Polystyrene ¹³C chemical shifts were measured as a function of miscible binary solvent compositions and temperature. The NMR data were used to calculate “association constants” as a measure of specific interactions of the solvent components with all sites on the polymer. In mixtures of acetone and diethyl ether, ¹³C-NMR indicates a weak interaction between the polystyrene phenyl ring and the diethylether solvent component. In the polystyrene/MCP/acetone system, present NMR data reveal no preferential interactions. Additional NMR measurements were performed on polystyrene in mixtures of CCl₄/acetone. From these results, it is concluded that although preferential polymer-solvent interactions are present in some cosolvent systems, they are not a prerequisite for such behavior.     

Deuterated Disaccharides for the Investigation of Protein-Carbohydrate Interactions-Application of Bioaffinity-and STD-NMR

ABSTRACT

NMR spectroscopic analysis of carbohydrates often suffers from severe overlap of resonance signals, especially in ¹H NMR spectra. Therefore, we synthesized four 2,3,4-trideuterio-α-L-fucose containing disaccharides, α-L-Fuc-(1→6)-β-D-GlcNAc-OMe 1, α-L-Fuc-(1→4)-β-D-GlcNAc-OMe 2, α-L-Fuc-(1→3)-β-D-GlcNAc-OMe 3, and α-L-Fuc-(1→2)-β-D-Gal-OMe 4. Compounds 1 to 4 are well suited to be subjected to NMR conformational analysis because their ¹H NMR spectra show almost no overlap of signals. The deuterated disaccharides 1 to 4 will therefore be used as NMR probes for the exploration of fucose-binding proteins. With a mixture of the corresponding non-deuterated disaccharides it is demonstrated that recently developed parallel NMR screening protocols, Bio-Affinity NMR and STD-NMR, deliver fast and robust tools to assay the compounds synthesized for protein-binding affinity.     

Hochtemperatur-Capillar-Gas-Chromatographie von Kohlenwasserstoffen, Fetts?urederivaten, Cholesterin-, Wachsestern und Triglyceriden am Beispiel des Bienenwachses

Zusammenfassung Durch Einsatz einer OV-101-fusedsilica-Capillare wird es möglich, sÄmtliche Lipidklassen des Bienenwachses schnell und zuverlÄssig in einem Arbeitsgang gas-chromatographisch zu trennen. Durch die Kontrolle von Kohlenwasserstoffen, Fettsäuren, Mono- und Diglyceriden, Sterin- und Wachsestern sowie Triglyceriden lassen sich QualitÄtsmÄngel von Bienenwachs oder Bienenwachsprodukten nachweisen und die Art eventueller VerfÄlschungen ermitteln. Für eine Reihe von Vergleichssubstanzen der oben genannten Stoffklassen werden relative Retentionszeiten (bezogen auf 5-Cholestan) angegeben.

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High-temperature capillary GLC of hydrocarbons, fatty-acid derivatives, cholesterol esters, wax esters and triglycerides in beeswax analysis

Summary By means of an OV-101 fused-silica capillary column, it has become possible to separate all the lipid classes of beeswax within one GLC run in a rapid and reliable way. Control of hydrocarbons, fatty acids, mono- and diglycerides, sterol and wax esters and triglycerides allows the detection of quality deviations of beeswax or beeswax products. Likewise, substances used for adulteration can be determined. For a number of substances of the above mentioned lipid classes, relative retention times (related to 5-cholestane) are given.

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Zur Zeit als Stipendiatin des Senats von Berlin tÄtig im Institut für Sozialmedizin und Epidemiologie des Bundesgesundheitsamtes     

Solvent–solute and solute–solute interactions from NMR in nematic phases

Abstract

The use of NMR spectroscopy of molecules oriented in liquid-crystalline media to study solvent–solute and solute–solute interactions in π-systems such as benzene–chloroform and in charge transfer complexes, for example pyridineiodine, is illustrated. Changes in molecular order and chemical shifts as a result of complexation are employed in such studies. The extraordinary symmetry of C₆₀ has also been investigated by using a mixture of liquid crystals of opposite diamagnetic anisotropies indicating, thereby, negligible solvent–solute/solute–solute interactions.     

An Accurate Method for Cholesterol Analysis in Bile

Abstract

An accurate method for quantitative analysis of cholesterol in human bile is presented. Bile cholesterol was extracted in a single solvent (chloroform) in single step and ¹H NMR spectra of the extract were obtained by suppressing chloroform signal by presaturation. Cholesterol was quantitatively estimated through integral area of its H‐18 methyl signal which invariably appears distinctly in the nuclear magnetic resonance (NMR) spectrum. Precision and accuracy were determined from the recovery of added cholesterol from bile. Excellent correlation was observed between added and recovered cholesterol (R²=1). Direct and accurate analysis of cholesterol following simple extraction method as presented here may have important implications.