Lipoic acid formulations for the removal of arsenic and mercury from museum artifact materials

Museums currently face a tremendous task of identification, mitigation, and remediation of pesticides from artifacts in order to protect museum workers and the general public. Additionally artifacts are being repatriated by Native American tribes for use in cultural ceremonies which may subject the practitioner to health risks. Arsenic and mercury salts are among the most persistent poisons used and so a critical challenge is removing these hazardous metals without damaging the material composition or decorations of the objects. At this time, there are no feasible procedures that can meet both of these objectives. Reported here is the development of a procedure involving concentrated aqueous reduced lipoic acid solutions for the removal of arsenic and mercury pesticides from substrate materials commonly encountered in museums.     

New investigations into the Uluburun resin cargo

Resin found within Canaanite amphorae from the Late Bronze Age shipwreck discovered off the coast of southwest Turkey at Uluburun has previously been identified as Pistacia sp. Although evidence from Egypt suggests that this resin was in high demand and typically transported in such amphorae, it has also been proposed that the amphorae contained wine, with the resin used to seal the interior surfaces and to flavour and/or preserve the wine. To attempt to resolve this question, we have analysed five samples of pistacia resin found in amphorae from the shipwreck using a range of analytical techniques which have used in the past for the analysis of wine residues: spot tests, FT-IR, and HPLC-MS-MS. As well as the archaeological samples, we have analysed modern samples of pistacia resin, leaves and fruit to determine the effectiveness of each technique and to exclude the possibility of false positive results. In addition to the analyses for wine we also detail analysis (GC-MS) of the terpenoids for the purpose of further molecular characterisation of the resin. Bulk stable isotope analysis was used in comparison with similar resins to attempt to identify the geographical origin of the resin.     

Archaeological collagen: Why worry about collagen diagenesis?

DNA appears to decay by random chain scission resulting in a predictable range of fragment lengths. Collagen decay has also been modelled in this same way, although it has become increasingly evident that collagen decay does not follow this same pattern. Radiocarbon and stable isotope analysis now use ultra-filtration to isolate large fragments (>30% of original polymer length) even in Pleistocene bone. How then does collagen decay? This study contrasts experimentally degraded samples with collagen extracted from forensic, archaeological and fossil bone. In experimentally degraded bone, values for amino acid and elemental (C:N) composition, bulk δ ¹³C, δ ¹⁵N, and aspartic acid racemisation (AAR) changed very little until 99% of the collagen was lost, suggesting that the collagen triple helix and polypeptide chains remained remarkably intact. This suggestion was demonstrated directly by examining the integrity of individual polypeptide chains using cyanogen bromide (CNBr) cleavage followed by SDS-PAGE electrophoresis. In ancient samples, AAR values remain remarkably stable and the pattern of CNBr-cleavage was only replaced with a smear of smaller polypeptides in the oldest (Pleistocene) bones investigated. Smearing may reflect both modification of the methionine resides (the sites of CNBr-cleavage) and/or partial hydrolysis of the collagen molecule. The findings reveal why it is not usually necessary to worry about collagen diagenesis; it is mostly intact. However, evidence of partial deterioration of the oldest bone samples suggests that alternative purification strategies may increase yields in some samples.     

透闪石玉物相构成及沁蚀演化机理新解

中国是世界上玉文化源远流长的地区,随着玉文化研究的深入和玉学的兴起,玉石的物相构成及受沁演化机理成为学界和出土古玉鉴定中的重要问题。由于埋藏环境的作用,许多玉器出土时的面貌和成分结构已发生很大改变。本研究运用扫描电子显微镜及能谱仪(SEM-EDX)、显微激光拉曼光谱仪(MLRM)和傅里叶变换红外光谱仪(FTIR)等分析设备,对湖北省京山市苏家垄遗址春秋时期M88号墓棺内出土的4件玉器残片以及1件现代透闪石玉原石开展比较研究。研究确认透闪石玉中除了纤维状的矿物成分,还包含玻璃相的高级脂肪酸盐,分布于晶界及晶体间隙的玻璃相脂肪酸盐在玉石晶链间形成缓冲,使透闪石玉具有较高的韧性,不易崩碎。当腐蚀发生时,脂肪酸盐会变质分解溶出,部分会在玉石裂隙及疏松处富集并吸附其他物质,致使玉石受沁。脂肪酸盐大量流失后,透闪石玉晶链因失去缓冲而极易碎裂。此时,链状结构中Ca-O键和Fe-O键因强度低于Mg-O键而优先断裂流失,使得玉石内阳起石结构减少,外观由半透明向不透明转变,甚至白化。关于古代玉石中脂肪酸盐来源及其对玉石影响的研究,为古玉研究开拓了新的途径。     

馆藏砖石质文物有害盐中多种无机及有机酸阴离子的定量分析

博物馆环境空气中无机或有机酸性污染气体会腐蚀馆藏砖石质文物并使其表面出现有害盐。常见的有害盐种类复杂,可能同时含有无机和有机酸阴离子。为进一步认识文物盐害和分析盐害产生的原因,本研究建立了一种基于离子色谱的有害盐中无机和有机酸阴离子定量分析方法。该方法可同时测定馆藏砖石质文物上有害盐中氟离子、氯离子、溴离子、硝酸根、亚硝酸根、磷酸根、硫酸根、甲酸根、乙酸根、丙酸根、丁酸根、戊酸根等十二种阴离子。采用2～30 mmol/L KOH淋洗液梯度洗脱,能够在35 min的检测时间下实现该十二种阴离子的快速分离与准确检测。所有阴离子的标准曲线的相关系数均高于0.995,检出限为0.001～0.022μg/mL,定量限为0.004～0.073μg/mL;加标回收率为81.8%～107.0%。该方法采用超纯水作为溶剂,样品处理简单,易于操作;具有成本低廉、检测时间短和准确性高的特点;可定量计算有害盐中多种无机及有机酸阴离子的质量分数。将该方法应用于中国国家博物馆馆藏“汉并天下”瓦当和仿制玉炉表面有害盐中的无机及有机酸阴离子的分析,可为分析盐害发生的原因,阻止、延缓及预测盐害的发生提供依据。     

老化丝织品的氨基酸分析研究

为了解氨基酸分析能否成为有效的研究丝织品老化原因及检测丝织品老化程度的方法,选用经光老化、热老化和水解老化的现代白色丝织品和出土于湖北、内蒙古、青海的古代丝织品为样品,将称好的样品用6mol／L的HCl在110℃恒温烘箱中水解22小时,然后用美国Waters公司产的氨基酸自动分析仪进行分离及检测,根据色谱图中各个氨基酸的峰面积得出各个氨基酸的百分含量。实验结果表明,光老化和热老化时,丝织品强度的损失与酪氨酸含量的降低呈线性关系;水解老化时,丝织品强度的损失与天门冬氨酸含量的降低呈线性关系。结果说明,氨基酸分析从分子水平上给出各种老化的特征及老化程度,无论是对于机理研究还是对于老化程度的判定,都很有实用意义。     

Aspartic acid racemization variability in ancient human remains: implications in the prediction of ancient DNA recovery

The extent of racemization of aspartic acid (Asp) – expressed as d/l ratio – has been used as a marker of biomolecular degradation in ancient remains. However, Asp racemization rate is highly variable, and depends on biochemical and geochemical factors. In this paper we aim to determine to which extent the fraction analyzed and the kind of sample used may influence the d/l Asp ratios. Other factors, such as burial site and sample preservation conditions, are also considered.     

A new method to remove copper corrosion stains from stone surfaces

This paper reports on a methodological study carried out in order to propose a cleaning procedure to remove stains produced by bronze corrosion products on surface of limestone (namely travertine); the procedure is effective and more environmentally friendly than the methods commonly used today. Several copper complexing or chelating agents were considered, including three amino acids and compared with some ion exchange resins. After a first laboratory phase on pure copper products and on artificially stained quarry samples, the optimized procedure was tested on the pedestal of a bronze statue in the Sapienza campus, in Rome. Colorimetry and ICP/OES were used to evaluate the efficiency of the cleaning procedure.     

The geochronological potential of isoleucine epimerisation in cassowary and megapode eggshells from archaeological sites

Our research demonstrates that the extent of isoleucine epimerisation (A/I) in fragments of avian eggshells provides geochronological information in archaeological contexts. In the archaeological sequence of Hay Cave, northern Queensland, Australia, there is an excellent correspondence between the A/I values of Australian brush-turkey (Alectura lathami) eggshells (n = 99) and independent geochronological control (n = 16 radiocarbon ages including 4 on eggshell calcite). The A/I values identify three phases of deposition during the Holocene at Hay Cave. In contrast to the Alectura eggshell A/I values, a poor correspondence was observed between the A/I values of cassowary (Casuarius) eggshells from Toé (n = 35) and Kria caves (n = 23) (Ayamaru Plateau, Papua) and the depths from which the specimens were recovered in these stratified sequences. Given coherent archaeofauna trends and radiocarbon chronologies (n = 8 and 2 eggshell calcite radiocarbon ages at Toé and Kria, respectively) with respect to depth, the variable A/I values are not explicable in terms of mixing. Rather, the variability is most likely due to exposure of the eggshells to the high temperatures of campfires. Despite the variability, eggshells with relatively low A/I values amongst specimens recovered from similar depths (and therefore presumably least influenced by high temperatures) exhibit a gradual increase in A/I with respect to depth, as expected in a stratified deposit. From this observation it is suggested that the identification of heated eggshells will increase confidence in geochronological information provided by A/I. These studies illustrate the complications that arise from campfire-induced acceleration of amino acid racemisation and emphasise that although this phenomenon is common, it is not universally encountered in archaeological contexts.     

Experimental chemical degradation compared to natural diagenetic alteration of collagen: implications for collagen quality indicators for stable isotope analysis

Stable isotopic ratios from archaeological bone collagen are valid palaeodietary indicators, but depend on sufficiently well preserved molecules and several collagen quality criteria have to be fulfilled (mostly collagen wt%, C%; N%, C/N molar ratio). For a reassessment of these quality criteria, and a better understanding of the chemical degradation of bone collagen, experimentally degraded modern bones and 54 archaeological human bones were investigated. In the course of the experimental degradation, alterations of isotopic ratios were paralleled by altered collagen quality criteria. The contrary was found in the case of the archaeological specimens. This implies that the commonly used collagen quality criteria may be insufficient and do not guarantee that stable isotopic values of the gelatine extracts will still represent the original biological signal.