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Images of ancient Egyptians wearing distinctive, cone-shaped objects on their heads have, in the absence of physical examples, long elicited scholarly debate. Did people wear these cones, or were they a purely iconographic device? What was their function and meaning? Recent excavations at the Amarna cemeteries now provide the first material examples of head cones. Spectroscopic analyses indicate that their primary constituent is a biological wax, and not fat or incense, as sometimes speculated. The authors tentatively suggest that the Amarna cones were symbols meant to enhance the rebirth or personal fertility of the deceased in the afterlife. Keywords: Egypt, Amarna, Akhetaten, Akhenaten, head cones, burial rites, Introduction For around 1500 years, from the early New Kingdom to the Ptolemaic period (c. 1549-30 BC), some visual representations of ancient Egyptians show individuals wearing a striking cone-shaped item [...]

Historically, many canvas paintings were infused with wax–resin mixtures that have discolored over time, distorting the aesthetics of the work, limiting treatment options, and introducing unstable materials into the object. Removal of the wax–resin is often desirable, but before works of art can be treated, a protocol to evaluate the efficacy of the treatment must be established. A mock-up painting was infused with a known amount of a wax–resin mixture made from beeswax and dammar; this material was then extracted through six intervals of exposure to solvent-loaded and dry sheets of Evolon® CR, a non-woven textile with a high sorbent capacity. Samples from the Evolon® CR sheets from each extraction round were analyzed using thermal separation probe gas chromatography–mass spectrometry (TSP-GC/MS). Normalization of peak areas related to beeswax and dammar to those of Evolon® CR revealed the relative amount of wax and resin removed throughout the extraction. The data show that, under these test conditions, the beeswax and dammar appear to be extracted with the same relative efficiency, information that cannot be provided through UV-induced visible fluorescence imaging of the Evolon® CR sheets or weight data alone, but which is critical to capture as it has implications for treatment success and the long-term stability of an artwork. [ABSTRACT FROM AUTHOR]

Copyright of Journal of the American Institute for Conservation is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of the American Institute for Conservation is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article examines the choice of pigments by artist Barnett Newman to create his colours non-destructive techniques in his series of paintings "Who's Afraid of red, yellow, and blue." Topics discussed include description made by Newman on the earliest painting in the series, finding on visual inspection made when creating the series, and Newman's 1965 interview with Davis Sylvester.

A collection of studio materials belonging to the Brazilian neo-concrete artist Hélio Oiticica (1937–1980) was analyzed to identify the pigments and binding media present in paint mixtures created by the artist and in Brazilian house, artist, and craft paints. The labels on some of the paint mixtures link them to specific artworks, including Invenções 6, 12, 23, and 34 (1959–1962), and Penetrável 1 (1961), and although the artworks themselves were not available for analysis, Oiticica's methodical journals include paint recipes for these objects. The findings reveal that Oiticica used a relatively narrow range of red and yellow pigments in the mixtures, and the majority of the paint mixtures appear to be oil or oils mixed with alkyds, sometimes with additional additives, including fungicides and extenders. The journal notes are often brief and incomplete, listing only a few paint mixtures for a given work, although many more paint mixtures exist in the collection. These samples, the only physical legacy remaining for much of Oiticica's work that was destroyed in a 2009 fire, offer an unparalleled glimpse into the materials used by this seminal artist and suggest a greater complexity to his works than has thus far been appreciated. [ABSTRACT FROM AUTHOR]

Yves Klein (1928–1962) is best known for his intensely blue monochromatic works made with International Klein Blue (IKB), a synthetic ultramarine blue pigment bound in a poly(vinyl acetate) binder. However, he also made monochromes in other colors, including red and pink, the pigments of which have never been elucidated. Analysis of one sculpture, three paintings, and one screenprint by micro-Fourier transform infrared spectroscopy (µ-FTIR), Raman and surface-enhanced Raman (SERS) spectroscopies, portable X-ray fluorescence spectroscopy (p-XRF), and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX), revealed that Klein used, knowingly or unknowingly, a variety of pink and red pigments, including Para Red, rhodamine 6G, rhodamine B, eosin Y, and alizarin lakes. The unexpected variety of pigments contrasts with his use of a single blue pigment and suggests he may not have held a singular vision of what constituted an iconic red or pink color. [ABSTRACT FROM AUTHOR]

Photography is one of the few fine art forms that were initially developed by scientists such as Herschel and Talbot; however, in the modern chemistry curriculum, photography has become divorced from its scientific beginnings and resides in the studio arts department of most universities. An upper-level undergraduate experiment is described in which students duplicate William Henry Fox Talbot's original silver-based photographic methods and analyze their prints by X-ray fluorescence spectroscopy. The students are able to successfully make prints and experimentally confirm whether the prints had been halide stabilized, thiosulfate-fixed, or toned with sulfur, selenium, or gold. Their experimental results are discussed in the context of preservation of museum collections and photograph conservation. This experiment introduced students to the field of conservation science, where chemistry is applied to the investigation and preservation of artistic or cultural materials, activities that often involve the re-creation of historic techniques. (Contains 1 table and 2 figures.)

The kinetics of tyrosyl radical, oxyferryl heme and peroxidase inactivation were examined in reactions of PGHS-1 reconstituted with heme or mangano protoporphyrin IX with a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), and ethyl hydrogen peroxide (EtOOH). Inactivation of the peroxidase activity during the reaction of PGHS-1 with EtOOH or 15-HPETE correlated with oxyferryl heme decay but not with changes in tyrosyl radical intensity or EPR line shape.

The 18:0-holo-acyl carrier protein delta(sup)9 desaturase reactivity is probed using fatty acids with single oxygen atom replacing the methylene groups in a C-18 fatty acyl chain. Results demonstrate desaturation, acyloxy chain scission, and 'register-shift' in binding of substrate. Data indicate that the desaturase-catalyzed reactions may initiate at the C-10 position.

Hydrogen bonding betweenTyr385 and Tyr348 is shown to be an important structural factor in the interaction of prostaglandin H synthase-2 (PGHS-2) with aspirin. One factor controlling the efficiency of coupling between the PGHS peroxidase and cycloogenase reactions is the rate of Tyr385 radical formation.

The reactions of the multiprotein diiron enzyme complex with stearoyl-acyl carrier protein are discussed. The changes in diiron enzymes in electronic configuration at metal centers are carried out by spectroscopic methods.

Hydroperoxides induce formation of a tyrosyl radical on Tyr385 in prostaglandin H synthase (PGHS). The Tyr385 radical initiates hydrogen abstraction from arachidonic acid, thereby mechanistically connecting the peroxidase and cyclooxygenase activities.

The article presents a laboratory experiment intended for undergraduate chemistry students that introduces them to the field of conservation science in which chemistry is applied in the investigation and preservation of artistic or cultural materials. Students use X-ray fluorescence spectroscopy to analyze duplicate prints they create via scientist William Henry Fox Talbot's original silver-based photographic methods.

Plant α-dioxygenases (PADOX) are hemoproteins in the myeloperoxidase family. We have used a variety of spectroscopic, mutagenic, and kinetic approaches to characterize the heme environment in Arabidopsis thaliana PADOX-1. Recombinant PADOX-1 purified to homogeneity contained 1 mol of heine bound tightly but noncovalently per protein monomer. Electronic absorbance, electron paramagnetic resonance, and magnetic circular dichroism spectra showed a high spin ferric heme that could be reduced to the ferrous state by addition. Cyanide bound relatively weakly in the ferric PADOX-1 heme vicinity (Kd ∼10 mM) but did not shift the heme to the low spin state. Cyanide was a very strong inhibitor of the fatty acid oxygenase activity (Ki ∼5 μM) and increased the Km value for oxygen but not that for fatty acid. Spectroscopic analyses indicated that carbon monoxide, azide, imidazole, and a variety of substituted imidazoles did not bind appreciably in the ferric PADOX-1 heme vicinity. Substitution of His-163 and His389 with cysteine, glutamine, tyrosine, or methionine resulted in variable degrees of perturbation of the heme absorbance spectrum and oxygenase activity, consistent with His-389 serving as the proximal heme ligand and indicating that the heme has a functional role in catalysis. Overall, A. thaliana PADOX-1 resembles a b-type cytochrome, although with much more restricted access to the distal face of the heme than seen in most other myeloperoxidase family members, explaining the previously puzzling lack of peroxidase activity in the plant protein. PADOX-1 is unusual in that it has a high affinity, inhibitory cyanide-binding site distinct from the distal heme face and the fatty acid site. [ABSTRACT FROM AUTHOR]

Membrane bound Prostaglandin H synthase (PGHS) is a key enzyme in prostanoid biosynthesis. It has two distinct enzyme activities: a cyelooxygenase activity that converts arachidonic acid (AA) to PGG2, and a peroxidase that converts PGG2 to PGH2. Understanding the protein orientation on the membrane will provide insights into the substrate presentation and the product release. We have determined the PGHS-1 orientation on the microsomal membrane using optical linear dichroism and EPR spectroscopy to define the orientation of the heme group. The oriented microsome membrane was prepared by partial dehydration of sheep seminal vesicle microsome sedimented onto film. Linear dichroism was determined as dichroic ratio between vertical and horizontal polarized light on the oriented membrane. A dichroic ratio of 1.05 of the heme Sorer band was obtained, indicating that the protein is partially oriented. Orientation-dependent changes of EPR signals were determined for both the rhombic signals at gx=6.25, gy=5.27 and the axial signal at gaxial=5.95 for the high-spin heine using a goniometer, The polar plot of gx and gy signal intensities against the angle between the external field and the membrane normal showed a period of 2π with two minimal gy signal and two maximal gx signal at 90 and 270 degree. These analyses give strong indication that the PGHS heme is almost perpendicular to the membrane. Inhibitor-treated PGHS-1 showed essentially the same heme orientation. Our determination of the PGHS-1 heme orientation is in contrast to that implied by X-Ray crystallographic data which predicted a 20 degree tilt from the membrane normal. These results will require reevaluation of the mechanism of AA access to the substrate channel and the product release as well as structural changes caused by crystallization. [ABSTRACT FROM AUTHOR]

Prostaglandin H synthase-1 (PGHS-1) is a bifunctional heme protein catalyzing both a peroxidase reaction, in which peroxides are converted to alcohols, and a cyclooxygenase reaction, in which arachidonic acid is converted into prostaglandin G2. Reaction of PGHS-1 with peroxide forms Intermediate I, which has an oxyferryl heme and a porphyrin radical. An intramolecular electron transfer from Tyr385 to Intermediate I forms Intermediate II, which contains two oxidants: an oxyferryl heme and the Tyr385 radical required for cyclooxygenase catalysis. Self-inactivation of the peroxidase begins with Intermediate II, but it has been unclear which of the two oxidants is involved. The kinetics of tyrosyl radical, oxyferryl heme, and peroxidase inactivation were examined in reactions of PGHS-1 reconstituted with heme or mangano protoporphyrin IX with a lipid hydroperoxide, 15-hydroperoxyeicosatetraenoic acid (15-HPETE), and ethyl hydrogen peroxide (EtOOH). Tyrosyl radical formation was significantly faster with 15-HPETE than with EtOOH and roughly paralleled oxyferryl heme formation at low peroxide levels. However, the oxyferryl heme intensity decayed much more rapidly than the tyrosyl radical intensity at high peroxide levels. The rates of reactions for PGHS-1 reconstituted with MnPPIX were approximately an order of magnitude slower, and the initial species formed displayed a wide singlet (WS) radical, rather than the wide doublet radical observed with PGHS-1 reconstituted with heme. Inactivation of the peroxidase activity during the reaction of PGHS-1 with EtOOH or 15-HPETE correlated with oxyferryl heme decay, but not with changes in tyrosyl radical intensity or EPR line shape, indicating that the oxyferryl heme, and not the tyrosyl radical, is responsible for the self-destructive peroxidase side reactions. Computer modeling to a minimal mechanism was consistent with oxyferryl heme being the source of peroxidase inactivation.

Plant alpha-dioxygenases (PADOX) are hemoproteins in the myeloperoxidase family. We have used a variety of spectroscopic, mutagenic, and kinetic approaches to characterize the heme environment in Arabidopsis thaliana PADOX-1. Recombinant PADOX-1 purified to homogeneity contained 1 mol of heme bound tightly but noncovalently per protein monomer. Electronic absorbance, electron paramagnetic resonance, and magnetic circular dichroism spectra showed a high spin ferric heme that could be reduced to the ferrous state by dithionite. Cyanide bound relatively weakly in the ferric PADOX-1 heme vicinity (K(d) approximately 10 mm) but did not shift the heme to the low spin state. Cyanide was a very strong inhibitor of the fatty acid oxygenase activity (K(i) approximately 5 microm) and increased the K(m) value for oxygen but not that for fatty acid. Spectroscopic analyses indicated that carbon monoxide, azide, imidazole, and a variety of substituted imidazoles did not bind appreciably in the ferric PADOX-1 heme vicinity. Substitution of His-163 and His-389 with cysteine, glutamine, tyrosine, or methionine resulted in variable degrees of perturbation of the heme absorbance spectrum and oxygenase activity, consistent with His-389 serving as the proximal heme ligand and indicating that the heme has a functional role in catalysis. Overall, A. thaliana PADOX-1 resembles a b-type cytochrome, although with much more restricted access to the distal face of the heme than seen in most other myeloperoxidase family members, explaining the previously puzzling lack of peroxidase activity in the plant protein. PADOX-1 is unusual in that it has a high affinity, inhibitory cyanide-binding site distinct from the distal heme face and the fatty acid site.