Science Concentrates ART & ARTIFACTS
Spotting fake silks Analyzing amino acid signatures reveals forgeries among Persian silks held by the George Washington University Museum and the Textile Museum: twelve possible frauds that had not been previously 14C dated and one authentic sample that had been dated. Moini’s test analyzes the amino acids in silk. As proteins age, some of their amino acids reconfigure, switching from far-morecommon left-handed conformations (L) to right-handed ones (D). Aspartic acid is the amino acid most prone to this process; the higher the ratio of D- to L-aspartic acid in silk proteins, the older the silk sample. The 14C-dated authentic Buyid silk had an aspartic acid D:L ratio of 29.6%, very close to the expected 30% for a sample 1,000 years old. The ratio for 11 of the 12 dubious silks ranged widely, up to 51.8%. Moini also found abnormally high phenylalanine and tyrosine D:L ratios in most of the possible forgeries. These amino acids
This purported ancient Persian silk is a forgery, according to recent tests. reconfigure slowly enough that in naturally aged 1,000-year-old silks, D-phenylalanine and D-tyrosine are almost undetectable. To determine how forged silks might have been artificially aged, Moini’s graduate student Christopher Rollman took modern silks and heated them, shined light on them, or exposed them to a base at high temperatures. The last of these methods resulted in spiked D-aspartic acid, D-phenylalanine, and D-tyrosine levels. “We can reproduce the signatures exactly,” Moini says. “In my opinion, the paper is conclusive,” says Ernst Kenndler of the University of Vienna, adding that high levels of D-aspartic acid, D-phenylalanine, and D-tyrosine together indicate artificial aging of silk.—LOUISA DALTON, special to C&EN
DRUG DELIVERY
Microneedle skin patch fights fat Patch slowly and safely releases a drug that transforms white fat to brown in mice A new skin patch can burn fat at the site where it’s applied. Researchers have shown that in mice, dozens of tiny microneedles on the patch slowly and painlessly deliver a drug that transforms energy-storing white fat into calorie-burning brown fat (ACS Nano 2017, DOI: 10.1021/acsnano.7b04348). The device could offer an effective and safe way to fight obesity and diabetes, says codeveloper Zhen Gu of the University of North Carolina, Chapel Hill, and North Carolina State University. Mammals have two types of fatty tissue. White tissue stores energy and is linked to obesity, heart disease, and diabetes. In cold weather, it can turn into brown fat, which consumes energy and produces heat to keep us warm, countering weight gain. Scientists have identified drugs that can spur this process, but they can have serious side effects when taken as pills or injections. Last year, researchers showed that the
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C&EN | CEN.ACS.ORG | OCTOBER 16, 2017
drug rosiglitazone—approved by FDA to treat diabetes but also capable of transforming white into brown fat—could accumulate in the fat tissue of mice when packed into nanoparticles (Proc. Natl. Acad. Sci. USA 2016, DOI: 10.1073/ pnas.1603840113). Using a patch to deliver the drug locally “was extremely creative and smart to mitigate drug toxicity,” says Omid Farokhzad of Harvard Medical School, who was part of the earlier study. Gu, along with Li Qiang of Columbia
University and colleagues, loaded dextran nanoparticles with glucose oxidase enzyme and rosiglitazone. They coated the particles with alginate and packed them into a 7- by 7-mm hydrogel patch with 121 conical microneedles (scanning electron micrograph shown). When the microneedles puncture the top layer of the skin, blood glucose seeps into the hydrogel and reacts with the glucose oxidase, creating an acid that degrades the alginate and releases the drug. The team attached patches, changing them every three days for four weeks, to the shaved lower abdomen of obese mice. With the same food intake, the treated animals had 20% less subcutaneous fat in the area under the patch and lower fasting blood glucose levels. Translating the results from mice to humans could be difficult, says John B. Buse of the University of North Carolina School of Medicine. “Mice have much more brown fat than humans, and it is possible that the effect in humans will be less striking.”—PRACHI PATEL, special to C&EN
CR E D I T: TH E T EXT IL E M US E U M, WAS H I N GTO N , D.C. , 3. 24 0 , ACQ UI R E D BY G EO RG E H EW I T T M Y E RS I N 1 946 (SI L K ); ACS N A N O (M I CRO G RA P H )
Chemists have used telltale chemical traces to affirm suspicions of ancient silk forgeries. They show that amino acid analysis can tell real ancient silk from fake, and their analysis suggests the manner of deception (Anal. Chem. 2017, DOI: 10.1021/acs. analchem.7b02854). In 1924, archaeologists unearthed rare Persian silks from the Buyid period (A.D. 934–1062) at the burial site of Princess Bibi Shahrbanu in Iran. Shortly afterward, suspected fakes appeared in the antiquities market. Decades later, carbon-14 dating proved that at least some of the Buyid silks sold after 1930 are forgeries. Mehdi Moini, a forensic chemist at George Washington University, had previously developed a dating test that requires far less sample and is less expensive than 14C dating. He has now applied the method to threads from Buyid silk specimens
