Following the people and events that make up the research community at Duke

Tag: biology

Researchers created a tiny circuit through a single water molecule, and here’s what they found

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Graphic by Limin Xiang, Arizona State University

Many university labs may have gone quiet amid coronavirus shutdowns, but faculty continue to analyze data, publish papers and write grants. In this guest post from Duke chemistry professor David Beratan and colleagues, the researchers describe a new study showing how water’s ability to shepherd electrons can change with subtle shifts in a water molecule’s 3-D structure:

Water, the humble combination of hydrogen and oxygen, is essential for life. Despite its central place in nature, relatively little is known about the role that single water molecules play in biology.

Researchers at Duke University, in collaboration with Arizona State University, Pennsylvania State University and University of California-Davis have studied how electrons flow though water molecules, a process crucial for the energy-generating machinery of living systems. The team discovered that the way that water molecules cluster on solid surfaces enables the molecules to be either strong or weak mediators of electron transfer, depending on their orientation. The team’s experiments show that water is able to adopt a higher- or a lower-conducting form, much like the electrical switch on your wall. They were able to shift between the two structures using large electric fields.

In a previous paper published fifteen years ago in the journal Science, Duke chemistry professor David Beratan predicted that water’s mediation properties in living systems would depend on how the water molecules are oriented.

Water assemblies and chains occur throughout biological systems. “If you know the conducting properties of the two forms for a single water molecule, then you can predict the conducting properties of a water chain,” said Limin Xiang, a postdoctoral scholar at University of California, Berkeley, and the first author of the paper.

“Just like the piling up of Lego bricks, you could also pile up a water chain with the two forms of water as the building blocks,” Xiang said.

In addition to discovering the two forms of water, the authors also found that water can change its structure at high voltages. Indeed, when the voltage is large, water switches from a high- to a low-conductive form. In fact, it is may be possible that this switching could gate the flow of electron charge in living systems.

This study marks an important first step in establishing water synthetic structures that could assist in making electrical contact between biomolecules and electrodes. In addition, the research may help reveal nature’s strategies for maintaining appropriate electron transport through water molecules and could shed light on diseases linked to oxidative damage processes.

The researchers dedicate this study to the memory of Prof. Nongjian (NJ) Tao.

CITATION: “Conductance and Configuration of Molecular Gold-Water-Gold Junctions Under Electric Fields,” Limin Xiang, Peng Zhang, Chaoren Liu, Xin He, Haipeng B. Li, Yueqi Li, Zixiao Wang, Joshua Hihath, Seong H. Kim, David N. Beratan and Nongjian Tao. Matter, April 20, 2020. DOI: 10.1016/j.matt.2020.03.023

Guest post by David Beratan and Limin Xiang

Combining Up-Close Views of Science, Nature With the Magic of Light

Zinnia stamen by Thomas Barlow, Duke University

Thomas Barlow ’21 finds inspiration in small everyday things most people overlook: a craggy lichen growing on a tree, a dead insect, the light reflected by a pane of glass. Where we might see a flower, Barlow looks past the showy pink petals to the intricate parts tucked within.

The 20-year-old is a Duke student majoring in biology. By day, he takes classes and does research in a lab. But in his spare time, he likes to take up-close photographs using objects he finds outside or around the lab: peach pits, fireflies. But also pipettes, pencils.

A handheld laser pointer and flitting fireflies become streaks of light in this long-exposure image in Duke Forest. By Thomas Barlow.

Barlow got interested in photography in middle school, while playing around with his dad’s camera. His dad, a landscape architect, encouraged the hobby by enlisting him to take photos of public parks, gardens and playgrounds, which have been featured on various architects’ websites and in national publications such as Architecture Magazine. But “I always wanted to get closer, to see more,” Barlow said.

In high school he started taking pictures of still lifes. But he didn’t just throw flowers and fruit onto a backdrop and call it art. His compositions were a mishmash of insects and plants arranged with research gadgets: glass tubes, plastic rulers, syringes, or silicon wafers like those used for computer chips.

“I like pairing objects you would never find together normally,” Barlow said. “Removing them from their context and generating images with interesting textures and light.”

Sometimes his mother sends him treasures from her garden in Connecticut to photograph, like the pale green wings of a luna moth. But mostly he finds his subjects just steps from his dorm room door. It might be as easy as taking a walk through Duke Gardens or going for one of his regular runs in Duke Forest.

Having found, say, a flower bud or bumblebee, he then uses bits of glass, metal, mirrors and other shiny surfaces — “all objects that interact with light in some interesting way” – to highlight the interaction of light and color.

“I used to be really obsessed with dichroic mirrors,” pieces of glass that appear to change colors when viewed from different angles, Barlow said. “I thought they were beautiful objects. You can get so many colors and reflections out of it, just by looking at it in different ways.”

In one pair of images, the white, five-petaled flowers of a meadow anemone are juxtaposed against panels of frosted glass, a pipette, a mechanical pencil.

Another image pair shows moth wings. One is zoomed in to capture the fine details of the wing scales. The other zooms out to show them scattered willy-nilly around a shimmering pink circle of glass, like the remnants of a bat’s dinner plate.

Luna moth wings and wing scales with dichroic mirror, Thomas Barlow

For extreme close-ups, Barlow uses his Canon DSLR with a microscope objective mounted onto the front of a tube lens. Shooting this close to something so small isn’t just a matter of putting a bug or flower in front of the camera and taking a shot. To get every detail in focus, he takes multiple images of the same subject, moving the focal point each time. When he’s done he’s taken hundreds of pictures, each with a different part of the object in focus. Then he merges them all together.

At high magnification, Barlow’s flower close-ups reveal the curly yellow stamens of a zinnia flower, and the deep red pollen-producing parts of a tiger lily.

“I love that you can see the spikey pollen globules,” Barlow said.

Stomata and pollen on the underside of a tiger lily stamen, by Thomas Barlow

When he first got to Duke he was taking photos using a DIY setup in his dorm room. Then he asked some of the researchers and faculty he knew if there was anything photography-related he could do for their labs.

“I knew I was interested in nature photography and I wanted to practice it,” Barlow said.

One thing led to another, and before long he moved his setup to the Biological Sciences building on Science Drive, where he’s been photographing lichens for Daniele Armaleo and Jolanta Miadlikowska, both lichenologists.

“A lichen photo might not seem like anything special to an average person,” Barlow said. “But I think they’re really stunning.”

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