Chocolate is a Valentine’s Day must-have and popular among people with a sweet tooth. Many also claim it lifts mood or even acts as an aphrodisiac, and we’ve all heard someone say it's habit forming.

The compounds in chocolate that allegedly have positive effects come from the cacao bean, so the darker the chocolate, the more of these compounds it contains. Milk chocolate has less than dark chocolate, and white chocolate has nearly none because it includes no cocoa solids, only cocoa butter.

Chocolate contains upwards of 800 chemical compounds, just a handful of which are explored in this infographic. See more chemistry infographics like this one in C&EN's Periodic Graphics collection. Click to enlarge

Does science back up the common claims about chocolate? To find the answers, we’re taking a look at the chemistry behind this treat.

Michael Boyce, associate professor of biochemistry at Duke University in Durham, North Carolina. Credit: Michael Boyce.

Sugars aren't merely energy sources for our cells. They also play important signaling roles through a process called glycosylation, where they attach to proteins and lipids as tags. Although these sugar tags, called glycans, impact many cellular processes, they have long been understudied due to technical challenges. Now, advances in analytical tools like mass spectrometry are enabling scientists to examine the enormous complexity of glycans. Other advances also allow researchers to synthesize complex sugars, providing them with standards for analytical experiments.

Over the past 12 months, we’ve explored a variety of topics in genetics, cell biology, chemistry, and careers in the biomedical sciences. As we ring in the new year, we bring you our top three posts of 2019. If your favorite is missing, let us know what it is in the comments section below!

Amazing Organisms and the Lessons They Can Teach Us

Hawaiian bobtail squid. Credit: Dr. Satoshi Shibata.

Studying research organisms, such as those featured in this post, teaches us about ourselves. These amazing creatures, which have some traits similar to our own, may hold the key to preventing and treating an array of complex diseases.