PubChem presents at the American Chemical Society National Meeting in San Francisco (April 2-6, 2017)

On April 2-6, 2017, the 253rd American Chemical Society National Meeting will be held in San Francisco, CA, the theme of which is “Advanced Materials, Technologies, Systems & Processes”.  The PubChem team will be at the ACS meeting to present new developments and recent changes in PubChem.  Below are a list of presentations that will be given by the PubChem staff.


Day 1 (Sunday, April 2)


Day 2 (Monday, April 3)


Day 3 (Tuesday, April 4)


Day 4 (Wednesday, April 5)


Atomic mass changes in PubChem

PubChem is now using the latest International Union of Pure and Applied Chemistry (IUPAC) recommendations for atomic mass and isotopic composition information.  In addition, PubChem is now restricting the allowed isotopes for a given element to those with a half-life of one millisecond or greater.

Fundamental changes within atomic mass information

Hydrogen and DeuteriumNormally atomic mass updates are not blog worthy; however, there are some fundamental changes in the way masses are conceptualized that affect the atomic weight values computed for nearly all compounds in PubChem.

Molecular weight is one of the most frequently requested pieces of information about a chemical.  To compute a molecular weight of a molecule, one consults a periodic chart and sums the average atomic weights of the elements comprising the chemical, while considering any specified isotopic enrichment information.  Although the molecular weight computation seems straightforward, as greater degrees of precision in atomic masses are known, the chemical science community is recognizing complex issues with average atomic weight and isotopic data.

The abundance ratio between different isotopes of a given element is used to determine its average atomic weight.  As the sensitivity of measuring equipment has increased, scientists now notice a distinct difference in these abundance ratios depending on the material source of that element.  To reflect this variation, and as explained in this IUPAC technical report, many elements are now given an atomic weight interval, consisting of a range of known discrete values reflecting the varying isotopic abundance ratios found in different elemental material sources. For example, the atomic weight interval of carbon is 12.0096 to 12.0116.

Another complicating factor is that the abundance ratio of naturally occurring isotopes is not available for all elements.  Some elements like radon do not have any stable isotope and no characteristic isotopic composition in earthly materials.  It means that no average atomic weight can be determined!  There are also a growing number of elements that do not exist in nature, being “synthesized” in the lab.  These artificially created elements are metastable, rapidly decaying into other elements.  Importantly, because different isotopes of a given element decay at different rates, the isotopic abundance ratio between isotopes is time-dependent.

All of these considerations contribute to the uncertainty in atomic weight and isotopic information, which in turn impacts the molecular weight of a compound.

What changes did PubChem make?

All molecular weights in the PubChem Compound database were updated as such:

  • Adoption of “conventional atomic weights”Periodic Table
    To provide a single, representative average atomic-weight value for an element ignoring any material source uncertainties, the latest IUPAC recommendations include a concept of “conventional atomic weight value” whereby most or all atomic-weight variation in normal materials is covered (with an interval of ± 1 in the last digit).  PubChem has adopted this approach for the twelve elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine, and thallium) with standard atomic weights given as intervals.
  • Standard atomic weights updated
    Standard atomic weights in PubChem use the latest values provided by IUPAC (except when a conventional atomic weight value is used).  For the thirty-four elements without any abundance information (e.g., technetium), the atomic weight of the most stable, non-theoretical isotope was used, as found in the NuBase2012 evaluation ( of nuclear and decay properties.
  • Trimmed precision of molecular weights
    To take into account the uncertainties in elemental abundances and masses, the precision of all molecular weight values were reduced from six to three digits beyond the decimal point.
  • Updated allowed isotopes for elements
    The internal PubChem knowledgebase used to generate the PubChem Compound database from the PubChem Substance database was updated.  (Read this blog if you are not familiar with how these two databases differ from each other.)  As a part of this, only isotopes for elements with an experimentally measured half-life of one millisecond or greater were allowed when using the NuBase2012 evaluation of nuclear and decay properties (  This (slightly) modifies the scope of what can be found in the PubChem Compound database.

 Where can you learn more about this topic?

To learn more about this topic, please read the following:

  • Atomic weights of the elements 2013 (IUPAC Technical Report)
    Meija et al., Pure Appl. Chem. 2016; 88(3): 265-291.
    doi: 10.1515/pac-2015-0305
  • Isotopic compositions of the elements 2013 (IUPAC Technical Report)
    Meija et al., Pure Appl. Chem. 2016; 88(3): 293-306.
    doi: 10.1515/pac-2015-0503

New PubChem Data Sources Page

The PubChem Data Sources page is now updated.

What is the Data Sources page?

As an archive, PubChem contains information from hundreds of sources from all over the world.  Contributors can provide different types of content, such as substances, bioassays, and annotation.  The Data Sources page is an interface that helps one to determine, among other things, who provided what information.PubChem Data Sources

What changed?

As a part of an underlying technology update of PubChem, this page has been completely overhauled with a new look and feel.  The categorization describing the organization types providing content was simplified.  Sources of hierarchical classifications and textual annotations are now included.  There is now a unified data source table containing all primary information.  The updated interface provides new and improved capabilities to navigate as a function of data type, category, and country, while also including keyword searching, counts, and geographic visualization.

  • Filtering capability
    A panel (on the left-hand side of the screen) now summarizes (by count) key aspects of PubChem data sources.  By clicking the check boxes, one can filter the data sources listed.

By type
Classification of the type of information provided to PubChem.  This includes the ability to consider data ‘on-hold’ (to be released at a later date).

By category
General-purpose groupings that describe the contributing organization.

By status
Separates active contributors from legacy.  As explained in this post, some contributors or projects no longer exist (although their contributed data may still have substantial utility or value).

By geographic region
PubChem data contributors span the globe.  One can now filter and visualize by country.

PubChem - Nature Chemistry

  • Expanded sorting capability
    The improved Data Sources page allows users to sort by record counts and last-modified date.  For example, sort by last-modified date helps to identify organizations who recently updated their content.
  • Exploring sources on a mobile device
    As with other PubChem pages developed in recent years, great effort is taken to make the page adapt to the unique experience of mobile devices.  This means that without sacrificing features, the layout scales and complexity adjusts to match the appropriate screen size.
  • Improved individual data source page
    If you click on a data source link in PubChem, it now directs you to a dedicated page for that depositor.  Beyond showing contact information with its location displayed on a Google Map, it provides the date content was last updated and the current counts of submitted records.

An Update to PubChem Widgets

PubChem Widgets 2.0f is released. The update substantially updates all table-based widgets and classification widgets, while adding new capabilities and features. The autocomplete widget remains unchanged from the previous version.


What are PubChem Widgets?

PubChem content is enormous and changes on a daily basis.  Keeping an effective mirror of this corpus is not trivial.  PubChem Widgets enable scientific web developers to display PubChem content within webpages they design.  All data comes directly from PubChem and, therefore, obviates the need to mirror that content.  This makes it easier to harness the vast scientific knowledge within PubChem on your own webpage, such as summaries of patents, bioactivities and PubMed articles linked to a PubChem record. They can also be used to provide an autocomplete function that suggests a list of terms when you type input into a search field.


What is new in PubChem Widgets 2.0f?

  • Simpler to embed
    It is now simpler to embed a data view widget into any web page using PubChem Widgets 2.0f. All you need is to include an HTML iframe tag with a proper URL as the ‘src’ attribute. For instance, to embed a PubChem widget from the above example, add the following code to your webpage at the location where you want the widget to appear:

    <iframe class="pubchem-widget" 
            style="border: 0;  width: 100%; height: 250px;">

    The widget then renders the desired content for you.

  • Easier to resize
    The open source iframe resizer is able to resize an iframe automatically for you. To use it, add the following code to your page (only once, even if you have multiple PubChem widgets on the same page) just before the closing body tag:

    <script type="text/javascript" src=""></script>
    <script type="text/javascript">iFrameResize({log:false,checkOrigin:false}, '.pubchem-widget')</script>


How to convert to PubChem Widgets 2.0f?

Detailed instruction on how to convert PubChem Widgets 2.0f is given in this Conversion Guide.  PubChem Widgets 1.0 will be retired soon.  If you are using the PubChem Widgets 1.0 tables and classifications in your web pages, please update to PubChem Widgets 2.0f as soon as possible.  [Please note there is no change required for conversion of the autocomplete widgets.]


For more information on PubChem Widgets 2.0f, please read these pages:

PubChem presents at the 252nd ACS national meeting in Philadelphia

The 252nd American Chemical Society National Meeting will be held in Philadelphia, PA from August 21 to August 25, 2016.  At this meeting, whose theme is “of the people, by the people, for the people”, Drs. Stephen Bryant and Evan Bolton will be presented the Herman Skolnik Award honoring their leadership in the PubChem project.  See here for more details about the Herman Skolnik Award.

In addition, the PubChem team and collaborators will give a total of eight oral presentations at the meeting to present recent developments and updates in PubChem.

Monday, August 22

Tuesday, August 23

Wednesday, August 24

Thursday, August 25

The PubChem team is also involved in organizing several symposia at this meeting, including:

Important Changes to PubChem Web Protocols

PubChem will no longer use HTTP web URLs in favor of HTTPS by September 30, 2016.

What does this mean to you?

Currently, PubChem supports both HTTP and HTTPS web URLs. For example, both URLs and take you to PubChem. However, by September 30, 2016, the HTTP web protocol will be retired in favor of the HTTPS protocol. Furthermore, the HTTPS web protocol will be implemented according to the HTTPS-Only Standard. Any attempt to access PubChem after September 30, 2016 using a web URL starting with “http:” may no longer work.

For the most part, this change will be invisible to you as PubChem started to use HTTPS protocol in early 2014. Today, many sites are using HTTPS when linking to PubChem with an URL. However, those still accessing PubChem using the HTTP protocol will need to be updated to the HTTPS protocol.

Why the change?

On June 8, 2015, the US federal government issued a HTTPS-only policy for all publicly accessible Federal websites.  As a part of this mandate, the National Center for Biotechnology Information (NCBI) recently announced important changes to NCBI Web Protocols to adopt HTTPS on September 30, 2016. A webinar is available on the NCBI YouTube channel that explains how this will affect access to web pages. PubChem resides at NCBI and will adopt the same HTTPS-only policy.

Why is this change being mandated?

The unencrypted HTTP protocol does not protect data from interception or alteration, which can subject users to eavesdropping, tracking, and the modification of received data. The regular unencrypted HTTP protocols create some vulnerabilities and may expose potentially sensitive information about users to hackers. The information may include browser identities, website contents, search terms, user submitted information, and more. Many commercial organizations such as banks have already adopted HTTPS-only policies to protect users when using their websites and services.

HTTPS verifies the identity of a website or web service for a connecting client, and encrypts nearly all information sent between the website or service and the user. Protected information includes cookies, user agent details, URL paths, form submissions, and query string parameters. HTTPS is designed to prevent this information from being read or changed while in transit. HTTPS provides a layer of protection for web users, however, it may be worth noting that HTTPS has several important limitations. IP addresses and destination domain names are not encrypted during communication. Even encrypted traffic can reveal some information indirectly, such as time spent on site, or the size of requested resources or submitted information.

To learn more, visit these websites:


PubChem presents at the American Chemical Society National Meeting in San Diego (March 13-17, 2016)

On March 13-17, 2016, the 251st American Chemical Society National Meeting will be held in San Diego, CA, the theme of which is “Computers in Chemistry”.  The PubChem team will be at the ACS meeting to present new developments and recent changes in PubChem.  Below is a list of presentations that will be given by the PubChem staff.


Day 1 (Sunday, March 13)

Day 2 (Monday, March 14)

Day 3 (Tuesday, March 15)

Day 4 (Wednesday, March 16)

Day 5 (Thursday, March 17)