Scientists have developed a new laser-based technique for distinguishing enantiomers—molecules that exist as mirror-image forms. These chiral molecules may look nearly identical, yet they can behave very differently in biological systems, chemical reactions, and medicines. The new method uses twisted light to identify molecular handedness through measurable ion signals.
Molecular chirality can be compared to the relationship between a screw and its matching thread. A right-handed screw fits a right-handed thread, while a left-handed screw does not. In a similar way, specially structured laser light can interact differently with chiral molecules depending on whether their handedness matches the light’s twist.
Using Twisted Laser Light to Detect Chirality
Researchers from the Tata Institute of Fundamental Research (TIFR), the Indian Institute of Technology Mumbai, and the Indian Institute of Technology Hyderabad have engineered laser light with two forms of angular motion. In addition to spinning, the light twists as it travels forward, creating a structured beam that can act as a sensitive probe of molecular shape.
When this twisted light interacts with a chiral molecule, the resulting response depends on how the light’s twist corresponds to the molecule’s natural handedness. This difference produces measurable signals that can reveal which enantiomer is present.
Breaking Chiral Molecules Into Measurable Fragments
The experiments were conducted at the laser facility at TIFR Hyderabad. Researchers exposed gaseous samples of the chiral molecule R- or S-camphor to ultrashort laser pulses lasting a few hundred femtoseconds. The pulses had carefully controlled spin and orbital twist.
The intense laser pulses caused the camphor molecules to break apart and form charged fragments, or ions. Scientists analyzed these fragments using a time-of-flight mass spectrometer, which identifies ions by measuring how long they take to reach a detector. Smaller, lighter fragments generally arrive before heavier ones.
The experiments revealed a clear pattern: the number of ions produced varied according to the combination of the laser beam’s twist and the molecule’s handedness. By comparing fragment yields, the researchers could distinguish between the two mirror-image forms of camphor.
A More Direct Method for Identifying Molecular Handedness
Traditional techniques for detecting molecular chirality often rely on extremely small differences in light absorption. Other approaches measure the direction in which electrons are emitted. These methods may require complex instrumentation, precise beam alignment, angular measurements, or coincidence detection.
The new approach detects chirality directly through ion signals generated when molecules are broken apart by twisted laser light. This could simplify measurements while improving the sensitivity of chiral molecule detection.
Analyzing Molecules Without Solvents or Surfaces
The researchers studied the molecules in the gas phase, removing external influences from solvents, containers, and surfaces. This experimental setup allowed them to observe the fundamental interaction between structured light and molecular chirality more directly.
The twisted laser beams also amplified the difference between the two enantiomers. This produced stronger signals than those typically associated with conventional optical methods for measuring chirality.
Connecting Structured Light With Chiral Matter
The findings demonstrate a new way to match the “threads” of light and matter. Twisted laser beams can serve as powerful probes for identifying molecular handedness with greater simplicity and precision.
The technique could support future advances in chemistry, molecular physics, biology, and pharmaceutical research. Identifying the correct enantiomer is especially important in medicine because two mirror-image forms of the same compound can produce significantly different biological effects.
Source: www.sciencedaily.com