About

Songi Han is a Physical Chemist and Professor in the Department of Chemistry at Northwestern University, also affiliated with Northwestern's Applied Physics Program. She joined Northwestern University in July 2023 after a 20-year career as a Professor in the Department of Chemistry and Biochemistry at the University of California, Santa Barbara. Her research focuses on electron and nuclear spins as quantum reporters, sensors, and active signal transducers in life science chemistry. She serves on the Executive Committee of the International EPR Society since 2020 and is a Fellow of the International Society of Magnetic Resonance (ISMAR). Additionally, she is the inaugural chair of a new Gordon Research Conference on Magnetic Resonance and Quantum Information Science scheduled for 2026 and will serve as the Vice-Chair elect of the ACS PHYS division starting in Fall 2026.

Research topics

• Chemistry
• Biochemistry
• Biology
• Biophysics
• Psychology
• Statistics
• Materials science
• Neuroscience
• Thermodynamics
• Physics
• Chromatography
• Internal medicine
• Mathematics
• Medicine

Selected publications

• Enhancing Water Harvesting Efficiency in a Phosphonate Metal–Organic Framework through Controlled Defect Generation

  ACS Materials Letters · 2025-05-16 · 6 citations

  article

  Global access to drinking water shrinks yearly, yet the atmosphere─our largest sustainable water source─remains largely untapped. Metal–organic frameworks (MOFs), a tunable class of crystalline porous materials, are promising candidates for atmospheric water harvesting. The channel-pore MOF STA-16(Co) stands out due to its robust phosphonate-based structure, which provides high stability and excellent water uptake. However, STA-16(Co) suffers from slow water uptake kinetics. To address this limitation, we introduced defects into STA-16(Co) by selectively removing linkers through treatment with nitrilotriacetic acid, significantly improving water diffusion kinetics. The defective MOFs demonstrate markedly faster water saturation rates─delivering ∼50% more water in a 40 min cycle─while maintaining the same uptake capacity and isothermal behavior as pristine STA-16(Co). Solid-state nuclear magnetic resonance analysis confirms that localized defects enhance efficiency without altering the overall pore geometry. This study presents a straightforward and generalizable strategy to optimize water sorption in channel-based MOFs.

  PublisherDOI

• Structure-specific Mini-Prion Model for Alzheimer’s Disease Tau Fibrils

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-06-27

  preprintOpen accessSenior authorCorresponding

  Abstract A critical discovery of the past decade is that tau protein fibrils adopt disease-specific hallmark structures in each tauopathy. The faithful generation of synthetic fibrils adopting hallmark structures that can serve as targets for developing diagnostic and/or therapeutic strategies remains a grand challenge. We report on a rational design of synthetic fibrils built of a short peptide that adopts a critical structural motif in tauopathy fibrils found in Alzheimer’s Disease (AD) and Chronic Traumatic Encephalopathy (CTE). They serve as minimal prions with exquisite seeding competency, in vitro and in tau biosensor cells, for recruiting tau constructs ten times larger its size en route to AD or CTE fibril structures. We demonstrate that the generation of AD and CTE-like fibril structures is dramatically catalyzed in the presence of mini-AD prions and further influenced by salt composition in solution. Double Electron-Electron Resonance studies confirmed the preservation of AD-like folds across multi-generational seeding. Fibrils formed with the full AD/CTE-like core show strong seeding competency, with their templating effect dominating over the choice of salt composition that tunes the initial selection of AD- and CTE-like fibril populations. The mini-AD prions serve as a potent catalyst with templating capabilities that offer a novel strategy to design pathological tau fibril models.

  PublisherOA PDFDOI

• Pump-Induced Dipolar Order to Evaluate Electron Spin Coupling Networks and Many-Body Effects

  ChemRxiv · 2025-10-14

  articleSenior author

  Networks of coupled electron spins are integral to applications in dynamic nuclear polarization, quantum information science, and materials properties emerging from many-body correlations. A minimal condition for electron spin entanglement or many- body spin correlations is dipolar order, yet techniques for creating and characterizing electron dipolar order of paramagnetic species are not broadly available. Here, we generate pump-induced dipolar order between P1 centers in powdered diamond samples and probe its formation by ELDOR (ELectron DOuble Resonance) and OOP-ESEEM (Out-Of-Phase Electron Spin Echo Envelope Modulation). ELDOR experiments on P1 centers show electron spin hyperpolarization which we attribute to the generation of dipolar order and subsequent conversion to Zeeman order. Pump-initialized OOP- ESEEM directly detects P1 dipolar order, with simulations confirming the experimental signatures originate from a heterogeneous network of coupled P1 centers. These results establish new approaches for monitoring dipolar order formation and probing materials’ potential for many-body effects.

  PublisherDOI

• DEER of Singly Labelled Proteins to Evaluate Supramolecular Packing of Amyloid Fibrils

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-11-12

  preprintOpen access

  The formation of protein amyloid fibrils in the brain is a hallmark of various neurodegenerative diseases, including Alzheimer diseases and Parkinson diseases. Amyloid fibrils are highly ordered aggregates in which proteins folded in two-dimensional layers stack along one axis to form elongated linear assemblies. The specific conformations adopted by the proteins within each layer of the amyloid correlates with the pathology. Furthermore, their spreading and templating competency relies on strict in register packing of the folded proteins along the fibril growing axis. There is a need for tools to characterize not only the protein fold across the fibril cross section but also the spatial ordering of the proteins stacked along the amyloid fibril axis. We present an approach based on double electron electron resonance spectroscopy (DEER) using singly labelled tau protein assembled in amyloid fibrils that can deliver an apparent dimensionality of the supramolecular organization of tau fibrils. The parameters of the DEER background function can be used to assess the amyloid core location and packing order, and track time-resolved formation of aggregation intermediates. Showcasing the method on tau, we demonstrate that heparin-induced tau fibrils are mispacked while seeded aggregation can template amyloid fibrils with a higher packing order. This study benchmarks a new method that will provide critical structural insights into amyloid assemblies.

  PublisherDOI

• Protein-Like Polymer for Inhibition of Tau Fibril Propagation in Human-Derived Models of Neurodegeneration

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-02-03

  preprint

  Abstract The misfolding, aggregation, and spread of tau protein fibrils underlie tauopathies, a diverse class of neurodegenerative diseases for which effective treatments remain elusive. Among these are corticobasal dementia (CBD) and progressive supranuclear palsy (PSP), canonical examples of 4-repeat (4R) tauopathies characterized by tau isoforms exclusively with four microtubule-binding repeat domains. We target this 4R tau isoform-specific mechanism by focusing on misfolded tau’s distinctive stem-loop-stem structural motif formed by the junction of the 4R-defining alternatively spliced exon and the adjacent constitutive exon. A synthetic peptide based on this stem-loop-stem sequence can induce aggregation and spread in an isoform-specific manner. Here, we develop a protein-like polymer (PLP) in which multiple copies of this synthetic peptide form a brush-like structure capable of preventing tau aggregation by binding and capping fibril ends in vitro , in human brain organoids, and in cellular models with an EC50 of 105 ± 14 nM. PLPs demonstrate robust activity against fibrils derived from CBD and PSP patient brains and a PS19 mouse tauopathy model. Previous tau-targeted treatments have primarily focused on broad tau clearance, aggregation inhibition, or microtubule stabilization, often lacking isoform specificity and precision. In contrast, this approach targets the 4R tau isoform’s unique structural motif, offering a tailored therapeutic intervention for diseases like CBD and PSP. Supported by prior studies showing blood-brain barrier penetrance and safety profiles, this tau-binding PLP offers a promising translational path toward clinical applications in tauopathy treatment.

  PublisherDOI

• P1 center network in high-pressure high-temperature diamonds is a readily accessible source of nuclear hyperpolarization at 14 T

  ChemRxiv · 2025-01-09 · 2 citations

  preprintOpen accessSenior author

  We investigate nitrogen substitution defects, also known as P1 centers, in type 1b diamonds as a source of electron spin polarization that is readily transferred to 13C nuclear spins within the diamond matrix at 14 Tesla by dynamic nuclear polarization (DNP) at room temperature down to 35 K. The goal was to obtain a quantitative model for clustered P1 centers in diamonds generated under high pressure and high temperature (HPHT). The study relied on frequency-stepped measurements of DNP profiles under magic angle spinning (MAS) using the mm-wave output of a frequency-tunable gyrotron and a regular superconducting NMR magnet set at a single field. The gyrotron output frequency was controlled via the temperature of the gyrotron cavity over 260 MHz centered around 395.3 GHz and had an output power of ~1 W across this range. We observe 13C on/off signal enhancements of up to 700-fold at room temperature under MAS and in static mode, and 130-fold between 35K and 100 K. Modeling of the experimental results revealed the dominant role of P1 clusters harboring inter-P1 dipolar and exchange couplings exceeding 100 MHz in achieving effective 13C DNP at 14.1 T. Clustered P1 centers may be of great utility in generating highly enhanced 13C NMR signal in high-pressure high-temperature diamond as a source of contrast for NMR and MRI applications, or a major decoherence source in quantum sensing applications.

  PublisherOA PDFDOI

• Hydraulic Activation of the AsLOV2 Photoreceptor

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-06-25

  preprintOpen accessSenior authorCorresponding

  Abstract How proteins transduce light into mechanical energy remains a central question in biology. This study tests the hypothesis that blue light activation of the LOV2 (light, oxygen, voltage sensitive) domain of Avena sativa phototropin 1 (AsLOV2), gives rise to concerted water movement that induces protein conformational extensions. Using electron and nuclear magnetic resonance spectroscopy, along with molecular dynamics simulations at high pressure, we find AsLOV2 activation can be initiated by blue light or high pressure, followed by selective and concerted expulsion of low-entropy, tetrahedrally coordinated “wrap” water from the protein hydration shell. These findings suggest that interfacial water serves as constituents to reshape the protein’s free energy landscape during activation. Our study highlights hydration water as an active hydraulic fluid that can drive long-range conformational changes underlying protein mechanics upon light activation and offers a new concept for engineering externally controllable protein actuators. Abstract Figure

  PublisherOA PDFDOI

• Coherent Control over Nuclear Hyperpolarization Using an Optically Initializable Chromophore-Radical System

  Journal of the American Chemical Society · 2025-09-17

  articleOpen accessSenior authorCorresponding

  Chromophore radicals (CR) are emerging as important components for molecular quantum information science (QIS), especially in the context of quantum sensing. Here, we demonstrate that the optically hyperpolarized electrons in a 1,6,7,12-tetrakis(4-tert-butylphenoxy)-perylene-3,4,9,10-bis(dicarboximide) (tpPDI) covalently linked to a partially deuterated 1,3-bis(diphenylene)-d16-2-phenylallyl radical (BDPA-d16) can be coherently manipulated via pulsed dynamic nuclear polarization (DNP) methods to transfer polarization to nuclear spins and back. Under light illumination at 85 K, electron hyperpolarization in BDPA is enhanced 2.1- to 2.4-fold over thermal polarization and lasts for more than 100 ms. By applying nuclear orientation via electron spin-locking (NOVEL) DNP, this optically amplified electron hyperpolarization was successfully transferred to a 1H nuclear spin within the CR system and efficiently returned to the electron spin for readout via reverse-NOVEL. The NOVEL transfer efficiency of 65% amounts to a 688-fold nuclear spin hyperpolarization of the target nuclear spin, considering the 2.1-fold electron spin hyperpolarization. This reversible coherent manipulation of hyperpolarization transfer highlights the utility of CR systems to initialize and read out nuclear spin states in a disordered matrix at moderate cryogenic temperatures. Coupled with CRs’ environmental compatibility, tunability, and precise state initialization, these results highlight the promising role of nuclear spins in CRs for QIS applications, including quantum sensing and memory.

  PublisherDOI

• Hydrolytically Stable Phosphonate‐Based Metal–Organic Frameworks for Harvesting Water from Low Humidity Air

  Small · 2025-04-18 · 9 citations

  articleOpen access

  Abstract Harvesting water from air offers a promising solution to the global water crisis. However, existing sorbents often struggle in arid climates due to limitations such as low sorption capacities, hydrolytic instability, slow mass transport, high desorption enthalpy, and costly operation. Phosphonate‐based metal–organic frameworks (MOFs), known for their exceptional water stability, have not been extensively explored for water harvesting. This study systematically investigates the performance of STA‐12 (M═Co, Ni, Mg) and STA‐16 (M═Co, Ni), a series of stable phosphonate‐based MOFs, as water sorbents. STA‐12 MOFs demonstrate remarkable adsorption at ultra‐low humidity (<10%), while STA‐16(Co) exhibits a high water uptake capacity of 0.54 g g −1 at 10–50% relative humidity (RH) and 0.72 g g −1 at 34% RH. Molecular simulations and solid‐state NMR identified liquid‐like water, critical for harvesting applications, as the key contributor to the superior sorption performance of STA‐16(Co). Scalable aqueous synthesis methods are developed, producing tens of grams of MOFs per batch without high‐pressure equipment. A prototype device incorporating STA‐12(Ni) demonstrated the feasibility of these materials for real‐world water harvesting, showcasing their potential to address water scarcity in arid regions.

  PublisherOA PDFDOI

• Hydration and Polyelectrolyte Properties of Polymeric Zwitterions with Long Carbon Spacers

  Macromolecules · 2025-07-21 · 1 citations

  article

  The antifouling performance of polymeric zwitterions exceeds those of other antifouling coating design strategies and is thought to be related to their strong surface-hydration interactions. However, design rules that connect zwitterion molecular structure with measures of surface hydration and fouling have been slow to emerge. This work probes the effect of the spacer length between the anion and cation on the hydration and ion sorption characteristics of model, carboxybetaine-containing hydrogel materials. In these hydrogels, the relationship between water sorption (swelling) and network mechanics allows for direct insight into intermolecular interactions and hydration structure from a combination of macroscopic and molecular-scale measurements. Control over the hydrogel mesh size tunes the relative strength of interchain interactions, deconvoluting the opposing effects of zwitterion hydrophilicity and associative pairing interactions. Swelling measurements indicate that zwitterions with shorter spacers are less hydrophilic and engage in fewer interchain zwitterion pairing interactions than those with longer spacers. Zwitterions with increasing spacer lengths give rise to distinct deswelling and salt partitioning behaviors with the addition of salt, indicative of appreciable surface charge segregation that may create attractive interactions with foulants. Measurements by Overhauser dynamic nuclear polarization indicated little difference in local water dynamics near zwitterionic polymer surfaces. While the shorter zwitterions studied here are less hydrophilic, they are known to possess superior fouling resistance. This trend is perhaps a result of appreciable surface charges among zwitterions with long spacers rather than hydration interactions alone. The higher degree of fouling observed in zwitterions with long spacers may indicate the role of surface charges in these chemistries.

  PublisherDOI

Recent grants

• Dynamic nuclear polarization at 7 Tesla to enable and enhance the study of chemical structures and surfaces

  NSF · $700k · 2015–2019

• NIH Grant R21RR032401

  NIH · $164k · 2014

• IDBR: Novel Electron-Nuclear Dual Resonance Instrument with Arbitrary Microwave Pulse Shaping to Advance the Structure and Dynamics Study of Biological Systems

  NSF · $750k · 2012–2016

• Multifrequency microwave powered DNP instrument for MAS NMR

  NIH · $334k · 2016–2019

• High-field Dynamic Nuclear Polarization using Spin Probes and Intrinsic Defects at Local Interfaces of Polymers and Solids

  NSF · $527k · 2011–2015

Frequent coauthors

• Alexander Pines

  University of California, Berkeley

  82 shared

• Mark S. Sherwin

  University of California, Santa Barbara

  37 shared

• Asif Equbal

  New York University

  34 shared

• Chi‐Yuan Cheng

  Colgate-Palmolive (United States)

  32 shared

• Sandra G. García

  Universidad de Zaragoza

  32 shared

• Juliette A. Seeley

  MIT Lincoln Laboratory

  32 shared

• Josef Granwehr

  RWTH Aachen University

  29 shared

• Yann Fichou

  Université de Bordeaux

  27 shared

Labs

• Han LaboratoryPI

  Physical Chemist and Professor in the Department of Chemistry at Northwestern University

Education

• Ph.D., Chemistry

  University of California, Berkeley

  2005

• B.S., Chemistry

  University of California, Berkeley

  2000

Awards & honors

• 2024 Bruker Prize Lecture of the Royal Society Chemistry EPR
• 2023 Callaghan Lecturer Prize of the ISMAR
• 2021 EAS Award for Outstanding Achievements in Magnetic Reso…
• 2020 The Mary and Joseph A. Pignolio, St. Award of Universit…
• 2019 Biophysical Society Innovation Award