Science Highlights

Ordering of Molecular Rotor Monolayer on Aqueous Surface

June 2018
BBA - Biomembranes, 2018, 1860, pp 1414-1423

Antimicrobial peptides (AMPs) target bacterial cells mainly by electrostatic interactions. Studies indicate that the hydrophobicity of AMPs plays an important role on the selectivity. By using the X-ray reflectivity technique at NSF’s ChemMatCARS and other characterization tools, researchers from Illinois Institute of Technology and New York University have investigated the molecular basis for peptoid interactions with bacterial and eukaryotic lipid membranes on the sub-nanometer scale. 

Click here for more info

Thermally Persistent High-Spin Ground States in Octahedral Iron Clusters

November 7, 2018
J. Am. Chem. Soc., 2018, 140 (48), pp 16792-16806

In this paper, a series of isostructural octahedral hexairon clusters are shown to display spin ground states varying from S = 9/2 to S = 11, marking thus the record of the highest spin states that remain isolated up to 300 K. Such behavior is attributed to double exchange manifested in the strongly delocalized clusters. Consequences of the latter are the hyperfine splitting of the Mössbauer spectrum at low temperature and the emergence of SMM behavior. As seen in the structural metrics, the existence of magnetic anisotropy can be predicted by the asymmetry of the [Fe6] octahedron and further manipulated by simple solvation of the cluster. The latter provides a pathway by which the magnetic behavior can be tuned and enhanced by simple exploration of other auxiliary ligands.

Click here for details

Topology-Guided Stepwise Insertion of Three Secondary Linkers in Zirconium Metal–Organic Frameworks

May 28, 2018
J. Am. Chem. Soc., 2018, 140(24), pp 7710-7715

NPF-300 represents the first structure prototype that has the capability to introduce three distinct functional groups into a single MOF in a crystallographically ordered fashion. It is our expectation that NPF-300 can be used to build multifunctional MOF materials for a wide range of applications including gas storage/separation and synergistic/cooperative catalysis. 

Click here for details

Tunable Rh2(II,II) Light Absorbers as Excited-State Electron Donors and Acceptors Accessible with Red/Near-Infrared Irradiation

April 18, 2018
J. Am. Chem. Soc., 2018, 140 (15), pp 5161–5170

A series of four dirhodium formamidinate paddlewheel complexes with electron-accepting napthyridine-based ligands were synthesized, and their structural, electronic, and photophysical properties were investigated. The photophysical and excited-state redox properties of the new complexes presented herein illustrate the advantages of this rigid bimetallic architecture for tuning their ability to undergo photoinduced electron and hole transfer. Given a judicious choice of ligands, these complexes provide a new platform for solar energy conversion applications that require charge injection into n- and p-type semiconductors accessible with photons from the UV to the near-IR. 

Click here for details

Dissecting Porosity in Molecular Crystals: Influence of Geometry, Hydrogen Bonding, and [π···π] Stacking on the Solid-State Packing of Fluorinated Aromatics

April 14, 2018
J. Am. Chem. Soc., 2018, 140 (18), pp 6014–6026

Scientists from University of Houston, NFS’s ChemMatCARS, Texas Center for Superconductivity have performed one of the most comprehensive examinations of structure/porosity relationships among porous molecular crystals. More than a dozen potential precursors to porous molecular all-organic crystals were synthesized using a combination of Cu and Pd catalysis, protecting group chemistry on the nitrogen, and solvothermal synthesis.

Click here for details

Electron Injection from Photoexcited Metal–Organic Framework Ligands to Ru2 Secondary Building Units for Visible-Light-Driven Hydrogen Evolution

March 26, 2018
J. Am. Chem. Soc., 2018, 140 (16), pp 5326–5329

Scientists designed two novel MOFs built from Ru2 SBUs and realized photocatalytic HER by directly incorporating HER catalysts as the SBUs into photosensitizing MOFs. The proximity of photosensitizing porphyrin ligands to the catalytic Ru2 SBUs in the MOFs facilitated multielectron transfer, leading to 28 times higher HER activity than the homogeneous control. This work provides a blueprint for designing multifunctional MOFs with catalytic SBUs and photosensitizing ligands for photocatalytic and other applications.

Click here for details

Ordering of Molecular Rotor Monolayer on Aqueous Surface

March 23, 2018
PNAS, 2018, pp 201712789

The so-far-unknown 2D ferroelectric assemblies of dipolar molecular rotors would be of considerable interest for miniaturization of analog electronics. Researchers from Academy of Sciences of the Czech Republic, University of Colorado Boulder, and Advanced Light Source have examined the structure of a monolayer of molecular motors on aqueous subphase by using grazing-incidence X-ray diffraction at NSF’s ChemMatCARS. Results revealed a perfect triangular lattice formed at the aqueous surface, which is a prerequisite for ferroelectric action in a 2D dipolar array.

Click here for more info

Nanoscale View of Assisted Ion Transport across the Liquid-Liquid Interface

March 8, 2018
PNAS, 2018, pp 201701389

The selective separation of targeted metal ions is widely utilized in many industrial processes. Although important, the structure of ion–extractant complexes at the liquid-liquid interface, as well as the mechanism of ion transport across the interface, are generally unknown.  By combining the liquid X-ray scattering measurements at NSF’s ChemMatCARS and MD simulations, researchers from the University of Illinois at Chicago, the University of California at Santa Cruz, and NSF’s ChemMatCARS have revealed the detailed process of ion transport across the interface. 

Click here for more info

η2-SO2 Linkage Photoisomer of an Osmium Coordination Complex

March 5, 2018
Inorg. Chem., 2018, 57 (5), pp 2673–2677

η2-SO2 linkage photoisomerism in the osmium pentaammine coordination complex [Os(NH3)5(SO2)][Os(NH3)5(HSO3)]Cl4was discovered in the solid state by means of state-of-the-art in situ light-induced x-ray diffraction methods using synchrotron facilities, and a custom-built concerted optical absorption spectroscopy and microscopy apparatus. The corresponding Os-(η2-SO2) photoisomer is the first structurally characterized example of its kind, which, considering the thermal reversibility of the isomerism, represents a rare example of an osmium-based solid-state optical switch.

Click here for more information

Polycation Adsorption Impacts the Permeability of Membranes

January 1, 2018
Acta Biomaterialia, 2018, 65, pp 317-326

Polycations are a large class of macromolecules with applications in gene therapy. However, the ability of polycation gene carriers to escape from the vesicles is not well known. Researchers from Purdue University and their collaborates studied the interactions between them and lipids monolayers with various techniques including X-ray reflectivity conducted at NSF’ ChemMatCARS. Results suggest that polycation adsorption increases the overall integrity of the vesicle, however, it also causes deformation and permeabilization of the vesicle.

Click here for more info

Two-Step Adsorption of PtCl62– Complexes at a Charged Langmuir Monolayer: Role of Hydration and Ion Correlations

October 27, 2017
J. Phys. Chem. C, 2017, 121, pp 25377–25383

Amphiphile–ion interactions at aqueous interfaces play an important role in many biological, chemical, environmental, and industrial processes. With the assist of liquid surface X-ray scattering and X-ray fluorescence techniques, researchers from Argonne National Laboratory have studied the adsorption of large anionic complexes at a soft charged interface over wide bulk concentration range. The results suggest a two-step absorption process.  

Click here for more information

Mixing Behavior in Binary Anionic Gemini Surfactant–Perfluorinated Fatty Acid Langmuir Monolayers

September 5, 2017
Langmuir, 2017, 33, pp 10205-10215

Gemini surfactants are compounds of great academic interest and hold considerable potential for industrial and biomedical applications.  Researchers from the University of Saskatchewan have combined compression isotherm, Brewster angle microscopy, and liquid surface X-ray scattering to investigate the miscibility and structure of mixed gemini and perfluorinated surfactants films at the air-water interface.  The structure of the mixed film demonstrates a strong dependency on the mole ratio of the two components.

Click here for more info

Exciton Migration and Amplified Quenching on Two-Dimensional Metal–Organic Layers

May 3, 2017
J. Am. Chem. Soc., 2017, 139 (20), pp 7020–7029

The dimensionality dependence of resonance energy transfer is of great interest due to its importance in understanding energy transfer on cell membranes and in low-dimension nanostructures. Light harvesting two-dimensional metal–organic layers (2D-MOLs) and three-dimensional metal–organic frameworks (3D-MOFs) provide comparative models to study such dimensionality dependence with molecular accuracy.  The scientists at the Xiamen University, China and the University of Chicago, USA report the construction of 2D-MOLs and 3D-MOFs from a donor ligand and a doped acceptor ligand. These 2D-MOLs and 3D-MOFs are connected by similar hafnium clusters, with key differences in the topology and dimensionality of the metal–ligand connection. Energy transfer from donors to acceptors through the 2D-MOL or 3D-MOF skeletons is revealed by measuring and modeling the fluorescence quenching of the donors. We found that energy transfer in 3D-MOFs is more efficient than that in 2D-MOLs, but excitons on 2D-MOLs are more accessible to external quenchers as compared with those in 3D-MOFs. These results not only provide support to theoretical analysis of energy transfer in low dimensions, but also present opportunities to use efficient exciton migration in 2D materials for light-harvesting and fluorescence sensing.

Click here for more info

Direct Characterization of a Reactive Lattice-Confined Ru2 Nitride by Photocrystallography

March 1, 2017
J. Am. Chem. Soc., 2017, 139 (8), pp 2912–2915

Metal-oxygen and metal-nitrogen multiply bonded complexes are ubiquitous intermediates in synthetic as well as biological oxidation chemistry. While the effect of π-π* interaction between filled ligand orbital and vacant d-orbitals of early transition metals tend to stabilize the metal-ligand multiply bonded complexes of early transition metals, the same effect destabilizes the metal-ligand multiple bonds in mid-to-late transition metals due to π-π* interaction between filled ligand orbital and filled d-orbitals. These complexes are thus difficult to crystallographically characterize. Synthetic tuning of the ligands can stabilize these reactive complexes for characterization, but it typically renders the resulting complexes unreactive. The highlight of my research so far is demonstrating direct characterization of a reactive Ru2-nitride intermediate without altering its reactivity or stability, using photo-crystallography. The results obtained from photo-crystallographic experiments were in good agreement with the results obtained from EPR and EXAFS experiments, confirming the reliability of this method to characterize reactive molecules.

Click here for more info

Molecular Structure of Canonical Liquid Crystal Interfaces

February 8, 2017
J. Am. Chem. Soc., 2017, 139, pp 3841-3850

Liquid crystals (LCs) have been studied extensively, particularly in the context of display technologies and optical devices. The control of molecular orientation at the interface (LCs) is critical for these applications.  By using synchrotron X-ray reflectivity measurements and large-scale atomistic molecular dynamics simulations, researchers from the University of Chicago Institute for Molecular Engineering (including members of ChemMatCARS), the University of Illinois at Chicago Department of Physics, and the University of Wisconsin−Madison Department of Chemical Engineering have reconstructed a detailed picture of interfacial molecular organization at the air-liquid crystal interface.

Click here for more info

Atomic Number Dependent "Structural Transitions" in Ordered Lanthanide Monolayers: Role of the Hydration Shell

January 20, 2017
Langmuir, 2017, 33, pp 1412-1418

Solvent extraction is the chemical method to separate and refine lanthanide ions, where the extractant-ion interaction is the key to the process. Although all lanthanides should be chemically and physically quite similar, there are significant differences in the efficiency of extraction processes. Researchers from Northwestern University have revealed that hydration shell of lanthanide ions plays a vital role in the structure of the extraction-ion complex. Synchrotron grazing incidence X-ray diffraction is used to explore the two-dimensional structures of the interfacial complex, formed by a series of lanthanide ions and extractants.

Click here for more info

Robust Gold Nanoparticle Sheets by Ligand Cross-Linking at the Air–Water Interface

January 13, 2017
ACS Nano, 2017, 11, pp 1292-1300

Self-assembly of nanoparticles (NPs) into ordered two and three-dimensional (2D and 3D) structures gives access to materials with useful electronic, optical, and magnetic properties.  Researchers from University of Massachusetts and The University of Chicago have characterized the cross-linking of 2D Au-NPs at the air-water interface in situ by using techniques including AFM, XR, and GIXD. Highly elastic and robust films were obtained when an aqueous soluble PC-pyridine-substituted catalyst was introduced to the water subphase.

Click here for more info

Imparting amphiphobicity on Metal-Organic Framework materials

October 31, 2016
Nature Communications 7, 2016, pp 13300

Single-crystalline Metal-Organic Framework (MOF) materials show great promise for practical applications and have been extensively investigated for applications in gas storage and separation, carbon capture, catalysis etc.  However, in order to be practically applicable, they need to maintain their properties over long spans of time, under a variety of environments, including high levels of humidity and presence of organic vapors.  For this purpose, scientists from the Zhejiang University in China and from the University of South Florida developed a procedure for the functionalization of the exterior crystal surfaces with perfluoroalkyl groups, rendering them amphiphobic (i.e. both superhydrophobic and oleophobic).  The treated crystals are structurally identical to the untreated ones, as revealed by single crystal X-ray diffraction measurements performed at the ChemMatCARS Crystallography facility on 15-IDB.  Following the perfluoroalkyl treatment, the crystals withstood prolonged exposure to 100% relative humidity CO2 atmosphere, showing no degradation.

Self-assembly Process and Oligomeric State of peptide-polymer conjugates at the Air-Water Interface

October 26, 2016
Biomacromolecules, 2016, 17, pp 3964-3972

Coiled-coil peptide-polymer conjugates are an emerging class of biomaterials.  Combining the results from Langmuir isotherm, XR, and GIXD measurements, researchers from the University of California, Berkeley have investigated the peptide structure and the effect of PEGylation in governing the oligomeric state and self-assembly process of coiled-coil peptide-polymer conjugates.  PEGylated 3-helix amphiphiles exhibited a surface pressure dependent transition from a mixture of dimers and trimers at intermediate pressure to complete trimers at high pressure. Furthermore, the PEGylated 3-helix amphiphile was able to preserve the inter-helical distance at high surface pressure.

Click here for more information 

Basing Earth-abundant metal catalysts at Metal-Organic frameworks

October 10, 2016
Nat. Commun., 2016, 7, pp 12610

Studies of Earth-abundant metal catalysts have been performed by University of Chicago Chemistry department researchers, led by Prof. Wenbin Lin.  Recent results of these studies were published in the Nature Communications Aug. 2016 issue.  Using a straightforward metalation of Metal-Organic Framework (MOF) building units with cobalt and iron salts the researchers produced highly active and reusable single-site solid catalysts for a variety of organic reactions.  The molecular structure of the resulting catalysts was studied using single crystal diffraction, at the ChemMatCARS crystallography facility.  These results are of potential great economic significance showing that, using widely abundant metals, MOFs provide a platform for the development of highly active and affordable catalysts for the sustainable synthesis of fine chemicals. 

The Model Catalyst

September 30, 2016
J. Am. Chem. Soc., 2016, 138 (38), pp 12432–12439

Researchers used ChemMatCARS (Sector 15 at APS) to carry out detailed structural characterization of the catalyst binding sites in situ, such as single site catalysts on silica supports.  Octadecyltrioxysilane (OTOS) monolayers formed from octadecyltrimethoxysilane (OTMS) at the air−liquid interface after hydrolysis and condensation at low pH were chosen as a model system of surface binding sites in silica-supported Zn2+ catalysts. The results show that OTOS monolayers may serve as a platform for studying silica surface chemistry or hydroxyl-mediated reactions.

This work has been featured in APS Science Highlights

Metal−Organic Frameworks Stabilize Solution-Inaccessible Cobalt Catalysts for Highly Efficient Broad-Scope Organic Transformations

February 11, 2016
J. Am. Chem. Soc., 2016, 138 (9), pp 3241–3249

Researchers, led by Prof. Wenbin Lin from the University of Chicago, used ChemMatCARS crystallography facility in 15-ID-B highly to determined the structure of a robust, active, and reusable cobaltbipyridine- and cobalt-phenanthroline-based metal−organic framework (MOF) catalysts that the group has designed for alkene hydrogenation and hydroboration, aldehyde/ketone hydroboration, and arene C−H borylation. In alkene hydrogenation, the MOF catalysts tolerated a variety of functional groups and displayed unprecedentedly high turnover numbers of ∼2.5 × 106 and turnover frequencies of ∼1.1 × 105 h−1 .  MOFs thus provide a novel platform for discovering new base-metal molecular catalysts and exhibit enormous potential in sustainable chemical catalysis.

Surface Mechanical and Rheological Behaviors of PLGA–PEG Monolayers at the Air–Water Interface

January 2016
Langmuir, 2015, 31 (51), pp 13821-13833

Researchers using the ChemMatCARS 15-ID-C beamline at the APS are investigating PLGA-PEG monolayers due to the exhibition of protein resistance and reasonable chemical stability at the air-water interface. The results show that PLGA-PEG monolayers seem to have the potential to be used in lung surfactant applications.

Precise Molecular Fission and Fusion: Quantitative Self-Assembly and Chemistry of a Metallo-Cuboctahedron

September 10, 2015
Angew. Chem., 2015, 54 (32), pp 9224–9229

Scientists from University of Akron created the largest molecular spheres (a cuboctahedron) that were unequivocally characterized by synchrotron X-ray analysis performed at ChemMatCARS Advanced Crystallography facility.

Electric Field Effect on Phospholipid Monolayers at an Aqueous−Organic Liquid−Liquid Interface

July 23, 2015
J. Phys. Chem. B, 2015, 119 (29), pp 9319–9334

The electric potential difference across cell membranes, known as the membrane potential, plays an important role in the activation of many biological processes.  Using ChemMatCARS liquid surface scattering facility, researchers from University of Illinois at Chicago have investigated the effect of the membrane potential on the molecular ordering of lipids within a biomimetic membrane at an electrified oil/water interface.  Measurements at higher positive potentials illustrate a monotonic decrease in the lipid interfacial density and accompanying variations in the interfacial configuration of the lipid. 

A versatile environmental control cell for in situ guest exchange single-crystal diffraction

April 2015

Scientists, led by Prof. Jason Benedict from University at SUNY, Buffalo, Natural Sciences Complex, designed and commissioned successfully a versatile environmental control cell for in situ guest exchange single-crystal diffraction measurements at ChemMatCARS Advanced Crystallography facility.  The first experiment performed under dynamic gas-flow conditions revealed that the cell was capable of stabilizing a novel metastable intermediate in the dehydration reaction of a previously reported metal-organic framework.

Reversible Crystallization at the Air-Water Interface

February 17, 2015
Sci. Rep., 2015, 5, pp 8497

Experiments performed at the ChemMatCARS liquid surface scattering facility provided evidence of a reversible phase transition process, between a 2-dimensional monolayer and a 3-dimensional crystalline structure.  The transition is driven by changes in surface pressure and, since crystalline phase normally represents the lowest energy state of condensed matter, the reversibility of this process is counterintuitive.  The existence of 3-dimensional crystals in the compressed phase was confirmed by atomic force microscopy measurements and the results of the study were published in Scientific Reports.

The Temperature Dependent Photoswitching of a Classic Diarylethene Monitored by in Situ X-ray Diffraction

January 9, 2015
J. Phys. Chem. A, 2015, 119 (5), pp 884–888

Researchers from University of SUNY Buffalo have examined temperature dependence of the light-driven photocyclization reaction in a classic diarylethene the using ChemMatCARS Advanced Crystallography facility (15ID-B).  These organic photochromic molecules including diarylethenes are of particular interest for their numerous potential applications including high-density optical data storage and light-activated switches.  Understanding how these systems behave under nonstandard conditions is critical to developing guiding principles that can be used to design and engineer photochromic materials with tailor-made properties.