Colloidal Nanoparticles of High Entropy Materials: Capabilities, Challenges, and Opportunities in Synthesis and Characterization

Materials referred to as "high entropy" contain a large number of elements randomly distributed on the lattice sites of a crystalline solid, such that a high configurational entropy is presumed to contribute significantly to their formation and stability. High temperatures are typically required to achieve entropy stabilization, which can make it challenging to synthesize colloidal nanoparticles of high entropy materials. Nonetheless, strategies are emerging for the synthesis of colloidal high entropy nanoparticles, which are of interest for their synergistic properties and unique catalytic functions that arise from the large number of constituent elements and their interactions. In this Perspective, we highlight the classes of materials that have been made as colloidal high entropy nanoparticles as well as insights into the synthetic methods and the pathways by which they form. We then discuss the concept of "high entropy" within the context of colloidal materials synthesized at much lower temperatures than are typically required for entropy to drive their formation. Next, we identify and address challenges and opportunities in the field of high entropy nanoparticle synthesis. We emphasize aspects of materials characterization that are especially important to consider for nanoparticles of high entropy materials, including powder X-ray diffraction and elemental mapping with scanning transmission electron microscopy, which are among the most commonly used techniques in laboratory settings. Finally, we share perspectives on emerging opportunities and future directions involving colloidal nanoparticles of high entropy materials, with an emphasis on synthesis, characterization, and fundamental knowledge that is needed for anticipated advances in key application areas.

Correlating chemistry and mass transport in sustainable iron production

Steelmaking contributes 8% to the total CO2 emissions globally, primarily due to coal-based iron ore reduction. Clean hydrogen-based ironmaking has variable performance because the dominant gas-solid reduction mechanism is set by the defects and pores inside the mm- to nm-sized oxide particles that change significantly as the reaction progresses. While these governing dynamics are essential to establish continuous flow of iron and its ores through reactors, the direct link between agglomeration and chemistry is still contested due to missing measurements. In this work, we directly measure the connection between chemistry and agglomeration in the smallest iron oxides relevant to magnetite ores. Using synthesized spherical 10-nm magnetite particles reacting in H2, we resolve the formation and consumption of wüstite (Fe1-xO)-the step most commonly attributed to whiskering. Using X-ray diffraction, we resolve crystallographic anisotropy in the rate of the initial reaction. Complementary imaging demonstrated how the particles self-assemble, subsequently react, and grow into elongated "whisker" structures. Our insights into how morphologically uniform iron oxide particles react and agglomerate in H2 reduction enable future size-dependent models to effectively describe the multiscale aspects of iron ore reduction.

Temporal Evolution of Morphology, Composition, and Structure in the Formation of Colloidal High-Entropy Intermetallic Nanoparticles

Morphology-controlled nanoparticles of high entropy intermetallic compounds are quickly becoming high-value targets for catalysis. Their ordered structures with multiple distinct crystallographic sites, coupled with the "cocktail effect" that emerges from randomly mixing a large number of elements, yield catalytic active sites capable of achieving advanced catalytic functions. Despite this growing interest, little is known about the pathways by which high entropy intermetallic nanoparticles form and grow in solution. As a result, controlling their morphology remains challenging. Here, we use the high entropy intermetallic compound (Pd,Rh,Ir,Pt)Sn, which adopts a NiAs-related crystal structure, as a model system for understanding how nanoparticle morphology, composition, and structure evolve during synthesis in solution using a slow-injection reaction. By performing a time-point study, we establish the initial formation of palladium-rich cube-like Pd-Sn seeds onto which the other metals deposit over time, concomitant with continued incorporation of tin. For (Pd,Rh,Ir,Pt)Sn, growth occurs on the corners, resulting in a sample having a mixture of flower-like and cube-like morphologies. We then synthesize and characterize a library of 14 distinct intermetallic nanoparticle systems that comprise all possible binary, ternary, and quaternary constituents of (Pd,Rh,Ir,Pt)Sn. From these studies, we correlated compositions, morphologies, and growth pathways with the constituent elements and their competitive reactivities, ultimately mapping out a framework that rationalizes the key features of the high entropy (Pd,Rh,Ir,Pt)Sn intermetallic nanoparticles based on those of their simpler constituents. We then validated these design guidelines by applying them to the synthesis of a morphologically pure variant of flowerlike (Pd,Rh,Ir,Pt)Sn particles as well as a series of (Pd,Rh,Ir,Pt)Sn particles with tunable morphologies based on control of composition.

Chemical Insights into the Formation of Colloidal High Entropy Alloy Nanoparticles

Nanoparticles of high entropy alloys (HEAs) have distinct properties that result from their high surface-to-volume ratios coupled with synergistic interactions among their five or more constituent elements, which are randomly distributed throughout a crystalline lattice. Methods to synthesize HEA nanoparticles are emerging, including solution approaches that yield colloidal products. However, the complex multielement compositions of HEA nanoparticles make it challenging to identify and understand their reaction chemistry and the pathways by which they form, which hinders their rational synthesis. Here, we demonstrate the synthesis and elucidate the reaction pathways of seven colloidal HEA nanoparticle systems that contain various combinations of noble metals (Pd, Pt, Rh, Ir), 3d transition metals (Ni, Fe, Co), and a p-block element (Sn). The nanoparticles were synthesized by slowly injecting a solution containing all five constituent metal salts into oleylamine and octadecene at 275 °C. Using NiPdPtRhIr as a lead system, we confirmed the homogeneous colocalization of all five elements and achieved tunable compositions by varying their ratios. We also observed heterogeneities, including Pd-rich regions, in a subpopulation of the NiPdPtRhIr sample. Halting the reaction at early time points and characterizing the isolated products revealed a time-dependent composition evolution from Pd-rich NiPd seeds to the final NiPdPtRhIr HEA. Similar reactions applied to FePdPtRhIr, CoPdPtRhIr, NiFePdPtIr, and NiFeCoPdPt, with modified conditions to most efficiently incorporate all five elements into each HEA, also revealed similar Pd-rich seeds with system-dependent differences in the rates and sequences of element uptake into the nanoparticles. When moving to SnPdPtRhIr and NiSnPdPtIr, the time-dependent formation pathway was more consistent with simultaneous coreduction rather than through formation of reactive seeds. These studies reveal important similarities and differences among the pathways by which different colloidal HEA nanoparticles form using the same synthetic method, as well as establish generality. The results provide guidelines for incorporating a range of different elements into HEA nanoparticles, ultimately providing fundamental knowledge about how to define and optimize synthetic protocols, expand into different HEA nanoparticle systems, and achieve high phase purity.

Current Advances in Nanotechnology for the Next Generation of Sequencing (NGS)

This communication aims at discussing strategies based on developments from nanotechnology focused on the next generation of sequencing (NGS). In this regard, it should be noted that even in the advanced current situation of many techniques and methods accompanied with developments of technology, there are still existing challenges and needs focused on real samples and low concentrations of genomic materials. The approaches discussed/described adopt spectroscopical techniques and new optical setups. PCR bases are introduced to understand the role of non-covalent interactions by discussing about Nobel prizes related to genomic material detection. The review also discusses colorimetric methods, polymeric transducers, fluorescence detection methods, enhanced plasmonic techniques such as metal-enhanced fluorescence (MEF), semiconductors, and developments in metamaterials. In addition, nano-optics, challenges linked to signal transductions, and how the limitations reported in each technique could be overcome are considered in real samples. Accordingly, this study shows developments where optical active nanoplatforms generate signal detection and transduction with enhanced performances and, in many cases, enhanced signaling from single double-stranded deoxyribonucleic acid (DNA) interactions. Future perspectives on miniaturized instrumentation, chips, and devices aimed at detecting genomic material are analyzed. However, the main concept in this report derives from gained insights into nanochemistry and nano-optics. Such concepts could be incorporated into other higher-sized substrates and experimental and optical setups.

Plain language summary of a fingerprinting technique to monitor blood cancer

WHAT IS THIS SUMMARY ABOUT?

This is a plain language summary discussing the results of our study published in the journal Nanomedicine. The study describes how to improve the detection of blood cancer and chart the progress of recovery/remission to reassure patients living with cancer.

WHAT DID WE DO?

In our study, we used a new tool called Raman spectroscopy to detect molecules found uniquely in the blood plasma of people with, or recovering from, blood cancer. Our aim was to fine-tune this technique so that it could help doctors better determine if cancer was growing back or not responding to treatment. Gold nanoparticles were used to enhance the signal of these cancer-specific molecules so that Raman spectroscopy (also called nanoSERS) could better identify and expose the cancer in hiding.

WHAT IS THE IMPORTANCE OF THESE FINDINGS?

We discovered that this new tool (Raman spectroscopy using gold nanoparticles) can detect trace molecules in the blood found only when cancer cells are present or when a person's cancer is returning. This study, which has identified new potential for Raman spectroscopy as an early-screening tool, opens the possibility for the better monitoring of blood cancer. This could mean both less aggressive and fewer treatments for people diagnosed with this disease. This tool may also be useful for people seeking reassurance that their cancer remains dormant or will be identified for treatment sooner if it returns. These findings can also be applied more broadly, such as in helping scientists test the effectiveness of new treatments as they continue to get better at eliminating cancer cells.

Muon Irradiation of ZnO Rods: Superparamagnetic Nature Induced by Defects

In this work, through a combination of photoluminescence spectroscopy, X-ray powder diffraction and magnetic measurements, it is determined that ZnO rods, made hydrothermally using a combination of magnetic field with respect to the force of gravity, exhibit superparamagnetic properties which emerge from Zn defects. These Zn defects result in a size-dependent superparamagnetic property of the rods. Red emissions, characteristic of Zn vacancies, and magnetic susceptibility both increased with decreasing rod size. The ZnO rods have significantly larger superparamagnetic cluster sizes (one order of magnitude) and lower fluctuation rates when compared to other superparamagnetic particles.

Nanoparticle surface-enhanced Raman spectroscopy as a noninvasive, label-free tool to monitor hematological malignancy

Aim: Monitoring minimal residual disease remains a challenge to the effective medical management of hematological malignancies; yet surface-enhanced Raman spectroscopy (SERS) has emerged as a potential clinical tool to do so. Materials & methods: We developed a cell-free, label-free SERS approach using gold nanoparticles (nanoSERS) to classify hematological malignancies referenced against two control cohorts: healthy and noncancer cardiovascular disease. A predictive model was built using machine-learning algorithms to incorporate disease burden scores for patients under standard treatment upon. Results: Linear- and quadratic-discriminant analysis distinguished three cohorts with 69.8 and 71.4% accuracies, respectively. A predictive nanoSERS model correlated (MSE = 1.6) with established clinical parameters. Conclusion: This study offers a proof-of-concept for the noninvasive monitoring of disease progression, highlighting the potential to incorporate nanoSERS into translational medicine.

Minute-Made, High-Efficiency Nanostructured Bi2Te3 via High-Throughput Green Solution Chemical Synthesis

Scalable synthetic strategies for high-quality and reproducible thermoelectric (TE) materials is an essential step for advancing the TE technology. We present here very rapid and effective methods for the synthesis of nanostructured bismuth telluride materials with promising TE performance. The methodology is based on an effective volume heating using microwaves, leading to highly crystalline nanostructured powders, in a reaction duration of two minutes. As the solvents, we demonstrate that water with a high dielectric constant is as good a solvent as ethylene glycol (EG) for the synthetic process, providing a greener reaction media. Crystal structure, crystallinity, morphology, microstructure and surface chemistry of these materials were evaluated using XRD, SEM/TEM, XPS and zeta potential characterization techniques. Nanostructured particles with hexagonal platelet morphology were observed in both systems. Surfaces show various degrees of oxidation, and signatures of the precursors used. Thermoelectric transport properties were evaluated using electrical conductivity, Seebeck coefficient and thermal conductivity measurements to estimate the TE figure-of-merit, ZT. Low thermal conductivity values were obtained, mainly due to the increased density of boundaries via materials nanostructuring. The estimated ZT values of 0.8-0.9 was reached in the 300-375 K temperature range for the hydrothermally synthesized sample, while 0.9-1 was reached in the 425-525 K temperature range for the polyol (EG) sample. Considering the energy and time efficiency of the synthetic processes developed in this work, these are rather promising ZT values paving the way for a wider impact of these strategic materials with a minimum environmental impact.

Transfer of 1D Photonic Crystals via Spatially Resolved Hydrophobization

1D photonic crystals (1DPCs) are well known from a variety of applications ranging from medical diagnostics to optical fibers and optoelectronics. However, large-scale application is still limited due to complex fabrication processes and bottlenecks in transferring 1DPCs to arbitrary substrates and pattern creation. These challenges were addressed by demonstrating the transfer of millimeter- to centimeter-scale 1DPC sensors comprised of alternating layers of H₃ Sb₃ P₂ O₁₄ nanosheets and TiO₂ nanoparticles based on a non-invasive chemical approach. By depositing the 1DPC on a sacrificial layer of lithium tin sulfide nanosheets and hydrophobizing only the 1DPC by intercalation of n-octylamine via the vapor phase the 1DPC can be detached from the substrate by immersing the sample in water. Upon exfoliation of the hydrophilic sacrificial layer, the freestanding 1DPC remains at the water-air interface. In a second step, it can be transferred to arbitrary surfaces such as curved glass. In addition, the transfer of patterned 1DPCs is demonstrated by combining the sacrificial layer approach with area-resolved intercalation and etching. The fact that the sensing capability of the 1DPC is not impaired and can be modified after transfer renders this method a generic platform for the fabrication of photonic devices.

Silica Coated Iron/Iron Oxide Nanoparticles as a Nano-Platform for T2 Weighted Magnetic Resonance Imaging

The growing concern over the toxicity of Gd-based contrast agents used in magnetic resonance imaging (MRI) motivates the search for less toxic and more effective alternatives. Among these alternatives, iron-iron oxide (Fe@FeOx) core-shell architectures have been long recognized as promising MRI contrast agents while limited information on their engineering is available. Here we report the synthesis of 10 nm large Fe@FeOx nanoparticles, their coating with a 11 nm thick layer of dense silica and functionalization by 5 kDa PEG chains to improve their biocompatibility. The nanomaterials obtained have been characterized by a set of complementary techniques such as infra-red and nuclear magnetic resonance spectroscopies, transmission electron microscopy, dynamic light scattering and zetametry, and magnetometry. They display hydrodynamic diameters in the 100 nm range, zetapotential values around -30 mV, and magnetization values higher than the reference contrast agent RESOVIST®. They display no cytotoxicity against 1BR3G and HCT116 cell lines and no hemolytic activity against human red blood cells. Their nuclear magnetic relaxation dispersion (NMRD) profiles are typical for nanomaterials of this size and magnetization. They display high r2 relaxivity values and low r1 leading to enhanced r2/r1 ratios in comparison with RESOVIST®. All these data make them promising contrast agents to detect early stage tumors.

The Sub-Nanometer Scale as a New Focus in Nanoscience

Size is one of the central issues in nanoscience. The practical meaning of the term "sub-nanometric material (SNM)" requires two aspects: (1) its size should be at the atomic level; (2) it shows unique (size-related) properties compared to its nano-counterparts with larger sizes. Here, SNMs in the form of wires (SNWs) and the unique properties arising from their special size are reviewed. First, their polymer-like behavior, including rheological behavior and self-assembly, is dicussed. Their origins may stem from the special size and the ligands around the wire. Even a slight increase in diameter would risk the polymer-like behavior. Meanwhile, the ligands on SNWs are proportional to the inorganic entity at this scale. Consequently, surface ligands should have a profound impact on the properties, like catalysis, self-assembly, optics, etc. To reveal more potential applications, their applications in energy conversion are comprehensively reviewed. To some extent, characterization can greatly influence the way things are observed. Thus, some appropriate characterization techniques are briefly introduced. Finally, another emerging part of SNWs (atomic chain material) is briefly introduced. It is hoped that this review can provide new insights to this special scale.

Intermetallic Nanocrystals: Syntheses and Catalytic Applications

At the forefront of nanochemistry, there exists a research endeavor centered around intermetallic nanocrystals, which are unique in terms of long-range atomic ordering, well-defined stoichiometry, and controlled crystal structure. In contrast to alloy nanocrystals with no elemental ordering, it is challenging to synthesize intermetallic nanocrystals with a tight control over their size and shape. Here, recent progress in the synthesis of intermetallic nanocrystals with controllable sizes and well-defined shapes is highlighted. A simple analysis and some insights key to the selection of experimental conditions for generating intermetallic nanocrystals are presented, followed by examples to highlight the viable use of intermetallic nanocrystals as electrocatalysts or catalysts for various reactions, with a focus on the enhanced performance relative to their alloy counterparts that lack elemental ordering. Within the conclusion, perspectives on future developments in the context of synthetic control, structure-property relationships, and applications are discussed.

Tip in-light on: Advantages, challenges, and applications of combining AFM and Raman microscopy on biological samples

Scanning probe microscopies and spectroscopies, especially AFM and Confocal Raman microscopy are powerful tools to characterize biological materials. They are both non-destructive methods and reveal mechanical and chemical properties on the micro and nano-scale. In the last years the interest for increasing the lateral resolution of optical and spectral images has driven the development of new technologies that overcome the diffraction limit of light. The combination of AFM and Raman reaches resolutions of about 50-150 nm in near-field Raman and 1.7-50 nm in tip enhanced Raman spectroscopy (TERS) and both give a molecular information of the sample and the topography of the scanned surface. In this review, the mentioned approaches are introduced, the main advantages and problems for application on biological samples discussed and some examples for successful experiments given. Finally the potential of colocated AFM and Raman measurements is shown on a case study of cellulose-lignin films: the topography structures revealed by AFM can be related to a certain chemistry by the colocated Raman scan and additionally the mechanical properties be revealed by using the digital pulsed force mode. Microsc. Res. Tech. 80:30-40, 2017. © 2016 Wiley Periodicals, Inc.

Nanochemistry of Protein-Based Delivery Agents

The past decade has seen an increased interest in the conversion of food proteins into functional biomaterials, including their use for loading and delivery of physiologically active compounds such as nutraceuticals and pharmaceuticals. Proteins possess a competitive advantage over other platforms for the development of nanodelivery systems since they are biocompatible, amphipathic, and widely available. Proteins also have unique molecular structures and diverse functional groups that can be selectively modified to alter encapsulation and release properties. A number of physical and chemical methods have been used for preparing protein nanoformulations, each based on different underlying protein chemistry. This review focuses on the chemistry of the reorganization and/or modification of proteins into functional nanostructures for delivery, from the perspective of their preparation, functionality, stability and physiological behavior.

Magnesium as Novel Material for Active Plasmonics in the Visible Wavelength Range

Investigating new materials plays an important role for advancing the field of nanoplasmonics. In this work, we fabricate nanodisks from magnesium and demonstrate tuning of their plasmon resonance throughout the whole visible wavelength range by changing the disk diameter. Furthermore, we employ a catalytic palladium cap layer to transform the metallic Mg particles into dielectric MgH2 particles when exposed to hydrogen gas. We prove that this transition can be reversed in the presence of oxygen. This yields plasmonic nanostructures with an extinction spectrum that can be repeatedly switched on or off or kept at any intermediate state, offering new perspectives for active plasmonic metamaterials.

Hierarchy of Chemical Bonding in the Synthesis of Fe-Phthalocyanine on Metal Surfaces: A Local Spectroscopy Approach

Scanning tunneling spectroscopy (STS) has become a key tool for accessing properties of organometallic molecules adsorbed on surfaces. However, the rich variety of signatures makes it sometimes a difficult task to find out which feature is intrinsic to the molecule, i.e., relevant for a metal-ligand interaction or related to the interaction of the molecule with the substrate. Here we study the prototype covalent self-assembly of FePc and probe how electronic/magnetic properties at the local scale change as a function of temperature-induced step-by-step assembly, starting from TCNB (1,2,4,5- Tetracyanobenzene) molecular and Fe atomic precursors. Intermediate complexes with tetra-coordinated Fe atoms are then used both, as synthons for the FePc and as identifiers of specific features of the STS. As observed by STS and confirmed by spin-polarized DFT calculations, the occupied dπ states of Fe are present in both the FePc and Fe(TCNB)2 on Au(111). The main difference appears in the dz(2) states, which play a key role in magnetism as confirmed by the presence/absence of the Kondo resonance. A comprehensive picture is obtained by following with STS the hybridization of the dz(2) orbital of Fe to various substrates (Cu, Au and Co). Finally it is demonstrated that FePc units can be created by on-surface polymerization from the Fe(TCNB)2 network upon thermal annealing.

Ether- and alcohol-functionalized task-specific ionic liquids: attractive properties and applications

In recent years, the designer nature of ionic liquids (ILs) has driven their exploration and exploitation in countless fields among the physical and chemical sciences. A fair measure of the tremendous attention placed on these fluids has been attributed to their inherent designer nature. And yet, there are relatively few examples of reviews that emphasize this vital aspect in an exhaustive or meaningful way. In this critical review, we systematically survey the physicochemical properties of the collective library of ether- and alcohol-functionalized ILs, highlighting the impact of ionic structure on features such as viscosity, phase behavior/transitions, density, thermostability, electrochemical properties, and polarity (e.g. hydrophilicity, hydrogen bonding capability). In the latter portions of this review, we emphasize the attractive applications of these functionalized ILs across a range of disciplines, including their use as electrolytes or functional fluids for electrochemistry, extractions, biphasic systems, gas separations, carbon capture, carbohydrate dissolution (particularly, the (ligno)celluloses), polymer chemistry, antimicrobial and antielectrostatic agents, organic synthesis, biomolecular stabilization and activation, and nanoscience. Finally, this review discusses anion-functionalized ILs, including sulfur- and oxygen-functionalized analogs, as well as choline-based deep eutectic solvents (DESs), an emerging class of fluids which can be sensibly categorized as semi-molecular cousins to the IL. Finally, the toxicity and biodegradability of ether- and alcohol-functionalized ILs are discussed and cautiously evaluated in light of recent reports. By carefully summarizing literature examples on the properties and applications of oxy-functional designer ILs up till now, it is our intent that this review offers a barometer for gauging future advances in the field as well as a trigger to spur further contemplation of these seemingly inexhaustible and--relative to their potential--virtually untouched fluids. It is abundantly clear that these remarkable fluidic materials are here to stay, just as certain design rules are slowly beginning to emerge. However, in fairness, serendipity also still plays an undeniable role, highlighting the need for both expanded in silico studies and a beacon to attract bright, young researchers to the field (406 references).

In quest of a systematic framework for unifying and defining nanoscience

This article proposes a systematic framework for unifying and defining nanoscience based on historic first principles and step logic that led to a "central paradigm" (i.e., unifying framework) for traditional elemental/small-molecule chemistry. As such, a Nanomaterials classification roadmap is proposed, which divides all nanomatter into Category I: discrete, well-defined and Category II: statistical, undefined nanoparticles. We consider only Category I, well-defined nanoparticles which are >90% monodisperse as a function of Critical Nanoscale Design Parameters (CNDPs) defined according to: (a) size, (b) shape, (c) surface chemistry, (d) flexibility, and (e) elemental composition. Classified as either hard (H) (i.e., inorganic-based) or soft (S) (i.e., organic-based) categories, these nanoparticles were found to manifest pervasive atom mimicry features that included: (1) a dominance of zero-dimensional (0D) core-shell nanoarchitectures, (2) the ability to self-assemble or chemically bond as discrete, quantized nanounits, and (3) exhibited well-defined nanoscale valencies and stoichiometries reminiscent of atom-based elements. These discrete nanoparticle categories are referred to as hard or soft particle nanoelements. Many examples describing chemical bonding/assembly of these nanoelements have been reported in the literature. We refer to these hard:hard (H-n:H-n), soft:soft (S-n:S-n), or hard:soft (H-n:S-n) nanoelement combinations as nanocompounds. Due to their quantized features, many nanoelement and nanocompound categories are reported to exhibit well-defined nanoperiodic property patterns. These periodic property patterns are dependent on their quantized nanofeatures (CNDPs) and dramatically influence intrinsic physicochemical properties (i.e., melting points, reactivity/self-assembly, sterics, and nanoencapsulation), as well as important functional/performance properties (i.e., magnetic, photonic, electronic, and toxicologic properties). We propose this perspective as a modest first step toward more clearly defining synthetic nanochemistry as well as providing a systematic framework for unifying nanoscience. With further progress, one should anticipate the evolution of future nanoperiodic table(s) suitable for predicting important risk/benefit boundaries in the field of nanoscience. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s11051-009-9632-z) contains supplementary material, which is available to authorized users.

A simple route for renewable nano-sized arjunolic and asiatic acids and self-assembly of arjuna-bromolactone

While separating two natural nano-sized triterpenic acids via bromolactonization, we serendipitously discovered that arjuna-bromolactone is an excellent gelator of various organic solvents. A simple and efficient method for the separation of two triterpenic acids and the gelation ability and solid state 1D-helical self-assembly of nano-sized arjuna-bromolactone are reported.

Zwitterionic self-assembly of L-methionine nanogratings on the Ag(111) surface

The engineering of complex architectures from functional molecules on surfaces provides new pathways to control matter at the nanoscale. In this article, we present a combined study addressing the self-assembly of the amino acid L-methionine on Ag(111). Scanning tunneling microscopy data reveal spontaneous ordering in extended molecular chains oriented along high-symmetry substrate directions. At intermediate coverages, regular biomolecular gratings evolve whose periodicity can be tuned at the nanometer scale by varying the methionine surface concentration. Their characteristics and stability were confirmed by helium atomic scattering. X-ray photoemission spectroscopy and high-resolution scanning tunneling microscopy data reveal that the L-methionine chaining is mediated by zwitterionic coupling, accounting for both lateral links and molecular dimerization. This methionine molecular recognition scheme is reminiscent of sheet structures in amino acid crystals and was corroborated by molecular mechanics calculations. Our findings suggest that zwitterionic assembly of amino acids represents a general construction motif to achieve biomolecular nanoarchitectures on surfaces.