Distinct Packing Research Articles

First principles crystal engineering of nonlinear optical materials. I. Prototypical case of urea.

The crystalline materials with nonlinear optical (NLO) properties are critically important for several technological applications, including nanophotonic and second harmonic generation devices. Urea is often considered to be a standard NLO material, due to the combination of non-centrosymmetric crystal packing and capacity for intramolecular charge transfer. Various approaches to crystal engineering of non-centrosymmetric molecular materials were reported in the literature. Here we propose using global lattice energy minimization to predict the crystal packing from the first principles. We developed a methodology that includes the following: (1) parameter derivation for polarizable force field AMOEBA; (2) local minimizations of crystal structures with these parameters, combined with the evolutionary algorithm for a global minimum search, implemented in program USPEX; (3) filtering out duplicate polymorphs produced; (4) reoptimization and final ranking based on density functional theory (DFT) with many-body dispersion (MBD) correction; and (5) prediction of the second-order susceptibility tensor by finite field approach. This methodology was applied to predict virtual urea polymorphs. After filtering based on packing similarity, only two distinct packing modes were predicted: one experimental and one hypothetical. DFT + MBD ranking established non-centrosymmetric crystal packing as the global minimum, in agreement with the experiment. Finite field approach was used to predict nonlinear susceptibility, and H-bonding was found to account for a 2.5-fold increase in molecular hyperpolarizability to the bulk value.

Exciton Coupling of Merocyanine Dyes from H- to J-type in the Solid State by Crystal Engineering.

A key issue for the application of π-conjugated organic molecules as thin film solid-state materials is the packing structure, which drastically affects optical and electronic properties due to intermolecular coupling. In this regard, merocyanine dyes usually pack in H-coupled antiparallel arrangements while structures with more interesting J-type coupling have been rarely reported. Here we show that for three highly dipolar merocyanine dyes, which exhibit the same π-scaffold and accordingly equal properties as monomers in solution, the solid-state packing can be changed by a simple variation of aliphatic substituents to afford narrow and intense absorption bands with huge hypsochromic (H) or bathochromic (J) shifts for their thin films and nanocrystals. Time-dependent density functional theory calculations show that the energetic offset of almost 1 eV magnitude results from distinct packing motifs within the crystal structures that comply with the archetype H- or J-aggregate structures as described by Kasha's exciton theory.

Bicyclo[3.2.0]heptane as a Core Structure for Conformational Locking of 1,3-Bis-Pharmacophores, Exemplified by GABA.

The synthesis and X-ray crystal structures of syn and anti 4-N-Boc-aminobicyclo[3.2.0]heptane-1-carboxylic acids are described. The placement of the N-Boc-amino groups in the two stereoisomers in either pseudo-equatorial or pseudo-axial positions renders the molecules conformationally locked, with N-Boc-protected γ-aminobutyric acid (GABA) embedded within the bicyclic core. Despite the different conformations of the urethane and distinct crystal packing, the bicyclic core units of the two stereoisomers adopt virtually identical structures. They correspond to in silico models of the parent bicyclic core and a systematic array of disubstituted derivatives. The study documents an intrinsic property of the bicyclo[3.2.0]heptane core to favor adoption of a boat-like conformation, which is largely unaffected by various substitution patterns. The structural concepts are useful in the design of molecules with spatial and directional fixation of pharmacophoric groups.

A perpendicular phenyl-induced exceedingly efficient solid-state excited state intramolecular proton transfer fluorophore based on 2-(2-hydroxyphenyl)benzothiazole

Fluorescent solid-state organic materials have been intensively researched in recent years. In this study, two 2-(2-hydroxyphenyl)benzothiazole (HBT) derivatives: phenylethylene-modified HBT (HBT-s-Ph) and diphenylethylene-modified HBT (HBT-d-Ph), were synthesized by facile Suzuki cross-coupling reactions. In toluene solutions, the fluorescence quantum yield (Φf) of HBT-s-Ph is slightly larger than that of HBT-d-Ph, because of the presence of a stronger intramolecular H-bond in HBT-s-Ph than in HBT-d-Ph. In crystalline forms, both of their Φf has substantial improvement, and the Φf of HBT-d-Ph reaches 78%, which is twice that of HBT-s-Ph. The crystal structure revealed that the striking emission enhancement of HBT-d-Ph was attributable to its distinct molecular packing model and the resultant relatively weak intermolecular interactions induced by the single phenyl group cis to the HBT moiety.

Graph-intersecting set systems and LYM inequalities

For a graph H, an H-intersecting collection is a collection of packings on a ground set [n] with V(H) parts where, for every edge ab of H, every two distinct packings in the collection, P1 and P2, satisfy P1a∩P2b≠Ø. We give a general method for producing LYM-like inequalities for H-intersecting collections, for any graph H. Our technique involves counting permutations having a certain “following” pattern of sets from the collection. For every graph H, we provide the optimal set of permutations to count, encoded by the arcs of a “follow digraph” F. We fully characterize the relationship between graphs H and follow digraphs F. Our inequalities inherently bound the maximum number of packings in H-intersecting collections, and for specific graphs H, we use them to derive bounds. If H is the star on 3 vertices, then an H-intersecting collection has size at most 12a+ba=O(φn∕n), where φ=12(1+5), a≈φb, and a+2b=n. If H is Kv with a loop on each vertex, with v≥3, then an H-intersecting collection has size at most 14⌊2n∕v⌋⌊n∕v⌋, for all n≥22v∕3, improving a bound given by Poljak and Tuza by a factor of 2. Assuming that optimal H-intersecting collections have a limiting behaviour, we derive a simplified form for our inequalities. When H is a complete graph Kv with a loop on each vertex, then, under these assumptions, we prove that an H-intersecting collection has size at most 1v2−v2n∕v+2n∕v+1(1+o(1)), which improves our bound for large enough n and v.

Fused Bis-Benzothiadiazoles as Electron Acceptors

Fused bis-benzothiadiazoles with different molecular geometries, namely, linear benzoquinone-fused bis(benzothiadiazole) (Q-BBT) and V-shaped sulfone-fused bis(benzothiadiazole) (S-BBT), were synthesized. Single crystal analysis of Q-BBT and S-BBT revealed profoundly distinct packing modes, which must be ascribed to the different molecular shapes. Experimental and theoretical studies indicated that both compounds give rise to electron-accepting materials. This work thus also contributes to the diversity of electron acceptors based on bis-benzothiadiazole moieties and highlights the important role of molecular shape for the solid-state packing of organic conjugated materials.

Singlet Fission via an Excimer-Like Intermediate in 3,6-Bis(thiophen-2-yl)diketopyrrolopyrrole Derivatives.

Singlet fission (SF) in polycrystalline thin films of four 3,6-bis(thiophen-2-yl)diketopyrrolopyrrole (TDPP) chromophores with methyl (Me), n-hexyl (C6), triethylene glycol (TEG), and 2-ethylhexyl (EH) substituents at the 2,5-positions is found to involve an intermediate excimer-like state. The four different substituents yield four distinct intermolecular packing geometries, resulting in variable intermolecular charge transfer (CT) interactions in the solid. SF from the excimer state of Me, C6, TEG, and EH takes place in τSF = 22, 336, 195, and 1200 ps, respectively, to give triplet yields of 200%, 110%, 110%, and 70%, respectively. The transient spectra of the excimer-like state and its energetic proximity to the lowest excited singlet state in these derivatives suggests that this state may be the multiexciton (1)(T1T1) state that precedes formation of the uncorrelated triplet excitons. The excimer decay rates correlate well with the SF efficiencies and the degree of intermolecular donor-acceptor interactions resulting from π-stacking of the thiophene donor of one molecule with the DPP core acceptor in another molecule as observed in the crystal structures. Such interactions are found to also increase with the SF coupling energies, as calculated for each derivative. These structural and spectroscopic studies afford a better understanding of the electronic interactions that enhance SF in chromophores having strong intra- and intermolecular CT character.

Two Polymorphic Forms of a Six-Coordinate Mononuclear Cobalt(II) Complex with Easy-Plane Anisotropy: Structural Features, Theoretical Calculations, and Field-Induced Slow Relaxation of the Magnetization

A mononuclear cobalt(II) complex [Co(3,5-dnb)2(py)2(H2O)2] {3,5-Hdnb = 3,5-dinitrobenzoic acid; py = pyridine} was isolated in two polymorphs, in space groups C2/c (1) and P21/c (2). Single-crystal X-ray diffraction analyses reveal that 1 and 2 are not isostructural in spite of having equal formulas and ligand connectivity. In both structures, the Co(II) centers adopt octahedral {CoN2O4} geometries filled by pairs of mutually trans terminal 3,5-dnb, py, and water ligands. However, the structures of 1 and 2 disclose distinct packing patterns driven by strong intermolecular O-H···O hydrogen bonds, leading to their 0D→2D (1) or 0D→1D (2) extension. The resulting two-dimensional layers and one-dimensional chains were topologically classified as the sql and 2C1 underlying nets, respectively. By means of DFT theoretical calculations, the energy variations between the polymorphs were estimated, and the binding energies associated with the noncovalent interactions observed in the crystal structures were also evaluated. The study of the direct-current magnetic properties, as well as ab initio calculations, reveal that both 1 and 2 present a strong easy-plane magnetic anisotropy (D > 0), which is larger for the latter polymorph (D is found to exhibit values between +58 and 117 cm(-1) depending on the method). Alternating current dynamic susceptibility measurements show that these polymorphs exhibit field-induced slow relaxation of the magnetization with Ueff values of 19.5 and 21.1 cm(-1) for 1 and 2, respectively. The analysis of the whole magnetic data allows the conclusion that the magnetization relaxation in these polymorphs mainly takes place through a virtual excited state (Raman process). It is worth noting that despite the notable difference between the supramolecular networks of 1 and 2, they exhibit almost identical magnetization dynamics. This fact suggests that the relaxation process is intramolecular in nature and that the virtual state involved in the two-phonon Raman process lies at a similar energy in polymorphs 1 and 2 (∼20 cm(-1)). Interestingly, this value is recurrent in Co(II) single-ion magnets, even for those displaying different coordination number and geometry.

Surface Assembly Configurations and Packing Preferences of Fibrinogen Mediated by the Periodicity and Alignment Control of Block Copolymer Nanodomains.

The ability to control the specific adsorption and packing behaviors of biomedically important proteins by effectively guiding their preferred surface adsorption configuration and packing orientation on polymeric surfaces may have utility in many applications such as biomaterials, medical implants, and tissue engineering. Herein, we investigate the distinct adhesion configurations of fibrinogen (Fg) proteins and the different organization behaviors between single Fg molecules that are mediated by the changes in the periodicity and alignment of chemically alternating nanodomains in thin films of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer (BCP). Specifically, the adsorption characteristics of individual Fg molecules were unambiguously resolved on four different PS-b-PMMA templates of dsa PS-b-PMMA, sm PS-b-PMMA, com PS-b-PMMA, and PS-r-PMMA. By direct visualization through high resolution imaging, the distinct adsorption and packing configurations of both isolated and interacting Fg molecules were determined as a function of the BCP template-specific nanodomain periodicity, domain alignment (random versus fully aligned), and protein concentration. The three dominant Fg adsorption configurations, SP∥, SP⊥, and TP, were observed and their occurrence ratios were ascertained on each PS-b-PMMA template. During surface packing, the orientation of the protein backbone was largely governed by the periodicity and alignment of the underlying PS-b-PMMA nanodomains whose specific direction was explicitly resolved relative to the polymeric nanodomain axis. The use of PS-b-PMMA with a periodicity much smaller than (and comparable to) the length of Fg led to a Fg scaffold with the protein backbone aligned parallel (and perpendicular) to the nanodomain major axis. In addition, we have successfully created fully Fg-decorated BCP constructs analogous to two-dimensional Fg crystals in which aligned protein molecules are arranged either side-on or end-on, depending on the BCP template. Our results demonstrate that the geometry and orientation of the protein can be effectively guided during Fg self-assembly by controlling the physical dimensions and orientations of the underlying BCP templates. Finally, the biofunctionality of the BCP surface-bound Fg was assessed and the Fg/BCP construct was successfully used in the Ca-P nanoparticle nucleation/growth and microglia cell activation.

Evolutionary relationships between heme-binding ferredoxin α + β barrels.

BackgroundThe α + β barrel superfamily of the ferredoxin-like fold consists of a functionally diverse group of evolutionarily related proteins. The barrel architecture of these proteins is formed by either homo-/hetero-dimerization or duplication and fusion of ferredoxin-like domains. Several members of this superfamily bind heme in order to carry out their functions.ResultsWe analyze the heme-binding sites in these proteins as well as their barrel topologies. Our comparative structural analysis of these heme-binding barrels reveals two distinct modes of packing of the ferredoxin-like domains to constitute the α + β barrel, which is typified by the Type-1/IsdG-like and Type-2/OxdA-like proteins, respectively. We examine the heme-binding pockets and explore the versatility of the α + β barrels ability to accommodate heme or heme-related moieties, such as siroheme, in at least three different sites, namely, the mode seen in IsdG/OxdA, Cld/DyP/EfeB/HemQ and siroheme decarboxylase barrels.ConclusionsOur study offers insights into the plausible evolutionary relationships between the two distinct barrel packing topologies and relate the observed heme-binding sites to these topologies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12859-016-1033-6) contains supplementary material, which is available to authorized users.

Directly Insight Into the Inter- and Intramolecular Interactions of CL-20/TNT Energetic Cocrystal through the Theoretical Simulations of THz Spectroscopy.

Compared with cocrystal coformers, an explosive cocrystal has distinctive packing arrangements and complex intermolecular interactions. Identifying the spectral signatures of an explosive cocrystal and understanding the molecular low-frequency modes by means of the spectrum in the terahertz range are of great worth to the explicit mechanism of cocrystal formation. In this work, on the basis of the joint molecular dynamics (MD) simulations and solid-state density functional theory (DFT) calculations, we have investigated the terahertz (THz) absorption spectra of the CL-20/TNT cocrystal and its different directions as well as cocrystal coformers and determined the systematic and all-sided assignments of corresponding THz vibration modes. The THz spectral comparison of the cocrystal with different directions and the cocrystal coformers indicates that the CL-20/TNT cocrystal has five fresh low-frequency absorption features as unique and discernible peaks for identification, in which 0.25, 0.73, and 0.87 THz are attributed to intensive crystalline vibrations; 0.87 THz is also caused by C-H···O hydrogen-bonding bending vibrations; 1.60 and 1.85 THz features originate from C-H···O hydrogen-bond stretching vibrations. Additionally, the THz spectrum of the (001) direction of the CL-20/TNT cocrystal verifies that the molecular conformation of the CL-20 is the same as that in the β-polymorph, other than the initial conformation of raw material ε-CL-20.

Two-Dimensional Bipyramid Plasmonic Nanoparticle Liquid Crystalline Superstructure with Four Distinct Orientational Packing Orders.

Anisotropic plasmonic nanoparticles have been successfully used as constituent elements for growing ordered nanoparticle arrays. However, orientational control over their spatial ordering remains challenging. Here, we report on a self-assembled two-dimensional (2D) nanoparticle liquid crystalline superstructure (NLCS) from bipyramid gold nanoparticles (BNPs), which showed four distinct orientational packing orders, corresponding to horizontal alignment (H-NLCS), circular arrangement (C-NLCS), slanted alignment (S-NLCS), and vertical alignment (V-NLCS) of constituent particle building elements. These packing orders are characteristic of the unique shape of BNPs because all four packing modes were observed for particles with various sizes. Nevertheless, only H-NLCS and V-NLCS packing orders were observed for the free-standing ordered array nanosheets formed from a drying-mediated self-assembly at the air/water interface of a sessile droplet. This is due to strong surface tension and the absence of particle-substrate interaction. In addition, we found the collective plasmonic coupling properties mainly depend on the packing type, and characteristic coupling peak locations depend on particle sizes. Interestingly, surface-enhanced Raman scattering (SERS) enhancements were heavily dependent on the orientational packing ordering. In particular, V-NLCS showed the highest Raman enhancement factor, which was about 77-fold greater than the H-NLCS and about 19-fold greater than C-NLCS. The results presented here reveal the nature and significance of orientational ordering in controlling plasmonic coupling and SERS enhancements of ordered plasmonic nanoparticle arrays.

Luminescent mechanochromism of a chiral complex: distinct crystal structures and color changes of racemic and homochiral gold(i) isocyanide complexes with a binaphthyl moiety.

Luminescent mechanochromism of a chiral gold(i) complex is investigated. The racemic and homochiral forms of the gold(i) complex possess distinct crystal packing arrangements with different emission colors. Upon mechanical stimulation, both crystals transform into amorphous powders that exhibit similar emission colors.

Self-assembly synthesis, structural features, reversible temperature-induced dehydration/hydration, and magnetic and luminescence properties of lanthanide(iii) compounds derived from 5-fluoronicotinic acid

A new series of eight lanthanide coordination compounds, namely [Ln(5-Fnic)3(H2O)3]2·2H2O (Ln = La (1), Pr (2), Nd (3), Eu (4), Gd (5), and Tb (6)), [Tm(5-Fnic)2(H2O)4]2[5-Fnic]2·2H2O (7), and [Eu(5-Fnic)2(phen)2(NO3)(H2O)]·2H2O (8) were generated by a hydrothermal self-assembly method in H2O from the corresponding lanthanide metal(III) nitrates, with 5-fluoronicotinic acid (5-FnicH) as the main building block, and an optional (for 8) 1,10-phenanthroline (phen) as an ancillary ligand. All the products (1–8) were fully characterized by IR spectroscopy, elemental analysis, thermogravimetric analysis, and powder and single-crystal X-ray diffraction analyses. Compounds 1–6 are isostructural and reveal neutral dilanthanide(III) molecular units, 7 is ionic and has a cationic Tm2 core, whereas 8 displays a mononuclear structure. Distinct crystal packing patterns driven by strong intermolecular hydrogen bonds were observed in 1–6, 7, and 8, resulting in the 0D → 3D (1–7) or 0D → 1D (8) extension of the structures into H-bonded networks; their topological analysis and classification were performed. Products 1 and 3–8 constitute the first La, Nd, Eu, Gd, Tb, and Tm coordination compounds derived from 5-fluoronicotinic acid. The magnetic properties of compounds 2, 3, 5, and 7 were investigated. Besides, products 4, 6, and 8 exhibit a reversible temperature-induced dehydration/hydration behavior, which also influences their solid state luminescence properties that were studied in detail. The intensity of the emission bands of the dehydrated samples greatly increases after thermal removal of water molecules and then returns back to the original level upon exposure to water. This reversible behavior is more pronounced in 8 given the additional presence of phenanthroline moieties.

Packing of elastic wires in flexible shells

The packing problem of long thin filaments that are injected into confined spaces is of fundamental interest for physicists and biologists alike. How linear threads pack and coil is well known only for the ideal case of rigid containers, though. Here, we force long elastic rods into flexible spatial confinement borne by an elastic shell to examine under which conditions recently acquired knowledge on wire packing in rigid spheres breaks down. We find that unlike in rigid cavities, friction plays a key role by giving rise to the emergence of two distinct packing patterns. At low friction, the wire densely coils into an ordered toroidal bundle with semi-ellipsoidal cross-section, while at high friction, it packs into a highly disordered, hierarchic structure. These two morphologies are shown to be separated by a continuous phase transition. Our findings demonstrate the dramatic impact of friction and confinement elasticity on filamentous packing and might drive future research on such systems in physics, biology and even medical technology toward including these mutually interacting effects.

Distinct Packings of Supramolecular Building Blocks in Metal-Organic Frameworks Based on Imidazoledicarboxylic Acid.

When the supramolecular building block packings (face-centered, body-centered, and primitive cubic) with different interactions (hydrogen and coordination bonding) were controlled, four new structures based on octahedral M(II) (M = Zn, Ni, Mn) and imidazoledicarboxylate were constructed. The interaction modes between the supramolecular building blocks affect the water stability of the structures. Furthermore, with uncoordinated carboxylate O atoms in the structures, these compounds demonstrate a strong capability of capturing metal ions in the solution.

Conformational polymorphism on styrl quinolinium salts of 2-[(E)-2-(4-hydroxy-3-methoxystyrl)-1-methyl]-quinolinium 4-chlorobenzenesulfonate (HMQ-CBS): Potential nonlinear optical crystals for terahertz application

Polymorphism is an important phenomenon to investigate the relationship between the chemical structures and properties of functional materials. Here, we demonstrate the existence of conformational polymorphism in the terahertz (THz) compounds of 2-[(E)-2-(4-hydroxy-3-methoxystyrl)-1-methyl]-quinolinium 4-chlorobenzenesulfonate (abbreviated as HMQ-CBS). There are two different crystalline phases (I and II, respectively). X-ray structural analyses reveal that HMQ-CBS crystallizes in the monoclinic crystallographic system with the non-centrosymmetric space group Pc for phase-I, and centrosymmetric space group of P21/n for phase-II. These two different crystalline phases exhibit the distinct anionic orientations and crystal packings, leading to significantly different nonlinear optical (NLO) properties. Second harmonic generation (SHG) measurements reveal that crystals in phase-I possess the SHG efficiency of about 0.5 times that of N, N-dimethylamino-N-methylstilbazolium p-toluenesulphonate (DAST), which indicates that HMQ-CBS in phase-I might be a potential NLO crystal for THz application. In contrast, crystals in the phase-II show no SHG responses. Comparison of their crystal structures and NLO properties enables us to understand the correlation between molecular conformational changes and bulk NLO properties, and sheds light on the design of organic THz materials.

A New Low Melting-Point Polymorph of Fenofibrate Prepared via Talc Induced Heterogeneous Nucleation

Fenofibrate is one of the most commonly prescribed hyperlipidemia agents. Despite its high lipophilicity and ultralow aqueous solubility, most commercially available formulations use micronized crystalline fenofibrate form I, which has a low dissolution rate and poor oral bioavailability. Little is known about the crystallization of other polymorphs from supercooled amorphous fenofibrate. This study reports a new fenofibrate polymorph (form III) obtained via a controlled heterogeneous nucleation method using low quantity (1% w/w) of the generally recognized as safe (GRAS) oral pharmaceutical excipient talc. Form III has a low melting point of 50 °C, and crystallization of form I immediately occurs after the melting of form III. The microscopic, thermal, and spectroscopic characterizations of form III confirmed the distinct molecular packing difference between the new form and other known forms. The discovery of this new form will enrich the understanding of the molecular behavior of fenofibrate and bring ...

Band Structure Engineering by Substitutional Doping in Solid-State Solutions of [5-Me-PLY(O,O)]2B(1-x)Be(x) Radical Crystals.

We report the substitutional doping of solid-state spiro-bis(5-methyl-1,9-oxido-phenalenyl)boron radical ([2]2B) by co-crystallization of this radical with the corresponding spiro-bis(5-methyl-1,9-oxido-phenalenyl)beryllium compound ([2]2Be). The pure compounds crystallize in different space groups ([2]2B, P1̅, Z = 2; [2]2Be, P2₁/c, Z = 4) with distinct packing arrangements, yet we are able to isolate crystals of composition [2]2B(1-x)Be(x), where x = 0-0.59. The phase transition from the P1̅ to the P2₁/c space group occurs at x = 0.1, but the conductivities of the solid solutions are enhanced and the activation energies reduced for values of x = 0-0.25. The molecular packing is driven by the relative concentration of the spin-bearing ([2]2B) and spin-free ([2]2Be) molecules in the crystals, and the extended Hückel theory band structures show that the progressive incorporation of spin-free [2]2Be in the lattice of the [2]2B radical (overall bandwidth, W = 1.4 eV, in the pure compound) leads to very strong narrowing of the bandwidth, which reaches a minimum at [2]2Be (W = 0.3 eV). The results provide a graphic picture of the structural transformations undergone by the lattice, and at certain compositions we are able to identify distinct structures for the [2]2B and [2]2Be molecules in a single crystalline phase.

Reduced Cytotoxicity of Graphene Nanosheets Mediated by Blood-Protein Coating.

The advent and pending wide use of nanoscale materials urges a biosafety assessment and safe design of nanomaterials that demonstrate applicability to human medicine. In biological microenvironment, biomolecules will bind onto nanoparticles forming corona and endow nanoparticles new biological identity. Since blood-circulatory system will most likely be the first interaction organ exposed to these nanomaterials, a deep understanding of the basic interaction mechanisms between serum proteins and foreign nanoparticles may help to better clarify the potential risks of nanomaterials and provide guidance on safe design of nanomaterials. In this study, the adsorption of four high-abundance blood proteins onto the carbon-based nanomaterial graphene oxide (GO) and reduced GO (rGO) were investigated via experimental (AFM, florescence spectroscopy, SPR) and simulation-based (molecular dynamics) approaches. Among the proteins in question, we observe competitive binding to the GO surface that features a mélange of distinct packing modes. Our MD simulations reveal that the protein adsorption is mainly enthalpically driven through strong π-π stacking interactions between GO and aromatic protein residues, in addition to hydrophobic interactions. Overall, these results were in line with previous findings related to adsorption of serum proteins onto single-walled carbon nanotubes (SWCNTs), but GO exhibits a dramatic enhancement of adsorption capacity compared to this one-dimensional carbon form. Encouragingly, protein-coated GO resulted in a markedly less cytotoxicity than pristine and protein-coated SWCNTs, suggesting a useful role for this planar nanomaterial in biomedical applications.