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2017
Xiao, Q, Sherman SE, Wilner SE, Zhou X, Dazen C, Baumgart T, Reed EH, Hammer DA, Shinoda W, Klein ML, Percec V.  2017.  Janus dendrimersomes coassembled from fluorinated, hydrogenated, and hybrid Janus dendrimers as models for cell fusion and fission, 2017/08/07. Proceedings of the National Academy of Sciences. AbstractWebsite
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Smail, R, Jezorek RL, Lejnieks J, Enayati M, Grama S, Monteiro M, Percec V.  2017.  Acetone-water biphasic mixtures as solvents for ultrafast SET-LRP of hydrophobic acrylates, 2017. Polymer Chemistry. :-.: The Royal Society of Chemistry AbstractWebsite

Acetone is an excellent solvent for polymers including poly(acrylate)s and a well understood and established reagent for organic synthesis. Therefore, it is surprising that being also the least expensive organic solvent after methanol, so far it did not become a common solvent for metal catalyzed living radical polymerizations. Here we report the elaboration of acetone-water biphasic mixtures as solvents for ultrafast single electron transfer living radical polymerization (SET-LRP) that provides close to 100% conversion of methyl and n-butyl acrylates to the corresponding polymers with near quantitative chain-end functionality in 20 to 35 min reaction time at room temperature. Two methodologies were elaborated for this process. The first involves the generation of Cu(0) nano-colloidal particles as catalyst via the in situ reduction of Cu(II)Br2 with NaBH4 by two different procedures. The second involves the use of non-activated Cu(0) wire as catalyst. Control experiments for the organic reactions of acetone and monomers with CuBr2 and other reagents have been used to eliminate the bromination of acetone and monomer, the aldol condensation of acetone, and the hydrolysis of CuBr2 to Cu(OH)2. Control experiments have also established that the most probable deactivating species, at least in the case of the first methodology, may not be CuBr2, but bromocuprates. Addition of tetra-n-butylammonium bromide was found to increase the linearity of the first order kinetic plots of the first SET-LRP process. We expect that these results will help establish acetone and other ketones as common solvents for metal catalyzed LRPs of both hydrophobic and hydrophilic monomers.

Andreopoulou, KA, Peterca M, Wilson DA, Partridge BE, Heiney PA, Percec V.  2017.  Demonstrating the 81-Helicity and Nanomechanical Function of Self-Organizable Dendronized Polymethacrylates and Polyacrylates, 2017. MacromoleculesMacromolecules. 50(14):5271-5284.: American Chemical Society AbstractWebsite
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Sherman, SE, Xiao Q, Percec V.  2017.  Mimicking Complex Biological Membranes and Their Programmable Glycan Ligands with Dendrimersomes and Glycodendrimersomes, 2017. Chemical ReviewsChemical Reviews. : American Chemical Society AbstractWebsite
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Lligadas, G, Grama S, Percec V.  2017.  Recent Developments in the Synthesis of Biomacromolecules and their Conjugates by Single Electron Transfer–Living Radical Polymerization, 2017. BiomacromoleculesBiomacromolecules. : American Chemical Society AbstractWebsite
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Grama, S, Lejnieks J, Enayati M, Smail RB, Ding L, Lligadas G, Monteiro MJ, Percec V.  2017.  Searching for efficient SET-LRP systems via biphasic mixtures of water with carbonates, ethers and dipolar aprotic solvents, 2017. Polymer Chemistry. :-.: The Royal Society of Chemistry AbstractWebsite

The recently developed "programmed" water/organic solvent biphasic reaction medium is the most efficient approach to expand the advantages of SET-LRP to next generation solvents and to enhance the performance of the current solvents employed in this polymerization methodology. This system has been successfully applied to families of solvents not accessible so far by SET-LRP such as polar and nonpolar non-disproportionation solvents. Here we report a series of screening experiments on biphasic mixtures of water with linear diethyl and dimethyl carbonates, cyclic propylene and ethylene carbonates, the cyclic ethers THF and dioxane, and with dipolar aprotic solvents. Two general methodologies were applied in the catalytic process: the accelerated "multicomponent" Cu(0) generated by the in situ reduction of Cu(ii)Br2 with NaBH4 and the "single component" Cu(0) wire. All carbonates and ethers provide linear kinetic SET-LRP experiments when solvent/water = 8/2, v/v were used while under the same conditions dipolar aprotic solvents increased their apparent rate constant of polymerization up to about 3.5 times from the values obtained in the absence of water. These remarkable results demonstrate the power of the biphasic water/organic solvent mixture to the elaboration of new solvent systems for SET-LRP.

Moreno, A, Garcia D, Galia M, Ronda JC, Cadiz V, Lligadas G, Percec V.  2017.  SET-LRP in the Neoteric Ethyl Lactate Alcohol, 2017. BiomacromoleculesBiomacromolecules. : American Chemical Society AbstractWebsite
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Lligadas, G, Grama S, Percec V.  2017.  SET-LRP Platform to Practice, Develop and Invent, 2017. BiomacromoleculesBiomacromolecules. : American Chemical Society AbstractWebsite
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Jezorek, RL, Enayati M, Smail R, Lejnieks J, Grama S, Monteiro M, Percec V.  2017.  Stirring rate provides dramatic acceleration of the ultrafast interfacial SET-LRP in biphasic acetonitrile-water mixtures, 2017. Polymer Chemistry. :-.: The Royal Society of Chemistry AbstractWebsite

The influence of stirring rate on the SET-LRP of methyl acrylate and n-butyl acrylate catalyzed with Cu(0) wire in methanol and with Cu(0) generated by the reduction of Cu(II)Br2 with NaBH4 by two different methodologies in biphasic acetonitrile-water mixtures was investigated. In all cases tris(2-dimethylaminoethyl)amine (Me6-TREN) was used as ligand and the polymerizations were carried out at 25 [degree]C. No effect of the stirring rate on the rate of SET-LRP was observed in methanol when Cu(0) wire was used as a catalyst and the reaction mixture exhibited a single homogeneous phase. However, a dramatic acceleration of the already ultrafast interfacial SET-LRP was observed in biphasic acetonitrile-water mixtures for both methodologies employed for the generation of Cu(0) directly in the reaction mixture. No increase in the dispersity of the resulting polymers was observed when the rate of the reaction was increased by stirring. This is contrary to rate of polymerization increased by catalyst concentration. Mechanistic hypothesis for this increase in rate of SET-LRP in biphasic acetonitrile-water systems was advanced. This catalytic-like effect of the stirring rate is expected to be of interest for both laboratory and technological applications.

Sahoo, D, Peterca M, Aqad E, Partridge BE, Heiney PA, Graf R, Spiess HW, Zeng X, Percec V.  2017.  Tetrahedral Arrangements of Perylene Bisimide Columns via Supramolecular Orientational Memory, 2017. ACS NanoACS Nano. 11(1):983-991.: American Chemical Society AbstractWebsite
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Lligadas, G, Enayati M, Grama S, Smail R, Sherman SE, Percec V.  2017.  Ultrafast SET-LRP with Peptoid Cytostatic Drugs as Monofunctional and Bifunctional Initiators, 2017. BiomacromoleculesBiomacromolecules. : American Chemical Society AbstractWebsite

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Jishkariani, D, MacDermaid CM, Timsina YN, Grama S, Gillani SS, Divar M, Yadavalli SS, Moussodia R-O, Leowanawat P, Berrios Camacho AM, Walter R, Goulian M, Klein ML, Percec V.  2017.  Self-interrupted synthesis of sterically hindered aliphatic polyamide dendrimers. Proceedings of the National Academy of Sciences. AbstractWebsite

2,2-Bis(azidomethyl)propionic acid was prepared in four steps and 85% yield from the commercially available 2,2-bis(hydroxymethyl)propionic acid and used as the starting building block for the divergent, convergent, and double-stage convergent–divergent iterative methods for the synthesis of dendrimers and dendrons containing ethylenediamine (EDA), piperazine (PPZ), and methyl 2,2-bis(aminomethyl)propionate (COOMe) cores. These cores have the same multiplicity but different conformations. A diversity of synthetic methods were used for the synthesis of dendrimers and dendrons. Regardless of the method used, a self-interruption of the synthesis was observed at generation 4 for the dendrimer with an EDA core and at generation 5 for the one with a PPZ core, whereas for the COOMe core, self-interruption was observed at generation 6 dendron, which is equivalent to generation 5 dendrimer. Molecular modeling and molecular-dynamics simulations demonstrated that the observed self-interruption is determined by the backfolding of the azide groups at the periphery of the dendrimer. The latter conformation inhibits completely the heterogeneous hydrogenation of the azide groups catalyzed by 10% Pd/carbon as well as homogeneous hydrogenation by the Staudinger method. These self-terminated polyamide dendrimers are enzymatically and hydrolytically stable and also exhibit antimicrobial activity. Thus, these nanoscale constructs open avenues for biomedical applications.

Holerca, MN, Sahoo D, Peterca M, Partridge BE, Heiney PA, Percec V.  2017.  A Tetragonal Phase Self-Organized from Unimolecular Spheres Assembled from a Substituted Poly(2-oxazoline). Macromolecules. 50:375-385., Number 1 AbstractWebsite
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2016
Xiao, Q, Yadavalli SS, Zhang S, Sherman SE, Fiorin E, da Silva L, Wilson DA, Hammer DA, André S, Gabius H-J, Klein ML, Goulian M, Percec V.  2016.  Bioactive cell-like hybrids coassembled from (glyco)dendrimersomes with bacterial membranes, 2016/03/01. Proceedings of the National Academy of Sciences. 113(9):E1134-E1141. AbstractWebsite

A library of amphiphilic Janus dendrimers including two that are fluorescent and one glycodendrimer presenting lactose were used to construct giant dendrimersomes and glycodendrimersomes. Coassembly with the components of bacterial membrane vesicles by a dehydration–rehydration process generated giant cell-like hybrid vesicles, whereas the injection of their ethanol solution into PBS produced monodisperse nanometer size assemblies. These hybrid vesicles contain transmembrane proteins including a small membrane protein, MgrB, tagged with a red fluorescent protein, lipopolysaccharides, and glycoproteins from the bacterium Escherichia coli. Incorporation of two colored fluorescent probes in each of the components allowed fluorescence microscopy to visualize and demonstrate coassembly and the incorporation of functional membrane channels. Importantly, the hybrid vesicles bind a human galectin, consistent with the display of sugar moieties from lipopolysaccharides or possibly glycosylated membrane proteins. The present coassembly method is likely to create cell-like hybrids from any biological membrane including human cells and thus may enable practical application in nanomedicine.

Xiao, Q, Zhang S, Wang Z, Sherman SE, Moussodia R-O, Peterca M, Muncan A, Williams DR, Hammer DA, Vértesy S, André S, Gabius H-J, Klein ML, Percec V.  2016.  Onion-like glycodendrimersomes from sequence-defined Janus glycodendrimers and influence of architecture on reactivity to a lectin, 2016/01/19. Proceedings of the National Academy of Sciences. 113(5):1162–1167. AbstractWebsite

A library of eight amphiphilic Janus glycodendrimers (GDs) with d-mannose (Man) headgroups, a known routing signal for lectin-mediated transport processes, was constructed via an iterative modular methodology. Sequence-defined variations of the Janus GD modulate the surface density and sequence of Man after self-assembly into multilamellar glycodendrimersomes (GDSs). The spatial mode of Man presentation is decisive for formation of either unilamellar or onion-like GDS vesicles. Man presentation and Janus GD concentration determine GDS size and number of bilayers. Beyond vesicle architecture, Man topological display affects kinetics and plateau level of GDS aggregation by a tetravalent model lectin: the leguminous agglutinin Con A, which is structurally related to endogenous cargo transporters. The agglutination process was rapid, efficient, and readily reversible for onion-like GDSs, demonstrating their value as versatile tools to explore the nature of physiologically relevant glycan/lectin pairing.

Peterca, M, Imam MR, Hudson SD, Partridge BE, Sahoo D, Heiney PA, Klein ML, Percec V.  2016.  Complex Arrangement of Orthogonal Nanoscale Columns via a Supramolecular Orientational Memory Effect, 2016. ACS NanoACS Nano. 10(11):10480-10488.: American Chemical Society AbstractWebsite
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Vorobii, M, Pop-Georgievski O, de los Santos Pereira A, Kostina NY, Jezorek R, Sedlakova Z, Percec V, Rodriguez-Emmenegger C.  2016.  Grafting of functional methacrylate polymer brushes by photoinduced SET-LRP, 2016. Polymer Chemistry. :-.: The Royal Society of Chemistry AbstractWebsite

Photoinduced surface-initiated single electron transfer living radical polymerization (SET-LRP) is a versatile technique for the preparation of polymer brushes. The vast diversity of compatible functional groups, together with a high end-group fidelity that enables precise control of the architecture, makes this approach an effective tool for tuning the properties of surfaces. We report the application of photoinduced SET-LRP for the surface-initiated grafting of polymer brushes from a wide range of methacrylate monomers for the first time. The living character of the process was demonstrated by the linear evolution of the polymer brush thickness in time, the ability to reinitiate the polymerization for the preparation of well-defined block copolymers, and also by X-ray photoelectron spectroscopy depth profiling. The surface patterning with these brushes could be achieved simply by restricting the irradiated area. The ability of poly(methacrylate) brushes prepared in this way to prevent non-specific protein adsorption is also demonstrated, indicating the suitability of this procedure for advanced applications.

Enayati, M, Jezorek RL, Percec V.  2016.  A multiple-stage activation of the catalytically inhomogeneous Cu(0) wire used in SET-LRP, 2016. Polymer Chemistry. :-.: The Royal Society of Chemistry AbstractWebsite

The surface of Cu(0) wire used as catalyst in the single electron-transfer living radical polymerization (SET-LRP) is inhomogeneous since it contains predominantly a combination of Cu(111) and Cu(100) faces of the face centered cubic unit cell of the copper single crystal. The ratio between the areas of these two orientations is determined by the method of fabrication of the copper wire. The activity of these faces towards SET reactions is substrate dependent, and therefore, aside from the Cu2O available on the surface, the ratio between the areas of these two crystal faces determines the catalytic activity of the wire. The inhomogeneous morphology of the Cu(0) wire is well established and known in the scientific community of metallurgy but apparently is not known by the community of the polymer chemistry. Here, we report a multiple-stage activation of the catalytically inhomogeneous Cu(0) wire used in SET-LRP by a combination of acetone washing, razor blade scratching, and either reduction or acid dissolution of the Cu2O from the surface. An increase of Cu(0) wire activity up to 82% was accomplished via this new and simple activation method.

Ho, M-S, Partridge BE, Sun H-J, Sahoo D, Leowanawat P, Peterca M, Graf R, Spiess HW, Zeng X, Ungar G, Heiney PA, Hsu C-S, Percec V.  2016.  Screening Libraries of Semifluorinated Arylene Bisimides to Discover and Predict Thermodynamically Controlled Helical Crystallization, 2016. ACS Combinatorial ScienceACS Combinatorial Science. 18(12):723-729.: American Chemical Society AbstractWebsite

Synthesis, structural and retrostructural analysis of a library containing sixteen self-assembling perylene (PBI), 1,6,7,12-tetrachloroperylene (Cl4PBI), naphthalene (NBI), and pyromellitic (PMBI) bisimides functionalized with environmentally friendly AB3 chiral racemic semifluorinated minidendrons at their imide groups via m = 0, 1, 2, and 3 methylene units is reported. These semifluorinated compounds melt at lower temperatures than homologous hydrogenated compounds, permitting screening of all their thermotropic phases via structural analysis to discover thermodynamically controlled helical crystallization from propeller-like, cogwheel, and tilted molecules as well as lamellar-like structures. Thermodynamically controlled helical crystallization was discovered for propeller-like PBI, Cl4PBI and NBI with m = 0. Unexpectedly, assemblies of twisted Cl4PBIs exhibit higher order than those of planar PBIs. PBI with m = 1, 2, and 3 form a thermodynamically controlled columnar hexagonal 2D lattice of tilted helical columns with intracolumnar order. PBI and Cl4PBI with m = 1 crystallize via a recently discovered helical cogwheel mechanism, while NBI and PMBI with m = 1 form tilted helical columns. PBI, NBI and PMBI with m = 2 generate lamellar-like structures. 3D and 2D assemblies of PBI with m = 1, 2, and 3, NBI with m = 1 and PMBI with m = 2 exhibit 3.4 Å π–π stacking. The library approach applied here and in previous work enabled the discovery of six assemblies which self-organize via thermodynamic control into 3D and 2D periodic arrays, and provides molecular principles to predict the supramolecular structure of electronically active components.Synthesis, structural and retrostructural analysis of a library containing sixteen self-assembling perylene (PBI), 1,6,7,12-tetrachloroperylene (Cl4PBI), naphthalene (NBI), and pyromellitic (PMBI) bisimides functionalized with environmentally friendly AB3 chiral racemic semifluorinated minidendrons at their imide groups via m = 0, 1, 2, and 3 methylene units is reported. These semifluorinated compounds melt at lower temperatures than homologous hydrogenated compounds, permitting screening of all their thermotropic phases via structural analysis to discover thermodynamically controlled helical crystallization from propeller-like, cogwheel, and tilted molecules as well as lamellar-like structures. Thermodynamically controlled helical crystallization was discovered for propeller-like PBI, Cl4PBI and NBI with m = 0. Unexpectedly, assemblies of twisted Cl4PBIs exhibit higher order than those of planar PBIs. PBI with m = 1, 2, and 3 form a thermodynamically controlled columnar hexagonal 2D lattice of tilted helical columns with intracolumnar order. PBI and Cl4PBI with m = 1 crystallize via a recently discovered helical cogwheel mechanism, while NBI and PMBI with m = 1 form tilted helical columns. PBI, NBI and PMBI with m = 2 generate lamellar-like structures. 3D and 2D assemblies of PBI with m = 1, 2, and 3, NBI with m = 1 and PMBI with m = 2 exhibit 3.4 Å π–π stacking. The library approach applied here and in previous work enabled the discovery of six assemblies which self-organize via thermodynamic control into 3D and 2D periodic arrays, and provides molecular principles to predict the supramolecular structure of electronically active components.

Gavrilov, M, Zerk TJ, Bernhardt PV, Percec V, Monteiro MJ.  2016.  SET-LRP of NIPAM in water via in situ reduction of Cu(ii) to Cu(0) with NaBH4, 2016. Polymer Chemistry. 7(4):933-939.: The Royal Society of Chemistry AbstractWebsite

The direct and quantitative reduction of the air-stable Cu(ii)Br2/Me6TREN to Cu(0) by NaBH4 represents a new method for the aqueous single electron transfer-living radical polymerization (SET-LRP) of water soluble polymers. By changing the stoichiometry of NaBH4 to Cu(ii)Br2, any desired ratio of Cu(ii)Br2 to Cu(0) could be obtained with no evidence of Cu(i) species. This quantitative reduction to Cu(0) in combination with rapid disproportionation of Cu(i)Br/Me6TREN in water resulted in activation by Cu(0) initially and during the polymerization. Polymerizations of NIPAM produced polymer within minutes and with controlled and narrow molecular weight distributions in agreement with ideal 'living' radical behavior. The direct in situ thio-bromo 'click' reaction produce polymers with stable chain-end functionality, eliminating the concern of hydrolysis of the halide end-group (i.e. Br). It was found that the end-group functionality was greater than 95%, and for the very rapid polymerizations close to 100%.

Enayati, M, Smail RB, Grama S, Jezorek RL, Monteiro MJ, Percec V.  2016.  The synergistic effect during biphasic SET-LRP in ethanol-nonpolar solvent-water mixtures, 2016. Polymer Chemistry. 7(47):7230-7241.: The Royal Society of Chemistry AbstractWebsite

Single electron transfer-living radical polymerization (SET-LRP) of n-butyl acrylate (BA) catalyzed by Cu(0) generated via in situ reduction of Cu(ii)Br2 with NaBH4 proceeds in triphase in ethanol-water mixtures since poly(butyl acrylate) (PBA) is not soluble in ethanol beyond a certain molecular weight and concentration. This triphase consists of the PBA gel swelled in the organic phase and the water phase containing Cu(ii)Br2 and hexamethylated tris(2-aminoethyl)amine (Me6-TREN). Addition of at least 10% hexanes or other nonpolar and non-disproportionating solvents to the ethanol-water reaction mixture transforms SET-LRP of BA from a triphasic to a biphasic system. A synergistic effect was observed in the biphasic system, which was caused by the addition of hexanes that corresponds to a volumetric ratio of 4/3/3 for ethanol/hexanes/water, when the volume fraction of hexanes ([curly or open phi]Hex) is constant at 0.3, and 4/4/2 while the volume fraction of water ([curly or open phi]H2O) is constant at 0.2. Other nonpolar, non-disproportionating solvents such as ethyl acetate, toluene, anisole, diethyl carbonate and cyclohexane were all shown to mediate the SET-LRP of BA in ethanol-nonpolar solvent-water mixtures at a 4/4/2 (v/v/v) ratio. These experiments demonstrate for the first time the ability to use a diversity of non-disproportionating, nonpolar solvents in conjunction with miscible polar solvents and water in biphasic SET-LRP. This new methodology is important from mechanistic and also from technologic points of view since it expands the scope of polymer synthesis via SET-LRP from disproportionating to non-disproportionating nonpolar solvents.

Enayati, M, Jezorek RL, Monteiro M, Percec V.  2016.  Ultrafast SET-LRP of Hydrophobic Acrylates in Multiphase Alcohol-Water Mixtures, 2016. Polymer Chemistry. ASAP: The Royal Society of Chemistry AbstractWebsite

A solution of a hydrophobic nonpolar acrylate such as n-butyl acrylate (BA) in a large diversity of alcohols is immiscible with a solution containing tris(2-dimethylaminoethyl)amine (Me6-TREN) and Cu(II)Br2 in water. Addition of NaBH4 to this biphasic mixture reduces instantaneously the Cu(II)Br2 to red Cu(0). When a biphasic mixture containing an alcohol, Me6-TREN, methyl 2-bromopropanoate (MBP), Cu(II)Br2 and water was combined with NaBH4 in an inexpensive test tube at 25 [degree]C under a blanket of N2, an ultrafast single electron transfer-living radical polymerization (SET-LRP) of the hydrophobic monomer in a two- or three-phase reaction mixture took place. First order kinetics up to 100% monomer conversion in less than 20 min with narrow molecular weight distribution of the resulting polyacrylate were observed regardless of the rate of the polymerization. The rate of this SET-LRP can be mediated both by the ratio between alcohol and water and by the ratio between Cu(II)Br2 and NaBH4. At the end of the polymerization all Cu(II)X2 is available only in the water phase that can be isolated leading to colorless polymers that are virtually free of any copper. This new multiphase polymerization methodology provides access to the synthesis of hydrophobic nonpolar polyacrylates by SET-LRP.

Xiao, Q, Wang Z, Williams D, Leowanawat P, Peterca M, Sherman SE, Zhang S, Hammer DA, Heiney PA, King SR, Markovitz DM, André S, Gabius H-J, Klein ML, Percec V.  2016.  Why Do Membranes of Some Unhealthy Cells Adopt a Cubic Architecture?, 2016 ACS Central Science. 2(12):943-953.: American Chemical Society AbstractWebsite

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Roche, C, Sun H-J, Leowanawat P, Araoka F, Partridge BE, Peterca M, Wilson DA, Prendergast ME, Heiney PA, Graf R, Spiess HW, Zeng X, Ungar G, Percec V.  2016.  A supramolecular helix that disregards chirality, 2015/11/16/onlin. Nat. Chem.. 8:80-89.: Nature Publishing Group AbstractWebsite

The functions of complex crystalline systems derived from supramolecular biological and non-biological assemblies typically emerge from homochiral programmed primary structures via first principles involving secondary, tertiary and quaternary structures. In contrast, heterochiral and racemic compounds yield disordered crystals, amorphous solids or liquids. Here, we report the self-assembly of perylene bisimide derivatives in a supramolecular helix that in turn self-organizes in columnar hexagonal crystalline domains regardless of the enantiomeric purity of the perylene bisimide. We show that both homochiral and racemic perylene bisimide compounds, including a mixture of 21 diastereomers that cannot be deracemized at the molecular level, self-organize to form single-handed helical assemblies with identical single-crystal-like order. We propose that this high crystalline order is generated via a cogwheel mechanism that disregards the chirality of the self-assembling building blocks. We anticipate that this mechanism will facilitate access to previously inaccessible complex crystalline systems from racemic and homochiral building blocks.