Edvinas Orentas

Catalysis with Anion–π Interactions

The conclusion is inevitable: Increasing stabilization of an anionic transition state with increasing π-acidity of the catalyst is observed; thus, anion-π interactions can contribute to catalysis.

A quantitative model for the transcription of 2D patterns into functional 3D architectures

Self-sorting on surfaces is one of the big challenges that must be addressed in preparing the organic materials of the future. Here, we introduce a theoretical framework for templated self-sorting on surfaces, and validate it experimentally. In our approach, the transcription of two-dimensional information encoded in a monolayer on the surface into three-dimensional supramolecular architectures is quantified by the intrinsic templation efficiency, a thickness-independent value describing the fidelity of transcription per layer. The theoretical prediction that exceedingly high intrinsic efficiencies will be needed to experimentally observe templated self-sorting is then confirmed experimentally. Intrinsic templation efficiencies of up to 97%, achieved with a newly introduced templated synthesis strategy, result in maximal 47% effective templation efficiency at a thickness of 70 layers. The functional relevance of surface-templated self-sorting and meaningful dependences of templation efficiencies on structural modifications are demonstrated.

Toward oriented surface architectures with three coaxial charge-transporting pathways.

We report a synthetic method to build oriented architectures with three coaxial π-stacks directly on solid surfaces. The approach operates with orthogonal dynamic bonds, disulfides and hydrazones, self-organizing surface-initiated polymerization (SOSIP), and templated stack-exchange (TSE). Compatibility with naphthalenediimides, perylenediimides, squaraines, fullerenes, oligothiophenes, and triphenylamine is confirmed. Compared to photosystems composed of two coaxial channels, the installation of a third channel increases photocurrent generation up to 10 times. Limitations concern giant stack exchangers that fail to enter SOSIP architectures (e.g., phthalocyanines surrounded by three fullerenes), and planar triads that can give folded or interdigitated charge-transfer architectures rather than three coaxial channels. The reported triple-channel surface architectures are as sophisticated as it gets today, the directionality of their construction promises general access to multichannel architectures with multicomponent gradients in each individual channel. The reported approach will allow us to systematically unravel the ultrafast photophysics of molecular dyads and triads in surface architectures, and might become useful to develop conceptually innovative optoelectronic devices.

Enantioselective self-sorting on planar, π-acidic surfaces of chiral anion-π transporters

Self-sorting at interfaces is one of the big challenges we face to prepare the functional organic materials of the future. As a first and decisive step to self-sorting into π-stacks or bundles, we here elaborate self-sorting of π-dimers in solution. Design, synthesis and study of planar naphthalenediimides (NDIs) with one shielded and one free chiral π-surface to direct self-assembly into dimers are described. Stereoisomers are isolated by chiral, preparative HPLC and characterized by X-ray crystallography. NMR studies show that racemates with almost planar, nearly identical π-surfaces prefer uniform self-sorting into homodimers at large differences in π-acidity and alternate self-sorting into heterodimers at small differences in π-acidity. In contrast, enantiomers self-sort “narcissistically” into heterodimers and diastereomers show moderate preference for homodimers. Whereas the lessons learned from dimerization are directly applicable to self-sorting of π-stacks on surfaces, anion transport in lipid bilayers is shown to require a more subtle, somewhat inverse interpretation, with diastereomeric transporters differing dramatically in activity but the least visible supramolecule being confirmed as the best performer.

Composition- and Size-Controlled Cyclic Self-Assembly by Solvent- and C60-Responsive Self-Sorting.

Synthesis, solvent-, and guest-controlled self-assembly, and self-sorting of new hydrogen-bonded chiral cavity receptors are reported. The design of the cavity is based on the cyclic self-aggregation of monomers containing the 4H-bonding ureidopyrimidinone motif fused with the bicylo[3.3.1]nonane framework. Selective formation of kinetically inert cyclic tetramers is observed in chloroform, while in toluene an equilibrium between tetrameric and pentameric forms exists. The high affinity of the tetrameric aggregates toward C60 and C70 is observed in aromatic solvents. The host-guest interaction of unconventional π-acidic supramolecular receptors for fullerenes is turned off and on by changing the solvent, whereas the selection of size and the very composition of the cavity aggregate is controlled by either the change of solvent or the addition of fullerene guest, making our systems a new type of self-sorting device.

Chirality, a never-ending source of confusion

Abstract In this Discussion a few points of confusion concerning chirality are clarified. The term chirodescriptive is proposed for such space groups that lack inversion centres, reflection planes, glide planes or rotary-inversion axes and thus can contain enantiopure, chiral objects. It is pointed out that chiral compounds can (and often do) crystallise in non-chirodescriptive space group when they occur as racemates and in such cases there is no incompatibility between chirality and mirror planes or centres of inversions. We also propose the term raceomorphism to describe the relationship between a conglomerate and a collection of racemic crystals of the same compound.

An Enantiopure Hydrogen-Bonded Octameric Tube: Self-Sorting and Guest-Induced Rearrangement.

The assembly of a discrete hydrogen-bonded molecular tube from eight small identical monomers is reported. Tube assembly was accomplished by means of selective heterodimerization between isocytosine and ureidopyrimidinone hydrogen-bonding motifs embedded in an enantiopure bicyclic building block, leading to the selective formation of an octameric supramolecular tube. Upon introduction of a fullerene guest molecule, the octameric tube rearranges into a tetrameric inclusion complex and the hydrogen-bonding mode is switched. The dynamic behavior of the system is further explored in solvent- and guest-responsive self-sorting experiments.

Recent Progress with Functional Biosupramolecular Systems

The objective of this account is to summarize our recent progress with functional biosupramolecular systems concisely. The functions covered are artificial photosynthesis, anion transport, and sensing in lipid bilayer membranes. With artificial photosynthesis, the current emphasis is on the construction of ordered and oriented architectures on solid surfaces. Recent examples include the zipper assembly of photosystems with supramolecular n/p-heterojunctions and oriented antiparallel redox gradients. Current transport systems in lipid bilayers reveal new interactions at work. Examples include anion-macrodipole or anion-π interactions. Current attention with membrane-based sensing systems shifts from biosensor approaches with enzymatic signal generation to aptamers (i.e., the DNA version of immunosensing) and differential sensing with dynamic polyion-counterion transporters. The functional diversity accessible with biosupramolecular systems is highlighted, as is the critical importance of cross-fertilization at intertopical convergence zones.

A Remarkably Complex Supramolecular Hydrogen-Bonded Decameric Capsule Formed from an Enantiopure C2-Symmetric Monomer by Solvent-Responsive Aggregation

The formation of an unprecedented decameric capsule in carbon disulfide, held together by the combination of double and triple hydrogen bonds between isocytosine units embedded in an enantiomerically pure bicyclic framework is reported. The aggregation occurs via symmetry breaking of the enantiopure intrinsically C2-symmetric monomer brought about by solvent, induced tautomerization of the hydrogen-bonding unit. We show that the topology of the aggregate is responsive to the solvent in which the assembly takes place. In this study we demonstrate that in carbon disulfide the chiral decameric cavity aggregate consisting of three forms of the same monomer, differing in their hydrogen bonding to each other is selectively formed, representing a tube-like structure capped with two C2-symmetric monomers. The large cylindrical cavity produced selectively accommodates one partially solvated C60 molecule, and molecular dynamic simulations revealed the special role of the solvent in the inclusion mechanism. The strategy described herein represents the first step toward the creation of a new class of hydrogen-bonded tubular objects from only one small symmetric building block by solvent-responsive aggregation.

N‐Protected 1,2‐Oxazetidines as a Source of Electrophilic Oxygen: Straightforward Access to Benzomorpholines and Related Heterocycles by Using a Reactive Tether

A hitherto unknown reactivity of a strained four-membered heterocycle, 1,2-oxazetidine, is reported. When reacted with organometallic compounds, this reagent provides electrophilic oxygen with a nitrogen-terminated two-carbon-atom tether. The synthetic versatility of the products obtained was demonstrated in various transformations, leading to efficient synthesis of six-, seven-, and eight-membered heterocyclic systems of pharmaceutical importance.