Prolinyl Phosphoramidates of Nucleotides with Increased Reactivity

Nucleoside monophosphates (NMPs) are the subunits of RNA. They are incorporated into growing complementary strands when sequences are copied in enzyme-free reactions using organic leaving groups at the phosphates. Amino acids are rarely considered as leaving groups, but proline can act as a leaving group when N-linked to NMPs, so that prolinyl NMPs hydrolyze in aqueous buffer at 37 °C, with half-life times as short as 2.4 h, and they act as monomers in enzyme-free primer extension. Still, their level of reactivity is insufficient for practical purposes, requiring months for some extensions. Herein we report the synthesis of eight substituted prolinyl AMPs together with seven related compounds and the results of a study of their reactivity. A δ-carboxy prolinyl NMP was found to be converted with a half-life time of just 11 min in magnesium-free buffer, and a δ-isopropyl prolinyl NMP was shown to react sevenfold faster than its prolinyl counterpart in enzyme-free genetic copying of RNA. Our results indicate that both anchimeric and steric effects can be employed to increase the reactivity of aminoacidyl nucleotides, i.e. compounds that combine two fundamental classes of biomolecules in one functional entity.

Non-Aqueous Poly(dimethylsiloxane) Organogel Sponges for Controlled Solvent Release: Synthesis, Characterization, and Application in the Cleaning of Artworks

Polydimethylsiloxane (PDMS) organogel sponges were prepared and studied in order to understand the role of pore size in an elastomeric network on the ability to uptake and release organic solvents. PDMS organogel sponges have been produced according to sugar leaching techniques by adding two sugar templates of different forms and grain sizes (a sugar cube template and a powdered sugar template), in order to obtain materials differing in porosity, pore size distribution, and solvent absorption and liquid retention capability. These materials were compared to PDMS organogel slabs that do not contain pores. The sponges were characterized by Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) and compared with PDMS slabs that do not contain pores. Scanning electron microscopy (SEM) provided information about their morphology. X-ray micro-tomography (XMT) allowed us to ascertain how the form of the sugar templating agent influences the porosity of the systems: when templated with sugar cubes, the porosity was 77% and the mean size of the pores was ca. 300 μm; when templated with powdered sugar, the porosity decreased to ca. 10% and the mean pore size was reduced to ca. 75 μm. These materials, porous organic polymers (POPs), can absorb many solvents in different proportions as a function of their polarity. Absorption capacity, as measured by swelling with eight solvents covering a wide range of polarities, was investigated. Rheology data established that solvent absorption did not have an appreciable impact on the gel-like properties of the sponges, suggesting their potential for applications in cultural heritage conservation. Application tests were conducted on the surfaces of two different lab mock-ups that simulate real painted works of art. They demonstrated further that PDMS sponges are a potential innovative support for controlled and selective cleaning of works of art surfaces.

Regioisomers of singly bridged calix[6]crown-6 and their heavy alkali metal complexes: a molecular baseball glove for caesium(I)

We report the formation of heavy alkali metal complexes of bicyclic host molecules including the caesium(I) complex that catches the central metal ion with the deep pocket of the host similar to a baseball glove. For this, three regioisomers of singly bridged calix[6]crown-6 [1,2-bridged (H4 L 1,2), 1,3-bridged (H4 L 1,3) and 1,4-bridged (H4 L 1,4)] have been synthesized by alkyl-ation of calix[6]arene with penta-ethyl-ene glycol di-tosyl-ate in the presence of M 2CO3 (M = Na, K, Rb and Cs). The larger the cation size of the metal carbonate, the higher the yield of the H4 L 1,4 isomer, indicating the size-based template effect. A combination of H4 L 1,2 and RbOH allowed isolation of the mononuclear rubidium(I) complex (1) in which the metal center is six-coordinated in a loose fashion, the remaining two oxygen donors in the crown loop and two phenols in the calix rim are uncoordinated. Notably, the complexation of H4 L 1,2 with CsOH yielded the mononuclear caesium(I) complex (2), in which all possible ten binding sites on the deep and good-fit pocket participate in coordination via high cooperativity between the crown loop and calix rim, similar to a baseball glove. In dipolar organic solution, the caesium(I) complex 2 remains intact. H4 L 1,4 afforded a dicesium(I) complex (3) and adjacent complexes are linked by intermolecular cation-π interactions, giving rise to a pseudo one-dimensional coordination polymer. These results provide insight into the metal carbonate-dependent synthesis of calix[6]crowns and the influence of regioisomers on caesium(I) complexation.

Cell-Selective siRNA Delivery Using Glycosylated Dynamic Covalent Polymers Self-Assembled In Situ by RNA Templating

Dynamic covalent libraries enable exploring complex chemical systems from which bioactive assemblies can adaptively emerge through template effects. In this work, we studied dynamic covalent libraries made of complementary bifunctional cationic peptides, yielding a diversity of species from macrocycles to polymers. Although polymers are typically expressed only at high concentration, we found that siRNA acts as a template in the formation of dynamic covalent polymers at low concentration in a process guided by electrostatic binding. Using a glycosylated building block, we were able to show that this templated polymerization further translates into the multivalent presentation of carbohydrate ligands, which subsequently promotes cell uptake and even cell-selective siRNA delivery.

Ring-to-Cage Structural Conversion via Template Effect in a Gold(I) Metallosupramolecular System

A unique example of a ring-to-cage structural conversion in a multinuclear gold(I) coordination system with d-penicillamine (d-H2 pen) is reported. The reaction of [Au2 Cl2 (dppe)] (dppe=1,2-bis(diphenylphosphino)ethane) with d-H2 pen in a 1:1 ratio gave [Au4 (dppe)2 (d-pen)2 ] ([1]), in which two [Au2 (dppe)]2+ units are linked by two d-pen S atoms in a cyclic form so as to have two bidentate-N,O coordination arms. The subsequent reaction of [1] with Cu(OTf)2 afforded [Au4 Cu(dppe)2 (d-pen)2 ]2+ ([2]2+ ), in which a CuII ion is chelated by the two coordination arms in [1] to form an AuI4 CuII bicyclic metallocage. A similar reaction using Cu(NO3 )2 was accompanied by the ring expansion of [1] to [Au8 (dppe)4 (d-pen)4 ], leading to the production of [Au8 Cu2 (dppe)4 (d-pen)4 ]4+ ([3]4+ ). In [3]4+ , two CuII ions are each chelated by the two coordination arms to form an AuI8 CuII2 tricyclic metallocage, accommodating a nitrate ion. The use of Ni(NO3 )2 or Ni(OAc)2 instead of Cu(NO3 )2 commonly gave a tricyclic metallocage of [Au8 Ni2 (dppe)4 (d-pen)4 ]4+ ([4]4+ ), but a water molecule was accommodated inside the AuI8 NiII2 metallocage.

A new structural motif for an enantiomerically pure metallosupramolecular Pd₄L₈ aggregate by anion templating

An enantiomerically pure BINOL-based bis(3-pyridyl) ligand 1 assembles into a homochiral [Pd4(1)8] complex upon coordination to tetravalent Pd(II) ions. The formation of this aggregate is templated by two tetrafluoroborate counterions that are encapsulated in two peripheral cavities. The resulting structure is a new structural motif for this kind of metallosupramolecular assemblies that arranges the palladium ions in a distorted tetrahedral fashion and forces ligand 1 to adopt two different conformations. Both phenomena are unique and cause an overall three-dimensional structure that has another confined, chiral, and hydrophilic central cavity.