A New Variant of Emissive RNA Alphabets

A new fluorescent ribonucleoside alphabet (^mthN) consisting of pyrimidine and purine analogues, all derived from methylthieno[3,4-d]pyrimidine as the heterocyclic core, is described. Large bathochromic shifts and high microenvironmental susceptibility of their emission relative to previous alphabets derived from thieno[3,4-d]pyrimidine (^thN) and isothiazole[4,3-d]pyrimidine (^tzN) scaffolds are observed. Subjecting the purine analogues to adenosine deaminase, guanine deaminase and T7 RNA polymerase indicate that, while varying, all but one enzyme tolerate the corresponding ^mthN/^mthNTP substrates. The robust emission quantum yields, high photophysical responsiveness and enzymatic accommodation suggest that the ^mthN alphabet is a biophysically viable tool and can be used to probe the tolerance of nucleoside/tide-processing enzymes to structural perturbations of their substrates.     

Selection of phage-displayed antibodies with high affinity and specificity by electrophoresis in microfluidic devices

A method development aimed for high-throughput and automated antibody screening holds great potential for areas ranging from fundamental molecular interactions to the discovery of novel disease markers, therapeutic targets, and monoclonal antibody engineering. Surface display techniques enable efficient manipulation of large molecular libraries in small volumes. Specifically, phage display appeared as a powerful technology for selecting peptides and proteins with enhanced, target-specific binding affinities. Here, we present a phage-selection microfluidic device wherein electrophoresis was performed under two orthogonal electric fields through an agarose gel functionalized with the respective antigen. This microdevice was capable of screening and sorting in a single round high-affinity phage-displayed antibodies against virus glycoproteins, including human immunodeficiency virus-1 glycoprotein 120 or the Ebola virus glycoprotein (EBOV-GP). Phages were differentially and laterally swept depending on their antigen affinity; the high-affinity phages were recovered at channels proximal to the application site, whereas low-affinity phages migrated distal after electrophoresis. These experiments proved that the microfluidic device specifically designed for phage-selection is rapid, sensitive, and effective. Therefore, this is an efficient and cost-effective method that allowed highly controlled assay conditions for isolating and sorting high-affinity ligands displayed in phages.     

Facile Synthesis of an Octagermacubane with Two Three-Coordinate Germanium(0) Atoms and its Unique Radical Anion

Thermolysis of a 1 : 1 mixture of tris(di-tert-butylmethylsilyl)germane 9 and bis(di-tert-butylmethylsilyl)germane 17 at 100 °C produces unexpectedly octagermacubane 18 , having two 3-coordinate Ge⁰ atoms (40 % yield). 18 was characterized by X-ray crystallography and it is a singlet biradical (according to DFT quantum mechanical calculations and the absence of an EPR signal). Reactions of 18 with CH₂Cl₂ and H₂O yield the novel dichloro-octagermacubane 24 and hydroxy-octagermacubane 25 , respectively. Reduction of 18 with tBuMe₂SiNa in THF produces an isolable octagermacubane radical anion 26-Na . Based on X-ray crystallography, EPR spectroscopy and DFT quantum mechanical calculations, 26-Na is classified as a Ge-centered radical anion.     

Small molecule antagonists of cell-surface heparan sulfate and heparin–protein interactions

Surfen, bis-2-methyl-4-amino-quinolyl-6-carbamide, was previously reported as a small molecule antagonist of heparan sulfate (HS), a key cell-surface glycosaminoglycan found on all mammalian cells. To generate structure–activity relationships, a series of rationally designed surfen analogs was synthesized, where its dimeric structure, exocyclic amines, and urea linker region were modified to probe the role of each moiety in recognizing HS. An in vitro assay monitoring inhibition of fibroblast growth factor 2 binding to wild-type CHO cells was utilized to quantify interactions with cell surface HS. The dimeric molecular structure of surfen and its aminoquinoline ring systems was essential for its interaction with HS, and certain dimeric analogs displayed higher inhibitory potency than surfen and were also shown to block downstream FGF signaling in mouse embryonic fibroblast cells. These molecules were also able to antagonize other HS–protein interactions including the binding of soluble RAGE to HS. Importantly, selected molecules were shown to neutralize heparin and other heparinoids, including the synthetic pentasaccharide fondaparinux, in a factor Xa chromogenic assay and in vivo in mice. These results suggest that small molecule antagonists of heparan sulfate and heparin can be of therapeutic potential for the treatment of disorders involving glycosaminoglycan–protein interactions.     

Synthesis by Si-H bond lithiation of novel half-pincer and pincer silyllithium compounds and their molecular structures

Structural Chemistry - The synthesis and the X-ray structural analysis of novel pincer and half-pincer silyllithiums: Ar2 (N)(tBu2MeSi)SiLi (Ar(N) = o-dimethylbenzylamine) (2a),...     

Mechanistic Aspects of Gas‐Phase Hydrogen‐Atom Transfer from Methane to [CO].+ and [SiO].+: Why Do They Differ?

The reactivity of the two diatomic congeneric systems [CO]^.+ and [SiO]^.+ towards methane has been investigated by means of mass spectrometry and quantum‐chemical calculations. While [CO]^.+ gives rise to three different reaction channels, [SiO]^.+ reacts only by hydrogen‐atom transfer (HAT) from methane under thermal conditions. A theoretical analysis of the respective HAT processes reveals two distinctly different mechanistic pathways for [CO]^.+ and [SiO]^.+, and a comparison to the higher metal oxides of Group 14 emphasizes the particular role of carbon as a second‐row p element.     

Preparation and Regioselective Metalation of Bis(trimethylsilyl)methyl‐Substituted Aryl Derivatives

A range of bis(trimethylsilyl)methyl‐substituted aryl derivatives was prepared by using a Kumada–Corriu cross‐coupling reaction. The regioselective metalation of the resulting bis(trimethylsilyl)methyl‐substituted aryl derivatives bearing this bulky silyl group allowed the generation of functionalized aromatics. A regioselective switch in the presence or in the absence of the bis(trimethylsilyl)methyl group has been demonstrated. Furthermore, this silyl group was converted into a formyl group or a styryl group, enhancing the scope of application of such bis(trimethylsilyl)methyl‐substituted arenes.     

Neutron scattering study of water confined in periodic mesoporous organosilicas

A series of quasi-elastic neutron scattering measurements were performed using IN6 at the Institute Laue Langevin for a mesoporous organosilica material with phenyl functions, called phenyltriethoxysilane (PTES). The aim of the experiment was to study the diffusion dynamics of nano-scale water clusters inside the hydrophobic pores as a function of temperature and hydration. By fitting the Debye-Waller factor, the data show clearly the different behavior between water, both inside and outside the hydrophobic pores, which resembles bulk water. The mean thermal displacement 〈u²〉 of the external water increases with T almost linearly up to 353 K, while the internal water quickly reaches the maximum at T∼323 K, indicating the confinement by an averaged pore diameter of the porous organosilica.     

Preconcentrative separation of chromium(III) species from chromium(VI) by cloud point extraction and determination by flame atomic absorption spectrometry

Microchimica Acta - We describe a high-throughput technique for the determination of chromium species in water samples by flame atomic absorption spectrometry (FAAS) after preconcentrative...