Organocatalytic synthesis of carbohydrates

The key role of carbohydrates in biological processes and their visible existence in our everyday life have stimulated the interest of leading research groups on the smart and simple synthesis of common and rare sugar molecules. Now, more than 120 years after Fischer's first synthesis of (D)-glucose (1890), we are witnessing important development in this field of total synthesis. Using modern methods of direct activation of carbonyl compounds chemists can prepare sugars in an elegant and efficient way similar to that of Nature. This tutorial review presents recent impressive progress in the area of de novo synthesis of carbohydrates by using organocatalytic direct aldol reaction as a key step.     

Photosensitised oxidation of a water pollutant using sulphonated porphyrin

Photodegradation of endocrine disrupting butylparaben (BP) in aerated aqueous solutions was studied using 4,4′,4″,4‴-(porphine-5,10,15,20-tetrayl)tetrakis(benzenesulphonic acid) (TPPS₄), as a sensitiser. Influence of various parameters, such as initial sensitiser and BP concentration, pH of the reaction solution and oxygen content in the reaction solution, on the photosensitised oxidation was examined. It was found that the dominant pathway of BP degradation occurred in the reaction with molecular singlet oxygen ¹O₂, i.e. via photosensitised oxidation mechanism of type II. Kinetic parameters of the BP reaction with ¹O₂ were estimated.     

Infrared studies of the potential controlled adsorption of sodium dodecyl sulfate at the Au(111) electrode surface

Quantitative subtractively normalized interfacial Fourier transform infrared reflection spectroscopy (SNIFTIRS) was used to determine the conformation and orientation of sodium dodecyl sulfate (SDS) molecules adsorbed at the single crystal Au(111) surface. The SDS molecules form a hemimicellar/hemicylindrical (phase I) structure for the range of potentials between -200 ≤ E < 450 mV and condensed (phase II) film for electrode potentials ≥500 mV vs Ag/AgCl. The SNIFTIRS measurements indicate that the alkyl chains within the two adsorbed states of SDS film are in the liquid-crystalline state rather than the gel state. However, the sulfate headgroup is in an oriented state in phase I and is disordered in phase II. The newly acquired SNIFTIR spectroscopy measurements were coupled with previous electrochemical, atomic force microscopy, and neutron reflectivity data to improve the current existing models of the SDS film adsorbed on the Au(111) surface. The IR data support the existence of a hemicylindrical film for SDS molecules adsorbed at the Au(111) surface in phase I and suggest that the structure of the condensed film in phase II can be more accurately modeled by a disordered bilayer.     

Tautomerization in 2,7,12,17‐Tetraphenylporphycene and 9‐Amino‐2,7,12,17‐tetraphenylporphycene: Influence of Asymmetry on the Direction of the Transition Moment

Femtosecond transient absorption anisotropy studies have been performed for two porphycenes of different symmetry. In 2,7,12,17‐tetraphenylporphycene, the chemical identity of two trans forms implies a change in the S₀–S₁ transition‐moment direction upon tautomerization. Exploiting this phenomenon, the rates of double hydrogen transfer in both the S₀ and S₁ states (1.4×10¹² s^?1 and 2.7×10¹¹ s^?1, respectively) have been determined by performing time‐resolved anisotropy studies. In the asymmetric 9‐amino‐2,7,12,17‐tetraphenylporphycene, tautomerization occurs with a similar rate in the ground state. In the S₁ state, the reaction is hindered in its vibrationally relaxed form, but the excitation spectra suggest that it may occur for an unrelaxed molecule. Unlike all porphycenes that have been studied so far, 9‐amino‐2,7,12,17‐tetraphenylporphycene does not reveal significant changes in anisotropy owing to intramolecular double hydrogen transfer; rather, the transition‐moment directions are similar in the two tautomeric forms. Analysis of the molecular orbitals allows for an explanation of the “locking” of the transition moments: it is due to a large splitting of the two HOMO orbitals, which retain the order of their energies in the two tautomers.     

Asymptotic porosity of planar harmonic measure

We study the distribution of harmonic measure on connected Julia sets of unicritical polynomials. Harmonic measure on a full compact set in ? is always concentrated on a set which is porous for a positive density of scales. We prove that there is a topologically generic set $\mathcal{A}$ in the boundary of the Mandelbrot set such that for every $c\in \mathcal{A}$ , β>0, and λ∈(0,1), the corresponding Julia set is a full compact set with harmonic measure concentrated on a set which is not β-porous in scale λ ⁿ for n from a set with positive density amongst natural numbers.     

Calculation of the potential energy curves of the HgZn dimer

Potential energies for the ground and several excited states of the HgZn excimer molecule have been calculated in order to assist experimenters in assigning the observed spectral bands. The CI-singles procedure, followed by a second-order Møller-Plesset perturbation theory correction were applied for the valence electrons. The core electrons were replaced by an effective-core potential. The effect of spin-orbit interaction was not investigated. The calculated energy curves are compared with other available theoretical data, as well as with preliminary experimental assignments.     

Cellular delivery of dinucleotides by conjugation with small molecules: targeting translation initiation for anticancer applications

Targeting cap-dependent translation initiation is one of the experimental approaches that could lead to the development of novel anti-cancer therapies. Synthetic dinucleoside 5′,5′-triphosphates cap analogs are potent antagonists of eukaryotic translation initiation factor 4E (eIF4E) in vitro and could counteract elevated levels of eIF4E in cancer cells; however, transformation of these compounds into therapeutic agents remains challenging – they do not easily penetrate into cells and are susceptible to enzymatic cleavage. Here, we tested the potential of several small molecule ligands – folic acid, biotin, glucose, and cholesterol – to deliver both hydrolyzable and cleavage-resistant cap analogs into cells. A broad structure–activity relationship (SAR) study using model fluorescent probes and cap–ligand conjugates showed that cholesterol greatly facilitates uptake of cap analogs without disturbing the interactions with eIF4E. The most potent cholesterol conjugate identified showed apoptosis-mediated cytotoxicity towards cancer cells.

Ligand assisted cellular delivery of negatively charged dinucleotides, which are potential antagonists of the protooncogenic protein eIF4E.     

High‐Mobility and Low Turn‐On Voltage n‐Channel OTFTs Based on a Solution‐Processable Derivative of Naphthalene Bisimide

In organic electronics solution‐processable n‐channel field‐effect transistors (FETs) matching the parameters of the best p‐channel FETs are needed. Progress toward the fabrication of such devices is strongly impeded by a limited number of suitable organic semiconductors as well as by the lack of processing techniques that enable strict control of the supramolecular organization in the deposited layer. Here, the use of N,N′‐bis(4‐n‐butylphenyl)‐1,4,5,8‐naphthalenetetracarboxylic‐1,4:5,8‐bisimide (NBI‐4‐n‐BuPh) for fabrication of n‐channel FETs is described. The unidirectionally oriented crystalline layers of NBI‐4‐n‐BuPh are obtained by the zone‐casting method under ambient conditions. Due to the bottom‐contact, top‐gate configuration used, the gate dielectric, Parylene C, also acts as a protective layer. This, together with a sufficiently low LUMO level of NBI‐4‐n‐BuPh allows the fabrication and operation of these novel n‐channel transistors under ambient conditions. The high order of the NBI‐4‐n‐BuPh molecules in the zone‐cast layer and high purity of the gate dielectric yield good performance of the transistors.