New cellulose-supported reagent: a sustainable approach to guanidines

[reaction: see text] A new cellulose-supported reagent for the synthesis of guanidine in aqueous medium is reported starting from commercially available functionalized cellulose beads. Primary and secondary amines, anilines, and amino acids were transformed to the corresponding guanidines in high yields and under very mild conditions.     

Phosphotyrosine phosphatases acting on band 3 in human erythrocytes of different age: PTP1B processing during cell ageing

The phosphorylation of tyrosine residues of human red blood cell (RBC) band 3 is regulated in vivo by constitutively active tyrosine-kinases (PTKs) and phosphotyrosine-phosphatases (PTPs), identified so far as, respectively, p72(syk) and p56/53(lyn), and PTP1B and SHPTP-2. Tyr-phosphorylation of band 3 increases upon reduction of cell volume as in hypertonic media or during Ca(2+)-induced membrane vesiculation. We show here that old RBCs display higher Tyr-phosphorylation levels of band 3 than younger cells under hypertonic conditions, at least in part due to the reduced cell volume of old RBCs, a condition of lowered threshold for activation of volume-sensitive PTKs. We have also analysed the membrane-bound PTP activity and the relative abundance of PTP1B (as the main membrane-associated PTP) in RBCs of different age. Immunodetection of PTP1B in purified ghost membranes revealed that the catalytic, N-terminal domain of the PTP is partially cleaved, in an age-dependent manner, from the membrane-bound domain, and it is lost during the preparation of ghost membranes. This suggests that erythrocytes may undergo in vivo activation of the Ca(2+)-dependent calpain system that proteolytically regulates PTP1B activity, as already documented for other cell types. On the other hand, the assay of the PTP activity that remains associated with the membranes of RBCs of different age indicated that the PTP undergoes oxidative inactivation that can be further differentiated into reversible and irreversible components.     

Generalized notions of symmetry of ODEs and reduction procedures

This paper describes the notion of σ‐symmetry, which extends the one of λ‐symmetry, and its application to reduction procedures of systems of ordinary differential equations (ODEs) and of dynamical systems (DS) as well. We also consider orbital symmetries, which give rise to a different form of reduction of DS. Finally, we discuss how DS can be transformed into higher order ODEs, and how these symmetry properties of the DS can be transferred into reduction properties of the corresponding ODEs. Many examples illustrate the various situations. Copyright © 2013 John Wiley & Sons, Ltd.     

Susceptibility to hydrolysis of phenylboronic pinacol esters at physiological pH

Boronic acids and their esters are highly considered compounds for the design of new drugs and drug delivery devices, particularly as boron-carriers suitable for neutron capture therapy. However, these compounds are only marginally stable in water. Hydrolysis of some phenylboronic pinacol esters is described here. The kinetics is dependent on the substituents in the aromatic ring. Also the pH strongly influences the rate of the reaction, which is considerably accelerated at physiological pH. Therefore, care must be taken when considering these boronic pinacol esters for pharmacological purposes.      

A Theoretical and Experimental Investigation of the Spectroscopic Properties of a DNA‐Intercalator Salphen‐Type ZnII Complex

The photophysical and DNA‐binding properties of the cationic zinc(II) complex of 5‐triethylammonium methyl salicylidene ortho‐phenylenediiminato (ZnL²⁺) were investigated by a combination of experimental and theoretical methods. DFT calculations were performed on both the ground and the first excited states of ZnL²⁺ and on its possible mono‐ and dioxidation products, both in vacuo and in selected solvents mimicked by the polarizable continuum model. Comparison of the calculated absorption and fluorescence transitions with the corresponding experimental data led to the conclusion that visible light induces a two‐electron photooxidation process located on the phenylenediiminato ligand. Kinetic measurements, performed by monitoring absorbance changes over time in several solvents, are in agreement with a slow unimolecular photooxidation process, which is faster in water and slower in less polar solvents. Moreover, structural details of ZnL–DNA binding were obtained by DFT calculations on the intercalation complexes between ZnL and the d(ApT)₂ and d(GpC)₂ dinucleoside monophosphate duplexes. Two main complementary binding interactions are proposed: 1) intercalation of the central phenyl ring of the ligand between the stacked DNA base pairs; 2) external electrostatic attraction between the negatively charged phosphate groups and the two cationic triethylammonium groups of the Schiff‐base ligand. Such suggestions are supported by fluorescence titrations performed on the ZnL/DNA system at different ionic strengths and temperatures. In particular, the values of the DNA‐binding constants obtained at different temperatures provided the enthalpic and entropic contributions to the binding and confirmed that two competitive mechanisms, namely, intercalation and external interaction, are involved. The two mechanisms are coexistent at room temperature under physiological conditions.     

Confinement effects on the interaction of native DNA with Cu(II)-5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate in C(12)E(4) liquid crystals

Confinement effects of native calf thymus DNA interacting with the complex Cu(ii)-5-(triethylammoniummethyl)salicylidene ortho-phenylendiiminate (CuL(2+)) perchlorate in tetraethylene glycol monododecyl ether (C(12)E(4)) liquid crystals have been investigated by UV absorption spectrophotometry, circular dichroism (CD) and small angle X-ray scattering (SAXS). The results indicate the occurrence of dramatic structural changes of both the DNA and the CuL(2+)-DNA system, when going from aqueous solution to C(12)E(4) liquid crystals, due to confinement constrains imposed by the closed structure of C(12)E(4) reverse micelles. Further marked departures from the behaviour observed in aqueous solution have been emphasized by registering the spectral response of DNA and CuL(2+)-DNA confined in C(12)E(4) reverse micelles after thermal treatment. It has been also ascertained that the confinement causes the formation of a more compact and thermoresistant DNA structure accompanied by a transition from the right- to left-handed form while a tight CuL(2+)-DNA binding has been revealed by the appearance of a broad induced CD band in the range 350-450 nm. From a biological point of view, these findings stress the need to account for confinement effects and the peculiarity of drug-DNA interactions occurring within the intra-cellular environment.     

Influence of ions on the structural organization of dipolar liquids probed by the noncoincidence effect: experimental and quantum chemical results

The C=O stretching [nu(C=O)] Raman bands of the carbonyl solvents, S (acetone and acetophenone), in some electrolytic solutions of lithium and sodium salts (M(+)X(-)) are analyzed. The large and negative values of the noncoincidence effect (NCE=nu(ani)-nu(iso)) measured for the component of this band generated by the solvent-ion interactions are interpreted in the light of the results of ab initio quantum chemical calculations performed for clusters of type (S)nM(+) and also on the basis of the transition dipole coupling mechanism between pairs of nu(C=O) oscillators. The effects of the size of the ion M(+) and of the solvation number n on the NCE are analyzed. It is shown that the decrease of the NCE resulting from the change in the size of the ion M(+) from Li(+) to Na(+) is appreciably counterbalanced by the increase of the NCE arising form the change in the ion solvation number n from 4 for Li(+) to 6 for Na(+).     

Photophysical behavior of open-shell first-row transition-metal octabutoxynaphthalocyanines: CoNc(OBu)8 and CuNc(OBu)8 as case studies

Ultrafast photodynamics and density functional theory/time-dependent density functional theory (DFT/TDDFT) results for complexes of Co and Cu with 5,9,14,18,23,27,32,36-octabutoxynaphthalocyanine [CoNc(OBu)8 and CuNc(OBu)8] are reported. As a basis for this work, details concerning the syntheses of these complexes and the corresponding Zn complex (used as a reference) are given. Transient absorption spectrometry with femtosecond time resolution combined with a detailed DFT/TDDFT analysis has been employed to construct a complete picture of the excited-state dynamics after Q-band excitation of the Co and Cu complexes and to gain an understanding of the relationship between the nature of the metal center and the excited-state lifetime. The Co complex was shown to return to its ground state via two competing channels: a (2)T1(pi, pi*) state that decayed with a lifetime of 1 ps and a low-lying (2)(d, d) state that repopulated the ground-state surface with a lifetime of 15 ps. CuNc(OBu)8 showed ground-state repopulation from the (2)T1(pi, pi*) state via a lower-lying ligand-to-metal charge-transfer (LMCT) state that was completed within a few nanoseconds. The photophysical behavior of the cobalt and copper complexes was compared to that previously reported for the nickel analog in an effort to highlight the effect of the central metal on the nature and rates of the deactivation pathways. The results described in this work provide basic knowledge that is relevant to the use of these compounds as photothermal sensitizers in cancer therapy.