Hierarchical porphyrin self-assembly in aqueous solution

In aqueous solution meso-tetrakis(4-phosphonatophenyl)porphyrin shows self-aggregation processes controlled by the "sergeant-soldier rule". After partial protonation of the external phosphonic groups, it is possible (i) to further protonate the inner nitrogen atoms of the molecules or (ii) to allow, over time, the system to aggregate. Therefore, the two procedure lead to a different system evolution, producing species with different chemico-physical properties.     

A chemometric study of active parameters and their interaction effects in a nebulized sheath-liquid electrospray interface for capillary electrophoresis-mass spectrometry

A chemometrics approach has been used for evaluating the effect of four experimental parameters when coupling capillary electrophoresis (CE) to electrospray ionization-mass spectrometry (ESI-MS). Electrospray voltage, sheath-liquid flow rate, nebulizing gas flow rate, and spray needle position in respect to the MS orifice were varied according to a full factorial design. In addition to main effects, two interaction effects could be identified as significant when measuring the peak intensity of the analytes, from a sample mixture containing peptides and pharmaceuticals. The first interaction effects, between the nebulizing gas flow rate and the sheath-liquid flow rate, and the second interaction effect, between the nebulizing gas flow rate and the spray position, could further explain the impact that these variables have on the spray performance. The number of theoretical plates and the baseline noise were also measured. The sheath-liquid flow was found to significantly affect the separation efficiency, while the noise level mainly was controlled by the nebulizing gas flow. The same factorial design was also used for a CE capillary with lower internal diameter (ID) and the effects of the same variables were compared on those capillaries using equal injection volume for both capillaries. Similar trends were obtained in both capillaries but capillary ID was shown to be a significant variable when evaluating both capillaries in a single model. It was found that a capillary with 25 microm ID provided improved CE-MS performance over than corresponding 50 microm ID capillary. Enhanced sensitivity was obtained using the narrow-bore capillary, and at lower sheath-liquid flow rate the 25 microm ID capillary also gave rise to more efficient peaks.     

Helical coordination polymers and cyclic dimers formed from heteroleptic thioether-dipyrrinato copper(II) complexes

Heteroleptic copper complexes containing an acetylacetonato ligand and a thioether derivatized dipyrrinato ligand are shown to form oligomers and polymers in the solid state.     

An experimental and theoretical approach to the molecular structure of 3‐{[4‐(3‐Methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐ indol‐2‐one

The title molecule, 3‐{[4‐(3‐methyl‐3‐phenyl‐cyclobutyl)‐thiazol‐2‐yl]‐hydrazono}‐1,3‐dihydro‐indol‐2‐one (C₂₂H₂₀N₄O₁S₁), was prepared and characterized by ¹H NMR, ¹³C NMR, IR, UV–visible, and single‐crystal X‐ray diffraction. The compound crystallizes in the monoclinic space group P21 with a = 8.3401(5), b = 5.6976(3), c = 20.8155(14) Å, and β = 95.144(5)°. Molecular geometry from X‐ray experiment and vibrational frequencies of the title compound in the ground state has been calculated using the Hartree–Fock with 6‐31G(d, p) and density functional method (B3LYP) with 6‐31G(d, p) and 6‐311G(d, p) basis sets, and compared with the experimental data. The calculated results show that optimized geometries can well reproduce the crystal structural parameters, and the theoretical vibrational frequencies values show good agreement with experimental data. Density functional theory calculations of the title compound and thermodynamic properties were performed at B3LYP/6‐31G(d, p) level of theory. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Efficient synthesis of 4-aminoquinazoline and thieno[3,2-d]pyrimidin-4-ylamine derivatives by microwave irradiation

[reaction: see text] A simple, efficient, and high-yielding synthesis of quinazolin-4-ylamine and thieno[3,2-d]pyrimidin-4-ylamine derivatives is reported under microwave irradiation conditions. Reaction conditions including temperature, solvent, and reaction time have been studied. An efficient parallel workup procedure was developed to generate a small library (23 compounds) in a short time period.     

Kinetics and mechanism of *NO2 reacting with various oxidation states of myoglobin

Nitrogen dioxide ((*)NO(2)) participates in a variety of biological reactions. Of great interest are the reactions of (*)NO(2) with oxymyoglobin and oxyhemoglobin, which are the predominant hemeproteins in biological systems. Although these reactions occur rapidly during the nitrite-catalyzed autoxidation of hemeproteins, their roles in systems producing (*)NO(2) in the presence of these hemeproteins have been greatly underestimated. In the present study, we employed pulse radiolysis to study directly the kinetics and mechanism of the reaction of oxymyoglobin (MbFe(II)O(2)) with (*)NO(2). The rate constant of this reaction was determined to be (4.5 +/- 0.3) x 10(7) M(-1)s(-1), and is among the highest rate constants measured for (*)NO(2) with any biomolecule at pH 7.4. The interconversion among the various oxidation states of myoglobin that is prompted by nitrogen oxide species is remarkable. The reaction of MbFe(II)O(2) with (*)NO(2) forms MbFe(III)OONO(2), which undergoes rapid heterolysis along the O-O bond to yield MbFe(V)=O and NO(3-). The perferryl-myoglobin (MbFe(V)=O) transforms rapidly into the ferryl species that has a radical site on the globin ((*)MbFe(IV)=O). The latter oxidizes another oxymyoglobin (10(4) M(-1)s(-1) < k(17) < 10(7) M(-1)s(-1)) and generates equal amounts of ferrylmyoglobin and metmyoglobin. At much longer times, the ferrylmyoglobin disappears through a relatively slow comproportionation with oxymyoglobin (k(18) = 21.3 +/- 5.3 M(-1)s(-1)). Eventually, each (*)NO(2) radical converts three oxymyoglobin molecules into metmyoglobin. The same intermediate, namely MbFe(III)OONO(2), is also formed via the reaction peroxynitrate (O(2)NOO(-)/O(2)NOOH) with metmyoglobin (k(19) = (4.6 +/- 0.3) x 10(4) M(-1)s(-1)). The reaction of (*)NO(2) with ferrylmyoglobin (k(20) = (1.2 +/- 0.2) x 10(7) M(-1)s(-1)) yields MbFe(III)ONO(2), which in turn dissociates (k(21) = 190 +/- 20 s(-1)) into metmyoglobin and NO(3-). This rate constant was found to be the same as that measured for the decay of the intermediate formed in the reaction of MbFe(II)O(2) with (*)NO, which suggests that MbFe(III)ONO(2) is the intermediate observed in both processes. This conclusion is supported by thermokinetic arguments. The present results suggest that hemeproteins may detoxify (*)NO(2) and thus preempt deleterious processes, such as nitration of proteins. Such a possibility is substantiated by the observation that the reactions of (*)NO(2) with the various oxidation states of myoglobin lead to the formation of metmyoglobin, which, though not functional in the gas transport, is nevertheless nontoxic at physiological pH.     

Selective formation of non-conjugated olefins by samarium(II)-mediated elimination/isomerization of allylic benzoates

Aromatic allylic benzoates can be selectively transformed to the corresponding benzoate eliminated olefin by the action of samarium diiodide. Depending on the substrate and the elimination conditions, high selectivity for the non-conjugated alkene product can be achieved.