Synthesis of New Chlorin e6 Trimethyl and Protoporphyrin IX Dimethyl Ester Derivatives and Their Photophysical and Electrochemical Characterizations

In view of increasing demands for efficient photosensitizers for photodynamic therapy (PDT), we herein report the synthesis and photophysical characterizations of new chlorin e₆ trimethyl ester and protoporphyrin IX dimethyl ester dyads as free bases and Zn^II complexes. The synthesis of these molecules linked at the β‐pyrrolic positions to pyrano[3,2‐c]coumarin, pyrano[3,2‐c]quinolinone, and pyrano[3,2‐c]naphthoquinone moieties was performed by using the domino Knoevenagel hetero Diels–Alder reaction. The α‐methylenechromanes, α‐methylenequinoline, and ortho‐quinone methides were generated in situ from a Knoevenagel reaction of 4‐hydroxycoumarin, 4‐hydroxy‐6‐methylcoumarin, 4‐hydroxy‐N‐methylquinolinone, and 2‐hydroxy‐1,4‐naphthoquinone, respectively, with paraformaldehyde in dioxane. All the dyads as free bases and as Zn^II complexes were obtained in high yields. All new compounds were fully characterized by 1D and 2D NMR techniques, UV/Vis spectroscopy, and HRMS. Their photophysical properties were evaluated by measuring the fluorescence quantum yield, the singlet oxygen quantum yield by luminescence detection, and also the triplet lifetimes were correlated by flash photolysis and intersystem crossing (ISC) rates. The fluorescence lifetimes were measured by a time‐correlated single photon count (TCSPC) method, fluorescence decay associated spectra (FDAS), and anisotropy measurements. Magnetic circular dichroism (MCD) and circular dichroism (CD) spectra were recorded for one Zn^II complex in order to obtain information, respectively, on the electronic and conformational states, and interpretation of these spectra was enhanced by molecular orbital (MO) calculations. Electrochemical studies of the Zn^II complexes were also carried out to gain insights into their behavior for such applications.     

Viscosities of solutions of electrolytes and nonelectrolytes inN-methylacetamide at 35° and 55°C

The viscosities of dilute solutions of a number of tetraalkylammonium and alkali metal halides, tetraphenylarsonium chloride, sodium tetraphenylborate, and tetrabutylammonium tetrabutylborate, as well as several nonelectrolytes have been measured in the high dielectric constant solvent N-methylacetamide (NMA) at 35 and 55°C. The relative viscosities were fitted to the extended Jones-Dole equation, = 1 + AC^1/2 + BC + DC². The pattern of behavior of the B coefficients is roughly similar to that observed in H₂O. However, the small ions have exceptionally large B values in this solvent due to strong solvation effects, while the large organic ions do not display the sharp crossing of the Einstein law, B=2.5 _V, characteristic in H₂O of hydrophobic interaction. The D coefficients roughly parallel the B behavior and display remarkably regular ionic trends. This suggests that they arise largely from hydrodynamic origins. Nonelectrolytes have small or negative B coefficients showing that the Einstein law is not applicable at the molecular level and that nonelectrolytes are poor models for structurally similar ions. A simple mixture law is presented as an alternative to the Einstein law to explain the B coefficients.     

The Diels–Alder reactions of para-benzoquinone nitrogen-derivatives: an experimental and theoretical study

An experimental and theoretical study of the comparative reactivity and selectivity of the Diels–Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent para-benzoquinones. DFT calculations support these experimental results.     

The preparation of n-octylaniline and its application in the extraction of noble metals

n-Octylaniline was prepared by nitration of n-octylbenzene followed by reduction with tin and hydrochloric acid and also by the high-temperature reaction of aniline with 1-octanol in the presence of zinc chloride. Little difference was found in the efficiency of extraction of noble metals with the products prepared by the two methods. The first method gives better yields of n-octylaniline and the formation of emulsions in the extraction is not a serious problem provided that the reagent is distilled before use. The para-isomer of n-octylaniline shows a slightly greater tendency than the ortho-isomer to form emulsions in noble metal extractions.