a Treatment of meso 2-ethylhexyl-3-mercaptopropionate substituted porphyrins with base at room temperature generated a porphyrin thiolate anion which in situ reacted in a nucleophilic aromatic substitution (S N Ar) reaction with remaining thioether derivative. This reaction yielded S-linked bisporphyrins in good yields, with mechanistic insight obtained via displacement reactions. Additionally, S N Ar of the thioether chain was achieved using S-and organolithium nucleophiles.Owing to their biological and medical importance, 1 the synthesis of organosulfur compounds has been the focus of thorough investigations. 2 One important development is the nucleophilic aromatic substitution (S N Ar) with the thiolate anion. 3 Typically, thiolate S N Ar only occurs with activated aryls with leaving groups such as halides or tosylates, 4 requiring a very strong base, elevated temperature and/or the use of metal catalysts. 3c,5 Additionally, it is often hindered via competing oxidation reactions to form disulfide bonds ( Fig. 1). 6 In a remarkable S N Ar, sulfur-linked porphyrin dimers were generated via a simple deprotection of a thioether appended porphyrin. While our initial goal was the synthesis of a free thiol group directly attached to the porphyrin macrocycle via base deprotection, bisporphyrin products were observed predominantly. Such sulfur linked bisporphyrins have not previously been reported and are easily produced, in contrast to other heteroatom linked porphyrin arrays which generally require many synthetic steps. 7These were generated via S N Ar by the thiolate at the meso position of the substituted porphyrin, with isooctyl-3-mercaptopropionate acting as an excellent leaving group. Substitution reactions on porphyrins are limited, 8 at best, and typically require highly specific activated systems and high temperatures. However, this room temperature in situ S N Ar of a seemingly unactivated porphyrin in such fashion represents, to the best of our knowledge, the first reaction of this type to be documented. This is somewhat reminiscent of previous work in our group, whereby using organolithium reagents a variety of substituents can be introduced to the porphyrin periphery via S N type reactions. 9Porphyrins bearing thiol and thioether substituents have a diverse range of optical applications due to their ability to form self-assembled monolayers (SAMs) on gold surfaces 10 and this attribute formed the basis for our interest in thioporphyrins. Adopting a versatile Pd-catalyzed porphyrin-sulfur bond forming reaction developed by Itoh and Mase, 11 a library of novel isooctyl-3-mercaptopropionate substituted porphyrins, so-called protected thiols, were synthesized. 12This involved a Pd-catalyzed reaction of bromoporphyrins 1a-i and the thiol 2-ethylhexyl-3-mercaptopropionate in good to excellent yields of 66-87%. These protected thiols have the potential to be used in Au-NP formulation or as a photosensitizer delivery system in PDT, 13 but our primary goal was for their use in deprotection reactions (Table 1). A...

Structural, magnetic, and spectroscopic data on a Mn 3+ spin-crossover complex with Schiff base ligand 4-OMe-Sal 2 323, isolated in crystal lattices with five different counteranions, are reported. Complexes of [Mn(4-OMe-Sal 2 323)]X where X = ClO 4 – ( 1 ), BF 4 – ( 2 ), NO 3 – ( 3 ), Br – ( 4 ), and I – ( 5 ) crystallize isotypically in the chiral orthorhombic space group P 2 1 2 1 2 with a range of spin state preferences for the [Mn(4-OMe-Sal 2 323)] + complex cation over the temperature range 5–300 K. Complexes 1 and 2 are high-spin, complex 4 undergoes a gradual and complete thermal spin crossover, while complexes 3 and 5 show stepped crossovers with different ratios of spin triplet and quintet forms in the intermediate temperature range. High-field electron paramagnetic resonance was used to measure the zero-field splitting parameters associated with the spin triplet and quintet states at temperatures below 10 K for complexes 4 and 2 with respective values: D S =1 = +23.38(1) cm –1 , E S =1 = +2.79(1) cm –1 , and D S =2 = +6.9(3) cm –1 , with a distribution of E parameters for the S = 2 state. Solid-state circular dichroism (CD) spectra on high-spin complex 1 at room temperature reveal a 2:1 ratio of enantiomers in the chiral conglomerate, and solution CD measurements on the same sample in methanol show that it is stable toward racemization. Solid-state UV–vis absorption spectra on high-spin complex 1 and mixed S = 1/ S = 2 sample 5 reveal different intensities at higher energies, in line with the different electronic composition. The statistical prevalence of homochiral crystallization of [Mn(4-OMe-Sal 2 323)] + in five lattices with different achiral counterions suggests that the chirality may be directed by the 4-OMe-Sal 2 323 ligand.

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Time-resolved fluorescence measurements were used to quantify partitioning of three different 7-aminocoumarin derivatives into DPPC vesicle bilayers as a function of temperature. The coumarin derivatives were structurally equivalent except for the degree of substitution at the 7-amine position. Calculated log P (octanol: water partitioning) coefficients, a common indicator that correlates with bioconcentration, predict that the primary amine (coumarin 151 or C151) would experience a ∼40-fold partition enrichment in polar organic environments (log P C151 = 1.6) while the tertiary amine’s (coumarin 152 or C152) concentration should be >500 times enhanced (log P C152 = 2.7). Both values predict that partitioning into lipid membranes is energetically favorable. Time-resolved emission spectra from C151 in solutions containing DPPC vesicles showed that within detection limits, the solute remained in the aqueous buffer regardless of temperature and vesicle bilayer phase. C152 displayed a sharp uptake into DPPC bilayers as the temperature approached DPPC’s gel–liquid crystalline transition temperature, consistent with previously reported results ([J. Phys. Chem. B201712140614070]). The secondary amine, synthesized specifically for these studies and dubbed C151.5 with a measured log P value of 1.9, partitioned into the bilayer’s polar head group with no pronounced temperature dependence. These experiments illustrate the limitations of using a gross descriptor of preferential solvation to describe solute partitioning into complex, heterogeneous systems having nanometer-scale dimensions. From a broader perspective, results presented in this work illustrate the need for more chemically informed tools for predicting a solute tendency for where and how much it will bioconcentrate within a biological membrane.

only partially removed from the surface by 2-propanol, regardless of the concentration. For the same amount of alcohol, the 1y0 solution of 2-propanol was more effective than the pure