Synthesis of porphyrin indolin-2-one conjugates via palladium-catalyzed amination reactions

New porphyrin indolin-2-one conjugates were synthesized via palladium-catalyzed amination reactions of iodinated and dibrominated indolin-2-one derivatives with (2-amino-5,10,15,20-tetraphenylporphyrinato)nickel(II). The combination of palladium catalysts and the phosphine ligand dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl (XPhos) is an effective methodology for catalyzing the coupling of 5-iodo-, 5,7-dibromo- and 4,6-dibromo-1,3,3-trimethylindolin-2-one with 2-aminoporphyrin to give the corresponding mono-(2-aminoporphyrinyl)- and di-(2-aminoporphyrinyl)-substituted indolin-2-ones in satisfactory yields under mild conditions. The mono brominated porphyrinic derivatives also underwent cross-coupling reactions under similar catalytic conditions. The studies also demonstrated that the course of the coupling process depends on factors, such as the catalytic system, number and position of the halogen substituents and the heating condition. Insights into the reactivity trends of the 5-iodo; 4,6- and 5,7-dibrominated indolin-2-one derivatives was carried out using theoretical calculations performed using density-functional theory with the B3LYP functional.     

Comparative study of 110mAg(I) removal from aqueous media by humic substances

Journal of Radioanalytical and Nuclear Chemistry - In this study, humic substances—dry cowdung powder and humic acid were used for the removal of precious metal ion Ag(I) from aqueous...     

Assembly of the Entire Carbon Backbone of a Stereoisomer of the Antitumor Marine Natural Product Hemicalide

A strategy for the assembly of the entire carbon backbone of a stereoisomer of the antitumor marine natural product hemicalide has been investigated. The devised convergent approach relies on Horner–Wadsworth–Emmons and Julia–Kocienski olefination reactions for the construction of the C6=C7 and C34=C35 double bonds, respectively, an aldol reaction to create the C27−C28 bond, and a Suzuki–Miyaura cross-coupling as the endgame to form the C15−C16 bond.     

Determination of lysinoalanine by high performance liquid chromatography

This work suggests an HPLC method for qualitative and quantitative determination of N^ε(2-amino-2-carboxyethyl)-L -lysine (LAL). LAL was released from total hydrolysates of various proteins of animal origin and derivatized with dansyl chloride. The performance of two different columns, Spherisorb 3S TG and μ-Bondapack C₁₈, was compared; better resolution and quantitative response were obtained with the former. The mobile phase was a mixture of 0.01 M phosphate buffer (pH 7) and acetonitrile. Linear response and quantitative repeatability were tested for both detectors used (UV-Vis set at 254 nm; fluorimetric set at λ_ex(max) = 360 nm and λ_em(max) = 525 nm). For LAL standard the minimum detectable amount was 0.05 ng, whereas for LAL in actual samples the amount was 0.5 ng (40 μg/g of analyzed proteins). Good analytical repeatability was obtained, resulting in CV % of 4.7 and 3.8 for UV and fluorimetric detectors, respectively. LAL recovery was determined using both detectors; the values obtained were 94 % (fluorimetric) and 92 % (UV). Greater noise levels were observed with the fluorimetric detector and its higher sensitivity could not, therefore, be fully utilized. The highest amounts of LAL were found in the casein (2816 μg/g) and cooked albumin (615 μg/g) samples.     

Asymmetric 1,3‐Dipolar Cycloadditions of 2‐Diazocyclohexane‐1,3‐diones and Alkyl Diazopyruvates

The 1,3‐dipolar cycloaddition reactions of 2‐diazocyclohexane‐1,3‐dione ( 7a ; Table 1) and of alkyl diazopyruvates ( 11a – e ; Table 3) to 2,3‐dihydrofuran and other enol ethers have been investigated in the presence of chiral transition metal catalysts. With Rh^II catalysts, the cycloadditions were not enantioselective, but those catalyzed by [Ru^IICl₂( 1a )] and [Ru^IICl₂( 1b )] proceeded with enantioselectivities of up to 58% and 74% ee, respectively, when diazopyruvates 11 were used as substrates. The phenyliodonium ylide 7c yielded the adduct 8a in lower yield and poorer selectivity than the corresponding diazo precursor 7a (Table 2) upon decomposition with [Ru(pybox)] catalysts. This suggests that ylide decomposition by Ru^II catalysts, contrary to that of the corresponding diazo precursors, does not lead to Ru‐carbene complexes as reactive intermediates. Our method represents the first reproducible, enantioselective 1,3‐cycloaddition of these types of substrates.     

Understanding and controlling the efficiency of Au24M(SR)18 nanoclusters as singlet-oxygen photosensitizers

Singlet oxygen, ¹O₂, can be generated by molecules that upon photoexcitation enable the ³O₂ → ¹O₂ transition. We used a series of atomically precise Au₂₄M(SR)₁₈ clusters, with different R groups and doping metal atoms M. Upon nanosecond photoexcitation of the cluster, ¹O₂ was efficiently generated. Detection was carried out by time-resolved electron paramagnetic resonance (TREPR) spectroscopy. The resulting TREPR transient yielded the ¹O₂ lifetime as a function of the nature of the cluster. We found that: these clusters indeed generate ¹O₂ by forming a triplet state; a more positive oxidation potential of the molecular cluster corresponds to a longer ¹O₂ lifetime; proper design of the cluster yields results analogous to those of a well-known reference photosensitizer, although more effectively. Comprehensive kinetic analysis provided important insights into the mechanism and driving-force dependence of the quenching of ¹O₂ by gold nanoclusters. Understanding on a molecular basis why these molecules may perform so well in ¹O₂ photosensitization is instrumental to controlling their performance.

Atomically precise Au₂₄M(SR)₁₈ clusters were used as singlet-oxygen photosensitizers. Comprehensive kinetic analysis provided insights into the mechanism and driving-force dependence of the quenching of ¹O₂ by gold nanoclusters.     

A molecular switch in amyloid assembly: Met35 and amyloid beta-protein oligomerization

Aberrant protein oligomerization is an important pathogenetic process in vivo. In Alzheimer's disease (AD), the amyloid beta-protein (Abeta) forms neurotoxic oligomers. The predominant in vivo Abeta alloforms, Abeta40 and Abeta42, have distinct oligomerization pathways. Abeta42 monomers oligomerize into pentamer/hexamer units (paranuclei) which self-associate to form larger oligomers. Abeta40 does not form these paranuclei, a fact which may explain the particularly strong linkage of Abeta42 with AD. Here, we sought to determine the structural elements controlling paranucleus formation as a first step toward the development of strategies for treating AD. Because oxidation of Met(35) is associated with altered Abeta assembly, we examined the role of Met(35) in controlling Abeta oligomerization. Oxidation of Met(35) in Abeta42 blocked paranucleus formation and produced oligomers indistinguishable in size and morphology from those produced by Abeta40. Systematic structural alterations of the C(gamma)(35)-substituent group revealed that its electronic nature, rather than its size (van der Waals volume), was the factor controlling oligomerization pathway choice. Preventing assembly of toxic Abeta42 paranuclei through selective oxidation of Met(35) thus represents a potential therapeutic approach for AD.     

Enzyme‐Mediated Preparation of Chiral 1,3‐Dioxane Odorants

The enantiomerically enriched diastereoisomers of the chiral 1,3‐dioxane odorants Floropal^® ( 1 ) and Magnolan^® ( 2 ) were prepared by an enzyme‐mediated approach. Their olfactory properties were evaluated to investigate differences in the odor perception for the stereoisomers.     

Correlation analysis of characteristic infrared spectral data of hydantoin derivatives: evidence for vibrational coupling

The characteristic vibrations (ν_CO and ν_CC) of a large number of hydantoin derivatives are reported. Especially the very fine correlations ν_CO(sym) versus ν_CO(asym) (r²=0.985) but also successful correlations of the vibration wave numbers to HAMMETT's substituent constants and some other experimental parameters (pK_s, OxPot, RedPot) as well, corroborate reassignments of previously obtained results [Monatsh. Chem. 92 (1961) 361] and prove the doublet obtained in the region of the CO stretching vibrations to be the symmetrical and anti-symmetrical vibrational modes of a mechanically coupled system of two quasi-symmetrical CO bonds.