Effects of substituents on synthetic analogs of chlorophylls. Part 3: The distinctive impact of auxochromes at the 7- versus 3-positions

Assessing the effects of substituents on the spectra of chlorophylls is essential for gaining a deep understanding of photosynthetic processes. Chlorophyll a and b differ solely in the nature of the 7-substituent (methyl versus formyl), whereas chlorophyll a and d differ solely in the 3-substituent (vinyl versus formyl), yet have distinct long-wavelength absorption maxima: 665 (a) 646 (b) and 692 nm (d). Herein, the spectra, singlet excited-state decay characteristics, and results from DFT calculations are examined for synthetic chlorins and 13(1)-oxophorbines that contain ethynyl, acetyl, formyl and other groups at the 3-, 7- and/or 13-positions. Substituent effects on the absorption spectra are well accounted for using Gouterman's four-orbital model. Key findings are that (1) the dramatic difference in auxochromic effects of a given substituent at the 7- versus 3- or 13-positions primarily derives from relative effects on the LUMO+1 and LUMO; (2) formyl at the 7- or 8-position effectively "porphyrinizes" the chlorin and (3) the substituent effect increases in the order of vinyl < ethynyl < acetyl < formyl. Thus, the spectral properties are governed by an intricate interplay of electronic effects of substituents at particular sites on the four frontier MOs of the chlorin macrocycle.     

Synthesis, characterization, DNA binding and cleavage properties and anticancer studies of ruthenium(III) Schiff base complexes

A Schiff base (HL) has been synthesized and characterized by physico-chemical, spectroscopic and X-ray crystallography studies. Three of its Ru(III) complexes were synthesized and characterized by analytical and spectroscopic studies. The DNA binding properties of HL and its Ru(III) complexes have been investigated by electronic absorption spectroscopy. Also, HL and its Ru(III) complex [RuCl₂(AsPh₃)L] were tested for DNA cleavage properties. The results showed that the complex cleaves DNA more rapidly than the free ligand. Further, an in vitro study of the cytotoxicity of HL and the complex [RuCl₂(AsPh₃)L] was carried out.     

Eddy-current-resistant SmCo5/CaF2 magnets produced via high-energy milling in polar and non-polar liquids

Processes of high-energy ball milling of SmCo₅ alloys were compared for three single-liquid environments without using additional surfactants. Both coarsely grained as-cast and nanocrystalline pre-milled SmCo₅ precursors showed tendency toward formation of thin flakes if milled in polar liquids (acetone and ethanol) in a marked contrast to milling in non-polar heptane. CaF₂ dielectric powder added prior to milling in the polar liquids tends to become attached on the flake surfaces. Milling in heptane in the presence of CaF₂ produces flake-like SmCo₅ particles which with increasing the milling time are found to incorporate an increasing amount of CaF₂. The SmCo₅—5 wt% CaF₂ mixtures milled for the optimum time in both the polar and non-polar liquids were successfully hot-pressed into laminated composite magnets having intrinsic coercivity of 25–30 kOe, maximum energy product of approximately 6.5 MG Oe and electrical resistivity of 500–600 μΩ cm, which is more than 7 times the resistivity of conventional Sm–Co magnets.     

Catalytic oxidation and C–C coupling reactions of new ruthenium(III) Schiff base complexes containing PPh<Subscript>3</Subscript> or AsPh<Subscript>3</Subscript> co-ligands

New mononuclear ruthenium(III) Schiff base complexes of the type [RuX₂(EPh₃)(L)] (X = Cl or Br; E = P or As; L = monobasic tridentate Schiff base derived from o-aminophenol or o-aminothiophenol with ethylacetoacetate or ethylbenzoylacetate) have been synthesized. The Schiff base ligands chelate to ruthenium through O, N, and O/S by dissociation of the phenolic proton/thiophenolic proton forming chelate rings. These complexes have been characterized by physico-chemical and spectroscopic methods. Cyclic voltammetric data of all the complexes showed Ru(III)/Ru(IV) oxidation and Ru(III)/Ru(II) reduction within the range of 0–1.5 V and 0 to −1.5 V with respect to Ag/AgCl, respectively. The complexes were tested as catalysts in the oxidation of alcohols using molecular oxygen at ambient temperature, and also in C–C coupling reactions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Synthesis and Crystal Structure of a New Schiff Base 4-[(2-hydroxy-benzylidene)-amino]-<Emphasis Type="Italic">N</Emphasis>-(5-methyl-isoxazol-3-yl)-benzenesulfonamide

Abstract  The structure of the title compound (C₁₇H₁₅N₃O₄S)₂ the schiff base, bis(N-(5-methyl-3-isoxazolyl)-4-[(2-hydroxy benzylidene)-amino]) benzene sulfonamide was elucidated by H¹, C¹³ NMR, UV–VIS and IR spectroscopic techniques. The X-ray structure was determined in order to establish the conformation of the molecule. The compound crystallizes in the triclinic space group P-1, with a = 11.419(1), b = 11.426(0), c = 13.316(1) ?, α = 71.94(2), β = 89.79(1), γ = 89.14(2)° and Z = 4. Two benzene rings and azomethine group are practically coplanar, as a result of intramolecular hydrogen bonds involving the hydroxy O atom and azomethine N atom. The component species further interact via N–H···N and C–H···O hydrogen bonds and π–π stacking interactions. Index Abstract  The title compound (C₁₇H₁₅N₃O₄S)₂, Schiff base, bis(N-(5-methyl-3-isoxazolyl)-4-[(2-hydroxy benzylidene)-amino]) benzene sulfonamide was synthesized by the condensation of 4-amino-N-(5-methyl-3-isoxazolyl) benzene sulfonamide (SMZ) and 2-hydroxy benzaldehyde (SA). Its structure was confirmed by single crystal X-ray diffraction analysis. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Cyclic chlorophosphites as scaffolds for the one-pot synthesis of α-aminophosphonates under solvent-free conditions

New α-aminophosphonates of the type (OCH₂CMe₂CH₂O)P(O)CH(NHCO₂R)(R′) [6a-i, 7a-e, and 8a-c] have been synthesized in high yields by a three-component reaction using (OCH₂CMe₂CH₂O)PCl (3), benzamide (or urethane or benzyl carbamate), and an aldehyde without using any catalyst under solvent-free conditions. This route can be readily adapted for bis-aminophosphonates as well as optically active binaphthoxy α-aminophosphonates; it also tolerates the phenolic -OH group as shown by the synthesis of hydroxy functionalized aminophosphonates. Partial hydrolysis of compounds 7a-d leads to products in which the phosphorinane ring is cleaved first. Compounds (OCH₂CMe₂CH₂O)P(O)CH[NHC(O)Ph](9-anthryl) (6f) and optically pure (R,S)-(−)-(C₂₀H₁₂O₂)P(O)CH(NHCO₂Et)(Ph) (14a) were characterized by X-ray crystallography.     

Synthesis of size-controlled cobalt ferrite particles with high coercivity and squareness ratio

Cobalt ferrite particles with diameters ranging from a few micrometer to about 15 nm were synthesized using a modified oxidation process. The fine control of the particle size was achieved by introducing various concentrations of Fe(3+) ions at the beginning of the reaction. Among the particle sizes obtained by using this method, particles with a grain size of about 36 nm showed a magnetization (M(s)) of 64 emu/g and a maximum coercivity (H(c)) of 2020 Oe at room temperature. The corresponding squareness ratio was found to be 0.53.     

Ruthenium(II) carbonyl complexes with tridentate Schiff bases and their antibacterial activity

The products obtained by reacting ruthenium (II) complexes [RuHCl(CO)(PPh₃)₂(B)] [B = PPh₃, pyridine (py) or piperidine (pip)] with tridentate Schiff base ligands derived by condensing salicylaldehyde or o-vanillin with o-aminophenol and o-aminothiophenol, have been characterised by analytical, i.r., electronic, ¹H-n.m.r. and ³¹P-n.m.r. spectral studies and formulated as [Ru(L)(CO)(PPh₃)(B)] (L = bifunctional tridentate Schiff base anion, B = PPh₃, py or pip). An octahedral structure has been tentatively proposed for the new complexes. Some have been tested for the in vitro growth inhibitory activity against bacteria Escherichia coli, Bacillus sp. and Pseudomonas sp.     

Supramolecular interactions in salts/cocrystals involving pyrimidine derivatives of sulfonate/carboxylic acid

The crystal structures of three compounds involving aminopyrimidine derivatives are reported, namely, 5-fluorocytosinium sulfanilate–5-fluorocytosine–4-azaniumylbenzene-1-sulfonate (1/1/1), C₄H₅FN₃O⁺·C₆H₆NO₃S⁻·C₄H₄FN₃O·C₆H₇NO₃S, I , 5-fluorocytosine–indole-3-propionic acid (1/1), C₄H₄FN₃O·C₁₁H₁₁NO₂, II , and 2,4,6-triaminopyrimidinium 3-nitrobenzoate, C₄H₈N₅⁺·C₇H₄NO₄⁻, III , which have been synthesized and characterized by single-crystal X-ray diffraction. In I , there are two 5-fluorocytosine (5FC) molecules (5FC-A and 5FC-B) in the asymmetric unit, with one of the protons disordered between them. 5FC-A and 5FC-B are linked by triple hydrogen bonds, generating two fused rings [two R₂²(8) ring motifs]. The 5FC-A molecules form a self-complementary base pair [R₂²(8) ring motif] via a pair of N—H…O hydrogen bonds and the 5FC-B molecules form a similar complementary base pair [R₂²(8) ring motif]. The combination of these two types of pairing generates a supramolecular ribbon. The 5FC molecules are further hydrogen bonded to the sulfanilate anions and sulfanilic acid molecules via N—H…O hydrogen bonds, generating R₄⁴(22) and R⁶₆(36) ring motifs. In cocrystal II , two types of base pairs (homosynthons) are observed via a pair of N—H…O/N—H…N hydrogen bonds, generating R₂²(8) ring motifs. The first type of base pair is formed by the interaction of an N—H group and the carbonyl O atom of 5FC molecules through a couple of N—H…O hydrogen bonds. Another type of base pair is formed via the amino group and a pyrimidine ring N atom of the 5FC molecules through a pair of N—H…N hydrogen bonds. The base pairs (via N—H…N hydrogen bonds) are further bridged by the carboxyl OH group of indole-3-propionic acid and the O atom of 5FC through O—H…O hydrogen bonds on either side of the R₂²(8) motif. This leads to a DDAA array. In salt III , one of the N atoms of the pyrimidine ring is protonated and interacts with the carboxylate group of the anion through N—H…O hydrogen bonds, leading to the primary ring motif R₂²(8). Furthermore, the 2,4,6-triaminopyrimidinium (TAP) cations form base pairs [R₂²(8) homosynthon] via N—H…N hydrogen bonds. A carboxylate O atom of the 3-nitrobenzoate anion bridges two of the amino groups on either side of the paired TAP cations to form another ring [R₃²(8)]. This leads to the generation of a quadruple DADA array. The crystal structures are further stabilized by π–π stacking ( I and III ), C—H…π ( I and II ), C—F…π ( I ) and C—O…π ( II ) interactions.