Structural and Spectroscopic Characterization of Iron(III) Dioxoporphodimethene Complexes and Their Autoreduction to an Iron(II) Complex in Pyridine

Three iron complexes of the meso-dioxo derivative of octaethylporphryin (trans-H(2)OEPO(2)) were characterized by X-ray diffraction. Green ClFe(III)(trans-OEPO(2)).1.5C(6)H(6) crystallizes in the monoclinic space group P2(1)/c with a = 13.766(3) ?, b = 19.075(3) ?, c = 15.217(3) ?, beta = 99.87(2) degrees at 123 K with Z = 4. Refinement of 2712 reflections with F > 6.0sigma(F) and 223 parameters yielded R = 0.0624, R(w) = 0.0596. The iron complex contains a domed dioxoporphodimethene macrocyclic ligand. The observation of a five-coordinate iron(III) ion with an axial Fe-Cl distance of 2.232(2) ? and in-plane Fe-N distances averaging 2.082 ? is consistent with its high-spin (S = (5)/(2)) character. This monomer is readily converted to the green {Fe(III)(trans-OEPO(2))}(2)O using aqueous hydroxide. {Fe(III)(trans-OEPO(2))}(2)O crystallizes in the monoclinic space group C2/c with a = 23.541(8) ?, b = 15.392(5) ?, c = 18.686(8) ?, and beta = 90.09(3) degrees at 294 K with Z = 8. Refinement of 3472 reflections with F > 6.0sigma(F) and 393 parameters yielded R = 0.0484, R(w) = 0.0527. The complex possesses a crystallographically imposed 2-fold symmetry axis that passes through the oxo ligand. The dioxoporphodimethene ligands within the molecule are roof-shaped and fold away from each other. The axial Fe-O distance is 1.749(1) ? with longer in-plane Fe-N distances (average 2.077 ?). The Fe-O-Fe angle of 165.4(2) degrees deviates significantly from linearity and is more acute than related porphyrin complexes. Pyridine solutions of either the iron(III) monomer or &mgr;-oxo dimer autoreduce over a period of days to give (py)(2)Fe(II)(trans-OEPO(2)). This red compound crystallizes in the space group P2(1) with a = 19.177(4) ?, b = 20.039(4) ?, c = 10.547(2) ?, and beta = 100.36(3) degrees at 130 K with Z = 2. Refinement of 5090 reflections with one restraint and 984 parameters yielded R1 = 0.0684, wR2 = 0.1763. The complex crystallizes with two distinct molecules in the asymmetric unit; each molecule contains a different degree of disorder with respect to the trans meso oxygen atoms (50/50, 71/29). Each independent molecule exhibits severe ruffling of the macrocycle. The six coordinate iron(II) center is diamagnetic. The axial Fe-N(pyridine) distances average 1.98 ?, and the in-plane Fe-N(pyrrole) distances average 1.95 ?. A common trend observed for the dioxoporphodimethene macrocycle in all of these structures is an elongation toward the trans oxidized meso carbons. These complexes were originally prepared as cis and trans isomeric mixtures that can be enriched in the trans isomer by fractional crystallization. This is evident in their distinctive (1)H NMR spectra. In addition, these compounds are characterized by electron impact mass spectrometry and UV-visible, ESR, and infrared spectroscopies.     

Energetics of protein-cyclodextrin interactions

The energetics of interaction of a range of cyclodextrins with folded and unfolded proteins has been examined by sensitive microcalorimetry techniques. Weak interaction with exposed amino acid residues promotes unfolding and dissociation of proteins. The possibility that such interactions may facilitate the use of cyclodextrins as chaperone-mimics in the refolding of denatured protein has been explored with the enzyme phosphoglycerate kinase. Up to 40% regain of activity can be achieved in some cases.     

A Product Formed from Glycylglycine in the Presence of Vanadate and Hydrogen Peroxide: The (Glycylde-N-hydroglycinato-kappa(3)N(2),N(N)(),O(1))oxoperoxovanadate(V) Anion

A crystalline glycylglycine complex of monoperoxovanadate has been obtained and its X-ray structure determined. The coordination is pentagonal bipyramidal with the peroxo group and a tridentate glycylglycine occupying the equatorial positions. The axial positions of the anion are occupied by the oxo ligand and by one oxygen of the peroxo group of the adjacent anion. The latter interaction establishes the seventh bond and produces a dimeric structure in the crystalline material. NMR studies of its dissolution in water combined with previously reported results from equilibrium measurements show that the dimer dissociates in water to the monomeric precursor. It is proposed that this monomer corresponds to the complex responsible for the inhibition of the vanadium-catalyzed decomposition of hydrogen peroxide by glycylglycine. Crystal structure of [NEt(4)][VO(O(2))(GlyGly)].1.58H(2)O: monoclinic, space group P2(1); Z = 4; a = 10.618(2) ?; b = 14.803(2) ?; c = 11.809(2) ?; beta = 101.37(2) degrees; V = 1819.7 ?(3); T = 198 K; R(F)() = 0.029 for 2664 data (I(o) >/= 2.5sigma(I(o))) and 431 variables.     

Reaping Numbers of Boolean Algebras

A subset A of a Boolean algebra B is said to be (n,m)-reapedif there is a partition of unity p B of size n such that |{b p:b a 0}| m for all a A. The reaping number r_n,m (B) ofa Boolean algebra B is the minimum cardinality of a set A B\{0}which cannot be (n,m)-reaped. It is shown that for each n, thereis a Boolean algebra B such that r_n+1,2(B) r_n,2(B). Also, {r_n,m(B):mn } consists of at most two consecutive cardinals. The existenceof a Boolean algebra B such that r_n,m (B) r_n',m' (B) is equivalentto a statement in finite combinatorics which is also discussed.     

Structures of two ketals derived from a pentacyclic cage diketone

The structure of a compound derived from a symmetrical cage diketone in which one of the ketone C=O groups has been converted into a ketal is reported. An investigation into reasons for the selective functionalization resulted in the isolation of acis, cisoid, cis linear triquinane derivative in which both ketones are converted to ketals that share a transannular oxygen atom. Crystal data:2, monoclinic,P2₁/c,a=7.6298(9),b=7.673(3),c=22.125(3)Å,=97.59(1)°,V=1283.9(5)ų, andR=0.048 (1001 reflections);4, triclinic,P¯1,a=7.3864(9),b=9.6362(9),c=10.3889(9)Å,=75.749(6),=76.300(8), =83.100(8)°,V=694.8(4)ų, andR=0.088 (1284 reflections).     

Yields of Br* (4P1/2) as a function of wavelength in the photodissociation of Br2 and IBr

A flashlamp-pumped tunable dye laser has been used to study the photochemical production of Br* (4²P_1/2) atoms from Br₂ and IBr exc     

β-lithiations of carboxamides. Synthesis of β-substituted-α,β-unsaturated amides

N-Methyl-2-methyl-3-(benzotriazol-l-yl)propanamide, on treatment with butyllithium forms a dianion which on treatment with alkyl and benzyl halides, aldehydes and ketones affords monosubstituted products; with ethyl p-toluate, a lactam is formed. The alkylated derivatives eliminate benzotriazole in the presence of base to afford trisubstituted α,β-unsaturated amides.     

Homopolar- and Heteropolar Bond Dissociation Energies and Heats of Formation of Radicals and Ions in the Gas Phase. I. Data on organic molecules

The literature data on heteropolar and homopolar 2-center bond dissociation energies in organic molecules in the gas phase and the corresponding heats of formation of radicals and ions have been critically evaluated. Data for more than 500 bonds are represented in tabular form together with the pertinent literature references. Selected electron affinities and π-bond dissociation energies have also been incorporated. The follow-up paper will discuss some empirical general aspects of these data particularly regarding the effect of structure on the bond dissociation energies.     

Construction of functional porphyrin polystyrene nano-architectures by ATRP

A series of mono-functionalized metallo-porphyrin polystyrenes have been synthesized using atom transfer radical polymerization and their self-assembling behavior was studied by electron microscopy showing that the polystyrene tail-length influences the aggregate architecture.     

Site-specific detection of S-nitrosylated PKB alpha/Akt1 from rat soleus muscle using CapLC-Q-TOF(micro) mass spectrometry

Protein Kinase Balpha(PKBalpha, or Akt1) is believed to play a crucial role in programmed cell death, cancer progression and the insulin-signaling cascade. The protein is activated by phosphorylation at multiple sites and subsequently phosphorylates and activates eNOS. Free cysteine residues of the protein may capture reactive, endogenously produced nitric oxide (NO) as S-nitrosothiols. Site-specific detection of S-nitrosylated cysteine residues, usually at low stoichiometry, has been a major challenge in proteomic research largely due to the lack of mass marker for S-nitrosothiols that are very labile under physiologic conditions. In this report we describe a sensitive and specific MS method for detection of S-nitrosothiols in PKB alpha/Akt1 in rat soleus muscle. PKB alpha/Akt1 was isolated by immunoprecipitation and 2D-gel electrophoresis, subjected to in-gel tryptic digestion, and cysteinyl nitrosothiols were reacted with iodoacetic acids [2-C(12)/C(13) = 50/50] under ascorbate reduction conditions. This resulted in the production of relatively stable carboxymethylcysteine (CMC) immonium ions (m/z 134.019 and m/z 135.019) within a narrow argon collision energy (CE = 30 +/- 5 V) in the high MS noise region. In addition, free and disulfide-linked cysteine residues were converted to carboxyamidomethylcysteines (CAM). Tryptic S-nitrosylated parent ion was detected with a mass accuracy of 50 mDa for the two CMC immonium ions at the triggered elution time during capillary liquid chromatography (LC) separation. A peptide containing Cys(296) was discriminated from four co-eluting tryptic peptides under lock mass conditions (m/z 785.8426). S-nitrosothiol in the tryptic peptide, ITDFGLBKEGIK (B: CAM, [M + 2H](2+) = 690.86, Found: 690.83), is believed to be present at a very low level, since the threshold for the CMC immonium trigger ions was set at 3 counts/s in the MS survey. The high levels of NO that are produced under stress conditions may result in increased S-nitrosylation of Cys(296) which blocks disulfide bond formation between Cys(296) and Cys(310) and suppresses the biological effects of PKB alpha/Akt1. With the procedures developed here, this process can be studied under physiological and pathological conditions.