Detection limits and error estimation in analysis

Summary The results of theoretical calculations of the standard deviation in atomic spectrometry and analytical chemistry are discussed. Methods for the estimation of random errors and detection limits are proposed.     

Meso-oxidation of some metalloporphyrins

Treatment of porphyrins with thallium(III) trifluoroacetate in the presence of trifluoroacetic acid results in uncontrolled oxidation at the macrocyclic meso-positions, presumably via radical processes. For example, a mixture of the thallium(III) α γ-dioxoporphodimethene (4a; R = Et), the αβγ-trioxo compound (3), and octaethylxanthoporphyrinogen (6) is obtained when octaethylporphyrin (1; R = Et) is oxidised in the presence of air. More controlled oxidation is achieved when the meso-trifluoroacetoxyporphyrin complexes (8a, b) or metallo-oxophlorins (7a, b) are treated with mild bases in air, the major products being metallo-αγ-dioxoporphodimethenes (4b, c).β-Hydroxy-α-oxophlorins (16) are isolated and characterised for the first time; aspects of the chemistry of this novel oxygenated porphyrin system are reported.     

Photochemistry of metalloporphyrins in aqueous solutions

The fluorescence spectra of Ga(III), In(III), Ge(IV) and Sn(IV) tetramethyl pyridine porphyrin showed a small stokes shift ca 400 ± 100 cm⁻¹ attributed to the similarity between their ground and excited states. The one and two electron reduction products of the metalloporphyrins were studied by steady-state method. The nature of the product was dependent upon the pH of the reaction medium. Chlorin and phlorin were obtained at low and high pH's, respectively. Sn TMPyP was the only metalloporphyrin which yielded the Π-radical anion whose stability is due to the high electronegativity of Sn(IV).     

Crystal solvates of porphyrins and metalloporphyrins

The published data on the crystal solvates with nonpolar aromatic and electron-donor compounds obtained using different research methods as well as our own experimental results obtained by thermogravimetric analysis of the porphyrins and metalloporphyrins of natural and synthetic origin are generalized. The influence of the molecular structure of the porphyrins and metalloporphyrins on the composition, structural parameters, thermal and energy stability of crystal solvates formed through specific ??-and ??-complexes with molecular ligands are considered.     

Nonlinear absorption dynamics in tetrapyridyl metalloporphyrins

Nonlinear absorption dynamics of Zn(2+), Cu(2+), and Ni(2+) tetrapyridyl porphyrins in chloroform/methanol solutions were investigated at 532 nm with the Z-scan technique. Additional techniques such as UV-vis absorption spectroscopy and time-resolved fluorescence were used to obtain parameters that are important for the analysis of the population dynamics. A marked difference was observed in the nonlinear absorption and excited-state dynamics of closed (ZnTPyP)- and open-shell metalloporphyrins (CuTPyP and NiTPyP). ZnTPyP presents a reverse saturable absorption whose dynamics can be completely described by means of a simple five-energy-level diagram. On the other hand, CuTPyP and NiTPyP have a different excited-state dynamics, presenting a saturable absorption behavior and faster relaxation rates that were attributed to the presence of unfilled d shells of the central ion.     

Vibronic transitions in single metalloporphyrins.

Structural and electronic properties of single zinc etioporphyrin molecules adsorbed on Al2O3/NiAl(110) were probed by a low-temperature scanning tunneling microscope (STM). Scanning tunneling spectroscopy (STS) revealed progressions of spectral features corresponding to the vibronic states of individual molecules that depend strongly on the molecular conformations. Vibronic features observed by STS were compared with the results from fluorescence induced by tunneling electrons (tunneling-induced fluorescence, TIF).     

One-pot general synthesis of metalloporphyrins

A new general one-pot method for the synthesis of various metalloporphyrins has been developed from pyrrole and substituted aldehydes using transition metal salts. This method allows higher working concentrations than those previously reported. Along with the reported metalloporphyrins, some new metalloporphyrins were synthesized in good yield.     

疏水性金属卟啉的合成及催化性能研究

本文合成了一类带疏水性长链的对称卟啉及其金属配合物, 研究了该类金属卟啉在CH2Cl2/H2O两相体系中催化苯乙烯的环氧化反应性能。通过以上研究, 发现催化反应体系中水相PH值对烯烃环氧化反应有很大影响; 改变金属卟啉的疏水性对催化反应影响不大; 具不同中心金属离子的金属卟啉有不同的催化活性, 催化活性顺序为:Mn>Co>Ni>Cu。     

Solvent effects in molecular complexes of porphyrins and metalloporphyrins

The apparent stability constants for porphyrin and metalloporphyrin complexes with an electron acceptor have been determined in mixed solvents. The variation of the apparent stability with solvent composition is evaluated in terms of solvation of the complex and reactant species and in terms of the exclusion of the solvent from the solvation sheath of the reactants, according to the equilibrium AS _a +DS _b =CS _x +yS.     

Capillary GC and GC-MS of porphyrins and metalloporphyrins

Summary Despite their inherent low volatility, a wide range of alkyl porphyrins and their various metallo-derivatives have been successfully analysed by gas chromatography on wall coated open tubular (WCOT) capillary columns. As a result of their superior peak shape (comparable ton-alkanes of similar retention times) and relatively low Kovat's retention indices (3300–3900), the bis(trialkylsiloxy)Si(IV) derivatives offer the greatest potential for the GC analysis of geological mixtures of alkyl porphyrins. Similar derivatives of porphyrins of biomedical importance, possessing polar side chains, are also amenable to GC and GC-MS analysis.Presented at the 14th International Symposium on Chromatography London, September, 1982     

CARS-spectra of excited states of metalloporphyrins

It is shown that resonance coherent anti-Stokes Raman scattering (RCARS) spectra of Cu- and Ni-octaethylporphyrins contain lines corresponding to molecule vibrations both in the ground and excited electronic states. Mechanisms are given which lead to the appearance of vibrations in the excited state in RCARS spectra. The RCARS methods are shown to be promising for comparing molecule vibrations in different electronic states.     

Nuclear magnetic resonance shifts in paramagnetic metalloporphyrins and metalloproteins

We report the first detailed investigation of the (1)H, (13)C, (15)N, and (19)F nuclear magnetic resonance (NMR) spectroscopic shifts in paramagnetic metalloprotein and metalloporphyrin systems. The >3500 ppm range in experimentally observed hyperfine shifts can be well predicted by using density functional theory (DFT) methods. Using spin-unrestricted methods together with large, locally dense basis sets, we obtain very good correlations between experimental and theoretical results: R(2) = 0.941 (N = 37, p < 0.0001) when using the pure BPW91 functional and R(2) = 0.981 (N = 37, p < 0.0001) when using the hybrid functional, B3LYP. The correlations are even better for C(alpha) and C(beta) shifts alone: C(alpha), R(2) = 0.996 (N = 8, p < 0.0001, B3LYP); C(beta), R(2) = 0.995 (N = 8, p < 0.0001, B3LYP), but are worse for C(meso), in part because of the small range in C(meso) shifts. The results of these theoretical calculations also lead to a revision of previous heme and proximal histidine residue (13)C NMR assignments in deoxymyoglobin which are confirmed by new quantitative NMR measurements. Molecular orbital (MO) analyses of the resulting wave functions provide a graphical representation of the spin density distribution in the [Fe(TPP)(CN)(2)](-) (TPP = 5,10,15,20-tetraphenylporphyrinato) system (S = (1)/(2)), where the spin density is shown to be localized primarily in the d(xz) (or d(yz)) orbital, together with an analysis of the frontier MOs in Fe(TPP)Cl (S = (5)/(2)), Mn(TPP)Cl (S = 2), and a deoxymyoglobin model (S = 2). The ability to now begin to predict essentially all heavy atom NMR hyperfine shifts in paramagnetic metalloporphyrins and metalloproteins using quantum chemical methods should open up new areas of research aimed at structure prediction and refinement in paramagnetic systems in much the same way that DFT methods have been used successfully in the past to predict/refine elements of diamagnetic heme protein structures.     

Theoretical analysis of core size effect in metalloporphyrins

Density functional theory has been applied to a series of unsubstituted planar metalloporphyrins (MPs) to elucidate how geometry and frequencies correlate with the metal-nitrogen distance, referred to as the core size. Different transition metals can invoke expansion or contraction of the porphyrin core due to electronic effects resulting from the amount of d-electron pairing as well as occupancy of the d(x(2)(-y(2))) orbital. A full vibrational analysis consisting of all in-plane and out-of-plane frequencies was carried out, and the resulting modes were plotted against core size for a linear analysis and grouped within symmetry blocks. The modes were separated according to planarity, and all modes with a large slope and best fit greater than 0.8 were considered sensitive to metal-nitrogen distances. All planar skeletal modes above 1450 cm(-1), including the pyrolle ring deformations, are found to be core-size sensitive. The most significant out-of-plane modes sensitive to core size are gamma(8) and gamma(9), which are infrared active and grouped within the A(2u) symmetry block. The present work also opens possible quantitative applications for the correlation of spectroscopic properties of MPs and heme proteins with actual structural parameters.     

Nuclear magnetic resonance of paramagnetic metalloporphyrins

The present article reviews and discusses proton magnetic resonance studies on metalloporphyrins which provide good models for heme proteins in their physical and chemical properties. Emphasis is given on the discussion of the₁Hnmr work done in our laboratory.