Harry Morris

Oxygen free radical generating mechanisms in the colon: do the semiquinones of vitamin K play a role in the aetiology of colon cancer?

It is proposed that bile acids (deoxycholic acid), the K vitamins, iron(II) complexes and oxygen interact to induce an oncogenic effect in the colon by the generation of free radicals. In the relatively low oxidising/reducing conditions of the colonic lumen the K vitamins exist in the reduced form; however, if absorbed into the mucosa they have the capacity to be chemically oxidised and to enter into a redox cycle yielding oxygen radicals. The semiquinone radical of K(1) (phylloquinone) has been stabilised in bile acid mixed micelles and investigated by electron paramagnetic resonance spectroscopy and quantum chemical calculations. The estimated half-life of the radical was about 30 min which confirms a remarkably high stability in aqueous micellar solution. A model is presented in which the reduced K vitamins may initiate superoxide radical, O2(-*) generation leading to Fe(II) mediated Fenton reactions in the stem colon cells.

Quantitative electron paramagnetic resonance (EPR) spectrometry with a TE104 double rectangular cavity Part 1. A simple alignment procedure for the precision positioning of the sample

Abstract The Bruker TE104 double rectangular cavity is commonly utilized for quantitative electron paramagnetic resonance (EPR) spectrometric measurements. The sample, together with an appropriate standard, can be studied simultaneously within such a cavity under identical states of machine tuning and parameter settings. However, even under such conditions, there still remain sources of error arising from sample size, shape and positioning of the sample tube within the cavity. In this paper such sources of error have been investigated and a procedure to minimize the errors by precision insertion of the sample tubes within the TE104 cavity is described.

Effect of hydrogenation on electronic and distant magnetic properties in copper(II) complexes with derivatives of tetrahydrosalen and salen. X-ray crystal structure of [Cu{Bu,Me(saltmen)}] complex

Abstract The salen complex CuL and the corresponding tetrahydrosalen complex Cu[H4]L were investigated by ESR spectroscopy and molecular orbital calculations [H2L = N,N′-bis(3-tert-butyl-5-methylsalicylidene)-2,3-diamino-2,3-dimethylbutane; H2[H4]L = N,N′-bis(2-hydroxy-3-tert-butyl-5-methylbenzyl)-2,3-diamino-2,3-dimethylbutane]. X-ray structure determination of CuL confirmed a slightly distorted planar geometry of the CuN2O2 coordination core. The ESR spectra of CuL at both 78 K and room temperature revealed that very well resolved lines cannot be attributed to the interaction with copper nuclear spin and 14N donor nuclei alone. Computer simulation showed that in addition to copper hyperfine (giso = 2.094, |ACu(iso)| = 270 MHz, room temperature) and nitrogen superhyperfine structure [|AN(iso)| = 46 MHz] a distant interaction with two equivalent protons is also present [|AH(iso)| = 23 MHz]. These protons are attached to the carbon atoms adjacent to 14N nuclei. In contrast the number of lines in the spectrum of the hydrogenated analogue Cu[H4]L is greatly reduced. At room temperature only a quintet with considerable smaller nitrogen shf constant [|AN(iso)|] = 25 MHz is observed. Thus, both factors planarity and conjugation, are essential for the observation of distant hydrogen shf splitting in CuL. The ESR findings are in good agreement with calculated spin densities by QR-INDO/1 method.

Quantitative electron paramagnetic resonance (EPR) spectrometry with a TE104 double rectangular cavity Part 2. Analysis of sample and TE104 cavity error sources associated with the movement of line-like samples into the TE104 cavity

Abstract In this study the sample- and double TE 104 cavity-associated error sources have been analysed. It was found that in quantitative EPR experiments, the EPR signal intensity of identical full-length cavity line-like samples, which were packed by the same procedure with the same powdered material into identical sample tubes, then precision inserted into the same positions within the double TE 104 cavity using a special sample insertion procedure, and measured using the same instrumental parameters, could be obtained with experimental errors of about 3–5%. However, if the procedures for packing and inserting the powdered samples into the cavity were not used, the associated experimental errors could be over 20%. The errors associated with the movement of a full-length cavity line-like sample (30 mm length) into the double TE 104 cavity have been analysed. This analysis has shown that the experimental dependence of the EPR signal intensity upon the movement of the sample along the x -axis of the double TE 104 cavity exhibited a 12.5 mm wide plateau over which the EPR signal intensity remained constant within an experimental error 0.5–0.8%. Because the centre of the plateau coincided with the situation in which centre of the sample was positioned in the cavity centre, this position is recommended for quantitative EPR measurements. The existence of the plateau in the case of full-length cavity line-like samples was found to be the principal difference when compared with the corresponding dependence for point-like samples.

A study of copper(II) carboxylato complexes with the biological ligands nicotinamide and papaverine

The X-band Electron Spin Resonance spectra, ESR, of Cu(II) complexes with the carboxylic acids, HCOOH, CH3COOH, ClCH2COOH, Cl2CHCOOH, Cl3CCOOH, F2ClCOOH, CH3CH2COOH, niflumic acid and the ligands nicotinamide and papaverine have been studied. The compounds form either mononuclear or binuclear structures which can be qualitatively correlated with the strengths of the acid and base. Analysis of the spin Hamiltonian parameters for the monomeric species indicate that the molecule has nearly axial symmetry ðgk . g’Þ with the unpaired electron in the dx2 –y 2 orbital. In many cases the perpendicular feature is sufficiently well resolved showing superhyperfine features due to the nitrogen ligand nuclei. Ak varies over the range 130 ! 188 G and the variation appears to arise as a consequence of changes in gk: The dimeric species show ESR spectra typical of Cu(II)-carboxylate complexes which consist of 3 (4 if E – 0) lines. These are assigned to Bz1; Bx2;y2 and Bz2 since the Q-band spectra of similar molecules indicate that the Bx1;y1 transition(s) lies below Bz2 which is itself near zero field. The observed seven-line hyperfine coupling on the Bz1 transition of some of the dimeric complexes is due to the two equivalent copper nuclei ðI ¼ I1 þ I2 ¼ 3Þ: The singlet – triplet separation has been estimated from the spin Hamiltonian parameters to give values of l2Jl in the range of approximately 220– 290 cm 21 which are typical of the compounds of this type.

Electron paramagnetic resonance signal intensity of a line-like sample with a variable length situated at an arbitrary position along the common sample-cavity axis. Theoretical prediction versus experimental measurement

The integral equations used for the theoretical prediction of the relative EPR-signal intensity of variable length line-like samples situated at the central position of a microwave cavity have been computed numerically for the cases where: (i) the microwave field is non-uniform but the modulation field is uniform, and (ii) the microwave and modulation fields are non-uniform. In both cases, stress is placed on the variable length of the sample and the length of the active part of the microwave cavity. The theoretically predicted and experimentally observed electron paramagnetic resonance (EPR) signal intensity are in a very good agreement for sample lengths from 1.3 to 50 mm. However, for the cases where the sample length is greater than that of the cavity, the theoretical equations and experimental results can only be reconciled if the cavity is assumed to have an active length, *a=40 mm, considerably greater than the actual length of the cavity, a=23.5 mm. Comparison of the theoretically predicted and experimentally obtained EPR-signal intensities indicate that those parts of the sample situated in the upper and lower sample access holes of the rectangular cavity can contribute significantly to the measured signal intensity. The possible influence of this phenomenon as a significant source of error in quantitative EPR measurements is discussed. The integral equations have been generalised to describe the signal intensity for line-like sample positioned at any point along the common sample-cavity axis.

ESR spectra of dimeric copper(II) compounds of CuX2(H2O)2 and CuX2(pý) (X = 2-fluoro-6-chlorobenzoate; py = pyridine)

Abstract Temperature-dependent ESR studies of dimeric copper(II) carboxylate adducts of the general formula [CuX 2 L] 2 (where X = 2-fluoro-6-chloro-benzoate; L = H 2 O and pyridine) are reported. The observed resonance lines are used to calculate the zero-field splitting parameters D and E . Agreement between observed and calculated resonance lines is excellent. The spin Hamiltonian and zero-field splitting parameters are used to estimate the antiferromagnetic interaction: for [CuX 2 H 2 O] 2 ·2H 2 O, this is −2 J = 366 cm −1 , and for [CuX 2 L] 2 (L = pyridine), −2 J = 386 cm −1 .

From a point-like to an arbitrarily shaped sample: A survey of equations for electron paramagnetic resonance signal intensity calculations

A set of original, analytical equations useful for theoretical calculation of the electron paramagnetic resonance (EPR) signal intensity are presented for the multitude of sample shapes, which range from point-like, line-like, planar, rectangular, cubical, circular, cylindrical, spherical to an irregularly shaped sample. The samples can be situated at any available position within the prescribed part of the microwave cavity (a central cylinder of diameter 11 mm and length 23.5 mm, in either a Bruker single TE102 or double TE104 rectangular cavity, with the modulation coils situated in the left and right side cavity walls, which is connected to a X-band, field-modulated CW Bruker EPR spectrometer). The theoretical computations of EPR signal intensity can be used in the computer simulations in which: (i) the EPR signal intensity profiles are constructed; (ii) the optimal sample positions in the cavity to give a maximum value of signal intensity are found; (iii) the errors associated with sample positioning within the cavity when compared to a second sample of a different size, shape or position are studied.

Influence of the movement of cylindrical samples with variable internal diameter and variable length along thex-axis of a double TE104 and a single TE102 rectangular cavity on the EPR signal intensity: A sample shape study

The response of the cavity to the movement of cylindrical samples with internal diameters from 0.7 to 4 mm and lengths from 5 to 50 mm along thex-axis of the Bruker double TE104 and single TE102 rectangular cavity has been analyzed. Independently of sample internal diameter, the experimentally observed dependences of the electron paramagnetic resonance (EPR) signal intensity versus sample position in the cavity showed the following: (i) a sharp maximum for sample lengths from 5 to 20 mm; (ii) a “plateau”, over which the signal intensity remained constant within experimental errors of 0.47–1.16%, for lengths from 30 to 40 mm; and (iii) a “sloping plateau” region, which could be approximated by the linear function (correlationr = 0.96–0.98) for the 50 mm sample. Theoretical predictions of the experimental dependences of the signal intensity versus sample position in the cavity were calculated with the “modified” and “revised” sine-squared function, and the correlation between observed and theoretically computed dependences is very good. Additionally, the experimental dependence of the signal intensity versus the sample internal diameter and length for cylindrical samples situated at the position in the cavity at which the signal intensity was a maximum was likewise numerically approximated by the surface fitting with the Lorentzian cumulative additive function (correlationr = 0.999). The experimental dependence of the signal intensity versus the sample internal diameter for the given sample length is nonlinear. The samples with internal diameters of 0.7 and 1 mm gave the total maximum of signal intensity for the 40 mm sample, however, the samples with internal diameters of 2, 3 and 4 mm gave the total maximal value of signal intensity, which was identical for both the 30 and 40 mm samples. The experimental dependence of the EPR signal intensity versus the sample volume clearly showed that the samples with identical volumes, however, with different shapes, can give significantly different signal intensities (with differences ca. 200–400%). Then, the comparison of cylindrical samples with identical volumes but different shapes may be a serious source of significant errors in quantitative EPR spectroscopy. Cylindrical samples to be compared should be of identical shape. Accurate and precise positioning of each sample in the microwave cavity is essential.

Hydrogen radioisotopic labelling studies using muonium: properties of thiyl radicals potentially relevant to cellular membrane damage

Thiyl radicals (RS·) are formed labelled with muonium atoms (a radioisotope of hydrogen with a positive muon as the nucleus) and detected using the muon spin rotation (MuSR) method. This approach is shown to be extremely effective in the study of thiyl radicals, in non‐aqueous (membrane‐like) environments, from which details of the structures of these reactive free radicals and their reaction kinetics were determined. In this regard, the method is superior to conventional ESR spectroscopy, to which thiyl radicals are undetectable in liquid solution, and to pulse‐radiolysis experiments, which are limited to aqueous media; the rate constants for the reactions of thiyl radicals with lipids but also with antioxidants such as β‐carotene and (SH)glutathione are found to be enhanced in non‐aqueous media. Copyright