An Electron Paramagnetic Resonance (EPR) spectroscopy study on the γ-irradiation sterilization of the pharmaceutical excipient l-histidine: Regeneration of the radicals in solution.

The effects of γ-radiation sterilization on the parenteral excipient l-histidine were analysed by means of EPR spectroscopy. The irradiation process was found to induce the formation of a deamination radical which was persistent in the solid state. The nature and reactivity of the radicals following dissolution in water was evaluated using spin-trapping EPR experiments. The deamination radical was found to regenerate in solution in the presence of trace metals, potentially leading to radical induced degradation reactions occurring up to an hour after the dissolution process. Understanding this process is significant for the improved design of parental pharmaceutical formulations in which unwanted radical reactions after γ-radiation sterilization could lead to degradation of active ingredients.

Fluorescence-detected magnetic field effects on radical pair reactions from femtolitre volumes.

We show that the effects of applied magnetic fields on radical pair reactions can be sensitively measured from sample volumes as low as ∼100 femtolitres using total internal reflection fluorescence microscopy. Development of a fluorescence-based microscope method is likely to be a key step in further miniaturisation that will allow detection of magnetic field effects on single molecules.

Probing a chemical compass: novel variants of low-frequency reaction yield detected magnetic resonance.

We present a study of a carotenoid-porphyrin-fullerene triad previously shown to function as a chemical compass: the photogenerated carotenoid-fullerene radical pair recombines at a rate sensitive to the orientation of an applied magnetic field. To characterize the system we develop a time-resolved Low-Frequency Reaction Yield Detected Magnetic Resonance (tr-LF-RYDMR) technique; the effect of varying the relative orientation of applied static and 36 MHz oscillating magnetic fields is shown to be strongly dependent on the strength of the oscillating magnetic field. RYDMR is a diagnostic test for involvement of the radical pair mechanism in the magnetic field sensitivity of reaction rates or yields, and has previously been applied in animal behavioural experiments to verify the involvement of radical-pair-based intermediates in the magnetic compass sense of migratory birds. The spectroscopic selection rules governing RYDMR are well understood at microwave frequencies for which the so-called 'high-field approximation' is valid, but at lower frequencies different models are required. For example, the breakdown of the rotating frame approximation has recently been investigated, but less attention has so far been given to orientation effects. Here we gain physical insights into the interplay of the different magnetic interactions affecting low-frequency RYDMR experiments performed in the challenging regime in which static and oscillating applied magnetic fields as well as internal electron-nuclear hyperfine interactions are of comparable magnitude. Our observations aid the interpretation of existing RYDMR-based animal behavioural studies and will inform future applications of the technique to verify and characterize further the biological receptors involved in avian magnetoreception.

Spin-locking in low-frequency reaction yield detected magnetic resonance.

The purported effects of weak magnetic fields on various biological systems from animal magnetoreception to human health have generated widespread interest and sparked much controversy in the past decade. To date the only well established mechanism by which the rates and yields of chemical reactions are known to be influenced by magnetic fields is the radical pair mechanism, based on the spin-dependent reactivity of radical pairs. A diagnostic test for the operation of the radical pair mechanism was proposed by Henbest et al. [J. Am. Chem. Soc., 2004, 126, 8102] based on the combined effects of weak static magnetic fields and radiofrequency oscillating fields in a reaction yield detected magnetic resonance experiment. Here we investigate the effects on radical pair reactions of applying relatively strong oscillating fields, both parallel and perpendicular to the static field. We demonstrate the importance of understanding the effect of the strength of the radiofrequency oscillating field; our experiments demonstrate that there is an optimal oscillating field strength above which the observed signal decreases in intensity and eventually inverts. We establish the correlation between the onset of this effect and the hyperfine structure of the radicals involved, and identify the existence of 'overtone' type features appearing at multiples of the expected resonance field position.

Magnetic field effects in flavoproteins and related systems.

Within the framework of the radical pair mechanism, magnetic fields may alter the rate and yields of chemical reactions involving spin-correlated radical pairs as intermediates. Such effects have been studied in detail in a variety of chemical systems both experimentally and theoretically. In recent years, there has been growing interest in whether such magnetic field effects (MFEs) also occur in biological systems, a question driven most notably by the increasing body of evidence for the involvement of such effects in the magnetic compass sense of animals. The blue-light photoreceptor cryptochrome is placed at the centre of this debate and photoexcitation of its bound flavin cofactor has indeed been shown to result in the formation of radical pairs. Here, we review studies of MFEs on free flavins in model systems as well as in blue-light photoreceptor proteins and discuss the properties that are crucial in determining the magnetosensitivity of these systems.

Chemical engineering of molecular qubits.

We show that the electron spin phase memory time, the most important property of a molecular nanomagnet from the perspective of quantum information processing, can be improved dramatically by chemically engineering the molecular structure to optimize the environment of the spin. We vary systematically each structural component of the class of antiferromagnetic Cr(7)Ni rings to identify the sources of decoherence. The optimal structure exhibits a phase memory time exceeding 15 µs.

Radiofrequency polarization effects in zero-field electron paramagnetic resonance.

Optically detected zero-field electron paramagnetic resonance spectroscopy is used to show that weak linearly and circularly polarized radiofrequency magnetic fields affect the recombination reactions of spin-correlated radical pairs to different extents; the spectra are shown to be consistent with the radical pair mechanism.

Radiofrequency polarization effects in low-field electron paramagnetic resonance.

Low-field optically detected EPR spectra of photochemically formed transient radical ion pairs are reported for weak circularly and linearly polarized radiofrequency (RF) fields. The spectra are found to be strongly dependent on the polarization and frequency of the RF field and on the angle between the static magnetic field and the plane containing the RF field. The spectra are discussed in terms of resonances arising from Zeeman and hyperfine interactions; the conditions for validity of the rotating frame approximation are determined. Knowledge of the latter is important when using low-field EPR as a diagnostic test for the operation of the radical pair mechanism.

A semi-solid drug delivery system for epidermal growth factor in corneal epithelial wound healing.

PURPOSE: To examine the effects of EGF, delivered from a semi-solid drug delivery system, on corneal epithelial wound healing following anterior keratectomy wound creation in the eyes of New Zealand white rabbits. METHODS: A semi-solid drug delivery system based on a Carbopol gel was developed. Following creation of a 7.5 mm circular anterior keratectomy wound, 50 microL of either a placebo gel or an EGF-containing gel, was instilled in the inferior fornix. The gel remained in the eye for 8 hours, at which time it was removed. Anaesthesia was maintained for the entire 8-hour period. Wound healing was evaluated by quantitative morphometry. We evaluated 0.04, 0.1, 0.2, 0.4, and 1% EGF concentrations in the gel. Tear EGF concentrations and histology of the healing corneas were also examined. RESULTS: The enhancement factor (ratio of the healing rate with the EGF gel and control gel) was 1.13 +/- 0.12, 1.40 +/- 0.14, 1.29 +/- 0.12, 1.80 +/- 0.22, and 1.09 +/- 0.12 for the gels containing 0.04, 0.1, 0.2, 0.4, and 1% EGF by mass, respectively. The increases in the rate of wound healing were significant with the 0.1, 0.2 and 0.4% gel formulations. Histologically, the 0.4% gels resulted in cellular hyperplasia after 5 days of healing. Differences between the placebo gel-treated and EGF-containing gel-treated eyes were evaluated at both 2 and 5 days. The concentration of EGF in the tears during the treatment period was approximately constant for both the 1% and 0.04% gels. The average tear concentration during the instillation period was 2.87 +/- 0.36 micrograms/mL and 200.61 ng/mL +/- 116.10 for the 1% and 0.04% gels respectively. CONCLUSIONS: Treatment with EGF in a Carbopol gel carrier for a period of 8 hours results in significant wound healing enhancement (p < 0.05). The optimum EGF loading in the gel was determined to be 0.4%. A slow release gel may be an effective way to deliver EGF to the corneal surface.

Continuous epidermal growth factor delivery in corneal epithelial wound healing.

PURPOSE: To investigate the effects of a single prolonged exposure to recombinant epidermal growth factor on the healing of anterior keratotomy wounds in New Zealand white rabbits. METHODS: After wounding, eyes were perfused for 1, 2, 4, and 8 hours with either epidermal growth factor solution at a concentration of 50 micrograms/ml or balanced saline solution using a Morgan therapeutic lens (Mortan Inc, Missoula MT) and a syringe pump. Furthermore, concentration response was evaluated by perfusing with epidermal growth factor solutions at concentrations of 5, 50, 100 and 500 micrograms/ml for 4 hours. Wound healing rates were determined by quantitative morphometry of the wound area. The ratio of healing rates of eyes perfused with epidermal growth factor and control eyes provided a measure of the effect of epidermal growth factor on wound healing, and was defined as the epidermal growth factor enhancement factor. RESULTS: The enhancement factor was found to be 1.04 +/- 0.08, 1.17 +/- 0.07, 1.43 +/- 0.09, and 1.59 +/- 0.07 for perfusion times of 1, 2, 4, and 8 hours, respectively. The concentration response enhancement factors were 0.99 +/- 0.08, 1.43 +/- 0.09, 1.21 +/- 0.09, and 0.95 +/- 0.07 for the 5, 50, 100, and 500 micrograms/ml 4-hour perfusions, respectively. CONCLUSION: The results indicated that continuous epidermal growth factor exposures of as few as 2 hours produced a significant increase in healing rates (P < 0.05); increasing the time of exposure further increases the rate of wound healing. Results from the concentration response experiments showed that the optimum epidermal growth factor concentration for enhancing epithelial wound healing is approximately 50 micrograms/ml.

Malignant acanthosis nigricans. A case report.

PURPOSE: The authors present a case of malignant acanthosis nigricans that has two unusual aspects. The first is involvement of the lid margins with confluent papillomata, causing severe visual impairment, and the second is the association with lung malignancy. METHODS: A 65-year-old Portuguese man presented with decreased vision, papillomatous lid lesions, pruritus, and progressive thickening of the skin of his face, neck, axillae, and inguinal creases. A diagnosis of acanthosis nigricans was made after skin biopsy. Systemic investigations showed a suprahilar mass, and biopsy was positive for squamous cell carcinoma of the lung. RESULTS: The patient underwent excision of papillomata from all four lid margins, and this was repeated 1 year later. He also completed a course of palliative radiotherapy. CONCLUSION: Malignant acanthosis nigricans is rarely associated with lung neoplasms, being more commonly a manifestation of intra-abdominal malignancies. Of note in this case is the extensive ocular involvement and visual impairment.

Collagen shields: efficacy, safety and comfort in the treatment of human traumatic corneal abrasion and effect on vision in healthy eyes.

To study the efficacy, safety and comfort of porcine collagen shields in the treatment of traumatic corneal abrasion, patients with corneal abrasions that had occurred within 24 hours before examination were treated with either a collagen shield (18 patients) or tight patching (12 patients). There was no significant difference in the rate of healing or the proportion of corneas healed between the two groups. The collagen shield was significantly more comfortable than the patch (p < 0.05). After 1 hour of wear the collagen shield allowed useful vision (mean 20/100) in nine healthy volunteer subjects. Collagen shields may be of benefit in carefully selected cases of traumatic corneal abrasion.

Corneal changes in Tay-Sachs disease.

Tay-Sachs disease is a well-known inherited disease leading to an accumulation of gangliosides in the brain and retina. Our report is based on a case of Tay-Sachs disease in a non-Jewish infant where pathologic changes were noted in corneal endothelium as well as in the retina.