Photolysis of thyroxine and its analogs in the near UV permitted synthesis in good yield of picogram to gram quantities of thyroid hormone metabolites. Preparation of the same metabolites by classical chemical synthesis requires multistep procedures. Specifically labeled metabolites of high specific activity (e.g., those carrying the label in the nonphenolic ring) were obtained by photolysis of appropriately labeled thyroxine or 3,3 ,5 -triiodothyronine (reverse triiodothyronine). Some of these labeled metabolites, which are required for metabolic studies (3-iodothyronine and 3,3 -diiodothyronine, labeled in the nonphenolic ring), had not previously been obtained by other methods. Irradiation of thyroxine and reverse triiodothyronine in 150 mM methanolic ammonium hydroxide with >340-nm light caused removal of one iodine atom from the phenolic ring with formation of 3,5,3 -triiodothyronine and 3,3 -diiodothyronine, respectively. Irradiation with higher-energy light (>300 nm) led to stepwise removal of additional iodine atoms. Those in the phenolic ring were removed preferentially, so that 3,5-diiodothyronine and 3-iodothyronine, respectively, were formed. The iodine atoms in the nonphenolic ring were lost more slowly. Tetraiodothyroacetic acid followed a similar photodeiodination pattern. Photolysis with light in the near UV is a simple method for the synthesis of thyroid hormone metabolites.
In vocoder systems speech is spectrally analysed with filter banks containing 16 to 19 narrowband filters. Digital techniques can be used to realize these filter banks in an economical manner by using single time multiplexed second order filters. A hardware implementation of a fourth and an eighth order filter, realized with one time-shared second order section is described. A software package is developed to simulate the filter performance, and validate the experimentally measured response. The CMOS design of a programmable filter is presented. A second order section is time multiplexed to realize up to 32 poles of filtering. The configuration is mask programmable and the filter coefficients are programmable with a UV-PROM. The bank of contiguous bandpass filters for vocoder use can be implemented with three multi-function filter chips.
The deposition of multilayer coatings for reflective filters in the extreme UV region is controlled by measuring the reflection of soft x-rays during the coating process. The x-ray source is aligned for every layer at the angle at which the maximas and minimas coincide with the peaks and valleys of the standing wave of the filter. The accuracy of the positioning between source and substrate has to be better than 1/50 degrees.
The increase in fluorescent chromophores within the human ocular lens is age related, leading to an increasingly yellow core (nucleus) that presumably results from UV radiation exposure. In approximately 10% of our population this process progresses more rapidly, resulting in the formation of the brown (nuclear) cataract. Some lenticular discoloration may be beneficial, since it enables the mature lens to filter UV and short-wavelength visible radiation, thus protecting the retina from potential photodamage. Aphakic primate retinas can be irreversibly damaged by exposure to approximately 5 mW.cm-2 long-wavelength UV (greater than 325 nm) radiation. Photosensitized damage to the lens and retina with psoralen plus UV radiation (320-400 nm) (PUVA) has been demonstrated in experimental animals, and cataracts have recently been reported in patients given PUVA therapy. A new method to screen patients for lens damage is by enhanced fluorescence measurements. This method, UV slit-lamp densitography, permits detection of lenticular photodamage at a molecular level, years before visible opacities become manifest by conventional slit-lamp examination. This procedure has also demonstrated a significantly lower level of lens fluorescence (hence decreased filtering capacity) in patients with retinal degenerative diseases, suggesting UV photodamage as a factor in the progression and perhaps pathogenesis of these conditions.