Light-sensitive System Research Articles

Influence of Drug Loading and Gel Structure on in-Vitro Release Kinetics from Photopolymerized Gels

AbstractPrecious work has shown that stabls and homogenous poly HEMA gels can be prepared using a visible light sensitive initiator system. Gels were prepared from solutions of water and poly-2-hydroxyethyl methacrylate monomer. At concentrations of water greater than 10% v/v, translucent gel resulted. However, polymerization solvents such as glycerol and tertiary butyl alcohol (T.B.T.A) gave transparent, flexible gels over a wider range of concentrations. Subsequent work showed that changes in polymerization solvent and monomer concentration brought about changes in the mechanical and structural properties of the gels.In this work, the effects of drug loading and polymerization solvents on in vitro drug release rate from the photopolymerized polyHEMA gels were studied. Polymerization solvents used included glycerol and tertiary butyl alcohol. Results indicated that the release rate in vitro was a diffusion-controlled process except at high drug concentrations in poly HEMA - T.B.T.A. gels when a departure...

Blue light-dependent regulation of cytoplasmic ribosomal RNA synthesis in Chlorella

Effect of blue and red light on ribosomal RNA synthesis in autotrophic synchronous cultures of Chlorella pyrenoidosa (strain 211-8b) is studied by pulse labeling experiments with tritiated guanosine. Nucleic acids were separated by electrophoresis on polyacrylamide gels. Compared with darkness and red light (679 nm), blue light (457 nm) of equal quantum flux (0.5-5x10(-10) Einstein cm-2 s-1) stimulates incorporation into ribosomal RNA. This blue light effect is observed in the cytoplasmic ribosomal RNA after 5 min of illumination, whereas the stimulation of chloroplast ribosomal RNA synthesis by blue light appears later. Maturation of chloroplast ribosomal RNA is slower than that of cytoplasmic ribosomal RNA. The blue light effect on the cytoplasmic ribosomal RNA formation does not require chloroplast RNA or protein synthesis as shown by inhibitor studies with rifampicin or lincomycin. The blocking of cytoplasmic protein synthesis by cycloheximide inhibits the blue light effect on ribosomal RNA formation. It is concluded that the cytoplasmic ribosomal RNA transcription is controlled by a blue light sensitive system.

Using light sensitive semiconductor-metal system in holographic research

Using light sensitive semiconductor-metal system in holographic research

Factors Influencing Expression of Oxidant Damage to Plants

This paper suggests that the mechanism that controls resistance of plants to oxidant pollutants may be similar to the one that controls resistance to other extremes in environmental factors. From the literature the following generalizations can be made in regard to the factors that affect the sensitivity of plants to oxidant air pollutants during growth: plants are more sensitive when grown under a short photo-period, a long dark period prior to exposure increases sensitivity; plants grown under low light intensities are more sensitive to ozone and less sensitive to PAN; low temperatures for one to several days prior to exposure reduce sensitivity; plants grown under drought conditions are less sensitive; plants grown under relatively low fertility levels are more sensitive. Sensitivity at time of exposure increases with increasing light intensity. Sensitivity of plants exposed under natural conditions is affected more by light intensity than by temperature. Temperature has an inverse effect on sensitivity, when plants are exposed under controlled lighting conditions. High carbon dioxide levels, at time of exposure, reduce sensitivity. Plants exposed under any soil conditions that produce a water stress in the plant show an increased resistance. Plant sensitivity, at time of exposure, increases with an increase inmore » humidity. Injury from PAN is mediated by a light-sensitive system within the plant. Sulfur dioxide reacts synergistically, with both ozone and nitrogen dioxide, on sensitive plant tissues. 101 references.« less

Phototropic "Indifference" and the Light-Sensitive System of Phycomyces

1. Sporangiophores of Phycomyces of high sensitivity to light, stimulated by exposure to unilateral illumination of sufficiently high intensity, fail to give the usual phototropic response. This condition is known as phototropic "indifference." 2. Sporangiophores which exhibit such indifference are nevertheless shown to give a distinct direct growth response as a consequence of the same unilateral illumination. The state of indifference is therefore not characterized by the absence of photic excitation, but by the failure of the light to evoke a differential acceleration of growth on the two sides of the sporangiophore. 3. Stimulation of sensitive "indifferent" sporangiophores by flashes of light of progressively reduced duration of exposure leads to the discovery of a critical duration below which indifference is abolished and phototropic bending occurs. 4. The critical duration of exposure to light for the appearance of the phototropic response corresponds to the critical duration of exposure for minimum reaction time in the direct growth response. 5. Phototropic bending therefore appears when the action of light on one side of the sporangiophore is submaximal. Conversely, indifference is due to equal and maximal photochemical action on both sides.

PHOTOTROPISM AND THE LIGHT-SENSITIVE SYSTEM OF PHYCOMYCES

1. The reaction time of the direct growth response of the sporangiophore of Phycomyces to light consists of a series of at least three major identifiable components: (a) an exposure period during which photochemical change occurs; (b) a latent period involving products directly consequent upon the photochemical action; and (c) an action-time occupying a further interval before the growth acceleration appears. 2. The reaction time of the phototropic response of the sporangiophore following stimulation by unilateral illumination is also compound, and is made up of at least three components comparable to those of the direct growth response. 3. The reaction time of each mode of response is constant for a particular intensity of illumination, provided that the duration of the exposure period exceeds a certain value. Below that value the reaction time increases progressively as the exposure time decreases. 4. The reaction time of each mode of response is found to vary similarly as a function of the duration of exposure to light. It is therefore concluded that the two responses are based on the same light-sensitive system. This conclusion accords with the conception of plant phototropism developed by Blaauw. 5. If a constant representing the action-time is subtracted from the reaction times for either mode of response, the reciprocals of the resulting numbers follow a linear sequence when plotted against the durations of the exposure to light. The rate of the process occurring during the latent period is therefore considered to be directly proportional to the amount of preceding photochemical change.

The Light-Sensitive System as the Basis of the Photic Responses of Phycomyces

The Light-Sensitive System as the Basis of the Photic Responses of Phycomyces