Primary Chromophore Research Articles

Clarifying the role of carboxyl functionality in squaraines towards aggregation and self-assembly through photophysical characterization and BSA interactions

The demand for near-infrared (NIR) probes with robust and stable fluorescence signals has surged, driven by their applications in optical sensing and bioimaging. Squraine dyes as NIR fluorescent probes have gained significant traction. However, understanding their behavior in aqueous media is important for their successful application. Herein we report the synthesis and photophysical characterization of carboxy-functionalized unsymmetrical squaraine dyes capable of light absorption and emission in the near-infrared (NIR) wavelength region. Structural variations in alkyl chain length, and spacer chain length between the primary chromophore and –COOH group were systematically introduced to investigate their impact on self-assembly in aqueous media leading to dye aggregation and their differential interactions with Bovine Serum Albumin (BSA) as a model protein. In phosphate buffer (PB) the absorption intensity decreased drastically along with pronounced shoulders due to dye aggregation leading to complete fluorescence quenching. However, in the presence of BSA, the intensity of shoulder bands reduced coupled with a sharp increase in the absorption associated with monomeric dye with the increasing concentration of BSA, indicating the prevention of dye aggregation owing to dye-BSA interactions. The prevention of dye aggregation due to dye-BSA interaction also led to a tremendous increase in the fluorescence intensities as a function of the increasing BSA concentrations. Site-selective study off BSA showed that these dyes bind preferably at Site-II using hydrophilic interactions. Thus, these dyes show great potential as FRET or fluorescent on/off probes for biosensing, non-covalent labeling of proteins, and fluorescent probes for bioimaging.

Magmatic-hydrothermal evolution of the aquamarine-bearing Yamrang Pegmatite, Eastern Nepal: Insights from beryl, garnet, and tourmaline mineral chemistry

The Ikhabu Pegmatite Field (IPF) in the Nepal Himalaya is a newly discovered rare-element (REL) pegmatite field that hosts the Yamrang pegmatite, the primary source of the famous Nepalese aquamarines. In this contribution, we provide a comprehensive description of the geology of both the IPF and the Yamrang pegmatite, offering insights into the evolutionary stages of the Yamrang pegmatite based on its internal texture and the mineral chemistry of beryl, garnet, and tourmaline. The Yamrang pegmatite is classified as a beryl-columbite subtype of REL pegmatite, exhibiting axial symmetric zonation and is differentiated into five mineralogical-textural zones during magmatic and hydrothermal stages. The magmatic stage involves undercooling, disequilibrium crystallization, and fractional crystallization whereas the hydrothermal stage comprises alkali-enriched fluid exsolution, the formation of miarolitic cavities, and the crystallization of aquamarine. Yamrang aquamarines are enriched in FeO, up to 1.1 wt%, with Fe2+ as the primary chromophore, resulting in their blue color. Two types of beryl have been identified: magmatic beryl in zones 3 and 4 and hydrothermal beryl in miarolitic cavities (zone 5). Magmatic beryls are characterized by their alkali-poor to sodic composition, prismatic to columnar habit, homogeneous texture, and the presence of Fe-Al octahedral substitution. In contrast, hydrothermal beryls belong to the sodic to Li-Cs beryl group, with tabular to acicular habit, weak compositional zoning, and channel-tetrahedral substitution. Yamrang garnet belongs to the almandine-spessartine series, while the tourmalines are Mg-Ca rich dravite-schorl to Fe-Mn rich schorl variety. Alkali-poor to Li-Cs beryl with low REE contents, spessartine garnet (spessartine component, Xsps ∼ 52) with high HREE, and schorl with high Ti but low Li, Pb, and REE contents suggests that the Yamrang Pegmatite is an intermediate-fractionated REL pegmatite. Potential pegmatite evolution indicators for IPF include high alkali, Fe, Mn, and Rb contents in beryl, high Xsps in garnet, and an increase in Li, Fe, Mn, Zn, Ga, and Nb, alongside depletion of Mg, Ca, Ti, and Ta in schorl. The identification of a rare metal pegmatite field in the Nepalese Himalaya reinforces the general rare metal mineralization potential of the entire Himalaya region.

On the unusual Stokes shift in the smallest PPE dendrimer building block: Role of the vibronic symmetry on the band origin?

1,3-Bis(phenylethynyl)benzene is the primary chromophore of the light-harvesting polyphenylene ethynylene (PPE) dendrimers. It is experimentally known to share the same absorption spectrum as its pair of diphenylacetylene (aka. tolane) meta-substituted branches yet exhibits an unusual Stokes shift of about 2000 cm-1 with respect to its band origin (corresponding to the loss of one vibrational quantum within the antisymmetric acetylenic stretching) in its emission spectrum. We suggest, in the present work, the unusual but plausible involvement of molecular symmetry selection rules in a situation where the Born-Oppenheimer approximation is far to be valid. Our hypothesis is comforted with quantum dynamics simulations of absorption and emission UV-visible spectra based on the quantum chemistry data and a diabatic vibronic coupling Hamiltonian model.

Role of opsins and light or heat activated transient receptor potential ion channels in the mechanisms of photobiomodulation and infrared therapy

Photobiomodulation (otherwise known as low level light therapy) is an emerging approach for treating many diseases and conditions such as pain, inflammation, wound healing, brain disorders, hair regrowth etc. The light used in this therapy generally lies in the red and near-infrared spectral regions. Despite many positive studies for treating different conditions, this therapy still faces some skepticism, which has prevented its widespread adoption in clinics. The main reasons behind this skepticism are the lack of comprehensive information about the molecular, cellular, and tissular mechanisms of action, which underpin the positive effects of photobiomodulation. Moreover, there is also another therapeutic application using longer wavelength infrared radiation, involving either infrared saunas or heat lamps which are powered by electricity, as well as infrared emitting textiles and garments which are solely powered by the wearer's own body heat. In recent years, much knowledge has been gained about the mechanism of action underlying these treatments, which will be summarized in this review. There are three broad classes of primary chromophores, which have so far been identified. One is mitochondrial cytochromes (including cytochrome c oxidase), another is opsins and light or heat-sensitive calcium ion channels, and a third is nanostructured water clusters. Light sensitive ion channels are activated by the absorption of light by the chromophore proteins, opsin-3 and opsin-4, while mitochondrial chromophores are activated by red or near-infra red (NIR) light up to about 850 nm. However NIR light at 980 nm or longer wavelengths can activate transient receptor potential (TRP) ion channels, probably after being absorbed by nanostructured water clusters. Heat-activated TRP channels undergo a conformational change triggered by only small temperature changes. Here we will discuss the role of opsins and light or heat activated TRP channels in the mechanism of photobiomodulation and infrared therapy.

En bloc resection for nonmuscle-invasive bladder cancer: selecting a proper laser.

To discuss the most recent surgical lasers that have been made available to us and to evaluate their potential in performing en bloc resection of nonmuscle invasive bladder cancer. Laser en bloc resection of bladder tumors (ERBT) can be performed with a number of laser systems including Ho:YAG, GreenLight, diode, Tm:YAG and thulium fiber lasers (TFL). The data that is currently available suggests that the water-targeting devices (utilizing water as a primary chromophore - Ho:YAG, Tm:YAG, TFL) may have a number of advantages over hemoglobin-targeting systems (potassium titanyl phosphate:YAG, lithium triborate:YAG). One recent addition to the surgical armamentarium Moses effect enhanced Ho:YAG and the TFL (being able to work both in quasi-continuous and SuperPulsed modes) necessitates careful discussion and comparison with the other available devices. The majority of available lasers have proven to be safe to use and compared to electrocautery allow for lower rates of obturator nerve reflex and result in fewer bleeding complications. The minimal penetration depth and decreased peak power of Tm:YAG and TFLs render them the devices of choice when it comes to ERBT. Unfortunately, more studies on ERBT with TFL are needed in order for us to make a sound assessment of the respective pros and cons.

Laser endoscopic procedures on the prostate: it is the small details that count.

This review aims to highlight the pros and cons of each laser device and to consider additional possible milestones for the development of laser technologies in the surgical treatment of benign prostate hyperplasia. Over the last three decades, lasers' role in endourology has gone from strength to strength. Specifically, the primary techniques where laser surgery for BPO relief is concerned are vaporization and enucleation. The idea behind vaporization is that lasers are able to vaporize substantial amounts of tissue due to deep ablation depth and increased power. The most efficient devices for vaporization are those affecting hemoglobin as primary chromophore and/or using a continuous firing mode (KTP/LBO:YAG, diode lasers, Tm:YAG). As for enucleation, multiple devices have been suggested for the adequate anatomical enucleation of the prostate (EEP). As it is a skill-dependent technique, the EEP is effective irrespective of which device the surgeon uses. However, some devices have shown significant advances where enucleation is concerned. The choice of device should be based primarily on the technique the surgeon prefers. Although the most suitable lasers for vaporization are hemoglobin-targeting and/or continuous wave devices, the EEP may be done with any enough powered laser, yet some provides specific effects which you should be aware before the surgery.

Focus on UV-Induced DNA Damage and Repair—Disease Relevance and Protective Strategies

The protective ozone layer is continually depleting due to the release of deteriorating environmental pollutants. The diminished ozone layer contributes to excessive exposure of cells to ultraviolet (UV) radiation. This leads to various cellular responses utilized to restore the homeostasis of exposed cells. DNA is the primary chromophore of the cells that absorbs sunlight energy. Exposure of genomic DNA to UV light leads to the formation of multitude of types of damage (depending on wavelength and exposure time) that are removed by effectively working repair pathways. The aim of this review is to summarize current knowledge considering cellular response to UV radiation with special focus on DNA damage and repair and to give a comprehensive insight for new researchers in this field. We also highlight most important future prospects considering application of the progressing knowledge of UV response for the clinical control of diverse pathologies.

Skin Chromophore Estimation from Mobile Selfie Images using Constrained Independent Component Analysis

Human skin is made up of two primary chromophores: melanin, the pigment in the epidermis giving skin its color; and hemoglobin, the pigment in the red blood cells of the vascular network within the dermis. The relative concentrations of these chromophores provide a vital indicator for skin health and appearance. We present a technique to automatically estimate chromophore maps from RGB images of human faces captured with mobile devices such as smartphones. The ultimate goal is to provide a diagnostic aid for individuals to monitor and improve the quality of their facial skin. A previous method approaches the problem as one of blind source separation, and applies Independent Component Analysis (ICA) in camera RGB space to estimate the chromophores. We extend this technique in two important ways. First we observe that models for light transport in skin call for source separation to be performed in log spectral reflectance coordinates rather than in RGB. Thus we transform camera RGB to a spectral reflectance space prior to applying ICA. This process involves the use of a linear camera model and Principal Component Analysis to represent skin spectral reflectance as a lowdimensional manifold. The camera model requires knowledge of the incident illuminant, which we obtain via a novel technique that uses the human lip as a calibration object. Second, we address an inherent limitation with ICA that the ordering of the separated signals is random and ambiguous. We incorporate a domain-specific prior model for human chromophore spectra as a constraint in solving ICA. Results on a dataset of mobile camera images show high quality and unambiguous recovery of chromophores.

Research Techniques Made Simple: Cutaneous Colorimetry: A Reliable Technique for Objective Skin Color Measurement

Skin color evaluation contributes to assessment of an individual's cutaneous phenotype. Skin color changes provide important clues to disease progression or treatment response. Skin color is also a predictor of skin cancer risk. Melanin pigment, blood flow, skin thickness, and photoaging contribute to skin color. Melanin, hemoglobin, bilirubin, and carotene are the primary chromophores of skin color. Their concentrations vary depending on the individual's phenotype, anatomic location, external insults of chemical irritants and UVR, and physiological changes. The evaluation and perception of skin color are often subjective. Objective quantification of skin color can be achieved with colorimetric devices such as tristimulus colorimeters. These devices compute the intensity of light reflected from skin and correlate with pigmentation and erythema. Cutaneous color and color changes can be quantified under color organization systems, such as the CIELAB color space, which is standardized by the Commission Internationale de l'Eclairage (CIE). The CIELAB expresses color's lightness, red/green intensity, and yellow/blue intensity, as L*, a*, and b* values, respectively. Additionally, skin color's full spectral characteristics and cutaneous physiology can be measured with spectrophotometers. This article outlines basic principles of the CIELAB color system and how to optimally use colorimetric devices as a skin research tool.

Progressive aging changes in the optical properties of Rat brain

The objective of this study to investigate how molecular changes caused by aging effects the absorption and fluorescence of cerebral cortex during the postnatal development in the rat. The aging dependent changes in the absorption and fluorescence properties of native chromophores in rat cerebral cortex were studied at postnatally from neonatal stage to adulthood at days 5,10, 15, and 45. The primary chromophores in brain are responsible for specific absorption and/or fluorescence emission are collagen, tryptophan, NADH, flavins and water. The evolution in the relative concentrations of these key chromophores in the rat brains progressively with increasing age is presented. Understanding changes in the optical properties with age will help in developing better understanding the underlying development of molecular components in the brain and for imaging strategies for methods like optical tomography and multiphoton brain imaging.

Mechanisms and applications of the anti-inflammatory effects of photobiomodulation.

Photobiomodulation (PBM) also known as low-level level laser therapy is the use of red and near-infrared light to stimulate healing, relieve pain, and reduce inflammation. The primary chromophores have been identified as cytochrome c oxidase in mitochondria, and calcium ion channels (possibly mediated by light absorption by opsins). Secondary effects of photon absorption include increases in ATP, a brief burst of reactive oxygen species, an increase in nitric oxide, and modulation of calcium levels. Tertiary effects include activation of a wide range of transcription factors leading to improved cell survival, increased proliferation and migration, and new protein synthesis. There is a pronounced biphasic dose response whereby low levels of light have stimulating effects, while high levels of light have inhibitory effects. It has been found that PBM can produce ROS in normal cells, but when used in oxidatively stressed cells or in animal models of disease, ROS levels are lowered. PBM is able to up-regulate anti-oxidant defenses and reduce oxidative stress. It was shown that PBM can activate NF-kB in normal quiescent cells, however in activated inflammatory cells, inflammatory markers were decreased. One of the most reproducible effects of PBM is an overall reduction in inflammation, which is particularly important for disorders of the joints, traumatic injuries, lung disorders, and in the brain. PBM has been shown to reduce markers of M1 phenotype in activated macrophages. Many reports have shown reductions in reactive nitrogen species and prostaglandins in various animal models. PBM can reduce inflammation in the brain, abdominal fat, wounds, lungs, spinal cord.

Chromophores in lignin-free cellulosic materials belong to three compound classes. Chromophores in cellulosics, XII

The chromophore release and identification method isolates well-defined chromophoric substances from different cellulosic matrices, such as highly bleached pulps, cotton linters, bacterial cellulose, viscose or lyocell fibers, and cellulose acetates. The chromophores are present only in extremely low (ppm to ppb) concentrations. The concept of primary and secondary chromophores is introduced, with primary chromophores arising only from the polysaccharides inherent to cellulosic materials. Secondary chromophores also include atoms from the chemicals used to process the cellulose. Most primary chromophores belong to one of three compound classes: hydroxy-[1,4]-benzoquinones, hydroxy-[1,4]-naphthoquinones, and hydroxyacetophenones. Among them, three individual compounds dominate: 2,5-dihydroxy-[1,4]-benzoquinone, 5,8-hydroxy-[1,4]-naphthoquinone, and 2,5-dihydroxyacetophenones, amounting to more than 80 % of the total isolated chromophores in most cases. In lignin-free cellulosics, these three compounds can thus be regarded as key chromophores. The prevalence of these molecules is due to both exceptionally strong resonance stabilization, as reflected in delocalized double bonds, and their ready reformation from carbohydrate degradation products by recondensation reactions. The findings that (a) most chromophores in lignin-free cellulosic materials belong to only three compound classes and that (b) three chromophore compounds make up the bulk of the chromophore mixtures are foundational for future bleaching research: Based on this knowledge, specific searches for optimized bleaching conditions can now concentrate on these compounds and still cover the vast majority of chromophores.

Multispectral Endoscopic Imaging of Colorectal Dysplasia In Vivo

Light provides a broad range of colors in the visible and near-infrared (400–900 nm) spectrum that can be used to transmit information about molecular expression in normal and diseased tissues. The absorbance spectrum of hemoglobin, the primary chromophore in tissue, is shown in Fig. 1A. Genetic changes that occur in cancer transformation can be heterogeneous, and several signaling pathways may be activated concurrently.1 Moreover, molecular activity levels may vary between individual patients, at different time points, and within the tumor. Thus, a single genetic mutation is unlikely to characterize most disease processes over a general population. Unfortunately, most endoscopic imaging methods are sensitive to only one molecular parameter.2 Thus, a methodology that can image multiple molecular targets simultaneously is better suited to address the heterogeneity of cancer and achieve disease detection with high sensitivity and specificity desired for efficient surveillance. In addition, these multiplexed strategies can potentially visualize the interactions between signaling pathways and allow for better understanding of disease pathogenesis on a systems level. Figure 1 A) The visible and near-infrared spectrum of light provides a broad range of colors to generate molecular images from digestive tract mucosa that can be collected with a B) 1.6 mm diameter multispectral scanning fiber endoscope. C) Excitation is delivered ... Recently, significant progress has been made in advancing new methods of endoscopic imaging to target disease in the digestive tract, including the development of novel instruments and specific contrast agents.3 In this video journal, we aim to demonstrate the application of a novel, multispectral endoscope that uses a scanning fiber to image multiple targets at the same time. Fluorescence imaging can be achieved with high target-to-background ratios, and allow us to see the different target expression patterns in an Apc-mutation dependent mouse model of spontaneous colorectal adenomas using multiple peptides as targeting ligands.4

Decreased Efficiency of Potassium-Titanyl-Phosphate Laser Photoselective Vaporization Prostatectomy with Long-Term 5 alpha–Reductase Inhibition Therapy: Is it True?

5 Alpha-reductase inhibitors (5ARIs) reduce angiogenesis in benign prostatic tissue. This has been postulated to affect the efficiency of the potassium-titanyl-phosphate (KTP) laser during photoselective vaporization prostatectomy (PVP), which has hemoglobin as its primary chromophore. We evaluate KTP laser PVP as treatment for benign prostatic hyperplasia (BPH) in patients on long-term 5ARIs. We prospectively evaluated our initial 12 month KTP laser PVP experience with patients without or with 5ARIs. Transurethral PVP was performed with the use of an 80W KTP side-firing laser system. Voiding trials were performed 2 hours after surgery. International Prostate Symptom Score (IPSS), maximum flow rate (Qmax), and postvoid residual (PVR) were measured preoperatively and at 1, 4, 12, 24, and 52 weeks after surgery. One hundred sixty consecutive patients were identified, of which 117 were not on a 5ARI and 43 were on either finasteride or dutasteride for at least 6 months. Mean prostate volumes were 72.8 +/- 49.5 cm3 and 70.8 +/- 49.1 cm3 (P = 0.39), respectively. There were no significant differences in the parameters of laser time (32.0 +/- 27.6 minutes and 37.0 +/- 36.2 minutes) and energy usage (97.4 +/- 91.6 kJ and 103.3 +/- 86.0 kJ). All were outpatient procedures with the majority of patients catheter-free at discharge. All patients were able to discontinue their prostate medications after surgery. IPSS, Qmax, and PVR values showed significant improvement within each group, but the degree of improvement between the 2 groups did not show statistical significance. Our experience suggests that 5ARIs do not have a detrimental effect on the efficiency and efficacy of KTP laser PVP.

Benzil-Tethered Precipitons for Controlling Solubility: A Round-Trip Energy-Transfer Mechanism in the Isomerization of Extended Stilbene Analogues

We are investigating photoresponsive molecules called "precipitons" that undergo a solubility change co-incident with isomerization. Isomerization can be induced by light or by catalytic reagents. Previous work demonstrated that covalent attachment of a metal complex, Ru(II)(bpy)3, greatly accelerates photoisomerization and influences the photostationary state. In this paper, we describe precipitons (1,2-biphenylethenes; analogous to stilbenes) that are activated by a covalently attached organic sensitizer (benzil). We find that isomerization of these stilbene analogues is little effected by the presence of benzil in solution but that the intramolecular benzil effect is to increase the rate of isomerization and to significantly change the photostationary state. What is most interesting about these observations is that the precipiton is the primary chromophore in this bichromophoric system (precipiton absorbance is many times greater than benzil absorbance in the 300-400 nm range), yet the neighboring benzil has a significant effect on the rate and the photostationary state. The effect of unattached benzil on the rate was small, about a 24% increase in rate as compared with 4-6-fold changes for an attached benzil. We speculate that the isomerization process occurs by a "round-trip" energy-transfer mechanism. Initial excitation of the precipiton chromophore initiates a sequence that includes (1) formation of the precipiton singlet state, (2) singlet excitation transfer from the precipiton unit to the benzil, (3) benzil-centered intersystem crossing to the localized benzil triplet state, (4) triplet energy transfer from the benzil moiety back to the precipiton, and (5) isomerization.

Determination of the debris produced from poly(ethylene terephthalate) during KrF excimer laser ablation

Pulsed UV laser beams, which are widely used in the processing of polymers, have many advantages because their photon energy is higher than the binding energy of polymers. Fabricating polymers with a UV laser process is faster, cleaner, and more convenient than with other processes. Nevertheless, some problems occur in the precision microprocessing of polymers. For example, the formation and deposition of surface debris, which is produced from the breakdown of either polymer chains or radical bonds. To determine the formation and origin of surface debris, a KrF excimer laser beam (248 nm) was used in the processing of poly(ethylene terephthalate) (PET). The investigation of the debris formation was facilitated by UV–vis spectroscopy, ATR FT-IR spectroscopy, and NMR spectroscopy. The UV–vis absorption peak indicates that the primary chromophore in the PET is benzoate. Furthermore, because benzoate causes the primary absorption, the absorbed energy is transferred by heat generation to an unsaturated ester. The ATR FT-IR spectrometer measurements show that the phenyl systems in the benzoate are demolished by ablation. This phenomenon indicates that the photochemical reaction causes the benzoate bonds to break down, and this breakdown in turn causes the carbonization to leave debris on the PET.

Characterization of the purity and stability of commercially available dichlorotriazine chromophores used in nonlinear optical materials

Nonlinear optical (NLO) materials consisting of organic chromophores have unique optical properties due to the polar molecular structure and noncentrosymmetric ordering of the chromophores. Chromophores with dichlorotriazine moieties can be incorporated with a consistent polar ordering into layer-by-layer films via covalent reaction with a nucleophilic polymeric species. While the manufacture of optical materials traditionally requires highly pure reagents, commercially available azo dyes originally manufactured for textile industry use are usually impure. The purities of three commercially available chromophores, Reactive Red 2, Reactive Orange 4, and Reactive Brown 23, that are being used in NLO materials research were determined by HPLC and found to be highly variable. MALDI-TOF MS analysis of collected HPLC peaks was used to confirm the identity of the chromophores and impurities that resulted from basic hydrolysis. Additionally, since noncentrosymmetric deposition of these chromophores into NLO films occurs at basic pH and hydrolyzed chromophores are not reactive, the stability of the chromophores at pH 10.5 was determined. Base hydrolysis experiments also revealed whether other impurities in the dyes were reactive. Because the layer-by-layer method of making NLO films relies on covalent reaction, the presence of non-reactive impurities may not be a critical issue. However, reactive impurities can take up space and inhibit incorporation of the primary chromophore in the film, and if their dipole moment orientation is different, they may cancel out the molecular ordering of the primary chromophore and further decrease NLO performance.

Photophysical Study of Local Anesthetics in Reverse Micelles and Water-Ethanol Mixtures

Fluorescence emission from three tertiary amine local anesthetics, dibucaine (D), tetracaine (T), and procaine (P) was investigated in the membrane-mimetic environment of AOT/isooctane reverse micelles and water-ethanol mixtures. At room temperature all three show broad UV absorption bands and large Stokes' shifts in emission from aqueous medium. In reverse micelles the emission bands are blue-shifted, with the magnitude of this shift decreasing continuously as the waterto-surfactant molar ratio (w0) of the micelles is increased. The emission intensity of D is much stronger in water and in the interior of micelles than in ethanol, whereas for T and P the emission in water is much weaker than in ethanol and in micelles. Whereas the behavior in micelles is the result of the increased hydrophobicity with respect to bulk water in their interior, that in waterethanol mixtures may be explained on the basis of state reversal of the excited electronic levels of D with increasing hydrogen bonding capability of the solvent mixture. The steady-state anisotropy for both T and P is unusually high in bulk water (∼0.27) and increases with increasing w0 in micelles. However, the rotational correlation time of the anesthetics, as calculated using Perrin's equation, decreases with increasing w0, as expected from physical considerations relating the size of the water pool to the ease of rotational relaxation of probe molecules inside micelles. Together, these results point to a marked difference in emission properties between D on one hand and T and P on the other, arising from differences in electronic characters of their primary emitting chromophores—quinoline for D, para amino benzoate for T and P.

Photochemically induced redox reactions in seawater, II. Nitrogen and iodine

Abstract Experiments have been conducted to determine whether the speciation of the nitrate-nitrite and iodate-iodide redox couples is influenced by light and organic matter in both deionised and sea waters. The results obtained indicate that photochemical production of nitrite occurs and that the rate of this reaction is dependent on the concentration of organic matter present in the system. The findings suggest that nitrate undergoes not only direct photochemical reaction, acting itself as a primary chromophore, but also a photochemically induced reduction through organic matter. This reaction is, however, unlikely to influence productivity to any great extent as most phytoplankton can use both species as nutrients. It may, however, be a source of the highly reactive hydroxyl radical and of NO which has the potential to degas to the atmosphere and there help to regulate ozone concentration. Experiments conducted on the iodine redox system similarly indicate that photochemically induced production of iodide occurs. The results show that the reaction is not biologically mediated and that the presence of organic matter is essential for iodide photoproduction. At the concentrations of added iodate used in the experiments no direct 1:1 relationship between iodate and iodide is seen. It is suggested that, under these conditions, organic matter is not only essential for the photochemical production of iodide but that it is also the limiting species for the reduction reaction.

Induction of slowly developing alkali-labile sites in human P3 cell DNA by UVA and blue- and green-light photons: action spectrum.

Action spectra (365-520 nm) for the formation of DNA single-strand breaks (SSB) and slowly developing alkali-labile sites (SDALS) in human teratocarcinoma P3 cells in culture were determined. Induction of SDALS results from the absorption of blue- and green-light photons. The spectrum has a broad peak that is maximal between 400 nm to 500 nm and declines sharply above and below these wavelength regions. Negligible yields of SDALS were produced by photons at wavelengths of 365 nm or shorter and at 520 nm or longer, whereas for SSB, the action ioffeases with shorter wavelength throughout the whole spectral range studied. The configuration of the SDALS action spectrum suggests that the primary chromophore, and therefore possibly the photosensitizer, is a mixture of porphyrin and flavin residues.