IoT-Based Sensor Data Fusion for Determining Optimality Degrees of Microclimate Parameters in Commercial Greenhouse Production of Tomato.

Optimum microclimate parameters, including air temperature (T), relative humidity (RH) and vapor pressure deficit (VPD) that are uniformly distributed inside greenhouse crop production systems are essential to prevent yield loss and fruit quality. The objective of this research was to determine the spatial and temporal variations in the microclimate data of a commercial greenhouse with tomato plants located in the mid-west of Iran. For this purpose, wireless sensor data fusion was incorporated with a membership function model called Optimality Degree (OptDeg) for real-time monitoring and dynamic assessment of T, RH and VPD in different light conditions and growth stages of tomato. This approach allows growers to have a simultaneous projection of raw data into a normalized index between 0 and 1. Custom-built hardware and software based on the concept of the Internet-of-Things, including Low-Power Wide-Area Network (LoRaWAN) transmitter nodes, a multi-channel LoRaWAN gateway and a web-based data monitoring dashboard were used for data collection, data processing and monitoring. The experimental approach consisted of the collection of meteorological data from the external environment by means of a weather station and via a grid of 20 wireless sensor nodes distributed in two horizontal planes at two different heights inside the greenhouse. Offline data processing for sensors calibration and model validation was carried in multiple MATLAB Simulink blocks. Preliminary results revealed a significant deviation of the microclimate parameters from optimal growth conditions for tomato cultivation due to the inaccurate timer-based heating and cooling control systems used in the greenhouse. The mean OptDeg of T, RH and VPD were 0.67, 0.94, 0.94 in January, 0.45, 0.36, 0.42 in June and 0.44, 0.0, 0.12 in July, respectively. An in-depth analysis of data revealed that averaged OptDeg values, as well as their spatial variations in the horizontal profile were closer to the plants' comfort zone in the cold season as compared with those in the warm season. This was attributed to the use of heating systems in the cold season and the lack of automated cooling devices in the warm season. This study confirmed the applicability of using IoT sensors for real-time model-based assessment of greenhouse microclimate on a commercial scale. The presented IoT sensor node and the Simulink model provide growers with a better insight into interpreting crop growth environment. The outcome of this research contributes to the improvement of closed-field cultivation of tomato by providing an integrated decision-making framework that explores microclimate variation at different growth stages in the production season.

Soft gripper for small fruits harvesting and pick and place operations.

Agriculture 4.0 presents several challenges for the automation of various operations, including the fundamental task of harvesting. One of the crucial aspects in the automatic harvesting of high value crops is the grip and detachment of delicate fruits without spoiling them or interfering with the environment. Soft robotic systems, particularly soft grippers, offer a promising solution for this problem, as they can operate in unstructured environments, manipulate objects delicately, and interact safely with humans. In this context, this article presents a soft gripper design for harvesting as well as for pick-and-place operations of small and medium-sized fruits. The gripper is fabricated using the 3D printing technology with a flexible thermoplastic elastomer filament. This approach enables the production of an economical, compact, easily replicable, and interchangeable gripper by utilizing soft robotics principles, such as flexible structures and pneumatic actuation.

Design and evaluation of a power tiller vegetable seedling transplanter with dibbler and furrow type.

Vegetable production plays a vital role in ensuring food security in Bangladesh. However, the majority of vegetable seedlings are currently transplanted manually, which is not only time-consuming but also labor-intensive and costly. In this context, a semi-automated transplanter can be considered as an alternative solution for mechanized seedling transplanting. To mechanize seedling operations, two types of transplanters were designed, fabricated and tested: the power tiller-operated semi-automatic dibbler vegetable seedling (DVS) transplanter and the furrow opener vegetable seedling (FVS) transplanter. The goal was to evaluate their performance and impact on field crop productivity. In the DVS transplanter design, the larger sprocket was adjusted to enhance the precision of hole-making by pressing the dibbler into the soil, creating holes where seedlings would be transplanted. On the other hand, the FVS transplanter utilized a furrow opener to create furrows, and the seedling is placed in these furrow at a specific distance from the furrow opener wall, where the distance between seedlings within the furrow could be adjusted based on the specific requirements of the seedling crop. The results of the evaluation indicated that both transplanters successfully planted seedlings without any missing placements, while hole covering was achieved at 115 and 118.2% for the DVS and FVS transplanters, respectively. The field capacity and field efficiency for both transplanters were determined to be 0.05 ha h-1 and 61.18%, respectively, with a coefficient of variation of 5% or less. Field tests conducted with brinjal crops at a forward speed of 1.2 km h-1 and a spacing of 0.7 × 0.6 m demonstrated that both designs yielded higher yield productivity compared to manual transplantation. Additionally, no issues related to vegetative development were observed. Both transplanters exhibited promising performance and significant potential in terms of accurately transplanting seedlings, and ensuring satisfactory transplantation quality. Furthermore, these transplanters offer several advantages, including less time-consuming, lower labor demands and even distribution of seedlings. This design encourages small to medium-level farmers seeking to engage in mechanized vegetable farming practices.

Light-activated tissue bonding for excisional wound closure: a split-lesion clinical trial.

BACKGROUND: Apposition of wound edges by sutures provides a temporary scaffold and tension support for healing. We have developed a novel tissue-sealing technology, photoactivated tissue bonding (PTB), which immediately crosslinks proteins between tissue planes, thereby sealing on a molecular scale. OBJECTIVES: To determine the effectiveness of PTB for superficial closure of skin excisions and to compare the results with standard epidermal suturing. METHODS: A split-lesion, paired comparison study of 31 skin excisions was performed. Following deep closure with absorbable sutures, one-half of each wound was superficially closed with nonabsorbable nylon sutures while the other half was stained with Rose Bengal dye and treated with green light. Overall appearance and scar characteristics were rated at 2weeks and 6months in a blinded manner by three dermatologists viewing photographs, by two onsite physicians and by patients. RESULTS: At 2weeks, neither sutured nor PTB-treated segments showed dehiscence; however, PTB-sealed segments showed less erythema than sutured segments as determined by photographic (P=0·001) and onsite evaluations (P=0·005). Overall appearance after PTB was judged better than after sutures (P=0·002). At 6months, scars produced by PTB were deemed superior to scars resulting from sutures in terms of appearance (P<0·001), width (P=0·002) and healing (P=0·003). Patients were more satisfied with the appearance of the PTB-sealed wound half after 2weeks and 6months (P=0·013 and P=0·003, respectively). CONCLUSIONS: A novel molecular suturing technique produces effective wound sealing and less scarring than closure with nylon interrupted epidermal sutures. Comparisons with better suturing techniques are warranted.

Effect of In Vitro Digestion on the Antioxidant and Angiotensin-Converting Enzyme Inhibitory Potential of Buffalo Milk Processed Cheddar Cheese.

The purpose of this study was to develop an in-vitro digestion protocol to evaluate the antioxidant potential of the peptides found in processed cheddar cheese using digestion enzymes. We first studied antioxidant and angiotensin-converting enzyme (ACE) inhibition and antioxidant activities of processed cheddar cheese with the addition of spices e.g., cumin, clove, and black pepper made from buffalo milk and ripened for 9 months. Then we conducted an in vitro digestion of processed cheddar cheese by gastric and duodenal enzymes. Freeze-dried water (WSE) and ethanol-soluble fractions (ESE) of processed cheddar cheese were also monitored for their ACE inhibition activity and antioxidant activities. In our preliminary experiments, different levels of spices (cumin, clove, and black pepper) were tested into a cheese matrix and only one level 0.2 g/100 g (0.2%) based on cheese weight was considered good after sensory evaluation. Findings of the present study revealed that ACE-inhibitory potential was the highest in processed cheese made from buffalo milk with the addition of 0.2% cumin, clove, and black pepper. A significant increase in ACE-inhibition (%) of processed cheddar cheese, as well as its WSE and ESE, was obtained. Lower IC50 values were found after duodenal phase digestion compared to oral phase digestion.

Assessment and Post-Intervention Recovery After Surgery for Lumbar Disk Herniation Based on Objective Gait Metrics from Wearable Devices Using the Gait Posture Index.

OBJECTIVE: Surgery for lumbar disk herniation (LDH) presents an option for patients when conservative measures fail. The objective of this clinical study is to investigate a novel, objective outcome measure in patients undergoing lumbar microdiscectomy. METHODS: Twenty-four patients were evaluated pre- and postoperatively using the Oswestry Disability Index (ODI), and a novel objective scoring tool, the Gait Posture index (GPi). The score is calculated from 4 key physical health metrics: daily step count, walking speed, step length, and walking posture. The GPi ranges from 0 (nonambulant) to 100 (excellent walking performance). Wearable accelerometers and observational recordings were used to evaluate the components of the GPi. The GPi was calculated and compared with the ODI, pre- and postintervention. The study was designed as a proof of concept and confirmation of validity for use of the GPi in LDH. RESULTS: At follow-up (average 66 ± 36 days), 23 of 24 patients had an improvement in their GPi after surgery. The average GPi of the cohort improved from 59.33 ± 16.06 to 85.75 ± 9.22 with P < 0.001, with significant changes in all 4 components. The average preoperative ODI was 54.54 ± 20.70, improving to 16.33 ± 14.095 with P < 0.001. The Pearson correlation coefficient was r = 0.56, indicating a correlation between change in ODI and change in GPi. CONCLUSIONS: The GPi score is a new, objective descriptor of mobility in spinal surgery which can be used to augment traditional subjective outcome scoring surveys such as the ODI. Significant changes are seen in the GPi and its constituent metrics in patients undergoing surgery for LDH.

A photobiological and photophysical-based study of phototoxicity of two chlorins.

To understand the fundamental determinants of phototoxic efficacy and absorbed photodynamic dose, the triplet state and photobleaching quantum yields in living cells, cellular uptake, intracellular localization, and correlation with cell viability were studied for the two purpurins tin ethyl etiopurpurin 1 (SnET2) and tin octaethylbenzochlorin (SnOEBC) in ovarian cancer cells (OVCAR5). Although the triplet yields of these two photosensitizers were not significantly affected by cellular incorporation, the photobleaching yields were shown to be 3 orders of magnitude higher for cellular-bound sensitizer than for free or albumin-bound photosensitizer and higher for SnET2 than for SnOEBC for all of the cases. The intracellular concentration of SnOEBC was half that of SnET2 after 3 h- and 24 h-incubation times for both 0.1 microM and 1.0 microM incubation concentrations. Despite the lower concentrations of SnOEBC, the phototoxicity of the two photosensitizers was comparable at 1-microM incubation concentration and was up to 10-fold higher for SnOEBC at the lower concentration. The subcellular localization established using confocal microscopy and molecular probes showed that both photosensitizers were primarily lysosomally localized. SnOEBC, however, had an extra-lysosomal, mitochondrial localization component. The photophysical measurements allowed calculation of the intracellular singlet oxygen production, which indicated that the photosensitizer-light dose reciprocity was limited by photobleaching for SnET2 but only minimally for SnOEBC, and this was confirmed through cell-survival studies. Taken together, these data indicate that the critical determinant of differences in phototoxicity between the two molecules was their relative rates of photobleaching and their subcellular localization. The study points to the importance of combining photosensitizer uptake and localization with photophysical measurements in the relevant biological milieu to reasonably interpret and/or predict photosensitization efficacies.

Photophysical properties of 3,3'-dialkylthiacarbocyanine dyes in organized media: unilamellar liposomes and thin polymer films.

All symmetrical dialkylthiacarbocyanine dyes, with the exception of the diethyl derivatives, are incorporated into liposomes. Absorption and fluorescence data indicate a solubilization site close to the bilayer surface with the alkyl chains penetrating into the lipid bilayer. Incorporation into organized assemblies affects the photophysical parameters of these dyes. Photoisomerization occurring from the first excited state becomes more difficult as the restrictive effect of the solubilization site increases. As a consequence, competing deactivation processes, such as fluorescence and triplet formation, become more efficient with the result that fluorescence quantum yields, triplet yields and singlet oxygen quantum yields are larger in liposomes than in homogeneous solution. Dihexylthiacarbocyanine iodide has a fluorescence quantum yield of 0.27 and 0.10 (25 degrees C) in dimyristoylphosphatidyl-choline liposomes and ethanol, respectively, and the singlet oxygen yield increases by a factor three to 0.006 on going from ethanol to liposomes. The effect of a highly organized environment is even more pronounced in thin polymer films. In these systems, photoisomerization is completely inhibited and only triplet formation is observed in the transient absorption spectrum.

Effects of structural modifications on the photosensitizing properties of dialkylcarbocyanine dyes in homogeneous and heterogeneous solutions.

The photophysical characterization of structurally modified symmetric dialkylthiacarbocyanine dyes in homogeneous and biomimetic media is reported. The aim of the two specific structural modifications was to increase singlet oxygen production, hence enhancing the photosensitizing properties of these cyanine dyes. Specifically, (1) the sulfur was exchanged with selenium in order to enhance intersystem crossing via an internal heavy atom effect and (2) substituents of differing size were introduced into the meso-position of the polymethine chain to reduce photoisomerization. The result of incorporation of an internal heavy atom (selenium) into the structure of the dye yields the expected effect: this modification results in a 22-fold increase in the rate of intersystem crossing, but does not change the remaining competing deactivation rates of the first excited singlet state. As a consequence, singlet oxygen quantum yields increase from 0.001 to 0.014 in ethanol and from 0.006 to 0.08 in unilamellar liposomes. In the case of the meso-substituted thiacarbocyanine dyes, a significant reduction in photoisomerization is indeed observed. However, this modification drastically enhances internal conversion which then becomes the main deactivation pathway of the first excited singlet state. As a result, very small fluorescence and singlet oxygen quantum yields are obtained, e.g. 0.006 and 0.001, respectively, in ethanol.

A wavelength dependent mechanism for rose bengal-sensitized photoinhibition of red cell acetylcholinesterase.

A 2-fold enhancement in the efficiency of rose bengal-photosensitized inhibition of red cell acetylcholinesterase activity was observed upon excitation of the dye in the ultraviolet (UV) (313 nm) compared to irradiation in the visible (514 or 550 nm). The measurements of efficiency of photosensitized enzyme inhibition were based on the effect produced when the same number of photons are absorbed by rose bengal (RB) at each wavelength. The mechanism for this unexpected enhancement of RB photosensitization upon UV excitation was investigated. The yield of singlet oxygen (O2(1 delta g], detected by time-resolved luminescence at 1270 nm, was independent of excitation wavelength for RB. Radicals were produced upon irradiation of RB at 313 nm but not at 514 nm as detected by bleaching of N,N-dimethylnitrosoaniline (RNO). Irradiation of RB at 313 nm but not at 514 nm appeared to cause homolytic cleavage of carbon-iodine bonds in the dye because iodine radicals, I, detected as I2 were produced with a quantum yield of 0.0041 +/- 0.0005 upon excitation in the UV. Photolysis of I2 in the presence of RNO caused bleaching of the RNO absorption at 440 nm, apparently resulting from reaction of I with RNO. Thus, the enhanced photosensitization upon UV excitation of RB is attributed to formation of I and/or RB. These results indicate that radicals, produced with low relative yield but having high reactivity compared to O2(1 delta g), can contribute to photosensitized enzyme inhibition and may represent an alternative mechanism for photodynamic therapy.

Evidence for peroxynitrite formation during S-nitrosoglutathione photolysis in air saturated solutions.

Flash photolysis of S-nitrosoglutathione (GSNO) in aerated solutions at pH 10 gave rise to an absorption with a maximum around 310-320 nm. This peak is spectrally similar to that displayed by ONOO-. The decay kinetics of this absorption was compared to that of authentic ONOO-, generated independently. An excellent correlation was obtained. Further proof of ONOO- generation was provided by HPLC studies showing the production of 3-nitrotyrosine on irradiation of GSNO in the presence of tyrosine at pH 7.4. In addition, the nitration yield was increased approximately 5-fold in the presence of bicarbonate and totally eliminated with DMPO, indicating the requirement of a radical intermediate for peroxynitrite production during S-nitrosothiol photolysis.

Photosensitized production of singlet oxygen.

Photosensitization is a simple and controllable method for the generation of singlet oxygen in solution and in cells. Methods are described for determining the yield of singlet oxygen in solution, for measurement of the rate of reaction between singlet oxygen and a substrate, and for comparing the effectiveness of singlet oxygen generated by different photosensitizers in cells. These quantitative measurements can lead to better understanding of the interaction of singlet oxygen with biomolecules.

Photochemical keratodesmos for repair of lamellar corneal incisions.

PURPOSE: To determine the efficacy of photochemical keratodesmos (PKD) for closing surgical incisions in the cornea of enucleated rabbit eyes compared with that achieved using sutures and self-sealing incisions. METHODS: A 3.5-mm incision, at an angle parallel to the iris, was made in the cornea of enucleated New Zealand White rabbit eyes. The intraocular pressure required to cause leakage (IOP(L)) from the untreated incision was then recorded. Photochemical keratodesmos treatment was then performed by application of a dye, Rose Bengal (RB), in saline solution to the surfaces of the incision wound, followed by laser irradiation at 514 nm from an argon ion laser. Immediately after treatment, the IOP(L) was measured. Both dose and laser irradiance dependencies were studied in five or more eyes for each condition and appropriate control eyes. The IOP(L)s were compared with those obtained using conventional interrupted 10-0 nylon sutures. Other dyes were tested in a similar fashion. RESULTS: The IOP(L) of 300 mm Hg was obtained using a fluence of 1270 J/cm(2) with an irradiance of 1.27 W/cm(2) (laser exposure time, 16 minutes 40 seconds). No sealing was observed using dye or light alone where control pressures of approximately 30 mm Hg were found. At higher dose (1524 J/cm(2)) and irradiance (3.82 W/cm(2); 6 minutes 35 seconds), PKD was less effective, which may be attributable to thermal effects. PKD produced IOP(L)s similar to those in closure by sutures. Other dyes such as riboflavin-5-phosphate and N:-hydroxy-pyridine thione also produced efficient bonding after PKD. Nonphotochemically active dyes did not produce significant increases in the IOP(L) at which leakage occurred. CONCLUSIONS: The increase in IOP(L) after PKD treatment, comparable with that with sutures, in enucleated rabbit eyes demonstrates the feasibility of this technique ex vivo.

On the nature of the active component of haematoporphyrin 'derivative'.

The active component of the photochemotherapeutic drug 'haematoporphyrin derivative' was studied by laser flash photolysis. The triplet extinction coefficient of this species was determined using a method in which the calculated value is dependent on the assumed molecular weight. This value was then incorporated in the evaluation of the quantum yield of triplet by a comparative technique. Since the maximum possible value of this yield is unity, it is shown that the molecular weight of the active component is greater than or equal to 3000, so that, on average, the drug molecule must contain at least 5 porphyrin units.

Permeation and metabolism of anti-HIV and endogenous nucleosides in human immune effector cells.

Numerous anti-HIV drugs are synthetic analogs of endogenous nucleosides. Therefore it is of interest to see if a facilitated nucleoside transport system exists to mediate their uptake into human immune effector cells that are known HIV targets. Nucleoside permeation and metabolism in lymphocytes, macrophages and bone marrow cells isolated from healthy human volunteers were studied, using uridine as the prototype endogenous nucleoside. There are saturable broad specificity nucleoside transport systems in all three cell types, all of which were inhibited by dipyridamole. The Vmax and Km values for uridine transport were 0.05 +/- 0.01 pmol/sec/10(6) cells and 18.4 +/- 4.2 microM, respectively, for lymphocytes, 0.04 +/- 0.01 pmol/sec/10(6) cells and 25.3 +/- 6.6 microM, respectively, for macrophages, and 0.03 +/- 0.01 pmol/sec/10(6) cells and 90.2 +/- 10.1 microM, respectively, for bone marrow mononuclear cells. Anti-HIV dideoxynucleosides such as azidothymidine (AZT), 2',3'-dideoxycytidine (DDC), 2',3'-dideoxyinosine (DDI), 2',3'-dideoxyadenosine (DDA), and 2',3'-dideoxythymidine (DDT) are not substrates of this nucleotide transport system; hence, little or no drug accumulated inside the cells after 60 sec. Equilibration of cells with uridine or dideoxynucleosides for 2 hr resulted in high levels of cellular uridine and DDA, low levels of cellular AZT, but undetectable levels of the other analogs in all three cell types. Active metabolite levels in lymphocytes as assayed by HPLC correlated with the drug permeation results. Our data demonstrated that DDC, DDI, and DDT are not substrates for the nucleoside transporter and cannot diffuse readily across the cell membrane of human immune effector cells. Future anti-HIV drug development efforts should consider drugs that are substrates of the nucleotide transporter to ensure rapid and complete uptake into target cells.

Strength training increases regional bone mineral density and bone remodeling in middle-aged and older men.

To determine the effects of strength training (ST) on bone mineral density (BMD) and bone remodeling, 18 previously inactive untrained males [mean age 59 +/- 2 (SE) yr] were studied before and after 16 wk of either ST (n = 11) or no exercise (inactive controls; n = 7). Total, spinal (L2-L4), and femoral neck BMD were measured in nine training and seven control subjects before and after the experimental period. Serum concentrations of osteocalcin, skeletal alkaline phosphatase isoenzyme, and tartrate-resistant acid phosphatase were measured before, during, and after the experimental program in all subjects. Training increased muscular strength by an average of 45 +/- 3% (P < 0.001) on a three-repetition maximum test and by 32 +/- 4% (P < 0.001) on an isokinetic test of the knee extensors performed at 60 degrees/s. BMD increased in the femoral neck by 3.8 +/- 1.0% (0.900 +/- 0.05 vs. 0.933 +/- 0.05 g/cm2, P < 0.05) and in the lumbar spine by 2.0 +/- 0.9% (1.180 +/- 0.06 vs. 1.203 +/- 0.06 g/cm2, P < 0.05). However, changes in lumbar spine BMD were not significantly different from those in the control group. There was no significant change in total body BMD. Osteocalcin increased by 19 +/- 6% after 12 wk of training (P < 0.05) and remained significantly elevated after 16 wk of training (P < 0.05). There was a 26 +/- 11% increase in skeletal alkaline phosphatase isoenzyme levels (P < 0.05) after 16 wk of training.(ABSTRACT TRUNCATED AT 250 WORDS)

Lacrimal gland hemangiopericytoma.

PURPOSE/METHODS: A 49-year-old woman with a left orbital mass was referred to an orbital clinic. Clinical investigation suggested a lacrimal gland lesion and the patient underwent lateral orbitotomy and excisional biopsy for a suspected pleomorphic adenoma in the lacrimal gland. RESULTS/CONCLUSION: Histopathologic evaluation disclosed a hemangiopericytoma originating within the lacrimal gland. Although hemangiopericytoma does not usually occur in this location, it may be added to the differential diagnosis of lacrimal gland enlargement.

Can cellular phototoxicity be accurately predicted on the basis of sensitizer photophysics?

The phototoxicity of three structurally related photosensitizers (PS), deuteroporphyrin IX (DP) and monobromo (Br-DP) and dibromo (Br2-DP) derivatives, was studied in murine L1210 leukemia cells. These compounds were chosen on the basis of heavy-atom-induced differences in triplet yield, phi T, and lifetime, tau T, and used as tools to test a model for phototoxicity based on photophysical parameters. All three porphyrins were found to localize preferentially in the plasma membrane of L1210 cells by confocal fluorescence microscopy. A poor correlation was observed between the measured photodynamic efficacies of these PS and a model using photophysical parameters determined by laser flash photolysis in homogeneous solution. However, an excellent correlation was obtained when the same parameters measured directly in the cells were used. The biological microenvironment of the porphyrins in cells induces significant changes in the photophysics of the PS. Reduction in fluorescence yield, phi F, and phi T observed for Br2-DP in cell suspensions arises from self association of the molecule due to increased hydrophobicity and high local concentrations. The photophysical model was also tested for its ability to handle variations in the oxygen dependence of cellular phototoxicity of these PS. The good correlation achieved between laser flash photolysis data determined in cells and the measured phototoxicity under air, 1.5% and 0.5% O2-saturated conditions, proves the intermediacy of singlet oxygen. This study gives further credence to the direct use of photophysical techniques to elucidate photochemical mechanisms in biological media while highlighting the potential pitfalls of using solution data to predict photosensitizing potential.

Photophysical properties of 3,3'-dialkylthiacarbocyanine dyes in homogeneous solution.

The photophysical properties of 3,3'-dialkylthiacarbocyanine iodides and chlorides were measured in various solvents. It was found that photoisomerization and fluorescence are the major contributors to the deactivation of the excited singlet state; intersystem crossing occurs with only a very low efficiency. In ethanol, a triplet yield of 0.004 and a singlet oxygen quantum yield of 0.002 were determined. The photophysical parameters of these dyes are not substantially influenced by the length of the alkyl chain or the size of the halide counterion. The substitution of an ethyl with an octadecyl-chain only slightly hinders photoisomerization, and the replacement of the chloride with an iodide reduces only marginally the fluorescence lifetimes and fluorescence quantum yields in chloroform. A significant external heavy-atom effect is observed using dibromoethane as a solvent: triplet and singlet oxygen yields increase 7-10-fold, and the triplet lifetime decreases from 55 microseconds to 15 microseconds.

Exclusive free radical mechanisms of cellular photosensitization.

In order to determine the specific effects of radical-induced reactions in the absence of complicating excited-state pathways, four different thiohydroxamic esters and their parent molecule, N-hydroxypyridine-2(1H)-thione, have been studied in murine L1210 leukemia cells for their ability to produce photobiological damage. Irradiation (lambda exc = 355 nm) of cells in the presence of thiopyridone esters, specific photolytic precursors of sulfur-, carbon- and oxygen-centered radicals, caused toxicity that was unambiguously demonstrated to result from radical photosensitization mechanisms. Cellular morphological changes were observed following irradiation but apoptosis was not found to take place. A good correlation was evident between lipid peroxidation, measured by the thiobarbituric acid method, and phototoxicity, assessed by the trypan blue exclusion assay, indicating that the ester derivatives exert their effects mainly in plasma and/or subcellular membranes. Irradiation performed under deaerated conditions also induced significant phototoxicity but the effects of deaeration were dependent on the ester used and are discussed in terms of the nature of the primary radical species generated in each case. Irradiation of L1210 cells in the presence of N-hydroxypyridine-2(1H)-thione, a nonspecific, photochemical source of hydroxyl radical, was also found to trigger phototoxicity and lipid peroxidation. However in this case, photodamage cannot yet be definitely attributed to a radical or type II mechanism although the apparent oxygen independence of phototoxicity would indicate that type II contribution is not significant.