POSTREPLICATION REPAIR IN uvrA AND uvrB STRAINS OF ESCHERICHIA COLI K-12 IS INHIBITED BY RICH GROWTH MEDIUM

Abstract Escherichia coli K-12 uvrA or uvrB strains grown to logarithmic phase in minimal medium showed higher survival after ultraviolet (UV) irradiation (254 nm) if plated on minimal medium (MM) instead of rich medium. This'minimal medium recovery'(MMR) was largely blocked by additional recA56 (92% inhibition) or lexA101 (77%) mutations, was partially blocked by additional recB21 (54%), uvrD3 (31%) or recF143 (22%) mutations, but additional polA1 or polA5 mutations had no effect on MMR. When incubated in MM after UV irradiation, the uvrB5 and uvrB5 uvrD3 strains showed essentially complete repair of DNA daughter-strand gaps (DSG) produced after UV radiation fluences up to ∼ 6 J/m² and ∼1 J/m², respectively, and then they accumulated unrepaired DSG as a linear function of UV radiation fluence. However, when they were incubated in rich growth medium after UV irradiation, they did not show the complete repair of DSG and unrepaired DSG accumulated as a linear function of UV radiation fluence. The fluence-dependent correlation observed for the uvrB and uvrB uvrD cells between UV radiation-induced killing and the accumulation of unrepaired DSG, indicates that the molecular basis of MMR is the partial inhibition of postreplication repair by rich growth medium. Rich growth medium can be just MM plus Casamino Acids or the 13 pure amino acids therein in order to have an adverse effect on survival, regardless of whether the cells were grown in rich medium or not before UV irradiation.     

INTERACTION OF IONIZING RADIATION AND ULTRAVIOLET-LIGHT IN DIPLOID YEAST STRAINS OF DIFFERENT SENSITIVITY*

Abstract— The interaction of ionizing radiation and UV-light regarding colony forming ability in 3 diploid yeast strains of Saccharomyces cerevisiae was investigated. A wild type and two radiation sensitive mutants were used. No difference in the response of the three strains could be detected when the UV dose was given first, but when ionizing radiation was applied shortly before UV, there were essential differences depending on the kind of mutation. The involvement of repair mechanisms in the interaction is discussed.     

Inactivation by Pulsed Light of Bacillus subtilis Spores with Impaired Protection Factors

The resistance to pulsed light (PL) of spores of Bacillus subtilis strain 168 and of strains with mutations increasing sensitivity to UV‐C or affecting spore structure was evaluated and compared to resistance to continuous UV‐C and moist heat, in order to reveal original mechanisms of inactivation by PL. Spores of B. subtilis strain 168 (1A1) and eight mutant strains (sspA, sspB, sspAB, cotA, gerE, cotE, uvrA and recA) were exposed to PL (up to 1.77 J cm^?2), continuous UV‐C (up to 147 mJ cm^?2) and moist heat at 90°C. Spores of the strains lacking proteins linked to coat formation or structure (cotA, gerE and cotE) were markedly more sensitive to PL than 1A1, while their sensitivity to continuous UV‐C or to moist heat was similar to the one of strain 1A1. Coat proteins had a major contribution to the resistance of B. subtilis spores to PL irradiation characterized by short‐time and high‐energy pulses of white light in the wavelengths 200–1100 nm. In contrast the role of coat proteins to UV‐C or to moist heat resistance was marginal or null.     

UV Signature Mutations

Sequencing complete tumor genomes and exomes has sparked the cancer field's interest in mutation signatures for identifying the tumor's carcinogen. This review and meta‐analysis discusses signatures and their proper use. We first distinguish between a mutagen's canonical mutations—deviations from a random distribution of base changes to create a pattern typical of that mutagen—and the subset of signature mutations, which are unique to that mutagen and permit inference backward from mutations to mutagen. To verify UV signature mutations, we assembled literature datasets on cells exposed to UVC, UVB, UVA, or solar simulator light (SSL) and tested canonical UV mutation features as criteria for clustering datasets. A confirmed UV signature was: ≥60% of mutations are C→T at a dipyrimidine site, with ≥5% CC→TT. Other canonical features such as a bias for mutations on the nontranscribed strand or at the 3′ pyrimidine had limited application. The most robust classifier combined these features with criteria for the rarity of non‐UV canonical mutations. In addition, several signatures proposed for specific UV wavelengths were limited to specific genes or species; UV's nonsignature mutations may cause melanoma BRAF mutations; and the mutagen for sunlight‐related skin neoplasms may vary between continents.     

THE EXPRESSION OF LIQUID HOLDING RECOVERY IN ULTRAVIOLET-IRRADIATED ESCHERICHIA COLI REQUIRES A DEFICIENCY IN GROWTH MEDIUM-DEPENDENT DNA REPAIR

Ultraviolet (UV) irradiated Escherichia coli K-12 recA cells (but not rec⁺ cells) show enhanced survival if they are held in buffer prior to plating for viability. To understand the role of the recA mutation in this liquid holding recovery (LHR) phenomenon, we have studied LHR in a temperature sensitive recA 200 mutant. The detection of LHR requires that the irradiated cells be recA when they are plated on growth medium, but the recA deficiency plays no role during liquid holding (LH). We conclude that it is the extreme sensitivity of recA cells in growth medium to unrepaired DNA daughter-strand gaps that magnifies the beneficial effects of the excision repair of DNA lesions during LH. Furthermore, we demonstrate a correlation between a strain's inability to perform growth medium dependent repair and its ability to express LHR. The relative amount of LHR was: recA > recF > lexA > recB > wild type (with the recB and wild-type strains showing negative LHR). Two strains did not show this correlation; the uvrD strain showed less LHR than expected from its UV radiation sensitivity, while the polA strain showed more. The molecular bases for these exceptions are explored.     

Determination of the Chemical Structure of Poly-β (-)-pinene by NMR Spectroscopy

This paper is dedicated to the memory of our friend and colleague Annalaura Segre.

The chemical structure of a series of β (-)-pinene polymers (PBP) obtained by radiation-induced polymerization, free radical initiation, cationic polymerization over a Friedel-Craft catalyst and by coordinative polymerization over a Ziegler-Natta catalyst has been fully elucidated by ¹H and ¹³C-NMR spectroscopy. 2D NMR techniques have been applied in order to assign all the NMR resonances to the structures of the PBP investigated. The NMR spectra show that the most regular PBP structure is obtained by radiation-induced polymerization followed by the free radical initiated polymerization. The most defective structure has been observed in the case of PBP prepared by cationic mechanism over a Friedel-Crafts catalyst. The discussion accounts for different types of defects and cross-links present in the PBPs investigated whose fundamental structure is based on the p-menthene repeating unit.

NMR self-diffusion measurements have been performed to evaluate the molecular weight of all the PBP investigated. The highest molecular weight (2600 Dalton) was found in the case of PBP prepared by Ziegler-Natta catalyst, while the lowest molecular weight was found in the case of PBP prepared by radiation-induced polymerization (about 1000 Dalton).     

叶酸介导的靶向性钆造影剂的制备及弛豫性能研究

在弱碱性的条件下，叶酸活化酯与牛血清白蛋白(BSA)反应生成叶酸-牛血清白蛋白偶联物(叶酸-BSA)，该偶联物再与二乙三胺五乙酸(DTPA)的酸酐反应，最后与GdCl₃进行螯合制得叶酸-BSA-(Gd-DTPA)_n。配合物的结构通过紫外光谱法进行了鉴定，并定量测定了配合物中叶酸、Gd-DTPA对BSA的偶联率。通过测定配合物的体外弛豫时间T₁，进一步分析其弛豫性能R₁。结果表明本研究制得的叶酸-BSA-(Gd-DTPA)_n配合物中叶酸的偶联率约为5，体外弛豫性能R1约为6×10^-3 L·mmol^-1·ms^-1，与未偶联叶酸的BSA-(Gd-DTPA)_n的弛豫性能无显著性差异，且比小分子Gd-DTPA的弛豫性能提高了3倍左右。     

Influence of UV Light Wavelength on Grafting of PVC

Abstract

PVC-(n-propyl xanthate) macroinitiators (PVC-nPX) with different fractions of xanthate groups were synthesized in THF/acetone solutions from PVC and potassium n-propyl xanthate (nPX). Methyl methacrylate (MMA) was grafted onto PVC-nPX macroinitiators using UV light of 254, 302, and 366 nm at 20 and 40°C. Reaction time was 1, 3, or 5 hours. Graft copolymerization and UV homopolymerization took place at the same time. Grafting was the most effective at a wavelength of 302 nm with a weight gain of copolymerization of up to 45%. The grafted copolymers were separated from the mixture by selective precipitation of THF solutions with hot ethanol and extraction with hot ethanol. The mechanism of grafting is discussed on the basis of the molecular weight of copolymers, on the quantity of homopolymers, on the structure of copolymers, and on the UV absorption of end groups.     

Features of Preparing the Butyl Acrylate–Acrylonitrile Copolymer by Radiation-Induced Emulsion Polymerization

Some specific features of the radiation-induced emulsion copolymerization of butyl acrylate and acrylonitrile and radiation-induced crosslinking of the resulting copolymer in the latex form were studied. The effect of polymerization conditions on the polymerization rate and the molecular mass of the polymer was determined. The copolymer was shown to undergo efficient crosslinking in the latex form by the action of -radiation. The radiation-chemical yield of crosslinking sites (G) and the average molecular mass (M _c) of chain segments between two adjacent network junctions were determined.     

MINIMUM DOSES OF ULTRAVIOLET RADIATION REQUIRED TO INDUCE MURINE SKIN EDEMA and IMMUNOSUPPRESSION ARE DIFFERENT and DEPEND ON THE ULTRAVIOLET EMISSION SPECTRUM OF THE SOURCE*

Many photoimmunological studies have used UV radiation sources that emit nonsolar UV spectral energy and UV doses based on nonimmunological endpoints, e.g. erythema and skin edema. Interpretation of these data has led to misunderstanding when extrapolated to hypothetical effects in humans exposed to solar UV. The purpose of this study was to: (1) establish UV dose response relationships for murine skin edema and immunosuppression, and (2) determine how different UV spectra affect these relationships. Back skin and ear minimum edema doses (MEdD) for Kodacel-filtered FS20 sunlamp UV (290–400nm) were greater than two-fold higher than those for unfiltered FS20 sunlamp UV (250–400nm). Xenon arc solar simulator UV (295–400nm) MEdD were > 10-fold higher than those for unfiltered sunlamp UV. Back skin and ear MEdD differed two- to five-fold between C3H/ HeN, SWR/J and HRA/Skh-1 mice. The minimum immunosuppression doses (MISD) in C3H mice showed similar UV source spectrum dependence. The solar simulator UV MISD was 5.4- and 1.5-fold higher than for unfiltered and Kodacel-filtered sunlamp UV MISD, respectively. Furthermore, MISD were from 3- to 50-fold higher than the MEdD for the three UV sources. The UV bioeffectiveness spectra indicated that UVC energy (250–290nm) contributed 12% and 18%, respectively, of the total skin edema and immunosuppression UV energy. These data demonstrate the variability in UV sensitivity among mouse strains, the significant differences between murine MEdD and MISD and how these differences are influenced by nonsolar regions (below 295 nm) of the UV spectrum.     

Photolyases and Cryptochromes in UV‐resistant Bacteria from High‐altitude Andean Lakes

“High‐altitude Andean Lakes” (HAAL) are pristine environments harboring poly‐extremophilic microbes that show combined adaptations to physical and chemical stress such as large daily ambient thermal amplitude, extreme solar radiation levels, intense dryness, alkalinity, high concentrations of arsenic (up to 200 ppm) and dissolved salts. In this work, we compared the UV resistance profiles, pigment content and photoreactivation abilities of three UV‐resistant bacteria isolated from distinct niches from HAALs, that is Acinetobacter sp. Ver3 (water, Lake Verde; 4400 m), Exiguobacterium sp. S17 (stromatolite, Lake Socompa, 3570 m) and Nesterenkonia sp. Act20 (soil, Lake Socompa, 3570 m). UV resistance ability of HAAL's strains indicate a clear adaptation to high radiation exposure encountered in their original habitat, which can be explained by genetic and physiological mechanisms named as the UV‐resistome. Thus, the UV‐resistome depends on the expression of a diverse set of genes devoted to evading or repairing the damage it provoked direct or indirectly. As pigment extraction and photoreactive assays indicate the presence of photoactive molecules, we characterized more in detail proteins with homology to photolyases/cryptochromes members (CPF). Phylogenetic analyses, sequence comparison and 3D modeling with bona fide CPF members were used to prove the presence of functional domains and key residues in the novel proteins.     

EFFECT OF UV IRRADIATION ON LETHAL INFECTION OF MICE WITH Candida albicans

Exposure of mice to UV radiation inhibits the induction and elicitation of the delayed-type hypersensitivity (DTH) response to Candida albicans. To determine whether UV irradiation also affects the pathogenesis of systemic C. albicans infection, C3H mice were exposed to a single dose of 48 kJ/m² UV-B radiation from FS40 sunlamps 5 days before or 5 days after sensitization with formalin-fixed C. albicans and challenged intravenously (i.v.) with a lethal dose of viable fungi 6 days after sensitization (11 or 1 days after UV irradiation). Exposing unsensitized mice to UV radiation 11 days before lethal challenge had no effect on survival, but the survival time of mice exposed to UV radiation 1 day before challenge was reduced by more than 50%. In the latter group, decreased survival time correlated with persistence of C. albicans in the brain and progressive growth of C. albicans in the kidneys. Sensitization of unirradiated mice with formalin-fixed C. albicans extended their survival time following lethal i.v. challenge with viable C. albicans. Exposing the mice to UV radiation 5 days before sensitization did not abrogate this beneficial effect of sensitization on survival, even though it significantly reduced the DTH response. Thus, immunity to systemic infection did not depend on the ability of the mice to exhibit a DTH response to C. albicans. The beneficial effect of sensitization on survival after lethal infection was abrogated, however, in mice exposed to UV radiation 1 day before lethal challenge with C. albicans. Furthermore, these mice were unable to contain the progressive growth of C. albicuns in the kidneys, in contrast to sensitized, unirradiated mice. The induction of cutaneous inflammation with turpentine had no effect on the survival rate of mice lethally infected with C. albicans, suggesting that inflammation alone is not sufficient to decrease the survival time of C. albicans-infected mice.     

XERODERMA PIGMENTOSUM FIBROBLASTS INCLUDING CELLS FROM XP VARIANTS ARE ABNORMALLY SENSITIVE TO THE MUTAGENIC AND CYTOTOXIC ACTION OF BROAD SPECTRUM SIMULATED SUNLIGHT

Abstract— The cytotoxic and mutagenic effects of broad spectrum simulated sunlight, as delivered by a Westinghouse Sun Lamp FS 20 filtered to eliminate wavelengths below 290 nm, were determined in diploid human skin fibroblasts which differ in their ability to repair pyrimidine dimers, and compared with results obtained with UV 254 nm radiation. The cell strains tested included normal fibroblasts; excision repair-deficient xeroderma pigmentosum (XP) cells from patients XP12BE (complementation group A). XP7BE (group D). and XP2BI (group G): and an XP variant patient (XP4BE) whose cells excise pyrimidinc dimers at a normal rate, but exhibit abnormal replication of DNA containing unexcised lesions. Cytotoxicity was assayed from loss of colony-forming ability. The group A cells were most sensitive to the killing effect of the Sun Lamp; the group D and G cells were slightly less sensitive; the XP variant cells showed intermediate sensitivity; and normal cells were most resistant. When the Sun Lamp survival curves for the group A, group D, the XP variant and normal cells were compared with their respective UV 254 nm survival curves, the relationships between the strains were virtually identical (i. e. the curves were related by a constant fluence modification factor). suggesting a common lesion for cell killing. The marker for mutagenesis was resistance to 6-thioguanine. The group A XP cells proved most sensitive to mutations induced by the simulated sunlight: the variant cells were intermediate; and the normal cells were the most resistant. Again, when the curves for mutations induced in these cell strains by simulated sunlight were compared with their respective 254 nm UV mutation curves, these were related by a constant fluence modification factor. suggesting a common lesion for mutagenesis. These results. taken together with published data indicating that at equicytotoxic levels of UV254 nm radiation and the filtered Sun Lamp. the number of pyrimidine dimers in the DNA of XP12BE cells was equal. support the hypothesis that the dimer is the lesion principally involved in both effects. Our data also support the hypothesis that mutations are involved in the sunlight-induced skin cancer of XP patients.     

Oligolysine‐Conjugated Zinc(II) Phthalocyanines as Efficient Photosensitizers for Antimicrobial Photodynamic Therapy

A series of zinc(II) phthalocyanines conjugated with an oligolysine chain (n=2, 4, and 8) were synthesized and characterized by using various spectroscopic methods. As shown by using UV/Vis and fluorescence spectroscopic methods, these compounds were nonaggregated in N,N‐dimethylformamide, and gave a weak fluorescence emission and high singlet oxygen quantum yield (Φ_Δ=0.86–0.89) as a result of their di‐α‐substitution. They became slightly aggregated in water with 0.05 % Cremophor EL, but they could still generate singlet oxygen effectively. The antimicrobial photodynamic activities of these compounds were then examined against various bacterial strains, including the Gram‐positive methicillin‐sensitive Staphylococcus aureus ATCC 25923 and methicillin‐resistant Staphylococcus aureus ATCC BAA‐43, and the Gram‐negative Escherichia coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. Generally, the dyes were much more potent toward the Gram‐positive bacteria. Only 15 to 90 nM of these photosensitizers was required to induce a 4 log reduction in the cell viability of the strains. For Escherichia coli, the photocytotoxicity increased with the length of the oligolysine chain. The octalysine derivative showed the highest potency with a 4 log reduction concentration of 0.8 μM . Pseudomonas aeruginosa was most resistant to the photodynamic treatment. The potency of the tetralysine derivative toward a series of clinical strains of Staphylococcus aureus was also examined and found to be comparable with that toward the nonclinical counterparts. Moreover, the efficacy of these compounds in photodynamic inactivation of viruses was also examined. They were highly photocytotoxic against the enveloped viruses influenza A virus (H1N1) and herpes simplex virus type 1 (HSV1), but exhibited no significant cytotoxicity against the nonenveloped viruses adenovirus type 3 (Ad3) or coxsackievirus (Cox B1). The octalysine derivative also showed the highest potency with an IC₅₀ value of 0.05 nM for the two enveloped viruses.     

Combined Experimental and Computational Studies on the Physical and Chemical Properties of the Renewable Amide, 3‐Acetamido‐5‐acetylfuran

The pK_a of 3‐acetamido‐5‐acetylfuran (3A5AF) was predicted to be in the range 18.5–21.5 by using the B3LYP/6‐311+G(2d,p) method and several amides as references. The experimental pK_a value, 20.7, was determined through UV/Vis titrations. Its solubility was measured in methanol‐modified supercritical CO₂ (mole fraction, 3.23×10^?4, cloud points 40–80 °C) and it was shown to be less soluble than 5‐hydroxymethylfurfural (5‐HMF). Dimerization energies were calculated for 3A5AF and 5‐HMF to compare hydrogen bonding, as such interactions will affect their solubility. Infrared and ¹H nuclear magnetic resonance spectra of 3A5AF samples support the existence of intermolecular hydrogen bonding. The highest occupied molecular orbital, lowest unoccupied molecular orbital, and electrostatic potential of 3A5AF were determined through molecular orbital calculations using B3LYP/6‐311+G(2d,p). The π–π* transition energy (time‐dependent density functional theory study) was compared with UV/Vis data. Calculated atomic charges were used in an attempt to predict the reactivity of 3A5AF. A reaction between 3A5AF and CH₃MgBr was conducted. As 3A5AF is a recently developed renewable compound that has previously not been studied extensively, these studies will be helpful in designing future reactions and processes involving this molecule.     

PHOTOREVERSIBLE UV-INACTIVATION OF MESSENGER RNA IN AN INSECT EMBRYO (SMITTIA SPEC., CHIRONOMIDAE, DIPTERA)

Smittia embryos were UV-irradiated during intravitelline cleavage. At this stage, nuclei are heavily shielded by yolk-rich cytoplasm, and do not synthesize detectable amounts of RNA. Irradiation at 265, 285 and 295 nm wavelength caused biological inactivation, and pyrimidine dimer formation in maternal RNA as described earlier (Kalthoff, 1976; Jäckie and Kalthoff, 1978). In addition, we observed marked effects on protein synthesis: (1) The overall rate of [³⁵S]-methionine incorporation in vivo was reduced to less than half of the normal rate. (2) Two-dimensional gel electrophoresis revealed quantitative variations in the synthetic rate of some polypeptides, and the appearance of new ones in UV-irradiated embryos. (3) Translation of polyadenylated RNA from Smittia embryos in a cell-free system was inhibited by UV irradiation in vivo. (4) The apparent degradation, during early embryogenesis, of maternal polyadenylated RNA was retarded in UV-irradiated embryos. Exposure to light (400 nm) after UV caused partial photoreversal of all UV effects observed. Both the photoreactivable sector of UV-inactivation, and the photoreactivated portion of UV inhibition of protein synthesis, were correlated with the amounts of pyrimidine dimers generated in maternal RNA by UV irradiation at the three wavelengths used. These correlated effects were produced most efficiently by 295 nm radiation, indicating the involvement of photosensitizing components in the embryos. Our data show, for the first time to our knowledge, that animal mRNA, after UV irradiation, can be photoreactivated in vivo. Moreover, our results strongly suggest that the photorepairable lesions consist of pyrimidine dimers generated in a photosensitized reaction.     

Synthesis,characterization, biological screening and molecular docking of Zn(II) and Cu(II) complexes of 3,5-dichlorosalicylaldehyde-N4-cyclohexylthiosemicarbazone

A 3,5-dichlorosalicylaldehyde-N⁴-cyclohexylthiosemicarbazone (C₁₄H₁₆Cl₂N₃OS) and its complexes [Zn(dsct)(phen)]·DMF ( 1 ), [Zn(dsct)(bipy)]·DMF ( 2 ), [Cu(dsct)(bipy)]·DMF ( 3 ) (phen = 1,10-phenathroline, bipy = 2,2’bipyridine) were synthesized and characterized by CHN analysis, FT-IR, UV–vis and NMR spectra. The molecular structure of the thiosemicarbazone (H₂dsct) and its complexes have been resolved using single crystal XRD studies. In the complexes, thiosemicarbazone exist in the thioiminolate form and acts as dideprotonated tridentate ligand coordinating through phenolic oxygen, thioiminolate sulfur and azomethine nitrogen. The antibacterial activity of the prepared compounds were screened against Escherichia coli, Salmonella typhi, Enterobacter aerogenes, Shigella dysentriae, Bacillus cereus, Staphylococcus aureus. All the complexes showed activity against bacterial strains E.coli and Salmonella typhi. The thiosemicarbazone showed activity against three bacterial strains such as E. coli, Enterobacter aerogenes and Shigella dysentriae. Complex 2 showed very good antibacterial activity as compared to standard drug (Ampicillin) against the bacterial strain, Salmonella typhi. Finally, the thiosemicarbazone and its complexes have been used to accomplish molecular docking studies against an Epidermal Growth Factor Receptor (EGFR) and breast cancer mutant 3hb5-oxidoreductase to determine the most preferred mode of interaction. The results confirm that the complex [Cu (dsct)(bipy)]·DMF( 3 ) showed the highest docking score as compared to other complexes under study. The [Cu(dsct)(bipy)]·DMF( 3 ) complex was evaluated for their anticancer activities against breast cancer cell line (MCF-7) and normal L929 (Mouse Fibroblast) cell line. It was found that the compound showed an LC₅₀ of 6.25 μg/mL against breast cancer cell line (MCF-7).     

Accurate Zygote‐Specific Discrimination of Single‐Nucleotide Polymorphisms Using Microfluidic Electrochemical DNA Melting Curves

We report the first electrochemical system for the detection of single‐nucleotide polymorphisms (SNPs) that can accurately discriminate homozygous and heterozygous genotypes using microfluidics technology. To achieve this, our system performs real‐time melting‐curve analysis of surface‐immobilized hybridization probes. As an example, we used our sensor to analyze two SNPs in the apolipoprotein E (ApoE) gene, where homozygous and heterozygous mutations greatly affect the risk of late‐onset Alzheimer’s disease. Using probes specific for each SNP, we simultaneously acquired melting curves for probe–target duplexes at two different loci and thereby accurately distinguish all six possible ApoE allele combinations. Since the design of our device and probes can be readily adapted for targeting other loci, we believe that our method offers a modular platform for the diagnosis of SNP‐based diseases and personalized medicine.     

Characterizations of iron-rich clay modified electrodes and their applications in optical recognition

Optical recognition was studied with modified electrodes based on iron-rich clays. According to energy-dispersive X-ray spectroscopy (EDX), several clay minerals including montmorillonite K10 (mont. K10) contain a lot of iron. Cyclic voltammetry suggested that electrochemically active iron species exist in most iron-rich clays and are likely to reside at different sites. The associated electrochemical activity is strongly pH-dependent and photosensitive. Under UV irradiation (λ ≤ 420 nm), these iron species were activated, and a pronounced photocurrent resulted. When these electrodes were flow-injected with 2-pyridylcarboxylic acids (λ_ab,max = 260 nm), the originally monotonic photocurrent could be modulated into a more recognizable a.c. pattern and the 260 nm optical signal became distinguishable. The photoresponse was highly reproducible, and the response time (t₉₀) was less than 10s.     

SYNTHESIS AND OPTICAL-ELECTRONIC PROPERTIES OF POLY [METHYLTETRAPHENYLPHENYLSILYLENE-CO- BIS（METHYLPHENYLSILYL）ACETYLENE]

Poly(methyltetraphenylphenylsilylene-co-bis(methylphenylsilyl)acetylene) (PSA) was synthesized by the cocondensation reaction of methyltetraphenylphenyldichlorosilane and bis(chloromethylphenylsilyl)acetylene with sodium in toluene. The PSA thus obtained was soluble in most organic solvents, and its molecular weight was smaller than that of poly[(disilanylene)acetylenes] with alkyl- or aryl-substitution because of the great steric congestion of tetraphenylphenyl groups. The optical and electronic properties of the polymer were investigated. The results show that PSA has strong UV absorption and fluorescence emission, the maximum UV absorption wavelength of PSA is 330 nm, which shows a considerable red-shift in comparison with that of poly(methylphenylsilylene-co-methylphenylsilylacetylene) (PSI) and alkylsubstituted poly[(disilanylene)acetylenes]. A strong photoluminescence band at 470 nm in THF and 432 nm in benzene can be observed in the visible region, respectively. Treatment of the films of PSA with I2 vapor afforded conducting films. The conductivity of PSA thin film doped with I2 was measured to be 0.35 Scm-1 in the air which is lower than that of poly(methyltetraphenylphenylsilylene-co-bis(methylphenylsilyl)phenylene), but higher than that of σ-π polymers without tetraphenylphenyl groups. As an explanation, the tetraphenylphenyl group is a large π-electron-conjugated group; after being introduced to the Si atoms of the polysilanes, the interaction between π-electrons of the tetraphenylphenyl groups and the σ-electrons conjugated along the Si-Si bonds is increased strongly, and the σ-electrons can be conjugated more extensively along the main chain of the polysilanes.