Transmission photoelasticity of centrally loaded generally and specially orthotropic beams

Transmission photoelastic patterns for generally and specially orthotropic beams and an isotropic beam are presented. Theoretical isochromatic and isoclinic results for these beams, calculated from classical elasticity stress equations and stress-optic laws, are also presented and compared with experiment. The agreement between the theory and experiment is excellent. For the orthotropic beams, a stressoptic law which accounts for the effects of residual birefringence was used. The residual birefringence observed for the composite used in this study is greater than one fringe order and results from a matrix residual tension which is about one fourth of the resin's ultimate tensile strength. Finally, the influence of such a large residual birefringence on beam and calibration photoelastic data is discussed in detail. Paper was presented at the 1986 SEM Spring Conference on Experimental Mechanics, held in New Orleans, LA on June 8–13.     

Die Chroms?ure?tzung von Polyolefinoberfl?chen und Adhiisivbindung

Ohne Zusammenfassung     

Synthesis of 14C-radiolabelled trimethyllead chloride

Two synthetic routes to ¹⁴C-labelled trimethyllead chloride ((CH₃)₃PbCl) from ¹⁴C-methyl iodide (CH₃I) were investigated. Alkylation of (CH₃)₃PbCl with labelled methylmagnesium halide, on a microscale, was less efficient for the synthesis of tetramethyllead ((CH₃)₄Pb) than was an electrochemical reduction of labelled CH₃I at a sacrificial lead cathode. In the Grignard approach, unlabelled decyl bromide served as an initiator for the reaction of ¹⁴C-CH₃l with excess Mg and as a carrier during the subsequent alkylation of (CH₃)₃PbCl. In the electrochemical approach a two-compartment cell, using dimethylformamide as solvent and sodium perchlorate as supporting electrolyte, offered several advantages over a single compartment reactor. The labelled (CH₃)₄Pb from both reactions was isolated by extraction, converted to (CH₃)₃PbCl by controlled oxidation with HCl and purified by thin layer chromatography.     

Comparison of characterization methods in high frequency sonochemical reactors of differing configurations

The aim of this study was to compare different characterization methods in order to evaluate the sonochemical efficiency of a cavitational reactor. The selected characterization methods were calorimetry and dosimetry based on potassium iodide oxidation or nitrite and nitrate ion formation. The effects of experimental parameters on physical and chemical effects of ultrasound were quantified with two transducers at a frequency of 366 kHz. The studied factors comprised temperature (16–28 °C), acoustic power (6–38 W), power density (4–61 W L^?1) and reactor configuration (D_{reactor 1} = 65 mm, D_{reactor 2} = 102 mm). Spectrophotometry was compared to ionic chromatography as a method to quantify nitrite and nitrate ions. Spectrometry was shown to be as representative as ionic chromatography. The reaction system based on the formation of both nitrite and nitrate ions was demonstrated to be as reliable as a potassium iodide dosimeter. The representativity of calorimetry was limited since part of acoustic energy was assumed to be used in the chemical reactions observed by dosimetry. Similar sonochemical efficiencies resulted from an increase of sonified surface (D_{reactor 1} = 65 mm vs. D_{reactor 2} = 102 mm) coupled to a 2-time decrease in power density at a constant emitting surface. The effect of emitting-to-sonified surface area ratio on the acoustic field was apparently limited by the height of the liquid.     

Signal enhancement in laser diode thermal desorption‐triple quadrupole mass spectrometry analysis using microwell surface coatings

Laser‐diode thermal desorption (LDTD) is an ionization source usually coupled to triple quadrupole mass spectrometry (QqQMS) and specifically designed for laboratories requiring high‐throughput analysis. It has been observed that surface coatings on LDTD microwell plates can improve the sensitivity of the analysis of small polar molecules. The objective of the present study is to understand and quantify the effect of microwell surface coatings on signal intensity of small organic molecules of clinical, environmental, and forensic interest. Experiments showed that the peak areas of diclofenac, chloramphenicol, salicylic acid, and 11‐nor‐9‐carboxy‐Δ⁹‐tetrahydrocannabinol obtained by LDTD‐QqQMS increased by up to 3 orders of magnitude when using microwells coated with ethylenediaminetetraacetic acid (EDTA). Tests with different chelating agents and polytetrafluoroethylene as microwell surface coatings showed that nitrilotriacetic acid gave significantly higher peak areas for five out of the nine compounds that showed signal enhancement using chelating agents as coatings. Scanning electron microscopy studies of EDTA‐coated and uncoated microwells showed that analytes deposited in the former formed more uniform and thinner films than in the latter. The enhancement effect of surface coatings in LDTD‐QqQMS was explained mainly by the formation of homogenous and thinner layers of nanocrystals of analytes that are easier to desorb thermally than the layers formed when the analytes dry in direct contact with the bare stainless‐steel surface. Chemisorption of some analytes to the stainless‐steel surface of the microwell plate appeared to be a minor factor. Surface coatings widen the number of compounds analyzable by LDTD‐QqQMS and can also improve sensitivity and limits of detection.     

Ultraviolet-B-induced inactivation of human OGG1, the repair enzyme for removal of 8-oxoguanine in DNA

The OGG1 proteins are DNA N-glycosylases-apurinic-apyrimidinic lyases that are responsible for the removal of 8-oxo-7,8-dihydroguanine (8-oxoG) base in DNA. The human enzyme (hOGG1) is a monomer of 345 amino acids containing 10 buried tryptophan (Trp) residues that are very sensitive to UVB irradiation. The photolysis quantum yield of these Trp residues is about 0.3 and 0.1 in argon- and air-saturated solutions, respectively. Matrix-assisted laser desorption-ionization-time-of-flight mass spectrometry shows that several cleavage sites are identical under aerobic and anaerobic photolysis of Trp residues; one of them includes the active site. Western blots and polyacrylamide gel electrophoresis indicate that fragments of high molecular size are also formed. In addition to common photochemical paths with argon-saturated solutions, specific reactions occur in air-saturated solutions of hOGG1. The photolysis rate is inhibited by more than 50% on binding of hOGG1 to a 34mer oligonucleotide containing a single 8-oxoG-C base pair. Binding to the oligonucleotide with 8-oxoG-C induced a 20% quenching of the hOGG1 fluorescence, suggesting interaction of nucleic acid bases with the Trp residue(s) responsible for the photolysis. Using 2,6-diamino-4-hydroxy-5-N-methylformamidopyrimidine (Me-FapyG) and 8-oxoG as substrates, it is shown that protein photolysis induces photoinactivation of the DNA N-glycosylase activities. The excision of 8-oxoG is more affected than that of Me-FapyG at the same dose of UVB irradiation under both air and argon conditions. Besides the role of Trp residues, the possible involvement of Cys 253 in the photoinactivation process of hOGG1 is discussed.     

Nanoscopic assemblies between supramolecular redox active metallodendrons and gold nanoparticles: synthesis,characterization, and selective recognition of H2PO4-, HSO4-, and adenosine-5'-triphosphate (ATP2-) anions

Tri- and nonaferrocenyl thiol dendrons have been synthesized and used to assemble dendronized gold nanoparticles either by the ligand-substitution method from dodecanethiolate-gold nanoparticles (AB(3) units) or Brust-type direct synthesis from a 1:1 mixture of dodecanethiol and dendronized thiol (AB(9) units). The dendronized colloids are a new type of dendrimers with a gold colloidal core. Two colloids containing a nonasilylferrocenyl dendron have been made; they bear respectively 180 and 360 ferrocenyl units at the periphery. These colloids selectively recognize the anions H(2)PO(4)(-) and adenosine-5'-triphosphate (ATP(2)(-)) with a positive dendritic effect and can be used to titrate these anions because of the shift of the CV wave even in the presence of other anions such as Cl(-) and HSO(4)(-). Recognition is monitored by the appearance of a new wave at a less positive potential in cyclic voltammetry (CV). The anion HSO(4)(-) is also recognized and titrated by the dendronized colloid containing the tris-amidoferrocenyl units, because of the progressive shift of the CV wave until the equivalence point. These dendronized colloids can form robust modified electrodes by dipping the naked Pt electrode into a CH(2)Cl(2) solution containing the colloids. The robustness is all the better as the dendron is larger. These modified electrodes can recognize H(2)PO(4)(-), ATP(2)(-) and HSO(4)(-), be washed with minimal loss of adsorbed colloid, and be reused.     

SELECTIVE DNA THYMINE DIMERIZATION DURING UVA IRRADIATION IN THE PRESENCE OF A SATURATED PYRIDOPSORALEN

Abstract— It has been recently shown that UVA (320–400 nm) irradiation of DNA in the presence of pyridopsoralens induces the formation of thymine cyclobutane dimers in addition to monoadducts. In this work, we measured the potency of a saturated pyridopsoralen to photosensitize DNA, despite its inability to covalently attach to DNA. First, from spectroscopic fluorescence measurements, we have shown that both analogs, saturated and unsaturated pyridopsoralens, namely 4',5'-dihydro-7-methyl-pyrido[3,4-clpsoralen (DH-MePyPs) and 7-methylpyrido[3,4-c]psoralen, exhibit a similar global affinity for DNA. Secondly, we demonstrated, by footprinting experiments, that exposure of a DNA sequence to 365 nm UV radiation in the presence of DH-MePyPs results in selective cyclobutane thymine dimerization. Thymines located in the immediate proximity of the 5'-TA-3' step are exclusively affected and the frequency of this photoprocess depends on flanking sequences. We thus probe a selective thymine dimer photosensitizer. Results are discussed in terms of drug affinity and physical properties of the helix at the binding site.     

Tetraaza analogues of lithium and sodium alums: synthesis and X-ray structures of the single strand polymer [Li(THF)2(Al[SO2(NtBu)2]2)] infinity and the contact ion pairs [Na(15-crown-5)][Al(SO2(NtBu)2)2] and ([Na(15-crown-5)][O2S(mu-NBn)2Al(mu-NBnSO2NBn)])2

The reaction of an alkali metal aluminohydride MAlH4 (M = Li, Na) with N,N'-bis-(tert-butyl)sulfamide or N,N'-bis-(benzyl)sulfamide in THF produces the complex ions (Al[SO2(NR)2]2)- (R = tBu, Bn). The X-ray structures of [Li(THF)2(Al[SO2(NtBu)2]2)] infinity (1), [Na(15-crown-5)][Al(SO2(NtBu)2)2], (2) and ([Na(15-crown-5)][O2S(mu-NBn)2Al(mu-NBnSO2NBn)])2 (3.3THF) are reported. The two diazasulfate ligands [SO2(NtBu)2]2- are N,N' chelated to Al3+ in both 1 and 2. In the lithium derivative 1 the spirocyclic (Al[SO2(NtBu)2]2)- anions are bridged by the bis-solvated cations Li(THF)2+ to give a polymeric strand. In the sodium salt 2 the complex anion is O,O' chelated to Na+, which is further encapsulated by a 15-crown-5 ligand to give a monomeric ion-pair complex. By contrast, the benzyl derivative 3 forms a dimer in which the terminal [SO2(NBn)2]2- ligands are (N,N'),(O,O') bis-chelated to Al3+ and Na+, respectively, and the bridging ligands adopt a novel N,O-chelate, N'-monodentate bonding mode. The central core of 3 consists of two four-membered AlOSN rings bridged by two NtBu groups. Crystal data: 1, orthorhombic, Pna2(1), a = 20.159(5) degrees, b = 10.354(3) degrees, c = 15.833(4) degrees, alpha = beta = gamma = 90 degrees, V = 3304.7(15) A3, Z = 4; 2, monoclinic, P2(1)/n, a = 16.031(2) A, b = 9.907(2) A, c = 23.963(4) A, beta = 103.326(2) degrees, Z = 4; 3, triclinic, P1, a = 12.7237(11) A, b = 14.0108(13) A, c = 16.2050(14) A, alpha = 110.351(2) degrees, beta = 111.538(2) degrees, gamma = 97.350(2) degrees, Z = 1.     

Photophysical properties of glucoconjugated chlorins and porphyrins and their associations with cyclodextrins

Glucoconjugated analogues of the meta-hydroxyphenyl porphyrin (m-THPP) and meta-hydroxyphenyl chlorin (m-THPC) has been recently synthesized. The characteristics of their triplet states have been determined with regard to their involvement in the photodynamic (PDT) efficiency. In the case of porphyrin derivatives, triplet quantum yields (Phi(T)) were ranging from 0.42 to 0.55 and triplet life times (tau(T)) from 1 to 5 micros. High reaction rate constants (k(q)) with molecular oxygen (k(q): 1.2-1.6 x 10(9)s(-1)) have been found. The triplet lifetimes of chlorin derivatives were about four times higher than those of porphyrins whereas the Phi(T) and k(q) values remained quite similar. Singlet oxygen yields of glucosylated and non-glucosylated porphyrins and chlorins were not significantly different within experimental errors (Phi(Delta)((1)O(2)): 0.41-0.58). Furthermore, it has been shown that glucoconjugated photosensitizers could undergo associations with the methyl-beta-cyclodextrin (Me-beta-CD) which exhibit high triplet lifetimes and singlet oxygen yields ranging from 0.27 to 0.48.