bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the aggregation of bilirubins using vapor pressure osmometry
Authors: Boiadjiev Stefan E. , Lightner David A. 
Published: March 2009

AbstractBilirubin and its analogs are carboxylic acids that engage in intramolecular hydrogen bonding and are thus thought to be monomelic in solution, although the evidence for the molecularity in solution is indirect. Contrastingly, the dimethyl esters favor intermolecular hydrogen bonding and are thought to be dimeric, yet they, like the bilirubin (acids), exhibit essentially no concentration dependence of their NH nmr chemical shifts upon dilution from 10−2 to 10−5 (or even 10−6) M in chloroform‐d. Vapor phase osmometry (vpo) studies of chloroform solutions of eight bilirubins and their dimethyl esters clearly indicate that the former are monomelic, while the latter are dimeric — except when a β‐methyl group (but not an α*‐methyl) is present in each methyl propionate chain. Bilirubin mono‐esters might be monomelic or dimeric in solution. Using vpo to study some seven mono‐esters or mono acids, we found that the pigments were monomelic in chloroform.
Synthesis of novel azonia Helicenes containing terminal thiophene rings
Authors: Sato Kiyoshi , Yamagishi Takamichi , Arai Sadao 
Published: March 2009

AbstractThe Knoevenagel condensation of the 9‐methyl derivatives of thieno[3,2‐a]‐ and thieno[2,3‐a]‐quinolizinium salts (2b and 3b) with appropriate arylaldehydes yielded 9‐(arylvinyl)thieno[3,2‐a]‐ and 9‐(arylvinyl)thieno[2,3‐a]quinolizinium salts (4a‐c and 5a‐c), respectively, which underwent photocyclization to give a series of novel hetero[5]helicenes (6a,b and 7a‐d) containing quinolizinium and thiophene rings.
An improved coupling procedure for the barton‐zard pyrrole synthesis
Authors: Bobál Pavel , Lightner David A. 
Published: March 2009

AbstractAn improved final step in the Barton‐Zard pyrrole synthesis uses inexpensive potassium carbonate as base in the coupling‐cyclization reaction of vic‐nitro‐acetates with isocyanides. In this modification the isolated yields of synthetically useful 2‐carboalkoxypyrroles (1a,b and 3) and 2‐(p‐toluenesulfonyl)pyrroles (2a,b) consistently rise to the 78‐89% range. Conversion of 2a to 5‐(p‐toluenesulfonyl)‐2‐pyrrolinone 4 is conveniently and directly achieved by reaction with 30% hydrogen peroxide in acetic acid, thus circumventing the commonly used two step procedure involving bromination followed by solvolysis.
Synthesis of 2‐amino‐4h‐thiazolo[5,4‐b]indole and characterization of its colored conversion products with protein tyrosine phosphatase inhibitory activity
Authors: Breinholt Jens , Jeppesen Claus Bekker , Branner Sven , Olsen Carl Erik , Møller Niels Peter Hundahl , Nielsen Bjarne Hilmer , Andersen Henrik Sune 
Published: March 2009

AbstractIn DMSO‐solution 2‐amino‐4H‐thiazolo[5,4‐b]indole is converted into a complex mixture of colored products. The three major conversion end‐products, of which two are inhibitors of protein tyrosine phos‐phatases (PTPs), were isolated by chromatographic methods and their structures characterized by spectro‐scopic analysis, including NMR and MS combined with computer assisted structure elucidation, and, finally, confirmed by independent chemical synthesis. Synthesis of 2‐amino‐4H‐thiazolo[5,4‐b]indole as well as its N‐acetyl derivatives prepared from either oxindole or 2‐bromo‐1‐(2‐nitro‐phenyl)ethanone is described.
Synthesis and spectroscopic studies of 5‐arylidene‐3‐substituted tetramic acids as possible substrates for catalytic asymmetric hydrogenation
Authors: Athanasellis Giorgos , Gavrielatos Efstathios , Igglessi‐Markopoulou Olga 
Published: March 2009

AbstractA new series of 5‐arylidene‐3‐substituted tetramic acids 6–19 have been synthesized by a condensation reaction of 3‐butanoyl tetramic acid 3, 3‐ethoxycarbonyl tetramic acid 4 and 3‐acetyl tetramic acid 5 with a variety of substituted benzaldehydes. The structures of the isolated compounds 6–19 have been elucidated using FT‐IR, 1H and 13C‐NMR spectroscopy, FAB‐MS spectroscopy as well as elemental analyses.
Synthesis of two novel classes of tetracycles bearing tetrahydro ring system from benzothiazole: 7,8,9,10‐tetrahydrothiazolo[5,4‐a]acridine and 1,2,3,4‐tetrahydro‐12H‐benzothiazolo[2,3‐b] quinazolin‐12‐one
Authors: Robin Maxime , Mialhe Stéphane , Pique Valérie , Faure Robert , Galy Jean‐Pierre 
Published: March 2009

AbstractNovel 7,8,9,10‐tetrahydrothiazolo[5,4‐a]acridine and 1,2,3,4‐tetrahydro‐12H‐benzothiazolo[2,3‐b]‐quinazolin‐12‐one derivatives were synthesized in one step from the corresponding benzothiazoles. These two new tetracyclic skeletons were unambiguously characterized and are presently in pharmacological tests.
Formation of nitrogen‐containing heterocycles using di(imidazole‐1‐yl)methanimine
Authors: Wu Yong‐Qian , Limburg David C. , Wilkinson Douglas E. , Hamilton Gregory S. 
Published: March 2009

AbstractA mild and efficient synthesis of five‐ and six‐membered nitrogen containing heterocyclic compounds, in which di(imidazole‐1‐yl)methanimine serves as a one‐carbon source, is reported.
Preparation of a clinically investigated ras farnesyl transferase inhibitor
Authors: Maligres Peter E. , Waters Marjorie S. , Weissman Steven A. , McWilliams J. Christopher , Lewis Stephanie , Cowen Jennifer , Reamer Robert A. , Volante R. P. , Reider Paul J. , Askin David 
Published: March 2009

AbstractThe synthesis of ras farnesyl‐protein transferase inhibitor 1 is described on a multi‐kilogram scale. Retrosynthetic analysis reveals chloromethylimidazole 2 and a piperazinone 3 as viable precursors. The 1,5‐disubstituted imidazole system was regioselectively assembled via an improved Marckwald imidazole synthesis. A new imidazole dethionation procedure has been developed to convert the Marckwald mercaptoim‐idazole product to the desired imidazole. This methodology was found to be tolerant of a variety of functional groups providing good to excellent yields of 1,5‐disubstituted imidazoles. A new Mitsunobu cycliza‐tion strategy was developed to prepare the arylpiperazinone fragment 3.
Polar effects in free‐radical reactions. A novel homolytic acylation of heteroaromatic bases by aerobic oxidation of aldehydes, catalysed by N‐hydroxyphthalimide and Co salts
Authors: Minisci Francesco , Recupero Francesco , Cecchetto Andrea , Punta Carlo , Gambarotti Cristian , Fontana Francesca , Pedulli Gian Franco 
Published: March 2009

AbstractA new process for the homolytic acylation of protonated heteroaromatic bases is described; an N‐oxyl radical (PINO) generated from N‐hydroxyphthalimide by air oxygen and Co(II) abstracts a hydrogen atom from an aldehyde. The resulting nucleophilic acyl radical adds to a heteroaromatic base, which is then rearo‐matised in a chain process. Quinazoline has an anomalous behaviour, giving 3H‐quinazolin‐4‐one as the only reaction product.
Syntheses of diazadithiacrown ethers containing appended coumarin or 1‐aminonaphthalene sidearms
Authors: Song Hua‐Can , Xu Zun‐Le , Chen Yi‐Wen , Yao Jun‐Hua , Bradshaw Jerald S. , Savage Paul B. , Izatt Reed M. 
Published: March 2009

AbstractSix crown ethers containing two coumarin (11, 13,14,16,17 and 19) or two 1‐aminonaphthalene (15 and 20) fragments as sidearms and two crown ethers bearing one coumarin (12 and 18) arm were synthesized by a nucleophilic substitution of the secondary macrocyclic amine function on the alkyl halide. The major products of these reactions were the diazadithiacrown ethers containing two sidearms. In some cases, one‐armed diazadithiacrown ethers were separated as minor products, although more than 2.5 mmoles of alkyl halide were used for 1.0 mmole of macrocyclic diamine.
Reactions of 3‐benzylindole‐2‐carbohydrazides: Synthesis of new 10‐Benzyl‐1,2‐dihydro‐1‐oxo‐1,2,4‐triazino[4,5‐a]indoles and 3‐Benzyl‐2‐(1,3,4‐oxadiazol‐2‐yl)indoles
Authors: Maddirala Shambabu Joseph , Gokak Vidya S. , Basanagoudar Linganagouda D. 
Published: March 2009

Abstract3‐Benzylindole‐2‐carbohydrazides (4) on reaction with triethylorthoformate in a polar solvent like DMF yielded only 10‐benzyl‐1,2‐dihydro‐1‐oxo‐1,2,4‐triazino[4,5‐a]indoles (5) while (4) on reaction with triethylorthoacetate in DMF yielded both 10‐benzyl‐4‐methyl‐1,2‐dihydro‐1‐oxo‐1,2,4‐triazino[4,5‐a]indoles (5) and 3‐benzyl‐2‐(5‐methyl‐1,3,4‐oxadiazol‐2‐yl)indoles (6) instead of only the triazinoindoles as expected. The oxadiazolylindoles (6) were also synthesized by refluxing (4) with excess of orthoesters. The structures of the compounds formed were characterized by their analytical and spectral data.
4H‐thieno[3,4‐e]‐ and 4H‐pyrazolo[4,3‐e]‐1,2,4‐thiadiazine 1,1‐dioxides synthesis, chemical properties and evaluation of their Potential Cardiovascular Activity
Authors: Vega Salvador , Arranz María Esther 
Published: March 2009

AbstractThis paper deals with the synthesis of a number of new 4H‐thieno[3,4‐e] and 4H‐pyrazolo[4,3‐e]‐1,2,4‐thiadiazine 1,1‐dioxide derivatives 1, the study of their chemical behavior in some alkylation reactions and the evaluation of their vasorelaxant effects on spontaneous motility and on tension responses to increased extracellular KCl concentrations in isolated rat portal vein.
Synthesis and reactivity of some imidazo‐, triazolo‐ and tetrazolo‐isoquinoline derivatives
Authors: Deady Leslie W. , Devine Shane M. 
Published: March 2009

Abstract1‐Acetylirrüno‐3‐methyl‐1H‐isochromene‐4‐carbonitrile, 1, reacts with glycine ethyl ester under basic conditions to give an imidazo[2,1‐a]isoquinoline derivative, while reaction with hydrazine hydrate in 1,4‐dioxane, with further chemistry, provides access to [1,2,4]triazolo[5,1‐a]isoquinoline, [1,2,4]triazolo[3,4‐a]isoquinoline and tetrazolo[5,1‐a]isoquinoline analogs. Benzene ring nitration and radical bromination of substituent methyl groups were investigated in the four tricycles, with some different positional reactivities being found. Two bromomethyl derivatives so produced were oxidised; ethyl 2‐bromomethyl‐6‐cyano‐5‐methylimidazo[2,1‐a]isoquinoline‐3‐carboxylate gave the anticipated ethyl 6‐cyano‐2‐formyl‐5‐methylimidazo[2,1‐a]isoquinoline‐3‐carboxylate (which reacted further with hydrazine to form a new system, 8,9‐dihydro‐6‐methyl‐8‐oxopyridazino[4′,5′:4,5]imidazo[2,1‐a]isoquinoline‐5‐carbonitrile), while 5‐bromomethyl‐2‐methyl[1,2,4]triazolo[5,1‐a]isoquinoline‐6‐carbonitrile unexpectedly gave directly another new system, 5,6‐dihydro‐5‐hydroxy‐2‐methyl‐7H‐pyrrolo[3,4‐c][1,2,4]triazolo[5,1‐a]isoquinolin‐7‐one.
Synthesis and biological evaluation of benzo[7,8]chromeno[5,6‐b][1,4]oxazin‐3‐ones
Authors: Nicolaides Demetrios N. , Gautam Daman R. , Litinas Konstantinos E. , Hadjipavlou‐Litina Dimitra J. , Kontogiorgis Christos A. 
Published: March 2009

AbstractThe O‐methylmonoximes 2,3 of stenocarpoquinone‐A and β‐lapachone reacted with methyl phenylacetate to give 1,4‐benzoxazine derivatives 8a, 8b and oxazole 11a. Compound 8a was transformed to compounds 13I, 13II, 14. Treatment of compound 14 with osmium tetroxide afforded compounds 15, 16 and esterification of the latter gave the bis‐ and mono‐ esters 17I, 17II, 18. All products are strongly fluorescent. Compounds 8a,b, 11a, 13–18 (azabenzo analogues of khellactones) were tested for their ability to interact with DPPH, to compete with dimethylsulfoxide for hydroxyl radicals, to inhibit soybean lipoxygenase and trypsin activities in vitro. Compounds 16 and 17II were found to compete significantly with dimethylsulfoxide for hydroxyl radicals, whereas compounds 8a, 11a, 14 and 17I were found to inhibit strongly soybean lipoxygenase.
Synthesis of dihydrothieno[2,3‐b]pyridines based on titanium(IV) chloride‐mediated michael reactions of 2‐amino‐4,5‐dihydro‐3‐thiophenecarbonitriles with α,β‐unsaturated ketones
Authors: Maruoka Hiroshi , Yamazaki Motoyoshi , Tomioka Yukihiko 
Published: March 2009

Abstract2‐Arnino‐4,5‐dihydro‐3‐thiophenecarbonitriles 1a‐c reacted with α,β‐unsaturated ketones (e.g. methyl vinyl ketone 2 and benzalacetone 3) in the presence of titanium(IV) chloride to give the corresponding Michael adducts 4a‐c and 5a‐c. Thermal treatment of compounds 4a‐c and 5a‐c with titanium(IV) chloride caused intramolecular cyclocondensation to yield the corresponding tetrahydrothieno[2,3‐b]pyridines 6a‐c and 7a‐c. Aromatization of 6a‐c and 7a‐c with potassium tert‐butoxide in refluxing tert‐butyl alcohol pro ceeded smoothly to afford the corresponding dihydrothieno[2,3‐b]pyridines 8a‐c and 9a‐c.
New many fold 1,2,3‐selenadiazole aromatic derivatives
Authors: Al‐Smadi Mousa , Ratrout Samer 
Published: March 2009

AbstractThe many fold aromatic ketones 2a‐d are versatile compounds for the synthesis of the many fold 1,2,3‐selenadiazole aromatic derivatives 5a‐d. The preparation starts with the reaction between the many fold bromomethylene benzene derivatives 1a‐d and 4‐hydroxyacetophenone, which are transformed through the reaction with semicarbazide hydrochloride or ethylhydrazine carboxylate into the corresponding semicarbazones derivatives 3a‐d or hydrazones 4a‐d. The reaction with selenium dioxide leads to regiospecific ring closure of semicarbazones or hydrazones to give the many fold 1,2,3‐selenadiazole aromatic derivatives in high yield.
A novel synthesis of 1‐substituted 2H‐isoquinolin‐3‐ones
Authors: Cánepa Alicia S. , Bravo Rodolfo D. 
Published: March 2009

AbstractThe intramolecular cyclization of 2‐acylphenylacetonitriles 1 under strongly acidic conditions easily affords 1‐substituted 2H‐isoquinolin‐3‐ones 2 in excellent yields.
Effect of reconstitution of sorghum with or without enzymes on production performance and immunocompetence in broiler chicken
Authors: Manwar Satish J , Mandal Asit B 
Published: March 2009

AbstractBACKGROUND: The presence of tannins and phytic acid in sorghum causes anti‐nutritional effects that include reduced growth rate, feed intake, feed efficiency and nutrient digestibility in broiler chicken. Therefore, in the present investigation efforts were made to reveal the effect of reconstitution of sorghum with or without enzymes on production performance and immunocompetence in broiler chicken.RESULTS: The body weight gain, feed conversion ratio, energy and protein utilization efficiency were better in birds fed reconstituted sorghum in comparison to those fed untreated sorghum. The intake of feed in different treatments did not vary in comparison to the control group. The feed cost per unit weight gain or meat yield apparently reduced due to reconstitution. There was significant improvement in nitrogen corrected apparent metabolizable energy (AMEn) of diets containing reconstituted sorghum. The serum biochemical parameters such as total cholesterol, triglycerides and uric acid were not affected due to dietary treatments. The cell‐mediated immune response to phytohaemagglutinin‐P was better in sorghum‐fed groups. However, the humoral response to sheep red blood cells remained unaffected owing to the substitution of the maize by sorghum or its processed form.CONCLUSION: The results suggest that the reconstitution of sorghum was beneficial in improving the growth performance and nutrient utilization in broiler chicken. However, supplementation of enzymes to raw sorghum‐based diets or addition of enzymes during reconstitution of sorghum did not further improve the growth performance of broilers. Copyright © 2009 Society of Chemical Industry
Stability and antioxidative properties of acylated anthocyanins in three cultivars of red cabbage (Brassica oleracea L. var. capitata L. f. rubra)
Authors: Pliszka Barbara , Huszcza‐Ciołkowska Grażyna , Mieleszko Emilia , Czaplicki Sylwester 
Published: March 2009

AbstractBACKGROUND: Red cabbage is rich in acylated anthocyanins. The aim of the experiment has been to determine the stability of anthocyanins in extracts of red cabbage cultivars and examine their antioxidative properties. The (high‐performance liquid chromatographic) HPLC profile of anthocyanins characteristic of each red cabbage cultivar has also been determined.RESULTS: We have used three red cabbage cultivars: cv. Koda, Haco POL and Kissendrup SWE. The HPLC assays enabled us to distinguish nine anthocyanin compounds, which were all classified as cyanidin derivatives. These compounds occurred in different proportions in the three culitvars of red cabbage. The differences were observed in the degradation index of anthocyanins in extracts from the red cabbage cultivars examined, both stored at + 2 °C and frozen. The highest trolox equivalent antioxidant capacity (TEAC) was attained for anthocyanins from cv. Haco POL red cabbage, whereas the lowest value was determined for cv. Koda.CONCLUSION: There were differences in the stability and antioxidative properties of anthocyanin compounds in red cabbage extracts among the cultivars evaluated (Koda, Haco POL and Kissendrup SWE). The highest stability and strongest antioxidative properties were assigned to anthocyanins in extracts from cv. Haco POL. The HPLC profiles imply differences in proportions of anthocyanin compounds present in the three red cabbage cultivars. Copyright © 2009 Society of Chemical Industry
Biomimetic carbocationic polymerizations III: Investigation of isoprene polymerization initiated by dimethyl allyl bromide
Authors: Puskas Judit E. , Peruch Frédéric , Deffieux Alain , Dabney David E. , Wesdemiotis Chrys , Li Haibo , Lindsay Allia 
Published: March 2009

AbstractNatural rubber (poly(1,4‐cis‐isoprene), NR) is a polymer of considerable industrial importance due to its exceptional properties. It is mostly produced from the cultivation of Hevea brasiliensis, and to a limited extent from Parthenium argentatum. Till date none of the synthetic equivalent of NR exists. Recently we suggested that the mechanism of NR biosynthesis is based on carbocationic polymerization, similarly to that of natural oligoisoprenoids forming by enzyme‐catalyzed prenylation. In this article we present proof of concept of a new bio‐inspired synthetic route towards the synthesis of polyisoprenes based on carbocationic polymerization initiated by dimethyl allyl bromide (DMABr)/TiCl4. It is shown that using this strategy, 1,4‐oligoisoprene carrying a dimethyl allyl head group is produced in both cis and trans configurations, together with cyclized sequences. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2172–2180, 2009
Soluble narrow‐band‐gap copolymers containing novel cyclopentadithiophene units for organic photovoltaic cell applications
Authors: Li Kuang‐Chieh , Hsu Ying‐Chan , Lin Jiann‐T'Suen , Yang Chang‐Chung , Wei Kung‐Hwa , Lin Hong‐Cheu 
Published: March 2009

AbstractFive novel conjugated copolymers (P1–P5) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with arylcyanovinyl and keto groups in different molar ratios) were synthesized and developed for the applications of polymer solar cells (PSCs). Polymers P1–P5 covered broad absorption ranges from UV to near infrared (400–900 nm) with narrow optical band gaps of 1.38–1.70 eV, which are compatible with the maximum solar photon reflux. Partially reversible p‐ and n‐doping processes of P1–P5 in electrochemical experiments were observed, and the proper molecular design for highest occupied molecular orbital (HOMO)/lowest unoccupied molecular orbital (LUMO) levels of P1–P5 induced the highest photovoltaic open‐circuit voltage in the PSC devices, compared with those previously reported CPDT‐based narrow‐band‐gap polymers. Powder X‐ray diffraction (XRD) analyses suggested that these copolymers formed self‐assembled π‐π stacking and pseudobilayered structures. Under 100 mW/cm2 of AM 1.5 white‐light illumination, bulk heterojunction PSC devices containing an active layer of electron donor polymers P1–P5 mixed with electron acceptor [6,6]‐phenyl C61 butyric acid methyl ester (PCBM) in the weight ratio of 1:4 were investigated. The PSC device containing P1 gave the best preliminary result with an open‐circuit voltage of 0.84 V, a short‐circuit current of 2.36 mA/cm2, and a fill factor of 0.38, offering an overall power conversion efficiency (PCE) of 0.77% as well as a maximal quantum efficiency of 23% from the external quantum efficiency (EQE) measurements. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2073–2092, 2009
Synthesis, characterization, and properties of regioregular conjugated polymers containing quaterthiophene and an acceptor repeating units
Authors: Chen Hui , Lu Yong , Ong Teng‐Teng , Hu Xiao , Ng Siu‐Choon 
Published: March 2009

AbstractNovel donor–acceptor type polymers consisting of alternating quaterthiophene and an electron withdrawing moiety, pyrazinyl or pyridinyl, have been prepared using Stille coupling approach with moderate yields. The polymers were highly soluble in common organic solvents such as tetrahydrofuran and chloroform. The structure and optical properties of the polymers were characterized by NMR, UV‐vis and fluorescence spectroscopy, and cyclic voltammetry, respectively. The polymer having pyrazine unit exhibited a red‐shift in both absorption and emission in comparison with those analogs containing pyridine because of strong electron withdrawing character of the pyrazinyl group. The polymer containing pyrazinyl as acceptor units also depicted decrease in its optical and electrochemical bandgap relative to those polymers containing 2,5‐ or 2,6‐pyridine moieties. The electrochemical behavior showed facile n‐doping and p‐doping properties of those polymers consisting of alternating quaterthiophene and the acceptor moiety. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2163–2171, 2009
Genotype–environment interactions affect flower and fruit herbivory and plant chemistry ofArabidopsis thalianain a transplant experiment
Authors: Mosleh Arany A. , de Jong T. J. , Kim H. K. , van Dam N. M. , Choi Y. H. , van Mil H. G. J. , Verpoorte R. , van der Meijden E. 
Published: March 2009

AbstractLarge differences exist in flower and fruit herbivory between dune and inland populations of plants ofArabidopsis thaliana(Brassicaceae). Two specialist weevilsCeutorhynchus atomusandC. contractus(Curculionidae) and their larvae are responsible for this pattern in herbivory. We test, by means of a reciprocal transplant experiment, whether these differences reflect environmental influences or genetic variation in plant defense level. All plants suffered more damage after being transplanted to the dune site than after being transplanted to the inland site. Plants of inland origin suffered more flower and fruit herbivory than plants of dune origin when grown at the dune transplant site, but differences were much smaller at the inland site. Both flower damage by adult weevils and fruit damage by their larvae were subject to significant genotype × environment interactions. The observed pattern in herbivory is a strong indication for local adaption of plant defense to the level of herbivory byCeutorhynchus.In order to identify the mechanism of defense, a quantitative analysis of glucosinolates was performed on the seeds with HPLC. Highly significant differences were found in glucosinolate types and total concentration. These patterns were mainly determined by the origin of the plants (dune or inland) and by a genotype × environment interaction. Herbivory was not significantly correlated to the concentration of glucosinolates in seeds. We therefore analyzed the total metabolic composition of seeds, using NMR spectroscopy and multivariate data analysis. Major differences in chemical composition were found in the water–methanol fractions: more glucosinolate and sucrose in the dune and more fatty acids, lipids and sinapoylmalate in the inland populations. We discuss which of these chemical factors could explain the marked differences in damage between populations.