Reactions of the carcinogen N-acetoxy-4-acetamidostilbene with nucleosides.

The carcinogen N-acetoxy-4-acetamidostilbene (N-AcO-AAS) yields multiple products in reactions with guanosine, adenosine or cytidine in aqueous acetone. The major product from the reaction with cytidine is a deamination product, 1-(4-acetamidophenyl)-1-(3-uridyl)-2-hydrosy-2-phenylethane. Three minor products were unstable and were characterized only by their UV spectra and pK values. Adenosine yielded two major products, one of them 1-(4-acetamidophenyl)-1-(N6-adenoxyl)-2-hydroxy-2-phenylethane, and the second 3-(beta-D-ribosyl)-7-phenyl-8-(4-acetamidophenyl)-7,8 dihydroimidazo [2,1-i] purine. The major adduct with guanosine is 1-(4-acetamidophenyl)-1-(1-guanosyl)-2-hydroxy-2-phenylethane. One minor adduct also appears to be a guanosine-N-1 derivative, while two other minor adducts yield 1-(4-acetamidophenyl)-2-phenyl-1, 2-ethanediol on acid hydrolysis, and thus appear to be O6-derivatives. None of the guanine adducts isolated had the properties of N-7, C-8 or N2 adducts. In this respect, N-Aco-AAS appears to behave more like a classical alkylating agent than like previously studied N-acetoxy-N-arylacetamides, although the target organs of 4-acetamidostilbene are the same as those of other N-arylacetamides.     

In vivo interactions of acrylonitrile with macromolecules in rats

The irreversible binding of [2,3-14C]acrylonitrile (VCN) to proteins, RNA and DNA of various tissues of male Sprague-Dawley rats after a single oral dose of 46.5 mg/kg (0.5 LD50) has been studied. Proteins were isolated by chloroform-isoamyl alcohol-phenol extraction. RNA and DNA were separated by hydroxyapatite chromatography. Binding of VCN to proteins was extensive and was time dependent. Radioactivity in nucleic acids was registered in the liver and the target organs, stomach and brain. DNA alkylation, which increased by time, was significantly higher in the target organs, brain and stomach (119 and 81 pmol/mg, respectively, at 24 h) than that in the liver. The covalent binding indices for the liver, stomach and brain at 24 h after dosing were, 5.9, 51.9 and 65.3, respectively. These results suggest that VCN is able to act as a multipotent carcinogen by alkylation of DNA in the extrahepatic target tissues, stomach and brain.     

Persistence of methylated bases in ribonucleic acid of syrian golden hamster liver after administration of dimethylnitrosamine.

1. Syrian golden hamster liver ribosomal RNA was isolated up to 96 h after administration of [14C]dimethylnitrosamine at 25 mg/kg or 2.5 mg/kg body weight. 2. The chemical alkyation products, 7-methylguanine, 3-methylcytosine, O6-methylguanosine and 1-methyladenosine, were measured after acidic or enzymic hydrolysis of the RNA to bases or mononucleosides followed by ion-exchange chromatography. 3. Between 7 and 96 h, the relative amounts of alkylation products did not change with time even though the absolute amounts fell by approx. 80% and 51% after the high and low doses respectively. 4. The results suggest that base specific excision repair does not exist for RNA alkylation products in this experimental system.     

Reaction of urethane with nucleic acids in vivo

1. [1-(14)C]Ethyl carbamate, ethyl [carboxy-(14)C]carbamate, [1-(14)C]ethanol and sodium hydrogen [(14)C]carbonate were injected intraperitoneally into C57 mice, and nucleic acids and proteins were separated from the liver and lungs with phenol as described by Kirby (1956). 2. Chromatographic analysis of the hydrolytic products of the urethane-labelled RNA showed the presence of a single radioactive compound differing in behaviour from the major pyrimidine nucleotides and purines. 3. The products from RNA labelled by [1-(14)C]ethyl carbamate or ethyl [carboxy-(14)C]carbamate appeared chromatographically identical but could not be detected in the RNA of mice given [1-(14)C]ethanol or sodium hydrogen [(14)C]-carbonate. 4. The labelled product appeared to be the ethyl ester of cytosine-5-carboxylic acid formed by the reaction of urethane with RNA in vivo. 5. A direct reaction between labelled urethane or the labelled metabolite of urethane, [1-(3)H]-ethyl N-hydroxycarbamate, and RNA was not detected.     

The specificity of different classes of ethylating agents toward various sites in RNA.

The alkyl products of neutral in vitro ethylation of TMV-RNA by [14C]diethyl sulfate, [14C]ethyl methanesulfonate, and [14C]ethylnitrosourea have been determined and found to differ significantly depending on the ethylating agent. Diethyl sulfate and ethyl methanesulfonate ethylate the bases of TMV-RNA in the following order: 7-ethylguanine greater than 1-ethyladenine, 3-ethylcytidine greater than 7-ethyladenine, 3-ethyladenine, O6-ethylguanosine, 3-ethylguanine. Ethyl methanesulfonate was more specific for the 7 position of guanine, and other derivatives were found in lesser amounts than with diethyl sulfate. Neither reagent caused the formation of detectable amounts (smaller than 0.26 percent) of 1-ethylguanine, 1,7-diethylguanine, N2-ethylguanine, N6-ethyladenine, N4-ethylcytidine, or 3-ethyluridine. Identified ethyl bases account for over 85% of the total radioactivity of [14C]ethyl methanesulfonate and [14C]diethyl sulfate treated TMV-RNA. Phosphate alkylation accounts for about 13 and 1%, respectively, In contrast, [14C]ethylnitrosourea-treated TMV-RNA, while reacting to a similar extent (15-70 ethyl groups/6400 nucleotides), is found to cause considerably more phosphate alkylation. Upon either U4A RNase or acid hydrolysis up to 60% of the radioactivity is found as volatile ethyl groupw in the form of [14C]ethanol, and a further 15% appears to be primarily ethyl phosphate and nucleosides with ethylated phosphate. Of the remaining radioactivity, half is found as O6-ethylguanosine, the major identified ethyl nucleoside. Other ethyl bases found in ethylnitrosourea-treated TMV-RNA are 7-ethylguanine greater than 1-ethyladenine, 3-ethyladenine, 7-ethyladenine, 3-ethylcytidine, and 3-ethylguanine. It appears that ethylnitrosourea preferentially alkylates oxygens, and that formation of phosphotriesters is by far the predominant chemical event. Since the number of ethyl groups introduced into TMV-RNA by ethylnitrosourea is similar to the number of lethal events, one may conclude that phosphate alkylation leads to loss of infectivity. None of the three ethylating agents studied are strongly mutagenic on TMV-RNA or TMV. The role of phosphate alkylation in regard to in vivo mutagenesis and oncogenesis remains to be established. At present it appears possible that the extent of this reaction may correlate better with the oncogenic effectiveness of different ethylating agents, than the extent of any base reaction. Unfractionated HeLa cell RNA is ethylated primarily in acid labile manner even by diethyl sulfate and ethyl methanesulfonate, a fact that is attributed to its high content of low molecular weight trna rich in terminal phosphates which alkylate readily.     

Comparison of sister-chromatid exchange induction caused by nitrosoureas that alkylate or alkylate and crosslink DNA

We have investigated the induction of sister-chromatid exchanges (SCEs) in 9L rat brain tumor cells treated with the alkylating agent 1-ethyl-1-nitrosourea (ENU) and 3-(4-amino-2-methyl-5-pyrimidinyl)methyl-1-(2-chloroethyl)-1-nitrosourea (ACNU), an agent that both alkylates and crosslinks DNA. Induction of SCEs by ACNU was found to be 143-fold greater than for ENU. However, on an equimolar basis, the alkylation of DNA by 14C-ACNU was approximately 3.2-fold higher than for 14C-ENU. After correction for this difference was made, the induction of SCEs by ACNU was calculated to be 45-fold greater than for ENU. While DNA alkylation products formed by ACNU and ENU are similar, the chloroethyl alkylation product(s) of ACNU can form DNA-interstrand crosslinks; the ethyl alkylation product(s) of ENU cannot. Based on these findings, we propose that the increased induction of SCEs caused by ACNU is a result of the formation of DNA interstrand crosslinks.     

Protein composition of nuclear ribonucleoprotein particles isolated from liver of rats in the early stages of feeding of 3'-methyl-4-dimethylaminoazobenzene and from hepatoma induced by the same carcinogen.

The feeding of carcinogenic 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB) in the early stages results in a change in the protein composition of the nuclear ribonucleoprotein particles of the rat liver. These particles are associated with newly synthesized RNA and it is assumed that they are involved in the processing and in the transport of this RNA. After 6 weeks of feeding of this azocarcinogen, the amount of one of the main polypeptides (apparent molecular weight 42 000) is decreased and after 10 weeks of feeding the particles are devoid of this polypeptide completely. Feeding of the non-carcinogenic p-aminoazobenzene (AB) is without any effect. The loss of this polypeptide is not characteristic for the malignant transformation. In the nuclear ribonucleoprotein particles isolated from hepatoma which has been induced by 3'-MeDAB this polypeptide is present in even higher proportion to other polypeptides than it is in particles isolated from liver cells of control animals. The 3'-MeDAB binds to the proteins of the liver nuclear ribonucleoprotein particles and interferes with the RNA processing. It is proposed that the changes in the composition of the protein moiety of the particles reflect changes in the population of liver cells leading finally to the selection of hepatoma cells which are resistant to the toxic effect of 3'-MeDAB on RNA processing.     

Facile synthesis of carbon-11-labeled sEH/PDE4 dual inhibitors as new potential PET agents for imaging of sEH/PDE4 enzymes in neuroinflammation

To develop PET tracers for imaging of neuroinflammation, new carbon-11-labeled sEH/PDE4 dual inhibitors have been synthesized. The reference standard N-(4-methoxy-2-(trifluoromethyl)benzyl)benzamide (1) and its corresponding desmethylated precursor N-(4-hydroxy-2-(trifluoromethyl)benzyl)benzamide (2) were synthesized from (4-methoxy-2-(trifluoromethyl)phenyl)methanamine and benzoic acid in one and two steps with 84% and 49% overall chemical yield, respectively. The standard N-(4-methoxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide (MPPA, 4) and its precursor N-(4-hydroxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide (5) were synthesized from methyl 4-piperidinecarboxylate, propionyl chloride and (4-methoxy-2-(trifluoromethyl)phenyl)methanamine in two and three steps with 62% and 34% overall chemical yield, respectively. The target tracers N-(4-[¹¹C]methoxy-2-(trifluoromethyl)benzyl)benzamide ([¹¹C]1) and N-(4-[¹¹C]methoxy-2-(trifluoromethyl)benzyl)-1-propionylpiperidine-4-carboxamide ([¹¹C]MPPA, [¹¹C]4) were prepared from their corresponding precursors 2 and 5 with [¹¹C]CH₃OTf through O-[¹¹C]methylation and isolated by HPLC combined with SPE in 25–35% radiochemical yield, based on [¹¹C]CO₂ and decay corrected to end of bombardment (EOB). The radiochemical purity was >99%, and the molar activity (A_M) at EOB was 370–740 GBq/μmol with a total synthesis time of 35–40-minutes from EOB.     

Monuron metabolism in excised gossypium hirsutum leaves: Aryl hydroxylation and conjugation of 4-chlorophenylurea*

A new glycoside was isolated as a minor metabolite in excised cotton leaves treated with either [carbonyl-¹⁴C] or [ring-¹⁴C] 3-(4-chlorophenyl)-1-methylurea and 4-chlorophenylurea. The aglycone from β-glucosidase or hesperidinase hydrolysis was identified as 4-chloro-2-hydroxyphenylurea by TLC, radioisotope dilution and MS.     

The in vivo incorporation of mannose, retinol and mevalonic acid into phospholipids of hamster liver

Hamsters were injected intraperitoneally with [¹⁴C]mannose, [¹⁴C]retinol and [³H]mevalonic acid. The livers were removed, extracted with chloroform-methanol and the lipids chromatographed on DEAE-cellulose and silicic acid. The hamster liver lipid contained a component which could be labelled with mannose and mevalonic acid. The properties of this compound were in accord with it being dolichyl-mannosyl-phosphate, a possible lipid intermediate required for the biosynthesis of some glycoproteins. [¹⁴C]Retinol and [¹⁴C] mannose were incorporated into another phospholipid which was labile to mild alkali conditions commonly used for the preparation of dolichyl-mannosyl-phosphate. The retinol labelled compound had similar properties to $\text{in vitro}$ prepared mannosyl-retinyl-phosphate.     

Versatile nuclearity in copper complexes with ortho functionalized 1,3-bis(aryl)triazenido ligands

The synthesis, characterization and crystal structures of three new copper complexes derived from 1,3-bis(aryl)triazenido ligands bearing either a methoxycarbonyl, methylthio or a hydroxymethyl group in the ortho position of one of the aromatic rings are reported. In addition to the coordination of the triazenido fragment, the Lewis basic groups coordinate to the copper centers to form complexes with different nuclearity: {1-[2-(methoxycarbonyl)phenyl]-3-[4-methylphenyl]}triazene and {1-[2-(methylthio)phenyl]-3-[4-methylphenyl]}triazene form stable dinuclear and tetranuclear Cu(I) complexes, respectively. Reaction of {1-[2-(hydroxymethyl)phenyl]-3-[4-methylphenyl]}triazene with either Cu(I) or Cu(II) results in a novel Cu(II) hexanuclear macrocyclic complex.     

The mode of action of cytotoxic and antitumor 1-nitroacridines. II. In vivo enzyme-mediated covalent binding of a 1-nitroacridine derivative, Ledakrin or Nitracrine, with dna and other macromolecules of mammalian or bacterial cells

Earlier evidence, in Part I of this paper, has shown that cytotoxic and antitumor 1-nitroacridines did not primarily exert their potent inhibitory effects on cultured mammalian cells by physicochemical binding with DNA, although it undoubtedly occurred (Chem.-Biol. Interact., 43 (1983) 131). As a result it was investigated (i) whether 9-14C- or 1'-14C-labeled derivatives of their representative, 1-nitro-9-/3'-dimethylamino-n-propylamino/acridine (Ledakrin or Nitracrine), were capable of covalent binding with nucleic acids and other suitable macromolecules in target cells in vivo and/or (ii) whether activation of the agent in the cell was a necessary prerequisite for such binding. Using the criteria of resistance to exhaustive extractions with trichloroacetic acid and/or organic solvents, [14C]Ledakrin was found to bind covalently, with relatively little discrimination, with: (i) intracellular macromolecules, including DNA, of cultured tumor HeLa cells (370-2500 DNA base pairs/one Ledakrin molecule; (ii) experimental animal tumor Ehrlich ascites (Eat) cells in vivo (650-5880 DNA base pairs/one Ledakrin molecule); (iii) bacterial Bacillus subtilis SB 1058 cells (7000-33 000 Ledakrin links/one cell genome); (iv) NADPH-fortified rat liver homogenates in vitro (25.6 nmol/mg microsomal protein under air). These results far exceed the common levels reported for alkylating agents or chemical carcinogens. Unlike [ethyl-14C]quinacrine, compared in vitro, covalent macromolecules binding with Ledakrin in vitro, and most probably in vivo, can be equated to NADPH-dependent activation(s) by oxidoreductase systems and the presence of DNA alone was not satisfactory in itself to attain Ledakrin binding. Fractionation of the enzymatic digest of 14C-associated DNA, isolated from Eat cells exposed in vivo to [9-14C]Ledakrin, by Sephadex LH-20 column chromatography followed by mass spectrometry analyses of modified nucleosides, indicated that both mono- and dinucleosidical Ledakrin metabolites were the products of an in vivo reaction. This implied that the lethal reaction of the drug could be its cross-linking of the target macromolecules and/or its monofunctional attack on vitally important cellular components.     

Metabolism of xanthine and hypoxanthine in the tea plant (Thea sinensis L.).

1. The metabolism of xanthine and hypoxanthine in excised shoot tips of tea was studied with micromolar amounts of [2(-14)C]xanthine or [8(-14)C]hypoxanthine. Almost all of the radioactive compounds supplied were utilized by tea shoot tips by 30 h after their uptake. 2. The main products of [2(-14)C]xanthine and [8(-14)C]hypoxanthine metabolism in tea shoots were urea, allantoin and allantoic acid. There was also incorporation of the label into theobromine, caffeine and RNA purine nucleotides. 3. The results indicate that tea plants can catabolize purine bases by the same pathways as animals. It is also suggested that tea plants have the ability to snythesize purine nucleotides from glycine by the pathways of purine biosynthesis de novo and from hypoxanthine and xanthine by the pathway of purine salvage. 4. The results of incorporation of more radioactivity from [8(-14)C]hypoxanthine than from [2(-14)C]xanthine into RNA purine nucleotides and caffeine suggest that hypoxanthine is a more effective precursor of caffeine biosynthesis than xanthine. The formation of caffeine from hypoxanthine is a result of nucleotide synthesis via the pathway of purine salvage.     

The stability of rat liver ribonucleic acid in vivo after methylation with methyl methanesulphonate or dimethylnitrosamine

1. RNA was isolated from rat liver at selected times after the intraperitoneal injection of either [¹⁴C]methyl methanesulphonate (50mg/kg) or [¹⁴C]dimethylnitrosamine (2mg/kg). These doses were chosen to minimize effects due to toxicity. 2. Two methods of extraction and purification of RNA were used and an analysis of the radioactivity present was made by column chromatography of acid hydrolysates of the purified RNA. 3. The extent of methylation of guanine, the principal site of alkylation in rat liver RNA, was determined at times up to 14 days after injection. Although dimethylnitrosamine is a potent liver carcinogen and methyl methanesulphonate is not carcinogenic to rat liver, the rate of disappearance of 7-methylguanine from RNA was similar for both compounds, with a half-life of about 3.5 days. 4. An estimate of the biological half-life of rRNA was made by using [³H]orotic acid. A half-life of 5 days was obtained and this was not affected by injecting animals with unlabelled methyl methanesulphonate at the same dosage of 50mg/kg used in the studies of RNA methylation. 5. After administration of labelled orotic acid, reutilization of labelled RNA degradation products probably results in an overestimation of the biological half-life for rRNA. It is suggested that non-toxic doses of methylating agents such as methyl methanesulphonate and dimethylnitrosamine may prove to be a more effective way of accurately estimating the biological turnover of RNA species.     

Biosynthesis and metabolism of indole-3-ethanol and indole-3-acetic acid by Pinus sylvestris L. needles

Combined gas chromatography-mass spectrometry has been used to identify indole-3-ethanol (IEt) in a purified extract from needles of Pinus sylvestris L. Quantitative estimates obtained by high-performance liquid chromatography with fluorescence detection, corrected for samples losses occurring during purification, indicate that Pinus needles contain 46±4 ng g^-1 IEt. This compares with 24.5±6.5 ng g^-1 indole-3-acetic acid (IAA) and 2.3±0.4 ng g^-1 indole-3-carboxylic acid (ICA) (Sandberg et al. 1984, Phytochemistry, 23, 99–102). Metabolism studies with needles incubated in a culture medium in darkness revealed that both [3-¹⁴C]-tryptophan and [2-¹⁴C]tryptamine mine are converted to [¹⁴C]IEt. It was also shown that [3-¹⁴C]IEt acted as a precursor of [¹⁴C]IAA. The observed metabolism appears to be enzymic in nature. The [2-¹⁴C]IAA was not catabolised to [¹⁴C]ICA in detectable quantities implying that, at best, only a minor portion of the endogenous ICA pool in the Pinus needles originates from IAA.Abbreviations DEAE diethylaminoethyl - GC-MS gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - IAA indole-3-acetic acid - ICA indole-3-carboxylic acid - IEt indole-3-ethanol - PVP polyvinylpyrrolidone     

Crystal structure and catalytic activity of a copper(II) complex based on a tetradentate bis-benzimidazole diamide ligand

A dimeric copper(II) complex bridged via a new tetra dentate bis benzimidazole diamide ligand [N,N′-bis(benzimidazolyl-2-yl)(methyl)pentane diamide](GBGA) with the composition [Cu₂(GBGA)₂(NO₃)₂](NO₃)₂ has been isolated and characterized. The X-ray structure of the above complex reveals that the unit cell consists of two centrosymmetric, crystallographically independent molecules, but differing in the coordination mode of ion. In one case ion is symmetric bidentate while in the other case it is monodentate. The coordination around Cu(II) is either a trigonally distorted octahedron (where the N2–O2 equatorial plane is formed by two benzimidazole N atoms and two carbonyl O atoms) or a distorted square pyramidal. The copper(II) complex carries out the selective oxidation of cinnamyl alcohol (allylic), geraniol (aliphatic-allylic) and 3-pyridyl carbinol (hetero aryl alcohol) to their respective aldehydes in the presence of tertiary butyl hydroperoxide as an alternative source of oxygen. The catalytic efficiency has been found to be much higher for the analogous copper(II) complex formed with the corresponding N-octylated ligand (O-GBGA). The percentage yield of the products viz geranial, cinnamyl aldehyde and 3-pyridyl carbinal varies between 34% and 57%. While the respective turnovers are 13-, 19- and 32-fold with respect to the copper(II) catalyst. A higher turnover in the case of 3-pyridyl carbinol is due to the transformation of the parent Cu(II) catalyst (having a N2–O2 type equatorial plane) to a more active Cu(II) species which have been shown to have a 4N donor equatorial plane as identified by low temperature EPR spectroscopy. Such a switch from a carbonyl O donor to an amine N donor of the peptidic link in the ligand may be important for the redox functioning of copper(II) bound to small peptides.     

Inhibition of aquaporin-1 expression by RNAi protects against aristolochic acid I-induced apoptosis in human proximal tubular epithelial (HK-2) cells

The aim of this study was to investigate the protective effect of inhibition of aquaporin-1 (AQP1) expression against aristolochic acid I (AA-I)-induced apoptosis. HK-2 cells impaired by AA-I were used in this study as the cell model of aristolochic acid nephropathy. Apoptosis was studied by different methods, including 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assays, flow cytometry, and caspase 3 activity assays. We compared AA-I-mediated apoptosis in HK-2 cells with or without knockdown of AQP1 expression by RNA interference. MTT assays showed that AA-I inhibited the viability of HK-2 cells in a time- and concentration-dependent manner. Apoptosis was evidenced by the results of the Annexin V/propidium iodide assay and the occurrence of a sub-G1 peak in cell-cycle analysis. The activity of caspase 3 was found to have been increased by AA-I in a concentration-dependent manner. However, AQP1 RNA interference provided protection against injury in cells treated with AA-I (40 μM) for 24 h and attenuated the number of apoptotic cells. These results suggested that AQP1 plays an important role in AA-I-induced apoptosis and that inhibition of AQP1 expression may protect HK-2 cells from AA-I-induced apoptotic damage.     

Complementary addressed alkylation of Escherichia coli 16S rRNA with 2',3'-O-[4-2-chloroethyl)-N-methylamino]benzylidene derivatives of deoxyribooligonucleotides. II. The nature of rapid interaction at 0 degrees C

Fast non-covalent interactions of 16S rRNA Escherichia coli with 14C labeled 2',3'-O-[4-N-(2-chloroethyl)-N-methylamino]benzylidene derivatives of deoxyribooligonucleotides d(pACCTTGTT)rA, d[pTTACGATC)rU, d(pTTTGCTCCCC)rA (less than[14C]CHRCl-reagents) observed at 0 degrees C were investigated. It was shown, that 16S rRNA and [14C]CHRCl-reagents at 0 degrees C form stable complexes which can not be disrupted under mild acidic conditions (pH 4, 40 degrees C) and under denaturing conditions (7 M urea, 50 degrees C), but are completely disrupted in the course of centrifugation in sucrose density gradient in the presence of SDS. Formation of such complexes of 16S rRNA with greater than[14C]CHRCl-reagents at 0 degrees C was observed due to the presence in the reagent preparation of a number of unidentified products, formed in the course of the synthesis of benzylidene derivatives, and having a hydrophobicity larger, than those for greater than CHRCl-derivatives of deoxyribooligonucleotide. Preparation of [14C]CHRCl-reagents, subjected for purification by reverse-phase chromatography, were unable to form such a complex with 16S rRNA at 0 degrees C. Studies on the complementary addressed modification at 0 degrees C (or incubation at 0 degrees C) with the use of the oligonucleotide benzylidene derivatives not purified from hydrophobic contaminations may lead to alkylation within these complexes during subsequent treatments and in such a way give incorrect information about the level of alkylation within the complex under investigation.     

Evidence that multiple species of aminoacylated transfer RNA are present in regenerating optic axons of goldfish

This study reports that 4S RNA present in regenerating optic axons of goldfish is likely to be transfer RNA. Evidence is also presented which indicates that this transfer RNA is similar to transfer RNA found in tectal cells and that its aminocylation is likely to occur both in retinal ganglion cells prior to axonal transport as well as in the axon itself. Fish with regenerating optic nerves received intraocular injections of [³H]uridine followed 4 days later by intracranial injections of [¹⁴C]uridine. Radioactive tectal 4S RNA was isolated 6 days after [³H]uridine injections and chromatographed by BD cellulose chromatography. Optical density as well as radioactivity profiles for both [¹⁴C]4S RNA (from tectal cells) and [³H]4S RNA (90% of which originated from regenerating optic axons) were found to be similar toE. coli transfer RNA optical density profiles, indicating that the intra-axonal 4S RNA is likely to be transfer RNA. Moreover, comparisons of³H/¹⁴C suggest that intra-axonal and cellular 4S RNAs are composed of similar species of transfer RNA. Results of other experiments indicated that aminoacylation of axonally transported tRNA occurs both in the retina and in optic axons subsequent to axonal transport.     

Homoleptic copper(II) and copper(I) complexes of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline. Six-coordinate copper(I) in solution

Reaction of 5,6-dihydro-5,6-epoxy-1,10-phenanthroline (L) with Cu(ClO₄)₂·6H₂O in methanol in 3:1 M ratio at room temperature yields light green [CuL₃](ClO₄)₂·H₂O (1). The X-ray crystal structure of the hemi acetonitrile solvate [CuL₃](ClO₄)₂·0.5CH₃CN has been determined which shows Jahn-Teller distortion in the CuN₆ core present in the cation [CuL₃]²⁺. Complex 1 gives an axial EPR spectrum in acetonitrile-toluene glass with g_|| = 2.262 (A_|| = 169 × 10⁻⁴ cm⁻¹) and g_⊥ = 2.069. The Cu(II/I) potential in 1 in CH₂Cl₂ at a glassy carbon electrode is 0.32 V versus NHE. This potential does not change with the addition of extra L in the medium implicating generation of a six-coordinate copper(I) species [CuL₃]⁺ in solution. B3LYP/LanL2DZ calculations show that the six Cu-N bond distances in [CuL₃]⁺ are 2.33, 2.25, 2.32, 2.25, 2.28 and 2.25 Å while the ideal Cu(I)-N bond length in a symmetric Cu(I)N₆ moiety is estimated as 2.25 Å. Reaction of L with Cu(CH₃CN)₄ClO₄ in dehydrated methanol at room temperature even in 4:1 M proportion yields [CuL₂]ClO₄ (2). Its ¹H NMR spectrum indicates that the metal in [CuL₂]⁺ is tetrahedral. The Cu(II/I) potential in 2 is found to be 0.68 V versus NHE in CH₂Cl₂ at a glassy carbon electrode. In presence of excess L, 2 yields the cyclic voltammogram of 1. From ¹H NMR titration, the free energy of binding of L to [CuL₂]⁺ to produce [CuL₃]⁺ in CD₂Cl₂ at 298 K is estimated as −11.7 (±0.2) kJ mol⁻¹.