PHYTOCHROME STATES IN ETIOLATED PEA SEEDLINGS: FLUORESCENCE AND PRIMARY PHOTOREACTIONS AT LOW TEMPERATURES

Emission spectra of the red phytochrome form (Pr) and fluence time-response curves of the Pr fluorescence intensity changes were measured in etiolated pea seedlings at low temperatures (80–150 K) in connection with its phototransformations into the initial photoproduct (Lr) and back upon actinic red (667 nm) and far-red (696 nm) illumination. The variable fluorescence reaches 45% at 85 K and decreases with the rise of temperature. Three kinetic components of the changes were found in the direct (Pr→Lr) and back (Lr→Pr) photoreactions belonging to three states of phytochrome: “slow”, “fast” and “very fast” (respective indices: s, f and vf). The amplitudes of the components and rate constants to reach photoequilibrium were determined in the direct and back photoreactions at different temperatures, and from this, their quantum yields, extent of the Pr?Lr phototransformation and activation energy of the reactions were evaluated for the three Pr and Lr states. The yields differ from each other by approximately a factor of 10 and those for the direct and back photoreactions are close to each other. The proportion of the amplitudes of the variable fluorescence of the three phytochrome states changes with temperature and upon the Pr→Lr photo-transformation and the Pr states differ in the position of their emission spectra by 3–5 nm. A close similarity between the Pr and Lr properties was observed, which implies a symmetrical scheme of their photoreactions. It is suggested that the three phytochrome species may originate in different conformational states of the chromophore and they independently transform in parallel photoreactions into the respective photoproducts: Prvf?Lrvf, Prf?Lrf and Prs?Lrs.     

Syntheses, spectroscopic characteristics and thermolytic rearrangements of bis-[(trimethylgermyl)methyl]platinum(II) and bis-[(trimethylstannyl)methyl]platinum(II) complexes

The preparations and spectroscopic characteristics are reported of a series of (trimethylgermyl)methyl- and (trimethylstannyl)methylplatinum(II) complexes with diene and P-donor ancillary ligands, cis-Pt(CH₂GeMe₃)₂L₂ (L = PPh₃ or PPh₂Me; L₂ = dppe or cod) and cis-Pt(CH₂SnMe₃)₂L₂ (L = PPh₃; L₂ =cod). Thermolysis of toluene solutions of cis-Pt(CH₂GeMe₃)₂(PPh₃)₂ leads to cis-Pt(Me)(CH₂GeMe₂CH₂GeMe₃)(PPh₃)₂ via β-alkyl migration, after (non-rate-limiting) phosphine dissociation. Estimated activation parameters (ΔH_{298 K}^‡ = 126 ± 3 kJ mol⁻¹, ΔS^‡ = + 17 ± 7 J mol⁻¹ K⁻¹ and hence Δ_{298 K}^‡ = 121 ± 5 kJ mol⁻¹) suggest that this system is more migration labile than its silicon analogue, primarily as a result of a lower activation enthalpy. While cis-Pt(CH₂GeMe₃)₂(PPh₂Me)₂ reacts similarly but less readily, Pt(CH₂GeMe₃)₂(dppe)₂ is inert at operable temperatures. Thermolysis of Pt(CH₂GeMe₃)₂(cod) generates 1,1,3,3,-tetramethyldi-1,3-germacyclobutane as the major organogermanium product, while from cis-Pt(CH₂SnMe₃)₂(PPh₃)₂, 1,1,3,3-tetramethyldi-1,3-stannacyclobutane predominates. Mechanistic implications are discussed.     

Synthesis, Characterization, and Electrochemistry of sigma-Bonded Cobalt Corroles in High Oxidation States

The synthesis, electrochemistry, spectroscopy, and structural characterization of two high-valent phenyl sigma-bonded cobalt corroles containing a central cobalt ion in formal +IV and +V oxidation states is presented. The characterized compounds are represented as phenyl sigma-bonded cobalt corroles, (OEC)Co(C(6)H(5)) and [(OEC)Co(C(6)H(5))]ClO(4), where OEC is the trianion of 2,3,7,8,12,13,17,18-octaethylcorrole. The electronic distribution in both molecules is discussed in terms of their NMR and EPR spectroscopic data, magnetic susceptibility, and electrochemistry.     

NMR determination of enantiomeric composition of 1-substituted 3-amino-1,2-dicarba-closo-dodecaboranes using Eu(hfc)3

Experimental conditions for determination of enantiomeric composition of 1-substituted 3-aminocarboranes by ¹H and ¹³C NMR spectroscopy using chiral shift reagent Eu(hfc)₃ have been found.     

Separation of nickel from other elements by cation-exchange chromatography in dimethylglyoxime/hydrochloric acid/acetone media

Nickel can be separated from Zn, Co, Cu(II), Mn(II), Fe(III), U(VI) and other elements which readily form chloro complex ions, by eluting them with 0.5 M HCl/93% acetone from AG50W-X4 resin. Nickel is then eluted selectivity with 0.5 M HCl/95% acetone containing 0.1 M dimethylglyoxime, while the alkali and alkaline-earth elements, Al, Ti(IV), Sc, Y, La, lanthanides, Zr, Hf and Th are still retained. Separations are sharp and quantitative.     

Perchlorate analysis using solid-phase extraction cartridges

Perchlorate is a compound of increasing concern as an environmental contaminant and is being regulated at increasingly stringent levels. Reliable methods are needed to consistently analyze perchlorate at low concentration levels. This research investigates the use of solid-phase extraction cartridges as an alternative to large-volume injection loops to achieve low-level (microg/L level) perchlorate quantitation. The method involves commercially available strong anion exchange (SAX) cartridges. Water samples are filtered (100 to 1000 mL) using the cartridge, which removes the perchlorate from the solution by anion exchange. Then, after the desired volume is filtered, the perchlorate is extracted using 4 mL of 1% NaOH. In addition, a cleanup method is developed to remove competing anions (chloride, sulfate, and carbonate) that are often found in environmental samples. Analyses are performed with an ion chromatograph using a 10-microL injection loop, yielding a perchlorate method detection limit (MDL) of 210 microg/L. One-liter volumes of a 2-microg/L perchlorate spiked deionized water solution are filtered with SAX SPE. Following extraction and analysis, an MDL of 0.82 microg/L is obtained, comparable to that found for 1-mL injection loop systems (reported as low as 0.53 microg/L). MDL studies are then conducted on perchlorate-amended groundwater (solution concentration of 70 microg/L) and surface water (solution concentration of 10 microg/L) using a filtration volume of 200 mL. The MDLs are 6.7 microg/L for the groundwater and 2.4 microg/L for the surface water.     

Steric and Electronic Effects, Enantiospecificity, and Reactive Orientation in DNA Binding/Cleaving by Substituted Derivatives of [SalenMn(III)](+)

Twenty-six derivatives of [SalenMn(III)](+) (1) bearing halogen, nitro, amino, ether, alkyl, or aryl substituents on the aromatic rings and/or at the imine positions or containing 1,3-propylene-, 1,2-phenylene-, 1,2-cyclohexane-, or 1,2-diphenylethylenediamine in place of ethylenediamine as the bridging moiety have been synthesized. The DNA binding/cleaving properties of these complexes in the presence of terminal oxidants have been examined using DNA affinity cleaving techniques. Active derivatives produced DNA cleavage from the minor groove at sites containing multiple contiguous A:T base pairs. For aryl-substituted derivatives, DNA cleavage efficiency was found to vary with both the identity and position of attachment of substituents. The precise patterns of cleavage at A:T target sites varied with the position of attachment of substituents, but not with the identity of the substituents. The results suggest that substituents alter specificity through both steric and electronic effects. The 3,3'-difluoro and -dichloro derivatives produced cleavage patterns that match those of the parent complex, suggesting that the activated form of 1 produces cleavage from an orientation in which the concave edge of the complex faces away from the floor of the DNA minor groove. Bridge modifications yield complexes with reduced DNA cleaving activity relative to 1. DNA cleaving efficiency was found to vary with both the structure and stereochemistry of the bridge. Cleavage efficiency for the complex derived from (R,R)-cyclohexanediamine was 5 times greater than that for the (S,S) enantiomer. Cleavage patterns produced by the enantiomeric complexes at A:T rich target sites were different, demonstrating enantiospecific recognition and cleavage of right-handed double-helical DNA.     

Calculations on bound and autoionizing states,and continuum radiative properties for Li− and Na−

Semi-empirical model potential calculations have been performed for bound and continuum properties of Li^? and Na^?. The calculated electron affinities of the 2s²¹S state of Li^? and the 3s²¹S and 3p²³P^e states of Na^? are in agreement with the calculations of Norcross and with experimental data. Positions of possible autoionizing states are calculated using projection and root stabilization methods. The Stieltjes imaging method of Langhoff is employed to compute the photodetachment cross sections of Li^? and Na^? and the results are in excellent agreement with the close-coupling calculations of Moores and Norcross. A comparison of variational and numerical results for the coupled time-dependent Hartree-Fock photoionization of helium shows that good Stieltjes imaging results can be obtained with a very small basis set for the variational calculation. The continuous photoemission profile for the 3p²³P^e state of Na^? is also obtained.     

Synthesis, characterization, biocide and toxicological activities of di-n-butyl- and diphenyl-tin(IV)-salicyliden-beta-amino alcohol derivatives

The one pot reaction of salicylaldehyde 1, beta-amino alcohols 2a-2c, and di-n-butyltin(IV) oxide 3a or diphenyltin(IV) oxide 3b produced five diorganotin(IV) compounds, 4a-4c, 5a, and 5c, in good yields. All compounds were characterized by IR, (1)H, (13)C, and (119)Sn NMR spectroscopy, and elemental analysis; furthermore, compounds 4b, 4c, 5a, and 5c were characterized by X-ray diffraction analysis. After the structural characterization, all of the compounds were tested in vitro against Bacillus subtilis (Gram-positive, strain ATCC 6633), Escherichia coli (Gram-negative, strain DH5alpha), Pseudomonas aeruginosa (Gram-negative, strain BH3), Desulfovibrio longus (strain DSM 6739), and Desulfomicrobium aspheronum (strain DSM 5918) to assess their antimicrobial activity. Compounds 4 and 5 demonstrated a wide range of bactericidal activities against the tested aerobic (one Gram-positive and two Gram-negative subtypes) and anaerobic bacteria (two sulfate-reducing bacteria, SRB). Compound 5 had better bactericidal performances than compound 4. For all of the compounds, the acute toxicity was measured using luminescent bacteria toxicity (LBT-Microtox) tests to track their further environmental impact. According to these results and in order to fulfill environmental regulations, the toxicity of the compounds studied herein can be modulated through the proper selection of the disubstituted tin(IV) moiety.     

Photo- and thermoinduced generation of 1,3-diaryl carbonyl ylides from 2,3-diaryloxiranes 1,3-dipolar cycloadditions to dipolarophiles

A group of symmetrically substituted 2,3-diaryloxiranes have been studied as photoprecursors for carbonyl ylides. The stereochemistry of the adducts obtained upon interception of these 4n pi-transient systems with a variety of dipolarophiles provides information on the mode(s) of electrocyclic opening of the oxiranes to carbonyl ylides, as well as the mechanism of the 4n + 2 cycloaddition process. The stereochemistry of the dipolarophiles is preserved in the cycloadducts, which is consistent with a concerted addition process; however, solvent effects, steric hindrance, and possibly secondary orbital overlap factors all may play a role in determining the product distribution.