Excited-state dynamics of carotenoids in light-harvesting complexes. 1. Exploring the relationship between the S1 and S* states

Dispersed transient absorption spectra collected at variable excitation intensities in combination with time-resolved signals were used to explore the underlying connectivity of the electronic excited-state manifold of the carotenoid rhodopin glucoside in the light-harvesting 2 complex isolated from Rhodopseudomonas acidophila. We find that the S state, which was recently identified as an excited state in carotenoids bound in bacterial light-harvesting complexes, exhibits a different response to the increase of excitation intensity than the S(1) state, which suggests that the models used so far to describe the excited states of carotenoids are incomplete. We propose two new models that can describe both the time-resolved and the intensity-dependent data; the first postulates that S(1) and S* are not populated in parallel after the decay of the initially excited S(2) state but instead result from the excitation of distinct ground-state subpopulations. The second model introduces a resonantly enhanced light-induced transition during excitation, which promotes population to higher-lying excited states that favors the formation of S* over S(1). Multiwavelength target analysis of the time-resolved and excitation-intensity dependence measurements were used to characterize the involved states and their responses. We show that both proposed models adequately fit the measured data, although it is not possible to determine which model is most apt. The physical origins and implications of both models are explored.     

Cyclization and rearrangements of diterpenoids. IX. Isomerization of (1R,2S,7S,10S,11R,12S,13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.01,10.02,7.011,13]pentadecane by fluorosulfonic acid

It has been shown that the opening of the cyclopropane ring in (1R, 2S, 7S, 10S, 11R, 12S, 13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.0^1,10.0^2,7.0^11,13]pentadecane takes place under the action of fluorosulfonic acid at all three carbon-carbon bonds, but at low temperatures the main isomerization product is (1R, 2S, 7S, 10S, 12S, 13S)-2,6,6,10,12-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadecan-13-ol, and at the ordinary temperature the main products are (1R, 2S, 7S, 11S, 12R, 13R)-2,6,6,11,13-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadeca-9-ene and (1S, 2R, 11S, 12R, 15R)-2,7,7,11,15-pentamethyltetracyclo[10.2.1.0^2,11.0^3,8]pentadeca-3(8)-ene.     

Trace-element emissions from Western U. S. coal-fired power plants

The Lawrence Livermore Laboratory program to evalute the trace elements in stack emissions from coal-fired power plants is described. Stack sampling and analysis of fly ash at modern, western U. S. power plants is discussed. Scanning-electron-microscope techniques are shown to be essential for accurate sizing of stack particles sampled with cascade impactors. Particle-size distributions for volatile and nonvolatile trace elements are reported. Comparisons show that the trace elemet enrichment factors of western and eastern U. S. coal-fired power plants are significantly different. This work was performed under the auspices of the U.S. Energy Research and Development Administration, under contract No. W-7405-Eng. 48.     

Cyclization and rearrangements of diterpenoids. IX. Isomerization of (1R,2S,7S,10S,11R,12S,13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.01,10.02,7.011,13]pentadecane by fluorosulfonic acid

It has been shown that the opening of the cyclopropane ring in (1R, 2S, 7S, 10S, 11R, 12S, 13S)-2,6,6,10,12-pentamethylpentacyclo[10.2.1.0^1,10.0^2,7.0^11,13]pentadecane takes place under the action of fluorosulfonic acid at all three carbon-carbon bonds, but at low temperatures the main isomerization product is (1R, 2S, 7S, 10S, 12S, 13S)-2,6,6,10,12-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadecan-13-ol, and at the ordinary temperature the main products are (1R, 2S, 7S, 11S, 12R, 13R)-2,6,6,11,13-pentamethyltetracyclo[10.2.1.0^1,10.0^2,7]pentadeca-9-ene and (1S, 2R, 11S, 12R, 15R)-2,7,7,11,15-pentamethyltetracyclo[10.2.1.0^2,11.0^3,8]pentadeca-3(8)-ene.Institute of Chemistry, Moldavian SSR Academy of Sciences, Kishinev. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 497–500, July–August, 1989.     

The role of N.S. Kurnakov in creating new generations of researchers

The major milestones in the pedagogic activity of N.S. Kurnakov are listed. The characteristic properties of his teaching activity, his approaches, methods, and his principal ideas as regards the organization of teaching chemistry at a higher school are presented with attracting the memoirs of his disciplines and associated.     

Interaction of the 5'-ends of 28S RNA in dimerization of hamster ribosomes.

Free ribosomes extracted from hamster cells and 28S RNA purified from these ribosomes are known to form dimers. We find that spleen phosphodiesterase inhibits ribosomal dimer formation, but only when a free 5'-hydroxyl end group, produced by the action of alkaline phosphatase, is present. Hence, formation of dimer ribosomes probably involves interaction at or near the phosphorylated 5'-ends of 28S RNA. Dimer RNA molecules show a modal length, when measured on electrom micrographs, of 2.1 mum, which is about double the length of 28S RNA. Electron micrographs of 115S dimer ribosomes often show profiles consistent with our interpretation that in dimers the 28S RNA chains are loosely linked by their 5'-ends.     

E.S.R. and D.S.C. investigations of phase transitions in polymorphic 4-n-alkoxybenzylidene-4′-n-alkylanilines

Abstract

It is shown that the McMillan parameter M = T _SAN/T _N1 (where T _SAN and T _NI are respectively the temperatures of the smectic A to nematic (SAN) and the nematic to isotropic (NI) phase transitions) is useful in analysing the crossover between second and first order behaviour of the S_NN transition in the nO.m homologous liquid crystal series (the 4-n-alkoxybenzylidene-4′-n-alkylanilines). Using a phase diagram of orientational ordering versus M for this series, as obtained in this work (from E.S.R. and D.S.C), a symmetric tricritical point with mean field exponent β₂ = 1 is demonstrated. In a preliminary study of E.S.R. linewidth parameters B and C of nitroxide spin probes dissolved in members of the nO.m series exhibiting a first order S_AN transition, critical-type divergences are observed near this transition. In the case where M is closer to 0.959 (the value at the tricritical point), these divergences appear similar to those previously observed in related nO.m members with a second order S_AN transition; however, they are considerably enhanced for an M value closer to unity (i.e. more removed from the tricritical point). This indicates the importance of coupling between orientational and positional order parameters in the observed critical-type divergences.     

Photoreactivation of killing in Streptomyces. II. Kinetics of formation and photolysis of pyrimidine dimers and adducts in S. coelicolor and S. griseus PHR-1

Abstract— A pyrimidine adduct, 6-4‘-[pyrimidine-2’-one] thymine (PO-T)?, observed in DNA hydrolysates of 254-nm ultraviolet (u.v.) irradiated conidia of Streptomyces coelicolor, increases linearly with u.v. dose up to 2 × 10⁵ ergs/mm². Yields of thymine dimer (T○) and uracil-thymine dimer (U○) level off at much lower doses. Initial relative rates of formation of these u.v. photoproducts are: 1:1.3:4.8 for PO-T, T○ and U○, respectively. Similar results were obtained with a Streptomyces griseus mutant, PHR-1. An equation is derived to estimate the ratio of the amount of PO-T to the total amount of thymine-derived photoproducts at low (biological) u.v. doses. The observed PO-T fractions compare well with the calculated values. Rapid photolysis of the precursor of PO-T was observed by post-u. v. treatment at 313 nm of conidia of S. coelicolor and of S. griseus PHR-1. The photolysis was much slower at 365 nm and did not occur at all at 405 nm. Pyrimidine dimers were not appreciably affected by post-u. v. treatment at the above wavelengths in these Streptomyces strains. Both of these strains are phenotypically photoreactivation-deficient, and the present results indicate that they do not possess active photoreactivating enzyme. In earlier papers[3,4,5], the pyrimidine adduct found in acid hydrolysates of DNA was loosely referred to as “uracil-thymine adduct (U-T adduct)”. Such terminology is not strictly correct. The pyrimidine adduct in acid hydrolysates is PO-T (sometimes called P₂B), which could theoretically result from removal of ammonia from a C-T adduct or removal of water from a U-T adduct (see [6]).     

Nitrosyl-Metallkoordinationsverbindungen. II. Synthese und Eigenschaften von Kobalt- und Eisenkomplexen des Typs M(S,S) (N,N) NO

Nitrosyl Metal Coordination Compounds. II. Syntheses and Properties of Cobalt and Iron Complexes of the Type M(S, S) (N, N) NO Neutral complex compounds of the type M(S, S)(N, N)NO, with M = Co, Fe; S,S = malonitrildithiolate and N,N = azomethines of biacetyl with the amines aniline (acal) 1 , p-toluidine (acto) 2 , p-chloraniline (acca) 3 , and p-anisidine (acan) 4 , have been synthesized. By menas of molar measurements, IR, ESCA, and ESR spectroscopy including magnetic measurements it was established that the cobalt complexes 1a – 4a are diamagnetic, with a 5-fold coordinated square pyramidale structure, with a formally trivalent central metal ion and a negative charged NO ligand [Co(d⁶)NO^?]²⁺. Iron complexes 1b — 4b coordinated in the same manner are paramagnetic with one unpaired electron located at the iron atom. The existence of the coordination unity [Fe(d⁵)NO^?]²⁺ is obvoius.     

Imaging studies of the photodissociation of H2S+ cations. II

Ion imaging methods have been used to explore the photodissociation dynamics of state-selected H(2)S(+) and D(2)S(+) cations. Predissociation following one photon excitation to the A (2)A(1) state at wavelengths (385< or =lambda(phot)< or =420 nm) in the vicinity of the first dissociation threshold results in formation of ground state S(+) fragment ions; the partner H(2)(D(2)) fragments are deduced to be rotationally "cold." Two photon dissociation processes are also observed, resonance enhanced at the energy of one absorbed photon by the predissociating A state levels. Two photon excitation at these wavelengths is deduced to populate an excited state of (2)A(1) symmetry, which dissociates to electronically excited S(+)((2)D) products, together with vibrationally excited H(2)(D(2)) cofragments. Ground state SH(+)(SD(+)) fragments, attributable to a one photon dissociation process, are observed once lambda(phot)< or =325 nm. Two photon induced production of SH(+)(SD(+)) fragments is also observed, at all wavelengths studied (i.e., at all lambda(phot)< or =420 nm). These SH(+)(SD(+)) fragments are deduced to be formed in their singlet (i.e., a (1)Delta and b (1)Sigma(+)) excited states, with high levels of rotational excitation. The observed product branching and energy disposals are discussed within the context of the (limited) available knowledge relating to the excited electronic states of the H(2)S(+) cation.     

The accessibility of antigenic determinants of ribosomal protein S4 in situ.

Antibodies to Escherichia coli ribosomal protein S4 react with S4 in subribosomal particles, eg, the complex of 16S RNA with S4, S7, S8, S15, S16, S17, and S19 and the RI reconstitution intermediate, but they do not react with intact 30S subunits. Antibodies were isolated by three different methods from antisera obtained during the immunization of eight rabbits. Some of these antibody preparations, which contained contaminant antibodies directed against other ribosomal proteins, reacted with subunits, but this reaction was not affected by removal of the anti-S4 antibody population. Other antibody preparations did not react with subunits. It is concluded that the antigenic determinants of S4 are accessible in some protein deficient subribosomal particles but not in intact 30S subunits.     

Ion Chromatographic Determination of Phosphorus in Eight U.S.G.S. Standard Rocks

Abstract

A method is described for the analysis of phosphorus in geological samples involving the decomposition of the sample with hydrofluoric acid in a quartz tube and the measurement of phosphate ion concentration using an ion chromatograph (Dionex 10) with an anion separator column (Wescan anion 269-001). The detection limit is between 0.05-0.5% P₂O₅ in the original sample. Multiple analyses of eight U.S.G.S. standard rocks yielded a relative standard deviation range between 2.37-16.67%. In excess of 15 samples can be analyzed in an 8 hour day.     

Metallocyclopeptide complexes with MII(S.Cys)4 chromophores

The tetracysteinyl peptide cyclo[Lys1,12](Gln-Cys-Gly-Val-Cys-Gly-Lys-Cys-Ile-Ala-Cys-Lys) ([symbol: see text] L(Cys.SH)4) was synthesized by solid-phase methods using an Fmoc/t-Bu/allyl strategy on a PAL-PEG-PS support. The formation of the 1:1 complexes with M = Fe2+, Co2+, and Ni2+ was observed by spectrophotometric monitoring of reactions in aqueous solution at pH 7.5. Size exclusion chromatography indicated that the peptide is a monomer and the complexes are dimers [M2([symbol: see text]L(Cys.S)4)2] in aqueous buffer at pH 7.5. Cobalt and nickel K-edge X-ray absorption data and EXAFS analysis of [Co2([symbol: see text] L(Cys.S)4)2] and [Ni2([symbol: see text] L(Cys.S)4)2] as lyophilized solids are reported. Derived bond distances are Co-S = 2.30 A and Ni-S = 2.21 A. From the collective results provided by absorption spectra, K-edges, EXAFS, and bond length comparisons with known structures, it is shown that [Fe2([symbol: see text] L(Cys.S)4)2] and [Co2([symbol: see text] L(Cys.S)4)2] possess distorted tetrahedral structures and [Ni2([symbol: see text] L(Cys.S)4)2] has distorted square planar stereochemistry. The Co(II) chromophore is particularly distinctive of the assigned structure, displaying three components of the parent tetrahedral ligand field transition 4A2-->4T1(P) (610, 685, 740 nm). The observed structures conform to the intrinsic stereochemical preferences of the metal ions. Structures for the binuclear complexes are suggested. These are the first characterized metal complexes of a cysteinyl cyclopeptide and among the few well-documented complexes of synthetic cyclopeptides. This study is a desirable first step in the design of cyclic peptides for the binding of mononuclear and polynuclear metal centers.     

Conformational changes of the S2YZ* intermediate of the S2 to S3 transition in photosystem II

The paper extends earlier studies on the S(2)Y(Z)* intermediate that is trapped by illumination in the temperature range 77 K to 190 K of untreated samples poised in the S(2)...Q(A) state. X-band EPR experiments on untreated and glycerol (50% v/v) treated samples at 10 K indicate that the intermediate consists of two components. A wide one with a splitting of ca 170 G, and a narrow one characterized by a splitting of ca 120 G (untreated), or 124 G (glycerol-treated samples). Lower temperatures of illumination in the above temperature range favor the wide component, which at 10 K decays faster than the narrow one. Re-illumination at 10 K after decay of the signal trapped at 77-190 K induces only the narrow component. Rapid scan experiments in the temperature range 77-190 K reveal high resolution spectra of the isolated tyz Z* radical and no evidence of alternative radicals. The two split signals are accordingly assigned to different conformations of the S(2)Y(Z)* intermediate A point-dipole simulation of the spectra yields "effective distances" between the spin densities of Y(Z)* and the Mn(4)Ca center of 5.7 ? for the wide and 6.4 ? for the narrow component. The results are discussed on the basis of a molecular model assuming two sequential proton transfers during oxidation of tyr Z. The wide component is assigned to a transient S(2)Y(Z)* conformation, that forms during the primary proton transfer.     

Photoreactivation of killing in Streptomyces. 3. Action spectra for photolysis of pyrimidine dimers and adducts in S. griseus and S. griseus PHR-1

Abstract— Photolysis of tritium-labelled thymine-derived photoproducts by 254-nm ultraviolet radiation (u.v.) in conidia of Streptomyces griseus was measured by chromatography of cell hydrolysates. The relative photolysis cross-sections of uracilthymine dimer (UT○) at various wavelengths are the same as those of thymine-thymine dimer (TT○), and their ratios at 313, 365, 405 and 436 nm are 2:1:2:3. Except at 436 nm, these relative values agree very well with cross-sections previously reported for photoreactivation of u.v. killing in this organism, leading to the conclusion that photoreactivation in the wild type is due to repair of cyclobutane-type pyrimidine dimers. In a mutant showing restricted photoreactivation (S. griseus PHR-1), post-u.v. treatments at the above wavelengths did not affect UT○ and TT○ in the conidia, supporting the earlier suggestion that this organism does not contain active PR enzyme. Another u.v. photoproduct, the precursor of a pyrimidine adduct (PO-T) that appears in cell hydrolysates, was removed from both wild-type and mutant cells very efficiently at 313 nm. This is presumably a direct photochemical reaction. In addition, in wild-type cells, the precursor of PO-T appeared to be inefficiently removed photoenzymatically at all wavelengths. Removal of the precursor of PO-T appears to be biologically significant, however, only in the mutant.     

Polymer battery R&D in the U.S.

Polymer electrolytes that have been developed for battery applications fall into two general classes, neat or “pure” polymer and plasticized or gel in which the polymer is combined with a conducting organic electrolyte. The polyethylene oxide (PEO) and its modifications are typical of the “pure” polymer electrolytes. They have poor conductivity at room temperatures, but at elevated temperatures, their conductivity is of the order of 10⁻³ to 10⁻⁴ S/cm. The PEO electrolytes have found application in the high temperature (>60°C) lithium metal anode battery systems. The high temperature necessary for good operation makes them unsuitable for use in small consumer appliances. The polymer electrolyte battery development activities have resulted in several high performance battery systems now just entering the market. Not all of the developments have resulted in commercial cell production. The commercialization activities of high performance lithium‐ion (Li‐Ion) batteries have been based on two general plastic polymer systems: poly‐vinylidene difluoride‐hexafluoropropylene copolymer (PVdF‐HFP) and polyacrylates. The polymer cells are expected to have advantages in manufacturing, flexibility, thin cell formats and lightweight packaging. Important parameters in PVdF gel electrolyte performance include the electrolyte type (combination of organic carbonates), temperature, and HFP copolymer content. Li‐Ion coin cells fabricated with a polyolefin separator with either liquid electrolyte or with the PVdF gel polymer electrolyte have equivalent performance.     

M. S. Tswett and the 1918 Nobel Prize in Chemistry

Summary The general recognition of M. S. Tswett and his achievements are discussed, with special emphasis to his nomination for the 1918 Nobel Prize in Chemistry.     

55Mn pulse ENDOR at 34 GHz of the S0 and S2 states of the oxygen-evolving complex in photosystem II

55Mn pulse ENDOR experiments at 34 GHz (Q-band) are reported for the S0 and S2 states of the oxygen-evolving complex of photosystem II. Their numerical analysis (i) shows that in both states all four Mn ions are magnetically coupled, (ii) allows a refinement of the hyperfine interaction (HFI) parameters obtained earlier for the S2 state at X-band (Peloquin, J. M.; Campbell, K. A.; Randall, D. W.; Evanchik, M. A.; Pecoraro, V. L.; Armstrong, W. H.; Britt, R. D. J. Am. Chem. Soc. 2000, 122, 10926-10942), (iii) provides the first reliable 55Mn HFI tensors for the S0 state, and (iv) leads to the suggestion that the Mn oxidation states in S0 and S2 are Mn4(III, III, III, IV) and Mn4(III, IV, IV, IV), respectively. In addition, a Q-band EPR spectrum is reported for the S0 state, and inversion-recovery experiments at 4.5 K directly show that the electron spin-lattice relaxation for the S0 state is about 2 orders of magnitude faster than that for the S2 state.     

Isomers among the carbon sulfides C4S6--synthesis and crystal structures of alpha,alpha-C4S6, alpha,beta-C4S6, and of a second polymorph of the diiodine adduct alpha,beta-C4S6.I2

The reaction of the alpha and beta forms of C3S5(2-) with thiophosgene yields two isomeric carbon sulfides alpha,alpha-C4S6 and alpha,beta-C4S6, respectively. The crystal structures of both compounds could be determined for the first time. Both structures are made up of almost planar molecules. The alpha,alpha-isomer (1,3-dithiolo-(4,5-d)-1,3-dithol-2,5-dithione) is D2h-symmetric, while the alpha,beta-isomer is approximately Cs-symmetric. In the molecules of both isomers the two different C3S5 units are retained without significant alterations of structural parameters. alpha,alpha-C4S6 is unstable with respect to alpha,beta-C4S6. The molecular rearrangement can be induced by a short thermal treatment at 150 degrees C. Significant differences are found in the mass spectra fragmentation patterns. Only alpha,beta-C4S6 shows an intense signal for C3S2+ and is therefore a potential source for the synthesis of carbon subsulfide via flash vacuum pyrolysis. Only alpha,beta-C4S6 forms a stable adduct with I2. alpha,beta-C4S6.I2 was already known (F. L. Lu, K. M. Keshavarz-K, G. Srdanov, R. H. Jacobson and F. Wudl, J. Org. Chem., 1989, 54, 2165, ), but a second polymorph is formed on crystallisation from a different solvent. The two polymorphic forms do not show differences in the structures of the individual molecules but show a different packing pattern. alpha,beta-C4S6.I2 is remarkably thermally stable. Thermal analysis shows that I2 cleavage occurs in that temperature region above 200 degrees C when C-S bonds are broken and CS2 and I2 are simultaneously liberated. Performed at 270 degrees C thermolysis of alpha,beta-C4S6.I2 yields under cleavage of I2 and CS2 a black polymeric carbon sulfide (CS)x which is probably a mixture of graphitic carbon and unidentified amorphous polymeric carbon sulfides.     

Stability analysis of the two rotational isomers of meta-fluorobenzaldehyde in the S0, S1, and S2 electronic states

For a determination of the stabilization energy between the two rotational isomers of m-fluorobenzaldehyde, the S(1,2)<--S0 absorption spectra were observed in fluid n-hexane solutions at 293 and 198 K. After employing a simulation method for the spectra, we succeeded in determining the stabilization energies in the ground and the relevant excited state at the same time. The energy was estimated to be 1.7 +/- 0.5 kJ mol(-1) for S0 and also for S1 while it was 2.9 +/- 0.5 kJ mol(-1) for S2. Ab initio calculations at MP2/6-311G** computational level predicted that the O-cis form in the S0 state is more stable by 1.9 +/- 0.5 kJ mol(-1) than the counterpart rotamer, O-trans form. In summary, a schematic energy level diagram of the two rotational isomers will be illustrated for the S0, S1, and S2 states in the fluid system.