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101.
-Thermoluminescence emission at 110 K (Z-band) was markedly diminished when thylakoid membranes were exposed to red light during or after Z-band charging with blue light. Analysis of this phenomenon showed that deactivation of Z-band-emitting chlorophyll species occurred preferentially on the low temperature side of the glow curve, and red light of670–680 nm was most efficient in the deactivation. In order to test our hypothesis that this detrapping is related to local heating effects caused by dissipation of absorbed energy, we measured thermoluminescence glow curves and Z-band emission spectra from spinach leaf discs and thylakoid membranes during induction of nonphotochemical chlorophyll fluorescence quenching. Pretreatment of the plant material was designed to achieve different levels of (1) de-epoxidized xanthophylls in the photosynthetic apparatus and (2) the proton concentration in the thylakoid lumen. In comparison, measurements were performed in aggregated and trimeric light-harvesting pigment-protein complexes of photosystem II. We observed on all three levels of organization that a higher capacity of excitation energy dissipation was accompanied by a stronger red light-induced detrapping of Z-band thermoluminescence.  相似文献   
102.
The study of ternary systems is interesting because it introduces the concept of molecular preference/competition into the system where one molecule may be displaced because the association between the other two is significantly stronger. Current definitions of a tertiary system indicate that solvent molecules are excluded from the molecule count of the system and some of the latest definitions state that any molecule that is not a solid in the parent form at room temperature should also be excluded from the molecule count. In the structure of the quinoline adduct hydrate of tryptaminium 3,5‐dinitrobenzoate, 3C10H13N2+·3C7H3N2O6·2C9H7N·2H2O, the asymmetric unit comprises multiple cation and anion species which are conformationally similar among each type set. In the crystal, a one‐dimensional hydrogen‐bonded supramolecular structure is generated through extensive intra‐ and inter‐unit aminium N—H…O and N—H…N, and water O—H…O hydrogen bonds. Within the central‐core hydrogen‐bonding associations, conjoined cyclic R44(10), R53(10) and R44(12) motifs are generated. The unit is expanded into a one‐dimensional column‐like polymer extending along [010]. Present also in the crystal packing of the structure are a total of 19 π–π interactions involving both cation, anion and quinoline species [ring‐centroid separation range = 3.395 (3)–3.797 (3) Å], as well as a number of weak C—H…O hydrogen‐bonding associations. The presence of the two water molecules in the crystal structure is considered to be the principal causative factor in the low symmetry of the asymmetric unit.  相似文献   
103.
Cell-penetrating peptides as delivery vehicles for biology and medicine   总被引:2,自引:0,他引:2  
Cell-penetrating peptides (CPPs) have found numerous applications in biology and medicine since the first synthetic cell-permeable sequence was identified two decades ago. Numerous types of drugs have been transported into cells using CPPs, including small-molecule pharmaceuticals, therapeutic proteins, and antisense oligonucleotides. Improved agents for medical imaging have been generated by conjugation with CPPs, with the appended peptides promoting cellular uptake and in some cases, cell-type specificity. Organelle-specific CPPs have also been generated, providing a means to target specific subcellular sites. This review highlights achievements in this area and illustrates the numerous examples where peptide chemistry was exploited as a means to provide new tools for biology and medicine.  相似文献   
104.
The combined influence of surface topography and charge of a polymer surface on the adsorption of the protein avidin has been investigated. Atomic force microscopy contact mode imaging and charge writing were used to create defined topographical roughness and electrostatic charge patterns on the surface of polystyrene. Increased avidin adsorption was found on nanometer-size topographical patterns, but the adsorption remained unaffected by electrostatic patterns.  相似文献   
105.
PalladiumII and nickelII halide complexes of the ferrocenyl polyphosphines 1,1',2,3-tetrakis(diphenylphosphino)ferrocene (1), and 1,1',2-tris(diphenylphosphino)-4-tert-butylferrocene (5) were prepared and characterized by multinuclear NMR. The metallo-ligand 1, the palladium [Pd2Cl4(1)] (3b) and nickel [NiCl2(5)] (6) coordination complexes were additionally characterized by X-ray diffraction crystallography. The behavior of 1 toward coordination to nickel and palladium was surprisingly different because the coordination of a second metal center after the initial 1,2-phosphorus-bonding of nickel was markedly difficult. The preference of nickel for 1,2-P coordination on 1,1'-bonding was confirmed by the exclusive formation of 6 from 5. The changes noted between the solid state structure of the ligand 1 and the structure obtained for the dinuclear palladium complex 3b reveal the rotational flexibility of this tetraphosphine. This flexibility is at the origin of the unique framework for a metallocenic dinuclear metal complex in which both coexist a 1,1'-heteroannular chelating P-bonding and a 2,3-homoannular chelating P-bonding with two palladium centers. Some reported specimens of ferrocenyl polyphosphines of constrained geometry have previously revealed that phosphorus lone pair overlap can lead to very intense "through-space" 31P31P nuclear spin-spin coupling constants (JPP) ( J. Am. Chem. Soc. 2004, 126 (35), 11077-11087] in solution phase. In these cases, an internuclear distance between heteroannular phosphorus atoms below 4.9 A, with an adequate orientation of the lone-pairs in the solid state and in solution, was a necessary parameter. The flexibility of the new polyphosphines 1 and 5 does not allow that spatial proximity (internuclear distances between heteroannular phosphorus above 5.2 A in the solid state); accordingly the expected through-space nuclear spin-spin coupling constants were not detected in any of their coordination complexes nor in 1.  相似文献   
106.
Mitochondria are important targets for cancer chemotherapy and other disease treatments. Gaining access to this organelle can be difficult, as the inner membrane is a barrier limiting diffusive transport. A mitochondrial molecular carrier would be a boon to the development of organelle-specific therapeutics. Here, we report a significant advance in the development of mitochondrial transporters-synthetic cell-permeable peptides that are able to enter mitochondria. Efficient uptake of these mitochondria-penetrating peptides (MPPs) is observed in a variety of cell types, and organellar specificity is attained with sequences that possess specific chemical properties. The MPPs identified are cationic, but also lipophilic; this combination of characteristics facilitates permeation of the hydrophobic mitochondrial membrane. The examination of a panel of MPPs illustrates that mitochondrial localization can be rationally controlled and finely tuned by altering lipophilicity and charge.  相似文献   
107.
Renormalized kinetic theory for the long range collective oscillations of turbulent plasmas is developed through infinite order summations of the interactions in the Vlasov-Poisson self-consistent field equations. Three levels of renormalized turbulence theory are derived, and the simply renormalized equations are solved for the problem of ion acoustic instability. The physical predictions of renormalized turbulence theory are discussed and used to interpret several experiments on ion acoustic turbulence.  相似文献   
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