Spectroscopic evidence for triplet excitation energy transfer among carotenoids in the LH2 complex from photosynthetic bacterium <Emphasis Type="Italic">Rhodopseudomonas palustris</Emphasis>

The LH2 complex from Rhodopsudomonas (Rps.) palustris is unique in the heterogeneous carotenoid compositions. The dynamics of triplet excited state Carotenoids (³Car* has been investigated by means of sub-microsecond time-resolved absorption spectroscopy both at physiological temperature (295 K) and at cryogenic temperature (77K). Broad and asymmetric T _n ←T ₁ transient absorption was observed at room temperature following the photo-excitation of Car at 532 nm, which suggests the contribution from various carotenoid compositions having different numbers of conjugated C=C double bonds (N_c=c). The triplet absorption bands of different carotenoids, which superimposed at room temperature, could be clearly distinguished upon decreasing the temperature down to 77 K. At room temperature the shorter-wavelength side of the main T_n04T₁ absorption band decayed rapidly to reach a spectral equilibration with a characteristic time constant of ∽1 μs, the same spectral dynamics, however, was not observed at 77 K. The aforementioned spectral dynamics can be explained in terms of the triplet-excitation transfer among heterogeneous carotenoid compositions. Global spectral analysis was applied to the time-resolved spectra at room temperature, which revealed two spectral components peaked at 545 and 565 nm, and assignable to the T_n04 T₁ absorption of Cars with Nc=c=11 and Nc=c=13, respectively. Surprisingly, the decay time constant of a shorter-conjugated Car, i.e. 0.72 ώs (aerobic) and 1.36 ώs (anaerobic), is smaller than that of a longer-conjugated Car, i.e. 2.12 us (aerobic) and 3.75 ώs (anaerobic), which is contradictory to the general rule of carotenoids and relative polyenes. The results are explained in terms of triplet-excitation transfer among different types of Cars. It is postulated that two Cars with different conjugation lengths coexist in an α, β-subunit in the LH2 complex.     

Enhancement of the light-scattering ability of coatings by using hollow pigments

The light-scattering properties of coatings based on monodisperse polymeric spheres of two different diameters (ca 0.5 and 1 m) were evaluated from reflectance measurements as a function of the wavelength from 400 to 700 nm. Some of these plastic pigments were hollow and it was noted that these particles gave coatings with a greater light-scattering ability than coatings based on solid particles of a similar size. It was possible to estimate the contribution of the internal pores to the scattering ability of the coating layers by saturating the layers with an oil of a refractive index similar to that of the polymeric pigment particles. A simple model accounting for the scattering provided by the internal pores of the hollow particles is suggested. The agreement between the experimental results and the prediction of the model is fair. It was noted that the light scattering coefficient of the coatings increased when the external diameter of their constituent hollow particles increased from ca 0.5 to 1 m.     

微波萃取花生壳天然黄色素及其稳定性研究

对福建产花生壳进行了微波萃取天然黄色素及其稳定性的研究 .研究表明微波萃取的工艺条件是 :以pH =3,体积分数 70 %的乙醇水溶液作提取剂 ,原料与提取剂配比为 1g∶5mL ,微波辐射功率为 12 0W ,辐射时间2 4 0s.对该色素稳定性研究结果表明 ,该色素为水溶性色素 ,属黄酮类色素 ,适用pH值范围比较宽 ,尤其碱性状态效果最佳 ,对光、热稳定性好 ,大多数食品添加剂对色素稳定性影响不大 ,对氧化剂H2 O2 的耐受能力较差 ,对还原剂Na2 SO3 的耐受能力强     

紫荆花红色素开发利用的研究

首次报道紫荆花红色素的提取纯化方法及红色素的理化性质，并与玫瑰茄红色素作对比研究，证实同属于花青甙类化合物，又经急性毒性试验证明其毒性极低，故紫荆花天然红色素具有开发利用的价值。     

New perylene polyimides containing p‐n diblocks for sensitization in TiO2 solar cells

Three novel perylene polyimides (PPIs) containing p‐n diblock units were designed and synthesized for use in dye‐sensitized mesoporous TiO₂ solar cells. They all dissolve in m‐cresol and N‐methyl‐2‐pyrrolidone (NMP). Their visible light absorption, electrochemical and photoelectrochemical properties were systematically studied. The polyimides have band gap energies of 2.16, 2.19 and 2.25 eV deduced from ultraviolet–visible absorption spectra, and electron affinity (E_a) and ionization potential (IP) of ?3.93 and 6.10 eV for PPI1, ?3.94 and 6.13 eV for PPI2, ?3.93 and 6.59 eV for PPI3, respectively, deduced from cyclic voltammogram. Experimental data show that introduction of 4,4′‐bisaminetriphenylamine cannot only greatly enhance optic‐electro conversion efficiency, but also enhance the dissolubility which in favorable for making the devices. The relationship of structure and properties of PPI is discussed and the mechanism of photocurrent generation is explained. Copyright © 2004 John Wiley & Sons, Ltd.     

Flexibility and Rigidity of Proteins and Protein–Pigment Complexes

Proteins may be rigid or flexible to various degrees as required for optimal function. Flexibility of large parts of a protein, which rearrange or move, is particularly interesting and will be discussed in this article. We differentiate between several categories, although the boundaries between them are diffuse: flexibility of peptide segments, order–disorder transitions of spatially contiguous regions, and domain motions. The domains may be flexibly linked to allow rather unrestricted motions or the motions may be constrained to certain modes. The various categories of large-scale flexibility will be illustrated with the following examples: (1) Small protein proteinase inhibitors are rather rigid molecules which provide binding surfaces complementary to their cognate proteases but show also limited segmental flexibility and adaptation. (2) Large plasma proteinase inhibitors exhibit large conformational changes after interaction with proteases probably for regulatory purposes. (3) Pancreatic serine proteases employ a disorder–order transition of their activation domain as a means to regulate enzymic activity. (4) Immunoglobulins show rather unrestricted and also hinged domain motions in different parts of the molecule probably to allow binding to antigens in different arrangements. (5) Citrate synthase adopts open and closed forms by a hinged domain motion to bind substrates and release products and to perform the catalytic condensation reaction, respectively. (6) Riboflavin synthase, a bifunctional multienzyme complex, catalyzes two consecutive reactions by means of two subunits, α and β. The β-subunits form a shell, in which the α-subunits are enclosed. Diffusional motion of the catalytic intermediates is therefore restricted. In addition, rearrangement of the N-terminal segment occurs during the assembly of the β-subunit. In contrast, rigidity is dominant in the structures of the light-harvesting complexes and the photosynthetic reaction centers involved in photosynthetic light reactions. These are large protein–pigment complexes in which the proteins serve as matrices to hold the pigments in the appropriate conformation and relative arrangement. Since motion would contribute to deactivation of the photoexcited states of the pigments and diminish the efficiency of light-energy and electron transfer, the functional role of rigidity is easy to rationalize for these proteins.     

掺铬铝酸钇红色颜料的合成、结构和性能表征

研究了高温固相合成制备掺铬铝酸钇红色颜料的方法，着重考察了灼烧温度（1000-1400℃）、灼烧时间（1-2h）、主要原料配比（Al／Y：1：0．5—1：1．5，Cr2O3％：0．3％-5％）等实验条件对产物结构和色泽的影响。XRD等方法对样品进行的相态分析表明，主相为铝酸钇石榴石相；运用反射光谱对红色颜料的色泽进行了反射峰位和相关强度的表征。当Y2O3：Al2O3摩尔比为1：1，掺杂3％的Cr2O3作显色剂，在少量矿化剂存在时，在1300℃下灼烧1 h，得到了色坐标为x=0．577，Y=0．401的红色陶瓷颜料。     

Topical Problems in the Biosynthesis of Red Blood Pigment

Uroporphyrinogen III plays a key role in the biosynthesis of heme, the red pigment of blood. In vivo studies with specifically ¹⁴C- and ³H-labeled precursors have revealed that the formation uroporphyrinogen III in the organism follows several primary and subsidiary pathways. Model experiments on the pattern of biosynthesis have led to simple and effective methods of synthesizing uroporphyrin analogs and have shown that their production is strongly favored thermodynamically. The biologically porphyrins important thus available permit a mechanistic explanation of the light-induced dermatoses in porphyria diseases and suggest promising medical applications in diagnosis and therapy.     

Phytochrome,the Visual Pigment of Plants

Plants require light for photosynthesis. In order to adapt to the light conditions in their particular habitat, they have developed various photoreceptor systems. Of these, phytochrome allows even two-color vision in the red/far-red region. The photoreceptor phytochrome is of interest not only to botanists, but also to natural product chemists, photochemists, biochemists, photobiologists, and recently molecular biologists. Despite numerous studies, there are still considerable gaps in our knowledge of this photoreceptor. This article first describes the basic structural studies of the tetrapyrrole chromophore and its photochemical cis–trans isomerization, which is the source of the chromoprotein's photochromism. In the section on the protein moiety, beside other topics, the domain structure of phytochrome and the conformational changes during phototransformation are discussed. Finally, the known phytochrome genes are used to derive phylogenetic relationships, and possible structure–function relationships are discussed.     

催化光度法测定痕量甲醛

基于磷酸介质中甲醛催化溴酸钾氧化溴甲酚紫的褪色反应 ,建立了测定痕量甲醛的方法。方法的检出限为 1.0× 10 - 5g·L- 1,线性范围为 0 .0 2 0～ 0 .4 8μg·ml- 1,方法简便 ,用于空气中测定痕量甲醛 ,结果满意。