Lipophilic derivative of rhodamine 19: characterization and spectroscopic properties

A new octadecylamide derivative of rhodamine 19 was synthesized by reaction of rhodamine 19 ethyl ester (rhodamine 6 G) with octadecylamine. This lipophilic dye exists in two forms: as a cationic species containing a secondary amide group and as an electrically neutral molecule containing an additional ring closed between the oxygen of the amide group and the central carbon of the xanthene part. Both forms were isolated and characterized in detail by means of elemental analysis, mass spectrometry, IR, NMR and UV-VIS spectroscopy. Depending on the hydrogen ion activity in solution and the availability of solvent hydrogen for hydrogen bond formation, the cationic form easily converted into a neutral one and vice versa. On the basis of absorption and emission UV-VIS spectroscopic data, the equilibrium of the two forms was studied in various solvents. An increase in dye concentration in acidified methanol/water mixture (volume fraction of water, ?=80%) led to aggregation of the cationic molecules. Using the UV-VIS absorption data, a corresponding dimerization constant was evaluated.     

Dimerization of Acetylenic Amides

Summary.  Dimers of substituted acetylenic amides were obtained when triethylamine was used as refluxing solvent and acid acceptor instead of pyridine in the reaction of substituted acetylenic amides with triphosgene. Unsubstituted acetylenic amides resulted in the corresponding quinazolinone. Received October 22, 2001. Accepted (revised) November 22, 2001     

C50富勒烯及其二聚物C100、C101的光学性质

运用B3LYP方法在6-31G*基组水平上对C50富勒烯以及它的两个不同二聚物C100、C101的几何构型进行了全优化. 在优化所得构型的基础上, 采用TDB3LYP方法在3-21G*基组水平上对其激发态性质、电子吸收光谱进行了研究, 根据计算得到的态态间跃迁偶极矩和跃迁能等数据, 结合使用态求和公式进一步计算得到了它们不同光学过程中的三阶非线性极化率. 结果表明, 当C50富勒烯二聚以后, 其电子吸收光谱的最大波长吸收峰发生了明显的红移, 三阶非线性极化率有了较大的提高. 其中, [5,5]-[5,5]哑铃型二聚物C101有着比[2+2]闭环型二聚物C100更大的三阶非线性极化率.     

消除甲基丙烯酸酯类单体阴离子聚合副反应的几种主要方法

本文论述了甲基丙烯酸酯类单体阴离子聚合过程中主要副反应的机理，重点讨论了三类主要的化合物（金属烷氧基化合物，金属卤化物和冠醚类化合物）对于甲基丙烯酸酯类单体阴离子活性中心的稳定作用。     

A monomeric bacteriochlorophyll triplet state (B) in reaction centres of Rhodobacter sphaeroides R26, studied by absorption-detected magnetic resonance

Using absorption-detected magnetic resonance, a new triplet state was observed in reaction centres of Rhodobacter sphaeroides R26 at 7 K. Its zero-field splitting parameters &|;D&|; = 220.5 × 10⁻⁴ cm⁻¹ and &;|;E&|; = 65.4 × 10⁻⁴ cm⁻¹, its spin polarization and its microwave-induced absorption spectrum indicate that it belongs to one of the accessory monomeric bacteriochlorophyll molecules and that it is populated through the same excitation path as the primary donor triplet ³P₈₇₀, via the radical pair ³[P₈₇₀⁺H⁻].     

Sharp upper bound for the first non-zero Neumann eigenvalue for bounded domains in rank-1 symmetric spaces

In this paper, we prove that for a bounded domain in a rank- symmetric space, the first non-zero Neumann eigenvalue where denotes the geodesic ball of radius such that

and equality holds iff . This result generalises the works of Szego, Weinberger and Ashbaugh-Benguria for bounded domains in the spaces of constant curvature.

     

氨基酸化学振荡反应活性中心的研究

我们已经报导了一系列氨基酸参与的化学振荡反应，获得了各振荡体系中反应物的浓度范围和典型振荡波形．初步拟定了反应机理，得到了振荡反应诱导期和周期的表观活化能以及各反应物初始浓度与诱导期或周期之间的定量关系［l，2］．然而，综观各振荡体系，不同结构的氨基酸一Bfoi－Mn‘＋－H。SO。一丙团（Act）体系中的BrOS、Mn‘＋、Act起振浓度变化很小，而各种氨基酸的最低起振浓度却存在着相当大的差异，且与酸度密切相关．为此，本文固定你对5］。二0．04mol·din－’；卜n‘＋o二0．016mol·din－‘；［Actfo二0．054mol·din－…     

The chloroplast thylakoid membrane system is a molecular conveyor belt

Light drives photosynthesis, but paradoxically light is also the most variable environmental factor influencing photosynthesis both qualitatively and quantitatively. The photosynthetic apparatus of higher plants is adaptable in the extreme, as exemplified by its capacity for acclimation to very bright sunny or deeply shaded conditions. It can also respond to rapid changes in light such as sunflecks. In this paper I offer a model that i) explains the thylakoid membrane organisation into grana stacks and stroma lamellae, ii) proposes a role for rapid D1 protein turnover and LHCII phosphorylation, and iii) suggests a mechanism for photoinhibition. I argue that the photosynthetic membrane system is dynamic in three dimensions, so much so that, in the light, it is in constant motion and operates in a manner somewhat analogous to a conveyor belt. D1 protein degradation is proposed to be the motor that drives this system. Photoinhibition is suggested to be due to the arrest of D1 protein turnover.Abbreviations D1 protein photosystem II reaction centre protein - 32 kDa rapidly turning over, herbicide, Q_B binding protein - LHCII light-harvesting chlorophylla/b binding protein of PS II - PS II centres PS II complete with LHCII located in grana stacks - Pre-PS II PS II complexes consisting only of the 47, 43 kDa and D2 proteins - D2 diffusely staining, reaction centre polypeptide, 34 kDa, of PS II - CP43 chlorophylla binding protein, 43 kDa, of PSII - CP47 chlorophylla binding protein, 47 kDa, of PSII - PS II centres PS II complex with newly inserted D1 protein but devoid of LHCII     

A new Si tetramer structure on Si (001)

Interactions between Si ad-dimers on Si (001) have been studied by molecular dynamics simulations using the Stillinger–Weber potential. The interactions determine the formation of clusters from diffusing dimers. We show different pathways for the formation of multiple-dimer clusters and propose a new tetramer (T_CC) structure formation by two diffusing dimers interacting. This tetramer structure has been found to be energetically stable with respect to isolated ad-dimers. Moreover, their local bonding configuration is very similar to the B-type step edge which is known to be the favoured adsorption site for epitaxial growth. The proposed tetramer may play a crucial role as the nucleus of the new epitaxial layer on Si (001).     

The conformational features of palytoxin in aqueous solution

Conformational features of palytoxin and acetylated palytoxin were investigated by detailed analyses of NOESY spectra. The conformational differences between palytoxin and acetylated palytoxin may account for the difference in the assembly state of palytoxin, which exists as an associated dimer, and the acetylated derivative, which exists as a monomer in aqueous solution. Two palytoxin units in the dimer may come in contact with each other at the hydrophobic region (C21-40) and the region around two conjugated double bonds (C60-84). The amino group of palytoxin is important for biological activities via Na/K ATPase, but it was not found to be involved in the contact faces of the two palytoxin units. This information should aid in revealing how palytoxin interacts with Na/K ATPase.