New chiral selectors: design and synthesis of 6-TBDMS-2,3-methyl beta-cyclodextrin 2-2' thioureido dimer and 6-TBDMS-2,3-methyl (or 2-methyl-3-acetyl) beta-cyclodextrin bearing an (R) Mosher acid moiety

Cyclodextrin (CD) derivatives are important selectors for analytical chiral recognition. Their enantioselectivities and chemical properties depend on ring size and on nature, number and location of substituents. This paper describes the synthesis of 6-O-TBDMS-2,3-O-methyl beta-cyclodextrins bearing in position 2 either a single (R)-Mosher acid moiety or a second CD unit, in view of their possible application as chiral selectors. Most synthetic steps were successfully carried out under high-intensity ultrasound using a new sonochemical reactor developed in the authors' laboratory. 6-O-TBDMS-2-O-methyl-3-[(S)-2-methylbutyl]-beta-CD was also synthesized and tested with gas chromatography; the enantiorecognition power of the other CD derivatives is also being tested. A computational study of model structures to design these CD derivatives.     

八肽胆囊收缩素激活钙离子通道和酪氨酸激酶诱导豚鼠心肌细胞内的游离钙增高

探讨八肽胆囊收缩素(CCK-8)对豚鼠单个心肌细胞内游离钙浓度([Ca2+]i的影响及其信号转导机制.Fluo 3-AM标记酶消化法分离的单个心室肌细胞,用激光共聚焦显微镜测定细胞内[Ca2+]i的浓度.[Ca2+]i的变化用荧光强度(Fi)和相对荧光强度(Fi/F0%)表示.实验结果如下(1)在含Ca2+1.0 mmol/L的Tyrode's液中,CCK-8(1～104pmoVL)均可引起[Ca2+]i快速显著上升(P＜0.01).(2)用钙离子鳌合剂EGTA(3 mmol/L)和钙离子通道阻断剂nisoldipine(0.5μmol/L)预孵育心肌细胞5 min,CCK-8(102pmol/L)仅可引起[Ca2+]i缓慢轻度上升(P＜0.01).(3)用非选择性CCK受体拮抗剂丙谷胺(proglumide 6μmo1/L)或酪氨酸激酶抑制剂genistein(1 μmol/L)预孵育心肌细胞5 min,则完全抑制CCK-8诱导的[Ca2+]i升高(P＜0.01).CCK-8可通过激活其受体控制的Ca2+通道,引起Ca2+内流,诱导细胞内Ca2+释放,引起豚鼠单个心肌细胞内[Ca2+]i上升,此作用可能由酪氨酸激酶介导.     

Tertiary structure of human alpha1-acid glycoprotein (orosomucoid). Straightforward fluorescence experiments revealing the presence of a binding pocket

Binding of hemin to alpha1-acid glycoprotein has been investigated. Hemin binds to the hydrophobic pocket of hemoproteins. The fluorescent probe 2-(p-toluidino)-6-naphthalenesulfonate (TNS) binds to a hydrophobic domain in alpha1-acid glycoprotein with a dissociation constant equal to 60 microM. Addition of hemin to an alpha1-acid glycoprotein-TNS complex induces the displacement of TNS from its binding site. At saturation (1 hemin for 1 protein) all the TNS has been displaced from its binding site. The dissociation constant of hemin-alpha1-acid glycoprotein was found equal to 2 microM. Thus, TNS and hemin bind to the same hydrophobic site: the pocket of alpha1-acid glycoprotein. Energy-transfer studies performed between the Trp residues of alpha1-acid glycoprotein and hemin indicated that efficiency (E) of Trp fluorescence quenching was equal to 80% and the F?rster distance, R0 at which the efficiency of energy transfer is 50% was calculated to be 26 A, revealing a very high energy transfer.     

Field and laboratory studies of Ophryoglena sp. (Ciliata: Ophryoglenidae) infection in zebra mussels,Dreissena polymorpha (Bivalvia: Dreissenidae)

This study, conducted in the Dnieper-Bug Canal in Belarus, is the first to monitor the seasonal (June-November) dynamics of infection with the parasitic ciliate Ophryoglena sp. in a zebra mussel (Dreissena polymorpha) population. Mean population prevalence and intensity of infection varied, respectively, from 11 to 62% and from 0.9 to 24.1 ciliates/mussel. Mean prevalence was highly correlated with mussel length in mussels <20 mm (R(2)=0.97) and was lower in larger mussels. Mean infection intensity in mussels 1-25 mm long was similarly correlated with their size (R=0.98), reached a maximum in the 20-25 mm size-class, and then sharply decreased, thus providing evidence, albeit limited, that high intensity of infection might be lethal. Transinfection of zebra mussels by Ophryoglena sp. was achieved in the laboratory-a first for a protozoan parasite of D. polymorpha; from an initial complete lack of infection, mean prevalence and intensity rose, respectively, to 86.7% and 8.3 ciliates/mussel.     

The significance of inter- and intraspecific variation in bacterivorous and herbivorous protists

This paper reviews the emerging evidence on the significance of inter- and intraspecific variation in the feeding behaviour of aquatic protists. Small heterotrophic nanoflagellates (HNF) have been identified as the primary bacterial consumers in most aquatic environments. Recent research using novel techniques such as flow cytometry and high resolution video microscopy revealed that their feeding strategies and grazing rates are diverse. There is an important conceptual difference between uptake rates measured in short-term (min to h) experiments and grazing rates averaged over a longer-term (d). This is because the latter are strongly affected by digestion rates which are species-specific, i.e. the same bacterial prey may be digested differently by various grazers, and the same predator may selectively digest variable prey. Planktonic ciliates are the most important algal consumers in many lakes and marine systems. Large species-specific differences in their feeding behaviour and growth rates have been documented for closely related species. Intraspecific variation, which is, most likely, caused by varying clonal composition may be as important as interspecific variation. Finally, there is some evidence that the individual variability within a given population is generally large, both among bacterivorous HNF and among herbivorous ciliates. The consequences of this diversity becoming apparent at the levels of the species, population, clone and individual need to be considered by aquatic ecologists in their conceptual models. This revised version was published online in August 2006 with corrections to the Cover Date.     

A generalized mover-stayer model for panel data

A generalized mover-stayer model is described for conditionally Markov processes under panel observation. Marginally the model represents a mixture of nested continuous-time Markov processes in which sub-models are defined by constraining some transition intensities to zero between two or more states of a full model. A Fisher scoring algorithm is described which facilitates maximum likelihood estimation based only on the first derivatives of the transition probability matrices. The model is fit to data from a smoking prevention study and is shown to provide a significant improvement in fit over a time-homogeneous Markov model. Extensions are developed which facilitate examination of covariate effects on both the transition intensities and the mover-stayer probabilities.     

Distribution of Acid and Alkaline Zones on the Cell Surface of Chara corallina under Stationary and Local Illumination

A scanning microprobe technique was used to study pH distribution near the cell surface of Chara corallina Klein ex Willd. under variations of light intensity, dark–light transitions, and local illumination of various cell parts. In darkness, the H⁺-transporting activity of plasmalemma was distributed homogeneously over the cell surface. However, after exposing the cell to weak light (irradiance 0.2–0.5 W/m²), individual alkaline peaks with pH of 1–2 units were observed in the longitudinal pH profile. The peaks in the longitudinal pH profile became more numerous with the increase in light intensity. The plot of pH as a function of light intensity included a steep transition from zero to its maximum amplitude. In strong light (100 W/m²), the pH bands alternated along the cell length with a periodic length of about 7 mm. It is shown that the light-induced formation of ring-shaped bands with H⁺-exporting and H⁺ sink activities is preceded by the appearance of irregularly located spots (patches). When small cell parts were illuminated and the light spot was suddenly shifted along the cell to another position, the alkaline bands reorganized in two ways. In some cases, this treatment was followed by a gradual shift in the band position (without attenuation in the peak height) toward the illuminated area. In other cases, the initial band disappeared after such treatment, and a new alkaline band emerged in the vicinity of the illuminated area. Despite the apparent similarity of regular bands in the longitudinal pH profiles, the properties of individual bands (variable sensitivity to light intensity changes, the ability of bands to move along the cell under external treatment) differ substantially. It is supposed that the light-induced formation of the pH profile is based on primary fluctuations of photosynthetic and transport activities in the chloroplast layer and the plasmalemma, as well as on further rearrangements of membrane domains that stabilize band locations.     

Inbreeding and true seed in tetrasomic potato. III. Early selection for seedling vigor in open-pollinated populations

Tuber yield in open-pollinated (OP) offspring of potato cultivars appears to be correlated with the proportion of hybrids within each population. OP true potato seed (TPS) from ten selected clones was tested in an experiment at two Peruvian locations, San Ramón (mid-altitude warm tropics) and Huancayo (highland cool tropics), to investigate the early selection effect on OP populations. Another experiment in La Molina (dry coast) was included to confirm the results from these other two locations. The results clearly showed that plant survival, tuber yield and berry number can be increased by a strong early selection. Likewise, the results suggested that the most-promising OP offspring for TPS production could be derived from tetraploid clones with a high rate of outcrossing. This experiment demonstrates that high tuber yield may be obtained in OP TPS cultivars with little effort, using early selection for seedling vigor in the nursery. Genetic interpretation of this response to early selection indicates that both the intensity of selection and non-additive genetic variation for tuber yield account for these observed gains. Received: 15 December 2000 / Accepted: 4 April 2001     

The sniff is part of the olfactory percept

In this review, we use data obtained primarily from humans to argue that sniffs are not merely a stimulus carrier but are rather a central component of the olfactory percept. We argue that sniffs 1) are necessary for the olfactory percept, 2) affect odorant intensity perception and identity perception, 3) drive activity in olfactory cortex, 4) are rapidly modulated in an odorant-dependent fashion by a dedicated olfactomotor system, and 5) are sufficient to generate an olfactory percept of some sort even in the absence of odor.