: Self-assembled monolayers (SAMs) of n-alkanethiolates on gold, silver, and copper have been intensively studied both as model organic surfaces and as modulators of metal surface properties. Sensitivity restrictions imposed by monolayer coverage and the low surface area of planar metal substrates, however, limit the characterization of these films in molecualar terms to surface enhancement techniques. As a result, key aspects such as film dynamics and alkyl chain ordering remain ill-defined. The characterization of the thermal behavior of SAMs is important not only for the design of stable, well-ordered organic superlattices, but also for the fundamental understanding of the factors that drive molecular interactions in two dimensions. Phase properties in SAMs have been addressed here through the synthesis of gold nanoparticles of 20-30 A in diameter and fully covered with alkylthiol chains. These thiolmodified gold nanoparticles with large surface areas have enabled the monolayer film structure to be uniquely characterized by transmission FT-IR spectroscopy, NMR spectroscopy, and differential scanning calorimetry. Our studies reveal that for long-chain thiols ( 2 C,,), the alkyl chains exist predominantly in an extended, all-trans ordered conformation at 25 "C. Furthermore, calorimetry, variable

Caladenia is very unusual in that it contains species that attract pollinators by two different strategies, food and sexual deception. Among the sexually deceptive species, baiting for pollinators has shown that within populations orchid species are typically pollinated by a single species of thynnine wasp. However, some wasp species can be pollinators of more than one species of orchid usually when their ranges do not overlap. There is a trend for closely related orchids to exploit wasps from the same genus, with different lineages of orchids often pollinated by different genera. Very little is known about pollination of food-deceptive Caladenia species, although it is evident they attract a suite of generalist food-seeking insects. Food-deceptive species have a higher pollination rate than do sexually deceptive species. Studies of population genetics and pollen movements are few, although they suggest a pattern of fine-scale genetic structuring within populations, owing to predominantly restricted seed dispersal and low genetic differentiation among populations as a consequence of rare long-distance seed-dispersal events. Both evolutionary and ecological research of Caladenia will greatly benefit from a better understanding of the insect species involved in pollination, their ecological requirements and the ecological and genetic consequences of food and sexual deception.

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The polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) technique has been used in situ to determine the orientation and molecular structure of an equimolar mixture of poly-(L-lactide) (PLLA) and poly(D-lactide) (PDLA) spread at the air-water interface. The characteristics of the compression isotherm and of the PM-IRRAS spectra give clear evidence for the presence of a PLLA/PDLA stereocomplex. One of the most striking features in the PM-IRRAS spectra of the stereocomplex is the derivative shape of the band due to the CdO stretching vibration, providing a spectral signature of the presence of polylactide helices oriented parallel to the water surface. The positive and the negative components of the CdO band observed at 1749 and 1765 cm -1 are assigned to the A and E modes of the helical structure, respectively. This assigment was confirmed by recording transmission spectra of the transferred stereocomplex at normal and oblique incidence. Compression of the monolayer past 17 Å 2 / repeat unit results in the formation of a bilayer structure. The surface pressure-area isotherm and the PM-IRRAS features suggest that the structure of the film at the air-water interface is similar to the three-dimensional crystal structure of the PLLA/PDLA stereocomplex. In the bulk crystalline structure, the molecules adopt a 31-helix conformation, and a segment of a PLLA molecule is paired with a segment of a PDLA molecule, resulting in a racemic unit cell. The PM-IRRAS technique is thus shown to provide detailed insight into the structure of these polymeric Langmuir films and definitely shows that helical polymeric structures can be directly observed at the air-water interface. † This paper is dedicated to the memory of Prof. G. Ronald Brown.

This study confirms for the first time that highly specific pollination by fungus gnats is achieved by sexual deception in Pterostylis. It is predicted that sexual deception will be widespread in the genus, although the diversity of floral forms suggests that other mechanisms may also operate.

Whereas short-term regulation of insulin biosynthesis at the level of translation is well accepted, glucosedependent transcriptional control is still believed to be a longterm effect occurring after more than 2 hr of glucose stimulation. Because pancreatic ␤ cells are exposed to elevated glucose levels for minutes rather than hours after food uptake, we hypothesized the existence of a short-term transcriptional control. By studying the dynamics of newly synthesized (prepro)insulin RNA and by employing on-line monitoring of gene expression in single, insulin-producing cells, we were able to provide convincing evidence that insulin gene transcription indeed is affected by glucose within minutes. Exposure of insulinoma cells and isolated pancreatic islets to elevated glucose for only 15 min resulted in a 2-to 5-fold elevation in (prepro)insulin mRNA levels within 60-90 min. Similarly, insulin promoter-driven green fluorescent protein expression in single insulin-producing cells was significantly enhanced after transient glucose stimulation. Thus, short-term signaling, such as that involved in insulin secretion, also may regulate insulin gene transcription.Insulin is of vital importance in maintaining glucose homeostasis in mammals. This, and its unique role as the only anabolic peptide hormone, necessitates strict regulation and fast-acting mechanisms guaranteeing efficient insulin biosynthesis and secretion. Although pancreatic beta cells secrete only part of their stored hormone in response to elevated glucose concentrations, biosynthesis of (prepro)insulin (PPI) is started immediately to rapidly replenish the insulin stores. It is commonly believed that glucose exhibits its immediate, or short-term, effect on insulin biosynthesis at the posttranscriptional and translational levels rather than at the level of transcription. Elevated glucose concentrations have been shown to enhance the stability of PPI mRNA (1), translation initiation (2), and translation elongation (2, 3). The effect of glucose on the generation of the PPI mRNA is commonly accepted to be a long-term effect, occurring after more than 2 hr of exposure to elevated glucose levels (4). To this end, the molecular mechanisms underlying glucose-stimulated insulin gene transcription mainly have been studied after incubation with high glucose concentrations over several hours or even days (5-15). According to this view, mechanisms regulating PPI gene transcription are dissociated from the immediate glucose effect and from short-term signaling associated with the regulation of translation or insulin secretion. However, from the physiological point of view pancreatic beta cells are exposed to elevated glucose levels for minutes rather than hours after food-uptake. Therefore, we hypothesized the existence of a short-term control, allowing glucose to exert physiological regulation at the level of insulin gene transcription.The aim of the present study was to evaluate whether glucose stimulation for only 15 min, thus mimicking the physiological situati...

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Ins(1,4,5)P3(InsP3)-induced Ca2+ release and [3H]InsP3 binding were measured in rat cerebellar microsomes in the presence or absence of caffeine. The quantal Ca2+ release was shown to occur in an apparently co-operative fashion with a Hill coefficient (h) of 2.2. Half-maximal Ca2+ release was observed at 900 nM-InsP3. Addition of caffeine caused changes both to the concentration of InsP3 required to cause half-maximal Ca2+ release (3.9 microM at 50 mM-caffeine) and to the apparent co-operativity (h = 1.0 at 50 mM-caffeine). Under standard conditions for [3H]InsP3 binding, caffeine had no effect, and it had no effect on InsP3 metabolism. Cyclic AMP also had no effect on the quantal release induced by InsP3. These results are consistent with the view that caffeine affects the opening (Ca2+ release) events rather than the ligand-binding events in the operation of the InsP3-sensitive Ca2+ channel.