Conditional Response to Stress in Yeast

All living cells respond to sudden, adverse changes in their environment by evoking a stress response. Here we focus mainly on the response of the model eukaryotic organism Saccharomyces cerevisiae (bakers yeast) to an increase in external osmolarity. We summarize data demonstrating that stress responses largely depend on the existing environmental growth conditions. Nutrients and other medium parameters such as external pH determine how yeast cells sense osmotic stress circumstances and subsequently elicit adaptive responses. It is likely that the composition of cell wall and plasma membrane plays an important role in this process.     

Camphor cryoscopy by differential thermal analysis

The determination of the freezing point depression of organic solutions with camphor as solvent was performed by means of DTA. Amounts of 50–100μg substance and 1–2 mg camphor were weighed on a platinum wire, the camphor being pressed to a pellet by a glass press. The temperature difference between the glass tubes with pure camphor and with solution was recorded versus temperature, while the samples were cooled in a previously heated aluminium block. The difference between the recorded deviations from a straight line was found to be a measure of the freezing point depression. Errors less than 5 % were computed for various samples.     

Synthesis of adamantane monomers and their properties

Conclusion Syntheses were reported for new adamantane monomers, namely the allyl and propargyl esters of 1-adamantanecarboxylic acid, the diallyl and dipropargyl esters of 1,3-adamantanedicarboxylic acid and di-1-adamantyl maleate. These esters are capable of undergoing thermal copolymerization with -cyanoacrylate esters.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2808–2809, December, 1986.     

Activation and transfer of oxygen XIII evidence for C10A as the primary nucleophilic additions site of N1-alkylflavinium cations

The formation of a primary adduct and its successive trapping were carried out with a deuteriated and non-deuteriated nucleophile. The addition sites were ascertained by NMR-specta. The consequences for the structure of ESR-silent blue flavin transients are discussed.     

Synthesis and Stereochemistry of Some New 1,3-Oxathiane Derivatives

Summary. The synthesis and stereochemistry of some new 2,5-substituted 1,3-oxathiane derivatives are reported. The anancomeric or flexible structure of the derivatives and some peculiar cases of prochirality are revealed by NMR investigations.     

Ordering surfaces on the nanoscale: implications for protein adsorption

Monolayer-protected metal nanoparticles (MPMNs) are a newly discovered class of nanoparticles with an ordered, striped domain structure that can be readily manipulated by altering the ratio of the hydrophobic to hydrophilic ligands. This property makes them uniquely suited to systematic studies of the role of nanostructuring on biomolecule adsorption, a phenomenon of paramount importance in biomaterials design. In this work, we examine the interaction of the simple, globular protein cytochrome C (Cyt C) with MPMN surfaces using experimental protein assays and computational molecular dynamics simulations. Experimental assays revealed that adsorption of Cyt C generally increased with increasing surface polar ligand content, indicative of the dominance of hydrophilic interactions in Cyt C-MPMN binding. Protein-surface adsorption enthalpies calculated from computational simulations employing rigid-backbone coarse-grained Cyt C and MPMN models indicate a monotonic increase in adsorption enthalpy with respect to MPMN surface polarity. These results are in qualitative agreement with experimental results and suggest that Cyt C does not undergo significant structural disruption upon adsorption to MPMN surfaces. Coarse-grained and atomistic simulations furthermore elucidated the important role of lysine in facilitating Cyt C adsorption to MPMN surfaces. The amphipathic character of the lysine side chain enables it to form close contacts with both polar and nonpolar surface ligands simultaneously, rendering it especially important for interactions with surfaces composed of adjacent nanoscale chemical domains. The importance of these structural characteristics of lysine suggests that proteins may be engineered to specifically interact with nanomaterials by targeted incorporation of unnatural amino acids possessing dual affinity to differing chemical motifs.     

Cautions regarding the physical interpretation of statistically based separation of the ortho substituent effect into inductive,mesomeric, and steric components—I: The composition of taft EsO constants

It is shown that the interpretation of the Taft E_s^O values in terms of predominating inductive, mesomeric, and steric effects depends strongly upon the sample size. Nevertheless, the results obtained indicate that the E_s^O constants are a function of the steric effects and to a lesser extent of the mesomeric effects of the substituents.     

Lipid bilayer deposition and patterning via air bubble collapse

We report a new method for forming patterned lipid bilayers on solid substrates. In bubble collapse deposition (BCD), an air bubble is first "inked" with a monolayer of phospholipid molecules and then touched to the surface of a thermally oxidized silicon wafer and the air is slowly withdrawn. As the bubble shrinks, the lipid monolayer pressure increases. Once the monolayer exceeds the collapse pressure, it folds back on itself, depositing a stable lipid bilayer on the surface. These bilayer disks have lateral diffusion coefficients consistent with high quality supported bilayers. By sequentially depositing bilayers in overlapping areas, fluid connections between bilayers of different compositions are formed. Performing vesicle rupture on the open substrate surrounding this bilayer patch results in a fluid but spatially isolated bilayer. Very little intermixing was observed between the vesicle rupture and bubble-deposited bilayers.     

Ultrafast charge-transfer dynamics of donor-substituted truxenones

The photophysics of two donor-substituted truxenone derivatives has been studied by femtosecond time-resolved transient absorption spectroscopy. The systems consist of a central truxenone acceptor with three triarylamine (TARA) branches which act as electron donors. Upon excitation in the visible regime an electron is transferred from the donor to the acceptor, generating a charge-separated state. This state can be probed via the characteristic absorption of the TARA radical cation around 700 nm. A second absorption band around 420 nm exhibits the same kinetics and is assigned to an absorption of the radical anion of the truxenone moiety. The back electron transfer and the recovery of the ground state can be interpreted within the framework of Marcus theory. To study the dependence of the back electron transfer on the electronic coupling, the distance between the donor and the acceptor was adjusted. Two solvents were employed, dimethylsulfoxide and dichloroethane. A biexponential decay of the bands assigned to the charge-separated state was observed, with time constants in the picosecond range. Surprisingly, the rates for electron back transfer do not follow the simple picture of the donor-acceptor distance being the determining factor. The observations are explained within a model that additionally takes steric interactions between the donor and the acceptor into account.