Electronic detection of the enzymatic degradation of starch

[reaction: see text] The enzymatic degradation of starch can be monitored electronically using single-walled carbon nanotubes (SWNTs) as semiconducting probes in field-effect transistors (FETs). Incubation of these devices in aqueous buffer solutions of amyloglucosidase (AMG) results in the removal of the starch from both the silicon surfaces and the side walls of the SWNTs in the FETs, as evidenced by direct imaging and electronic measurements.     

Self-assembling structures of long-chain phenyl glucoside influenced by the introduction of double bonds

Four long-chain phenyl glucoside amphiphiles possessing a saturated or unsaturated long alkyl chain group as the self-assembling unit of a highly organized molecular architecture were synthesized. Their self-assembling properties were investigated by EF-TEM, SEM, CD, FT-IR, and XRD. Compound 2 possessing one double bond in the lipophilic portion showed twisted helical fibers, which formed a bilayered structure with a 3.59 nm period, while compound 3 showed the helical ribbons and left-handed nanotubular structures with 150-200 nm inner diameters and ca. 20 nm of wall. Very interestingly, compound 4 possessing three double bonds showed a nanotubular structure with ca. 70 nm of inner diameter through a helical ribbon, which formed a loose bilayered structure with 4.62 nm. These results indicate that self-assembling properties strongly depend on the number of cis double bonds.     

Mechanistic study of thermal behavior and combustion performance of epoxy resins: I homopolymerized TGDDM

Tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) undergoes homopolymerization on heating. Intramolecular reactions which compete with crosslinking favor the formation of cyclic structures with increasing thermal and fire resistance of the resin, whereas physical mechanical properties tend to decrease. The mechanism of thermal decomposition of TGDDM is studied by thermogravimetry, differential scanning calorimetry and thermal volatilization analysis with characterization of volatiles evolved and residue left. Thermal degradation of poly-(TGDDM) starts at 260°C with elimination of water from secondary alcoholic groups which is a typical pathway for epoxy resin degradation. Resulting unsaturations weaken bonds in the β-position and provoke the first chain breaking at allyl–amine and allyl–either bonds. With increasing temperature, saturated alkyl–ether bonds and alkyl carbon–carbon bonds are broken first, followed by the most stable alkyl–aryl bonds at T>365°C. The combustion performance of TGDDM is discussed on the basis of the thermal degradation behavior.     

Temperature dependence of the distribution of the first passage time: results from discontinuous molecular dynamics simulations of an all-atom model of the second beta-hairpin fragment of protein G

More than 22 000 folding kinetic simulations were performed to study the temperature dependence of the distribution of first passage time (FPT) for the folding of an all-atom Gō-like model of the second beta-hairpin fragment of protein G. We find that the mean FPT (MFPT) for folding has a U (or V)-shaped dependence on the temperature with a minimum at a characteristic optimal folding temperature T(opt). The optimal folding temperature T(opt) is located between the thermodynamic folding transition temperature and the solidification temperature based on the Lindemann criterion for the solid. Both the T(opt) and the MFPT decrease when the energy bias gap against nonnative contacts increases. The high-order moments are nearly constant when the temperature is higher than T(opt) and start to diverge when the temperature is lower than T(opt). The distribution of FPT is close to a log-normal-like distribution at T > or = T(opt). At even lower temperatures, the distribution starts to develop long power-law-like tails, indicating the non-self-averaging intermittent behavior of the folding dynamics. It is demonstrated that the distribution of FPT can also be calculated reliably from the derivative of the fraction not folded (or fraction folded), a measurable quantity by routine ensemble-averaged experimental techniques at dilute protein concentrations.     

Reactions of dimethyl acetylenedicarboxylate—VI : Reaction with aldehyde and ketone phenylhydrazones

Benzaldehyde phenylhydrazone with dimethyl acetylenedicarboxylate gives dimethyl 1,3-diphenylpyrazoline-4,5-dicarboxylate, dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate and trimethyl 1-phenylpyrazole-3,4,5-tricarboxylate; p-chlorobenzaldehyde phenylhydrazone gives trimethyl 1-phenyl-3,4,5-tricarboxylate and 1,2-(bis-phenylazo)-1,2-di-p-chlorophenylethane. Under similar conditions, p-tolualdehyde phenylhydrazone gives only trimethyl 1-phenylpyrazole-3,4,5- tricarboxylate. Acetophenone phenylhydrazone with dimethyl acetylenedicarboxylate gives dimethyl 1,3-diphenylpyrazole-4,5-dicarboxylate. Benzophenone phenylhydrazone, on the other hand, gives a mixture of dimethyl 1,3-diphenylpyrazoline-4,5-dicarboxylate and dimethyl 1,3-diphenylpyrazole-4,5- dicarboxylate. Benzyl methyl ketone and dimethyl acetylenedicarboxylate gives an enamine maleate, which is the Michael addition product.     

Symmetry allowed π4s+π2s additions silacyclopentadienes

π⁴s+π²s cycloaddition of hexaphenylsilacyclopentadiene with ethyl acrylate gives rise to a bicyclosilaheptene derivative. High resolution NMR studies have shown that the ester group in this adduct is in the endo position and that the ester methylene protons are magnetically inequivalent. Similar cycloadditions of hexaphenylsilacyclopentadiene, 1,1-dimethyl-2,3,4,5-tetraphenylsilacyclopentadiene, 1-methyl-1,2,3,4,5-pentaphenylsilacyclopentadiene, and 1-methyl-1-vinyl-2,3,4,5-tetra-phenylsilacyclopentadiene with dienophiles like acrylonitrile, maleic anhydride and dibenzoylacetylene have been carried out. The stereochemistry of these adducts has been deduced on the basis of NMR studies. Mass spectral fragmentation studies of some of the silabicycloheptenes have been carried out.     

The indole side chain of tryptophan as a versatile pi-donor

Single-armed, 15- and 18-membered lariat ether receptor systems having indolylethyl side arms bind Na+ and K+ in the ring. The indole residue serves as a pi-donor to the ring-bound cation. Whether the five- or six-membered ring interacts most directly with Na+ or K+ depends on whether the sidearm is attached to indole's 3- or 5-position. This suggests that structural as well as electronic factors are important in pi-complexation of alkali metal cations.     

Comparative study of photodynamic properties of 13,15-N-cycloimide derivatives of chlorin p6

Comparative study of 13,15-[N-(2-hydroxyethyl)]cycloimide chlorin p6 (2), 13,15-(N-acetoxy)cycloimide chlorin p6 (3), 13,15-(N-hydroxy)cycloimide chlorin p6 methyl ester (4) and 13,15-(N-methoxy)cycloimide chlorin p6 methyl ester (5) together with the previously investigated 13,15-[N-(3-hydroxypropyl)]cycloimide chlorin p6 (1) was performed. The dependence of the key photodynamic properties of 1-5 on the introduced substituents was analyzed. The photoinduced cell-killing activity of 4 is 100- and 280-fold higher than that of chlorin p6 and Photogem, respectively, as estimated on A549 human lung adenocarcinoma cells. The activity is reduced eight times in the order 4 > 5 > 1 > 2 > 3. The intracellular accumulation of 1-5 occurs in cytoplasm in a monomeric form bound to the lipids of cellular membranes. This form of 1, 2, 3, 4 and 5 is characterized by the high quantum yield of singlet oxygen generation, which depends on the introduced substituents, 0.66, 0.59, 0.35, 0.51 and 0.73, respectively. The photostability is two-fold less for 1 and four-fold less for 2, 3 and 5 than for 4. The rates of cellular uptake and efflux of 1-5 vary widely, thus providing the way to optimize the pharmacological properties of the photosensitizer (PS) using the respective substituents. Modifying the substituents, 1-5 were targeted to different cellular organelles. The enhanced accumulation in the Golgi apparatus and mitochondria complemented with diffuse staining of intracellular membranous structures is a property of 1-4. Compound 5 accumulates selectively in the lipid droplets and stains weakly perinuclear structures. Temperature-sensitive mechanisms of transport are responsible for the 1-4 uptake. Diffusion can play a role in the internalization of 5 but not of 1-4. Endocytosis via caveolae, clathrin-dependent and adenosine triphosphate-dependent pathways are not noticeably involved in the 1-5 internalization. Independently from their intracellular localization 1, 4 and 5 are highly efficient near-IR PS, which induce predominantly an apoptotic type of cell death under conditions providing ca 50% level of phototoxicity and necrosis at the 100% level of phototoxicity.