Theoretical studies of the geometries of H2GeLiCl and its insertion reaction with R-H (R = F,OH, NH2)

The geometries and insertion reactions of germylene derivative H₂GeLiCl with R-H (R = F, OH, NH₂) have been investigated at the B3LYP/6-311+G^* level of theory. The potential barriers of the three reactions are 93.5, 151.3, and 194.1 kJ/mol, including the zero-point vibration energy corrections, respectively. The mechanisms of all the three reactions are identical, i.e., an intermediate has been located during the insertion reaction. The intermediate could dissociate to substituted germylene and LiCl as a barrier process. Correspondingly, the reaction free energies for the three reactions are −7.4, 49.9, and 64.4 kJ/mol, respectively.

     

The lipidated membrane anchor of full length N-Ras protein shows an extensive dynamics as revealed by solid-state NMR spectroscopy

Many proteins involved in signal transduction are equipped with covalently attached lipid chains providing a hydrophobic anchor targeting these molecules to membranes. Despite the considerable biological significance of this membrane binding mechanism for 5-10% of all cellular proteins, to date very little is known about structural and dynamical features of lipidated membrane binding domains. Here we report the first comprehensive study of the molecular dynamics of the C-terminus of membrane-associated full-length lipidated Ras protein determined by solid-state NMR. Fully functional lipid-modified N-Ras protein was obtained by chemical-biological synthesis ligating the expressed water soluble N-terminus with a chemically synthesized (2)H or (13)C labeled lipidated heptapeptide. Dynamical parameters for the lipid chain modification at Cys 181 were determined from static (2)H NMR order parameter and relaxation measurements. Order parameters describing the amplitude of motion in the protein backbone and the side chain were determined from site-specific measurements of (1)H-(13)C dipolar couplings for all seven amino acids in the membrane anchor of Ras. Finally, the correlation times of motion were determined from temperature dependent relaxation time measurements and analyzed using a modified Lipari Szabo approach. Overall, the C-terminus of Ras shows a versatile dynamics with segmental fluctuations and axially symmetric overall motions on the membrane surface. In particular, the lipid chain modifications are highly flexible in the membrane.     

Composition-ratio determination of Chrome Azurol S (CAS) with Cu(2+) and research on dynamic reaction process of CAS with EDTA

The composition-ratio of Chrome Azurol S (CAS) with Cu(2+) and dynamic reaction process of CAS with EDTA were studied by spectrophotometry. The composition-ratio of Cu(2+) with CAS (2:1) was successfully determined using the method of lines and EDTA complexing substitution. The effects of temperature, time, pH, concentration of cetyltrimethylammonium bromide (CTMAB), and concentration of Cu(2+) on the absorption spectrum were also discussed. By optimizing experimental conditions, the dynamic process of displacement of CAS, which forms the ternary compound Cu-CAS-CTMAB, by EDTA were determined. The test results indicated that EDTA can replace 99.6% of the CAS quickly when heated. The system reached equilibrium finally. This research method can be applied to the qualitative and quantitative analysis of related Cu complexes.     

Deposition of DNA-functionalized gold nanospheres into nanoporous surfaces

We report the deposition of DNA-conjugated gold nanospheres into arrays of surface nanopores obtained from hexagonally ordered thin polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer films on silicon. The deposition occurs spontaneously from aqueous solution and is driven by either electrostatic interactions or specific DNA hybridization events between the DNA nanospheres and the surface nanopores. To mitigate this spontaneous deposition, we have chemically modified the nanopores with either positively charged aminosilanes or oligonucleotide probe sequences. The deposition of DNA nanospheres into the surface nanopores was characterized by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). We have observed preferential immobilization of individual DNA nanospheres within the nanopores, based on the size matching between the two entities. The inclusion density and selectivity of DNA nanosphere deposition into the surface nanopores was found to depend predominantly on the methods through which the nanoporous surfaces were prepared and chemically functionalized.     

Phase‐separated,conducting composites from polyaniline and benzobisthiazole rigid‐rod polymer

As an alternative method for processing polyaniline (PANI) from its conducting (protonated) state, vacuum casting of PANI from a methanesulfonic acid (MSA) solution provided films with electrical conductivity values of about 130–150 S/cm. In addition, we similarly prepared blended films of PANI · MSA and poly(p‐phenylene benzobisthiazole) (PBZT). This process eliminated the need for a subsequent protonation step and had the additional advantage that the conjugated PBZT may provide alternative conducting pathways. Conductivity values of the composite films ranged from 100 pS/cm to 124 S/cm, and the films displayed critical concentration behavior with a PANI threshold concentration of 2.75% and a critical exponent of 4. Transmission electron micrographs displayed phase‐separated regions with PANI forming a continuous network at high concentrations. Thermogravimetric analysis results demonstrated the thermal and thermooxidative stability advantage of the blends due to the PBZT component. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2539–2548, 2001     

Unusual dependence of particle architecture on surfactant concentration in partially fluorinated decylpyridinium templated silica

A series of porous silica particles is prepared with different concentrations of the fluorinated cationic surfactant 1-(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10)-heptadecafluorodecyl)pyridinium chloride (HFDePC) to trace the changes in pore structure and particle morphology as the surfactant concentration increases. At the lowest concentration studied (1.5 mmol/L), the product consists of small round particles with close-packed cylindrical mesopores. As the HFDePC concentration increases, macroporous voids are introduced to create multi-chambered hollow particles with mesoporous walls. With a still higher concentration of HFDePC the macropore volume decreases, and elongated, tactoid-like nanoparticles are formed with random mesh-phase pores oriented with silica layers perpendicular to the main axis of the particles. Further increasing the concentration of HFDePC eventually leads to the formation of round particles with disordered pores. These changes are consistent with increasing HFDePC concentration favoring increasingly oblate or disklike micelles. The process of forming the elongated particles with random mesh-phase structure is investigated by TEM of chilled and dried samples. The results indicate that the oriented tactoid-like structure forms spontaneously within 2 min by co-assembly of silica and HFDePC rather than by preferred growth perpendicular to the layers. The particle shape and layer orientation are consistent with what would be expected for a liquid-crystal particle with orientation-dependent surface tension. Finally, we compare samples prepared with a high HFDePC and with good or poor mixing. With inadequate mixing, a gel layer forms at the top of the sample which is composed of elongated mesoporous particles with a thick coating of microporous silica. The lower particulate phase contains small disordered particles similar to those obtained in a well-mixed sample. Presumably, the structure of the upper layer results from initial immiscibility of the precursor and slow diffusion of silicates out of the gel.     

Detection of mitochondrial DNA mutations using temporal temperature gradient gel electrophoresis

Mitochondrial disorders are a group of clinically and genetically heterogeneous diseases. Common recurrent mitochondrial DNA (mtDNA) point mutations account for the molecular defects of a small proportion of patients. In order to identify mtDNA mutations, comprehensive mutational analysis of the entire mitochondrial genome is necessary. We developed the temporal temperature gradient gel electrophoresis (TTGE) method to screen for mutations in mtDNA. The entire mitochondrial genome was amplified using 32 pairs of overlapping primers followed by TTGE analysis of the DNA fragments. TTGE method was first validated on 200 DNA fragments containing known mutations or polymorphisms. On TTGE, homoplasmic nucleotide substitutions show a single band shift and heteroplasmic mutations show multiple banding patterns. The known mutations or polymorphisms were correctly identified. TTGE was then used to screen for unknown mutations in the mitochondrial genome. DNA banding patterns, deviated from wild-type, suggestive of either homoplasmic or heteroplasmic mutations, were followed by direct DNA sequencing to identify the mutations. Numerous mutations and polymorphisms were detected. The results demonstrated that TTGE detects and distinguishes heteroplasmic mutations from homoplasmic polymorphisms. It also detects heteroplasmic changes in the background of a homoplasmic polymorphism. Overall, TTGE was proven to be a simple, rapid, sensitive, and effective mutation detection method.     

The Design of Biodegradable Microcarriers for Induced Cell Aggregation

PLLA microspheres were aminolyzed in hexanediamine/propanol solution to introduce free amino groups on their surface, which were further transferred into aldehyde groups by a treatment of glutaraldehyde. Chitosan‐graft‐lactose was then covalently coupled via Schiff base formation. Morphological variation and chitosan‐graft‐lactose immobilization were characterized. In vitro culture of rabbit auricular chondrocytes demonstrated that the PLLA microcarriers could effectively support the cell attachment and particularly induce cell aggregation on their surface. The formed cell aggregates/microcarriers composite showed higher viability and extracellular matrix production. Thus, the PLLA microcarriers can be potentially used as an injectable delivery system for cartilage repair.

     

Carbon monoxide-assisted synthesis of single-crystalline Pd tetrapod nanocrystals through hydride formation

Carbon monoxide can adsorb specifically on Pd(111) to induce the formation of unique Pd nanostructures. In the copresence of CO and H(2), single-crystalline Pd tetrapod nanocrystals have now been successfully prepared. The Pd tetrapods are enclosed by (111) surfaces and are yielded through hydride formation. Density functional theory calculations revealed that the formation of PdH(x) in the presence of H(2) reduces the binding energy of CO on Pd and thus helps to decrease the CO coverage during the synthesis, which is essential to the formation of the PdH(x) tetrapod nanocrystals. In addition to tetrapod nanocrystals, tetrahedral nanocrystals were also produced in the copresence of CO and H(2) when the reaction temperature was ramped to further lower the CO coverage. Upon aging in air, the as-prepared PdH(x) nanocrystals exhibited a shape-dependent hydrogen releasing behavior. The conversion rate of PdH(x) tetrapod nanocrystals into metallic Pd was faster than that of tetrahedral nanocrystals.     

Reversible changes in solution pH resulting from changes in thermoresponsive polymer solubility

Pendant groups on polymers that have lower-critical solution temperature (LCST) properties experience a water-like environment below the LCST where the polymer is soluble but are less hydrated above the LCST when the polymer phase separates from solution. When these pendant groups are amphoteric groups like carboxylate salts or ammonium salts, the change in solvation that accompanies the polymer precipitation event significantly changes these groups' acidity or basicity. These changes in acidity or basicity can lead to carboxylate salts forming carboxylic acid groups by capturing protons from the bulk solvent or ammonium salts reverting to the neutral amine by release of protons to the bulk solvent, respectively. When polymers like poly(N-isopropylacrylamide) that contain a sufficient loading of such comonomers are dissolved in solutions whose pH is near the pK(a) of the pendant acid or basic group and undergo an LCST event, the LCST event can change the bulk solution pH. These changes are reversible. These effects were visually followed using common indicators with soluble polymers and or by monitoring solution pH as a function of temperature. LCST events triggered by the addition of a kosmotropic salt lead to similar reversible solution pH changes.