Long-range order of organized oligonucleotide monolayers on Au(111) electrodes

Oligonucleotides modified by a hexamethylene linker group adsorb on gold electrodes via Au-S bond formation. We have obtained novel data for adsorption of thiol-modified (HS) single-strand HS-10A and double-stranded HS-10AT oligonucleotides and for analogous thiol-free 10A (A = adenine) and 10T (T = thymine) nonspecifically adsorbed as reference molecules. Mercaptohexanol has served as a second reference molecule. The data are based on cyclic and differential pulse voltammetry, interfacial capacitance data, and in situ scanning tunneling microscopy (STM) directly in an aqueous buffer solution, with electrochemical potential control of both the sample electrode and the tip. All the data are based on single-crystal, atomically planar Au(111)-electrode surfaces. The high sensitivity of such surfaces provides accurate HS-10A and HS-10AT electrode coverages on the basis of the reductive desorption of the Au-S bond. The coverage is high and in keeping with dense monolayers of adsorbed HS-10A and HS-10AT in an upright or tilted orientation, with the oligonucleotide backbone repelled from the strongly negatively charged electrode surface. Adsorbed thiol-free 10A only gives a Au(111)-reconstruction peak, while 10T shows a subtle pattern involving pronounced voltammetric adsorption peaks indicative of both nonspecific adsorption via single thymine units and potential-dependent structural reorganization in the surface layer. In situ STM supports these findings at the molecular level. In situ STM of HS-10A discloses large, highly ordered domains at strongly negative sample potentials. Reversible domain formation and disordering could, moreover, be controlled by an electrochemical potential variation in the negative and positive directions, respectively. 10A and 10T did not form ordered adsorbate domains, substantiating that domain formation rests on adsorption of thiol-modified oligonucleotide adsorption in an upright or tilted orientation. The comprehensive, high-resolution information reported may hold prospects for single-molecule electronic conduction and molecular-scale mapping of oligonucleotide hybridization.     

First Measurement of the Gerasimov-Drell-Hearn Sum Rule for 1H from 0.7 to 1.8 GeV at ELSA

To verify the fundamental Gerasimov-Drell-Hearn (GDH) sum rule for the first time experimentally, we measured the helicity dependent total photoabsorption cross section with circularly polarized real photons and longitudinally polarized nucleons in the photon energy range 0.68-1.82 GeV with the tagged photon facility at ELSA. The experiment was carried out with a 4pi detection system, a circularly polarized tagged photon beam, and a frozen spin polarized proton target. The contribution to the GDH sum rule in this photon energy range is [49.9+/-2.4(stat)+/-2.2(syst)] microb.     

Convergent synthesis of fully functionalized ring C allocolchicinoids. Benzannulation approach

[reaction: see text]. A novel convergent approach to fully functionalized ring C allocolchicinoids is developed which is based on the benzannulation reaction of Fischer carbene complexes with alkynes. The efficacy of this strategy was established with the conversion of bromide 1a (R1 = Me, R2 = H) to the biaryl phenol 3a (R = Me, R(L) = Pr, R(S) = H) via the carbene complex 2a. Bromide 1b (R1 = t-Bu, R2 = OMe) was then used for the analogous preparation of the diastereomeric allocolchicinoids 3b (R = Me, R(L) = Pr, R(S) = H).     

Observation of a 1/t decay law for hot clusters and molecules in a storage ring

The exponential law is valid both for decay from a single quantum state into a continuum and for an ensemble maintained in thermal equilibrium. For statistical decay of an ensemble of isolated systems with a broad energy distribution, the exponential decay is replaced by a 1/t distribution. We present confirmation of this decay law by experiments with cluster anions in a small electrostatic storage ring. Deviations from the 1/t law for such an ensemble give important information on the dynamics of the systems. As examples, we present measurements revealing strong radiative cooling of anions of both metal clusters and fullerenes.     

Graded nanostructures produced by sliding and exhibiting universal behavior

Nanostructured copper was produced by deformation under large sliding loads. In the near surface layers, 10 nm scale microstructures form and coarsen with increasing depth from the surface. The graded structure enables characterization of the structural scale over several orders of magnitude. Analysis reveals that universal scaling of the microstructure exists from 10,000 to 10 nm. The limit of scale is pushed to an order of magnitude of the ultimate scale at which the crystallinity is lost. This universality opens the door for easy manufacture of ever finer scale components by deformation.     

Distance in stratified graphs

A graph G is stratified if its vertex set is partitioned into classes, called strata. If there are k strata, then G is k-stratified. These graphs were introduced to study problems in VLSI design. The strata in a stratified graph are also referred to as color classes. For a color X in a stratified graph G, the X-eccentricity e _X(v) of a vertex v of G is the distance between v and an X-colored vertex furthest from v. The minimum X-eccentricity among the vertices of G is the X-radius rad_X G of G and the maximum X-eccentricity is the X-diameter diam_X G. It is shown that for every three positive integers a, b and k with ab, there exist a k-stratified graph G with rad_X G = a and diam_X G = b. The number s _X denotes the minimum X-eccetricity among the X-colored vertices of G. It is shown that for every integer t with rad_X G t diam_X G, there exist at least one vertex v with e _X(v) = t; while if rad_X G t s _X, then there are at least two such vertices. The X-center C _X(G) is the subgraph induced by those vertices v with e _X(v) = rad_X G and the X-periphery P _X (G) is the subgraph induced by those vertices v with e _X(G) = diam_X G. It is shown that for k-stratified graphs H ₁, H ₂,..., H _k with colors X ₁, X ₂,..., X _k and a positive integer n, there exists a k-stratified graph G such that C X _i(G) H _i (1 ; i ; k1) and for i j. Those k-stratified graphs that are peripheries of k-stratified graphs are characterized. Other distance-related topics in stratified graphs are also discussed.     

Transverse asymmetry AT' from the quasielastic 3He(e,e') process and the neutron magnetic form factor

We have measured the transverse asymmetry A(T') in 3He(e,e(')) quasielastic scattering in Hall A at Jefferson Laboratory with high precision for Q2 values from 0.1 to 0.6 (GeV/c)(2). The neutron magnetic form factor G(n)(M) was extracted based on Faddeev calculations for Q2 = 0.1 and 0.2 (GeV/c)(2) with an experimental uncertainty of less than 2%.     

Direct evidence for the breakdown of the N = 8 shell closure in 12Be

We derive the formalism to obtain spatial distributions of collisional correlation times for macroscopic particles undergoing granular flow from pulsed gradient spin echo nuclear magnetic resonance diffusion data. This is demonstrated with an example of axial motion in the shear flow regime of a 3D granular flow in a horizontal rotating cylinder at one rotation rate.     

Electron microscopy study of tubular crystals (BiS)1+delta(NbS2)n

Big crystals (mm-sized) with anomalous tubular morphology were synthesised in the Bi-Nb-S system. Their structural study by electron microscopy and related techniques revealed that they can be described as misfit layer structures, a type of composite modulated structures. The misfit monolayer approximately BiNbS3 and bilayer approximately BiNb2S5 phases appear as well in the preparation but with lamellar morphology as it is typical for these kind of compounds. They consist of periodical intergrowth of pseudotetragonal layers BiS (Q) with pseudohexagonal layers NbS2 (H). approximately BiNbS3 has a stacking sequence ...Q,H,Q,H,... and approximately BiNb2S5 has a stacking sequence ...Q,H,H,Q,H,H,... Backscattered electron imaging, wavelength dispersive X-ray spectroscopy and transmission electron microscopy of transversal cross-sections of single tubular crystals showed that these crystals present a strong compositional and inter-laminar stacking disorder along the tube radius. This disorder is suggested to be the cause for the original wrapping of the layers that gives rise to the tubes. Besides the disordered areas, some ordered slabs have been found with stacking sequences corresponding to binary 3R-NbS2 (approximately 6 A), approximately BiNb2S5 (approximately 17.4 A) (which dominate in the crystal) and to a new related phase approximately BiNb4S9 with a stacking sequence ...Q,H,H,H,H,Q,H,H,H,H,... and a periodicity of approximately 29.2 A.