Tailoring of Surfaces with Ultrathin Layers for Controlled Binding of Biopolymers and Adhesion and Guidance of Cells

Various strategies are described for the bio-functionalization of solid substrates by design of interfacial architectures. The first approach is based on the self-assembly process of long-chain thiol molecules from solution to a (noble) metal surface. If some of these building blocks carry a binding site (ligand) for proteins (receptors, antibodies, etc.) the metal surface can be tailored for maximum specific binding while simultaneously minimizing nonspecific adsorption. The second concept is based on polymers that are covalently attached to (oxide) surfaces. The preparation of these (end-) grafted functional polymers involves either the binding of preformed macromolecules to corresponding sites at the surface of the support or the recently introduced “grafting-from” method, by which an initiator molecule is first covalently bound to the surface and then activated — either by heat or light — in the presence of suitable monomer units such that a polymer chain grows from the solid/solution interface. Finally, the functionalization of patterned surfaces by peptide chains that mimic the binding domains of cell adhesion proteins is summarized. It is demonstrated that not only the selective adhesion of neuronal cells can then be controlled, but also their development with the outgrowth of dendrites and axons.     

Comparison of Formulae for the Determination of Fluorescent and Non–fluorescent Whiteness

The prediction capabilities of simple whiteness formulae based on photometer reflectance readings (A, G, B) as compared to linear formulae with adjustable parameters based on chromaticity values (x, y, Y) have been investigated. For each formula, the instrumentally determined whiteness was compared with visually estimated whiteness using the plates of the Ciba–Geigy Plastic White (CGPW) Scale as a standard. This was carried out for a set of 48 fluorescent cotton cloth samples previously studied, as well as for a new set of 86 non–fluorescent cotton cloth samples. As expected, the AGB formulae were inferior to those based on chromaticity values; however, the Taube formula performed quite well for fluorescent samples. On the set of non–fluorescent samples, a formula having green hue preference was required; the Berger formula was found to be the most successful among the simple AGB formulae.     

The carbon-isotopic composition of Proterozoic carbonates: Riphean successions from northwestern Siberia (Anabar Massif, Turukhansk Uplift)

Thick carbonate-dominated successions in northwestern Siberia document secular variations in the C-isotopic composition of seawater through Mesoproterozoic and early Neoproterozoic (Early to early Late Riphean) time. Mesoproterozoic dolomites of the Billyakh Group, Anabar Massif, have delta 13C values that fall between 0 and -1.9 permil versus PDB, with values in the upper part of the succession (Yusmastakh Formation) consistently higher than those of the lower (Ust'-Il'ya and Kotuikan formations). Consistent with available biostratigraphic and radiometric data, delta 13C values for Billyakh carbonates compare closely with those characterizing early Mesoproterozoic carbonates (about 1600-1200 Ma) worldwide. In contrast, late Mesoproterozoic to early Neoproterozoic limestones and dolomites in the Turukhansk Uplift exhibit moderate levels of secular variation. Only the lowermost carbonates in the Turukhansk succession (Linok Formation) have delta 13C values that approximate Billyakh values. Higher in the Turukhansk succession, delta 13C values vary from -2.7 to +4.6 permil (with outliers as low as -5.0 permil interpreted as diagentically altered). Again, consistent with paleontological and radiometric data, these values compare well with isotopic values from 1200 to 850 Ma successions elsewhere. Five sections measured in different parts of the Turukhansk basin show nearly identical patterns of variation, confirming that carbonate delta 13C correlates primarily with time and not facies. The Siberian sections illustrate the potential of integrated biostratigraphic and chemostratigraphic data in the intra- and interbasinal correlation of Mesoproterozoic and early Neoproterozoic rocks.     

Morphology and crack toughness behaviour of nanostructured block copolymer/homopolymer blends

The crack initiation and propagation behaviour of styrene-butadiene (SB) star block copolymer/polystyrene blends (ST3/PS) forming PS-rich and polybutadiene (PB)-rich nanosized domains by self-assembling have been investigated using the essential-work-of-fracture (EWF) approach. Three morphological transitions have been observed, which are crucial to understand the crack toughness behaviour: (i) 0-30 wt.% PS homopolymer: A co-continuous domain structure of PS-rich and PB-rich domains has been observed. For PS homopolymer fraction (?_PS) < 10 wt.% PS homopolymer (i.e. only pure ST3) the rubbery PB-rich phase forms the major phase and for ?_PS > 10 wt.% the glassy PS-rich phase. (ii) At 40-60 wt.% PS homopolymer, a layer-like morphology is formed where the PS-rich layer thickness is ?50 nm, a critical dimension, which is crucial for understanding the ductile-to-semiductile transition. (iii) For 80 wt.% PS homopolymer, PS-rich phase starts to form the matrix combined with a transition from shear stress dominated (shear yielding) to normal stress dominated behaviour (PS-like crazes). The co-continuous morphology at 20 wt.% and 30 wt.% PS is capable of improving toughness of block copolymers, demonstrated by the observed maximum in the non-essential work of fracture and thus explaining a new way of toughening of polymers while retaining high transparency. The correspondence between the ductile-to-semiductile transition and the change in the shape of plastic zone from circular to elliptical as revealed from strain field analysis could be clearly reaffirmed by the observed transition from shear to normal force induced deformation in the fractured surface analysis of these blends. The conceptual correspondence of βw_p and w_e with T_J and δ_0.2 respectively reveal that resistance against crack propagation (βw_p and T_J) is morphology sensitive while the resistance against crack initiation (w_e and δ_0.2) is matrix sensitive.     

A new approach for handling and transferring of thin semiconductor materials

 Based on the fracture mechanics analysis of crack propagation, the phenomenon of subcritical crack growth was utilized for a controlled debonding of directly wafer-bonded interfaces. The approach allowed the well-defined separation of bonded wafers although the bond strength was high due to thermal annealing. The achieved splitting velocity depended on the wafer material, the wafer thickness ratio, the bonding process parameters, and the environmental conditions during cleaving. In combination with wafer bonding, the method can be used for a temporary stiffening and handling of thin and brittle wafers during fabrication, even if the wafers are exposed to high process temperatures. The approach can also be applied to fabricate micromechanical systems (MEMS). Received: 12 July 2001/Accepted: 26 February 2002 This paper was presented at the Conference of Micro System Technologies 2001 in March 2001.     

Mismatch discrimination in oligonucleotide hybridization reactions using single strand binding protein. A surface plasmon fluorescence study

We describe the use of surface plasmon- and surface plasmon fieldenhanced fluorescence spectroscopy for the detection of hybridization reactions between surface-attached probe oligonucleotides and complement strands binding from solution. These targets, exhibiting different base mismatches relative to the probe 15-mer sequences, carry a fluorophore at their 5'-end thus allowing for sensitive detection and quantification of association, k_on, and dissociation, k_off, rate constants, as well as affinity constants, K_a. We demonstrate that by the competitive binding / replacement of single strand binding proteins the mismatch discrimination can be further enhanced.     

Formylation products of thioamides. XIII. Reaction of N-(3-aminothioacryloyl)-formamidines with amines – Synthesis of Pyrimidine Derivatives

N-(3-Aminothioacryloyl)-formamidines 3 react with primary amines to give either 4(1H)-pyrimidinthiones 6 or transaminated N-(3-aminothioacryloyl)-formamidines 5 . Alkylation of the latter compounds gives rise to cyclised 6(1H)-pyrimidinimines 7 . The 4(1H)-pyrimidinthiones 6 can be S-alkylated to 4-alkylmercaptopyrimidinium salts 8 . Subsequent substitution of the alkylmercapto group of the 8 results in the formation of 4-aminopyrimidinium salts 9 , which can also be obtained starting from the 3 by a reversed reaction sequence that is first by S-alkylation to 3-alkylmercapto-2-azapentamethinium salts 10 and subsequent reaction with primary amines.     

DEFECT CORRECTION WITH A FULLY COUPLED INEXACT NEWTON METHOD

Abstract

We examine the characteristics of a fully coupled inexact Newton method using defect correction to obtain high-order solutions for two problems: natural convection in a square cavity and mixed-convection flow over a backward step. Newton's method produces a linearized system with a Jacobian matrix and a residual vector, each of which can be formed using different discrete operators. Solution accuracy depends on the discretization used for the residuals. Defect correction employs low-order operators for the Jacobian but high-order operators for the residuals. We employ an O(h³) convection operator in the residual vector and upwinding in the Jacobian. We find that defect correction is an efficient and effective way to achieve high-order solutions.