Short-Range Structural Correlations in Amorphous 2D Polymers.

Many 2D covalent polymers synthesized as single layers on surfaces show inherent disorder, expressed for example in their ring-size distribution. Systems which are expected to form the thermodynamically favored hexagonal lattice usually deviate from crystallinity and include high numbers of pentagons, heptagons, and rings of other sizes. The amorphous structure of two different covalent polymers in real space using scanning tunneling microscopy is investigated. Molecular dynamics simulations are employed to extract additional information. We show that short-range correlations exist in the structure of one polymer, i. e. that polygons are not tessellating the surface randomly but that ring neighborhoods have preferential compositions. The correlation is dictated by the energy of formation of the ring neighborhoods.

The threshold algorithm: Description of the methodology and new developments.

Understanding the dynamics of complex systems requires the investigation of their energy landscape. In particular, the flow of probability on such landscapes is a central feature in visualizing the time evolution of complex systems. To obtain such flows, and the concomitant stable states of the systems and the generalized barriers among them, the threshold algorithm has been developed. Here, we describe the methodology of this approach starting from the fundamental concepts in complex energy landscapes and present recent new developments, the threshold-minimization algorithm and the molecular dynamics threshold algorithm. For applications of these new algorithms, we draw on landscape studies of three disaccharide molecules: lactose, maltose, and sucrose.

The switch from sulfonylurea to preprandial short- acting insulin analog substitution has an immediate and comprehensive beta-cell protective effect in patients with type 2 diabetes mellitus.

BACKGROUND: Supplementary insulin therapy provides assistance to meal-time insulin secretion in patients with type 2 diabetes and may have protective effects on beta-cell function. METHODS: This study explored the immediate effect of supplementary insulin therapy on beta- cell function in patients with glimepiride monotherapy (five women, 15 men; 61.8 +/- 6.4 years old; body mass index, 31.1 +/- 4.4 kg/m(2); hemoglobin A1c, 7.0 +/- 1.3%). After 1 week of continued glimiperide therapy, the patients were randomized either to continue with their oral treatment or to switch to a fixed-dose supplementary insulin therapy (8 U of insulin aspart subcutaneously before each meal) for another week. Oral glucose tolerance tests (OGTTs) after drug uptake were performed at days 7 and 14, with measurement of glucose, insulin, C-peptide, intact and total proinsulin, glucagon, lactate, free fatty acids, and adiponectin. RESULTS: Significant reductions from baseline were seen in the supplementary insulin therapy group for the fasting values of insulin (from 13.1 +/- 5.1 microU/mL to 10.6 +/- 5.2 microU/mL, P < 0.01), intact proinsulin (from 18.3 +/- 11.2 pmol/L to 10.3 +/- 4.6 pmol/L, P micro 0.05), total proinsulin (from 43.3 +/- 22.7 pmol/L to 29.7 +/- 14.5 pmol/L, P < 0.01), split proinsulin (from 24.9 +/- 13.8 pmol/L to 19.4 +/- 10.8 pmol/L, P micro 0.01), and the degree of beta-cell dysfunction (P < 0.05). Also, lower values for intact and total proinsulin and split proinsulin in the OGTT were observed in this group during the OGTT at the end point, while no changes at all occurred in the glimepiride group. CONCLUSIONS: A fixed low-dose preprandial insulin aspart therapy resulted in an overall beta-cell protection with an improved fasting beta-cell secretion profile already within 1 week. Our study indicates that supplementary insulin therapy might be a reasonable alternative to bedtime basal insulin injections for initiation of insulin therapy in patients with type 2 diabetes.