X-ray crystal structure of trans-bis(pyridin-3-yl)ethylene: comparing the supramolecular structural features among the symmetrical bis(n-pyridyl)ethylenes (n = 2, 3, or 4) constitutional isomers

The molecular structure of trans-bis(pyridin-3-yl)ethylene (3,3′-bpe), C12H10N2, as determined by single-crystal X-ray diffraction is reported. The molecule self-assembles into two dimensional arrays by a combination of C—H...N hydrogen bonds and edge-to-face C—H...π interactions that stack in a herringbone arrangement perpendicular to the crystallographic c-axis. The supramolecular forces that direct the packing of 3,3′-bpe as well as its packing assembly within the crystal are also compared to those observed within the structures of the other symmetrical isomers trans-1,2-bis(n-pyridyl)ethylene ( n , n ′-bpe, where n = n′ = 2 or 4).

All-Purpose Packing Cups for Hyper Compressor

Hyper compressors are designed for LDPE production, compressing ethylene up to 3500bar with only two stages of compression, in order to reach conditions for the polymerization. The high operating and fluctuating pressure strongly impact design and life of all cylinder components. The packing cups are among the most stressed components of a hyper compressor cylinder. They are particularly subjected to very high pulsating pressures, thus fatigue and wear. Therefore, they are periodically replaced during maintenance and are critical for availability of the hyper compressor. A typical hyper compressor packing assembly contains 5 to 6 disc shaped packing cups that contain the plunger sealing rings at the internal diameter. The packing cups are provided with lube oil ducts to lubricate the sealing elements. Typically these ducts extend axially through the assembly to the injection points. For that purpose each packing cup could have a different number of lube oil passages. Moreover, at the external diameter are located passages for packing cooling oil. For these reasons each of the packing cups is a unique part with different machining features. In order to optimize the availability of spare parts and standardize the product, a new design of hyper compressor packing cups has been evaluated, called further “all-purpose packing cup”. The idea was to make the packing cups all equal to each other, and potentially to reduce manufacturing and warehousing costs. This idea has been realized by introducing in a single all-purpose cup, multiple sectors angularly offset with each other. Each sector contains the oil ducts required for a given cup position in the assembly. By rotating the cup about the plunger axis by e.g. 90° or 180° the desired sector can be activated (put in fluid communication with adjacent lube oil ducts). In this way the “all-purpose packing cup” can be mounted in each of the 5 to 6 different positions in the packing assembly. The all-purpose cup design has been analyzed by a well validated FEA approach on the high cycle fatigue and flaw propagation safety margins. The analysis was performed considering all multiple possible load combinations where, depending on the assembly configuration, different active lube oil holes (holes that deliver oil to the plunger) were pressurized while all remaining ducts were left unpressurized.

Industrial Application of Research Results of Packings on Safety Relevant Valves in Nuclear Power Plants

In a NPP approximately 380 safety relevant valves are installed. The main requirements are the safety and operational availability as well as a adequate leak tightness of the sealings and stem packings. Based upon the research results of the MPA-Stuttgart, Germany on packing features specific procedures for handling, assembly and maintenance of packings and analytical inputs for the design calculation have been developed. Depending on the valve size, especially on the stem diameter, the packing influences the necessary stem force for the closing and opening function due to the amount of friction force. The complying equations of the valve calculation guideline were derived from the research results and rely on covering material characteristics of the approved packing rings such as friction coefficient and the vertical/horizontal force transfer factor of the stressing force. The industrial application often requires a more detailed calculation and handling of the actually installed packing configurations especially if existing valves are considered for redesign measures and recalculation. Therefore additionally mock-up tests of existing packing configurations have been performed in cooperation with the packing manufacturer in order to get very specific material coefficients as input data for the calculations. This paper presents the application of research results to design calculation of safety relevant valves as well as the development of procedures for the packing assembly and maintenance.

Modeling and characterization of the amino propeptide of collagenα1(XI), a regulatory domain in collagen fibrillar architecture.

Connective tissues such as cartilage, tendon, skin, bone, and arteries are composite bio-materials that contain predominantly water, collagen, proteoglycans and hyaluronic acid. Like any composite material, the components themselves and their interactions dictate the properties of the material. Fibrillar collagens are the principal structural molecules of the connective tissues and require regulated assembly and growth. Previous work from our lab indicates that the amino propeptide (Npp) domain of collagen type XI α1 chain regulates fibril diameter growth. Npp is a globular domain that is thought to sterically hinder the dense packing assembly of collagen molecules in fibrils. This mechanism of regulating collagen fibril assembly may be more complex than steric hindrance. We hypothesize that the Npp domain has a more dynamic role in establishing the structure/function relationship of collagen fibrils in connective tissues. In this study, the molecular structure of Npp was predicted by modeling. The model predicted putative binding sites for heparan sulfate and divalent cations. These predicted binding sites were evaluated empirically by fluorescence spectroscopy and surface plasmon resonance.