Stabilization centers in various proteins

Interactions among residues together with their interactions with the surrounding medium determine the unique structure of globular proteins. An algorithm was recently developed to locate residues participating in cooperative long-range interactions, called stabilization center residues, that are primarily responsible for preventing the decay of the 3D structure. While our statistical analysis showed that interactions of stabilization center residues hardly influence the formation of the various secondary structure elements, the distribution of the stabilization center residues is rather uneven among the secondary structure elements. Here we analyzed the frequency and distribution of the stabilization center residues and their interacting pairs in secondary structure classes to learn about the effect of secondary structure on the formation and properties of stabilization centers and about the types of interactions responsible for stabilization of proteins of various secondary structure classes. It was found that residues from the same secondary structure tend to interact with each other in the stabilization centers of all classes. It is also suggested that the folding-unfolding equilibrium is governed by different principles for class all-α than for the rest of the classes. Received: 24 April 1998 / Accepted: 17 September 1998 / Published online: 7 December 1998     

Cyclizations to new azolopyridazines and related ring systems

In the course of our recent synthetic activity in the area of ring closure reactions we have found that relatively little had been published on azolopyridazines and related compounds, and this circumstance prompted us to explore novel pathways to such ring systems. In the present short review three such approaches from our laboratory leading to various fused azoles are discussed.     

(E)-2-Benzylidenebenzocyclanones: Part X. Determination of log P of (E)-3-benzylidene-2,3-dihydro-1-benzopyran-4-ones by RP-TLC. Effect on log P of Incorporation of Oxygen Atom into Carbocyclic Chalcone Analogues

JPC – Journal of Planar Chromatography – Modern TLC - log P values of 14 biologically active (E)-3-(X-benzylidene)-2,3-dihydro-1-benzopyran-4-ones (3) have been determined by an...     

Synthesis and Applications of Cinchona Squaramide-Modified Poly(Glycidyl Methacrylate) Microspheres as Recyclable Polymer-Grafted Enantioselective Organocatalysts

This work presents the immobilization of cinchona squaramide organocatalysts on poly(glycidyl methacrylate) solid supports. Preparation of the well-defined monodisperse polymer microspheres was facilitated by comprehensive parameter optimization. By exploiting the reactive epoxy groups of the polymer support, three amino-functionalized cinchona derivatives were immobilized on this carrier. To explore the effect of the amino linker, these structurally varied precatalysts were synthesized by modifying the cinchona skeleton at different positions. The catalytic activities of the immobilized organocatalysts were tested in the Michael addition of pentane-2,4-dione and trans-β-nitrostyrene with excellent yields (up to 98 %) and enantioselectivities (up to 96 % ee). Finally, the catalysts were easily recovered five times by centrifugation without loss of activity.     

Synthesis of 3‐Alkyl and Arylapomorphines

The synthesis of 3‐alkyl and arylapomorphines 18–20 has been accomplished by using the Suzuki–Miyaura cross‐coupling reaction of vinyl‐ and allylhalide morphinanedienes or arylhalide apocodeines and arylboronic acids.     

DÖME: revitalizing a low-background counting chamber and developing a radon-tight sample holder for gamma-ray spectroscopy measurements

There was an emerging need at the Nuclear Analysis and Radiography Department of the Centre for Energy Research, Hungarian Academy of Sciences, Budapest to be able to perform low level radioactivity measurements of various samples from in-beam activation and from environmental studies. Important aspects of reusing the low-background chamber called DÖME, which had been unused for some years, were the development of an easily reusable radon-tight sample container and the setup of a measurement system capable of counting extended samples in close-in geometry. As a result of our efforts a special sample container made of HDPE (High-density Polyethylene) was developed, and it is proved that the probability of a radon loss larger than the 2 % of its radioactive decay constant is <95 %. Due to the lack of reference samples, containing the same radionuclides as the unknown sample, the absolute method of measuring the activity concentration of nuclides in the sample had to be applied, which implied the reliable determination of the full-energy peak efficiency. A method called efficiency transfer combined with the correction for true coincidence summing effects is proven to be providing appropriate results and applied.     

New approach for the synthesis of 3H-pyrrolo[2,3-c]isoquinoline derivatives

Synthesis of new 2,3-diaryl-3H-pyrrolo[2,3-c]isoquinoline derivatives has been elaborated starting from isoquinoline-3-amine. Buchwald–Hartwig arylation and subsequent iodination in position 4 afforded 3-arylamino-4-iodoisoquinolines. These compounds were subjected to Sonogashira cross-coupling reactions with some selected acetylenes, and the resulting coupled products underwent cyclization in the presence of tetrabutylammonium fluoride to give title derivatives.     

Synthesis and ring transformation of novel tetracyclic fused as-triazines

Summary Eight new tetracyclic fused as-triazines (4–6,8,11–13, and15) have been synthesized by conversion and subsequent ring transformation of 1,2-diaminoisoquinolinium (2) and -quinolinium salts (9) with 4-benzoyl-5-phenylfuran-2,3-dione (1). Selective alkylations of the new products revealed that these reactions are governed mainly by the electronic density of the lone pairs as well as by steric effects.Dedicated to em. Univ. Prof. Dr. E. Ziegler on the occasion of his 80th birthday     

Quantification of Conversion Degree and Monomer Elution from Dental Composite Using HPLC and Micro-Raman Spectroscopy

The purpose of the study was to analyze the correlation between the quantity of eluted monomers from dental resin-based composite using reverse-phase HPLC and the degree of conversion (DC) using micro-Raman spectroscopy, and to evaluate the influence of the energy of polymerization delivered on the composite material and the applied resin layer thickness on these properties. There was direct proportion in degree of conversion and inverse proportion in monomer elution when the energy of light polymerization was increased from 20 to 40 J cm⁻²; however, further increase in energy density did not influence significantly the DC and the elution of monomers. Investigating the depth of cure significant differences could be measured both in DC and the elution of monomers. 1 mm layer increment up to 3 mm from the top led to 10 % decrease in DC and 30–35 % increase in monomer elution. Further increase in depth from 3 to 4 mm caused 30 % drop in DC and 55 % increase in the amount of leached monomers. The overall result of the findings indicates that direct correlation exists between DC of composite and the elution of unreacted monomers.