Elimination of C-8-functional groups from driman-8<Emphasis Type="Italic">α</Emphasis>,11-diol-11-monoacetate and-diacetate

The dehydration products of driman-8α,11-diol-11-monoacetate that are formed upon reaction with several dehydrating agents and the products from elimination of the C-8 acetoxy group in driman-8α,11-diol diacetate were investigated in detail. A new effective synthesis of drimenylacetate from driman-8α, 11-diol-11-monoacetate by its regioselective dehydration using methanesulfonic acid trimethylsilyl ether was developed. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 340–343, July–August, 2007.     

Exact solutions for the entropy production rate of several irreversible processes

We investigate thermal conduction described by Newton's law of cooling and by Fourier's transport equation and chemical reactions based on mass action kinetics where we detail a simple example of a reaction mechanism with one intermediate. In these cases we derive exact expressions for the entropy production rate and its differential. We show that at a stationary state the entropy production rate is an extremum if and only if the stationary state is a state of thermodynamic equilibrium. These results are exact and independent of any expansions of the entropy production rate. In the case of thermal conduction we compare our exact approach with the conventional approach based on the expansion of the entropy production rate near equilibrium. If we expand the entropy production rate in a series and keep terms up to the third order in the deviation variables and then differentiate, we find out that the entropy production rate is not an extremum at a nonequilibrium steady state. If there is a strict proportionality between fluxes and forces, then the entropy production rate is an extremum at the stationary state even if the stationary state is far away from equilibrium.     

SERS assessment of the cancer-specific methylation pattern of genomic DNA: towards the detection of acute myeloid leukemia in patients undergoing hematopoietic stem cell transplantation

In this label-free surface-enhanced Raman scattering (SERS) study of genomic DNA, we demonstrate that the cancer-specific DNA methylation pattern translates into specific spectral differences. Thus, DNA extracted from an acute myeloid leukemia (AML) cell line presented a decreased intensity of the 1005 cm⁻¹ band of 5-methylcytosine compared to normal DNA, in line with the well-described hypomethylation of cancer DNA. The unique methylation pattern of cancer DNA also influences the DNA adsorption geometry, resulting in higher adenine SERS intensities for cancer DNA. The possibility of detecting cancer DNA based on its SERS spectrum was validated on peripheral blood genomic DNA samples from n = 17 AML patients and n = 17 control samples, yielding an overall classification of 82% based on the 1005 cm⁻¹ band of 5-methylcytosine. By demonstrating the potential of SERS in assessing the methylation status in the case of real-life DNA samples, the study paves the way for novel methods of diagnosing cancer.

Graphical abstract

     

Model Systems for Evidencing the Mediator Role of Riboflavin in the UVA Cross-Linking Treatment of Keratoconus

Riboflavin under UVA radiation generates reactive oxygen species (ROS) that can induce various changes in biological systems. Under controlled conditions, these processes can be used in some treatments for ocular or dermal diseases. For instance, corneal cross-linking (CXL) treatment of keratoconus involves UVA irradiation combined with riboflavin aiming to induce the formation of new collagen fibrils in cornea. To reduce the damaging effect of ROS formed in the presence of riboflavin and UVA, the CXL treatment is performed with the addition of polysaccharides (dextran). Hyaluronic acid is a polysaccharide that can be found in the aqueous layer of the tear film. In many cases, keratoconus patients also present dry eye syndrome that can be reduced by the application of topical solutions containing hyaluronic acid. This study presents physico-chemical evidence on the effect of riboflavin on collagen fibril formation revealed by the following methods: differential scanning microcalorimetry, rheology, and STEM images. The collagen used was extracted from calf skin that contains type I collagen similar to that found in the eye. Spin trapping experiments on collagen/hyaluronic acid/riboflavin solutions evidenced the formation of ROS species by electron paramagnetic resonance measurements.     

Kinetics of the thermal isomerization of 1,1,2,2‐tetramethylcyclopropane

Reaction rates for the structural isomerization of 1,1,2,2‐tetramethylcyclopropane to 2,4‐dimethyl‐2‐pentene have been measured over a wide temperature range, 672–750 K in a static reactor and 1000–1120 K in a single‐pulse shock tube. The combined data from the two temperature regions give Arrhenius parameters E_a=64.7 (±0.5) kcal/mol and log₁₀(A, s^?1) = 15.47 (±0.13). These values lie at the upper end of the ranges of E_a and log A values (62.2–64.7 kcal/mol and 14.82–15.55, respectively) obtained from three previous experimental studies, each of which covered a narrower temperature range. The previously noted trend toward lower E_a values for structural isomerization of methylcyclopropanes as methyl substitution increases extends only through the dimethylcyclopropanes (1,1‐ and 1,2‐); E_a then appears to increase with further methyl substitution. In contrast, the pre‐exponential factors for isomerization of cyclopropane and all of the methylcyclopropanes through tetramethylcyclopropane lie within ±0.3 of log₁₀(A, s^?1) = 15.2 and show no particular trend with increasing substitution. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 483–488, 2006     

Superacid cyclization of certain aliphatic sesquiterpene derivatives in ionic liquids

Superacid cyclization was demonstrated for the first time to be successful in those ionic liquids with functional groups that are stable in the reaction medium using aliphatic sesquiterpene derivatives as examples. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 354–356, July–August, 2006.     

Multifunctional materials based on polyazomethines derived from 2,5‐dihydroxy‐1,4‐benzoquinone and siloxane diamines

New polyazomethines have been synthesized by the reaction between 2,5‐dihydroxy‐1,4‐benzoquinone and siloxane diamines differing by the siloxane sequence length. A dimer has also been prepared as a model compound. The products were characterized by spectral (FTIR and ¹H‐NMR) and elemental analyses, GPC, viscosity measurements, solubility tests, and transmission electron microscopy (TEM). The different properties have been investigated by adequate techniques: thermal (DSC and TGA), spectral (UV–vis and fluorescence spectroscopy), redox (Differential Pulse Voltammetry). pH‐sensitivity and metal complexing ability were also evaluated. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1862–1872, 2008     

Consideration concerning interlaboratory test for cement in the last 20 years

Since 1988, over 40 laboratories representing research institutes, cement plants, pre-cast units, hydro plant construction companies, industrial construction companies, building companies, etc. from nine countries—Romania, Republic of Moldova, Croatia, Serbia, Macedonia, Bulgaria, Hungary, Ukraine and Lebanon—take part every year in an interlaboratory test organized by our laboratory. The subject of the interlaboratory test for cement was 37 laboratory tests: 12 chemical determinations, 7 physical tests and 9 mechanical tests carried out with 2 types of sand, from CEPROCIM and from each participant laboratory. The paper presents the evolution of two statistical parameters (standard deviation of reproducibility and/or coefficient of variation) for a period of 20 years and for 11 laboratory tests. The results strongly prove that interlaboratory test is one of the most efficient tools to establish a common language for all the participant laboratories performing cement testing procedures.