On the critical difference of almost bipartite graphs

Journal of Algebraic Combinatorics - A set $$S\subseteq V$$ is independent in a graph $$G=\left( V,E\right) $$ if no two vertices from S are adjacent. The independence number $$\alpha (G)$$ is the...     

New improvements in oligonucleotide synthesis by use of the p-nitrophenylethyl phosphate blocking group and its deprotection by DBU or DBN

Phosphate protection in the phosphotriester approach is improved by the new, versatile p-nitrophenylethyl group due to its stability in the condensation step and its clean removal by DBU and DBN respectively.     

Nucleotide. XV. Synthese und Eigenschaften von 2′-O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleosid-3′-phosphotriestern,Ausgangssubstanzen für Oligonucleotid-Synthesen

Nucleotides. XV. Synthesis and Properties of 2′O-t-Butyldimethylsilyl-5′-O-monomethoxytritylribonucleoside-3′-phosphotriesters, Starting Materials for Oligonucleotide Syntheses The syntheses of two types of fully blocked ribonucleoside 3′-phosphotriesters 6–14 have been achieved in excellent yields from 2′-O-t-butyldimethylsilyl-5′-O-monomethoxytrityl-ribonucleosides 1–5 by phosphorylation with 2-chloro- and 2,5-dichlorophenylphosphorodichloridate respectively and subsequent treatment by cyanoethanol to 6 , 8 , 10 , 12 and 14 and by p-nitrophenylethanol to 7 , 9 , 11 and 13 . These phosphotriesters are valuable starting materials for oligonucleotide syntheses due to the fact that the corresponding phosphotriesters 15–23 with free HO? C(5′) could be obtained by detritylation and the 3′-phosphodiester triethylammonium salts 24–32 by deblocking of the cyanoethyl and the 2,5-dichlorophenyl group respectively. All newly synthesized compounds have been characterized by UV.-and NMR.-spectra as well as C, H, N elementary analyses.     

Radiative relaxation quantum yields for synthetic eumelanin

We report absolute values for the radiative relaxation quantum yield of synthetic eumelanin as a function of excitation energy. These values were determined by correcting for pump beam attenuation and emission reabsorption in both eumelanin samples and fluorescein standards over a large range of concentrations. Our results confirm that eumelanins are capable of dissipating >99.9% of absorbed UV and visible radiation through nonradiative means. Furthermore, we have found that the radiative quantum yield of synthetic eumelanin is excitation energy dependent. This observation is supported by corrected emission spectra, which also show a clear dependence of both peak position and peak width on excitation energy. Our findings indicate that photoluminescence emission in eumelanins is derived from ensembles of small chemically distinct oligomeric units that can be selectively pumped. This hypothesis lends support to the theory that the basic structural unit of eumelanin is oligomeric rather than heteropolymeric.     

Structural Investigation of Guest-to-Host and Ligand-Ligand Interactions in Werner Clathrates of [Ni(4-Etpy)4(NCS)2]⋅ nG Type (G = Naphthalene Derivatives). The Crystal Structure of [Ni(4-Etpy)4(NCS)2]⋅1-Methylnaphthalene

The stoichiometry and spectral properties of [Ni(4-Etpy)4(NCS)2]nG clathrates have been studied where n = 2 for G = 1-BrN (N = naphthalene), n = 1 or 2 for G = 1-MeN, and n = 0.5 for 2-MeN and 2-BrN. The complexes under study show electronic absorption spectra typical of an octahedral environment of the Ni(II) central atom. The differences found in IR spectra for the (CN) and (Ni–-NNCS) vibrations are discussed. The crystal structure of [Ni(4-Etpy)4(NCS)2]1-MeN was determined by X-ray diffraction and refined to R = 0.0586. Discrete non-centrosymmetric [Ni(4-Etpy)4(NCS)2] molecules form layers of a host structure and the space between the layers is occupied by 1-MeN. The relationship between interatomic distances in the host complex of similar clathrates are discussed.     

Nucleotides. Part XXVIII. Chemical syntheses of the 2′-5′-cordycepin-trimer core

The chemical synthesis of 3′-deoxyadenyly-(2′-5′)-3′-deoxyadenylyl-(2′-5′)-3′-deoxyadenosine ( 30 ; trimeric cordycepin) is described by three different routes using various protecting groups and applying the phosphotriester approach. The intermediates have been isolated and characterized by elemental analyses and spectroscopic means. High yields of 30 have been obtained on deprotection making this biologically very active compound available in preparative scale.     

Few-electron corrections of statistical exchange potential in low-energy electron scattering

In order to allow for the relative increase of self-interaction in few-electron systems, a reduction factor is introduced into the statistical free-electron exchange potential. This net-exchange potential has been used in the calculation of elastic electron scattering by rare-gas atoms in the low-energy region from 0 to 10 eV. Whereas former attempts to treat these phenomena as simple potential scattering have failed, in this work at least a crude qualitative agreement with experimental data has been achieved in most cases.