Almost all trees share a complete set of immanantal polynomials

Let χ be an irreducible character of the symmetric group S_n. For an n-by-n matrix A = (a_ij), define If G is a graph, let D(G) be the diagonal matrix of its vertex degrees and A(G) its adjacency matrix. Let y and z be independent indeterminates, and define L(G) = yD(G) + zA(G). Suppose t_n is the number of trees on n vertices and s_n is the number of such trees T for which there exists a nonisomorphic tree T? such that d_χ(xl - L(T)) = d_x(xl - L(T?)) for every irreducible character χ of S_n. Then lim_n→∞ S_n/t_n = 1. © 1993 John Wiley & Sons, Inc.     

Mussel adhesive protein mimetic polymers for the preparation of nonfouling surfaces

A new biomimetic strategy for modification of biomaterial surfaces with poly(ethylene glycol) (PEG) was developed. The strategy exploits the adhesive characteristics of 3,4-dihydroxyphenylalanine (DOPA), an important component of mussel adhesive proteins, to anchor PEG onto surfaces, rendering the surfaces resistant to cell attachment. Linear monomethoxy-terminated PEGs were conjugated either to a single DOPA residue (mPEG-DOPA) or to the N-terminus of Ala-Lys-Pro-Ser-Tyr-Hyp-Hyp-Thr-DOPA-Lys (mPEG-MAPD), a decapeptide analogue of a protein found in Mytilus edulis adhesive plaques. Gold and titanium surfaces were modified by adsorption of mPEG-DOPA and mPEG-MAPD from solution, after which surface analysis by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectroscopy confirmed the presence of immobilized PEG on the surface. The ability of modified surfaces to resist cell attachment was examined by culturing 3T3 fibroblasts on the surfaces for up to 14 days. Quantitative image analysis revealed that cell adhesion to mPEG-DOPA and mPEG-MAPD modified surfaces decreased by as much as 98% compared to control surfaces. Modified Ti surfaces exhibited low cell adhesion for up to 2 weeks in culture, indicating that the nonfouling properties of mPEG-DOPA and mPEG-MAPD treated surfaces persist for extended periods of time. This strategy paradoxically exploits the strong fouling characteristics of MAP analogues for antifouling purposes and may be broadly applied to medical implants and diagnostics, as well as numerous nonmedical applications in which the minimization of surface fouling is desired.     

Comparative molecular field analysis and molecular modeling studies of 20-(S)- camptothecin analogs as inhibitors of DNA topoisomerase I and anticancer/antitumor agents

Conformational studies and comparative molecular field analysis (CoMFA) were undertakenfor a series of camptothecin (CPT) analogs to correlate topoisomerase I inhibition with thesteric and electrostatic properties of 32 known compounds. The resulting CoMFA modelshave been used to make predictions on novel CPT derivatives. Using the newly derived MM3parameters, a molecular database of the 32 CPT analogs was created. Various point atomiccharges were generated and assigned to the MM3 minimized structures, which were used inpartial least-squares analyses. Overall, CoMFA models with the greatest predictive validitywere obtained when both the R- and S-isomers were included in the data set, andsemiempirical charges were calculated for MM3 minimized low-energy lactone structures. Across-validated R2 of 0.758 and a non-cross-validated R2 of 0.916 were obtained for MM3minimized structures with PM3 ESP charges for the 32 CPT analogs. The derived QSARequations were used to assign topoisomerase I inhibition values for compounds in this studyand compounds not included in the original data set. Prior to its appearance in the literature,an IC50 of 103 nM was predicted for the 10,11-oxazole derivative. This CoMFA predictedvalue compared favorably with the recently reported value of 150 nM. The CoMFA modelwas also evaluated by predicting the activities of recently reported 11-aza CPT and trionederivatives. The predicted activity (IC50 = 249 nM) for 11-aza CPT compared well with thereported value of 383 nM.     

Catalytic enantioselective transamination of alpha-keto esters: an organic approach to enzymatic reactions

The half-transamination reaction of alpha-keto esters with pyridoxamine or 4-picolylamine was found to be catalysed by different metal catalysts in organic solvents giving moderate yields and enantioselectivities of up to 37% ee for methyl-3-indole pyruvate.     

The role of solvent in conjugate additions leading to cis and trans-1-Alkyl-2-aryl-3-carbo(aroyl)aziridines

In the formation of cis- and trarn-1-alkyl-2-aryl-3-carbo(aroyl)aziridines a change in solvent from benzene to rnethanol in the α-bromochalone-primary amine reaction produced an increase in cic isotner. However, the same solvent change resulted in a decrease in the cis/trans ratio when these same aziridines were prepared by the ehalcone-halogen-primary amine reaction. These results are rationalized in terms of both an open and chelated enol intermediate thought to be crucial in the relative product formations. Other mechanistic considerations in the product formations are presented.     

Unusual C25 steroids produced by a sponge-derived Penicillium citrinum

[structure: see text] Structurally unique steroids, isocyclocitrinol A (1) and 22-acetylisocyclocitrinol A (2), were isolated from the extract of a saltwater culture of sponge-derived Penicilliun citrinum. The structures were established by analysis of 1D and 2D NMR data. The absolute structures were determined on the basis of X-ray structure analysis and application of modified Mosher's method. Furthermore, the structure of cyclocitrinol (3a) previously isolated from a terrestrial P. citrinum was revised as 3b. Compounds 1 and 2 showed weak antibacterial activity against Staphylococcus epidermidis and Enterococcus durans.     

Manadomanzamines A and B: a novel alkaloid ring system with potent activity against mycobacteria and HIV-1

Two novel alkaloids, named manadomanzamines A (1) and B (2), were isolated from an Indonesian sponge Acanthostrongylophora sp. (Haplosclerida: Petrosiidae). Their structures were elucidated and shown to be a novel organic skeleton related to the manzamine type alkaloids. Their absolute configuration and conformation were determined by CD, NOESY, and molecular modeling analysis. The microbial community analysis for the sponge that produces these unprecedented alkaloids has also been completed. Manadomanzamines A (1) and B (2) exhibited strong activity against Mycobacterium tuberculosis (Mtb) with MIC values of 1.9 and 1.5 mug/mL, respectively. Manadomanzamines A and B also exhibit activities against human immunodeficiency virus (HIV-1) and AIDS opportunistic fungal infections.     

On the angular correlation of electrons in configuration interaction wavefunctions

In a recent study of angular correlation of electrons in the ground state of the helium atom was examined using both configuration interaction (CI) and Hylleraas wavefunctions. It was concluded that little reliance should be placed on properties involving angular correlation which are derived from CI wavefunctions. In contradiction with this conclusion, we have observed a rapid convergence of the natural orbital CI expansion to the correct angular correlation behavior of the Kinoshita helim atom wavefunction.     

Virtual strain gage size study

Experimental Techniques -