Quantum mechanical calculations on phosphate hydrolysis reactions

Multiple biological processes are regulated by kinases and phosphatases. This study aims to provide nonenzymatic models for phosphorylation and dephosphorylation of serine, threonine, and tyrosine phosphate using ab initio guantum mechanical calculations. We reduce the problem to methyl phosphate hydrolysis to model serine/threonine, and the hydrolysis of phenyl phosphate to model the tyrosine. HF, B3LYP, and MP2 calculations with a 6‐31+G(d) basis set were employed. The effect of water as a catalyst was also analyzed. As expected, the activation energy barrier is lowered. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 43–51, 2000     

Kristallstruktur von Kaliumtriflat‐Butyrolacton, [K3(O3SCF3)3(O2C4H6)2]

Crystal Structure of Potassium Triflate‐butyrolactone, [K₃(O₃SCF₃)₃(O₂C₄H₆)₂] Single Crystals of [K₃(O₃SCF₃)₃(O₂C₄H₆)₂] ( 1 ) have been obtained as a by‐product from the reaction of KNPPh₃ with Yb(O₃SCF₃)₃ in THF with subsequent addition of butyrolactone. The structure of 1 consists of three symmetry‐independent potassium ions which are linked by the oxygen atoms of the triflate ions and the butyrolactone molecules to give a supramolecular structure with layers normal to the crystallographic b‐axis. The carbonyl oxygen atoms of both butyrolactone molecules show a μ₃‐bridging function between three K⁺ ions, one of them is, in addition, coordinated by the ring O‐atom in a chelate manner. 1 : Space group P2₁/c, Z = 4, lattice dimensions at 193 K: a = 1155.0(1), b = 1537.2(1), c = 1531.1(1) pm, β = 100.623(7)°, R = 0.0484.     

Auger spectrometric studies on fracture surfaces of tool steel

The fracture surfaces of tool steel K-13 (Hungarian Standard) were studied by Auger electron spectroscopy. Notched specimens of 3 × 3 mm² were fractured in UHV (6 × 10⁻⁸ Pa) with a fracturer (Riber FR 100) and studied with a CMA analyser (Riber OPC 103). With our modification the fracturer was operated within the −150°C −+230°C temperature range. The fracture surfaces were tested with a scanning electron microscope (JEOL JSM 35). The evaluation of Auger spectra was based on the PHI (PALMBERG et al.). Handbook, however the backscattering correction of Jablonski was applied in some cases. The choice of adequate fracturing temperature proved to be very important. Low temperature fracture of this steel alloy is producing very rigid transgranular fracture. The effects of sample heat treatment and of fracturing temperature as well were studied in details. The Auger spectra of fracture surfaces are strongly affected by the heat treatment of the samples. The grain boundary fracture surface of a sample austenitized at 1100°C quenched and tempered at 600°C exhibited a strong enrichment of P, correlating with the enrichment of Cr, V and Mo. The transgranular fracture surface of the same sample but without tempering corresponded to the bulk composition. In some cases and spots on the fracture surfaces, giant S or P peaks were associated with secondary phases (inclusions) on the SEM pictures.     

Photoinduced charge-transfer dehydrogenation in a gas-phase metal-DNA base complex: Al-cytosine

An Al-cytosine association complex has been generated via laser ablation of a mixture of aluminum and cytosine powders that were pressed into a rod form. The ionization energy of the complex is found to be 5.16 +/- 0.01 eV. The photoionization efficiency spectrum of Al-cytosine has also been collected. DFT calculations indicate that binding of Al to cytosine manifests a significant weakening of the N-H bond, predicted to have a strength of 1.5 eV in the complex, and a significant stabilization of the oxo tautomeric form relative to the hydroxy forms. The predicted ionization energy of 5.2 eV agrees well with the experimental value. The threshold for dehydrogenation/ionization of Al-cytosine, forming (Al-cytosine-H)+, is found to occur at photoexcitation energies between 11.4 and 12.8 eV. This is a two-photon process that is proposed to occur via photoinduced electron transfer from Al to an antibonding (sigma) orbital localized on N-H. In the context of this mechanism, this work constitutes the first time charge transfer between a metal and DNA base has been photoinitiated in the gas phase.     

Tertiary amine catalyzed polymerizations of α‐amino acid N‐carboxyanhydrides: The role of cyclization

Sarcosine N‐carboxyanhydride, D,L ‐alanine N‐carboxyanhydride, D,L ‐phenylalanine N‐carboxyanhydride, and D,L ‐leucine N‐carboxyanhydride were polymerized with pyridine or N‐ethyldiisopropylamine as the catalyst. With pyridine, cyclic oligo‐ and polypeptides were obtained in addition to water‐initiated or water‐terminated chains. The cyclopeptides were the main products in the case of sarcosine N‐carboxyanhydride and D,L ‐phenylalanine N‐carboxyanhydride. The fraction of cycles was particularly high when N‐methylpyrrolidone was used as the reaction medium. These results suggested the existence of a pyridine‐catalyzed zwitterionic mechanism. However, cyclopeptides were also obtained with N‐ethyldiisopropylamine as the catalyst. In this case, N‐deprotonation of N‐carboxyanhydrides, followed by the formation of N‐acyl N‐carboxyanhydride chain ends, was the most likely initiation mechanism. Various chain‐growth mechanisms were examined. In the case of γ‐benzyl ester‐L ‐glutamate N‐carboxyanhydride, side reactions such as the formation of pyroglutamoyl end groups were detected. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4680–4695, 2006     

Classification of resolvable balanced incomplete block designs — the unitals on 28 points

Approaches for classifying resolvable balanced incomplete block designs (RBIBDs) are surveyed. The main approaches can roughly be divided into two types: those building up a design parallel class by parallel class and those proceeding point by point. With an algorithm of the latter type — and by refining ideas dating back to 1917 and the doctoral thesis by Pieter Mulder — it is shown that the list of seven known resolutions of 2-(28, 4, 1) designs is complete; these objects are also known as the resolutions of unitals on 28 points. This research was supported in part by the Academy of Finland, Grants No. 107493, 110196, and 117499.     

Multicyclic polyethers by the polycondensation of 1,2‐ or 1,3‐dicyanotetrafluorobenzene with flexible diphenols

1,2‐Dicyanotetrafluorobenzene (1,2‐DCTB) was polycondensed with various flexible diphenols in a molar ratio of 1:2, and experimental parameters such as the concentration and temperature were varied. Certain diphenols allowed a complete substitution of all C? F bonds, so perfect multicyclic polyethers (B_nCN, where B stands for bridge units, C represents cycles, and N is the degree of polymerization) were the main reaction products. Despite complete conversion, gelation was avoidable under optimized reaction conditions. However, in the case of 1,3‐dicyanotetrafluorobenzene (1,3‐DCTB), complete tetrasubstitution was not feasible with a feed ratio of 1:2. Yet, because of the inductive and mesomeric electronic interactions of all substituents in 1,3‐DCTB, the three C? F groups in the ortho position with respect to the cyano groups were significantly more reactive than the fourth C? F bond. Therefore, polycondensations with diphenols in a 3:2 feed ratio showed a relatively clean course, yielding soluble multicycles of structure B_{n /2}CN. All the multicyclic polyethers were amorphous and possessed molar mass distributions with polydispersities greater than 2. Heating with Cu²⁺ salts caused crosslinking of the multicycles derived from 1,2‐DCTB because of the formation of phthalocyanine complexes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5546–5556, 2006