Photoinduced electron transfer in platinum(II) terpyridinyl acetylide complexes connected to a porphyrin unit

A series of six new dyads consisting of a zinc or magnesium porphyrin appended to a platinum terpyridine acetylide complex via a para-phenylene bisacetylene spacer are described. Different substituents on the 4' position of the terpyridinyl ligand were explored (OC7H15, PO3Et2, and H). The ground-state electronic properties of the dyads are studied by electronic absorption spectroscopy and electrochemistry, and they indicate some electronic interactions between the porphyrin subunit and the platinum complex. The photophysical properties of these dyads were investigated by steady-state, time-resolved, and femtosecond transient absorption spectroscopy in N,N-dimethylformamide solution. Excitation of the porphyrin unit leads to a very rapid electron transfer (2-20 ps) to the nearby platinum complex followed by an ultrafast charge recombination, thus preventing any observation of the charge separated state. The variation in the rate of the photoinduced electron transfer in the series of dyads is consistent with Marcus theory. The results underscore the potential of the para-phenylene bisacetylene bridge to mediate a rapid electron transfer over a long donor-acceptor distance.     

Nucleocyclitols. Synthesis of substituted purinyl-muco-inositol derivatives

Several carbocyclic nucleoside analogs possessing a 6-substituted purine linked to a mesylated muco-inositol were synthesized. The coupling of triethylamine-activated 6-chloropurine with 2,3-anhydro-l,5,6-tri-O-(methanesulfonyl)-epi-inositol gave a 6-chloro purinyl muco-inositol amenable to further synthetic transformations in the heterocyclic moiety by substitution of the chlorine atom by nitrogen nucleophiles such as methylamino, diethylamino, benzylamino, hydrazino, morpholino, hydroxylamino, piperidino, and glycyl groups.     

Spectrophotometric determination of indium in nickel alloys and zinc ores with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea

A sensitive method for the spectrophotometric determination of indium with 1-(2-pyridylmethylideneamine)-3-(salicylideneamine)thiourea is proposed. A yellow complex is formed at pH 4.5 (succinate buffer) in a medium containing 40% dimethylformamide, and the absorbance is measured at 415 nm. The molar absorptivity is 6.2 x 10(4)l.mole(-1).cm(-1). The relative standard deviation of the procedure is 1.5%. The method has been applied to determination of indium in a nickel alloy and three zinc ores, with prior isolation of indium by co-precipitation with ammonia and extraction into n-butyl acetate from 5M hydrobromic acid.     

Determination of Binding Constants of Polyethylene Glycol Vancomycin Derivatives to Peptide Ligands Using Affinity Capillary Electrophoresis

Vancomycin (Van) from Streptomyces orientalis has been derivatized with polyethylene glycol [PEG; PEG-550 (1), 750 (2), 1,100 (3), 2,000 (4), 5,000 (5), and 8,000 (6) g mol⁻¹] at the N-terminus of the glycopeptide backbone and their binding to d-Ala-d-Ala terminus peptides assessed using affinity capillary electrophoresis (ACE). Utilizing ACE, a plug of Van-PEG and non-interacting standards are injected and electrophoresed. Analysis of the change in the relative migration time ratio of the Van-PEG species, relative to the non-interacting standards, as a function of the concentration of peptide, yields a value for the binding constant (K _b). Values of K _b for N-acetyl-d-Ala-d-Ala, 7 to the Van-PEG derivatives are weaker than those for N _α,N _ε-diacetyl-Lys-d-Ala-d-Ala, 8 (for example, values of K _b for 7-1 and 8-1 are 1.8 and 47.7 × 10³ M⁻¹, respectively). These results demonstrate that derivatization of Van with PEG has little effect on the affinity of d-Ala-d-Ala peptide ligands to it. The findings further prove the versatility of ACE and its ability to estimate binding parameters of ligands to antibiotics.     

Determination of fat-soluble vitamins in yogurt by HPLC with electrochemical detection

A method employing HPLC with electrochemical detection for the rapid and simultaneous determination of vitamins A, D(3) and E is described. The method uses a C-18 reverse phase column and 2.5 mM HAcO-NaAcO in methanol-water (99:1, v/v) solution as the mobile phase. The compounds are quantified using amperometric detection with a glassy carbon electrode at a potential of + 1300 mV (vs. Ag/AgCl) and the results are compared with those obtained using UV detection at a wavelength of 280 nm. The method was successfully applied to the analysis of vitamins A, D(3) and E in yogurt samples. After saponification, fat-soluble vitamins were extracted and the methanolic solution of the extracts was injected directly into the chromatographic system, avoiding the clean-up step which is necessary when no electrochemical detection is used. Good recovery percentages were obtained.     

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) to estimate binding constants of receptors to ligands

Partial filling multiple injection affinity capillary electrophoresis (PFMIACE) is used to determine binding constants between vancomycin (Van) from Streptomyces orientalis, teicoplanin (Teic) from Actinoplanes teicomyceticus and ristocetin (Rist) from Nocardia lurida to d-Ala-d-Ala terminus peptides and carbonic anhydrase B (CAB, E.C.4.2.1.1) to arylsulfonamides. Two variations of PFMIACE are described herein. In the first technique, the capillary is partially filled with ligand at increasing concentrations, a non-interacting standard, three or four separate plugs of receptor each separated by small plugs of buffer, a plug containing a second non-interacting standard, and then electrophoresed in buffer. Upon continued electrophoresis, equilibrium is established between the ligand and receptors causing a shift in the migration time of the receptors with respect to the non-interacting standards. This change in migration time is utilized for estimating multiple binding constants (K_b) for the same interaction. In the second technique, separate plugs of sample containing non-interacting standards, peptide one, buffer, and peptide two, were injected into the capillary column. The capillary is partially filled with a series of buffers containing an antibiotic at increasing concentrations and electrophoresed. Peptides migrate through the column at similar electrophoretic mobilities since their charge-to-mass ratios are approximately the same but remain as distinct zones due to the buffer plug between peptides. Upon electrophoresis, the plug of antibiotic flows into the peptide plugs affecting a shift in the migration time of the peptides with respect to the non-interacting standards occurs due to formation of the of the antibiotic-peptide complex. The shift in the migration time of the peptides upon binding to the antibiotic is used for the Scatchard analysis and measurement of a K_b. The PFMIACE technique expands the functionality and potential of ACE as an analytical tool to examine receptor-ligand interactions. In PFMIACE, a smaller amount of sample is required in the assay compared to both conventional ACE and MIACE. Furthermore, a wide array of data is obtained from a single experiment, thus, expediting the assay of biological species.     

BIOLOGICAL CHEMILUMINESCENCE

Abstract
The nucleobase 5-methylcytosine ( I ) is a minor component of eukaryotic DNA thought to be important in regulation of gene expression. The photochemical reactions of this nucleobase and its 2'-deoxyribonucleoside, 5-methyl-2'-deoxycytidine ( II ), in water have been studied. These reactions lead, respectively, to 3-amino-2-methylacrylamidine ( Ib ) and 3-(2- erythro - d -pentopyranos-1-yl) amino-2-methylacrylamidine ( IIb ) as the main photoproducts. The structure of the photoproducts was established by spectroscopic methods (¹H and ¹³C NMR, UV spectroscopy, electron impact and liquid secondary ion mass spectrometry); in the case of Ib , confirmatory evidence was obtained by chemical methods (photolysis of 5-methyl[2–¹³C]cytosine, hydrolysis of N -carbomethoxy-3-amino-2-methylacryl-amidine and reaction of Ib with 1,1'-carbonyldiimidazole to give I ). The quantum yield for formation of Ib was determined to be 1.8 × 10^-3at pH 7.5 while the quantum yield for formation of IIb has a lower value of 0.2 × 10^-3 at pH 7.5. These quantum yields depend strongly on pH and reach maximum values of 2.0 × 10^-3 at pH 7.0 ( Ib ) and 0.6 × 10^-3 at pH 5.0 ( IIb ). The mechanism of formation of Ib (or IIb ) is proposed to involve nucleophilic attack of water on the C-2 position of photoexcited I (or II ), followed by ring opening and decarboxylation of an intermediate carbamic acid.     

Global minima of (C60)nCa, (C60)nF and (C60)nI clusters

Likely candidates for the lowest potential energy minima of (C₆₀)_nCa²⁺, (C₆₀)_nF⁻ and (C₆₀)_nI⁻ clusters are located using basin-hopping global optimisation. In each case, the potential energy surface is constructed using the Girifalco form for the C₆₀ intermolecular interaction, an averaged Lennard–Jones C₆₀–ion interaction, and a polarisation potential, which depends on the first few non-vanishing C₆₀ multipole polarisabilities. We find that the ions generally occupy the interstitial sites of a (C₆₀)_n cluster, the coordination shell being tetrahedral for Ca²⁺ and F⁻. The I⁻ ion has an octahedral coordination shell in the global minimum for (C₆₀)₆I⁻, however for 12  n  8 the preferred coordination geometry is trigonal prismatic.