Modification of aluminum chips for LDI mass spectrometry of proteins

Matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI TOFMS) combined with affinity chromatography on immobilized phenylboronic acid agarose gels was used for selective enrichment and detection of specifically modified proteins such as glycated proteins in complex biological samples. Physicochemical grafting of hydrophilic polymers on aluminum surface was developed to reduce nonspecific protein sorption and to create a proper support layer for a three-dimensional affinity hydrogel. Grafted agarose allowed the fixation of three-dimensional agarose hydrogel on the chip surface. Both pinched polymers and hydrogels were effectively derivatized. 3-Aminophenylboronic acid (mPBA) was covalently immobilized as an affinity ligand to achieve specific binding of glycated plasma proteins. Alternatively, the affinity sorbent was immersed into the hydrogel to increase binding capacity. MALDI TOFMS was used to evaluate binding efficiency and molecular mass changes of human serum albumin due to glycation. Glycated proteins were captured directly on the chip with high selectivity and efficacy, and low nonspecific binding. Thus they could easily be characterized by MALDI TOFMS.     

The reaction of tricarbon with acetylene: an ab initio/RRKM study of the potential energy surface and product branching ratios

Ab initio calculations of the potential energy surface for the C3(1Sigmag+)+C2H2(1Sigmag+) reaction have been performed at the RCCSD(T)/cc-pVQZ//B3LYP/6-311G(d,p) + ZPE[B3LYP/6-311G(d,p)] level with extrapolation to the complete basis set limit for key intermediates and products. These calculations have been followed by statistical calculations of reaction rate constants and product branching ratios. The results show the reaction to begin with the formation of the 3-(didehydrovinylidene)cyclopropene intermediate i1 or five-member ring isomer i7 with the entrance barriers of 7.6 and 13.8 kcal/mol, respectively. i1 rearranges to the other C5H2 isomers, including ethynylpropadienylidene i2, singlet pentadiynylidene i3, pentatetraenylidene i4, ethynylcyclopropenylidene i5, and four- and five-member ring structures i6, i7, and i8 by ring-closure and ring-opening processes and hydrogen migrations. i2, i3, and i4 lose a hydrogen atom to produce the most stable linear isomer of C5H with the overall reaction endothermicity of approximately 24 kcal/mol. H elimination from i5 leads to the formation of the cyclic C5H isomer, HC2C3, +H, 27 kcal/ mol above C3+C2H2. 1,1-H2 loss from i4 results in the linear pentacarbon C5+H2 products endothermic by 4 kcal/mol. The H elimination pathways occur without exit barriers, whereas the H2 loss from i4 proceeds via a tight transition state 26.4 kcal/mol above the reactants. The characteristic energy threshold for the reaction under single collision conditions is predicted be in the range of approximately 24 kcal/mol. Product branching ratios obtained by solving kinetic equations with individual rate constants calculated using RRKM and VTST theories for collision energies between 25 and 35 kcal/mol show that l-C5H+H are the dominant reaction products, whereas HC2C3+H and l-C5+H2 are minor products with branching ratios not exceeding 2.5% and 0.7%, respectively. The ethynylcyclopropenylidene isomer i5 is calculated to be the most stable C5H2 species, more favorable than triplet pentadiynylidene i3t by approximately 2 kcal/mol.     

Isomeric identification by laser control mass spectrometry

The influence shaped femtosecond laser pulses have on molecular photofragmentation and ionization, coupled with the intrinsic sensitivity of mass spectrometry, results in a powerful tool for fast, accurate, reproducible and quantitative isomeric identification. Complex phase functions are introduced to enhance differences during the laser-molecule interactions, which depend on geometric structure, resulting in different fragmentation fingerprints. A full account is given on the setup and results leading to a technique that can be used to distinguish between compounds normally indistinguishable by conventional electron ionization mass spectrometry. We demonstrate geometric and structural isomer identification of cis-/trans-3-heptene, cis-/trans-4-methyl-2-pentene, o-/p-cresol and o-/p-xylene. For the positional isomers of xylene we present a complete dataset consisting of 1024 different phases to explore phase complexity. A selection of two phases from that data can then be used to achieve quantitative identification in mixtures of xylene isomers. Finally, we evaluate receiver operational curves obtained from our experimental data to demonstrate the reliability that can be achieved by femtosecond laser control mass spectrometry.     

Jahn-Teller and related effects in the silver trimer. I. The ab initio calculation of spectroscopically observable parameters for the X 2E' and A 2E" electronic states

Extensive ab initio calculations were performed for the X2E' and A2E" states of Ag3, using a newly constructed basis set for Ag. An important goal of these calculations is to guide the analysis of the experimentally observed A 2E"-X2E' electronic spectrum. Vibrational frequencies of Ag(3) for both the X and A states are reported. Spectroscopically obtainable parameters describing the Jahn-Teller effect are calculated for the X and A states. The magnitude of the spin-orbit effects for this relativistic system was also calculated for the X2E' and A 2E" states. Using all this information, the X-A electronic spectrum is predicted for Ag(3). Additionally, the geometries and symmetries of the global minima and saddle points as well as the barrier to pseudorotation around the moat of the potential energy surface are determined for both states.     

On the orientational dependence of resolution in 1H solid-state NMR, and its role in MAS, CRAMPS and delayed-acquisition experiments

Numerical simulations and experiments are used to show that the spin dynamics of the dipolar-coupled networks in solids is often strongly dependent on crystallite orientation. In particular, different rates of dephasing of the magnetisation mean that NMR signals obtained at longer dephasing times are dominated by orientations in which the local dipolar coupling strength is relatively weak. This often leads to a distinct improvement in spectral resolution as the dephasing time is increased. The effects are particularly noticeable under magic-angle spinning (MAS), but are also observed when homonuclear decoupling is used to reduce the rate of dipolar dephasing. Numerical simulation is seen to be a powerful and easily used tool for understanding the behaviour of solid-state NMR experiments involving dipolar-coupled networks. The implications for solid-state NMR spectra of abundant spins acquired under MAS and homonuclear decoupling are discussed, as well as insights provided into the performance of 'delayed-acquisition' and 'constant-time' experiments.     

Satellites of Xe transitions induced by infrared active vibrational modes of CF4 and C2F6 molecules

Absorption and luminescence excitation spectra of Xe/CF(4) mixtures were studied in the vacuum UV region at high resolution using tunable synchrotron radiation. Pressure-broadened resonance bands and bands associated with dipole-forbidden states of the Xe atom due to collision-induced breakdown of the optical selection rules are reported. The spectra display in addition numerous satellite bands corresponding to transitions to vibrationally excited states of a Xe-CF(4) collisional complex. These satellites are located at energies of Xe atom transition increased by one quantum energy in the IR active v(3) vibrational mode of CF(4) (v(3) = 1281 cm(-1)). Satellites of both resonance and dipole-forbidden transitions were observed. Satellites of low lying resonance states are spectrally broad bands closely resembling in shape their parent pressure-broadened resonance bands. In contrast, satellites of dipole-forbidden states and of high lying resonance states are spectrally narrow bands (FWHM ～10 cm(-1)). The satellites of dipole-forbidden states are orders of magnitude stronger than transitions to their parent states due to collision-induced breakdown of the optical selection rules. These satellites are attributed to a coupling of dipole-forbidden and resonance states induced by the electric field of the transient CF(4) (v(3) = 0 ? v(3) = 1) dipole. Similar satellites are present in spectra of Xe/C(2)F(6) mixtures where these bands are induced by the IR active v(10) mode of C(2)F(6). Transitions to vibrationally excited states of Xe-CF(4)(C(2)F(6)) collision pairs were also observed in two-photon LIF spectra.     

Synthesis, characterization, and cytotoxic activity of novel potentially pH-sensitive nonclassical platinum(II) complexes featuring 1,3-dihydroxyacetone oxime ligands

The reaction of 1,3-dihydroxyacetone oxime with diam(m)minediaquaplatinum(II) under basic conditions produced zwitterionic diam(m)mine(3-hydroxy-2-(oxidoimino)propan-1-olato-κ(2)N,O)platinum(II) complexes featuring the N,O-chelating ligand. Upon reaction with hydrochloric acid, it was possible to isolate either the singly protonated species still exhibiting the intact N,O-chelate or the open-chain chlorido complex. All complexes were characterized in detail with multinuclear ((1)H, (13)C, and (195)Pt) NMR spectroscopy, ESI mass spectrometry, and in one case X-ray diffraction. Cytotoxicity was investigated in three human cancer cell lines (CH1, SW480, and A549). The obtained IC(50) values are in the medium or even low micromolar range, remarkable for platinum complexes having N(3)O or N(3)Cl coordination spheres. To study the solution behavior of the prepared complexes at physiologically relevant proton concentrations, time-dependent (1)H NMR measurements were performed for the ethane-1,2-diamine-containing series at pH values of 7.4, 6.0, and exemplarily 5.0. While the zwitterionic complex proved to be stable at both pH 7.4 and 6.0, the protonated species were deprotonated at pH 7.4, tending toward ring opening in slightly acidic environments, as characteristic for many solid tumors. Finally, the open-chain form stayed intact at pH 6.0, being completely converted into its chelated analogue at pH 7.4. A pH-dependent evaluation of antiproliferative effects of the two latter complexes at pH 7.4 and pH 6.0 revealed an activation under slightly acidic conditions, which might be of interest for further in vivo studies.     

2-Oxo-2-polyfluoroalkylethane-1-sulfones and -sulfamides in the Biginelli and ‘retro-Biginelli’ reactions

2-Oxo-2-polyfluoroalkylethane-1-sulfones and -sulfamides react with aryl aldehydes and urea under Biginelli reaction conditions to yield 4-hydroxy-4-polyfluoroalkyl-5-sulfonyl-6-aryl-tetrahydropyrimidinones. The latter compounds on reaction with hexamethylenetetramine (HMTA) under thermal conditions undergo ‘retro-Biginelli’ reaction involving replacement of the 6-aryl substituent of the pyrimidinone cycle with a hydrogen atom donated by HMTA. Hexamethylenetetramine was employed for the first time in place of formaldehyde in the reported one-step Biginelli protocol for the synthesis of fluorinated sulfonyl-containing 6-unsubstituted tetrahydropyrimidinones.