Differential interactions of isomeric amino sugars with insulin studied under electrospray ionisation mass spectrometry

Protein-ligand interactions were studied for bovine insulin-amino sugar systems under electrospray ionisation mass spectrometry conditions. The isomeric amino sugars showed differences in the relative abundance of 1:1 protein-ligand complex formation. The electrospray ionisation and tandem mass spectrometry results of the complex clearly demonstrated that the differences in the interaction of isomeric sugars with insulin are mainly due to the differences in their gas-phase basicity. The same phenomenon is replicated in the formation of complexes between insulin and other ligands, such as amino acids, as well as in the binding of the amino sugars with amyloid β 1-40 peptide.     

Differentiation of diasteromeric α-sulfanyl-β-amino acid derivatives by electrospray ionization tandem mass spectrometry

A set of diastereomeric α-sulfanyl-β-amino acid derivatives, which are important building blocks for pharmaceuticals with potent biological activity, are studied by electrospray ionization tandem mass spectrometry. The collision induced dissociation (CID) spectra of [M+H](+), [M+NH(4)](+), [M+Na](+) and [M+Li](+) of the diastereomers were studied, among them the CID of [M+Na](+) and [M+Li](+) showed consistent differences in the relative abundance of characteristic ions that enabled distinction of the anti isomers from syn isomers. The decomposition pathways for the diagnostic ions were arrived at based on high-resolution mass spectrometry data, multiple mass spectrometry data, deuterium labeling experiments and the mass shift in accordance with the substituents located at different places. Loss of (R(1)-C(6)H(4)-CH=NH) and (Cat-NH-SO(2)R(2)) from [M+Cat](+), where Cat=Na and Li, and the product ions as a results of McLafferty rearrangement involving either >S=O or >C=O group were found to be diagnostic. The McLafferty rearrangement product ions involving >S=O group were more abundant in syn isomers while those involving >C=O group were more abundant in anti isomer. The selectivity observed in the decomposition of [M+Li](+) ions was found to be similar to that of [M+Na](+) ions, but in few cases the differences are marginal in the decomposition [M+Li](+) ions.     

Quantization noise in binary holograms

The signal-to-noise (S/N) ratio in the reconstructed image from a binary hologram has been quantitatively related to the amplitude and phase quantization levels. The S/N ratio increases monotonically with increasing number of quantization levels. This observation is further supported by experimental results.     

The synthesis of XTT: A new tetrazolium reagent that is bioreducible to a water-soluble formazan

A new tetrazolium salt, XTT, has been synthesized. XTT is reduced by a considerable variety of cell lines to a water-soluble formazan. XTT appears to merit further investigation as a reagent for broader application to cell culture assay systems.     

Self-assembly of a fluorescent chiral zinc(II) complex that leads to supramolecular helices

The chiral Zn(II) complex [ZnLCl(2)], 1 {L = 4-methyl-2,6-di[(S)-(+)-1-phenylethyliminomethyl] phenol}, self-assembles via C-H...Cl hydrogen bonding into supramolecular helices. Complex 1 exhibits emission in solution at room temperature in the visible range. Crystal data for 1: orthorhombic space group P2(1)2(1)2(1), a = 9.614(2) A, b = 13.825(3) A, c = 18.667(3) A, V = 2481.1(8) A(3), Z = 4.     

Near-infrared absorption in symmetric squarylium and croconate dyes: a comparative study using symmetry-adapted cluster-configuration interaction methods

Symmetric croconate (CR) and squarylium dyes (SQ) are well-known near-infrared (NIR) dyes and, in general, are considered to be donor-acceptor-donor type molecules. It is established in the literature that CR dyes absorb in a longer wavelength region than the corresponding SQ dyes. This has been attributed to the CR ring being a better acceptor than the SQ ring. Thus increasing the donor capacity should lead to a bathochromic shift in both SQ and CR. On the other hand, some experiments reported in the literature have revealed that increasing the conjugation in the donor part of the SQ molecule leads first to red shift, which upon a further increase of the conjugation changes to a blue shift. Hence, to understand the role of the central ring and the substitutions in the absorption of these dyes, we carried out high-level symmetry-adapted cluster-configuration interaction (SAC-CI) calculations of some substituted SQ and CR dyes and compare the absorption energy with the existing experimental data. We found that there is very good agreement. We also carried out SAC-CI calculations of some smaller model molecules, which contain the main oxyallyl substructure. We varied the geometry (angle) of the oxyallyl subgroup and the substitution in these model molecules to establish a correlation with the bathochromic shift. We found that the charge transfer is very small and does not play the key role in the red shift, but on the other hand, the perturbation of the HOMO-LUMO gap (HLG) from both the geometry and substitution seems to be responsible for this shift. We suggest as a design principle that increasing the donor capacity of the groups may not help in the red shift, but introducing groups which perturb the HLG and decrease it without changing the MO character should lead to a larger bathochromic shift.     

Role of the oxyallyl substructure in the near infrared (NIR) absorption in symmetrical dye derivatives: A computational study

It is well-known from experimental studies that the oxyallyl-substructure-based squarylium and croconium dyes absorb in the NIR region of the spectrum. Recently, another dye has been reported (J. Am. Chem. Soc. 2003, 125, 348) which contains the same basic chromophore, but the absorption is red-shifted by at least 300 nm compared to the former dyes and is observed near 1100 nm. To analyze the reasons behind the large red shift, in this work we have carried out symmetry-adapted cluster-configuration interaction (SAC-CI) studies on some of these NIR dyes which contain the oxyallyl substructure. From this study, contrary to the earlier reports, it is seen that the donor groups do not seem to play a major role in the red-shift of the absorption. On the other hand, on the basis of the results of the high-level calculations carried out here and using qualitative molecular orbital theory, it is observed that the orbital interactions play a key role in the red shift. Finally, design principles for the oxyallyl-substructure-based NIR dyes are suggested.     

Studies in sigmatropic rearrangements of N-prenylindole derivatives--a formal enantiomerically pure synthesis of tryprostatin B

Rearrangement of N(a)-prenyl-N(b)-acetyltryptamine, induced by BF3.Et2O at low temperature, leads to a 2-prenyl derivative, and thence to the tricyclic tryptamine 7 and the indoline 8. Similarly, N(a)-prenyl-N(b)-phthaloyl-l-tryptophan methyl ester furnished the corresponding 2-prenyl derivative 16, a known advanced precursor of tryprostatin B. Density functional (B3LYP) calculations for the putative rearrangement transition state for N-prenylskatole show that prior coordination of BF3 to the indolic nitrogen changes the character of the subsequent sigmatropic pericyclic shifts from being entirely covalent to acquiring a significant degree of ionic character. The shifting prenyl group favours the endo over the exo mode of the transition state by 4.1 kcal mol(-1).