Formation of Peptide Radical Cations (M<Superscript>+·</Superscript>) in Electron Capture Dissociation of Peptides Adducted with Group IIB Metal Ions

Peptides adducted with different divalent Group IIB metal ions (Zn²⁺, Cd²⁺, and Hg²⁺) were found to give very different ECD mass spectra. ECD of Zn²⁺ adducted peptides gave series of c-/z-type fragment ions with and without metal ions. ECD of Cd²⁺ and Hg²⁺ adducted model peptides gave mostly a-type fragment ions with M^+• and fragment ions corresponding to losses of neutral side chain from M^+•. No detectable a-ions could be observed in ECD spectra of Zn²⁺ adducted peptides. We rationalized the present findings by invoking both proton-electron recombination and metal-ion reduction processes. As previously postulated, divalent metal-ions adducted peptides could adopt several forms, including (a) [M + Cat]²⁺, (b) [(M + Cat – H) + H]²⁺, and (c) [(M + Cat – 2H) + 2H]²⁺. The relative population of these precursor ions depends largely on the acidity of the metal–ion peptide complexes. Peptides adducted with divalent metal-ions of small ionic radii (i.e., Zn²⁺) would form predominantly species (b) and (c); whereas peptides adducted with metal ions of larger ionic radii (i.e., Hg²⁺) would adopt predominantly species (a). Species (b) and (c) are believed to be essential for proton-electron recombination process to give c-/z-type fragments via the labile ketylamino radical intermediates. Species (c) is particularly important for the formation of non-metalated c-/z-type fragments. Without any mobile protons, species (a) are believed to undergo metal ion reduction and subsequently induce spontaneous electron transfer from the peptide moiety to the charge-reduced metal ions. Depending on the exothermicity of the electron transfer reaction, the peptide radical cations might be formed with substantial internal energy and might undergo further dissociation to give structural related fragment ions.     

Ceramicines E-I, new limonoids from Chisocheton ceramicus

Five new limonoids, ceramicines E-I (1-5), have been isolated from the bark of Chisocheton ceramicus. The structures and relative stereochemistry of them were fully elucidated based on 1D- and 2D-NMR data. Ceramicines E-I (1-5) exhibited moderate cell growth inhibitory activities on a range of cell lines (HL-60, A549, MCF7, and HCT116). The absolute structure of previously isolated ceramicine B (6) was also elucidated by circular dichroism (CD) and X-ray analysis.     

Crystallographic and infrared spectroscopic study of bond distances in Ln[Fe(CN)6]·4H2O (Ln=lanthanide)

Along with crystallographic data of Ln[Fe(CN)₆]·4H₂O (Ln=lanthanide), the infrared spectra are reassigned to examine bond length trends across the series of Ln. The changes in mean Ln-O, Ln-N, CN and Fe-C distances are discussed and the bond natures of Ln-N and Ln-O are studied by bond length linear or quadratic fitting and comparisons with relevant ionic radii. The two different CN bond distances have been simulated by the covalo-electrostatic model.     

Structure of sputtered Co-Se thin films prepared for an application in catalysis

Co-Se thin films prepared by magnetron sputtering have shown significant activity for the oxygen reduction reaction. One sample, after sectioning by ultramicrotomy, was studied by high-resolution scanning transmission electron microscopy (HRSTEM) and scanning Auger microscopy (SAM), and X-ray diffraction (XRD) was used for characterizing further samples. These thin films were shown to have Co-Se nanocrystals embedded into Se-rich matrices. The TEM and XRD results were consistent with the nanocrystallites being non-stoichiometric with structures related to those of monoclinic Co_1−xSe (x=0.125-0.25).     

New D‐A‐A’‐Configured Small Molecule Donors Employing Conjugation to Red‐shift the Absorption for Photovoltaics

Four new donor‐acceptor‐acceptor’ (D‐A‐A’)‐configured donors, CPNT , DCPNT , CPNBT , and DCPNBT equipped with naphtho[1,2‐c:5,6‐c′]bis([1,2,5]‐thiadiazole) (NT) or naphtho[2,3‐c][1,2,5]thiadiazole (NBT) as the central acceptor (A) unit bridging triarylamine donor (D) and cyano or dicyanovinylene acceptor (A’), were synthesized and characterized. All molecules exhibit bathochromic absorption shifts as compared to those of the benzothiadiazole (BT)‐based analogues owing to improved electron‐withdrawing and quinoidal character of NT and NBT cores that lead to stronger intramolecular charge transfer. Favorable energy level alignments with C₇₀, together with the good thermal stability and the antiparallel dimeric packing render CPNT and DCPNT suitable donors for vacuum‐processed organic photovoltaics (OPV)s. OPVs based on DCPNT : C₇₀ active layers displayed the best power conversion efficiency (PCE)=8.3%, along with an open circuit voltage of 0.92 V, a short circuit current of 14.5 mA cm^?2 and a fill factor of 62% under 1 sun intensity, simulated AM1.5G illumination. Importantly, continuous light‐soaking with AM 1.5G illumination has verified the durability of the devices based on CPNT :C₇₀ and DCPNT : C₇₀ as the active blends. The devices were examined for their feasibility of indoor light harvesting under 500 lux illumination by a TLD‐840 fluorescent lamp, giving PCE=12.8% and 12.6%, respectively. These results indicate that the NT‐based D‐A‐A’‐type donors CPNT and DCPNT are potential candidates for high‐stability vacuum‐processed OPVs suitable for indoor energy harvesting.     

A solid-state 23Na NMR study of monovalent cation binding to double-stranded DNA at low relative humidity

We report a solid-state (23)Na NMR study of monovalent cation (Li(+), Na(+), K(+), Rb(+), Cs(+) and NH(4) (+)) binding to double-stranded calf thymus DNA (CT DNA) at low relative humidity, ca 0-10%. Results from (23)Na--(31)P rotational echo double resonance (REDOR) NMR experiments firmly establish that, at low relative humidity, monovalent cations are directly bound to the phosphate group of CT DNA and are partially dehydrated. On the basis of solid-state (23)Na NMR titration experiments, we obtain quantitative thermodynamic parameters concerning the cation-binding affinity for the phosphate group of CT DNA. The free energy difference (DeltaG degrees ) between M(+) and Na(+) ions is as follows: Li(+) (-1.0 kcal mol(-1)), K(+) (7.2 kcal mol(-1)), NH(4) (+) (1.0 kcal mol(-1)), Rb(+) (4.5 kcal mol(-1)) and Cs(+) (1.5 kcal mol(-1)). These results suggest that, at low relative humidity, the binding affinity of monovalent cations for the phosphate group of CT DNA follows the order: Li(+) > Na(+) > NH(4) (+) > Cs(+) > Rb(+) > K(+). This sequence is drastically different from that observed for CT DNA in solution. This discrepancy is attributed to the different modes of cation binding in dry and wet states of DNA. In the wet state of DNA, cations are fully hydrated. Our results suggest that the free energy balance between direct cation-phosphate contact and dehydration interactions is important. The reported experimental results on relative ion-binding affinity for the DNA backbone may be used for testing theoretical treatment of cation-phosphate interactions in DNA.     

Consideration of some sampling problems in the on-line analysis of batch processes by low-field NMR spectrometry

A low-field medium-resolution NMR spectrometer, with an operating frequency of 29 MHz for 1H, has been assessed for on-line process analysis. A flow cell that incorporates a pre-magnetisation region has been developed to minimise the decrease in the signal owing to incomplete polarisation effects. The homogeneous esterification reaction of crotonic acid and 2-butanol was monitored using a simple sampling loop; it was possible to monitor the progression of the reaction through changes in CH signal areas of butanol and butyl crotonate. On-line analysis of heterogeneous water-toluene mixtures proved more challenging and a fast sampling loop system was devised for use with a 5 L reactor. The fast sampling loop operated at a flow rate of 8 L min(-1) and a secondary sampling loop was used to pass a sub-sample through the NMR analyser at a slower (mL min(-1)) rate. It was shown that even with super-isokinetic sampling conditions, unrepresentative sampling could occur owing to inadequate mixing in the reactor. However, it was still possible to relate the 1H NMR signal obtained at a flow rate of 60 mL min(-1) to the composition of the reactor contents.     

Luminescent alkynylplatinum(II) complexes of 2,6-bis(N-alkylbenzimidazol-2'-yl)pyridine-type ligands with ready tunability of the nature of the emissive states by solvent and electronic property modulation

A new class of luminescent alkynylplatinum(II) complexes of tridentate bis(N-alkylbenzimidazol-2'-yl)pyridines (bzimpy), [Pt(R,R'-bzimpy)(C[triple chemical bond]C-R')]X (X=PF(6), OTf), and one of their chloro precursor complexes, [Pt(R,R'-bzimpy)Cl]PF(6), have been synthesized and characterized; one of the alkynyl complexes has also been structurally characterized by X-ray crystallography. Electrochemical studies showed that the oxidation wave is alkynyl ligand-based in nature with some mixing of the metal center-based contribution, whereas the two quasi-reversible reduction couples are mainly bzimpy-based reductions. The electronic absorption and luminescence properties of the complexes have also been investigated. In solution, the high-energy and intense absorption bands are assigned as the pi-pi* intraligand (IL) transitions of the bzimpy and alkynyl ligands, whereas the low-energy and moderately intense absorptions are assigned to an admixture of metal-to-ligand charge-transfer (MLCT) (dpi(Pt)-->pi*(R,R'-bzimpy)) and ligand-to-ligand charge-transfer (LLCT) (pi(C[triple chemical bond]C-R')-->pi*(R,R'-bzimpy)) transitions. Upon variation of the electronic effects of the arylalkynyl ligands, vibronic-structured or structureless emission bands, originating from triplet metal-perturbed intraligand (IL) or an admixture of triplet metal-to-ligand charge-transfer (MLCT) and ligand-to-ligand charge-transfer (LLCT) excited states respectively, were observed in solution. Interestingly, two of the complexes showed a dual luminescence that was sensitive to the polarity of the solvents. Upon cooling from 298 K to 155 K, drastic color, UV/Vis, and luminescence changes were observed in a butyronitrile solution of 1, and were ascribed to the formation of aggregate species through PtPt and pi-pi stacking interactions. DFT and time-dependent DFT (TD-DFT) calculations have been performed to verify and elucidate the results of the electrochemical and photophysical properties.     

Functionalized europium nanorods for in vitro imaging

Emissive europium hydroxide nanorods (ENR) (20 nm x 500 nm) functionalized by a surface coating of chromophore-containing organically modified silicate (ORMOSIL) layer, have been synthesized and characterized by high-resolution transmission electron microscopy (TEM). Low-temperature photophysical characterization of the functionalized nanorods (FENR) demonstrated a strong red 5D0 luminescence both in solid and in suspended solutions. Potentials of this nanorod material for live cell imaging have also been explored. Both the bare and functionalized nanorods are able to enter living human cells with no discernible cytotoxicity. Chromophore-to-Eu3+ energy-transfer in the functionalized nanorods enables staining of the cytoplasm of living human cells. This is confirmed by costaining with fluorescent dextran. The red chromophore-sensitized luminescence from the internalized nanorods in live human lung carcinoma cells (A549) can be observed by confocal microscopy 2 h after loading and reaches maximal emission after 24 h.     

Complexation of the vulcanization accelerator tetramethylthiuram disulfide and related molecules with zinc compounds including zinc oxide clusters (Zn4O4)

Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn(2+), ZnMe(2), Zn(OMe)(2), Zn(OOCMe)(2), and the heterocubane cluster Zn(4)O(4) with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me(2)NCS(2)(*), Me(2)NCS(3)(*), Me(2)NCS(2)(-), and Me(2)NCS(3)(-) have been studied by quantum chemical methods at the MP2/6-31+G(2df,p)//B3LYP/6-31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe(2)相似文献