{[Ca5(C8H4O4)5(H2O)9]·8H2O}n: the first crystallographically characterized non‐transition metal salt of isophthalic acid

The reaction of CaCO₃ with isophthalic acid in water yields nona­aqua­penta‐μ‐isophthalato‐pentacalcium octahydrate, {[Ca₅(C₈H₄O₄)₅(H₂O)₉]·8H₂O}_n, a complex polymeric one‐dimensional column structure bearing metal–carboxyl­ate bonds and Ca‐bound terminal and bridging water mol­ecules, in addition to hydrogen‐bonded water mol­ecules of crystallization. The asymmetric unit comprises half of the formula unit, with one Ca²⁺ ion located on a twofold axis, and contains 16 unique strong O—H⋯O hydrogen bonds, some of which link the columns together.     

Comparison of three different configurations of dual ultramicroelectrodes for the decomposition of S-Nitroso-L-glutathione and the direct detection of nitric oxide

Podoplanin (PDP) is a small transmembrane protein and widely present in various specialized cells throughout the human body. It is a specific marker for identification of lymphatic vessel and a candidate marker for cancer stem cells in squamous cell carcinoma of the lung. We report on method for the highly selective determination of PDP by using a surface plasmon resonance imaging (SPRI) that exploits the highly selective interaction between PDP and anti-human PDP monoclonal antibody (IgG). The sensor has a dynamic range between 0.25 and 1.0?ng?mL^?1, and a detection limit of 15?pg?mL^?1. It was applied to the determination of PDP in blood plasma and tissue homogenates from paired normal and lung tumor tissue.

Palladium-catalyzed intramolecular allylic alkylation of α-sulfinyl carbanions: a new asymmetric route to enantiopure γ-lactams

Asymmetric intramolecular palladium-catalyzed allylic alkylation allowing access to disubstituted sulfinyl γ-lactams is described. The use of unsaturated amides bearing a sulfinyl group of defined absolute configuration together with enantiopure BINAP as the ligand in a biphasic medium provided good diastereoselectivities with clear solvent effect.     

Organocatalysts for the controlled "immortal" ring-opening polymerization of six-membered-ring cyclic carbonates: a metal-free, green process

Six-membered cyclic carbonates, namely trimethylene carbonate (TMC), 3,3-dimethoxytrimethylene carbonate (DMTMC) and 3-benzyloxytrimethylene carbonate (BTMC), undergo controlled "immortal" ring-opening polymerization (iROP) under mild conditions (bulk, 60-150 °C), by using organocatalysts, including an amine [4-N,N-dimethylaminopyridine (DMAP)], a guanidine [1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD)], or a phosphazene [2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP)], in the presence of an alcohol [benzyl alcohol (BnOH), 1,3-propanediol (PPD), glycerol (GLY)] that acts as both a co-initiator and a chain-transfer agent. Remarkably, such organocatalysts remain highly active in the iROP of technical-grade, unpurified TMC. Under optimized conditions, as much as 100,000 equivalents of TMC were fully converted by as little as 10 ppm of BEMP with the simultaneous growth of as many as 200 polymer chains, allowing the preparation of high molar mass poly(trimethylene carbonate)s (up to 45,800 g mol(-1)). These catalyst systems enable among the highest activities (TOF=55,800 h(-1)) and productivities (TON=95,000) ever reported for the ROP of TMC.     

Human serum albumin self-assembly on weak polyelectrolyte multilayer films structurally modified by pH changes

Adsorption of proteins onto film surfaces built up layer by layer from oppositely charged polyelectrolytes is a complex phenomenon, governed by electrostatic forces, hydrogen bonds, and hydrophobic interactions. The amounts of the interacting charges, however, both in polyelectrolytes and in proteins adsorbed on such films are a function of the pH of the solution. In addition, the number and the accessibility of free charges in proteins depend on the secondary structure of the protein. The subtle interplay of all these factors determines the adsorption of the proteins onto the polyelectrolyte film surfaces. We investigated the effect of these parameters for polyelectrolyte films built up from weak "protein-like" polyelectrolytes (i.e., polypeptides), poly(L-lysine) (PLL), and poly(glutamic acid) (PGA) and for the adsorption of human serum albumin (HSA) onto these films in the pH range 3.0-10.5. It was found that the buildup of the polyelectrolyte films is not a simple function of the pure charges of the individual polyelectrolytes, as estimated from their respective pKa values. The adsorption of HSA onto (PLL/PGA)n films depended strongly on the polyelectrolyte terminating the film. For PLL-terminated polyelectrolyte films, at low pH, repulsion, as expected, is limiting the adsorption of HSA (having net positive charge below pH 4.6) since PLL is also positively charged here. At high pH values, an unexpected HSA uptake was found on the PGA-ending films, even when both PGA and HSA were negatively charged. It is suggested that the higher surface rugosity and the decrease of the alpha-helix content at basic pH values (making accessible certain charged groups of the protein for interactions with the polyelectrolyte film) could explain this behavior.     

A Comparison of Silica C and Silica Gel in HILIC Mode: The Effect of Stationary Phase Surface Area

In order to assess the effect of silica gel structure on retention in hydrophilic interaction chromatography, a test system was developed which used quaternary ammonium ions as probes with tetramethylammonium acetate (TMAA) as the counter-ion competing against the interaction of the test probes with ionised silanols in the stationary phase. Four silica gel columns and a silica hydride column were examined. Retention times were obtained for the test probes at 20, 40, 60, 80 and 90 % acetonitrile (ACN) with all the mobile phase mixtures containing 10-mM TMAA buffer at pH 6.0. All phases gave “U”-shaped plots for log k against percentage of ACN with the steepest rise in retention occurring between 80 and 90 % ACN. Benzyltrimethylammonium, the smallest quaternary ammonium ion, was the most strongly retained probe at 90 % ACN and was most retained on a high surface area 60 Å Kromasil column and least retained on a 300 Å ACE silica gel column. The ionic strength of the mobile phase was varied at 80 and 90 % ACN and plots of log k against the inverse of buffer strength followed by fitting of second-order polynomial curves allowed an assessment of the contribution from HILIC to the mixed HILIC/ion-exchange retention mechanism. Toluene and pentylbenzene were used to assess the decrease in accessible pore volume due to water absorption in HILIC mode.     

Structure-guided optimization of small molecule c-Abl activators

c-Abl kinase is maintained in its normal inactive state in the cell through an assembled, compact conformation. We describe two chemical series that bind to the myristoyl site of the c-Abl kinase domain and stimulate c-Abl activation. We hypothesize that these molecules activate c-Abl either by blocking the C-terminal helix from adopting a bent conformation that is critical for the formation of the autoinhibited conformation or by simply providing no stabilizing interactions to the bent conformation of this helix. Structure-based molecular modeling guided the optimization of binding and activation of c-Abl of these two chemical series and led to the discovery of c-Abl activators with nanomolar potency. The small molecule c-Abl activators reported herein could be used as molecular tools to investigate the biological functions of c-Abl and therapeutic implications of its activation.     

Probing Protonation Sites of Isolated Flavins Using IR Spectroscopy: From Lumichrome to the Cofactor Flavin Mononucleotide

Infrared spectra of the isolated protonated flavin molecules lumichrome, lumiflavin, riboflavin (vitamin B₂), and the biologically important cofactor flavin mononucleotide are measured in the fingerprint region (600–1850 cm^?1) by means of IR multiple‐photon dissociation (IRMPD) spectroscopy. Using density functional theory calculations, the geometries, relative energies, and linear IR absorption spectra of several low‐energy isomers are calculated. Comparison of the calculated IR spectra with the measured IRMPD spectra reveals that the N10 substituent on the isoalloxazine ring influences the protonation site of the flavin. Lumichrome, with a hydrogen substituent, is only stable as the N1‐protonated tautomer and protonates at N5 of the pyrazine ring. The presence of the ribityl unit in riboflavin leads to protonation at N1 of the pyrimidinedione moiety, and methyl substitution in lumiflavin stabilizes the tautomer that is protonated at O2. In contrast, flavin mononucleotide exists as both the O2‐ and N1‐protonated tautomers. The frequencies and relative intensities of the two C?O stretch vibrations in protonated flavins serve as reliable indicators for their protonation site.     

A self-assembled complex with a titanium(IV) catecholate core as a potential bimodal contrast agent

A ditopic chelating ligand (H(6)4) that bears catechol and diethylenetriamine-N,N,N',N',N'-pentaacetate (DTPA) has been designed and shown to specifically bind lanthanide(III) ions at the DTPA core ([Ln(H(2)4)(H(2)O)](-)) and further self-assemble with titanium(IV), thereby giving rise to the formation of a supramolecular metallostar complex with a lanthanide(III)-to-titanium(IV) ratio of 3:1, [(Ln4)(3)Ti(H(2)O)(3)](5-) (Ln=La, Eu, Gd). The efficacy of the metallostar complex as a potential bimodal optical/magnetic resonance imaging (MRI) agent has been evaluated. Nuclear magnetic relaxation dispersion (NMRD) measurements for the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex have demonstrated an enhanced r(1) relaxivity that corresponds to 36.9 s(-1) mM(-1) per metallostar molecule at 20 MHz and 310 K, which is a result of a decreased tumbling rate. The ability of the complex to bind to human serum albumin (HSA) was also examined by relaxometric measurements. In addition, upon UV irradiation the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex exhibits broad-band green emission in the range 400-750 nm with a maximum at 490 nm. Taking into account the high relaxivity and luminescence properties, the [(Gd4)(3)Ti(H(2)O)(3)](5-) complex is a good lead compound for the development of efficient bimodal contrast agents.     

Investigation of the photoinduced magnetization of copper octacyanomolybdates nanoparticles by X-ray magnetic circular dichroism

Through an extensive set of SQUID magnetic measurements, X-ray absorption spectroscopy, and X-ray magnetic circular dichroism, we have determined the nature of the metastable photomagnetic phase in the cyano-bridged 3D network Cs(2)Cu(7)[Mo(CN)(8)](4). The photomagnetic effect is induced by the photoconversion of Mo(IV) ions in low spin (LS) configuration (S = 0) into Mo(IV) ions in high spin (HS) configuration (S = 1). The magnetic and spectroscopic measurements fully support the LS to HS conversion, whereas the previously invoked charge transfer mechanism Mo(IV) + Cu(II) ? Mo(V) + Cu(I) can be completely ruled out.