NMR study of 5-substituted pyrazolo[3,4-c]pyridine derivatives

Substituted pyrazolopyridines are potent inhibitors of phosphodiesterases and cyclin-dependent kinases. In this study, NMR was used to investigate the potential N1-H and N2-H tautomerism of 5-substituted pyrazolo[3,4-c]pyridine derivatives. Six compounds were fully characterized by using (1)H, (13)C, and (15)N chemical shifts and indirect (1)H--(13)C and (1)H--(15)N coupling constants. The (1)H NMR spectra were measured over a broad range of temperatures. All of the compounds were shown to exist predominantly in the N1-H tautomeric form. Complementary quantum-chemical calculations of the chemical shieldings and indirect spin-spin couplings support the structural conclusions drawn.     

Metastable liquid clusters in super- and undersaturated protein solutions

Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the solution, have been known to form in solutions of proteins and small-molecule substances. Here, with the protein lumazine synthase as a test system, using dynamic and static light scattering and atomic force microscopy, we demonstrate submicron size clusters of dense liquid. In contrast to the macroscopic dense liquid, these clusters are metastable not only with respect to the crystals, but also with respect to the low-concentration solution: the characteristic cluster lifetime is limited to approximately 10 s, after which they decay. The cluster population is detectable only if they occupy >10(-6) of the solution volume and have a number density >105 cm-3 for 3 to 11% of the monitored time. The cluster volume fraction varies within wide limits and reaches up to 10(-3). Increasing protein concentration increases the frequency of cluster detection but does not affect the ranges of the cluster sizes, suggesting that a preferred cluster size exists. A simple Monte Carlo model with protein-like potentials reproduces the metastable clusters of dense liquid with limited lifetimes and variable sizes and suggests that the mean cluster size is determined by the kinetics of growth and decay and not by thermodynamics.     

Polyoxomolybdenum(V/VI)-sulfite compounds: synthesis, structural, and physical studies

Reaction of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) in the mixed-solvent system H(2)O/CH(3)CN (pH = 5) resulted in the formation of the tetranuclear cluster (NH(4))(4)[Mo(4)(VI)SO(16)] x H(2)O (1), while the same reaction in acidic aqueous solution (pH = 5) yielded (NH(4))(4)[Mo(5)(VI)S(2)O(21)] x 3H(2)O (2). Compound {(H(2)bipy)(2)[Mo(5)(VI)S(2)O(21)] x H(2)O}(x) (3) was obtained from the reaction of aqueous acidic solution of Na(2)Mo(VI)O(4) x 2H(2)O with (NH(4))(2)SO(3) (pH = 2.5) and 4,4'-bipyridine (4,4'-bipy). The mixed metal/sulfite species (NH(4))(7)[Co(III)(Mo(2)(V)O(4))(NH(3))(SO(3))(6)] x 4H(2)O (4) was synthesized by reacting Na(2)Mo(VI)O(4) x 2H(2)O with CoCl(2) x 6H(2)O and (NH(4))(2)SO(3) with precise control of pH (5.3) through a redox reaction. The X-ray crystal structures of compounds 1, 2, and 4 were determined. The structure of compound 1 consists of a ring of four alternately face- and edge-sharing Mo(VI)O(6) octahedra capped by the trigonal pyramidal sulfite anion, while at the base of the Mo(4) ring is an oxo group which is asymmetrically shared by all four molybdenum atoms. Compound 3 is based on the Strandberg-type heteropolyion [Mo(5)(VI)S(2)O(21)](4-), and these coordinatively saturated clusters are joined by diprotonated 4,4'-H(2)bipy(2+) through strong hydrogen bonds. Compound 3 crystallizes in the chiral space group C2. The structure of compound 4 consists of a novel trinuclear [Co(III)Mo(2)(V)SO(3)(2-)] cluster. The chiral compound 3 exhibits nonlinear optical (NLO) and photoluminescence properties. The assignment of the sulfite bands in the IR spectrum of 4 has been carried out by density functional calculations. The cobalt in 4 is a d(6) octahedral low-spin metal atom as it was evidenced by magnetic susceptibility measurements, cw EPR, BVS, and DFT calculations. The IR and solid-state UV-vis spectra as well as the thermogravimetric analyses of compounds 1-4 are also reported.     

Direct and Indirect Chemiluminescence: Reactions,Mechanisms and Challenges

Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (¹O₂) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date.     

Tetra‐μ‐acetato‐κ8O:O′‐bis[(N1,N2‐di‐p‐anisylformamidine‐κN2)ruthenium(II)](Ru—Ru): an example of an axial bis‐adduct of {Ru2}4+ tetracarboxyl­ate with N‐donor ligands

The title compound, [Ru₂(C₂H₃O₂)₄(C₁₅H₁₆N₂O₂)₂], lies on a crystallographic inversion center and exhibits an Ru—Ru bond length of 2.2847 (8) Å. There are weak intramolecular hydrogen‐bonding interactions between the N¹,N²‐di‐p‐anisylformamidine (HDAniF) ligands and the bridging acetate ligands. The molecule is one of the few examples of a crystallographically characterized axial bis‐adduct of a {Ru₂}⁴⁺ complex with two N‐donor ligands.     

A Reevaluation of the Ambident Reactivity of the Guanine Moiety Towards Hydroxyl Radicals

Radically different : Contrary to previous proposals, the main reaction of the HO^. radical with guanosine or 2′‐deoxyguanosine is the hydrogen abstraction from the NH₂ moiety to give a guanyl radical. This radical, characterized by a broad band in the visible region (around 610 nm), undergoes tautomerization to the most stable isomer.

     

Photophysical behavior of terpyridine-lanthanide ion complexes incorporated in a poly(N,N-dimethylacrylamide) hydrogel

Poly(N,N-dimethylacrylamide) hydrogel forms complexes with terpyridine and various trivalent ions, like Eu(3+), Tb(3+), Gd(3+), and In(3+). The hydrogel can be obtained in three different phases: swollen with water, lyophilized (i.e., dried by freeze-drying), where it loses the solvent but preserves the swollen configuration, and dried in the air where it shrinks. The three hydrogel phases affect the type of complex formed between terpyridine and the metal ion. Thus, in the swollen and lyophilized phases, metal-centered emission can be obtained by energy transfer from the excited ligand. In the shrunk phase, an intense green fluorescence is emitted, which is ligand-centered and is independent of the complexed ion. In the absence of any ion, the ligand emits blue luminescence, independently of the hydrogel phase. In the presence of europium(III) ions, blue, green, or red emission can be thus produced at appropriate compositions and hydrogel phases. Analysis of the photophysical behavior of the polymer-ligand-metal ion complex is related with the photophysical behavior of the ligand and its complexes in various pure solvents.     

On the accuracy of the IWM–CFC approximation in differentially rotating relativistic stars

A circular restricted three-body problem describes the motion of a test particle around two massive bodies in circular orbits. In this system, orbital decay caused by a gravitational radiation reaction between the two primary bodies is considered but the direct effect of gravitational radiation on the test particle is neglected. We adopt distance- and time-scale transformations to Newtonian problems so that systems without orbital decay will not depend on separation between the primaries but systems with orbital decay will depend on this separation. If a regular or chaotic orbit is given in a Newtonian system, the starting separation of the primaries varies according to the corresponding decay system. Thus, insights into the chaotic behaviour of a third body in a decay case are provided. For a large initial separation between the primaries, the chaos that exists in a Newtonian problem may be retained for a long enough time scale of dissipative evolution before the primaries coalesce. The final state of a third body is escape attributed to orbital decay.     

Bioflavonoid profile of citrus juices from Greece

High‐performance liquid chromatography with confirmation by UV–visible photodiode array detector–positive electrospray ionization–mass spectrometry [HPLC‐UV–vis‐DAD‐(+ESI)‐MS] with enhanced fragmentation by appropriate adjustment of the cone voltage was used to determine bioflavonoid content of five citrus species (tangerine, sanguine, sour orange, lemon and grapefruit) cultivated in Greece which come from citrus varieties analyzed for the first time. The main groups of bioflavonoids found in the juice of the citrus species according to HPLC retention times, spectral data and literature references were O‐glycosylated flavanones and flavones, C‐glucosylated flavones, O‐glucosylated flavones, O‐C‐glucosylated flavones like saponarin and a phenolic derivative. Copyright © 2012 John Wiley & Sons, Ltd.