New Statistical Results on the Angular Distribution of Gamma-Ray Bursts

We presented the results of several statistical tests of the randomness in the angular sky-distribution of gamma-ray bursts in BATSE Catalog. Thirteen different tests were presented based on Voronoi tesselation, Minimal spanning tree and Multifractal spectrum for five classes (short1, short2, intermediate, long1, long2) of gamma-ray bursts, separately. The long1 and long2 classes are distributed randomly. The intermediate subclass, in accordance with the earlier results of the authors, is distributed non-randomly. Concerning the short subclass earlier statistical tests also suggested some departure from the random distribution, but not on a high enough confidence level. The new tests presented in this article suggest also non-randomness here.Comment: in GAMMA-RAY BURSTS 2007: Proceedings of the Santa Fe Conferenc

Factor analysis of the spectral and time behavior of long GRBs

A sample of 197 long BATSE GRBs is studied statistically. In the sample 11 variables, describing for any burst the time behavior of the spectra and other quantities, are collected. The application of the factor analysis on this sample shows that five factors describe the sample satisfactorily. Both the pseudo-redshifts coming from the variability and the Amati-relation in its original form are disfavored.Comment: In GAMMA-RAY BURSTS 2007: Proceedings of the Santa Fe Conferenc

Catalytic Conversion of Fructose to γ‑Valerolactone in γ‑Valerolactone

The one-pot conversion of fructose to γ-valerolactone (GVL) in GVL as solvent was confirmed by monitoring the dehydration of ¹³C₆-d-fructose to ¹³C₆-5-(hydroxymethyl)-2-furaldehyde (¹³C₆-HMF), the hydration of ¹³C₆-HMF to ¹³C₅-levulinic and ¹³C-formic acids, followed by their conversion to ¹³C₅-GVL

Exploration of Interfacial Hydration Networks of Target–Ligand Complexes

Interfacial hydration strongly influences interactions between biomolecules. For example, drug–target complexes are often stabilized by hydration networks formed between hydrophilic residues and water molecules at the interface. Exhaustive exploration of hydration networks is challenging for experimental as well as theoretical methods due to high mobility of participating water molecules. In the present study, we introduced a tool for determination of the complete, void-free hydration structures of molecular interfaces. The tool was applied to 31 complexes including histone proteins, a HIV-1 protease, a G-protein-signaling modulator, and peptide ligands of various lengths. The complexes contained 344 experimentally determined water positions used for validation, and excellent agreement with these was obtained. High-level cooperation between interfacial water molecules was detected by a new approach based on the decomposition of hydration networks into static and dynamic network regions (subnets). Besides providing hydration structures at the atomic level, our results uncovered hitherto hidden networking fundaments of integrity and stability of complex biomolecular interfaces filling an important gap in the toolkit of drug design and structural biochemistry. The presence of continuous, static regions of the interfacial hydration network was found necessary also for stable complexes of histone proteins participating in chromatin assembly and epigenetic regulation

Valorization of the Exoskeletons of Crustaceans in Seafood Wastes to Chemicals in Renewable Solvents: A Catalytic and Mechanistic Study

Levulinic acid (LA) and γ-valerolactone (GVL) are considered valuable platform chemicals that can be derived from various types of biomass ranging from food wastes to agricultural residues. Herein, the valorization of the exoskeletons of crustaceans in seafood wastes into LA, GVL, acetic acid (AA), and ammonium (NH4)+ was studied including the catalytic and mechanistic aspects. Chitin was used as a model compound to optimize the conditions for converting the exoskeletons of crustaceans in seafood wastes using acetic acid (AA) and GVL as bio-originated renewable solvents. The same conditions were applied to convert various pretreated seafood wastes, such as the exoskeletons of crabs and lobsters. The decalcification of the crustacean samples using phosphoric acid was also studied. GVL was also used as a solvent to produce formic acid (FA), LA, NH4+, and GVL to simplify the product purification process. The reaction mixture of chitin (0.41 g, equivalent to 2 mmol of N-acetyl-glucosamine) in a mixture of 10 mL of GVL and 1.5 mL of 5 M H2SO4 was heated at 150 °C for 4 h followed by neutralization with additional NH4+ (NH4OH) to result in two phases due to the salting out effect of (NH4)2SO4. Ru-based Shvo’s catalyst was then added to the organic phase for transfer hydrogenation of LA with FA as the hydrogen donor to yield GVL. Uniformly labeled N-acetyl-[13C6]glucosamine (UL-13C6-NAG) was used to confirm the formation of 13C5-GVL in 12C5-GVL via 13C5-LA and 13C-FA. Detailed in situ NMR studies revealed the presence of two bicyclic compounds, protonated salt of 1,6-anhydro-2-deoxy-2-ammonio-glucopyranose (AGluNPH+) and 1,6-anhydro-2-deoxy-2-ammonio-glucofuranose (AGluNFH+), as proposed key intermediates of the of UL-13C6-NAG conversion

Catalytic Conversion of Fructose, Glucose, and Sucrose to 5‑(Hydroxymethyl)furfural and Levulinic and Formic Acids in γ‑Valerolactone As a Green Solvent

The conversion of fructose, glucose, and sucrose to 5-(hydroxymethyl)­furfural (HMF) and levulinic acid (LA)/formic acid (FA) was investigated in detail using sulfuric acid as the catalyst and γ-valerolactone (GVL) as a green solvent. The H₂SO₄/GVL/H₂O system can be tuned to produce either HMF or LA/FA by changing the acid concentration and thus allowing selective switching between the products. Although the best yields of HMF were around 75%, the LA/FA yields ranged from 50% to 70%, depending on the structure of the carbohydrates and the reaction parameters, including temperature, acid, and carbohydrate concentrations. While the conversion of fructose is much faster than glucose, sucrose behaves like a 1:1 mixture of fructose and glucose, indicating facile hydrolysis of the glycosidic bond in sucrose. The mechanism of the conversion of glucose to HMF or LA/FA in GVL involves three intermediates: 1,6-anhydro-β-d-glucofuranose, 1,6-anhydro-β-d-glucopyranose, and levoglucosenone

[Tl^III(dota)]⁻: An Extraordinarily Robust Macrocyclic Complex

The X-ray structure of {C­(NH₂)₃}­[Tl­(dota)]·H₂O shows that the Tl³⁺ ion is deeply buried in the macrocyclic cavity of the dota^4– ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) with average Tl–N and Tl–O distances of 2.464 and 2.365 Å, respectively. The metal ion is directly coordinated to the eight donor atoms of the ligand, which results in a twisted square antiprismatic (TSAP′) coordination around Tl³⁺. A multinuclear ¹H, ¹³C, and ²⁰⁵Tl NMR study combined with DFT calculations confirmed the TSAP′ structure of the complex in aqueous solution, which exists as the Λ­(λλλλ)/Δ­(δδδδ) enantiomeric pair. ²⁰⁵Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl­(dota)]⁻ + H⁺ ⇆ [Tl­(Hdota)] to be determined, which turned out to be p<i>K</i>^H_Tl(dota) = 1.4 ± 0.1. [Tl­(dota)]⁻ does not react with Br^–, even when using an excess of the anion, but it forms a weak mixed complex with cyanide, [Tl­(dota)]⁻ + CN^– ⇆ [Tl­(dota)­(CN)]^2–, with an equilibrium constant of <i>K</i>_mix = 6.0 ± 0.8. The dissociation of the [Tl­(dota)]⁻ complex was determined by UV–vis spectrophotometry under acidic conditions using a large excess of Br^–, and it was found to follow proton-assisted kinetics and to take place very slowly (∼10 days), even in 1 M HClO₄, with the estimated half-life of the process being in the 10⁹ h range at neutral pH. The solution dynamics of [Tl­(dota)]⁻ were investigated using ¹³C NMR spectroscopy and DFT calculations. The ¹³C NMR spectra recorded at low temperature (272 K) point to <i>C</i>₄ symmetry of the complex in solution, which averages to <i>C</i>_4<i>v</i> as the temperature increases. This dynamic behavior was attributed to the Λ­(λλλλ) ↔ Δ­(δδδδ) enantiomerization process, which involves both the inversion of the macrocyclic unit and the rotation of the pendant arms. According to our calculations, the arm-rotation process limits the Λ­(λλλλ) ↔ Δ­(δδδδ) interconversion