Anion separation by selective crystallization of metal-organic frameworks

A novel approach for the separation of anions from aqueous mixtures was demonstrated, which involves their selective crystallization with metal-organic frameworks (MOFs) containing urea functional groups. Self-assembly of Zn2+ with the N,N'-bis(m-pyridyl)urea (BPU) linker results in the formation of one-dimensional MOFs including various anions for charge balance, which interact to different extents with the zinc nodes and the urea hydrogen-bonding groups, depending on their coordinating abilities. Thus, Cl-, Br-, I-, and SO4(2-), in the presence of BPU and Zn2+, form MOFs from water, in which the anions coordinate the zinc and are hydrogen-bonded to the urea groups, whereas NO3- and ClO4- anions either do not form MOFs or form water-soluble discrete coordination complexes under the same conditions. X-ray diffraction, FTIR, and elemental analysis of the coordination polymers precipitated from aqueous mixtures containing equivalent amounts of these anions indicated total exclusion of the oxoanions and selective crystallization of the halides in the form of solid solutions with the general composition ZnCl(x)Br(y)I(z).BPU (x + y + z = 2), with an anti-Hofmeister selectivity. The concomitant inclusion of the halides in the same structural frameworks facilitates the rationalization of the observed selectivity on the basis of the diminishing interactions with the zinc and urea acidic centers in the MOFs when going from Cl- to I-, which correlates with decreasing anionic charge density in the same order. The overall crystal packing efficiency of the coordination frameworks, which ultimately determines their solubility, also plays an important role in the anion crystallization selectivity under thermodynamic equilibration.     

Thermodynamic study of a series lithium β-diketonates

Thermal behaviour of a series of lithium β-diketonates: Li(dpm) (dpm=dipivaloylmethanate (2,2,6,6-tetramethylheptane-3,5- dionate)), Li(pta) (pta=pivaloyltrifluoracetonate (2,2-dimethyl-6,6,6-trifluoro-3,5-hexanedionate)), Li(tfa) (tfa=trifluoracetylacetonate (1,1,1-trifluoro-2,4-pentandionate)), Li(hfa) (hfa=hexafluoracetylacetonate (1,1,1,5,5,5-hexafluoro-2,4-pentandionate)) has been investigated. Gas phase composition of these complexes has been established. Temperature dependences of vapor pressure of lithium compounds were obtained by static and dynamic methods, and thermodynamic parameters were calculated. Dependence of compound volatility on ligand structure is shown. For Li(dpm) detailed investigation has been done by differential scanning calorimetry (DSC).     

Development of a solid‐phase microextraction LC–MS/MS method for determination of oxidative stress biomarkers in biofluids

Recently the connection between oxidative stress and various diseases, including cancer and Alzheimer's, attracts notice as a pathway suitable for diagnostic purposes. 8‐Oxo‐deoxyguanosine and 8‐oxo‐deoxyadenosine produced from the interaction of reactive oxygen species with DNA become prominent as biomarkers. Several methods have been developed for their determination in biofluids, including solid‐phase extraction and enzyme‐linked immunosorbent assays. However, still, there is a need for reliable and fast analytical methods. In this context, solid‐phase microextraction offers many advantages such as flexibility in geometry and applicable sample volume, as well as high adaptability to high‐throughput sampling. In this study, a solid‐phase microextraction method was developed for the determination of 8‐oxo‐deoxyguanosine and 8‐oxo‐deoxyadenosine in biofluids. The extractive phase of solid‐phase microextraction consisted of hydrophilic–lipophilic balanced polymeric particles. In order to develop a solid‐phase microextraction method suitable for the determination of the analytes in saliva and urine, several parameters, including desorption solvent, desorption time, sample pH, and ionic strength, were scrutinized. Analytical figures of merit indicated that the developed method provides reasonable interday and intraday precisions (<15% in both biofluids) with acceptable accuracy. The method provides a limit of quantification for both biomarkers at 5.0 and 10.0 ng/mL levels in saliva and urine matrices, respectively.     

Triggering the Directional Selectivity of a Ring‐Closure Reaction Leads to Pyridoazacarbazoles with Anticancer Properties

We herein describe a facile and versatile synthetic route to the tetracyclic system of 6‐substituted 5,6‐dihydro‐11H‐pyrido[3,2‐i]‐1‐azacarbazoles with promising anticancer properties. These derivatives are built up by an elegant one‐step base‐catalyzed synthetic procedure from commercially available building blocks. One additional step provides the corresponding skeleton hitherto unknown in the literature. The possibility to synthesize a large library of compounds with various substitution patterns utilizing this method underlines the importance of this synthetic procedure.     

Architectural control of polystyrene physical properties using branched anionic polymerization initiated at ambient temperature

Ambient temperature-initiated anionic polymerization has generated branched polystyrenes of varying molecular weights and architectures by inclusion of a distyryl branching comonomer into a conventional sec-Butylithium-initiated polymerization of styrene. Primary chain length control within the branched polymers, and restriction of the branching points to varying segments of the primary chains, led to variations of glass transition temperature with no direct correlation to the branched polymer molecular weight but a strong relationship to the length of individual chains comprising the branched macromolecules.     

Carbohydrate Hydrolase-Inhibitory Activity of Juice-Based Phenolic Extracts in Correlation to Their Anthocyanin/Copigment Profile

Red fruits and their juices are rich sources of polyphenols, especially anthocyanins. Some studies have shown that such polyphenols can inhibit enzymes of the carbohydrate metabolism, such as α-amylase and α-glucosidase, that indirectly regulate blood sugar levels. The presented study examined the in vitro inhibitory activity against α-amylase and α-glucosidase of various phenolic extracts prepared from direct juices, concentrates, and purees of nine different berries which differ in their anthocyanin and copigment profile. Generally, the extracts with the highest phenolic content—aronia (67.7 ± 3.2 g GAE/100 g; cyanidin 3-galactoside; chlorogenic acid), pomegranate (65.7 ± 7.9 g GAE/100 g; cyanidin 3,5-diglucoside; punicalin), and red grape (59.6 ± 2.5 g GAE/100 g; malvidin 3-glucoside; quercetin 3-glucuronide)—showed also one of the highest inhibitory activities against α-amylase (326.9 ± 75.8 μg/mL; 789.7 ± 220.9 μg/mL; 646.1 ± 81.8 μg/mL) and α-glucosidase (115.6 ± 32.5 μg/mL; 127.8 ± 20.1 μg/mL; 160.6 ± 68.4 μg/mL) and, partially, were even more potent inhibitors than acarbose (441 ± 30 μg/mL; 1439 ± 85 μg/mL). Additionally, the investigation of single anthocyanins and glycosylated flavonoids demonstrated a structure- and size-dependent inhibitory activity. In the future in vivo studies are envisaged.     

Comparative study of the photochemistry of the azidopyridine 1-oxides

The photochemistry of azidopyridine 1-oxides was studied using an array of glass and matrix isolation techniques. As with room temperature, the photochemistry of 4-azidopyridine 1-oxide is dominated by triplet nitrene chemistry. However, in the case of the 3-azide, matrix photolysis indicates the formation of diazabicyclo[4.1.0]hepta-2,4,6-triene N-oxide and diazacycloheptatetraene N-oxide intermediates as well as triplet nitrene.     

Poly(ethylene glycol)-supported tetrahydroxyphenyl porphyrin: a convenient,recyclable catalyst for photooxidation reactions

[reaction: see text] A new poly(ethylene glycol)-supported porphyrin has been prepared and its ability as a promoter in photooxidation reactions has been studied. The PEG-supported catalyst exhibits high activity, comparable to that of a nonanchored sensitizer, and it is easily removable by filtration from the reaction mixture. The polymer-bound porphyrin has been recycled up to six times with no loss of chemical and stereochemical efficiency.     

2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides: synthesis,stereospecificity, some chemical transformations,and conformational analysis

The synthesis of methyl 5-O-benzoyl-2-chloro-2,3-dideoxy-3-fluoro-beta-d-ribofuranoside (5) and its use as a glycosylating agent for persilylated thymine, N(6)-benzoyladenine, and N(4)-benzoylcytosine are described (Scheme 1). The 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides 10-12 synthesized were transformed to 2',3'-dideoxy-3'-fluoro-alpha- and -beta-d-erythro-pentofuranoside nucleosides of thymine (13a,b), adenine (14a,b), and cytidine (15a,b) by treatment with tributyltin hydride in the presence of alpha,alpha'-azobisisobutyronitrile (Scheme 2). Treatment of 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides with 1 M MeONa/MeOH under reflux for 1-5 h afforded 2',3'-didehydro-2',3'-dideoxy-2'-chloro-d-pentofuranosyl nucleosides as the principal products (47-81%) of the reaction, along with recovered starting nucleoside (11-33%) (Scheme 3). Easy HF elimination was also observed in the case of the 2'-azido-2',3'-dideoxy-3'-fluoro-beta-d-ribofuranosides of thymine (17) and adenine (20) (Scheme 3). The role of conformational peculiarities of 2'-chloro-2',3'-dideoxy-3'-fluoro-d-ribonucleosides as well as of 17 and 20 in the observed exclusive elimination of HF is discussed. The conformational analysis of a rather broad palette of 2,3-dideoxy-3-fluoro-2-(X-substituted)-d-ribofuranosides was performed with the aid of the PSEUROT (version 6.3) program, using (i) the recently reparametrized Karplus-type relation (Chattopadhyaya and co-workers. J. Org. Chem. 1998, 63, 4967) and (ii) empirical bond angle correction terms suggested by us. The predictive power of the Brunck and Weinhold model (J. Am. Chem. Soc. 1979, 101, 1700) of the gauche effect between atoms and groups as a conformational driving force acting upon the pentofuranose ring is explored. Their model invokes maximum antiperiplanar sigma <--> sigma stabilization when the donating bond is the least polar one and the acceptor orbital is at the most polarized bond and is found at least as satisfactory, and in various specific cases more so than, as rationalizations on the basis of the preference of the gauche vs the trans conformation of two vicinal electronegative substituents (Wolfe. Acc. Chem. Res. 1972, 5, 102).