X-ray and IR spectroscopic studies of specific intermolecular interactions inN′-substituted isonicotinohydrazides

_N-Thenylidene- andN-(o-nitrobenzylidene)hydrazides of isonicotinic acid have been studied by X-ray structural analysis and IR spectroscopy. In the crystalline state, these molecules are linked through intermolecular N—H ... Np_y hydrogen bonds. Carbonyl groups are not involved in intermolecular hydrogen bonds. However, it was found that the C=O group participates in an attractive interaction with the sulfur atom of the thiophene group. The energy of this interaction is comparable with the energies of intermolecular C=O ... H—N hydrogen bonds in amides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 896–900, April, 1996.     

Kinetics and mechanism of base hydrolysis of Reinecke's salt revisited – specific salt effects

The kinetics of base hydrolysis of the trans-[Cr(NH₃)₂(NCS)₄]^– anion follows the rate law: -d[complex]/dt = k ₀ + k ₁[OH^–] (50–70 °C, [OH^–] = 0.1–1.9 M and = 2.0 M). The specific salt effect has been investigated for eight aqueous media: NaCl, NaBr, NaI, NaClO₄, KCl, KBr, CsCl and CsBr. The alkali-independent path (k ₀) does not show any specific effect of inert electrolyte ions, the activation parameters: H = 113.5 ± 0.4 kJ mol^–1 and S = 24.1 ± 1.3 J mol^–1 K^–1 are interpreted in the frame of a dissociative interchange mechanism (I _d). For the alkali-dependent path (k ₁) the specific salt effect is observed for cations of the inert electrolyte, showing an important role for ion-pair formation between the cations and reagent complex anion in the activation process. A linear correlation between lnk ₁ and lnK ₀ (K ₀ – ion-pair formation constant) has been found for the cations studied. The dissociative, via conjugate base, mechanism (D _CB) has been proposed for the alkali-dependent path.     

Are defect models consistent with the entropy and specific heat of glass formers?

We show that pointlike defect model of glasses cannot explain the thermodynamic properties of glass formers, as for example, the excess specific heat close to the glass transition, contrary to the claim of Garrahan and Chandler [Proc. Natl. Acad. Sci. U.S.A. 100, 9710 (2003)]. More general models and approaches in terms of extended defects are also discussed.     

Synthesis and specific nootropic activity of (–)-cytisine derivatives with carbamide and thiocarbamide moieties in their structure

N-(methylcytisinyl)-N′-substituted ureas, N-substituted cytisine-12-carbamides, and cytisine-12-thiocarbamide were prepared by reaction of (–)-cytisine with urea and thiourea and of (–)-cytisine and its 12-N-methyl-3-amino derivative with isocyanates. Their specific nootropic activity was studied in vivo. The therapeutic index was determined for the lead compound. Promising candidates for further pharmacological testing were found.     

A highly sensitive and specific enzyme immunoassay for detection of β-amanitin in biological fluids

Polyclonal antisera to -amanitin were generated in sheep and used to construct a competitive ELISA for measurement of the toxin in human serum and urine. The assay had a detection limit of about 80 pg mL^–1, a dynamic range of 80–2,000 pg mL^–1, a cross reactivity of 22% with -amanitin, and no cross reactivities with cyclic peptides from algal sources. Assay responses in buffer, serum, and urine were remarkably similar. Coupling of the toxin to carrier proteins was carried out by previously unreported methods. The key step that allowed the construction of the highly sensitive assay was the introduction of a novel heterologous hapten derivative made of -amanitin-cyanuric chloride derivative. The new derivative overcame the problems of bridge binding that was, in this case, particularly serious with the homologous hapten derivative. The study demonstrated that the developed antiserum and ELISA procedure can be used to detect -amanitin and related toxins from Amanita phalloides in human serum and urine samples from suspected poison cases and enable early treatment to be administered.     

Novel triphenylamine-based fluorescent probe for specific detection and bioimaging of OCl−

Hypochlorite (OCl^?) plays important roles both in physiological and pathological processes, the detection of which is of great significance. Herein, a novel fluorescent probe based on the triphenylamine-type schiff base derivative (TPAD) was developed to detect OCl^?. Probe TPAD exhibited specific fluorescence response toward ClO^? with the fluorescence quenching rate up to 80%, and the detection limit was estimated to be 0.8?μM. The sensing mechanism study demonstrated that TPAD reacted with ClO^?via an oxidation process, which was evidenced by MS and NMR characterization. Moreover, owing to the excellent sensing properties and negligible cytotoxicity, TPAD was successfully applied in the bioimaging of OCl^? in living A549?cells.     

Polymorph specific RMSD local order parameters for molecular crystals and nuclei: α-, β-, and γ-glycine

Crystal nucleation is important for many processes including pharmaceutical crystallization, biomineralization, and material synthesis. The progression of structural changes which occur during crystal nucleation are often described using order parameters. Polymorph specific order parameters have been developed for crystallization of spherically symmetric particles; however, polymorph specific order parameters for molecular crystals remain a challenge. We introduce template based polymorph specific order parameters for molecular crystals. For each molecule in a simulation, we compute the root mean squared deviation (RMSD) between the local environment around the molecule and a template of the perfect crystal structure for each polymorph. The RMSD order parameters can clearly distinguish the α-, β-, and γ-glycine polymorph crystal structures in the bulk crystal and also in solvated crystallites. Surface melting of glycine crystallites in supersaturated aqueous solution is explored using the newly developed order parameters. The solvated α-glycine crystallite has a thinner surface melted layer than the γ-glycine crystallite. α-glycine forms first out of aqueous solution, so surface melted layer thickness may provide insight into interfacial energy and polymorph selection.     

Solar blind photocell – a simple element specific detector in Hg, As and Se speciation

An element-specific detection method, based on atomic absorption spectrometry (AAS) using solar blind photocells instead of a dispersion system, is described for the determination of Hg-, As-, and Se-species. Spectrometric investigations of AAS background lamps for As and Se measured with a CsI-cathode photocell shows its quality as narrow band detector. Species determination can be carried out subsequently to prior separation by HPLC or GC. The LODs for alkylated Hg species were below 1 ng/L, and for methylated As species below 1 μg/L. The relative standard deviation was < 10%. With the components described the production of cheap and automated dedicated speciation spectrometers is possible. Received: 18 May 1999 / Revised: 6 September 1999 / Accepted: 13 September 1999     

Spectroscopic investigation of novel donor–acceptor chromophores as specific application agents for opto-electronics and photonics

Donor–acceptor chromophores were synthesized by Knoevenagel condensation and characterized by using spectroscopic measurements (FT-IR, ¹H NMR, ¹³C NMR, and mass) and elemental analyses. UV–Vis and fluorescence spectroscopic studies provided that these dyes are good absorbent and fluorescent. The results of photostability study showed that photobleaching of Dyes 2 and 4 was more significant than that of Dyes 1 and 3, providing that Dyes 1 and 3 are more photostable than Dyes 2 and 4. In addition, all dyes included in this study are found to be sensitive to the polarity of the microenvironment provided by different solvents based on the results of fluorescence polarity studies.     

Preservation and detection of specific antibody—peptide complexes by matrix-assisted laser desorption ionization mass spectrometry

The direct detection of an antibody-peptide complex is reported by matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). Experimental conditions have been found in which specific, noncovalent interactions in solution are maintained throughout the sample preparation and ionization process. Mass measurements based on the ion signals for the intact antibody and 1:1 antibody-peptide complex reveal that specific noncovalent associations between a monoclonal antibody and a peptide, which comprises the determinant of the corresponding antigen, are maintained in the gas phase. These results support the wider application of MALDI-MS to studies of the structure and specificity of macromolecular complexes important to immune and other biological function.     

MS/MS fragmentation-guided search of TMG-chitooligomycins and their structure-activity relationship in specific β-N-acetylglucosaminidase inhibition

The reducing tetrasaccharide TMG-chitotriomycin (1) is an inhibitor of β-N-acetylglucosaminidase (GlcNAcase), produced by the actinomycete Streptomyces anulatus NBRC13369. The inhibitor shows a unique inhibitory spectrum, that is, selectivity toward enzymes from chitin-containing organisms such as insects and fungi. Nevertheless, its structure-selectivity relationship remains to be clarified. In this study, we conducted a structure-guided search of analogues of 1 in order to obtain diverse N,N,N-trimethylglucosaminium (TMG)-containing chitooligosaccharides. In this approach, the specific fragmentation profile of 1 on ESI-MS/MS analysis was used for the selective detection of desired compounds. As a result, two new analogues, named TMG-chitomonomycin (3) and TMG-chitobiomycin (2), were obtained from a culture filtrate of 1-producing Streptomyces. Their enzyme-inhibiting activity revealed that the potency and selectivity depended on the degree of polymerization of the reducing end GlcNAc units. Furthermore, a computational modeling study inspired the inhibitory mechanism of TMG-related compounds as a mimic of the substrate in the Michaelis complex of the GH20 enzyme. This study is an example of the successful application of a MS/MS experiment for structure-guided isolation of natural products.     

Discovery of a potent and highly β1 specific proteasome inhibitor from a focused library of urea-containing peptide vinyl sulfones and peptide epoxyketones

Syringolins, a class of natural products, potently and selectively inhibit the proteasome and show promising antitumour activity. To gain insight in the mode of action of syringolins, the ureido structural element present in syringolins is incorporated in oligopeptide vinyl sulfones and peptide epoxyketones yielding a focused library of potent new proteasome inhibitors. The distance of the ureido linkage with respect to the electrophilic trap strongly influences subunit selectivity within the proteasome. Compounds 13 and 15 are β5 selective and their potency exceeds that of syringolin A. In contrast, 5 may well be the most potent β1 selective compound active in living cells reported to date.     

New insight into anionic cyclizations of alkynyl- and ortho-dialkynylarenes: a specific reactivity of 3-alkynyl-2-chloro- and 2,3-dialkynylquinoxalines and related compounds toward CH-acids’ carbanions

The reactivity of 3-alkynyl-2-chloroquinoxalines, 2,3-dialkynylquinoxalines, and some related pyrazine derivatives toward carbanions of the CH-acids (malononitrile, ethyl cyanoacetate, diethyl malonate, 1,3-dimethylbarbituric acid) has been studied. Most of the observed reactions proceeded as tandem or cascade cyclizations yielding polynuclear heterocyclic compounds. The process starts with the addition of a nucleophile to an alkyne triple bond. Depending on the nature of the used C-nucleophile, the thus formed anionic adduct underwent further cyclization via (i) intramolecular nucleophilic substitution of the chlorine atom, (ii) intramolecular acylation of the ring nitrogen atom by the ester side chain or (iii) intramolecular nucleophilic attack on the second CC bond. Reactions of 3-alkynyl-2-chloro- and 2,3-dialkynylpyrazines with 1,3-dimethylbarbituric acid in the presence of t-BuOK were accompanied by recyclization of the 1,3-dimethylbarbituric acid moiety.     

A colorimetric method for protein assay via exonuclease III-assisted signal attenuation strategy and specific DNA–protein interaction

Taking advantage of exonuclease III (Exo III)-assisted signal attenuation strategy and the protection of DNA from Exo III-mediated digestion by specific DNA–protein interaction, a colorimetric method is proposed in this paper for protein assay. Specifically, in the absence of target protein, Exo III-assisted signal attenuation can be achieved by digesting the report DNA in a complex formed by the hybridization of a report DNA and a probe DNA. Nevertheless, in the presence of target protein, the binding of the analyte to the probe DNA will inhibit the Exo III-assisted nucleotides cleavage, so that cyclic signal attenuation is blocked. Therefore, a bridge can be established between the concentration of target protein and the degree of the attenuation of the obtained signal, and the relationship can be shown by the surface plasmon changes caused by the report DNA-induced aggregation of DNA-modified gold nanoparticles (AuNPs). Our method can also have considerable sensitivity and selectivity, which has been demonstrated by the assay of human α-thrombin. Furthermore, by simply changing the sequence of the probe DNA, we can expand the application of our method to not only aptamer binding proteins but also DNA binding proteins, thus we have also used this method to analyze a specific serological marker for systemic lupus erythematosus (SLE) in this study. With a broad detection range of 1.3–133 nM and a detection limit of 0.61 nM (S/N = 3), it may hold great promise for clinical application.     

4-C-Me-DAB and 4-C-Me-LAB - enantiomeric alkyl-branched pyrrolidine iminosugars - are specific and potent α-glucosidase inhibitors; acetone as the sole protecting group

The syntheses of 4-C-Me-DAB [1,4-dideoxy-1,4-imino-4-C-methyl-d-arabinitol] from l-erythronolactone and of 4-C-Me-LAB [from d-erythronolactone] require only a single acetonide protecting group. The effect of pH on the NMR spectra of 4-C-Me-DAB [pK_a of the salt around 8.4] is discussed and illustrates the need for care in the analysis of both coupling constants and chemical shift. 4-C-Me-DAB (for rat intestinal sucrase K_i 0.89 μM, IC₅₀ 0.41 μM) is a competitive—whereas 4-C-Me-LAB (for rat intestinal sucrase K_i 0.95 μM, IC₅₀ 0.66 μM) is a non-competitive—specific and potent α-glucosidase inhibitor. A rationale for the α-glucosidase inhibition by DAB, LAB, 4-C-Me-DAB, 4-C-Me-LAB and isoDAB—but not isoLAB—is provided. Both are inhibitors of endoplasmic reticulum (ER) resident α-glucosidase I and II.     

What are the practical limits for the specific surface area and capacitance of bulk sp~2 carbon materials?

The possible practical limits for the specific surface area and capacitance performance of bulk sp~2 carbon materials were investigated experimentally and theoretically using a variety of carbon materials. We find the limit for the specific surface area to be 3500–3700 m~2 g~(-1), and based on this, the corresponding best capacitance was predicted for various electrolyte systems. A model using an effective ionic diameter for the electrolyte ions was proposed and used to calculate the theoretical capacitance. A linear dependence of experimental capacitance versus effective specific surface area of various sp~2 carbon materials was obtained for all studied ionic liquid, organic and aqueous electrolyte systems. Furthermore, excellent agreement between the theoretical and experimental capacitance was observed for all the tested sp~2 carbon materials in these electrolyte systems, indicating that this model can be applied widely in the evaluation of various carbon materials for supercapacitors.     

Dual-active-site Fe/Cu single-atom nanozymes with multifunctional specific peroxidase-like properties for S2− detection and dye degradation

Designing single-atom nanozymes with densely exposed metal atom active sites and enhancing catalytic activity to detect pollutants remain a serious challenge. Herein, we reported a single-atom nanozyme with layered stacked Fe/Cu dual active sites (Fe/Cu-NC SAzyme) synthesized via hydrothermal and high-temperature pyrolysis using folic acid as a template. Compared with Fe-NC and Cu-NC SAzyme, Fe/Cu-NC SAzyme has higher peroxidase-like activity, which indicates that the doping of synthesized Fe/Cu bimetals can improve the catalytic activity and that the atomic loading of Fe and Cu in Fe/Cu-NC is 5.5 wt% and 2.27 wt%, respectively. When S²⁻ is added to the Fe/Cu-NC catalytic system, a high-sensitivity and high-selectivity S²⁻ colorimetric sensing platform can be established, with a wide linear range (0.09–6 µmol/L) and a low detection limit (30 nmol/L), which can be used to detect S²⁻ in environmental water samples. What's more, the Fe/Cu-NC SAzyme can activate peroxymonosulfate (PMS) to degrade 99.9% of rhodamine B (RhB) within 10 min with a degradation kinetics of 0.5943 min⁻¹. This work details attractive applications in Fe/Cu-NC SAzyme colorimetric sensing and dye degradation.