8-(p-CF3-cinnamyl)-modified purine nucleosides as promising fluorescent probes

Natural nucleotides are not useful as fluorescent probes because of their low quantum yields. Therefore, a common methodology for the detection of RNA and DNA is the application of extrinsic fluorescent dyes coupled to bases in oligonucleotides. To overcome the many limitations from which fluorescent nucleotide-dye conjugates suffer, we have developed novel purine nucleosides with intrinsic fluorescence to be incorporated into oligonucleotide probes. For this purpose we synthesized adenosine and guanosine fluorescent analogues 7-25, conjugated at the C8 position with aryl/heteroaryl moieties either directly, or via alkenyl/alkynyl linkers. Directly conjugated analogues 7-14, exhibited high quantum yields, φ >0.1, and short λ(em) (<385 nm). Alkynyl conjugated analogues 22-25, exhibited low quantum yields, φ <0.075, and λ(em)<385 nm. The alkenyl conjugated analogues 15-21, exhibited λ(em) 408-459 nm. While analogues 15,16, and 20 bearing an EDG on the aryl moiety, exhibited φ <0.02, analogues 17, and 21 with EWG on the aryl moiety, exhibited extremely high quantum yields, φ ≈ 0.8, suggesting better intramolecular charge transfer. We determined the conformation of selected adenosine analogues. Directly conjugated analogue 8 and alkynyl conjugated analogue 22, adapted the syn conformation, whereas alkenyl conjugated analogue 15 adapted the anti conformation. Based on the long emission wavelengths, high quantum yields, anti conformation and base-paring compatibility, we suggest analogues 17 and 21 for further development as fluorescent probes for the sensitive detection of genetic material.     

Biomolecule-nanoparticle hybrids as functional units for nanobiotechnology

Biomolecule-metal or semiconductor nanoparticle (NP) hybrid systems combine the recognition and catalytic properties of biomolecules with the unique electronic and optical properties of NPs. This enables the application of the hybrid systems in developing new electronic and optical biosensors, to synthesize nanowires and nanocircuits, and to fabricate new devices. Metal NPs are employed as nano-connectors that activate redox enzymes, and they act as electrical or optical labels for biorecognition events. Similarly, semiconductor NPs act as optical probes for biorecognition processes. Double-stranded DNA or protein chains that are modified with metallic nanoclusters act as templates for the synthesis of metallic nanowires. The nanowires are used as building blocks to assemble nano-devices such as a transistor or a nanotransporter.     

A Light-Fronts Approach to a Two-Center Time-Dependent Dirac Equation

The two center time dependent Dirac equation, for an electron in the external field of two colliding ultrarelativistic heavy ions is considered. In the ultrarelativistic limit, the ions are practically moving at the speed of light and the electromagnetic fields of the ions are confined to the light fronts by the extreme Lorentz contraction and by the choice of gauge, designed to remove the long-range Coulomb effects. An exact solution to the ultrarelativistic limit of the two-center Dirac equation is found by using light-front variables and a light-fronts representation. Previously unexplained experimental results obtained at CERN's SPS are explained in this way and predictions are made as to where one should look, in momentum space, and in space-time, if one wants to study and observe non-perturbative electromagnetic pair-production effects in extremely relativistic heavy-ion collisions.     

Preliminary toxicological studies of selected water‐soluble polymer–platinum conjugates

The objective of this preliminary investigation of a number of water‐soluble carrier‐bound platinum(II) complexes for potential use in cancer chemotherapy was to assess the toxicological behavior of representative platinum coordination compounds anchored to, or incorporated into, polymeric carriers via polymer‐attached amine ligands. The conjugates included linear polyaspartamides (1–4, 6, 7), each composed of a major fraction of subunits featuring side‐chain‐attached tertiary amino groups as water‐solubilizing entities, and a minor fraction of subunits comprising the anchored platinum complexes, again as side‐chain components. Whereas in 1–4 the platinum atom was polymer‐bound through a single amino group, both 6 and 7 contained polymer‐attached cis‐diamine‐chelating ligands coordinating to the metal center. Also included in this study was a linear polyamidoamine (5), which contained a poly(ethylene oxide) segment in the backbone in addition to intrachain ethylenediamine segments acting as cis‐diamine chelating ligands for coordination to the platinum center. The compounds were injected as aqueous (phosphate‐buffered saline) solutions into the tail veins of CD‐1 mice (four to eight mice per conjugate), and the maximally tolerated dose was determined for each compound. For polyaspartamides 1–4 the dose levels ranged from about 25 mg Pt (kg body weight⁻¹) (in conjugate 4) to 500 mg Pt kg⁻¹ (in compound 1), the latter conjugate proving some 100‐fold less toxic than cisplatin (3–4 mg Pt kg⁻¹), which was included in this study for comparison. Low toxicity (tolerated dose 160 mg Pt kg⁻¹) was also observed for the intrachain cis‐diamineplatinum complex polymer (5). The polyaspartamide conjugates 6 and 7, on the other hand, both characterized by a cis‐diamineplatinum complex system in the side chain, were toxic even below the dose level of 20–25 mg Pt kg⁻¹. The preliminary findings of this study, while providing a basis for more extensive and broad‐based toxicological studies, will serve to direct and optimize structural conjugate designs in forthcoming synthetic programs. Copyright © 2000 John Wiley & Sons, Ltd.     

Diethyl chlorophosphite: a versatile reagent

Diethyl chlorophosphite (DECP) was previously described as a reducing agent for nitro compounds to the corresponding amines (Fischer, B.; Sheihet, L. J. Org. Chem. 1998, 63, 393). Here, the utility of this reagent was extended to chemical conversions of other oxygenated functional groups. In this paper we report on the scope of the reaction of DECP with N-oxides, epoxides, sulfones, sulfoxides, hydroxylamines, ketoximes, and aldoximes. The chemoselectivity of DECP is described, and conditions for a stepwise multiple conversion of functional groups on the same molecule with this reagent are provided.     

Bioinspired Artificial Photosynthetic Systems

Mimicking photosynthesis using artificial systems, as a means for solar energy conversion and green fuel generation, is one of the holy grails of modern science. This perspective presents recent advances towards developing artificial photosynthetic systems. In one approach, native photosystems are interfaced with electrodes to yield photobioelectrochemical cells that transform light energy into electrical power. This is exemplified by interfacing photosystem I (PSI) and photosystem II (PSII) as an electrically contacted assembly mimicking the native Z-scheme, and by the assembly of an electrically wired PSI/glucose oxidase biocatalytic conjugate on an electrode support. Illumination of the functionalized electrodes led to light-induced generation of electrical power, or to the generation of photocurrents using glucose as the fuel. The second approach introduces supramolecular photosensitizer nucleic acid/electron acceptor complexes as functional modules for effective photoinduced electron transfer stimulating the subsequent biocatalyzed generation of NADPH or the Pt-nanoparticle-catalyzed evolution of molecular hydrogen. Application of the DNA machineries for scaling-up the photosystems is demonstrated. A third approach presents the integration of artificial photosynthetic modules into dynamic nucleic acid networks undergoing reversible reconfiguration or dissipative transient operation in the presence of auxiliary triggers. Control over photoinduced electron transfer reactions and photosynthetic transformations by means of the dynamic networks is demonstrated.     

Analogues of uracil nucleosides with intrinsic fluorescence (NIF-analogues): synthesis and photophysical properties

Uridine cannot be utilized as fluorescent probe due to its extremely low quantum yield. For improving the uracil fluorescence characteristics we extended the natural chromophore at the C5 position by coupling substituted aromatic rings directly or via an alkenyl or alkynyl linker to create fluorophores. Extension of the uracil base was achieved by treating 5-I-uridine with the appropriate boronic acid under the Suzuki coupling conditions. Analogues containing an alkynyl linker were obtained from 5-I-uridine and the suitable boronic acid in a Sonogashira coupling reaction. The uracil fluorescent analogues proposed here were designed to satisfy the following requirements: a minimal chemical modification at a position not involved in base-pairing, resulting in relatively long absorption and emission wavelengths and high quantum yield. 5-((4-Methoxy-phenyl)-trans-vinyl)-2'-deoxy-uridine, 6b, was found to be a promising fluorescent probe. Probe 6b exhibits a quantum yield that is 3000-fold larger than that of the natural chromophore (Φ 0.12), maximum emission (478 nm) which is 170 nm red shifted as compared to uridine, and a Stokes shift of 143 nm. In addition, since probe 6b adopts the anti conformation and S sugar puckering favored by B-DNA, it makes a promising nucleoside analogue to be incorporated in an oligonucleotide probe for detection of genetic material.     

Acetyl Chloride-Methanol as a Convenient Reagent for: A) Quantitative Formation of Amine Hydrochlorides B) Carboxylate Ester Formation C) Mild Removal of N-t-Boc-Protective Group.

Hydrogen chloride qualitatively generated in situ by the addition of acetyl chloride to alcoholic solutions is a useful reagent for carboxylic acid esterification, N-t-Boc deprotection and phosphoramide solvolysis reactions.     

Quality management in hematology laboratory improved preanalytics variables

Clinical decisions based on laboratory test values are correctly made when a preanalytical stage is properly performed. In this study we demonstrated that introduction of quality management procedures to Hematology laboratory at Medical Center and Health Care Center have helped to solve problems in the preanalytic stage. Blood clotting is a highly complicated process, which begins during blood withdrawal from vessels. In order to minimize in-vitro changes during collection, transportation and storage, the following steps were followed: centralization of blood collection, strict keeping of time interval between blood withdrawal to testing or freezing and purchasing of adequate freezer for storage. As a result, fibrin clots in frozen plasma were reduced from 10.6% to zero within 13 months and thus, the number of rejected samples decreased. Cooperation with ex-hospital customer who had introduced quality management system and established center for blood collection, separation and distribution have encouraged the introduction of new procedures.     

Photoaffinity labeling on magnetic microspheres (PALMm) methodology for topographic mapping: preparation of PALMm reagents and demonstration of biochemical relevance

Photoaffinity labeling (PAL) is a technique widely used for identifying the binding-site within proteins. Although the classic method is both versatile and powerful, it suffers significant disadvantages, such as the need to radiolabel the PAL ligand, and the need to conduct highly complicated separations of both the labeled protein and the labeled peptides derived from it. Here, we propose a novel and universal methodology--Photo-Affinity Labeling on Magnetic microspheres (PALMm) designed to simplify and shorten the PAL protocol. In this context, we describe the preparation of PALMm reagents and the evaluation of their biochemical relevance regarding two ATP-binding enzymes: hexokinase and apyrase.