A high temperature and high sensitivity micro-thermobalance

A thermobalance which ensures a sensivity of 1 × 10^?6 g and an excellent stability up to 1500 C has been developed. A sample, which is suspended from one end of the beam of the balance, is heated in a compact furnace with a small heat capacity. Temperature is measured by a Pt-PtRh (10%) thermocouple placed close to the sample. Use of an alumina mantle ensures easy control of atmosphere: at room temperature, the evacuation can be done to 1 × 10^?4 Torr, and stable operation can be done up to 1500 C in air inert gas at a flow-rate smaller than 50 ml min^?1. It is also possible to use a corrosive gas as atmosphere. In a blank test with platinum cell support (6.5 mm diam. and 0.1 mm thick) suspended in an air stream of 50 ml min^?1 and heated up to 1500 C at 10 C min^?1, the drift was smaller than 20 × 10^?6 g and the reproducibility was better than 10×10^?6 g. This paper refers to the construction of the thermobalance, and its performances. And some examples of high temperature thermogravimetry through the results of analyses of CaCO₃, quick lime and byproduct lime are also reported.     

A new high sensitivity thermobalance

A new thermobalance is described which gives a direct plot of percentage weight loss versus sample temperature, without the need for replotting the results. The unit operates over the range ambient to 1000°C and features a miniature water-cooled furnace in conjunction with an electronic microbalance, giving sensitivities of 1–250 mg for full scale deflection on a potentiometric recorder. Heating rates of 1–100°C/minute are available and the furnace will cool from 1000°C to 50°C in less than four minutes. Typical applications of the unit are illustrated by reference to a number of inorganic and polymer systems.     

Polymeric PARACEST agents for enhancing MRI contrast sensitivity

Linear polymers of PARACEST agents were prepared by using classical free radical chain polymerization conditions. The Eu3+-polymers exhibited similar intermediate-to-slow water exchange and CEST characteristics as the Eu3+-monomers. This provided an avenue to lower the detection limit of these imaging agents substantially and makes them potentially useful as MRI sensors for molecular imaging.     

含杂环并具有高自旋基态的双自由基体系的理论设计

以—·N—O—为自旋中心(SC),间苯为铁磁耦合单元(FC),苯、吡啶、哒嗪、嘧啶、吡嗪、三嗪为端基(EG),设计一系列新型稳定高自旋分子.另外以—·N—O—为SC,苯、吡啶、哒嗪、嘧啶、吡嗪、三嗪为FC,苯为EG,又设计另一系列新型稳定高自旋分子,并通过AM1—CI方法计算,研究了不同杂环作为端基或耦合单元对高自旋分子自旋多重度稳定性的影响.     

Contrast agents for magnetic resonance imaging synthesized with ring-opening metathesis polymerization

A monomer for ring-opening metathesis polymerization (ROMP) has been developed that also functions as a portion of a GdIII chelating moiety for a magnetic resonance imaging contrast agent. An increase in per GdIII relaxivity was shown upon transition from monomer to polymer. Additionally, extremely large molecular relaxivities were achieved through incorporation of multiple GdIII ions per polymer. The nature of ROMP-derived polymers allows for functionalization of the monomer units and termini through orthogonal chemistry. This strategy is the basis for a new class of highly sensitive, targeted imaging agents.     

Phthalonitrile-based high temperature resin

An aromatic, diether-linked phthalonitrile resin, prepared from 4,4′-bis(3,4-dicyanophenoxy)biphenyl, exhibits excellent thermo-oxidative properties. The resin is easily processed from the melt of the monomer in a controlled manner as a function of the amine curing agent and processing temperatures. Polymerization occurs by a cyclic addition reaction without the formation of volatile by-products. The polymerization reaction can be stopped at a prepolymer stage. The prepolymer can be stored indefinitely at ambient conditions without further reaction. The modulus and viscoelastic properties of the resin were found to be a function of the postcuring conditions.     

Synthesis of hydroxyl-terminated polybutadiene possessing high content of 1,4-units via anionic polymerization

<正>The hydroxyl-terminated polybutadiene(HTPB) possessing high content of 1,4-units was synthesized by anionic polymerization of butadiene,using alkyllithium containing silicon-protected hydroxyl group as initiator and cyclohexane as solvent.The polymers were characterized by GPC,IR and ~1H-NMR.The mechanical properties of cured films were also evaluated.The results show that the content of 1,4-units for HTPBs made by anionic polymerization reaches up to 90%.The molecular weight distribution is very narrow(≤1.05).The functionality of hydroxyl groups approaches 2.Compared with free radical HTPB,the elongation at break of anionic HTPB films increased by 70%,while the tensile strength remained nearly unchanged.This new HTPB can be very useful in solid propellant.     

Effect of polymer matrix on temperature sensitivity of temperature sensitive paints

The thermal quenching behaviors of the temperature sensitivity paints(TSP) composed of europium(Ⅲ) thenoyltrifluoroacetonate(Eu TTA) and Eu-phenanthrene complex(Eu-2) in polystyrene(PS), polymethylmethacrylate(PMMA) and epoxy resin(EP) were investigated. It is found that both the emission intensity and temperature sensitivity were not only affected by the luminescence probes, but also by the polymer matrix. The interaction between probes and matrix results in the alteration of both the non-radiation decay rate and the activation energy of the non-radiative process for the thermal quenching process, i.e. larger activation energy of the non-radiative process shows higher temperature sensitivity and less emission intensity. Therefore, it was confirmed that the temperature sensitivity and luminescent intensity of TSP depended not only on the luminescence probes but also on the polymer matrix.     

Bisquaternary-drug membrane electrodes with high sensitivity

The construction and performance characteristics of ion-selective plastic membrane electrodes for succinylcholine, hexamethonium and decamethonium are described. The electrodes, based on ion-pair complexes with triphenylstillbenyl borate (TPSB), show near-Nernatian responses over the range 10^?2–10^?6 M or less, with very low limits of detection at around 10^?7 M. The responses are not affected by pH in the range 2–10. The selectivity relative to some inorganic ions, amino acids, neurotransmitters, drugs and various drug excipients is reported.     

Rational design of a DNA wire possessing an extremely high hole transport ability

DNA is a promising conductive biopolymer. However, there are problems that need to be solved to realize real DNA wires. These include the low efficiency of hole transport and the serious oxidative damage that can occur during hole transport. We have demonstrated a protocol for the design of a DNA wire that can effectively mediate hole transport that is not adversely affected by oxidation during hole transport through the DNA duplex. We have synthesized a stable and effective DNA wire by incorporating a designer nucleobase, benzodeazaadenine derivatives, which have lower oxidation potentials and wider stacking areas but are not decomposed during hole transport.     

Photo-driven liquid crystal cell with high sensitivity

The photo-driven LC cell was assembled by sandwiching the liquid crystal material between two quartz or ITO plates covered with a 'command layer', which was fabricated from azobenzene-grafted ladder-like polysilsesquioxanes. The improved response sensitivity of the photo-driven cell, which means a lower threshold driving UV light intensity and a faster risetime, was achieved in two ways: pre-rubbing of the command surface and application of an assisting critical in-plane mode electric field. The response behaviour of the photo-driven cell was measured in situ and data were collected by computer. The results show that the risetime (4 s) under a weak UV intensity of 0.5 mWcm -2 is shorter than previously reported (several tens of seconds) under a greater UV intensity of 3-5 mWcm -2. The improved photo-driven LC cell holds out promise of potential applications in photo-addressing and photo-recording.     

Photo-driven liquid crystal cell with high sensitivity

The photo-driven LC cell was assembled by sandwiching the liquid crystal material between two quartz or ITO plates covered with a 'command layer', which was fabricated from azobenzene-grafted ladder-like polysilsesquioxanes. The improved response sensitivity of the photo-driven cell, which means a lower threshold driving UV light intensity and a faster risetime, was achieved in two ways: pre-rubbing of the command surface and application of an assisting critical in-plane mode electric field. The response behaviour of the photo-driven cell was measured in situ and data were collected by computer. The results show that the risetime (4 s) under a weak UV intensity of 0.5 mWcm -2 is shorter than previously reported (several tens of seconds) under a greater UV intensity of 3-5 mWcm -2. The improved photo-driven LC cell holds out promise of potential applications in photo-addressing and photo-recording.     

Low and high temperature bromination of exocyclic dienes: high temperature bromination. Part 16

The electrophilic addition of bromine to an exocyclic diene, 5,6-dimethylenebicyclo[2.2.1]hept-2-ene, in CCl₄ at 0°C led to the formation of non-rearranged (73%) and rearranged products (27%). However, high temperature bromination of the exocyclic diene at 77°C suppressed the formation of the rearranged products. Similarly, bromination of 9,10-dimethylenetricyclo[6.2.1.0^2,7]undeca-2,4,6-triene at −10°C gave only the exo-1,2-addition product. Bromination at +5°C resulted in the formation of a mixture consisting of exo-1,2- and 1,4-addition products in a ratio of (1:4). High temperature bromination at 77°C resulted in the formation of the endo-1,2-addition product. Furthermore, it has been shown that the 1,4-addition product converts smoothly to the 1,2-addition product. The formation mechanism of the products is discussed and supported by calculations.     

Polypeptides possessing catalytic properties

The catalytic properties of synthetic polypeptides containing L-amino acids with the sequences H-(His-Glu)_n-OH, H-(Ser-Glu)_n-OH, H-(His-Tyr)_n-OH, and H-(Trp-Glu)_n-OH in the hydrolysis of p-NPA (para-nitrophenyl acetate) are considered. The dependences of the rates of the polypeptide-catalyzed hydrolysis of p-NPA on the pH of the medium, the temperature, and the concentration of p-NPA are discussed. V_max, K_m, and K″ — the effective rate constants of the hydrolysis of p-NPA — and K₂ — the constant for the splitting out of p-nitrophenol from the substrate — have been found and calculated.     

Polypeptides possessing catalytic properties

The catalytic properties of synthetic polypeptides containing L-amino acids with the sequences H-(His-Glu)_n-OH, H-(Ser-Glu)_n-OH, H-(His-Tyr)_n-OH, and H-(Trp-Glu)_n-OH in the hydrolysis of p-NPA (para-nitrophenyl acetate) are considered. The dependences of the rates of the polypeptide-catalyzed hydrolysis of p-NPA on the pH of the medium, the temperature, and the concentration of p-NPA are discussed. V_max, K_m, and K — the effective rate constants of the hydrolysis of p-NPA — and K₂ — the constant for the splitting out of p-nitrophenol from the substrate — have been found and calculated.V. I. Lenin Tadzhik State University, Dushanbe. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 503–506, July–August, 1984.     

Strategies for increasing the sensitivity of gadolinium based MRI contrast agents

Gadolinium(III) complexes are often used in clinical MRI to increase contrast by selectively relaxing the water molecules near the complex. There is a desire to improve the sensitivity (relaxivity) of these contrast agents in order to detect molecular targets. This tutorial review describes the molecular factors that contribute to relaxivity and illustrates with recent examples how these can be optimized. It may be of interest to senior undergraduates and more advanced researchers interested in lanthanide chemistry, biophysics, and/or molecular imaging.     

The temperature dependence of radiation sensitivity of large molecules

The change in radiation sensitivity with temperature is quantitatively the same for biological macromolecules and synthetic polymers. The mechanism(s) for this effect is (are) due to secondary processes occurring after the primary ionization and are associated with the presence of free radicals.     

A high sensitivity titration calorimeter using pyroelectric sensor

A new sensitive isothermal titration microcalorimeter using polyvinylidene difluoride (PVDF) as detector has been developed. Heat pulses of less than 0.4 μJ can be detected and the baseline noise level (p-p) is 40 nW. The calorimeter is constructed with one reaction cell (0.7 ml) insulated by several radiation shields inside a vacuum chamber. The performance of the instrument was examined by measuring the heat of protonation of Tris with HCl. The enthalpy of reaction was found to be ?49±1 kJ·mol^?1, in good agreement with the reported value of ?47.5 kJ·mol^?1.