18F-labeling techniques for positron emission tomography

Much research effort has been made to understand various biological processes at levels of molecules using molecular imaging techniques.Because of great sensitivity,high resolution,and rapid detection,positron emission tomography(PET)imaging is becoming one of the most used imaging techniques for medical diagnose and pre-clinical studies.Here we provide a review on molecular imaging and PET imaging.An introduction is also provided on18F-fluorine labeling techniques for the preparation of PET imaging probes.A summary and comparison of currently available18F-fluorine labeling methods is provided.The perspectives for18F-fluorine labeling techniques are also given.     

NMR studies of bond orders in heteroaromatic systems

Fifty-seven values for the ortho-benzylic coupling constant ⁴J_{Me? C?C? H} (henceforth denoted as ⁴J_OB) were obtained for a variety of heteroaromatic systems. It was shown that a good correlation exists between ⁴J_OB when the methyl group is not α to the heteroatom and the SCF-MO bond order. This method can therefore be used as an experimental means of determining bond orders in heteroaromatic systems. An examination of bond alternation in thirteen heteroaromatic systems has given a measure of relative “degree of aromaticity” for a larger number of systems than previously reported by any single method.     

The influence of shear rate, temperature and chain conformation on the critical concentration c

 When viscometry is used, a crossover phenomenon is observed separating the dilute solutions into extremely dilute solutions and dilute solutions. The critical concentration c ^**, determined from this crossover phenomenon, strongly depends on the shear rate in the solution. At very high values of shear rate the critical concentration c ^** becomes very low and depends only on the contour length of the elongated chains of different polymers. An increase of the temperature induces an increase of c ^** because the relaxation time of the chains decreases. If a polymer adopts a rodlike conformation (in a given solvent at a given temperature) the excluded volume of its chains increases and its critical concentration c ^** decreases. Received: 14 October 1996 Accepted: 3 March 1997     

Determination of the silver content of ancient silver coins by neutron activation analysis

A reactor neutron activation analysis procedure for the determination of the silver content of silver coins is described. The samples are irradiated for 1 s, cooled for 85 s and measured for 60 s with a Ge-detector. The analysis is based on the measurement of¹¹⁰Ag and¹⁰⁸Ag. Aluminium is used for flux monitoring and pulse pile-up correction. A calibration curve is prepared by irradiating and measureing a series of discs with known silver contents. An average precision of ±2.1% is obtained. The analysis of coins with known silver contents shows good agreement with the given values. The analysis time is 2.5 minutes per sample.     

Elementary derivation of long-range moments of two coupled centrosymmetric systems

The expression for the long-range dipole moment of a pair of non-identical centrosymmetric systems (varying as R^?7) in terms of frequency-dependent polarizabilities and hyperpolarizabilities is recovered more simply than hitherto. An expression in terms of frequency-dependent quantities for the quadrupole moment of an identical pair (∞ R^?6) is given for the first time.     

Predictions of the bond length and vibrational frequency of Ge2

We present a pseudopotential local spin density calculation of the bond length, vibrational frequency, and binding energy for the ³Σ_g^? state of the germanium dimer. Predictions for the equilibrium bond length and vibrational frequency are given. An overestimate of the binding energy is obtained; this is consistent with other local spin density calculations for sp bonded diatomic molecules.     

Spectral properties of helium‐like ions under strongly coupled plasma conditions

Systematic investigations have been performed to study the effect of strongly coupled plasma on the dynamic polarizabilities, low‐lying energy levels, oscillator strengths, and transition probabilities for the helium isoelectronic ions Li⁺, Be²⁺, B³⁺, C⁴⁺, N⁵⁺, O⁶⁺, F⁷⁺, and Ne⁸⁺. An ion‐sphere (IS) model of the plasma has been adopted and time‐dependent perturbation theory has been applied to calculate the energy levels and other transition properties. Systematic trend is observed for the spectroscopic properties along the isoelectronic sequence under a given plasma strength and also for a given ion under different plasma strengths. The ionization potential for a given ion is found to decrease, and the number of bound excited states has become finite under increased plasma strengths. The spectral line shifts under such plasma environment have been calculated. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Alpha-spectrometry in nuclear fuel analysis

A survey is given of the analysis of actinide nuclides by means ofa-spectrometry in high-level radioactivity process solutions resulting from reprocessing of spent U-Th fuel. Separation of fission products and isolation of the nuclides²²⁸Th,²³¹Pa,²³²U,²³⁷Np and²³⁸Pu are performed by adsorption, ion-exchange, extraction chromatography and extraction techniques. After separation, samples for quantitative determination are prepared by electrodeposition and measured using a silicon-surface barrier detector combined with a multichannel analyzer. An error estimation is given.     

The relationship between proton-proton NMR coupling constants and substituent electronegativities—I : An empirical generalization of the karplus equation

A new coupling constant-torsion angle relation for the three-bond ¹H-¹H spin-spin coupling constant is formulated. The relation includes a correction for the electronegativity of substituents. The correction term is written as a function of the electronegativity, the H-C-C-H torsion angle, and the orientation of each substituent relative to the coupled protons. A dataset consisting of 315 experimental coupling constants was used to derive six empirical parameters by means of an iterative least-squares minimization procedure. The precision of the proposed equation, expressed as the root-mean-square deviation (0.48 Hz), is superior to any hitherto reported. It is shown that separate treatment of CH₂CH₂, CH₂CH and CHCH fragments even improves this precision. An application in the field of monosubstituted cyclohexanes is given.     

Extraction chromatography in the DHDECMP(XAD-4)-HNO3 system

An organic resin impregnated with DHDECMP was prepared for extraction chromatography and used for separation of the actinide elements. A known amount of inert support, Amberlite XAD-4, was contacted with a given amount of the extractant and water. By contacting the three phases for several hours at room temperature, the resin can be modified regardless of its mesh size. It is loaded with (1.13±0.03) g of DHDECMP per 1 g of the support. A given amount of the modified resin was contacted 50 times with fresh 3M nitric acid solution to remove the loosely bound extractant from the support. its amount was less than 1 weight%. As an application,²⁴¹Am was recovered from 3.5M nitric acid waste solution on a column of the modified resin. Decontamination factor for the effluent was 10⁵, while approximately 113 mg of²⁴¹Am was obtained in 0.3M nitric acid eluting solution with 95% efficiency.     

An average fock operator technique of approximate open-shell LCAO-MO-SCF calculation

The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF ^av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE ^ac with the UHF-energy shows thatE _UHF<E ^ac in each case revealing some kind of an upper bound nature ofE ^ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed.     

Time resolved molecular spectroscopy using high power solid state lasers in pulse transmission mode. A re-examination of the Sn← S1 spectra of naphthalene and anthracene

A nanosecond laser spectrometer consisting of a 3nsec ruby/Nd PTM laser, fast detection system and high brightness analysing source is described. An analysis of the geometry considerations is given for crossed beam and collinear arrangement. The excited-state absorption spectra of naphthalene in 3MP at 85°K and 293°K from 14000 to 30000 cm^?1 are given. The results provide a direct method to evaluate the quantum yields for fluorescence φ_f and intersystem crossing φ_T. Also the excited-state absorption spectra of anthracene in PMM from 16000 to 26000 cm^?1 and in 3MP from 26000 to 36000 cm^?1 are reported.     

Heavy fermions: An induced interaction approach

A review of the induced interaction model and its application to the heavy-fermion metals is given. Emphasis is placed on understanding some of the features of the calculation of Bedell and Quader. In particular it is proposed that some of the approximations used by Bedell and Quader can be understood within the context of a two-band Fermi liquid. An application of Fermi liquid theory to UPt₃ allows us to extract the Landau parameter F^a_o. The value obtained for F^a_o is close to that predicted by the induced interaction model. Some arguments are presented for using an isotropic Fermi liquid to describe the main features of heavy-fermion systems.     

Theory of excimer vibrational relaxation and U.V. emission in solid neon

A quantitative explanation is provided for the observed UV emission from Ne₂^* molecules in solid neon. An expression involving only known molecular quantities and lattice parameters is given for the rate of vibrational relaxation of an excimer, initially formed in a highly excited level, by interaction with the phonons. This expression is used to show that relaxation cannot proceed to the ground vibrational level of Ne₂^* during the radiative lifetime of the excimer (at the low temperatures at which the experiments are done). The calculation brings out that the vibrational population is concentrated at the n = 3 level when radiation takes place. The lineshape for dissociative UV emission from the n = 3 state of the excimer is computed, and found in very good agreement with experiment.     

Hydration of the ions Al3+ and Cu2+. An ab initio SCF study

Ab initio calculations are reported for the systems Al(H₂O)_n³⁺ and Cu(H₂O)_n²⁺ with n up to 7. The calculated binding energies increase monotically up to n = 6, with equal binding energies for n = 6 and 7 for the Al³⁺ cation. An estimate of the enthalpy of hydration of Al³⁺ is given, based on model calculations with one or two water molecules from the second solvation shell. An SN1 (dissociative) mechanism for the exchange of the water molecules from the first hydration shell of Al³⁺ appears energetically favorable if the leaving molecule remains in the second hydration shell.     

Application of radioisotopes in the field of nuclear medicine

A comprehensive review has been made to discuss the role of various radionuclides of lanthanide series elements in the field of nuclear medicine. The role of several pharmaceuticals labeled with radiolanthanides and used for investigative purposes like measurement of cerebral blood flow, bone density measurement, bone marrow imaging, etc., have been described. The role of lanthanide radionuclides in radiation synovectomy, radioimmunotherapy, etc., have also been discussed. Methods of preparation of some representative radiopharmaceuticals like¹⁵³Sm-EDTMP,¹⁵³Sm-HYP, have been presented. An outline on the production of carrier free radioisotopes of lanthanide series elements has been given.     

Unusual peak defocusing in capillary GC on hexakis(2,6-diO-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase

An unusual peak defocusing effect influencing chromatographic performance over a limited range of elution temperatures is described for hexakis(2,6-di-O-pentyl-3-O-acetyl)-α-cyclodextrin stationary phase. Since this phenomenon is likely to be dependent on minor details of the cyclodextrin molecule, full assignment of the ¹H- and ¹³C-NMR-spectra are given.     

FT–NMR investigation of 13C?11B coupling. A reappraisal

An earlier short communication on this topic reports some incorrect ¹¹B? ¹³C coupling parameters. The correct data are given together with some ¹⁰B coupling and isomer shift data.     

A modified synthesis of mosher's acid and its use in a sensitive stereoisomer analysis of amino acid derivatives

A convenient and sensitive method for stereoisomer analysis of amino acid derivatives is described. It is based on the ¹⁹F NMR-analysis of mixtures containing epimers of N-.-methoxy-.-trifluoromethyl-phenylacetyl alanine (MTPA). An improved procedure for the synthesis of MTPA is given.