Anton F. Schreiner

CHARACTERIZATION OF CISPLATIN ADDUCTS OF OLIGONUCLEOTIDES BY FAST ATOM BOMBARDMENT MASS SPECTROMETRY

The products of the reaction of the antitumor drug cisplatin (cis-diamminedichloroplatinum(II)) with four oligonucleotide tetramers, d(GpCpGpC), d(GpGpCpC), d(TpGpApT), and d(TpGpCpT), were separated by gel permeation chromatography and characterized by negative- and positive-ion fast atom bombardment (FAB) mass spectrometry. Fragment ions indicating the oligonucleotide sequence and the position of cisplatin binding were observed in MS/MS spectra following collisional activation and B/E-linked scanning. Positive-ion FAB MS/MS spectra were characterized by platinum-containing product ions. Nonplatinated sequence ions and internal fragment ions were present primarily in the negative-ion spectra. The most prominent fragment ions containing platinum were [HB2.Pt.B3H]+ and [HB1.Pt.B2H]+, where B1, B2, and B3 were bases in the oligonucleotide tetramer, one of which was usually guanine. Both singly and doubly charged platinum complexes were observed, probably indicating reduction of Pt(II) during the FAB ionization process. The location of the platinum complex bound to each oligonucleotide sequence could be determined, and the binding sites observed by mass spectrometry were similar to those previously determined by other methods. FAB ionization with collisional activation and MS/MS analysis could serve as a new method for structural analysis of platinated oligonucleotides.

Photolytic dechlorination of 4-chlorophenol in O2-saturated aqueous solutions in the absence of photocatalysts or additives using ArF* (193 nm) and KrF* (248 nm) excimer lasers

Abstract One of the toxic products from chlorine bleaching of wood pulp is 4-chlorophenol (4-CP). Detoxification of such compounds usually requires their dechlorination. The present study involves a fairly detailed comparison of the attempt and success of the photolytic dechlorination of 4-CP in O 2 -saturated aqueous solutions using ArF ∗ (193 nm) and KrF ∗ (248 nm) excimer laser radiation at higher (1.1 × 10 −2 M) and lower (4.5 × 10 −4 M) starting substrate concentrations and comparisons of quantum yield (φ), product distributions, etc. At the higher starting substrate concentration (1.1 × 10 −2 M) the average initial quantum yields, i.e. early in the reaction process, for the disappearance of 4-CP (φ ≈2 0.30) and for the generation of chloride ions (φ ≈2 0.25) were about the same for both 193 and 248 nm radiation. However, when the number of photons absorbed ( n ) became greater than about 3 × 10 20 , more chloride ions (higher φ) were generated with the 193 nm radiation than with the 248 nm radiation. Oligomers were the major products for both wavelengths of radiation, but the quantity of oligomers generated was greater using the 193 nm radiation. At 248 nm a significant amount of hydroquinone was generated, whereas hydroquinone was not detected with the 193 nm radiation. In addition, a significant amount of 4-chlorocatechol was generated during the direct photolysis of 4-CP using either wavelength of radiation. This is a new result for the photolysis of 4-CP at a wavelength longer than 193 nm in the absence of added H 2 O 2 . At the lower starting substrate concentration (4.5 × 10 −4 M) the average initial quantum yields for the disappearance of 4-CP (φ ≈2 0.55) and for the generation of chloride ions (φ ≈2 0.45) were both much greater using the 193 nm radiation than with the 248 nm radiation and 0.10 respectively). At 193 nm oligomers were still the major products generated, but the fraction of oligomeric products generated was less than the fraction at the higher substrate concentration. This is consistent with the fact that at the lower substrate concentration a significant amount of hydroquinone was generated at 193 nm, whereas it was not detected at this wavelength for the higher substrate concentration. During the 248 nm photolysis of 4-CP at this lower starting substrate concentration, hydroquinone was the only major product generated in these experiments. Oligomers were not observed at this lower substrate concentration using 248 nm radiation, whereas oligomers were generated at the higher substrate concentration. The results demonstrate the utility of using an excimer laser for the photolytic dechlorination of 4-CP without added photocatalysts or additives. It is also possible to suggest a number of explanations, given in the text, which are consistent with our findings.

Photolytic dechlorination of 4-chlorophenol using an ArF* excimer laser

A photochemical study of the dechlorination of 4-chlorophenol (I) in O 2 - and N 2 -saturated aqueous solutions under 193 nm radiation was carried out using an ArF * excimer laser. Higher (1.07×10 -2 M) and lower (4.49×10 -4 M) initial concentrations were studied. At the higher substrate concentration, the quantum yields for the disappearance of I (Φ0.30) and for the generation of chloride ions (Φ0.25) were independent of the dissolved gas (O 2 - or N 2 -saturated). It is also of interest that a significant amount of 4-chlorocatechol was generated at this higher substrate concentration. Finding 4-chlorocatechol is a new result for the direct photolysis of I in the absence of added H 2 O 2 . For the lower substrate concentration, the average quantum yields for the initial disappearance of I (Φ0.55) and for the initial generation of chloride ions (Φ0.45) were both larger than the quantum yields obtained with the higher substrate concentration. It was found beyond the initial radiation times (n>3×10 20 photons absorbed by the solutions), that the dechlorination of I in the O 2 -saturated solutions was slightly more efficient than the N 2 -saturated solutions, whereas initially they were approximately the same for both the O 2 - and N 2 -saturated solutions. Different products from the dechlorination of I were observed depending on the initial substrate concentration. At the higher initial substrate concentration, the major products from the dechlorination of I were oligomers. At the lower initial substrate concentration, hydroquinone was the major product in O 2 -saturated solutions, but oligomers were still the major product when these solutions were N 2 -saturated. Explanations for the observations are given and are consistent with these findings

Molecular and crystal structures of halopentaamminerhodium-(III) complexes, [Rh(NH3)5Cl]Cl2 and [Rh(NH3)5Br]Br2

The crystal and molecular structures of the title compounds have been determined by three-dimensional single-crystal X-ray techniques. All crystallographic details are fully reported. The major chemical conclusion for the pair, [Rh(NH3)5Cl]Cl2 and [Rh(NH3)Br]Br2, is that neither Cl nor Br exert a static intramoleculartrans effect. Furthermore, the two halogens have the same static electronic structural effect on the [RhIII(NH3)5] fragment. The conclusions shed much light on spectroscopic, thermodynamic and kinetic data of other compounds.

THE QUANTITATIVE INTEPRETATION OF A/D PARAMETERS FOR ELECTRONIC EXCITATION MO ASSIGNMENTS OF TRANS-[M(CO)4(P(n-Bu)3)2] (M = Cr, Mo, AND W) BASED ON ELECTRONIC MCD AND COMPLETE OPERATOR MATRIX 〈Lz〉 EVALUATION

Abstract Electronic absorption (EA) and magnetic circular dichroism (MCD) spectra of trans-[M(CO)4(P(n-Bu)3)2] (M = Cr, Mo, W) of five bands from ∼20.0 × 103 to ∼45.5 × 103 cm−1 were measured. The EA spectra exhibit three dominant bands, I-III, at about 27 × 103 cm−1, 30 × 103 cm−1, and 39 × 103 cm−1, respectively. Corresponding MCD spectra in the region of both hands I and III are dominated by the presence of positive A-terms, indicative of transitions to degenerate excited states. A-terms and dipole strength (D) parameters were extracted by rigorous spectral deconvolution for the Cr complex; the spectra of the Mo and W analogs are quite similar. Since these are charge transfer bands and a number of the 2-center and 3-center integrals of 〈Lz〉 will be large, multi-zeta all-center operator matrix computations were used to evaluate signs and magnitudes of MCD A/D parameters for all degenerate excited-state electronic configurations of statically electric dipole allowed g → u (MLCT, or ·M → π∗(CO)) type tran...

A combination spectrophotometer for measuring electronic absorption, natural circular dichroism, and magnetic circular dichroism spectra

The design, construction, and evaluation of a combination spectrometer for measuring electronic absorption (EA), natural circular dichroism (CD), and magnetic circular dichroism (MCD) are described. Around the optical components of a JASCO ORD/UV‐5 spectropolarimeter, a new EA/CD/MCD instrument was built with the realized intentions of increasing sensitivity and upgrading the analog tube type circuitry to a solid‐state digitally, computer‐controlled spectrophotometer. It is a flexible, dynamic, and user‐controllable system, interfaced to an Apple II Plus computer, for studying instrument and signal parameters. The monochromator (M), photoelastic modulator (PEM), photomultiplier tube applied voltage (PMHV), and photomultiplier tube dc output current (PMdc) are under complete and independent software control. Our system has two unique aspects for obtaining the circular dichroism. First, the ac signal is measured with a voltage‐to‐frequency (V/f) converter; and, second, both the ac and the dc are independent...

Radiative Recombinations in be-Doped Alx Ga1-x As

Abstract Six types of systematic photoluminescence (PL) surements (T ≥ 77 K) were carried out on single crystals of AlxGa1-xAs (x ~ 0.3) undoped or doped with Be by LPE or ion implantation. The multimea-surements approach was employed in order to ascertain that the highest-energy radiative recombination was in fact band-to-band (BTB), and consequently to obtain accurate activation energies. LPE doped crystal luminescence consisted of a high-energy BTB peak and a lower energy shoulder (observed near 77K) assigned to free electron to bound (FTB) hole reconbination at the Be acceptor center. All Be implanted AlxGa1-xAs specimens had BTB radiative recombinations at T ≥ 77 K. The lower energy FTB shoulder, observed between 85 and 77K, appeared only for crystals annealed at or above 800°C, i.e., the higher temperatures are necessary to activate the implanted Be dopant in AlxGal-xAs. In addition to the BTB and FTB peaks, a PL peak at ~ 1.29 eV is attributed to implantation damaqe.

Readily constructed modular polarization‐emission scanning spectrometer

A modular polarization spectrometry system for the measurement of the degree of polarization (linear or circular) of luminescence intensity is described. It is based on polarization modulation with a photoelastic modulator and two lock‐in amplifiers for signal recovery. Interfaced to the spectrometer is a microcomputer configured with CRT monitor, disk drive, and digital printer to provide system control and to permit digital data storage and data manipulations such as multiple scan averaging and averaged background subtraction. The system described is capable of measuring linearly polarized emission, linearly polarized excitation luminescence, and circularly polarized emission spectra. The modular design also allows the spectrometer to be rapidly and easily modified for the measurement of circular dichroism, magnetic circular dichroism, or magnetic circularly polarized emission. The system performance is demonstrated.

Growth and photoluminescence study of several single crystal segments relevant to monolithic semiconductor cascade solar cells

Several representative single crystal stacked layers of III–V compound and alloy semiconductors were grown which are spatial regions relevant to a monolithic cascade solar cell, including the substrate, n-GaAs(Si), which was pre-growth heat treated in H2(g) prior to its use. These structures were then studied by cryogenic laser excited photoluminescence (PL), and the substrate portion was explored in a depth profiling mode. Within the forbidden band gap region up to seven recombinations were observed and identified for undoped GaAs layers or the GaAs(Si) substrate, and several other PL recombinations were observed for undoped AlxGa1−xAs and AlyGa1−ySbzAs1−z layers. In addition to the valence and conduction bands, these optical bands are also associa ted with the presence of CGa, SiGa, SiAs, CuGa, VAs, VGa and vacancy-impurity complexes involving several of these defect types even in the absence of intentional doping. The findings also relate to problems of self-compensation and type inversion, so that the need for growth modifications is indicated.

High‐current transistor‐based regulator for the stabilization of 450‐W xenon lamps

A stable high‐current transistor‐based regulator has been designed to stabilize 450‐W dc xenon arc lamps. The circuit employs commercially available components. The regulator provides stabilization beyond that found in commercial optical instruments. The improvements using this circuit are a 0.20% ac‐to‐dc regulation representing a 44% decrease in the peak‐to‐peak ac ripple, achievement of nondrifting dc level, and being able to use the spectrometer immediately following lamp ignition.