Ellak I. von Nagy-Felsobuki

Tyrosine hydroxylase phosphorylation: regulation and consequences

The rate‐limiting enzyme in catecholamine synthesis is tyrosine hydroxylase. It is phosphorylated at serine (Ser) residues Ser8, Ser19, Ser31 and Ser40 in vitro, in situ and in vivo. A range of protein kinases and protein phosphatases are able to phosphorylate or dephosphorylate these sites in vitro. Some of these enzymes are able to regulate tyrosine hydroxylase phosphorylation in situ and in vivo but the identity of the kinases and phosphatases is incomplete, especially for physiologically relevant stimuli. The stoichiometry of tyrosine hydroxylase phosphorylation in situ and in vivo is low. The phosphorylation of tyrosine hydroxylase at Ser40 increases the enzymes activity in vitro, in situ and in vivo. Phosphorylation at Ser31 also increases the activity but to a much lesser extent than for Ser40 phosphorylation. The phosphorylation of tyrosine hydroxylase at Ser19 or Ser8 has no direct effect on tyrosine hydroxylase activity. Hierarchical phosphorylation of tyrosine hydroxylase occurs both in vitro and in situ, whereby the phosphorylation at Ser19 increases the rate of Ser40 phosphorylation leading to an increase in enzyme activity. Hierarchical phosphorylation depends on the state of the substrate providing a novel form of control of tyrosine hydroxylase activation.

Theoretical studies of the structures of some mono- and di-substituted benzenes

Abstract The structures of some monosubstituted benzenes have been optimized at the ab initio STO—3G level, and, in some cases, also using split valence base sets. It is found that the geometries obtained are in reasonable agreement with experimental gas phase values, particularly as far as substituent induced trends are concerned. The work has been extended to para-disubstituted benzenes to examine the contribution of quinonoid forms. The geometrical evidence and interaction energies obtained indicate that such forms are of minor significance in the neutral molecules, but can be quite significant in ions such as the para-nitrophenoxide anion.

Photoelectron spectra of sulfur dibromide and selenium dibromide

Abstract The photoelectron spectra of gaseous products from reactions of atomic/molecular bromine with powdered sulfur and selenium analysed with a visual assessment stripping program (VASP) yield the He(I) spectra of SBr 2 (sulfur dibromide) and SeBr 2 (selenium dibromide). The proposed assignments are consistent with the results of valence-electron-only model-potential (VEOMP) calculations.

Electrospray Mass Spectrometry of Aqueous Solutions of Isopolyoxo-tungstates

Electrospray mass spectrometry (ESMS) has been conducted on aqueous solutions of isopolyoxotungstate systems. There is direct evidence that the desorption process in the ESMS technique has resulted in significant chemical effects, resulting in the detection of many new anions and cations. For the ammonium polyoxotungstate system, negative-ion ESMS yields ions of the form [HWmO3m+1]−, [WmO3m+1]2−, and [HWmO3m+2]3− (with the latter being better formulated as [H2W2mO6m+4]6−). For the alkali metal polyoxotungstate systems ions of the form [WmO3m+1A]− and [WmO4mA2m−2]2− (where A=Li+, Na+, K+) were observed. For positive-ion ESMS two series were observed, namely, the [WmO4mA2m+1]+ and [WmO4mA2m+2]2+ ions. In the ammonium polyoxotungstate system, aggregates of both the [HWmO3m+1]− and the [WmO3m+1]2− series can be classified as open-chained structures of tetrahedra that are corner shared, whereas the more highly charged anions [H2W2mO6m+4]6− are consistent with closed-packed structures which are based on the structure of paratungstate-B [H2W12O42]10−. For the alkali metal tungstate systems, the ESMS spectra are consistent with open-chained structures of octahedral units that are edge shared, with a terminating tetrahedral unit. Linear correlations suggest that the assembly of these aggregates occurs via an additive polymerization mechanism for which the additive moieties (WO3, WO2+2, and W2O8A4) in aqueous solution can be identified.

New isopolyoxovanadate ions identified by electrospray mass spectrometry

Abstract Ammonium metavanadate in aqueous solution at pH 4.5 displays in electrospray mass spectrometry experiments the presence of the two series of anions [HxVyOz]− (x=0, 1; y=1–9; z=3–23) and [HxVyOz]2− (x=0, 1; y=3–17; z=9–44) as well as [H2VO4]−, [V10O28]6− and [H5V10O28]− ions. Further, the cation series [Hm+1(VO3)m]+ (m=1–6), [Hm−1VmO3m−1]+ (m=4–10) and [Hm−3VmO3m−2]+ (m=6–11) are observed. The series of protonated and unprotonated anions differ by {V2O5} units, the formal building block in these clusters. A range of polyoxovanadates not previously reported have been observed.

Unknown isopolyoxovanadate species detected by electrospray mass spectrometry

Abstract Electrospray mass spectrometry (ES MS) has been used to identify many previously unknown isopolyvanadate anions and cations in aqueous solutions under non-equilibrium conditions. There is direct evidence that the evaporation process in ES MS has resulted in significant chemical effects, thereby generating many of these previously undetected species. As a consequence, ES MS offers insight into the polymerisation process. For the ammonium metavanadate system, negative-ion ES MS yielded two series, namely: [HxVyOz]− (x=0 to 1; y=1 to 10; z=3 to 26) and [HxVyOz]2− (x=0, 1; y=3 to 17; z=9 to 44). Also, the [H2VO4]−, [V10O28]6− and [H5V10O28]− anions were detected. In the positive-ion mode, three series of polyoxovanadate cations were observed, namely: [Hm+1(VO3)m]+, [Hm−1VmO3m−1]+ and [Hm−3VmO3m−2]+. For the alkali metal metavanadate systems ions of the form [AVmO3m−2]− (m=2, 4, 6; A=Li+, Na+ and K+) were detected. In the positive-ion mode, at least two series of the form [Am+1(VO3)m]+ and [Am+3VmO3m+1]+ were observed. In all series, the protonated and unprotonated ions differed by {V2O5} mass units (characterised by ES MS as the formal building block in these clusters). At high cone-voltages, mixed-valence polyoxovanadate anions were observed for all the systems studied. On the other hand, for the positive-ion mode, the only mixed-valence polyoxovandates cations detected were for the potassium system.

Conformational and UV photoelectron spectroscopy analysis of the chalcogenobispyridines

Abstract It is now possible to review the conformational and electronic behaviours of the isomers of chalcogenobispyridines and related compounds, so providing information on the link between the geometric and electronic properties, and providing some insight into their observed and anticipated physical and biological activities. Moreover, observations can now be made on the effect of the bridging atoms (O, S, Se, Te) and positional isomerism on conformation and electronic distributions; on the balance between resonance and inductive effects; and on the energetics of conformer interconversion. As a result of the non-rigid nature of the chalcogenobispyridines and related compounds, it is necessary to determine the preferred geometries to calculate the ionization energies (IEs). For the entire family of the chalcogenobispyridines, the minimum energy structures predict the pyridine ring planes to be nearly perpendicular, allowing maximum overlap of the chalcogen valence orbitals with the π system of only one of the pyridine rings. Rotational barrier height calculations do not support the fully conjugated planar forms on steric grounds, but suggest that a range of near-isoenergetic conformers surround the minimum structure. Ab initio methods (such as restricted Hartree-Fock (HF) methods) were found to assign incorrectly the UV photoelectron spectra of these pyridine-based compounds. While HF methods were shown to be reasonably successful for the prediction of the IEs of the π-type molecular orbitals (MOs), they failed to position the IEs correctly for the long-pair nitrogen MOs (n N ), so requiring the use of computer-intensive configuration interaction (CI) methods. Bands caused by distinct conformers could not be resolved in the UV photoelectron spectra of the chalcogenobispyridines. Conformational analyses predicted low energy pathways for concerted disrotatory motion, permitting a smooth transition between near isoenergetic rotamers. The calculated IEs of the most populated conformers were found to be within the instrumental resolution, so were difficult to resolve. This was supported by the production of ‘synthetic’ spectra. Within the composite-molecule model, correlations with the IEs of pyridine and the methylchalcogenopyridines assisted in the spectral assignment of the chalcogenobispyridines. For each congener, the first IE was assigned to ionization from an anti-bonding π−n x combination in which the contribution of pyridine π character was found to decrease down the group. The spectra recorded with different radiation sources were valuable in identifying bands associated primarily with the chalcogen character.

Electrospray ionisation mass spectroscopic characterisation of isopolyoxo-niobates and -tantalates

Abstract The electrospray ionisation mass spectrometric (ESI MS) characterisation of potassium isopolyoxo-niobate and -tantalate solutions (at pH 11, 10 −3 M), including the mixed Nb/Ta oxometalate system, primarily yields ions that are based on the M 6 O 19 moiety (with some protonation of most species being evident). In both positive ion and negative ion modes, moieties of the form [A m M 6 O 19 ] n ± , [A m M 6 O 18 ] n ± , [A m M 6 O 17 ] n ± and [A m M 6 O 16 ] n − (with A=H and/or K, M=Nb and/or Ta) are evident, with the last three types of species being derived from a formal [M 6 O 19 ] 8− species by the progressive loss of three O 2− ions. In negative ion mode, polymeric species containing 4, 8, 10, 12 and 14 metal atoms are also observed in the single metal systems, many of which can be related by {M 2 O 5 } polymerisation units. Most of these are hydrated species, such as [A 6 M 8 O 24 (H 2 O) n ] 2− and [A 3 M 12 O 33 (H 2 O) n ] 3− (both with M=Nb and Ta), [A 5 Ta 12 O 34 (H 2 O) n ] 3− and [A 3 Nb 14 O 38 (H 2 O) n ] 3− , and are not observed in the ‘mixed’ Nb/Ta oxometalate system.

Electrospray identification of new polyoxochromate species

Abstract Electrospray ionization mass spectrometry (ESI MS) has been conducted on the ammonium and alkali metal (A=Li + , Na + and K + ) dichromate systems. A large number of previously unknown polyoxochromate species have been characterized. Major series that have been identified include [A x +1 H x Cr VI x O 4 x ] + (Li + , x =1–5; Na + , x =1–7; K + , x =1–4) and [A 2 x− 1 Cr VI x O 4 x −1 ] + (Li + , x =2, 3; Na + , x =2–4; K + , x =2, 3) in the alkali metal dichromate systems, and [HCr VI x O 3 x +1 ] − ( x =1–5) in the ammonium dichromate system. Several series also contain mixed oxidation state species, ranging from Cr(V) to Cr(II) in conjunction with Cr(VI), which is consistent with the ease of reduction of Cr(VI). Negative ion ESI MS spectra clearly demonstrate the existence of [HCrO 4 ] − as the most abundant ion at −20 V, suggesting that its existence in solution is not just hypothetical, as was previously thought. The polymerization units for the series observed include {AHCrO 4 }, {A 2 CrO 4 } and {CrO 3 }, with the latter prominent in the alkali metal systems. This presumably arises from the fragmentation of dichromate, A 2 Cr 2 O 7 →{A 2 CrO 4 }+{CrO 3 }. Moreover, the ESI MS of the dichromate compounds have illustrated that the preservation of tetrahedral stereochemistry is of paramount importance for these systems, which leads to only limited polymerization compared to the related molybdate and tungstate systems.

Ab initio calculations on first row transition metal hydrides TMHn+ and helides TMHe(n+1)+ (TM = Sc-Cu, n = 0-2)

Ab initio metods have been employed to investigate first row transition metal hydrides and helides of form: TMHn+ (where n = 0–2) and TMHen+ (where n = 1–3), respectively. Multi-configurational SCF and IC-MRCI methods have been used, along with all-electron ROHF-UCCSD(T) methods, in order to compare trends in the bonding of these series. Equilibrium geometries, dissociation energies and vibrational frequencies have been determined for the low-lying electronic states. A comparison with the diatomic first row transition metal hydrides illustrates the limit of isoelectronic approaches and so further highlights the unique binding properties of helium.