Enthalpies of combustion of 2,2-trans-4,6- (1) and 4,4,6,6-tetramethyl- (2) and 2,4,4,6,6- (3) and 2,2,4,4,6-pentamethyl-1,3-dioxanes (4) were determined to estimate their enthalpies of formation in the gas phase. By comparing the latter with the corresponding enthalpies estimated based on the various bond–bond interactions allowed to determine the chair–2,5-twist energy difference (ΔHCT = 29.8 kJ mol–1) for 1 since C-13 shift correlations indicate that it escapes to the 2,5-twist form where the 2-methyl groups are isoclinal and 4- and 6-methyl groups pseudoequatorial to avoid syn-axial interactions. Compounds 2 and 3 in turn give the values 21.0 and 21.6 kJ mol–1 for the 4,6-diaxial Me,Me-interaction. Finally compound 4, which retains the chair conformation to avoid pseudoaxial interactions in the twist forms gives the value 19.5 kJ mol–1 for the 2,4-diaxial Me,Me-interaction indicating that its chair form appears to be somewhat deformed.

As a continuum to our work with coumarins, 12 psoralens were synthesized and evaluated for their anti‐inflammatory activity. Psoralens were prepared in three steps; at first, 7‐hydroxycoumarins were synthesized by von Pechmann condensation and then converted to 7‐(2‐oxopropoxy)coumarins. In the final step, a fused furan ring was introduced in an intramolecular ring‐formation reaction. Based on a SciFinder search, two out of the 12 synthesized psoralen derivatives (compounds 9 and 12) were found to be novel. The derivatives displayed anti‐inflammatory activity by suppressing iNOS and IL‐6 expression, but their mechanism of action seemed to be dependent on the substitution. Compound 6 with propyl side chain inhibited NF‐κB mediated transcription, while compound 10 with a phenyl substituent down‐regulated iNOS expression in a posttranscriptional manner. The results introduce psoralen derivatives as promising anti‐inflammatory compounds with potential for treatment of conditions involving iNOS and/or IL‐6‐mediated adverse responses.

A number of 7-hydroxycoumarins have been synthesised by Pechmann cyclisation using differently substituted resorcinols employing perchloric acid as the condensing agent. All the compounds have been characterised by analytical and spectroscopic methods. The anti-inflammatory properties were tested with LPS-induced inflammation in J774 macrophages. Expression of iNOS and COX-2 was determined by Western blot, NO by nitrite assay and IL-6 by ELISA analyses. Fifteen of the tested 7-hydroxycoumarins also inhibited IL-6 production but none of them had any major inhibitory effect on COX-2 expression.

AbstractNovel 7‐hydroxycoumarin derivatives (III) are synthesized by Pechmann cyclization.

The gas-phase behavior and stability of [RuX2(CO)(2)(dcbpy)], [OsX2(CO)(2)(dcbpy)], and [OsI2(CO)(2)(mcbpy)] (X = Cl, Br, I; dcbpy = 2,2'-bipyridine-4,4'-dicarboxylic acid; mcbpy = 2,2'-bipyridine-4-carboxylic acid) were studied by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Negative-ion ESI produced abundant singly and doubly deprotonated molecules for all of the compounds, without apparent changes in the metal atom oxidation state or the ligand coordination. The characteristic fragment ions resulting from the decarboxylation (loss of CO2) in one of the carboxylic acid substituents of the dcbpy ligand were also observed. The gas-phase fragmentation was investigated by means of collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) techniques. The most favored fragmentation pathway included the loss of CO2, followed by one or two decarbonylations. Fragmentation was observed to be both qualitatively and quantitatively dependent on the metal atom and the surrounding ligands. Generally, the compounds of osmium were considerably more stable than those of ruthenium, owing to the higher metal-carbonyl bond energies. On the basis of the ionic structures observed experimentally, the fragmentation processes were also investigated computationally at the DFT level of theory. The most likely fragmentation routes predicted by the calculations agreed well with the experimental findings. The computational structures of the different fragment anions provided additional information about the effect of the carboxylic acid substituents on the stability of the ruthenium and osmium complexes.

Chiral discrimination of seven enantiomeric pairs of beta-3-homo-amino acids was studied by using the kinetic method and trimeric metal-bound complexes, with natural and unnatural alpha-amino acids as chiral reference compounds and divalent metal ions (Cu2+ and Ni2+) as the center ions. The beta-3-homo-amino acids were selected for this study because, first of all, chiral discrimination of beta-amino acids has not been extensively studied by mass spectrometry. Moreover, these beta-3-homo-amino acids studied have different aromatic side chains. Thus, the emphasis was to study the effect of the side chain ( electron density of the phenyl ring, as well as the difference between phenyl and benzyl side chains) for the chiral discrimination. The results showed that by the proper choice of a metal ion and a chiral reference compound, all seven enantiomeric pairs of beta-3-homo-amino acids could be differentiated. Moreover, it was noted that the beta-3-homo-amino acids with benzyl side chains provided higher enantioselectivity than the corresponding phenyl ones. However, increasing or decreasing the electron density of the aromatic ring by different substituents in both the phenyl and benzyl side chains had practically no role for chiral discrimination of beta-3-homo-amino acids studied. When copper was used as the central metal, the phenyl side chain containing reference molecules (S)-2-amino-2-phenylacetic acid (L-Phg) and (S)-2-amino-2-(4-hydroxyphenyl)-acetic acid (L-4'-OHPhg) gave rise to an additional copper-reduced dimeric fragment ion, [Cu-I(ref)(A)](+). The inclusion of this ion improved noticeably the enantioselectivity values obtained. Copyright (C) 2010 John Wiley & Sons, Ltd.

Molecular recognition of Glu, Glc(2)-Glc(6) and Mal(3) by a tetrakis(bile acid)-porphyrin conjugate has been studied by using EST-FTICR mass spectrometry. The bile acid conjugate was observed to form 1:1 noncovalent complexes with saccharides, The conjugate was found to have size-selectivity towards saccharides with three or more glucose residues. The Glc(3) and Glc(4) also formed kinetically the most stable complexes. The electron capture dissociation (ECD) experiments revealed that in complexation of an oligosaccharide three glucose residues interact with the bile acid conjugate, whereas additional glucose residues are susceptible to fragmentation. The ECD results also showed the significance of the porphyrin centre for complexation of an intact oligosaccharide. It is obvious that the complexation of an intact sugar requires at least one bile acid side arm and the porphyrin centre.

Differentiation of beta-amino acid enantiomers with two chiral centres was investigated by kinetic method with trimeric metal-bound complexes. Four enantiomeric pairs of beta-amino acids were studied: cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)- and trans-(1S,2S)-2-aminocyclopentanecarboxylic acids (cyclopentane beta-amino acids), and cis-(1R,2S)-, cis-(1S,2R)-, trans-(1R,2R)-, and trans-(1S,2S)-2-aminocyclohexanecarboxylic acids (cyclohexane beta-amino acids). The results showed that the choice of metal ion (Cu(2+), Ni(2+)) and chiral reference compound (alpha- and beta-amino acids) had an effect on the enantioselectivity. Especially, aromaticity of the reference compound was noted to enhance the enantioselectivity. The fixed-ligand kinetic method, a modification of the kinetic method, was then applied to the same beta-amino acids, with dipeptides used as fixed ligands. With this method, dipeptide containing an aromatic side chain enhanced the enantioselectivity.

The reactions between the diphosphino-alkynyl gold complexes (XC6H4C2Au)PR2-C6H4-PR2(AuC2C6H4X) with Cu+ lead to the formation of a family of heterometallic clusters of the general formula [{Au3Cu2(C2C6H4X)6}Au3(PR2C6H4PR2)3][PF6]2 (X = NO2, H, OMe, NMe2; R = C6H5, NC4H4). These complexes adopt the same structural pattern and consist of a heterometallic alkynyl cluster [Au3Cu2(C2C6H4X)6]- "wrapped" by the cationic [Au3(PR2C6H4PR2)3]3+ "belt". The novel compounds were characterized by NMR spectroscopy and ESI-MS measurements. A systematic study of their luminescence properties revealed efficient room-temperature phosphorescence in solution with remarkably weak quenching by molecular oxygen. The photophysical experiments demonstrate that the increase in the electron donor ability of the alkynyl ligands and the electron-withdrawing character of the diphosphines results in the bathochromic shift of emission maxima (in the 576-686 nm range) and a decrease in the luminescence quantum yield. The electronic structure calculations showed that variations of X or R substituents have very little effect on the structural parameters but display a significant influence on the electronic properties of the clusters and characteristics of luminescence. The metal-centered triplet emission within the heterometallic alkynyl cluster is suggested to play a key role in the observed phosphorescence.

Twenty-two substituted 7-hydroxycoumarins were studied by negative ion electrospray ionization collision- induced dissociation (CID) mass spectrometry. Fragmentation pathways were also investigated by computation method using the B3LYP density functional theory. In general, the most important fragmentations of the 7- hydroxycoumarin [M - H](-) ions were the elimination of CO(2) and CO which agreed with the calculated energies of the proposed fragmentation reactions. In most cases, methyl group elimination was also favorable. Methyl group elimination occurred in three different ways, the most interesting being hydrogen rearrangement from a neighboring alkyl group to a ring carbon, which led to a benzyl radical formation. In some cases, CH(2)CO elimination was observed as well. Isomeric compounds gave rise to different CID spectra.

The H-bonding in alkylammonium complexes of phosphonate cavitands were studied by mass spectrometric methods and theoretical calculations. The alkylammonium ions included primary, secondary, and tertiary methyl- and ethylammonium ions. Their complexation with mono-, tetra-, and two di-phosphonate cavitands, which differ according to the number and position of H-bond acceptor P = O groups, was evaluated by using different competition experiments, energy-resolved CID, gas-phase H/D-exchange, and ligand-exchange reactions, together with ab initio theoretical optimization of the complexes. The phosphonate cavitands with two or more adjacent P = O groups were found to be selective towards secondary alkylammonium ions, due to simultaneous formation of two stable hydrogen bonds. In the ion-molecule reactions (both H/D- and ligand-exchange), the formation of two stable hydrogen bonds was observed either to slow down the reaction or to completely prevent it. This was, however, limited to situations where two hydrogen bonds are formed between the H-bond donor sites of the alkyl ammonium ion and the vicinal H-bond acceptor sites of the cavitand.

The gas-phase recognition of native amino acids and the conformational properties of three glucosylthioureidocalix[4]arenes (1-3) were studied theoretically and experimentally using ab initio calculations, ESI-FTICR, H-1 and C-13 NMR MS. The conformational and complexation properties of the glucocalixarenes were dependent on the number of glucose units at the upper rim and the length of the alkyl chains at the lower rim of the calixarene skeleton. ESI-MS experiments showed the compounds to form 1:1 complexes with the amino acids, with a marked preference for amino acids containing an aromatic nucleus and an additional H-bonding group in their side chain (Trp, Tyr, Phe >> Ser, Leu and Asp). The experimental data were rationalized by the results of ab initio calculations. ESI-MS competitions carried out with enantiomeric-labelled (EL) amino acids showed enantiomeric selectivities ranging from 0.61 (Phe(D)/Phe(L) with ligand 3) to 2.58 (Tyr(D)/Tyr(L) with ligand 2). In gas-phase hydrogen-deuterium (H/D) exchange reactions, diglucosylcalix[4] arene 2 exhibited extremely slow exchange rates, which were attributed to the close proximity and strong hydrogen bonding between the facing glucosylthioureido groups. H/D exchange rates were much higher for the tetraglucosylcalix[4] arenes 1 and 3 and their amino acid complexes, and the more rigid tetrapropoxy derivative 3 showed more selective H/D exchange reactions than the calixarene 1. Bi-or trimodal H/D exchange distribution was observed for the tetraglucosyl derivatives indicating that these ligands exist in multiple isomeric forms in gas phase.

Metal complex formation was investigated for di-exo-, di-endo- and trans-2,3- and 2,5-disubstituted trinorbornanediols, and di-exo- and di-endo- 2,3-disubstituted camphanediols using different divalent transition metals (Co(2+), Ni(2+), Cu(2+)) and electrospray ionization quadrupole ion trap mass spectrometry. Many metal-coordinated complex ions were formed for cobalt and nickel: [2M+Met](2+), [3M+Met](2+), [M-H+Met](+), [2M-H+Met](+), [M+MetX](+), [2M+MetX](+) and [3M-H+Co](+), where M is the diol, Met is the metal used and X is the counter ion (acetate, chloride, nitrate). Copper showed the weakest formation of metal complexes with di-exo-2,3-disubstituted trinorbornanediol yielding only the minor singly charged ions [M-H+Cu](+), [2M-H+Cu](+) and [2M+CuX](+). No clear differences were noted for cobalt complex formation, especially for cis-2,3-disubstituted isomers. However, 2,5-disubstituted trinorbornanediols showed moderate diastereomeric differentiation because of the unidentate nature of the sterically more hindered exo-isomer. trans-Isomers gave rise to abundant [3M-H+Co](+) ion products, which may be considered a characteristic ion for bicyclo[221]heptane trans-2,3- and trans-2,5-diols. To differentiate cis-2,3-isomers, the collision-induced dissociation (CID) products for [3M+Co](2+), [M+CoOAc](+), [2M-H+Co](+) and [2M+CoOAc](+) cobalt complexes were investigated. The results of the CID of the monomeric and dimeric metal adduct complexes [M+CoOAc](+) and [2M-H+Co](+) were stereochemically controlled and could be used for stereochemical differentiation of the compounds investigated. In addition, the structures and relative energies of some complex ions were studied using hybrid density functional theory calculations.

ABSTRACT The effects of different structural features on the thermostability of Thermopolyspora flexuosa xylanase XYN10A were investigated. A C-terminal carbohydrate binding module had only a slight effect, whereas a polyhistidine tag increased the thermostability of XYN10A xylanase. In contrast, glycosylation at Asn26, located in an exposed loop, decreased the thermostability of the xylanase. The presence of a substrate increased stability mainly at low pH.

Chiral differentiation of four enantiomeric pairs of β -amino acids, cis -(1 R ,2 S )-, cis -(1 S ,2 R )-, trans -(1 R ,2 R )-, and trans -(1 S ,2 S )-2-aminocyclopentanecarboxylic acids (cyclopentane β -amino acids), and cis -(1 R ,2 S )-, cis -(1 S ,2 R )-, trans -(1 R ,2 R )-, and trans -(1 S ,2 S )-2-aminocyclohexanecarboxylic acids (cyclohexane β -amino acids) was performed successfully by using host-guest complexes and ion/molecule reactions. The experiments were conducted by using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. The effect of a chiral host molecule was tested by using three different host compounds; (+)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, (−)-(18-Crown-6)-2,3,11,12-tetracarboxylic acid, and β -cyclodextrin. This is the first time that small enantiomeric pairs with two chiral centers have been differentiated using ion/molecule reactions and host-guest complexes.

Two gas oil Samples, untreated feed and hydrotreated product oil, were analyzed. Both basic and acidic polar species were detected by electrospray ionization (ESI) Fourier transform ion Cyclotron resonance mass spectrometry, and the detected species were characterized on the basis of their elemental compositions. Samples were real refinery samples, with one sample being a certain distillation fraction of crude Oil (feed) and the other sample being a hydrotreated feed oil (product). Comparison of the compositions of untreated and hydrotreated oil provides insight into (1) compounds that are resistant to processing, (2) compounds that are removed/degraded by processing, and (3) new compounds that are produced during processing. N-1 class compounds were found to be the most abundant basic species in both oil samples. In addition, the proportion of N-1 class compounds was clearly greater in the product oil than in the feed oil, which indicates that these basic species must be resistant to removal by hydrotreatment. All basic NxOy-, NxSz-, arid NxOySz-containing compounds that were detected in the feed oil were completely removed by hydrotreatment. However. some of the OySz Compounds remained in the oil after hydrotreatment. Negative-ion ESI revealed that the majority of the acidic polar species in the product sample were IN, compounds, which was also the predominant class in the feed sample. The second most abundant species were the O-y-containing compounds. All of the O-1 compounds that were detected in the feed oil were degraded during the hydrotreatment process, as were the O-2 compounds with double-bond equivalent (DBE) values > 4. Acidic NxOy-, NxSz-, OySz-, and NxOySz-containing compounds were not completely removed by the processing, but the relative abundances of these species were no longer significant in the product oil.

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. The molecular recognition properties of the third-generation tetraphosphonate cavitands toward alcohols and water at the gas-solid interface have been evaluated by means of three complementary techniques and compared to those of the parent mono- and diphosphonate cavitands. The combined use of ESI-MS and X-ray crystallography defined precisely the host-guest association at the interface in terms of type, number, strength, and geometry of interactions. Quartz crystal microbalance (QCM) measurements then validated the predictive value of such information for sensing applications. The importance of energetically equivalent multiple interactions on sensor selectivity and sensitivity has been demonstrated by comparing the molecular recognition properties of tetraphosphonate cavitands with those of their mono- and diphosphonate counterparts.

Chicken avidin is a key component used in a wide variety of biotechnological applications. Here we present a circularly permuted avidin (cpAvd4→3) that lacks the loop between β‐strands 3 and 4. Importantly, the deletion of the loop has a positive effect on the binding of 4′‐hydroxyazobenzene‐2‐carboxylic acid (HABA) to avidin. To increase the HABA affinity of cpAvd4→3 even further, we mutated asparagine 118 on the bottom of the ligand‐binding pocket to methionine, which simultaneously caused a significant drop in biotin‐binding affinity. The X‐ray structure of cpAvd4→ 3(N118M) allows an understanding of the effect of mutation to biotin‐binding, whereas isothermal titration calorimetry revealed that the relative binding affinity of biotin and HABA had changed by over one billion‐fold between wild‐type avidin and cpAvd4→3(N118M). To demonstrate the versatility of the cpAvd4→3 construct, we have shown that it is possible to link cpAvd4→3 and cpAvd5→4 to form the dual‐chain avidin called dcAvd2. These novel avidins might serve as a basis for the further development of self‐organising nanoscale avidin building blocks.

The noncovalent complexation of tetraethyl and tetraphenyl resorcinarenes with mono-, di-, and oligosaccharides was studied with negative-polarization electrospray ionization quadrupole ion trap and electrospray ionization Fourier-transform ion cyclotron resonance mass-spectrometric analysis. The saccharides formed 1:1 complexes with deprotonated resorcinarenes, which exhibited clear size and structure selectivity in their complexation. In the case of the monosaccharides, hexoses formed much more abundant and kinetically stable complexes than pentoses or deoxyhexoses. A comparison of the mono-, di-, and oligosaccharides revealed that both the relative abundance and stability of the complexes increase up to biose and triose, but start to decrease after that point, as the length of the oligosaccharide is increased. This behavior was rationalized by comparing the lowest-energy conformations of the complexes formed between the resorcinarene and oligosaccharides. This comparison was achieved by using theoretical calculations and X-ray crystal studies.