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Hydrogen gas, H2, is generated in serpentinizing hydrothermal systems, where it has supplied electrons and energy for microbial communities since there was liquid water on Earth. In modern metabolism, H2 is converted by hydrogenases into organically bound hydrides (H–), for example, the cofactor NADH. It transfers hydrides among molecules, serving as an activated and biologically harnessed form of H2. In serpentinizing systems, minerals can also bind hydrides and could, in principle, have acted as inorganic hydride donors—possibly as a geochemical protoenzyme, a ‘geozyme’— at the origin of metabolism. To test this idea, we investigated the ability of H2 to reduce NAD+ in the presence of iron (Fe), cobalt (Co) and nickel (Ni), metals that occur in serpentinizing systems. In the presence of H2, all three metals specifically reduce NAD+ to the biologically relevant form, 1,4-NADH, with up to 100% conversion rates within a few hours under alkaline aqueous conditions at 40 °C. Using Henry's law, the partial pressure of H2 in our reactions corresponds to 3.6 mm, a concentration observed in many modern serpentinizing systems. While the reduction of NAD+ by Ni is strictly H2-dependent, experiments in heavy water (2H2O) indicate that native Fe can reduce NAD+ both with and without H2. The results establish a mechanistic connection between abiotic and biotic hydride donors, indicating that geochemically catalysed, H2-dependent NAD+ reduction could have preceded the hydrogenase-dependent reaction in evolution.

The possible evolutionary significance of pyrophosphate (PPi) has been discussed since the early 1960s. Lipmann suggested that PPi could have been an ancient currency or a possible environmental source of metabolic energy at origins, while Kornberg proposed that PPi vectorializes metabolism because ubiquitous pyrophosphatases render PPi forming reactions kinetically irreversible. To test those ideas, we investigated the reactions that consume phosphoanhydride bonds among the 402 reactions of the universal biosynthetic core that generates amino acids, nucleotides, and cofactors from H2, CO2, and NH3. We find that 36% of the core’s phosphoanhydride hydrolyzing reactions generate PPi, while no reactions use PPi as an energy currency. The polymerization reactions that generate ~80% of cell mass – protein, RNA, and DNA synthesis – all generate PPi, while none use PPi as an energy source. In typical prokaryotic cells, aminoacyl tRNA synthetases (AARS) underlie ~80% of PPi production. We show that the irreversibility of the AARS reaction is a kinetic, not a thermodynamic effect. The data indicate that PPi is not an ancient energy currency and probably never was. Instead, PPi hydrolysis is an ancient mechanism that imparts irreversibility, as Kornberg suggested, functioning like a ratchet’s pawl to vectorialize the life process toward growth. The two anhydride bonds in nucleoside triphosphates offer ATP-cleaving enzymes an option to impart either thermodynamic control (Pi formation) or kinetic control (PPi formation) upon reactions. This dual capacity explains why nature chose the triphosphate moiety of ATP as biochemistry’s universal energy currency.

The metabolism of cells contains evidence reflecting the process by which they arose. Here, we have identified the ancient core of autotrophic metabolism encompassing 404 reactions that comprise the reaction network from H2, CO2, and ammonia (NH3) to amino acids, nucleic acid monomers, and the 19 cofactors required for their synthesis. Water is the most common reactant in the autotrophic core, indicating that the core arose in an aqueous environment. Seventy-seven core reactions involve the hydrolysis of high-energy phosphate bonds, furthermore suggesting the presence of a non-enzymatic and highly exergonic chemical reaction capable of continuously synthesizing activated phosphate bonds. CO2 is the most common carbon-containing compound in the core. An abundance of NADH and NADPH-dependent redox reactions in the autotrophic core, the central role of CO2, and the circumstance that the core’s main products are far more reduced than CO2 indicate that the core arose in a highly reducing environment. The chemical reactions of the autotrophic core suggest that it arose from H2, inorganic carbon, and NH3 in an aqueous environment marked by highly reducing and continuously far from equilibrium conditions. Such conditions are very similar to those found in serpentinizing hydrothermal systems.

Life as we know it would not exist without water. However, water molecules not only serve as a solvent and reactant but can also promote hydrolysis, which counteracts the formation of essential organic molecules. This conundrum constitutes one of the central issues in origin of life. Hydrolysis is an important part of energy metabolism for all living organisms but only because, inside cells, it is a controlled reaction. How could hydrolysis have been regulated under prebiotic settings? Lower water activities possibly provide an answer: geochemical sites with less free and more bound water can supply the necessary conditions for protometabolic reactions. Such conditions occur in serpentinising systems, hydrothermal sites that synthesise hydrogen gas via rock-water interactions. Here, we summarise the parallels between biotic and abiotic means of controlling hydrolysis in order to narrow the gap between biochemical and geochemical reactions and briefly outline how hydrolysis could even have played a constructive role at the origin of molecular self-organisation.

Hydrogen gas, H2, is generated in alkaline hydrothermal vents from reactions of iron containing minerals with water during a geological process called serpentinization. It has been a source of electrons and energy since there was liquid water on the early Earth, and it fuelled early anaerobic ecosystems in the Earth’s crust1–3. H2is the electron donor for the most ancient route of biological CO2fixation, the acetyl-CoA (or Wood-Ljungdahl) pathway, which unlike any other autotrophic pathway simultaneously supplies three key requirements for life: reduced carbon in the form of acetyl groups, electrons in the form of reduced ferredoxin, and ion gradients for energy conservation in the form of ATP4,5. The pathway is linear, not cyclic, it releases energy rather than requiring energy input, its enzymes are replete with primordial metal cofactors6,7, it traces to the last universal common ancestor8and abiotic, geochemical organic syntheses resembling segments of the pathway occur in hydrothermal vents today9,10. Laboratory simulations of the acetyl-CoA pathway’s reactions include the nonenzymatic synthesis of thioesters from CO and methylsulfide11, the synthesis of acetate12and pyruvate13from CO2using native iron or external electrochemical potentials14as the electron source. However, a full abiotic analogue of the acetyl-CoA pathway from H2and CO2as it occurs in life has not been reported to date. Here we show that three hydrothermal minerals — awaruite (Ni3Fe), magnetite (Fe3O4) and greigite (Fe3S4) — catalyse the fixation of CO2with H2at 100 °C under alkaline aqueous conditions. The product spectrum includes formate (100 mM), acetate (100 μM), pyruvate (10 μM), methanol (100 μM), and methane. With these simple catalysts, the overall exergonic reaction of the acetyl-CoA pathway is facile, shedding light on both the geochemical origin of microbial metabolism and on the nature of abiotic formate and methane synthesis in modern hydrothermal vents.

Rock–water–carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe3O4) plus H2. The hydrogen can generate native metals such as awaruite (Ni3Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H2 and CO2 under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate—intermediates of the acetyl-CoA pathway, the most ancient pathway of CO2 fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni0 in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO2-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase—the only enzyme on Earth that reduces N2—is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe3O4 and H2, the catalyst and reductant for industrial CO2 hydrogenation and for N2 reduction via the Haber–Bosch process. In both industrial processes, an Fe3O4 catalyst is matured via H2-dependent reduction to generate Fe5C2 and Fe2N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways.

Step-Scan-FTIR spectroscopy has been used to measure the infrared spectrum of xanthone in the triplet state using chloroform as solvent. Xanthone is an important triplet sensitizer and therefore suitable as model system. Xanthone was excited at 266 nm and its IR triplet spectrum measured in the range 1000–1750 cm−1. The spectrum was analyzed by comparison with DFT/B3LYP/TZVP/COSMO calculations. Further on the results were compared to gas phase IR measurements of triplet xanthone and calculations of isolated xanthone. Mainly based on the calculations we tried to identify the geometry changes from the electronic ground state to the first triplet state.

If life on Earth started out in geochemical environments like hydrothermal vents, then it started out from gasses like CO 2 , N 2 and H 2 . Anaerobic autotrophs still live from these gasses today, and they still inhabit the Earth's crust. In the search for connections between abiotic processes in ancient geological systems and biotic processes in biological systems, it becomes evident that chemical activation (catalysis) of these gasses and a constant source of energy are key. The H 2 –CO 2 redox reaction provides a constant source of energy and anabolic inputs, because the equilibrium lies on the side of reduced carbon compounds. Identifying geochemical catalysts that activate these gasses en route to nitrogenous organic compounds and small autocatalytic networks will be an important step towards understanding prebiotic chemistry that operates only on the basis of chemical energy, without input from solar radiation. So, if life arose in the dark depths of hydrothermal vents, then understanding reactions and catalysts that operate under such conditions is crucial for understanding origins.

The structures of the phenol (Ph)-acetylene (A) clusters PhA1,2,3 and Ph2A1 are assigned on the basis of isomer and mass specific IR-UV double resonance spectroscopy and compared to the structure of the PhA cocrystal. The structures of the PhA1,2,3 clusters are dominated by phenol-acetylene π-hydrogen bonds whereas Ph2A1 binds via OH···OH···C≡C interaction with dominating Ph-Ph hydrogen bond like in the phenol dimer and acetylene attached to the free OH group of the proton acceptor phenol. The macroscopic crystal is a clathrate of phenol with acetylene with hydrogen bridges only between the phenol molecules and not between phenol and acetylene. (1) A possible aggregation pathway is proposed in which larger phenol clusters like Ph6 are cyclic with no free OH available anymore to which acetylene could attach as proton acceptor.

The fluorescence kinetics of 1,6-diphenyl-1,3,5-hexatriene (DPH) dissolved in cyclohexane was investigated as a function of temperature, concentration and 355 nm excitation pulse energy. At concentrations above 2.5 μM and excitation energies above 1 mJ a long-lived, very intense emission, which appears within less than 5 ns and lasts up to 70 ns, is observed. During the first 50 ns the decay does not follow an exponential but rather a linear behaviour. In oxygen saturated solutions the long-lived emission is suppressed and solely short-lived fluorescence with τ 1-state and competes with the formation of DPH-O2 contact charge-transfer complexes and intersystem crossing which both quench the fluorescence. Our investigations show that even the small amount of oxygen dissolved in nitrogen saturated solutions has a distinct influence on the fluorescence kinetics of DPH.

Vibronic spectra of 9H-adenine, 9-acetyladenine and several alkyladenines have been recorded by resonant two-photon ionization spectroscopy of the laser-desorbed molecules, entrained in a molecular beam. While adenine and the alkyladenines exhibit similar electronic spectra, 9-acetyladenine behaves considerably different. Theoretical absorption spectra of 9H-adenine and 9-acetyladenine were calculated using the combined density functional theory/multi-reference configuration interaction approach and using second order coupled cluster theory, in order to explain striking differences in the experimental spectra. The major differences between the 9H-adenine and the 9-acetyladenine absorption spectra can be traced back to the different configurations, which contribute to the excitations, both of the lowest ππ* and the nπ* states. While the excitations in 9H-adenine are localized in the chromophore, they show considerable charge transfer character from the chromophore to the acetyl group in the case of 9-acetyladenine.

Photocatalytic splitting of water was carried out in a two-phase system. Nanocrystalline titanium dioxide was used as photocatalyst and potassium hexacyanoferrate(III)/(II) as electron transporter. Generated hydrogen was chemically stored by use of a 1,4-benzoquinone/1,4-hydroquinone system, which was used as a recyclable fuel in a commercialised direct methanol fuel cell (DMFC). The electrical output of the cell was about half compared to methanol. The conversion process for water splitting and recombination in a fuel cell was monitored by UV-Vis spectroscopy and compared to a simulated spectrum. Products of side reactions, which lead to a decrease of the overall efficiency, were identified based on UV-Vis investigations. A proof of principle for the use of quinoide systems as a recyclable hydrogen storage system in a photocatalytic water splitting and fuel cell cyclic process was given.

Isomer- and mass-selective UV and IR-UV double resonance spectra of the BA3, B2A, and B2A2 clusters of benzene (B) and acetylene (A) are presented. Cluster structures are assigned by comparison with the UV and IR spectra of benzene, the benzene dimer, as well as the BA, BA2, and B2A clusters. The intermolecular vibrations of BA are identified by dispersed fluorescence spectroscopy. Assignment of the cluster structures is supported by quantum chemical calculations of IR spectra with spin-component scaled second-order Møller-Plesset (SCS-MP2) theory. Initial propositions for various structures of the BA3 and B2A2 aggregates are generated with model potentials based on density functional theory combined with the symmetry-adapted perturbation theory (DFT-SAPT) approach. Shape and relative cluster stabilities are then confirmed with SCS-MP2. T-shaped geometries are the dominant structural motifs. Higher-energy isomers are also observed. The detected cluster structures are correlated with possible cluster formation pathways and their role as crystallization seeds is discussed.

Four donor-(π-conjugated-bridge)-acceptor type dyes A-D were designed and synthesized. These new compounds use an unconventional 4-hydroxy-1,3-thiazole building block as an additional chromophore for light harvesting and to extend the π-conjugated system of the molecules. The synthetic route involved a double N-arylation Hartwig–Buchwald reaction using Pd(dba)2 as precatalyst and P(tBu)3 as ligand. Two different triarylamines and a 4-methoxyphenyl group were used as electron donor moieties. The electron acceptor (anchoring) group was 2-cyanoacrylic acid for all dyes, whereas the π-spacer was varied and the influence was investigated. The dyes were thoroughly characterized using photophysical and electrochemical methods and by density functional theory calculations. Additionally, they were evaluated in nanocrystalline TiO2-based dye-sensitized solar cells (DSSCs). The DSSCs were prepared with and without deoxycholic acid (DCA) as a co-adsorbent to inhibit dye aggregation. The efficiencies obtained were low for DSSCs fabricated without DCA, but were significantly improved for DCCS with co-adsorbed DCA. Additionally, the X-ray structure of dye D was obtained, demonstrating the stereochemistry and planar geometry of the molecule. The DSSC based on dye A showed an efficiency of η = 1.70% (Jsc = 4.49 mA cm−2, VOC = 0.61 V, FF = 0.62) under 100 mW cm−2 simulated AM 1.5 G solar irradiation compared to η = 4.1% of the standard N3 obtained under same conditions.

Phenothiazinyl rhodanylidene acetic acid merocyanine dyes with variable substitution pattern on the peripheral benzene ring were synthesized in good to excellent yields by Knoevenagel condensation of the corresponding phenothiazinyl aldehydes and rhodanine-N-acetic acid. The electronic properties were investigated by cyclic voltammetry, absorption, and fluorescence spectroscopy. Electron releasing substitution leads to an appreciable lowering of the oxidation potential, bathochromic shift of the absorption band, and minimization of the emission quantum yield. Not least as a consequence of these properties, the compounds are interesting for use as chromophores in dye-sensitized solar cells (DSSC). DSSCs were constructed and successfully tested by determining the characteristic parameters such as incident-photon-to-electron conversion efficiency (IPCE), fill factor (FF), and overall efficiency.

Photocatalytic splitting of water was carried out in a two-phase system. The efficiencies of different types of nanocrystalline semiconductors were investigated and compared with commercialised TiO2 nanopowder. Generated hydrogen was chemically stored by use of a quinoid system, which seems to be useable for fuel cells. Solar light sensitive nanocomposites of CdSe/TiO2 and CdSxSey/TiO2 type were prepared and their good photocatalytic performance was demonstrated. In the visible range of 400 - 600 nm CdSxSey/TiO2 composites show comparable good results as in the UV range, which is very promising for their use as solar light water splitters. The concept of sensitising TiO2 with different kind of semiconductor nanoparticles, which is already known from quantum dot sensitised solar cells (QDSC), was demonstrated here for water splitting as well. Furthermore the kinetics of the storage reaction was investigated by UV-Vis spectroscopy and found to proceed via a consecutive reaction with an 1:1 charge transfer complex of quinone and hydroquinone as intermediate. The electron transfer process via a Fe2+/Fe3+ redox couple was investigated by UV-Vis spectroscopy as well as by a dye reaction on the TiO2 surface. A light microscopic view of the surface of larger aggregates of TiO2 nanoparticles indicated different areas of photocatalytic activity with photocatalysis preferentially at catalyst edges. The global electron transfer process could be traced by following the dye colour in real time.

Gr?tzel cells were prepared by using CdSe- and CdSxSey-nanoparticles as sensitizer. The quantum dots were incorporated in various sizes and concentrations in a TiO2 nanoparticle layer by a simple mixing procedure. The advantage of this method compared to anchoring of nanoparticles to TiO2 by linker molecules or chemical bath deposition is that we are able to control the ratio between TiO2 and CdSe or CdSxSey more precisely and over a larger range of concentrations. TiO2 solar cells sensitized by this technique achieved photon-to-current conversion efficiencies (IPCE) of ~40% in the range of 300 - 500 nm with a maximum IPCE of ~70% at 400 nm (sulphide/sulphate electrolyte). The best results at wavelengths above 500 nm were achieved with CdSxSey/TiO2 cells at a molar ratio of 6:1 (S:Se) with IPCE of 40% at 500 nm and still 15% at 800 nm. Quantum efficiencies obtained with iodine/iodide electrolyte were lower and lead to an overall efficiency of 0.32%. The CdSxSey sensitized solar cells show enhanced stability compared to CdSe based systems and the use of the iodine/iodide electrolyte increases cell endurance further.

We present gas phase Fourier Transform Infrared (FTIR) spectra of the homologue series of α, ω-diphenylpolyenes consisting of trans- and cis-stilbene, diphenylbutadiene (DPB) and diphenylhexatriene (DPH) obtained by a fast thermal heating technique that enables vaporization without decomposition. Infrared marker bands for the cis-isomers of the polyenes have been identified by density functional calculations at the B3LYP/TZVP level of theory. The all trans isomers of DPB and DPH do not interconvert to the cis-isomers in the gas phase at 200 °C.

The FTIR spectrum of pyrazine in the gas phase has been measured and analyzed using automated evolutionary algorithms. For the stronger bands, the rotational constants for ground and vibrationally excited states, the correct band types and in some cases centrifugal distortion constants could be extracted. Several hot hands have been identified and assigned by comparison to a cubic force field calculation at the MP2/6-311G(d,p) level of theory. Vibrationally averaged rotational constants for the excited bands can give a further guidance in the assignment of the vibrational bands.

BACKGROUND: Photo-crosslinkable polymers are well known and commercially applied as photoresists. But so far they have not been applied as membrane materials for separation processes. They would offer certain advantages in membrane fabrication over conventional crosslinked polymer materials. Therefore, in this work, a poly[ethene-stat-(methacrylic acid)] (PEMAA) which is a potential membrane polymer for different separation problems was functionalised with photo-crosslinkable maleimide side groups. RESULTS: It has been shown that PEMAA can be used as basic polymer material and a conversion with 3-hydroxypropylmaleimide is possible in order to obtain a photo-crosslinkable polymer. Investigation of the crosslinking mechanism was performed using stationary infrared and UV-visible spectroscopy as well as nanosecond transient spectroscopy absorption measurements of a rotating film. Intense transient absorption of the maleimide-esterified PEMAA occurs at 250 nm in the film pointing to maleimide anion formation and crosslinking via an ionic dimerisation mechanism. CONCLUSION: It is found that crosslinking reactions can be observed spectroscopically in situ using a maleimide-functionalised PEMAA. Furthermore, experiments can be performed in the liquid phase (polymer in solution) as well as in the solid phase (polymer film) using a rotating polymer film sample. Maleimide anion formation and crosslinking via an ionic dimerisation mechanism can be investigated by variation of the polymer structure as well as the structure of the maleimide side groups. Copyright © 2009 Society of Chemical Industry

Guanosine monophosphate (GMP) in aqueous solutions has been studied with femtosecond broad-band transient absorption spectroscopy and by quantum-mechanical calculations. The sample was excited at 267 or 287 nm and probed between 270 and 1000 nm with 100 fs resolution, for various pH values between 2 and 7. At pH 2, when the guanine ring is ground-state protonated (GMPH(+)), we observe isosbestic behavior indicating state-to-state relaxation. The relaxation is biexponential, tau(1) = 0.4 ps, tau(2) = 2.2 ps, and followed by slower internal conversion with tau(3) = 167 ps. For nonprotonated GMP in the pH range 7-4, we find biexponential decay in the region 400-900 nm (tau(1) = 0.22 ps, tau(2) = 0.9 ps), whereas, between 270 and 400 nm, the behavior is triexponential with one growing, tau(1) = 0.25 ps, and two decaying, tau(2) = 1.0 ps, tau(3) = 2.5 ps, components. The excited-state evolution is interpreted with the help of quantum-chemical calculations, performed at the time-dependent PBE0 level accounting for bulk solvent effects and specific solvation. The computed dynamics involves L(a) and L(b) bright excited states, whereas the n(0)pi* and pisigma* dark excited states play a minor role. Independent of the pH, the photoinduced evolution involves ultrafast L(b)--L(a) conversion (tau(ba)100 fs) and exhibits the presence of a wide planar plateau on L(a). For neutral GMP a barrierless path connects this region to a conical intersection (CI) with the ground state, giving an account of the ultrafast decay of this species. For protonated GMPH(+) the system evolves into a stable minimum L(a min) characterized by out-of-plane displacement of NH and CH groups, which explains the longer (167 ps) fluorescence lifetime.

We reinvestigated the stationary singlet absorption spectrum of flavone and its transient triplet spectrum at excitation wavelengths of 266 and 355 nm in cyclohexane as solvent. The S 0 –S n spectra obtained by Density Functional/Multi Reference Configuration Interaction (DFT/MRCI) calculations agree well with experiment. The calculated intense T 1 –T n transitions qualitatively reproduce the experimental band maxima observed at ∼330, 365 and 600 nm in cyclohexane.

We present size- and isomer-selective IR–UV double resonance spectra of two pyrazine dimer isomers. The most stable isomer has a planar structure, stabilized by two CH ��� N contacts. The other isomer has a stacked, cross-displaced structure. Our assignment is supported by B3LYP-D calculations. RI-MP2 calculations tend to overestimate the stability of the stacked and T-shaped isomers.

Die grundlegendenStrukturmotiveder Elementarzellen knnten im Prinzip mit der Struktur vonNanokristallen verglichen werden, die bei der adiabatischenAbkhlung in berschallexpansionen entstehen. Allerdingsknnen kooperative Effekte zu isomeren Kristallstrukturenfhren, die nicht notwendigerweise den globalen Mini-mumsstrukturen der Cluster entsprechen. Jedoch werdenunter den Nichtgleichgewichtsbedingungen der berschall-expansionen oft auch hherenergetische Clusterisomere ge-bildet. Dadurch wird die Mglichkeit geschaffen, die Motiveder Elementarzellen in Form von isolierten Clustern zu un-tersuchen. Im Folgenden werden die Strukturen kleinerBenzol-Acetylen-Cluster vorgestellt und mit der Struktur des1:1-Cokristalls verglichen.Starke C [3]H···p-Wechselwirkungen ( 2.5 kcalmol

We present the first gas phase Fourier transform infrared (FTIR) spectra of flavone, 3-hydroxyflavone, 5-hydroxyflavone, 6-hydroxyflavone and 3-methoxyflavone by using a fast thermal heating technique to vaporize them without decomposition. The intramolecular OH···O C hydrogen bond strength increases from 3HF (5-ring) to 5HF (6-ring) as evidenced by the increasing red-shift and band width of the OH stretch vibration. C O stretch and OH in-plane bend motions are coupled in the 5- and 6-rings and give rise to two intense IR bands in the range 1600–1700 cm −1 . 6HF is not able to form an intramolecular hydrogen bond.

Electronic and vibrational gas phase spectra of 1-methylthymine (1MT) and 1-methyluracil (1MU) and their clusters with water are presented. Mass selective IR/UV double resonance spectra confirm the formation of pyrimidine-water clusters and are compared to calculated vibrational spectra obtained from ab initio calculations. In contrast to Y. He, C. Wu, W. Kong; J. Phys. Chem. A, 2004, 108, 94 we are able to detect 1MT/1MU and their water clusters via resonant two-photon delayed ionization under careful control of the applied water-vapor pressure. The long-living dark electronic state of 1MT and 1MU detected by delayed ionization, survives hydration and the photostability of 1MT/1MU cannot be attributed solely to hydration. Oxygen coexpansions and crossed-beam experiments indicate that the triplet state population is probably small compared to the (1)n pi* and/or hot electronic ground state population. Ab initio theory shows that solvation of 1MT by water does not lead to a substantial modification of the electronic relaxation and quenching of the (1)n pi* state. Relaxation pathways via (1)pi pi*(1)-n pi*(1) and (1)pi pi*-S(0) conical intersections and barriers have been identified, but are not significantly altered by hydration.

Silver nanoparticles (Ag NPs) stabilized by a thermoresponsive polymer, poly(N-isopropylacrylamide) (PNIPAM), have been synthesized by the reduction of silver ions with NaBH(4) in aqueous solutions. The obtained Ag NPs are very stable at room temperature due to the extended coil conformation of the PNIPAM chain at temperatures below its volume phase transition temperature ( approximately 32 degrees C). At higher temperatures (such as 45 degrees C) above the phase transition of PNIPAM, only minute aggregation between Ag NPs was observed, showing that the collapsed PNIPAM chains still retain the ability to stabilize Ag NPs. The PNIPAM-stabilized Ag NPs were then characterized as a function of the thermal phase transition of PNIPAM by UV-vis spectroscopy, dynamic light scattering, transmission electron microscopy, and cyclic voltammeter. Consistent results were obtained showing that the phase transition of PNIPAM has some effect on the optical properties of Ag NPs. Switchable electrochemical response of the PNIPAM-stabilized Ag NPs triggered by temperature change was observed.

We present the first gas phase Fourier transform infrared (FTIR) spectra of the uncapped (natural) amino acids glycine, alanine, threonine, cysteine, methionine and capped methionine by using a fast thermal heating technique up to around 520 K to vaporize them. The experimental spectra taken in the range 700–4000 cm −1 show no sign of decomposition and are in good agreement with ab initio calculated frequencies and intensities of the non-zwitterionic form of the amino acids.

The change of the phenol dimer (PH2) structure upon electronic excitation is determined by a Franck-Condon analysis of the intensities in the fluorescence emission spectra obtained via excitation of seven different vibronic bands. A total of 547 emission band intensities are fitted, together with the changes of rotational constants upon electronic excitation of fi ve isotopomers. These rotational constants are taken from previously published [Schmitt et al. ChemPhysChem 2006, 7, 1241-1249] high-resolution LIF measurements. The geometry change upon electronic excitation of the pipi* state of the donor moiety can be described by a strong shortening of the hydrogen bond, a shortening of the CO bond in the donor moiety, an overall symmetric expansion of the donor phenol ring, and a nearly unchanged acceptor moiety. The resulting geometry changes are interpreted on the basis of ab initio calculations.

We present near- and mid-infrared−UV double resonance spectra of the natural dipeptide H−Pro-Trp−OH. Two conformers are present in the supersonic expansion: a stretched conformer with fully extended backbone and a folded conformer with an OH···OCpep hydrogen bond. Both conformers are stabilized by dispersion interaction between indole ring and peptide backbone and a NHpep/Nproline contact. The vibrational and conformational assignment is supported by DFT and MP2 calculations. An adequate description of the energetic order of different conformers requires the explicit inclusion of dispersion and geometry optimization at the MP2 level. We will address the very sensitivity of the observed conformations to the structure of the end groups.

A micelle-based method to synthesize dispersed polyaniline (PANI)−Au composite particles by direct oxidation of aniline using AuCl4- as the oxidant is presented. The obtained composite particles have a core−shell structure, where Au nanoparticles of 20 nm mean diameter are encapsulated by PANI of well-defined tetrahedron shape with 150 nm average edge length. The polaron band of the dispersed PANI−Au composite particles is centered at 745 nm and is rather narrow compared to the broad 835 nm absorption of PANI synthesized by the IUPAC procedure. The surface plasmon absorption of Au nanoparticles normally centered at around 520 nm is absent in the composite particles with oxidized PANI. Our results point to a strong electronic interaction between the encapsulated Au nanoparticles and the shell of oxidized PANI. Films and pellets produced from these composite particles show a twofold higher conductivity than IUPAC PANI.

In this paper the conformational landscape of amphetamine in the neutral ground state is examined by both spectroscopy and theory. Several spectroscopic methods are used: laser-induced fluorescence (LIF), resonance-enhanced two-photon ionization (R2PI), dispersed fluorescence and IR/R2PI hole burning spectroscopy. The latter two methods provide for the first time vibrationally resolved spectra of the neutral ground state of dl -amphetamine and the amphetamine–(H 2 O) 1,2 complexes. Nine stable conformers of the monomer were found by DFT (B3LYP/6-311++G(d,p)) and ab initio (MP2/6-311++G(d,p)) calculations. For conformer analysis the vibrations observed in the IR/R2PI hole burning and dispersed fluorescence spectra obtained from single vibronic levels (SVLF) of a selected conformer were compared with the results of an ab initio normal mode analysis. By this procedure three S 0 → S 1 transitions in the R2PI spectrum were assigned to three different conformer structures. Another weak transition earlier attributed to another conformer could be assigned to a vibronic band of one of the three conformers. Furthermore spectra of amphetamine–(H 2 O) 1,2 are tentatively assigned.

By using laser-induced heating, we prepared Au-Ag nanoalloys via three different procedures: (i) mixture of Au nanoparticles and Ag(+) ions irradiated by a 532 nm laser, (ii) mixture of Au and Ag nanoparticles irradiated by a 532 nm laser, and (iii) mixture of Au and Ag nanoparticles irradiated by a 355 nm laser. Procedure i is advantageous for the production of spherical alloy nanoparticles; in procedures ii and iii, nanoalloys with a sintered structure have been obtained. The morphology of the obtained nanoalloys depends not only on the laser wavelength but also on the concentration of nanoparticles in the initial mixture. When the total concentration of Ag and Au nanoparticles in the mixture is increased, large-scale interlinked networks have been observed upon laser irradiation. It is expected that this selective heating strategy can be extended to prepare other bi- or multi-metallic nanoalloys.

The carotenoid r , r -astaxanthin (3 R ,3′ R -dihydroxy-4,4′-diketo-β-carotene) forms different types of aggregates in acetone–water mixtures. H-type aggregates were found in mixtures with a high part of water (e.g. 1:9 acetone–water mixture) whereas two different types of J-aggregates were identified in mixtures with a lower part of water (3:7 acetone–water mixture). These aggregates were characterized by recording UV/vis-absorption spectra, CD-spectra and fluorescence emissions. The sizes of the molecular assemblies were determined by dynamic light scattering experiments. The hydrodynamic diameter of the assemblies amounts 40 nm in 1:9 acetone–water mixtures and exceeds up to 1 μm in 3:7 acetone–water mixtures. Scanning tunneling microscopy monitored astaxanthin aggregates on graphite surfaces. The structure of the H-aggregate was obtained by molecular modeling calculations. The structure was confirmed by calculating the electronic absorption spectrum and the CD-spectrum where the molecular modeling structure was used as input.

Gold nanoparticles with an average diameter of approximately 20 nm were prepared in an aqueous solution by a wet chemistry method. The parent gold nanoparticles were then capped with a 4-aminothiophenol protecting layer and transferred into toluene by tuning the surface charge of the modified nanoparticles. Gold nanoparticles before and after phase transfer were subjected to photofragmentation by a pulsed 532 nm laser. The effects of solvent properties and surface chemistry on the photofragmentation of the gold nanoparticles have been investigated. Fast photofragmentation has been observed in the organic solvent in which the dielectric constant, heat capacity, and thermal conductivity are lower. The results suggest new approaches for the preparation of very small gold clusters from gold nanoparticles.

We present the first gas-phase Fourier transform infrared (FT-IR) spectra of uncapped (natural) amino acids using a fast thermalheating technique up to around 570 K. The experimental spectra of phenylalanine, proline, valine, leucine and isoleucine in therange 900–3700 cm 1 show no sign of decomposition and are in good agreement with ab initio calculated frequencies and intensitiesat the B3LYP/6-31G(d,p) level, if non-hydrogen bonded structures are assumed at the high temperatures of the experiment. 2005 Elsevier B.V. All rights reserved. 1. IntroductionGas-phaseinfraredspectraarefreefromsolventinter-actionsandcanbecompareddirectlywithabinitiocalcu-lations of harmonic and anharmonic vibrationalfrequencies [1,2]. In addition, gas-phase spectra can becomparedwithspectrainliquidphase,solutionsandma-trixisolation,inordertoassestheinteractionwiththesol-vent and neighboring molecules [3,4]. So far, gas-phasespectra are available only for molecules with a sufficienthigh vapor pressure or thermal stability. Especially bio-molecules, like amino acids and peptides, have very lowvapor pressures and are well known for their thermalinstability.Indeed,allnaturalaminoacidsdecomposebe-foreoruponsublimationtosomeextent[5],thereforepre-venting easy measurements of gas-phase infrared spectrainstatic,thermallyheatedgascells.Somegas-phasespec-tra ofamino acids were measured using thermally heatednozzles [6–8] or laser desorption techniques [9–11]. Sinceboth sources yield only very low number densities, sensi-tivedetectionschemeslikeREMPI[6,7,9],IR-CRLAS[8]or microwave spectroscopy [10,11] are required.However,onlythreenaturalaminoacids,namelyphenyl-alanine, tryptophane and tyrosine, have chromophoreswithlowlyingelectronicstatesandaresuitedforREMPIdetection in combination with IR-UV double resonanceexperiments.In earlier experiments, we could show that we can ob-tain gas-phase FT-IR spectra of solid samples of adenine[12], thymine [13], cytosine [14] and benzotriazol [15] byrapid heating to about 250–300 C. Thermodynamicalpropertiesoftheketo/enolequilibriumcouldbeobtainedfrom measurements at different temperatures [15]. In thiswork,wepresentaslightlymodified,butnonetheless,verysimplerapidheatingset-up,whichcanbeappliedtother-mally very unstable molecules, too. We report the firstgas-phase FT-IR spectra of five different natural aminoacids: valine (Val), proline (Pro), phenylalanine (Phe),iso-leucine (Ile), and leucine (Leu). The spectra are com-pared to density functional calculations at the B3LYP/6-31G(d,p) level of theory, underlining once again thegood quality of density functional methods in describingthe harmonic vibrations of monomeric species.2. ExperimentalThe measurements were performed in a simple heatedgas cell (see Fig. 1). A stainless steel tube, 9 cm long and3 cm in diameter, is sealed at both ends with NaCl

Gold nanoparticles were surface modified with an ionizable and pH-sensitive monolayer of thiobarbituric acid (TBA). By variation of the pH value of the solution, nanoparticle aggregates can be produced in a controlled way. The aggregates thus prepared were irradiated with an intense pulsed laser at 532 nm. The products in solution were examined by transmission electron microscopy (TEM) and optical absorption spectroscopy. The TEM images of the products revealed that the nanoparticle aggregates dissociate upon laser irradiation and form much smaller gold nanoparticles. The optical absorption spectra measured simultaneously show the gradual disappearance of the absorbance band of the aggregates at around 680 nm. Additionally, a blue shift (from 534 to 524 nm) of the resonance absorbance corresponding to isolated nanoparticles has been observed. All the observations suggest that the colloidal solution becomes more stable after laser irradiation. Both the reduced nanoparticle size and the stabilizing TBA ligands present on the particle surface contribute to the acquired stability of the colloidal solutions.

The change in structure of 7-azaindole upon electronic excitation was determined by a Franck-Condon analysis of the intensities in the fluorescence emission spectra obtained via excitation of six different vibronic bands. A total of 107 emission band intensities were fit, together with the changes in the rotational constants of four 7-azaindole isotopomers. The geometry change of the ring framework upon electronic excitation from the electronic ground state to the 1Lb state (ππ*) can be described by an overall expansion of the pyridine ring of 7-azaindole, with minor changes of the pyrrole ring. The resulting geometry changes are interpreted on the basis of ab initio calculations.

The peptides Trp-Gly, Gly-Trp and Trp-Gly-Gly were investigated by UV–UV and IR–UV hole burning spectroscopy. Solid samples of the three peptides were vaporised into an argon jet by laser desorption. The IR–UV spectra of different conformers of the peptides were assigned by comparison with the IR–UV spectra of tryptophan [Snoek et al., Phys. Chem. Chem. Phys., 2001, 3, 1819], the free peptide bond in N-acetyl tryptophan methyl amide [Dian et al., J. Chem. Phys., 2002, 117, 10688] and ab initio calculations performed at the DFT B3LYP 6-31G(d,p) level. Apart from an NH⋯NH2 interaction, the peptide backbone of one conformer of each dipeptide is unfolded. The second conformer of Gly-Trp shows a COOH⋯OC hydrogen bond and the second conformer of Trp-Gly-Gly a hydrogen bond between the peptide backbone and the NH group of the indole ring.

Tryptophan ethylester (Trp–OEt) and the dipeptides glycine–tryptophan (Gly–Trp), tryptophan–serine (Trp–Ser) and proline–tryptophan (Pro–Trp) exhibit complex R2PI spectra in the region from 34 550 to 35 600 cm −1 . The number of conformers observed for all four molecules in the investigated spectral range by UV–UV double resonance spectroscopy is surprisingly small. The spectrum of Trp–OEt consists of bands from three different conformers with redmost bands at 34 811, 34 705 and 34 548, respectively. The dipeptide spectra each consist of lines of two conformers in the investigated spectral range from 34550 to 35600 cm −1 for Gly–Trp, 34 300 to 34 960 cm −1 for Trp–Ser and 34 650 to 35 100 cm −1 for Pro–Trp. Our results on Gly–Trp are in agreement with previous observations by Levy and co-workers.