Soft-tissue evidence for homeothermy and crypsis in a Jurassic ichthyosaur

Ichthyosaurs are extinct marine reptiles that display a notable external similarity to modern toothed whales. Here we show that this resemblance is more than skin deep. We apply a multidisciplinary experimental approach to characterize the cellular and molecular composition of integumental tissues in an exceptionally preserved specimen of the Early Jurassic ichthyosaur Stenopterygius. Our analyses recovered still-flexible remnants of the original scaleless skin, which comprises morphologically distinct epidermal and dermal layers. These are underlain by insulating blubber that would have augmented streamlining, buoyancy and homeothermy. Additionally, we identify endogenous proteinaceous and lipid constituents, together with keratinocytes and branched melanophores that contain eumelanin pigment. Distributional variation of melanophores across the body suggests countershading, possibly enhanced by physiological adjustments of colour to enable photoprotection, concealment and/or thermoregulation. Convergence of ichthyosaurs with extant marine amniotes thus extends to the ultrastructural and molecular levels, reflecting the omnipresent constraints of their shared adaptation to pelagic life

Finding intersections between electronic excited state potential energy surfaces with simultaneous ultrafast X-ray scattering and spectroscopy

Light-driven molecular reactions are dictated by the excited state potential energy landscape, depending critically on the location of conical intersections and intersystem crossing points between potential surfaces where non-adiabatic effects govern transition probabilities between distinct electronic states. While ultrafast studies have provided significant insight into electronic excited state reaction dynamics, experimental approaches for identifying and characterizing intersections and seams between electronic states remain highly system dependent. Here we show that for 3d transition metal systems simultaneously recorded X-ray diffuse scattering and X-ray emission spectroscopy at sub-70 femtosecond time-resolution provide a solid experimental foundation for determining the mechanistic details of excited state reactions. In modeling the mechanistic information retrieved from such experiments, it becomes possible to identify the dominant trajectory followed during the excited state cascade and to determine the relevant loci of intersections between states. We illustrate our approach by explicitly mapping parts of the potential energy landscape dictating the light driven low-to-high spin-state transition (spin crossover) of [Fe(2,2′-bipyridine)3]2+, where the strongly coupled nuclear and electronic dynamics have been a source of interest and controversy. We anticipate that simultaneous X-ray diffuse scattering and X-ray emission spectroscopy will provide a valuable approach for mapping the reactive trajectories of light-triggered molecular systems involving 3d transition metals

Chemical Evaluation of Eumelanin Maturation by ToF-SIMS and Alkaline Peroxide Oxidation HPLC Analysis

Residual melanins have been detected in multimillion-year-old animal body fossils; however, confident identification and characterization of these natural pigments remain challenging due to loss of chemical signatures during diagenesis. Here, we simulate this post-burial process through artificial maturation experiments using three synthetic and one natural eumelanin exposed to mild (100 °C/100 bar) and harsh (250 °C/200 bar) environmental conditions, followed by chemical analysis employing alkaline hydrogen peroxide oxidation (AHPO) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results show that AHPO is sensitive to changes in the melanin molecular structure already during mild heat and pressure treatment (resulting, e.g., in increased C-C cross-linking), whereas harsh maturation leads to extensive loss of eumelanin-specific chemical markers. In contrast, negative-ion ToF-SIMS spectra are considerably less affected by mild maturation conditions, and eumelanin-specific features remain even after harsh treatment. Detailed analysis of ToF-SIMS spectra acquired prior to experimental treatment revealed significant differences between the investigated eumelanins. However, systematic spectral changes upon maturation reduced these dissimilarities, indicating that intense heat and pressure treatment leads to the formation of a common, partially degraded, eumelanin molecular structure. Our findings elucidate the complementary nature of AHPO and ToF-SIMS during chemical characterization of eumelanin traces in fossilized organismal remains

Dinuclear metal complexes modelling active sites of metallohydrolases

To study the active sites of dinuclear metallohydrolases new metal complexes that model these sites both in structure and function have been synthesized using two new phenol based dinucleating ligands, 2-(N-isopropyl-N-((2-pyridyl)methyl)aminomethyl)-6-(N-(carboxylmethyl)-N-((2-pyridyl)methyl)aminomethyl)-4-methylphenol (IPCPMP) and 2,6-Bis[N-(N-(carboxymethyl)-N-(pyridylmethyl)amine)methyl]-4-methylphenolate (BCPMP). Both ligands contain pyridyl, tertiary amine and carboxylate groups but in IPCPMP one carboxylate donor is exchanged for a non-coordinating group yielding an unsymmetric ligand while BCPMP is symmetric with identical sets of ligands on either side of the phenol group. Zinc complexes of both these ligands have been structuraly characterized revealing tetratetranuclear complexes are formed when reacting IPCPMP with zinc acetate or ZnCl2 and sodium pivalate. Infrared spectroscopy indicate that the tetranuclear complexes dissociate in solution yielding two dinuclear complexes. The symmetric ligand BCPMP only yielded a dinuclear complex. Complexes of both ligand enhance the rate of phosphoester cleavage. For the substrate 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) an in situ prepared complex of the unsymmetric ligand yielded higher activity than the corresponding complex of the symmetric ligand. A zinc complex of the unsymmetric ligand also enhanced the hydrolysis of bis(2,4-dinitrophenyl)-phophate (BDNPP) and displayed saturation behaviour with respect to both pH and substrate concentration. Potentiometric studies support the formulation of the active catalyst as a dinuclear zinc complex with two terminally coordinated hydroxides where one act as nucleophile in the hydrolysis of BDNPP. The unsymmetric ligand has also been used to form a mononuclear Fe(III) complex that systematically and selectively can be used to synthesize heterodinuclear metalcomplexes. Several of these have been characterized by X-ray crystallography revealing close to identical structures for complexes of the fomula [Fe(III)M(II)(IPCPMP) (OAc)2(CH3OH)][PF6] (M = Zn, Co, Ni). A FeMn complex of the same formula is believed to have a very similar structure. The complexes have been studied by a range of different methods in both solid state (IR and Mössbauer spectroscopy as well as Magnetic susceptibility) and solution (IR and UV-vis spectroscopy) These complexes enhance the transesterification of HPNP but display different reactivities with the highest for the FeCo complex. They also enhance the hydrolysis of BDNPP and display significantly different pH dependencies. The results are used to discuss various mechanistic possibilities and it appears that the complexes use slightly different mechanisms partly depending on the pH of the solution. A FeCu derivative with the formula [{FeCu(IPCPMP)(OAc)}2(m-O)][PF6]2 has also been structurally characterized and has a tetranuclear structure where two heterodinuclear parts are bridged by a m-oxido group. Its structure and spectroscopic properties have been used to explain peculiarities in the reactivity and spectroscopic properties of the FeZn derivative

Insertion of carbon dioxide into (PCP)Pd-II-Me bonds

A (PCP)PdMe complex has been synthesized and structurally characterized, displaying a very long Pd-Me bond. It is reactive toward CO2 insertion, giving the corresponding acetate in quantitative yield. The methyl complex can be regenerated using ZnMe2, and catalytic carboxylation is possible in benzene

Asymmetric dinuclear metal complexes as models for active sites in hydrolases and redox enzymes

Recent advances in the synthesis of biomimetic asym. dinuclear transition metal complexes are reviewed. Emphasis is put on description of asym. model complexes for the active sites of the enzymes purple acid phosphatase, zinc phosphotriesterase, urease, Cu, Zn superoxide dismutase, tyrosinase, and catechol oxidase

Symmetrical and unsymmetrical dizinc complexes as models for the active sites of hydrolytic enzymes.

Dinuclear carboxylate-bridged zinc complexes of one symmetric and one asymmetric phenolate-based ligand catalyse the transesterification of 2-hydroxypropyl-p-nitrophenyl phosphate (HPNP) at different rates, with an unsymmetrical complex being more active than a symmetric one

Chemical evaluation of eumelanin maturation by tof-sims and alkaline peroxide oxidation hplc analysis

Residual melanins have been detected in multimillion-year-old animal body fossils; how-ever, confident identification and characterization of these natural pigments remain challenging due to loss of chemical signatures during diagenesis. Here, we simulate this post-burial process through artificial maturation experiments using three synthetic and one natural eumelanin exposed to mild (100◦C/100 bar) and harsh (250◦C/200 bar) environmental conditions, followed by chemical analysis employing alkaline hydrogen peroxide oxidation (AHPO) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). Our results show that AHPO is sensitive to changes in the melanin molecular structure already during mild heat and pressure treatment (resulting, e.g., in increased C-C cross-linking), whereas harsh maturation leads to extensive loss of eumelanin-specific chemical markers. In contrast, negative-ion ToF-SIMS spectra are considerably less affected by mild maturation conditions, and eumelanin-specific features remain even after harsh treatment. Detailed analysis of ToF-SIMS spectra acquired prior to experimental treatment revealed significant differences between the investigated eumelanins. However, systematic spectral changes upon maturation reduced these dissimilarities, indicating that intense heat and pressure treatment leads to the formation of a com-mon, partially degraded, eumelanin molecular structure. Our findings elucidate the complementary nature of AHPO and ToF-SIMS during chemical characterization of eumelanin traces in fossilized organismal remains

A monocarboxylate-bridged diiron(III) mu-oxido complex that catalyzes alkane oxidation by hydrogen peroxide

Reaction of the ligand 2-(N-isopropyl-N-{(2-pyridyl)methyl}aminomethyl)- 6-(N-(carboxymethyl)-N-((2-pyridyl)-methyl) aminomethyl)- 4-methylphenol (H2IPCPMP) with two equivalents of Fe(ClO4)(2) and two equivalents of sodium pivalate in air leads to the formation of the mu-oxido, mu-carboxylato-bridged diiron complex [{Fe(H-IPCPMP)}(2)(mu-O)(Piv)]ClO4 (1) (Piv = pivalate). Complex 1 is capable of catalysing the oxidation of cyclohexane or 1,2-cis-dimethylcyclohexane by hydrogen peroxide, leading to the formation of the corresponding cyclohexanone and cyclohexanol, as well as a small amount of cyclohexyl hydroperoxide

Ultrafast excited state dynamics of [Cr(CO)4(bpy)] : Revealing the relaxation between triplet charge-transfer states

Ultrafast excited state dynamics of [Cr(CO)4(bpy)] upon metal-to-ligand charge-transfer (1MLCT) transition have been studied by pump-probe absorption spectroscopy in CH3CN, pyridine and CH2Cl2 solvents. Intersystem crossing (ISC) was found to be very fast (∼100 fs) and efficient, while the formation of the photoproduct with one axial CO dissociated is significantly less competitive, indicating a barrier along the dissociative coordinate. As a refinement of the previous dynamic model [I. R. Farrell, et al., J. Am. Chem. Soc., 1999, 121, 5296-5301], we show that a conventional downhill energy relaxation concept dominates the observed dynamics. Experimentally, we have identified the consecutive population of two triplet states as a result of triplet electronic relaxation convoluted with vibrational and solvent relaxation (the overall time is 2.7-6.9 ps depending on solvent), as well as the overall depopulation of the excited state through the lowest triplet state (57-84 ps). Adaptive excitation pulse shaping could not achieve optimization of the photoproduct quantum yield via re-distribution of only low-frequency vibrational modes during excitation, indicating that the two low-lying 1MLCT states, Cr(3d) → π∗bpy and Cr(3d) → π∗CO, are not coupled