Electrostatic potential at the retinal of three archaeal rhodopsins: implications for their different absorption spectra

The color tuning mechanism of the rhodopsin protein family has been in the focus of research for decades. However, the structural basis of the tuning mechanism in general and of the absorption shift between rhodopsins in particular remains under discussion. It is clear that a major determinant for spectral shifts between different rhodopsins are electrostatic interactions between the chromophore retinal and the protein. Based on the Poisson-Boltzmann equation, we computed and compared the electrostatic potential at the retinal of three archaeal rhodopsins: bacteriorhodopsin (BR), halorhodopsin (HR), and sensory rhodopsin II (SRII) for which high-resolution structures are available. These proteins are an excellent test case for understanding the spectral tuning of retinal. The absorption maxima of BR and HR are very similar, whereas the spectrum of SRII is considerably blue shifted--despite the structural similarity between these three proteins. In agreement with their absorption maxima, we find that the electrostatic potential is similar in BR and HR, whereas significant differences are seen for SRII. The decomposition of the electrostatic potential into contributions of individual residues, allowed us to identify seven residues that are responsible for the differences in electrostatic potential between the proteins. Three of these residues are located in the retinal binding pocket and have in fact been shown to account for part of the absorption shift between BR and SRII by mutational studies. One residue is located close to the beta-ionone ring of retinal and the remaining three residues are more than 8 A away from the retinal. These residues have not been discussed before, because they are, partly because of their location, no obvious candidates for the spectral shift among BR, HR, and SRII. However, their contribution to the differences in electrostatic potential is evident. The counterion of the Schiff base, which is frequently discussed to be involved in the spectral tuning, does not contribute to the dissimilarities between the electrostatic potentials.     

Cochlear sensitivity in the lesser spear-nosed bat, <Emphasis Type="Italic">Phyllostomus discolor</Emphasis>

Behavioral auditory thresholds of Phyllostomus discolor are characterized by two threshold minima separated by an insensitive region at about 55 kHz (Esser and Daucher 1996). To investigate whether these characteristics are due to cochlear properties, we recorded distortion product otoacoustic emissions (DPOAEs) and calculated relative DPOAE threshold curves, which proved to be a good measure of cochlear sensitivity. Our results indicate that in P. discolor, cochlear sensitivity, as assessed by DPOAE recordings, does not show a threshold maximum at 55 kHz. The DPOAE threshold curves display an absolute minimum at approximately 30 kHz, and from that frequency region, the threshold continuously increases without any pronounced irregularities. The frequency tuning properties of the cochlea, as assessed by DPOAE suppression tuning curves (STCs) reveal broad filter bandwidths with Q10dB values between 3.4 and 10.7. There are no frequency-specific specializations of cochlear tuning. The characteristic pattern of subsequent threshold maxima and minima at high frequencies observed in behavioral studies seems to be shaped by transfer characteristics of the outer ear and/or neuronal processing in the ascending auditory pathway rather than by cochlear mechanics.     

Unassisted Water Splitting Using a GaSbxP(1−x) Photoanode

Here, unbiased water splitting with 2% solar‐to‐hydrogen efficiency under AM 1.5 G illumination using new materials based on GaSb_0.03P_0.97 alloy is reported. Freestanding GaSb_xP_1?x is grown using halide vapor phase epitaxy. The native conductivity type of the alloy is modified by silicon doping, resulting in an open‐circuit potential (OCP) of 750 mV, photocurrents of 7 mA cm^?2 at 10 sun illumination, and corrosion resistance in an aqueous acidic environment. Alloying GaP with Sb at 3 at% improves the absorption of high‐energy photons above 2.68 eV compared to pure GaP material. Electrochemical Impedance Spectroscopy and illuminated OCP measurements show that the conduction band of GaSb_xP_1?x is at ?0.55 V versus RHE irrespective of the Sb concentration, while photocurrent spectroscopy indicates that only radiation with photon energies greater than 2.68 eV generate mobile and extractable charges, thus suggesting that the higher‐laying conduction bands in the Γ 1 valley of the alloys are responsible for exciton generation.     

早期声音暴露对蝙蝠中脑下丘听神经元频率调谐特性发育的影响

本实验对鼠耳蝠出生后不同时期进行纯音暴露,采用常规电生理不方法研究出生后早期声音暴露出蝙蝠中脑下丘听神经元频率调谐特性发育的影响及影响的临界期。结果表明,出生后第１,３周开始声暴露的实验组,其神经元调于暴露声频段的数量较对照组和出生后第５周开始声暴露的实验组明显增多,且音调筑构出现扭曲,神经元频率调谐曲线的Ｑ１０－ｄＢ值也较高。     

猫外膝体神经元非寻常的方位调谐特性──Ⅱ．在去视皮层猫和视觉剥夺猫（Dark－reared cats）的研究

以移动的正弦光栅作为刺激,用玻璃微电极记录以冰冻法毁损皮层１７、１８、１９区和外侧上雪氏回区后的猫外膝体的单细胞反应,测定了５７９个细胞的方位调谐特性,另外还在视觉剥夺猫外膝体测定了３４４个细胞的方位调谐特性,与正常猫相似,去视以猫和视觉剥夺猫外膝体的少数细胞具有非寻常的方位调谐特性,包括具蝴蝶形调谐曲线的方位调谐特性、双调谐的方位调谐特性和最优方位随刺激空间的不同而变化的方位调谐特性。结果表明外     

Organic Salts as a Route to Energy Level Control in Low Bandgap,High Open‐Circuit Voltage Organic and Transparent Solar Cells that Approach the Excitonic Voltage Limit

A new series of organic salts with selective near‐infrared (NIR) harvesting to 950 nm is reported, and anion selection and blending is demonstrated to allow for fine tuning of the open‐circuit voltage. Extending photoresponse deeper into the NIR is a significant challenge facing small molecule organic photovoltaics, and recent demonstrations have been limited by open‐circuit voltages much lower than the theoretical and practical limits. This work presents molecular design strategies that enable facile tuning of energy level alignment and open‐circuit voltages in organic salt‐based photovoltaics. Anions are also shown to have a strong influence on exciton diffusion length. These insights provide a clear route toward achieving high efficiency transparent and panchromatic photovoltaics, and open up design opportunities to rapidly tailor molecules for new donor–acceptor systems.     

Modern termites inherited the potential of collective construction from their common ancestor

Animal collective behaviors give rise to various spatial patterns, such as the nests of social insects. These structures are built by individuals following a simple set of rules, slightly varying within and among species, to produce a large diversity of shapes. However, little is known about the origin and evolution of the behavioral mechanisms regulating nest structures. In this study, we discuss the perspective of inferring the evolution of collective behaviors behind pattern formations using a phylogenetic framework. We review the collective behaviors that can be described by a single set of behavioral rules, and for which variations of the environmental and behavioral parameter values produce diverse patterns. We propose that this mechanism could be at the origin of the pattern diversity observed among related species, and that, when they are placed in the proper conditions, species have the behavioral potential to form patterns observed in related species. The comparative analysis of shelter tube construction by lower termites is consistent with this hypothesis. Although the use of shelter tubes in natural conditions is variable among species, most modern species have the potential to build them, suggesting that the behavioral rules for shelter tube construction evolved once in the common ancestor of modern termites. Our study emphasizes that comparative studies of behavioral rules have the potential to shed light on the evolution of collective behaviors.     

Can spectral cues contribute to species separation in closely related grasshoppers?

 The acridid grasshoppers Chorthippus biguttulus and Ch. mollis, which are closely related and often sympatric species, were compared intra- and interspecifically with regard to the spectra of their calling and courtship songs and of the sound-induced vibrations of the tympanal membrane, as well as the threshold curves of the tympanal nerve. In the low-frequency range but not in the ultrasound region, the maxima of these various curves fall at distinctly different frequencies in the two species. It is shown that the low-frequency sensitivity of the auditory system in both species, especially in females, is well matched to the conspecific song spectra but not to those of the heterospecific songs. Whether these characteristics actually contribute to species discrimination remains to be determined by behavioural tests. Accepted: 23 August 1996