Metal detection within cell studies has been quickly growing, with fast-paced development and discovery. Iron in particular, is at the heart of many important biological processes and diseases (DNA synthesis, ferroptosis, iron deficiency anemia, etc.).[2] Creating iron probes is a significant challenge due to iron’s coordination chemistry which is selective on the type of ligand it will bind to. Fe2+ will form stable low-spin complexes with strong-field ligands. In contrast, Fe3+ will generate high-spin complexes due to the stability of the d5 electron configuration, which as a +3 ion is also more selectively bound. Activity-based probes of cellular iron metabolism are primarily for Fe2+, by using its redox activity to promote chemical reactions that induce fluorescence, acting as “turn-on” probes.[1] In contrast, iron-complexation-based (recognition-based) probes of cellular iron metabolism are primarily used for Fe3+ due to its paramagnetism, thereby causing “turn-off” of fluorescence.[3] This work aims to highlight the recent development of iron probes within the literature and discuss their advantages and disadvantages. This review is expected to provide researchers with sufficient background for promising future work on iron probes and suggestions to avoid challenges. 

The earlier work on iron targeting peptides includes the synthesis of previously reported iron chelating mitochondrial probes with a dansyl fluorophore.[1] This work found that the two-photon fluorescence of the dansyl fluorophore made it difficult to conduct cell studies. Therefore, an alternative fluorophore, thiazole orange, has been coupled unto a 6-sequence SS-peptide. Thiazole orange would not require the two-photon experiment for cell studies (single photon instead). Another benefit of using thiazole orange is its intense fluorescence response and signal sensitivity.[2] The TO-Fx-r-Fx-r-Fx-r peptide was inspired by the work from Horton et al. (2008).[3] This peptide is different from the dansyl one because localization of (Cx-d-arginine)6-NH2 is not as easily perturbed when it is conjugated to fluorophores, chelators etc.

 Sulfur dimer is an important molecular constituent in atmospheric and cometary spectra. S2 has been detected in the volcanic plumes on Jupiter’s moon Io [1]. S2 has also been seen in UV spectra of comet IRAS-Araki-Alcock 1983d [2], comet Hyakutake [3] and comet Shoemaker–Levy 9 [4]. 

An S2 line list has been generated by using available spectroscopic constants from the literature and the program PGOPHER [5]. The line list contains the primary B3Σ−u- X3Σ−g (ν’=0-27, ν’’=0-5,7) electronic transition, with predissociated bands from ν’≥10. Similar to the Schumann-Runge Bands of O2, the S2 predissociated bands are caused by the spin-orbit interaction with the crossing ungerade electronic states [6]. These diffuse S2 UV bands require the inclusion of predissociated line widths in order to generate reliable cross-section spectra. HAPI is currently being modified to calculate absorption cross-sections with the inclusion of predissociated line widths. This new functionality with HAPI will allow for the calculation of spectra for any molecule with predissociated line widths. With the new predissociation calculation within HAPI we are able to accurately reproduce the available photoabsorption cross-section spectra from [7] at 370K and 823K.

The primary isotopologue 32S2 makes up the majority of the line list, with the 34S2 isotopologue available for a single B-X (10,0) band. The S2 line list also includes the B″3Πu- X3Σ−g (ν’=0-21, ν’’=0-5,7) electronic bands, where the B″ state strongly interacts with the B state. The f1Δu - a1Δg (1,2) band has also been included in the line list, its band head is visible at 35791.7 cm-1. In summary, we present the new HITRAN-formatted S2 line list and its validation against laboratory absorption and emission spectra.

 The ability to model and interpret spectra in diverse planetary environments is a cornerstone for the successful scientific outputs of current and future planetary remote sensing missions. For instance, NASA’s Juno Mission has been taking microwave data from Jupiter’s deep atmosphere (dominated by H2, He and to lesser extent H2O) and is interpreting this data by using NH3 opacity models educated by laboratory measurements [1,2,3,4,5,6,7,8,9,10]. Future missions to Venus (dominated by CO2) will aim to investigate the recent tentative microwave detections of PH3 [11,12] and its potential correlation with SO2 within the middle/upper cloud deck. In this work, we assess the accuracy of the HITRAN2020 [13] parameters at reproducing the experimental microwave spectra of NH3, SO2 and PH3 by using the HITRAN Application Programming Interface (HAPI) [14]. HITRAN has always contained air- and self-broadening data, however, newly included broadening data (He, H2, CO2 and H2O) [15,16,17] are used in this work and demonstrate an improvement in opacity calculations applicable to planetary atmospheres. Symmetric line shapes, such as the Voigt line shape, do not properly fit microwave data that are close to zero wavenumbers. Instead alternative asymmetric profiles must be used, such as the Van Vleck & Weisskopf or Gross line shapes. These are suitable for most molecules, for instance in this work, PH3 opacity is calculated with the Van Vleck & Weisskopf line shape. However, for NH3, the high density of lines in inversion mode, requires invoking the Ben-Reuven line shape, which contains additional terms for line coupling and pressure shifts. Similarly, for SO2 broadened by CO2 a Ben-Reuven line shape provides a better application of CO2 induced line shifts values, rather than the expected Van Vleck & Weisskopf line shape. 

The HITRAN2020 edition includes newly added or updated planetary broadening parameters applicable to modeling and interpreting spectra of planetary and exoplanetary atmospheres [1]. These new parameters include broadening due to ambient pressure of H2O [2], He, H2, and CO2 [3]. Planetary broadeners were first added to the database during the HITRAN2016 edition for the line lists of; SO2, NH3, HF, HCl, OCS, and C2H2 [4]. Since then, He, H2, and CO2 broadening parameters, as well as their temperature dependencies, and in some cases, pressure-induced shifts have been added and/or updated for the line lists of; CO2, N2O, CO, SO2, OH, OCS, H2CO, HCN, PH3, H2S, and GeH4 [3]. By using these planetary broadeners, in conjunction with the HITRAN Application Programming Interface (HAPI) [5], a reliable planetary reference opacity can be calculated. As a test case, this work investigates how the HITRAN broadening data can be used to model spectra under Jovian and Venusian conditions, with resultant opacities compared to available laboratory data [6-9]. Specifically, opacities of NH3 broadened by H2, He, and H2O are tested against laboratory data that are utilized by the Juno mission to retrieve atmospheric molecular constituents of Jupiter [10, 11]. In addition, due to the recent tentative detection of PH3 on Venus [12] and subsequent studies regarding correlation of the signal with lines of SO2 [13, 14], the opacities of PH3 and SO2 under Venusian conditions are also modeled. Overall, this work demonstrates how HITRAN and HAPI along with the newly included planetary broadeners can be utilized to generate opacities under diverse planetary conditions.

New ESA and NASA missions to Venus will be equipped with spectrometers targeting relevant molecular species. It is therefore essential that the HITRAN database provides the best available spectroscopic parameters for the primary constituents and trace gases in the atmosphere of Venus. This refers not only to the traditional HITRAN parameters but also to the line-shape parameters due to ambient pressure of CO2, relevant collision-induced absorption, and CO2 line-mixing. Some notable updates were made towards these goals for HITRAN2020. The laser spectrometer onboard of DaVinci+ mission will be measuring several key atmospheric constituents on Venus, including SO2, OCS, CO, CO2 and H2O, and their isotopologues [1], all of which have been updated in HITRAN2020, including revising or adding broadening parameters due to pressure of CO2 [2]. Moreover, the line list of SO2 was improved and expanded by incorporating additional bands [3], isotopologues [4], and broadening parameters; in particular, SO2 perturbed by CO2 [5]. There have been important updates to the spectral parameters of H2O, CO2, CO, and OCS, with the inclusion of numerous additional bands (in the case of H2O, CO2 and OCS) along with an update of the line shape parameters. In addition, the line list of PH3 has been improved for the dyad, pentad and octad regions. Furthermore, several new molecules have been added to HITRAN for the first time which are relevant for Venus, such as SO [6] and CS2 [7]. In summary, a comprehensive overview of the important updates and remaining deficiencies in HITRAN relevant for the exploration of Venus is detailed in this work.

The HITRAN (high-resolution transmission molecular spectroscopic database) is an international standard for reference molecular spectroscopy, particularly in simulating planetary and terrestrial atmospheric spectra [1]. HITRAN recently added new broadening parameters that are relevant to planetary atmospheres for many chemical species in the database. For NH3, new broadening parameters include H2, He, CO2 [2] and H2O [3]. These additional broadening parameters for NH3 allowed for validations of HITRAN data with the HITRAN Application Programming Interface (HAPI) [4] against the NH3 opacity models and laboratory data utilized by the Juno Mission. The Juno spacecraft carries with it a microwave radiometer which probes the atmospheric composition of Jupiter in the microwave range (0.02-0.73 cm−1 ) [5,6]. At these frequencies, Jupiter’s atmospheric spectra is dominated by the inversion of NH3 and is broadened by H2, He, and H2O. This work required three new line shapes to be incorporated into HAPI in order to accurately compare to available laboratory data and standard NH3 opacity models (the Ben-Reuven [7], Gross [8] and Van Vleck and Weisskopf [9] line shapes). The results of this work demonstrate that HAPI can be used with HITRAN data, to model NH3 opacities under Jovian conditions in the microwave region. It also shows great promise to produce opacities for other species of interest to the planetary community.

 The HITRAN (high-resolution transmission) molecular spectroscopic database is an international standard for reference molecular spectroscopy, particularly in simulating planetary and terrestrial atmospheric spectra [1]. Recently, new H2-, He-, CO2- [2, 3] and H2O-broadening [4] parameters, which are relevant to planetary and exoplanetary atmospheres, have been added to HITRAN for many chemical species. Proof-of-concept comparisons for NH3 have been performed against opacity models and laboratory data utilized by the Juno Mission, using the HITRAN Application Programming Interface (HAPI) [5]. The microwave radiometer on Juno is probing the atmospheric composition of Jupiter in the microwave range (0.02-0.73 cm-1) [6, 7]. At these frequencies, Jupiter’s atmospheric spectra is dominated by the inversion of NH3 and is broadened by H2, He, and H2O. Additionally, due to the recent tentative detections of PH3 on Venus [8], and the potential of spectral blending between transitions of PH3 and SO2, we have compared SO2 and PH3 absorption in the microwave region to experimental observations. The results of this work demonstrate that HAPI can be used with HITRAN data to produce atmospheric opacities under Jovian conditions in the microwave region.

HITRAN (high-resolution transmission molecular spectroscopic database) is an international standard for reference molecular spectroscopy, particularly in simulating planetary atmospheric spectra [Gordon et al., 2017]. HITRAN recently added parameters for broadening of ammonia lines not only by “traditional” air and self, but also by H2, He, CO2 [Wilzewski et al., 2016] and H2O [Tan et al., 2019]. With these additional broadening parameters applied to HITRAN, the efficacy of their application on the inversion spectrum of ammonia in the microwave region has been tested by using the HITRAN Application Programming Interface (HAPI) [Kochanov et al., 2016] and comparing it with modern widely used models and laboratory data. In particular, this work is comparing to the laboratory studies and opacity models utilized by the Juno mission for interpretation of Jupiter’s atmospheric composition. The Juno spacecraft carries with it a microwave radiometer which operates in the 0.02-0.73 cm-1 range to retrieve the abundance of molecular constituents from the microwave signature of Jupiter [Janssen et al., 2017, Bolton et al., 2017]. At these frequencies, the microwave opacity of the Jovian atmosphere is dominated by the inversion of the ammonia (NH3) molecule. To make accurate comparisons to laboratory data and corresponding NH3 opacity models, this work required three new line shapes to be incorporated into HAPI (the Ben-Reuven [1966], Gross [1955] and Van Vleck and Weisskopf [1945] line shapes). The results of this work demonstrate that using HAPI and HITRAN data, with a Ben-Reuven [1966] line shape, can accurately reproduce the opacity of NH3 under Jovian conditions.

 The HITRAN database is a compilation of molecular spectroscopic parameters used to simulate and analyze the transmission and emission of light in gaseous media, especially the planetary atmospheres [1]. HITRAN contains data that is provided by researchers and collaborators throughout the spectroscopic community. These contributors receive credit for their contributions through the bibliography of citations produced alongside the data returned by an online search. Prior to the work presented here, HITRAN created these bibliographies manually, which is a tedious, time consuming and error-prone process. The application described here is able to create bibliographic entries in the database automatically, which reduces both the frequency of mistakes and the workload for the its administrators. This new system uniquely identifies each reference from its digital object identifier (DOI) and retrieves the corresponding bibliographic information from any of several online services, including the SAO/NASA Astrophysics Data Systems (ADS) [2] and CrossRef APIs. Once parsed into a relational database, the software is able to produce bibliographies in any of several formats, including HTML and BibTeX for use on websites or printed articles. The application is provided free-of-charge for general use by any scientific database. This work was made possible due to the Smithsonian Astrophysical Observatory Latino Initiative Program and is funded by the National Science Foundation under Grant No. 1745460.