An urgent need for COP27: confronting converging crises.

The last 12 months have provided further evidence of the potential for cascading ecological and socio-political crises that were warned of 12 months ago. Then a consensus statement from the Regional Action on Climate Change Symposium warned: "the Earth's climatic, ecological, and human systems are converging towards a crisis that threatens to engulf global civilization within the lifetimes of children now living." Since then, the consequences of a broad set of extreme climate events (notably droughts, floods, and fires) have been compounded by interaction with impacts from multiple pandemics (including COVID-19 and cholera) and the Russia-Ukraine war. As a result, new connections are becoming visible between climate change and human health, large vulnerable populations are experiencing food crises, climate refugees are on the move, and the risks of water, food, and climate disruption have been visibly converging and compounding. Many vulnerable populations now face serious challenges to adapt. In light of these trends, this year, RACC identifies a range of measures to be taken at global and regional levels to bolster the resilience of these populations in the face of such emerging crises. In particular, at all scales, there is a need for globally available local data, reliable analytic techniques, community capacity to plan adaptation strategies, and the resources (scientific, technical, cultural, and economic) to implement them. To date, the rate of growth of the support for climate change resilience lags behind the rapid growth of cascading and converging risks. As an urgent message to COP27, it is proposed that the time is now right to devote much greater emphasis, global funding, and support to the increasing adaptation needs of vulnerable populations.

Temperature Dependence of Desorbed Ions and Neutrals and Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization.

Two separate temperature-dependent experiments were performed to investigate the ionization mechanism of ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) of matrix 2,5-dihydroxybenzoic acid (2,5-DHB). First, the angular resolved intensity and velocity distributions of neutrals desorbed from the 2,5-DHB solid sample through UV laser (355 nm) pulse irradiation were measured using a rotating quadrupole mass spectrometer. Second, the desorbed neutrals, at an angle normal to the surface, and the desorbed ions were simultaneously detected for each laser shot using the quadrupole mass spectrometer and a time-of-flight mass spectrometer, respectively. Both experiments were conducted at two initial temperatures: 100 and 300 K. The measurements from these two experiments were used to calculate the initial temperature dependence of the ion-to-neutral ratio. The results closely agreed with the predictions of the temperature-dependent ion-to-neutral ratio using the thermal model, indicating that thermally induced proton transfer is the dominant reaction that generates initial ions of 2,5-DHB in UV-MALDI.

Advantage of spatial map ion imaging in the study of large molecule photodissociation.

The original ion imaging technique has low velocity resolution, and currently, photodissociation is mostly investigated using velocity map ion imaging. However, separating signals from the background (resulting from undissociated excited parent molecules) is difficult when velocity map ion imaging is used for the photodissociation of large molecules (number of atoms ≥ 10). In this study, we used the photodissociation of phenol at the S1 band origin as an example to demonstrate how our multimass ion imaging technique, based on modified spatial map ion imaging, can overcome this difficulty. The photofragment translational energy distribution obtained when multimass ion imaging was used differed considerably from that obtained when velocity map ion imaging and Rydberg atom tagging were used. We used conventional translational spectroscopy as a second method to further confirm the experimental results, and we conclude that data should be interpreted carefully when velocity map ion imaging or Rydberg atom tagging is used in the photodissociation of large molecules. Finally, we propose a modified velocity map ion imaging technique without the disadvantages of the current velocity map ion imaging technique.

Laser Pulse Width Dependence and Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization.

Ultraviolet laser pulses at 355 nm with variable pulse widths in the region from 170 ps to 1.5 ns were used to investigate the ionization mechanism of matrix-assisted laser desorption/ionization (MALDI) for matrices 2,5-dihydroxybenzoic acid (DHB), α-cyano-4-hydroxycinnamic acid (CHCA), and sinapinic acid (SA). The mass spectra of desorbed ions and the intensity and velocity distribution of desorbed neutrals were measured simultaneously for each laser shot. These quantities were found to be independent of the laser pulse width. A comparison of the experimental measurements and numerical simulations according to the multiphoton ionization, coupled photophysical and chemical dynamics (CPCD), and thermally induced proton transfer models showed that the predictions of thermally induced proton transfer model were in agreement with the experimental data, but those of the multiphoton ionization model were not. Moreover, the predictions of the CPCD model based on singlet-singlet energy pooling were inconsistent with the experimental data of CHCA and SA, but were consistent with the experimental data of DHB only when some parameters used in the model were adjusted to extreme values. Graphical Abstract ᅟ.

Theoretical investigation of low detection sensitivity for underivatized carbohydrates in ESI and MALDI.

Electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mainly generate protonated ions from peptides and proteins but sodiated (or potassiated) ions from carbohydrates. The ion intensities of sodiated (or potassiated) carbohydrates generated by ESI and MALDI are generally lower than those of protonated peptides and proteins. Ab initio calculations and transition state theory were used to investigate the reasons for the low detection sensitivity for underivatized carbohydrates. We used glucose and cellobiose as examples and showed that the low detection sensitivity is partly attributable to the following factors. First, glucose exhibits a low proton affinity. Most protons generated by ESI or MALDI attach to water clusters and matrix molecules. Second, protonated glucose and cellobiose can easily undergo dehydration reactions. Third, the sodiation affinities of glucose and cellobiose are small. Some sodiated glucose and cellobiose dissociate into the sodium cations and neutral carbohydrates during ESI or MALDI process. The increase of detection sensitivity of carbohydrates in mass spectrometry by various methods can be rationalized according to these factors. Copyright © 2016 John Wiley & Sons, Ltd.

Formation of Metal-Related Ions in Matrix-Assisted Laser Desorption Ionization.

In a study of the metal-related ion generation mechanism in matrix-assisted laser desorption ionization (MALDI), crystals of matrix used in MALDI were grown from matrix- and salt-containing solutions. The intensities of metal ion and metal adducts of the matrix ion obtained from unwashed crystals were higher than those from crystals washed with deionized water, indicating that metal ions and metal adducts of the matrix ions are mainly generated from the surface of crystals. The contributions of preformed metal ions and metal adducts of the matrix ions inside the matrix crystals were minor. Metal adducts of the matrix and analyte ion intensities generated from a mixture of dried matrix, salt, and analyte powders were similar to or higher than those generated from the powder of dried droplet crystals, indicating that the contributions of the preformed metal adducts of the matrix and analyte ions were insignificant. Correlation between metal-related ion intensity fluctuation and protonated ion intensity fluctuation was observed, indicating that the generation mechanism of the metal-related ions is similar to that of the protonated ions. Because the thermally induced proton transfer model effectively describes the generation of the protonated ions, we suggest that metal-related ions are mainly generated from the salt dissolution in the matrix melted by the laser. Graphical Abstract ᅟ.

Ionization Mechanism of Matrix-Assisted Laser Desorption/Ionization.

In past studies, mistakes in determining the ionization mechanism in matrix-assisted laser desorption/ionization (MALDI) were made because an inappropriate ion-to-neutral ratio was used. The ion-to-neutral ratio of the analyte differs substantially from that of the matrix in MALDI. However, these ratios were not carefully distinguished in previous studies. We begin by describing the properties of ion-to-neutral ratios and reviews early experimental measurements. A discussion of the errors committed in previous theoretical studies and a comparison of recent experimental measurements follow. We then describe a thermal proton transfer model and demonstrate how the model appropriately describes ion-to-neutral ratios and the total ion intensity. Arguments raised to challenge thermal ionization are then discussed. We demonstrate how none of the arguments are valid before concluding that thermal proton transfer must play a crucial role in the ionization process of MALDI.

Ion-to-Neutral Ratios and Thermal Proton Transfer in Matrix-Assisted Laser Desorption/Ionization.

The ion-to-neutral ratios of four commonly used solid matrices, α-cyano-4-hydroxycinnamic acid (CHCA), 2,5-dihydroxybenzoic acid (2,5-DHB), sinapinic acid (SA), and ferulic acid (FA) in matrix-assisted laser desorption/ionization (MALDI) at 355 nm are reported. Ions are measured using a time-of-flight mass spectrometer combined with a time-sliced ion imaging detector. Neutrals are measured using a rotatable quadrupole mass spectrometer. The ion-to-neutral ratios of CHCA are three orders of magnitude larger than those of the other matrices at the same laser fluence. The ion-to-neutral ratios predicted using the thermal proton transfer model are similar to the experimental measurements, indicating that thermal proton transfer reactions play a major role in generating ions in ultraviolet-MALDI.

Fluorescence spectroscopy of UV-MALDI matrices and implications of ionization mechanisms.

Matrix-assisted laser desorption ionization (MALDI) has been widely used in the mass analysis of biomolecules; however, there are a lot of debates about the ionization mechanisms. Previous studies have indicated that S1-S1 annihilation might be a key process in the generation of primary ions. This study investigates S1-S1 annihilation by examining the time-resolved fluorescence spectra of 12 matrices. No S1-S1 annihilation was observed in six of these matrices (3-hydroxy-picolinic acid, 6-aza-2-thiothymine, 2,4-dihydroxy-acetophenone, 2,6-dihydroxy-acetophenone, 2,4,6-trihydroxy-acetophenone, and ferulic acid). We observed two matrix molecules reacting in an electronically excited state (S1) in five of these matrices (2,5-dihydroxybenzoic acid, α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxy-acetophenone, 2,3-dihydroxybenzoic acid, and 2,6-dihydroxybenzoic acid), and S1-S1 annihilation was a possible reaction. Among these five matrices, no S1-S1 annihilation was observed for 2,3-dihydroxybenzoic acid in typical peak power region of nanosecond laser pulses in MALDI, but a very small value of reaction rate constant was observed only in the high peak power region. The excited-state lifetime of sinapinic acid was too short to determine whether the molecules reacted in an electronically excited state. No correlation was observed between the ion generation efficiency of MALDI and S1-S1 annihilation. The results indicate that the proposal of S1-S1 annihilation is unnecessary in MALDI and energy pooling model for MALDI ionization mechanism has to be modified.

Contribution of thermal energy to initial ion production in matrix-assisted laser desorption/ionization observed with 2,4,6-trihydroxyacetophenone.

RATIONALE: Although several reaction models have been proposed in the literature to explain matrix-assisted laser desorption/ionization (MALDI), further study is still necessary to explore the important ionization pathways that occur under the high-temperature environment of MALDI. 2,4,6-Trihydroxyacetophenone (THAP) is an ideal compound for evaluating the contribution of thermal energy to an initial reaction with minimum side reactions. METHODS: Desorbed neutral THAP and ions were measured using a crossed-molecular beam machine and commercial MALDI-TOF instrument, respectively. A quantitative model incorporating an Arrhenius-type desorption rate derived from transition state theory was proposed. Reaction enthalpy was calculated using GAUSSIAN 03 software with dielectric effect. Additional evidence of thermal-induced proton disproportionation was given by the indirect ionization of THAP embedded in excess fullerene molecules excited by a 450 nm laser. RESULTS: The quantitative model predicted that proton disproportionation of THAP would be achieved by thermal energy converted from a commonly used single UV laser photon. The dielectric effect reduced the reaction Gibbs free energy considerably even when the dielectric constant was reduced under high-temperature MALDI conditions. With minimum fitting parameters, observations of pure THAP and THAP mixed with fullerene both agreed with predictions. CONCLUSIONS: Proton disproportionation of solid THAP was energetically favorable with a single UV laser photon. The quantitative model revealed an important initial ionization pathway induced by the abrupt heating of matrix crystals. In the matrix crystals, the dielectric effect reduced reaction Gibbs free energy under typical MALDI conditions. The result suggested that thermal energy plays an important role in the initial ionization reaction of THAP.

Ion intensity and thermal proton transfer in ultraviolet matrix-assisted laser desorption/ionization.

The ionization mechanism of ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI) was investigated by measuring the total cation intensity (not including sodiated and potasiated ions) as a function of analyte concentration (arginine, histidine, and glycine) in a matrix of 2,4,6-trihydroxyacetophenone (THAP). The total ion intensity increased up to 55 times near the laser fluence threshold as the arginine concentration increased from 0% to 1%. The increases were small for histidine, and a minimal increase occurred for glycine. Time-resolved fluorescence intensity was employed to investigate how analytes affected the energy pooling of the matrix. No detectable energy pooling was observed for pure THAP and THAP/analyte mixtures. The results can be described by using a thermal proton transfer model, which suggested that thermally induced proton transfer is crucial in the primary ion generation in UV-MALDI.

Does decarboxylation make 2,5-dihydroxybenzoic acid special in matrix-assisted laser desorption/ionization?

RATIONALE: Among the six positional isomers of dihydroxybenzoic acid (DHB), 2,5-DHB is a more favorable matrix for use in matrix-assisted laser desorption/ionization (MALDI) than the other isomers because of its high ion-generation efficiency at 337 and 355 nm. The generation of hydroquinone or p-benzoquinone through the decarboxylation of 2,5-DHB has been suggested to play a crucial role in the ion-generation efficiency of 2,5-DHB. METHODS: The mass spectra of desorbed neutrals generated from MALDI were measured using electron impact ionization (70 eV) and a quadrupole mass spectrometer and vacuum ultraviolet (118 nm) photoionization and a time-of-flight mass spectrometer. The mass spectra of desorbed ions generated from MALDI were investigated using a time-of-flight mass spectrometer. The dissociation barrier height and dissociation rate of decarboxylation were calculated by an ab initio method and RRKM theory. RESULTS: Decarboxylation of neutral 2,5-DHB and 2,5-DHB cations was not observed. Theoretical calculations indicated that decarboxylation of neutral 2,5-DHB and 2,5-DHB cations is too slow to occur. CONCLUSIONS: The high ion-generation efficiency of the 2,5-DHB matrix at 337 and 355 nm is not related to decarboxylation.

Thermal proton transfer reactions in ultraviolet matrix-assisted laser desorption/ionization.

One of the reasons that thermally induced reactions are not considered a crucial mechanism in ultraviolet matrix-assisted laser desorption ionization (UV-MALDI) is the low ion-to-neutral ratios. Large ion-to-neutral ratios (10(-4)) have been used to justify the unimportance of thermally induced reactions in UV-MALDI. Recent experimental measurements have shown that the upper limit of the total ion-to-neutral ratio is approximately 10(-7) at a high laser fluence and less than 10(-7) at a low laser fluence. Therefore, reexamining the possible contributions of thermally induced reactions in MALDI may be worthwhile. In this study, the concept of polar fluid was employed to explain the generation of primary ions in MALDI. A simple model, namely thermal proton transfer, was used to estimate the ion-to-neutral ratios in MALDI. We demonstrated that the theoretical calculations of ion-to-neutral ratios exhibit the same trend and similar orders of magnitude compared with those of experimental measurements. Although thermal proton transfer may not generate all of the ions observed in MALDI, the calculations demonstrated that thermally induced reactions play a crucial role in UV-MALDI.

Is energy pooling necessary in ultraviolet matrix-assisted laser desorption/ionization?

RATIONALE: Energy pooling has been suggested as the key process for generating the primary ions during ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). In previous studies, decreases in fluorescence quantum yields as laser fluence increased for 2-aminobenzoic acid, 2,5-dihydroxybenzoic acid (2,5-DHB), and 3-hydroxypicolinic acid were used as evidence of energy pooling. This work extends the research to other matrices and addresses whether energy pooling is a universal property in UV-MALDI. METHODS: Energy pooling was investigated in a time-resolved fluorescence experiment by using a short laser pulse (355 nm, 20 ps pulse width) for excitation and a streak camera (1 ps time resolution) for fluorescence detection. RESULTS: The excited-state lifetime of 2,5-DHB decreased with increases in laser fluence. This suggests that a reaction occurs between two excited molecules, and that energy pooling may be one of the possible reactions. However, the excited-state lifetime of 2,4,6-trihydroxyacetophenone (THAP) did not change with increases in laser fluence. The upper limit of the energy pooling rate constant for THAP is estimated to be approximately 100-500 times smaller than that of 2,5-DHB. CONCLUSIONS: The small energy pooling rate constant for THAP indicates that the potential contribution of the energy pooling mechanism to the generation of THAP matrix primary ions should be reconsidered.

Selective enhancement of carbohydrate ion abundances by diamond nanoparticles for mass spectrometric analysis.

Diamond nanoparticles (DNPs) were incorporated into matrix-assisted laser desorption/ionization (MALDI) samples to enhance the sensitivity of the mass spectrometer to carbohydrates. The DNPs optimize the MALDI sample morphology and thermalize the samples for thermally labile compounds because they have a high thermal conductivity, a low extinction coefficient in UV-vis spectral range, and stable chemical properties. The best enhancement effect was achieved when matrix, DNP, and carbohydrate solutions were deposited and vacuum-dried consecutively to form a trilayer sample morphology. It allows the direct identification of underivatized carbohydrates mixed with equal amount of proteins because no increase in the ion abundance of proteins was achieved. For dextran with an average molecular weight of 1500, the trilayer method typically improves the sensitivity by 79- and 7-fold in comparison to the conventional dried-droplet and thin-layer methods, respectively.

MALDI mechanism of dihydroxybenzoic acid isomers: desorption of neutral matrix and analyte.

Angular resolved velocity distributions of laser desorbed neutral matrices (dihydroxybenzoic acids, DHB) and analytes (tryptophan) embedded in these matrices were investigated at 322 nm by a modified crossed molecular beam apparatus. Desorbed ions generated from MALDI were measured by a time-of-flight mass spectrometer. Desorptions of neutral matrix and analyte from 2,3-DHB, 2,4-DHB, 2,5-DHB, 2,6-DHB, and 3,5--DHB at 322 nm have similar properties, but the ion intensities are in the order 2,3DHB ≅ 2,6-DHB > 2,5-DHB ≅ 2,4-DHB > 3,5-DHB. It indicates that the combination of various parameters related to neutral species, including absorption coefficient, sublimation energy, contact of analyte and matrix in crystal, and plume dynamics of desorbed species are not crucial in the determination of MALDI process for DHB isomers. The difference of matrix activity of DHB isomers at this wavelength must result from the other properties, like the excited state lifetime, proton affinity, gas-phase basicity, acidity, ionization energy, or the other properties related to the primary reactions in ion generation.

Analysis of initial reactions of MALDI based on chemical properties of matrixes and excitation condition.

This investigation concerns the initial chemical reactions that affect the ionization of matrixes in matrix-assisted laser desorption/ionization (MALDI). The study focuses on the relaxations of photon energy that occur on a comparable time scale to that of ionization, in which the available laser energy is shared and the ionization condition is changed. The relaxations include fluorescence, fragmentation, and nonradiative relaxation from the excited state to the ground state. With high absorption cross section and long excited-state lifetime, photoionization of matrix plays an important role if sufficient laser energy is used. Under other conditions, thermal ionization of the molecule in the ground state is predicted to be one of the important reactions. Evidence of change in the branching ratio of initial reactions with the matrix and the excitation wavelength was obtained with α-cyano-4-hydroxycinnamic acid, sinapinic acid, 2,5-dihydroxybenzoic acid, and 2,4,6-trihydroxyacetophenone. These matrixes are studied by obtaining their mixed crystal absorption spectra, fluorescence properties, laser-induced infrared emission, and product ions. The exact ionization pathway depends on the chemical properties of matrixes and the excitation conditions. This concept may explain the diversity of experimental results observed in MALDI experiments, which provides an insight into the ensemble of chemical reactions that govern the generation of ions.

High ion yields of carbohydrates from frozen solution by UV-MALDI.

An aqueous acetonitrile solution containing oligosaccharides (maltopentaose and polysaccharides) and a matrix (2,5-dihydroxybenzoic acid) was frozen at 100 K for mass analysis using ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI). Compared with conventional UV-MALDI (i.e., using a dry analyte/matrix mixture), a frozen solution generates more oligosaccharide ions and less fragments from postsource decay. Furthermore, the ion signal is long-lasting, and the analyte distribution features enhanced homogeneity. The ion generation efficiency for this procedure is 20-30 times greater than that for a conventional dried mixture. Interestingly, the percentages for maltopentaose fragmentation from postsource decay for the frozen samples are close to zero (<2%), as compared with the 17% and 40% values found for dried samples at low and high laser fluences, respectively. Comparisons with other UV matrixes (α-cyano-4-hydroxycinnamic acid and sinapinic acid) and ionic liquids (2,5-dihydroxybenzoic acid + pyridine and α-cyano-4-hydroxycinnamic acid + butylamine) were investigated, and possible mechanisms are discussed.

Plume expansion dynamics of matrix-assisted laser desorption ionization.

High-resolution angular and velocity distributions for neutral analytes (tryptophan and poly-tryptophan) and matrix (2,4,6-trihydroxyacetophenon, THAP) are measured by using 355 nm laser desorption. The information suggests that two separate mechanisms dominate the angular and velocity distributions at the beginning and before the end of desorption. A molecular jet-like isentropic expansion dominates the plume expansion at the beginning of desorption. This only occurs at high surface temperature, thus resulting in a large velocity normal to the surface and a very narrow angular distribution. Most of the analytes are produced under these conditions. Before the end of desorption, the surface temperature decreases and the mechanism of thermal desorption at low vapor pressure takes over. The velocities become small and the angular distribution is close to cosθ. Only a very small amount of analytes are generated under these conditions. Compared to tryptophan, poly-tryptophan has a much narrower angular distribution, thereby suggesting that it is only produced at the higher surface temperatures.