Monometallic salts derived from complex anions of group 10 metal ions with p-tolylsulfonyldithiocarbimate ligand: Synthesis, characterization and properties

New monometallic complex salts of the form X-2[M(L)(2)] [M = Ni2+, X = (CH3)(2)NH2+(1); M = Ni2+, X = (CH3)(4)N+ (2); M = Ni2+, X = (C2H5)(4)N+(3); M = Ni2+, X = (C3H7)(4)N+(4); M = Ni2+; X = (C6H13)(4)N+) (5); M = Pd2+,X = (CH3)(2)NH2+(6); M = Pd2+, X= (C2H5)(4)N+(7); M = Pd2+, X= (C3H7)(4)N+(8); M = Pd2+, X = (C6H13)(4)N+ (9); M = Pt2+, X = (CH3)(2)NH2+(10); L = p-tolylsulfonyldithiocarbimate (CH3C6H4SO2N=CS22 )] have been prepared and characterized by elemental analysis, IR, H-1 and C-13 NMR and UV-Vis spectroscopy; 1, 3, 4 and 5 by X-ray crystallography. In 1, 3, 4 and 5, the Ni atom is four coordinate with a square planar environment being bonded to four sulfur atoms from two bidentate ligands. All the salts are weakly conducting (sigma(rt) = 10 (7) to 10 (14) Scm (1)) because of the lack of significant S center dot center dot center dot S intermolecular interactions between complex anions [M(L)(2)](2) in the solid state however, they show behavior of semiconductors in the temperature range 353-453 K. All the Pd(II) and Pt(II) salts exhibited phtotolumeniscent emissions near visible region in solution at room temperature.

Gut microbial activity, implications for health and disease: the potential role of metabolite analysis

Microbial metabolism of proteins and amino acids by human gut bacteria generates a variety of compounds including phenol, indole, and sulfur compounds and branched chain fatty acids, many of which have been shown to elicit a toxic effect on the lumen. Bacterial fermentation of amino acids and proteins occurs mainly in the distal colon, a site that is often fraught with symptoms from disorders including ulcerative colitis (UC) and colorectal cancer (CRC). In contrast to carbohydrate metabolism by the gut microbiota, proteolysis is less extensively researched. Many metabolites are low molecular weight, volatile compounds. This review will summarize the use of analytical methods to detect and identify compounds in order to elucidate the relationship between specific dietary proteinaceous substrates, their corresponding metabolites, and implications for gastrointestinal health.

Synthesis, structure and electrochemical properties of some thiosemicarbazone complexes of ruthenium

Reaction of salicylaldehyde thiosemicarbazone (L-1), 2-hydroxyacetophenone thiosemicarbazone (L-2) and 2-hydroxynapthaldehyde thiosemicarbazone (L-3) with [Ru(dmso)(4)Cl-2] affords a family of three dimeric complexes (1), (2) and (3) respectively. Crystal structure of the complex (3) has been determined. In these complexes, each monomeric unit consists of one ruthenium center and two thiosemicarbazone ligands, one of which is coordinated to ruthenium as O,N,S-donor and the other as N,S-donor forming a five-membered chelate ring. Two such monomeric units remain bridged by the sulfur atoms of the O,N,S-coordinated thiosemicarbazones. Due to this sulfur bridging, the two ruthenium centers become so close to each other, that a ruthenium-ruthenium single bond is also formed. All the complexes are diamagnetic in the solid state and in dimethylsulfoxide solution show intense absorptions in the visible and ultraviolet region. Origin of these spectral transitions has been established from DFT calculations. Cyclic voltammetry on the complexes shows two irreversible ligand oxidations on the positive side of SCE and two irreversible ligand reductions on the negative side.

Ruthenium mediated C–H activation of benzaldehyde thiosemicarbazones: Synthesis, structure and, spectral and electrochemical properties of the resulting complexes

Reaction of five 4R-benzaldehyde thiosemicarbazones (R = OCH3, CH3, H, Cl and NO2) with [ Ru(PPh3)(3)(-CO)(H) Cl] in refluxing methanol in the presence of a base (NEt3) affords complexes of two different types, viz. 1-R and 2-R. In the 1-R complexes the thiosemicarbazone is coordinated to ruthenium as a dianionic tridentate C,N,S-donor via C-H bond activation. Two triphenylphosphines and a carbonyl are also coordinated to ruthenium. The tricoordinated thiosemicarbazone ligand is sharing the same equatorial plane with ruthenium and the carbonyl, and the PPh3 ligands are mutually trans. In the 2-R complexes the thiosemicarbazone ligand is coordinated to ruthenium as a monoanionic bidentate N, S-donor forming a four-membered chelate ring with a bite angle of 63.91(11)degrees. Two triphenylphosphines, a carbonyl and a hydride are also coordinated to ruthenium. The coordinated thiosemicarbazone ligand, carbonyl and hydride constitute one equatorial plane with the metal at the center, where the carbonyl is trans to the coordinated nitrogen of the thiosemicarbazone and the hydride is trans to the sulfur. The two triphenylphosphines are trans. Structures of the 1-CH3 and 2-CH3 complexes have been determined by X-ray crystallography. All the complexes show intense transitions in the visible region, which are assigned, based on DFT calculations, to transitions within orbitals of the thiosemicarbazone ligand. Cyclic voltammetry on the complexes shows two oxidations of the coordinated thiosemicarbazone on the positive side of SCE and a reduction of the same ligand on the negative side.

Immunomodulatory effects of a probiotic drink containing Lactobacillus casei Shirota in healthy older volunteers

PURPOSE: There is growing evidence that probiotics confer health benefits to the host by modulating immune function, especially in older people, where immunosenescence is a feature even of healthy ageing. The aim of this study was to investigate the effect of a probiotic drink containing Lactobacillus casei Shirota (LcS) on immune function in a healthy non-immunocompromised older population. METHODS: Thirty healthy old volunteers were recruited into a randomized placebo-controlled, single-blind crossover study. The volunteers were supplemented with the probiotic drink containing 1.3 × 10(10) CFU LcS or skimmed milk per day for 4 weeks, followed by 4 weeks of washout and were crossed over to the other treatment. Peripheral blood and saliva samples were collected at baseline and end of each treatment. RESULTS: Probiotic consumption was associated with a significant increase in natural killer (NK) cell activity relative to baseline and a significant decrease in the mean fluorescence intensity of CD25 expression in the resting T cells compared with placebo. Additionally, there was a trend towards an increased ratio of IL-10 to IL-12 relative to baseline after LcS intake. CONCLUSIONS: Consumption of a probiotic drink containing LcS improved NK cell activity and tended to produce a more anti-inflammatory cytokine profile in an older population.

The interplay of secondary Hg⋯S, Hg⋯N and Hg⋯π bonding interactions in supramolecular structures of phenylmercury(ii) dithiocarbamates

Three new phenylmercury(II) and one mercury(II) dithiocarbamate complexes viz. PhHg S2CN(PyCH2) Bz (1), PhHg S2CN(PyCH2)CH3 (2), PhHg S2CN(Bz)CH3 (3), and [Hg (NCS2(PyCH2)Bz)(2)] (4) (Py = pyridine; Bz = benzyl) have been synthesized and characterized by elemental analyses, IR, electronic absorption, H-1 and C-13 NMR spectroscopy. The crystal structures of 1, 2 and 3 showed a linear S-Hg-C core at the centre of the molecule, in which the metal atom is bound to the sulfur atom of the dithiocarbamate ligand and a carbon atom of the aromatic ring. In contrast the crystal structure of 4 showed a linear S-Hg-S core at the Hg(II) centre of the molecule. Weak intermolecular Hg center dot center dot center dot N (Py) interactions link molecules into a linear chain in the case of 1, whereas chains of dimers are formed in 2 through intermolecular Hg center dot center dot center dot N (Py) and Hg center dot center dot center dot S interactions. 3 forms a conventional face-to-edge dimeric structure through intermolecular Hg center dot center dot center dot S secondary bonding and 4 forms a linear chain of dimers through face-to-face Hg center dot center dot center dot S secondary bonding. In order to elucidate the nature of these secondary bonding interactions and the electronic absorption spectra of the complexes, ab initio quantum chemical calculations at the MP2 level and density functional theory calculations were carried out for 1-3. Complexes 1 and 2 exhibited photoluminescent properties in the solid state as well as in the solution phase. Studies indicate that Hg center dot center dot center dot S interactions decrease and Hg center dot center dot center dot N interactions increase the chances of photoluminescence in the solid phase

Geo-Engineering to Confine Climate Change: Is it at all Feasible?

Paul Crutzen (2006) has suggested a research initiative to consider whether it would be feasible to artificially enhance the albedo of the planet Earth to counteract greenhouse warming. The enhancement of albedo would be achieved by intentionally injecting sulfur into the stratosphere. The rational for proposing the experiment is the observed cooling of the atmosphere following the recent major volcanic eruptions by El Chichon in 1984 and Mount Pinatubo in 1991 (Hansen et al., 1992). Although I am principally not against a research initiative to study such a potential experiment, I do have important reservations concerning its general feasibility. And its potential feasibility, I believe, must be the key motivation for embarking on such a study. Here I will bring up three major issues, which must be more thoroughly understood before any geo-engineering of climate could be considered, if at all. The three issues are (i) the lack of accuracy in climate prediction, (ii) the huge difference in timescale between the effect of greenhouse gases and the effect of aerosols and (iii) serious environmental problems which may be caused by high carbon dioxide concentration irrespective of the warming of the climate.

Spatial patterns of gluten protein and polymer distribution in wheat grain

The starchy endosperm is the major storage tissue in the mature wheat grain and exhibits quantitative and qualitative gradients in composition, with the outermost cell layers being rich in protein, mainly gliadins, and the inner cells being low in protein but enriched in high-molecular-weight (HMW) subunits of glutenin. We have used sequential pearling to produce flour fractions enriched in particular cell layers to determine the protein gradients in four different cultivars grown at two nitrogen levels. The results show that the steepness of the protein gradient is determined by both genetic and nutritional factors, with three high-protein breadmaking cultivars being more responsive to the N treatment than a low-protein cultivar suitable for livestock feed. Nitrogen also affected the relative abundances of the three main classes of wheat prolamins: the sulfur-poor ω-gliadins showed the greatest response to nitrogen and increased evenly across the grain; the HMW subunits also increased in response to nitrogen but proportionally more in the outer layers of the starchy endosperm than near the core, while the sulfur-rich prolamins showed the opposite trend.

Electrochemical sensing of 2D condensation in amyloid peptides

The interfacial behavior of the model amyloid peptide octamer YYKLVFFC (peptide 1) and two other amyloid peptides YEVHHQKLVFF (peptide 2) and KKLVFFA (peptide 3) at the metal|aqueous solution interface was studied by voltammetric and constant current chronopotentiometric stripping (CPS). All three peptides are adsorbed in a wide potential range and exhibit different interfacial organizations depending on the electrode potential. At the least negative potentials, chemisorption of peptide 1 occurs through the formation of a metal sulfur bond. This bond is broken close to −0.6 V. The peptide undergoes self-association at more negative potentials, leading to the formation of a “pit” characteristic of a 2D condensed film. Under the same conditions the other peptides do not produce such a pit. Formation of the 2D condensed layer in peptide 1 is supported by the time, potential and temperature dependences of the interfacial capacity and it is shown that presence of the 2D layer is reflected by the peptide CPS signals due to the catalytic hydrogen evolution. The ability of peptide 1 to form the potential-dependent 2D condensed layer has been reported neither for any other peptide nor for any protein molecule. This ability might be related to the well-known oligomerization and aggregation of Alzheimer amyloid peptides.

Bounding the role of black carbon in the climate system: a scientific assessment

Black carbon aerosol plays a unique and important role in Earth’s climate system. Black carbon is a type of carbonaceous material with a unique combination of physical properties. This assessment provides an evaluation of black-carbon climate forcing that is comprehensive in its inclusion of all known and relevant processes and that is quantitative in providing best estimates and uncertainties of the main forcing terms: direct solar absorption; influence on liquid, mixed phase, and ice clouds; and deposition on snow and ice. These effects are calculated with climate models, but when possible, they are evaluated with both microphysical measurements and field observations. Predominant sources are combustion related, namely, fossil fuels for transportation, solid fuels for industrial and residential uses, and open burning of biomass. Total global emissions of black carbon using bottom-up inventory methods are 7500 Gg yr�-1 in the year 2000 with an uncertainty range of 2000 to 29000. However, global atmospheric absorption attributable to black carbon is too low in many models and should be increased by a factor of almost 3. After this scaling, the best estimate for the industrial-era (1750 to 2005) direct radiative forcing of atmospheric black carbon is +0.71 W m�-2 with 90% uncertainty bounds of (+0.08, +1.27)Wm�-2. Total direct forcing by all black carbon sources, without subtracting the preindustrial background, is estimated as +0.88 (+0.17, +1.48) W m�-2. Direct radiative forcing alone does not capture important rapid adjustment mechanisms. A framework is described and used for quantifying climate forcings, including rapid adjustments. The best estimate of industrial-era climate forcing of black carbon through all forcing mechanisms, including clouds and cryosphere forcing, is +1.1 W m�-2 with 90% uncertainty bounds of +0.17 to +2.1 W m�-2. Thus, there is a very high probability that black carbon emissions, independent of co-emitted species, have a positive forcing and warm the climate. We estimate that black carbon, with a total climate forcing of +1.1 W m�-2, is the second most important human emission in terms of its climate forcing in the present-day atmosphere; only carbon dioxide is estimated to have a greater forcing. Sources that emit black carbon also emit other short-lived species that may either cool or warm climate. Climate forcings from co-emitted species are estimated and used in the framework described herein. When the principal effects of short-lived co-emissions, including cooling agents such as sulfur dioxide, are included in net forcing, energy-related sources (fossil fuel and biofuel) have an industrial-era climate forcing of +0.22 (�-0.50 to +1.08) W m-�2 during the first year after emission. For a few of these sources, such as diesel engines and possibly residential biofuels, warming is strong enough that eliminating all short-lived emissions from these sources would reduce net climate forcing (i.e., produce cooling). When open burning emissions, which emit high levels of organic matter, are included in the total, the best estimate of net industrial-era climate forcing by all short-lived species from black-carbon-rich sources becomes slightly negative (�-0.06 W m�-2 with 90% uncertainty bounds of �-1.45 to +1.29 W m�-2). The uncertainties in net climate forcing from black-carbon-rich sources are substantial, largely due to lack of knowledge about cloud interactions with both black carbon and co-emitted organic carbon. In prioritizing potential black-carbon mitigation actions, non-science factors, such as technical feasibility, costs, policy design, and implementation feasibility play important roles. The major sources of black carbon are presently in different stages with regard to the feasibility for near-term mitigation. This assessment, by evaluating the large number and complexity of the associated physical and radiative processes in black-carbon climate forcing, sets a baseline from which to improve future climate forcing estimates.

Observations of the eruption of the Sarychev volcano and simulations using the HadGEM2 climate model

In June 2009 the Sarychev volcano located in the Kuril Islands to the northeast of Japan erupted explosively, injecting ash and an estimated 1.2 ± 0.2 Tg of sulfur dioxide into the upper troposphere and lower stratosphere, making it arguably one of the 10 largest stratospheric injections in the last 50 years. During the period immediately after the eruption, we show that the sulfur dioxide (SO2) cloud was clearly detected by retrievals developed for the Infrared Atmospheric Sounding Interferometer (IASI) satellite instrument and that the resultant stratospheric sulfate aerosol was detected by the Optical Spectrograph and Infrared Imaging System (OSIRIS) limb sounder and CALIPSO lidar. Additional surface‐based instrumentation allows assessment of the impact of the eruption on the stratospheric aerosol optical depth. We use a nudged version of the HadGEM2 climate model to investigate how well this state‐of‐the‐science climate model can replicate the distributions of SO2 and sulfate aerosol. The model simulations and OSIRIS measurements suggest that in the Northern Hemisphere the stratospheric aerosol optical depth was enhanced by around a factor of 3 (0.01 at 550 nm), with resultant impacts upon the radiation budget. The simulations indicate that, in the Northern Hemisphere for July 2009, the magnitude of the mean radiative impact from the volcanic aerosols is more than 60% of the direct radiative forcing of all anthropogenic aerosols put together. While the cooling induced by the eruption will likely not be detectable in the observational record, the combination of modeling and measurements would provide an ideal framework for simulating future larger volcanic eruptions.

Efficacy of increased resistant starch consumption in human type 2 diabetes

Resistant starch (RS) has been shown to beneficially affect insulin sensitivity in healthy individuals and those with metabolic syndrome, but its effects on human type 2 diabetes (T2DM) are unknown. This study aimed to determine the effects of increased RS consumption on insulin sensitivity and glucose control and changes in postprandial metabolites and body fat in T2DM. Seventeen individuals with well-controlled T2DM (HbA1c 46.6±2 mmol/mol) consumed, in a random order, either 40 g of type 2 RS (HAM-RS2) or a placebo, daily for 12 weeks with a 12-week washout period in between. At the end of each intervention period, participants attended for three metabolic investigations: a two-step euglycemic–hyperinsulinemic clamp combined with an infusion of [6,6-2H2] glucose, a meal tolerance test (MTT) with arterio-venous sampling across the forearm, and whole-body imaging. HAM-RS2 resulted in significantly lower postprandial glucose concentrations (P=0.045) and a trend for greater glucose uptake across the forearm muscle (P=0.077); however, there was no effect of HAM-RS2 on hepatic or peripheral insulin sensitivity, or on HbA1c. Fasting non-esterified fatty acid (NEFA) concentrations were significantly lower (P=0.004) and NEFA suppression was greater during the clamp with HAM-RS2 (P=0.001). Fasting triglyceride (TG) concentrations and soleus intramuscular TG concentrations were significantly higher following the consumption of HAM-RS2 (P=0.039 and P=0.027 respectively). Although fasting GLP1 concentrations were significantly lower following HAM-RS2 consumption (P=0.049), postprandial GLP1 excursions during the MTT were significantly greater (P=0.009). HAM-RS2 did not improve tissue insulin sensitivity in well-controlled T2DM, but demonstrated beneficial effects on meal handling, possibly due to higher postprandial GLP1.

The inclusion of forage mixtures in the diet of growing dairy heifers: impacts on digestion, energy utilisation, and methane emissions

Intensive farming focusing on monoculture grass species to maximise forage production has led to a reduction in the extent and diversity of species-rich grasslands. However, plant communities with higher species number (richness) are a potential strategy for more sustainable production and mitigation of greenhouse gas (GHG) emissions. Research has indicated the need to understand opportunities that forage mixtures can offer sustainable ruminant production systems. The objective of the two experiments reported here were to evaluate multiple species forage mixtures in comparison to ryegrass-dominant pasture, when conserved or grazed, on digestion, energy utilisation, N excretion, and methane emissions by growing 10–15 month old heifers. Experiment 1 was a 4 × 4 Latin square design with five week periods. Four forage treatments of: (1) ryegrass (control); permanent pasture with perennial ryegrass (Lolium perenne); (2) clover; a ryegrass:red clover (Trifolium pratense) mixture; (3) trefoil; a ryegrass:birdsfoot trefoil (Lotus corniculatus) mixture; and (4) flowers; a ryegrass:wild flower mixture of predominately sorrel (Rumex acetosa), ox-eye daisy (Leucanthemum vulgare), yarrow (Achillea millefolium), knapweed (Centaurea nigra) and ribwort plantain (Plantago lanceolata), were fed as haylages to four dairy heifers. Measurements included digestibility, N excretion, and energy utilisation (including methane emissions measured in respiration chambers). Experiment 2 used 12 different dairy heifers grazing three of the same forage treatments used to make haylage in experiment 1 (ryegrass, clover and flowers) and methane emissions were estimated using the sulphur hexafluoride (SF6) tracer technique. Distribution of ryegrass to other species (dry matter (DM) basis) was approximately 70:30 (clover), 80:20 (trefoil), and 40:60 (flowers) for experiment 1. During the first and second grazing rotations (respectively) in experiment 2, perennial ryegrass accounted for 95 and 98% of DM in ryegrass, and 84 and 52% of DM in clover, with red clover accounting for almost all of the remainder. In the flowers mixture, perennial ryegrass was 52% of the DM in the first grazing rotation and only 30% in the second, with a variety of other flower species occupying the remainder. Across both experiments, compared to the forage mixtures (clover, trefoil and flowers), ryegrass had a higher crude protein (CP) content (P < 0.001, 187 vs. 115 g kg −1 DM) and DM intake (P < 0.05, 9.0 vs. 8.1 kg day −1). Heifers in experiment 1 fed ryegrass, compared to the forage mixtures, had greater total tract digestibility (g kg −1) of DM (DMD; P < 0.008, 713 vs. 641) and CP (CPD, P < 0.001, 699 vs. 475), and used more intake energy (%) for body tissue deposition (P < 0.05, 2.6 vs. −4.9). For both experiments, heifers fed flowers differed the most compared to the ryegrass control for a number of measurements. Compared to ryegrass, flowers had 40% lower CP content (P < 0.001, 113 vs. 187 g kg −1), 18% lower DMD (P < 0.01, 585 vs. 713 g kg −1), 42% lower CPD (P < 0.001, 407 vs. 699 g kg −1), and 10% lower methane yield (P < 0.05, 22.6 vs. 25.1 g kg −1 DM intake). This study has shown inclusion of flowers in forage mixtures resulted in a lower CP concentration, digestibility and intake. These differences were due in part to sward management and maturity at harvest. Further research is needed to determine how best to exploit the potential environmental benefits of forage mixtures in sustainable ruminant production systems.

Increased whole grain consumption does not affect blood biochemistry, body composition or gut microbiology in healthy low habitual whole grain consumers

Background Whole grain (WG) foods have been suggested to reduce the risk of cardiovascular disease, but studies are inconsistent and effects on cardiovascular risk markers are not clear. Objective The objective of this study was to assess the impact of increasing WG consumption to at least 80 g/d on overall dietary intake, body composition, blood pressure (BP), blood lipids, blood glucose, gastrointestinal microbiology and gastrointestinal symptoms in healthy, middle-age adults with habitual WG intake < 24 g/d. The trial was registered as ISRCTN36521837. Methods Eligible subjects (12 men, 21 women, aged 40-65 y and BMI 20-35 kg/m2) were identified using food frequency questionnaires and subsequently completed 3-day food diaries (3DFD) to confirm habitual WG consumption. Subjects consumed diets high in WG (> 80 g/d) or low in WG (< 16 g/d, refined grain [RG] diet) in a crossover study, with 6-week intervention periods, separated by a 4-week washout. Adherence was achieved by specific dietary advice and provision of a range of cereal food products. The 3DFD, diet compliance diaries and plasma alkylresorcinols (ARs) were used to verify compliance. Results On the WG intervention, consumption increased from 28 g/d to 168 g/d (P < 0.001), accompanied by an increase in plasma ARs (P < 0.001) and total fiber intake (P < 0.001), without any effect on energy or other macronutrients. While there were no effects on studied parameters, there were trends towards increased 24 h fecal weight (P = 0.08) and reduction in body weight (P = 0.10) and BMI (P = 0.08) during the WG compared to the RG period. Conclusion A combination of dietary advice and provision of commercially available food items enabled subjects with a low-moderate habitual consumption of WG to substantially increase their WG intake, but there was little effect on blood biochemical parameters, body composition, BP, fecal measurements or gut microbiology.

Aerosol microphysics simulations of the Mt.~Pinatubo eruption with the UM-UKCA composition-climate model

We use a stratosphere–troposphere composition–climate model with interactive sulfur chemistry and aerosol microphysics, to investigate the effect of the 1991 Mount Pinatubo eruption on stratospheric aerosol properties. Satellite measurements indicate that shortly after the eruption, between 14 and 23 Tg of SO2 (7 to 11.5 Tg of sulfur) was present in the tropical stratosphere. Best estimates of the peak global stratospheric aerosol burden are in the range 19 to 26 Tg, or 3.7 to 6.7 Tg of sulfur assuming a composition of between 59 and 77 % H2SO4. In light of this large uncertainty range, we performed two main simulations with 10 and 20 Tg of SO2 injected into the tropical lower stratosphere. Simulated stratospheric aerosol properties through the 1991 to 1995 period are compared against a range of available satellite and in situ measurements. Stratospheric aerosol optical depth (sAOD) and effective radius from both simulations show good qualitative agreement with the observations, with the timing of peak sAOD and decay timescale matching well with the observations in the tropics and mid-latitudes. However, injecting 20 Tg gives a factor of 2 too high stratospheric aerosol mass burden compared to the satellite data, with consequent strong high biases in simulated sAOD and surface area density, with the 10 Tg injection in much better agreement. Our model cannot explain the large fraction of the injected sulfur that the satellite-derived SO2 and aerosol burdens indicate was removed within the first few months after the eruption. We suggest that either there is an additional alternative loss pathway for the SO2 not included in our model (e.g. via accommodation into ash or ice in the volcanic cloud) or that a larger proportion of the injected sulfur was removed via cross-tropopause transport than in our simulations. We also critically evaluate the simulated evolution of the particle size distribution, comparing in detail to balloon-borne optical particle counter (OPC) measurements from Laramie, Wyoming, USA (41° N). Overall, the model captures remarkably well the complex variations in particle concentration profiles across the different OPC size channels. However, for the 19 to 27 km injection height-range used here, both runs have a modest high bias in the lowermost stratosphere for the finest particles (radii less than 250 nm), and the decay timescale is longer in the model for these particles, with a much later return to background conditions. Also, whereas the 10 Tg run compared best to the satellite measurements, a significant low bias is apparent in the coarser size channels in the volcanically perturbed lower stratosphere. Overall, our results suggest that, with appropriate calibration, aerosol microphysics models are capable of capturing the observed variation in particle size distribution in the stratosphere across both volcanically perturbed and quiescent conditions. Furthermore, additional sensitivity simulations suggest that predictions with the models are robust to uncertainties in sub-grid particle formation and nucleation rates in the stratosphere.