Steric Changes Research Articles

Steric sea level variability (1993–2010) in an ensemble of ocean reanalyses and objective analyses

Quantifying the effect of the seawater density changes on sea level variability is of crucial importance for climate change studies, as the sea level cumulative rise can be regarded as both an important climate change indicator and a possible danger for human activities in coastal areas. In this work, as part of the Ocean Reanalysis Intercomparison Project, the global and regional steric sea level changes are estimated and compared from an ensemble of 16 ocean reanalyses and 4 objective analyses. These estimates are initially compared with a satellite-derived (altimetry minus gravimetry) dataset for a short period (2003–2010). The ensemble mean exhibits a significant high correlation at both global and regional scale, and the ensemble of ocean reanalyses outperforms that of objective analyses, in particular in the Southern Ocean. The reanalysis ensemble mean thus represents a valuable tool for further analyses, although large uncertainties remain for the inter-annual trends. Within the extended intercomparison period that spans the altimetry era (1993–2010), we find that the ensemble of reanalyses and objective analyses are in good agreement, and both detect a trend of the global steric sea level of 1.0 and 1.1 ± 0.05 mm/year, respectively. However, the spread among the products of the halosteric component trend exceeds the mean trend itself, questioning the reliability of its estimate. This is related to the scarcity of salinity observations before the Argo era. Furthermore, the impact of deep ocean layers is non-negligible on the steric sea level variability (22 and 12 % for the layers below 700 and 1500 m of depth, respectively), although the small deep ocean trends are not significant with respect to the products spread.

The interaction between delayed rectifier channel alpha-subunits does not involve hetero-tetramer formation.

We have previously reported a physiologically relevant interaction between KCNQ1 (Q1) and KCNH2 (H2). While the H2 C-terminus has been suggested to play a role, so far, no more detailed information regarding the interaction site is available. The methods used in the study are cell culture, PCR for mutagenesis, patch clamp for ion current recordings, co-immunoprecipitation for determination of protein interaction. Co-expression of Q1 and H2 resulted in an increase of I H2 (tails after +50mV; Q1 + H2, 36 ± 6pA/pF; H2, 14 ± 2pA/pF; n = 10; 12; P < 0.05). Upon expressing a non-conductive (dominant-negative) Q1-pore mutation (dnQ1), there was still an increase in I H2 (tails after +50mV; H2 + dnQ1, 24 ± 4pA/pF; n = 10; P < 0.05) making the pore region unlikely as an interaction site. Experiments using the KCNH2-pore blocking agent quinidine supported these findings. If Q1 and H2 formed hetero-tetramers, steric changes within the pore should change the quinidine half-inhibitory concentrations (IC50). However, I H2 sensitivity did not significantly change in the presence or absence of Q1 (IC50 341 ± 63 vs. 611 ± 293nmol/L, respectively, P = n.s.), providing further evidence that the pore is not a likely H2-Q1 interaction site. To obtain further insights into the role of intra-cytoplasmic structures, we used both C- and N-terminally truncated mutant H2 proteins. Both H2 mutants co-immunoprecipitated with Q1, suggesting no specific role of C- or N-termini. Accordingly, rather than these, the transmembrane domains of the α-subunits appear relevant for the interaction. Our results largely exclude the formation of hetero-tetramers between H2 and Q1 comprising the pore region or H2 C- or N-termini.

Pd-catalyzed directed ortho-C-H alkenylation of phenylalanine derivatives.

A practical Pd-catalyzed ortho-olefination of enantioenriched N-(SO2Py)-protected aryl-alanine and norephedrine derivatives with electron-deficient alkenes has been developed using N-fluoro-2,4,6-trimethylpyridinium triflate as the terminal oxidant. The reaction occurs efficiently with excellent monosubstitution selectivity and without loss of enantiopurity. This cross-coupling proved to be broad in scope, tolerating a variety of steric and electronic changes to both coupling partners. Removal of the directing group under mild conditions provides access to optically active tetrahydroisoquinoline-3-carboxylic acid derivatives (Tics) with good diastereocontrol and with very small erosion of enantiomeric purity.

The effect of steric changes on the isoselectivity of dinuclear indium catalysts for lactide polymerization.

A series of (±)- and (R,R)-tridentate diamino, ortho/para disubstituted phenolate proligands H(NNO(R)) with various phenolate substituents was synthesized and used to prepare indium dichloride complexes (NNO(R))InCl2via salt metathesis of the deprotonated ligands with indium trichloride. These complexes are dinuclear in the solid state, in contrast to previously reported complexes with t-butyl or methyl phenolate substituents. Solution state (1)H and PGSE NMR spectroscopy suggests that a fast exchange between the monomeric and dimeric forms of these complexes may exist in solution and is likely influenced by the chirality of the complexes undergoing aggregation. The indium dichloride complexes were utilized to synthesize dinuclear indium ethoxide complexes via salt metathesis with sodium ethoxide. These complexes were active for the polymerization of lactide. In situ and bulk polymerization data confirmed differences in the activity and selectivity of these systems based on the phenolate substituents as well as the ligand chirality.

Sea-level changes in Iceland and the influence of the North Atlantic Oscillation during the last half millennium

We present a new, diatom-based sea-level reconstruction for Iceland spanning the last ∼500 years, and investigate the possible mechanisms driving the sea-level changes. A sea-level reconstruction from near the Icelandic low pressure system is important as it can improve understanding of ocean–atmosphere forcing on North Atlantic sea-level variability over multi-decadal to centennial timescales. Our reconstruction is from Viðarhólmi salt marsh in Snæfellsnes in western Iceland, a site from where we previously obtained a 2000-yr record based upon less precise sea-level indicators (salt-marsh foraminifera). The 20th century part of our record is corroborated by tide-gauge data from Reykjavik. Overall, the new reconstruction shows ca 0.6 m rise of relative sea level during the last four centuries, of which ca 0.2 m occurred during the 20th century. Low-amplitude and high-frequency sea-level variability is super-imposed on the pre-industrial long-term rising trend of 0.65 m per 1000 years. Most of the relative sea-level rise occurred in three distinct periods: AD 1620–1650, AD 1780–1850 and AD 1950–2000, with maximum rates of ∼3 ± 2 mm/yr during the latter two of these periods. Maximum rates were achieved at the end of large shifts (from negative to positive) of the winter North Atlantic Oscillation (NAO) Index as reconstructed from proxy data. Instrumental data demonstrate that a strong and sustained positive NAO (a deep Icelandic Low) generates setup on the west coast of Iceland resulting in rising sea levels. There is no strong evidence that the periods of rapid sea-level rise were caused by ocean mass changes, glacial isostatic adjustment or regional steric change. We suggest that wind forcing plays an important role in causing regional-scale coastal sea-level variability in the North Atlantic, not only on (multi-)annual timescales, but also on multi-decadal to centennial timescales.

Relative contributions of ocean mass and deep steric changes to sea level rise between 1993 and 2013

Regional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996 and 2006 are assessed through a full-depth SLR budget using full-depth in situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003 to 2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large-scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo-Atlantic sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr−1 for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8%, and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m is considered.

Long-term sea-level change revisited: the role of salinity

Of the many processes contributing to long-term sea-level change, little attention has been paid to the large-scale contributions of salinity-driven halosteric changes. We evaluate observed and simulated estimates of long-term (1950-present) halosteric patterns and compare these to corresponding thermosteric changes. Spatially coherent halosteric patterns are visible in the historical record, and are consistent with estimates of long-term water cycle amplification. Our results suggest that long-term basin-scale halosteric changes in the Pacific and Atlantic are substantially larger than previously assumed, with observed estimates and coupled climate models suggesting magnitudes of ∼25% of the corresponding thermosteric changes. In both observations and simulations, Pacific basin-scale freshening leads to a density reduction that augments coincident thermosteric expansion, whereas in the Atlantic halosteric changes partially compensate strong thermosteric expansion via a basin-scale enhanced salinity density increase. Although regional differences are apparent, at basin-scales consistency is found between the observed and simulated partitioning of halosteric and thermosteric changes, and suggests that models are simulating the processes driving observed long-term basin-scale steric changes. Further analysis demonstrates that the observed halosteric changes and their basin partitioning are consistent with CMIP5 simulations that include anthropogenic CO2 forcings (Historical), but are found to be inconsistent with simulations that exclude anthropogenic forcings (HistoricalNat).

Mean sea level variability in the North Sea: Processes and implications

AbstractMean sea level (MSL) variations across a range of time scales are examined for the North Sea under the consideration of different forcing factors since the late 19th century. We use multiple linear regression models, which are validated for the second half of the 20th century against the output of a tide+surge model, to determine the barotropic response of the ocean to fluctuations in atmospheric forcing. We find that local atmospheric forcing mainly initiates MSL variability on time scales up to a few years, with the inverted barometric effect dominating the variability along the UK and Norwegian coastlines and wind controlling the MSL variability in the south from Belgium up to Denmark. On decadal time scales, MSL variability mainly reflects steric changes, which are largely forced remotely. A spatial correlation analysis of altimetry observations and gridded steric heights suggests evidence for a coherent signal extending from the Norwegian shelf down to the Canary Islands. This fits with the theory of longshore wind forcing along the eastern boundary of the North Atlantic causing coastally trapped waves to propagate over thousands of kilometers along the continental slope. Implications of these findings are assessed with statistical Monte‐Carlo experiments. It is demonstrated that the removal of known variability increases the signal to noise ratio with the result that: (i) linear trends can be estimated more accurately; (ii) possible accelerations (as expected, e.g., due to anthropogenic climate change) can be detected much earlier. Such information is of crucial importance for anticipatory coastal management, engineering, and planning.

Spatial variations of sea level along the coast of Thailand: Impacts of extreme land subsidence, earthquakes and the seasonal monsoon

The study addresses two important issues associated with sea level along the coasts of Thailand: first, the fast sea level rise and its spatial variation, and second, the monsoonal-driven seasonal variations in sea level. Tide gauge data that are more extensive than in past studies were obtained from several different local and global sources, and relative sea level rise (RSLR) rates were obtained from two different methods, linear regressions and non-linear Empirical Mode Decomposition/Hilbert–Huang Transform (EMD/HHT) analysis. The results show extremely large spatial variations in RSLR, with rates varying from ~1mmy−1 to ~20mmy−1; the maximum RSLR is found in the upper Gulf of Thailand (GOT) near Bangkok, where local land subsidence due to groundwater extraction dominates the trend. Furthermore, there are indications that RSLR rates increased significantly in all locations after the 2004 Sumatra–Andaman Earthquake and the Indian Ocean tsunami that followed, so that recent RSLR rates seem to have less spatial differences than in the past, but with high rates of ~20–30mmy−1 almost everywhere. The seasonal sea level cycle was found to be very different between stations in the GOT, which have minimum sea level in June–July, and stations in the Andaman Sea, which have minimum sea level in February. The seasonal sea-level variations in the GOT are driven mostly by large-scale wind-driven set-up/set-down processes associated with the seasonal monsoon and have amplitudes about ten times larger than either typical steric changes at those latitudes or astronomical annual tides.

Mechanisms of Global-Mean Steric Sea Level Change

Abstract Global-mean sea level change partly reflects volumetric expansion of the oceans because of density change, otherwise known as global-mean steric sea level change. Owing to nonlinearities in the equation of state of seawater, the nature of processes contributing to recent observed global-mean steric sea level changes has not been well understood. Using a data-constrained ocean state estimate, global-mean steric sea level change over 1993–2003 is revisited, and contributions from ocean transports and surface exchanges are quantified using closed potential temperature and salinity budgets. Analyses demonstrate that estimated decadal global-mean steric sea level change results mainly from a slight, time-mean imbalance between atmospheric forcing and ocean transports over the integration period: surface heat and freshwater exchanges produce a trend in global-mean steric sea level that is mainly offset by the redistribution of potential temperature and salinity through small-scale diffusion and large-scale advection. A set of numerical experiments demonstrates that global-mean steric sea level changes simulated by ocean general circulation models are sensitive to the regional distribution of ocean heat and freshwater content changes.

Spectroscopic Studies of Single and Double Variants of M Ferritin: Lack of Conversion of a Biferrous Substrate Site into a Cofactor Site for O2 Activation

Ferritin has a binuclear non-heme iron active site that functions to oxidize iron as a substrate for formation of an iron mineral core. Other enzymes of this class have tightly bound diiron cofactor sites that activate O2 to react with substrate. Ferritin has an active site ligand set with 1-His/4-carboxylate/1-Gln rather than the 2-His/4-carboxylate set of the cofactor site. This ligand variation has been thought to make a major contribution to this biferrous substrate rather than cofactor site reactivity. However, the Q137E/D140H double variant of M ferritin, has a ligand set that is equivalent to most of the diiron cofactor sites, yet did not rapidly react with O2 or generate the peroxy intermediate observed in the cofactor sites. Therefore, in this study, a combined spectroscopic methodology of circular dichroism (CD)/magnetic CD (MCD)/variable temperature, variable field (VTVH) MCD has been applied to evaluate the factors required for the rapid O2 activation observed in cofactor sites. This methodology defines the coordination environment of each iron and the bridging ligation of the biferrous active sites in the double and corresponding single variants of frog M ferritin. Based on spectral changes, the D140H single variant has the new His ligand binding, and the Q137E variant has the new carboxylate forming a μ-1,3 bridge. The spectra for the Q137E/D140H double variant, which has the cofactor ligand set, however, reflects a site that is more coordinately saturated than the cofactor sites in other enzymes including ribonucleotide reductase, indicating the presence of additional water ligation. Correlation of this double variant and the cofactor sites to their O2 reactivities indicates that electrostatic and steric changes in the active site and, in particular, the hydrophobic nature of a cofactor site associated with its second sphere protein environment, make important contributions to the activation of O2 by the binuclear non-heme iron enzymes.

ジチエニルエテン類3種の光異性化反応におけるエネルギーと立体化学変化および置換基効果等のMOPAC-PM6法によるシミュレーション解析

ジチエニルエテン類のフォトクロミズムは次世代の分子レベルスイッチなどとして期待されている．本報では，その3種タイプの光閉環/光開環の可逆反応におけるポテンシャルエネルギー，立体化学変化，置換基効果等の実験データを，小さい計算負荷のMOPAC-PM6法を用いてシミュレーションした．6π開環異性体はタイプ1，3(3hと3m)および5であり，閉環異性体は対応の2，4および6である．そのシミュレーションはB3LYP/6-31GやCASSCF (10,10)レベルによる既存データと比較，検証した．タイプ1と3の結晶状態での光反応では，反応炭素間距離RCC と環化反応の量子収率 φOCとの間には，RCCが 4 Å以下の3h(4'-H)5ではφOCがほぼ1であり，4 Å以上の結晶では0というデータがある．本法のシミュレーションでは基底状態と励起状態の両方につき，開環体の安定配座(anti-parallel)からの動的解析で上記現象を再現した．RCCが4 Å以下の開環体の励起では，HSOMOなどのフロンティア軌道の6π末端間相互作用が，励起一重項(3h* と5*：RCC約2.1 Å)を容易にもたらし，閉環体にする．RCCが4 Å以上の1および3m(4'-Me) の光環化は起り難く，一方溶液中では6π面の容易な変化が推定され，上記現象が合理的に説明される．閉環体2および4から，その励起一重項(2*と4*：RCC約1.6 Å)を経た開環反応過程も明らかにした．6からは6* ではなく，5* の生成が観察された．それは，6から5への光開環反応の量子収率φCO が比較的に高い原因の一つを示唆している．本報のPM6法での計算精度はB3LYP/6-31G レベルのそれと遜色ないものが多かったが，補正すべき点もあり，その補正量を指摘した．多様な分子設計や反応系解析への，PM6法の活用が期待される．

Tuning coordination modes of pyridine/thioether Schiff base (NNS) ligands to mononuclear manganese carbonyls.

We have investigated the coordination modes of NNS Schiff base, thioether ligands to manganese(I) carbonyls. The ligands contain ortho substituted pyridines (H, CH3, OCH3, fluorophenyl) and varying substituents (H, CH3) at the Schiff base linkage. In general, reaction of [Mn(CO)5Br] with a tridentate NNS ligand in CH2Cl2 affords species in which the thioether-S may be bound or unbound to the manganese center, depending on the steric and electronic substitution in the ligand framework; as a result, the complexes exhibit two or three carbonyl ligands, respectively. Aldehyde-derived ligand frames ((R1)N(H)NS) generally afford complexes of type [((R)NNS)Mn(CO)3Br] (1(CO), 2(CO), 3(CO); R = H, OCH3, CH3) that exhibit incomplete ligation of the chelate (S not bound) in X-ray structures. In contrast, use of the iminomethyl ligand (N(Me)NS) affords a complex of formula [(N(Me)NS)Mn(CO)2Br] (4(CO)), in which the mixed N/thioether-S stabilizes the {Mn(CO)2}(+) fragment. In solid state IR spectra, complexes of type [((R)NNS)Mn(CO)3Br] (1(CO) through 3(CO)) afford three ν(CO) in the range ~2060-1865 cm(-1); the dicarbonyl complex [(N(Me)NS)Mn(CO)2Br] (4(CO)) exhibits two carbonyl stretches in the range ~1920-1845 cm(-1). Prolonged storage of the tricarbonyl [((Me)NNS)Mn(CO)3Br] (3(CO)) in presence of trace dioxygen affords the dibromide species [((Me)NNS)Mn(Br)2] (3(Br)), in which the thioether S reliably binds to the Mn(II) center. Complexes 1(CO)-3(CO) exhibit simple, diamagnetic (1)H NMR spectra in CD2Cl2. The S-ligated complex 4(CO) exhibits spectra consistent with a mixture of an S-bound (6-coordinate) and S-unbound (5-coordinate) species as represented by [(N(Me)NS)Mn(CO)2Br] ↔ [(N(Me)NS)Mn(CO)2Br]. Lastly, we obtained crystal structures of the S-bound and S-unbound conformers derived from the same ligand--the fluorophenyl derived (FPh)NNS, namely [((FPh)NNS)Mn(CO)3Br] (5(CO-a)) and [((FPh)NNS)Mn(CO)2Br] (5(CO-b)). This report represents several examples of a thioether-stabilized {Mn(CO)2}(+) fragment, a deviation from the usual 'piano stool' Mn(I) tricarbonyl motif. We highlight that coordination of these NNS ligands to Mn(I) carbonyls occurs on a soft conformational landscape, and that ligand substituents can be rationally employed to favor the desired coordination mode.

Co-expression of γ2 Subunits Hinders Processing of N-Linked Glycans Attached to the N104 Glycosylation Sites of GABAA Receptor β2 Subunits

GABAA receptors, the major mediators of fast inhibitory neuronal transmission, are heteropentameric glycoproteins assembled from a panel of subunits, usually including α and β subunits with or without a γ2 subunit. The α1β2γ2 receptor is the most abundant GABAA receptor in brain. Co-expression of γ2 with α1 and β2 subunits causes conformational changes, increases GABAA receptor channel conductance, and prolongs channel open times. We reported previously that glycosylation of the three β2 subunit glycosylation sites, N32, N104 and N173, was important for α1β2 receptor channel gating. Here, we examined the hypothesis that steric effects or conformational changes caused by γ2 subunit co-expression alter the glycosylation of partnering β2 subunits. We found that co-expression of γ2 subunits hindered processing of β2 subunit N104 N-glycans in HEK293T cells. This γ2 subunit-dependent effect was strong enough that a decrease of γ2 subunit expression in heterozygous GABRG2 knockout (γ2(+/-)) mice led to appreciable changes in the endoglycosidase H digestion pattern of neuronal β2 subunits. Interestingly, as measured by flow cytometry, γ2 subunit surface levels were decreased by mutating each of the β2 subunit glycosylation sites. The β2 subunit mutation N104Q also decreased GABA potency to evoke macroscopic currents and reduced conductance, mean open time and open probability of single channel currents. Collectively, our data suggested that γ2 subunits interacted with β2 subunit N-glycans and/or subdomains containing the glycosylation sites, and that γ2 subunit co-expression-dependent alterations in the processing of the β2 subunit N104 N-glycans were involved in altering the function of surface GABAA receptors.

Sea level changes at Tenerife Island (NE Tropical Atlantic) since 1927

Hourly sea level observations measured by five tide gauges at Santa Cruz harbor (Tenerife Island), in the Northeastern Tropical Atlantic, have been merged to build a consistent and almost continuous sea level record starting in 1927. Datum continuity was ensured using high precision leveling information. The time series underwent a detailed quality control in order to remove outliers, time drifts, and datum shifts. The resulting sea level record was then used to describe the low frequency (interannual to decadal) sea level variability at Tenerife. It was found that at interannual and longer time scales, the observed sea level changes are primarily driven by steric sea level variations. Such steric changes are originated by coastal trapped waves induced by longshore winds along the continental coast and propagate poleward. Observed sea level rise at Tenerife was 2.09 ± 0.04 mm/yr since 1927. According to the hydrographic observations in the area, only half of this trend was attributed to steric sea level changes for the top 500 m, at least since 1950.

열팽창 효과를 직접 고려한 미래 지구온난화에 의한 북서태평양에서의 상세 해수면 상승 연구

In order to consider the effect of steric sea level change directly, we developed the regional version ocean circulation model (ReMOM) using the GFDL MOM version 4 which does not use the Boussinesq approximation. The GFDL CM2.1’s SRES A1B and B1 results from IPCC were used for the initial and boundary conditions in the northwestern Pacific. The sea surface temperature and sea surface height were increased by about 2oC and 30cm for SRES A1B, and about 1oC and 22 cm for SRES B1 after 100 years, respectively. East Sea was affected by steric effect more than Yellow Sea. It caused by the warmer Tsushima current passing the Korea strait due to global warming. The sea level rises by the direct steric effect were higher than by the indirect steric effect.

Illuminating Photoswitchable Catalysis

Through the realization of conceptually new approaches aimed at controlling chemical reactions using light, the field of photoswitchable catalysis has seen rapid development over the past three decades. Although many photoswitchable catalysts are heterogeneous and utilize photosensitive surfaces, such as TiO2 and CdSe, significant attention has also been directed toward homogeneous analogues, primarily by capitalizing on the steric changes that accompany the E → Z photoisomerizations of azobenzene or stilbene derivatives. More recently, photochromic diarylethene moieties have been used to switch the intrinsic catalytic activities and selectivities through alteration of the steric and electronic properties displayed by a supporting ligand. In addition to detailing the aforementioned advances, this perspective summarizes other important developments in photoswitchable catalysis and offers a viewpoint on the future outlook of the field.

Satellite‐derived interannual ocean bottom pressure variability and its relation to sea level

[1] Knowledge of the relationship between bottom pressure pb and sea level ζ is important for understanding ocean circulation and climate. We use recent Gravity Recovery and Climate Experiment (GRACE) Release-05 data along with altimetry to investigate the relationship between ζ and pb over long periods (>1 year) and large scales (>750 km). Elevated pb signals are observed over deep extratropical regions (e.g., Southern Ocean basins) and shallow or semi-enclosed areas (e.g., Indonesian and Nordic seas). In these places, considerable ζ variance is explained by pb variance. Correlation between ζ and pb is significant in many regions, including instances of significant negative correlation suggestive of active baroclinic processes. Results exemplify the good quality of GRACE Release-05 data and demonstrate that contemporary regional ζ variability cannot always be interpreted in terms of steric changes alone.

Steric effects and mechanism in the formation of hemi‐acetals from aliphatic aldehydes

Some physical properties (pKa, log POW, boiling points) of hexanoic acid 1 (X = COOH) and its seven isomers 2, 3, 4, 5, 6, 7, 8 (X = COOH) are reported.Hexanal 1 (X = CHO) and its seven isomeric aldehydes 2, 3, 4, 5, 6, 7, 8 (X = CHO) are shown to equilibrate, in methanol solution, with their hemi‐acetals. Logarithms of equilibrium constants correlate with values of Es for the isomeric C5H11 substituents, and with logs of relative rates for saponification of the corresponding methyl esters with ρ = 0.52, reflecting the reduced steric demand of hydrogen compared to oxygen in the quaternization of ester and aldehydic carbonyl groups. Rates of equilibration have also been measured in buffered methanol. For hexanal, with a 2:1 Et3N:AcOH buffer, the buffer‐independent contribution is dominated by the methoxide catalysed pathway. Rates in this medium have been determined for isomers 1, 2, 3, 4, 5, 6, 7, 8 (X = CHO), and their logarithms do not correlate with logarithms of equilibrium constants for hemi‐acetal formation or with substituent steric parameters derived from ester formation or saponification, indicating that the steric changes associated with full quaternization of the carbonyl group are not mirrored in the transition structures for hemi‐acetal formation. It is suggested that transition states for hemi‐acetal formation are relatively early so that steric interactions are effectively those between the nucleophile and ground state conformations of the aldehydes. A comparison of the entropies of hemi‐acetal formation with entropies of activation has provided a basis for a suggested transition structure. Comparisons with acid chloride hydrolyses are made. © 2013 The Authors. Journal of Physical Organic Chemistry published by John Wiley &amp; Sons Ltd.

Steric sea level change in twentieth century historical climate simulation and IPCC-RCP8.5 scenario projection: A comparison of two versions of FGOALS model

To reveal the steric sea level change in 20th century historical climate simulations and future climate change projections under the IPCC’s Representative Concentration Pathway 8.5 (RCP8.5) scenario, the results of two versions of LASG/IAP’s Flexible Global Ocean-Atmosphere-Land System model (FGOALS) are analyzed. Both models reasonably reproduce the mean dynamic sea level features, with a spatial pattern correlation coefficient of 0.97 with the observation. Characteristics of steric sea level changes in the 20th century historical climate simulations and RCP8.5 scenario projections are investigated. The results show that, in the 20th century, negative trends covered most parts of the global ocean. Under the RCP8.5 scenario, global-averaged steric sea level exhibits a pronounced rising trend throughout the 21st century and the general rising trend appears in most parts of the global ocean. The magnitude of the changes in the 21st century is much larger than that in the 20th century. By the year 2100, the global-averaged steric sea level anomaly is 18 cm and 10 cm relative to the year 1850 in the second spectral version of FGOALS (FGOALS-s2) and the second grid-point version of FGOALS (FGOALS-g2), respectively. The separate contribution of the thermosteric and halosteric components from various ocean layers is further evaluated. In the 20th century, the steric sea level changes in FGOALS-s2 (FGOALS-g2) are largely attributed to the thermosteric (halosteric) component relative to the pre-industrial control run. In contrast, in the 21st century, the thermosteric component, mainly from the upper 1000 m, dominates the steric sea level change in both models under the RCP8.5 scenario. In addition, the steric sea level change in the marginal sea of China is attributed to the thermosteric component.