Attributing northern high-latitude precipitation change over the period 1966-2005 to human influence

Wan, Hui,Zhang, Xuebin,Zwiers, Francis,Min, Seung-Ki Springer-Verlag 2015 Climate dynamics Vol.45 No.7

Attribution of extreme temperature changes during 1951–2010

Kim, Y. H.,Min, S. K.,Zhang, X.,Zwiers, F.,Alexander, L. V.,Donat, M. G.,Tung, Y. S. Springer Science + Business Media 2016 Climate dynamics Vol.46 No.5

<P>An attribution analysis of extreme temperature changes is conducted using updated observations (HadEX2) and multi-model climate simulation (CMIP5) datasets for an extended period of 1951-2010. Compared to previous HadEX/CMIP3-based results, which identified human contributions to the observed warming of extreme temperatures on global and regional scales, the current results provide better agreement with observations, particularly for the intensification of warm extremes. Removing the influence of two major modes of natural internal variability (the Arctic Oscillation and Pacific Decadal Oscillation) from observations further improves attribution results, reducing the model-observation discrepancy in cold extremes. An optimal fingerprinting technique is used to compare observed changes in annual extreme temperature indices of coldest night and day (TNn, TXn) and warmest night and day (TNx, TXx) with multi-model simulated changes that were simulated under natural-plus-anthropogenic and natural-only (NAT) forcings. Extreme indices are standardized for better intercomparisons between datasets and locations prior to analysis and averaged over spatial domains from global to continental regions following a previous study. Results confirm previous HadEX/CMIP3-based results in which anthropogenic (ANT) signals are robustly detected in the increase in global mean and northern continental regional means of the four indices of extreme temperatures. The detected ANT signals are also clearly separable from the response to NAT forcing, and results are generally insensitive to the use of different model samples as well as different data availability.</P>

Human subcortical brain asymmetries in 15,847 people worldwide reveal effects of age and sex

Guadalupe, Tulio,Mathias, Samuel R.,vanErp, Theo G. M.,Whelan, Christopher D.,Zwiers, Marcel P.,Abe, Yoshinari,Abramovic, Lucija,Agartz, Ingrid,Andreassen, Ole A.,Arias-Vá,squez, Alejandro,Aribi Springer US 2017 Brain imaging and behavior Vol.11 No.5

<P>The two hemispheres of the human brain differ functionally and structurally. Despite over a century of research, the extent to which brain asymmetry is influenced by sex, handedness, age, and genetic factors is still controversial. Here we present the largest ever analysis of subcortical brain asymmetries, in a harmonized multi-site study using meta-analysis methods. Volumetric asymmetry of seven subcortical structures was assessed in 15,847 MRI scans from 52 datasets worldwide. There were sex differences in the asymmetry of the globus pallidus and putamen. Heritability estimates, derived from 1170 subjects belonging to 71 extended pedigrees, revealed that additive genetic factors influenced the asymmetry of these two structures and that of the hippocampus and thalamus. Handedness had no detectable effect on subcortical asymmetries, even in this unprecedented sample size, but the asymmetry of the putamen varied with age. Genetic drivers of asymmetry in the hippocampus, thalamus and basal ganglia may affect variability in human cognition, including susceptibility to psychiatric disorders.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1007/s11682-016-9629-z) contains supplementary material, which is available to authorized users.</P>

Conformation-Specific Spectroscopy of Asparagine-Containing Peptides: Influence of Single and Adjacent Asn Residues on Inherent Conformational Preferences

Blodgett, Karl N.,Fischer, Joshua L.,Lee, Jaeyeon,Choi, Soo Hyuk,Zwier, Timothy S. American Chemical Society 2018 The Journal of physical chemistry A Vol.122 No.44

<P>The infrared and ultraviolet spectra of a series of capped asparagine-containing peptides, Ac-Asn-NHBn, Ac-Ala-Asn-NHBn, and Ac-Asn-Asn-NHBn, have been recorded under jet-cooled conditions in the gas phase in order to probe the influence of the Asn residue, with its −CH<SUB>2</SUB>-C(═O)-NH<SUB>2</SUB> side chain, on the local conformational preferences of a peptide backbone. The double-resonance methods of resonant ion-dip infrared (RIDIR) spectroscopy and infrared-ultraviolet hole-burning (IR-UV HB) spectroscopy were used to record single-conformation spectra in the infrared and ultraviolet, respectively, free from interference from other conformations present in the molecular beam. Ac-Asn-NHBn spreads its population over two conformations, both of which are stabilized by a pair of H-bonds that form a bridge between the Asn carboxamide group and the NH and C═O groups on the peptide backbone. In one the peptide backbone engages in a 7-membered H-bonded ring (labeled C7<SUB>eq</SUB>), thereby forming an inverse γ-turn, stabilized by a C6/C7 Asn bridge. In the other the Asn carboxamide group forms a C8/C7 H-bonded bridge with the carboxamide group facing in the opposite direction across an extended peptide backbone involving a C5 interaction. Both Ac-Ala-Asn-NHBn and Ac-Asn-Asn-NHBn are found exclusively in a single conformation in which the peptide backbone engages in a type I β-turn with its C10 H-bond. The Asn residue(s) stabilize this β-turn via C6 H-bond(s) between the carboxamide C═O group and the same residue’s amide NH. These structures are closely analogous to the corresponding structures in Gln-containing peptides studied previously [Walsh, P. S. et al. <I>PCCP</I><B>2016</B>, <I>18</I>, 11306-11322; Walsh, P. S. et al. <I>Angew. Chem. Int. Ed.</I><B>2016</B>, <I>55</I>, 14618-14622], indicating that the Asn and Gln side chains can each configure so as to stabilize the same backbone conformations. Spectroscopic and computational evidence suggest that glutamine is more predisposed than asparagine to β-turn formation via unusually strong side-chain-backbone hydrogen-bond formation. Further spectral and structural similarities and differences due to the side-chain length difference of these similar amino acids are presented and discussed.</P> [FIG OMISSION]</BR>

Conformer-Specific and Diastereomer-Specific Spectroscopy of <i>αβα</i> Synthetic Foldamers: Ac-Ala−β_ACHC-Ala-NHBn

Blodgett, Karl N.,Zhu, Xiao,Walsh, Patrick S.,Sun, Dewei,Lee, Jaeyeon,Choi, Soo Hyuk,Zwier, Timothy S. American Chemical Society 2018 The Journal of physical chemistry A Vol.122 No.14

<P>The folding propensities of a capped, cyclically constrained, mixed <I>α/β</I> diastereomer pair, (<I>SRSS)</I> Ac-Ala−β<SUB>ACHC</SUB>-Ala-NHBn (hereafter <I>RS</I>) and (<I>SSRS)</I> Ac-Ala−β<SUB>ACHC</SUB>-Ala-NHBn (<I>SR</I>), have been studied in a molecular beam using single-conformation spectroscopic techniques. These <I>α/β</I>-tripeptides contain a cyclohexane ring across each C<SUB>α</SUB><I>-</I>C<SUB>β</SUB> bond, at which positions their stereochemistries differ. This cyclic constraint requires any stable species to adopt one of two ACHC configurations: equatorial C═O/axial NH or equatorial NH/axial C═O. Resonant two-photon ionization (R2PI) and infrared-ultraviolet hole-burning (IR-UV HB) spectroscopy were used in the S<SUB>0</SUB>-S<SUB>1</SUB> region of the UV chromophore, revealing the presence of three unique conformational isomers of <I>RS</I> and two of <I>SR</I>. Resonant ion-dip infrared spectra were recorded in both the NH stretch (3200-3500 cm<SUP>-1</SUP>) and the amide I (1600-1800 cm<SUP>-1</SUP>) regions. These experimental vibrational frequencies were compared with the scaled calculated normal-mode frequencies from density functional theory at the M05-2X/6-31+G(d) level of theory, leading to structural assignments of the observed conformations. The <I>RS</I> diastereomer is known in crystalline form to preferentially form a C11/C9 mixed helix, in which alternating hydrogen bonds are arranged in near antiparallel orientation. This structure is preserved in one of the main conformers observed in the gas phase but is in competition with both a tightly folded C7<SUB>eq</SUB>/C12/C8/C7<SUB>eq</SUB> structure, in which all four amide NH groups and four C═O groups are engaged in hydrogen bonding, as well as a cap influenced C7<SUB>eq</SUB>/NH···π/C11 structure. The <I>SR</I> diastereomer is destabilized by inducing backbone dihedral angles that lie outside the typical Ramachandran angles. This diastereomer also forms a C11/C9 mixed helix as well as a cap influenced bifurcated C7<SUB>ax</SUB>-C11/NH···π/C7<SUB>eq</SUB> structure as the global energy minimum. Assigned structures are compared with the reported crystal structure of analogous <I>α/β</I>-tripeptides, and disconnectivity graphs are presented to give an overview of the complicated potential energy surface of this tripeptide diastereomer pair.</P> [FIG OMISSION]</BR>

Conformation-specific spectroscopy of capped glutamine-containing peptides: role of a single glutamine residue on peptide backbone preferences

Walsh, Patrick S.,Dean, Jacob C.,McBurney, Carl,Kang, Hyuk,Gellman, Samuel H.,Zwier, Timothy S. The Royal Society of Chemistry 2016 Physical chemistry chemical physics Vol.18 No.16

<P>The conformational preferences of a series of short, aromatic-capped, glutamine-containing peptides have been studied under jet-cooled conditions in the gas phase. This work seeks a bottom-up understanding of the role played by glutamine residues in directing peptide structures that lead to neurodegenerative diseases. Resonant ion-dip infrared (RIDIR) spectroscopy is used to record single-conformation infrared spectra in the NH stretch, amide I and amide II regions. Comparison of the experimental spectra with the predictions of calculations carried out at the DFT M05-2X/6-31+G(d) level of theory lead to firm assignments for the H-bonding architectures of a total of eight conformers of four molecules, including three in Z-Gln-OH, one in Z-Gln-NHMe, three in Ac-Gln-NHBn, and one in Ac-Ala-Gln-NHBn. The Gln side chain engages actively in forming H-bonds with nearest-neighbor amide groups, forming C8 H-bonds to the C-terminal side, C9 H-bonds to the N-terminal side, and an amide-stacked geometry, all with an extended (C5) peptide backbone about the Gln residue. The Gln side chain also stabilizes an inverse gamma-turn in the peptide backbone by forming a pair of H-bonds that bridge the gamma-turn and stabilize it. Finally, the entire conformer population of Ac-Ala-Gln-NHBn is funneled into a single structure that incorporates the peptide backbone in a type I beta-turn, stabilized by the Gln side chain forming a C7 H-bond to the central amide group in the beta-turn not otherwise involved in a hydrogen bond. This beta-turn backbone structure is nearly identical to that observed in a series of X-(AQ)-Y beta-turns in the protein data bank, demonstrating that the gas-phase structure is robust to perturbations imposed by the crystalline protein environment.</P>