{"id":2610,"date":"2010-09-24T11:04:13","date_gmt":"2010-09-24T09:04:13","guid":{"rendered":"http:\/\/localhost\/azgad\/wordpress\/?p=2610"},"modified":"2010-09-24T11:04:13","modified_gmt":"2010-09-24T09:04:13","slug":"%d7%97%d7%93%d7%a9%d7%95%d7%aa-%d7%9e%d7%92%d7%96%d7%a8%d7%aa-%d7%9e%d7%95%d7%9c%d7%a7%d7%95%d7%9c%d7%95%d7%aa-%d7%94%d7%9e%d7%99%d7%9d-%d7%94%d7%a8%d7%90%d7%a9-%d7%9c%d7%9e%d7%a2%d7%9c%d7%94-%d7%94","status":"publish","type":"post","link":"https:\/\/azgad.com\/?p=2610","title":{"rendered":"\u05d7\u05d3\u05e9\u05d5\u05ea \u05de\u05d2\u05d6\u05e8\u05ea \u05de\u05d5\u05dc\u05e7\u05d5\u05dc\u05d5\u05ea \u05d4\u05de\u05d9\u05dd: \u05d4\u05e8\u05d0\u05e9 \u05dc\u05de\u05e2\u05dc\u05d4, \u05d4\u05d6\u05e0\u05d1 \u05dc\u05de\u05d8\u05d4"},"content":{"rendered":"

.
\nAdvanced laser spectroscopy exposes the
\nunique organization of water molecules under
\n model membrane surfaces<\/strong><\/p>\n

.
\nThe behavior of water molecules as they
\ncontact biological substances has long puzzled
\n scientists. The first few layers of interfacial
\nwater can display complex arrangements that
\ndistinctly influence biochemical reactivity and
\n function. Mapping these interfaces, however,
\n is extremely difficult because chemical
\nsignatures of surface-bound water are often
\nswamped by bulk liquid signals. Now, researchers
\nled by Tahei Tahara from the Riken Institute
\nhave developed a laser spectroscopy technique
\n that conclusively determines the orientation of
\n water molecules beneath charged lipid layers\u2014
\nthe primary components of cell membranes.
\n.
\nPhospholipids are fatty acid molecules that
\ncontain two parts: hydrophobic \u2018tails\u2019 made of
\nlong hydrocarbon chains and hydrophilic \u2018heads\u2019
\n comprised of charged phosphate groups
\nand other organic units. At the air\u2013water interface,
\n phospholipids spontaneously form into monolayer
\n films, with their tails extending into the air and
\ntheir heads immersed in water. The structure
\nand orientation of water molecules below such
\nmonolayers has been a matter of controversy.
\nSome investigators suggest that the partially
\npositive-charged hydrogen atoms of water
\norientate \u2018up\u2019 or \u2018down\u2019 to align with the lipid
\nhead charge, while others suggest the opposite
\n outcome.
\n.
\nTahara and colleagues resolved this debate by
\nusing an optical technique called heterodyne-
\ndetected vibrational sum frequency generation
\n (HD-VSFG) spectroscopy, which has extremely
\nhigh surface sensitivity. HD-VSFG combines two
\n laser beams with different frequencies at an
\ninterface to generate a sum-frequency signal;
\nwhen vibrations of surface molecules resonate
\n with the applied laser, the sum-frequency signal
\n rapidly shoots up\u2014instantly identifying which
\nchemicals are present. Because this signal
\noriginates from non-linear surface polarization
\n effects, it contains only contributions from
\n interfacial species. \u201cHD-VSFG automatically
\nprobes the depths of water layers that are
\ndifferent from the bulk,\u201d says Tahara.
\n.
\nDetermining the orientation of surface water
\nrequired heterodyne detection, a method that
\ndetermines the phase of weak signals via interference
\n with a reference beam. According to Tahara,
\nperforming such measurements required
\nprecisely sensing changes to the signal light\u2019s
\noptical phase\u2014meaning the researchers had to
\n control the laser beams with nanometer-scale
\naccuracy.
\n.
\nThe teams\u2019 experiments on three different lipid
\n monolayers revealed that the interfacial structures
\nare governed by the net charge of the heads:
\n water hydrogen atoms pointed up with anionic
\nlipid heads, and faced downwards in the presence
\n of cationic. \u201cThis is totally different from the
\nsituation for reactions in aqueous solutions,\u201d
\nsays Tahara, who believes that the results will
\nshed light on important reactions that take place
\n at cell membranes, such as enzyme activation.
\n.<\/p>\n","protected":false},"excerpt":{"rendered":"

. Advanced laser spectroscopy exposes the unique organization of water molecules under model membrane surfaces . The behavior of water molecules as they contact biological substances has long puzzled scientists. The first few layers of interfacial water can display complex arrangements that distinctly influence biochemical reactivity and function. Mapping these interfaces, however, is extremely difficult … <\/p>\n

\u05d4\u05de\u05e9\u05d9\u05db\u05d5 \u05d1\u05e7\u05e8\u05d9\u05d0\u05d4<\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_monsterinsights_skip_tracking":false,"_monsterinsights_sitenote_active":false,"_monsterinsights_sitenote_note":"","_monsterinsights_sitenote_category":0,"footnotes":""},"categories":[10],"tags":[312,154,513,311,49],"class_list":["post-2610","post","type-post","status-publish","format-standard","hentry","category-10","tag-312","tag-154","tag-513","tag-311","tag-49","nodate","item-wrap"],"_links":{"self":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/2610","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=2610"}],"version-history":[{"count":4,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/2610\/revisions"}],"predecessor-version":[{"id":2614,"href":"https:\/\/azgad.com\/index.php?rest_route=\/wp\/v2\/posts\/2610\/revisions\/2614"}],"wp:attachment":[{"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=2610"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=2610"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/azgad.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=2610"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}