Hi Kirk,
It's been sometime since I ran this experiment, but yesterday I was able
to optimize the gradients at the lower values of 9000 and around 18000
(17580) on our 800. In fact, the lower gradient levels also worked with
the original experiment obtained from Lewis Kay's group, so I'm not
exactly sure why myself and others have had problems with this experiment
in the past. I'd be curious to learn if you also could get the experiment
to work with the lower gradient levels.
Eugene
Eugene DeRose, Ph.D.
NIEHS NMR Laboratory Manager
Contractor to NIEHS/DIR
919.541.1981
derose_at_niehs.nih.gov
On 1/14/14 12:13 PM, "Kirk Marat" <Kirk.Marat_at_umanitoba.ca> wrote:
>The gradients suggested by Eugene seem to work OK, and gzlvl11 seemed to
>optimize right at 29400. I think at 110 us that this should be fairly
>safe for the probe. For a gradient coil resistance of 1 Ohm this is only
>about 6 milliJoules of energy.
>
>If I understand correctly, it is the ratio of the coherence selection
>gradients that is critical, not the absolute values (as long as they are
>"strong enough"). I would think that one could scale back all the
>coherence selection gradients by some fraction if one was concerned about
>the probe. Eugene's values of 9000 and 17680 are about the same ratio,
>but I am not sure why these wouldn't work on his 600 and 800.
>
>Cheers!
>Kirk
>
>Kirk Marat, Ph. D. NMR Facility Manager
>Dept. of Chemistry, University of Manitoba
>Winnipeg, Manitoba
>R3T 2N2, Canada
>
>Ph: (204) 474-6259 FAX: (204) 474-7608
>
>
>> -----Original Message-----
>> From: DeRose, Eugene (NIH/NIEHS) [C] [mailto:derose_at_niehs.nih.gov]
>> Sent: January 9, 2014 5:04 PM
>> To: Tara Sprules, Dr.; ammrl_at_ammrl.org
>> Subject: Re: AMMRL: BioPack gNcpmgex_NH experiment
>>
>> Tara makes a good point. We may have been able to get away with running
>> the experiment at the higher gradient strength because the length of the
>> gradient gt11 is only 110 us in this experiment. I would not want to
>>try
>> running at such a high gradient level with a longer gradient delay.
>>
>> Since we are also very interested in this pulse sequence, I decided to
>> retry the sequence on our Inova 500 equipped with a Cold Probe, and was
>> surprised to find that the sequence works well with gzlvl8=9000 and
>> gzlvl=17680 after optimization. On our system, these values are close
>>to
>> the gradient strengths of 15 and 28.9 G/cm given in the original paper
>>by
>> Mulder et al. JACS 2001. In the past, I was not able to get the
>> experiment to work with these lower gradient strengths on our 600 and
>>800,
>> but plan to recheck this when I have time.
>>
>> Eugene
>>
>> Eugene DeRose, Ph.D.
>> NIEHS NMR Laboratory Manager
>> Contractor to NIEHS/DIR
>> 919.541.1981
>> derose_at_niehs.nih.gov
>>
>>
>>
>> On 1/7/14 1:43 PM, "Tara Sprules, Dr." <tara.sprules_at_mcgill.ca> wrote:
>>
>> >Just a quick point: check back to see what the gradient levels should
>>be
>> >in G/cm and make sure you use the gzcal for your system to get the
>>gzlvl
>> >you should use.. On our systems gzcal is roughly 0.2, so where a Lewis
>> >Kay sequence calls for a 29.4 G/cm gradient, and uses a gzlvl of 29400,
>> >we need to use 14600. We'd been using a couple of sequences with gzlvls
>> >of 29400 at one point when our gradient coil got fried: I was told we
>> >were using gradients that were too high, so ever since then I make sure
>> >to go back to the original publications to find the strength in G/cm.
>> >
>> >Tara
>> >________________________________________
>> >From: DeRose, Eugene (NIH/NIEHS) [C] [derose_at_niehs.nih.gov]
>> >Sent: Monday, January 06, 2014 1:34 PM
>> >To: Kirk Marat; ammrl_at_ammrl.org
>> >Subject: Re: AMMRL: BioPack gNcpmgex_NH experiment
>> >
>> >Hi Kirk,
>> >
>> >This experiment was originally written by Frans Mulder in Lewis Kay's
>> >group. Upon comparing the parameters from the original experiment
>> >(N15_CPMG_Rex_NH2_fm_500_v2) with the BioPack parameters, I noticed
>>that
>> >the gradient levels gzlvl5, gzlvl8 and gzlvl11 do not agree. The
>>correct
>> >values from the original experiment should be gzlvl5=-6000,
>>gzlvl8=15000,
>> >and gzlvl11=29400. I hope this helps.
>> >
>> >Best regards,
>> >Eugene
>> >
>> >Eugene DeRose, Ph.D.
>> >NIEHS NMR Laboratory Manager
>> >Contractor to NIEHS/DIR
>> >919.541.1981
>> >derose_at_niehs.nih.gov
>> >
>> >
>> >
>> >On 1/3/14 4:25 PM, "Kirk Marat" <Kirk.Marat_at_umanitoba.ca> wrote:
>> >
>> >>Happy New Year everyone.
>> >>
>> >>Has anyone had any experience with the N15 T2 exchange experiment
>> >>(gNcpmgex_NH) in BioPack? We can't seem to get it to work or even see
>> >>any signal in the first increment, even when the number of CPMG
>>cycles is
>> >>very low. Other BioPack sequences seem to work fine, suggesting that
>>the
>> >>probe calibration file is fine. Checking on the SPINSIGHTS site, it
>> >>appears that at least one other person has had trouble with this
>> >>experiment (in both VJ 3.2 and 4), but there was no real fix that I
>>could
>> >>see.
>> >>
>> >>This is an INOVA600 running VnmrJ 3.2A.
>> >>
>> >>Thanks!
>> >>Kirk
>> >>
>> >>Kirk Marat, Ph. D. NMR Facility Manager
>> >>Dept. of Chemistry, University of Manitoba
>> >>Winnipeg, Manitoba
>> >>R3T 2N2, Canada
>> >>
>> >>Ph: (204) 474-6259 FAX: (204) 474-7608
>> >>
>> >>
>> >
>
Received on Wed Jan 15 2014 - 06:22:59 MST